JP2010150654A - Composite particle, and method for producing composite particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite particle having sufficient dispersibility in a dispersion medium, and to provide a method for producing the same. <P>SOLUTION: The composite particle is composed of a metal particle and a covering layer formed on at least a part of the surface of the metal particle and comprising the basic carbonate of a metal, and simultaneously satisfies the conditions in inequality; 0.5≤(ρ/ρ<SB>0</SB>) and inequality; (S/S<SB>0</SB>)≤1.2; wherein ρ denotes the measured value of bulk density of the composite particle based on a measurement method prescribed in JIS-R-1628; ρ<SB>0</SB>denotes true density of the composite particle based on a dry density measurement method according to a constant volume expansion method; S denotes the measured value of the specific surface area of the composite particle based on a BET single point method; and S<SB>0</SB>denotes the theoretical calculation value of the specific surface area of the composite particle calculated on the basis of the arithmetic means particle size of the composite particle calculated on the basis of the SEM (Scanning Electron Microscope) image of the composite particle and the true density of the composite particle. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to composite particles having at least one of magnetic and conductive properties and a method for producing the composite particles. More specifically, the present invention relates to composite particles used for imparting at least one of magnetic and conductive properties to materials used for electronic components, for example, and a method for producing the composite particles.

  Conventionally, composite particles having at least one of magnetic and conductive properties have been used, for example, for the purpose of imparting conductivity and magnetism to materials used in electronic components mounted on electrical and electronic equipment. . As this composite particle, there is known a particle in which a coating layer containing an inorganic compound is formed on at least a part of the surface of a metal particle having at least one of magnetic and conductive properties.

  Examples of the material imparted with at least one of magnetic property and electrical conductivity by containing such composite particles (hereinafter referred to as “composite particle-containing material”) include, for example, using a composite particle to conduct a polymer material. Conductive films and the like have been developed. The application range of the composite particles has been expanded to electrical and electronic devices used in a wide range of fields such as biomedical and life science, which are expected to expand in the future.

  In recent years, the electrical and electronic devices described above are increasingly required to be smaller and have higher capacity. As a result, the composite particles used in these electronic component materials are also of sub-micron size or even nano size, and the particle shape and particle size distribution are within a desired range to some extent. Things that are well-organized are now being demanded.

  In general, the composite particles are a dispersion treatment step of obtaining a liquid, slurry, or paste in which metal particles as a main component are dispersed in a dispersion medium, and an inorganic compound is added to the liquid, slurry, or paste obtained in this step. It is manufactured through a coating layer forming step of adding and forming a coating layer.

  However, metal particles having a particle size of sub-micron size or less, and further, metal particles having a nano size have a large surface area and high surface activity, so that aggregation easily occurs in the dispersion treatment step. A large shearing force is required to solve the aggregated state of the aggregated particles once aggregated. Further, even if the aggregated state of the aggregated particles is solved, reaggregation tends to occur. In particular, metal particles having magnetism are more likely to be aggregated because of their magnetic cohesion.

  In general, composite particles in which a coating layer is formed on aggregated particles in which metal particles are aggregated are generally difficult to bond the coating layer to the metal particles with sufficient strength. Therefore, the coating layer may be peeled off from the surface of the metal particles by a coating layer forming step, heat treatment when manufacturing a composite particle-containing material using the composite particles, or the like. On the other hand, while maintaining the characteristics required for the metal particles (at least one of magnetic and conductive characteristics), studies have been made to modify the surface of the metal particles to prevent the aggregation of the metal particles. (Patent Documents 1 and 2 below).

  For example, Patent Document 1 intends to reduce aggregated particles in which metal particles (Ni powder) that induce peeling of the coating layer (coating layer) are aggregated (see paragraph [0014] of Patent Document 1). A coating layer (coating layer) is formed by depositing (coating) an inorganic compound of a metal other than Ni on the surface of a powder (metal particles) obtained by co-precipitation of a metal containing Ni as a main component and a metal compound other than nickel. Ni powder (composite particles) is proposed.

Further, for example, Patent Document 2 examines the component composition of a conductive paste containing composite particles used to contain composite particles in the material of an internal conductor film (conductive film) mounted on an electronic component. Prevents the occurrence of structural defects (delamination and cracks) by preventing the coating layer (coating layer) from falling off (peeling) from the composite particles during the heat treatment when manufacturing the internal conductor film using paste. Proposals intended to be made. More specifically, a conductive paste in which BaTiO ₃ is added to Ni powder (composite particles) in which the surface of Ni particles (metal particles) is coated (coated) with SiO ₂ has been proposed.
JP 2003-129106 A JP 2003-317542 A

  However, even with the above-described prior art, sufficient bonding between the metal particles of the composite particles and the coating layer cannot be ensured, and when the coating layer forming step or the composite particle-containing material is produced, The present inventors have found that peeling of the coating layer from the surface of the metal particles cannot be sufficiently prevented by heat treatment or the like. For this reason, there is still room for improvement from the viewpoint of obtaining composite particles having sufficient dispersibility in the dispersion medium, and thus sufficient dispersibility in the composite particle-containing material.

  Therefore, the present invention has been made in view of the above-described problems of the prior art, and provides composite particles having sufficient dispersibility in a dispersion medium, and thus sufficient dispersibility in a composite particle-containing material. Objective. Moreover, this invention aims at providing the manufacturing method of the composite particle which can obtain the composite particle of the above-mentioned this invention more reliably.

  As a result of intensive studies to achieve the above object, the present inventors have ensured sufficient dispersibility in the dispersion medium by sufficiently securing the bondability between the metal particles of the composite particles and the coating layer. Has found that it is extremely effective in achieving the above object to make the composite particles satisfy the conditions represented by the following formulas (1) and (2), and the present invention has been achieved.

That is, the present invention
Metal particles,
A coating layer that is formed on at least a part of the surface of the metal particles and contains a basic carbonate of metal (hereinafter also referred to as “metal for coating layer”);
Contains
It has a configuration that simultaneously satisfies the conditions of the following formula (1) and formula (2).
Provide composite particles.
0.5 ≦ (ρ / ρ ₀ ) (1)
(S / S ₀ ) ≦ 1.2 (2)
[In Formula (1),
ρ is a measurement value of the bulk density of the composite particles based on the measurement method defined in JIS-R-1628,
ρ ₀ is a measured value of the true density of the composite particles based on a dry density measurement method by a constant volume expansion method,
Respectively,
In formula (2),
S is a measured value of the specific surface area of the composite particle based on the BET 1-point method,
S ₀ is a theoretical calculated value of the specific surface area of the composite particle calculated based on the arithmetic average particle diameter of the composite particle calculated based on the SEM image of the composite particle and the true density of the composite particle;
Respectively. ]

Since the composite particles of the present invention have a configuration that simultaneously satisfies the conditions represented by the formulas (1) and (2), the bondability between the metal particles and the coating layer can be sufficiently ensured.
And the composite particle of this invention will have sufficient dispersibility in a dispersion medium and by extension sufficient dispersibility in a composite particle containing material.

