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

Abstract

The present invention pertains to a nickel powder or an aggregate of nickel particles having a 50%-particle diameter D50 of 100 nm or less in a number distribution obtained through measurement performed with scanning electron microscope observation. The contained amount of boron (B) elements in the nickel particles is 0.1-1.0 mass%. Further, when measurement by TOF-SIMS is performed in a range from the outermost surface of the powder to a sputtering depth of 10 nm, in terms of SiO2, of the powder, a ratio (Amax / A1), which is obtained by dividing the maximum value Amax of the ratio of the detected ion number of B elements with respect to the detected ion number of Ni elements by the ratio A1 of the detected ion number of B ions with respect to the detected ion number of Ni ion at the outermost surface of the powder, is 12 or more. The present invention also provides a production method for reducing Ni ions, by forming a nickel-hydrazine complex and then adding thereto a boron element-containing reductive compound. The present invention further provides a conductive composition and a conductive film, in which said nickel powder is used.

Description

[Technical Field]

[0001] The present invention relates to a nickel powder, a method for producing the same, a conductive composition, and a conductive film. [Background technology]

[0002] To achieve miniaturization and high capacitance in electronic components such as multilayer ceramic capacitors (MLCCs) used in electronic devices, there is a demand for increased wiring density and improved dimensional stability in the wiring formation within the electronic devices. To achieve these demands, for example, the use of metal particles with small particle diameters as a constituent material for the wiring structure has been investigated.

[0003] Patent Document 1 discloses composite microparticles in which a core material is made of a composite compound of nickel, a noble metal element, boron, etc., and the surface of the core material is coated with a metal oxide, with the aim of solving the problems of shrinkage during sintering and oxidation of metals.

[0004] Furthermore, Patent Document 2 discloses a conductive powder in which Ni-B alloy powder is deposited on the surface of Ni powder in order to impart oxidation resistance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US 2002 / 146564 A1 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-68090 Summary of the Invention

[0006] When the metal particles described in Patent Documents 1 and 2 are used as raw materials for manufacturing a wiring structure, it is sometimes impossible to form a wiring structure with low electrical resistance.

[0007] The present invention therefore relates to a nickel powder with low electrical resistivity.

[0008] The present invention provides a nickel powder comprising an aggregate of nickel particles containing elemental boron, The content of the boron element is 0.1% by mass or more and 2.0% by mass or less, The 50% particle size D50 in the number distribution measured by scanning electron microscope observation is 100 nm or less, In the measurement of the depth direction of the powder by time-of-flight secondary ion mass spectrometry, when the range from the outermost surface of the powder to a sputter depth of 10 nm in terms of SiO2 of the powder is measured, the ratio of the number of detected ions of boron ions to the number of detected ions of nickel ions at the outermost surface of the powder is defined as A1, and the maximum value of the ratio of the number of detected ions of boron ions to the number of detected ions of nickel ions in the powder is defined as A max When A1 is max The ratio (A max / A1) is 12 or more.

[0009] The present invention also provides a nickel powder comprising an aggregate of nickel particles containing elemental boron, The content of the boron element is 0.1% by mass or more and 2.0% by mass or less, The 50% particle size D50 in the number distribution measured by scanning electron microscope observation is 100 nm or less, The nickel powder has a NiB content of 81% or less relative to the total amount of NiB, Ni2B, and Ni3B when measured in the depth direction of the powder by time-of-flight secondary ion mass spectrometry over a range from the outermost surface of the powder to a sputtering depth of 10 nm in terms of SiO2 of the powder.

[0010] The present invention also provides a nickel powder comprising an aggregate of nickel particles containing elemental boron, The content of the boron element is 0.1% by mass or more and 2.0% by mass or less, The 50% particle size D50 in the number distribution measured by scanning electron microscope observation is 100 nm or less, The present invention provides a nickel powder having a coefficient of variation (CV) value represented by the following formula (1) of 20% or less. CV value (%) = (standard deviation of particle size (nm) obtained by scanning electron microscope observation) / (arithmetic mean particle size (nm)) × 100 (1)

[0011] The present invention also provides a method for producing nickel powder, comprising the steps of mixing a water-soluble nickel source and hydrazine to form a nickel-hydrazine complex, and then further adding a reducing compound containing boron element to reduce the nickel ions. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1(a) is a scanning electron microscope image of the nickel powder of Example 1, and FIG. 1(b) is a scanning electron microscope image of the nickel powder of Comparative Example 1. [Figure 2] FIG. 2(a) is a graph showing the ratio of the number of detected boron ions to the number of detected nickel ions at each sputtering depth in SiO2 equivalent when the nickel powders of Examples 1 to 3 and Comparative Example 1 were measured in the depth direction by time-of-flight secondary ion mass spectrometry, and FIG. 2(b) is a graph showing the first derivative of the ratio of the number of detected boron ions to the number of detected nickel ions in the graph of FIG. 2(a) with respect to the sputtering depth. [Figure 3] FIG. 3 shows the 1H-NMR spectra of the nickel-hydrazine complexes produced in Examples 3, 4, 6 and 7. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention relates to a nickel powder comprising an aggregate of nickel particles mainly containing nickel element, and a method for producing the same. Prior to describing the nickel powder, a preferred method for producing the nickel powder will be described.

[0014] This production method first involves mixing a water-soluble nickel source with hydrazine to form a complex of nickel ions and hydrazine (hereinafter also referred to as a nickel-hydrazine complex). Thereafter, a reducing compound containing boron element is further added to reduce the nickel ions. This step preferably involves forming the nickel-hydrazine complex in an aqueous solution mainly composed of water, and then adding the reducing compound containing boron element to the aqueous solution. One embodiment of this production method will be described below. In the preferred embodiment described below, a reaction system mainly composed of water will be described as an example. By adopting such a method, it is possible to sufficiently proceed with the reduction reaction, thereby obtaining particles with small diameters and small particle size variations, and it is also advantageous in that it is possible to suppress the incorporation of impurities such as carbon element.

[0015] 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 nickel-hydrazine complex to be formed in the reaction solution. That is, in this production method, hydrazine is used as a complexing agent for nickel ions. By reducing nickel ions under these conditions, nickel with low electrical resistance is abundantly present on the particle surface, and nickel powder with a sharp particle size distribution can be efficiently obtained. An embodiment of the conditions for forming a nickel-hydrazine complex will be described later. Whether or not a nickel-hydrazine complex is formed in the first reaction solution can be determined by, for example, 1 This can be determined by H-NMR. 1 The measurement conditions by H-NMR will be described in detail in the Examples below.

