JP2001131603A - Composite metallic superfine grain and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite metallic superfine grain uniform in diameter, excellent in dispersion stability and property stability as the grain and capable of being manufactured on an industrial scale and its manufacturing method. SOLUTION: A positively charged cationic core metal 12 having 1-20 nm diameter is surrounded by an anionic organic material 14 to constitute the composite metallic superfine grain, and the grain is manufactured by heating a low-temperature decomposable low-molecular-weight organometallic salt, such as a metallic salt, e.g. a carbonate, a formate or an acetate, in a non- aqueous solvent in the presence of the anionic organic material above the decomposition temperature of the metallic salt and below the decomposition temperature of the anionic organic material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to composite metal ultrafine particles and a method for producing the same, and more particularly to composite metal ultrafine particles having excellent dispersion stability and capable of being produced on an industrial scale.

[0002]

2. Description of the Related Art As a method for producing ultrafine metal particles having a particle diameter of 100 nm or less, ultrafine metal particles are condensed from a gas phase by evaporating a metal in a vacuum and in the presence of a small amount of gas to obtain ultrafine metal particles. A device for obtaining fine metal fine particles is generally known. However, in the method using such a physical process, the variation in the particle size distribution is large, and the grain boundary remains even after heat treatment.
It is not suitable for mass production because a uniform metal film cannot be obtained and the amount of generated metal ultrafine particles is small.In addition, electron beams, plasma, laser,
Since an apparatus such as induction heating is required, the cost increases.

[0003] In addition, when such ultrafine metal particles are used, if they are taken out into the air alone, they will agglomerate.
It must be used by dispersing it in a solvent using a surfactant or the like, but it is insufficient in terms of dispersion stability such as storage stability.

For this reason, the metal organic compound is heated at a temperature equal to or higher than the decomposition start temperature and lower than the complete decomposition temperature of the metal organic compound in an inert gas atmosphere in which oxygen is cut off. Ultra-fine metal particles mainly composed of a metal component derived from a metal component substantially consisting of the metal component, the periphery of which is surrounded by an organic compound, and a method for producing the same have been proposed. It requires an atmosphere, has a high decomposition temperature, and can be used only in a specific area.

[0005]

In the case of ultrafine metal particles, if they are assembled in a state of particles in a bare state, the particles are easily adhered to each other, and aggregation or chaining occurs. For this reason,
In order to stabilize the ultrafine metal particles in a state separated from each other, it is necessary to form some kind of protective film on the surface of the fine metal particles. Heretofore, ultrafine metal particles are considered to be electrically neutral, and therefore, a nonionic surfactant or a nonionic substance such as gelatin or polyvinyl alcohol has been generally used as the protective film. .

[0006] The same applies to the case where the central metal component and the metal organic compound are surrounded by a metal ultra-fine particle surrounded by a metal organic compound that functions as a protective film. Are thought to be bound by an intermolecular affinity such as van der Waals force.

However, in order for the ultrafine metal particles to be stable as particles even at a higher metal concentration, for example, the metal part at the center and the protective film around the metal part do not have an intermolecular affinity having a relatively small energy, but have a certain energy. It is desirable to have a strong bonding force.

The inventors have found that in the process of thermally decomposing certain metal salts, ultrafine metal particles having cationity are formed. Therefore, if there is an anionic organic substance or the like which forms a preferable protective film at the time when the cationic metal ultrafine particles are formed, the anionic organic substance or the like is stably ion-bonded to the surface of the metal ultrafine particles. ,
The composite metal ultrafine particles have a stable protective film formed thereon.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a composite metal ultrafine particle having a more uniform particle size, excellent dispersion stability and excellent property stability as particles, and capable of being manufactured on an industrial scale. It is intended to provide a manufacturing method.

[0010]

The invention according to claim 1 is a composite metal ultrafine particle having a structure in which a positively charged core metal having a diameter of 1 to 20 nm is surrounded by a large number of anionic substances. .

It is known that the melting point of metal particles decreases as the particle size decreases, but the effect starts to appear at 20 nm or less, and the effect becomes remarkable at 10 nm or less. Accordingly, the average particle diameter of the core metal (metal ultrafine particles) is preferably 1 to 20 nm, and 1 to 10 nm.
Particularly preferred is nm. In addition, the core metal and the anionic substance are strongly ion-bonded, and the anionic substance serves as a protective film for protecting the core metal, thereby improving the dispersion stability in the solvent, and as a particle. Can improve the property stability.

According to a second aspect of the present invention, the metal component of the core metal is Cu, Ag, Au, In, Si, Ti, G
e, Sn, Fe, Co, Ni, Ru, Rh, Pd, O
2. The composite metal ultrafine particle according to claim 1, wherein the composite metal ultrafine particle is at least one of s, Ir, Pt, V, Cr and Bi.

