Nickel particles and method for producing nickel particles

Abstract

A nickel particle has a surface region containing an alloy of nickel and a metal element M. The metal element M is at least one selected from the group consisting of bismuth, copper, iron, and molybdenum. The content of the metal element M with respect to the entire nickel particle is 0.09 to 15.8 mass%. When a region from the surface to a sputtering depth of 5 nm in terms of SiO2 is measured in the depth direction of the nickel particle by X-ray photoelectron spectroscopy analysis, the maximum value of the proportion of the number of atoms of the metal element M with respect to the total number of atoms of the nickel element and the metal element M in the region is set as X (at%), and when the nickel particle is measured by ICP emission spectroscopy analysis, the proportion of the number of atoms of the metal element M with respect to the total number of atoms of the nickel element and the metal element M is set as Y (at%), the value of X / Y is 0.5 to 35.

Description

TECHNICAL FIELD

[0001] The present application relates to a nickel particle and a method for producing the same. BACKGROUND

[0002] For the formation of internal electrodes of a multilayer ceramic capacitor (hereinafter also referred to as "MLCC") used in electronic devices, a nickel particle has generally been used. In the production of an MLCC, in the case where a laminate of a dielectric layer and an internal electrode containing a nickel particle is simultaneously fired, it is possible that a defect is generated in the internal electrode due to a difference in the sintering temperature of raw materials. In order to prevent such an undesirable situation, it is required to improve the sintering resistance of the nickel particle.

[0003] For example, in Patent Literature 1, a technique is disclosed in which a nickel powder containing tin or bismuth obtained by a PVD method or a CVD method is used for the formation of an internal electrode of an MLCC. In this document, it is described that by adding a non-magnetic metal such as tin to the nickel powder, the crystal structure of nickel is distorted, whereby the sintering temperature of the nickel powder is increased.

[0004] In Patent Literature 2, a technique is disclosed in which a nickel powder having a substantially spherical particle shape and being surface-treated with tin is used for the formation of an internal electrode of an MLCC. Further, in this document, it is also disclosed that bismuth is used in addition to tin for surface treatment. In this document, it is described that according to the nickel powder described in this document, the sintering behavior is improved.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: International Publication No. 2014 / 080600

[0008] Patent Literature 2: Japanese Patent Application Publication No. 2018-104819 SUMMARY

[0009] However, with the recent high performance of electronic devices, it is required to further prevent an undesirable situation in an MLCC due to a defect that can be generated in an internal electrode. In order to cope with this requirement, not only an improvement in sintering resistance but also a prevention of an excessive increase in the resistance of the electrode when the internal electrode is formed using the nickel particle are expected for the nickel particle.

[0010] Therefore, an object of the present application is to provide a nickel particle having high sintering resistance without excessively increasing the resistance.

[0011] The present application provides a nickel particle having a surface region containing an alloy of nickel and a metal element M,

[0012] The metal element M is at least one selected from the group consisting of bismuth, copper, iron, and molybdenum,

[0013] The content of the metal element M with respect to the entire nickel particle is 0.09 to 15.8 mass%,

[0014] When the region from the surface to a sputtering depth of 5 nm in terms of SiO2 is measured in the depth direction of the nickel particle by X-ray photoelectron spectroscopy analysis, the maximum value of the proportion of the number of atoms of the metal element M with respect to the total number of atoms of the nickel element and the metal element M in the region is set to X (at%), and when the nickel particle is measured by ICP emission spectroscopy analysis, the proportion of the number of atoms of the metal element M with respect 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 0.5 to 35.

[0015] Further, the present application provides a method for producing a nickel particle, which heats a mixed solution containing a nickel hydroxide particle, a polyhydric alcohol, a polyvinylpyrrolidone, and a polyethyleneimine to produce a nickel particle,

[0016] 30 to 200 parts by mass of the polyvinylpyrrolidone is used with respect to 1 part by mass of the polyethyleneimine,

[0017] The nickel hydroxide particle is reduced to a nickel parent particle by the heating,

[0018] In a state where a part of the nickel hydroxide particle remains, the mixed solution is mixed with a compound of a metal element M, the compound is reduced to the metal M, and a surface region containing an alloy of nickel and the metal element M is formed on the nickel parent particle,

[0019] The metal element M is at least one selected from the group consisting of bismuth, copper, iron, and molybdenum. DETAILED DESCRIPTION

[0020] The nickel particle of the present application has a nickel parent particle and a surface region containing an alloy of nickel and a metal element M (hereinafter, also referred to as "nickel / metal M alloy") on the surface of the parent particle. The "nickel parent particle" in the present specification means a particle substantially composed of a nickel element and containing inevitable elements in the remaining part. The inevitable elements are, for example, oxygen and carbon elements derived from oxygen and carbon dioxide in the atmosphere, and a nitrogen element which can be mixed in during the production of the nickel particle.

[0021] The nickel parent particle in the nickel particle has a surface region containing a nickel / metal M alloy on the surface thereof. The "nickel / metal M alloy" in the present specification means a nickel-based alloy containing the metal element M described later. The nickel / metal M alloy is substantially composed of an alloy of the nickel element and the metal element M, and contains inevitable elements in the remaining portion. In the surface region containing the nickel / metal M alloy, a part of the metal element M can also exist in the state of the metal element M as such (i.e., in the state of a metal). Alternatively, a part of the metal element M can also exist in the state of a compound of the metal element M. Alternatively, the metal element M can also exist in a state in which two or more of them are combined. In the case where the metal element M exists in the state of a compound of the metal element M in the surface region containing the nickel / metal M alloy, as the compound, for example, an oxide, a hydroxide, a sulfide, a sulfoxide, a boride, a phosphide, or the like containing the metal M can be exemplified, but is not limited thereto. 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 advantages originally possessed by the nickel particle of the present application. The "substantially contains only an alloy with nickel" in the present specification means the following gist: the surface region is intentionally excluded from containing the metal element M other than the alloy with nickel, and a trace amount of the metal element M in the state of the metal element M as such or a compound of the metal element M inevitably mixed during the production of the nickel particle is allowed.

[0022] The metal element M in the nickel particle is preferably at least one selected from the group consisting of bismuth, copper, iron, and molybdenum. By the metal element M being bismuth, copper, iron, or molybdenum, it is possible to further improve the sinter resistance without excessively increasing the electric resistance of the nickel particle. The metal element M can use only one of bismuth, copper, iron, and molybdenum, or can use two or more in any combination. In the following description, when referring to the metal element M (or metal M), it means bismuth, copper, iron, or molybdenum or any two or more combination thereof depending on the context.

[0023] The fact that the nickel particle contains the nickel / metal M alloy in the surface region thereof can be confirmed by the following method.

[0024] Specifically, first, it is confirmed by measurement using X-ray photoelectron spectroscopy (hereinafter also referred to as "XPS") that the nickel particle contains the metal element M in the surface region thereof, and that the metal element M is mainly in the state of a metal. Next, it is confirmed that the a-axis length in the X-ray diffraction peak of the nickel particle is elongated compared to the a-axis length in the X-ray diffraction peak obtained by the measurement of the nickel particle alone. The elongation of the a-axis length in the X-ray diffraction peak means that the substance has been solid-solved. Therefore, according to the fact that the metal element M is confirmed to exist in the surface region of the nickel particle in the state of a metal by the measurement by XPS, and according to the fact that the metal element M is confirmed to be solid-solved with nickel by the comparison of the a-axis lengths, it is possible to confirm that the nickel particle contains the nickel / metal M alloy in the surface region thereof.

[0025] The proportion of the metal element M contained in the surface region of the nickel particles can be determined by XPS. In detail, when the region from the surface to a sputtering depth of 5 nm in terms of SiO2 (hereinafter, this region is also referred to as "particle surface region") is measured in the depth direction of the nickel particles by XPS, the maximum value of the proportion of the number of atoms of the metal element M with respect to the total number of atoms of the nickel element and the metal element M, i.e., the value of X, in the particle surface region is preferably 0.5 at% or more. The "maximum value" described above refers to the maximum value of the value of X in the case where the values of X measured in the thickness direction of the particle surface region are different. The presence of the metal element M in the form of a site having a value of X of 0.5 at% or more is preferable from the viewpoint of further improving the sinter resistance of the nickel particles described later.

[0026] In the case where the metal element M is bismuth, the value of X (at%) is more preferably 1 at% or more, even more preferably 2 at% or more, further preferably 3 at% or more, still further preferably 7 at% or more, and particularly preferably 14 at% or more, from the same viewpoint as described above. In addition, the value of X (at%) is more preferably 70 at% or less, even more preferably 35 at% or less, further preferably 30 at% or less, still further preferably 20 at% or less, and particularly preferably 15 at% or less.

