JP2021161495A - Nickel particle and method for producing the same, as well as conductive composition - Google Patents

Abstract

To provide a nickel particle that has excellent low-temperature sinterability.SOLUTION: The nickel particle of the present invention has a 50% particle diameter D50 in the number distribution measured by scanning electron microscopy of less than 50 nm, and has a crystallite size obtained from the half value width of a peak due to (111) plane of nickel by Scherrer's equation in X-ray diffraction measurement of less than 15 nm. Further, a method for producing nickel particle comprising a step of mixing a water-soluble nickel source, a metal element source nobler than nickel, and a reducing compound to reduce the nickel source is also provided. Further, a conductive composition containing the nickel particle and an organic solvent is also provided.SELECTED DRAWING: Figure 1

Description

The present invention relates to nickel particles, a method for producing the same, and a conductive composition.

With the recent trend of energy saving worldwide, semiconductor elements called power devices have been actively used as power conversion / control devices such as inverters. Unlike integrated circuits such as memories and microprocessors, power devices are for controlling high current and high voltage, so the amount of heat generated during driving tends to be very large. Therefore, the bonding material for bonding the power device to the substrate is required to have high bonding reliability against the thermal stress generated by the repeated operation of On / Off of the device. In addition to this, in order not to affect the performance of the manufactured power device, a bonding material capable of exhibiting bonding performance at a bonding temperature of 300 ° C. or lower is also desired.
Metal particles containing silver and copper have been studied as bonding materials that can satisfy such performance, but these metals have a large difference in thermal expansion coefficient from semiconductors such as Si and SiC used in power devices. In addition, the joint reliability against thermal stress may not be sufficient. Therefore, in order to ensure the bonding reliability, a bonding material containing a metal such as nickel, which is relatively close to the coefficient of thermal expansion of the semiconductor, is desired.

The applicant has proposed a nickel fine powder containing 0.01 to 2% by mass of phosphorus with respect to the mass of nickel and having a particle size of 0.5 μm or less (Patent Document 1). This nickel fine powder has a uniform particle size and is excellent in heat shrinkage characteristics.

Further, Patent Document 2 discloses nickel fine particles having a nickel hydroxide film and having a predetermined mass ratio of nickel hydroxide, carbon element and oxygen element. It is also disclosed that the nickel fine particles can form a bonding layer having a high share strength.

Japanese Unexamined Patent Publication No. 2000-313906 Japanese Unexamined Patent Publication No. 2014-162967

When the nickel particles described in Patent Documents 1 and 2 are used as a raw material for producing a bonding material, the meltability of the particles at the time of sintering is not sufficient due to the high melting point of nickel, and the desired bonding is performed. Sometimes it was not possible to form a layer.

Therefore, an object of the present invention is to provide nickel particles having excellent low-temperature sinterability.

In the present invention, the 50% particle size D50 in the number distribution measured by scanning electron microscopy is less than 50 nm.
Provided are nickel particles having a crystallite size of less than 15 nm determined by Scheller's equation from the full width at half maximum of a peak derived from the (111) plane of nickel in an X-ray diffraction measurement.

The present invention also provides a method for producing nickel particles, which comprises a step of mixing a water-soluble nickel source, a metal element source nobler than nickel, and a reducing compound to reduce nickel ions.

Furthermore, the present invention provides a conductive composition containing the nickel particles and a solvent.

According to the present invention, nickel particles having excellent low-temperature sinterability are provided.

FIG. 1 is a scanning electron microscope image of nickel particles of an example before and after firing observed at a magnification of 150,000.

The nickel particles of the present invention have a 50% particle diameter D50 in the number distribution of preferably less than 50 nm, more preferably 40 nm or less, still more preferably 30 nm or less when observed from directly above with a scanning electron microscope. By having such a D50, sinterability at a low temperature can be effectively exhibited. Further, when the particles are contained in a conductive paste or the like and used, a bonding material exhibiting good filling property can be obtained. On the other hand, from the viewpoint of achieving both sinterability at low temperature and handleability of particles, D50 is realistically 10 nm or more. Nickel particles having such D50 can be produced, for example, by a production method described later.

