JP2526398B2 - Method for producing composite ultrafine particles - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite of nanometer-scale ultrafine particles in a gas atmosphere containing pressure or pressure reduction.

[0002]

2. Description of the Related Art In recent years, handling of substances on a nanometer scale level has become important in various fields such as catalysts, electronic devices, and functional materials. For example, the construction of thin films at the nanometer level is an important technology in electronic devices and the like, and is now a fairly generalized technology.

On the other hand, nanometer-scale ultrafine particles are
Its utility value is highly evaluated in a wide variety of fields as described above regardless of whether it is metallic or non-metallic, and in particular, metallic ultra-fine particles have unique properties and are not found in ordinary bulk metals, It has attracted attention as a new functional material because it exhibits properties that further emphasize the properties of bulk metal, such as improved magnetic properties, increased chemical reactivity, selective absorption of light, and low-temperature sinterability.

The characteristics of such metallic ultrafine particles can be dramatically improved by combining the metallic ultrafine particles with the nonmetallic ultrafine particles such as ceramic ultrafine particles to form composite ultrafine particles. At the same time, it has the potential to create substances with new functions that conventional ultrafine particles of a single substance do not have.

Specifically, the use of an ultrafine hetero interface formed by different types of ultrafine particles, for example, application to semiconductors, sensors, etc., and the impartation of high functionality by controlling the structure of ceramics microscopically, etc. Applications are possible. Therefore, as a method for producing such composite ultrafine particles,
A method in which a binary alloy is melted by arc plasma, each alloying element is evaporated at the same time, and vapors of different substances are condensed in the same space has been proposed as an active plasma-metal reaction method (Journal of the Japan Institute of Metals (1989)). Vol. 53, No. 9, pp. 936-945).

[0006]

However, according to the above-mentioned active plasma-metal reaction method, the bonding form of the composite ultrafine particles, that is, the number of the ultrafine particles constituting the composite ultrafine particles, the bonding ratio thereof and the like are controlled. In addition to the problem that it is extremely difficult to efficiently produce composite ultrafine particles having an arbitrary bonding morphology, a device for generating an arc plasma and a device for maintaining the arc plasma at a predetermined temperature There is a problem that the heating energy is costly and the manufacturing cost is very high.

In view of the above problems, the present invention can control the bonding morphology of different kinds of ultrafine particles constituting nanometer-order composite ultrafine particles, and can be manufactured at a relatively low cost. It is an object of the present invention to provide a method for producing fine particles.

[0008]

Means for Solving the Problems In the method for producing composite ultrafine particles according to the present invention for achieving the above object, the particle size is
nm-several tens of nm are separately generated in the first step, the second step of electrically charging the ultrafine particles generated in the first step to the opposite polarity, and the second step The third step of mixing the charged ultrafine particles in a gas atmosphere , and passing the mixed ultrafine particles into an alternating electric field.
And a fourth step in which the number ratio of constituent particles is 1: 1 or
Prepared composite ultrafine particles composed of 1: 2
And a method for producing composite ultrafine particles .

Further , preferably, it occurs in the first step.
At least one of the two types of ultrafine particles
Must be composite ultrafine particles produced in the third or fourth step.
To prepare composite ultrafine particles composed of required number ratio
It is also possible to do so.

The ultrafine particles to be used in the present invention are particles having a particle size of approximately 0.1 μm (100 nm) or less, preferably ultrafine particles having a size of several nm to several tens nm. In order to produce the composite ultrafine particles, it is necessary to produce the ultrafine particles that can be the constituent particles in the first step. The necessary conditions for the constituent particles are that they are first dispersed ultrafine particles that are not aggregated, and second that they have a particle size that is as uniform as possible.

