CN116981526A

CN116981526A - Nickel powder and method for producing nickel particles

Info

Publication number: CN116981526A
Application number: CN202280019284.1A
Authority: CN
Inventors: 西野光彦; 佐佐木隆史; 井手仁彦
Original assignee: Mitsui Mining and Smelting Co Ltd
Current assignee: Mitsui Mining and Smelting Co Ltd
Priority date: 2021-04-26
Filing date: 2022-04-11
Publication date: 2023-10-31
Also published as: JP7406047B2; KR20240000452A; TW202302872A; JPWO2022230650A1; WO2022230650A1

Abstract

The nickel powder of the present invention has a number-cumulative particle diameter D at 50% by number of cumulative particles in a particle size distribution based on the equivalent diameter of circles calculated by measurement with a scanning electron microscope ₅₀ At time D ₅₀ Is 50nm to 200nm, and has D ₅₀ The presence ratio of particles having a particle diameter of 1.5 times or more is 0.5% by number or less. When the standard deviation of the particle diameters in the particle size distribution is σ (nm), it is preferable that (σ/D ₅₀ ) The value of x 100 (%) is 14% or less. When Cs is the crystallite size measured by WPPF, cs/D is also preferable ₅₀ The value of (2) is0.3 to 0.6.

Description

Nickel powder and method for producing nickel particles

Technical Field

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

Background

Nickel particles are generally used for forming internal electrodes of a multilayer ceramic capacitor (MLCC). With miniaturization and high capacity of MLCCs, nickel particles used to form internal electrodes need to be further micronized. From this point of view, patent document 1 proposes a nickel powder having a diameter of 0.09 μm or less in an amount of 50%. According to this document, the nickel powder is produced by a vapor phase reduction method in which nickel chloride gas is brought into contact with a reducing gas, or a spray pyrolysis method in which a thermally decomposable nickel compound is sprayed to thermally decompose.

Prior art literature

Patent literature

Patent document 1 International publication No. 2015/156080 pamphlet

Disclosure of Invention

The nickel powder described in patent document 1 contains nickel particles of fine particles. However, since the nickel powder is produced by a gas phase method, it is difficult to control the particle size, and as a result, the particle size distribution tends to be widened. Thus, the nickel powder contains coarse nickel particles in addition to fine nickel particles at a high ratio to some extent. The presence of coarse nickel particles may cause short-circuiting between internal electrodes and a decrease in withstand voltage of the MLCC.

Accordingly, the present invention has an object to provide a nickel powder which is fine particles and contains a small proportion of coarse particles, and a method for easily producing the nickel powder.

The present invention provides a nickel powder, wherein the cumulative number is 50 in the particle size distribution based on the equivalent diameter calculated by the measurement of a scanning electron microscopeThe number cumulative particle diameter at several% is set to D ₅₀ In the time-course of which the first and second contact surfaces,

D ₅₀ is 50nm to 200nm,

with D ₅₀ The presence ratio of particles having a particle diameter of 1.5 times or more is 0.5% by number or less.

In addition, as a preferred method for producing the nickel powder, the present invention provides a method for producing nickel particles,

which is a method for producing nickel particles by heating a liquid containing nickel hydroxide particles, a polyol, polyvinylpyrrolidone and polyethyleneimine,

the polyvinylpyrrolidone is used in an amount of 30 to 200 parts by mass based on 1 part by mass of the polyethyleneimine.

Drawings

Fig. 1 (a) is a graph showing the measurement result of the thermomechanical analysis of the nickel powder obtained in example 2, and fig. 1 (b) is a graph showing the result of the second order differentiation of the graph shown in fig. 1 (a).

Fig. 2 (a) is a schematic diagram showing a process of producing nickel powder according to the present invention, and fig. 2 (b) is a schematic diagram showing a process of producing conventional nickel powder.

Fig. 3 is a scanning electron microscope image of the nickel powder obtained in example 2.

Fig. 4 is a scanning electron microscope image of the nickel powder obtained in comparative example 2.

Detailed Description

The present invention will be described below based on preferred embodiments. The present invention relates to nickel powder as an aggregate of nickel particles of fine particles. In the following description, when "nickel powder" is mentioned, depending on the context, it may refer to powder as an aggregate of nickel particles, and each nickel particle constituting the powder.

As described above, the nickel powder of the present invention is composed of fine nickel particles. The nickel particles are composed of nickel element and unavoidable impurities, or of nickel-based alloys and unavoidable impurities. The particle size of the nickel particles was measured by observing the nickel powder of the present invention with a Scanning Electron Microscope (SEM). In detail, SEM is used toThe nickel particles constituting the nickel powder were photographed at a magnification of 50000 times, and the area of the photographed nickel particles was determined. From this area, the circle equivalent diameter was calculated. The particle size distribution was determined based on the calculated equivalent circle diameter. The particle size distribution is measured as the circle equivalent diameter on the horizontal axis of the graph and as the number frequency on the vertical axis. In the particle size distribution curve thus obtained, the number-cumulative particle diameter at which the cumulative number is 50% by number is defined as D ₅₀ . Particle size D thus defined ₅₀ The value of (2) is preferably 50nm to 200 nm. By making the particle diameter D of the nickel powder of the present invention ₅₀ Within this range, when the nickel powder of the present invention is used as an internal electrode of various applications such as an MLCC, there is an advantage that it is difficult to cause a short circuit between the internal electrodes. From the viewpoint of making this advantage more remarkable, the particle diameter D of the nickel powder ₅₀ More preferably from 50nm to 180nm, still more preferably from 50nm to 150nm, still more preferably from 50nm to 90 nm.

