Nickel particles and methods for manufacturing nickel particles

Abstract

A nickel particle having a surface region comprising an alloy of nickel and a metallic element M. The metallic element M is selected from at least one of tin and zinc. The content of metallic element M relative to the total nickel particle is 0.16% to 11.4% 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 particle by X-ray photoelectron spectrophotometry, the maximum value of the ratio of the number of atoms of metallic element M to the total number of atoms of nickel and metallic element M in this region is set as X (at%). When measuring the nickel particle by ICP-luminescence spectrophotometry, the ratio of the number of atoms of metallic element M to the total number of atoms of nickel and metallic element M is set as Y (at%), and the value of X / Y is 1.5 to 30.

Description

Technical Field

[0001] This invention relates to nickel particles and methods for manufacturing the same. Background Technology

[0002] Nickel particles are generally used in the formation of the internal electrodes of multilayer ceramic capacitors (MLCCs) used in electronic devices. During the manufacturing of MLCCs, when the laminate containing the nickel particles and the dielectric layer are sintered simultaneously, defects may occur in the internal electrodes due to differences in the sintering temperatures of the raw materials. To prevent such defects, it is necessary to improve the sintering resistance of the nickel particles.

[0003] For example, Patent Document 1 discloses a technique for using nickel powder containing tin or zinc, obtained by PVD or CVD, to form the internal electrodes of MLCCs. This document describes how adding non-magnetic metals such as tin to the nickel powder distorts the crystal structure of the nickel, thereby increasing the sintering temperature of the nickel powder.

[0004] Patent Document 2 discloses a technique for forming internal electrodes of MLCCs using nickel powder with a generally spherical particle shape and surface-treated with tin. Furthermore, this document also discloses the use of zinc for surface treatment in addition to tin. The document states that the sintering behavior of the nickel powder described herein is improved.

[0005] Existing technical documents

[0006] Patent documents

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

[0008] Patent Document 2: Japanese Patent Application Publication No. 2018-104819 Summary of the Invention

[0009] However, with the increasing performance of electronic devices in recent years, there is a growing demand to further prevent defects in the internal electrodes of MLCCs. To meet this requirement, it is desirable not only to further improve the sintering resistance of nickel particles, but also to avoid excessively increasing the resistance of the electrodes when using nickel particles to form internal electrodes.

[0010] Therefore, the objective of this invention is to provide nickel particles with high sintering resistance without excessively increasing resistance.

[0011] This invention provides a nickel particle having a surface region comprising an alloy containing nickel and the metallic element M.

[0012] The aforementioned metallic element M is selected from at least one of tin and zinc.

[0013] The content of the aforementioned metallic element M relative to the total content of the aforementioned nickel particles is 0.16% to 11.4% by mass.

[0014] 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 is set as X (at%). 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 is set as Y (at%), and the value of X / Y is 1.5 to 30.

[0015] Furthermore, this invention provides a method for manufacturing nickel particles, which involves heating a mixture comprising nickel hydroxide particles, polyol, polyvinylpyrrolidone, and polyethyleneimine to produce nickel particles.

[0016] Relative to 1 part by weight of polyethyleneimine, use 30 to 200 parts by weight of polyvinylpyrrolidone.

[0017] The nickel hydroxide particles are reduced to nickel parent particles by the above heating process.

[0018] With some of the aforementioned 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 containing an alloy of nickel and metallic element M on the nickel parent particles.

[0019] The aforementioned metallic element M is selected from at least one of tin and zinc. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope image of the nickel particles obtained in Example 3.

[0021] Figure 2 This is a scanning electron microscope image of the nickel particles obtained in Comparative Example 2. Detailed Implementation

[0022] The present invention will now be described based on its preferred embodiments. The nickel particles of the present invention have nickel parent particles and a surface region on the surface of the parent particles comprising an alloy containing nickel and metallic element M (hereinafter also referred to as "nickel / metallic M alloy"). In this specification, "nickel parent particle" refers to a particle substantially composed of nickel element and containing unavoidable elements in the remaining portion. Unavoidable elements include, for example, oxygen from the atmosphere, oxygen from carbon dioxide, carbon, and nitrogen element that may be introduced during the manufacturing process of the nickel particles.

[0023] The nickel parent particles in the nickel particles have a surface region comprising a nickel / metal M alloy on their surface. In this specification, "nickel / metal M alloy" refers to a nickel-based alloy comprising the metallic element M, as described later. The nickel / metal M alloy is substantially composed of an alloy of nickel and metallic element M, and inevitably contains other elements in the remainder. In the surface region comprising the nickel / metal M alloy, a portion of metallic element M may exist in its elemental state (i.e., in a metallic state). Alternatively, a portion of metallic element M may exist in its compound state. Alternatively, metallic element M may exist in a combination of two or more states. When metallic element M exists in the surface region comprising the nickel / metal M alloy in the state of a compound of metallic element M, examples of such compounds include, but are not limited to, oxides, hydroxides, sulfides, sulfur oxides, borides, phosphides, etc., containing metallic M. In particular, it is preferable from the viewpoint of maximizing the inherent advantages of the nickel particles of the present invention that the metallic element M in the surface region comprising the nickel / metal M alloy substantially comprises only an alloy with nickel. In this specification, "substantially contains only alloys with nickel" means the following: intentionally excluding the aforementioned surface areas from containing metallic element M other than alloys with nickel, and allowing trace amounts of elemental or compound metallic element M that are inevitably mixed in during the manufacturing process of nickel particles.

[0024] The metallic element M in the nickel particles is preferably selected from at least one of tin and zinc. By using tin or zinc as the metallic element M, the sintering resistance can be further improved without excessively increasing the resistivity of the nickel particles. The metallic element M can be either tin or zinc, or both. In the following description, when referring to the metallic element M (or metal M), it means tin or zinc, or both, depending on the context.

[0025] The presence of nickel / metal M alloy in the surface area of ​​nickel particles can be confirmed by the following methods.