[0016] The first reaction solution may be prepared by adding the raw materials simultaneously to a solvent such as pure water, or by adding the raw materials to the solvent in any order. From the viewpoint of improving the ease of handling during production, it is preferable to prepare a nickel raw material solution in advance by mixing a water-soluble nickel source with a solvent such as pure water, and then mix the nickel raw material solution with solid hydrazine or an aqueous hydrazine solution to form a complex between nickel ions and hydrazine. In this case, the nickel raw material solution is prepared in a hydrazine-free state.

[0017] Examples of water-soluble nickel sources used in the nickel raw material solution include various nickel compounds, such as nickel formate, nickel acetate, nickel malonate, and nickel succinate, nickel nitrate, nickel sulfate, and other nickel organic acid salts, nickel chloride, and other nickel inorganic acid salts, nickel chloride, and other halides, and nickel hydroxide, and these nickel compounds may be anhydrous or hydrated. These nickel compounds may be used alone or in combination of two or more.

[0018] The content of the water-soluble nickel source in the nickel raw material 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, expressed in terms of the molar concentration of nickel element.

[0019] Hydrazine may be used in the form of anhydrous form, a hydrate such as monohydrate, a liquid hydrazine compound such as hydrazine carbonate or hydrazine bromate, or a solid hydrazine compound such as hydrazine hydrochloride, hydrazine nitrate, or hydrazine sulfate. In this specification, these hydrazines or compounds derived from hydrazine may be collectively referred to simply as "hydrazine." In either case, from the viewpoint of efficiently forming a complex with nickel ions, the amount of hydrazine added is preferably 2 to 12 moles, more preferably 4 to 10 moles, per mole of nickel element.

[0020] The solvent used in preparing the first reaction liquid may be at least one of water and an organic solvent, such as alcohols (e.g., monohydric alcohols and polyhydric alcohols), ethers (e.g., polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers), esters, ketones, nitrogen-containing heterocyclic compounds, amides, amines, saturated hydrocarbons, etc.

[0021] Among these, from the viewpoint of reducing production costs and improving production efficiency due to ease of handling during production, it is preferable to use at least one of water and a hydrophilic organic solvent as the solvent used in preparing the first reaction liquid, and it is more preferable to use water alone. Using water alone also has the advantage of being able to reduce the unintended inclusion of impurities such as carbon element in the produced nickel particles. As the hydrophilic organic solvent, monohydric alcohols such as methanol, ethanol, 1-propanol, and 2-propanol, and dihydric alcohols such as ethylene glycol, propylene glycol, and diethylene glycol are preferably used.

[0022] The first reaction solution is preferably prepared by adding a ligand compound other than hydrazine to the water-soluble nickel source and hydrazine. The inclusion of the ligand compound improves the particle size uniformity of the resulting nickel powder and reduces the CV value, which is an index of particle size variation. Furthermore, aggregation of the resulting particles can be suppressed.

[0023] The ligand compound added to the first reaction solution has a functional group with a lone electron pair in its chemical structure. Therefore, the ligand compound functions as a complexation promoter that coordinates with nickel ions during the particle formation process, facilitating the formation of nickel complexes in the reaction solution. Additionally, after particle formation, the ligand compound's functional groups coordinate with atoms on the particle surface to form steric hindrances, thereby advantageously functioning as a dispersant that enhances the dispersibility of particles.

[0024] Examples of the ligand compounds include high molecular weight organic compounds and low molecular weight organic compounds. These compounds can be used alone or in combination. Furthermore, these compounds may each independently be an anhydride or a hydrate. The polymeric organic compound referred to in the present invention refers to one having a weight-average molecular weight of 10,000 or more. Examples of such polymeric organic compounds include polyvinylpyrrolidone, sodium carboxymethylcellulose, and polyoxyalkylene compounds. Examples of low-molecular-weight organic compounds include linear or branched monovalent, divalent, or trivalent carboxylic acids, aliphatic or aromatic organic acids such as hydroxy acids, and aliphatic or aromatic organic amines such as primary amines, secondary amines, tertiary amines, and aromatic amines.

[0025] Among these, from the viewpoint of reducing production costs and reducing the content of impurities such as carbon and nitrogen elements when the nickel powder is obtained, it is preferable to use a low-molecular-weight organic compound as the ligand compound, and it is more preferable to use a saturated or unsaturated aliphatic organic acid. Specific examples of the aliphatic organic acid include aliphatic monocarboxylic acids having 1 to 12 carbon atoms, such as lauric acid, undecanoic acid, caproic acid, acetic acid, formic acid, and crotonic acid, and aliphatic hydroxy acids, such as lactic acid, malic acid, and citric acid.

[0026] When a ligand compound is further contained, the content of the ligand compound in the first reaction solution is preferably 0.1 to 0.8 mol, more preferably 0.2 to 0.6 mol, per mol of nickel element. By adding the ligand compound in this range, after the nickel particles are generated, the ligand compound is adsorbed onto the particle surface, slowing particle growth, thereby reducing particle size and particle size variation (e.g., CV value). In addition, when the ligand compound functions as a dispersant, the steric repulsion between particles caused by the dispersant can suppress aggregation of the generated particles. Furthermore, unintended contamination of impurities such as carbon element can be reduced.

[0027] If the content of the ligand compound is within the above range, even when the obtained nickel powder is used, for example, for electrodes of electronic components or for electrode catalysts of fuel cells, the intended conductivity and catalytic activity of nickel can be improved and the occurrence of voids and cracks due to gases derived from impurities can be suppressed. From the viewpoint of making these effects more pronounced, the content of the ligand compound is preferably as small as possible.

[0028] One embodiment of the conditions for forming a complex of nickel ions and hydrazine is a method in which a water-soluble nickel source is mixed with hydrazine under acidic conditions. Specifically, one example is a method in which the pH of a nickel raw material solution is adjusted in advance to be acidic, and then various types of hydrazine are mixed into the nickel raw material solution. By adjusting the conditions to be as described above, it is possible to suppress the precipitation of nickel hydroxide due to the hydroxide of the nickel salt or nickel salt, which are raw materials, before mixing with hydrazine, and to efficiently form a nickel-hydrazine complex.

[0029] Acidic conditions refer to a pH of less than 7.0, preferably 2.0 to 6.5, and more preferably 3.0 to 6.0. Various acids and basic substances can be used to adjust the pH. To achieve acidic conditions, for example, organic acids such as citric acid, acetic acid, formic acid, and lauric acid or salts thereof can be added as the ligand compounds described above, or at least one inorganic acid such as hydrochloric acid, nitric acid, and sulfuric acid can be further added to the nickel raw material solution. Examples of basic substances that can be used include sodium hydroxide, potassium hydroxide, and aqueous ammonia.