When the above particle size distribution curve was obtained, the equivalent circle diameter was obtained for 5000 or more nickel particles. For the calculation of the equivalent circle diameter, image analysis particle size distribution measurement software (Mac-View manufactured by mountain Co., ltd.) was used. The minimum unit of nickel particles as an observation target was determined as to whether or not the particle interface of one particle which was considered to be independent was observed by SEM. Therefore, even if an aggregate constituted by a plurality of particles is observed, in the case where a particle interface is observed in the aggregate, a region defined by the particle interface is regarded as one particle.

The nickel powder of the present invention preferably has a small ratio of coarse particles in addition to the fine particles of nickel constituting the nickel powder. When the nickel powder of the present invention is used for, for example, an internal electrode of an MLCC, the presence of coarse particles may cause a short circuit between the internal electrodes. By reducing the presence ratio of coarse particles in the nickel powder, the short circuit can be effectively prevented. From this viewpoint, the nickel powder of the present invention preferably has D ₅₀ The presence ratio of particles having a particle diameter of 1.5 times or more (hereinafter also referred to as "coarse particle presence ratio") is 0.5% by number or less, more preferably 0.3% by number or less, and still more preferably 0.1% by number or less.

The closer the coarse particle presence ratio is to 0%, the more effective it is to prevent the occurrence of a short circuit between the internal electrodes, but if the coarse particle presence ratio is as low as about 0.01%, the occurrence of a short circuit between the internal electrodes can be effectively prevented.

As the scale of coarse particles, a particle having D is selected ₅₀ The reason why the particles having a particle diameter of 1.5 times or more are found to be: at D ₅₀ The particle size of 1.5 times or more becomes one cause of roughening of the surface of the conductive film when forming the conductive film, which is extremely closely related to occurrence of short-circuiting between internal electrodes of the MLCC.

The nickel powder of the present invention is preferably fine particles, and in addition to the low presence ratio of coarse particles, the particle size is preferably as uniform as possible. In other words, a concentration of the particle size distribution curve is preferred. The concentration of the particle size distribution curve can be evaluated by the coefficient of variation of the particle size. The coefficient of variation is represented by (sigma/D) when the standard deviation of particle diameters in the particle size distribution is represented by sigma (nm) ₅₀ ) Values defined by x 100 (%). The nickel powder of the present invention preferably has a coefficient of variation of 14% or less, from the viewpoint of improving the surface smoothness of the internal electrode of the MLCC formed from the nickel powder. The coefficient of variation is preferably 13% or less, more preferably 12% or less, from the viewpoint of further improving the surface smoothness of the internal electrode.

The closer the coefficient of variation is to 0%, the more favorable the surface smoothness of the internal electrode is, but if the coefficient of variation is as low as about 5%, the surface of the internal electrode can be smoothed to a sufficient degree.

In the nickel powder of the present invention, the nickel particles constituting the powder are preferably high in crystallinity. The high crystallinity of the nickel particles means that the nickel powder of the present invention is difficult to thermally shrink at low temperatures. In other words, when the nickel powder of the present invention is applied to the sintering step, the heat shrinkage finishing temperature increases. In the case of manufacturing an MLCC using the nickel powder of the present invention, it is advantageous in that the heat shrinkage finish temperature of the nickel powder in the sintering step, which is one step of manufacturing, can be made as close as possible to the sintering temperature of the dielectric powder, and that the heat shrinkage finish temperature due to sintering is high. Bringing the heat shrinkage end temperature of the nickel powder close to the sintering temperature of the dielectric powder means that the shrinkage degree of the nickel powder and the dielectric powder is close. Therefore, the increase in the heat shrinkage finish temperature of the nickel powder of the present invention is advantageous in that the occurrence of defects due to the mismatch in shrinkage degree between the nickel powder and the dielectric powder can be effectively prevented.

By relative particle size D ₅₀ The ratio of crystallite size Cs (nm), cs/D ₅₀ Methods for evaluating crystallinity of nickel particles are often used in the technical field of metal powders. Cs/D ₅₀ The larger the value of (c) is, the higher the crystallinity of the nickel particles can be evaluated. From this point of view, in the nickel powder of the present invention, cs/D ₅₀ The value of (2) is preferably 0.3 or more, more preferably 0.34 or more, and still more preferably 0.38 or more.

Cs/D ₅₀ The larger the value of (C) is, the more advantageous the increase in the heat shrinkage finishing temperature of the nickel powder is, in the present invention, the Cs/D is ₅₀ The value of (2) is preferably 0.6 or less, so that the heat shrinkage finish temperature of the nickel powder can be sufficiently increased, and Cs/D is from this viewpoint ₅₀ The value of (2) is more preferably 0.55 or less, still more preferably 0.50 or less.

