Nickel powder, its manufacturing method, conductive composition and conductive film

Abstract

To provide a nickel powder that has high sintering resistance and a low degree of agglomeration between particles.SOLUTION: Provided is a nickel powder that comprises an aggregate of nickel particle. The nickel particle contain tin element on the surface thereof and the contained amount of tin element is 1.5 mass% or more and 30 mass% or less. The nickel powder has a 50% particle size D50 in the number distribution measured by scanning electron microscope observation of 100 nm or less. When measuring the region from the outermost surface to a sputtering depth of 5 nm in conversion of SiO2 in the depth direction of the nickel powder by XPS analysis, the nickel powder has, in the region, a site where the maximum value X1 of the ratio X of the number of atoms of tin element to the total number of atoms of nickel element and tin element is 0.15 at.% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a nickel powder containing elemental tin. [Background technology]

[0002] In order to achieve miniaturization and high capacitance in electronic components such as multilayer ceramic capacitors (hereinafter also referred to as "MLCC") used in electronic devices, for example, increasing the density of wiring in the wiring formation within the electronic device and improving the dimensional stability of the wiring are required. To achieve these requirements, for example, the use of metal particles with small particle diameters as a constituent material of the wiring structure has been considered.

[0003] For example, Patent Document 1 proposes nickel powder that has been surface-treated with tin, has a tin content of less than 1.5 mass %, and has an average particle size of 0.03 μm to 0.5 μm. The publication states that the addition of a small amount of tin to this nickel powder suppresses resin decomposition in a dried nickel paste film and improves the sintering resistance of the nickel powder. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-104819 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 does not verify the extent to which the sintering behavior of the nickel powder described therein has been improved, and the extent of the improvement is unclear. Furthermore, because nickel particles are magnetic, magnetic aggregation of particles is likely to occur, but the nickel powder described therein does not take any measures to prevent aggregation. It is therefore an object of the present invention to provide a nickel powder that has high resistance to sintering and low degree of agglomeration of particles. [Means for solving the problem]

[0006] The present invention provides a nickel powder comprising an aggregate of nickel particles or nickel-based alloy particles, the nickel particles or nickel-based alloy particles contain tin element on their surfaces, and the content of the tin element is 1.5% by mass or more and 30% by mass or less; The nickel powder has a 50% particle diameter D 50 is 100 nm or less, When the region from the outermost surface to a sputtering depth of 5 nm in terms of SiO2 in the depth direction of the nickel powder is measured by X-ray photoelectron spectroscopy, the maximum value X1 of the ratio X of the number of tin atoms to the total number of nickel and tin atoms in the region is 0.1 5% The present invention provides a nickel powder having the above-mentioned portions.

[0007] The present invention also provides a method for determining the 50% particle diameter D in the number distribution measured by scanning electron microscopy. 50 A method for producing a nickel powder comprising an aggregate of nickel particles or nickel-based alloy particles having a particle size of 100 nm or less and containing tin element on the surface thereof, The present invention provides a method for producing nickel powder, which comprises mixing a slurry containing nickel base particles or nickel-based alloy base particles with an aqueous solution in which a water-soluble tin compound is dissolved, so that the tin content is 1.5 to 50.0 mass % relative to 100 mass % which is the total of tin and nickel, and reducing the tin compound to metallic tin to form a layer containing tin on the surface of the nickel base particles or nickel-based alloy base particles. [Effects of the Invention]

[0008] The present invention provides a nickel powder that has high resistance to sintering and low levels of particle agglomeration. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a graph showing the absolute value of the differential value obtained by differentiating the TMA shrinkage (%) measured by thermomechanical analysis for the nickel powders obtained in the examples and comparative examples with respect to temperature T (°C), i.e., ΔTMA / ΔT, on the y-axis and temperature T on the x-axis. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below based on preferred embodiments. The present invention relates to a nickel powder consisting of an aggregate of nickel particles or nickel-based alloy particles. In the following description, the term "nickel powder" may refer to a powder that is an aggregate of nickel particles or nickel-based alloy particles, or to the individual nickel particles or nickel-based alloy particles that make up the powder, depending on the context.

[0011] In the present invention, nickel particles refer to particles that are essentially composed of nickel element, with the balance containing unavoidable elements. Examples of unavoidable elements include oxygen element derived from oxygen or carbon dioxide in the atmosphere, carbon element, and nitrogen element derived from hydrazine. Nickel-based alloy particles refer to particles that contain 50 at% or more of nickel element, are essentially composed of an alloy of nickel element and other elements, and contain the balance containing unavoidable elements. Examples of elements contained in nickel-based alloys include, but are not limited to, tin, copper, silver, palladium, platinum, gold, boron, and phosphorus. In the following description, to avoid complexity, nickel particles and nickel-based alloy particles will be collectively referred to simply as "nickel particles."

[0012] The nickel powder of the present invention is preferably composed of fine nickel particles. The particle size of the nickel particles is measured by observing the nickel powder of the present invention with a scanning electron microscope (SEM). In detail, the nickel particles that make up the nickel powder are observed with an SEM at a magnification of 100,000 times, and 200 or more particles that do not overlap are randomly selected from the observed SEM image to determine the area of ​​the nickel particles. The circle equivalent diameter (Heywood diameter) is calculated from the area. The particle size distribution is determined based on the calculated circle equivalent diameter. The particle size distribution is plotted on the graph with the circle equivalent diameter on the horizontal axis and the number frequency on the vertical axis. In the particle size distribution obtained in this way, the number cumulative particle size at 50% of the cumulative number is defined as D 50 The particle size D defined in this way is 50 The value is preferably 100 nm or less, more preferably 5 nm or more and 100 nm or less, even more preferably 10 nm or more and 90 nm or less, and even more preferably 20 nm or more and 80 nm or less. The particle size D of the nickel powder of the present invention 50 When the nickel powder of the present invention is used in various applications, for example, as an internal electrode of an MLCC, the nickel particles are less likely to agglomerate, which allows for the formation of a smooth and thin internal electrode layer and reduces the likelihood of short circuits between the internal electrodes. Furthermore, when the nickel powder of the present invention is used as an electrode catalyst for an SOFC (solid oxide fuel cell), a PCFC (proton conducting fuel cell), an SOEC (solid oxide electrolysis cell), or a PCEC (proton conducting water electrolysis cell) (hereinafter, these are also collectively referred to as "SOFC, etc."), the nickel particles are less likely to agglomerate, which increases the specific surface area of ​​the nickel powder as a whole and increases the catalytic activity.

