JP3404520B2 - Method for producing ultrafine particles and high-density crystals thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ultrafine particles, particularly nanometer order, used for developing functional materials, nonlinear optical materials, high-precision catalysts, high-performance composite materials, etc., which are based on quantum effects expressed by the size effect of particles. The present invention relates to the production of ultrafine particles having a diameter and crystals thereof.

[0002]

2. Description of the Related Art When a substance is made into ultra-fine particles on the order of nanometers (nm), it has a possibility of exhibiting properties different from those in the bulk state, for example, a drastic drop in melting point and a quantum effect. Is commonly known. Development of next-generation technologies utilizing such newly developed properties is being actively conducted, and specific application examples thereof include high-performance composite materials, catalysts, nonlinear optical materials, storage elements, and so on. It extends to technical fields in the field. However, at present, with regard to atomization of substances, which is an essential elemental technology for these technological developments, it is not always possible to obtain sufficient particles such as particle size, uniformity, and crystallinity of the atomized particles. First, this is one of the bottleneck of technological development,
It has become a major technical challenge. This will be described below.

Generally, in order to produce fine particles, from the viewpoint of particle diameter, they are roughly classified into a breakdown method and a built-up method. At present, the breakdown method is considered to be limited to submicron order particle size, and is not suitable for producing particles of nm order size. Therefore, a build-up method is mainly used to obtain particles on the order of nm. The vapor phase method and the liquid phase method are known as the methods for the build-up.

As the liquid phase method, a method mainly utilizing a chemical reaction using reverse micelles is adopted.
Recently, methods utilizing the thermal decomposition of organic compounds such as metallic soap have been proposed. However, although the liquid phase method has an advantage that a large amount of fine particles can be easily produced, since a chemical reaction is used, impurities are mixed in the particles and fine particles of several nm or less are generated. It has drawbacks such as difficulty in manufacturing.

On the other hand, the vapor phase method is a method of mainly vaporizing a pure substance and then condensing the vapor, so that a high-purity substance is easily obtained, and it is suitable for an electronic device using a semiconductor substance or the like. Although it is convenient and has the advantage that ultrafine particles of 1 nm or less can be obtained relatively easily, it has disadvantages such as low production efficiency and poor energy efficiency. By the way, since nm-order fine particles produced by the vapor phase method are in a dilute state dispersed in a gas, it is necessary to concentrate them in a stage of secondary treatment or processing. The simplest and easiest method of concentration is collection with a filter or the like, but simple collection causes aggregation and fusion between the collected particles, and it is extremely difficult to obtain particles in a completely isolated state. Have difficulty. Therefore, in order to prevent aggregation and fusion between particles, a method of concentrating using a fusion prevention stabilizer has been proposed.

Cationic surfactants and alkanes having a thiol group have been tried as the anti-fusing stabilizer, and the method of using them is to spray the anti-fusing agent to form fine particles. A method of collecting and a method of trapping with liquid nitrogen in an organic solvent have been used. However, the collection of particles using these methods is not always sufficient, and the inertial collision force, which is the collection driving force in the former case, and the temperature differential migration force in the latter case, do not necessarily affect all generated particles. However, there is a problem that the capture efficiency is low.

Further, the collection by the filter can be expected to be effected by the inertial collision force and the diffusing force effective for the fine particles, and can be easily carried out by appropriately adjusting the layer thickness of the filter and the packing density of the fibers and the like. It is possible. However, when the filter is used for collecting fine particles, there is a problem that not only the agglomeration and fusion between particles described above occur but also a major drawback of the filter is clogging. In particular, liquid particles are likely to be clogged due to the surface tension after collection, and it is presumed that these are the reasons why they were not adopted by the former two.

Next, the problems of the shape and internal structure of nanometer fine particles, which are important for the development of applied technology of nanometer-order fine particles, will be mentioned. Conventionally, regarding the shape and internal structure of fine particles produced by various methods including a liquid phase method and a gas phase method, the internal structure has a difference in crystallinity depending on the production method, while the shape is There is almost no difference due to the method, most of the fine particles are amorphous, and generally, they are spherical. However, in order to exhibit the quantum size effect and the like, it is predicted that control at the atomic level is indispensable, as seen in the production of two-dimensional nm-order thin films and the like. Atomic level control of nano-sized particles must control not only the inside of the particles but also the surface. The control of the fine particle surface means, in the first place, the fine particles having crystal faces formed,
There is a demand for the production of ultrafine particles having crystal planes. As described above, at present, an efficient method for producing ultrafine particles of the nm order existing in an isolated state using a vapor phase method and a method for producing ultrafine particle crystals of a close-packed structure in which the ultrafine particles are arranged at high density As for, there is still no known satisfactory method.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned actual situation in the prior art. That is, an object of the present invention is to provide a method for efficiently producing colloidal ultrafine particles in which individual particles of nanometer (nm) order prepared by a vapor phase method exist in a stable isolated state. It is in. Another object of the present invention is to provide an ultrafine particle crystal having a close-packed structure in which nm-order colloidal ultrafine particles existing in an isolated state are arranged at a high density without coalescence.

