JP2002241810A - Equipment and method for manufacturing metallic ultrafine particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide equipment and a method for manufacturing metallic ultrafine particles which enable effective suppression of the adhesion of the resultant metallic ultrafine particles to the tip of a discharge electrode even in the period until arc discharge becomes stabilized in forming the metallic ultrafine particles using arc discharge. SOLUTION: For example, the distance (interelectrode distance) between the discharge electrode 13 and a target 5 is gradually extended after the initiation of the arc discharge by providing a position-changing mechanism 15 for moving a torch 12, by which the adhesion of the resultant metallic ultrafine particles to the tip of the discharge electrode 13 can be suppressed, or the interelectrode distance can also be extended gradually in the period from immediately after the initiation of the arc discharge until the arc discharge becomes stabilized by using, as the above target, a target having a shape with a size larger in height direction than in width direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for producing ultrafine metal particles, and more particularly, to suppressing the consumption of the tip of an electrode when producing ultrafine metal particles using arc discharge for a long time. And a method and apparatus for producing ultrafine metal particles capable of maintaining the arc discharge for a long time.

[0002]

2. Description of the Related Art Conventionally, it has been known to use arc discharge as a technique for producing ultrafine metal particles having a diameter of nm units among metal fine particles. In this technique, generally, a voltage is applied between a discharge electrode (cathode) arranged in close proximity and a metal base material (anode) serving as a target to generate an arc discharge, whereby metal ultrafine particles are formed. Further, by using hydrogen gas or a mixed gas of hydrogen gas and an inert gas as an atmospheric gas (this method is referred to as a hydrogen arc method), a metal particle having a particle size of about several tens nm is obtained. Fine particles can be obtained.

However, in the technique of generating ultrafine metal particles represented by the hydrogen arc method, since the generated ultrafine metal particles easily adhere to the tip of the discharge electrode, the tip is deformed or melts off. It will be exhausted. As a result, it has been difficult to perform arc discharge for a long time. Specifically, since the formed metal ultrafine particles adhere to the tip of the discharge electrode containing tungsten as a main component and the tip is alloyed, the melting point of the tip is higher than the original melting point of the discharge electrode. Is also considered to decrease, and deformation and burn-through are likely to occur.

In order to solve the above problems,
For example, Japanese Patent No. 1594485 (Japanese Patent Publication No. 60-768)
No. 2) discloses an apparatus for producing metal fine particles,
By providing the gas flow generating means, a gas flow (shielding gas) containing hydrogen gas is formed near the discharge electrode to reduce the concentration of the ultrafine metal particles near the discharge electrode. The shield gas prevents the ultrafine metal particles from adhering to the tip of the discharge electrode, so that the tip of the discharge electrode can be prevented from being consumed.

[0005]

However, in the above prior art, no consideration is given to the period until the arc discharge is stabilized between the discharge electrode and the metal base material. Therefore, it has not been possible to more reliably suppress the ultrafine metal particles generated at the tip of the discharge electrode from adhering to the tip of the discharge electrode.

In the production of ultrafine metal particles by the hydrogen arc method, at the start of arc discharge, the arc (electrode interval) between the discharge electrode (cathode) and the metal base material (anode) is shortened. Discharge is easily generated, and thereafter, the distance between the electrodes is increased with the dissolution of the metal base material, and the arc discharge is stabilized, so that the generation of metal ultrafine particles and the blowing direction thereof are stabilized.

The phenomenon in which the generated ultrafine metal particles adhere to the tip of the discharge electrode occurs regardless of the period before the arc discharge is stabilized or during the period after the arc discharge is stabilized. However, during the above-mentioned period, since the arc discharge is not stable, the generation of the ultrafine metal particles and the blowing direction thereof are also unstable. The phenomenon that metal ultrafine particles adhere to the tip of the electrode cannot be suppressed.

That is, in the above-described conventional technique, during the period after the arc discharge is stabilized, the adhesion of the ultrafine metal particles to the tip of the discharge electrode can be effectively suppressed, but the arc discharge is stabilized. In the previous period, the adhesion of the ultrafine metal particles could hardly be suppressed, and as a result, it was actually difficult to effectively avoid the consumption of the tip of the discharge electrode. Become.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to produce a metal ultrafine particle using an arc discharge even when the arc discharge is stabilized. Another object of the present invention is to provide an apparatus and a method for producing ultrafine metal particles which can effectively suppress the generated ultrafine metal particles from adhering to the tip of the discharge electrode.

[0010]

In order to solve the above-mentioned problems, an apparatus for producing ultrafine metal particles according to the present invention is provided with a discharge electrode and a metal base material provided at a position close to the discharge electrode. And an arc power supply connected to these electrodes, and an apparatus for producing ultrafine metal particles that generates an arc discharge by applying a voltage between the discharge electrode and the holding electrode from the arc power supply At
Further, by changing at least one of the positions of the discharge electrode and the holding electrode, a position changing means for gradually increasing the distance between the discharge electrode and the metal base material, and at least the operation of the position changing means, It is characterized by comprising control means for controlling in response to a change in the state of the arc discharge from immediately after the start of the arc discharge until the arc discharge is stabilized.