Here, in the present invention, when (ρ / ρ ₀ ) represented by formula (1) is 0.5 or more, good dispersibility of the composite particles is obtained in the dispersion medium, and when it is less than 0.5, the dispersion is performed. The present inventors have found that the dispersibility of the composite particles is lowered in the medium, the aggregation of the composite particles is likely to proceed, and the fusion of the aggregated composite particles proceeds by the heat treatment in producing the composite particle-containing material. This is confirmed by observation of an SEM image.

On the other hand, the value of (ρ / ρ ₀ ) shown in equation (1) is preferably as large as possible, but the theoretical upper limit is 1.0. In addition, the maximum filling rate of true spheres with the same particle size is theoretically 0.74, but the actual particles have a distribution in particle size and are not perfect spheres but an irregular shape. Since particles of the same material have the same surface potential, the repulsive force increases as the particles approach each other. For this reason, it is not easy to obtain the theoretical maximum filling rate. The value is about .5.

In order to further increase the value of (ρ / ρ ₀ ), for example, the optimum particle size distribution is selected based on the concept of filling small particles into gaps between large particles and filling smaller particles into the gaps. To do. Such selection of the particle size distribution is generally performed by mixing particles having a particle size distribution peak in about two or three different sizes. If the optimum particle size distribution is selected in this way, the theoretical maximum filling rate can be 0.74 or higher, and the upper limit value of (ρ / ρ ₀ ) is 1.0.

However, widening the particle size distribution may cause other disadvantages. For example, when a conductive film containing composite particles is used to form a coating film and heat treatment to produce a conductor film, fusion between particles starts at a lower temperature for smaller particles than for larger particles. To do. For this reason, fusion between particles occurs over a wide temperature range during heat treatment, and the heat treatment conditions to be determined become complicated, or there is a difference in physical properties between the part fused first and the part to be fused from now on. For this reason, structural defects or the like may occur. Therefore, although the value of (ρ / ρ ₀ ) is 1.0 or less, the upper limit value of (ρ / ρ ₀ ) is more preferably 0.74 in order to prevent the above disadvantages.

Furthermore, in the present invention, when (S / S ₀ ) represented by formula (2) is 1.2 or less, good dispersibility of the composite particles can be obtained in the dispersion medium. The present inventors have found that the dispersibility of the composite particles is reduced and the aggregation of the composite particles is likely to proceed, and that the present inventors have developed a light scattering type particle size distribution meter (“LB” manufactured by Horiba, Ltd.). -550 ").

On the other hand, the value of (S / S ₀ ) shown in equation (2) is preferably as small as possible, but the theoretical lower limit is 1.0. Therefore, from the viewpoint of more reliably obtaining the effects of the present invention, (S / S ₀ ) is more preferably 1.0 to 1.1.

  As described above, in the present invention, ρ represents a measurement value of the bulk density of the composite particles based on the measurement method defined in JIS-R-1628. Specifically, for example, the measurement can be performed manually using a tapping method.

  The “bulk density” refers to a density when a measurement container having a certain volume is filled with composite particles and the inner volume is defined as the volume. This volume includes the following five types of volumes. That is, (I) the volume of the composite particle itself, (II) the volume of the closed pores in the composite particle, (III) the volume of the space on the surface of the composite particle, (IV) the gap between the composite particle and the composite particle (V) is the volume of the gap between the composite particle and the measurement container.

In the present invention, ρ ₀ represents a measured value of the true density of the composite particles based on a dry density measuring method by a constant volume expansion method. More preferably, in the present invention, ρ ₀ represents a measured value of the true density of the composite particles measured with a dry automatic densimeter “Acpic 1330” manufactured by Shimadzu Corporation.

  The “true density” indicates a density in which only the volume occupied by the composite particle itself is a volume for density calculation. However, if there is a space (closed pore) that is not connected to the outside inside the composite particle (metal particle or coating layer), the gas used for measurement cannot reach the internal space, so the measurement result is so-called It may correspond to “apparent density”. Therefore, the “true density” used in the present invention includes a case corresponding to an “apparent density”.

  Further, in the present invention, S indicates a measured value of the specific surface area of the composite particle based on the BET one-point method. More preferably, in the present invention, S represents a measured value of the specific surface area of the composite particle based on the BET single point method measured by “Macsorb HM model-1201” manufactured by Mountec Co., Ltd.

S ₀ represents the theoretical calculated value of the specific surface area of the composite particle calculated based on the arithmetic average particle diameter of the composite particle calculated based on the SEM image of the composite particle and the true density of the composite particle. In the present invention, the “arithmetic mean particle diameter of composite particles calculated based on SEM image” is more preferably a composite photographed using “scanning electron microscope S-4800” manufactured by Hitachi, Ltd. The particle diameter of 100 composite particles was measured from the SEM image of the particles, and an arithmetic average value was calculated (hereinafter referred to by using the symbol “d”). If the unit of S ₀ is m ² · g ⁻¹ , the unit of d is nm and the unit of ρ ₀ is g · cm ⁻³ , S ₀ can be expressed by the following formula (4).
S ₀ = 6000 · (ρ ₀ · d) ⁻¹ (4)

Moreover, it is preferable that the composite particle of this invention has the structure which satisfy | fills the conditions of following formula (3) further simultaneously in addition to said Formula (1) and said Formula (2).
0.15 ≦ W ≦ 0.35 (3)
[Wherein, W is the half-width of three diffraction peaks with the peak intensity of 1st to 3rd among diffraction peaks obtained by powder X-ray diffraction spectrum measurement using CuKα characteristic X-rays. The arithmetic mean value of is shown. The unit is deg. ]

  Here, in the present invention, when W shown in the formula (3) is 0.35 or less, there is less disorder of the crystal lattice on the surface of the metal particles, and the coating layer is formed without impairing the original properties of the metal particles. It is preferable. On the other hand, if W shown in Formula (3) is not less than 0.15, it is preferable that the particles are not enlarged due to aggregation or bonding of metal particles. From the viewpoint of obtaining the effects of the present invention more reliably, W is more preferably 0.2 to 0.3.