[0026] Specifically, firstly, X-ray photoelectron spectrophotometry (hereinafter also referred to as "XPS") was used to confirm that the nickel particles contained a metallic element M in their surface region, and that this metallic element M was primarily in a metallic state. Next, it was confirmed that the a-axis length of the X-ray diffraction peaks of the aforementioned nickel particles was elongated compared to the a-axis length of the X-ray diffraction peaks obtained from prior measurements of only the nickel particles. This elongation of the a-axis length in the X-ray diffraction peaks indicates that the substance has undergone solid solution. Therefore, based on the confirmation by XPS that the metallic element M exists in a metallic state in the surface region of the nickel particles, and based on the confirmation by the comparison of the a-axis lengths that the metallic element M has undergone solid solution with nickel, it can be confirmed that the nickel particles contain a nickel / metal M alloy in their surface region.

[0027] The proportion of metallic element M contained in the surface region of nickel particles can be determined by XPS. Specifically, 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 (hereinafter referred to as the "particle surface region") by XPS, the maximum value of the ratio of the number of atoms of metallic element M to the total number of atoms of nickel and metallic element M in this particle surface region, i.e., the value of X, is preferably 0.5 at% or more. The aforementioned "maximum value" refers to the maximum value of the value of X among multiple different values ​​measured along the thickness direction of the particle surface region. The presence of metallic element M with a value of X of 0.5 at% or more is preferred from the viewpoint of further improving the sintering resistance of the nickel particles described later. From the same viewpoint, the value of X (at%) is more preferably 0.5 at% or more, more preferably 1 at% or more, and even more preferably 2 at% or more. Furthermore, from the same viewpoint, the value of X (at%) is more preferably 70 at% or less, more preferably 30 at% or less, and even more preferably 20 at% or less. The method for determining the value of X will be described in the examples described later.

[0028] The term "outermost surface of nickel particles" as used above refers to the outermost part of the nickel particles containing surface treatment agents such as organic acids or amines, when such agents are present on the surface of the nickel particles. When no surface treatment agent is present on the surface of the nickel particles, it refers to the surface of the particles themselves.

[0029] The nickel particles preferably contain 0.16% to 11.4% by mass of metallic element M relative to the total nickel particles. By maintaining the content of metallic element M within this range relative to the nickel particles, the sintering resistance can be further improved without excessively increasing the resistivity of the nickel particles.

[0030] When the metallic element M is tin, from the same perspective as above, the tin content relative to the total nickel particles is more preferably 0.3% by mass or more, more preferably 0.4% by mass or more, and even more preferably 1% by mass or more. Furthermore, the tin content relative to the total nickel particles is more preferably 6% by mass or less.

[0031] When the metallic element M is zinc, from the same perspective as above, the zinc content relative to the total nickel particles is more preferably 0.2% by mass or more, more preferably 0.4% by mass or more, and even more preferably 0.5% by mass or more. Furthermore, the zinc content relative to the total nickel particles is more preferably 6.7% by mass or less, and more preferably 3.4% by mass or less.

[0032] The content of metallic element M relative to the total nickel particles can be determined by ICP luminescence spectrophotometry, which will be described later.

[0033] The nickel particles of the present invention are provided with the condition that the content of metallic element M relative to the total amount of nickel particles meets the above-mentioned range. In this total amount of nickel particles, the ratio (at%) of the number of atoms of metallic element M to the total number of atoms of nickel and metallic element M is preferably 0.15 at% to 6 at%. The presence of metallic element M with a Y value within this range is preferred from the viewpoint of further improving the sintering resistance without excessively increasing the resistivity of the nickel particles. From the same viewpoint, the value of Y is particularly preferred to be 0.2 at% or more, especially preferably 0.5 at% or more. Furthermore, the value of Y is particularly preferred to be 6 at% or less, especially preferably 3 at% or less.

[0034] 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 (118.7 for tin and 65.4 for zinc) to convert this percentage 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.

[0035] The inventors of this invention have determined that the relationship between the values ​​of X and Y affects the sintering resistance of nickel particles. Specifically, it has been determined that by setting the X / Y value to 1.5 to 30, the temperature at which the nickel particles begin to shrink during sintering increases, i.e., the sintering resistance increases. When the nickel particles of this invention, with their high sintering resistance, are used to manufacture, for example, MLCCs, the temperature at which the internal electrode shrinks due to the sintering of the nickel particles is as close as possible to the temperature at which the dielectric layer shrinks due to the sintering of the dielectric particles during the firing process, as a manufacturing step. Reducing the temperature difference between the shrinkage of the internal electrode and the dielectric layer is advantageous from the perspective of minimizing the overlap in the shrinkage time of the internal electrode and the dielectric layer during the heating process of the firing process. Specifically, in the firing process of MLCCs, it is advantageous from the viewpoint that structural defects such as cracks and delamination (interlayer peeling at the interface between the internal electrode and the dielectric layer) caused by the difference in temperature and shrinkage rate of the internal electrode and the dielectric layer can be effectively prevented.

[0036] From the viewpoint of further highlighting the above advantages, the X / Y value in the nickel particles is more preferably 3.7 or higher. Furthermore, the X / Y value in the nickel particles is more preferably 20 or lower, more preferably 15 or lower, even more preferably 13 or lower, and even more preferably 10 or lower.

[0037] In the particle surface region, the ratio of the number of atoms of metal element M to the total number of atoms of nickel and metal element M can be constant or variable in the depth direction. If the ratio is not constant in the depth direction, it can decrease continuously or stepwise from the surface of the nickel particle towards the center. In particular, when measuring the region from the outermost surface of the nickel particle to a sputtering depth of 20 nm (converted to SiO2) using XPS, the decrease in the ratio from the outermost surface towards the sputtering depth of 20 nm is preferable from the perspective of further improving the sintering resistance of the nickel particle. In this case, when the maximum value of the ratio in the region from the outermost surface of the nickel particle to a sputtering depth of 5 nm is set as X, and the maximum value of the ratio at a sputtering depth of 20 nm is set as X1, a value of X / X1 of 3.0 to 15 is preferable from the perspective of further improving the sintering resistance of the nickel particle. From the same viewpoint, a value of X / X1 of 3.8 or higher is more preferable, and even more preferable is 4.3 or higher. Furthermore, the value of X / X1 is more preferably 10 or less, more preferably 7.8 or less, and even more preferably 6.1 or less. The method for measuring X1 will be described in the examples described later.

[0038] Regarding the value of X1 itself, from the viewpoint of further improving the sintering resistance of nickel particles, it is preferably 0.2 to 10, more preferably 0.5 to 6, even more preferably 0.7 to 4.1, and even more preferably 1.7 to 4.1.

