JP5063624B2 - Method for producing nickel fine particles - Google Patents

Description

  The present invention relates to nickel fine particles having an average particle diameter of nanometers to several tens of nanometers and a method for producing the same.

  Recently, there has been a demand for downsizing and high integration of electronic components mounted inside electronic devices in accordance with downsizing and high integration of electronic devices. Circuit boards and capacitors in electronic components (for example, multilayer ceramic capacitors formed by alternately laminating and firing dielectric layers (ceramic layers) and internal electrode layers) are also strongly required to be thin and multilayer. .

  When forming such an internal electrode layer of a capacitor or an electric circuit of a substrate, conventionally, a conductive material prepared in a paste or slurry containing an expensive noble metal material such as silver, platinum, or palladium is used. Materials (hereinafter collectively referred to as “conductor paste”) are applied to a predetermined portion with a predetermined film thickness and fired to form the electrode layer, the substrate circuit, and the like. Was. Recently, in place of the noble metal material, a relatively inexpensive and highly reliable conductor paste containing nickel has been widely used. As a nickel powder contained in the conductor paste, the above-mentioned thinning and multilayering are realized. Is preferably a nickel fine particle (nickel nanoparticle) having a nanometer (nm) size (nanosize) particle size (that is, an average particle size or a median diameter of particle size distribution).

  Various techniques have been proposed for producing nickel fine particles. For example, Non-Patent Documents 1 to 3 disclose a method of generating nickel particles by adding hydrazine to nickel chloride and reducing it under basic conditions. In Patent Document 1, a metal salt such as nickel hydroxide is dissolved or dispersed in an organic solvent such as reducing ethylene glycol together with a solid catalyst such as chloroplatinic acid, and a microwave is applied to the solution. A method for producing nickel particles by irradiation is disclosed. For example, Patent Document 2 discloses a method in which nickel hydroxide is produced by reducing nickel hydroxide with hydrogen gas and then crushing it with a jet mill equipped with a high-speed classification rotor to remove coarse particles before reaggregation. ing.

JP 2000-256707 A JP 2003-89806 A

Chou K., et al., "Studies on the chemical synthesis of nanosized nickel powder and its stability", J. Nanopart. Res., 2001, 3, p.127-132 Duan Y., et al., "Structure study of nickel nanoparticles", Mater. Chem. Phys., 2004, 87, p.452-454 Park J. W., et al., "Preparation of fine Ni powders from nickel hydrazine complex", Mater. Chem. Phys., 2006, 97, p.371-378

  However, in the above-described method, for example, in the methods disclosed in Patent Documents 1 and 2, a special apparatus is necessary for producing nickel fine particles. In addition, in the methods disclosed in Non-Patent Documents 1 to 3, hydrazine is added to nickel chloride, and nickel chloride is reduced to form nickel fine particles, typically by mixing a mixed solution of nickel chloride and hydrazine at a high temperature. (For example, in Non-Patent Document 1, the reaction temperature must be 80 ° C. or higher), it is necessary to add other components such as a catalyst and a dispersant to advance the reduction reaction, or the reduction reaction In order to proceed the reaction, it is difficult to adjust the reaction conditions for smoothly proceeding the reaction, for example, by adjusting the liquidity of the mixed solution to be basic (for example, by adding sodium hydroxide). Further, the produced nickel fine particles are easily altered by oxidation or the like, and it is difficult to stably exist for a long time.

  This invention is made | formed in view of this point, The main objective is to provide the method of manufacturing simply the nanosized nickel fine particle which can exist stably over a long period of time. It is another object to provide nickel nanoparticles produced using such a method.