[0030] Another embodiment of adjusting the conditions to form a complex between nickel ions and hydrazine is to prepare the first reaction liquid under non-heating conditions. Specifically, a nickel raw material solution and, if necessary, a ligand compound are premixed under non-heating conditions, and then various hydrazines are mixed with the nickel raw material solution. Non-heating conditions are, for example, a temperature range of 5°C or higher and lower than 40°C. By preparing the first reaction solution under such conditions, the reduction of nickel ions by hydrazine does not proceed, or the reaction rate of complex formation can be maintained at a rate sufficiently higher than the reduction reaction rate. Therefore, the reduction of nickel ions, as described below, can be efficiently carried out while maintaining the conditions for forming a complex between nickel ions and hydrazine. These conditions may be employed alone or in combination with the acidic conditions described above.

[0031] Next, the first reaction solution in which the nickel-hydrazine complex is produced is mixed with a reducing compound containing boron element to obtain a second reaction solution. This reduces the nickel ions to obtain an aggregate of nickel particles. The first reaction solution in which the nickel-hydrazine complex is produced is brought to a neutral or basic condition with a pH of 7.0 or higher by the addition of hydrazine. Furthermore, as described below, it is also preferable to heat the second reaction solution to carry out the reduction reaction in order to improve production efficiency.

[0032] From the viewpoint of appropriately controlling the reduction reaction, it is preferable to prepare a reducing solution containing a reducing compound containing boron element separately from the first reaction solution prior to the preparation of the second reaction solution. In this production method, the reducing compound containing boron element is used as a reducing agent for nickel ions. As with the preparation of the first reaction solution, the preparation of the reducing solution is advantageously carried out under non-heating conditions, since this suppresses the hydrolysis reaction in the solution of the reducing compound containing boron element, allows the reduction reaction to proceed sufficiently, and allows the production of particles with small diameters and small particle size variation.

[0033] The solvent for preparing the reducing solution can be the same as the solvent used in preparing the first reaction solution. Specifically, from the viewpoint of reducing the unintended incorporation of impurities such as carbon into the generated nickel particles, it is preferable to use at least one of water and a hydrophilic organic solvent, and it is more preferable to use only water, as the solvent for preparing the reducing solution. Furthermore, from the viewpoint of suppressing a decrease in reducing power due to hydrolysis of the reducing compound containing boron, when water is used as the solvent, it is preferable to add the reducing compound containing boron under basic conditions with a pH of 9.0 or higher. A basic substance such as sodium hydroxide, potassium hydroxide, or aqueous ammonia can be used to adjust the pH.

[0034] The reducing compound containing boron element may be at least one of borohydride and aminoborane. The reducing compound containing boron element may be in a solid or liquid state. Among these, from the viewpoint of efficiently proceeding the reduction reaction of nickel ions, it is more preferable to use a borohydride as the reducing compound containing boron element.

[0035] As the borohydride, it is preferable to use a water-soluble borohydride or a salt thereof, such as sodium borohydride, ammonium borohydride, potassium borohydride, lithium borohydride, aluminum borohydride, or zinc borohydride. As the aminoborane, it is preferable to use a secondary aminoborane, such as diethylaminoborane or dimethylaminoborane, or a tertiary aminoborane, such as triethylaminoborane or trimethylaminoborane. The above-mentioned borohydrides and aminoboranes can be used alone or in combination of two or more.

[0036] When mixing the first reaction liquid and the reducing solution, one may be added to the other and mixed, or these solutions may be mixed simultaneously. Furthermore, these solutions may be mixed all at once or sequentially, such as by dropwise addition. In either case, mixing the first reaction liquid and the reducing solution from start to finish under non-heating conditions is preferred, as this allows the reduction reaction to proceed slowly, resulting in small particle sizes and reduced variation in particle size of the resulting particles.

[0037] Among the above-mentioned mixing methods, it is preferable to prepare the second reaction solution by gradually adding the reducing solution to the first reaction solution. By carrying out this sequential addition, the progress of the reduction reaction of nickel ions from the nickel-hydrazine complex can be appropriately controlled, and the nickel and nickel boride produced by the reduction can be gently precipitated. As a result, particles with a large amount of nickel element present on the surface and small particle diameters can be efficiently produced, and the particle aggregates obtained thereby have a sharp particle size distribution.

[0038] When mixing the first reaction liquid with the reducing solution, it is preferable to adjust the pH of the second reaction liquid to a neutral or basic condition of 7.0 or higher, since this suppresses decomposition of reducing compounds containing hydrazine or boron element and allows for efficient reduction of nickel ions. To achieve the above-mentioned pH condition in the second reaction liquid, for example, the first reaction liquid prepared by the above-mentioned method may be mixed with the reducing solution. When the second reaction liquid is heated as described below, it is preferable to adjust the pH of the second reaction liquid before heating (i.e., before heating).

[0039] When the reducing solution is added successively, the rate of addition is preferably 0.005 L / min to 10 L / min, more preferably 0.05 L / min to 1 L / min.

[0040] In preparing the second reaction liquid, the reducing solution is mixed so that the total content of the reducing compounds containing boron in the second reaction liquid is preferably 0.05 to 1.5 mol, more preferably 0.1 to 1.0 mol, per 1 mol of nickel. By adjusting the total content of the reducing compounds containing boron to such a ratio, it is possible to efficiently produce particles with a large amount of nickel present on the surface and small particle size, and the particle aggregate obtained thereby has a sharp particle size distribution.

[0041] In this production method, by sequentially adding hydrazine, a complexing agent, and a reducing compound containing boron element, it is possible to efficiently produce particles that contain boron element and in which the amount of nickel element increases from the particle center toward the particle surface, and which have small particle diameters, and the inventors speculate that the reason why the particle aggregates have a sharp particle size distribution is as follows.

