JP5744580B2 - Method for producing metal composite nickel nanoparticles containing iron oxide and metal composite nickel nanoparticles containing iron oxide - Google Patents

Description

  The present invention relates to a method for producing metal composite nickel nanoparticles containing iron oxide and metal composite nickel nanoparticles containing iron oxide.

Nickel nanoparticles are cheaper than noble metal nanoparticles such as silver nanoparticles and are chemically more stable than noble metal nanoparticles, so they are expected to be used for electrodes in catalysts, magnetic materials, and multilayer ceramic capacitors. Yes. Conventionally, nickel nanoparticles have been obtained by solid phase reaction or liquid phase reaction.
Known solid-phase reactions include chemical vapor deposition of nickel chloride and thermal decomposition of nickel formate salt. In the liquid phase reaction, a nickel salt such as nickel chloride is directly reduced with a strong reducing agent such as sodium borohydride, a reducing agent such as hydrazine is added in the presence of NaOH, and the precursor [Ni (H ₂ NNH ₂ ) ₂ ] A method of thermal decomposition after forming SO ₄ · 2H ₂ O, a method of hydrothermal synthesis by putting a nickel complex such as nickel chloride or a nickel complex containing an organic ligand into a pressure vessel together with a solvent, etc. It has been.

In order for nickel nanoparticles to be suitably used for applications such as the above-described catalyst, magnetic material, and electrode, it is necessary to be able to control the particle size to be small and uniform so as to be less than 150 nm, for example.
For example, when used for an internal electrode application of a multilayer ceramic capacitor, the particle size control is important in preventing delamination and cracks described later.

However, in the case of the chemical vapor deposition method among solid phase reactions, the particles are enlarged from submicron to micron order. Moreover, in the case of the method by thermal decomposition, particles are aggregated because the reaction temperature is high. Moreover, the manufacturing method by these solid-phase reactions tends to be high in the manufacturing cost of nickel nanoparticles compared with the manufacturing method by a liquid phase reaction.
On the other hand, in the case of a method using a strong reducing agent in the liquid phase reaction, since nickel is immediately reduced, it is difficult to control the reaction in order to obtain particles having a desired particle size. In addition, in the case of the method of passing through the precursor, the precursor is in the form of a gel, the subsequent reduction reaction becomes heterogeneous, and in the case of hydrothermal synthesis, the reaction temperature is high, so in each case, avoid aggregation. Can not.

  Regarding a liquid phase reaction technique, a technique is disclosed in which nickel nanoparticles are obtained by mixing a nickel precursor, an organic amine, and a reducing agent, followed by heating (Patent Document 1). According to this technique, it is said that the control of the size and shape of the nickel nanoparticles is easy. However, since this production method uses a strong reducing agent such as tetrabutylammonium borohydride, it is difficult to control the reduction reaction, and it is not always necessary to obtain nickel nanoparticles with sufficiently controlled particle size. It is considered unsuitable.

  By the way, the multilayer ceramic capacitor is obtained by alternately laminating ceramic dielectrics and internal electrodes and pressing them, and then sintering and integrating them. At this time, for example, the sintering temperature of the nickel nanoparticles as the internal electrode material is as low as several hundred degrees Celsius compared to the sintering temperature of the ceramic dielectric exceeding 1,000 ° C. There is a risk that delamination and cracks may occur due to differences in the behavior such as volume change. With respect to such a problem during sintering, the conventional technology such as Patent Document 1 described above does not take any effective measures.

  As a technique for increasing the sintering temperature of metal nanoparticles while optimizing the particle size and distribution of the metal nanoparticles, for example, for copper powder, metal copper fine particles or metal whose surface is oxidized A metal copper fine particle is disclosed in which a metal salt aqueous solution is added to a slurry of copper fine particles and the pH is adjusted to fix a metal oxide or the like on the surface (Patent Document 2). However, since this technique involves a complicated manufacturing process, it is considered difficult to obtain inexpensive nickel nanoparticles.

In addition, the inventors of the present invention first manufactured by heating a solution containing a Lewis base such as nickel formate hydrate, fatty acid amine and a solvent, and a general formula Ni (HCOO) ₂ (L ¹ ) (L ² ) (however, L ¹ and L ^{2 each} represent a Lewis base ligand, and L ¹ and L ² may be the same or different from each other), which discloses a nickel complex ( Patent Document 3).

JP 2010-37647 A JP 2000-345201 A JP 2010-64983 A

  An object of the present invention is to produce nickel nanoparticles having a moderately high sintering temperature while using a liquid phase reaction technique to optimize the particle size and distribution.

  As a result of intensive research on nickel nanoparticles, the present inventors have made it possible to contain an appropriate amount of iron in the production of nickel nanoparticles, and completely separate the complex formation reaction and the reduction reaction of the nickel precursor. The inventors have found that the above problems can be solved by using a specific heating method, and have completed the present invention.

That is, in the method for producing metal composite nickel nanoparticles containing iron oxide according to the present invention, a mixture of nickel carboxylate, iron salt and primary amine is heated to a temperature in the range of 100 ° C to 165 ° C. A complexing reaction liquid producing step for obtaining a complexing reaction liquid;
A nanoparticle slurry generating step of heating the complexing reaction liquid to a temperature of 170 ° C. or higher by microwave irradiation to obtain a metal composite nickel nanoparticle slurry containing iron oxide;
It has.

  The method for producing metal composite nickel nanoparticles containing iron oxide according to the present invention includes, in the reaction solution generation step, instead of the mixture, the mixture of the nickel carboxylate and the primary amine, and the iron salt. And the mixture of primary amines may be heated separately, and the resulting reaction solutions may be mixed.

  Moreover, the manufacturing method of the metal composite nickel nanoparticle containing the iron oxide which concerns on this invention may perform the said reaction liquid production | generation process in presence of an organic solvent.

