JP2002241806A - 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 stable formation of high-quality metallic ultrafine particles by stably maintaining the shape of an arc column in forming the metallic ultrafine particles using arc discharge. SOLUTION: In order to maintain the shape of the arc column, the distance (interelectrode distance D) between a discharge electrode 13 and a target 5 is maintained nearly constant. In particular, the maintenance of the interelectrode distance D can be done more easily and more accurately by detecting the discharge voltage in the case where arc discharge is initiated and changing the position of the discharge electrode 13 in such a way that the discharge voltage can be held at a nearly constant value.

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 a method for producing ultrafine metal particles using arc discharge for a long period of time. The present invention relates to an apparatus and a method for producing ultrafine metal particles, which stabilize the conditions for producing ultrafine metal particles by maintaining the time substantially constant.

[0002]

2. Description of the Related Art Conventionally, it has been known to use an arc discharge as a technique for producing ultrafine metal particles having a particle 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.

In the technique for producing ultrafine metal particles represented by the hydrogen arc method, in order to stabilize the amount and particle size of the resulting ultrafine metal particles, an arc column (electron generated between a cathode and an anode, And an arc composed of ion plasma)
It is important to maintain the shape of the stably. That is,
If the shape of the arc column changes, the conditions for generating the ultrafine metal particles differ, and the generation speed and the particle diameter change, thereby deteriorating the quality of the ultrafine metal particles.

[0004]

However, in the technology relating to the conventional hydrogen arc method, little consideration has been given to maintaining the shape of the arc column in a stable manner. This leads to the problem that it cannot be manufactured.

[0005] The general method for producing ultrafine metal particles by the hydrogen arc method is a batch-type production method in which one arc discharge is completed when a target (metal base material) is consumed. Normally, when the target is consumed, its volume is also reduced. Therefore, if the arc discharge continues, the distance between the discharge electrode and the target gradually increases. As a result, the shape of the arc column changes with the progress of the arc discharge.

In a conventional apparatus for producing ultrafine metal particles using the hydrogen arc method, arc discharge is generated in a state where both the discharge electrode and the target are held so as not to change their positions. Therefore, the distance between the discharge electrode and the target always changes due to the consumption of the target, so that the shape of the arc column could not be maintained, and as a result, high-quality metal ultrafine particles could not be manufactured. .

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to stably maintain the shape of an arc column when generating ultrafine metal particles using arc discharge. Therefore, it is an object of the present invention to provide an apparatus and a method for producing ultrafine metal particles, which can stably produce high-quality ultrafine metal particles.

[0008]

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, a voltage detecting means for detecting a discharge voltage accompanying the occurrence of arc discharge, and changing a position of one of the discharge electrode and the holding electrode to change an interval between the discharge electrode and the metal base material. It is characterized by comprising a position changing means and a control means for maintaining the discharge voltage at a substantially constant value by controlling at least the operation of the position changing means.

According to the above arrangement, the control means controls the operation of the position changing means more reliably by detecting the discharge voltage of the arc discharge by the voltage detection means and using the detected discharge voltage as a control parameter. be able to. As a result, even if the metal base material is gradually consumed due to the generation of the ultrafine metal particles, the shape of the arc column is stabilized by maintaining the electrode interval between the discharge electrode and the metal base material substantially constant. And the ultrafine metal particles can be stably generated for a long time.

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 an electrode for discharge and a metal base material in close proximity to each other, and applying a voltage between the electrodes to form an arc. In the method for producing metal ultrafine particles for generating electric discharge, at least one of the above-mentioned electric discharge electrode and the metal base material so as to maintain the electric discharge voltage at a substantially constant value after detecting the electric discharge voltage accompanying the occurrence of arc discharge. Is changed.

According to the above method, the discharge voltage of the arc discharge is detected and used as a control parameter, so that the discharge electrode can be used even if the metal base material is gradually consumed by the generation of ultrafine metal particles. In addition, it is possible to stabilize the shape of the arc column by maintaining the electrode interval, which is the interval between the metal base materials, substantially constant. As a result, ultrafine metal particles can be stably generated for a long time.

In order to solve the above-mentioned problems, the method for producing ultrafine metal particles according to the present invention comprises disposing an electric discharge electrode and a metal base material in close proximity to each other, and applying a voltage between them to form an arc. In the method for producing metal ultrafine particles for generating electric discharge, the distance between the discharge electrode and the metal base material, which changes due to the consumption of the metal base material by the occurrence of arc discharge, is maintained at a substantially constant value. The position of at least one of the electrode and the metal base material is changed.