[0042] When nickel ions are brought into contact with hydrazine, a complex of nickel ions and hydrazine is stably formed, with the reduction reaction not proceeding or proceeding at a rate much slower than the rate of complex formation. When this complex is brought into contact with a reducing compound containing boron, the nickel ions are reduced from the nickel complex by the reducing power of the reducing compound containing boron, which is added later in addition to hydrazine, and nickel boride (Ni boride) is formed due to the reaction between the boron derived from the reducing compound containing boron and the nickel ions. xA large amount of fine particles of nickel boride (B; X is an integer of 1 to 3) are produced in the second reaction solution. Then, using the nickel boride fine particles produced in the second reaction solution as nuclei, nickel ions are reduced by a reducing compound containing hydrazine and boron element, gradually precipitating metallic nickel or nickel boride on the particle surface, resulting in particle growth. Since this particle growth occurs simultaneously for each fine particle in the second reaction solution, the particle growth for each particle is controlled to be uniform. As a result, the amount of nickel element present increases toward the particle surface, the particles become smaller in diameter, and an aggregate of particles with a sharp particle size distribution is thought to be efficiently obtained. Furthermore, the constituent particles of the powder obtained in this manner are typically spherical in shape.

[0043] On the other hand, as shown in the comparative example described later, when hydrazine and a reducing compound containing boron are added simultaneously, nickel ions in the solution are directly reduced by the reducing compound containing boron, such as a borohydride, which has a strong reducing power, before the nickel-hydrazine complex is sufficiently formed. This causes the reduction reaction to proceed too quickly, making it difficult for the nucleation reaction and the particle growth reaction to occur independently and sequentially. As a result, the resulting particles may aggregate or have non-uniform particle sizes.

[0044] From the viewpoint of efficiently promoting the reduction of nickel ions and obtaining nickel particles with small particle diameters uniformly and with high productivity, it is preferable to prepare the second reaction solution under non-heating conditions and then perform aging under heated conditions. The heating conditions for the second reaction solution are preferably 40°C or higher and 90°C or lower, more preferably 60°C or higher and 80°C or lower, and heating is maintained until aging is complete. The aging time is preferably 10 minutes or longer and 120 minutes or shorter. Furthermore, from the viewpoint of uniformly causing the reduction reaction to occur and obtaining nickel powder with little variation in particle diameter, it is also preferable to continue stirring the second reaction solution from the start to the end of aging.

[0045] The nickel particles thus obtained may be washed by a decantation method or the like, and then dispersed in water or an organic solvent such as alcohol to form a conductive composition in the form of a slurry, ink, paste, etc., as described below. The washed nickel particles may also be dried to form a dry powder, which is an aggregate of the particles.

[0046] Preferred embodiments of the nickel powder obtained by the above-described preferred production method will be described below. The embodiments described below can be combined with each other.

[0047] The nickel particles constituting the nickel powder contain nickel as the main component and also boron. The boron contained in the nickel particles is derived from the reducing compound containing boron in the above-mentioned manufacturing method. The inclusion of boron appropriately reduces the coercive force of metallic nickel, thereby suppressing magnetic aggregation and improving the powder's ease of handling.

[0048] As long as the effects of the present invention are achieved, it is not excluded that the nickel particles inevitably contain elements other than nickel and boron, such as oxygen, carbon, nitrogen, or sulfur. These other elements that may be inevitably mixed in may originate from oxygen or carbon dioxide in the atmosphere, or from production raw materials such as hydrazine and the nickel source.

[0049] The content of boron element in the nickel particles is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more to exhibit oxidation resistance and sintering resistance. Furthermore, to fully exhibit the electrical conductivity of nickel, the content is preferably 2.0% by mass or less, more preferably 1.5% by mass or less, and even more preferably 1.0% by mass or less. In addition, the coercive force of metallic nickel is appropriately reduced, improving the handleability of the powder. The presence or absence of boron element in nickel particles and its content can be measured by, for example, time-of-flight secondary ion mass spectrometry (TOF-SIMS) or inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0050] The nickel content in the nickel particles is more than 50% by mass, preferably 80% to 99% by mass, and more preferably 85% to 97% by mass. When the nickel content is in this range, the electrical conductivity of nickel is fully exhibited, resulting in reduced electrical resistance. The presence or absence of nickel element in nickel particles and its content can be measured by the same method as that for measuring boron element.

[0051] The nickel powder preferably has a median particle size D50 in the number distribution measured by scanning electron microscope observation of 100 nm or less, more preferably 90 nm or less, and even more preferably 80 nm or less. Furthermore, a D50 of more than 20 nm is practical, and preferably 30 nm or more. By having such a D50, defects such as discontinuities in the resulting conductive film of an electrode or the like can be reduced. Furthermore, when the powder is used by being incorporated into a conductive paste or the like, good filling properties can be achieved. As a result, the powder and conductive film have reduced electrical resistance.

[0052] D50 can be measured by the following method. First, from a scanning electron microscope image of nickel powder at a magnification of 150,000 times, 200 or more particles that do not overlap are randomly selected and their particle sizes (Heywood diameter) are measured. Next, a particle size distribution based on the number standard is obtained from the particle sizes of each particle obtained. The median particle size of the particle size distribution based on the number standard is then defined as D50 in the present invention.

[0053] As described above, the nickel particles contain boron element, and it is preferable that the ratio of nickel element to boron element is different between the particle surface and the particle center. Specifically, when nickel powder is measured in the depth direction using time-of-flight secondary ion mass spectrometry (TOF-SIMS) in a range from the outermost surface of the powder to a sputtering depth of 10 nm in terms of SiO2 of the powder, the ratio of the number of detected boron ions to the number of detected nickel ions at the outermost surface of the nickel powder is defined as A1. Further, the maximum value of the ratio of the number of detected boron ions to the number of detected nickel ions in a range from the outermost surface of the nickel powder to a sputtering depth of 10 nm in terms of SiO2 under the same conditions is defined as A max In this case, A for A1 max The ratio (A max / A1) is preferably 12 or more, more preferably 12 or more and 5,000 or less, even more preferably 20 or more and 5,000 or less, even more preferably 20 or more and 3,000 or less, and even more preferably 20 or more and 1,000 or less.

[0054] The above-mentioned A max The / A1 ratio indicates that the relative abundance of boron element increases continuously or stepwise when observing from the surface to the inside of the powder sample. This coincides with the change trend of the relative abundance of boron element in each particle. That is, when observing each particle from the particle surface to the particle center, it indicates that the relative abundance of boron element in the particle increases continuously or stepwise. On the other hand, the more uniformly the boron and nickel elements are distributed in the particles, the higher the A max The / A1 ratio is close to 1. In the case of nickel powder consisting of particles containing boron or particles with a layer on the surface, as in the prior art, the A max The / A1 ratio tends to be small. max The / A1 ratio being in the above-mentioned range indicates that a large amount of nickel element is present on the particle surface, which allows the electrical conductivity of nickel to be fully exhibited, resulting in a powder with low electrical resistance.