According to the above configuration, the interval between the discharge electrode and the metal base material is gradually increased until the arc discharge is stabilized after the start of the arc discharge. Therefore, the generated metal ultrafine particles hardly adhere to the tip of the discharge electrode, and stable arc discharge can be continued for a long time. Further, since the consumption of the tip of the discharge electrode is suppressed, the life of the discharge electrode is prolonged. As a result, ultrafine metal particles can be manufactured stably and at low cost for a long time.

[0012] In addition to the above configuration, the apparatus for producing ultrafine metal particles according to the present invention further includes a current detecting means for detecting a current flowing along with the occurrence of arc discharge, and a voltage change accompanying the occurrence of arc discharge. And at least one of voltage detection means for detecting, the control means, as a change in the state of arc discharge, the current detection means,
And the operation of the position changing means is controlled using at least one detection result of the voltage detecting means.

According to the above arrangement, the detection result obtained by at least one of the current detecting means and the voltage detecting means is used as a parameter for changing the state of the arc discharge. Therefore, the control unit can more reliably control the operation of the position changing unit, and can maintain the arc discharge in a predetermined state while avoiding an excessive increase in the electrode interval. As a result, the adhesion of the ultrafine metal particles to the discharge electrode can be effectively suppressed even during the period before the arc discharge is stabilized.

An apparatus for producing ultrafine metal particles according to the present invention is characterized in that, in addition to the above configuration, the position changing means changes only the position of the discharge electrode.

According to the above configuration, the distance between the electrodes is changed by changing only the position of the discharge electrode. Since the discharge electrode often has a substantially bar shape, by moving the discharge electrode in the axial direction (longitudinal direction), it is possible to reduce the volume required for position change as compared with the holding electrode. As a result, it is possible to simplify the configuration of the position changing means and, consequently, the configuration of the entire manufacturing apparatus.

In order to solve the above-mentioned problems, the method for producing ultrafine metal particles according to the present invention comprises disposing a discharge electrode and a metal base material in close proximity, and applying a voltage between them in an atmosphere containing hydrogen gas. In the method for producing ultrafine metal particles that generate arc discharge by applying a voltage, the interval between the discharge electrode and the metal base material is gradually increased from immediately after the start of the arc discharge until the arc discharge is stabilized. Features.

According to the above method, the interval between the discharge electrode and the metal base material is gradually increased until the arc discharge is stabilized after the start of the arc discharge. Therefore, the generated metal ultrafine particles hardly adhere to the tip of the discharge electrode, and stable arc discharge can be continued for a long time. Further, since the consumption of the tip of the discharge electrode is suppressed, the life of the discharge electrode is prolonged. As a result, ultrafine metal particles can be manufactured stably and at low cost for a long time.

In order to solve the above-mentioned problems, another method for producing ultrafine metal particles according to the present invention is to dispose a discharge electrode and a metal base material in close proximity to each other in an atmosphere containing hydrogen gas. In the method for producing ultrafine metal particles that generate an arc discharge by applying a voltage to the metal base material, a shape in which the height direction is larger than the width direction in a state where the metal base material is disposed close to the discharge electrode. It is characterized by the use of

According to the above method, since a metal base material having a height direction larger than the width direction is used, the height direction becomes smaller immediately after the start of arc discharge. Therefore, the electrode interval gradually increases, and even during the period before the arc discharge is stabilized, the adhesion of the ultrafine metal particles can be surely suppressed. Moreover, since the same manufacturing apparatus as in the past can be used,
It is not necessary to use a manufacturing apparatus having a complicated configuration. Therefore, metal ultrafine particles can be produced for a long time at lower cost.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] The first embodiment of the present invention will be described below with reference to FIGS. Note that the present invention is not limited to this.

The apparatus and method for manufacturing ultrafine metal particles according to the present embodiment have a movable torch structure such as an electrode support frame on which an electrode for discharge is mounted, and can maintain the arc discharge simultaneously with the start of the arc discharge. In addition, the interval between the discharge electrode and the metal base material (electrode interval) is enlarged.

Specifically, as shown in FIG. 1, the apparatus for producing ultrafine metal particles according to the present embodiment includes a particle generator 10 for generating ultrafine metal particles by arc discharge, A gas supply unit 20 for supplying an atmosphere gas containing a gas, a particle collection unit 30 for collecting the generated ultrafine metal particles, and a control unit 4 for controlling the operation of the manufacturing apparatus
0. In FIG. 1, broken arrows indicate transmission paths of control signals, thin solid lines indicate electrical connection paths, and thick solid lines (between the position change mechanism 15, the torch 12, and the discharge electrode 13, which will be described later) indicate mechanical parts. Shows a typical relationship.

As shown in FIG. 2, the particle generator 10 includes a chamber 11, a torch (electrode supporting frame / torch mechanism) 12, a discharge electrode 13, a holding table (hearth / holding electrode) 14, A position changing mechanism (position changing means) 15;
Arc power supply 16 and current monitor (current detection means) 17
And a voltage monitor (voltage detecting means) 18.

The chamber 11 is a box having a space where an arc discharge can be generated between the discharge electrode 13 and the target (metal base material) 5. The specific configuration is not particularly limited, and a conventionally known configuration can be suitably used. However, as shown in FIG. 2, it is preferable to supply an atmospheric gas from one side to the other side. Atmospheric gas is discharged from the side.