D50 can be measured by, for example, the following method. First, from a scanning electron microscope image of nickel particles at a magnification of 150,000 times, 1000 or more particles in which the particles do not overlap are randomly selected and the particle size (Haywood diameter) is measured. Then, from the obtained particle size of each particle, a particle size distribution based on the number standard is obtained. Then, the median particle size of the particle size distribution based on the number standard can be set to D50 in the present invention.

The nickel particles have a crystallite size of preferably less than 15 nm, more preferably 13 nm or less, still more preferably 10 nm or less. With such a crystallite size, many crystallites can be present in one particle and many interfaces between the crystallites can be formed. Therefore, when the particles are heated, the atoms at the crystallite interface can be formed. Diffusion can be activated. As a result, the meltability of the particles at a low temperature can be increased, and the sinterability can be improved. Such an improvement in low-temperature sinterability is more remarkable as the crystallite size is smaller. Such nickel particles can be produced, for example, by a production method described later.

The crystallite size of nickel particles is measured based on Scheller's equation from the half width of the diffraction peak derived from the (111) plane of nickel obtained by X-ray diffraction measurement. The X-ray diffraction measurement can be performed using, for example, an X-ray diffraction measuring device "RINT-TTR-III" manufactured by Rigaku Co., Ltd. CuKα (X-ray wavelength: 0.154056 nm) is used as the X-ray source, and the tube voltage is 50 kV and the tube current is 300 mA. The measurement range is 2θ = 20 to 90 °, the scan speed is 20 ° / min, and the scan step is 0.02 °. For the analysis, for example, software "PDXL" manufactured by Rigaku Co., Ltd. can be used to remove the background, and then Scheller's formula (D = Kλ / βcosθ) can be used to calculate the crystallite size. In Scheller's equation, D is the crystallite size (nm), K is the Scheller constant (0.9400), λ is the wavelength of X-rays (nm), β is the full width at half maximum (rad), and θ is the diffraction angle (rad). be.
The nickel particles may have an FCC crystal structure and an HCP crystal structure, but the nickel particles of the present invention preferably have an FCC crystal structure having a (111) plane.

Since both D50 and the crystallite size of the nickel particles having the above structure are less than the predetermined values, the temperature of the atoms in the particles existing at the surface of the nickel particles and the crystallite interface in the particles rises. Since the particles are easily diffused together with the particles, softening and melting of the particles are likely to occur even under low temperature heating conditions. The result is nickel particles with excellent sinterability at low temperatures. Further, even under conditions where sintering is difficult to proceed as compared with heating in a reducing atmosphere such as hydrogen gas, such as heating in an inert atmosphere such as nitrogen gas, the sintering property of nickel particles is high. It will be expensive. Such particles can be suitably used as a constituent material contained in a bonding material such as a material for die bonding.

It is also preferable that the nickel particles contain a phosphorus element and the phosphorus element content is in a predetermined range. Specifically, the content of the phosphorus element in the nickel particles is preferably 0.01% by mass or more and 10.0% by mass or less, more preferably 0.01% by mass or more and 8% by mass or less, and further preferably. It is 1% by mass or more and 7% by mass or less. Although the form of phosphorus present in the nickel particles is not clear, by setting the content of phosphorus element in such a range, a melting point drop can be generated and the sinterability at low temperature can be further improved. Such nickel particles can be produced, for example, by a production method described later. The presence or absence of the phosphorus element and its content in the nickel particles can be measured by, for example, inductively coupled plasma emission spectroscopy.

It is also preferable that the nickel particles contain a metal element that is more noble than nickel as the first metal, and the content of the metal element is in a predetermined range. The "metal element nobler than nickel" refers to a metal element having a higher standard electrode potential than nickel alone, and is also referred to as a "second metal element" in the following description. In the present invention, as the second metal element, preferably one or more of copper, silver and noble metals such as palladium, platinum and gold, more preferably one or more of palladium, platinum and gold, and even more preferably palladium are used. ..