The value of the crystallite size Cs itself is preferably 15nm or more and 70nm or less, more preferably 18nm or more and 70nm or less, and still more preferably 23nm or more and 70nm or less, from the viewpoint of sufficiently increasing the heat shrinkage end temperature of the nickel powder.

As a method for measuring the crystallite size, various methods are known in the art of metal powders, and the crystallite size in the present specification refers to a value measured by WPPF (whole powder pattern fitting, full powder pattern alignment) method. As a method for measuring the crystallite size, the scherrer method is known in addition to the WPPF method, and in the case where the degree of deformation of the crystal is large, the value of the crystallite size obtained by the scherrer method lacks reliability, so that the WPPF method with low risk is used in the present invention.

Details of the method for measuring the crystallite size by the WPPF method are described in examples described later.

As described above, the nickel powder of the present invention preferably has a high heat shrinkage finish temperature during sintering. Specifically, from the viewpoint of bringing the heat shrinkage finish temperature of nickel powder in the sintering step, which is one step of manufacturing an MLCC, as close as possible to the sintering temperature of dielectric powder, it is preferable that the heat shrinkage finish temperature is 650 ℃ to 1000 ℃. From this viewpoint, the heat shrinkage end temperature is preferably 680 ℃ or higher and 980 ℃ or lower, more preferably 700 ℃ or higher and 980 ℃ or lower.

The heat shrinkage end temperature of the nickel powder was measured by Thermal Mechanical Analysis (TMA), and the measurement conditions of TMA were 1 vol% hydrogen/99 vol% nitrogen atmosphere and a heating rate of 10 ℃/min. Fig. 1 (a) shows the measurement results of TMA obtained for the nickel powder obtained in example 2 described below.

In the graph obtained by performing second order differentiation on the graph of the relationship between the temperature measured by TMA and the displacement amount, the temperature of the peak top among the peaks protruding upward is defined as the heat shrinkage end temperature. Fig. 1 (b) shows a graph obtained by differentiating the graph of fig. 1 (a) in the second order. In fig. 1 (b), the temperature indicated by the arrow is the heat shrinkage end temperature. When 2 or more peaks are observed in the graph of the second order differential, the peak observed on the highest temperature side is focused on, and the temperature of the peak top of the peak is taken as the heat shrinkage end temperature.

The nickel powder of the present invention preferably has a low degree of heat shrinkage in addition to a high heat shrinkage end temperature. As described above, the low level of thermal shrinkage of the nickel powder is advantageous in that the occurrence of defects due to mismatch in the shrinkage levels between the nickel powder and the dielectric powder can be effectively prevented in the sintering step, which is a step of manufacturing the MLCC. From this viewpoint, the nickel powder of the present invention preferably has a heat shrinkage at 900 ℃ of 30% or less, more preferably 28% or less, and still more preferably 25% or less. The more the heat shrinkage of the nickel powder is close to zero, the more preferable.

The heat shrinkage amount of the nickel powder was set to 1% by volume of hydrogen/99% by volume of nitrogen in the TMA atmosphere measured by TMA in the same manner as the above heat shrinkage end temperature. The temperature rise rate was set at 10℃per minute. The displacement (%) on the vertical axis of the graph obtained by TMA measurement is the heat shrinkage referred to in the present specification.

In the nickel powder of the present invention, nickel particles constituting the same are composed of nickel element and unavoidable impurities, or nickel base alloy and unavoidable impurities. In any case, the amount of unavoidable impurities is preferably as small as possible from the standpoint of preventing failures that may occur when the nickel powder of the present invention is used to produce an MLCC, or from the standpoint of maintaining the quality of the MLCC.

In the nickel powder of the present invention, the amount of carbon contained in the nickel powder is preferably as small as possible. Carbon is easily mixed from an organic substance used in the production of the nickel powder of the present invention. Since the organic substance is relatively hydrophilic, in the preparation of a paste in the step of producing an electrode of an MLCC using the nickel powder of the present invention, the solvent used in the paste (the solvent is hydrophobic) may have low affinity with the organic substance (relatively hydrophilic as described above), and thus the characteristics of the paste such as fluidity may be deteriorated. If the fluidity of the paste is deteriorated, the surface of the sintered film formed from the paste becomes rough, which is a cause of the problem.

In the nickel powder of the present invention, it is preferable that the surface of the nickel particles is treated with a hydrophobic organic material after reducing the amount of carbon derived from the organic material mixed during production. When the hydrophobic organic substance is present on the surface of the nickel particles, the affinity of the solvent used in the paste with the hydrophobic organic substance present on the surface of the nickel particles may be high at the time of preparing the paste in the step of manufacturing the electrode of the MLCC, and thus the characteristics of the paste, such as fluidity, may be good.

From the above point of view, the content of the carbon (C) element in the nickel powder of the present invention is preferably 3 mass% or less, more preferably 2.5 mass% or less, and even more preferably 2 mass% or less.

From the same viewpoint, in the nickel powder of the present invention, the value of the content/specific surface area of the carbon element is preferably 0.01 g/(m) ² Per g) of above and 0.35 g/(m) ² Per g) or less, more preferably 0.03 g/(m) ² Per g) of above and 0.30 g/(m) ² Per g) or less, more preferably 0.05 g/(m) ² Per g) of above and 0.27 g/(m) ² Per g) or below, moreFurther preferably 0.05 g/(m) ² Per g) of above and 0.20 g/(m) ² /g) is below.