[0039] The cumulative particle size D of the nickel particles in this invention is calculated when the cumulative number of nickel particles is 50%. 50 The preferred value is 20 nm to 200 nm. In other words, the nickel particles of the present invention are preferably microparticles. The particle size D of the nickel particles is determined by... 50 Within this range, the nickel particles of the present invention, when used as internal electrodes in various applications such as MLCCs, have the advantage of becoming less prone to short circuits between these internal electrodes. From the viewpoint of further enhancing this advantage, the particle size D of the nickel particles... 50 More preferably, the particle size is 20nm–170nm; even more preferably, 20nm–150nm; further preferably, 40nm–150nm; and even more preferably, 40nm–100nm. The particle size D of the nickel particles... 50 The determination was performed by observing the nickel particles using a scanning electron microscope (SEM). Specifically, the nickel particles were photographed using the SEM at a magnification of 50,000, and the area of ​​the photographed nickel particles was calculated. The equivalent circle diameter was calculated from this area. Based on the calculated equivalent circle diameter, the particle size distribution was determined. The particle size distribution is plotted with the equivalent circle diameter on the horizontal axis and the frequency of occurrence on the vertical axis. In the particle size distribution curve obtained through this operation, the cumulative number of particles at 50% of the total number of particles is defined as D. 50 .

[0040] When obtaining the aforementioned "particle size distribution curve," the equivalent circle diameter was calculated for more than 5000 nickel particles. The equivalent circle diameter was calculated using image analysis particle size distribution measurement software (Mac-View, manufactured by MOUNTECH Co., Ltd.). The smallest unit of the nickel particle being observed was determined by whether a particle interface, identified as a single particle, was observed using SEM. Therefore, even if an agglomerate containing multiple particles was observed, if a particle interface was observed within that agglomerate, the area defined by that particle interface was considered a single particle.

[0041] Preferably, the nickel particles of the present invention are not only microparticles, but also have a low proportion of coarse particles. When the nickel particles of the present invention are used, for example, as internal electrodes in MLCCs, the presence of coarse particles can potentially cause short circuits between these internal electrodes. By reducing the proportion of coarse particles in the nickel particles, this short circuit can be effectively prevented. From this viewpoint, the nickel particles of the present invention have a D... 50The proportion of particles with a diameter of 1.5 times or more (hereinafter also referred to as "the proportion of coarse particles") is preferably 0.5% or less, more preferably 0.3% or less, and even more preferably 0.1% or less.

[0042] The closer the proportion of coarse particles is to 0%, the more effective it is in preventing short circuits between internal electrodes. However, as long as the proportion of coarse particles is as low as about 0.01%, it can effectively prevent short circuits between internal electrodes.

[0043] Selected as the scale for coarse particles, having D 50 The reason for the particles having a diameter more than 1.5 times that of the present invention is that the inventors of the present invention discovered that: in D 50 When the particle size is more than 1.5 times larger, it becomes one of the reasons why the surface of the conductive film becomes rough during the formation of the conductive film, which is closely related to the short circuit between the internal electrodes of the MLCC.

[0044] The nickel particles of this invention preferably have a low proportion of microparticles and coarse particles, and also exhibit the most uniform particle size. In other words, the particle size distribution curve is preferably sharp. The sharpness of the particle size distribution curve can be evaluated by the coefficient of variation of the particle size. The coefficient of variation is calculated by using (σ / D) when the standard deviation of the particle size in the particle size distribution is set to σ (nm). 50 The value is defined as ()×100 (%). The fact that the variation coefficient of the nickel particles in this invention is 14% or less is preferred from the viewpoint of reducing the surface roughness of the conductive film formed by these nickel particles. From the viewpoint of further reducing the surface roughness of the conductive film, the variation coefficient is more preferably 13% or less, and even more preferably 12% or less.

[0045] The closer the variation coefficient is to 0%, the more it helps to reduce the surface roughness of the conductive film. However, as long as the variation coefficient is as low as about 8%, the surface roughness of the conductive film can be reduced to the level that should be fully satisfied.

[0046] The nickel particles of the present invention preferably have high nickel crystallinity. High nickel crystallinity means that the nickel particles of the present invention begin to shrink during sintering. In other words, high nickel crystallinity means that, as described above, the nickel particles exhibit high sintering resistance.

[0047] The crystallinity of nickel is determined by the crystallite size Cs (nm) relative to the grain size D. 50 The ratio of (nm) is Cs / D 50 The evaluation method is frequently used in the field of metal powder technology. (Cs / D) 50 The higher the Cs / D value, the higher the crystallinity of nickel can be evaluated. From this perspective, in the nickel particles of this invention, Cs / D... 50The value is preferably 0.3 or higher, more preferably 0.34 or higher, and even more preferably 0.37 or higher.

[0048] Cs / D 50 The higher the value of Cs / D, the higher the temperature at which nickel particles begin to shrink during sintering. However, in this invention, as long as Cs / D... 50 The optimal value for Cs / D is below 0.6, which is sufficient to significantly increase the temperature. From this perspective, Cs / D 50 The value is more preferably 0.55 or less, and even more preferably 0.52 or less.

[0049] Regarding the value of the crystallite size Cs itself, from the viewpoint of fully increasing the temperature at which nickel particles begin to shrink during sintering, it is preferably 15 nm to 70 nm, more preferably 18 nm to 70 nm, and even more preferably 20 nm to 70 nm.

[0050] Various methods are known in the field of metal powder technology for measuring crystallite size, but the crystallite size referred to in this specification is the value obtained by measurement using the WPPF (whole powder pattern fitting) method. Besides the WPPF method, the Scherrer method is also known for measuring crystallite size; however, when the degree of crystal distortion is large, the crystallite size value obtained based on the Scherrer method becomes unreliable. Therefore, the WPPF method, which has fewer concerns, is used in this invention.

[0051] Details of the method for determining the crystallite size of nickel based on the WPPF method will be described in the examples described later.

[0052] The nickel particles of the present invention preferably do not excessively increase resistance. When such nickel particles are used, for example, as internal electrodes of MLCCs, the performance of the MLCC can be further improved. Therefore, to avoid excessively increasing resistance, it is preferable to control the crystal structure of the nickel particles in a manner that increases the pure nickel content in nickel particles having a surface region comprising a nickel / metal M alloy. From this viewpoint, in the nickel particles of the present invention, the a-axis length of the crystal lattice in the nickel crystal structure is preferably... More preferably Further preferred

[0053] The a-axis length of the crystal lattice in the crystal structure of nickel particles can be determined using an X-ray diffraction apparatus employing CuKα1 rays, as described in the embodiments described later. For analytical determination, it is obtained using the WPPF method, as described in the embodiments described later.