The content of the second metal element in the nickel particles is preferably 0.02% by mass or more and 0.50% by mass or less, more preferably 0.04% by mass or more and 0.30% by mass or less, and further preferably. It is 0.06% by mass or more and 0.10% by mass or less. The existence mode of the second metal element may be a simple substance or an alloy with nickel, which is the first metal. By setting the content of the second metal element in such a range, nickel particles having a lower melting point and more excellent sinterability at a low temperature can be obtained at a reduced production cost. Such nickel particles can be produced, for example, by a production method described later. The presence or absence of the second metal element and its content can be measured by, for example, inductively coupled plasma emission spectroscopy.

As the shape of the nickel particles, one or more of various shapes such as a spherical shape, a flake shape, and a polyhedral shape can be adopted. In the bonding material containing nickel particles, the shape of the nickel particles is preferably spherical from the viewpoint of excellent sinterability at low temperature and the viewpoint of increasing the density of the bonded body obtained after sintering. The term “spherical” as used herein means that the circularity coefficient measured by the following method is 0.75 or more, and more preferably 0.80 or more. For the circularity coefficient, 200 particles in which the particles do not overlap were randomly selected from the scanning electron microscope images of the particles to be measured, and the area of the two-dimensional projection image of the particles was S and the peripheral length was L. Occasionally, the circularity coefficient of the particles is calculated from the equation of 4πS / L ² , and the arithmetic average value of the circularity coefficient of each particle is taken as the above-mentioned circularity coefficient. When the two-dimensional projection image of the particle is a perfect circle, the circularity coefficient of the particle is 1, so it can be said that the higher the value of the circularity coefficient, the closer the particle is to a true sphere. Therefore, the circularity coefficient of the nickel particles is preferably 1 or less, and 0.95 or less is realistic.

BET specific surface area of the nickel particles is preferably not more than 15.0 m ² / g or more 40.0m ² / g, still more preferably not more than 20.0 m ² / g or more 35.0 m ² / g. Since the size of the BET specific surface area and the small particle size are generally correlated, when the BET specific surface area is in such a range, the particle size of the nickel particles is sufficiently reduced and the low temperature sinterability is achieved. It is advantageous in that it can further increase. The BET specific surface area can be measured by a nitrogen adsorption method (BET one-point method) using, for example, "Macsorb HM model-1201" manufactured by Mountech Co., Ltd. The amount of the measurement sample was 0.1 to 0.2 g, the adsorbed gas was a nitrogen-helium mixed gas containing 30% by volume of nitrogen and 70% by volume of helium as a carrier gas, and the preliminary degassing condition was helium /. The temperature is 75 ° C. for 20 minutes in a nitrogen atmosphere.

Next, a preferred method for producing the nickel particles described above will be described. The present production method comprises a step of mixing a water-soluble nickel source, a second metal element source and a reducing compound to reduce nickel ions. This method is preferably performed under wet conditions. That is, in this method, it is preferable to reduce nickel ions in an aqueous solution in which a water-soluble nickel source, a second metal element source and a reducing compound are mixed to generate nickel particles. The manufacturing method under wet conditions will be described below as an example.

First, a reaction solution in which a water-soluble nickel source, a second metal element source and a reducing compound are mixed is prepared. In this step, each raw material may be added to a solvent such as pure water at the same time to prepare a reaction solution, or each raw material may be added to the solvent in an arbitrary order to prepare a reaction solution. From the viewpoint of making it easier to control the reduction reaction of nickel ions and improving the handleability during production, a nickel raw material solution in which a water-soluble nickel source and a second metal element source are mixed in a solvent such as pure water, and a reducing compound. It is preferable to separately prepare a reducing solution prepared by mixing the above with a solvent such as pure water, and then mix the nickel raw material solution and the reducing solution to prepare a reaction solution, and start the nickel ion reduction reaction. In this case, the nickel raw material solution is free of reducing compounds. Similarly, the reducing solution is free of both a water-soluble nickel source and a secondary metal element source.
In particular, it is preferable to use only water as the solvent for preparing the nickel raw material solution, the reducing solution and the reaction solution, because it is possible to reduce the mixing of unintended impurities into the obtained nickel particles. In the following description, a production method in which a nickel raw material solution and a reducing solution are prepared independently and then these solutions are mixed to prepare a reaction solution will be described as an example.