According to a third aspect of the present invention, the anionic substance is an ionic organic substance.
Or the composite metal ultrafine particles according to 2. The invention according to claim 4 is the composite metal ultrafine particle according to claim 3, wherein the ionic organic substance is a fatty acid having 5 or more carbon atoms, alkylbenzenesulfonic acid or alkylsulfonic acid.

[0014] The invention according to claim 5 is a low-molecular-weight organic metal such as a metal salt, more preferably a carbonate, formate or acetate, which is decomposable in a non-aqueous solvent and in the presence of an ionic organic substance. A method for producing ultrafine composite metal particles, comprising heating a salt at a temperature not lower than the decomposition reduction temperature of the metal salt and not higher than the decomposition temperature of the ionic organic substance. Since such composite metal ultrafine particles can be produced by a chemical process in a liquid phase, mass production can be performed in a normal atmosphere using a simple apparatus without using a large-scale vacuum apparatus. Possible and inexpensive. In addition, since the particle size is uniform, all the particles are fused at a constant temperature.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows the structure of a composite metal ultrafine particle according to an embodiment of the present invention. The composite metal ultrafine particle 10 includes a positively charged core metal 12 substantially composed of a metal component, And an ionic organic substance 14 as an anionic substance surrounding the periphery of the core metal 12. That is, the composite metal ultrafine particles 10
It is composed of an organic anionic substance and a metal component derived from a starting metal salt, for example, a carbonate, formate or acetate, the center of which is composed of a core metal 12, around which an ionic organic substance 14 is formed. Surrounding.

The ionic organic substance 14 is composed of the core metal 12
It plays a role as a protective film of
By coating the periphery of the core metal 12 with the ionic organic substance 14, the composite metal ultrafine particles 10 having a small tendency to aggregate in a solvent and having excellent dispersion stability are formed. In addition, the ionic organic substance 14 and the core metal 12 exist in a state where a part or the whole thereof is firmly bonded by ionic bonding, and the conventional metal superconductor stabilized by being coated with a surfactant. Unlike fine particles, they have high property stability as particles and are stable even at higher metal concentrations.

The ratio of the core metal 12 in the ultrafine composite metal particles 10 is usually about 50 to 90% by weight. For example, when it is used as a metal material to be embedded in a wiring groove, about 60 to 90% by weight is used. In particular, the content is preferably 70 to 90% by weight.

The core metal 12 of the ultrafine composite metal particles 10
Has an average particle size of usually about 1 to 20 nm, preferably 1 to 20 nm.
It is about 10 nm. It is known that the melting point of metal particles decreases as the particle size decreases, but the effect starts to appear at 20 nm or less, and the effect becomes significant at 10 nm or less. Therefore, with this configuration, it becomes possible to melt the core metal 12 of the ultrafine composite metal particle 10 at a temperature lower than the original melting point of the metal. For example, the melting point of silver is 1233K (960
° C), but in the case of ultrafine silver particles having a particle diameter of 5 nm, silver melts at about 220 ° C.

Thus, for example, in the case of composite metal ultrafine particles constituted by using silver ultrafine particles having a particle diameter of 5 nm as the core metal 12 and surrounding the ionic organic material 14 with the ionic organic material, The decomposition temperature of 14 is 2
By heating to 220 ° C. if the temperature is 20 ° C. or lower, or to the decomposition temperature of the ionic organic substance 14 if the temperature is higher than 20 ° C., it is possible to form a film composed of only the mutually fused silver.

The ultrafine composite metal particles 10 are used to decompose a metal salt, for example, a carbonate, formate or acetate, in a non-aqueous solvent and in the presence of an ionic organic substance at a temperature not lower than the decomposition and reduction temperature and decompose the ionic organic substance. It can be produced by heating below the temperature.

The metal component of the core metal 12 is C
u, Ag, Au, In, Si, Ti, Ge, Sn, F
e, Co, Ni, Ru, Rh, Pd, Os, Ir, P
At least one of t, V, Cr and Bi is used, and as the ionic organic substance, a fatty acid having 5 or more carbon atoms, alkylbenzenesulfonic acid or alkylsulfonic acid is used.

The heating temperature is equal to or higher than the decomposition reduction temperature of a metal salt, for example, a carbonate, formate or acetate, and equal to or lower than the decomposition temperature of an ionic organic substance. For example, in the case of silver acetate, since the decomposition start temperature is 200 ° C., the temperature may be maintained at 200 ° C. or higher and at a temperature at which the ionic organic substance does not decompose.
In this case, the heating atmosphere is preferably an inert gas atmosphere in order to make it difficult for the ionic organic substance to be decomposed. However, heating can be performed even in the atmosphere by selecting a non-aqueous solvent.

After the heating is completed, purification is performed by a known purification method. The purification may be performed by, for example, centrifugation, membrane purification, solvent extraction, or the like.