In order to achieve the above object, the method for producing nickel fine particles provided by the present invention provides a nickel hydroxide dispersion in which nickel hydroxide particles having an α-type crystal structure are dispersed in an aqueous solvent, and the above preparation And adding a reducing agent to the dispersion to produce metallic nickel fine particles from nickel hydroxide in the dispersion.
In the method for producing nickel fine particles (powdered nickel fine particles or an aggregate of nickel fine particles) according to the present invention, nickel hydroxide (α-Ni (OH) ₂ ) having an α-type crystal structure as a nickel (Ni) source When nickel hydroxide is reacted with a reducing agent and reduced, fine metallic nickel is produced. The nickel hydroxide is used, for example, in a state prepared by mixing with water to form a dispersion or slurry. When a reducing agent (for example, prepared as an aqueous solution) is added to the nickel hydroxide in this state and mixed, In the mixed liquid, the nickel hydroxide is easily reduced to produce (precipitate) metallic nickel. Therefore, according to this manufacturing method, nickel fine particles can be easily manufactured by reducing α-type nickel hydroxide.

In a preferred embodiment of the method for producing nickel fine particles disclosed herein, metallic nickel fine particles are produced in which the average particle diameter based on TEM observation is in the range of 1 nm to 50 nm.
Here, the average particle diameter based on the TEM observation refers to a particle diameter (equivalent circle diameter) measured from a microscope image by a transmission electron microscope (TEM) using a microscope.

Here, in good preferable aspect of the method for manufacturing the nickel microparticles disclosed, as the reducing agent, use borohydride compound or an aluminum hydride compound. More preferably, sodium borohydride is used.
According to such an embodiment, it is preferable to use a metal hydride as the reducing agent, more preferably a borohydride compound (more preferably sodium borohydride; NaBH ₄ ) or an aluminum hydride compound (eg, lithium aluminum hydride; LiAlH ₄ ) (for example, an aqueous solution of the metal hydride is mixed with the nickel hydroxide). As a result, nickel fine particles (nickel nanoparticles) can be easily produced under normal temperature and pressure without exposing the mixed liquid of the metal hydride and the nickel hydroxide to high temperature conditions or high pressure conditions. .

In a further preferred aspect of the nickel fine particle production method disclosed herein, the reducing agent is added so as to be in a concentration range of 0.1M to 3.0M.
According to this aspect, the concentration of the reducing agent in the mixed liquid (dispersion) of the reducing agent and the nickel hydroxide after the addition of the reducing agent is within the above range (preferably 1.5M to 3.0M, More preferably, the nickel nanoparticles can be produced more efficiently by adding to the nickel hydroxide dispersion so as to be 2.0 M to 3.0 M).

In another preferable aspect of the method for producing nickel fine particles disclosed herein, nickel nitrate (Ni (NO ₃ ) ₂ ) or nickel sulfate (NiSO ₄ ) and alkali metal water are used as the nickel hydroxide having the α-type crystal structure. Nickel hydroxide produced by preparing an aqueous solution mixed with an oxide is used.
According to this aspect, the nickel hydroxide having the α-type crystal structure is produced by reacting nickel nitrate or nickel sulfate with an alkali metal hydroxide (typically sodium hydroxide), thereby producing the nickel hydroxide. The liquidity of the mixed liquid at the time of production is already basic. Therefore, in order to promote the reduction reaction from nickel hydroxide to metallic nickel, it is not necessary to make the mixed liquid basic again. This makes it possible to efficiently generate nickel fine particles without requiring an extra step or reagent for making it basic again.

The nickel hydroxide having the α-type crystal structure prepared as described above preferably has an average particle diameter in the range of 0.5 nm to 30 nm.
According to such an embodiment, nickel fine particles having an average particle diameter in the above range can be suitably generated by using nickel hydroxide (fine particles) having such an average particle diameter.

  Moreover, this invention provides the nickel microparticles (microparticle group, ie, powder) manufactured by the manufacturing method disclosed here as another aspect. Such nickel fine particles are separated by, for example, filtering the above mixed liquid containing the nickel fine particles, and the filtrate (residue) can be washed and dried to obtain nickel powder.

It is an X-ray-diffraction spectrum of the alpha nickel hydroxide produced | generated by the method which concerns on an Example (Example 1). 2 is an X-ray diffraction spectrum of β-type nickel hydroxide produced by a method according to an example (Example 2). It is a TEM photograph of nickel fine particles produced | generated by the method which concerns on an Example (Example 5). It is a TEM photograph of nickel fine particles produced | generated by the method which concerns on an Example (Example 7). It is a X-ray-diffraction spectrum which shows the time change of the deposit containing the nickel fine particle obtained by the method which concerns on an Example (Example 9). It is an X-ray-diffraction spectrum which shows the time change of the deposit containing the nickel fine particle obtained by the method which concerns on an Example (Example 11).