[0054] The crystallite size and a-axis length of the crystal lattice in the nickel crystal structure of the present invention are achieved, for example, by adjusting the proportion of metallic element M contained in the surface region of the nickel particles and reducing the thickness of the surface region containing the nickel / metal M alloy of the nickel particles. Alternatively, they can be achieved by appropriately adjusting the conditions in the nickel particle manufacturing method described later.

[0055] The degree of sintering resistance of the nickel particles of the present invention can be evaluated using these nickel particles as the object and through thermomechanical analysis (TMA). In the present invention, the temperature at which the TMA shrinkage rate (%) based on room temperature (25°C) reaches 5% is defined as the shrinkage initiation temperature. It is preferable that this temperature is 500°C or higher from the viewpoint of further improving the sintering resistance of the nickel particles. From the viewpoint of making this advantage even more significant, 530°C or higher is more preferred, 550°C or higher is even more preferred, and 570°C or higher is even more preferred.

[0056] Next, a preferred method for manufacturing the nickel particles of the present invention will be described. In this manufacturing method, the nickel particles are manufactured by a so-called polyol method. The polyol method refers to a method that uses a polyol as a solvent that also acts as a reducing agent. In the polyol method, a reduction reaction to nickel master particles is generated by heating the polyol in a state where nickel is present in the chemical species. Before the reduction reaction is completed, a compound of metal element M is mixed in, and further heating is performed to generate a reduction reaction to metal M, thereby forming a surface region containing a nickel / metal M alloy on the nickel master particles.

[0057] In this manufacturing method, the use of nickel hydroxide as the chemical species for generating nickel particles is preferred from the viewpoint of successfully obtaining the target nickel particles. Nickel hydroxide is added to a mixture containing a polyol, polyvinylpyrrolidone (hereinafter also referred to as "PVP"), and polyethyleneimine (hereinafter also referred to as "PEI"). From an operability point of view, nickel hydroxide in a particulate form is preferred.

[0058] The polyol contained in the mixture is used as a solvent as described above and also as a reducing agent for nickel hydroxide.

[0059] Examples of polyols that can be used include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, dipropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, and polyethylene glycol. These polyols can be used alone or in combination of two or more. Ethylene glycol is preferred among these polyols because it has a high proportion of hydroxyl groups relative to its molecular weight, resulting in high reducing properties. Furthermore, it is liquid at room temperature and has excellent workability.

[0060] If the amount of polyol used is considered from the perspective of its use as a reducing agent, it can be adjusted appropriately according to the amount of nickel hydroxide in the mixture, so there is no need to set special limits. On the other hand, if it is intended to function as a solvent, since the properties of the mixture change depending on the concentration of the polyol in the mixture, there is a certain appropriate concentration range. From this point of view, the concentration of the polyol in the mixture is preferably set in the range of 50% by mass to 99.8% by mass.

[0061] PVP is used as a dispersant for nickel hydroxide. PVP is preferred because it is highly effective as a dispersant, sharpening the particle size distribution of nickel particles generated by reduction. The molecular weight of these PVPs can be appropriately adjusted according to their water solubility and dispersing ability. The amount of PVP in the mixture is preferably set to 0.01 to 30 parts by mass relative to 100 parts by mass of nickel converted from nickel hydroxide. By setting it within this range, sufficient dispersion effect can be achieved without excessively increasing the viscosity of the mixture.

[0062] PEI has the following function: during the formation of nickel nuclei in the mixture, it reduces the number of nickel ions in the mixture, so that nucleation and nucleus growth do not occur simultaneously. This is because: (a) PEI has non-covalent electron pairs that interact with nickel ions, enabling it to coordinate with them; (b) PEI has a large number of these non-covalent electron pairs; and (c) PEI has hydrogen bond sites that can interact with the surface of nickel hydroxide present in an undissolved state in the mixture.

[0063] By including PEI in the mixture, nickel nucleation and the growth of the generated nuclei can proceed sequentially. As a result, fine nickel particles with uniform particle size can be successfully obtained. In contrast, in conventional reduction-based nickel particle manufacturing, coarse particles are easily generated and particle size inhomogeneity tends to occur because nucleation and nucleus growth occur simultaneously.

[0064] From the above perspective, it is advantageous to use branched PEI compared to linear PEI. Similarly, it is preferred to use PEI with a number-average molecular weight of 600–10000, particularly preferred to use PEI with a number-average molecular weight of 800–5000, and especially preferred to use PEI with a number-average molecular weight of 1000–3000.

[0065] In particular, in this manufacturing method, by setting the ratio of PVP to PEI in the mixture to a specific range, the sequential generation and growth of nickel nuclei become reliable. Specifically, relative to 1 part by mass of PEI, it is preferable to use 30 to 200 parts by mass of PVP, more preferably 40 to 150 parts by mass of PVP, and even more preferably 50 to 130 parts by mass of PVP.

[0066] The amount of PEI in the mixture is appropriately set based on the PVP amount, provided that the ratio of PVP to PEI meets the above-mentioned range.

[0067] The mixture can also contain a noble metal catalyst. This allows for the formation of fine nuclei of the noble metal in the initial stages of reduction, providing a starting point for the smooth reduction of nickel. Noble metal catalysts can be, for example, water-soluble salts of noble metals or other noble metal compounds. Examples of water-soluble salts of noble metals include water-soluble salts of palladium, silver, platinum, and gold. When using palladium as the noble metal, palladium chloride, palladium nitrate, palladium acetate, and ammonium palladium chloride can be used. When using silver, silver nitrate, silver lactate, silver oxide, silver sulfate, silver cyclohexanoate, and silver acetate can be used. When using platinum, platinum chloride, potassium platinum chloride, and sodium platinum chloride can be used. When using gold, auric acid chloride and sodium auric acid chloride can be used. Palladium nitrate, palladium acetate, silver nitrate, and silver acetate are preferred due to their low cost and economic efficiency. The noble metal catalyst can be added in the form of the aforementioned compounds or in the form of an aqueous solution obtained by dissolving the compound in water. The amount of noble metal catalyst contained in the mixture is preferably 0.01 to 5 parts by mass relative to 100 parts by mass of nickel (converted to nickel), and particularly preferably 0.01 to 1 part by mass.