In the nickel powder of the present invention, as described above, the amount of alkali metal element, halogen element, and sulfur element is preferably as small as possible in addition to the amount of carbon.

Examples of the alkali metal element include sodium element and potassium element. If these elements are mixed into an MLCC, they may cause degradation of the performance of the MLCC.

Examples of the halogen element include chlorine element. Halogen elements and sulfur elements are corrosive elements, and thus, the manufacturing apparatus of the MLCC may be corroded by these elements.

From the above point of view, the content of sodium element in the nickel powder of the present invention is preferably 50ppm or less, more preferably 30ppm or less, and still more preferably 10ppm or less.

The content of potassium element is preferably 50ppm or less, more preferably 30ppm or less, and still more preferably 10ppm or less.

The content of chlorine element is preferably 500ppm or less, more preferably 300ppm or less, and still more preferably 50ppm or less.

The content of sulfur element is preferably 500ppm or less, more preferably 300ppm or less, and still more preferably 50ppm or less.

In the present specification, ppm is a mass basis. The sodium, potassium, and sulfur contents can be measured by ICP emission spectrometry with respect to a solution obtained by dissolving nickel powder, for example, with an acid. Chlorine can be measured by ion chromatography.

Next, a preferred method for producing the nickel powder of the present invention will be described. In the present production method, nickel powder is produced by a so-called polyol method. The polyol method is a method of producing nickel particles by heating a polyol in a state where a chemical nucleus (chemical bond) of nickel is present in the polyol using the polyol as a reducing agent and a solvent, thereby generating a reduction reaction.

In the present production method, nickel hydroxide is preferably used as the chemical core of nickel for producing nickel particles from the viewpoint that the target nickel powder can be obtained smoothly. Nickel hydroxide is added to a mixed solution containing a polyol, polyvinylpyrrolidone (hereinafter also referred to as "PVP") and polyethylenimine (hereinafter also referred to as "PEI") to form a reaction solution.

As described above, the polyol contained in the reaction liquid serves as a solvent and also as a reducing agent for nickel hydroxide.

As the polyhydric alcohol, for example, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1, 2-propanediol, dipropylene glycol, 1, 2-butanediol, 1, 3-butanediol, 1, 4-butanediol, 2, 3-butanediol 1, 5-pentanediol, polyethylene glycol, and the like can be used. These polyols may be used singly or in combination of 2 or more. The ethylene glycol in these polyols is preferable because it has a high ratio of hydroxyl groups to molecular weight, and therefore has high reducing performance, and is liquid at ordinary temperature and excellent in handleability.

The amount of the polyhydric alcohol to be used is not particularly limited, as it is appropriately adjusted depending on the amount of nickel hydroxide in the reaction solution from the viewpoint of using the polyhydric alcohol as a reducing agent. On the other hand, when functioning as a solvent, the properties of the reaction solution change according to the concentration of the polyol in the reaction solution, and thus there is a certain range of suitable concentration. From this viewpoint, the concentration of the polyol in the reaction liquid is preferably set in the range of 50 mass% or more and 99.8 mass% or less.

PVP is used as a dispersant for nickel hydroxide. PVP is preferable because it has a remarkable effect as a dispersant and can concentrate the particle size distribution of nickel particles generated during reduction. The molecular weight of the PVP may be appropriately adjusted according to the degree of water solubility and dispersibility. The amount of PVP in the reaction solution is preferably 0.01 to 30 parts by mass based on 100 parts by mass of nickel converted from nickel hydroxide. When the viscosity is set within this range, the dispersion effect can be sufficiently exhibited without excessively increasing the viscosity of the reaction solution. In addition, PVP has a number average molecular weight of preferably 5000 to 200000, particularly preferably 5000 to 150000, particularly preferably 5000 to 100000, in terms of being sufficiently uniformly adsorbed on the particle surface and suppressing aggregation.

PEI has the effect of reducing the number of nickel ions in the reaction solution during the formation of nickel nuclei in the reaction solution, and causing the formation of nuclei to be performed at a different time from the growth of nuclei. The reason for this is that: (a) PEI has unshared electron pairs with interactions with nickel ions and is capable of coordinate bonding with nickel ions; (b) PEI has a plurality of said unshared electron pairs; and (c) PEI has hydrogen bond sites capable of interacting with the surface of nickel hydroxide present in an undissolved state in the reaction liquid.

The presence of PEI in the reaction solution enables the sequential formation of nickel nuclei and the growth of the nuclei formed, as shown in FIG. 2 (a). As a result, nickel powder having fine particles and a uniform particle diameter can be obtained smoothly. In contrast, in the production of conventional nickel powder by reduction, as shown in fig. 2 (b), since the nucleation and the nucleation occur simultaneously, coarse particles are easily formed, and the particle size is easily deviated.

From the above viewpoints, the use of branched PEI is advantageous over the use of linear PEI. From the same point of view, PEI having a number average molecular weight of 600 or more and 10000 or less, particularly preferably 800 or more and 5000 or less, and particularly preferably 1000 or more and 3000 or less is also preferably used.