Various methods for producing ultrafine particles in gas or under reduced pressure have been proposed. As a method for producing ultrafine particles satisfying the above-mentioned conditions, the resistance wire previously devised by the present inventors is used. There is a simple method. This is to wrap a linear ultrafine particle material around the surface of the resistance wire, or
This is a method in which a powdery ultrafine particle material is adhered, and the resistance wire is heated by energizing the resistance wire to melt and evaporate the ultrafine particle material, and then to generate ultrafine particles by condensation (Japanese Patent Laid-Open No. Hei 10 (1999) -242242). See 3-178332).

Next, the ultrafine particles generated in a dispersed state in a gas atmosphere are charged in the second step. Generally, glow discharge or corona discharge under reduced pressure is mainly used as the method, but any method may be used as long as the charging efficiency is good. Further, it is not always necessary to charge all the generated ultrafine particles.

The ultrafine particles that have passed through the charging device are preferably passed between the deflection electrodes to remove uncharged particles or abnormally charged particles, but it is not necessary to make the purification purity of the composite ultrafine particles to be high. You don't have to. By the above method, two types of charged ultrafine particles having opposite polarities are produced.

Next, these charged ultrafine particles are mixed in the third step. If each of the ultrafine particles is suspended in the gas, stirring or mechanical mixing with a double nozzle or the like is performed. It is possible. Further, even if one side is under reduced pressure, mixing with a double nozzle or the like is possible.

When both are under reduced pressure, the mixture can be promoted by utilizing the electrostatic force of each charged ultrafine particle by passing through an appropriate AC electric field in the fourth step. In addition, the method of passing through this AC electric field is
It can also be applied when ultrafine particles are suspended in gas.

What is required in these processes is to bring two kinds of ultrafine particles having opposite polarities close to each other. Therefore, it is even more preferable to use the mechanical mixing method in the third step and the electrical mixing method in the fourth step together. By going through each of the above steps, two types of ultrafine particles are combined to produce composite ultrafine particles, but since the single substance ultrafine particles that are not finally combined have different electrical characteristics. It can be easily removed by using a deflection electrode or the like.

[0017]

[Operation] The method for producing composite ultrafine particles according to the present invention has the above constitution, and the two types of ultrafine particles generated in the first step are electrically reversed in polarity in the second step. By being charged, when mixed in the third step, the two types of ultrafine particles are attracted by the electrostatic force of each other and bonded to form a composite.

In the case where the fourth step is provided, when the ultra-fine particles charged with opposite polarities pass through the AC electric field, the ultra-fine particles meander in the directions opposite to each other. The ultrafine particles have a higher probability of approaching each other, and the binding is promoted. Furthermore, by using at least one of the two types of ultrafine particles generated in the first step as the composite ultrafine particles produced in the third step or the fourth step, a composite ultrafine particle composed of three or more types of ultrafine particle materials is obtained. It becomes possible to produce fine particles.

[0019]

Embodiments of the present invention will now be described with reference to the drawings. In Example 1 of the present invention shown in FIG. 1, sodium chloride was used as one ultrafine particle material A and silver was used as the other ultrafine particle material B. The reason why sodium chloride and silver are used is that the bonding morphology can be easily observed from the difference in crystallinity and the image intensity by an electron microscope.

First, as devices used in the first step, an ultrafine particle generator 1 for producing ultrafine particles of sodium chloride and an ultrafine particle generator 2 for producing ultrafine particles of silver are provided. . These ultra fine particle generators 1,
No. 2 was previously proposed by the present inventors by JP-A-3-178332, in which sodium chloride is adhered to the surface of the resistance wire of one ultrafine particle generator 1 and the other ultrafine particle generator 2 A silver wire is intermittently wound around the surface of the resistance wire of
By energizing these resistance wires, the resistance wires generate heat, and the ultrafine particle materials A and B are separately melted and evaporated, and then ultrafine particles are generated by condensation.

In this first step, the respective ultrafine particle generators 1 and 2 under atmospheric pressure respectively produce sodium chloride ultrafine particles shown in the electron microscope photograph of FIG. 3 and silver ultrafine particles shown in the electron microscope photograph of FIG. Was generated. All of these ultrafine particles are in a dispersed state, and the sodium chloride ultrafine particles have a cubic crystal shape, whereas the silver ultrafine particles have an elliptic shape.