[0013] The nickel particles contain tin element on their surfaces. When a surface treatment agent such as an organic acid is present on the surface of the nickel particles, the "surface of the nickel particles" refers to the surface portion of the particles excluding the surface treatment agent. When no surface treatment agent is present on the surface of the nickel particles, the "surface of the nickel particles" refers to the surface of the particles themselves. The tin element may exist on the surface of the nickel particles in the form of simple tin (i.e., metallic tin). Alternatively, the tin element may exist on the surface of the nickel particles in the form of a divalent or tetravalent tin compound. Alternatively, the tin element may exist on the surface of the nickel particles in the form of an alloy with nickel. Alternatively, the tin element may exist in a combination of two or more of these. When tin element is present on the surface of nickel particles in the form of the tin compound, examples of the tin compound include, but are not limited to, oxides, hydroxides, sulfides, sulfates, borides, phosphides, etc. containing tin.

[0014] The nickel powder of the present invention has improved particle dispersibility due to the reduction in magnetism caused by the inclusion of tin, a non-magnetic metal, on the surface of the nickel particles. In other words, the nickel powder of the present invention has suppressed magnetic aggregation between particles. From this viewpoint, the nickel powder of the present invention has a particle diameter D measured by SEM observation. 50 is within the above-mentioned range, the volume cumulative particle size D at 50 volume %, 10 volume % and 90 volume % of the cumulative volume measured by a laser diffraction scattering particle size distribution measurement method, which indicates the agglomeration size of nickel particles. LD50、 D LD10 and D LD90 are preferably in the following ranges: That is, D LD50 is preferably 0.9 μm or more and 5.0 μm or less, more preferably 1.0 μm or more and 4.0 μm or less, and even more preferably 1.1 μm or more and 3.0 μm or less. LD10 is preferably 0.05 μm or more and 0.9 μm or less, more preferably 0.1 μm or more and 0.8 μm or less, and even more preferably 0.3 μm or more and 0.7 μm or less. LD90 is preferably 5 μm or more and 25 μm or less, more preferably 6 μm or more and 20 μm or less, and even more preferably 7 μm or more and 15 μm or less.

[0015] The proportion of tin atoms contained in the surface of nickel particles can be confirmed by X-ray photoelectron spectroscopy (hereinafter also referred to as "XPS"). Specifically, when the region from the outermost surface to a sputtering depth of 5 nm in terms of SiO2 in the depth direction of the nickel powder is measured by XPS (hereinafter also referred to as the "particle surface region"), the maximum value of X1, which is the ratio X of the number of tin atoms to the total number of nickel and tin atoms in the particle surface region, is 0.1 5% It is preferable that the value of X1 is 0.1 or more. 5% It is preferable that the tin element is present so as to have a portion where X1 is 0.2 or more, from the viewpoint of further improving the sintering resistance of the nickel powder. 0% Above, especially 0.4 0% The closer the value of X1 is to 1, the higher the sintering resistance of the nickel powder is, so it is preferable. 0% If the temperature is high enough, the sintering resistance of the nickel powder is sufficiently high to be satisfactory. In order to further increase the sintering resistance of the nickel powder, the value of X1 is set to 0.1 at any three points in the depth direction of the particle surface region. 5% Above, especially 0.2 0% Above, especially 0.3 0% It is preferable that this is equal to or greater than this. The "outermost surface of the nickel powder" refers to the outermost surface of the surface treatment agent when a surface treatment agent such as an organic acid or an amine is present on the surface of the nickel particle. When no surface treatment agent is present on the surface of the nickel particle, the "outermost surface of the nickel powder" refers to the surface of the particle itself.

[0016] By containing tin element on the surface of the nickel particles in the above ratio, the nickel powder of the present invention is less susceptible to magnetic aggregation and also exhibits the following three sintering resistance properties. First, it increases the temperature at which nickel particles begin to sinter and shrink. Second, the temperature at which the absolute value of the rate of change of shrinkage with temperature becomes maximum shifts to the higher temperature side. Third, the absolute value of the rate of change of shrinkage with temperature becomes smaller. The nickel powder of the present invention has high sintering resistance in terms of the three aspects described above. Due to the first and second effects, when, for example, an MLCC is manufactured using a composition containing the nickel powder of the present invention, the temperature at which the internal electrode layers shrink due to sintering of nickel particles during the MLCC firing process, which is one of the manufacturing steps, can be made as close as possible to the temperature at which the dielectric layers shrink due to sintering of dielectric particles. Reducing the difference in the temperatures at which the internal electrode layers and the dielectric layers shrink means that the times at which the internal electrode layers and the dielectric layers shrink overlap during the temperature rise process of the firing process. The third effect means that the internal electrode layers shrink slowly during the temperature rise process of the firing process. The nickel powder of the present invention exhibits these three effects that indicate sintering resistance, which is advantageous from the viewpoint of effectively preventing the occurrence of structural defects such as cracks and delamination (interlayer peeling at the interface between the internal electrode layer and the dielectric layer) caused by differences in the temperature and shrinkage rate at which the internal electrode layer and the dielectric layer shrink during the firing process of MLCCs. The high sintering resistance of the nickel powder of the present invention is also advantageous when used as an electrode catalyst for the hydrogen electrode of an SOFC or PCFC. The environment at the hydrogen electrode of an SOFC or PCFC during operation is a high-temperature, reducing atmosphere of 600°C or higher, and conventional nickel powder is prone to sintering when exposed to this environment, which can lead to a decrease in catalytic activity. In contrast, the nickel powder of the present invention has high sintering resistance, so it is less likely to sinter at the operating temperatures of an SOFC or PCFC, and is less likely to experience a decrease in catalytic activity due to this. SOEC and PCEC are technologies for producing hydrogen through the reverse reaction of the chemical reaction that occurs in SOFC and PCFC. The structures of SOEC and PCEC are the same as those of SOFC and PCFC, respectively. Therefore, it is advantageous to use the nickel powder of the present invention as an electrode catalyst for the hydrogen electrode of SOEC and PCEC, just as with SOFC and PCFC.