[0027] In the case where the metal element M is copper, the value of X (at%) is more preferably 1 at% or more, even more preferably 2 at% or more, further preferably 4 at% or more, still further preferably 8 at% or more, and particularly preferably 12 at% or more, from the same viewpoint as described above. In addition, the value of X (at%) is more preferably 70 at% or less, even more preferably 35 at% or less, further preferably 20 at% or less, and still further preferably 14 at% or less.

[0028] In the case where the metal element M is iron, the value of X (at%) is more preferably 1 at% or more, even more preferably 2 at% or more, further preferably 4 at% or more, and still further preferably 7 at% or more, from the same viewpoint as described above. In addition, the value of X (at%) is more preferably 70 at% or less, even more preferably 35 at% or less, further preferably 30 at% or less, still further preferably 20 at% or less, and particularly preferably 9 at% or less.

[0029] In the case where the metal element M is molybdenum, from the same viewpoint as described above, the value of X (at%) is more preferably 1 at% or more, still more preferably 2 at% or more, further preferably 4 at% or more, and yet further preferably 8 at% or more. In addition, the value of X (at%) is more preferably 70 at% or less, still more preferably 35 at% or less, further preferably 30 at% or less, and yet further preferably 10 at% or less.

[0030] The method for measuring the value of X will be described in the Examples described later.

[0031] The so-called "outermost surface of the nickel particle" described above means the outermost surface of the nickel particle including the surface treatment agent when the surface treatment agent such as an organic acid or an amine is present on the surface of the nickel particle. When the surface treatment agent is not present on the surface of the nickel particle, it means the surface of the particle itself.

[0032] The nickel particle preferably contains 0.09 to 15.8 mass% of the metal element M with respect to the entire nickel particle. By adjusting the content of the metal element M with respect to the nickel particle within this range, it is possible to further improve the sintering resistance without excessively increasing the electric resistance of the nickel particle.

[0033] In the case where the metal element M is bismuth, from the same viewpoint as described above, the content of the bismuth element with respect to the entire nickel particle is more preferably 0.3 mass% or more, still more preferably 0.4 mass% or more, further preferably 1 mass% or more, and yet further preferably 6.7 mass% or more. In addition, the content of the bismuth element with respect to the entire nickel particle is more preferably 15.8 mass% or less, still more preferably 13 mass% or less, further preferably 11.4 mass% or less, and yet further preferably 10 mass% or less.

[0034] In the case where the metal element M is copper, from the same viewpoint as described above, the content of the copper element with respect to the entire nickel particle is more preferably 0.4 mass% or more, still more preferably 1 mass% or more, further preferably 2.1 mass% or more, and yet further preferably 4.3 mass% or more. In addition, the content of the copper element with respect to the entire nickel particle is more preferably 11.4 mass% or less, still more preferably 7.6 mass% or less, further preferably 6.5 mass% or less, yet further preferably 6 mass% or less, and particularly preferably 5.4 mass% or less.

[0035] In the case where the metal element M is iron, from the same viewpoint as described above, the content of the iron element with respect to the entire nickel particle is more preferably 0.09% by mass or more, further more preferably 0.28% by mass or more, still further preferably 0.40% by mass or more, yet further preferably 0.47% by mass or more. In addition, the content of the iron element with respect to the entire nickel particle is more preferably 11.4% by mass or less, further more preferably 6% by mass or less, still further preferably 2.87% by mass or less, yet further preferably 1.91% by mass or less, particularly preferably 0.96% by mass or less.

[0036] In the case where the metal element M is molybdenum, from the same viewpoint as described above, the content of the molybdenum element with respect to the entire nickel particle is more preferably 0.4% by mass or more, further more preferably 1% by mass or more, still further preferably 1.1% by mass or more, yet further preferably 1.6% by mass or more. In addition, the content of the molybdenum element with respect to the entire nickel particle is more preferably 11.4% by mass or less, further more preferably 6.4% by mass or less, still further preferably 6% by mass or less, yet further preferably 4.9% by mass or less, particularly preferably 3.3% by mass or less.

[0037] The content of the metal element M with respect to the entire nickel particle can be measured by the ICP emission spectrometry described later.

[0038] The nickel particle of the present application, with the proviso that the content of the metal element M with respect to the entire nickel particle satisfies the range described above, has a value (at%) of Y, which is the ratio of the number of atoms of the metal element M with respect to the total number of atoms of the nickel element and the metal element M in the entire nickel particle, preferably 0.1 at% to 7 at%. The presence of the metal element M in such a manner that the value of Y becomes within the range is preferable from the viewpoint of further improving the sintering resistance without excessively increasing the electric resistance of the nickel particle.

[0039] In the case where the metal element M is bismuth, from the same viewpoint as described above, the value of Y is more preferably 0.1 at% or more, further more preferably 0.2 at% or more, still further preferably 0.3 at% or more, yet further preferably 0.5 at% or more, particularly preferably 2 at% or more. In addition, the value of Y is more preferably 6 at% or less, further more preferably 5 at% or less, still further preferably 4 at% or less, yet further preferably 3 at% or less.

[0040] In the case where the metal element M is copper, from the same viewpoint as described above, the value of Y is more preferably 0.2 at% or more, further more preferably 0.5 at% or more, still further preferably 1 at% or more, yet further preferably 2 at% or more, particularly preferably 4 at% or more. In addition, the value of Y is more preferably 7 at% or less, further more preferably 6 at% or less, still further preferably 5 at% or less.

[0041] When the metallic element M is iron, from the same point of view as described above, the value of Y is more preferably 0.1at% or more, more preferably 0.2at% or more, even more preferably 0.3at% or more, and even more preferably 0.5at% or more. Furthermore, the value of Y is more preferably 6at% or less, more preferably 3at% or less, even more preferably 2at% or less, and even more preferably 1at% or less.

[0042] When the metallic element M is molybdenum, from the same viewpoint as above, the value of Y is more preferably 0.2 at% or more, more preferably 0.3 at% or more, even more preferably 0.5 at% or more, even more preferably 0.7 at% or more, and particularly preferably 1 at% or more. Furthermore, the value of Y is more preferably 6 at% or less, more preferably 4 at% or less, even more preferably 3 at% or less, and even more preferably 2 at% or less.

[0043] The proportion of metallic element M atoms in the nickel particles, i.e., the value of Y, is determined by ICP-C (Inductively Coupled Propagation) spectrophotometry. Specifically, firstly, the nickel particles are analyzed using ICP-C to determine the proportion of nickel and metallic element M. Then, the proportion of nickel (mass%) is divided by the atomic weight of nickel (58.7) to convert this proportion into the number of nickel atoms, A. Ni Furthermore, the percentage (mass%) of metallic element M is divided by the atomic weight of metallic element M (bismuth 209, copper 63.6, iron 55.9, molybdenum 96), and this percentage is converted into the number of atoms A of metallic element M. M Then, calculate the number of atoms of metallic element M relative to the number of atoms of nickel element A. Ni The number of atoms A of metallic element M M The proportion (A) M / (A Ni +A M ()×100), calculate the value of Y above.

[0044] As a result of the research by the inventors of the present application, it was ascertained that the relationship of the value of X to the value of Y has an influence on the sintering resistance of the nickel particles. In detail, it was ascertained that by setting the value of X / Y to 0.5 to 35, the temperature at which the nickel particles start to shrink by sintering, i.e., the sintering resistance, becomes high. The nickel particles of the present application, which have high sintering resistance, in the case where they are used to manufacture, for example, an MLCC, can make the temperature at which the internal electrode shrinks by sintering of the nickel particles in the firing process, which is one process of the manufacturing, as close as possible to the temperature at which the dielectric layer shrinks by sintering of the dielectric particles. Reducing the difference between the temperatures at which the internal electrode and the dielectric layer shrink each is advantageous from the aspect that the times at which the internal electrode and the dielectric layer shrink overlap during the temperature increase process in the firing process. In particular, in the firing process of the MLCC, it is advantageous from the viewpoint that the generation of structural defects such as cracks, delamination (interlayer peeling at the interface of the internal electrode and the dielectric layer) due to the difference in the temperature and the shrinkage rate at which the internal electrode and the dielectric layer shrink can be effectively prevented.

[0045] In the case where the metal element M is bismuth, from the viewpoint of making the above-mentioned advantages further significant, the value of X / Y in the nickel particles is more preferably 1.5 or greater, even more preferably 3.7 or greater, further preferably 4 or greater, still further preferably 5 or greater, and particularly preferably 7 or greater. The value of X / Y in the nickel particles is more preferably 30 or less, even more preferably 25 or less, further preferably 20 or less.

