JPH06145725A - Production of fine grain - Google Patents

Abstract

PURPOSE:To suppress the formation of coarse grains and to obtain fine grains having a uniform grain size, at the time of producing fine grains by an evaporating method in an arc type gas, by fixing arc plasma or controlling its movement. CONSTITUTION:A magnet 10 for fixing arc plasma on the surface of a raw material member or controlling its movement is arranged, e.g. in a Ti fine grain producing method by an evaporating method in an arc type gas. A substrate 7 is set in a vacuum vessel 4, thereafter, the vacuum vessel 4 is evacuated to a prescribed pressure, and then, an Ar gas 9 is fed to the vacuum vessel 4 to set the pressure to a prescribed value. Next, an electric current is sent through the magnet 10 to generate a magnetic field. After that, a voltage is impressed from an electric source 5 to an upper Ti electrode 1 and a lower Ti electrode 2 to generate arc plasma between the electrodes 1 and 2. The arc plasma at this time is fixed on the central part of the electrode 2 and is stabilized. The electrode 1 is heated and evaporated by the heat of the arc plasma, by which the objective Ti fine grains are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for mass-producing high-purity fine particles at high speed, in which fine particles are produced by removing surface oxides of a raw material member, which is a raw material of fine particles. It is characterized by providing uniform fine particles.

[0002]

2. Description of the Related Art The term "fine particles" refers to particles having a particle size smaller than 1 .mu.m, and because of their unique physical properties, they have been applied to various high-performance electronic parts, chemical products and the like. In particular, high-purity fine particles with uniform particle size have the effects of lowering the firing temperature and improving the characteristics when producing high-performance ceramic electronic components by firing, and that it is possible to realize high-density magnetic recording media. Alternatively, various applications are popular because of its high chemical activity compared to bulk materials and the ability to provide high performance catalysts.

There are various conventional methods for producing fine particles. Among them, the so-called arc-type gas evaporation method using arc plasma as a heat source is capable of producing high-purity fine particles because it is produced in a high-purity atmosphere, or in order to heat and evaporate the raw material with arc plasma having large thermal energy. It has excellent characteristics compared to other manufacturing methods, such as that it can manufacture a large amount of fine particles of high melting point materials such as ceramics at high speed.

FIG. 3 is a schematic view of an apparatus showing a typical example of a conventional arc-type gas evaporation method (reference material: ultrafine particles; Tatsu Hayashi, Ryoji Ueda, Akira Tasaki, edited; Mita Publishing Co., pp. 49-).
p. 51). An example of the procedure for producing fine particles in this conventional example will be described below.

The upper electrode 21 and the lower electrode 22 are installed on an upper electrode part 26 and a sample table 23, respectively, and a vacuum container 24
Is evacuated to, for example, 3 × 10 ^-6 Torr. After that, argon gas as a plasma gas is introduced into the vacuum container 24 and set to 300 Torr. Subsequently, when a DC voltage is applied to the upper electrode 21 and the lower electrode 22 by the power supply 25, arc plasma is generated between these electrodes. The lower electrode 22 is heated, melted and evaporated by the heat of this arc plasma.

The vaporized atoms from the lower electrode 22 thus vaporized are cooled by collision with the atmospheric gas argon, so that they are supersaturated and condensed to form fine particles of the lower electrode material. That is, in this case, the raw material for producing the fine particles is the lower electrode 22. The smoke in the figure is observed because the fine particles rise due to the air flow, and is provided as fine particles after being collected by the collector 27.

In the case of producing fine particles of Si, for example, in this conventional example, if the upper electrode 21 and the lower electrode 22 are made of Si as described in the above cited reference material, the particle size becomes 0. It can be manufactured with a thickness of about 1 μm.

[0008]

However, when fine particles are produced by the above-mentioned conventional technique, arc plasma is generated in the upper electrode and the lower electrode as described in the above cited reference. During the period, red-hot droplets are generated which are enough to be visually observed. Then, there is a problem that coarse particles having a particle diameter much larger than the particle diameter of the fine particles formed by cooling the droplets are generated. Such coarse particles have a particle diameter of several tens of μm depending on the conditions for producing the fine particles, and when mixed in the fine particles, the firing temperature is lowered, the characteristics are improved, and the chemical activity is high as described above. It hinders features such as this. Therefore, it becomes difficult to provide various high-performance electronic parts, chemical products, and the like.