[0017] To make the above advantages more pronounced, the tin content in the nickel powder is preferably 1.5% by mass or more, more preferably 3.0% by mass or more, and even more preferably 5.0% by mass or more. Also, the tin content in the nickel powder is preferably 30.0% by mass or less, more preferably 25% by mass or less, and even more preferably 20.0% by mass or less. The content of tin element in nickel powder can be measured by ICP atomic emission spectrometry using a solution obtained by dissolving nickel powder in acid.

[0018] The nickel particles preferably contain tin on their surfaces and also near the surfaces. In particular, it is preferable that the tin be unevenly distributed at a predetermined content ratio on the surfaces of the nickel particles and in their vicinity, from the viewpoint of enhancing the sintering resistance of the nickel powder without impairing the inherent properties of the nickel powder. In other words, the nickel particles constituting the nickel powder of the present invention preferably comprise a core portion made of a nickel matrix and a shell portion located outside the core portion and in which the tin is unevenly distributed. The "core portion made of a nickel matrix" refers to a portion that is essentially composed of nickel, with the remainder containing unavoidable elements, or a portion that contains 50 at% or more nickel, is essentially composed of an alloy of nickel and other elements, with the remainder containing unavoidable elements. The nickel particles constituting the nickel powder of the present invention contain tin element on the surface and in the vicinity thereof, but may also contain tin in the core portion.

[0019] In the particle surface region, the ratio X of the number of tin atoms to the total number of nickel and tin atoms may be constant or variable in the depth direction. When the value of X is not constant in the depth direction, the value of X may decrease continuously or stepwise from the surface to the center of the particle. In particular, when measuring the region from the outermost surface of the nickel powder to a sputtering depth of 20 nm in SiO2 equivalent by XPS, it is preferable that the value of X gradually decreases from the outermost surface to a sputtering depth of 20 nm, as this further improves the sintering resistance of the nickel powder. In this case, when the maximum value of X in the region from the outermost surface of the nickel powder to a sputtering depth of 5 nm is X1 and the value of X at a sputtering depth of 20 nm is X2, the value of X1 / X2 is preferably 1.0 or more and 5.0 or less, in order to further improve the sintering resistance of the nickel powder. The value of X1 / X2 is more preferably 1.5 or more, even more preferably 2.0 or more. Furthermore, the value of X1 / X2 is more preferably 4.0 or less, even more preferably 3.0 or less.

[0020] In nickel particles, it is preferable that a region where tin is unevenly distributed exists with a predetermined thickness on the particle surface and in the region nearby, from the viewpoint of further improving the sintering resistance of the nickel powder. From this viewpoint, when the region from the outermost surface of the nickel powder to a sputtering depth of 20 nm in SiO2 equivalent is measured by XPS, when X1 is the maximum ratio X of the number of tin atoms to the total number of nickel and tin atoms in the range from the outermost surface to a sputtering depth of 5 nm, and the average value X2 of X at a sputtering depth of 20 nm is A (= (X1 + X2) / 2), the sputtering depth at which the value of X in the depth direction becomes A is preferably 1.0 nm to 10.0 nm, more preferably 2.0 nm to 8.0 nm, and even more preferably 3.0 nm to 6.0 nm.

[0021] It is preferable that tin element is present in the form of an oxide on the surface of the nickel particles. The reason for this is that when tin element present on the surface of the nickel particles is in the form of an oxide, the tin atoms are less likely to diffuse than when tin element is present in the form of metal tin, and therefore nickel atoms inside the particles are also less likely to diffuse, thereby increasing the sintering resistance of the nickel powder. From this perspective, when the particle surface region of the nickel powder is measured in the depth direction by XPS, it is preferable that the value of S2 / S1, which is the ratio of the detection intensity S2 of tin oxide to the detection intensity S1 of tin element, is 0.80 or more, particularly 0.85 or more, and especially 0.90 or more. The closer the value of S2 / S1 is to 1, the higher the sintering resistance of the nickel powder, which is preferable. From the viewpoint of further increasing the sintering resistance of the nickel powder, it is preferable that the value of S2 / S1 at any three points in the depth direction of the particle surface region is 0.80 or more, particularly 0.85 or more, and especially 0.90 or more. When the tin element present on the surface of the nickel particles is in the form of an oxide, the type of the oxide is not particularly limited. For example, the tin element may be present in the form of SnO and / or SnO, or in the form of a composite oxide of tin with nickel or other elements. Even if tin element exists in the form of oxide, when the nickel powder of the present invention is used for, for example, an internal electrode of an MLCC, the nickel powder is sintered in a reducing atmosphere, and the tin oxide is reduced at that time, so that the electrical conductivity of the nickel powder is not affected.Furthermore, when the nickel powder of the present invention is used for, for example, an electrode catalyst of an SOFC or the like, fuel (e.g., hydrogen) is supplied to the electrode catalyst, and the tin oxide is reduced at that time, so that the electrical conductivity and catalytic activity of the nickel powder are not affected.