[0046] In the case where the metal element M is copper, from the viewpoint of making the above-mentioned advantages further significant, the value of X / Y in the nickel particles is more preferably 0.5 or greater, even more preferably 1 or greater, further preferably 1.5 or greater, still further preferably 2 or greater. The value of X / Y in the nickel particles is more preferably 30 or less, even more preferably 15 or less, further preferably 13 or less, still further preferably 10 or less, particularly preferably 7 or less, and especially preferably 3 or less.

[0047] In the case where the metal element M is iron, from the viewpoint of making the above-mentioned advantages further significant, the value of X / Y in the nickel particles is more preferably 1 or greater, even more preferably 1.5 or greater, further preferably 3.7 or greater, still further preferably 5 or greater, and particularly preferably 10 or greater. The value of X / Y in the nickel particles is more preferably 30 or less, even more preferably 25 or less, further preferably 20 or less, and still further preferably 15 or less.

[0048] In the case where the metal element M is molybdenum, the value of X / Y in the nickel particle is more preferably 1 or greater, even more preferably 1.5 or greater, further preferably 3 or greater, still further preferably 3.7 or greater, and particularly preferably 5 or greater, from the viewpoint of making the above-described advantages more remarkable. The value of X / Y in the nickel particle is more preferably 30 or less, even more preferably 15 or less, further preferably 13 or less, still further preferably 10 or less, and particularly preferably 7 or less.

[0049] The value of the proportion of the number of atoms of the metal element M with respect to the total number of atoms of the nickel element and the metal element M in the surface region of the particle can be constant in the depth direction, or can vary. In the case where the value of the proportion is not constant in the depth direction, the value of the proportion can decrease continuously or stepwise, for example, from the surface toward the center of the nickel particle. In particular, when the region from the surface of the nickel particle to a sputtering depth of 20 nm in terms of SiO2 is measured by XPS, it is preferable that the value of the proportion decrease from the surface toward the sputtering depth of 20 nm, from the viewpoint of further improving the sinter resistance of the nickel particle. In this case, when the maximum value of the proportion in the region from the surface of the nickel particle to a sputtering depth of 5 nm is set to X, and the maximum value of the proportion at the sputtering depth of 20 nm is set to X1, it is preferable that the value of X / X1 be 0.1 to 15, from the viewpoint of further improving the sinter resistance of the nickel particle.

[0050] In the case where the metal element M is bismuth, the value of X / X1 is more preferably 1 or greater, even more preferably 1.5 or greater, and further preferably 2 or greater, from the same viewpoint as described above. In addition, the value of X / X1 is more preferably 10 or less, even more preferably 7.8 or less, further preferably 6.1 or less, still further preferably 4 or less, particularly preferably 3 or less, and especially preferably 2.5 or less.

[0051] In the case where the metal element M is copper, the value of X / X1 is more preferably 0.1 or greater, even more preferably 0.5 or greater, and further preferably 1 or greater, from the same viewpoint as described above. In addition, the value of X / X1 is more preferably 10 or less, even more preferably 7.8 or less, further preferably 6.1 or less, still further preferably 5 or less, and particularly preferably 3 or less.

[0052] In the case where the metal element M is iron, the value of X / X1 is more preferably 0.1 or greater, even more preferably 0.5 or greater, and further preferably 1 or greater, from the same viewpoint as described above. In addition, the value of X / X1 is more preferably 10 or less, even more preferably 7.8 or less, further preferably 6.1 or less, still further preferably 5 or less, and particularly preferably 2 or less.

[0053] In the case where the metal element M is molybdenum, the value of X / X1 is more preferably 0.1 or more, much more preferably 1 or more, and further preferably 2 or more, from the same viewpoint as described above. In addition, the value of X / X1 is more preferably 10 or less, much more preferably 7.8 or less, further preferably 6.1 or less, much further preferably 5 or less, and particularly preferably 3 or less.

[0054] The method for measuring X1 will be described in the Examples described later.

[0055] In the case where the metal element M is bismuth, the value of X1 itself is more preferably 0.2 or more, much more preferably 0.5 or more, further preferably 0.7 or more, much further preferably 1.7 or more, particularly preferably 2 or more, and especially preferably 5 or more, from the viewpoint of further improving the sintering resistance of the nickel particles. In addition, the value of X1 itself is more preferably 15 or less, much more preferably 10 or less, and further preferably 7 or less.

[0056] In the case where the metal element M is copper, the value of X1 itself is more preferably 0.2 or more, much more preferably 0.5 or more, further preferably 0.7 or more, much further preferably 1 or more, particularly preferably 1.7 or more, especially preferably 3 or more, and particularly especially preferably 5 or more, from the viewpoint of further improving the sintering resistance of the nickel particles. In addition, the value of X1 itself is more preferably 20 or less, much more preferably 15 or less, and further preferably 10 or less.

[0057] In the case where the metal element M is iron, the value of X1 itself is more preferably 0.2 or more, much more preferably 0.5 or more, further preferably 0.7 or more, much further preferably 1 or more, particularly preferably 1.7 or more, especially preferably 2 or more, and particularly especially preferably 4 or more, from the viewpoint of further improving the sintering resistance of the nickel particles. In addition, the value of X1 itself is more preferably 15 or less, much more preferably 10 or less, and further preferably 6 or less.

[0058] In the case where the metal element M is molybdenum, the value of X1 itself is more preferably 0.2 or more, much more preferably 0.5 or more, further preferably 0.7 or more, much further preferably 1 or more, particularly preferably 1.7 or more, especially preferably 2 or more, and particularly especially preferably 4 or more, from the viewpoint of further improving the sintering resistance of the nickel particles. In addition, the value of X1 itself is more preferably 15 or less, much more preferably 10 or less, further preferably 6 or less, and much further preferably 5 or less.

[0059] The number of the nickel particles of the present application at the number cumulative particle diameter of 50% is the number cumulative particle diameter, i.e., D50. 50The value of D is preferably 20 nm to 200 nm. In other words, the nickel particles of the present application are preferably microparticles. By adjusting the particle diameter D of the nickel particles to be within this range, when the nickel particles of the present application are used as internal electrodes of MLCCs, for example, the advantage of making it less likely to cause short-circuiting between the internal electrodes is obtained. From the viewpoint of making this advantage even more remarkable, the particle diameter D of the nickel particles is preferably 20 nm to 150 nm, more preferably 40 nm to 150 nm, and even more preferably 40 nm to 100 nm. 50 The value of D is preferably 20 nm to 200 nm. In other words, the nickel particles of the present application are preferably microparticles. By adjusting the particle diameter D of the nickel particles to be within this range, when the nickel particles of the present application are used as internal electrodes of MLCCs, for example, the advantage of making it less likely to cause short-circuiting between the internal electrodes is obtained. From the viewpoint of making this advantage even more remarkable, the particle diameter D of the nickel particles is preferably 20 nm to 150 nm, more preferably 40 nm to 150 nm, and even more preferably 40 nm to 100 nm. 50 The value of D is preferably 20 nm to 200 nm. In other words, the nickel particles of the present application are preferably microparticles. By adjusting the particle diameter D of the nickel particles to be within this range, when the nickel particles of the present application are used as internal electrodes of MLCCs, for example, the advantage of making it less likely to cause short-circuiting between the internal electrodes is obtained. From the viewpoint of making this advantage even more remarkable, the particle diameter D of the nickel particles is preferably 20 nm to 150 nm, more preferably 40 nm to 150 nm, and even more preferably 40 nm to 100 nm. 50 The particle diameter D of the nickel particles is measured by observing the nickel particles with a scanning electron microscope (SEM). In detail, the nickel particles are photographed with an SEM at a magnification of 50,000 times, and the area of the photographed nickel particles is calculated. The equivalent circle diameter is calculated from this area. Based on the calculated equivalent circle diameter, the particle size distribution is calculated. The particle size distribution is a graph in which the equivalent circle diameter is taken as the horizontal axis and the number frequency is taken as the vertical axis. In the particle size distribution curve obtained by such an operation, the number cumulative particle diameter at which the cumulative number is 50% is defined as D 50 .

[0060] When the "particle size distribution curve" described above is obtained, the equivalent circle diameters of 5,000 or more nickel particles are calculated. For the calculation of the equivalent circle diameters, an image analysis particle size distribution measuring software (Mac-View manufactured by MOUNTECH Corporation) is used. The smallest unit of the nickel particles observed is determined by whether or not the particle interface observed as an independent one particle is observed with the SEM. Therefore, even if a coagulation block containing multiple particles is observed, when the particle interface is observed in the coagulation block, the region divided by the particle interface is recognized as one particle.