[0055] When measuring the depth direction of nickel powder using TOF-SIMS, the ratio of the number of detected boron ions to the number of detected nickel ions at a sputtering depth of 10 nm from the outermost surface of the nickel powder in terms of SiO2 is defined as A2. max The ratio of A2 to A max / A2) is preferably 1.35 or more and 3.00 or less, more preferably 1.40 or more and 2.80 or less, and even more preferably 1.50 or more and 2.60 or less.

[0056] The above-mentioned A2 is equivalent to the average of the number of detected boron ions relative to the number of detected nickel ions in multiple particles, so the above-mentioned A max A divided by A2 max The / A2 ratio represents the concentration gradient in which the boron element changes continuously throughout the powder. max The / A2 ratio indicates that the relative abundance ratio of boron element in the particle increases continuously from the particle surface to the particle center, and that the relative abundance ratio of nickel element in the particle increases continuously from the particle center to the particle surface. max By satisfying the preferred range of the / A2 ratio, the electrical conductivity of nickel can be more fully exhibited, resulting in a powder with even lower electrical resistance.

[0057] The above-mentioned A max , A1 and A2 can be measured using TOF-SIMS by the following method. The measurement sample for TOF-SIMS is nickel powder formed into a pellet using a press. Specifically, approximately 10 mg of the powder sample is weighed into an aluminum container with dimensions of φ5.2 mm and height 2.5 mm, and pressure is applied to the aluminum container using a press (manufactured by AS ONE, product number: 1-312-01) and an adapter (product number: 1-312-03) at a specified stroke (25 mm) to remove the nickel powder pellet supported in the aluminum container. The pellet obtained by the above method is then sputtered from the surface of the sample to the interior in a depth direction using a TOF-SIMS, while the scattered ions are mass analyzed, and a mass spectrum in the depth direction is obtained, with the depth from the outermost surface being the sputtering depth [nm] (SiO2 equivalent). From the numbers of nickel ions and boron ions detected at each sputtering depth, the ratio of the number of boron ions detected to the number of nickel ions detected at each sputtering depth is calculated. The analytical conditions shown below are common to all TOF-SIMS measurements in this specification.

[0058] TOF-SIMS equipment: TRIFT IV, manufactured by ULVAC-PHI, Inc. Primary ion species: Au + Measurement mode: positive Measurement range: 100 μm x 100 μm Neutralization gun use: Yes Sputtered ion species: Au + Sputtering area: 200 μm x 200 μm Sputtering yield: 3.2 [nm / min] (SiO2 equivalent) Sputtering interval: 3 [s] Sputtering mode: Phased Profile

[0059] For the mass spectrum obtained by measurement at each sputtering depth, the sum of the peak intensities (counts) present in a specific mass number m / z range is calculated as the number of detected ions (counts) for each fragment. Note that the mass conversion (calibration) of the time of flight is performed using the peaks of CH3, C2H3, C3H5, and Ni.

[0060] The mass number m / z ranges of each fragment are as follows: B: m / z = 10.500 ~ 11.499 Ni: m / z = 57.500 ~ 58.000 NiB: m / z = 68.500 ~ 69.000 Ni2B: m / z = 126.500 ~ 127.000 Ni3B: m / z = 184.500 ~ 185.000

[0061] The mass number m / z range of each fragment is preferably within the following range. B: m / z = 10.900 ~ 11.100 Ni: m / z = 57.850 ~ 57.950 NiB: m / z = 68.850 ~ 69.000 Ni2B: m / z = 126.800 ~ 127.000 Ni3B: m / z = 184.700 ~ 184.950

[0062] The nickel powder is composed of nickel boride (hereinafter referred to as Ni) in the range from the outermost surface of the powder to a sputtering depth of 10 nm in terms of SiO2. x B, where X is an integer of 1 to 3.) is preferably present in a predetermined range. Specifically, when measured in the depth direction of the powder by TOF-SIMS within the above-mentioned depth range, W1 is the sum of the ratios of the number of detected NiB ions to the number of detected nickel ions at each sputtering depth in the range from the outermost powder surface to a sputtering depth of 10 nm (SiO2 equivalent). Also, under the same conditions, W2 is the sum of the ratios of the number of detected NiB ions to the number of detected nickel ions at each sputtering depth. Also, under the same conditions, W3 is the sum of the ratios of the number of detected NiB ions to the number of detected nickel ions at each sputtering depth. The percentages P1, P2, and P3 of W1, W2, and W3 relative to the total value (W1 + W2 + W3) of NiB, NiB, and NiB are the abundance ratios (%) of NiB, NiB, and NiB, respectively.

[0063] In this case, the abundance ratio P1 of NiB relative to the total amount of NiB, Ni2B, and Ni3B is preferably 81% or less, more preferably 50% to 80%, and even more preferably 55% to 78%. By being in the above-mentioned ratio range, sintering resistance and oxidation resistance are effectively exhibited, resulting in a powder with low electrical resistance.

[0064] Furthermore, the abundance ratio P2 of Ni2B relative to the total value of NiB, Ni2B, and Ni3B is preferably 14% or more and 45% or less, more preferably 20% or more and 40% or less, and even more preferably 25% or more and 35% or less. Since Ni2B has lower electrical resistance than NiB, by having the ratio in the above range, the powder has even lower electrical resistance.

[0065] Furthermore, the abundance ratio P3 of Ni3B relative to the total value of NiB, Ni2B, and Ni3B is preferably 5% or more and 25% or less, more preferably 8% or more and 20% or less, and even more preferably 10% or more and 15% or less. Since Ni3B has lower electrical resistance than NiB, by having the ratio in the above range, the powder has even lower electrical resistance.

[0066] Furthermore, it is preferable that the nickel powder has a predetermined peak when the relationship between the ratio of the number of boron ions detected to the number of nickel ions detected by TOF-SIMS and the sputtering depth (nm) in terms of SiO2 is plotted. Specifically, by TOF-SIMS, the ratio of the number of detected boron ions to the number of detected nickel ions is measured in the depth direction of the powder. Taking the sputter depth (nm) in terms of SiO2 as x and the ratio of the number of detected boron ions to the number of detected nickel ions as y, consider the function y = f(x) thus obtained, and the first derivative y = f′(x) obtained by differentiating this function y = f(x) with respect to the sputter depth x. At this time, when the first derivative y = f′(x) is plotted, it is preferable that the first derivative has an intersection with y = 0 and a peak including a negative maximum value of -0.01 or less where the slope of the tangent line in the first derivative changes from negative to positive. For example, in Example 3 shown in FIG. 2(b) described later, point P is the intersection and point Q is the peak. By having both the intersection and the peak as described above, when plotting the relationship between the ratio of the number of detected boron ions to the number of detected nickel ions by TOF-SIMS and the sputter depth (nm) in terms of SiO2, it has a predetermined peak.

