WO2001008795A1

WO2001008795A1 - Fine particle manufacturing method using laser beam

Info

Publication number: WO2001008795A1
Application number: PCT/KR2000/000666
Authority: WO
Inventors: Man-Soo Choi; Dong-Geun Lee
Original assignee: Choi Man Soo; Lee Dong Geun
Priority date: 1999-08-02
Filing date: 2000-06-26
Publication date: 2001-02-08
Also published as: KR20010016692A

Abstract

A method of manufacturing fine particles includes the steps of producing fine particles of a material targeted for manufacture by a physical or chemical method, irradiating a laser beam into the aggregates of the produced fine particles that exist in gases so that fine particles coalesce to form spherical particles, and trapping the spherical particles.

Description

FINE PARTICLE MANUFACTURING METHOD USING LASER BEAM

Technical Field

The present invention relates to a method for manufacturing fine particles including ceramic particles, metallic particles, glass particles or composite particles using a physical method or a chemical method, and more particularly, to a method for controlling the size, morphology, crystalline phase and composition of fine unagglomerate particles at high concentrations by facilitating coalescence of the fine aggregate particles by irradiating a laser beam into the produced tine aggregate particles. Background Art

In order to physically manufacture fine particles, a solid or liquid material is heated to be evaporated, cooled to be super-saturated and is then recondensed. Here, for the purpose of evaporating the solid or liquid material, various heating methods are used, including heating using a laser beam, heating using an electrical heater or heating using an arc discharge. Once the solid or liquid material is evaporated, the evaporated material is super-saturated and recondensed in the same procedure to produce fine particles.

In a chemical method ot manufacturing fine particles, the fine particles are produced by various chemical reactions induced by various means, such as plasma, microwave, an electrical heater or a combustion flame burner.

However, in the aforementioned physical and chemical method for manufacturing fine particles, in order to manufacture particles at high concentrations, aggregate particles shaped of a bunch ot grapes and composed of small primary particles are generally produced. Since the aggregate particles have a collision cross- sectional area much larger than spherical particles ot the same volume, they grow rapidly Now, a conventional method tor manutacturmg fine particles using a general physical method w ill be described with reference to FIG. 1 FIG. 1 schematically shows a method for manufacturing particles by evaporating a material targeted for manufacture by an arc discharge. As shown, tungsten or graphite 1 is used as a positive electrode and a target material 2 is used as a negative electrode. Then, if a strong direct current (DC) is applied to the positive and negative electrodes, the target material 2 is evaporated within an evaporation space 5 to generate an arc 3.

Then, an inert gas 4 such as helium is injected in a direction indicated by an arrow to transfer the generated arc 3 to a particle trapping device 10. The transferred arc 3, that is, a vaporized material, passes through a cooler 9 to be recondensed and turned to be particles in a solid phase The particles are trapped in the particle trapping device 10 by an electrical trapping method or a cold trapping method Here, the pressures ot the evaporation space 5 the cooler 9 and the particle trapping device 10 are controlled by using a vacuum pump connected through an exhaust duct 15 However, according to the conventional method tor manufacturing fine particles at high concentrations, a vaporized material is cooled in a cooler to cause super-saturation, thereby producing an aggregate 20 having a shape like that of a bunch of grapes, that is, many primary particles 21 are connected to one another, as shown in FIG. 2. Now, a conventional chemical method for manufacturing fine particles will be described with reference to FIG. 5. As shown, a chemical precursor material 100 is injected into a chemical reactor 102 and the chemical precursor material 100 is heated using a heater 101 such as an electrical heater or a combustion flame burner, the heater 101 installed outside the chemical reactor 102. Alternatively, as shown in FIG. 6, a microwave 111 is formed in a reactor 102 using a plasma generator or microwave generator 110 installed outside the reactor 102, thereby causing a chemical reaction of the chemical precursor material 100.

In the case ot producing oxide particles 120, high-purity oxygen ozone or water vapor is contained in the chemical precursor material 100 miected into the reactor 102 In the case ot producing non-oxide particles such as silicon (Si) particles oxygen, ozone or water vapor is not nηected If the chemical precursor material 100 injected into the reactor 102 is heated to a high temperature or becomes a plasma state, a chemical reaction occurs to nucleate extremely small particles 120 and the particles collide with each other to grow. Here, in view of economic manufacture, the particles must be in a high concentration per unit volume. To this end, a heavily concentrated chemical precursor material is injected into a reactor to produce aggregates 81 and 20, thereby accelerating the growth of particles.