  In the method for producing metal composite nickel nanoparticles containing iron oxide according to the present invention, the iron salt may be iron (II) carboxylate or iron (III) carboxylate.

  In addition, the method for producing metal composite nickel nanoparticles containing iron oxide according to the present invention, at least before the nanoparticle slurry generation step, from a metal salt group consisting of a palladium salt, a silver salt, a platinum salt and a gold salt. You may further have the metal salt addition process which adds the 1 or 2 or more metal salt selected.

  The metal composite nickel nanoparticles containing iron oxide according to the present invention have a total amount of nickel element, iron element and oxygen element of 95 parts by mass or more with respect to 100 parts by mass of metal composite nickel nanoparticles, Is in the range of 5 to 50 parts by mass with respect to 100 parts by mass of the total amount of nickel element and iron element, the average particle size is in the range of 30 nm to 150 nm, and the iron oxide contains triiron tetroxide. The main component.

  The method for producing metal composite nickel nanoparticles containing iron oxide according to the present invention comprises heating a mixture of nickel carboxylate, iron salt and primary amine at a temperature in the range of 100 ° C. to 165 ° C. to complex. A step of obtaining a reaction liquid, and a step of heating the complexing reaction liquid to a temperature of 170 ° C. or higher by microwave irradiation to obtain a metal composite nickel nanoparticle slurry containing iron oxide. The particle size and distribution of the nickel nanoparticles can be optimized, and in particular, metal composite nickel nanoparticles having a high sintering temperature can be obtained. Metal composite nickel nanoparticles having a high sintering temperature can be suitably used, for example, as a material for internal electrodes of a multilayer ceramic capacitor.

Moreover, since the metal composite nickel nanoparticle containing the iron oxide according to the present invention contains triiron tetroxide (Fe ₃ O ₄ ) as a main component of the iron oxide, for example, an internal electrode of a multilayer ceramic capacitor It is suitable as a material.

It is a figure which shows the structure of each nickel acetate complex, (a) shows bidentate coordination, (b) shows monodentate coordination, (c) shows the state which the carboxylate ion coordinated to the outer sphere, respectively. . 1 is a view showing an SEM photograph of nanoparticles obtained in Example 1. FIG. 2 is a diagram showing an X-ray diffraction pattern of nanoparticles obtained in Example 1. FIG. It is a figure which shows the behavior of the thermal expansion shrinkage | contraction of the nanoparticle obtained in Example 1. FIG. 4 is a view showing an SEM photograph of nanoparticles obtained in Example 2. FIG. 4 is a view showing an SEM photograph of nanoparticles obtained in Example 3. FIG. 4 is a view showing an SEM photograph of nanoparticles obtained in Comparative Example 1. FIG. It is a figure which shows the behavior of the thermal expansion contraction of the nanoparticle obtained by the comparative example 1. FIG. It is a figure which shows the behavior of the thermal expansion contraction of the nanoparticle obtained in Example 5. FIG.

  Embodiments of the present invention will be described in detail. First, a method for producing metal composite nickel nanoparticles containing iron oxide according to the present embodiment (hereinafter sometimes abbreviated as “nanoparticles”) will be described.

[Method for producing metal composite nickel nanoparticles containing iron oxide]
In the method for producing metal composite nickel nanoparticles containing iron oxide according to the present embodiment, a mixture of nickel carboxylate, iron salt and primary amine is heated at a temperature in the range of 100 ° C to 165 ° C. A complexing reaction solution generating step for obtaining a complexing reaction solution, and nanoparticles for obtaining a metal composite nickel nanoparticle slurry containing iron oxide by heating the complexing reaction solution to a temperature of 170 ° C. or higher by microwave irradiation A slurry generation step. In the complexation reaction liquid production step, a complex formation reaction between nickel carboxylate and primary amine and iron salt and primary amine is performed to produce a reaction liquid containing nickel complex and iron complex. In the nanoparticle slurry production step, Then, the nickel complex and the iron complex and the unreacted nickel ion and iron ion are reduced to produce a metal composite nickel nanoparticle slurry containing iron oxide.

<Complexation reaction liquid production process>
The complexing reaction solution generation step is a one-pot in which the complexation reaction of nickel carboxylate and iron salt with a primary amine is carried out in one pot in which the reaction is continuously performed without isolation and purification of the intermediate product. Can be obtained in a high yield, which is preferable. At this time, in the complexation reaction liquid production step, instead of the above mixture, (1) a mixture of nickel carboxylate and primary amine and (2) a mixture of iron salt and primary amine are separately heated and obtained. You may mix each reaction liquid.

(Nickel carboxylate)
The nickel carboxylate (nickel salt of carboxylic acid) is not limited to the type of carboxylic acid. For example, the carboxy group may be one monocarboxylic acid, or the carboxy group has two or more carboxylic acids. It may be. Moreover, acyclic carboxylic acid may be sufficient and cyclic carboxylic acid may be sufficient. As such nickel carboxylate, nickel acyclic monocarboxylate can be suitably used. Among the nickel acyclic monocarboxylates, nickel acetate or nickel propionate having a longer straight chain than nickel acetate, It is more preferable to use nickel acid or the like. By using these acyclic nickel monocarboxylates, for example, the resulting nanoparticles are more easily formed in a uniform shape, with variations in shape being more suppressed. The nickel carboxylate may be an anhydride or a hydrate.

In addition, it is possible to use inorganic salts such as nickel chloride, nickel nitrate, nickel sulfate, nickel carbonate, nickel hydroxide instead of nickel carboxylate, but in the case of inorganic salts, dissociation (decomposition) is high temperature. In the process of reducing the dissociated nickel ions (or nickel complex), heating at a higher temperature is required, which is not preferable. It is also possible to use nickel salts composed of organic ligands such as Ni (acac) ₂ (β-diketonato complex) and nickel stearate. However, using these nickel salts increases the cost of raw materials. It is not preferable.