[0067] It is also preferable that both the intersection and the peak in the above-mentioned first derivative are included in the range of 0 < x ≦ 10, which corresponds to the range from the outermost surface of the nickel powder to a sputter depth of 10 nm in terms of SiO2 of the powder. Furthermore, it is also preferable that the position on the x-axis where the peak is observed is greater than the position on the x-axis where the intersection is observed, on the condition that the range is 0 < x ≦ 10. That is, it is preferable that the peak is observed in a range where x is greater than the intersection. The position on the x-axis of the peak is determined based on the position of the negative peak top in the first derivative.

[0068] The observation of the desired peak within a predetermined sputtering depth indicates that the abundance of boron in the nickel particles increases relatively from the particle surface to the particle center, and also indicates that the abundance of nickel in the particles increases relatively from the particle center to the particle surface. Therefore, the observation of such a peak indicates that the high abundance of nickel at the surface can reduce electrical resistance, and the moderate content of boron in the particles can reduce the coercive force of metallic nickel while fully exhibiting the sintering resistance and oxidation resistance of the particles. Furthermore, a negative maximum value of −0.01 or less indicates a sufficiently large concentration gradient in which the relative abundance of boron decreases continuously from the particle center to the particle surface, while the relative abundance of nickel increases continuously. This allows for the production of a powder with sufficiently low electrical resistance for use as an electrode material.

[0069] The nickel powder preferably has a coefficient of variation (CV), which is an index of small particle size variation, within a predetermined range. Specifically, the coefficient of variation (CV), expressed by the following formula (1), is preferably 20% or less, more preferably 18% or less, and even more preferably 16% or less. While a lower coefficient of variation (CV) is preferable, a value of 5% or more is practical. A CV value within this range ensures uniform nickel particle size and high particle dispersibility. Furthermore, when a conductive composition containing nickel particles is applied to another component, a smooth thin layer can be obtained. Furthermore, the thickness of the conductive film obtained by sintering a thin layer of the conductive composition can be made less variable, reducing electrode discontinuities.

[0070] CV value (%) = (standard deviation of particle size (nm) obtained by scanning electron microscope observation) / (arithmetic mean particle size (nm)) × 100 (1)

[0071] The standard deviation of particle diameter in the above formula (1) can be calculated from the particle size distribution based on the number standard prepared when measuring and calculating D50. The arithmetic mean particle size of the nickel powder is the particle size at the arithmetic mean value of the particle size distribution based on the number standard created when measuring and calculating D50.

[0072] The nickel particles may have one or more of various shapes, such as spherical, flake, or polyhedral. In a bonding material containing nickel particles, the nickel particles are preferably spherical. The spherical particle shape can increase the density of a sintered body obtained after sintering a powder containing the particles. Furthermore, when the powder is used as a wiring material, the density of the wiring and the dimensional stability of the wiring can be increased.

[0073] The particle shape being spherical means that the circularity coefficient measured by the following method is 0.65 or more, more preferably 0.70 or more. The circularity coefficient is determined by randomly selecting 200 particles that do not overlap each other from a scanning electron microscope image of the particles to be measured, and calculating the circularity coefficient of the particle as 4πS / L, where S is the area of ​​the two-dimensional projection image of the particle and L is the perimeter. 2 The circularity coefficient is calculated from the formula, and the arithmetic mean value of the circularity coefficients of each particle is taken as the circularity coefficient mentioned above. If the two-dimensional projected image of a particle is a perfect circle, the circularity coefficient of the particle is 1, so the higher the circularity coefficient value, 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 or less is realistic.

[0074] The carbon element content in the nickel powder is preferably 1.5 mass % or less, more preferably 1.0 mass % or less, and even more preferably 0.5 mass % or less, and realistically 0.1 mass % or more, from the viewpoint of keeping the electrical resistance low when the nickel powder is used, for example, in electrodes, conductive pastes, etc. The carbon element content can be measured, for example, using a carbon analyzer EMIA-Expert manufactured by Horiba, Ltd.

[0075] 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. Inorganic coatings can improve oxidation resistance and sintering resistance by coating with inorganic oxides that are stable against heat and oxygen, such as SiO2 and ZrO2. As for organic surface treatments, for example, attaching organic dispersants such as amines and carboxylic acids to the particle surfaces can suppress particle aggregation and improve particle dispersibility.

[0076] The volume resistivity (Ω·cm) of the nickel powder of the present invention is 1×10 3 It is preferable that the volume resistivity (Ω·cm) is 1×10 or less from the viewpoint of suitably using the material as a conductive composition, etc., as will be described later. 2 The volume resistivity (Ω·cm) is measured by the method described in the examples below.

[0077] Nickel powder is preferably used as a metal filler to be blended into a conductive composition. The conductive composition contains nickel powder as a metal filler and a solvent, and preferably contains a binder resin. Examples of the form of the conductive composition include a conductive slurry, a conductive ink, and a conductive paste.

[0078] Examples of solvents used in the conductive composition include water, alcohols, ketones, esters, ethers, and hydrocarbons. Among these, at least one of alcohols such as terpineol and dihydroterpineol, and ethers such as ethyl carbitol and butyl carbitol is preferred. Examples of binder resins used in the conductive composition include at least one of acrylic resins, epoxy resins, polyester resins, polycarbonate resins, and cellulose resins.

[0079] The conductive composition can be applied to the surface of the target surface by a predetermined means to form a coating film, thereby forming a conductive film having a desired pattern. If necessary, the coating film may 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, allowing 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.

[0080] The conductive film described above can be used to form, for example, wiring circuits on printed wiring boards or electrodes on chip components. It 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. It can also be used as a bonding material for bonding substrates and chips, such as a die-bonding material.

[0081] The conductive composition or conductive film described above can be used as an electrode catalyst for a battery or an electrode catalyst for a water electrolysis cell, and is particularly suitable for use as a catalyst for a hydrogen electrode. Examples of such batteries or water electrolysis cells include, but are not limited to, solid oxide fuel cells (SOFCs), proton conducting fuel cells (PCFCs), solid oxide electrolysis cells (SOECs), and proton conducting water electrolysis cells (PCECs). [Example]

[0082] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0083] Example 1 (1) Preparation of nickel raw material solution Nickel sulfate hexahydrate was used as the water-soluble nickel source. 26.285 g of nickel sulfate hexahydrate and 5.161 g of trisodium citrate as a ligand compound were dissolved in 400.0 g of pure water, and then the solution was stirred at room temperature (25°C) for 30 minutes to obtain a nickel raw solution. The pH of this aqueous solution at 25°C was 5.7. The content of the water-soluble nickel source in the nickel raw solution, expressed as a molar concentration of nickel element, was 0.25 mol / L.