[0010]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that a gas treated with a specific particle stabilizer contains a gas containing ultrafine particles of nm order. When passed, in the filter, the particle stabilizer adheres to the individual particles, and the ultrafine particles are collected in a state where they exist in an isolated state. When the collected filter is washed with a solvent, a colloidal ultrafine particle solution is obtained. Therefore, it was found that the colloidal ultrafine particles can be heat-treated to obtain ultrafine particle crystals having a densely arranged and close-packed structure, and the present invention has been completed.

That is, according to the present invention, the ultrafine particle-containing gas produced in the gas phase is passed through a fine particle capturing filter in which a particle stabilizer for preventing aggregation and fusion between the ultrafine particles is adsorbed in advance. A method for producing ultrafine particles, which comprises capturing ultrafine particles on the filter, attaching a particle stabilizer to the ultrafine particles, and then washing the filter with a solvent to obtain a colloidal ultrafine particle solution. Is provided. The fine particle capturing filter is preferably obtained by immersing the filter in a solution containing a particle stabilizer that prevents aggregation and fusion of ultrafine particles and then drying.

Further, according to the present invention, the colloidal ultrafine particles obtained by the above-mentioned method are heat-treated, so that the individual particles are not aggregated or fused and are isolated to form a high-density array state and aggregate. And a crystal plane, which provides a method for producing a high-density ultrafine particle crystal.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. In the present invention, as the material used for producing the colloidal ultrafine particle solution, any material can be used as long as it can produce ultrafine particles of nm order by a vapor phase method, and examples thereof include silver, gold, platinum, germanium, and iron. Metals such as cobalt, cadmium sulfide, metal sulfides such as zinc sulfide, and semiconductor compounds such as silicon. Further, as a method for obtaining the ultrafine particles of the material, various conventionally known gas phase methods, for example, ultrafine particle generation method by heating furnace, hot wire type aerosol generation method, etc. Any fine particles can be used as long as they are dispersed, but it is preferable to use ultra fine particles generated by a hot-wire type aerosol generating method under atmospheric pressure which can easily generate ultra fine particles and save energy.

Next, in order to collect the ultrafine particles dispersed in the gas in an isolated state with high efficiency, a filter is used as a collector. It is important to use a filter in which a particle stabilizer is adsorbed in advance as this filter. That is, in the present invention, by passing the ultrafine particle-containing gas through the filter to which the particle stabilizer is adsorbed, the ultrafine particles to which the particle stabilizer is attached are collected by the filter.

As the filter for trapping fine particles used in the present invention, either a filter in which a particle stabilizer is physically adsorbed or chemically adsorbed can be used. Among them, the filter is immersed in an organic solvent containing a particle stabilizer. After that, it is preferable that the particle stabilizer is uniformly deposited on the surface of the particle collecting part, that is, the surface of the filter-filled fiber by removing the solvent by drying. According to this method, the microparticles are collected on the filter-filled fibers and, at the same time, come into contact with the particle stabilizer. As a result, the fine particles are covered with the particle stabilizer due to the surface tension, and the collected fine particles come close to each other without directly contacting each other to be in a high density state.

As the filter used in the present invention, any conventionally known filter that can collect small-diameter particles can be used, either natural fibers or synthetic fibers, but it has low reactivity with particles and has high heat resistance. Those having are preferable, and specifically, nylon fiber, tetron fiber, aramid fiber, teflon fiber and the like are used. In addition, as the fiber diameter, from the viewpoint of ensuring the porosity and the strength of the filter, several μm
It is preferably in the range of several tens of μm, more preferably about 5 to 20 μm, and specifically, a filter made of nylon fibers of about 10 μm is suitable.

The particle stabilizer to be adsorbed on the filter is required to be an organic compound which prevents agglomeration and fusion of the used material fine particles and has an affinity or a binding property with the material fine particles. , An organic compound having a functional group such as a thiol group or a surfactant is used, and specifically, dodecanethiol, octanethiol, alkanethiols such as octadecanethiol, and cationic surfactants such as alkyltrimethylammonium are used. preferable.