(Iron salt)
As the iron salt, an appropriate iron compound can be used. For example, it may be a halide or iron iron carboxylate. More preferably, divalent iron (II) carboxylate or trivalent iron (III) carboxylate is used as the iron salt. By using the iron salt together with nickel carboxylate, the obtained nanoparticles become a composite metal, and the sintering temperature is increased compared to the metal nickel nanoparticles obtained when no iron salt is used.

  The amount of iron contained in the nanoparticles can be controlled by the amount of iron salt used. The amount of iron salt to be used is preferably such that the amount of iron element in the obtained nanoparticles is in the range of 5 to 50 parts by mass with respect to 100 parts by mass of the total amount of nickel element and iron element, Preferably it shall be in the range of 5-40 mass parts. If the amount of iron salt used is too small, it will be difficult to improve the sintering temperature of the resulting nanoparticles, and if the amount of iron salt used is excessive, it will be difficult to use under high temperature conditions. In the sintering process of the nanoparticles, thermal expansion of the nanoparticles is likely to occur. For example, when the nanoparticles are used for an internal electrode of a multilayer ceramic capacitor, there is a possibility of causing delamination or cracks.

  In addition, about the thermal expansion of the nanoparticle of this invention, when evaluated, for example with a thermomechanical analyzer (TMA; Thermomechanical Analysis), the thermal expansion of a nanoparticle can be confirmed especially at the temperature of 800 degreeC or more.

(Primary amine)
The primary amine can form a complex with nickel ions, and effectively exhibits a reducing ability for nickel complexes (or nickel ions). On the other hand, secondary amines have great steric hindrance and may hinder good formation of nickel complexes, and tertiary amines cannot be used because they do not have the ability to reduce nickel ions.

  The primary amine is not particularly limited as long as it can form a complex with nickel ions, and can be a solid or liquid at room temperature. Here, room temperature means 20 ° C. ± 15 ° C. The primary amine that is liquid at room temperature also functions as an organic solvent for forming the nickel complex. In addition, even if it is a primary amine solid at normal temperature, there is no particular problem as long as it is liquid by heating at 100 ° C. or higher, or can be dissolved using an organic solvent.

  The primary amine may be an aromatic primary amine, but an aliphatic primary amine is preferred from the viewpoint of easy nickel complex formation in the reaction solution. Aliphatic primary amines can control the particle size of the produced nanoparticles, for example, by adjusting the length of the carbon chain, and in particular, produce nanoparticles having an average particle size in the range of 50 nm to 100 nm. This is advantageous. From the viewpoint of controlling the particle size of the nanoparticles, the aliphatic primary amine is preferably selected from those having about 6 to 20 carbon atoms. The larger the number of carbons, the smaller the particle size of the resulting nanoparticles. Examples of such amines include octylamine, trioctylamine, dioctylamine, hexadecylamine, dodecylamine, tetradecylamine, stearylamine, oleylamine, myristylamine, and laurylamine. For example, oleylamine exists in a liquid state under the temperature conditions in the nanoparticle production process, and therefore can efficiently proceed with a reaction in a homogeneous solution.

Since the primary amine functions as a surface modifier during the production of the nanoparticles, secondary aggregation can be suppressed even after removal of the primary amine. The primary amine is also preferable from the viewpoint of ease of processing operation in the washing step of separating the solid component of the produced nanoparticles after the reduction reaction from the solvent or the unreacted primary amine. Further, the primary amine is preferably one having a boiling point higher than the reduction temperature from the viewpoint of ease of reaction control when the nickel complex is reduced to obtain nickel nanoparticles. That is, the aliphatic primary amine preferably has a boiling point of 180 ° C. or higher, more preferably 200 ° C. or higher, and preferably has 9 or more carbon atoms. Here, for example, the boiling point of C ₉ H ₂₁ N (nonylamine) of an aliphatic amine having 9 carbon atoms is 201 ° C. The amount of primary amine is preferably 2 mol or more, more preferably 2.2 mol or more, and more preferably 4 mol or more with respect to 1 mol of nickel. When the amount of primary amine is less than 2 mol, it is difficult to control the particle diameter of the nickel nanoparticles obtained, and the particle diameter tends to vary. The upper limit of the amount of primary amine is not particularly limited, but is, for example, about 20 mol or less from the viewpoint of productivity.

(Organic solvent)
In order to proceed the reaction in a homogeneous solution more efficiently, an organic solvent other than the primary amine may be newly added. When an organic solvent is used, the organic solvent may be mixed with the nickel carboxylate and the primary amine. However, when the organic solvent is added after first mixing the nickel carboxylate and the primary amine to form a complex, It is more preferable because it efficiently coordinates to a nickel atom. The organic solvent that can be used is not particularly limited as long as it does not inhibit the complex formation between the primary amine and the nickel ion. For example, the organic solvent having 4 to 30 carbon atoms, 7 to 30 carbon atoms, and the like. A saturated or unsaturated hydrocarbon organic solvent, an alcohol organic solvent having 8 to 18 carbon atoms, or the like can be used. Moreover, from the viewpoint of enabling use even under heating conditions by microwave irradiation, it is preferable to select an organic solvent having a boiling point of 170 ° C. or higher, more preferably in the range of 200 to 300 ° C. It is better to choose one. Specific examples of such an organic solvent include tetraethylene glycol and n-octyl ether.