[0084] (2) Preparation of reducing solution Sodium borohydride was used as a reducing compound containing boron. 1.135 g of sodium borohydride was dissolved in 100.0 g of pure water at room temperature to obtain a reducing solution. The pH of this aqueous solution at 25°C was 9.8.

[0085] (3) Synthesis of nickel particles A first reaction solution was prepared by adding 40.048 g of hydrazine monohydrate as a complexing agent all at once to the room temperature nickel raw material solution prepared in step (1) and mixing it, and this was stirred at room temperature (25°C) for 30 minutes to form a nickel-hydrazine complex. The molar ratio of hydrazine to nickel element was 8.0, and the pH of the first reaction solution at 25°C was 10.4. Next, the entire amount of the reducing solution prepared in step (2) was added dropwise to the first reaction solution at a rate of 0.5 L / min, and the mixture was stirred at room temperature (25°C) for 10 minutes to obtain a second reaction solution. The molar ratio of sodium borohydride to nickel was 0.30.

[0086] Subsequently, the second reaction liquid was heated to a liquid temperature of 70°C, and aging was carried out by stirring for 80 minutes while maintaining this temperature. Finally, the second reaction solution after aging was decanted with pure water and then solvent-substituted with ethanol. The solution was then concentrated by decantation and vacuum-dried to obtain the desired dry powder of nickel particles. A scanning electron microscope image of the nickel powder obtained in this example is shown in Figure 1(a).

[0087] Example 2 A dry powder of nickel particles was obtained in the same manner as in Example 1, except that 1.892 g of sodium borohydride was used in preparing the reducing solution. The molar ratio of sodium borohydride to elemental nickel was 0.50.

[0088] Example 3 A dry powder of nickel particles was obtained in the same manner as in Example 1, except that 2.648 g of sodium borohydride was used in preparing the reducing solution. The molar ratio of sodium borohydride to elemental nickel was 0.70.

[0089] Example 4 Dry powder of nickel particles was obtained in the same manner as in Example 3, except that trisodium citrate dihydrate was not used as a ligand compound in the preparation of the nickel raw material solution. The molar ratio of trisodium citrate to elemental nickel was 0.

[0090] Example 5 Dry powder of nickel particles was obtained in the same manner as in Example 3, except that 10.323 g of trisodium citrate dihydrate was dissolved in 400.0 g of pure water in the preparation of the nickel raw material solution. The molar ratio of trisodium citrate to elemental nickel was 0.35.

[0091] Example 6 Dry powder of nickel particles was obtained in the same manner as in Example 3, except that 15.484 g of trisodium citrate dihydrate was dissolved in 400.0 g of pure water in the preparation of the nickel raw material solution. The molar ratio of trisodium citrate to elemental nickel was 0.53.

[0092] Example 7 Dry powder of nickel particles was obtained in the same manner as in Example 3, except that 20.646 g of trisodium citrate dihydrate was dissolved in 400.0 g of pure water in the preparation of the nickel raw material solution. The molar ratio of trisodium citrate to elemental nickel was 0.70.

[0093] Example 8 A dry powder of nickel particles was obtained in the same manner as in Example 2, except that in preparing the nickel raw material solution, in addition to nickel sulfate hexahydrate and trisodium citrate, 0.587 g of a dispersant (Marialim FA-1150AM-08, manufactured by NOF Corporation) was used and dissolved in 400 g of pure water. The molar ratio of sodium borohydride to elemental nickel was 0.50.

[0094] Comparative Example 1 In preparing the reducing solution, 1.892 g of sodium borohydride and 40.048 g of hydrazine monohydrate were dissolved in 100.0 g of pure water. This reducing solution was added all at once to the nickel raw material solution to obtain a second reaction solution. A dry powder of nickel particles was obtained in the same manner as in Example 1. A scanning electron microscope image of the nickel powder obtained in this comparative example is shown in Figure 1(b).

[0095] [Molar ratio of ligand compound to nickel element] The molar ratios of the ligand compound to the nickel element in the examples and comparative examples are shown in the following Tables 1 and 2. Note that in Example 4, no ligand compound was used, and therefore, in Table 2, this is indicated by "-".

[0096] [Measurement of particle size and calculation of CV value] The D50 (nm) of the nickel powders obtained in the examples and comparative examples was measured using the above-mentioned measurement method. In addition, the CV value was also calculated from the particle size distribution used for measuring and calculating D50. The results are shown in Tables 1 and 2 below.

[0097] [Measurement of boron element content] The boron element content in the nickel powders obtained in the examples and comparative examples was measured using an inductively coupled plasma optical emission spectrometer (manufactured by Hitachi High-Tech Science Corporation, model number: PS3520UV-DD). The results are shown in Tables 1 and 2 below.

[0098] [Measurement of carbon element content] The carbon element content of the nickel powders obtained in the examples and comparative examples was measured using a carbon analyzer (EMIA-Expert, manufactured by Horiba, Ltd.) The results are shown in Tables 1 and 2 below.

[0099] [Measurement of the ratio of the number of detected boron ions to the number of detected nickel ions] Based on the above-mentioned TOF-SIMS measurement method, the ratio A1 of the number of detected ions on the outermost surface of the powder, the maximum ratio A of the number of detected ions in the powder measurement results, max The ratio A2 of the number of ions detected at a sputtering depth of 10 nm from the powder surface in terms of SiO2 was measured. max / A1 ratio and A max The / A2 ratios were calculated for each sample, and the results are shown in Tables 1 and 2 below.

[0100] [Measurement of the proportion of nickel boride present] For the nickel powders of the examples and comparative examples, the abundance ratios P1 (%) of NiB, P2 (%) of NiB, and P3 (%) of NiB were calculated based on the above-mentioned TOF-SIMS measurement method. The results are shown in Tables 1 and 2 below.