An atmosphere gas pipe 23 and a shield gas pipe 24, which will be described later, are connected to the chamber 11, and supply the atmosphere gas into the chamber 11. Therefore, the atmosphere gas is supplied from the atmosphere gas pipe 23 and the shield gas pipe 24 as shown by the arrow A in the figure, and is discharged from the chamber 11 through the recovery filter 32 described later. ing.

The torch 1 is provided in the chamber 11.
2. Discharge electrode 13 and holding table 14 are arranged. The discharge electrode 13 is fixedly supported at the end of the torch 12, and the holding table 14 is arranged at a position near the discharge electrode 13, and allows the target 5 to be mounted thereon. It has a trapezoidal shape.

The torch 12 has a substantially rod shape having a length in the primary direction. The torch 12 stably holds the discharge electrode 13 at an end thereof while being connected to an arc power supply 16. ing. The specific configuration of the torch 12 is not particularly limited as long as the discharge electrode 13 can be stably held.

Further, as shown in FIG. 3, the torch 12 may be provided with a shield gas pipe 24 and a shield gas nozzle 25 for forming a shield gas around the discharge electrode 13. The shield gas is formed around the discharge electrode 13 after the arc discharge is stabilized in order to prevent the ultrafine metal particles from adhering to the discharge electrode 13.

In FIG. 3, since the shield gas nozzle 25 is arranged around the discharge electrode 13 in the torch 12, the atmosphere gas flows out from around the discharge electrode 13 along the axial direction (longitudinal direction). (Arrow B in the figure), a shielding gas is formed. In addition, the ultrafine metal particles generated by the arc discharge at this time, as shown by arrow C in the figure,
It blows out to the side opposite to the discharge electrode 13 arranged diagonally above the target 5. Note that the shield gas pipe 24 and the shield gas nozzle 25 are not necessarily provided in the torch 12, and may be provided near the discharge electrode 13 as another configuration.

The discharge electrode 13 is an electrode for generating an arc discharge with a target (metal base material) 5 which is a precursor of the ultrafine metal particles, and usually contains tungsten (W) as a main component. Is preferably used. A metal oxide is often added to the tungsten electrode, and generally, a material called “tritan” containing thorium oxide (ThO ₂ ) in a range of about 1 to 2% is preferable. Used for

The shape of the discharge electrode 13 is not particularly limited, but usually, as shown in FIG. 4, a tip having a sharpened end is preferably used to facilitate arc discharge. Used. The length and diameter are not particularly limited either. For example, length L = 35 mm, diameter φ =
Those having a size of about 4 mm are preferably used.

The holding table 14 holds the target 5 in a state of being mounted thereon, and applies a voltage to the target 5 from an arc power supply 16. The specific shape is not particularly limited as long as it has a trapezoidal shape and is configured to apply a voltage to the target 5 placed above. The material is not particularly limited as long as a voltage can be applied to the target 5, but copper is generally preferably used.

The holding table 14 is used for arc discharge.
The cooling is performed by cooling means (not shown) such as water cooling. Therefore, as shown in FIG. 2 and FIG. 3, usually, the metal particles are slightly crushed by their own weight and are rounded into a substantially elliptical sphere, so that ultrafine metal particles can be stably generated.

As means for holding the target 5, if the holding electrode is a holding electrode capable of applying a voltage to the target 5 while holding the target 5, the holding table 1
It is not limited to four.

The position changing mechanism 15 moves the torch 12 so that the discharge electrode 13 and the target 5 are moved.
(Electrode spacing) is changed.
Specifically, in the present embodiment, the torch 12 has a substantially rod shape, and the discharge electrode 13 is disposed at the end thereof. Therefore, when a motor is used as a driving source, for example, a rack-pinion Using a mechanism or a ball screw structure,
A configuration in which the torch 12 is moved along the longitudinal direction of the torch 12 can be suitably used. In FIG. 2,
For convenience of explanation, the position changing mechanism 15 is schematically illustrated.

In the present invention, as described later, it is important to gradually increase the electrode interval immediately after the start of arc discharge. Therefore, the discharge electrode 13 or the holder 1
4 or both the discharge electrode 13 and the holding table 14 may be moved, but preferably, only the discharge electrode 13 is moved by moving the torch 12 along its longitudinal direction. The movement in the axial direction is preferable because the space required for the movement can be made smaller and the configuration of the position changing mechanism 15 can be simplified.

The position changing mechanism 15 may be configured to change the electrode interval by moving the holding table 14. That is, as the position changing mechanism 15,
Any structure that can change the above-mentioned electrode interval may be used, and whether torch 12 or holding table 14 or both of them are moved is appropriately changed according to the structure of the manufacturing apparatus.

In this embodiment, as shown in FIG. 2 and FIG. 3, the discharge electrode 13 is applied to the target 5 placed and held on the holding table 14 in the direction of the flow of the atmosphere gas. It is preferable that arc discharge is performed in a state of being disposed obliquely upward on the upstream side in the direction of arrow A). Thereby, the metal ultrafine particles generated in the chamber 11 can be efficiently transported along with the flow of the atmospheric gas.
Note that the specific arrangement of the “diagonally above” is not particularly limited, but for example, in the present embodiment,
The torch 12 is disposed so as to be inclined by about 45 ° from the horizontal direction.