Next, as devices used in the second step, a particle charging device 3 for negatively charging the sodium chloride ultrafine particles and a particle charging device 4 for positively charging the silver ultrafine particles. It is provided. These particle charging devices 3, 4
Is a device for applying electric charges of opposite polarities to two types of ultrafine particles by glow discharge or corona discharge. The ultrafine sodium chloride particles and the ultrafine silver particles charged in the second step are agitated by the mechanical mixing device 5 in the next third step. In the present embodiment, agitation by a double nozzle in which a small-diameter inner tube is housed in a large-diameter outer tube is adopted, and the gas in the inner tube in which one charged ultrafine particle is suspended,
By sending out from the nozzle of the inner tube into the outer tube, the other charged ultrafine particles were mixed with the gas in the outer tube in which the particles were suspended.

In order to further promote the mixing of the two kinds of ultrafine particles, the fourth step is provided in this embodiment, and the composite ultrafine particles already bound in the third step and the two kinds of uncharged charged ultrafine particles. The particles are introduced into the electric mixing device 6 in a mixed state. In the electric mixer 6 of this embodiment, the electric field strength is
An AC electric field of 20 kV / m and a frequency of 1 Hz is generated, and the probability that two types of charged ultrafine particles having opposite polarities are brought close to each other to a distance where they can be bonded by electrostatic force is increased.

After the fourth step, electron micrographs of the composite ultrafine particles C taken without any special means for removing uncharged particles and abnormally charged particles are shown in FIGS. 5 and 6.
Shown in In any of these electron micrographs, the ultrafine silver particles have a strong image intensity and can be clearly confirmed, whereas the ultrafine sodium chloride particles have a weak image intensity, and some particles have a cubic crystal form, Since the image of some other particles is thin, it is difficult to confirm the contour, especially for minute ultrafine particles. However, when observed in detail, the shape of the silver ultrafine particles after composite formation is shown in FIG.
The presence of the sodium chloride ultrafine particles can be confirmed from the fact that, unlike the shape of the silver ultrafine particles shown in (1), it is deformed so that a part thereof is chipped.

As a result, most of the obtained composite ultrafine particles C consisted of two constituent particles consisting of one sodium chloride ultrafine particle and one silver ultrafine particle, and one sodium chloride ultrafine particle and one silver ultrafine particle. It can be seen that the number of particles is limited to two types, that is, three particles composed of two fine particles. That is, in the present embodiment, it was possible to manufacture the composite ultrafine particles C in which the constituent particles were limited to 2 or 3 and the bonding morphology thereof was defined by using two kinds of different types of ultrafine particles. Of. Further, in the case of the three constituent particles, it can be seen that the two silver ultrafine particles are not directly bonded but are bonded via the sodium chloride ultrafine particles. However, since the image of the sodium chloride ultrafine particles is thin in the electron micrograph, it seems that silver ultrafine particles are paired with a slight gap in some of the composite ultrafine particles C.

Next, in the second embodiment of the present invention shown in FIG. 2, the composite ultrafine particles C produced by the production method of the first embodiment are charged by the particle charging device 3 and another ultrafine particle material D is obtained.
After being melted and evaporated by the ultrafine particle generator 2, the charged composite ultrafine particles and the charged ultrafine particles, which are charged by the particle charging device 4 and have the opposite polarities, are mechanically mixed and electrically mixed. This is a method for producing composite ultrafine particles E composed of three kinds of ultrafine particle materials by combining them by 6.

As described above, by applying the existing composite ultrafine particles C to at least one of the two kinds of ultrafine particles generated in the first step, composite ultrafine particles composed of three or more kinds of ultrafine particle materials are produced. Further, by repeating the above-mentioned steps a plurality of times, it becomes possible to manufacture more complex composite ultrafine particles.