The divalent nickel ion is known as a ligand-substituted active species, and the ligand of the complex to be formed may easily change by ligand exchange depending on the temperature and concentration. For example in the step of heating the mixture of nickel carboxylate and primary amine to obtain a reaction solution, considering the steric hindrance of the carbon chain length of the amine or the like used, for example, as shown in FIG. 1, a carboxylate ion (R ₁ COO, R ₂ COO) may be coordinated by either bidentate coordination (a) or monodentate coordination (b), and when the amine concentration is in large excess, carboxylate ions are present in the outer sphere. The structure (c) to be taken may be taken. In order to obtain a homogeneous solution at the reaction temperature (reduction temperature), at least one of the ligands of A, B, C, D, E, and F must be coordinated with a primary amine. In order to take this state, it is necessary that the primary amine is excessively present in the reaction solution, and it is preferable that at least 2 mol per 1 mol of nickel ions is present, and 2.2 mol or more exist. It is more preferable that 4 mol or more is present.

  It is considered that iron ions behave similarly to nickel ions and form complexes. For this reason, the primary amine must be present in an excessive amount with respect to iron ions.

  This complexing reaction can proceed even at room temperature, but heating is performed at a temperature within the range of 100 ° C. to 165 ° C. in order to carry out the reaction reliably and more efficiently. This heating is particularly advantageous when a nickel carboxylate hydrate such as nickel acetate tetrahydrate is used as the nickel carboxylate. The heating temperature is preferably a temperature exceeding 100 ° C., more preferably a temperature of 105 ° C. or more, so that the ligand substitution reaction between the coordinating water coordinated with nickel carboxylate and the primary amine is efficient. The water molecule as the complex ligand can be dissociated, and the water can be discharged out of the system, so that the complex can be formed efficiently. In addition, the heating temperature is preferably 160 ° C. or less, more preferably from the viewpoint of separating from the subsequent heat reduction process by microwave irradiation of the nickel complex (or nickel ions) and completing the complex formation reaction. Is preferably 150 ° C. or lower.

  The heating time can be appropriately determined according to the heating temperature and the content of each raw material, but is preferably 10 minutes or more from the viewpoint of reliably completing the complex formation reaction. Although there is no upper limit on the heating time, heating for a long time is useless from the viewpoint of saving energy consumption and process time. The heating method is not particularly limited, and may be heating by a heat medium such as an oil bath or heating by microwave irradiation.

  The complex formation reaction between nickel carboxylate and primary amine (as well as iron salts) can be confirmed by the change in color of the solution when the solution obtained by mixing nickel carboxylate and primary amine is heated. it can. In addition, this complex formation reaction is carried out by measuring the absorption maximum wavelength of the absorption spectrum observed in the wavelength region of 300 nm to 750 nm using, for example, an ultraviolet / visible absorption spectrum measuring apparatus, and measuring the maximum absorption wavelength of the raw material (for example, nickel acetate). In tetrahydrate, the maximum absorption wavelength is 710 nm.), And this can be confirmed by observing the shift of the reaction solution with respect to. After complexation of nickel carboxylate and iron salt with primary amine is performed, the resulting reaction solution is heated by microwave irradiation to reduce the nickel ions of the nickel complex as described below. Then, the carboxylate ions coordinated to the nickel ions are simultaneously decomposed, and finally metal composite nickel nanoparticles containing nickel having an oxidation number of 0 are generated. In general, nickel carboxylate is hardly soluble under conditions other than using water as a solvent, and a solution containing nickel carboxylate and an iron salt needs to be a homogeneous reaction solution as a pre-stage of a heat reduction reaction by microwave irradiation. On the other hand, the primary amine used in the present embodiment is liquid at the operating temperature conditions, and is thought to be liquefied by coordination with nickel ions and iron ions to form a homogeneous reaction solution. It is done.

<Nanoparticle slurry production process>
The method for producing metal composite nickel nanoparticles containing iron oxide according to the present embodiment is obtained by complex formation reaction between nickel carboxylate and iron salt (or nickel carboxylate or iron salt) and primary amine. The reaction solution (or mixed solution) is heated to a temperature of 170 ° C. or higher by microwave irradiation. The temperature for heating by microwave irradiation is preferably 180 ° C. or higher, more preferably 200 ° C. or higher, from the viewpoint of suppressing variation in the shape of the obtained nanoparticles. The upper limit of the heating temperature is not particularly limited, but is preferably about 270 ° C. or less from the viewpoint of efficiently performing the treatment. The heating time is not particularly limited, and can be, for example, about 2 to 10 minutes. In addition, the use wavelength of a microwave is not specifically limited, For example, it is 2.45 GHz.

In the nanoparticle slurry generation step, since microwaves penetrate into the reaction liquid (or the mixed liquid), uniform heating is performed and energy can be directly applied to the medium, so that rapid heating can be performed. . As a result, the entire reaction solution can be brought to a desired uniform temperature, and the processes of reduction, nucleation, and nucleation of the nickel complex (or nickel ions) are simultaneously generated in the entire solution, and the single particle size distribution is narrow. Dispersed particles can be easily produced in a short time. In this manufacturing process, the iron complex (or iron ion) present in the reaction solution (or in the mixed solution) is mainly Fe ₃ O ₄ (triiron tetroxide), which is combined with nickel (zero-valent). it is conceivable that. Fe ₃ O ₄ (triiron tetroxide) is an X-ray diffractometer (XRD; X-ray).
diffraction). Note that Fe ₃ O ₄ may be present as an iron oxide in the form of NiFe ₂ O ₃ (nickel ferrite), which is a nickel substitutional solid solution.