[0022] The degree of sintering resistance of the nickel powder of the present invention can be evaluated by thermomechanical analysis (TMA) of the nickel powder. In the present invention, the temperature at which the TMA shrinkage rate (%) based on room temperature (25°C) is 5% is defined as the shrinkage onset temperature. From the viewpoint of further enhancing the sintering resistance of the nickel powder, the temperature is preferably 405°C or higher. From the viewpoint of making this advantage even more pronounced, the temperature is more preferably 440°C or higher, and even more preferably 480°C or higher.

[0023] The absolute value of the differential value obtained by differentiating the TMA shrinkage rate (%) with respect to temperature T, i.e., the temperature at which the value of ΔTMA / ΔT is maximum (hereinafter referred to as "T (ΔTMA / ΔT)max It is preferable that the temperature is 450°C or higher in order to further increase the sintering resistance of the nickel powder. (ΔTMA / ΔT) max More preferably, T is 500°C or higher, and even more preferably, 550°C or higher. (ΔTMA / ΔT) max The higher the temperature, the better from the viewpoint of sintering resistance of the nickel powder. (ΔTMA / ΔT) max If t is high, the sintering resistance of the nickel powder is sufficiently high to be satisfactory. The measurement conditions for TMA are a 1% by volume hydrogen / 99% by volume nitrogen atmosphere and a temperature rise rate of 10° C. / min (the measurement conditions for TMA described below are the same as these).

[0024] It is preferable that the value of ΔTMA / ΔT itself is small because the internal electrode layers gradually shrink during the temperature rise process in the firing process. From this point of view, the maximum value of ΔTMA / ΔT in the temperature range from 400 ° C to 800 ° C (ΔTMA / ΔT) max (ΔTMA / ΔT) is preferably 0.10 or more and 0.20 or less, more preferably 0.12 or more and 0.18 or less, and even more preferably 0.14 or more and 0.16 or less. max The reason for setting the temperature range from 400 to 800°C is that (ΔTMA / ΔT) in this temperature range maxIf the value of is within the above-mentioned range, when the nickel powder of the present invention is used as an internal electrode of an MLCC, the difference in temperature at which the internal electrode layer and the dielectric layer shrink is small, and the occurrence of structural defects such as cracks and delamination caused by this can be suppressed. Also, when the nickel powder of the present invention is used as an electrode catalyst for an SOFC or the like, sintering of nickel particles is suppressed at the operating temperature of the electrode catalyst, and the resulting decrease in catalytic activity is less likely to occur.

[0025] The nickel powder of the present invention preferably exhibits small shrinkage in the temperature range of 400°C to 800°C. In addition, the nickel powder of the present invention preferably exhibits small shrinkage in the temperature range of 100°C to 300°C. The temperature range of 100°C to 300°C corresponds to the thermal decomposition temperature of a binder (e.g., ethyl cellulose) in the process of manufacturing an internal electrode of an MLCC using the nickel powder of the present invention together with the binder. If the nickel powder exhibits small shrinkage in this temperature range, gas generated by thermal decomposition of the binder is more likely to volatilize to the outside, making it less likely for the gas to remain in the internal electrode. Residual gas causes structural defects due to thermal expansion of the gas during the temperature rise process, which contributes to a decrease in the performance of the MLCC. From this perspective, the maximum value of ΔTMA / ΔT (ΔTMA / ΔT) in the temperature range of 100°C to 300°C is max is 3.0×10 -2 Preferably, it is 1.0 x 10 or less. -4 Over 3.0 x 10 -2 More preferably, it is 5.0×10 or less. -3 Over 2.0 x 10 -2 More preferably, it is 7.0×10 or less. -3 Over 1.8 x 10 -2 It is even more preferred that: Furthermore, when tin is present on or near the surface of the nickel particles, the thermal decomposition of the binder proceeds more slowly in the temperature range of 100°C to 300°C, which also makes it difficult for gas to remain in the internal electrode. The reason for this is that nickel has a catalytic effect that promotes the thermal decomposition of the binder, and when tin is present on or near the surface of the nickel particles, the catalytic effect of nickel is suppressed.

[0026] (ΔTMA / ΔT) in the temperature range from 100℃ to 300℃ max To reduce the value of N2 / N1, it is preferable that the proportion of nickel element present on the surface of the nickel particles and in the vicinity thereof is metallic and the proportion of nickel element present in a compound state such as oxide or hydroxide is small. The reason for this is that when nickel exists in a compound state other than metal, gas is generated due to reduction of the nickel compound and the nickel particles shrink. From this perspective, when the particle surface region of the nickel powder is measured in the depth direction by XPS, it is preferable that the value of N2 / N1, which is the ratio of the detection intensity of metallic nickel to the detection intensity of nickel element N1, is 0.35 or more, particularly 0.40 or more, and especially 0.45 or more. The closer the value of N2 / N1 is to 1, the smaller the shrinkage of the nickel powder will be, which is preferable. From the viewpoint of further reducing the shrinkage of the nickel powder, it is preferable that the value of N2 / N1 at any three points in the particle surface region is 0.35 or more, particularly 0.40 or more, and especially 0.45 or more.

[0027] The nickel particles constituting the nickel powder of the present invention may have one or more of a variety of shapes, such as spherical, flake, or polyhedral. Spherical nickel particles are particularly preferred. Nickel powder containing spherical particles can increase the density of the sintered body obtained after sintering. Furthermore, when the powder is used as a wiring material, it can increase the density of the wiring and improve the dimensional stability of the wiring. Furthermore, when the powder is used as a catalyst, it can increase the specific surface area of ​​the entire nickel powder and enhance catalytic activity.

