JPS61200851A - Method and apparatus for preparing fine particle - Google Patents

Abstract

PURPOSE:To easily and efficiently form fine particles with a desired particle size, by generating the heat exciting reaction of a stock material not reacting at ambient temp. by dielectric breakdown plasma generated by condensing laser beam. CONSTITUTION:CO2-TEA laser beam from a laser oscillator 6 is one with about 0.5-1J/pulse class, a pulse lasting time of about 1 mus and peak output of about 1MW and condensed by a lens 7 to generate ionization action due to an ultra- high electromagnetic field in the vicinity of the focus of said lens and laser induced dielectric breakdown plasma is generated in a tubular passage 3. If stock gases A, B, for example, SuCl4 gas and O2 gas mixed in a stock material container 1 are guided to the side of a product container 2 through the passage 3, the gaseous mixture generates heat exciting reaction by rapid heating due to LIDB plasma P in the tubular passage 3 to form fine particles which are, in turn, transferred to the container 2 while the shapes thereof are held by quenching due to heat extinction.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a method for producing fine particles by thermally excitation reacting raw materials that do not react at room temperature with dielectric breakdown plasma generated by focusing laser light, and a method thereof. Regarding the apparatus for carrying out the implementation.

BACKGROUND ART In recent years, the utility value of fine particles (fine particles on the order of 100A) has increased in the field of ceramic technology, etc., and the demand for manufacturing technology for such fine particles has increased.

Conventionally, the following techniques are known as techniques for producing such fine particles.

1) Method C02- using excitation by absorption of laser light
Transversely Excited Atom
ospheric v -the (hereinafter simply CO□-TE
Using gaseous molecules that have a strong absorption band in the wavelength band (approximately 10 μm) of the A laser as a raw material, the raw material is irradiated with unfocused CO,-TEA laser light, and the molecules are reacted by absorption excitation. Generates fine particles.

II) Method 10' using DC arc plasma A gaseous raw material is introduced into the flame of DC arc plasma which reaches a high temperature to cause a thermally excited reaction, and then is rapidly cooled to generate fine particles.

m) Method using evaporation in low-pressure gas The metal in the screw is heated in low-pressure gas to evaporate it, and the evaporated metal molecules collide with the molecules of the low-pressure gas, releasing energy and cooling the metal. , a metal molecule gas is produced, which is condensed to produce fine particles.

<Problems to be solved by the invention> In the method 1) above, since the reaction is based on absorption excitation, the absorption band of Co2-TEA, such as siH, etc.
Only molecules that are strong in the laser wavelength band or have a broad absorption band can be used as raw materials, and there are restrictions on the types of raw materials. By using different powerful lasers in the visible to ultraviolet range, the range of raw materials that can be used can be expanded.
It is extremely disadvantageous in terms of power efficiency compared to the O□-TEA laser.

Further, in the method 1)), a large amount of electric power is required to generate DC arc plasma, and it is difficult to stabilize this plasma. Furthermore, there have been cases in which the magnetic effect obstructs the introduction of the raw material into the plasma.

Further, in the methods I) and l) above.

Because of the large thermal inertia, it was not possible to create the desired temperature range in a short period of time and within a limited range, resulting in poor controllability.

The present invention has been made in view of the conventional circumstances as described above,
Provided is a method for producing fine particles by a novel method in which electric destructive plasma is generated by a laser beam focused by a lens, and a raw material is subjected to a thermal excitation reaction using this plasma, and an apparatus for carrying out the method. The purpose is to

Means for Solving the Problems> The method for producing fine particles according to the present invention focuses laser light on a lens to generate dielectric breakdown plasma near its focal point, and injects gaseous raw material into the dielectric breakdown plasma. is characterized in that it generates fine particles through a thermally excited reaction. (191) The particle manufacturing apparatus according to the present invention includes a tubular passage through which a gaseous raw material is transferred, a lens having a focal point within the tubular passage, and a dielectric material that is focused by the lens and placed near the focal point within the tubular passage. A laser source that oscillates a laser beam that generates a destructive plasma, and a collection means that is connected to the tubular passage and that collects fine particles generated from a gaseous raw material by a thermally excited reaction caused by the dielectric destructive plasma. Features.

Effect> Dielectric breakdown plasma induced by laser light is generated in a limited range near the focal point of the blades 7 and e. For this reason, the gaseous raw material introduced into the plasma is rapidly heated to an extremely high temperature within the plasma to generate fine particles, and then the fine particles are transferred to the outside of the plasma or the plasma is extinguished, causing the fine particles to rise to an extremely high temperature. It is rapidly cooled and stabilized with a difference,
The particle size becomes constant. It was.