  In order to generate nanoparticles having a uniform particle size, a nickel complex is uniformly and sufficiently generated in a complexing reaction liquid generation step (a step where nickel complex is generated), and a nanoparticle slurry generation step ( In the step of heating by microwave irradiation), it is necessary to simultaneously generate and grow nickel (zero-valent) nuclei generated by reduction of the nickel complex (or nickel ions). In other words, by adjusting the heating temperature of the complexing reaction liquid generation step within the above specific range and ensuring that it is lower than the heating temperature of the nanoparticle slurry generation step, particles having a uniform particle size and shape can be obtained. Easy to generate. For example, if the heating temperature is too high in the complexing reaction liquid generation process, the formation of a nickel complex and the reduction reaction to nickel (zero valence) proceed simultaneously, and the generation of particles with a uniform particle shape in the nanoparticle slurry generation process May be difficult. In addition, if the heating temperature in the nanoparticle slurry generation step is too low, the reduction reaction rate to nickel (zero valence) is slowed and the generation of nuclei is reduced, so that not only the particles are enlarged, but also from the viewpoint of the yield of nanoparticles. Is also not preferred.

  Metal composite nickel nanoparticle slurry (nanoparticle slurry) obtained by heating by microwave irradiation, for example, standing and separating, removing the supernatant liquid, washing with a suitable solvent, and drying, Metal composite nickel nanoparticles (nanoparticles) are obtained.

  In the nanoparticle slurry generation step, the organic solvent described above may be added as necessary. As described above, it is a preferred embodiment of the present invention to use the primary amine used in the complex formation reaction as an organic solvent as it is.

<Addition of metal salt>
In the method for producing metal composite nickel nanoparticles containing iron oxide according to the present embodiment, at the latest, before irradiation with microwaves (before the nanoparticle slurry generation step), palladium salt, silver salt, platinum salt and gold It is preferable to further include a step of adding one or more metal salts selected from the group of metal salts consisting of salts.

  The metal salt does not particularly limit the type of salt. The use of hydrochloric acid, nitric acid, sulfuric acid and acetic acid as the acid (acid group) constituting the salt is a preferred embodiment. For the platinum salt and gold salt, for example, chloroplatinic acid or chloroauric acid is also a preferred embodiment.

  The amount of the metal salt is not particularly limited, but it is preferable that the metal salt is added in an amount of 0.01 parts by mass or more on a metal basis with respect to 100 parts by mass of the total amount of nickel element of nickel carboxylate and iron element of iron salt. . The upper limit of the amount of the metal salt is not particularly limited. For example, in consideration of the balance between the effect of the invention and the cost, the nickel element of the nickel carboxylate and the iron element of the iron salt are 10 parts by mass or less with respect to 100 parts by mass. Can be set to

  In the method for producing metal composite nickel nanoparticles containing iron oxide according to the present embodiment, the reaction solution (or mixed solution) is heated by microwave irradiation to reduce the nickel complex (or nickel ion) and nucleate. Each process of nucleation occurs simultaneously in the entire solution. At this time, it is considered that by adding the above-mentioned metal salt, nickel is generated and grown on the surface of the fine particles of palladium or silver generated earlier as nuclei. Thereby, it becomes easy to produce | generate the particle | grains in which the particle size and shape were arranged.

<Surface modifier>
In the method for producing metal composite nickel nanoparticles containing iron oxide according to the present embodiment, a surface modifier is used for the purpose of controlling the particle size of the nanoparticles and improving the dispersibility of the nanoparticles. Can be added. For example, a polymer resin such as polyvinyl pyrrolidone (PVP), polyethyleneimine, or polyacrylamide, a long-chain carboxylic acid such as myristic acid or oleic acid, a carboxylate, or the like can be added. However, if the surface modification amount of the obtained nanoparticles is large, when used as a conductive paste for nickel electrodes, paste density of nickel particles and firing at high temperatures may lead to a decrease in packing density, resulting in delamination and cracks. Therefore, the surface modification amount after washing the obtained nanoparticles is preferably as small as possible. Therefore, it is preferable that the addition amount of the surface modifier is in the range of 0.1 to 100 parts by mass with respect to 100 parts by mass of the total amount of nickel element and iron element of the iron salt. The surface modifier may be added at the stage of the mixture of nickel carboxylate, iron salt and primary amine in the complexing reaction liquid production process, or added to the complexation reaction liquid obtained in the complexation reaction liquid production process. However, the timing of addition is preferably after the complexation reaction or after the formation of the metal composite nickel nanoparticles.

By the method for producing metal composite nickel nanoparticles containing iron oxide according to the present embodiment described above, the particle size is 150 nm or less, more preferably in the range of 10 to 120 nm, and uniform, In particular, composite nickel nanoparticles having a sintering temperature higher by 50 ° C. or more (preferably 100 ° C. or more) than conventional nickel particles (for example, nickel nanoparticles disclosed in Patent Document 3) can be obtained. Thus, the composite nickel nanoparticles having a high sintering temperature can be suitably used as a material for internal electrodes of a multilayer ceramic capacitor, for example. In addition, metal composite nickel nanoparticles having a high ratio of Fe ₃ O ₄ obtained by using a raw material having a higher ratio of iron salt to nickel carboxylate are used in various important applications of Fe ₃ O ₄ such as magnetic fluids. It can be suitably used for high-quality toner or diagnostic medicine.

[Metal composite nickel nanoparticles]
Next, the metal composite nickel nanoparticles according to the present embodiment will be described.

  The metal composite nickel nanoparticles according to the present embodiment are metal composite nickel nanoparticles containing iron oxide, and the total amount of nickel element, iron element and oxygen element is 100 parts by mass of metal composite nickel nanoparticles. 95 parts by mass or more, the amount of iron element is in the range of 5 to 50 parts by mass with respect to 100 parts by mass of the total amount of nickel element and iron element, the average particle size is in the range of 30 nm to 150 nm, iron The oxide is composed mainly of triiron tetroxide.

  The metal composite nickel nanoparticles according to the present embodiment can be suitably obtained by the above-described method for producing metal composite nickel nanoparticles containing the iron oxide according to the present embodiment.