[0068] The mixture containing the above components is heated while being stirred to reduce nickel hydroxide. Although the heating temperature varies depending on the type of polyol used, heating at atmospheric pressure, preferably at 150°C to 200°C, more preferably at 170°C to 200°C, and even more preferably at 190°C to 200°C, ensures the smooth reduction of nickel hydroxide to nickel masterbatch.

[0069] Next, before the reduction reaction of nickel hydroxide is completed, a compound of metal element M is mixed into the above mixture. In other words, the compound of metal element M is mixed into the above mixture with a portion of nickel hydroxide remaining. Here, "before the reduction reaction of nickel hydroxide is completed" means before 80 mol% or more of the added nickel hydroxide is reduced. When metal element M is tin, from the viewpoint of smoothly forming a surface region containing a nickel / metal M alloy on the nickel parent particles in the reduction reaction of the compound of metal element M described later, at least one selected from sodium stannate trihydrate, tin(II), and tin(IV) chloride is preferably used as the compound, and sodium stannate trihydrate is particularly preferred. Furthermore, when metal element M is zinc, from the same viewpoint as above, at least one selected from zinc sulfate, zinc nitrate, zinc chloride, zinc hydroxide, and zinc oxide is preferably used as the compound, and zinc hydroxide is particularly preferred.

[0070] When the metallic element M is tin, from the viewpoint of smoothly forming a surface region containing an alloy of nickel and tin on the nickel master particles, it is preferable that the amount of tin compound in the mixture, converted to tin, is set to 0.016 parts by mass or more, more preferably 0.003 parts by mass or more, even more preferably 0.004 parts by mass or more, and even more preferably 0.01 parts by mass or more, relative to 1 part by mass of nickel added. Furthermore, it is preferable that the amount of tin compound in the mixture, converted to tin, is set to 0.12 parts by mass or less, more preferably 0.06 parts by mass or less, relative to 1 part by mass of nickel added.

[0071] When the metallic element M is zinc, from the viewpoint of smoothly forming a surface region containing an alloy of nickel and zinc on the nickel master particles, it is preferable that the amount of zinc compound in the mixture, converted into zinc, is set to 0.016 parts by mass or more, more preferably 0.002 parts by mass or more, even more preferably 0.004 parts by mass or more, and even more preferably 0.005 parts by mass or more, relative to 1 part by mass of nickel added. Furthermore, it is preferable that the amount of zinc compound in the mixture, converted into zinc, is set to 0.12 parts by mass or less, more preferably 0.070 parts by mass or less, and even more preferably 0.034 parts by mass or less, relative to 1 part by mass of nickel added.

[0072] Next, the mixture containing the compound of the aforementioned metallic element M is heated while being stirred to reduce nickel hydroxide and the compound in the mixture. Through this reduction reaction, the nickel hydroxide remaining in the mixture is reduced to nickel; when metallic element M is tin, the compound of metallic element M is reduced to tin; and when metallic element M is zinc, the compound of metallic element M is reduced to zinc. In this reduction reaction, by simultaneously reducing nickel hydroxide and the compound of metallic element M, a surface region containing a nickel / metallic element M alloy, in which nickel and metallic M are homogeneously dissolved, is formed on the surface of the nickel matrix particles. It should be noted that, as long as the effects of the present invention can be achieved, a portion of metallic element M may exist in its elemental state, in its compound state, or in a combination of two or more of these states.

[0073] While the heating temperature of the aforementioned mixture varies depending on the type of polyol and metal element M compound used, it is preferably 150°C to 200°C under atmospheric pressure, more preferably 170°C to 200°C, and even more preferably 190°C to 200°C. By setting the heating temperature within this range, nickel hydroxide and the metal element M compound can be simultaneously reduced, smoothly forming a surface region containing a nickel / metal M alloy on the surface of the nickel master particles.

[0074] Subsequently, as needed, the polyol in the obtained nickel particle dispersion is replaced with water, and then the replaced water is replaced again with methanol to wash the nickel particles, followed by vacuum drying. This operation enables the production of the nickel particles of the present invention.

[0075] In manufacturing nickel particles containing metallic element M, PVD or CVD methods can be used to add metallic element M to the nickel raw material. In this case, the nickel particles form a nickel / metal M alloy throughout. However, if the sintering resistance of the nickel particles is to be improved, the content of metallic element M, i.e., tin and / or zinc, in the nickel particles becomes too high, resulting in increased electrical resistance. Furthermore, due to the non-uniform particle size, the surface of the conductive film becomes rough when using these nickel particles to form a conductive film, potentially causing short circuits between the internal electrodes of the MLCC. Additionally, as another method for manufacturing nickel particles containing metallic element M, as described in Patent Document 2, a method is known to involve reducing all of nickel hydroxide and then adding a compound containing metallic element M. In this case, a layer of elemental metallic element M, i.e., tin and / or zinc, with a melting point lower than nickel, is formed on the surface of the nickel particles. However, the sintering resistance of these nickel particles does not increase because the particle surface is formed by a layer of elemental tin and / or zinc. In contrast, the nickel particles of the present invention, comprising nickel master particles and a nickel / metal M alloy disposed on their surface, can improve sintering resistance without excessively increasing electrical resistance. Furthermore, if the nickel particles of the present invention are used to form a conductive film, the surface of the conductive film can be made smooth. For these reasons, as described above, it is preferable to manufacture the nickel particles by simultaneously reducing the compound of nickel hydroxide and metal element M while a portion of nickel hydroxide remains.

[0076] Although the nickel particles produced by the above method are microparticles with a uniform particle size, their surface region containing a nickel / metal M alloy allows them to be used in various fields. In particular, they are suitable for the formation of internal electrodes in MLCCs.