The particle size of the fine particles can be easily controlled by controlling the temperature by adjusting the flow rate and concentration of the gaseous raw material or the plasma generation area.

<Example> An embodiment of the present invention will be described below with reference to the drawings.

First, a fine particle manufacturing apparatus for carrying out the method of the present invention will be described with reference to FIG. 1, which schematically shows its structure. The fine particle manufacturing device connects a raw material container 1 and a product container 2 with a cylindrical tubular passage 3.
It has a container that communicates with the Gaseous raw materials (hereinafter referred to as raw material gas) A and B are introduced into the raw material container 1.
The raw material gas A and the raw material gas B are heated to F/4 in the raw material container 1.
It is designed to be mixed well. still.

These raw material gas A and raw material gas B are a combination that does not react even if mixed at room temperature. Compared to the raw material container 1, the product container 2 is set at a lower pressure.

A mixed gas of raw material gas A and raw material gas B passes through the tubular passage 3 at a constant flow rate from the raw material container 1 side to the product container 2.
It flows to the side.

The raw material container 1 has a window 5 facing the opening on one end side of the tubular passage 3.
is provided, and the C02-TEA radar light from the laser oscillator 6 is focused by the lens 7, enters the container through the window 5, and is focused in the tubular passage 3. The window 5 and the lens 7 are made of KCI, NaCl, Ge, etc., which are transparent at the wavelength of the CO□-TEA laser, but they are not made of materials through which the laser light used in the CO,=TEA laser, etc. is transmitted. If so, there are no particular limitations on the material.

The CO2-TEA radar light from the laser oscillator 6 is about 0.
5 to about I J/pulae class, pulse duration 1
μs, with a peak output of about I MW, and is focused by the lens 7 to cause an ionization effect by an ultra-strong electromagnetic field near its focus, resulting in a laser-induced dielectric breakdown plasma (Laaer-induced dielectric breakdown plasma) in the tubular passage 3.
A breakdown plaama (hereinafter referred to as LIDB grammar) is generated. For example, 0.6-0.8J
A LIDB plasma P with a length of about 2-1 and a diameter of about 1 m is generated by the Co, -T EA laser beam of /pulsse.
Volume of IDB plasma P (approximately 0.02d: 2xlOmo
l) and the gas (as a diatomic molecule) (7Chi/m
olsK:30Cal/m0aIIK) TokaraLI
The DB bra X'-qp has an extremely high temperature of about 10'. This high temperature state is thought to relax on the order of m8.

Since a shock wave is observed, a thin cylinder of rapidly expanding high temperature gas remains in the tubular passage 3, and immediately thereafter rapidly cools down within about 10 ms due to expansion and radiation. That is, depending on the pulse of the laser oscillator 6, the lens 7
in a short time of about 1 μ8 at a predetermined location depending on the focal point of the
Rapid fever state reaching 0K (10k/s) and 10~IOK
A rapid cooling state in which the temperature drops at /S can be obtained.

This state occurs at a much higher frequency than high-frequency discharge (assuming the wavelength of the C02-TEA laser is 10 am).
3X10'm/8)÷(10xiO-'m) =3X1
This shows that high-frequency plasma at 0"Hz) can be repeated at 1) about 00pp. Note that the present invention can also use a continuous wave laser, and in the case of a continuous wave laser, unlike the pulsed laser described above, Rapid cooling is done using LIDB Plasma P.
This is done by moving the area out of the area where it occurs.

According to the fine particle manufacturing apparatus having the above configuration, the raw material gas and the raw material gas B mixed in the raw material container 1 flow through the tubular passage 3 to the product container 2 side. The rapid heating caused by the LIDB plasma P generates fine particles through a thermal excitation reaction within the chamber, and the fine particles generated by rapid cooling when the LIDB plasma disappears due to the pulsed laser retain their shape without further reaction and form a product. container 2
will be transferred to. Specifically, even if it is normally mixed as a raw material, 1
0□ with 5nC14 gas that reacts only at temperatures above 000℃
When using gas, 5n02 is obtained as C12 gas and fine particles, and other 80f7 compounds 1 such as 5b
C1,, hlc13. FeCl, .

The same applies to TlCl, etc. Further, nitrides, borides, carbides, etc. that are gaseous at room temperature can also be used as raw materials. Yet again.