  In the present invention, the diffraction peak obtained by powder X-ray diffraction spectrum measurement using CuKα characteristic X-rays is preferably measured using a powder X-ray diffraction spectrum measurement device “ULTIMA-III” manufactured by Rigaku Corporation. The peaks measured under the following conditions are shown. That is, X-ray tube (Cu, tube voltage: 40 kV, tube current: 40 mA), measurement conditions (measurement angle range of Bragg angle 2θ / degree: 10-90 degrees, sampling width: 0.01 degrees, scan speed: 4 Degree / minute, divergent slit: 1/2 degree, divergent longitudinal slit: 10 mm, scattering slit: 1/2 degree, light receiving slit: 0.3 m).

  Furthermore, in the composite particle of the present invention, the basic carbonate is preferably a rare earth metal basic carbonate. In such composite particles, the rare earth metal basic carbonate is chemically stable compared to other metal basic carbonates, and is difficult to form a composite compound with the metal particles. It is effective from the viewpoint that it can be coated without damaging. The basic carbonate is more preferably yttrium basic carbonate. Such composite particles are effective from the viewpoint that yttrium is a relatively large amount of rare earth metal and is inexpensive.

  Furthermore, in the composite particles of the present invention, it is preferable that the metal particles contain at least one element selected from the group consisting of Fe, Ni, Cu, Ag, and Au as a constituent element. Such composite particles are effective from the viewpoint of more reliably having at least one of magnetic and conductive properties in the composite particle-containing material. In the composite particles of the present invention, various elements can be selected depending on the application. Fe or Ni is preferable for imparting magnetism, Ni, Cu, Ag or Au is desirable for imparting conductivity, and Ag or Au is particularly desirable when rust is a problem.

  In the composite particle of the present invention, the metal particle preferably contains Ni as a constituent element. Such composite particles are effective from the viewpoint of reliably imparting both magnetism and conductivity to the composite particle-containing material because Ni has both magnetic properties and electrical conductivity.

  Furthermore, in the composite particles of the present invention, the metal particles preferably contain Ag as a constituent element. Since such composite particles have high Ag conductivity, they are effective from the viewpoint of more reliably imparting conductivity to the composite particle-containing material. Further, Ag has an advantage that it is less expensive than Au.

The present invention also provides:
A method for producing composite particles comprising metal particles and a coating layer formed on at least a part of the surface of the metal particles,
A suspension preparation step of preparing a suspension containing metal particles, a chemical species containing a metal (metal for coating layer) that is a material of the coating layer, and a chemical species containing carbonate ions;
A coating in which an alkaline aqueous solution in which a base is dissolved in water is added to the suspension obtained in the suspension preparation step to form a coating layer containing the basic carbonate of the metal on the surface of the metal particles. A layer forming step;
Contains
In the suspension preparation step, the amount of the chemical species including the metal in the suspension obtained after the suspension preparation step is the oxidation of the metal with respect to the metal particles in the suspension. The amount of the chemical species containing the metal is adjusted in advance so that the converted value is 0.001 to 10% by mass, and
By performing at least the coating layer forming step in an inert gas atmosphere,
Preparing composite particles having a configuration that simultaneously satisfies the conditions of the following formulas (1) and (2):
A method for producing composite particles is provided.
0.5 ≦ (ρ / ρ ₀ ) (1)
(S / S ₀ ) ≦ 1.2 (2)
[In Formula (1),
ρ is a measurement value of the bulk density of the composite particles based on the measurement method defined in JIS-R-1628,
ρ ₀ is a measurement of the true density of the composite particle,
Respectively,
In formula (2),
S is a measured value of the specific surface area of the composite particle based on the BET 1-point method,
S ₀ is a theoretical calculated value of the specific surface area of the composite particle calculated based on the arithmetic average particle diameter of the composite particle calculated based on the SEM image of the composite particle and the true density of the composite particle,
Respectively. ]

  As a result of intensive studies, the inventors have adjusted the addition amount of the chemical species including the metal in the suspension preparation step to the above range, and at least the coating layer forming step in an inert gas atmosphere. It has been found that what is performed below is extremely effective for obtaining the above-described composite particles of the present invention more reliably.

  Here, in the present invention, “the amount of the chemical species including the metal in the suspension obtained after the suspension preparation step is 0. 0 in terms of the oxide of the metal relative to the metal particles in the suspension. 001 to 10% by mass ”will be explained. In other words, the “metal oxide (metal oxide) equivalent value” means that the mass of a chemical species containing the metal is an oxide (metal oxide) containing a metal having the same chemical equivalent as the metal contained in the chemical species. The mass of the obtained metal oxide is expressed as a ratio to the mass of the metal particles.

For example, when the metal particles are nickel particles and the metal is yttrium, the mass of the chemical species that becomes a source of yttrium such as yttrium nitrate used in the manufacture of the composite particles of Example 1 to be described later is calculated as follows. The value obtained by converting the mass of yttrium oxide (Y ₂ O ₃ ) containing yttrium oxide having the same chemical equivalent as the yttrium contained in the yttrium, and expressing the mass of the obtained yttrium oxide (Y ₂ O ₃ ) as a ratio to the mass of the nickel particles. It is.

  As described above, in the suspension preparation step, the amount of chemical species including the metal in the suspension obtained after the suspension preparation step is calculated in advance so that the amount falls within the above range, and then the chemical including the metal is included. A suspension is prepared by determining the amount of seed added.

  By setting the amount of the chemical species including the metal within the above range, the composite particles of the present invention described above can be obtained more reliably. In addition, by setting the amount of the chemical species including the metal within the above-mentioned range, even the porous coating layer has a relatively thin thickness, and the influence of the increase in specific surface area due to the porous structure is sufficiently increased. A coating layer can be firmly formed on the surface of the metal particles in a suppressed state. Therefore, the composite particles obtained by the method for producing composite particles of the present invention can ensure sufficient dispersibility even with a small amount of dispersion medium, and can reduce the load on the dispersion treatment.

  When the amount of the chemical species including the metal for the coating layer is 0.001% by mass or more in terms of oxide of the metal with respect to the metal particles, the effect of preventing aggregation by covering the composite particles can be reliably obtained, If it is less than 0.001% by mass, the amount of coating is small, and the effect of preventing aggregation of the composite particles cannot be obtained with certainty. On the other hand, when the amount of the chemical species including the metal for the coating layer is 10% by mass or less in terms of oxide of the metal with respect to the metal particles, the characteristics of the metal particles (at least one of the characteristics of magnetism and conductivity) ) Is surely imparted to the composite particles, but if it exceeds 10% by mass, the mass fraction of the coating layer relative to the metal particles becomes too large, and the characteristics of the metal particles (at least one of the characteristics of magnetism and conductivity) May not be reliably applied to the composite particles. Furthermore, from the viewpoint of obtaining the effect of the present invention more reliably, the amount of the above-mentioned chemical species including the metal is 0.05 to 1 mass in terms of oxide of the metal with respect to the metal particles in the suspension. % Is more preferable.