[0028] A particle shape being spherical means that the circularity coefficient is 0.65 or more, more preferably 0.70 or more. The circularity coefficient is calculated by randomly selecting 200 particles that do not overlap each other from a scanning electron microscope image of the particle to be measured, and calculating the circularity coefficient as 4πS / L where S is the area of ​​the two-dimensional projection image of the particle and L is the perimeter. 2 It is the arithmetic mean value of the circularity coefficient calculated from the formula. If the two-dimensional projection image of a particle is a perfect circle, the circularity coefficient of the particle is 1, so the higher the numerical value of the circularity coefficient, the closer the particle is to a perfect sphere. The upper limit of the circularity coefficient of nickel particles is preferably closer to 1, but 0.95 is realistic.

[0029] As long as the effects of the present invention are achieved, the particles constituting the nickel powder may be coated with an organic or inorganic substance or subjected to a surface treatment. Examples of inorganic coatings include inorganic oxides such as SiO2 and ZrO2, which are stable against heat and oxygen. Coating with these stable inorganic oxides can further improve sintering resistance. Examples of organic surface treatments include attaching organic dispersants such as amines and carboxylic acids to the particle surfaces. This treatment can suppress particle aggregation and improve particle dispersibility.

[0030] Next, a preferred method for producing the nickel powder of the present invention will be described. This production method is roughly divided into a process for producing nickel base particles and a process for coating the nickel base particles with tin. Each process will be described below.

[0031] As a method for producing nickel base particles, any method known in the art can be used. For example, dry methods such as wet reduction and atomization can be used. From the viewpoint of easy control of the particle size of the nickel base particles, it is preferable to use the wet reduction method. Therefore, in the following explanation, a method for producing nickel base particles substantially composed of elemental nickel by the wet reduction method will be described.

[0032] Examples of nickel sources used in wet reduction methods include water-soluble nickel compounds. Examples of such nickel compounds include various nickel compounds, such as nickel organic acid salts (e.g., nickel formate, nickel acetate, nickel malonate, and nickel succinate), nickel inorganic acid salts (e.g., nickel nitrate and nickel sulfate), halides (e.g., nickel chloride), and hydroxides (e.g., nickel hydroxide). These nickel compounds may be anhydrous or hydrated. These nickel compounds may be used alone or in combination of two or more.

[0033] The water-soluble nickel compound is dissolved in water to obtain an aqueous solution of nickel ions. The concentration of nickel ions in the aqueous solution is preferably 0.01 mol / L or more and 2.0 mol / L or less, more preferably 0.05 mol / L or more and 1.5 mol / L or less, from the viewpoint of successful reduction precipitation of nickel base particles. A complexing agent can be added to the aqueous solution of nickel ions to control the reduction of the nickel ions. Examples of the complexing agent include polybasic acids such as citrates and other organic acids. The amount of complexing agent contained in the aqueous solution of nickel ions is preferably set to 0.1 to 2.0 moles per mole of nickel ions, in order to ensure successful reduction of the nickel ions. The aqueous solution of nickel ions may further contain various additives such as an antifoaming agent, if necessary.

[0034] Once the aqueous solution of nickel ions has been prepared, a reducing agent is added to reduce the nickel ions. Any reducing agent known in the art can be used without any particular limitations. Using a reducing agent that does not contain carbon is particularly preferable, since the resulting nickel base particles are substantially free of carbon. If the nickel base particles contain carbon, gas derived from the carbon element is likely to be generated during sintering, and this gas may unintentionally remain in the sintered body. From this perspective, it is preferable to use a carbon-free compound such as hydrazine, sodium borohydride, or sodium hypophosphite as the reducing agent.

[0035] The use of multiple reducing agents for the reduction of nickel ions is effective in obtaining fine nickel base particles with a uniform particle size. In one embodiment, the first reduction step is performed using sodium borohydride, followed by the second reduction step using hydrazine.

[0036] When performing the two-stage reduction, first, a water-soluble nickel source and hydrazine are mixed to form a complex of nickel ions and hydrazine (hereinafter also referred to as "nickel-hydrazine complex"), and then sodium borohydride is further added to reduce the nickel ions.

[0037] First, a water-soluble nickel source and hydrazine are mixed to prepare a first reaction solution. The first reaction solution is preferably prepared under conditions that allow a complex between nickel ions and hydrazine to be formed in the reaction solution. That is, in this production method, hydrazine is also used as a complexing agent for nickel ions. By reducing nickel ions under these conditions, nickel powder with a narrow particle size distribution and a large amount of nickel with low electrical resistance present on the particle surface can be efficiently obtained. An embodiment of the conditions for forming a complex between nickel ions and hydrazine will be described later.

[0038] In order to successfully reduce nickel ions, the amount of hydrazine used as the reducing agent is preferably 2 to 12 moles, more preferably 4 to 10 moles, per mole of elemental nickel. On the other hand, sodium borohydride is added in an amount of preferably 0.05 mol or more and 1.5 mol or less, more preferably 0.1 mol or more and 1.0 mol or less, per mol of nickel element.

[0039] The reduction of nickel ions using a reducing agent may be carried out in an unheated state or in a heated state. When the reduction of nickel ions is carried out in a heated state, it is preferable to heat the aqueous solution of nickel ions to a temperature of 60°C or higher and 90°C or lower.

[0040] Next, the nickel base particles are coated with tin. In this coating process, a slurry consisting of the post-reduction reaction solution containing nickel base particles or nickel-based alloy base particles and its dilution and washings is mixed with an aqueous solution in which a water-soluble tin compound is dissolved, and the tin compound is reduced to metallic tin, coating the nickel base particles with tin. When using a reaction solution after the reduction reaction, the tin compound may be reduced to metallic tin using unreacted reducing agent remaining in the reaction solution. Alternatively, a new reducing agent may be added. When using a washing solution obtained by diluting or washing the reaction solution, a sufficient amount of reducing agent is required to reduce the tin compound to metallic tin.