[0061] The nickel particles of the present application are preferably microparticles, and the proportion of the presence of coarse particles is small. When the nickel particles of the present application are used as internal electrodes of MLCCs, for example, the presence of coarse particles can become a cause of short-circuiting between the internal electrodes. By reducing the proportion of the presence of coarse particles in the nickel particles, the short-circuiting can be effectively prevented. From this viewpoint, in the nickel particles of the present application, the proportion of the presence of particles having a particle diameter of 1.5 times or more of D 50 is preferably 0.5% or less, more preferably 0.3% or less, and even more preferably 0.1% or less.

[0062] The closer the proportion of the presence of coarse particles is to 0%, the more effective the prevention of the occurrence of short-circuiting between the internal electrodes is, but as long as the proportion of the presence of coarse particles is as low as about 0.01%, the occurrence of short-circuiting between the internal electrodes can be effectively prevented.

[0063] The reason for selecting particles having a particle diameter of 1.5 times or more of D 50 is because the inventors of the present application found that when the particle diameter is 1.5 times or more of D 50 , one of the reasons that the surface of the conductive film becomes rough when the conductive film is formed is closely related to the generation of short-circuit between internal electrodes of the MLCC.

[0064] The nickel particles of the present application are preferably not only low in the proportion of the existence of fine particles and coarse particles, but also uniform in particle diameter as much 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 particle diameter. The coefficient of variation is a value defined by (σ / D 50 ) x 100 (%) when the standard deviation of particle diameter in the particle size distribution is set to σ (nm). It is preferable that the value of the coefficient of variation of the nickel particles of the present application be 14% or less from the viewpoint of reducing the surface roughness of the 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 further preferably 12% or less.

[0065] The closer the coefficient of variation is to 0%, the further the reduction of the surface roughness of the conductive film is facilitated, but as long as the coefficient of variation is as low as about 8%, the surface roughness of the conductive film can be reduced to a degree that should be sufficiently satisfactory.

[0066] The nickel particles of the present application are preferably high in crystallinity of nickel. The high crystallinity of nickel means that the temperature at which the nickel particles of the present application start to shrink by sintering increases. In other words, the high crystallinity of nickel means that the nickel particles exhibit high sintering resistance as described above.

[0067] The crystallinity of nickel is evaluated by the ratio of the crystallite size Cs (nm) to the particle diameter D 50 (nm), that is, Cs / D 50 . The larger the value of Cs / D 50 , the higher the crystallinity of nickel can be evaluated. From this viewpoint, in the nickel particles of the present application, the value of Cs / D 50 is preferably 0.3 or more, more preferably 0.34 or more, and further preferably 0.37 or more.

[0068] The larger the value of Cs / D 50 , the higher the temperature at which the nickel particles start to shrink by sintering, but in the present application, as long as the value of Cs / D 50 is preferably 0.6 or less, the temperature can be sufficiently increased, and from this viewpoint, the value of Cs / D 50 is more preferably 0.55 or less, and further preferably 0.52 or less.

[0069] The value of the crystallite size Cs is preferably 15 nm to 70 nm, more preferably 18 nm to 70 nm, and further preferably 20 nm to 70 nm from the viewpoint of sufficiently increasing the temperature at which the nickel particles start to shrink due to sintering.

[0070] As a method for measuring the crystallite size, various methods are known in the technical field of metal powder, but the crystallite size in the present specification refers to a value obtained by measurement by the WPPF (whole powder pattern fitting) method. As a method for measuring the crystallite size, the Scherrer method is known in addition to the WPPF method, but in the case where the degree of distortion of the crystal is large, the value of the crystallite size obtained based on the Scherrer method becomes less reliable, and therefore the WPPF method having less concern as described above is adopted in the present application.

[0071] Details of the method for measuring the crystallite size of nickel based on the WPPF method will be described in the Examples described later.

[0072] The nickel particles of the present application preferably do not excessively increase the electric resistance. In the case where such nickel particles are used for the internal electrode of, for example, an MLCC, the performance of the MLCC can be further improved. Therefore, for the purpose of not excessively increasing the electric resistance, it is preferred to control the crystal structure of the nickel particles in such a manner that the pure nickel component in the nickel particles having a surface region containing nickel / metal M alloy becomes more. From this viewpoint, in the nickel particles of the present application, the a-axis length of the crystal lattice in the crystal structure of nickel is preferably 0.150 nm to 0.160 nm, more preferably 0.152 nm to 0.158 nm, and further preferably 0.154 nm to 0.156 nm. More preferably, the a-axis length of the crystal lattice in the crystal structure of nickel is 0.154 nm to 0.156 nm. Further preferably, the a-axis length of the crystal lattice in the crystal structure of nickel is 0.154 nm to 0.156 nm. Still further preferably, the a-axis length of the crystal lattice in the crystal structure of nickel is 0.154 nm to 0.156 nm.

[0073] The a-axis length of the crystal lattice in the crystal structure of the nickel particles can be measured by an X-ray diffractometer using CuKα1 rays as described in the Examples described later. For the analysis, the WPPF method is used as described in the Examples described later.

[0074] The crystallite size in the crystal structure of nickel and the a-axis length of the crystal lattice in the present application are achieved, for example, by adjusting the proportion of the metal element M contained in the surface region of the nickel particles, and thinning the thickness of the surface region containing nickel / metal M alloy possessed by the nickel particles. On this basis or instead, it can also be achieved by appropriately adjusting the conditions in the manufacturing method of the nickel particles described later.

[0075] The degree of sintering resistance of the nickel particles of the present application can be evaluated by thermomechanical analysis (TMA) with the nickel particles as the subject. In the present application, the temperature at which the TMA shrinkage rate (%) with room temperature (25°C) as the reference becomes 5% is defined as the shrinkage start temperature. It is preferable that this temperature be 400°C or higher from the viewpoint of further improving the sintering resistance of the nickel particles. It is more preferable that this temperature be 450°C or higher, even more preferable that it be 500°C or higher, further preferable that it be 550°C or higher, and even further preferable that it be 570°C or higher from the viewpoint of making this advantage even more remarkable.

[0076] Next, a preferred production method for the nickel particles of the present application will be described. In this production method, the nickel particles are produced by the so-called polyol method. The polyol method refers to a method in which a polyol is used as a solvent that also serves as a reducing agent. In the polyol method, a reduction reaction to the nickel parent particles is produced by heating in a state in which a chemical species of nickel is present in the polyol, a compound of a metal element M is mixed before the end of this reduction reaction, and a reduction reaction to the metal M is produced by further heating, thereby forming a surface region containing a nickel / metal M alloy on the nickel parent particles.

[0077] In this production method, it is preferable that nickel hydroxide be used as the chemical species of nickel for producing the nickel particles from the viewpoint of smoothly obtaining the target nickel particles. The nickel hydroxide is added to a mixed solution containing a polyol, polyvinylpyrrolidone (hereinafter also referred to as "PVP"), and polyethyleneimine (hereinafter also referred to as "PEI"). From the viewpoint of operability, it is preferable that a nickel hydroxide having a particle-like form be used as the nickel hydroxide.

[0078] The polyol contained in the mixed solution is used as the solvent as described above and also as the reducing agent for the nickel hydroxide.

[0079] As the polyol, for example, 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, etc. can be used. These polyols can be used alone or in combination with two or more. Of these polyols, ethylene glycol is preferable because the proportion of the hydroxyl group with respect to the molecular weight is large, the reduction performance is high, and it is liquid at ordinary temperatures and excellent in operability.

[0080] The amount of the polyol used is not particularly limited if it is considered from the viewpoint of using it as a reducing agent, and it is only necessary to appropriately adjust it in accordance with the amount of the nickel hydroxide in the mixed solution. On the other hand, in the case where it is desired to function as a solvent, since the properties of the mixed solution change depending on the concentration of the polyol in the mixed solution, there is a certain appropriate 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%.

[0081] PVP is used as a dispersant for the nickel hydroxide. PVP is preferable because it can make the particle size distribution of the nickel particles generated by reduction sharp due to the effect as a dispersant. The molecular weight of these PVPs is only necessary to appropriately adjust in accordance with the degree of water solubility, dispersing ability. The amount of the PVP in the mixed solution is preferably set to 0.01 parts by mass to 30 parts by mass with respect to 100 parts by mass of the nickel hydroxide converted into nickel. By setting it to this range, the dispersing effect can be sufficiently exhibited without excessively increasing the viscosity of the mixed solution.