First, a nickel raw material solution containing a water-soluble nickel source and a second metal element source is prepared. Examples of the water-soluble nickel source include nickel organic acid salts such as nickel formate, nickel acetate, nickel malonate and nickel succinate, nickel inorganic acid salts such as nickel nitrate and nickel sulfate, halides such as nickel chloride, and nickel hydroxide. Hydroxide, etc., and various nickel compounds such as. These nickel compounds may be anhydrous or hydrated. These nickel compounds can be used alone or in combination of two or more.

The second metal element source contained in the nickel raw material solution is used to promote the reduction of nickel ions to obtain nickel particles having a desired particle size and crystallite size. As the secondary metal element source, for example, a water-soluble secondary metal such as a salt of a secondary metal such as silver, copper, palladium, platinum and gold and an inorganic acid such as nitrate, sulfuric acid, acetic acid and carbonic acid or an organic acid. Compounds are preferably used. This also has the advantage that the melting point drop of the obtained nickel particles can be appropriately expressed and the sintering characteristics at a lower temperature can be improved.

The content of the water-soluble nickel source in the nickel raw material solution is preferably 0.1 mol / L or more and 1.0 mol / L or less, preferably 0.3 mol / L or more and 0.7 mol / L or less, in terms of the molar concentration of the nickel element. More preferred.

The content of the second metal element source in the nickel raw material solution is preferably ^{5.0 × 10-5} or more and 5.0 × ^10-2 or less in terms of the molar ratio of the second metal element to the nickel element. More preferably, it is 0.0 × 10 ^-4 or more and 2.5 × 10 ^{-2 or less.} By containing the second metal element source in such a ratio, the particle size of the obtained nickel particles can be made small and easily controlled. Further, it is possible to obtain nickel particles in which the content of the second metal element is controlled within the above-mentioned range.

In preparing the nickel raw material solution, there are no particular restrictions on the order and method of adding the water-soluble nickel source and the second metal element source. For example, a solid water-soluble nickel compound and a solid secondary metal compound may be added to a solvent such as pure water in any order or at the same time to form a solution, and at least one of the water-soluble nickel compound and the secondary metal compound may be added. After being dissolved in pure water or the like in advance, these may be added in any order or at the same time and mixed to form a solution. In any case, from the viewpoint of increasing the reduction efficiency of nickel ions and obtaining nickel particles having a small particle size in the steps described later, after the preparation of the nickel raw material solution, the temperature is 40 ° C. or higher and 90 ° C. or lower with stirring. It is preferable to reduce the nickel ions by heating to.

Further, a reducing solution containing a reducing compound is prepared separately from the nickel raw material solution. The reducing compound used in this method is preferably water soluble. Examples of such reducing compounds include hydrazine compounds such as hydrazine, hydrazine hydrochloride, hydrazine sulfate and hydrous hydrazine, boron compounds such as sodium hydride and dimethylamine borane and salts thereof, sodium sulfite and sodium hydrogen sulfite. And sulfur oxo acidates such as sodium thiosulfate, nitrogen oxo salts such as sodium nitrite and sodium hyponitrite, phosphoric acids such as phosphite, sodium phosphite, hypophosphite and sodium hypophosphite, and The salt can be mentioned. These reducing compounds may be anhydrous or hydrated. These reducing compounds may be used alone or in combination of two or more.

It is preferable that the reducing solution has an alkaline condition having a pH of 8.0 or more at 25 ° C., because a reducing reaction of nickel ions proceeds satisfactorily when a reducing compound, particularly a hydrazine-based compound, is used. .. In this case, various acids and basic substances can be used for adjusting the pH as long as the effects of the present invention are exhibited, and for example, sodium hydroxide and ammonia can be used.