  Hereinafter, preferred embodiments of the present invention will be described. In addition, matters other than matters specifically mentioned in the present specification (for example, a method for producing α-type nickel hydroxide used as a raw material for nickel fine particles) and matters necessary for the implementation of the present invention (for example, produced nickel) The method of taking out the fine particles as a powder) can be grasped as a design matter of those skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  The method for producing nickel fine particles according to the present invention comprises an aggregate of nickel fine particles (nickel nanoparticles) having a nano-sized average particle size (typically 0.5 nm to 200 nm, for example, an average particle size of 1 nm to 100 nm) ( That is, a method for producing powdered nickel nanoparticles), which is a metal hydride (typical) as a reducing agent for a nickel hydroxide dispersion obtained by dispersing α-type nickel hydroxide in an aqueous solvent. Is characterized by adding a borohydride compound or an aluminum hydride compound). Therefore, as long as the above object can be achieved, the content and composition of other components (subcomponents) can be arbitrarily determined in light of various standards.

In the production method according to the present invention, nickel hydroxide (Ni (OH) ₂ ) powder can be preferably used as the nickel (Ni) source. The nickel hydroxide powder is composed of nickel hydroxide (α-Ni (OH) ₂ ) particles having an α-type crystal structure (or 50% by mass or more of the total is α-Ni (OH) ₂ . Powder) is preferable, but the nickel hydroxide particles having the α-type crystal structure may be the main component, and the nickel hydroxide particles having another crystal structure (typically β-type crystal structure) may be included as an accessory component. May be. The average particle diameter of the nickel hydroxide particles constituting such nickel hydroxide powder is preferably 0.1 nm to 50 nm (more preferably 0.5 nm to 30 nm). Such nickel hydroxide powder is used after being prepared in the form of a dispersion liquid or slurry dispersed in an aqueous solvent.

Regarding the dispersion (slurry) of nickel hydroxide particles (powder) having the α-type crystal structure, a commercially available nickel hydroxide (α-type nickel hydroxide) powder having an α-type crystal structure is used, and an aqueous solvent is added thereto. Can be obtained. Alternatively, for example, a dispersion (slurry) containing α-type nickel hydroxide particles having an average particle diameter in the above range as a main component can be easily prepared by the following method.
First, an alkali metal (typically sodium) hydroxide is added to an aqueous solution of nickel nitrate (Ni (NO ₃ ) ₂ ) or nickel sulfate (NiSO ₄ ) and stirred. Ni (NO ₃ ) ₂ or NiSO ₄ is preferably a salt having a high solubility in an aqueous solvent, and more preferably nickel nitrate. As the alkali metal hydroxide, sodium hydroxide (NaOH) can be preferably used as described above. An aqueous solution is prepared by dissolving the hydroxide in water (solvent), and Ni (NO ₃ ) ₂ or an aqueous solution of NiSO ₄ . The concentration of the hydroxide aqueous solution is a concentration at which hydroxide ions in the aqueous solution can be present in an amount more than can react with the nickel ions in the Ni (NO ₃ ) ₂ or NiSO ₄ aqueous solution without excess or deficiency. It is preferable that When the hydroxide aqueous solution is added, the hydroxide aqueous solution is dropped into the Ni (NO ₃ ) ₂ or NiSO ₄ aqueous solution at a rate of 1 mL for 1 to 5 seconds (eg, 1 mL for 4 seconds ± 1 second). (Addition) is preferable. Mixing of the above-mentioned Ni (NO ₃ ) ₂ or NiSO ₄ and the above-mentioned hydroxide can be carried out at room temperature, and it is not necessary to perform heating in order to advance the reaction between the two. At this time, the mixed solution is preferably added dropwise with stirring. Preferably, stirring is continued for a while (for example, about 3 to 5 minutes) even after the addition of the hydroxide.
After completion of the stirring, the mixed solution is centrifuged at a rotational speed of, for example, 3000 rpm to 8000 rpm (for example, 6000 rpm ± 1000 rpm) for 5 minutes to 10 minutes (for example, 7 minutes ± 1 minute). Thereby, nickel hydroxide can be precipitated.