According to the above method, the shape of the arc column can be maintained by keeping the distance between the discharge electrodes and the metal base material substantially constant. Therefore, by directly detecting the above-mentioned electrode interval or indirectly using parameters such as discharge voltage and maintaining the electrode interval at a constant value, the shape of the arc column is maintained, and the metal ultrafine particles are removed. It can be produced stably.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.
The following is a description based on FIGS. 1 to 7. Note that the present invention is not limited to this.

An apparatus and a method for producing ultrafine metal particles according to the present invention provide a discharge electrode and a target (metal base material) for maintaining the shape of an arc column when generating ultrafine metal particles by arc discharge. (Electrode spacing) is maintained substantially constant. In particular, in the present embodiment, a discharge voltage (arc voltage) accompanying an arc discharge is detected and used as a parameter to more accurately control the electrode interval to be kept constant.

Specifically, as shown in FIG. 2, 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. Note that the dashed arrows in FIG. 2 indicate the transmission path of the control signal, the thin solid line indicates the electrical connection path, and the thick solid line (between the position change mechanism 15-the torch 12-the discharge electrode 13 described later) indicates the mechanical connection Shows a typical relationship.

As shown in FIG. 3, 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. 3, preferably, an atmosphere gas is supplied from one side and the other is supplied. 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.

In the chamber 11, the torch 1
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.

As shown in FIG. 4, 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. This is because, when the metal ultrafine particles adhere to the tip of the discharge electrode 13, the discharge electrode 13 is excessively consumed due to deformation, melting, and the like.

In FIG. 4, 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 its 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 between the discharge electrode 13 and a target (metal base material) 5 which is a precursor of 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. 5, a shape having a sharpened tip is preferable in order to easily generate 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 placed thereon, and applies a voltage from the arc power supply 16 to the target 5. 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 FIGS. 3 and 4, 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 a 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. 3,
For convenience of explanation, the position changing mechanism 15 is schematically illustrated.

In the present invention, as will be described later, when the arc discharge is stable and the ultrafine metal particles are generated, the distance between the electrodes is maintained substantially constant in accordance with the consumption of the target 5. ing. Therefore, any one of the discharge electrode 13 and the holder 14 or both the discharge electrode 13 and the holder 14 may be moved, but preferably, the torch 12 is moved along its longitudinal direction. It is preferable to move only the discharge electrode 13 in the axial direction by moving it, because the space required for the movement can be made smaller and the configuration of the position changing mechanism 15 can be simplified.

Further, 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 the present invention, the positional relationship between the discharge electrode 13 and the holder 14 is not particularly limited. Therefore, as described later, the discharge electrode 13 may be disposed almost directly above the holding table 14, or may be placed and held on the holding table 14 as shown in FIGS. The arc discharge may be performed on the target 5 in a state where the discharge electrode 13 is disposed obliquely upward on the upstream side in the flow direction of the atmospheric gas (the direction of the arrow A).

The former configuration is used in a conventional general apparatus for producing ultrafine metal particles, and the latter configuration is a preferable configuration for improving the effect of suppressing the adhesion of ultrafine metal particles by the shield gas. It has become. That is, in the latter configuration, the metal ultrafine particles generated in the chamber 11 are efficiently transported by being carried by the flow of the atmospheric gas.
The shielding effect by the shielding gas can be improved. The specific arrangement of the “diagonally above” is not particularly limited. For example, in FIGS. 3 and 4, the torch 12 is arranged 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 generate an arc discharge between them (see FIG. 2). 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. 2, the current monitor 17 and the voltage monitor 18 generate an electric current (referred to as an arc current) flowing between the discharge electrode 13 and the target 5 due to the arc discharge, respectively, and (Referred to as arc voltage) is detected. As apparent from FIG. 2, the detection results of the current monitor 17 and the voltage monitor 18 are as follows.
Any of them is output to the control unit 40 and used for operation control of the position changing 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 unit 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 this embodiment, hydrogen (H ₂ ) gas and two kinds of inert gases of 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 atmosphere 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 is also connected to the particle recovery section 30 so that the supplied atmosphere gas is circulated by the gas circulation pump 35. It has become. 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.