Subsequently, nickel ions and preferably second metal ions are reduced in a reaction solution in which a nickel raw material solution and a reducing solution are mixed to obtain nickel particles. The mixing ratio of the nickel raw material solution and the reducing solution is preferably 100 parts by mass or more and 500 parts by mass or less of the nickel raw material solution with respect to 100 parts by mass of the reducing solution. Further, in the mixing of the nickel raw material solution and the reducing solution, one may be added to the other and mixed, or these solutions may be mixed at the same time. Further, these solutions may be mixed by batch addition or sequential addition by dropping or the like.
From the viewpoint of allowing the reduction reaction of nickel ions to proceed satisfactorily, it is preferable to set the pH of the reaction solution at 25 ° C. to an alkaline condition of 8.0 or more. In order to make the reaction solution alkaline, for example, the pH of the reducing solution may be changed to be high, or the mixing ratio of the reducing solution under alkaline conditions may be changed to make appropriate adjustments. can.

In the reduction reaction in the reaction solution, it is preferable to use a hydrazine compound as the reducing compound in the reducing solution from the viewpoint of having high reducing property and reducing the generation and mixing of unintended impurities after the reduction. It is more preferable to use hydrazine anhydride or hydrate from the viewpoint of being widely used industrially, inexpensive and easily available in large quantities. Further, from the viewpoint of facilitating the control of the grain growth of nickel after reduction and efficiently obtaining nickel particles having a small D50 and a small crystallite size, it is added to the hydrazine-based compound as a reducing compound in the reducing solution. Therefore, it is preferable to use phosphoric acid and a salt thereof, further preferably to use phosphoric acid salt, further preferably to use hypophosphite, and even more preferably to use sodium hypophosphite.
In particular, by using a palladium compound as the second metal element source and using a combination of hydrazine and phosphoroxate as the reducing compound, the reduction reaction of nickel ions and the progress of grain growth are appropriately controlled, and the particle size can be adjusted. It is preferable in that nickel particles having a small size and a small crystallite size can be obtained with high productivity.

By using a phosphoroxate in addition to hydrazine as the reducing compound in the reducing solution, nickel particles having a small D50 and a small crystallite size can be efficiently obtained. I'm guessing. First, the hydrazine in the reaction solution reduces the second metal ion derived from the second metal element source before the nickel ion, and very fine particles of the second metal element are generated in the reaction solution. Subsequently, with the fine particles of the second metal element generated in the reaction solution as nuclei, nickel is reduced and precipitated by hydrazine on the surface of the particles, and very fine nickel particles are generated. Furthermore, the second metal element particles reduced by hydrazine and the metallic nickel itself precipitated on the surface of the particles function as a catalyst, the reduction reaction of nickel ions by phosphoroxate is promoted, and the phosphorus element is contained in the nickel particles as the grains grow. Is taken in by. At this time, nickel grain growth occurs simultaneously in each particle in the reaction solution, and a large amount of nickel ions in the reaction solution are consumed during the grain growth. Therefore, the amount of nickel ions consumed for grain growth per particle. Is reduced, and grain growth for each particle is suppressed. As a result, it is considered that nickel particles having a small D50 and a small crystallite size can be efficiently obtained.

Further, as a preferable method of this method, by preparing a reaction solution using a reducing solution in which alkaline conditions are prepared in advance, nickel ions uniformly present in the nickel raw material solution are reduced in the reaction solution, which is caused by the reduction reaction. Nucleation and grain growth of the nickel proceed uniformly and simultaneously in the reaction solution. As a result, it is considered that atomization of each particle is efficiently achieved. On the other hand, when a reaction solution is prepared using a nickel raw material solution prepared in advance under alkaline conditions, the nickel ions and hydroxide ions in the nickel raw material solution react with each other to precipitate nickel hydroxide, which is mixed in the reaction solution. Therefore, it is considered difficult to produce nickel particles having both the above-mentioned D50 and crystallite size.

