TWI483796B - Nickel particles coated with nickel hydroxide and a method for producing the same - Google Patents

Description

Nickel particles coated with nickel hydroxide and method of producing the same

The present invention relates to a nickel particle whose surface is coated with nickel hydroxide and a method for producing the same.

A technique for increasing the dispersibility of nickel particles by covering the surface of nickel particles with nickel hydroxide is well known. For example, JP-A-2003-129103 discloses a method of heating a nickel powder in a hydrogen gas stream, reducing an oxide or hydroxide on the surface of the nickel particle, and immersing the nickel powder in water to use air. Foaming is performed to form nickel oxide or nickel hydroxide on the surface of the nickel powder.

Japanese Patent Laid-Open Publication No. 2004-330247 discloses a nickel powder containing Ni(OH) ₂ and NiO, and the composition of the surface is expressed in mol %, Ni: 5 to 20%, Ni ( OH) ₂ : 25 to 75%, NiO: 15 to 65%. The nickel powder can be obtained by reducing a nickel ion by dropwise adding an aqueous solution of a nickel salt to an aqueous solution of a reducing agent by a liquid phase reduction method.

Since the nickel powder described in each of the above documents is used in a state in which the surface thereof is coated with nickel oxide or hydroxide, the electrode film containing the nickel powder has a high electric resistance value and is fired in the metallic nickel powder. Defects that are difficult to fire in the temperature range.

Accordingly, the present invention provides a nickel hydroxide-coated nickel particle which can eliminate various disadvantages of the prior art described above and a method for producing the same.

The present invention provides a nickel particle coated with nickel hydroxide, characterized in that the surface of the surface is coated with nickel hydroxide bonded by a bonding force which can be removed by an external force, and the average particle diameter of the primary particles is 5~500nm.

Further, the present invention provides a method for producing nickel particles coated with nickel hydroxide, which is characterized in that it is suspended in a polyol, as a preferred method for producing the nickel particles coated with nickel hydroxide. When the nickel hydroxide particles are heated and reduced to nickel, the nickel hydroxide particles are not completely reduced, and the reaction is terminated in the middle of the reduction to form a plurality of minute nickel particles in the nickel hydroxide particles, and then the nickel hydroxide is formed. The particles are crushed to obtain a plurality of nickel particles having a thin layer of nickel hydroxide on the surface.

Hereinafter, the present invention will be described based on preferred embodiments thereof. The nickel particles coated with nickel hydroxide of the present invention are obtained by coating a surface of a core particle formed of metallic nickel with a thin layer of nickel hydroxide. The thin layer of nickel hydroxide may completely cover the entire surface of the nickel core particles, or may be partially covered in such a manner that a part of the surface of the nickel core particles is exposed.

The thin layer of nickel hydroxide contains hydroxide, its hydrate or both. By providing a thin layer of nickel hydroxide on the surface of the nickel core particles, the thin layer functions as a protective agent, and it is possible to effectively prevent particles from aggregating with each other. This advantageous effect is that when the particle diameter of the nickel particles coated with nickel hydroxide is extremely small, for example, the average particle diameter of the primary particles is preferably from 5 to 500 nm, more preferably from 5 to 300 nm. In addition, in the case where the nickel film coated with nickel hydroxide is subjected to reduction baking to form an electrode film, the nickel hydroxide layer functions as a sintering aid, so that low-temperature sinterability is improved. The average particle diameter of the primary particles of the nickel particles coated with nickel hydroxide can be measured by TEM (transmission electron microscope) observation of nickel particles coated with nickel hydroxide.

The thin layer of nickel hydroxide preferably has a thickness sufficient to sufficiently exhibit the above advantages. Specifically, the thickness of the thin layer of nickel hydroxide is also dependent on the particle diameter of the nickel core particles, and the thickness thereof is preferably from 1 to 50 nm, particularly preferably from 1 to 10 nm. The thickness of the nickel hydroxide thin layer can be measured, for example, by transmission electron microscopy (TEM) observation of nickel particles coated with nickel hydroxide.