Discard the supernatant after centrifugation, add an organic solvent (eg, acetone) to the remaining jelly-like precipitate (nickel hydroxide), and apply this to an ultrasonic bath for about 5 minutes, for example. Disperse in the organic solvent. Thereafter, centrifugation is performed again. Such separation conditions may be the same as described above, and are appropriately adjusted. After such centrifugation, the supernatant is discarded again, pure water is added to the remaining (jelly-like) precipitate, and the precipitate is dispersed in pure water in an ultrasonic bath in the same manner as described above. The amount of such pure water is appropriately adjusted according to the concentration of the desired dispersion (slurry). Finally, it is preferable to leave it for 10 minutes to 60 minutes (for example, 30 minutes ± 10 minutes) to completely volatilize the organic solvent that can remain in the dispersion.
As described above, a dispersion of α-type nickel hydroxide can be prepared. Depending on the purpose, another component (for example, a stabilizer or the like) may be appropriately added to such a dispersion as long as it does not adversely affect the reduction reaction with a reducing agent described later.

A metal hydride can be used as a reducing agent added to the nickel hydroxide dispersion prepared above. Preferred are borohydride compounds or aluminum hydride compounds, such as sodium borohydride (NaBH ₄ ), diisobutylaluminum hydride (referred to as DIBAH or DIBAL-H), or lithium aluminum hydride (LiAlH ₄ ). Can be mentioned. And particularly preferably NaBH _4. By using such a reducing agent, the α-type nickel hydroxide can be preferably reduced to nano-sized (for example, a particle diameter of 1 nm to 50 nm) metallic nickel (fine particles).

The metal hydride is preferably dissolved in an aqueous solvent and added to the nickel hydroxide dispersion as an aqueous solution. At this time, the metal hydride has a concentration of the metal hydride in the mixed liquid after addition of 1.0 M to 3.0 M (preferably 2.0 M to 3.0 M, for example, 2.2 M ± 0.2 M). It is prepared and added as an aqueous solution that falls within the range. When such a concentration is lower than 1.0M, it takes a long time to produce metallic nickel fine particles, and the produced metallic nickel fine particles are unstable and may be oxidized again if left standing for a while. Moreover, when the said density | concentration is significantly higher than 3.0M, since another side reaction may occur besides the reductive reaction in which metallic nickel fine particles are produced, there is a possibility that the yield of metallic nickel fine particles may be reduced. In the above concentration range, when the concentration of the metal hydride is high, a precipitate containing metal nickel fine particles described later is generated more quickly and stably, and the generated precipitate is more stable over a long period of time. Therefore, it can be taken out as a powder.
In order to prevent α-type nickel hydroxide in the nickel hydroxide dispersion from undergoing a phase change (typically changing to β-type nickel hydroxide), it is preferable that the aqueous solution of the metal hydride and the nickel hydroxide dispersion be used. The liquid is mixed at normal pressure and room temperature. At this time, an aqueous solution of metal hydride is preferably added dropwise to the nickel hydroxide dispersion at an appropriate dropping rate and mixed while stirring.
By such mixing, the nickel hydroxide is reduced by the reducing agent to produce metallic nickel. Such metallic nickel is obtained as a precipitate generated as fine particles in the mixed liquid. In order to completely precipitate the metal nickel fine particles, the mixed liquid is allowed to stand after the above mixing for 1 hour to 5 hours (preferably 2 hours or more, for example, 2 hours to 3 hours), and the precipitate is put into a reaction vessel. It is preferable to sink (deposit) on the bottom of the substrate.