[0041] After nickel base particles are produced in an aqueous solution by the above-described nickel base particle production process, a water-soluble tin compound is subsequently added to the aqueous solution as a tin source. Examples of water-soluble tin compounds include alkali-soluble tin salts. Examples of alkali-soluble tin salts that can be used include tin oxoacid salts. Examples of tin oxoacid salts that can be used include alkali metal stannates (X2SnO3 (X represents NH4, Li, Na, K, Rb, or Cs)), which are compounds of Sn(IV). Among these, sodium stannate and potassium stannate are more preferred because they are highly soluble in water, inexpensive, and easily available. However, the present invention is not limited to these. The amount of water-soluble tin compound added is preferably such that the tin element is 1.5% by mass or more and 50.0% by mass or less, particularly 5.0% by mass or more and 45.0% by mass or less, and especially 10.0% by mass or more and 40.0% by mass or less, relative to 100% by mass, which is the total of the tin element and the nickel element in the aqueous solution.

[0042] When the nickel ions are reduced while the aqueous solution of nickel ions is heated, the water-soluble tin compound can be added while the aqueous solution is still heated. The heating temperature can be set to the same temperature as that during the reduction of the nickel ions. On the other hand, when nickel ions are reduced in an unheated state, the water-soluble tin compound may be added to the aqueous solution while it is still unheated, or the water-soluble tin compound may be added to the aqueous solution after it is heated. Whether the water-soluble tin compound is added in a heated or unheated state, it is preferable to add the water-soluble tin compound and then age the aqueous solution for a predetermined period of time while stirring it. Since the reducing agent used to reduce the nickel ions remains in the aqueous solution or a newly added reducing agent is present, the aging reduces the tin compound to metallic tin, forming a layer containing tin element on the surface of the nickel base particles. When sodium borohydride is used as the reducing agent in the previous step, tin boride is partially formed. By adjusting the aging time, the thickness of the tin-containing layer formed on the surface of the nickel base particles can be adjusted. Generally, the longer the aging time, the thicker the tin-containing layer. From this perspective, the aging time is preferably set to 0.1 to 20 hours, more preferably 0.2 to 10 hours, and even more preferably 0.5 to 5 hours.

[0043] The nickel powder obtained in this manner has high sintering resistance and low particle aggregation due to the presence of tin element on the surfaces of the nickel particles that make up the nickel powder. Taking advantage of these characteristics, the nickel powder of the present invention can be used as a conductive composition used to form internal electrodes of multilayer ceramic capacitors. This conductive composition contains nickel powder as a metal filler, a solvent, and preferably a binder. Examples of the form of the conductive composition include a conductive slurry, a conductive ink, and a conductive paste. Alternatively, by utilizing the catalytic activity of nickel, the nickel powder of the present invention can be used as an electrode catalyst for fuel cells or electrolysis cells, or as a gas reforming catalyst used in the production of hydrogen by decomposing hydrocarbon compounds through a steam reforming reaction or in the methanation reaction of CO. When the nickel powder of the present invention is used as an electrode catalyst or gas reforming catalyst, it may be used by supporting a slurry containing a solvent similar to the solvent used in the conductive composition described below on a catalyst support.

[0044] Examples of solvents used in the conductive composition include water, alcohols, ketones, esters, ethers, and hydrocarbons. Among these, it is preferable to use at least one of alcohols such as terpineol and dihydroterpineol, ethers such as ethyl carbitol and butyl carbitol, and hydrocarbons such as hexane, heptane, and toluene. Examples of binder resins used in the conductive composition include acrylic resins, epoxy resins, polyester resins, polycarbonate resins, and cellulose resins, and it is preferable to use at least one of these. Using these resins allows the viscosity of the solvent to be adjusted, further improving workability.

[0045] The conductive composition can be applied to the surface of the target surface by a predetermined means, for example, to form a coating film and a conductive film having a desired pattern. If necessary, the coating film can be heated to form a conductive film. The nickel powder contained in the conductive composition has a small particle diameter and a sharp particle size distribution, which allows the formation of a high-density conductive film. As a result, the resulting conductive film is less likely to have unintended discontinuities and has low electrical resistance.

[0046] The conductive film described above can be used to form, for example, wiring circuits on printed wiring boards or electrodes on chip components, and can also be used as a material for filling vias in printed wiring boards or as an adhesive for surface-mounting electronic devices on printed wiring boards. [Example]

[0047] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

[0048] Example 1 An aqueous solution of nickel ions was prepared by dissolving nickel sulfate hexahydrate, trisodium citrate, and an antifoaming agent in pure water. The concentration of nickel ions in the aqueous solution was The concentration was 0.2 mol / L. Trisodium citrate was used in an amount of 0.2 mol per 1 mol of nickel ions. Hydrazine monohydrate was first added to this aqueous solution and the solution was stirred, then sodium borohydride was added and the solution was continued to be stirred. The solution was heated to 70°C. The amount of hydrazine monohydrate added was 8.0 moles per mole of nickel ions. The amount of sodium borohydride added was 0.7 moles per mole of nickel ions. Next, while maintaining the heating temperature, an aqueous solution containing dissolved sodium stannate was added at a rate of 40 ml / min in the amount shown in Table 1. After the addition, the aqueous solution was stirred while maintaining the heating temperature, and aging was carried out for the time shown in Table 4.

[0049] After aging, the reaction solution was cooled to room temperature and decanted with pure water until the sodium ion concentration was 10 ppm or less. Solvent substitution with 2-propanol was then performed three times. The reaction solution was then concentrated by decantation, and the solid matter was vacuum dried, in that order, to obtain the desired nickel powder.