The flow rate of the atmosphere gas supplied from the shield gas pipe 24 is not particularly limited as long as the flow rate of the shield gas can be formed. For example, a flow rate of about 5 L / min is exemplified. 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 a collecting filter 3
2, and a gas circulation pump 35 for recovering the ultrafine metal particles generated in the chamber 11 using the flow of the atmospheric gas.

In FIG. 3, 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 unit 40 controls at least the operation of the position changing mechanism 15 based on the state of the arc discharge. More preferably, as shown in FIG. Unit 20, particle collection unit 30
Such operations are also controlled.

Next, a method for producing ultrafine metal particles according to the present embodiment, that is, a method for maintaining the shape of arc discharge by the control unit 40 will be described.

As described above, in the production of ultrafine metal particles by the hydrogen arc method, in order to improve the quality of ultrafine metal particles, the shape of the arc column generated between the discharge electrode 13 and the target 5 must be improved. It is important to keep it stable. However, in the conventional configuration, since the torch 12 and the holding table 14 are almost completely fixed in the chamber 11, as the arc discharge proceeds, the target 5 becomes The electrode is gradually consumed, and accordingly, the electrode interval between the discharge electrode 13 and the target 5 is increased.

For example, as shown in FIG. 6, when the target 5 which has been melted by arc discharge to become a substantially spherical / elliptical sphere is consumed, the volume of the target 5 itself is reduced, and therefore, the substantially spherical / substantially elliptical. The diameter of the spherical target 5 becomes smaller. As a result, the above-mentioned electrode interval D, which is the interval between the discharge electrode 13 and the target 5, is enlarged by, for example, Δd.

Therefore, in order to keep the electrode interval D constant,
It is conceivable to change the position of at least one of the discharge electrode 13 and the target 5 by providing the position changing mechanism 15 or the like. It is usually difficult to change the position of at least one of the electrode 13 and the target 5.

In the present embodiment, the operation of the position change mechanism 15 is based on the finding that the electrode spacing D is also substantially constant when the discharge voltage associated with the arc discharge is substantially constant, which the present inventors independently found. The discharge voltage detected by the voltage monitor 18 is used for control. That is, in the apparatus or method for producing ultrafine metal particles according to the present invention, in order to make the arc column have a stable shape, the discharge voltage accompanying the arc discharge is detected by the voltage monitor 18 and the value of the discharge voltage is set to a fixed value. The operation of the position changing mechanism 15 is controlled by the control unit 40 as follows.

In the present embodiment, first, an experiment for previously determining the generation conditions for generating the ultrafine metal particles is performed, and based on the results of the experiment, the specific value of the discharge voltage (preferably the preferable discharge voltage for generating the ultrafine metal particles) keep determine a voltage value V _B). Then, the control unit 40, upon setting the value of the preferred voltage value V _B, controls the operation of the position change mechanism 15 as a preferred voltage value V _B is maintained at all times.

Specifically, an arc discharge is started by applying a high-frequency voltage between the discharge electrode 13 and the target 5 (holding table 14) from the arc power supply 16,
An arc column is formed. Since the formation of the arc column is due to dielectric breakdown occurring between the discharge electrode 13 and the target 5 (holding table 14), an arc current flows simultaneously with the formation of the arc column. Therefore, the start of arc discharge is 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. Thereafter, the high frequency voltage applied from the arc power supply 16 is switched to a DC voltage.

For example, the discharge electrode 13 is
As an example (see FIG. 4), an arrangement is made in such a manner as to be inclined with respect to .alpha., As shown in FIG. Since the target 5 is stable in terms of surface tension, the arc discharge is also stable at a constant electrode interval D, and the shape of the arc column is maintained substantially constant. Therefore, ultrafine metal particles are generated stably and blown out along the flow of the atmospheric gas (arrow A in the figure) (arrow C in the figure).

The target 5 gradually wears out with the generation of the metal ultrafine particles, and the electrode interval D increases, but the DC voltage V detected by the voltage monitor 18 is accordingly increased.
(Detection result) also changes. Where the control unit 40, the DC voltage value V is substantially suitable voltage V _B (V = V _B) As described above, performs control to suppress the expansion of the electrode spacing D by operating the position change mechanism 15.

As a result, as shown in FIG. 1 (b), even when the substantially spherical / elliptical target 5 is consumed and its diameter is reduced, the position changing mechanism 15 operates accordingly. Electrode spacing D between discharge electrode 13 and target 5
Is maintained substantially constant. Therefore, the shape of the arc column is also kept constant, and the generation and blowing direction of the ultrafine metal particles are stabilized along the flow direction of the atmospheric gas.