  Here, in the present invention, “inert gas” refers to a rare gas and a nitrogen gas. In the present invention, the “inert gas atmosphere” means an atmosphere in which the concentration of oxygen in the inert gas atmosphere is such that the oxidation state of the surface of the metal particles does not proceed (substantially does not contain oxygen). Atmosphere). The concentration of oxygen in the inert gas atmosphere is preferably 0.1% by volume or less, and more preferably 0.01% by volume or less. That is, the concentration of the inert gas is preferably 99.9% by volume or more, and more preferably 99.99% by volume or more.

  In addition, this “inert gas atmosphere” is performed using “inert gas atmosphere forming means” such as a dry room or a glove box, or a solution or suspension in a separable flask or the like. This can be achieved by bubbling with an inert gas for a long time to remove dissolved oxygen. The “inert gas” may contain about 1 to 3% by volume of hydrogen gas. Since hydrogen gas has reducibility, oxidation can be suppressed when a metal, particularly a metal that is easily oxidized, such as Ni, Fe, or Cu, is preferably used.

  Furthermore, according to the method for producing composite particles of the present invention, since at least the coating layer forming step is performed in an inert gas atmosphere, the characteristics of the metal particles (at least one of magnetism and conductivity) are not impaired. Composite particles can be produced. The detailed mechanism for obtaining such an effect has not been clearly elucidated.

  However, the present inventors perform at least the coating layer forming step in an inert gas atmosphere, so that the surface of the metal particles is immersed in a solution for forming the coating layer (a solution from which dissolved oxygen is sufficiently removed). However, it is presumed that the crystallinity change of the surface of the metal particles is prevented, and the characteristics of the metal particles (at least one of the characteristics of magnetism and conductivity) can be maintained. In addition, when the present inventors have conventionally formed a coating layer on a metal particle in a liquid, the surface of the metal particle is immersed in a liquid (a liquid containing dissolved oxygen), so that the crystallinity of the surface of the metal particle is reduced. It is presumed that the characteristics of the metal particles (at least one of the magnetic properties and the electrical conductivity) may be impaired.

  Moreover, from the viewpoint of obtaining the effect of the present invention more reliably, in the method for producing composite particles of the present invention, it is preferable to perform all the steps in an inert gas atmosphere.

  Furthermore, the method for producing composite particles of the present invention further includes an alkali treatment step in which the metal particles are heat-treated using an alkali solution containing a base in a dispersion medium before the suspension preparation step. It is preferable that In addition, it is preferable to perform this alkali treatment process also in inert gas atmosphere from a viewpoint of acquiring the effect of this invention more reliably.

  As described above, the present inventors have found that the bonding strength of the coating layer to the surface of the metal particles can be improved by heat-treating the metal particles using an alkali solution before the suspension preparation step. The detailed mechanism about the ability to improve the bond strength of the coating layer to the surface of the metal particles has not been clearly elucidated. The present inventors measured the powder X-ray diffraction spectrum using the CuKα characteristic X-ray described above that when the metal particles were heat-treated with an alkali solution, the hydroxyl groups were bonded to the surfaces of the metal particles. It is confirmed by. Therefore, the present inventors believe that the hydroxyl group bonded to the surface of the metal particle contributes to improving the bond between the coating layer formed on the surface of the metal particle and the surface of the metal particle in the coating layer forming step. I guess.

  ADVANTAGE OF THE INVENTION According to this invention, the composite particle which has sufficient dispersibility in a dispersion medium (or solvent), and hence sufficient dispersibility in a composite particle containing material can be provided. Further, according to the present invention, a method for producing composite particles that can more reliably obtain the composite particles of the present invention having sufficient dispersibility in the dispersion medium, and thus sufficient dispersibility in the composite particle-containing material. Can be provided.

  Hereinafter, a preferred embodiment of a composite particle of the present invention and a preferred embodiment of a method for producing a composite particle of the present invention will be described in detail with reference to the drawings. In the following description, duplicate description is omitted.

[Composite particles]
First, a preferred embodiment of the composite particle of the present invention will be described. The composite particles of the present embodiment have a configuration mainly including metal particles and a coating layer formed on at least a part of the surface of the metal particles and containing a basic carbonate of yttrium. And the composite particle of this embodiment has the structure which satisfy | fills the conditions of following formula (1) and following formula (2) mentioned previously further further.
0.5 ≦ (ρ / ρ ₀ ) (1)
(S / S ₀ ) ≦ 1.2 (2)

Here, in the formula (1), ρ is a measurement value of the bulk density of the composite particle based on the measurement method specified in JIS-R-1628, and ρ ₀ is the composite particle based on the dry density measurement method by the constant volume expansion method. Measured values of true density of each are shown. In the formula (2), S is a measured value of the specific surface area of the composite particle based on the BET 1-point method, S ₀ is an arithmetic average particle diameter of the composite particle calculated based on an SEM image of the composite particle, The theoretical calculated value of the specific surface area of the composite particle calculated based on the true density of the composite particle is shown.

  Since the composite particle of this embodiment has the structure which satisfy | fills the conditions represented by Formula (1) and Formula (2) simultaneously, it can fully ensure the bondability of a metal particle and a coating layer. Therefore, the composite particles of the present embodiment have sufficient dispersibility in the dispersion medium, and consequently sufficient dispersibility in the composite particle-containing material. Examples of the dispersion medium include water, organic substances such as an organic dispersion medium, a polymer (polymer), and a binder.

  Here, in the case of the conventional composite particles, if the coating layer is porous, a large amount of solvent and resin are required because the specific surface area is large. In the case of conventional composite particles, if the coating layer is porous, the bulk density of the composite particles will be smaller than the bulk density of the metal particles before coating, and the amount that can be dispersed in the dispersion medium will be relatively small. It was. For this reason, a large amount of dispersion medium is required to disperse in a large amount in the dispersion medium.

  On the other hand, the composite particles of the present embodiment have a configuration that satisfies the conditions represented by the formulas (1) and (2) at the same time, so that even the porous coating layer has a relatively small thickness. In addition, it is possible to adopt a configuration in which the coating layer can be firmly formed on the surface of the metal particles in a state where the influence of the increase in specific surface area due to the porous structure is sufficiently suppressed. Therefore, the composite particles of the present embodiment are excellent in the balance between the specific surface area and the density, and it is possible to ensure sufficient dispersibility even with a small amount of dispersion medium as compared with the conventional composite particles.