In manufacturing thin films or bulk materials by sintering fine particles, aggregates cause flow and packing problems to become porous, which adversely affect the mechanical strength and optical and magnetic properties of the produced bulk materials.

Thus in order to increase the quality and reliability in manufacturing various kinds ot tine powders, it is important to form particles that have a uniform size distribution, have a spherical shape and are as small as possible in the nanometer scale, and also to control the crystalline phase ot fine powders.

Disclosure of the Invention

To solve the above problems, it is an objective of the present invention to provide a method for manufacturing spherical fine particles smaller than those manufactured by the conventional method, by irradiating a laser beam into early stage fine aggregate particles formed by a conventional physical or chemical method to coalesce the aggregate particles so as to convert the same into spherical nanoparticles having the same volume as the fine aggregate particles, and by using the fact that the collision cross-sectional areas of the spherical nanoparticles are smaller than those of conventionally produced aggregate particles.

Since the nanoparticles coalesced by a laser beam collide with one another noticeably fewer times compared to the aggregate particles, the growth due to collision can be suppressed, thereby obtaining uniform, spherical particles which are finer. It is another objective ot the present invention to provide a method tor manufacturing spherical tine particles having uniformly distributed compositions by irradiating a laser beam into composite aggregate particles, thereby controlling the uniformity of composition in a particle. While fine particles are generated and grow in gases, the irradiation of laser beam on the aggregates causes rapid heating of particles and the transformed spherical particles may also experience rapid cooling right after passing the laser beam. This can be utilized to control the crystalline phase of fine particles..

To achieve the first objective of the present invention, there is provided a method of manufacturing fine particles includes the steps of producing fine particles of a material targeted for manufacture by a physical or chemical method, irradiating a laser beam into the aggregates of the produced tine particles so that tine aggregate particles coalesce to form spherical particles.

Also, the target material may consist ot two or more components and spherical composite particles are manufactured by irradiating a laser beam into the produced aggregates. Therefore according to the present invention, coalescence ot particles is rapidly facilitated by irradiating high-power laser beam into aggregate particles at the time of formation thereof, thereby converting the aggregate particles into spherical particles. Also, high-concentration spherical particles smaller than conventionally produced particles can be manufactured by using the fact that spherical particles have smaller collision areas than the aggregate particles of the same volume.

In particular, the present invention is very advantageously used in manufacturing nanoparticles of 100 nm or less

Brief Description of the Drawings The above objectives and advantages ot the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which-

FIG 1 is a schematic diagram illustrating a conventional method tor evaporating and condensing a material targeted tor manufacture by an arc discharge FIG 2 illustrates aggregates condensed by the method shown in FIG 1

FIG 3 is a schematic diagram tor explaining a method tor evaporating a material targeted for manufacture by irradiating a laser beam;

FIG. 4 is a schematic diagram for explaining a method for evaporating a material targeted for manufacture by an electrical resistance heating method;

FIG. 5 is a schematic diagram for explaining a method for manufacturing fine particles by inducing a chemical reaction of reactants using a conventional heater,

FIG. 6 is a schematic diagram for explaining a method for manufacturing fine particles by inducing a chemical reaction of reactants using a conventional plasma or microwave generator;

FIG 7 is a schematic diagram illustrating an apparatus for adopting the method tor manufacturing fine particles according to an embodiment ot the present invention,

FIG 8 is a schematic diagram partially illustrating an apparatus tor adopting the method tor manufacturing tine particles according to another embodiment ot the present invention, and FIG 9 is a schematic diagram partially illustrating an apparatus tor adopting the method for manufacturing tine particles according to a still another embodiment of the present invention

Best mode for carrying out the Invention Preferred embodiments of the present invention will now be described in more detail with reference to the accompanying drawings