Similarly, even when the discharge electrode 13 is arranged substantially perpendicular to the target 5, FIG.
As shown in (2), the target 5 finally having a substantially spherical / elliptical shape forms a stable arc column at a fixed electrode interval D and stably generates ultrafine metal particles. However, since the electrode spacing D is to enlarge depleted target 5 gradually along with the generation of the ultrafine metal particles, the DC voltage value V detected by the voltage monitoring 18 becomes almost suitable voltage V _B (V = V _B ) As described above, the position change mechanism 15 is operated to suppress an increase in the electrode interval D. As a result, FIG.
As shown in (2), since the electrode interval D between the discharge electrode 13 and the target 5 is maintained substantially constant, the shape of the arc column is also maintained constant, and the generation of ultrafine metal particles is stabilized.

The range of the high-frequency voltage for starting the arc discharge is not particularly limited. For example, in the manufacturing apparatus having the above-described configuration, a value of about 7 kV can be given. The range of the DC voltage (arc voltage / discharge voltage) after the start of arc discharge is not particularly limited, but is preferably in the range of 30 V to 50 V, and more preferably in the range of 20 V to 30 V. . 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.

Further, the range of the electrode interval D is as follows.
It is appropriately set depending on the output of the arc power supply 16 and the materials of the discharge electrode 13 and the target 5, and is not particularly limited. For example, as the discharge electrode 13, 1-2%
When a nickel electrode is used as the target 5 using a tungsten electrode containing thorium oxide, a range of 1.0 mm to 1.5 mm at the start of arc discharge and a range of 5 mm to 30 mm at the time of stable arc discharge. Can be mentioned.

The specific value of the preferred voltage value V _B also varies as appropriate depending on the electrode spacing D and the configuration of the device, and is not particularly limited. For example, under conditions where the electrode spacing D and the DC voltage are within the above ranges and the discharge electrode 13 is arranged obliquely with respect to the target 5 (see FIGS. 1 and 6 and the like), the voltage is about 30 V.

The method of controlling the position changing mechanism 15 by the control unit 40 is not particularly limited. For example, in the present embodiment, PID control (proportional-integral-differential control) is used.

As described above, in the present embodiment, by using the detection result (DC voltage value V) obtained by the voltage monitor as a parameter for maintaining the electrode interval D constant, the control unit can control the position change. The operation of the mechanism can be more reliably controlled. As a result, even if the arc discharge is stabilized and the target is gradually consumed, it becomes possible to maintain the electrode interval D substantially constant and stabilize the shape of the arc column, and to stabilize the ultrafine metal particles for a long time. Can be generated. Therefore, even when ultrafine metal particles are produced by batch processing using the hydrogen arc method, it is possible to adjust the production amount and particle size within a predetermined range, and to produce ultrahigh-quality ultrafine metal particles. It can be manufactured stably.

In this embodiment, the discharge voltage (the DC voltage value V) is used as a parameter in order to maintain the electrode interval D, which changes as the target wears out, at a substantially constant value. The present invention is not limited to this. That is, in the present invention, if the position of at least one of the discharge electrode and the target is changed so as to substantially correspond to the increase in the electrode interval D due to the consumption of the target, the electrode interval D is kept constant. Good.

Therefore, for example, when the particle size of the produced ultrafine metal particles can be measured, the measured value of the particle size is used as a parameter to control at least one of the position of the discharge electrode and the target. Alternatively, control may be performed to change at least one of the position of the discharge electrode and the position of the target using an image recognition system. In any of these cases, a suitable range of the particle size and the electrode interval may be set by conducting experiments in advance.

Further, the control for changing the electrode interval in the present invention is performed during a period after the arc discharge is stabilized, as is clear from the above description. It will not be implemented in the period until it is changed.

[0073]

As described above, the apparatus for producing ultrafine metal particles according to the present invention includes a voltage detecting means for detecting a discharge voltage accompanying the occurrence of arc discharge, and a position for one of the discharge electrode and the holding electrode. Position changing means for changing the distance between the discharge electrode and the metal base material, and control means for maintaining the discharge voltage at a substantially constant value by controlling at least the operation of the position changing means. It is a configuration provided with.