As described above, by reducing the α-type nickel hydroxide with the metal hydride, the nano-sized average particle diameter can be reduced only by the reduction step of adding the aqueous solution of the metal hydride to the nickel hydroxide dispersion. The metal nickel fine particle which has can be produced | generated. Further, such a reduction step may be carried out at normal pressure and room temperature, and the metal nickel fine particles can be easily precipitated simply by mixing the α-type nickel hydroxide dispersion and the metal hydride aqueous solution.
For example, when nickel chloride is reduced to metallic nickel, it is necessary to add sodium hydroxide or the like to a solution containing nickel chloride (typically an aqueous solution) to make the liquid basic. On the other hand, when α-type nickel hydroxide is produced by the above-described method, the dispersion containing the nickel hydroxide is not only basic but the aqueous solution of the metal hydride exhibits strong basicity. . Thereby, in the reduction process according to the present invention, it is not necessary to add a basic substance again in order to advance the reduction reaction, and it is possible to preferably prevent the process from becoming complicated and the cost from increasing.

  As described above, the metal nickel fine particles generated as a precipitate in the mixed liquid can be taken out in a powder state by using a method similar to the conventional method for taking out the precipitate. That is, for example, the mixed liquid is filtered to separate the precipitate as a filtrate from the filtrate, and the residue is washed with pure water to remove unreacted metal hydride and other salts, and then the remaining residue. To dry. Through such steps, fine powdered nickel metal particles can be obtained.

  The metal nickel fine particles produced in this manner are obtained as nickel nanoparticles having a nanosize particle diameter in the range of 1 nm to 50 nm as a particle diameter (average particle diameter) measured from a microscopic image based on TEM observation. Can do.

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the following examples.

<Example 1: Preparation of α-type nickel hydroxide dispersion>
An α-type nickel hydroxide dispersion (α-Ni (OH) ₂ ) was prepared as follows.
First, pure water was added to commercially available (Chem-Supply Pty. Ltd.) nickel nitrate (Ni (NO ₃ ) ₂ ) to prepare 50 mL of 0.2 M Ni (NO ₃ ) ₂ aqueous solution. Next, pure water was added to commercially available sodium hydroxide (NaOH) (manufactured by Asia Pacific Chemicals Ltd.) to prepare 50 mL of 0.4 M NaOH aqueous solution.
Next, the Ni (NO ₃ ) ₂ aqueous solution was stirred at a rotational speed of 350 rpm at room temperature, and the NaOH aqueous solution was dropped (added) thereto at a dropping rate of about 1 mL over 4 seconds. Thereafter, stirring was continued for about 4 minutes.
Next, an appropriate amount of acetone was added thereto, followed by centrifugation at a rotational speed of 6000 rpm for 7 minutes. The suspended matter was discarded, and acetone was further added to the jelly-like precipitate and dispersed again. Next, this was placed in an ultrasonic bath for about 5 minutes. Thereafter, it was centrifuged again at a rotational speed of 6000 rpm for 7 minutes.
Thereafter, the suspended matter was discarded and pure water was added to the jelly-like precipitate and dispersed. Next, it was placed in an ultrasonic bath for about 5 minutes. Finally, pure water was added to dilute to 100 mL, and left at room temperature for about 30 minutes to volatilize the remaining acetone as an excess.
A dispersion (slurry) of α-Ni (OH) ₂ was prepared as described above.

<Example 2: Preparation of β-type nickel hydroxide dispersion>
Next, a part of the α-Ni (OH) ₂ dispersion obtained in Example 1 above is taken out and refluxed at 80 ° C. for 2 hours, so that β-type nickel hydroxide (β-Ni ( OH) ₂ ) A dispersion (slurry) was prepared.

<Example 3: XRD measurement of each prepared nickel hydroxide dispersion>
A part of the α-Ni (OH) ₂ dispersion obtained in Example 1 was used for XRD measurement, and XRD measurement was performed. The measurement results are shown in FIG. Further, a part of the β-Ni (OH) ₂ dispersion obtained in Example 2 was used for XRD measurement, and XRD measurement was performed in the same manner as the α-Ni (OH) ₂ dispersion. The measurement results are shown in FIG. As shown in FIGS. 1 and ₂ , a characteristic diffraction peak was observed for each of α-Ni (OH) ₂ and β-Ni (OH) ₂ .