One of the characteristics of the nickel particles coated with nickel hydroxide is that the nickel hydroxide thin layer coats the surface of the nickel core particles with a relatively low bonding force which can be removed from the surface of the nickel core particles by an external force. In contrast, the nickel powder described in the above-mentioned Japanese Patent Laid-Open Publication No. 2003-129103, and the Japanese Patent Publication No. 2004-330247, the nickel hydroxide or nickel oxide is chemically used. The method is firmly bonded to the surface of the metallic nickel, so that it is difficult to remove it from the surface of the metallic nickel by an external force. The above-mentioned external force refers to a mechanical force applied when agglomerated particles are crushed or pulverized using a media mill such as a bead mill or a ball mill.

The fact that the thin layer of nickel hydroxide coats the surface of the nickel core particles with a low bonding force has the following advantages. In other words, when the nickel particles coated with nickel hydroxide are stored, the nickel hydroxide-coated nickel particles can be inhibited from agglomerating by the action of the thin layer of nickel hydroxide, thereby maintaining high dispersibility. Therefore, it is economical to perform surface modification treatment without using a polymer dispersant or the like.

As other advantages, the following advantages can be cited. In other words, when nickel particles coated with nickel hydroxide are used, an external force can be applied to the nickel particles coated with nickel hydroxide by a media mill such as a bead mill or a ball mill before use, and the nickel hydroxide coating can be easily removed. A thin layer that exposes the metallic nickel surface of the nickel core particles. When an ink or a paste containing nickel core particles obtained in this manner is used to form, for example, an electrode film, the film becomes uniform due to high dispersibility, and metal nickel can be surely ensured to contact each other, thereby The increase in resistance of the electrode film can be suppressed. Further, it is also possible to suppress an increase in the sintering temperature when the electrode film is formed by baking in a reducing atmosphere. In particular, as described above, since the nickel hydroxide layer itself functions as a sintering aid, the electrode film is formed by reduction calcination in a state in which nickel particles coated with nickel hydroxide are directly removed without removing the nickel hydroxide. It is also possible to suppress an increase in the sintering temperature or an increase in the resistance.

As an example of the bonding force of the nickel hydroxide thin layer, when the nickel hydroxide thin layer is substantially completely removed by the following conditions, it is considered that the nickel hydroxide thin layer coats the surface of the nickel core particle with a low bonding force. Using zirconia beads of Φ = 0.1 mm, 4.2 parts by weight of zirconia beads were added to 20% by weight of the slurry for 15 minutes.

Since the thin layer of nickel hydroxide is very thin, the particle diameter of the nickel core particles after removing the nickel hydroxide thin layer from the nickel particles coated with nickel hydroxide is not significantly different from the particle diameter of the nickel particles coated with nickel hydroxide. . That is, the particle diameter of the nickel core particles is set to be smaller than the range of the particle diameter of the nickel particles coated with nickel hydroxide, and is substantially the same as the range described above with respect to the particle diameter of the nickel particles coated with nickel hydroxide. .

In the present invention, the shape of the nickel particles coated with nickel hydroxide is not particularly limited, and various shapes can be employed depending on the method of production. The shape of the nickel particles coated with nickel hydroxide is generally substantially spherical. As described above, since the nickel hydroxide thin layer is very thin, the shape of the nickel particles coated with nickel hydroxide reflects the shape of the nickel core particles as the core. Therefore, the shape of the nickel core particles is also generally substantially spherical.

From the viewpoint of preventing aggregation of particles, the nickel particles coated with nickel hydroxide are preferably stored in a state of being dispersed in a slurry in water. The concentration of the nickel particles coated with nickel hydroxide in the slurry is preferably about 1 to 80% by weight from the viewpoint of workability or prevention of aggregation. In the slurry state, nickel particles coated with nickel hydroxide are less likely to be aggregated. However, it is also possible to further suppress aggregation by adding a dispersant or the like to the slurry.

Hereinafter, a preferred production method of the nickel hydroxide-coated nickel particles of the present invention will be described. The manufacturing method is roughly classified into: (a) a step of preparing nickel hydroxide particles; and (b) a reduction step of the prepared nickel hydroxide particles. Hereinafter, each step will be described.