  In the metal composite nickel nanoparticles according to the present embodiment, if the total amount of nickel element, iron element and oxygen element is too small, the organic amine volatilizes at a low temperature (200 to 300 ° C.). Particle mass loss tends to occur, and the nickel packing density decreases. As a result, for example, when nanoparticles are used for an internal electrode of a multilayer ceramic capacitor, there is a risk of delamination or cracks. In addition, about the mass loss of a nanoparticle, it can evaluate by thermal mass measurement (TGA), for example. Therefore, the total amount of nickel element, iron element, and oxygen element is more preferably 97 parts by mass or more, and further preferably 99 parts by mass or more with respect to 100 parts by mass of the metal composite nickel nanoparticles. The remainder of the metal composite nickel nanoparticles excluding nickel element, iron element and oxygen element is organic amine coating the surface of the nickel nanoparticles. The organic amine coated on the nanoparticles improves the stability and dispersibility of the nanoparticles.

  In the metal composite nickel nanoparticles according to the present embodiment, if the ratio of the iron element is too small, it becomes difficult to sufficiently raise the sintering temperature of the nanoparticles, whereas, if the ratio of the iron element is excessive, Thermal expansion of the nanoparticles is likely to occur during the sintering process. For example, when the nanoparticles are used for internal electrodes of a multilayer ceramic capacitor, there is a risk of delamination or cracking. Therefore, the amount of the iron element is preferably 5 to 40 parts by mass with respect to 100 parts by mass of the total amount of the nickel element and the iron element. The amount of each element such as iron and nickel can be measured with an elemental analyzer.

  The average particle diameter of the metal composite nickel nanoparticles is preferably in the range of 30 nm to 120 nm, more preferably in the range of 50 nm to 100 nm. In addition, when the average particle diameter of the metal composite nickel nanoparticles is 100 nm or less, the effect of sintering resistance (which means that the sintering temperature is high and sintering is difficult) is effectively exhibited. Here, the average particle diameter is an area average particle diameter of a powder photograph taken by SEM (scanning electron microscope) and randomly extracted 200 particles.

  Moreover, since it is a more preferable aspect that the particle size distribution is sharp, the Cv value (coefficient of variation) of the metal composite nickel nanoparticles is 0.5 or less, preferably 0.4 or less, more preferably 0.3 or less. It is. Here, the Cv value is an index representing relative dispersion, and the smaller the value, the sharper the particle size distribution. The Cv value is calculated by dividing the standard deviation by the average particle diameter.

In the metal composite nickel nanoparticles, the iron oxide is mainly composed of triiron tetroxide. Here, “the iron oxide is composed mainly of triiron tetroxide” means that the iron oxide contains triiron tetroxide in a sufficient amount to exert the effects of the present invention. In terms of elemental structure, it means that the nanoparticles contain an oxygen element in the range of preferably 10 to 45 parts by mass, more preferably 10 to 38 parts by mass with respect to 100 parts by mass of the iron element. From another viewpoint, an X-ray diffractometer (XRD; X-ray
The peak intensity ratio observed using diffraction) is preferably the maximum of Fe ₃ O ₄ when the peak diffraction intensity of nickel of the metal composite nanoparticles (2θ) = 44.50 ° is 100. The peak (2θ = 35.42 °) intensity is 1 to 500, the maximum peak of FeO is 1.0 or less, and the maximum peak (2θ = 33.15 °) intensity of α-Fe ₂ O ₃ (hematite) is 1.0. More preferably, the maximum peak intensity of Fe ₃ O ₄ is 5 to 250, the maximum peak of FeO (2θ = 54.37 °) is 0.1 or less, and the maximum of α-Fe ₂ O ₃ (hematite) is The peak is 0.1 or less.

  The shape of the metal composite nickel nanoparticle according to the present embodiment is, for example, spherical, pseudo-spherical, oblong, cubic, truncated tetrahedral, bipyramidal, octahedral, icosahedral, icosahedron Various shapes such as a face-piece shape may be used, but for example, from the viewpoint of improving the packing density when nanoparticles are used for internal electrodes of a multilayer ceramic capacitor, a spherical shape or a pseudospherical shape is preferable, and a spherical shape is more preferable. . Here, the shape of the nanoparticles can be confirmed by observing with a scanning electron microscope (SEM).

  The metal composite nickel nanoparticles according to the present embodiment are suitable as a material for internal electrodes of a multilayer ceramic capacitor, for example.

  The present invention will be further described with reference to examples and comparative examples. In addition, this invention is not limited to the Example demonstrated below. As for the particle diameter of the nanoparticles, a photograph of the powder was taken with an SEM (scanning electron microscope), 200 particles were randomly extracted from them, and the average particle diameter (area average diameter) and standard deviation were obtained. The Cv value (coefficient of variation) was calculated by (standard deviation) / (average particle size).

[Example 1]
Under a nitrogen atmosphere, 42.90 g of nickel acetate tetrahydrate, 8.94 g of iron (II) acetate and 690.00 g of oleylamine were mixed and then heated at 140 ° C. with stirring for 20 minutes. A blue reaction solution 1 was obtained. When the absorption spectrum of the reaction liquid 1 was measured using the UV-visible absorption spectrum measuring apparatus, the wavelength of the absorption maximum in a wavelength range of 300 nm to 800 nm was present at 370 nm and 610 nm. The absorption spectrum of the reaction solution 1 was shifted to a lower wavelength side with respect to 710 nm, which is the wavelength of the absorption maximum of nickel acetate tetrahydrate, so that a complex formation reaction was confirmed.

  Next, 0.14 g of silver nitrate was added to the reaction solution 1, and then the mixture was irradiated with microwaves and heated at 250 ° C. for 5 minutes in a nitrogen atmosphere to obtain a nanoparticle slurry 1. In the following examples and comparative examples, “heating at 250 ° C. for 5 minutes” means heating to 250 ° C. at a heating rate of 5.0 ° C./second by microwave and holding at that temperature for 5 minutes. Means.