In particular, in the present production method, by setting the ratio of PVP to PEI contained in the reaction solution to a specific range, as shown in fig. 2 (a), the nickel nuclei can be reliably formed and the nickel nuclei can be reliably grown in sequence. Specifically, PVP is preferably used in an amount of 30 to 200 parts by mass, more preferably 40 to 150 parts by mass, still more preferably 50 to 130 parts by mass, per 1 part by mass of PEI.

The amount of PEI in the reaction solution is appropriately set according to the amount of PVP, provided that the ratio of PVP to PEI satisfies the above range.

The reaction solution may contain a noble metal catalyst. Thus, fine core particles of noble metal are produced at the initial stage of reduction, and nickel is smoothly reduced from the core particles. As the noble metal catalyst, for example, a noble metal compound such as a water-soluble salt of a noble metal can be used. Examples of the water-soluble salts of noble metals include water-soluble salts of palladium, silver, platinum, gold, and the like. When palladium is used as the noble metal, for example, palladium chloride, palladium nitrate, palladium acetate, ammonium palladium chloride, or the like can be used. When silver is used, for example, silver nitrate, silver lactate, silver oxide, silver sulfate, silver cyclohexane, silver acetate, or the like can be used. When platinum is used, for example, chloroplatinic acid, potassium chloroplatinate, sodium chloroplatinate, or the like can be used. When gold is used, for example, chloroauric acid, sodium chloroaurate, and the like can be used. Among them, palladium nitrate, palladium acetate, silver nitrate and silver acetate are preferably used because of low cost and economical efficiency. The noble metal catalyst may be used in the form of the above-mentioned compound or in the form of an aqueous solution in which the compound is dissolved in water. The amount of the noble metal catalyst contained in the reaction solution is preferably 0.01 to 5 parts by mass, particularly preferably 0.01 to 1 part by mass, based on 100 parts by mass of nickel converted from nickel hydroxide.

The slurry containing the above components was heated while stirring, and nickel hydroxide was reduced. The heating temperature depends on the kind of the polyhydric alcohol used, but the reduction of nickel hydroxide can be smoothly performed by heating at atmospheric pressure at preferably 150 ℃ or higher and 200 ℃ or lower, more preferably 170 ℃ or higher and 200 ℃ or lower, still more preferably 190 ℃ or higher and 200 ℃ or lower.

Nickel particles are generated in the liquid by reduction of nickel hydroxide. As a side reaction of reduction, decomposition of PVP and PEI may occur to generate hydrophilic organic substances. If the organic substance adheres to the surface of the nickel particles, the surface of the nickel particles becomes hydrophilic. When a paste is prepared using nickel powder composed of nickel particles whose surfaces are hydrophilic, as described above, the characteristics of the paste, such as fluidity, may be deteriorated because the solvent used in the paste (which is hydrophobic) has low affinity for the organic substance (which is hydrophilic as described above). In order to prevent this, it is desirable to sufficiently wash the nickel particles produced. The washing is preferably carried out until the amount of carbon contained in the nickel powder after the washing is 0.25 g/(m) ² /g) is below.

In order to further reduce the amount of carbon contained in the nickel powder, it is preferable to treat the nickel powder after washing with an alkaline aqueous solution or the nickel powder without washing. By this treatment, hydrophilic organic substances present on the surfaces of the nickel particles can be further removed. Examples of the alkaline aqueous solution used for treating nickel powder include aqueous solutions of alkali metal hydroxide, alkaline earth metal hydroxide, alkali metal carbonate, alkali metal hydrogencarbonate, quaternary ammonium salt, and ammonia. Specifically, for example, aqueous solutions of sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, ammonia, sodium carbonate, sodium hydrogencarbonate, potassium carbonate, potassium hydrogencarbonate, ammonium carbonate, ammonium hydrogencarbonate, and the like can be used. These solutes of the alkaline aqueous solution may be used singly or in combination of 2 or more. Among these aqueous alkaline solutions, tetramethyl ammonium hydroxide, ammonia, ammonium carbonate and ammonium bicarbonate are preferable because they do not contain alkali metal elements.

The pH of the alkaline aqueous solution is preferably 7.5 to 14.0, more preferably 9.0 to 14.0. The treatment with the alkaline aqueous solution is preferably carried out until the amount of carbon contained in the nickel powder after washing is 0.10 g/(m) ² /g) is below.

The nickel powder thus obtained is preferably treated with a hydrophobic organic substance. When the nickel powder subjected to the treatment is used for preparing a paste, the nickel powder has a high affinity with an organic solvent contained in the paste, and therefore has an advantage of good characteristics of the paste such as fluidity. The paste is advantageous in that the fluidity of the paste is good in terms of being able to smooth the surface of a sintered film formed from the paste. From the viewpoint of preventing the hydrophobic organic matter excessively adsorbed on the particles from eluting into the paste, the treatment with the hydrophobic organic matter is preferably performed at a limit where the amount of carbon contained in the nickel powder after the treatment does not exceed the amount of carbon contained in the nickel powder immediately after the synthesis (i.e., before the washing with water or before the treatment with an alkaline aqueous solution).