For example, FeCj as a raw material? , is evaporated and condensed in an inert gas to create an aerosol, and the Hz of other raw materials is
It is also possible to obtain fine particles of Fe and HC/gas by mixing with a gas at room temperature and reacting with LIDB7-lasma P.

In addition to using a combination of an aerosol and a gas as raw materials as described above, fine particles can also be produced from a wide range of raw materials such as aerosols, etc. according to the present invention. Further, it is of course possible to supply two or more kinds of raw material gases into the raw material container 1, and these raw material gases may be mixed in advance and supplied to the raw material container 1.

Here, the pulse of the co2-TEA laser is 50 pp8
, the length 2 in the tubular passage 3 with a diameter 21) m1
1) The area of LIDB7 lasma P that occurs across the wound.
Since the flow rate of the raw material gas passing at 50 g is 1 m/II, the processing number is 3 d/s, and it is understood that it takes about 2 hours to process 1 mole of raw material gas with LIDB plasma at 1 atmosphere. . This means that manufacturing 1) 0F/
hr, and is relatively efficient compared to other currently known manufacturing methods. For example, 5nC
A'4 gas + 0□ gas → sno, fine particles + 2CJ2
In the case of gas, the total raw material gas is 2 moles to 1.50.77
When the SnO□ fine particles are generated, for example, the inside of the container is
Reduce pressure to torr.

Even if Bn gas is diluted to 50% with Ar gas, fine particles can be generated on the order of 55 E/hr.

tt, if we assume that the condensation during the process of rapidly cooling the fine particles generated in the LIDB plasma can be described by the theory of coalescence and aggregation of aerosols, then the average of fine particles is 6/! l 6
/! 1 Volume not OC (residence time) (volume concentration) (absolute A vs. temperature), so the average diameter of fine particles dp (XO+
4 (Partial pressure of raw material gas/Flow rate of raw material gas) (However, it is assumed that the absolute temperature is determined at the laser source and does not depend much on the reaction system.) Therefore.

In order to obtain fine particles with a smaller diameter, it is sufficient to lower the partial pressure of the raw material gas (lower the concentration of the raw material gas) or increase the flow rate of the raw material gas.However, when LIDB plasma is induced by a pulse laser.

In order to cause all of the raw material gas flowing in the tubular passage 3 to react with LIDB plasma, a restriction is imposed on the flow rate of the raw material gas. For this reason, when a pulse laser is used, it is easy to control the particle size of the generated fine particles by controlling the partial pressure of the raw material gas.

In this respect, it can be said that particle size control can be performed more easily if a continuous wave laser is used. In reality, the particle size of the generated fine particles is much more dependent on the raw material gas partial pressure than on the raw material gas flow rate, so even with a pulsed laser, it is sufficient to control the raw material gas partial pressure in the range of about 20 A to about 2000 A. Experiments have confirmed that particle size control is possible.

As mentioned above, the tubular passage 3 is approximately the diameter of the LIDB plasma.
Having a small diameter has the following advantages.

a) Since all the raw material gas passes through the LIDB plasma, the generation efficiency of fine particles is high.

b) Because the gas flow in the tubular passage is unidirectional.

Backflow from the product container 2 to the raw material container 1 is prevented, and regrowth of fine particles is prevented.

C) Since the raw material container 1 and the product container 2 are substantially separated, for example, the raw material chamber is heated above the condensation point and liquid nitrogen is introduced into the product container 2 to create a difference in temperature conditions between the two. Tashi,
Alternatively, a difference in pressure conditions can be established between the two by setting the original cap number 1 at high pressure and the product container 2 at low pressure, or by adsorbing to the surface of fine particles generated only in the product container 2 and modifying this surface. It is possible to easily set conditions such as adding a gaseous substance to be used.

Here, when the tubular passage 3 is made small in diameter as described above, while there is the above-mentioned advantage, the generated fine particles may be thermally deposited on the relatively low-temperature wall surface of the tubular passage 3, and the radial direction of the LIDB plasma may It is conceivable that the rapid expansion of the tube may damage the tubular passage 3 or cause harmful effects on the plasma due to decomposition and evaporation of the substances forming the tube wall. It is possible to reduce thermal deposition of fine particles by rapid expansion cooling into the product container 2. On the other hand, in order to more effectively prevent thermal deposition of particles and damage to the tubular passage 3, it is necessary to Just make it as thick as possible.