[0077] The present invention has been described above based on its preferred embodiments, but the present invention is not limited to the above embodiments. For example, the nickel particles of the present invention have a surface region comprising a nickel / tin alloy on their surface, but the inventors of the present invention have determined that the above advantages can be fully utilized even when zinc is used instead of tin to manufacture the nickel particles. In other words, the inventors of the present invention have determined that the above advantages can also be fully utilized with the following nickel particles, which have a surface region comprising a nickel / zinc alloy, the zinc content relative to the total content of the nickel particles is within a specified range, and when X-ray photoelectron spectrophotometry is used to measure the region from the outermost surface to a sputtering depth of 5 nm (converted to SiO2) in the depth direction of the nickel particles, the maximum value of the ratio of the number of zinc atoms to the total number of nickel and zinc atoms in this region is set as X2, and when the nickel particles are measured by ICP emission spectrophotometry, the ratio of the number of zinc atoms to the total number of nickel and zinc atoms is set as Y1, and the value of X2 / Y1 is within a specified range. Such nickel particles can be easily manufactured by using zinc instead of tin in the preferred manufacturing method of the nickel particles of the present invention described above. Furthermore, the advantages described above can also be fully utilized when nickel particles having a surface region comprising a nickel / tin / zinc alloy are manufactured by using zinc together with tin in the above manufacturing method.

[0078] The present invention has been described above based on its preferred embodiments, but the present invention is not limited to the above embodiments.

[0079] Regarding the above embodiments, the following nickel particles and their manufacturing method are further disclosed.

[0080] [1] A nickel particle having a surface region comprising an alloy containing nickel and the metallic element M,

[0081] The aforementioned metallic element M is selected from at least one of tin and zinc.

[0082] The content of the aforementioned metallic element M relative to the total content of the aforementioned nickel particles is 0.16% to 11.4% by mass.

[0083] 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 is set as X (at%). 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 is set as Y (at%), and the value of X / Y is 1.5 to 30.

[0084] [2] According to the nickel particles described in [1], wherein, in the particle size distribution based on the equivalent circle diameter calculated by measurement using a scanning electron microscope, the cumulative particle size when the cumulative number is 50% is set as D. 50 At that time, D 50 The range is 20nm to 200nm.

[0085] When the standard deviation of the particle size in the above particle size distribution is set to σ (nm), the coefficient of variation (σ / D) 50 The value of (%) is below 14%.

[0086] Variation coefficient (%) = (σ / D) 50 )×100

[0087] [3] According to the nickel particles described in [1] or [2], wherein, in the particle size distribution based on the equivalent circle diameter calculated by measurement using a scanning electron microscope, the cumulative particle size when the cumulative number is 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%.

[0088] [4] Nickel particles according to any one of [1] to [3], wherein, in the particle size distribution based on the equivalent circle diameter calculated by measurement using a scanning electron microscope, the cumulative particle size when the cumulative number is 50% is set as D. 50 When the crystallite size determined by the WPPF method is set as Cs (nm), Cs / D 50 The value is 0.3 to 0.6.

[0089] [5] A method for manufacturing nickel particles, wherein nickel particles are manufactured by heating a mixture comprising nickel hydroxide particles, polyol, polyvinylpyrrolidone and polyethyleneimine.

[0090] Relative to 1 part by weight of polyethyleneimine, use 30 to 200 parts by weight of polyvinylpyrrolidone.

[0091] The nickel hydroxide particles are reduced to nickel parent particles by the above heating process.

[0092] With some of the aforementioned 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 containing an alloy of nickel and metallic element M on the nickel parent particles.

[0093] The aforementioned metallic element M is selected from at least one of tin and zinc.

[0094] [6] A multilayer ceramic capacitor that uses nickel particles as described in any one of [1] to [4] in its internal electrodes.

[0095] Example

[0096] The present invention will now be described in more detail through embodiments. However, the scope of the present invention is not limited to the embodiments described. Unless otherwise specified, "%" refers to "mass %".

[0097] [Example 1]

[0098] A mixture 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 palladium nitrate aqueous solution (concentration: 100 g / L) to a 500 ml beaker. The polyethyleneimine was branched and had a number average molecular weight of 1800. The mixture was heated while stirring and subjected to a reduction reaction at 198 °C for 5 hours under atmospheric pressure. At this point, the reduction of nickel hydroxide was 80 mol% relative to the amount of nickel hydroxide added. Then, 0.5 g of sodium stannate trihydrate was added, and the reduction reaction was further carried out at 198 °C for 10 hours under atmospheric pressure. Heating was stopped to end the reduction, and the mixture was allowed to cool naturally to room temperature. This process was repeated to obtain a large quantity of nickel particles.

[0099] A magnet is placed at the bottom of a beaker containing the obtained nickel particle dispersion to attract the nickel particles. The supernatant of the dispersion is then removed.

[0100] After removing the magnet from the bottom of the beaker, add 50g of pure water and stir the dispersion for 10 minutes. Then, place the magnet back at the bottom of the beaker to attract the nickel particles. In this state, remove the supernatant from the dispersion. Repeat this process five times.

[0101] Next, 50g of methanol was added and the dispersion was stirred for 10 minutes. The supernatant was removed three times using a magnet to replace the solvent in the dispersion with methanol. Then, the dispersion was vacuum dried at 80°C to obtain nickel particles.

[0102] [Examples 2-6]

[0103] The amounts of palladium nitrate aqueous solution and sodium stannate 3-hydrate added, as well as the time from the initial heating of the mixture to the addition of sodium stannate 3-hydrate, were set as shown in Table 1. Except for these, nickel particles were obtained by operating in the same manner as in Example 1.

[0104] [Examples 7-12]

[0105] Instead of sodium stannate trihydrate, zinc hydroxide was added. The amounts of palladium nitrate aqueous solution and zinc hydroxide added were set as shown in Table 1. Except for these, nickel particles were obtained by operating in the same manner as in Example 1.

[0106] [Comparative Example 1]

[0107] A mixture 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 palladium nitrate aqueous solution (concentration: 100 g / L) to a 500 ml beaker. The polyethyleneimine was branched and had a number average molecular weight of 1800. The mixture was heated while stirring and the reduction reaction was carried out at 198 °C for 6.5 hours. Heating was then stopped to end the reduction, and the mixture was allowed to cool naturally to room temperature. Repeating this process yielded a large quantity of nickel particles.

[0108] A magnet is placed at the bottom of a beaker containing the obtained nickel particle dispersion to attract the nickel particles. The supernatant of the dispersion is then removed.

[0109] After removing the magnet from the bottom of the beaker, add 50g of pure water and stir the dispersion for 10 minutes. Then, place the magnet back at the bottom of the beaker to attract the nickel particles. In this state, remove the supernatant from the dispersion. Repeat this process five times.

