JP7320312B2 - Method for producing ultrafine particles - Google Patents

Description

The present invention relates to a method for producing ultrafine particles.

As one form of the method for producing ultrafine particles, JP-A-2019-136694 (Patent Document 1) and JP-A-2014-194059 (Patent Document 2) disclose a discharge vessel and a discharge vessel arranged inside the discharge vessel. A method for producing ultrafine particles using an ultrafine particle producing apparatus having a plurality of discharge electrodes and a power source for supplying power to the discharge electrodes is disclosed.

In the method for producing ultrafine particles disclosed in Cited Document 1, a particulate metal material is put into a discharge vessel, arc discharge is generated between a plurality of discharge electrodes, plasma is generated in the discharge vessel, and metal Ultrafine particles are generated from material particles.

JP 2019-136694 A

In the production apparatus used in the method for producing ultrafine particles described in Cited Document 1, a material supply device is provided at the bottom of the discharge vessel, a material supply pipe is piped from the material supply device to the center of the discharge vessel, and the carrier is passed through the material supply pipe. A particulate metal material is supplied into the discharge vessel together with the gas.
Since the manufacturing apparatus used in this manufacturing method requires a material supply device and a material supply pipe, the structure is complicated, the size increases, and the manufacturing cost increases.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing ultrafine particles that can produce ultrafine particles at low cost.

Using an ultrafine particle production apparatus comprising a discharge vessel, a plurality of discharge electrodes arranged inside the discharge vessel, and a power supply unit for supplying power to the discharge electrodes, the metal material placed in the discharge vessel and the plurality of discharge electrodes are separated. A method for producing ultrafine particles by generating an arc discharge between and generating plasma in a discharge vessel to generate ultrafine particles from a metal material,
The discharge vessel comprises a vertical cylindrical main body and an upper lid that covers the upper opening of the main body,
1. A method for producing ultrafine particles, comprising filling a discharge vessel with an aggregate of metal fibers having a wire diameter of 20 μm to 50 μm and a wire length of 50 mm to 200 mm as a metal material through a top opening.

According to the first aspect of the invention, when a high voltage is applied to the discharge electrode, an arc electric path is formed between the discharge electrode and the metal fiber, and the metal fiber melts and evaporates to produce ultrafine particles.
According to the present invention, instead of filling the discharge vessel with particulate or block-shaped metal material, the discharge vessel is filled with aggregates of metal fibers. The aggregate of metal fibers can be easily filled into the discharge vessel without a material supply device for supplying the metal material together with the carrier gas to the discharge vessel, as in the case of producing ultrafine particles from a particulate metal material. . Therefore, a manufacturing apparatus having a simple and small structure can be used, and the manufacturing cost can be reduced.

Since metal fibers are long unlike particles, the distance to the discharge electrode is shortened, the electrical resistance can be lowered, and a large current can flow.
In addition, since metal fibers have a large surface area, when oxygen is injected to produce metal oxide fine particles or nitrogen is injected to produce metal nitride fine particles into a discharge vessel containing a pure metal material, an oxidation reaction or nitriding reaction occurs. Reactions occur efficiently.

The particle shape and particle size distribution of the produced ultrafine particles can be adjusted by selecting the wire diameter, wire length, and packing density of the metal fibers.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially broken cross-sectional view showing an ultrafine particle manufacturing apparatus used in the ultrafine particle manufacturing method according to the first embodiment of the present invention; It is a top view which shows the same ultrafine particle manufacturing apparatus. It is a side view which shows the same ultrafine particle manufacturing apparatus. It is a power supply circuit diagram incorporated in the power supply unit of the same ultrafine particle manufacturing apparatus. It is a control panel circuit diagram built in the power supply section of the ultrafine particle manufacturing apparatus. FIG. 4 is an explanatory diagram of the operation of the power supply circuit and the operation panel circuit when operating the operation panel provided in the power supply section of the ultrafine particle manufacturing apparatus; Fig. 3 is a partially broken cross-sectional view showing a state in which a discharge vessel of the same ultrafine particle manufacturing apparatus is filled with metal fibers. FIG. 6 is an exploded perspective view showing the main parts of an ultrafine particle manufacturing apparatus used in the ultrafine particle manufacturing method according to the second embodiment of the present invention;

The present invention will be described below with reference to the drawings. 1 to 3 show an ultrafine particle manufacturing apparatus 10 used in the ultrafine particle manufacturing method according to the first embodiment of the present invention. The ultrafine particle production apparatus 10 includes a discharge vessel 11 and a power source section 12 . The discharge vessel 11 is assembled with a vertical cylindrical main body 13 , an upper lid 14 covering the upper opening of the main body 13 , and a lower lid 15 covering the lower opening of the main body 12 . The main body 13 is made of a heat-resistant quartz glass tube, and the upper lid 14 and the lower lid 15 are made of stainless steel.