Examples of the hydrophobic organic substance include various fatty acids and aliphatic amines. In view of the ability to produce a paste having good properties, it is particularly preferable to use a saturated or unsaturated fatty acid or aliphatic amine having 6 to 18 carbon atoms, and it is particularly preferable to use a saturated or unsaturated fatty acid or aliphatic amine having 10 to 18 carbon atoms. Specific examples of such fatty acids or aliphatic amines include benzoic acid, capric valeric acid, caproic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, palmitic acid, oleic acid, stearic acid, pentylamine, hexylamine, octylamine, decylamine, dodecylamine, laurylamine, oleylamine, and stearylamine.

In addition to fatty acids and aliphatic amines, sulfur-containing organic compounds such as mercapto compounds and mercaptans can be used as the hydrophobic organic compound. For example, decanethiol, dodecanethiol, octadecanethiol, and the like can be used.

Furthermore, a polymer containing a carboxyl group, a polymer containing an amino group, or the like may be used as the hydrophobic organic substance.

The hydrophobic organic substance may be used alone or in combination of at least 2 kinds.

The hydrophobic organic material may be a commercially available material. Examples of such commercial products include ESLEAM (registered trademark) of the company of daily oil.

The nickel powder manufactured by the method fully utilizes the characteristics of particles and uniform particle size, and can be used in various fields. Is particularly suitable for forming the internal electrodes of the MLCC.

Examples

The present invention will be described in further detail with reference to examples. However, the scope of the present invention is not limited to the embodiments. Unless otherwise specified, "%" means "% by mass".

[ example 1]

A slurry was prepared by adding 445g of ethylene glycol, 64g of nickel hydroxide particles, 12g of polyvinylpyrrolidone, 0.14g of polyethyleneimine and 0.06ml of an aqueous palladium nitrate solution (concentration: 100 g/l) in a 500ml beaker. The polyethyleneimine is branched and has a number average molecular weight of 1800. The number average molecular weight of polyvinylpyrrolidone was 40000. The slurry was heated while stirring, and the reduction reaction was performed at 198℃for 6 hours. Then, the heating was stopped to terminate the reduction, and the mixture was naturally cooled to room temperature. Thereby generating a large amount of nickel particles.

[ example 2]

In example 1, nickel powder was obtained in the same manner as in example 1, except that 0.2g of polyethyleneimine and 0.13ml of an aqueous palladium nitrate solution were used.

[ example 3]

In example 1, nickel powder was obtained in the same manner as in example 1, except that polyvinylpyrrolidone was changed to 14g, polyethylenimine was changed to 0.28g, and palladium nitrate aqueous solution was changed to 0.18 ml.

[ example 4 ]

In example 1, nickel powder was obtained in the same manner as in example 1, except that 18g of polyvinylpyrrolidone, 0.3g of polyethyleneimine and 0.8ml of palladium nitrate aqueous solution were used.

[ example 5 ]

A magnet was placed at the bottom of a beaker containing the nickel particle dispersion obtained by the reduction reaction of example 1, and the nickel particles were attracted and aggregated by the magnet. In this state, the supernatant of the dispersion is removed.

After removing the magnet, 50g of pure water was added and mixed, and the dispersion was stirred for 10 minutes. The magnet was again placed at the bottom of the beaker and the nickel particles were attracted to the magnet to accumulate. In this state, the supernatant of the dispersion was removed.

After removing the magnet, 50g of 5% aqueous ammonia solution was added, and the dispersion was stirred for 10 minutes. The magnet was again placed at the bottom of the beaker and the nickel particles were attracted to the magnet to accumulate. In this state, the supernatant of the dispersion was removed.

After removing the magnet, 50g of pure water was added and mixed, and the dispersion was stirred for 10 minutes. The magnet was again placed at the bottom of the beaker and the nickel particles were attracted to the magnet to accumulate. In this state, the supernatant of the dispersion is removed, thereby removing residual ammonia.

Then, 50g of methanol was added and stirred for 10 minutes, and removal of the supernatant was repeated 3 times with a magnet to replace the solvent with methanol.

A liquid obtained by dissolving 0.8g of ESLEAM (registered trademark) C2093I (manufactured by Nikko Co., ltd.) in 5g of methanol was added to the dispersion of nickel particles, and stirred for 60 minutes. Then, the supernatant was removed using a magnet to obtain surface-treated nickel particles.

[ example 6 ]

The same procedure as in example 5 was conducted except that the nickel particle dispersion obtained by the reduction reaction of example 2 was used, to obtain surface-treated nickel particles.

Example 7

The same procedure as in example 5 was conducted except that the nickel particle dispersion obtained by the reduction reaction of example 3 was used, to obtain surface-treated nickel particles.

Example 8

The same procedure as in example 5 was conducted except that the nickel particle dispersion obtained by the reduction reaction of example 4 was used, to obtain surface-treated nickel particles.