[0110] Next, 50g of methanol was added and the dispersion was stirred for 10 minutes. The supernatant was removed three times using a magnet to replace the solvent in the dispersion with methanol. Then, the dispersion was vacuum dried at 80°C to obtain nickel particle powder.

[0111] [Comparative Example 2]

[0112] Before carrying out the reduction reaction of nickel hydroxide, sodium stannate 3-hydrate was added, and otherwise the procedure was the same as in Example 1 to obtain nickel particles.

[0113] [Comparative Example 3]

[0114] A mixture 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 palladium nitrate aqueous solution (concentration: 100 g / L) to a 500 ml beaker. The polyethyleneimine was branched and had a number average molecular weight of 1800. The mixture was heated while stirring and the reduction reaction was carried out at 198 °C for 6.5 hours. Heating was then stopped to end the reduction, and the mixture was allowed to cool naturally to room temperature. Repeating this process yielded a large quantity of nickel particles.

[0115] A magnet is placed at the bottom of a beaker containing the obtained nickel particle dispersion to attract the nickel particles. The supernatant of the dispersion is then removed.

[0116] After removing the magnet from the bottom of the beaker, add 50g of pure water and stir the dispersion for 10 minutes. Then, place the magnet back at the bottom of the beaker to attract the nickel particles. In this state, remove the supernatant from the dispersion. Repeat this process five times.

[0117] Add 300g of pure water and hydrazine 1 hydrate to the dispersion and heat to 60°C. Then add 1g of sodium stannate 3 hydrate and stir for 5 hours to perform surface treatment on nickel particles using tin.

[0118] A magnet is placed at the bottom of a beaker containing the dispersion of the obtained nickel particles, and the nickel particles are attracted to the magnet. In this state, the supernatant of the dispersion is removed.

[0119] After removing the magnet from the bottom of the beaker, add 50g of pure water and stir the dispersion for 10 minutes. Then, place the magnet back at the bottom of the beaker to attract the nickel particles. In this state, remove the supernatant from the dispersion. Repeat this process five times.

[0120] Next, 50g of methanol was added and the dispersion was stirred for 10 minutes. The supernatant was removed three times by using a magnet to replace the solvent in the dispersion with methanol. Then, the dispersion was vacuum dried at 80°C to obtain nickel particle powder with tin surface treatment. As described in [Evaluation 1] below, 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.

[0121] [Evaluation 1]

[0122] For the nickel particles obtained in Examples 1-12 and Comparative Examples 1-3, the values ​​of X and X1 were determined by the following XPS analysis method.

[0123] In addition, the content of tin and zinc elements relative to the total nickel particles and the value of Y were determined by ICP emission spectrophotometry.

[0124] Furthermore, the particle size distribution is determined using the methods described above, and the particle size D is calculated. 50 The proportion and variation coefficient of coarse particles.

[0125] Furthermore, the a-axis length and crystallite size Cs of nickel based on the WPPF method were determined using the following method.

[0126] Furthermore, the methods described above are used to confirm whether the surface region of the nickel particles contains an alloy of nickel and tin, and whether it also contains an alloy of nickel and zinc.

[0127] The results are shown in Table 1 below. Furthermore, SEM images of the nickel particles obtained in Example 3 and Comparative Example 2 are shown in... Figure 1 and 2 middle.

[0128] [X-ray photoelectron spectrophotometry (XPS) determination]

[0129] For the test specimens used in XPS, a specimen obtained by forming nickel particles into granules using a press was employed. Specifically, approximately 10 mg of the particle specimen was added to an aluminum container with dimensions of φ5.2 mm and height of 2.5 mm. Then, using a press (AS ONE, model: 1-312-01) and adapter (model: 1-312-03), pressure was applied along with the aluminum container at a specified stroke (25 mm). Finally, the granulated nickel particles supported by the aluminum container were removed.

[0130] The obtained granular material was subjected to surface surface measurements and depth measurements from the sample surface toward the interior, performed using sputtering of Ar monomer ions. The measurement conditions are as follows.

[0131] • Measuring apparatus: VersaProbeIII manufactured by ULVAC-PHI Corporation

[0132] • Excitation X-rays: Monochromatic Al-Kα rays (1486.7 eV)

[0133] • Output power: 50W

[0134] Accelerating voltage: 15kV

[0135] • X-ray irradiation diameter: 200 μm φ

[0136] X-ray scanning area: 1000μm × 300μm

[0137] • Detection angle: 45°

[0138] • Bandpass energy: 26.0 eV

[0139] • Energy step size: 0.1 eV / step

[0140] Sputtered ion species: Ar monomeric ions

[0141] Sputtering rate: 3.3 nm / min (SiO2 conversion)

[0142] Sputtering interval: 20s

[0143] • Element to be determined: C 1s Ni 2p3 Sn 3d5 、Zn 2p3

[0144] • Energy correction value: C 1s CC and CH bonds (284.8 eV)

[0145] [Analysis of XPS data]

[0146] XPS data was analyzed using data parsing software (ULVAC-PHI's "MultiPak Ver9.9"). Shirley was used for the background mode.

[0147] [The value of X]

[0148] In Examples 1-6, Sn 3d5 The number of atoms relative to Ni 2p3 With Sn 3d5 The ratio of the total number of atoms of the two elements is set as X (at%). In Examples 7-12, Zn 2p3 The number of atoms relative to Ni 2p3 With Zn 2p3 The proportion of the total number of atoms of the two elements is set as X (at%).

[0149] [Determination of a-axis length and crystallite size Cs]

[0150] 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.

[0151] Device name: SmartLab (9KW); manufactured by Rigaku Corporation.