An upper cylinder 16 made of stainless steel is fitted on the upper part of the main body 13 and fixed with a heat-resistant adhesive. A flange 16 a is formed at the upper end of the upper cylinder 16 . On the other hand, the upper lid 14 is also formed with a flange 14a. The upper lid 14 is assembled to the main body 13 by joining the flange 14a and the flange 16a of the upper cylindrical body 16, clamping the combined flanges 14a and 16a with a ring-shaped clamp 17, and tightening them with screws 17a. The upper lid 14 can be removed from the main body 13 by loosening the screw 17a and removing the clamp 17. - 特許庁

Similarly, a lower cylindrical body 18 made of stainless steel is fitted to the lower part of the main body 13 and fixed with a heat-resistant adhesive. A flange 18a is formed at the lower end of the lower cylindrical body 18, and the lower lid 15 is also formed with a flange 15a. The flange 15a of the lower lid 15 and the flange 18a of the lower cylindrical body 18 are combined, and the combined flanges 15a and 18a are clamped by a ring-shaped clamp 19 and tightened with screws to be detachably attached to the main body 13. ing.

The discharge vessel 11 is supported by left and right frames 20 . A plate-like bracket 21 is welded to the lower portion of the upper cylindrical body 16 fixed to the upper portion of the main body 13 of the discharge vessel 11 and extends radially from the main body 13 . An insulator 22 is fixed to the upper end of each frame 20, and a bracket 21 and a terminal 24a of a positive current wire 24 are detachably fixed to the upper end of the insulator 22 by a wing nut 23. The discharge vessel 11 can be removed from the frame 20 by loosening the wing nut 23 .

The upper lid 14 is provided with a plurality of screw ports 14b. These screw ports 14b are provided for connection with a vacuum pump for evacuating the inside of the main body 13, connection with an inert gas supply pipe, or connection with an oxygen concentration sensor inside the main body 13. . In addition, a pressure gauge 25 for monitoring the pressure inside the main body 13 and an exhaust port 14c formed in the upper lid 14 are opened to avoid the risk of the main body 13 bursting when the pressure inside the main body 13 rises rapidly. A safety valve 26 for releasing the internal pressure of the main body 13 and a handle 14d for lifting the upper lid 14 are provided.

A spiral discharge electrode 27 is fixed to the back surface of the upper lid 14 with a screw 28 . The outer diameter of the spiral discharge electrode 27 is approximately the same as the inner diameter of the main body 13 , and when the upper cover 14 is placed over the main body 13 , it is incorporated so as to come into contact with the inner peripheral surface of the main body 13 .

A terminal 29 a of a negative pole conducting wire 29 is fastened to the lower lid 15 with a screw 30 . A needle-shaped discharge electrode 31 is erected on the lower lid 15 so as to extend to the middle of the main body 13 along the center of the spiral positive discharge electrode 27 .

Electric power is supplied from the power supply unit 12 to the ultrafine particle manufacturing apparatus 10 through the positive electrode line 24 and the negative electrode line 29 . The power supply unit 12 is provided with an operation panel 12a, and incorporates a power supply circuit 40 shown in FIG. 4 and an operation panel circuit 50 shown in FIG.

The power supply circuit 40b includes a first DC power supply 41 with an input power supply of AC 200V, an output of DC 60V to 26V, an output current of 200A, and a second DC power supply 42 with an output of 200V. The positive electrode of the first DC power source 41 is connected to the spiral discharge electrode 27 of the discharge vessel 11 via line 1, and the negative electrode of the first DC power source 41 is connected to the needle-shaped discharge electrode 31 of the discharge vessel 11 via line 2. It is connected to the.

The positive pole of the second DC power supply 42 is connected to the spiral discharge electrode 27 of the discharge vessel 11 via the line 3 , and the negative pole of the second DC power supply 42 is connected via the line 2 to the needle discharge electrode 31 of the discharge vessel 11 . It is connected to the.