In the step (a) of preparing nickel hydroxide particles, nickel hydroxide particles prepared using a nickel source may be used, or commercially available nickel hydroxide particles may be directly used. In any case, from the viewpoint of obtaining nickel particles uniformly coated with nickel hydroxide, the particle diameter of the nickel hydroxide particles is preferably from 1 to 30 μm, particularly preferably from 1 to 20 μm.

When a nickel source is used to prepare nickel hydroxide, for example, the following method can be employed. A water-soluble compound of nickel such as nickel acetate, nickel sulfate, nickel chloride, nickel bromide, nickel nitrate or the like is used as a nickel source. The compounds are dissolved in water to prepare an aqueous solution.

The concentration of nickel ions in the aqueous solution is not particularly limited, and the solubility of the above water-soluble nickel compound is the upper limit of the nickel ion concentration. In the aqueous solution, a dispersing agent such as polyvinylpyrrolidone or polyvinyl alcohol may be added as needed to improve the dispersibility of nickel hydroxide. A strong base such as potassium hydroxide or sodium hydroxide is added to the aqueous solution prepared as described above to form nickel hydroxide. If nickel hydroxide is formed at a low temperature (for example, greater than 0 ° C and 60 ° C or less), uniform nickel hydroxide is formed. On the other hand, when nickel hydroxide is formed at a high temperature (for example, more than 60 ° C and 100 ° C or less), nickel hydroxide having high crystallinity is formed.

In the reduction step of (b) nickel hydroxide particles, nickel hydroxide or commercially available nickel hydroxide produced as described above is dispersed in a polyol to form a slurry, and the slurry is used, and the slurry is used. The reduction method well known in the art, the polyol method, reduces nickel hydroxide. For the concentration of nickel hydroxide in the slurry, the concentration of nickel hydroxide can be smoothly reduced, and the concentration thereof is preferably from 10 to 200 g/l, particularly preferably from 20 to 100 g/l.

As the polyhydric alcohol, for example, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, dipropylene glycol, 1,2-butanediol, and 1,3-butyl can be used. Glycol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, polyethylene glycol, and the like. These polyols may be used singly or in combination of two or more. Among these polyols, ethylene glycol has a low boiling point and is liquid at normal temperature, and is excellent in handleability. The polyols function as a reducing agent for the nickel salt and also function as a solvent.

When the amount of use of the polyol is considered in view of the amount of the reducing agent, it can be appropriately adjusted depending on the amount of nickel in the reaction liquid, and thus it is not necessary to provide a particular limitation. On the other hand, in the case where the function of the solvent is to be exerted, since the properties of the reaction liquid change depending on the concentration of the polyol in the reaction liquid, there is a certain fixed concentration range. From this point of view, the concentration of the polyol in the reaction liquid is preferably in the range of 50 to 99.8% by weight.

The slurry of nickel hydroxide preferably contains a dispersing agent. As the dispersing agent, for example, a water-soluble polymer compound can be used. Examples of the water-soluble polymer compound include polyvinylpyrrolidone, polyacrylamide, and poly(2-methyl-2-). A nitrogen-containing organic compound such as oxazoline or the like, and polyvinyl alcohol. These dispersing agents may be used singly or in combination of two or more. Among these, in particular, the effect of polyvinylpyrrolidone as a dispersing agent is remarkable, and the particle size distribution of the nickel core particles produced by the reduction can be made sharp, which is preferable. The molecular weight of the polymer compound can be appropriately adjusted depending on the degree of water solubility or the dispersibility. The amount of the dispersing agent in the slurry of nickel hydroxide is preferably from 0.01 to 30 parts by weight based on 100 parts by weight of the nickel. By setting it within this range, the viscosity of the nickel hydroxide slurry is not excessively improved, and the dispersion effect can fully be exhibited.