FIG 7 is a schematic diagram illustrating an apparatus for adopting the method for manufacturing fine particles according to an embodiment of the present invention As shown, the fine particle manufacturing apparatus includes an evaporator 90 installed in a housing 80, for evaporating a material targeted for manufacture, a gas nozzle 63 tor meeting gas into the evaporated material to be condensed a beam irradiation apparatus (not shown) tor irradiating a laser beam 60 into tine aggregate particles produced from the evaporated material and a cooler 66 and a trapper 67, both tor trapping the produced particles Reference numeral 61 denotes a focusing lens tor focusing a laser beam reference numeral 70 denotes a w indow tor projecting the laser beam and reference numeral 68 denotes an exhaust path connected to a vacuum pump for adjusting the pressures of an evaporation space and a trapping space.

The evaporator 90 can be any conventional evaporation apparatus that is used in physical deposition. In other words, an evaporation method using an arc discharge, disclosed in U.S. Patent Nos. 4,732,369 and 5,472,749, an evaporation method using laser beam or electron beam irradiation disclosed in U.S Patent No.

5,534,314, or an evaporation method using electrical resistance or inductive heating disclosed in U.S Patent No 5,618,475, can be used, which will now be described in detail. The apparatus and method for evaporating a material targeted tor manufacture has been described above with reference to FIG 1 and a further explanation thereof will not be given FIG 3 shows an apparatus based on evaporation using laser beam irradiation.

Referring to FIG 3, a laser beam 30 is irradiated through a lens 31 and a window 32 into a solid or liquid material 22 targeted for manufacture prepared within an evaporation space 25 of a chamber 34 to evaporate the target material 22, so that it becomes a vapor phase 23 The vapor-phase material is carried by an inert gas 4 sprayed by a separate supply means so that it is exhausted through a vapor spray orifice 33 The evaporation apparatus using an electron beam is substantially the same as the evaporation apparatus using laser beam irradiation, except that a focusing lens and a window corresponding to the electron beam are provided

An alternative evaporation apparatus based on electrical resistance heating is shown in FIG 4. As shown, a rod-shaped target material 42 is placed into an evaporation space 35 of a chamber 46 and a DC or AC electrical field is applied from a power source 40 to an electric resistor 44 surrounding the evaporation space

35, for heating A ceramic insulator 45 is provided around the electric resistor 44 to reduce heat loss

One end 42 ot the target material 42 is melted by heating the resistor 44 and a vapor phase material evaporated therefrom is sprayed by a gas 4 through a vapor spraying orifice 43

inductive heating may be used instead ot electrical resistance heating.

Now, a method for manufacturing fine particles using the aforementioned apparatus according to the present invention will be described in detail.

Referring back to FIG. 7, a material targeted for manufacture (not shown) is evaporated by the aforementioned evaporation apparatus. The target material which can be adopted in the present invention is not specifically limited, inclusive of ceramic, metal, carbon, glass or composite, and compounds produced by combination thereof, can be used.

Then, a gas is supplied to inject a vapor-phase jet 83 The supplied gas is preferably an inert gas such as helium Also, according to the kind of particles produced, a reactant gas such as oxygen, nitrogen or argon can be used, not being limited by this embodiment ot the present invention

The vapor-phase jet 83 is exhausted through a vapor exhausting orifice (not shown) Gas 64 is additionally miected into the exhausted vapor-phase jet 83 through a gas nozzle 63 spaced an appropriate distance apart from the vapor exhausting orifice, thereby recondensing the jet 83 to produce particles As described above, the produced particles include small-sized aggregate particles 81 when high-concentration particles are produced. Although not shown, the particles may be produced by expansion as well as additional gas injection. According to the present invention, a laser beam 60 is irradiated into the produced aggregate particles that exist in gases through a focusing lens 61 The small-sized aggregate particles 81 are coalesced by laser beam irradiation, so that they form spherical nanoparticles 65. The produced spherical particles have a collision cross sections smaller than those of aggregates Thus, the growth rate of the spherical particles is reduced and small-sized spherical particles can be obtained by trapping the same using the conventional cooler 66 and trapper 67

According to another aspect ot the present invention, as shown in FIG. 8, in order to increase the irradiation efficiency of a laser beam a plurality of reflecting mirrors 69a and 69b are installed The laser beam travels in a plurality ot paths through the reflecting mirrors 69a and 69b thereby further increasing the coalescence effect ot particles Also although not shown a cylindrical lens is installed, instead of the focusing lens 61 shown in FIG. 7, and a plane laser beam having passed through the cylindrical lens is reflected by the reflecting mirrors 69a and 69b, thereby coalescing the particles.