The arc power supply 16 applies a high-frequency voltage (start voltage) to the discharge electrode 13 and the target 5, that is, the target 5 to be electrically connected to the holding table 14 in order to produce ultrafine metal particles. Voltage) to cause an arc discharge between them (see FIG. 1). In the present embodiment, the discharge electrode 13 is used as an anode (cathode) and the target 5 is used as a cathode (anode).
The positive pole is connected to the holding table 14.

As shown in FIG. 1, the current monitor 17 and the voltage monitor 18 respectively generate a current (referred to as an arc current) flowing between the discharge electrode 13 and the target 5 due to the arc discharge, and generate a voltage (the arc current). Arc voltage). As is clear from FIG. 1, the detection results of the current monitor 17 and the voltage monitor 18 are both output to the control unit 40 and used for the operation control of the position change mechanism 15 in the control unit 40. The specific configuration is not particularly limited, and a known ammeter or voltmeter generally used for detecting current and voltage can be preferably used.

As the target 5, any metal can be used. Generally, nickel (Ni), iron (Fe), and the like are often used. The shape of the target 5 is not particularly limited, and a desired metal may be formed into an appropriate shape so as to enable arc discharge. The metal ultrafine particles generated from the target 5 are as follows:
It is preferable that the average particle size is in the range of 1 nm to 100 nm.

The gas supply section 20 includes a gas tank 21a.
.21b.21c, gas supply valves 22a.22b.2
2c, atmosphere gas pipe 23, shield gas pipe 24
And an atmosphere gas for arc discharge including hydrogen gas is supplied into the chamber 11 (arrow A in the figure).

In the present embodiment, two kinds of inert gases, hydrogen (H ₂ ) gas and argon (Ar) or helium (He), are used as the atmosphere gas. Therefore, in order to supply these atmospheric gases, a gas tank 21a for hydrogen gas and a gas tank 2 for argon gas are used.
1b and a gas tank 21c for helium gas are provided. These gas tanks 21a, 21b, 21c
Are the atmosphere gas pipe 23 and the shield gas pipe 2
4, connected to the chamber 11;
The supply amount of each atmosphere gas can be adjusted by gas supply valves 22a, 22b, and 22c provided corresponding to the gas tanks 21a, 21b, and 21c, respectively.

The gas used as the atmospheric gas is not particularly limited, but it is very preferable to use hydrogen gas in the production of ultrafine metal particles. As the gas other than the hydrogen gas, various inert gases such as an argon gas and a helium gas are preferably used, but are not particularly limited.

The composition of the atmosphere gas is not particularly limited.
It is preferably at least volume%. Hydrogen gas concentration is 50
If it is at least% by volume, the production efficiency of ultrafine metal particles tends to be improved. In addition, the composition of an inert gas such as an argon gas or a helium gas is not particularly limited.

The atmosphere gas pipe 23 and the shield gas pipe 24 are connected to the chamber 11 as described above. The atmosphere gas pipe 23 mainly supplies the atmosphere gas. Piping for shielding gas 2
Numeral 4 supplies an atmosphere gas for a shield gas formed by a shield gas nozzle 25 arranged near the discharge electrode 13. Therefore, the shield gas pipe 24 may be configured to branch off from the atmosphere gas pipe 23.

The atmosphere gas pipe 23 not only branches the shield gas pipe 24 but also is connected to the particle collection section 30 so that the supplied atmosphere gas is collected by the collection pump 33 and the gas circulation pump. 35 circulates. The material and shape of each of the pipes 23 and 24 are not particularly limited, and a conventionally known gas stainless steel pipe or the like can be suitably used.

The pressure of the atmospheric gas in the chamber 11 is not particularly limited, but is generally preferably in the range of 40 kPa to 100 kPa. Further, the flow rate of the atmosphere gas supplied to the chamber 11 is not particularly limited, but the atmosphere gas pipe 2 which is a main supply pipe of the atmosphere gas is used.
In general, when supplied from 3, the flow rate is preferably such that the gas flow rate for transport is 0.7 m / s or more.

Further, the flow rate of the atmosphere gas supplied from the shield gas pipe 24 is not particularly limited as long as the shield gas can be formed. For example, a flow rate of about 5 L / min is mentioned. Can be. Normally, the supply amount of the atmosphere gas from the shield gas pipe 24 is an amount within an error range with respect to the supply amount of the atmosphere gas from the atmosphere gas pipe 23.

The above-mentioned particle collecting section 30 includes the collecting filter 3
2 and a gas circulation pump 35 for recovering ultrafine metal particles generated in the chamber 11 using the flow of the atmospheric gas.

In FIG. 2, the recovery filter 32 includes a discharge electrode 13 and a holding base 14 in the chamber 11.
And at a position where the atmospheric gas in the chamber 11 is discharged. Also, on the side where the discharge electrode 13 and the holder 14 are located,
The atmosphere gas pipe 23 and the shield gas pipe 24 are connected. Therefore, in the chamber 11, the collection filter 3 is located from the side where the discharge electrode 13 and the holding table 14 are located.
2, the flow of the atmospheric gas is formed (arrow A in the figure). As a result, the collection filter 32 collects the ultrafine metal particles.