A noble metal catalyst may also be contained in the slurry of nickel hydroxide. Thereby, fine nuclear particles of a noble metal are generated in an initial stage of reduction, and nickel is smoothly reduced by using the core particles as a starting point. 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 salt of the noble metal 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, palladium chloride chloride or the like can be used. In the case of using silver, for example, silver nitrate, silver lactate, silver oxide, silver sulfate, silver cyclohexanoate, silver acetate or the like can be used. In the case of using platinum, for example, chloroplatinic acid, potassium chloroplatinate, sodium chloroplatinate or the like can be used. In the case of using gold, for example, chloroauric acid, sodium chloroaurate or the like can be used. Among these, palladium nitrate, palladium acetate, silver nitrate, and silver acetate are inexpensive and economical, so that they can be preferably used. The noble metal catalyst may be added 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 slurry of nickel hydroxide is preferably 0.1 to 5 parts by weight, particularly preferably 0.5 to 1 part by weight, per 100 parts by weight of the precious metal of nickel.

Amino acid may also be contained in the slurry of nickel hydroxide. The formed nickel core particles can be further atomized by containing an amino acid. As the amino acid, for example, alanine, aspartame, aspartic acid, sitamine, glutamic acid, histidine, arginine, leucine, isoleucine, or amine can be used. Acid, cystine, methionine, phenylalanine, serine, valine and the like. These amino acids may be used singly or in combination of two or more. The amount of the amino acid in the slurry of nickel hydroxide is preferably from 1 to 50 parts by weight, particularly preferably from 20 to 40 parts by weight, per 100 parts by weight of the amino acid of the nickel. The amino acid may be either D or L.

An amine-based organic compound may also be contained in the slurry of nickel hydroxide. The amine-based organic compound functions as a reduction reaction controlling agent, and in addition to the effect of increasing the reduction rate, it also has a dispersing effect of the noble metal ultrafine particles formed at the initial stage of the reaction, and contributes to the refinement of the nickel core particles to be refined and granulated. Homogenization of the path. As the amine-based organic compound, a water-soluble polymer compound having an amine group or an imide group in the main chain or the side chain can be suitably used. Examples of such a water-soluble polymer compound include polyvinylamine, polyallylamine, polydiallylamine, and polyethyleneimine. Among these, polyethyleneimine or polyallylamine is preferred. The amount of the amine-based organic compound in the slurry of nickel hydroxide is preferably 20 g/l or less.

The slurry containing the above components is heated while stirring, and reduction of nickel hydroxide is performed. The heating temperature can be appropriately set depending on the degree of reduction of nickel hydroxide. Although depending on the type of polyol to be used, nickel hydroxide can be smoothly reduced by heating at atmospheric pressure and usually at 150 to 210 °C.

One of the features of the present production method is that the nickel hydroxide is not completely reduced, but the reaction is terminated in the middle of the reduction. Since the nickel hydroxide has a layer structure, when nickel hydroxide is reduced in the state of the particles, the polyols infiltrate into the layer structure of the nickel hydroxide to cause reduction of the entire particles. That is, not a reduction occurs from the surface of the nickel hydroxide particles toward the center, but a plurality of nickel nuclei are formed in the particles, and nickel core particles are generated from the core. Further, in the present production method, it is important to terminate the reduction reaction when a plurality of nickel core particles having a target particle diameter are formed. For the heating time, it is usually preferred to heat for 1 to 20 hours, particularly preferably 3 to 16 hours, under the condition that the heating temperature is within the above range. Fig. 1(a) shows a state in which the reduction reaction is terminated halfway through the mode. As shown in FIG. 1(a), in one nickel hydroxide particle 10, a plurality of nickel core particles 12 are dispersed in the nickel hydroxide substrate 11 which has not been reduced.