  For example, the present inventors have compared the particle size distribution of conventional composite particles by observation using a light scattering particle size distribution meter (light scattering particle size distribution meter “LB-550” manufactured by Horiba, Ltd.). The particle size distribution of the composite particles of the present embodiment (more specifically, composite particles of Examples 1 to 3 described later) is a plurality of types of dispersion media (water or ethanol). It has been confirmed that the particle size distribution of the primary particles is closer. In addition, the present inventors have observed this using a light scattering particle size distribution meter (light scattering particle size distribution meter “LB-550” manufactured by Horiba, Ltd.), compared with conventional composite particles. It was confirmed that the composite particles of the embodiment (specifically, composite particles of Examples 1 to 3 to be described later) are well dispersed in a polymer (EC vehicle (ethylcellulose polymer) manufactured by Nisshin Kasei Co., Ltd.). is doing.

Furthermore, the composite particle of this embodiment has a configuration that further satisfies the condition of the following formula (3) described above in addition to the formulas (1) and (2).
0.15 ≦ W ≦ 0.35 (3)
Here, in Formula (3), W is a diffraction peak obtained by powder X-ray diffraction spectrum measurement using CuKα characteristic X-rays. The arithmetic mean value of a half value width is shown, and a unit is deg.

[Metal particles]
Next, the metal particle which comprises the composite particle of this embodiment is demonstrated. This metal particle is a group consisting of Fe, Ni, Cu, Ag, and Au from the viewpoint of more reliably obtaining a composite particle having at least one of magnetic and electrical conductivity in the composite particle-containing material. It is preferable that at least one element selected from the above is included as a constituent element. These elements can be selected depending on the use of the composite particles of the present invention, Fe or Ni when imparting magnetism, Ni, Cu, Ag or Au when imparting conductivity, In particular, Ag or Au is preferable when rust becomes a problem.

  In addition, since Ni has both magnetism and conductivity, it is preferable that the metal particles contain Ni as a constituent element from the viewpoint of reliably imparting both magnetism and conductivity to the composite particle-containing material. Further, since Ag has high conductivity, it is preferable that the metal particles contain Ag as a constituent element from the viewpoint of more reliably imparting conductivity to the composite particle-containing material.

  In addition, as another element of said metal element, Co and Pt are mentioned preferably. The metal particles may be metal particles made of FePt alloy (metal compound), or may be metal particles made of CoPt alloy (metal compound). Pt is preferable from the viewpoint of conductivity and resistance to rust. Further, CoPt is preferable from the viewpoint of having magnetism and being difficult to rust. ),

  The arithmetic average particle diameter of the metal particles (the value calculated by the same method as the arithmetic average particle diameter calculated based on the SEM image of the composite particles described above) is said to obtain the effect of the present invention more reliably. From the viewpoint, it is preferably 10 nm to 1 μm, more preferably 30 nm to 500 nm, and further preferably 50 nm to 200 nm.

  In addition, when the metal particle which comprises the composite particle of this embodiment contains Ni as a structural element of a main component, the diffraction peak at the time of taking out the conditions of Formula (3) mentioned above is (111). ), (200), and (220) planes. Such composite particles have sufficient crystallinity, and are effective from the viewpoint of more reliably imparting at least one of magnetic and conductive properties to the composite particle-containing material.

[Coating layer]
Next, the coating layer formed on at least a part of the surface of the metal particles will be described.
The coating layer in this embodiment is a layer containing yttrium basic carbonate. Even when the coating layer has a porous structure, the coating layer is placed on the surface of the metal particle while sufficiently suppressing the influence of an increase in specific surface area by reducing the thickness and making it porous. From the viewpoint of forming firmly, the coating layer preferably contains yttrium basic carbonate as a main component, and the coating layer is more preferably made of yttrium basic carbonate. As a result, the composite particles of the present embodiment have sufficient dispersibility even with a small amount of dispersion medium compared to conventional composite particles, while maintaining at least one of the characteristics of magnetism and conductivity more reliably. Can be secured.

The yttrium basic carbonate preferably has a chemical composition represented by the following formula (5) and the following formula (6).
Y (OH) CO ₃ · nH ₂ O (5)
0.5 ≦ n ≦ 3 (6)

[Production method of composite particles]
Next, an embodiment of the method for producing composite particles of the present invention will be described.
The method for producing composite particles of the present embodiment mainly includes an alkali treatment step, a suspension preparation step, and a coating layer forming step. More specifically, the method for producing composite particles of the present embodiment includes (a) an alkali treatment step, (b) a suspension preparation step, (c) a dissolved oxygen purge step, and (d) a coating layer forming step. (E) a composite particle extraction step.

  In the method for producing composite particles of the present embodiment, the amount of chemical species including yttrium in the suspension preparation step is adjusted to the above-described range, and at least the coating layer forming step is performed in an inert gas atmosphere. Performed below. Thereby, it becomes possible to more reliably obtain the composite particles of the first embodiment that simultaneously satisfy the conditions of the expressions (1) and (2) described above in the method for manufacturing composite particles of the present embodiment. Hereinafter, each process of the manufacturing method of the composite particle of this embodiment is demonstrated.

(A) Alkali treatment step The alkali treatment step is a step of heat-treating the metal particles using an alkali solution containing a base in a dispersion medium. The heat treatment conditions can be appropriately selected by those skilled in the art so as to obtain the effects of the present invention. The heat treatment temperature is, for example, 90 to 90 from the viewpoint of more reliably forming a hydroxyl group on the surface of the metal particles. It is preferable that it is 110 degreeC. The heat treatment time is preferably 12 to 36 hours, for example.

  The base used in this step is not particularly limited as long as it can bond a hydroxyl group to the surface of the metal particles by heat treatment. Examples thereof include sodium hydroxide, potassium hydroxide, and ammonia. Further, a compound that generates ammonia by hydrolysis and raises the pH of the liquid, such as thorium carbonate, potassium carbonate, and urea.

  The dispersion medium used in this step is not particularly limited as long as it can cause a base to act on the surface of the metal particles in the heat treatment and can bond a hydroxyl group to the surface of the metal particles. Further, it may be one that can chemically react with a base in heat treatment to bond a hydroxyl group to the surface of the metal particles. For example, water or a mixed dispersion medium of water and alcohol such as ethanol or methanol, or a mixed dispersion medium of water and a dispersion medium having a hydroxyl group such as ethylene glycol or glycerin and miscible with water can be used.