<Example 4: Preparation of reducing agent>
Next, sodium borohydride (NaBH ₄ ) was employed as a reducing agent, and pure water was added to such NaBH ₄ powder (manufactured by Asia Pacific Chemicals Ltd.) to prepare an aqueous NaBH ₄ solution. Two types (1) and (2) were prepared as such aqueous solutions. The two types of NaBH ₄ aqueous solutions (1) and (2) have a NaBH ₄ concentration of 0.1M and 2.2M, respectively, in the mixed liquid obtained by adding the aqueous solution to the nickel hydroxide dispersion. It was prepared as follows.

<Example 5: Reaction of α-type nickel hydroxide dispersion and NaBH ₄ aqueous solution (1)>
Next, the NaBH ₄ aqueous solution (1) prepared in Example 4 above is added to and mixed with the α-Ni (OH) ₂ dispersion prepared in Example 1 above, so that the concentration of NaBH ₄ is 1. A liquid mixture was obtained that would result in 0M. This mixed liquid produced a brown to black precipitate after 20 to 30 minutes. And such a sediment completely settled to the bottom of the container in about 3 hours. This precipitate has magnetism, and formation of metallic nickel was confirmed. The precipitate in the mixed liquid turned greenish gray after about 215 hours. This was presumably because part of the precipitate was oxidized to produce nickel hydroxide again. However, no subsequent changes were observed in such precipitates.

<Example 6: TEM observation after reaction between α-type nickel hydroxide dispersion and NaBH ₄ aqueous solution (1)>
Next, TEM observation of the precipitate was performed. First, the α-Ni (OH) ₂ dispersion and the NaBH ₄ aqueous solution (1) are mixed, and the obtained mixed liquid is put into an approximately 1 g centrifuge tube, and 10 mL of water and 10 mL of acetone are poured therein. Shake well. The centrifuge tube was centrifuged at 6000 rpm for 7 minutes. After centrifugation, the upper layer portion was discarded, and 10 mL of acetone was newly poured and transferred to a glass bottle. The glass bottle was then placed in an ultrasonic bath for 10 minutes. A few drops of the slurry-like mixed liquid sufficiently dispersed in this way was dropped on a carbon grid and dried under an IR lamp for about 15 minutes to prepare a sample for TEM observation.
The TEM observation result of the obtained sample is shown in FIG. As shown in FIG. 3, it was confirmed that a plurality of particles were scattered in the sample, and these particles were metallic nickel particles. The average particle size of such particles was found to be about 5 nm from this TEM image.

<Example 7: Reaction of α-type nickel hydroxide dispersion and NaBH ₄ aqueous solution (2)>
Next, in the same manner as in Example 5, the aqueous NaBH ₄ solution (2) prepared in Example 4 above was added to and mixed with the α-Ni (OH) ₂ dispersion prepared in Example 1 above. A mixed liquid having a NaBH ₄ concentration of 2.2 M was obtained. This mixed liquid produced a black precipitate immediately after mixing. And this deposit settled to the bottom of the container completely in 2-3 hours. Similar to the case of Example 5 above, this precipitate had magnetism, and formation of metallic nickel was confirmed. In addition, it was suggested that the deposit in this liquid mixture has magnetism even after 100 days, and can be taken out in a usable state as a powder (solid) without oxidizing the precipitate.

<Example 8: TEM observation after reaction between α-type nickel hydroxide dispersion and NaBH ₄ aqueous solution (2)>
Next, TEM observation of the precipitate obtained in Example 7 was performed using the TEM observation sample prepared in the same manner as in Example 6. The result is shown in FIG. As shown in FIG. 4, a plurality of particles were scattered in the sample, and it was confirmed that these particles were metallic nickel particles. The average particle size of such particles was found to be about 30 nm from this TEM image.

<Example 9: Reaction of β-type nickel hydroxide dispersion with NaBH ₄ aqueous solution (1)>
Next, in the same manner as in Example 5 above, the aqueous NaBH ₄ solution (1) prepared in Example 4 above was added to and mixed with the β-Ni (OH) ₂ dispersion prepared in Example 2 above. A mixed liquid having a NaBH ₄ concentration of 1.0 M was obtained. This mixed liquid produced an off-white precipitate after 30 minutes. It was confirmed that bubbles were generated after 5 hours and the reduction reaction was continued. By 21 hours, a green lump started to appear again on the surface layer of the precipitate, and by 45 hours, the precipitate turned almost completely green.