[0101] [Determining the presence or absence of a peak] For the nickel powders of the examples and comparative examples, the ratio of the number of detected boron ions to the number of detected nickel ions was measured in the range from the powder surface to a sputtering depth of 10 nm in terms of SiO2. Then, the function y = f(x) was graphed by plotting the sputtering depth x on the horizontal axis and the ratio y of the number of detected ions on the vertical axis. This graph is shown in Figure 2(a). In addition, a graph was created of the first derivative y = f'(x) obtained by first differentiating the above function y = f(x) with respect to the sputtering depth x. This graph is shown in Figure 2(b). In the graph of y = f'(x), cases where both an intersection and a peak were observed are indicated as "present" in Tables 1 and 2, and cases where at least one of an intersection and a peak was not observed are indicated as "absent" in Tables 1 and 2. As shown in Figure 2(b), in the graph of the first derivative, intersections and peaks were observed in all Examples, while no peaks were observed in the Comparative Examples.

[0102] [Evaluation of Electrical Resistance] Approximately 30 mg of nickel powder from each of the examples and comparative examples was pressed into pellets, and the measurement samples were used to measure volume resistivity (Ω·cm). Pellets were formed using a MiNi-Pellet Press (Specac) and a 7 mm die, applying a pressure of 2 tons. Volume resistivity was measured using a Loresta-GP (Mitsubishi Chemical Analytech MCP-T610) with a four-terminal, four-probe method, with a QPP-type probe pressed against the pellet surface. The lower the volume resistivity, the higher the conductivity. The results are shown in Table 1. In the comparative example, the volume resistivity of the sample exceeded the upper limit of detection and could not be measured.

[0103] [Nickel-hydrazine complex 1 H-NMR measurement] The first reaction solution prepared in Examples 3, 4, 6, and 7 was centrifuged to obtain a precipitate, which was then dispersed in ethanol and centrifuged again to obtain a precipitate. This precipitate was vacuum dried at room temperature to obtain a solidified nickel-hydrazine complex. 1 The NMR spectrum obtained by H-NMR measurement is shown in Figure 3. As a result, a peak for the nickel-hydrazine complex was observed at a chemical shift of around 4 ppm. From this result, it was inferred that the nickel-hydrazine complex formed in the nickel raw material solution was [Ni(N2H4)4]SO4, [Ni(N2H4)3]SO4, or a mixture of these.

[0104] As shown in Figure 3 1 The H-NMR measurement conditions are as follows: Magnetic field: 14.1T ( 1 H 600MHz) Spectrometer: Bruker AVANCE NEO600 Measurement and data processing software: Bruker TopSpin NMR probe: 1.3mm MAS probe Sample rotation speed: 60kHz Chemical shift and radio frequency intensity standards: Adamantane. Chemical shift value standard: Adamantane 1 The H-NMR peak is set at 1.91 ppm. Measurement method: Single pulse method Radio frequency pulse width: 2.5 μsec Radio frequency pulse intensity: 100 kHz (irradiation center is 1.91 ppm) of adamantane 1 The peak intensity of the H-NMR spectrum is at its maximum with a radio frequency pulse width of 2.5 μsec. Radiofrequency pulse irradiation center: 4.7 ppm Interval between observation points: 2 μsec Number of observation points: 20,000 Number of spectral points: 65536 Window function: No window function is used

[0105] [Table 1]

[0106] [Table 2] [Industrial Applicability]

[0107] According to the present invention, a nickel powder having low electrical resistivity is provided.

Claims

1. A nickel powder consisting of an aggregate of nickel particles containing elemental boron, The content of the boron element is 0.1% by mass or more and 2.0% by mass or less, a 50% particle size D50 in a number distribution measured by observation with a scanning electron microscope of 100 nm or less; In the measurement of the depth direction of the powder by time-of-flight secondary ion mass spectrometry, the SiO ２ When measuring the range up to a sputtering depth of 10 nm in terms of the surface area of ​​the powder, the ratio of the number of detected boron ions to the number of detected nickel ions on the outermost surface of the powder is A １ The maximum ratio of the number of detected boron ions to the number of detected nickel ions in the powder is defined as A ｍａｘ When this is done, A １ A against ｍａｘ The ratio (A ｍａｘ / A １ ) is 12 or more.

2. A nickel powder consisting of an aggregate of nickel particles containing elemental boron, The content of the boron element is 0.1% by mass or more and 2.0% by mass or less, a 50% particle size D50 in a number distribution measured by observation with a scanning electron microscope of 100 nm or less; In the measurement of the depth direction of the powder by time-of-flight secondary ion mass spectrometry, the SiO ２ When measuring the range up to a sputtering depth of 10 nm in terms of conversion, NiB and Ni ２ B and Ni ３ A nickel powder in which the proportion of NiB relative to the total value of NiB and B is 81% or less.

3. The SiO of the powder from the outermost surface of the powder ２ In the range of 10 nm of sputtering depth in terms of NiB and Ni ２ B and Ni ３ Ni relative to the total value of B ３ The nickel powder according to claim 1 or 2, wherein the content of B is 5% or more and 25% or less.

4. The nickel powder according to any one of claims 1 to 3, wherein the coefficient of variation CV value represented by the following formula (1) is 20% or less. CV value (%)=(standard deviation of particle diameters (nm) obtained by scanning electron microscope observation) / (arithmetic mean particle diameter (nm))×100 (1)

5. The nickel powder according to any one of claims 1 to 4, wherein the carbon element content is 1.5 mass% or less.

6. The ratio of the number of detected boron ions to the number of detected nickel ions was measured in the depth direction of the powder by time-of-flight secondary ion mass spectrometry, and SiO ２ When considering a first derivative y = f '(x) obtained by first differentiating a function y = f (x) obtained by first differentiating the function y = f '(x) with respect to the sputtering depth x, where x is the sputtering depth (nm) in terms of converted value and y is the ratio of the number of detected ions of boron ions to the number of detected ions of nickel ions, the first derivative has an intersection point between y = f '(x) and y = 0, and a peak including a negative maximum value of -0.01 or less in a range where x is larger than the intersection point, in the range of 0 < x ≦ 10 of the first derivative. The nickel powder according to any one of claims 1 to 5,

7. A method for producing nickel powder, comprising the steps of mixing a water-soluble nickel source and hydrazine to form a nickel-hydrazine complex, and then adding a reducing compound containing boron element to reduce nickel ions, A method for producing nickel powder, comprising mixing a water-soluble nickel source and hydrazine under acidic conditions.

8. A conductive composition comprising the nickel powder according to any one of claims 1 to 6 and a solvent.

9. A conductive film formed using the conductive composition according to claim 8.

10. An electrode catalyst comprising the nickel powder according to any one of claims 1 to 6 and used as a hydrogen electrode of a fuel cell.

11. An electrode catalyst comprising the nickel powder according to any one of claims 1 to 6 and used as a hydrogen electrode of a water electrolysis cell.

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