In the preparation of the reaction solution, the total content of the reducing compound in the reaction solution is preferably 4 mol or more and 20 mol or less, more preferably 6 mol or more and 15 mol or less, based on 1 mol of the nickel element. , Mix the reducing solution. By setting the total content of the reducing compound to such a ratio, nickel particles having D50 and crystallite size within the above-mentioned ranges can be efficiently obtained.

When a hydrazine compound is used in combination with a phosphoric acid and a salt thereof as the reducing compound, the content of the hydrazine compound in the reaction solution is preferably 1 mol or more and 20 mol or less with respect to 1 mol of the nickel element. More preferably, it is 4 mol or more and 15 mol or less. The content of phosphorus oxo acid and its salt in the reaction solution is preferably 0.01 mol or more and 15 mol or less, and more preferably 0.1 mol or more and 10 mol or less with respect to 1 mol of the nickel element. By controlling the concentration of the reducing compound in these ranges, the reduction reaction of nickel ions and the progress of grain growth can be appropriately controlled, and nickel particles having a small particle size and a small crystallite size can be obtained with high productivity. Can be done. In addition, nickel particles having a phosphorus content in the above range can be obtained.

It is preferable to heat the reaction solution from the viewpoint of efficiently advancing the reduction of nickel ions in the reaction solution and obtaining nickel particles having a small particle size with high productivity. The heating conditions of the reaction solution are preferably 40 ° C. or higher and 90 ° C. or lower, particularly 60 ° C. or higher and 80 ° C. or lower, from the start of mixing the nickel raw material solution and the reducing solution to the end of the reaction. The time from the start time to the end time of mixing is preferably 15 minutes or more and 120 minutes or less. Further, from the viewpoint of uniformly causing the reduction reaction to obtain nickel particles having little variation in particle size, it is also preferable to continue stirring the reaction solution from the start of mixing to the end of the reaction.

The nickel particles thus obtained may be washed by a decantation method or the like and then dispersed in an organic solvent such as water or alcohol to form a slurry, ink, paste or the like. Further, the washed nickel particles may be dried to obtain a dry powder which is an aggregate of the particles.

The nickel particles obtained through the above steps have a small particle size and a small crystallite size. Further, the particles thus obtained are generally spherical. As long as the effect of the present invention is exhibited, it is excluded that the obtained nickel particles contain elements other than the phosphorus element and the second metal element, and that the surface of the nickel particles is inevitably slightly oxidized. It's not something to do.

Nickel particles are suitably used as a metal filler to be blended in a conductive composition. The conductive composition contains nickel particles as a metal filler and a solvent, and preferably contains a binder resin. Examples of the shape of the conductive composition include a conductive slurry, a conductive ink, and a conductive paste.

Examples of the solvent used in the conductive composition include water, alcohols, ketones, esters, ethers and hydrocarbons. Among them, at least one of alcohols such as tarpineol and dihydroterpineol, and ethers such as ethyl carbitol and butyl carbitol are preferable. Further, examples of the binder resin used in the conductive composition include at least one of acrylic resin, epoxy resin, polyester resin, polycarbonate resin, cellulose resin and the like.

The conductive composition can be applied, for example, by a predetermined means to form a wiring circuit of a printed wiring board or an electrode of a chip component. It can also be used as a via filling material in a printed wiring board or as an adhesive when surface-mounting an electronic device on a printed wiring board. In particular, the conductive composition containing nickel particles can be particularly preferably used as a bonding material for bonding a substrate and a chip, such as a material for die bonding.

The coefficient of thermal expansion of nickel is relatively close to the coefficient of thermal expansion of semiconductor chips such as Si and SiC. Therefore, when a conductive composition containing nickel is used as a bonding material in a wire bonding structure, it is difficult to apply a stress load to the package when a temperature change occurs, and the bonding reliability against thermal stress can be improved. However, nickel is a material with a high melting point and low meltability as compared with metals such as silver and copper, which are typical conductive materials, so that nickel has sufficient sinterability at low temperatures such as 300 ° C. or lower. In some cases, the desired performance could not be achieved in the target product.