The ones shown in FIGS. 2 to 4 maintain the advantages of the small diameter of the tubular passage 3 without reducing the particle generation efficiency,
In addition, this is a method that effectively prevents thermal deposition of fine particles and damage to the tubular passage 3.

In the one shown in FIG. 2, the tubular passage 3 is connected to the raw material container side portion 3a.
and a product container side portion 3b.

These image parts 3a and 3b are connected by a cylindrical soyoint member 3C having a porous member 3d such as a glass filter, and at least a portion of the tubular passage 3 surrounding the generation area of the LIDB plasma P has a diameter larger than the diameter of the LIDB plasma. That is. In addition, 8 in the figure is 0 S/G for sealing. Then, an inert gas such as Ar supplied from a supply source (not shown) into the inside of the nozzle member 3C passes through the porous member 3d and is evenly supplied around the LIDB plasma P in the tubular passage 3. ing. As a result, a layer of inert gas is formed near the wall inside the tubular passage 3, and the part near the wall that is not turned into plasma is replaced by the inert gas, so the diameter of the tubular passage 3 related to particle generation is substantially reduced. It has become smaller. Therefore, thermal deposition of fine particles and tubular passage 3
Fine particles can be produced while maintaining the advantages mentioned above without causing any damage.

What is shown in FIG. 3 is a raw material container side portion 3a of the tubular passage 3.
is made to have a small diameter comparable to that of LIDB plasma P, and the product container side portion 3b is made to have a large diameter.

These two subcommittees 3a and -3bt-0s/g 8 are connected to each other. Then, an inert gas such as Ar is supplied from a supply source not shown in Figure 1 to the chamber 72 section 3e provided at the tip of the product container side portion 3b in a laminar flow state along the inner wall surface of the product container side portion 3b. The area where the LIDB plasma P is generated is made substantially smaller in diameter by replacing the portion near the wall surface that is not converted into plasma with an inert gas.

The one shown in FIG.
These containers 1.degree. 2 are connected by a tubular passage 3 extending vertically and having a structure similar to that shown in FIG. 3 and 9.

The silicone oil supplied to the chatuba part 3e from a supply source (not shown) is made to flow down evenly along the inner wall surface of the product container side portion 3b surrounding the generation area of LIDB plasma P, so that the portion near the wall surface that is not converted into plasma is By replacing it with silicone oil, the generation area of LIDB plasma P is made substantially smaller in diameter. If the tubular passage 3 is made somewhat long, the fine particles can be collected in the silicone oil by utilizing thermal deposition of the fine particles on the wall surface.

The device shown in Fig. 1 mixes the raw material gases in the raw material container 1, so it has a volume I that is sufficient to form the raw material container 1, but several types of raw material gases are mixed in advance and supplied. In some cases, the raw material container 1 may have an extremely small capacity as shown in FIG. 5, or the raw material container may be omitted. Here, although not limited to the configuration shown in FIG. 5, this is to prevent particles in the source gas and generated fine particles from depositing on the window 5 and reducing the laser transmittance.

As shown in FIG. 6, an injection port 9 is provided in a round shape from the inside of the raw material container 1 toward the window 5, and an inert gas such as Ar is sprayed onto the air 5 from the injection port 9 to prevent the deposition of particles. It can also be prevented. In addition, if it is necessary to prevent only the deposition of fine particles on the window 5, use a lens 7 with a long focal length so that the area where the LIDB7 lasma P is generated is sufficiently far away from the window 5. Even if you keep them apart, you can achieve your goal.

Furthermore, when the raw material to be supplied has a high point, it is also possible to evaporate and condense the raw material once to generate a dust-containing airflow, and supply this as the raw material gas. For example, as shown in FIG. 7, a raw material A with a high boiling point is heated in a heater 1 and a raw material container 1, evaporated and condensed to form a solid or liquid particulate, and this is supplied into a raw material container 1. Ar to be done,
This raw material gas A is introduced into the tubular passage 3 on a carrier gas such as N2, and mixed with another raw material gas B supplied into the tubular passage 3 before the LIDB plasma P generation area, and is then mixed with the LIDB plasma P by the LIDB plasma P. It can be made to react.

In this case, the intermediate container for mixing raw material gas A and raw material gas B = iLIDB plasma P generation area υ
It may be placed in front. In addition to the heater 10, other known means may be used to heat the raw material A, such as heating by irradiating a CO2 laser for heating.