In the prior art, fine particles are provided after such coarse particles are separated by means such as a collector in the prior art example as shown in FIG.
That is, solving the essential suppression of coarse particles remains unsolved. As a result, the amount of coarse particles to be discarded cannot be ignored, and it is difficult to effectively use the fine particle raw material.

The formation of the coarse particles is not limited to the above-mentioned conventional technique example, but occurs in other conventional examples (for example, Masahiro Uda, Satoru Ohno; Journal of Welding Society; 44 (1975) p. 79).
9). It is a well known fact that the main cause is the surface oxide of the fine particle raw material member.

Such removal of the surface oxide of the fine particle raw material member can be considered as a mere extension of the above-mentioned conventional technique. The surface of the fine particle raw material member is heated to a temperature not lower than the decomposition temperature of the oxide by arc plasma. do it.
Although the present inventors tried such a thing in the early stage of the examination, they did not achieve a sufficient effect. This is because the arc plasma moves in a self-selective manner to obtain an oxide that emits thermoelectrons more easily than a clean surface. If the moving range of the arc plasma is limited to only the fine particle raw material, it does not become a serious problem. However, in reality, the arc plasma often moves to holding parts for the fine particle raw material member, other electrode parts, and the like. As a result, a part of the component is also evaporated, and it is difficult to provide high-purity fine particles by mixing with the fine particles.

[0012]

SUMMARY OF THE INVENTION Therefore, the present inventors have diligently made efforts to suppress the production of coarse particles in order to provide electronic parts and the like having excellent characteristics by utilizing the characteristics of fine particles as described above.

The invention according to claim 1 of the present application made from the above process is a method for producing fine particles by heating and evaporating a fine particle raw material member by arc plasma in a reduced pressure gas atmosphere, wherein arc plasma is used as the raw material. It is a method for producing fine particles, which is characterized in that it is fixed on the surface of a member or the movement of arc plasma is controlled.

In order to fix or control the arc plasma according to various fine particle producing conditions, a method of applying a magnetic field is preferable. At this time, the direction of the magnetic field is at least parallel to the electric field of the arc plasma on the surface of the fine particle raw material member, and the magnetic field strength distribution is characterized in that the circumference of the raw material member is larger than the central portion.

The invention according to claim 3 of the present application is a method for producing fine particles, which comprises heating and evaporating a fine particle raw material member by arc plasma in a reduced pressure gas atmosphere, wherein the raw material member is formed prior to the production of the fine particle. Is exposed to a non-oxidizing gas atmosphere containing atomic hydrogen, and then the raw material member is continuously heated and evaporated in a predetermined arc plasma gas atmosphere without being exposed to the oxidizing atmosphere.

[0016]

The operation of the invention according to claim 1 will be described below. The present inventors, while working on a series of suppression control of the generation of coarse particles, coarse particles frequently occur in the state where the arc plasma arbitrarily moves on the surface of the fine particle raw material member, but fixed at one point. We have come to discover that sometimes coarse particles are rarely produced.

The reason is that, when the arc plasma is fixed on the surface of the raw material member, the surface oxide on the surface of the raw material member at the fixing point is evaporated by the heat of the arc plasma, and a clean raw material member surface is exposed and the arc plasma is exposed. It is considered that this is because the gas evaporates, and the local gas expansion accompanying the thermal decomposition of the oxide is stopped, and the explosive evaporation of the molten metal of the raw material member does not occur.

It is a well known fact that the arc plasma can be variously controlled by a magnetic field. The present invention is
The direction and strength distribution of such a magnetic field are specified. That is, the direction of the magnetic field is at least parallel to the electric field of the arc plasma on the surface of the fine particle raw material member, and the magnetic field strength distribution is characterized in that the circumference of the raw material member is larger than the central portion. Since the direction of the magnetic field is at least parallel to the electric field of the arc plasma on the surface of the fine particle raw material member, electrons and ions in the arc plasma are less likely to dissipate across the magnetic field lines of the magnetic field. Further, since the magnetic field strength distribution is larger in the periphery of the raw material member than in the central portion, the magnetic pressure in the peripheral portion is higher than that in the central portion, and the arc plasma is confined in the central portion of the fine particle raw material member.
The fixation or control of the arc plasma can be realized by controlling the magnetic field strength according to the arc plasma condition, that is, the particle generation condition.

Next, the operation of the invention according to claim 3 of the present application will be described. In the second invention, the fine particle raw material member is reduced with atomic hydrogen prior to the production of fine particles, and then the raw material member is continuously heated and evaporated in a predetermined arc plasma gas atmosphere without being exposed to an oxidizing atmosphere. It has a feature.