  The obtained nanoparticle slurry 1 was allowed to stand and separated, and the supernatant liquid was removed, followed by washing three times with a mixed solvent having a volume ratio of methanol to toluene of 1: 4, and then vacuum drying maintained at 70 ° C. Drying with a machine for 6 hours gave nanoparticles (metal composite nickel nanoparticles) 1. The nanoparticles were a group of uniform particles having an average particle diameter of 60 nm (Cv value; 0.34). A scanning electron microscope (SEM) photograph of the nanoparticles 1 is shown in FIG.

The identification of the nanoparticle 1 was performed using a powder X-ray diffractometer (XRD) (manufactured by Rigaku Corporation, trade name: RINT2500). X-ray analysis diffraction angle (2θ) = 44.58 °, 51.84 °, 76.40 °, respectively, having nickel crystal plane (111), (200), (220) peaks. The powder was confirmed to be Ni having a face-centered cubic structure (fcc). Also, X-ray analysis diffraction angles (2θ) = 30.29 °, 35.66 °, 43.19 °, 57.16 °, 62.74 ° respectively derived from triiron tetroxide (Fe ₃ O ₄ ). The peak to be confirmed was confirmed. At this time, the maximum peak intensity of Fe ₃ O ₄ was 18 with respect to the maximum peak intensity 100 of Ni. Moreover, the peak of the nickel acetate complex which is a raw material, and the peak of nickel oxide, iron oxide (FeO), and ferric trioxide (α-Fe ₂ O ₃ ) were not confirmed. An X-ray diffraction pattern of the obtained nanoparticles 1 is shown in FIG.

  The behavior of thermal expansion and contraction of the nanoparticles 1 was confirmed using a thermomechanical analyzer (TMA) (Rigaku Corporation, trade name: Thermo plus EVO-TMA8310). The starting temperature at 5% thermal shrinkage of Nanoparticle 1 was about 420 ° C. The behavior of the thermal expansion and contraction of the nanoparticles 1 is shown in FIG. In addition, Table 1 shows the 5% heat shrink start temperature.

  The composition of the nanoparticles 1 was confirmed using an elemental analyzer. As a result of this elemental analysis, it was Ni; 82.9, Fe; 13.2, O; 2.5, C; 0.7, H; 0.1 (unit: mass%). From this analysis result, in terms of mass, the iron element was 15.9 with respect to the nickel element 100, and the oxygen element was 19.0 with respect to the iron element 100.

[Example 2]
Under a nitrogen atmosphere, 14.30 g of nickel acetate tetrahydrate, 2.98 g of iron (II) acetate and 225.00 g of oleylamine were mixed and then heated at 140 ° C. for 20 minutes with stirring. Reaction liquid 2 was obtained.

  Next, the reaction liquid 2 was irradiated with microwaves and heated at 250 ° C. for 5 minutes to obtain a nanoparticle slurry 2.

  The obtained nanoparticle slurry 2 was allowed to stand and separated, and the supernatant liquid was removed, followed by washing three times using a mixed solvent having a volume ratio of methanol and toluene of 1: 4, and then vacuum drying maintained at 70 ° C. Nanoparticles 2 were obtained by drying with a machine for 6 hours. Nanoparticle 2 was a group of spherical uniform particles having an average particle size of 120 nm (Cv value; 0.46). A scanning electron microscope (SEM) photograph of the nanoparticles 2 is shown in FIG. Moreover, the starting temperature in 5% of heat shrink of the obtained nanoparticle 2 was about 400 degreeC. In addition, Table 1 shows the 5% heat shrink start temperature.

[Example 3]
Reaction solution 3 was obtained in the same manner as in Example 1 except that 9.81 g of iron (III) acetate basic was used instead of 8.94 g of iron (II) acetate in Example 1, and then nano After obtaining the particle slurry 3, spherical uniform nanoparticles 3 having an average particle diameter of 60 nm (Cv value; 0.40) were obtained. A scanning electron microscope (SEM) photograph of the nanoparticles 3 is shown in FIG. It was confirmed that the starting temperature at 5% thermal shrinkage of the obtained nanoparticles 3 was about 420 ° C. Table 1 shows the 5% heat shrink start temperature.

[Examples 4 to 6]
The raw materials of nickel acetate tetrahydrate, iron (II) acetate and oleylamine were charged at the ratio (mass%) shown in Table 1, and prepared under the same conditions as in Example 1 to obtain nanoparticles 4-6. It was. Table 1 shows the average particle diameter, CV value, shape, and 5% heat shrinkage start temperature of each nanoparticle.

[Example 7]
Under a nitrogen atmosphere, 42.90 g of nickel acetate tetrahydrate and 490.0 g of oleylamine were mixed and then heated at 140 ° C. for 20 minutes with stirring to obtain a blue reaction solution 7a.

  Further, 8.94 g of iron (II) acetate and 20.0 g of oleylamine were mixed in a nitrogen atmosphere, and then heated at 140 ° C. for 20 minutes with stirring to obtain a brown reaction solution 7b.

  Mixing the reaction liquids 7a and 7b obtained as described above, adding 0.14 g of silver nitrate while stirring, and then heating at 250 ° C. for 5 minutes by irradiation with microwaves in a nitrogen atmosphere Thus, a nanoparticle slurry 7 was obtained.

  In the same manner as in Example 1, spherical uniform nanoparticles 7 having an average particle diameter of 65 nm (Cv value: 0.32) were obtained. The onset temperature at 5% thermal shrinkage of the obtained nanoparticles 7 was about 415 ° C. The results are shown in Table 1.

[Example 8]
After mixing 42.90 g of nickel acetate tetrahydrate, 8.94 g of iron (II) acetate and 390.00 g of oleylamine previously heated and dissolved in a 40 ° C. hot water bath under a nitrogen atmosphere. The blue reaction liquid 8 was obtained by heating at 140 ° C. for 20 minutes with stirring.