After the nickel hydroxide particles in the state shown in Fig. 1(a) were obtained, the slurry was cooled to room temperature, and then the particles were solid-liquid separated from the slurry. Since the nickel core particles 12 are not firmly bonded to the nickel hydroxide substrate 11, the nickel hydroxide particles are crushed by the external force during the repeated operations of the cleaning operation and the solid-liquid separation, and the nickel core particles 12 are self-imaged. Separated from the nickel hydroxide substrate 11 shown in 1 (a). As a result, as shown in FIG. 1(b), nickel hydroxide-coated nickel particles 20 coated with the nickel hydroxide thin layer 21 on the surface of the nickel core particles 22 are obtained. In addition, in FIG. 1(b), the nickel core particle 22 is uniformly covered with the nickel hydroxide thin layer 21 as a whole, but this state is shown by simplifying the actual state for understanding the present invention, and actually There are particles in which a part of the nickel core particles 22 are partially exposed, or particles in which the nickel core particles 22 are entirely covered by the thin layer 21 but the thickness thereof is not uniform. The nickel hydroxide-coated nickel particles 20 obtained in the above manner prevent the particles 20 from aggregating with each other by the action of the nickel hydroxide thin layer 21, and are highly dispersed in a medium such as water.

The above production method has an advantage that nickel hydroxide-coated nickel particles 20 which are fine particles and have high dispersibility can be obtained by a simple operation of controlling only the reaction time of reduction. Moreover, in the above manufacturing method, there is no need for a plurality of post-processing steps performed in the prior methods, or surface modification by controlling the environment.

The nickel particles coated with nickel hydroxide obtained in the above manner can be used, for example, in the form of ink or solder paste. In this case, in the state of storage before the preparation of the ink or the solder paste, the nickel particles coated with nickel hydroxide are maintained in a highly dispersed state in a medium such as water as described above, and thus, as shown in Fig. 1(c) As shown, the nickel particles 30 are obtained by removing the nickel hydroxide thin layer 21 immediately before the preparation of the ink or solder paste, and using the nickel particles as a raw material, a nickel ink or a nickel solder paste having high dispersibility maintained can be obtained. As described above, since the nickel hydroxide thin layer 21 coats the surface of the nickel core particle 22 with a lower degree of bonding force which can be removed from the surface of the nickel core particle 22 by an external force, it is easy to form a thin layer of nickel hydroxide. 21 removed. When the nickel ink or the nickel solder paste is used, the electrode film is formed by, for example, reduction baking, and the electrode film is relatively uniform and has low electrical resistance.

Alternatively, the nickel hydroxide particles coated with nickel hydroxide may be used to prepare an ink or a solder paste without removing the nickel hydroxide thin layer. When the ink or the solder paste is used, the electrode film is formed by, for example, reduction baking, and the low-temperature sinterability is improved by the action of the nickel hydroxide thin layer as a baking aid.

The nickel hydroxide-coated nickel particles produced by the above method are particularly suitable for forming internal electrodes of laminated ceramic capacitors.

[Examples]

Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the invention is not limited by the embodiment. Unless otherwise stated, "%" means "% by weight".

[Example 1]

In a 500 ml beaker, 445 g of ethylene glycol, 32.3 g of nickel hydroxide particles (average particle size of 5 μm), 4.3 g of polyvinylpyrrolidone, 10 g of polyethyleneimine, and 4 g of L-spermine were added. A slurry was prepared by using an acid, 0.69 ml of an aqueous solution of palladium nitrate (concentration: 100 g/l). The slurry was stirred while heating, and a reduction reaction was carried out at 190 ° C for 13 hours. Then, the heating was stopped to complete the reduction, and it was naturally left to cool to room temperature. In this manner, a plurality of nickel fine particles are formed in the nickel hydroxide particles. This state is equivalent to FIG. 2.

Next, the slurry is filtered, and the particles are subjected to solid-liquid separation by decantation using water, whereby nickel hydroxide particles are crushed, and nickel particles coated with nickel hydroxide present therein are separated. This state is equivalent to FIG. The average particle diameter of the primary particles obtained by TEM observation of the particles was 20 nm, and the thickness of the thin layer of nickel hydroxide was 2 nm on average. The shape of the particles is substantially spherical.

A 20% slurry of nickel hydroxide coated nickel particles obtained in the above manner was treated using a bead mill. Specifically, 4.2 parts by weight of zirconia beads (Nikkato Co., Ltd., 0.1 mm Φ) of Φ = 0.1 mm were mixed in a 20% slurry, and then treated for 30 minutes. By this treatment, a thin layer of nickel hydroxide coated with nickel particles of nickel hydroxide was removed to obtain spherical nickel particles having a surface on which nickel was exposed (the average particle diameter of the primary particles was 20 nm). This state corresponds to FIGS. 4(a) and (b). 4(a) and (b), the particles of the nickel fine particles obtained in the present example were uniformly arranged, and the dispersed state was very good.