[0050] [Examples 2 to 4 and Comparative Example 1] The amount of aqueous sodium stannate solution added and the aging time were as shown in Table 4. Other than these, nickel powder was obtained in the same manner as in Example 1.

[0051] Example 5 The nickel base particles were manufactured using the same process as in Example 1. After cooling the reaction solution to room temperature, decantation with pure water was performed until the sodium ion concentration was 10 ppm or less, and this was used as a washing solution. Pure water was added to the solution until the total weight reached 400 g, and 40.048 g of hydrazine monohydrate was added all at once. While the aqueous solution was heated and maintained at 70°C, an aqueous solution of sodium stannate prepared by dissolving 8.002 g of sodium stannate in pure water was added at a rate of 40 ml / min. While the solution was heated and maintained at 70°C, aging was performed for 5 hours after the addition was completed. After aging, nickel powder was obtained in the same manner as in Example 1.

[0052] 〔evaluation〕 The tin content of the nickel powders obtained in the examples and comparative examples was measured by ICP atomic emission spectroscopy. Furthermore, the values ​​of X1, X2 / X1, S2 / S1, and N2 / N1 were determined by the XPS analysis method described below, and the sputtering depth at which the value of X became A was also determined. Furthermore, SEM observation, TMA measurement, magnetization measurement, and laser diffraction / scattering particle size distribution measurement were performed using the methods described below. The results are shown in Table 4. The S2 / S1 and N2 / N1 values ​​in Table 4 are those at the outermost surface of the nickel powder. Figure 1 shows a graph in which the absolute value of the differential value obtained by differentiating the TMA shrinkage rate (%), which is the TMA measurement result, with temperature T (°C), i.e., ΔTMA / ΔT, is shown on the y-axis and temperature T on the x-axis.

[0053] [X-ray photoelectron spectroscopy (XPS) measurement] The measurement sample for XPS was prepared by molding nickel powder into pellets using a press. Specifically, approximately 10 mg of the powder sample was placed in an aluminum container measuring 5.2 mm in diameter and 2.5 mm in height. Next, using a press (manufactured by AS ONE, product number: 1-312-01) and an adapter (product number: 1-312-03), pressure was applied to the aluminum container at a predetermined stroke (25 mm). The nickel powder pellet supported in the aluminum container was then removed. The obtained pellet-shaped product was subjected to measurement of the outermost surface and measurement of the depth direction from the sample surface to the inside by sputtering with Ar monomer ions. The measurement conditions were as follows:

[0054] Measurement equipment: ULVAC-PHI VersaProbe III Excitation X-ray: Monochromated Al-Kα radiation (1486.7 eV) Output: 50W Acceleration voltage: 15kV ·X-ray irradiation diameter: 200μmφ X-ray scanning area: 1000μm×300μm Detection angle: 45° Pass energy: 26.0 eV Energy step: 0.1 eV / step Sputtered ion species: Ar monomer ions Sputtering rate: 3.3 nm / min (SiO2 equivalent) Sputtering interval: 20 seconds ·Measurement element: C 1s , Ni 2p3 , Sn 3d5 Energy correction value: C 1s CC and CH bonds (284.8 eV)

[0055] [XPS data analysis] XPS data were analyzed using data analysis software (ULVAC-PHI, "Multipack Ver. 9.9"), with Shirley as the background mode.

[0056] [Tin content: X] Ni 2p3 and Sn 3d5 Sn relative to the total number of atoms of the two elements 3d5 The ratio of the number of atoms in X (% ) was decided.

[0057] [S2 / S1] Sn 3d5 Peak separation analysis was performed using the least squares method with two peaks, a Sn metal peak and a Sn oxide peak, under the conditions described below. The range of each peak was set as shown in Table 1, and the half-width of the peak was a free parameter. The peak function used was a Voigt function with a Gaussian function ratio in the range of 70 to 100%.

[0058] [Table 1]

[0059] The areas of the Sn metal peak and the Sn oxide peak obtained by peak separation analysis were used as the detection intensity, and the sum of the area of ​​the Sn metal peak and the area of ​​the Sn oxide peak was taken as S1, and the area of ​​the Sn oxide peak was taken as S2. The ratio of S2 was defined as the proportion of Sn oxides present in the particle surface region, S2 / S1.

[0060] [N2 / N1] Ni 2p3 The peaks were analyzed by the least squares method under the following conditions: the half-width of each peak to be fitted was a free parameter, a Gaussian function was used as the peak function, and the peak energy was within the range shown in Table 2. The sum of the peak areas of peak numbers 1 to 4 obtained by peak separation analysis was defined as the peak area A1 of metallic Ni. The area of ​​peak number 5 was defined as the peak area A2 of NiO. The peak area of ​​peak number 6 was defined as the peak area A3 of other Ni compounds (Ni compounds other than NiO) including Ni2O3 and Ni(OH)2. The sum of the peak areas of peak numbers 7 to 9 was defined as the peak area A4 of the satellite peak derived from Ni oxide. A1 / (A1+A2+A3+A4) was defined as N2 / N1, which is the ratio of the detection intensity of metallic nickel to the detection intensity N1 of nickel element.

[0061] The peak parameters of peak numbers 1 to 4 shown in Tables 2 and 3 below are values ​​in a peak set for reproducing the actually measured spectrum based on the measurement results of a Ni metal plate from which the surface oxide film was removed with an Ar ion beam.