  Next, 0.14 g of silver nitrate and 300 g of tetraethylene glycol as a solvent were added to the reaction solution 8, and then the mixture was heated at 250 ° C. for 5 minutes in a nitrogen atmosphere to obtain a nanoparticle slurry 8. It was.

  The obtained nanoparticle slurry 8 was allowed to stand and separated, and the supernatant liquid was removed, followed by washing three times with a mixed solvent having a volume ratio of methanol and toluene of 1: 4, and then vacuum drying maintained at 70 ° C. The resultant was dried with a machine for 6 hours to obtain nanoparticles (metal composite nickel nanoparticles) 8. The nanoparticles 8 were a group of spherical uniform particles having an average particle diameter of 65 nm (Cv value; 0.31). The results are shown in Table 1.

[Comparative Example 1]
Example 1 except that instead of 42.90 g nickel acetate tetrahydrate in Example 1, 60.00 g nickel acetate tetrahydrate was used and no iron (II) acetate was used. In the same manner as in Example 1, spherical uniform metallic nickel nanoparticles having an average particle diameter of 100 nm (Cv value: 0.17) were obtained. A scanning electron microscope (SEM) photograph of the obtained metallic nickel nanoparticles is shown in FIG. Moreover, the starting temperature in 5% heat shrink of the obtained metal nickel nanoparticles was about 295 ° C. The behavior of this thermal expansion and contraction is shown in FIG.

[Reference Example 1]
In Example 1, instead of being irradiated with microwaves and heated at 250 ° C. for 5 minutes, a mantle heater was used to heat to 250 ° C. at a temperature rising rate of 5.0 ° C./second and held at 250 ° C. for 5 minutes. Except that, spherical nanoparticles having an average particle diameter of 60 nm (Cv value: 0.55) were obtained in the same manner as in Example 1. The starting temperature of the resulting nanoparticles at 5% thermal shrinkage was about 370 ° C.

The above results are summarized in Table 1. In Table 1, “pseudosphere” in Example 6 means a sphere like confetti having projections on the surface. “Fe / (Ni + Fe)” represents the mass ratio (%) of the iron element of the iron salt to the total mass part of the nickel element of the nickel carboxylate and the iron element of the iron salt at the time of charging, and “Ag / (Ni + Fe) ")" Indicates the mass ratio (%) of silver element of silver nitrate to the total mass part of nickel element of nickel carboxylate and iron element of iron salt at the time of preparation. Furthermore, the “strength ratio between Fe ₃ O ₄ and Ni” is the value obtained when the peak intensity at the diffraction angle (2θ) = 44.50 ° of nickel of the metal composite nanoparticles observed using XRD is 100. _It means the maximum peak (2θ = 35.42 °) intensity of ₃ O ₄ .

  From the results of Examples 1 to 7, it can be seen that the higher the Fe / (Ni + Fe) in the charged amount, the higher the 5% heat shrink start temperature. Moreover, from the results of Example 1 and Examples 3 to 8, it can be seen that uniform nanoparticles having a small average particle diameter can be obtained by adding silver nitrate. On the other hand, the starting temperature at 5% thermal shrinkage of the metallic nickel nanoparticles obtained in Comparative Example 1 was about 125 ° C. lower than that of the nanoparticles of Example 1. Further, in Reference Example 1, although a strong reducing agent was not used, microwave irradiation was not used as a heating means in the reduction process, and thus the Cv value exceeded 0.5.

Claims (6)

A complexing reaction liquid production step of heating a mixture of nickel carboxylate, iron salt and primary amine to a temperature in the range of 100 ° C. to 165 ° C. to obtain a complexing reaction liquid;
A nanoparticle slurry generating step of heating the complexing reaction liquid to a temperature of 170 ° C. or higher by microwave irradiation to obtain a slurry of metal composite nickel nanoparticles containing iron oxide;
Bei to give a,
In the metal composite nickel nanoparticles containing iron oxide, the total amount of nickel element, iron element and oxygen element is 95 parts by mass or more with respect to 100 parts by mass of metal composite nickel nanoparticles, and the amount of iron element is nickel element A method for producing metal composite nickel nanoparticles containing iron oxide , which is in the range of 5 to 50 parts by mass with respect to 100 parts by mass of the total amount of iron elements and having an average particle size in the range of 30 to 150 nm. In the reaction liquid generating step, instead of the mixture, the mixture of the nickel carboxylate and the primary amine and the mixture of the iron salt and the primary amine are each separately brought to a temperature in the range of 100 ° C to 165 ° C. The method for producing metal composite nickel nanoparticles containing iron oxide according to claim 1, wherein the reaction liquids obtained by heating are mixed.   The manufacturing method of the metal composite nickel nanoparticle containing the iron oxide of Claim 1 or 2 which performs the said reaction liquid production | generation process in organic solvent presence.   The method for producing metal composite nickel nanoparticles containing iron oxide according to claim 1 or 2, wherein the iron salt is iron (II) carboxylate or iron (III) carboxylate.   The metal salt addition step of adding one or more metal salts selected from a metal salt group consisting of a palladium salt, a silver salt, a platinum salt and a gold salt before the nanoparticle slurry generation step at the latest. Or the manufacturing method of the metal composite nickel nanoparticle containing the iron oxide of 2. Metal composite nickel nanoparticles containing iron oxide, wherein the total amount of nickel element, iron element and oxygen element is 95 parts by mass or more with respect to 100 parts by mass of metal composite nickel nanoparticles, and the amount of iron element is nickel It is in the range of 5 to 50 parts by mass with respect to 100 parts by mass of the total amount of element and iron element, the average particle size is in the range of 30 nm to 150 nm, and the iron oxide is mainly composed of triiron tetroxide. Metal composite nickel nanoparticles containing iron oxide, characterized in that.