In the present invention, the particle stabilizer used for preventing aggregation and fusion of particles is sufficient if it can form a monomolecular layer or a bimolecular layer around the ultrafine particles. If all the stabilizers are effectively used, the amount thereof does not need to be so large, and the amount of the particle stabilizer used at this time is a small amount to prevent the particles from agglomerating and fusing. It is sufficient that the range of several times to several tens of times is sufficient for the amount of ultrafine particles to be collected, and this action extends to the particles to be collected one after another. The above-mentioned method of the present invention, as compared with the conventional spraying method, etc., because the ultrafine particles are collected by the filter and at the same time, the particle stabilizer surrounds the periphery of the individual ultrafine particles by its surface tension. There is an advantage that it does not cause aggregation or fusion with the collected ultrafine particles.

By the way, in order to fully exhibit this trapping effect, the trapped fine particles and the particle stabilizer must be in good contact with each other. For that purpose, the particle stabilizer needs to adhere to the filler such as the filter fiber in a coating form. Therefore, in the present invention, it is preferable to employ a method in which the particle stabilizer is dissolved in a volatile organic solvent such as benzene, toluene, hexane, or octane, the filter is immersed therein, and then dried. According to this method
Since the particle stabilizer is uniformly adsorbed or adhered to the filter packing material, the captured ultrafine particles always come into contact with the particle stabilizer, and are collected in a high density in an isolated state.

Next, the filter which has collected the ultrafine particles by the above-mentioned method is immersed in an organic solvent such as benzene, toluene, hexane, octane or the like to be washed to obtain a stable solution containing colloidal ultrafine particles. Can be easily obtained.

The ultrafine particles collected by the above method are expected to be in a highly dense isolated state. However, since an optimum amount of the particle stabilizer and the like are present, a completely ideal high density state is obtained. Has not been achieved. The ideal state here is a state in which only a monomolecular layer or a bimolecular layer of the particle stabilizer exists between the isolated fine particles, and the structure has a close-packed structure. Therefore, in order to make an incomplete high-density structure into an ideal close-packed structure, it is necessary to remove unnecessary particle stabilizers existing between the particles. Conventionally, removal of this excess particle stabilizer has been performed by washing with a solvent, etc., but there is a high possibility that the particles will be washed and removed together, and this is not always a sufficient method and good yield etc. Was needed.

By the way, since the high-density state after collection does not always form an ideal close-packed structure as described above, this is caused by agglomeration and fusion between particles. In order to obtain an ideal close-packed structure divided by a monolayer or bilayer, which is the minimum amount of particle stabilizer capable of preventing We have found a method of applying heat treatment to the collected high-density ultrafine particles.

When a certain temperature is reached by the heat treatment according to the method of the present invention, the excess particle stabilizer evaporates and vaporizes, while the particle stabilizer bound to the ultrafine particles has a function of remaining due to its binding force. It is thought to be done. The binding force between the ultrafine particles and the particle stabilizer may be a physical binding force or a chemical binding force, but in general, both are stronger than the binding force between the particle stabilizer molecules. This is because the material having such characteristics is selected as the particle stabilizer. The temperature of this heat treatment varies depending on the type of particle stabilizer used, but is usually 10
It is preferable to perform heat treatment in the range of 0 to 300 ° C, preferably 150 to 200 ° C. If this is heat-treated under reduced pressure, the temperature can be further lowered.

The heat treatment of such high-density ultrafine particles causes another important action. That is, when the particle size is smaller than about 10 nanometers, the melting point is remarkably lowered due to the fineness of the particles, and for example, in the case of silver, the melting point is greatly lowered from about 980 ° C to 200 ° C or less. From another viewpoint, this phenomenon also causes a negative effect of causing aggregation or fusion between particles at the time of collection. From another point of view, it is also considered to be a factor that causes recrystallization of particles.

In the conventional method, when the nanometer fine particles are heated, the fine nanometer particles tend to be fused to each other and grow, whereas in the present invention, the particle stabilizer contained in the fine nanometer particles is It is thought to act in the direction of hindering growth. Therefore, there is a limit diameter determined by the temperature and the like, and particles having a diameter smaller than the limit diameter grow and crystallize, but the growth of the particles having a diameter larger than the limit diameter is hindered. Needless to say, this tendency results in uniform particle size. In the case of recrystallization by heat treatment, the surface of the particle can be made into a crystal plane by gradually heating for a sufficient time and then cooling. As described above, in the heat treatment process of the nm-order fine particles containing the particle stabilizer, not only the formation of the ideal close-packed structure described above can be realized, but also the crystal fine particles having the uniform particle diameter and the crystal planes. Can also result in the generation of

By the way, the recrystallization temperature and the temperature required for removing the excess grain stabilizer are not necessarily the same. Therefore, when treating these separately, it is possible to control the action thereof by changing the atmospheric pressure or the like as another control factor. That is, temperature and pressure are control factors for removing excess particle stabilizer, while
It is also possible to use only temperature as a controlling factor for recrystallization.