<Example 10: XRD measurement after reaction between β-type nickel hydroxide dispersion and NaBH ₄ aqueous solution (1)>
Here, with respect to the mixed liquid obtained in Example 9 above, changes in the state after 5 hours after mixing (5 hrs) and after 215 hours after mixing (215 hrs) were evaluated by XRD measurement. For the β-Ni (OH) ₂ dispersion before mixing, XRD measurement was performed for comparison (0 hrs). In such XRD measurement, the mixed liquid and β-Ni (OH) ₂ dispersion liquid after the elapse of each time are dropped into a predetermined container, and left to stand at room temperature for 20 to 30 minutes to dry, thereby XRD measurement. Samples were prepared. And XRD measurement of each sample was implemented. The result is shown in FIG. As a result, the product in the liquid mixture after each time (precipitate) In, beta-Ni (OH) ₂ has appeared a peak at the same position as, beta-Ni (OH) different products from the ₂ Was not confirmed.

<Example 11: Reaction of β-type nickel hydroxide dispersion and NaBH ₄ aqueous solution (2)>
Next, in the same manner as in Example 9, the aqueous solution of NaBH ₄ (2) prepared in Example 4 above was added to and mixed with the β-Ni (OH) ₂ dispersion prepared in Example 2 above. A mixed liquid having a NaBH ₄ concentration of 2.2 M was obtained. The mixed liquid produced a grayish precipitate immediately after mixing and turned black during 30 minutes. By the end of 5 hours, the settlement of the black precipitate was completely completed. By 21 hours, a green lump started to appear in the surface layer of the precipitate, and by 215 hours, the precipitate turned almost completely green.

<Example 12: XRD measurement after reaction between β-type nickel hydroxide dispersion and NaBH ₄ aqueous solution (2)>
Here, with respect to the mixed liquid obtained in Example 11 above, the change in the state after 5 hours after mixing (5 hrs) and after 215 hours after mixing (215 hrs) was changed in the same manner as in Example 10 above. Evaluation was made by XRD measurement. For the β-Ni (OH) ₂ dispersion before mixing, XRD measurement was performed for comparison (0 hrs). The result is shown in FIG. As a result, as in Example 10 above, in the product (precipitate) in the mixed liquid after the passage of each time (5 hrs and 215 hrs), a peak appears at the same position as β-Ni (OH) ₂ . No product different from β-Ni (OH) ₂ was observed.

As described above, according to this example, by adding an aqueous sodium borohydride solution as a reducing agent to a nickel hydroxide dispersion having an α-type crystal structure as a nickel source, However, the reduction reaction proceeds favorably, and the metallic nickel fine particles having nano-sized particle diameters that can exist stably over a long period of time can be easily obtained only through the reduction process.

Claims (6)

A method for producing nickel fine particles, comprising:
A nickel hydroxide dispersion in which α-type crystal structure nickel hydroxide particles are dispersed in an aqueous solvent, wherein 50% by mass or more of the total nickel hydroxide particles are α-type crystal structure nickel hydroxide particles. Preparing a nickel dispersion , and adding a borohydride compound and / or an aluminum hydride compound as a reducing agent to the prepared dispersion to produce metallic nickel fine particles from nickel hydroxide in the dispersion ,
Including the method.   2. The method according to claim 1, wherein metal nickel fine particles having an average particle diameter based on TEM observation are in the range of 1 nm to 50 nm. The method according to claim 1 or 2 , wherein sodium borohydride is used as the reducing agent. The method according to claim 1, wherein the reducing agent is added so as to be in a concentration range of 0.1M to 3.0M. As the nickel hydroxide of the α-type crystal structure, nickel hydroxide produced by preparing an aqueous solution of a mixture of nickel nitrate or nickel sulfate and an alkali metal hydroxide, according to any one of claims 1-4 Manufacturing method. The production method according to claim 5 , wherein the nickel hydroxide having the α-type crystal structure generated has an average particle diameter in a range of 0.5 nm to 30 nm.