[0062] [Table 2]

[0063] [Table 3]

[0064] [Scanning electron microscope (SEM) observation] The Ni powder was observed with an SEM under the following observation conditions, and the particle size of the Ni particles was determined by the method described above. Measurement equipment: JEOL Ltd. JSM-7900F Acceleration voltage: 1.0 kV Observation mode: GBSH-S Detector: Upper Extremity Detector (UED) Magnification: 100,000x

[0065] [Thermomechanical analysis (TMA) measurement] The TMA measurement device used was a TMA / SS6000 manufactured by Seiko Instruments Inc. 0.2–0.3 g of nickel powder was placed in a 5.0 mm diameter stainless steel mold and pressed to form a pellet at a pressure of 92 MPa. The pellet length of the resulting pellet was measured and used as the measurement sample. The sample was placed in the measurement device and heated at a rate of 10°C / min under a load of 49 mN in a 1% by volume hydrogen / 99% by volume nitrogen atmosphere. Measurements were started at room temperature (25°C), and a graph showing the relationship between temperature and shrinkage (%) was obtained. The shrinkage was calculated in percentage terms by dividing the displacement by the pellet length before measurement. The shrinkage was differentiated with respect to temperature and the absolute value was taken to obtain ΔTMA / ΔT at each temperature.

[0066] [Magnetization (VSМ) measurement] The saturation magnetization Ms, which is a parameter of the magnetic properties of the nickel powder, was measured using a vibrating sample magnetometer (VSM-5 manufactured by Toei Industry Co., Ltd.) in an external magnetic field of 10 kOe.

[0067] [Laser diffraction / scattering particle size distribution measurement] Approximately 50 mg of nickel powder was mixed with 50 mL of pure water containing 0.1% sodium hexametaphosphate, and the mixture was dispersed for 1 minute using an ultrasonic homogenizer (Nippon Seiki Seisakusho, US-150E) at an output of 1.0 A to prepare a slurry. The prepared slurry was then placed in a laser diffraction / scattering particle size distribution analyzer (Microtrackbell MT3300 EXII) through which pure water was circulated, and the particle size distribution was measured.

[0068] [Table 4]

[0069] As is clear from the results shown in Table 4, the nickel powders obtained in each example had a higher shrinkage starting temperature and T (ΔTMA / ΔT)max is high and (ΔTMA / ΔT) max It can be seen that is small. Although not shown in the table, in the nickel powder of each example, in the region from the outermost surface of the nickel powder to a sputtering depth of 20 nm in SiO2 equivalent, the value of X gradually decreased from the outermost surface toward a sputtering depth of 20 nm. Furthermore, the nickel powders obtained in each example have lower saturation magnetization values ​​and a smaller degree of particle aggregation than the nickel powder of Comparative Example 1, which indicates that magnetic aggregation is suppressed. 1, it can be seen that the position of the apex of the upward peak in each Example is on the higher temperature side than the position of the apex of the upward peak in Comparative Example 1. In particular, in Comparative Example 1, a small upward peak is observed around 200°C, whereas in each Example, no such peak is observed around the same temperature.

Claims

1. A nickel powder consisting of an aggregate of nickel particles or nickel-based alloy particles, the nickel particles or nickel-based alloy particles contain tin element on their surfaces, and the tin element content is 1.5% by mass or more and 30% by mass or less; The nickel powder has a 50% particle diameter D in the number distribution measured by observation with a scanning electron microscope. ５０ is 40 nm or more and 52 nm or less, X-ray photoelectron spectroscopy revealed that the nickel powder was composed of SiO ２ The nickel powder has a portion in which, when a region up to a sputtering depth of 5 nm in terms of a thickness is measured, the maximum value X1 of the ratio X of the number of tin atoms to the total number of nickel and tin atoms is 0.23% or more and 0.66% or less in the region.

2. X-ray photoelectron spectroscopy revealed that the nickel powder was composed of SiO ２ 2. The nickel powder according to claim 1, wherein, when a region up to a sputtering depth of 5 nm in terms of SiO 2 is measured, any of the regions has a region where the ratio of the detection intensity S2 of tin oxide to the detection intensity S1 of tin element is 0.80 or more.

3. X-ray photoelectron spectroscopy revealed that SiO ２ The nickel powder according to claim 1 or 2, wherein, when measuring a region up to a sputtering depth of 20 nm in terms of surface area, the value of X gradually decreases from the outermost surface to a sputtering depth of 20 nm.

4. X-ray photoelectron spectroscopy revealed that SiO ２ When measuring the area up to a sputtering depth of 20 nm in terms of surface area, ２ When the average value of X1 in the range of a sputtering depth of 5 nm in terms of nickel and tin atoms and the ratio X2 of the number of tin atoms to the total number of nickel and tin atoms at a sputtering depth of 20 nm is A, the sputtering depth at which the value of X is A is 1.0 nm or more and 10.0 nm or less. The nickel powder according to any one of claims 1 to 3.

5. A conductive composition comprising the nickel powder according to any one of claims 1 to 4 and a solvent.

6. A conductive film formed using the conductive composition according to claim 5 .

7. An electrode catalyst for use in a hydrogen electrode of a fuel cell, comprising the nickel powder according to any one of claims 1 to 4.

8. An electrode catalyst for use in a hydrogen electrode of a water electrolysis cell, comprising the nickel powder according to any one of claims 1 to 4.

9. A gas reforming catalyst comprising the nickel powder according to any one of claims 1 to 4.

10. 2. The method for producing nickel powder according to claim 1, a step of mixing a slurry containing nickel base particles or nickel-based alloy base particles with an aqueous solution having a water-soluble tin compound dissolved therein so that the tin content is 1.5 mass % or more and 50.0 mass % or less relative to 100 mass % of the total of tin and nickel, and reducing the tin compound to metallic tin to form a layer containing tin on the surfaces of the nickel base particles or nickel-based alloy base particles; A method for producing nickel powder, comprising adding the aqueous solution containing the water-soluble tin compound and then aging the mixture for 0.5 hours to 20 hours.

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