  By this step, it can be confirmed by powder X-ray diffraction spectrum measurement using CuKα characteristic X-rays that the hydroxyl group is bonded to the surface of the metal fine particles as described above. The present inventors believe that the hydroxyl group bonded to the surface of the metal particle contributes to improving the bond between the surface of the metal particle and the coating layer formed on the surface of the metal particle in the next coating layer forming step. I guess. In addition, from the viewpoint of more reliably maintaining the surface characteristics of the metal particles (at least one of the characteristics of magnetism and conductivity, crystallinity), the alkali treatment step is also performed in the inert gas atmosphere described above. Also good.

  From the viewpoint of preventing the aggregation of the metal particles, it is preferable in this step to stir the metal particles using an ultrasonic homogenizer, a ball mill, or the like to uncoagulate the metal particles in advance. Moreover, it is preferable to stir the metal particles using an ultrasonic homogenizer, a ball mill or the like during the alkali treatment.

(B) Suspension preparation step The suspension preparation step is a step of preparing a suspension containing metal particles, a chemical species containing yttrium as a material for the coating layer, and a chemical species containing carbonate ions. is there. In this suspension preparation step, as described above, the amount of chemical species including yttrium in the suspension obtained after the suspension preparation step is oxidized against the metal particles in the suspension. The addition amount of the chemical species containing yttrium is adjusted in advance so that it is 0.001 to 10% by mass, preferably 0.05 to 1% by mass in terms of yttrium.

  Examples of the chemical species containing yttrium used in this step include water-soluble salts such as yttrium nitrate and yttrium chloride. Alternatively, a solution obtained by dissolving yttrium oxide in an acid such as nitric acid may be used. Further, an yttrium alkoxide may be used. Examples of yttrium alkoxides include isopropoxy yttrium, triethoxy yttrium, trisdipivaloylmethanato yttrium, and trinormal butoxy yttrium.

  Moreover, as a chemical species containing the carbonate ion used at this process, sodium carbonate, sodium hydrogencarbonate, ammonium carbonate, ammonium hydrogencarbonate, etc. are mentioned, for example. In addition, urea and urea derivatives such as methylene diurea and monomethylol urea, which generate carbonate ions when heated in an aqueous solution, may be mentioned. In addition, what is necessary is just to adjust the addition amount of sodium hydrogencarbonate, for example so that the obtained suspension may contain the carbonate ion of the chemical equivalent equal to or more than the molar amount of a yttrium ion.

  Examples of the dispersion medium used for preparing the suspension in this step include water or a mixed dispersion medium of water and alcohol such as ethanol or methanol, or water and a hydroxyl group such as ethylene glycol or glycerin. A mixed dispersion medium with a dispersion medium that is miscible with retained water is preferred. Also in this step, from the viewpoint of sufficiently stirring the components in the suspension, it is preferable to stir while irradiating the suspension with ultrasonic waves using an ultrasonic homogenizer or the like. In addition, from the viewpoint of more reliably maintaining the surface characteristics of the metal particles (at least one of magnetic and conductive properties, crystallinity), the suspension preparation step is also performed under the inert gas atmosphere described above. It is preferable to carry out with.

(C) Dissolved oxygen purging step The dissolved oxygen purging step is a step of purging dissolved oxygen in the suspension obtained through the suspension preparation step with an inert gas. This purging can be performed by bubbling a rare gas or nitrogen gas into the suspension by a conventionally known method.

(D) Coating layer forming step In the coating layer forming step, an alkaline aqueous solution in which a base is dissolved in water is added to the suspension obtained in the suspension preparation step, and yttrium basic carbonate is formed on the surface of the metal particles. Forming a coating layer containing This coating layer forming step is performed in an inert gas atmosphere having a dissolved oxygen concentration of preferably 1 mg / L or less. Also in the coating layer forming step, from the viewpoint of sufficiently stirring the components in the liquid, it is preferable to stir while irradiating the suspension with ultrasonic waves using an ultrasonic homogenizer or the like.

  The base used in this step is not particularly limited as long as it can bond a hydroxyl group to the surface of the metal particles by heat treatment. Examples thereof include sodium hydroxide, potassium hydroxide, and ammonia. Moreover, the compound which generate | occur | produces ammonia by hydrolysis like sodium carbonate, potassium carbonate, and urea, and raises the pH of a liquid may be sufficient.

  In this step, an additive may be further added to promote the formation of the coating layer or to further suppress the aggregation of the metal particles or composite particles. As such additives, various surfactants (anionic, cationic, nonionic) and the like can be used. For example, sodium bis (2-ethylhexyl) sulfosuccinate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, polyoxyethylene glycol, polyoxyethylene sorbitan monolaurate (for example, Tween manufactured by Tokyo Chemical Industry Co., Ltd.) -20), poly (oxyethylene) -octylphenyl ether (for example, Triton X-100 manufactured by Cosmo Bio) may be used.

(E) Composite Particle Extraction Step The composite particle extraction step is a step of extracting composite particles from the liquid after the coating layer forming step by a solid-liquid separation method. This solid-liquid separation can be performed by, for example, filtration of the suspension containing the composite particles after the coating layer forming step by a conventionally known method. Thereafter, the obtained solid component is dried to obtain the composite particles of the present invention.

  Hereinafter, although the composite particle of this invention and the manufacturing method of the composite particle of this invention are further demonstrated with an Example and a comparative example, this invention is not limited to these Examples at all.

Example 1
(1) Alkali treatment step of metal particles First, nickel particles (average particle diameter: 200 nm) as metal particles are dispersed in water, ammonia water is added to make pH 11.5, and heat treatment is performed at 100 ° C. for 24 hours. did. Thereby, nickel particles having a nickel hydroxide layer formed on the surface layer were obtained.

  The presence of the nickel hydroxide layer on the surface of the nickel particles was confirmed by powder X-ray diffraction spectrum measurement using CuKα characteristic X-rays. More specifically, the measurement was performed under the following measurement conditions using a powder X-ray diffraction spectrum measurement apparatus “ULTIMA-III” manufactured by Rigaku Corporation. That is, X-ray tube (Cu, tube voltage: 40 kV, tube current: 40 mA), measurement conditions (measurement angle range of Bragg angle 2θ / degree: 10-90 degrees, sampling width: 0.01 degrees, scan speed: 4 Degree / minute, divergent slit: 1/2 degree, divergent longitudinal slit: 10 mm, scattering slit: 1/2 degree, light receiving slit: 0.3 mm).