In this regard, according to the conductive composition of the present invention, since nickel particles having a small particle size and a small crystallite size are contained, the nickel particles can be sintered at a low temperature. Further, the density of the nickel layer formed after sintering is high, and the bonding reliability with respect to conductivity and thermal stress is both high.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the scope of the present invention is not limited to such examples.

[Example 1]
(1) Preparation of Nickel Raw Material Solution Nickel acetate tetrahydrate was used as a water-soluble nickel source, and palladium nitrate was used as a second metal element source. 14.95 g of nickel acetate tetrahydrate and 3.53 g of an aqueous palladium nitrate solution having a palladium element concentration of 1.00 g / L (molar ratio of Pd element to Ni element: 5.5 × 10 ^-4 ) were added to 120. It was dissolved in 78 g of pure water to obtain a nickel raw material solution.

(2) Preparation of reducing solution Hydrazine monohydrate and sodium hypophosphite were used as reducing compounds. 12.04 g of hydrazine monohydrate and 25.48 g of sodium hypophosphite were mixed with 50.00 g of pure water and 15.00 g of sodium hydroxide to obtain a reducing solution.

(3) Synthesis of Nickel Particles The nickel raw material solution obtained in the above step (1) was stirred while heating at 80 ° C., and the reducing solution was mixed by batch addition to prepare a reaction solution. The molar ratio of the reducing compound to the nickel element was 8.0, the molar ratio of hydrazine monohydrate to the nickel element was 4.0, and the molar ratio of the amount of sodium hypophosphite to the nickel element was 4.0. ..
The reaction solution was heated from the start of mixing to the end of the reaction so as to maintain a temperature of 70 ° C. or higher and 90 ° C. or lower, and stirred for 1 hour for reaction. Then, decantation was carried out with pure water, and further solvent substitution was carried out with ethanol. Then, it was concentrated by decantation, and the solid content was vacuum dried in this order to obtain a dry powder of the desired nickel particles. The contents of phosphorus and palladium in the nickel particles are as shown in Table 1 below.

[Example 2]
In the reducing solution containing hydrazine monohydrate and sodium hypophosphate, the content of hydrazine monohydrate was changed to 23.14 g and the content of sodium hypophosphate was changed to 0.62 g. Nickel particles were produced in the same manner as in the above. The molar ratio of the reducing compound to the nickel element was 8.0, the molar ratio of hydrazine monohydrate to the nickel element was 7.9, and the molar ratio of sodium hypophosphite to the nickel element was 0.1. The contents of phosphorus and palladium in the nickel particles are as shown in Table 1 below.

[Example 3]
The same as in Example 1 except that the nickel acetate tetrahydrate was changed to 15.37 g of nickel sulfate hexahydrate (molar ratio of Pd element to Ni element: 5.5 × 10 ^-4). Nickel particles were produced. The contents of phosphorus and palladium in the nickel particles are as shown in Table 1 below.

[Example 4]
The amount of nickel acetate tetrahydrate added is 6.35 g, and the amount of palladium nitrate aqueous solution of 1.00 g / L in palladium element concentration is 5.41 g (molar ratio of Pd element to Ni element: 2.0 × 10 ^-3 ). Nickel particles were produced in the same manner as in Example 1 except that the nickel solution was prepared and only 7.66 g of hydrazine monohydrate was used as the reducing compound. The molar ratio of hydrazine monohydrate to the elemental nickel in the reaction solution was 6.0. The contents of phosphorus and palladium in the nickel particles are as shown in Table 1 below.

[Comparative Example 1]
In this comparative example, nickel particles were produced based on the method described in Example 9 of JP-A-2000-313906. This method uses a reaction solution in which a nickel source and a reducing compound are mixed without using a second metal element source.