Atomic hydrogen is chemically very active and has a large oxide reducing ability, and the surface oxide of the fine particle raw material can be easily removed. If the density of atomic hydrogen is high, the oxide removal time can be shortened, which is industrially advantageous. Such atomic hydrogen can be obtained by converting hydrogen gas into plasma. Further, since the surface oxide is removed in a gas atmosphere, a relatively large area can be processed, which is advantageous in the production of fine particles.

[0021]

EXAMPLES Examples of the present invention for producing Ti fine particles are shown below. 1 shows an embodiment of a fine particle manufacturing apparatus embodying the invention described in claim 1 of the present application.
FIG. 1A is an overall schematic view of an example of a Ti fine particle manufacturing apparatus, FIG.
(B) shows an arrangement example of magnets that generate a magnetic field for fixing or controlling the arc plasma in the present embodiment. In this embodiment, a solenoid coil electromagnet is used as the magnet.

The procedure for producing fine particles in this embodiment will be outlined. After placing the substrate 7 in the vacuum container 4, the vacuum pump (not shown) vacuum container 4 is evacuated to 3 × 10 ⁻⁶ Torr. Next, the argon gas 9 is supplied to the vacuum container 4,
Set the pressure to 300 Torr. Next, a current of 100 A is applied to the magnet 10 shown in FIG. 1B to generate a magnetic field.

After that, the upper Ti electrode 1 and the lower Ti electrode 2
When a voltage is applied from the power source 5 to the electrode, arc plasma is generated between the Ti electrodes, but the arc plasma at this time is fixed at the center of the lower electrode 2 and is stable. The lower Ti electrode 2 is heated and evaporated by the heat of arc plasma.

The Ti atoms evaporated in this way are condensed by collision with the atmospheric gas argon, and as a result, Ti fine particles are produced. Also in the present invention, red-hot droplets were generated at the initial stage of arc plasma generation. This is because the surface oxide originally present in the lower electrode 2 which is a fine particle raw material was removed by the heat of the arc plasma. However, since the arc plasma remained fixed, the droplets were not generated instantaneously. , Only smoke, which is the air flow of fine particles, is generated. To deposit the fine particles on the substrate 7, the shutter 8 is opened after only the smoke is observed as described above. The fine particles of Ti are
It is deposited on the substrate 7 by the rising airflow of argon gas heated by the arc plasma.

In this embodiment, the magnet 10 of the solenoid coil shown in FIG. 1B was used as a means for fixing the arc plasma on the surface of the raw material member or controlling the movement of the arc plasma. Here, this solenoid coil will be described. The magnetic field generated by the solenoid coil shown is
The electric field due to the arrangement of the upper electrode 1 and the lower electrode 2 is parallel to the surface of the lower electrode 2 which is a fine particle raw material. In the strength distribution of the magnetic field generated by the solenoid coil shown in the figure, the magnetic field strength at the peripheral portion of the lower electrode 2 is larger than the magnetic field strength at the central portion of the lower electrode 2.

In this embodiment, by setting the electric field and the magnetic field in this way, for example, when the current flowing through the solenoid coil is 100 A or more as described above, the arc plasma is generated in the lower electrode during the generation of fine particles. It remained fixed in the center. In this case, the Ti fine particles deposited on the substrate 7 had an average particle diameter of 50 nm, and no coarse particles having a particle diameter larger than 1 μm were observed.

When the current becomes smaller than 100 A, the arc plasma immediately after the generation gradually moves within the limited area in the central portion of the lower electrode 2, and as it moves, red-hot droplets are generated. Is observed to occur. This is because, as described above, the arc plasma self-selectively moves the oxide originally present on the surface of the electrode 2 below, but in the present embodiment, the current flowing through the magnet 10 is set to 10 A or more. In this case, the arc plasma did not move to the sample table 3 or the like.

As described above, once the surface oxide is removed, the arc plasma is stably generated at the portion where the distance between the upper electrode 1 and the lower electrode 2 is the shortest due to its nature. As a result, the droplets were not observed and only fine particles could be stably generated.

Next, an embodiment of the invention described in claim 3 of the present application will be described with reference to FIG. FIG. 2 is a sectional view showing the structure of a fine particle manufacturing apparatus embodying the present invention.

The procedure for producing fine particles in this example will be outlined. After the substrate 17 is installed in the vacuum container 14, the vacuum pump (not shown) vacuum container 14 is evacuated to 3 × 10 ⁻⁶ Torr.