The collection filter 32 is, for example, a membrane filter, a HEPA filter, or a UL filter.
A PA filter or the like is preferably used, but is not particularly limited as long as it has a filter structure capable of reliably collecting ultrafine metal particles. Further, the means for collecting the ultrafine metal particles is not limited to the filter structure, and a configuration such as a cyclone may be used.

The atmosphere gas discharged from the chamber 11 returns to the atmosphere gas pipe 23 through the gas circulation pump 35, and is returned to the chamber 11 and the pipes 23 and 24.
(Arrow A in the figure).

The vacuum pump 33 is connected to the main valve 3
The chamber 11 is connected to the chamber 11 through the chamber 4 and sucks and discharges the atmospheric gas from the chamber 11.

The control section 40 controls at least the operation of the position changing mechanism 15 in accordance with the change in the state of the arc discharge immediately after the start of the arc discharge until the arc discharge is stabilized. More preferably, as shown in FIG. 1, the operations of the arc power supply 16, the gas supply unit 20, the particle recovery unit 30, and the like are also controlled.

Next, the method for producing ultrafine metal particles according to the present embodiment, that is, the control unit 40 causes the generated ultrafine metal particles to adhere to the discharge electrode 13 even before the arc discharge is stabilized. A method for suppressing this will be described.

As described above, in the production of ultrafine metal particles by the hydrogen arc method, first, at the start of arc discharge, the discharge electrode 13 (cathode) and the target 5 (anode)
Is smaller than the interval before the arc discharge is stabilized, thereby facilitating the generation of the arc discharge. Then, the interval between the electrodes is increased with the melting of the target 5 and the arc discharge is stabilized, so that the generation of the metal ultrafine particles and the blowing direction thereof are stabilized.

Here, after the arc discharge is started, the period before the arc discharge is stabilized and the period after the arc discharge is stabilized are divided into the period after the arc discharge is stabilized. Therefore, the adhesion of the ultrafine metal particles to the discharge electrode 13 can be suppressed by the shield gas. On the other hand, in the period before the arc discharge is stabilized, the electrode gap is small, and the generation of metal ultrafine particles and the blowing direction are unstable. The attachment of fine particles cannot be suppressed.

Therefore, in this embodiment, the position change mechanism 1 is controlled by the control unit 40 immediately after the start of arc discharge.
5, the position of the discharge electrode 13 is changed by moving the torch 12 to gradually increase the electrode interval, thereby suppressing the adhesion of the ultrafine metal particles to the discharge electrode 13. I have.

At this time, the operation of the position changing mechanism 15 is controlled in accordance with the change in the state of the arc discharge. The parameter indicating the state change of the arc discharge is not particularly limited. For example, an arc current flowing along with the occurrence of arc discharge and an arc voltage (also referred to as discharge voltage) along with the occurrence of arc discharge are used. At least one, and preferably both, of the changes can be very well utilized. In the following description, a case where both the arc current and the arc voltage are detected and used for the control of the control unit 40 will be described.

First, the discharge electrode 1 is supplied from the arc power supply 16.
When a high-frequency voltage is applied between the target 3 and the target 5 (holding table 14), arc discharge is started as shown in FIG. At this point, the electrode interval D is set to be relatively small so that arc discharge easily occurs.

When the high-frequency voltage is applied by the arc power supply 16, the dielectric breakdown finally occurs, and the discharge electrode 1
An arc current flows at the same time as an arc discharge occurs between the target 3 and the target 5 (holding table 14). Therefore, the start of arc discharge can be detected by monitoring the generation of arc current by the current monitor 17.

The control unit 40 recognizes that the arc discharge has started based on the detection result that the arc current has been detected between the discharge electrode 13 and the target 5 by the current monitor 17. Since the period after the detection of the arc current is the period before the above-mentioned arc discharge is stabilized, the controller 40
Uses the detection result of the arc current as a parameter of the state change of the arc discharge, and uses the position change mechanism 1
5 is operated to start increasing the interval (electrode interval D) between the discharge electrode 13 and the target 5.

The range of the high frequency voltage is not particularly limited. For example, in this embodiment, about 7 k
V. Further, in the arc power supply 16, the high-frequency voltage is switched to the DC voltage (arc voltage) simultaneously with the start of the arc discharge. The range of the DC voltage at this time is not particularly limited, but is 30 V or more and 50 V or more.
V or less, more preferably 20 V or more and 30 V or less. Similarly, the range of the arc current associated with the arc discharge is not particularly limited, but is generally preferably in the range of 100A or more and 400A or less.

The range of the electrode interval D may be the output of the arc power source 16 or the discharge electrode 13 / target 5
It is appropriately set depending on the material of the material and the like, and is not particularly limited. For example, when a tungsten electrode containing 1 to 2% thorium oxide is used as the discharge electrode 13 and nickel or copper is used as the target 5, when the arc discharge starts, a range of 1.0 mm to 1.5 mm is used. After the arc discharge is stabilized, the range may be 5 mm or more and 30 mm or less.