[Comparative Example 1]

The same operation as in Example 1 was carried out except that the nickel hydroxide was completely reduced by a reduction reaction for 22 hours. The state of the nickel fine particles obtained in the above manner is shown in Figs. 5(a) and (b). 5(a) and (b), the particles of the nickel fine particles obtained in the comparative example were significantly agglomerated with each other.

As described in detail above, according to the present invention, nickel hydroxide on the surface of the nickel coating serves as a protective agent during storage, thereby preventing aggregation and improving the dispersibility of the particles. Further, since the nickel metal can be easily exposed by removing nickel hydroxide during use, the increase in electric resistance of the electrode film including the same can be suppressed. In the case where the reduction and calcination are carried out without removing nickel hydroxide, the nickel hydroxide functions as a sintering aid and the low-temperature sinterability is improved.

10. . . Nickel hydroxide particles

11. . . Nickel hydroxide matrix

12, 22. . . Nickel core particle

20. . . Nickel particles coated with nickel hydroxide

twenty one. . . Thin layer of nickel hydroxide

30. . . Nickel particles

In Fig. 1, Fig. 1(a) is a schematic view showing a state in which a plurality of nickel core particles are formed in nickel hydroxide particles, and Fig. 1(b) is a view showing hydrogen hydroxide in a state shown in Fig. 1(a). A schematic diagram of nickel particles coated with nickel particles obtained by nickel particles, and FIG. 1(c) shows a thin layer of nickel hydroxide removed from nickel particles coated with nickel hydroxide in the state shown in FIG. 1(b). State diagram of the state;

2 is an electron microscope image showing nickel hydroxide particles having a plurality of nickel core particles obtained in Example 1 (FIG. 1 (a) equivalent);

3 is a transmission electron microscope image of nickel hydroxide coated nickel particles obtained by crushing nickel hydroxide particles in the state shown in FIG. 2 (FIG. 1 (b) corresponding diagram);

In Fig. 4, Fig. 4(a) shows an electron microscope image of nickel particles obtained by removing nickel hydroxide from nickel hydroxide-coated nickel particles in the state shown in Fig. 3, and Fig. 4(b) shows Fig. 4 (a) an electron microscope image of a portion of the circle surrounded by the circle; and

In Fig. 5, Fig. 5(a) shows an electron microscope image of the nickel fine particles obtained in Comparative Example 1, and Fig. 5(b) shows an electron microscope image in which the portion surrounded by the circle in Fig. 5(a) is enlarged.

10. . . Nickel hydroxide particles

11. . . Nickel hydroxide matrix

12, 22. . . Nickel core particle

20. . . Nickel particles coated with nickel hydroxide

twenty one. . . Thin layer of nickel hydroxide

30. . . Nickel particles

Claims (4)

A nickel particle coated with nickel hydroxide, characterized in that the surface thereof is coated with nickel particles of nickel hydroxide, and the average particle diameter of the primary particles is 5 to 500 nm, and the nickel hydroxide can be removed by an external force. The claim 1 is coated with nickel hydroxide nickel particles, wherein the nickel hydroxide can be removed by applying an external force by a media mill. A method for producing nickel hydroxide coated with nickel hydroxide according to claim 1, characterized in that, when nickel hydroxide particles are heated and reduced to nickel in a state of being suspended in a polyol, the nickel hydroxide is not The particles are completely reduced, and the reaction is terminated in the middle of the reduction to form a plurality of minute nickel particles in the nickel hydroxide particles, and then the nickel hydroxide particles are crushed to obtain a plurality of nickel particles having a thin layer of nickel hydroxide on the surface. A method for producing nickel fine particles, comprising: producing nickel particles coated with nickel hydroxide according to the method of claim 3, and then applying an external force to the nickel particles coated with nickel hydroxide to coat nickel hydroxide Remove.