[0082] PEI has the following effects: during the generation of the nucleus of nickel in the mixed solution, the number of nickel ions in the mixed solution is reduced, and the nucleus generation and the nucleus growth are made to proceed at different times. The reason for this is because: (a) PEI has a non-covalent electron pair that has an interaction with nickel ions, and can be coordinated bonded to the nickel ions; (b) PEI has a large number of the above non-covalent electron pairs; and (c) PEI has a hydrogen bonding site that can interact with the surface of the nickel hydroxide that exists in the mixed solution in an undissolved state.

[0083] By the presence of PEI in the mixed solution, the nucleus generation of nickel and the growth of the generated nucleus can be sequentially performed. As a result, nickel particles that are fine and have a uniform particle diameter can be smoothly obtained. In contrast to this, in the conventional production of nickel particles based on reduction, since the nucleus generation and the nucleus growth occur at the same time, it is easy to generate coarse particles, and the particle diameter is easy to become uneven.

[0084] From the above viewpoint, as the PEI, it is advantageous to use a branched PEI compared to a linear PEI. From the same viewpoint, it is also preferable to use a PEI having a number average molecular weight of 600 to 10,000, particularly preferable to use a PEI having a number average molecular weight of 800 to 5,000, and especially preferable to use a PEI having a number average molecular weight of 1,000 to 3,000.

[0085] 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 sequential progress of the nucleation and the nucleate growth of nickel becomes reliable. In detail, 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 further preferably used, with respect to 1 part by mass of PEI.

[0086] The amount of PEI in the mixed solution is appropriately set in accordance with the amount of PVP, provided that the ratio of PVP to PEI satisfies the above range.

[0087] The mixed solution can also contain a noble metal catalyst. By this, fine core particles of the noble metal are generated in the initial stage of reduction, and nickel smoothly proceeds with reduction using the core particles as a starting point. As the noble metal catalyst, for example, a water-soluble salt of a noble metal or the like noble metal compound can be used. As examples of the water-soluble salt of a noble metal, water-soluble salts of palladium, silver, platinum, gold, and the like can be listed. In the case where palladium is used as the noble metal, for example, palladium chloride, palladium nitrate, palladium acetate, palladium ammonium chloride, and the like can be used. In the case where silver is used, for example, silver nitrate, silver lactate, silver oxide, silver sulfate, silver cyclohexanoate, silver acetate, and the like can be used. In the case where platinum is used, for example, chloroplatinic acid, potassium chloroplatinate, sodium chloroplatinate, and the like can be used. In the case where gold is used, for example, chloroauric acid, sodium chloroaurate, and the like can be used. Of these, palladium nitrate, palladium acetate, silver nitrate, and silver acetate are preferably used because they are inexpensive and have good economy. The noble metal catalyst can be used by being added 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, and particularly preferably 0.01 to 1 part by mass, with respect to 100 parts by mass of nickel hydroxide converted into nickel.

[0088] The mixed solution containing the above-mentioned components is heated while being stirred to perform reduction of the nickel hydroxide. The heating temperature also varies depending on the kind of the polyol used, but by performing heating at 150 to 200°C, more preferably at 170 to 200°C, and further preferably at 190 to 200°C under atmospheric pressure, reduction of the nickel hydroxide to the nickel parent particle can be smoothly performed.

[0089] Next, a compound of the metal element M is mixed in the above-mentioned mixed solution before the reduction reaction of the nickel hydroxide is completed. In other words, the compound of the metal element M is mixed in the above-mentioned mixed solution in a state where a part of the nickel hydroxide remains. The "before the reduction reaction of the nickel hydroxide is completed" herein means before 80 mol% or more of the nickel hydroxide is reduced with respect to the amount of the nickel hydroxide charged.

[0090] In the case where the metal element M is bismuth, from the viewpoint of smoothly forming the surface region containing the nickel / bismuth alloy on the nickel parent particle in the reduction reaction of the compound of the metal element M to be described later, at least one selected from the group consisting of bismuth nitrate, bismuth chloride, bismuth nitrate 5 hydrate, bismuth hydroxide, bismuth oxide, and bismuth carbonate is preferably used as the compound, and bismuth chloride is particularly preferably used.

[0091] In the case where the metal element M is copper, from the same viewpoint as described above, at least one selected from the group consisting of copper nitrate 3 hydrate, copper sulfate 5 hydrate, copper acetate 1 hydrate, copper hydroxide, cuprous oxide, and copper oxide is preferably used as the compound, and copper sulfate 5 hydrate is particularly preferably used.

[0092] In the case where the metal element M is iron, from the same viewpoint as described above, at least one selected from the group consisting of iron nitrate 9 hydrate, iron chloride 6 hydrate, iron sulfate 7 hydrate, iron hydroxide, and iron oxide is preferably used as the compound, and iron sulfate 7 hydrate is particularly preferably used.

[0093] In the case where the metal element M is molybdenum, from the same viewpoint as described above, at least one selected from the group consisting of sodium molybdate, potassium molybdate, calcium molybdate, and ammonium molybdate is preferably used as the compound, and sodium molybdate is particularly preferably used.

[0094] In the case where the metal element M is bismuth, from the viewpoint of smoothly forming the surface region containing the nickel / bismuth alloy on the nickel parent particle, it is preferable that the amount of the bismuth compound in the mixed solution is set to 0.003 parts by mass or more, more preferably 0.004 parts by mass or more, further preferably 0.01 parts by mass or more, and still further preferably 0.02 parts by mass or more, with respect to 1 part by mass of the nickel, in terms of bismuth. In addition, it is preferable that the amount of the bismuth compound in the mixed solution is set to 0.20 parts by mass or less, more preferably 0.16 parts by mass or less, further preferably 0.13 parts by mass or less, and still further preferably 0.12 parts by mass or less, with respect to 1 part by mass of the nickel, in terms of bismuth.

[0095] In the case where the metal element M is copper, from the viewpoint of smoothly forming a surface region containing an alloy of nickel and copper on the nickel parent particles, it is preferable that the amount of the copper compound in the mixed solution, converted into copper, be set to 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, further preferably 0.045 parts by mass or more, relative to 1 part by mass of the amount of nickel to be fed. In addition, it is preferable that the amount of the copper compound in the mixed solution, converted into copper, be set to 0.12 parts by mass or less, more preferably 0.082 parts by mass or less, even more preferably 0.07 parts by mass or less, further preferably 0.06 parts by mass or less, relative to 1 part by mass of the amount of nickel to be fed.

[0096] In the case where the metal element M is iron, from the viewpoint of smoothly forming a surface region containing an alloy of nickel and iron on the nickel parent particles, it is preferable that the amount of the iron compound in the mixed solution, converted into iron, be set to 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, further preferably 0.0047 parts by mass or more, relative to 1 part by mass of the amount of nickel to be fed. In addition, it is preferable that the amount of the iron compound in the mixed solution, converted into iron, be set to 0.12 parts by mass or less, more preferably 0.08 parts by mass or less, even more preferably 0.06 parts by mass or less, further preferably 0.030 parts by mass or less, still further preferably 0.020 parts by mass or less, relative to 1 part by mass of the amount of nickel to be fed.

[0097] In the case where the metal element M is molybdenum, from the viewpoint of smoothly forming a surface region containing an alloy of nickel and molybdenum on the nickel parent particles, it is preferable that the amount of the molybdenum compound in the mixed solution, converted into molybdenum, be set to 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, further preferably 0.016 parts by mass or more, relative to 1 part by mass of the amount of nickel to be fed. In addition, it is preferable that the amount of the molybdenum compound in the mixed solution, converted into molybdenum, be set to 0.12 parts by mass or less, more preferably 0.07 parts by mass or less, even more preferably 0.06 parts by mass or less, further preferably 0.051 parts by mass or less, still further preferably 0.034 parts by mass or less, relative to 1 part by mass of the amount of nickel to be fed.

[0098] Next, the mixed solution containing the compound of the metal element M above is heated while being stirred to reduce the nickel hydroxide and the compound in the mixed solution. By this reduction reaction, the nickel hydroxide remaining in the mixed solution is reduced to nickel, and in the case where the metal element M is bismuth, the compound of the metal element M is reduced to bismuth. Alternatively, in the case where the metal element M is copper, the compound of the metal element M is reduced to copper. Alternatively, in the case where the metal element M is iron, the compound of the metal element M is reduced to iron. Alternatively, in the case where the metal element M is molybdenum, the compound of the metal element M is reduced to molybdenum. In this reduction reaction, by simultaneously reducing the nickel hydroxide and the compound of the metal element M, a surface region containing nickel / metal M alloy in which nickel and metal M are homogeneously solid-solved is formed on the surface of the nickel parent particle. Note that as long as the effects of the present application can be exerted, it is permissible for a part of the metal element M to exist in the state of the metal element M as it is, in the state of the compound of the metal element M, or in a combination of two or more states thereof.