During the period from the start of the arc discharge until the arc discharge is stabilized, the control unit 40 controls the position changing mechanism 1 according to the melting of the target 5 as shown in FIG.
5 is controlled to increase the electrode interval D.

In this period, as indicated by an arrow E in the figure,
The generated ultrafine metal particles are generated while being blown in an upwardly inclined direction, not along the substantially horizontal direction (the direction of arrow A) in the chamber 11, which is the flow of the atmospheric gas. Therefore, the formation of the shielding gas does not effectively suppress the adhesion of the ultrafine metal particles. However, if the electrode interval D is gradually increased, the discharge electrode 13 is moved away from the blowing direction of the ultrafine metal particles. In addition, the adhesion of the ultrafine metal particles can be effectively suppressed.

Here, in the present embodiment, the voltage between the discharge electrode 13 and the target 5 is also detected by the voltage monitor 18 as described above. Therefore, the control unit 40 controls the operation of the position changing mechanism 15 so that the DC voltage as the detection result obtained from the voltage monitor 18 is maintained within the above range.

In order to effectively suppress the adhesion of the ultrafine metal particles to the discharge electrode 13, the electrode interval D is set so as to approach the maximum interval at which the arc discharge can be maintained after the start of the arc discharge. It is preferred to enlarge as quickly as possible. Although it is possible to confirm that the arc discharge is maintained by detecting the current with the current monitor 17, it is more strictly preferable to use the detection of the DC voltage with the voltage monitor 18. Therefore, the control unit 40 preferably controls the operation of the position change mechanism 15 based on the result of the detection of the DC voltage by the voltage monitor 18 (the parameter of the state change of the arc discharge), and always appropriately changes the electrode interval D. .

If the enlargement of the electrode interval D is too slow, it is not preferable because the generated ultrafine metal particles tend to adhere to the tip of the discharge electrode 13. On the other hand, if the expansion of the electrode interval D is too fast, the electrode interval D expands more than necessary and the arc discharge disappears, which is not preferable.

As described above, the detection result obtained by the current monitor 17 and the voltage monitor 18 is used as a parameter of the state change of the arc discharge, so that the control unit 40
Can more reliably control the operation of the position changing mechanism 15. As a result, it is possible to maintain the arc discharge in a predetermined state while avoiding the electrode gap D from being excessively enlarged, and even in the period before the arc discharge becomes stable, the discharge electrode 13 of the ultrafine metal particles is used. It is possible to effectively suppress the adhesion to the surface.

Thereafter, as shown in FIG. 5C, the target 5 is almost completely melted by the heat generated by the arc discharge.
The cooling of the holding table 14 finally results in a substantially spherical shape. In this state, since the shape of the target 5 is stable in terms of surface tension, arc discharge is also stable. Therefore, the control unit 40 performs control to stop the expansion of the electrode interval D based on the detection result of the DC voltage, whereby the generation and blowing direction of the metal ultrafine particles are also changed in the direction of the flow of the atmosphere gas (the direction of arrow A in the figure). )
(Arrow C in the figure). In other words, in this state, the period after the above-mentioned arc discharge stabilizes, so that a conventionally known shield gas as shown in FIG. 3 is formed to effectively suppress the adhesion of the ultrafine metal particles to the discharge electrode 13. can do.

In the present embodiment, the position changing mechanism 1
It is possible to operate the torch 5 manually, but in this case, the timing of changing the position of the torch 12 tends to shift. As a result, the electrode gap D is too small, so that the metal ultrafine particles adhere to the discharge electrode 13 or the arc gap disappears because the electrode gap D is too large.
Not very good.

As described above, in the manufacturing apparatus and the manufacturing method according to the present embodiment, the interval between the electrodes is gradually increased at least until the arc discharge is stabilized after the start of the arc discharge (the above-described period). I have. Therefore, the generated metal ultrafine particles hardly adhere to the tip of the discharge electrode,
It is possible to continue stable arc discharge for a long time. Further, since the consumption of the tip of the discharge electrode is suppressed, the life of the discharge electrode is prolonged. As a result, ultrafine metal particles can be manufactured stably and at low cost for a long time. In particular, since the control unit grasps the state change of the arc discharge by detecting the current and the voltage, the electrode interval can be changed more accurately based on the change, so that the arc discharge is reliably and stably maintained. You can also.

It should be noted that the control for changing the electrode spacing in the present invention is performed during the period until the arc discharge is stabilized, as is apparent from the above description, and is performed during the period after the arc discharge is stabilized. It is not implemented.

[Second Embodiment] A second embodiment of the present invention will be described below with reference to FIGS. Note that the present invention is not limited to this. Further, for convenience of explanation, members having the same functions as those used in the first embodiment are given the same reference numerals, and descriptions thereof are omitted.

In the first embodiment, the electrode spacing D is changed by providing the position changing mechanism 15 in the manufacturing apparatus. However, in the manufacturing method of the metal ultrafine particles according to the present embodiment, the shape of the target is changed. The electrode interval D is gradually increased by forming the elongated shape larger in the height direction than in the width direction and melting the target by the heat of the arc immediately after the start of the arc discharge.