  Then, from the diffraction pattern obtained under these measurement conditions, by confirming peaks such as the (001) plane and the (011) plane, which are peaks attributed to nickel hydroxide, It was confirmed that a nickel oxide layer was present. In addition, the average particle diameter of the nickel particles was determined by measuring the particle diameter of 100 composite particles from the SEM image of the composite particles photographed using “Scanning Electron Microscope S-4800” manufactured by Hitachi, Ltd. It is the value which calculated the arithmetic mean value.

(2) Suspension preparation step for preparing a suspension containing the metal particles and the coating layer material Next, water is added to the nickel fine particles, and the mixture is stirred while irradiating ultrasonic waves, and yttrium nitrate serving as an yttrium source. A solution in which sodium carbonate is dissolved (solvent: water) and a solution in which sodium hydrogen carbonate as a carbonate ion source is dissolved (solvent: water) are added, and metal particles, chemical species including yttrium, and carbonate ions are included. A suspension containing the chemical species was prepared.

The amount of yttrium nitrate added was adjusted so that the suspension obtained after the addition contained 0.1% by mass of yttrium nitrate in terms of yttrium oxide with respect to the nickel particles. Here, the “equivalent value of yttrium oxide” means that the mass of yttrium nitrate is converted to the mass of yttrium oxide (Y ₂ O ₃ ) containing yttrium having the same chemical equivalent as that of yttrium nitrate. It is a value expressed as a ratio of the mass of yttrium (Y ₂ O ₃ ) to the mass of nickel particles. Further, the amount of sodium hydrogen carbonate added was adjusted so that the suspension obtained in this step contained carbonate ions having a chemical equivalent to yttrium ions.

(3) Dissolved oxygen purge step of purging dissolved oxygen in the suspension with an inert gas Next, the suspension is sufficiently bubbled using nitrogen gas as an inert gas to dissolve the dissolved oxygen in the suspension. Was thoroughly purged.

(4) Coating layer forming step of forming a coating layer containing yttrium basic carbonate on the surface of the metal particles Next, 300 times the chemical equivalent to the chemical equivalent of yttrium nitrate contained in the yttrium nitrate used in the suspension preparation step An aqueous ammonia solution (ammonia concentration: 1.5 mol / L) containing an equivalent amount of ammonia was prepared. Then, the dissolved oxygen in the aqueous ammonia solution was sufficiently purged using nitrogen gas as an inert gas.

  Next, the aqueous ammonia solution is dropped over 2 hours while vigorously stirring the suspension obtained through the dissolved oxygen purging step in an inert gas atmosphere using nitrogen gas (oxygen concentration: 1 mg / L or less). did. Further, the liquid after completion of the dropping was also stirred for 2 hours in an inert gas atmosphere using the same nitrogen gas.

(5) Composite Particle Extraction Step Next, solid components were separated and extracted from the liquid after completion of dropping by a solid-liquid separation method. Next, this solid component was dried to obtain composite particles in which a coating layer containing yttrium basic carbonate as a main component was formed on the surface of nickel particles.

(6) Chemical composition analysis of composite particle coating layer The chemical composition of the composite particle coating layer obtained is represented by the following composition formula from the analysis results using FT-IR, TG-DTA, and ICP spectroscopic analysis. Identified as yttrium basic carbonate.
Composition formula: Y (OH) CO ₃ .nH ₂ O (n = 0.5-3).

<< Example 2 >>
In Example 1, “(2) Suspension preparation step of preparing a suspension containing metal particles and coating layer material”, the amount of yttrium nitrate added in the suspension obtained after the addition was changed to nickel particles. In the same manner as in Example 1 except that the amount of yttrium nitrate was adjusted to be 0.08% by mass in terms of yttrium oxide, the surface of the nickel particles was coated with yttrium basic carbonate as a main component. A composite particle having a layer formed was obtained.
Moreover, the chemical composition of the coating layer of the obtained composite particles was identified as yttrium basic carbonate as in Example 1 from the analysis results using FT-IR, TG-DTA, and ICP spectroscopy. .

Example 3
In Example 1, “(2) Suspension preparation step of preparing a suspension containing metal particles and coating layer material”, the amount of yttrium nitrate added in the suspension obtained after the addition was changed to nickel particles. In the same manner as in Example 1 except that the amount of yttrium nitrate was adjusted to be 0.17% by mass in terms of yttrium oxide, the surface of the nickel particles was coated with yttrium basic carbonate as a main component. A composite particle having a layer formed was obtained.
Moreover, the chemical composition of the coating layer of the obtained composite particles was identified as yttrium basic carbonate as in Example 1 from the analysis results using FT-IR, TG-DTA, and ICP spectroscopy. .

≪Comparative example 1≫
The composite particles of Comparative Example 1 were produced by the following procedure.
“(1) Alkali treatment step of metal particles” in Example 1 was not performed, but “(2) Suspension preparation step of preparing a suspension containing metal particles and the material of the coating layer” was performed. That is, as in Example 1, water was added to nickel fine particles, stirred while irradiating with ultrasonic waves, a solution in which yttrium nitrate serving as a yttrium source was dissolved (solvent: ion-exchanged water) was added, and metal particles, A suspension containing a chemical species containing yttrium was prepared. The amount of yttrium nitrate added was also the same as in Example 1.

  Next, “(4) coating containing yttrium basic carbonate on the surface of the metal particles was performed without performing the“ (3) dissolved oxygen purge step of purging dissolved oxygen in the suspension with an inert gas ”in Example 1. The coating layer forming step of forming a layer ”was performed. Here, in the (4) coating layer forming step of Comparative Example 1, stirring in an inert gas atmosphere using the nitrogen gas performed in Example 1, and the dissolved oxygen in the liquid using nitrogen gas as the inert gas No purging was performed.

  That is, similarly to Example 1, an aqueous ammonia solution containing 300 times the chemical equivalent of ammonia relative to the chemical equivalent of yttrium nitrate used in the suspension preparation step (ammonia concentration: 1.5 mol / L) Was prepared. In contrast to Example 1, the aqueous ammonia solution was not purged of dissolved oxygen using nitrogen gas as an inert gas.

  Thereafter, the aqueous ammonia solution containing the above-described dissolved oxygen was added dropwise over 2 hours while vigorously stirring the suspension in the atmosphere instead of under an inert gas atmosphere using nitrogen gas. Furthermore, the liquid after the completion of dropping was stirred for 2 hours in the air, not in an inert gas atmosphere using the same nitrogen gas.