[0099] The heating temperature of the mixed solution above varies depending on the polyol used and the kind of the compound of the metal element M, but is preferably 150°C to 200°C, more preferably 170°C to 200°C, and further preferably 190°C to 200°C at atmospheric pressure. By setting the heating temperature within this range, the nickel hydroxide and the compound of the metal element M can be simultaneously reduced, and a surface region containing nickel / metal M alloy can be smoothly formed on the surface of the nickel parent particle.

[0100] After that, as necessary, the polyol in the dispersion liquid of the nickel particle obtained is replaced with water, and then the replaced water is re-replaced with methanol to wash the nickel particle, and vacuum drying is performed. Such an operation enables the production of the nickel particle of the present application.

[0101] In the case of manufacturing the nickel particles containing the metal element M, the PVD method or the CVD method can be performed by adding a raw material of the metal element M to a nickel raw material. In this case, the nickel particles become to form the nickel / metal M alloy in the entire thereof. However, in the case where it is intended to improve the sintering resistance of the nickel particles, the content of the metal element M, i.e., bismuth, copper, iron and / or molybdenum in the entire of the nickel particles becomes too high, as a result, there is a problem that the electric resistance becomes high. In addition to this, since the particle diameter of the nickel particles becomes non-uniform, the surface of the conductive film becomes rough when the nickel particles are used to form the conductive film, there is a problem that it becomes one of the causes of the short circuit between the internal electrodes of the MLCC. Further, as another method of manufacturing the nickel particles containing the metal element M, as described in Patent Document 2, there is known a method of adding a compound of the metal element M after reducing the entire amount of nickel hydroxide. In this case, if bismuth and / or copper is used as the metal element M, a layer of the elementary substance of bismuth and / or copper having a lower melting point than nickel is formed on the surface of the nickel particles. However, the sintering resistance of the nickel particles does not become high due to the layer of the elementary substance of bismuth and / or copper formed on the surface of the particles. Further, in the case where iron and / or molybdenum is used as the metal element M, the elementary substance of iron and molybdenum easily oxidizes, a layer containing the iron oxide and / or the molybdenum oxide is formed on the surface of the nickel particles. In the case where the nickel particles on which such a layer is formed are fired at the time of manufacturing the MLCC, the oxides contained in the layer are absorbed by the dielectric layer, therefore the sintering resistance of the nickel particles also does not become high. In contrast to this, according to the nickel particles of the present application containing the nickel parent particles and the nickel / metal M alloy arranged on the surface thereof, it is possible to improve the sintering resistance without excessively increasing the electric resistance. Further, if the nickel particles of the present application are used to form the conductive film, it is possible to make the surface of the conductive film smooth. For these reasons, as described above, it is preferable to manufacture the nickel particles by simultaneously reducing the nickel hydroxide and the compound of the metal element M in the state where a part of the nickel hydroxide remains.

[0102] The nickel particles manufactured by the above method, although being fine particles and having a uniform particle diameter, can be used in various fields by utilizing the feature that the surface region thereof contains the nickel / metal M alloy on the surface of the nickel particles. In particular, it is suitably used for the formation of the internal electrodes of the MLCC.

[0103] The above has been described based on the preferred embodiments of the present application, but the present application is not limited to the above-described embodiments.

[0104] With respect to the above-described embodiments, the following nickel particles and the method of manufacturing the same are further disclosed.

[0105] (1) A nickel particle having a surface region containing an alloy of nickel and a metal element M,

[0106] The above metal element M is at least one selected from the group consisting of bismuth, copper, iron and molybdenum,

[0107] the content of the metal element M with respect to the entire nickel particle is 0.09 to 15.8 mass%,

[0108] when the region from the surface to a sputtering depth of 5 nm in terms of SiO2 is measured in the depth direction of the nickel particle by X-ray photoelectron spectroscopy analysis, the maximum value of the proportion 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 in the region is set to X (at%), and when the proportion 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%) when the nickel particle is measured by ICP emission spectroscopy analysis, the value of X / Y is 0.5 to 35.

[0109] 〔2〕 The nickel particle according to 〔1〕, wherein, in a particle size distribution based on the equivalent circle diameters calculated from the measurement using a scanning electron microscope, the number cumulative particle diameter at the cumulative number of 50% is set to D 50 , and D 50 is 20 nm to 200 nm,

[0110] 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 (σ / D 50 ) (%) is 14% or less.

[0111] the coefficient of variation (%) = (σ / D 50 ) x 100

[0112] 〔3〕 The nickel particle according to 〔1〕 or 〔2〕, wherein, in a particle size distribution based on the equivalent circle diameters calculated from the measurement using a scanning electron microscope, the number cumulative particle diameter at the cumulative number of 50% is set to D 50 , and the existence proportion of the particles having a particle diameter of 1.5 times or more of D 50 is 0.5% or less.

[0113] 〔4〕 The nickel particle according to any one of 〔1〕 to 〔3〕, wherein, in a particle size distribution based on the equivalent circle diameters calculated from the measurement using a scanning electron microscope, the number cumulative particle diameter at the cumulative number of 50% is set to D 50 , and when the crystallite size determined by the WPPF method is set to Cs (nm), the value of Cs / D 50 is 0.3 to 0.6.

[0114] 〔5〕 A method for producing a nickel particle, which heats a mixed solution containing a nickel hydroxide particle, a polyhydric alcohol, a polyvinylpyrrolidone, and a polyethylene imine to produce a nickel particle,

[0115] 30 parts by mass to 200 parts by mass of polyvinylpyrrolidone is used with respect to 1 part by mass of polyethyleneimine,

[0116] The nickel hydroxide particles are reduced to nickel parent particles by the above heating,

[0117] In a state where a part of the nickel hydroxide particles remains, the mixed solution is mixed with a compound of a metal element M, the compound is reduced to metal M, and a surface region containing an alloy of nickel and the metal element M is formed on the nickel parent particles,

[0118] The metal element M is at least one selected from the group consisting of bismuth, copper, iron, and molybdenum.

[0119] [6] A multilayer ceramic capacitor using the nickel particles described in any one of [1] to [4] in the internal electrodes.

[0120] Example

[0121] Hereinafter, the present application will be described in more detail by examples. However, the scope of the present application is not limited to the examples. Unless otherwise specified, "%" means "mass %".

[0122] [Example 1]

[0123] A mixed solution was prepared by adding 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 an aqueous solution of palladium nitrate (concentration: 100 g / 1) into a 500-ml beaker. The polyethyleneimine was a branched polyethyleneimine having a number average molecular weight of 1800. The mixed solution was heated while being stirred, and a reduction reaction was performed at 198°C under atmospheric pressure for 5 hours. At this time, the reduction of the nickel hydroxide was 80 mol% with respect to the amount of the nickel hydroxide charged. Next, 0.3 g of bismuth chloride was added, and a further reduction reaction was performed at 198°C under atmospheric pressure for 10 hours. The reduction was completed by stopping the heating and naturally cooling to room temperature. In this manner, a large amount of nickel particles was obtained.

[0124] A magnet was arranged at the bottom of a beaker containing a dispersion liquid of the obtained nickel particles, and the nickel particles were attracted to the magnet. In this state, the supernatant of the dispersion liquid was removed.

[0125] After the magnet was removed from the bottom of the beaker, 50 g of pure water was added, and the dispersion liquid was stirred for 10 minutes. Next, the magnet was arranged again at the bottom of the beaker, and the nickel particles were attracted to the magnet. In this state, the supernatant of the dispersion liquid was removed. The series of operations was repeated five times.

[0126] Next, methanol 50 g was added and the dispersion liquid was stirred for 10 minutes. The removal of the supernatant was repeated three times by using a magnet to replace the solvent in the dispersion liquid with methanol. After that, vacuum drying was performed at 80°C to obtain nickel particles.

[0127] [Examples 2 to 6]

[0128] The amount of addition of the aqueous palladium nitrate solution and the amount of addition of bismuth chloride, and the time from the start of heating of the mixed solution to the addition of bismuth chloride in the mixed solution were set as shown in Table 1. Other than these, the same operation as in Example 1 was performed to obtain nickel particles.

[0129] [Example 7]

[0130] Instead of bismuth chloride, copper sulfate 5 hydrate was added. The amount of addition of the aqueous palladium nitrate solution and the amount of addition of copper sulfate 5 hydrate were set as shown in Table 1. Other than these, the same operation as in Example 1 was performed to obtain nickel particles.

[0131] [Example 8]

[0132] Instead of bismuth chloride, iron sulfate 7 hydrate was added. The amount of addition of the aqueous palladium nitrate solution and the amount of addition of iron sulfate 7 hydrate were set as shown in Table 1. Other than these, the same operation as in Example 1 was performed to obtain nickel particles.