[0152] <Device Composition>

[0153] wavelength

[0154] Target: Cu

[0155] Wavelength type: Kα1

[0156] ·Kα1:

[0157] ·Kα2:

[0158] ·Kβ:

[0159] Kα12 intensity ratio: 0.4970

[0160] Horizontal polarization: 0.500

[0161] Diffraction device

[0162] • Goniometer: SmartLab

[0163] • Accessory base: Z-axis stage (separate)

[0164] Accessories: ASC6-Reflector

[0165] <Measurement Conditions>

[0166] Optical system properties: Lumped method

[0167] • CBO Select Slit: BB

[0168] • Parallel slit for incident light: Soller_slit_5.0deg

[0169] • Entrance slit: 2 / 3deg

[0170] • Length limiting slit: 10.0mm

[0171] • Light-receiving slit 1: 20.000mm

[0172] • Parallel slit for receiving light: Soller_slit_5.0deg

[0173] • Light-receiving slit 2: 20.000mm

[0174] Attenuator: On

[0175] • Detector: D / teX Ultra250

[0176] • Scan axis: 2θ / θ

[0177] • Scanning mode: Continuous

[0178] • Scan range: 5.0000~140.0000 deg

[0179] • Step size: 0.0100 deg

[0180] • Scanning speed / measurement time: 2.015572 deg / min

[0181] Data points: 13501

[0182] • Tube voltage: 45kV

[0183] Tube current: 200mA

[0184] HV: 0.00

[0185] <Preparation of Specimen for X-ray Diffraction>

[0186] Cover the nickel particles to be measured with the measuring holder, and use a glass plate to smooth them in such a way that the thickness of the layer formed by the nickel particles becomes 0.5 mm and the measuring surface becomes smooth.

[0187] Using the X-ray diffraction pattern obtained under the above-mentioned measurement conditions, analyze it using analysis software under the following conditions. In the analysis, correction was performed using the data obtained from the standard substance, lanthanum hexaboride powder (SRM660 series), provided by the National Institute of Standards and Technology (NIST) of the United States. The a-axis length and the crystallite size Cs were calculated using the WPPF method.

[0188] <Analysis Conditions of Measurement Data>

[0189] ·Analysis software: PDXL2 manufactured by Rigaku

[0190] ·Analysis method: WPPF method

[0191] ·Data processing: Automatic profile processing

[0192] (Rigaku Corporation PDXL User's Guide p.305)

[0193] 〔Evaluation 2〕

[0194] For the nickel particles obtained in Examples 1 to 12 and Comparative Examples 1 to 3, the shrinkage start temperature of the nickel particles, the resistivity 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.

[0195] 〔Measurement of Shrinkage Start Temperature〕

[0196] As the measurement device for TMA, TMA / SS6000 manufactured by Seiko Instruments Inc. was used. 0.2 to 0.3 g of nickel particles were placed in a stainless steel mold container with a diameter of φ5.0 mm, and compression molding was performed by applying a pressure of 92 MPa to the nickel particles to produce pellets. The pellet length of the obtained pellets was measured and used as the measurement object specimen. It was set in the measurement device, and the specimen was heated at 5 °C / min in an atmosphere of a load of 49 mN and 1 vol% hydrogen / 99 vol% nitrogen. The measurement was started from room temperature (25 °C), and a chart showing the relationship between temperature and shrinkage rate (%) was obtained. The shrinkage start temperature was determined from the obtained chart.

[0197] 〔Measurement of Resistivity〕

[0198] 0.1g of ethyl cellulose was dissolved in 4g of terpineol, and then 5g of nickel particles were added to obtain a mixture. This mixture was then mixed using a rotary mixer (THINKY Co., Ltd., "Awatori Rentaro" (registered trademark)). Next, the mixture was passed through a three-roll mill four times to break it up. The gap of the three-roll mill was set to 8μm. This process was repeated to obtain a coating solution.

[0199] The coating solution was applied to an alumina substrate to form a coating film. The coating film thickness was 30 μm. The coating film was sintered at 800 °C for 60 minutes under an atmosphere of 1 vol% hydrogen / 99 vol% nitrogen to obtain a sintered film. The resistivity (Ω·cm) of this sintered film was measured using a Loresta MCP-T600 four-probe resistivity measuring apparatus manufactured by Mitsubishi Analytech.

[0200] [Determination of surface roughness Rz]

[0201] The surface roughness Rz of the sintered film described above was measured using a SURFCOM 130A. The measurement conditions were set as follows: evaluation length of 6.0 mm and measurement speed of 0.6 mm / s.

[0202] [Table 1]

[0203]

[0204] As the results shown in Table 1 indicate, XPS measurements confirmed that the nickel particles obtained in Examples 1-6 contained metallic tin in their surface regions. Furthermore, the a-axis length of the nickel particles obtained in the examples was longer than that of the nickel particles obtained in Comparative Example 1, which did not use a tin compound. These results indicate that the nickel particles obtained in Examples 1-6 contained an alloy of nickel and tin in their surface regions.

[0205] Furthermore, as the results shown in Table 1 indicate, XPS measurements confirmed that the nickel particles obtained in Examples 7-12 contained metallic zinc in their surface regions. Moreover, the a-axis length of the nickel particles obtained in these examples was longer than that of the nickel particles obtained in Comparative Example 1, which did not use a zinc compound. These results indicate that the nickel particles obtained in Examples 7-12 contained an alloy of nickel and zinc in their surface regions.

[0206] Furthermore, as the results shown in Table 1 indicate, the nickel particles obtained in Examples 1-12 exhibited higher shrinkage initiation temperatures compared to the nickel particles obtained in Comparative Examples 1-3. This suggests that the nickel particles obtained in Examples 1-12 exhibit high sintering resistance.

[0207] In particular, as shown by the comparison between Examples 1-5 and Example 6, it is known that the resistivity of the sintered film obtained from the nickel particles can be controlled by controlling the amount of tin contained in the nickel particles.

[0208] Furthermore, compared to Comparative Example 2, where a nickel-tin alloy was formed in the nickel particles themselves, the surface of the sintered film in Examples 1-6, which produced nickel particles with surface regions containing a nickel-tin alloy, became smoother. From this, it is evident that the surface roughness of the sintered film is lower according to the nickel particles having surface regions containing a nickel-tin alloy.

[0209] Furthermore, if the corresponding embodiment 3 is taken as Figure 1 and corresponding to Comparative Example 2 Figure 2 By comparison, it can be seen that Figure 1 The nickel particles have a uniform particle size, in contrast, Figure 2 The nickel particles have uneven particle size.

[0210] Industrial availability

[0211] According to the present invention, nickel particles with high sintering resistance 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 tin and zinc. The content of the metallic element M relative to the total amount of nickel particles is 0.16% to 11.4% 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 luminescence 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 1.5 to 30.

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, comprising heating a mixture containing nickel hydroxide particles, a polyol, polyvinylpyrrolidone, and polyethyleneimine to manufacture nickel particles. 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 tin and zinc. The state of the nickel hydroxide particles remaining in the aforementioned part refers to the state before they have been reduced by more than 80 mol% relative to the amount of nickel hydroxide added.

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

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