In addition, the means for collecting the generated particulates is not limited to the one provided with the product container 2, but it is also possible to install a dust collector such as a cyclone, or to collect the particulates by cooling with a flowing liquid film or shower. Furthermore, an adsorbent gas supply device for the purpose of surface modification of the generated fine particles may be attached.

Further, in the embodiment, the laser beam focused by the lens 7 is made to enter the container through the window 5, but the window 5 can be omitted and a lens 7 is provided in the raw material container l, and this lens 7 can also serve as a window. You can also do it.

In addition, the laser used for LIDB plasma generation is CO2
Not only the laser but also other lasers can be used as long as various conditions are satisfied. The laser irradiation direction is not limited to the direction along the axis of the tubular passage 3, but can be irradiated from any direction such as a direction perpendicular to the tubular passage 3.
It is also possible to generate LIDB7 lasma by focusing the thus irradiated laser within the transparent tubular passage 3. For example, when irradiating a laser from a direction perpendicular to the tubular passage 3, it is preferable that the tubular passage 3 has an elongated rectangular cross section along the irradiation direction in order to achieve high efficiency.
On the other hand, when the laser is a film-like beam, it is preferable that the cross section is square. Furthermore, by irradiating the laser from the side of the tubular passage 3 in this way, it is possible to irradiate a large number of lasers along the tubular passage and freely establish the generation region of LIDB plasma, so that the pulse When controlling the particle size of fine particles being generated using a laser, the flow rate of the raw material gas can be easily used as a control parameter.

In addition, although the above-mentioned embodiments have shown the generation of fine particles from two or more types of raw material gases, the present invention has a method of producing fine particles from two or more types of raw material gases.
Co) 4→Ni+4CO It can also be applied to the generation of metal fine particles by thermal decomposition of transition extra space carbonyl. That is, Ni.

It can be used as a new refining method in which metals and ores such as Fe, Co, Mo, W, etc., which are reacted with CO to form cargonyl, are once converted into cargonyl and then refined into fine metal particles.

Incidentally, since the above reaction of N1(Co)4 is extremely toxic, it is recommended to use an apparatus as shown in Fig. @8 to carry out the reaction. That is, Ni (Co) from a raw material container 1 containing metal or light ore is thermally refined by LIDB plasma in a tubular passage 3, and the generated Ni fine particles are transferred to a product container 2.
Along with collecting.

The CO gas generated at the same time is circulated through the pipe 1) to the raw material container 1 and used for the production of N1 (Co), thereby preventing toxic gas from leaking to the outside.

In addition, the particle size distribution of the fine particles produced by the present invention is considered to be approximately lognormal distribution (self-preserving distribution) with a standard deviation of about 1.4, and the average particle size of the fine particles can be easily controlled. Therefore, the present invention can also be applied as a standard aerosol generator.

Furthermore, if the tubular passage 3 is made transparent.

It can also be applied as an emission spectrometer for analyzing CVD reactions.

<Effects of the Invention> According to the present invention, fine particles with extremely stable particle sizes can be produced from a wide range of raw materials using equipment that is simple and easy to handle, and the particle size can also be easily controlled. can do.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a microparticle manufacturing apparatus according to one embodiment of the present invention, FIGS. 2 to 4 are configuration diagrams each showing various aspects of the tubular passage, and A schematic configuration diagram showing a fine particle manufacturing apparatus using high boiling point raw materials, Figure 8 is N1 (
1 is a schematic configuration diagram showing a fine particle manufacturing apparatus applied to a thermal decomposition reaction of Co)4. In the drawing. 1 is a raw material container. 2 is a product container. 3 is a V-shaped passage. 6 is a laser oscillator. 7 is the lens. P is LIDB plasma. Patent author Hitoyoshi Akinori Sawa (1 other person) Representative Patent attorney Former Ishishibu (1 other person) Figure 1^ B Figure 2 Figure 3 Figure 8r Figure 5 Figure 7

Claims (2)

[Claims] (1) Fine particle production characterized by focusing laser light with a lens to generate dielectric breakdown plasma near its focal point, guiding a gaseous raw material into the dielectric breakdown plasma and generating fine particles through a thermally excited reaction. Method. (2) A tubular passage through which a gaseous raw material is transferred, a lens having a focal point within the tubular passage, and a laser beam that is focused by the lens and generates dielectric breakdown plasma near the focal point within the tubular passage. A device for producing fine particles, comprising: a laser source for generating a gaseous material; and a collecting means connected to the tubular passage for collecting fine particles generated from a gaseous raw material by a thermally excited reaction caused by the dielectric breakdown plasma.