[0027]

EXAMPLES The present invention will be specifically described below with reference to examples. A gas (ultrafine particle number concentration of about 5 × 10 ⁸ particles / cc) containing ultrafine particles of silver having a particle size distribution of about 1 to 20 nm generated by a hot-wire type aerosol generator was used under atmospheric pressure. On the other hand, a filter with a thickness of about 10 mm composed of 10 μm nylon fiber for collecting ultrafine particles is immersed in a toluene solution containing about 1% of dodecanethiol as a particle stabilizer so that no bubbles remain in the filter. After that, a filter dried at room temperature was obtained. By passing the gas containing ultrafine particles of silver generated from the above-mentioned aerosol generator at room temperature and normal pressure at a flow rate of about 10 to 20 cm / sec, through the filter thus obtained,
The ultrafine particles of silver were collected. When the gas after passing through the filter was inspected, it was found that the ultrafine silver particles were not contained, so it is considered that the silver fine particles contained in the gas were almost completely collected.

Then, the filter was thoroughly washed with toluene to obtain a colloidal ultrafine particle solution in which ultrafine silver particles (particle size: about 1 to 20 nm) were dispersed in toluene. FIG. 1 shows a photograph of ultrafine silver particles taken by an electron microscope after removing toluene from the obtained colloidal ultrafine particle solution. According to FIG. 1, it can be seen that the individual particles are in a state of being concentrated to some extent and in an isolated state.

Next, the ultrafine silver particles obtained by the above method were heated in nitrogen gas at about 170 ° C. for about 30 minutes. FIG. 2 is a photograph of the ultrafine silver particles obtained by this heat treatment, taken by an electron microscope. According to FIG. 2, the particles are very dense, the particle spacing is almost equivalent to two molecules of dodecanethiol, and it is found that the particles are in a state close to the closest packing structure. Further, comparing FIG. 2 and FIG. 1,
It can be seen that in FIG. 1, the particle size distribution of the particles is considerably wide, whereas in FIG. 2, the ratio of the minute particles is reduced and the particle size distribution width is narrowed, and the particles are uniformized. Regarding the shape of the particles, in Fig. 1, the shape is close to a circle, whereas in Fig. 2, the shadows of hexagons and triangles can be seen, which indicates that the particles have crystal faces. ing. In order to confirm the difference between FIG. 1 and FIG. 2, as a result of examining electron beam diffraction, the diffraction pattern showing an amorphous state is shown in FIG. 1, whereas the diffraction pattern showing a crystalline state is shown in FIG. It turned out to be.

[0030]

As described above, according to the present invention, it is possible to easily and efficiently obtain isolated particles of nm order, and further, it is possible to obtain a super close packed structure composed of the isolated particles. Fine particle crystals are considered to contribute to the development of properties that have been strengthened as an aggregate without impairing the properties of individual particles. For example, they are expressed by uniform microparticulation that has not been obtained in the past. By integrating quantum effects such as light emission as an aggregate, it is expected to be useful for practical application such as utilization as an optical material or electronic material.

[Brief description of drawings]

FIG. 1 is a photograph of ultrafine silver particles obtained by the method of the present invention.

FIG. 2 is a photograph of a silver high-density ultrafine particle crystal obtained by the method of the present invention.

Claims (7)

(57) [Claims] 1. An ultrafine particle-containing gas produced in a gas phase,
At the same time as capturing the ultrafine particles on the filter, by passing through a filter for capturing particles which adsorbs a particle stabilizer that prevents aggregation and fusion between the ultrafine particles in advance,
A method for producing ultrafine particles, characterized in that a colloidal ultrafine particle solution is obtained by attaching a particle stabilizer to the ultrafine particles and then washing the filter with a solvent. 2. The filter for trapping fine particles is obtained by immersing the filter in a solvent containing a particle stabilizer that prevents aggregation and fusion between ultrafine particles and then drying the filter. Item 2. The method for producing ultrafine particles according to Item 1. 3. The method for producing ultrafine particles according to claim 1, wherein the ultrafine particles are particles having a nanometer (nm) diameter. 4. The method for producing ultrafine particles according to claim 1, wherein the ultrafine particles are a semiconductor compound such as a metal, a metal oxide, a metal sulfide or silicon. 5. The method for producing ultrafine particles according to any one of claims 1 to 4, wherein the particle stabilizer is a thiol compound. 6. The thiol compound is dodecanethiol,
It is octane thiol or octadecane thiol, The manufacturing method of the ultrafine particle of any one of Claims 1-5 characterized by the above-mentioned. 7. By subjecting the colloidal ultrafine particles obtained in any one of claims 1 to 6 to a heat treatment, the individual particles are not aggregated or fused and are isolated to form a high-density array state and aggregate. And a method for producing a high-density ultrafine particle crystal having a crystal plane.