More specifically, as shown in FIG.
A long target (metal base material) 6 having a shape in which the height direction H is larger than the width direction W in a state where the target is placed and held on the substrate 4 and arranged close to the discharge electrode 13 is used. The extent to which the height direction H is larger than the width direction W is not particularly limited, but it is highly preferable that the ratio of the height direction H to the width direction W (H / W) be 1.5. 2.5 times or more
It is within the range of 2 times or less, and about 2 times is particularly preferable. In other words, the long target 6 used in the present embodiment has a substantially rod shape or a substantially column shape having a length in the primary direction.

The more specific shape of the long target 6 is not particularly limited as long as it has a substantially rod shape or a substantially columnar shape. However, considering the ease of processing, FIG. As shown, a substantially cylindrical shape or the like is preferably employed. As a practical level of size, for example, in the present embodiment, a substantially cylindrical long target 6 having a diameter φ = 5 mm and a height h = about 10 mm is preferably used.

Next, a method for producing ultrafine metal particles according to the present embodiment will be described.

First, the electrode interval D is set relatively small,
When a high-frequency voltage is applied between the discharge electrode 13 and the substantially circular target 6 (holding base 14) by the arc power supply 16, arc discharge is started as shown in FIG. You. Thereafter, the period before the arc discharge becomes stable.

Thereafter, as the arc discharge proceeds, the upper end of the substantially cylindrical long target 6 gradually melts, and the height direction H of the melted long target 6 decreases due to its own weight. As a result, the discharge electrode 13 and the long target 6
Is gradually increased.

During this period, as shown in FIG. 7B, as in the first embodiment, the generated metal ultrafine particles are substantially horizontally (arrow A) in the chamber 11 where the atmosphere gas flows. Is generated while blowing out in the direction inclined in the upward direction (the direction of arrow E in the figure) without following the direction of (). Therefore, even if the shield gas is formed, the adhesion of the ultrafine metal particles is not effectively suppressed. However, if the electrode interval D gradually increases with the melting of the long target 6, the discharge electrode 13 can be viewed relatively. Is moved away from the blowing direction of the ultrafine metal particles, so that the adhesion of the ultrafine metal particles is effectively suppressed.

As described in the first embodiment,
If the enlargement of the electrode interval D is too slow, the generated metal ultrafine particles are likely to adhere to the tip of the discharge electrode 13, which is not preferable. If the enlargement of the electrode interval D is too fast, the electrode interval increases more than necessary. And the arc discharge disappears,
Not preferred. Therefore, it is particularly preferable that the ratio (H / W) of the height direction H to the width direction W of the long target 6 is in the range of 1.5 times or more and 2.5 times or less.

Thereafter, as shown in FIG. 7C, the long target 6 is almost completely melted by the heat generated by the arc discharge, and finally becomes substantially spherical by cooling the holding table 14.
In this state, since the shape of the long target 6 is stable in terms of surface tension similarly to the target 5, the arc discharge is also stable. Therefore, the generation and blowing direction of the ultrafine metal particles are also stabilized along the flow direction of the atmospheric gas (the direction of arrow A in the figure) (arrow C in the figure). In other words, in this state, the period after the above-mentioned arc discharge stabilizes, so that the formation of a conventionally known shield gas (see FIG. 3) can effectively suppress the adhesion of the ultrafine metal particles to the discharge electrode 13. Can be.

As described above, in this embodiment, the manufacturing apparatus itself is the same as the conventional one, but a long target whose height direction is larger than the width direction is used as the target. Therefore, even during the period before the arc discharge is stabilized, the adhesion of the ultrafine metal particles can be surely suppressed, and the position change mechanism, the current monitor, the voltage monitor, etc. It is not necessary to use a complicated configuration such as a means for detecting an arc discharge state. Therefore, metal ultrafine particles can be produced for a long time at lower cost.

[0087]

As described above, the apparatus for manufacturing ultrafine metal particles according to the present invention changes the position of at least one of the discharge electrode and the holding electrode to increase the distance between the discharge electrode and the metal base material. Position change means for gradually expanding, and control means for controlling at least the operation of the position change means in accordance with a change in the state of the arc discharge from immediately after the start of the arc discharge until the arc discharge is stabilized. Configuration.

In the above configuration, the interval between the discharge electrode and the metal base material is gradually increased until the arc discharge is stabilized, so that the generated metal ultrafine particles are formed at the tip of the discharge electrode. With little adhesion, stable arc discharge can be continued for a long time. Further, since the consumption of the tip of the discharge electrode is suppressed, the life of the discharge electrode is prolonged. As a result, there is an effect that ultrafine metal particles can be stably manufactured at low cost for a long time.

In the apparatus for producing ultrafine metal particles,
In addition to the above configuration, the apparatus further includes at least one of a current detection unit that detects a current flowing with the occurrence of arc discharge and a voltage detection unit that detects a change in voltage with the occurrence of arc discharge. The control means is configured to control the operation of the position change means using the detection result of at least one of the current detection means and the voltage detection means as the change in the state of the arc discharge.

In the above configuration, since the detection result obtained by at least one of the current detecting means and the voltage detecting means is used as a parameter for changing the state of the arc discharge, the control means controls the operation of the position changing means more. Control can be performed more reliably. As a result, even in a period before the arc discharge is stabilized, an effect is obtained that the adhesion of the ultrafine metal particles to the discharge electrode can be effectively suppressed.