[Measurement of particle size]
The D50 (nm) of the nickel particles obtained in Examples and Comparative Examples was measured by the above-mentioned measuring methods, respectively. The results are shown in Table 1 below.

[Measurement of crystallite size]
The crystallite size (nm) of the nickel particles obtained in Examples and Comparative Examples is 2θ = 40 derived from the (111) plane of nickel with respect to the diffraction peak obtained by the above-mentioned X-ray diffraction measuring device and measurement conditions. Measurements were made based on the half width of the peaks observed in the range of ~ 50 °. The results are shown in Table 1 below.

[Measurement of phosphorus and palladium contents]
For each content of phosphorus and palladium in the nickel particles of Examples and Comparative Examples, the particles were dried at 105 ° C. for 2 hours, and then an inductively coupled plasma emission spectrophotometer (manufactured by Hitachi High-Tech Science Co., Ltd., model number: PS3520UV-DD). Was measured using. The results are shown in Table 1 below. When the content of phosphorus or palladium was less than 0.01% by mass, it was set as "<0.01" in the table.

[Evaluation of sinterability]
Using the nickel particles obtained in Examples and Comparative Examples, the sinterability was evaluated by the following method.
First, the nickel particles obtained in Examples and Comparative Examples were dispersed in tarpineol using a rotation / revolution mixer (Sinky Co., Ltd., Awatori Rentaro, model: ARE-500) to prepare a slurry. The solid content concentration of the slurry was 30% by mass.
Next, 1.0 g of the obtained slurry was introduced into an atmosphere furnace (KLO-30NL manufactured by Koyo Thermo System Co., Ltd.), and nitrogen flowed at a furnace temperature of 30 ° C. for 30 minutes to replace the atmosphere in the furnace with nitrogen. , The temperature was raised to 300 ° C. at a heating rate of 20 ° C./min in a nitrogen atmosphere, and the slurry was calcined at 300 ° C. for 30 minutes.

The scanning electron microscope images of the nickel particles of Example 1 before and after firing are shown in FIG. The shape of the nickel particles of Example 1 could be confirmed before firing. Further, after firing, a phenomenon in which the particles are bonded to each other to the extent that the interface of each particle cannot be clearly discriminated is observed, and it can be seen that the low-temperature sinterability is very good.

Further, for the nickel particles of each Example and Comparative Example, the BET specific surface area (m ² / g) of the nickel particles before and after firing under the above conditions was measured by the above method, and the BET ratio of the nickel particles before firing was measured. The ratio of the BET specific surface area of the nickel particles after firing to the surface area was calculated. The smaller the ratio of the specific surface area, the smaller the specific surface area due to the bonds between the particles, indicating that the low temperature sinterability is high. The results are shown in Table 1.
It can be seen that the nickel particles of the examples have a small ratio of the BET specific surface area and are excellent in low-temperature sinterability as compared with those of the comparative examples. The smaller the D50 and the crystallite size, the smaller the ratio of the BET specific surface area, indicating that the sinterability is improved.

Claims (7)

The 50% particle size D50 in the number distribution measured by scanning electron microscopy is less than 50 nm.
Nickel particles having a crystallite size of less than 15 nm determined by Scheller's equation from the full width at half maximum of the peak derived from the (111) plane of nickel in the X-ray diffraction measurement. The nickel particle according to claim 1, which contains a phosphorus element and has a phosphorus element content of 0.01% by mass or more and 10.0% by mass or less. The nickel particle according to claim 1 or 2, which contains a metal element nobler than nickel and has a content of the metal element of 0.02% by mass or more and 0.50% by mass or less. A method for producing nickel particles, comprising a step of reducing nickel by mixing a water-soluble nickel source, a metal element source nobler than nickel, and a reducing compound. The production method according to claim 4, wherein a hydrazine-based compound is used as the reducing compound. The production method according to claim 5, further using a phosphorus oxo acid or a salt thereof as the reducing compound. A conductive composition containing the nickel particles according to any one of claims 1 to 3 and a solvent.

Images