[0133] [Example 9]

[0134] Instead of bismuth chloride, sodium molybdate was added. The amount of addition of the aqueous palladium nitrate solution and the amount of addition of sodium molybdate were set as shown in Table 1. Other than these, the same operation as in Example 1 was performed to obtain nickel particles.

[0135] [Comparative Example 1]

[0136] A mixed solution was prepared by adding 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 an aqueous palladium nitrate solution (concentration: 100 g / 1) to a 500-ml beaker. The polyethyleneimine was a branched polyethyleneimine having a number average molecular weight of 1800. The mixed solution was heated while stirring, and a reduction reaction was performed at 198°C for 6.5 hours. The heating was stopped to end the reduction, and the mixture was allowed to cool naturally to room temperature. In this way, a large amount of nickel particles was obtained.

[0137] A magnet was arranged at the bottom of a beaker containing the dispersion liquid of the obtained nickel particles to attract the nickel particles to the magnet. In this state, the supernatant of the dispersion liquid was removed.

[0138] After removing the magnet from the bottom of the beaker, 50 g of pure water was added and the dispersion liquid was stirred for 10 minutes. Thereafter, the magnet was again arranged at the bottom of the beaker and the nickel particles were attracted to the magnet. In this state, the supernatant of the above dispersion liquid was removed. This series of operations was repeated 5 times.

[0139] Next, 50 g of methanol was added and the dispersion liquid was stirred for 10 minutes. The removal of the supernatant was repeated 3 times by using the magnet to replace the solvent in the dispersion liquid with methanol. Thereafter, vacuum drying was performed at 80°C to obtain a powder of the nickel particles.

[0140] [Comparative Example 2]

[0141] Bismuth chloride was added before performing the reduction reaction of the nickel hydroxide, and otherwise, the same operations as in Example 1 were performed to obtain nickel particles.

[0142] [Comparative Example 3]

[0143] A 500-ml beaker was charged with 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 an aqueous palladium nitrate solution (concentration: 100 g / 1) to prepare a mixed solution. The polyethyleneimine was a branched polyethyleneimine having a number average molecular weight of 1800. The mixed solution was heated while being stirred, and a reduction reaction was performed at 198°C for 6.5 hours. The heating was stopped to end the reduction, and the temperature was allowed to cool naturally to room temperature. In this manner, a large amount of nickel particles was obtained.

[0144] A magnet was arranged at the bottom of a beaker containing the dispersion liquid of the obtained nickel particles, and the nickel particles were attracted to the magnet. In this state, the supernatant of the above dispersion liquid was removed.

[0145] After removing the magnet from the bottom of the beaker, 50 g of pure water was added and the dispersion liquid was stirred for 10 minutes. Thereafter, the magnet was again arranged at the bottom of the beaker and the nickel particles were attracted to the magnet. In this state, the supernatant of the above dispersion liquid was removed. This series of operations was repeated 5 times.

[0146] After adding 300 g of pure water and hydrazine monohydrate to the dispersion liquid and warming to 60°C, 1 g of sodium stannate trihydrate was added, and stirring was performed for 5 hours to perform surface treatment of the nickel particles with tin.

[0147] A magnet was arranged at the bottom of a beaker containing the dispersion liquid of the obtained nickel particles, and the nickel particles were attracted to the magnet. In this state, the supernatant of the above dispersion liquid was removed.

[0148] After removing the magnet from the bottom of the beaker, pure water 50 g was added and the dispersion liquid was stirred for 10 minutes. After that, the magnet was again arranged at the bottom of the beaker and the nickel particles were attracted to the magnet. In this state, the supernatant of the above dispersion liquid was removed. This series of operations was repeated 5 times.

[0149] Next, methanol 50 g was added and the dispersion liquid was stirred for 10 minutes. The removal of the supernatant was repeated 3 times by using a magnet to replace the solvent in the dispersion liquid with methanol. After that, vacuum drying was performed at 80°C to obtain a powder of the nickel particles on which surface treatment by tin was performed. It was confirmed that the surface region of the nickel particles did not contain an alloy of nickel and tin, and a tin surface layer was formed, as described in [Evaluation 1] described later.

[0150] [Evaluation 1]

[0151] For the nickel particles obtained in Examples 1 to 9 and Comparative Examples 1 to 3, the values of X and X1 were found by the following XPS analysis method.

[0152] Further, the contents of the bismuth element, the copper element, the iron element, and the molybdenum element with respect to the entire nickel particles and the value of Y were found by ICP emission spectrometry.

[0153] Further, the particle size distribution was measured by the above method, and the particle diameter D 50 , the proportion of coarse particles, and the coefficient of variation were found.

[0154] Further, the a-axis length of nickel and the crystallite size Cs based on the WPPF method were found by the following method.

[0155] Further, it was confirmed whether or not an alloy of nickel and bismuth, whether or not an alloy of nickel and copper, whether or not an alloy of nickel and iron, and whether or not an alloy of nickel and molybdenum were contained in the surface region of the nickel particles, by the above method.

[0156] [X-ray photoelectron spectroscopy (XPS) measurement]

[0157] For the measurement target sample for XPS, a sample obtained by molding nickel particles into a pellet shape using a press machine was used. In detail, 10 mg or more of the particle sample was added to an aluminum container having dimensions of φ 5.2 mm and a height of 2.5 mm. Next, using a press machine (AS ONE, Model: 1-312-01) and an adapter (Model: 1-312-03), the aluminum container was pressurized with a prescribed stroke (25 mm). Next, the pellet-shaped product of the nickel particles supported by the aluminum container was taken out.

[0158] For the obtained pellet-shaped product, surface measurement and measurement in the depth direction from the surface of the sample toward the inside by sputtering using Ar monomer ions were performed. The measurement conditions were as follows.

[0159] • Measuring apparatus: VersaProbeIII manufactured by ULVAC-PHI Corporation

[0160] • Excitation X-rays: Monochromatic Al-Kα rays (1486.7 eV)

[0161] • Output power: 50W

[0162] Accelerating voltage: 15kV

[0163] • X-ray irradiation diameter: 200 μm φ

[0164] X-ray scanning area: 1000μm × 300μm

[0165] • Detection angle: 45°

[0166] • Bandpass energy: 26.0 eV

[0167] • Energy step size: 0.1 eV / step

[0168] Sputtered ion species: Ar monomeric ions

[0169] Sputtering rate: 3.3 nm / min (SiO2 conversion)

[0170] Sputtering interval: 20s

[0171] • Element to be determined: C 1s Ni 2p3 Sn 3d5 Bi 4f Cu 2p Fe 3p Mo 3d

[0172] • Energy correction value: C 1s CC and CH bonds (284.8 eV)

[0173] [Analysis of XPS data]

[0174] XPS data was analyzed using data parsing software (ULVAC-PHI's "MultiPak Ver9.9"). Shirley was used for the background mode.

[0175] [The value of X]

[0176] In Examples 1-6, Bi was used. 4f The number of atoms relative to Ni 2p3 with Bi 4f The ratio of the total number of atoms of the two elements is set as X (at%). In Example 7, Cu...2p The number of atoms relative to Ni 2p3 With Cu 2p The ratio of the total number of atoms of the two elements is set as X (at%). In Example 8, Fe... 3p The number of atoms relative to Ni 2p3 with Fe 3p The ratio of the total number of atoms of the two elements is set as X (at%). In Example 9, Mo is... 3d The number of atoms relative to Ni 2p3 with Mo 3d The proportion of the total number of atoms of the two elements is set as X (at%).

[0177] [Determination of a-axis length and crystallite size Cs]

[0178] The a-axis length and crystallite size Cs of the nickel particles obtained in the examples and comparative examples were calculated using the WPPF method based on the diffraction peaks derived from nickel obtained by X-ray diffraction.

[0179] Device name: SmartLab (9KW); manufactured by Rigaku Corporation.