[0028]

EFFECT OF THE INVENTION The method for producing composite ultrafine particles according to the present invention comprises a first step of separately generating two kinds of ultrafine particles having a particle diameter of several nm to several tens nm, and an ultrafine particle generated in the first step. The second step of electrically charging the particles to opposite polarities, the third step of mixing the ultrafine particles charged in the second step in a gas atmosphere, and the mixed ultrafine particles in an alternating electric field
It consists of a fourth step of passing through the inside, and the number ratio of constituent particles
To prepare composite ultrafine particles composed of 1: 1 or 1: 2
Since this is done, the following effects can be achieved .

The particle size generated in the first step is a few n
When two kinds of ultra-fine particles of m to several tens of nm are electrically charged with opposite polarities in the second step, the fineness of the particles is reduced .
Limited to charged for, mixing in the third step
Accordingly, the electrostatic force together two kinds of ultrafine particles 1
Ru can be complexed by coupling in pairs 1 or 1: 2.
Further, after the third step, the mixed ultrafine particles are subjected to an alternating current.
Since the fourth step was set up to pass through the world, two types of ultrafine
Particles approach each other to a distance where they can bond by electrostatic forces
The probability of doing so becomes high, and complexing can be promoted .
In addition, two types of ultrafine particles generated in the first step
At least one of them is manufactured in the third step or the fourth step
By using composite ultra fine particles,
Composite ultrafine particles with a more complex structure composed of ultrafine particle materials
Can be manufactured.

The composite ultrafine particles are formed by the method described above.
To control the number of ultrafine particles formed and their bonding state
Therefore, it is possible to use nano materials that are useful as electrical materials and functional materials.
Enables production of new materials controlled on a meter scale
It Specifically, ultrafine particles formed by different types of ultrafine particles
Use of hetero interfaces, for example for semiconductors, sensors, etc.
For controlling the production of ceramics
Greatly contributes to various industrial fields such as high functionality by
can do. In addition, a relatively simple device and method
To efficiently produce the target composite ultrafine particles
Therefore, the conventional activated plasma-metal reaction method, etc.
Cheaper than the method of manufacturing composite ultrafine particles
Can be.

[Brief description of drawings]

FIG. 1 is a block diagram showing a method for producing composite ultrafine particles in Example 1 of the present invention.

FIG. 2 is a block diagram showing a method for producing composite ultrafine particles in Example 2 of the present invention.

FIG. 3 is an electron micrograph of sodium chloride ultrafine particles generated in the first step of the present invention.

FIG. 4 is an electron micrograph of ultrafine silver particles generated in the first step of the present invention.

FIG. 5 is an electron micrograph of composite ultrafine particles compounded in the fourth step of the present invention.

FIG. 6 is an electron micrograph of composite ultrafine particles compounded in the fourth step of the present invention.

[Explanation of symbols]

1 Ultrafine Particle Generator 2 Ultrafine Particle Generator 3 Particle Charger 4 Particle Charger 5 Mechanical Mixer 6 Electric Mixer A Ultrafine Particle Material B Ultrafine Particle Material C Composite Ultrafine Particle D Ultrafine Particle Material E Composite Ultrafine Particle

Claims (2)

(57) [Claims] 1. A first step in which two types of ultrafine particles having a particle size of several nm to several tens nm are separately generated, and the ultrafine particles generated in the first step are electrically charged to opposite polarities. The second step, the third step of mixing the ultrafine particles charged in the second step in a gas atmosphere, and the mixed ultrafine particles
The fourth step of passing the
Composite ultrafine particles with a ratio of the number of offspring of 1: 1 or 1: 2
A method for producing composite ultrafine particles, characterized in that a child is prepared . 2. At least one of the two types of ultrafine particles generated in the first step is a composite ultrafine particle produced in the third step or the fourth step, and is composed in a required number ratio.
The method for producing composite ultrafine particles according to claim 1, wherein the composite ultrafine particles are prepared.