Comparative example 1

In this comparative example, nickel powder was produced using an aqueous system. Specifically, 900g of nickel sulfate hexahydrate, 35g of citric acid, and 12.5g of sodium phosphinate were dissolved in 1L of pure water to obtain an aqueous solution. The resulting aqueous solution was added to 760g of an aqueous solution of 25% sodium hydroxide concentration maintained at 60℃for 10 minutes, whereby nickel hydroxide was precipitated. 940g of hydrazine monohydrate was added to the suspension for 5 minutes while maintaining the liquid temperature of the suspension at 80℃to reduce the nickel hydroxide to nickel, thereby obtaining nickel powder.

Comparative example 2

In this comparative example, PEI was not used in example 1. Further, nickel powder was obtained in the same manner as in example 1, except that the palladium nitrate aqueous solution was changed to 0.4 ml.

[ evaluation 1]

The particle size distribution of the nickel powders obtained in examples and comparative examples was measured by the above method to obtain the particle size D ₅₀ Coarse particle presence ratio and coefficient of variation. As SEM, JSM-7100F manufactured by JSEINC Co., ltd.

The crystallite size by the WPPF method was determined by the following method.

The results are shown in Table 1 below. SEM images of the nickel powders obtained in example 2 and comparative example 2 are shown in fig. 3 and 4.

[ measurement of crystallite size by WPPF method ]

The crystallite size can be calculated from the diffraction peak from nickel measured by X-ray diffraction using WPPF method. The conditions for the X-ray diffraction measurement are described in detail in examples described later.

Device name SmartLab (9 KW): rigaku Corporation made of

Structure of device

Wavelength of

Target: cu (Cu)

Wavelength type: kα1

·Kα1：1.54059

·Kα2：1.54441

·Kβ：1.39225

Kα12 intensity ratio: 0.4970

Horizontal polarization ratio: 0.500

Diffraction device

Goniometer: smartLab

Fitting base: z-axis workbench alone

Fitting: ASC 6-reflectance < measurement Condition >)

Optical system properties: centralizing method

CBO selection slit: BB (BB)

Incident parallel slit: soller_slip_5.0 deg

Entrance slit: 2/3deg

Longitudinal limiting slit: 10.0mm

Light receiving slit 1:20.000mm

Light-receiving parallel slit: soller_slip_5.0 deg

Light receiving slit 2:20.000mm

Attenuator: open (Open)

Detector: D/teX Ultra250

Scanning axis: 2 theta/theta

Scanning mode: continuous and continuous

Scan range: 5.0000-140.0000 deg

Stride: 0.0100deg

Scan speed/measurement time: 2.015572deg/min

Data points: 13501 point

Guan Dianya: 45kV

Guan Dianliu: 200mA

·HV：0.00

Preparation method of sample for X-ray diffraction

The nickel powder to be measured was spread on the measuring holder, and the surface was smoothed by using a glass plate so that the thickness of the layer composed of the nickel powder was 0.5mm and the measuring surface was smooth.

Using the X-ray diffraction pattern obtained under the above measurement conditions, analysis was performed using analysis software under the following conditions. In the analysis, correction was performed using data obtained from lanthanum hexaboride powder (SRM 660 series), which is a standard substance supplied from National Institute of Standards and Technology (NIST). Crystallite size was calculated using WPPF method.

< analysis conditions of measured data >

Analysis software: PDXL2 manufactured by Rigaku

Analysis method: WPPF process

Data processing: automatic contour processing

(Rigaku Corporation PDXL user Manual p.305)

[ evaluation 2]

The amount of the impurity element contained in the nickel powder was quantified by the following method. Further, the specific surface area of the nickel powder was measured by the following method. These results are shown in table 2 below.

[ quantification of impurity element ]

1.00g of nickel powder was dissolved in 50ml of 15% aqueous nitric acid to obtain a solution. The solution was introduced into an ICP emission spectrometry device (Hitachi High-Technologies Corp. Manufactured by PS3520 VDDII) to measure the contents of sodium, potassium and sulfur.

Further, 1.00g of nickel powder was added to 20.0ml of pure water, and 2ml of a 2.5g/l aqueous silver nitrate solution and 10ml of a 70% aqueous nitric acid solution were further added thereto, followed by heating at 90 ℃. The aqueous solution was naturally cooled to room temperature, and 1ml of a 1.5g/l aqueous potassium bromide solution was added. The precipitate obtained was filtered off with suction, washed with pure water, dissolved in 20mL of 10g/l thiourea aqueous solution, and filtered. The solution was introduced into an ion chromatography apparatus (Metrohm Japan Ltd. 930 CompactICFlex) to measure the chlorine content.

Further, the amount of carbon contained in the nickel powder was measured before the washing with water (C1), after the treatment with an alkaline aqueous solution (C2) and after the surface treatment (C3) by the following methods.

A carbon/sulfur analyzer (CS 844, LECO Japan Corporation) was used. The nickel powders of examples and comparative examples were measured by placing 0.50g in a magnetic crucible. The carrier gas was set to oxygen (purity: 99.5%). The analysis time was set to 40 seconds.

[ determination of specific surface area ]

The specific surface area was measured by a nitrogen adsorption method using "Macsorb" manufactured by Mountech co.ltd. The amount of the powder was measured and set to 0.2g. The pre-degassing conditions were set to vacuum at 80℃for 30 minutes.