The composite metal ultrafine particles 1 thus produced
0 is dispersed in an appropriate organic solvent such as cyclohexane to prepare a composite metal ultrafine particle dispersion. Such a composite metal ultrafine particle dispersion is very transparent when the mixed metal ultrafine particles are mixed and stirred because the dispersed particles are very fine, and the type of the solvent, the ultrafine particle concentration, the temperature, and the like are appropriately selected. By doing so, physical properties such as surface tension and viscosity can be adjusted.

[0025]

Example 1 Oleic acid was used as an organic anionic substance, and silver acetate was used as a metal source. 0.5L naphthene-based high-boiling solvent with a boiling point of 250 ° C in a 1L eggplant-shaped flask
, And 10 g of silver acetate and 20 g of oleic acid were put therein, and heated at 240 ° C. for 3 hours. The color tone changed from colorless to light brown and further to purple with heating. After heating,
Acetone was added to perform precipitation purification.

When this modified powder was observed with a transmission electron microscope, it was found to be composed of ultrafine particles having a particle size of about 10 nm. Further, when powder X-ray diffraction was performed, a metallic silver core was confirmed.

When the powder composed of the ultrafine composite metal particles was dispersed in toluene and xylene, no precipitate was observed in any case, and a transparent state was obtained. That is,
It was confirmed that the material was in a solubilized state.

This was applied as a composite metal ultrafine particle dispersion to the surface of the substrate at 0.05 g / cm ² , dried, and then heated at about 250 ° C. in a nitrogen atmosphere. Then, it was easily baked to form a silver coating film.

[0029]

Example 2 Stearic acid was used as an organic anionic substance, and copper carbonate was used as a metal source. A paraffinic high-boiling solvent having a boiling point of 250 ° C. was placed in a 1-L eggplant-shaped flask.
Put 5L into it, 10g copper carbonate and 40 stearic acid.
g was heated at 300 ° C. for 3 hours. Upon heating, the color changed from light green to dark green to brown. After heating, methanol was added to perform precipitation purification.

The ultrafine composite metal particles were applied to a substrate in the same manner as in Example 1. However, if the heat treatment temperature is 3
The temperature was set to 00 ° C. Then, it was easily baked to form a copper coating film.

[0031]

Example 3 Sodium dodecylbenzenesulfonate was used as an organic anionic substance, and chloroplatinic acid was used as a metal source. 0.5 L of xylene (mixture of isomers) is placed in a 1 L eggplant-shaped flask, and 5 g of chloroplatinic acid and 20 g of sodium dodecylbenzenesulfonate are placed therein.
And heated at 150 ° C. for 3 hours. According to the heating,
The color changed from yellow to light brown to gray. After heating, acetone was added to perform precipitation purification.

The ultrafine composite metal particles were applied to a substrate in the same manner as in Example 1. However, if the heat treatment temperature is 2
The temperature was set to 00 ° C. Then, it was easily baked to form a platinum coating film.

[0033]

As described above, according to the present invention, a protective film for firmly ion-bonding a core metal having an average particle diameter of 1 to 20 nm and an anionic substance to protect the core metal on the anionic substance. As a result, the dispersion stability in the solvent is excellent, and the property stability as particles is enhanced for easy handling. It is possible to provide ultrafine composite metal particles that can maintain stability and are easy to control. In addition, since it can be manufactured by a chemical process in a liquid phase, mass production can be performed in a normal atmosphere using a simple apparatus without using a large-scale vacuum apparatus, and the cost is low. It is. In addition, since the particle size is uniform, all the particles are fused at a constant temperature.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing the structure of a composite metal ultrafine particle according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Composite metal ultrafine particle 12 Cationic core metal 14 Anionic organic substance

Claims (5)

[Claims] 1. Composite metal ultrafine particles having a structure in which a positively charged core metal having a diameter of 1 to 20 nm is surrounded by an anionic substance. 2. The metal component of the core metal is Cu, A
g, Au, In, Si, Ti, Ge, Sn, Fe, C
o, Ni, Ru, Rh, Pd, Os, Ir, Pt, V,
2. The composite metal ultrafine particle according to claim 1, wherein the composite metal ultrafine particle is at least one of Cr and Bi. 3. The composite metal ultrafine particle according to claim 1, wherein the anionic substance is an ionic organic substance. 4. The composite metal ultrafine particle according to claim 3, wherein the ionic organic substance is a fatty acid having 5 or more carbon atoms, alkylbenzenesulfonic acid or alkylsulfonic acid. 5. A composite metal comprising heating a metal salt in a non-aqueous solvent and in the presence of an ionic organic substance at a temperature not lower than the decomposition reduction temperature of the metal salt and not higher than the decomposition temperature of the ionic organic substance. A method for producing ultrafine particles.