  Next, in the same manner as in Example 1, the solid component containing nickel particles was separated and extracted from the liquid after completion of dropping by a solid-liquid separation method. Next, this solid component was dried to obtain composite particles in which a coating layer containing yttrium basic carbonate as a main component was formed on the surface of nickel particles.

[Dispersibility evaluation test in dispersion medium]
For the composite particles of Example 1 and the composite particles of Comparative Example 1, the values of ρ, ρ ₀ , S, S ₀ , (ρ / ρ ₀ ), (S / S ₀ ), W, and d The measurement was performed by the measurement method, measurement apparatus, and measurement conditions described above in “Means for Doing”. In Tables 1 and 2, d ₀ and d ₁ represent the following values, respectively.

d ₀ is the particle size (theoretical value) of the composite particle calculated by the following formula (A).
d ₀ = 6000 · (ρ ₀ · S) ⁻¹ (A)
d ₁ indicates the light scattering particle diameter of the composite particles obtained by “LB-550”, a light scattering particle size distribution measuring instrument manufactured by Horiba, Ltd. In this measurement, ion-exchange water was used as a dispersion medium for the composite particles, and the composite particles were dispersed in the ion-exchange water at a concentration of 0.1% by weight while irradiating with ultrasonic waves.

Moreover, the “dispersibility evaluation result” in Table 2 is based on d ₀ (theoretical value of particle diameter), d (arithmetic mean particle diameter based on SEM image), and d ₁ (light scattering particle diameter). It is the result of having evaluated the dispersibility to ion-exchange water. “Good” in “Dispersibility evaluation result” in Table 2 indicates a case where the light scattering measurement value d ₁ falls within 100 to 150% of the SEM particle diameter measurement value d. In addition, “Poor” in “Dispersibility evaluation result” in Table 2 indicates a case where the light scattering measurement value d ₁ exceeds 150% of the SEM particle size measurement value d.

  As is clear from the results shown in Tables 1 and 2, the formulas (1) to (1) are compared with the composite particles of Comparative Example 1 that do not satisfy the conditions of the formulas (1) to (3) described above. It was confirmed that the composite particles of Example 1, Example 2, and Example 3 that simultaneously satisfy the condition (3) have good dispersibility.

For example, the composite particles of Example 1, as is clear from figures that d and d _1, in the case where the dispersion medium was deionized water, the particle size distribution of composite particles, the particle size of the primary particles constituting this It is closer to the distribution (d ₀ ). Further, the composite particles of Example 1 also had good dispersibility in the ethylcellulose-based polymer.

  The composite particles obtained by the present invention have the characteristics that, when mixed with a solvent such as water or a polymer, they are less aggregated and easily dispersed, and the characteristics of the metal particles constituting the composite particles are not impaired. Therefore, the composite particles of the present invention can be suitably used for various polymer materials and electrical and electronic products, and can also be suitably used in a wide range of fields such as biomedical and life sciences. Moreover, the manufacturing method of the composite particle obtained by this invention can be utilized in order to manufacture said composite particle suitably.

Claims (9)

Metal particles,
Formed on at least a part of the surface of the metal particles, and a coating layer containing a basic carbonate of metal;
Contains
It has a configuration that simultaneously satisfies the conditions of the following formula (1) and formula (2).
Composite particles.
0.5 ≦ (ρ / ρ ₀ ) (1)
(S / S ₀ ) ≦ 1.2 (2)
[In Formula (1),
ρ is a measurement value of the bulk density of the composite particles based on the measurement method defined in JIS-R-1628,
ρ ₀ is a measured value of the true density of the composite particles based on a dry density measurement method by a constant volume expansion method,
Respectively,
In formula (2),
S is a measured value of the specific surface area of the composite particle based on the BET 1-point method,
S ₀ is a theoretical calculated value of the specific surface area of the composite particle calculated based on the arithmetic average particle diameter of the composite particle calculated based on the SEM image of the composite particle and the true density of the composite particle,
Respectively. ] 2. The composite particle according to claim 1, wherein in addition to the formula (1) and the formula (2), the composite particle further satisfies a condition of the following formula (3).
0.15 ≦ W ≦ 0.35 (3)
[Wherein, W is the half-width of three diffraction peaks with the peak intensity of 1st to 3rd among diffraction peaks obtained by powder X-ray diffraction spectrum measurement using CuKα characteristic X-rays. The arithmetic mean value of is shown. The unit is deg. ]   The composite particle according to claim 1, wherein the basic carbonate is a rare earth metal basic carbonate.   The composite particle according to claim 1, wherein the basic carbonate is yttrium basic carbonate.   The composite according to any one of claims 1 to 4, wherein the metal particle includes at least one element selected from the group consisting of Fe, Ni, Cu, Ag, and Au as a constituent element. particle.   The composite particles according to claim 1, wherein the metal particles contain Ni as a constituent element.   The composite particles according to claim 1, wherein the metal particles contain Ag as a constituent element. A method for producing composite particles comprising metal particles and a coating layer formed on at least a part of the surface of the metal particles,
A suspension preparation step of preparing a suspension containing metal particles, a chemical species containing a metal that is a material of the coating layer, and a chemical species containing carbonate ions;
A coating in which an alkaline aqueous solution in which a base is dissolved in water is added to the suspension obtained in the suspension preparation step to form a coating layer containing the basic carbonate of the metal on the surface of the metal particles. A layer forming step;
Contains
In the suspension preparation step, the amount of the chemical species including the metal in the suspension obtained after the suspension preparation step is the oxidation of the metal with respect to the metal particles in the suspension. The amount of the chemical species containing the metal is adjusted in advance so that the converted value is 0.001 to 10% by mass, and
By performing at least the coating layer forming step in an inert gas atmosphere,
Preparing composite particles having a configuration that simultaneously satisfies the conditions of the following formulas (1) and (2):
A method for producing composite particles.
0.5 ≦ (ρ / ρ ₀ ) (1)
(S / S ₀ ) ≦ 1.2 (2)
[In Formula (1),
ρ is a measurement value of the bulk density of the composite particles based on the measurement method defined in JIS-R-1628,
ρ ₀ is a measurement of the true density of the composite particle,
Respectively,
In formula (2),
S is a measured value of the specific surface area of the composite particle based on the BET 1-point method,
S ₀ is a theoretical calculated value of the specific surface area of the composite particle calculated based on the arithmetic average particle diameter of the composite particle calculated based on the SEM image of the composite particle and the true density of the composite particle;
Respectively. ] Before the suspension preparation step, further comprising an alkali treatment step of heat-treating the metal particles using an alkaline liquid containing a base in a dispersion medium.
The method for producing composite particles according to claim 8.