[0180] <Device Composition>

[0181] wavelength

[0182] Target: Cu

[0183] Wavelength type: Kα1

[0184] ·Kα1:

[0185] ·Kα2:

[0186] ·Kβ:

[0187] Kα12 intensity ratio: 0.4970

[0188] Horizontal polarization: 0.500

[0189] Diffraction device

[0190] • Goniometer: SmartLab

[0191] • Accessory base: Z-axis stage (separate)

[0192] Accessories: ASC6-Reflector

[0193] <Measurement Conditions>

[0194] Optical system properties: Lumped method

[0195] • CBO selection slit: BB

[0196] • Incident parallel slit: Soller_slit_5.0deg

[0197] • Incident slit: 2 / 3deg

[0198] • Length limit slit: 10.0mm

[0199] • Light receiving slit 1: 20.000mm

[0200] • Light receiving parallel slit: Soller_slit_5.0deg

[0201] • Light receiving slit 2: 20.000mm

[0202] • Attenuator: ON

[0203] • Detector: D / teX Ultra250

[0204] • Scan axis: 2theta / theta

[0205] • Scan mode: Continuous

[0206] • Scan range: 5.0000~140.0000deg

[0207] • Step: 0.0100deg

[0208] • Scan speed / measurement time: 2.015572deg / min

[0209] • Number of data points: 13501 points

[0210] • Tube voltage: 45kV

[0211] • Tube current: 200mA

[0212] • HV: 0.00

[0213] Preparation of a sample for X-ray diffraction

[0214] The nickel particles to be measured were spread over a measurement holder, and smoothing was performed using a glass plate so that the thickness of the layer formed by the nickel particles would be 0.5 mm and the measurement surface would be smooth.

[0215] The X-ray diffraction pattern obtained using the measurement conditions described above was analyzed using analysis software under the following conditions. In the analysis, correction was performed using data obtained from a standard substance, lanthanum hexaboride powder (SRM660 series), provided by the National Institute of Standards and Technology (NIST). The a-axis length and crystallite size Cs were calculated using the WPPF method.

[0216] <Measurement data analysis conditions>

[0217] • Analysis software: PDXL2 (Rigaku Corporation)

[0218] • Analysis method: WPPF method

[0219] • Data processing: Automatic profile processing

[0220] (Rigaku Corporation PDXL User's Guide p. 305)

[0221] 〔Evaluation 2〕

[0222] The shrinkage start temperature of the nickel particles, the resistivity of the sintered film containing the nickel particles, and the surface roughness Rz of the sintered film were measured by the following methods for the nickel particles obtained in Examples 1 to 9 and Comparative Examples 1 to 3. The results are shown in Table 1 below.

[0223] 〔Measurement of shrinkage start temperature〕

[0224] As the measuring device of TMA, TMA / SS6000 (Seiko Instruments Inc.) was used. 0.2 to 0.3 g of the nickel particles were put in a mold container made of stainless steel having a diameter of 5.0 mm, and a granule was produced by pressure molding in such a manner that a pressure of 92 MPa was applied to the nickel particles. The length of the granule obtained was measured, and the granule was used as a sample for measurement. The sample was set in the measuring device, and the sample was heated at 5°C / min under a load of 49 mN and an atmosphere of 1 vol% hydrogen / 99 vol% nitrogen. The measurement was started from room temperature (25°C), and a graph showing the relationship between the temperature and the shrinkage rate (%) was obtained. The shrinkage start temperature was calculated from the obtained graph.

[0225] 〔Measurement of resistivity〕

[0226] 0.1 g of ethyl cellulose was dissolved in 4 g of terpineol, and then 5 g of the nickel particles were added to obtain a mixture. The mixture was mixed using a rotation and revolution stirrer ("awatori rentaro (registered trademark)" (THINKY Co., Ltd.)). Then, the mixture was crushed in a three-roll mill for 4 times. The gap of the three-roll mill was set to 8 μm. The coating liquid was obtained by such operations.

[0227] The coating liquid was applied to an alumina substrate to form a coating film. The thickness of the coating film was 30 μm. The coating film was sintered at 800°C for 60 minutes in an atmosphere of 1 vol% hydrogen / 99 vol% nitrogen to obtain a sintered film. For the sintered film, the specific resistance (Ω-cm) was measured using Loresta MCP-T600 manufactured by Mitsubishi Analytech Co., Ltd. as a four-probe method specific resistance measuring device.

[0228] [Measurement of surface roughness Rz]

[0229] SURFCOM 130A was used to measure the surface roughness Rz of the above-described sintered film. The measurement conditions were set to an evaluation length of 6.0 mm and a measurement speed of 0.6 mm / s.

[0230] [Table 1]

[0231]

[0232] As indicated by the results shown in Table 1, it was confirmed by the measurement by XPS that the nickel particles obtained in Examples 1 to 9 contained the bismuth element, the copper element, the iron element, or the molybdenum element in the surface region thereof in a metallic state. Further, the a-axis length of the nickel particles obtained in the Examples was elongated as compared with the a-axis length of the nickel particles obtained in Comparative Example 1 which did not use the compounds of the bismuth element, the copper element, the iron element, and the molybdenum element. From these results, it was learned that the nickel particles obtained in Examples 1 to 6 contained an alloy of nickel and bismuth in the surface region thereof. In addition, it was learned that the nickel particles obtained in Example 7 contained an alloy of nickel and copper in the surface region thereof. In addition, it was learned that the nickel particles obtained in Example 8 contained an alloy of nickel and iron in the surface region thereof. In addition, it was learned that the nickel particles obtained in Example 9 contained an alloy of nickel and molybdenum in the surface region thereof.

[0233] In addition, as indicated by the results shown in Table 1, the nickel particles obtained in Examples 1 to 9 exhibited a high shrinkage start temperature as compared with the nickel particles obtained in Comparative Examples 1 to 3. From this, it was learned that the nickel particles obtained in Examples 1 to 9 exhibited a high sintering resistance.

[0234] In particular, as indicated by the comparison between Examples 1 to 5 and Example 6, it was learned that by controlling the amount of bismuth contained in the nickel particles, the specific resistance of the sintered film obtained from the nickel particles could be controlled.

[0235] In addition, the surface of the sintered film became smooth in Examples 1 to 6 which produced nickel particles having a surface region in which an alloy of nickel and bismuth was formed, as compared with Comparative Example 2 in which an alloy of nickel and bismuth was formed in the entire nickel particles. From these, it was learned that according to the nickel particles having a surface region containing an alloy of nickel and bismuth, the surface roughness of the sintered film was reduced.

[0236] Industrial applicability

[0237] According to the present application, nickel particles having high resistance to sintering can be provided without excessively increasing the resistance.

Claims

1. A nickel particle having a surface region comprising an alloy of nickel and metallic element M, The metallic element M is selected from at least one of bismuth, copper, iron, and molybdenum. The content of the metallic element M relative to the total amount of the nickel particles is 0.09% to 15.8% by mass. When measuring the region from the outermost surface to a sputtering depth of 5 nm (converted to SiO2) in the depth direction of the nickel particles by X-ray photoelectron spectrometry, the maximum value of the ratio of the number of atoms of metal element M to the total number of atoms of nickel and metal element M in this region, expressed as at%, is set as X. When measuring the nickel particles by ICP emission spectrometry, the ratio of the number of atoms of metal element M to the total number of atoms of nickel and metal element M, expressed as at%, is set as Y, and the value of X / Y is 0.5 to 35.

2. The nickel particles according to claim 1, wherein, In the particle size distribution based on the equivalent circle diameter calculated using scanning electron microscopy, the number-cumulative particle size at a cumulative number of 50% is set as D. 50 At that time, D 50 The range is 20nm to 200nm. When the standard deviation of the particle size in the particle size distribution is set to σ in nm, the coefficient of variation (σ / D) 50 The value is below 14%. Variation coefficient (%) = (σ / D) 50 )×100%.

3. The nickel particles according to claim 1, wherein, In the particle size distribution based on the equivalent circle diameter calculated using scanning electron microscopy, the number-cumulative particle size at a cumulative number of 50% is set as D. 50 At that time, having D 50 The proportion of particles with a diameter greater than 1.5 times that of the particle size is less than 0.5%.

4. The nickel particles according to claim 1, wherein, In the particle size distribution based on the equivalent circle diameter calculated using scanning electron microscopy, the number-cumulative particle size at a cumulative number of 50% is set as D. 50 When the crystallite size measured by the WPPF method is set to Cs in nm, Cs / D 50 The value is 0.3 to 0.

6.

5. A method for manufacturing nickel particles according to any one of claims 1 to 4, wherein nickel particles are manufactured by heating a mixture comprising nickel hydroxide particles, a polyol, polyvinylpyrrolidone, and polyethyleneimine. Relative to 1 part by weight of polyethyleneimine, use 30 to 200 parts by weight of polyvinylpyrrolidone. The nickel hydroxide particles are reduced to nickel parent particles by heating. With a portion of the nickel hydroxide particles remaining, the mixture is mixed with a compound of metallic element M, reducing the compound to metallic M, thus forming a surface region on the nickel parent particles that contains an alloy of nickel and metallic element M. The metallic element M is selected from at least one of bismuth, copper, iron and molybdenum.

6. A multilayer ceramic capacitor, wherein nickel particles according to any one of claims 1 to 4 are used in the internal electrodes.

Images