[ evaluation 3]

The surface roughness Rz of the sintered film containing the nickel powder, and the heat shrinkage finish temperature and heat shrinkage amount of the nickel powder obtained in examples and comparative examples were measured by the following methods. Further, the viscosity of the coating liquid used for producing the sintered film was measured. These results are shown in table 3 below.

[ Heat shrinkage end temperature and Heat shrinkage ]

As a measurement apparatus for TMA, EXSTAR 6000 manufactured by Seiko Instruments Inc. was used. 500mg of nickel powder was placed in a stainless steel cup having a diameter of 5.0mm, and the cup was press-molded under a pressure of 1.0MPa to prepare pellets. The obtained pellets were used as a sample to be measured, and the sample was set in a measuring apparatus. The sample was warmed at 10 c/min in a 1 vol% hydrogen/99 vol% nitrogen atmosphere. Measurement was started from room temperature (25 ℃) to obtain a graph showing the relationship between temperature and displacement (%).

[ surface roughness Rz of sintered film ]

0.1g of ethylcellulose was dissolved in 4g of terpineol, followed by adding 5g of nickel powder to obtain a mixture. The mixture was mixed using a rotation/revolution mixer (manufactured by "Awatori huntaro (registered trademark)", THINKY CORPORATION). The mixture was then broken up by passing it through a three-roll mill 4 times. The gap of the three-roll mill was set at 8. Mu.m. Thereby obtaining a coating liquid.

The viscosity (25 ℃) of the coating liquid was measured using HAAKE RheoStress3000 manufactured by Thermo Fisher Scientific.

The coating liquid is coated on a glass substrate to form a coating film. The wet thickness of the coating film was 35. Mu.m. The film was sintered at 350℃for 10 minutes in a nitrogen atmosphere to obtain a sintered film.

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

TABLE 1

TABLE 2

TABLE 3

As is apparent from the results shown in tables 1 to 3, the nickel powder obtained in each example had a high heat shrinkage termination temperature and the sintered film had a small surface roughness Rz.

In contrast, it is found that the nickel powder obtained in comparative example 1 has a low heat shrinkage finish temperature and the sintered film has a large surface roughness Rz.

The nickel powder obtained in comparative example 2 had a high heat shrinkage finish temperature, but had a large amount of coarse particles, and the sintered film had a large surface roughness Rz.

Further, as is clear from the comparison of examples 1 to 4 and examples 5 to 8, the nickel powder obtained by reduction was treated with an alkaline aqueous solution, and the viscosity of the coating liquid was lowered, thereby improving the smoothness of the surface of the sintered film.

Industrial applicability

According to the present invention, a nickel powder having a small content of fine particles and coarse particles can be provided. Therefore, the nickel powder is suitable for use as a material for forming internal electrodes of, for example, an MLCC. Further, according to the present invention, such nickel powder can be easily produced.

Claims

1. A nickel powder wherein the number-cumulative particle diameter at which the cumulative number is 50% in the particle size distribution based on the equivalent diameter calculated by measurement with a scanning electron microscope is set to D ₅₀ In the time-course of which the first and second contact surfaces,

D ₅₀ is 50nm to 200nm,

2. The nickel powder according to claim 1, wherein the standard deviation of the particle diameter in the particle size distribution is set to σ (nm), (σ/D ₅₀ ) The value of x 100 (%) is 14% or less.

3. The nickel powder according to claim 1 or 2, wherein Cs/D is measured by WPPF method, when Cs (nm) is the crystallite size ₅₀ The value of (2) is 0.3 to 0.6.

4. The nickel powder according to any of claims 1 to 3, wherein the content of sodium element is 50ppm or less, the content of potassium element is 50ppm or less, the content of chlorine element is 500ppm or less, and the content of sulfur element is 500ppm or less.

5. The nickel powder according to any one of claims 1 to 4, which has a heat shrinkage of 30% or less at 900 ℃ in a 1 vol.% hydrogen/99 vol.% nitrogen atmosphere.

6. The nickel powder according to any one of claims 1 to 5, which has a heat shrinkage end temperature of 650 ℃ or higher and 1000 ℃ or lower in a 1 vol.% hydrogen/99 vol.% nitrogen atmosphere at a heating rate of 10 ℃/min.

7. The nickel powder according to any of claims 1-6, wherein the value of the content/specific surface area of carbon element is 0.01 g/(m) ² Per g) of above and 0.35 g/(m) ² /g) is below.

8. A method for producing nickel particles by heating a liquid containing nickel hydroxide particles, a polyol, polyvinylpyrrolidone and polyethyleneimine, wherein,

9. The production method according to claim 8, wherein the liquid is heated to 150 ℃ or higher and 200 ℃ or lower.

10. The production method according to claim 8 or 9, wherein ethylene glycol is used as the polyol.

11. The method according to any one of claims 8 to 10, wherein a branched polyethylenimine having a number average molecular weight of 600 or more and 10000 or less is used as the polyethylenimine.

12. The production method according to any one of claims 8 to 11, wherein the produced nickel particles are washed with water or treated with an alkaline aqueous solution.

13. The production method according to claim 12, wherein the nickel particles after washing with water or the nickel particles after treatment with the alkaline aqueous solution are treated with a hydrophobic organic substance.