In the above apparatus for producing ultrafine metal particles, it is preferable that, in addition to the above-described configuration, the position changing means changes only the position of the discharge electrode.

In the above configuration, since only the position of the discharge electrode is changed to change the electrode interval, it is possible to make the volume required for the position change smaller than that of the holding electrode. As a result, there is an effect that the configuration of the position changing means and the configuration of the entire manufacturing apparatus can be simplified.

As described above, in the method for producing ultrafine metal particles according to the present invention, the interval between the discharge electrode and the metal base material is gradually increased from the start of the arc discharge until the arc discharge is stabilized. How to

In the above method, the gap between the discharge electrode and the metal base material is gradually increased until the arc discharge is stabilized. Metal ultrafine particles hardly adhered,
It is possible to continue stable arc discharge for a long time. Further, since the consumption of the tip of the discharge electrode is suppressed, the life of the discharge electrode is prolonged. As a result, there is an effect that metal ultrafine particles can be stably manufactured at low cost for a long time.

Further, as described above, in the method for producing another metal ultrafine particle according to the present invention, when the metal base material is disposed close to the discharge electrode, the height direction is larger than the width direction. This is a method using a shape having a different shape.

In the above method, since the height direction becomes smaller first from the shape of the metal base material, the electrode interval gradually increases, so that even during the period before the arc discharge is stabilized, it is ensured. In addition to suppressing the adhesion of the ultrafine metal particles, the manufacturing apparatus itself is the same as the conventional one, so that there is no need to use a manufacturing apparatus having a complicated configuration. Therefore, there is an effect that ultrafine metal particles can be produced for a long time at lower cost.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a control system of an apparatus for manufacturing ultrafine metal particles according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a schematic configuration of the manufacturing apparatus shown in FIG.

FIG. 3 is an explanatory diagram showing a configuration for forming a shielding gas provided in the manufacturing apparatus shown in FIG. 1;

FIG. 4 is an explanatory view showing a shape of a discharge electrode used in the manufacturing apparatus shown in FIG.

5A is an explanatory diagram showing a state of a target immediately after an arc discharge is started by the manufacturing apparatus shown in FIG. 1, and FIG. 5B is a diagram showing a state of the target until the arc discharge is stabilized; It is explanatory drawing which shows the production | generation state of metal ultrafine particle, (c) is explanatory drawing which shows the state of the target after arc discharge was stabilized, and the production | generation state of metal ultrafine particle.

FIG. 6 is an explanatory diagram showing an example of a long target used in the method for producing ultrafine metal particles according to the second embodiment of the present invention.

7A is an explanatory diagram showing a state of the long target immediately after the start of arc discharge when the long target shown in FIG. 6 is used, and FIG. 7B is a diagram illustrating a state where the arc discharge is stabilized. It is an explanatory view showing the state of the long target and the generation state of the ultrafine metal particles, and (c) is an explanatory view showing the state of the long target and the generation state of the ultrafine metal particles after the arc discharge is stabilized.

[Explanation of symbols]

 Reference Signs List 5 Target (metal base material) 6 Long target (metal base material) 13 Discharge electrode 14 Holder (holding electrode) 15 Position changing mechanism (position changing means) 16 Arc power supply 17 Current monitor (current detecting means) 18 Voltage monitor ( Voltage detection means) 40 control unit (control means)

Claims (5)

[Claims] A discharge electrode, a holding electrode provided at a position close to the discharge electrode for holding a metal base material, and an arc power supply connected thereto; In the apparatus for producing ultrafine metal particles, which generates an arc discharge by applying a voltage between the discharge electrode and the holding electrode, the position of at least one of the discharge electrode and the holding electrode is changed, Position changing means for gradually increasing the interval between the metal base materials; and at least the operation of the position changing means corresponds to a change in the state of the arc discharge immediately after the start of the arc discharge until the arc discharge is stabilized. An apparatus for producing ultrafine metal particles, comprising: a control means for controlling the temperature of the metal particles. 2. The control device according to claim 1, further comprising at least one of a current detecting means for detecting a current flowing in accordance with the occurrence of the arc discharge, and a voltage detecting means for detecting a change in a voltage in accordance with the occurrence of the arc discharge. 2. The ultrafine metal particles according to claim 1, wherein the means controls the operation of the position changing means by using at least one of the current detection means and the voltage detection means as a change in the state of the arc discharge. Manufacturing equipment. 3. The apparatus according to claim 1, wherein said position changing means changes only the position of the discharge electrode. 4. A method for producing ultrafine metal particles in which a discharge electrode and a metal base material are arranged close to each other and a voltage is applied between the electrodes and the metal base material, wherein the arc discharge is started immediately after the start of the arc discharge. A method for producing ultrafine metal particles, wherein the distance between the discharge electrode and the metal base material is gradually increased until the temperature is stabilized. 5. A method for producing ultrafine metal particles in which an electric discharge electrode and a metal base material are arranged close to each other and a voltage is applied between the electrodes and the metal base material to generate an arc discharge. A method for producing ultrafine metal particles, characterized in that a shape in which a height direction is larger than a width direction in a state of being arranged close to an electrode for use is used.