The present invention can also be applied to a chemical process in addition to the above-described physical process, which will now be described with reference to FIG. 9.

Referring to FIG. 9, a fine particle manufacturing apparatus according to the present invention includes a chemical precursor material injector (not shown) for injecting a reactant 100 into a chemical reactor 102, a reaction inducing apparatus 1 15 for chemically reacting the injected reactant 100 to produce particles, a beam irradiation apparatus (not shown) for irradiating a laser beam 160 into small-sized aggregate particles 81 produced in a chemical reactor 102, and a cooler 166 and a trapper 167, tor trapping the produced particles Here, reference numeral 168 denotes an exhaust path connected to a vacuum pump, for adjusting the pressures ot a reactor space and a trapping space. Reference numeral 120 denotes nucleated particles initially produced by the chemical reaction of the reactant, and reference numeral 65 is small-sized spherical particles converted from the small-sized aggregate particles 81 and coalesced by a laser beam 60

The reaction inducing apparatus 115 can be any conventional apparatuses that chemically produce particles. In other words, a heating apparatus (see FIG. 5) for inducing a chemical reaction by heating a reactant, or a plasma or microwave generator (see FIG. 6) for inducing a chemical reaction by generating plasma or microwave mside a chemical reactor, can also be used in the present invention.

Now, a method for manufacturing fine particles using the aforementioned apparatus will be described.

The reactant 100 is injected into the chemical reactor 102 and then the reactant 100 is subjected to a chemical reaction by the reaction inducing apparatus 1 15 installed outside the chemical reactor 102 to nucleate particles 120 The nucleated particles 120 are turned into the small-sized aggregate particles 81 by collision

Then the laser beam 160 which is focused through the focusing lens 161 and the window 170 is irradiated into the aggregate particles 81 so that the aggregate particles 81 coalesce, thereby producing spherical particles 65 while having the same volume. The thus-produced spherical particles 65 have collision cross-sectional areas much smaller than the aggregate particles 81 , thereby retarding the growth of particles and finally obtaining much smaller spherical nanoparticles.

In the case of producing oxide particles, a chemical precursor material containing high-purity oxygen, ozone or water vapor is injected into the reactor. In the case of producing non-oxide particles, oxygen, ozone or water vapor is not injected. .In the case where a material targeted for manufacture is a composite consisting of multiple components, a laser beam is irradiated into small-sized composite particles manufactured by the aforementioned manufacturing apparatus to facilitate coalescence of particles, thereby obtaining spherical composite particles.

According to the method for manufacturing small-sized spherical particles by enhancing the coalescence of particles that exist in gases using laser beam heating, spherical particles smaller than the conventional particles can be manufactured by irradiating a laser beam into a region at which small aggregate particles are formed in the conventional physical or chemical process. Also, the present invention can also be applied in manufacturing composite nanoparticles. Although the invention has been described using an exemplary preferred embodiment, various modifications and changes can be effected by one skilled in the art within the scope of the present invention, and it is Intended the scope of the invention be defined by the claims appended thereto.

Industrial Applicability

The present invention can be applied to manufacture of fine particles including ceramic particles, metallic particles, glass particles or composite particles using a physical or chemical method.

Claims

What is claimed is:

1. A method for manufacturing fine particles, comprising the steps of: producing fine particles of a material targeted for manufacture by a physical or chemical method; irradiating a laser beam into the aggregates of the produced fine particles that exist in gases so that fine particles coalesce to form spherical particles and the growth of particles is retarded; and trapping the spherical particles.

2. The method according to claim 1. wherein the target material consists of two or more components, and spherical composite particles are manufactured by irradiating a laser beam into the produced aggregates.

3. The method according to claim 1 , wherein the irradiation of laser beam on the aggregates causes particles to be rapidly heated and the transformed spherical particles are rapidly cooled right after passing the laser beam, thereby controlling the crystalline phase of fine particles.