In the above configuration, since the control means uses the discharge voltage detected by the voltage detecting means as a control parameter, the operation of the position changing means can be controlled more reliably. As a result, even if the metal base material is gradually consumed due to the generation of the ultrafine metal particles, it is possible to maintain the electrode gap almost constant and to stabilize the shape of the arc column, and to stabilize the ultrafine metal particles for a long time. This has the effect that it can be generated.

In the above apparatus for producing ultrafine metal particles, it is preferable that, in addition to the above 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.

Further, as described above, the method for producing ultrafine metal particles according to the present invention detects the discharge voltage accompanying the occurrence of arc discharge, and maintains the discharge voltage at a substantially constant value. This is a method of changing at least one of the position of the discharge electrode and the metal base material.

In the above method, the discharge voltage of the arc discharge is detected and used as a control parameter, so that even if the metal base material is gradually consumed due to the generation of the ultrafine metal particles, the electrode interval is kept substantially constant. It is possible to maintain and stabilize the shape of the arc column. As a result, there is an effect that metal ultrafine particles can be stably generated for a long time.

Further, in the method for producing ultrafine metal particles according to the present invention, even if the discharge voltage is not detected, the change is caused by the consumption of the metal base material due to the occurrence of arc discharge.
Any method may be used as long as at least one of the positions of the discharge electrode and the metal base material is changed so that the distance between the discharge electrode and the metal base material is maintained at a substantially constant value.

That is, the shape of the arc column can be maintained by maintaining the electrode interval substantially constant. Therefore, in the present invention, the electrode interval is directly detected, or indirectly detected using various parameters other than the discharge voltage,
By maintaining the electrode spacing at a constant value, there is an effect that the shape of the arc column can be maintained and metal ultrafine particles can be stably generated.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a state of an electrode interval in a state where arc discharge is stabilized by a manufacturing apparatus of ultrafine metal particles according to a first embodiment of the present invention, and FIG. (B) shows the state when the target is gradually consumed after the arc discharge is stabilized.

FIG. 2 is a block diagram showing a control system of the manufacturing apparatus for performing the arc discharge shown in FIG.

FIG. 3 is a schematic diagram showing a schematic configuration of the manufacturing apparatus shown in FIG.

FIG. 4 is an explanatory diagram showing a configuration for forming a shielding gas provided in the manufacturing apparatus shown in FIG. 2;

FIG. 5 is an explanatory view showing a shape of a discharge electrode used in the manufacturing apparatus shown in FIG.

FIG. 6 is an explanatory diagram showing an enlargement of an electrode interval due to consumption of a target due to execution of arc discharge.

7A and 7B are explanatory diagrams showing another example of the state of electrode spacing in a state where arc discharge is stabilized by the apparatus for manufacturing ultrafine metal particles shown in FIG. 1; FIG. 7A shows a state immediately after arc discharge is stabilized; And (b) shows the state at the time when the target is gradually consumed after the arc discharge is stabilized.

[Explanation of symbols]

 5 Target (Metal Base Material) 13 Discharge Electrode 14 Holder (Holding Electrode) 15 Position Changing Mechanism (Position Changing Means) 16 Arc Power Supply 18 Voltage Monitor (Voltage Detecting Means) 40 Control Unit (Control Means)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuhiko Karasawa 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto F-term in Murata Manufacturing Co., Ltd. 4K017 AA02 CA08 EA13

Claims (4)

[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; The apparatus for producing metal ultrafine particles that generates an arc discharge by applying a voltage between the electrode for use and the holding electrode, further comprising: voltage detection means for detecting a discharge voltage accompanying the occurrence of the arc discharge; A position changing means for changing a position of one of the holding electrodes to change an interval between the discharge electrode and the metal base material; and controlling the operation of at least the position changing means to make the discharge voltage substantially constant. And a control means for maintaining the value of the ultrafine metal particles. 2. The apparatus according to claim 1, wherein said position changing means changes only the position of the discharge electrode. 3. 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 to produce an arc discharge. A method for producing ultrafine metal particles, comprising detecting a voltage and changing at least one of the position of the discharge electrode and the metal base material so as to maintain the discharge voltage at a substantially constant value. 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 to generate an arc discharge, the method comprising the steps of: A metal which changes as the material is consumed, wherein at least one of the position of the discharge electrode and the metal base material is changed so as to maintain the distance between the discharge electrode and the metal base material at a substantially constant value. A method for producing ultrafine particles.