Next, hydrogen gas 19 is supplied to the vacuum container 14 and the pressure is set to 1 Torr. Power supply 15 in this state
From the upper electrode 11 to the positive electrode and the lower electrode 12 to the cathode 50
When a voltage of 0 V is applied, glow plasma of hydrogen is generated between the electrodes on the surface of the lower electrode 12.

When the voltage from the power supply 15 is turned off after the glow plasma is generated for 30 minutes, the hydrogen glow plasma disappears, so that the supply of the hydrogen gas 19 is stopped and the argon gas 20 is then supplied to the vacuum container. 14 and set to 300 Torr.

Subsequently, when a voltage is applied from the power supply 15 to the upper Ti electrode 11 and the lower Ti electrode 12, arc plasma is generated between the Ti electrodes, and the lower Ti electrode 12 is heated and evaporated by the heat of the arc plasma. To do. The Ti atoms thus evaporated are condensed by collision with the atmospheric gas argon, and as a result, Ti fine particles are generated.

In the present embodiment, since the lower electrode 12 which is a fine particle raw material was exposed to the hydrogen glow plasma of 1 Torr for about 30 minutes as described above, red-hot droplets were not observed even at the initial stage of arc plasma generation, and the arc Only fine smoke was observed with the plasma generation.

In this embodiment, the fine particles of Ti are deposited on the substrate 17 by the upward flow of argon gas heated by the arc plasma. In this embodiment,
The average particle size of the particles deposited on the substrate 17 was 50 nm, and no coarse particles having a particle size larger than 1 μm were observed.

In this embodiment, as described above, the time for exposing the fine particle raw material member to the hydrogen glow plasma, the plasma density of the hydrogen glow plasma, and the like are the processing conditions for removing the oxide on the surface of the fine particle raw material member. For example, in the glow plasma having a hydrogen gas pressure of 1 Torr and a voltage of 500 V, if the exposure time is shorter than 25 minutes, red-heated droplets are generated at the initial stage of the arc plasma generation of argon, and in some cases, the arc plasma reaches the sample stage. Sometimes moved.

The surface oxide can also be removed by hydrogen arc plasma. However, in this case, since the lower electrode 12 is heated and evaporated by the arc plasma of hydrogen, the effective utilization rate of the fine particle raw material member is slightly decreased. On the other hand, since the density of atomic hydrogen is higher than that of glow plasma, there is an advantage that the oxide removal time is much shorter.

[0038]

As described above, the effect of the present invention is that it is possible to produce a large amount of high-purity fine particles having a uniform particle size and having few coarse particles as compared with the prior art. Therefore, if the fine particles produced by the present invention are used, the firing temperature decreases when producing high-performance ceramic electronic components by firing,
It is possible to provide a high-performance catalyst because it has the effect of improving the characteristics, it is possible to realize a high-density magnetic recording medium, and because it has a higher chemical activity than the bulk material, the industrial effect is great. There is something.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an apparatus that embodies an embodiment of a method for producing fine particles of the present invention.

FIG. 2 is a block diagram of an apparatus embodying another embodiment of the present invention.

FIG. 3 is a block diagram of a conventional apparatus for producing fine particles.

[Explanation of symbols]

 1, 11 Upper electrode 2, 12 Lower electrode 4, 14 Vacuum container 5, 15 Power supply 7, 17 Substrate 9, 20 Argon gas 19 Hydrogen gas

Claims (3)

[Claims] 1. A method for producing fine particles, comprising heating and evaporating a fine particle raw material member by arc plasma in a reduced pressure gas atmosphere, wherein the arc plasma is fixed to the surface of the raw material member or the movement of the arc plasma is controlled. A method for producing fine particles, comprising: 2. A method for fixing or controlling the arc plasma is to apply a magnetic field, the direction of the magnetic field is at least parallel to the electric field of the arc plasma on the surface of the fine particle raw material member, and the magnetic field strength distribution is as described above. The method for producing fine particles according to claim 1, wherein the periphery of the raw material member is larger than the central portion. 3. A method for producing fine particles by heating and evaporating a fine particle raw material member by arc plasma in a reduced pressure gas atmosphere, wherein the raw material member is a non-oxidizing gas atmosphere containing atomic hydrogen prior to the production of fine particles. And then heating and evaporating the raw material member in a predetermined arc plasma gas atmosphere without exposing the raw material member to an oxidizing atmosphere.