Line 1 has a switch MCC and a diode D1 connected in series. Line 3 is connected in series with switch MCA, switch MCB and diode D1. A line 4 connecting the lines 2 and 3 is connected to a switch MCA and a capacitor C1. A line 5 connecting lines 3 and 4 incorporates a capacitor C2 and a switch MCA. In addition, a switch MCA is incorporated in line 6 connecting line 4 and line 5 .

The control panel circuit 50 is used by being connected to an AC 100V outlet. The connection between the outlet and the lines 7 and 8 of the control panel circuit 50 is switched by the main switch CP1. A line 9 connecting lines 7 and 8 incorporates a normally open switch S1 and two switches MCA. Two switches MCA are arranged in parallel. Similarly, line 10 incorporates normally open switch S1, timer T1, switch MCB and switch MCC. Switch MCB is connected to normally open switch S1 via normally closed switch S2. Switch MCC is connected to normally open switch S1 via normally open switch S3.

The configuration of the ultrafine particle manufacturing apparatus 10 is as described above, and the operation thereof will be described below. The wing nut 23 is loosened to remove the spiral discharge electrode 27 together with the top cover 14 of the discharge vessel 11 from the main body 13, and the main body 13 is filled with an aggregate of metal fibers 60 as shown in FIG. Then, the upper lid 14 is put on the main body 13 and the wing nut 23 is tightened to fix the upper lid 14 to the main body 13 . The screw port 14b of the upper lid 14 is closed. In this embodiment, as an example, aluminum fibers having a wire diameter of 20 to 50 μm, a wire length of 50 to 200 mm, and a bulk density of 0.2 to 0.3 g/cc are filled.

The operation panel 12a is switched to operate the ultrafine particle manufacturing apparatus 10. FIG. FIG. 6 shows an operation chart during operation. When the operation panel 12a is switched from "OFF" to "CHARGE", the switch MCA is closed and the two capacitors C1 and C2 are arranged in parallel and charged from the second DC power supply 42. When the operation panel 12a is switched from "charging" to "discharging", the timer T1 is activated, and during the predetermined time set by the timer T1, the two capacitors C1 and C2 are arranged in series, and the second DC power supply 42 is connected to the discharge container. 11 is applied with a high voltage of 200V. Then, when a predetermined period of time elapses and the application of the high voltage ends, the switch MCC is closed and a low voltage and large current is applied from the first DC power supply 41 .

According to the method for producing ultrafine particles according to the present embodiment, when a high voltage is applied to the discharge electrodes 27 and 31 of the discharge vessel 11, an arc electric path is formed between the discharge electrodes 27 and 31 and the metal fibers 60, and the metal fibers 60 melts and evaporates to produce aluminum ultrafine particles. Since most of the produced ultrafine particles are accumulated on the lower lid 15 of the discharge vessel 11, the lower lid 15 is removed and collected.

In the method for producing ultrafine particles according to the present embodiment, the discharge vessel 11 is filled with aggregates of metal fibers 60 such as aluminum fibers, instead of putting a particulate or block-shaped metal material into the discharge vessel 11 . In general, the more current that flows through a conductor, the greater the resistance. This is because magnetic lines of force are generated perpendicular to the direction of the current flowing according to Fleming's law, and a skin effect occurs that inhibits the current flowing through the center of the conductor. The cross-sectional area of a conductor is proportional to the cube of its diameter, and the surface area of a conductor is proportional to the square of its diameter. . Since the metal fiber 60 has a thin cross-sectional area, a large current can flow through it, effectively generating an arc discharge.

Since the metal fibers 60 are long unlike the particles, the distance to the discharge electrodes 27 and 31 is shortened, the electrical resistance can be lowered, and a large current can flow.
In addition, since the metal fibers 60 have a large surface area, when oxygen is injected to produce metal oxide fine particles or nitrogen is injected to produce metal nitride fine particles into the discharge vessel 11 containing a pure metal material, an oxidation reaction occurs. and nitriding reactions occur efficiently.

The aggregate of the metal fibers 60 can be easily formed into the discharge vessel 11 without a material supply device for supplying the metal material together with a carrier gas to the discharge vessel 11, as in the case of producing ultrafine particles from a particulate metal material. can be filled to Therefore, a manufacturing apparatus having a simple and small structure can be used, and the manufacturing cost can be reduced.

When the discharge vessel 11 is filled with an aggregate of metal fibers 60 , the metal fibers 60 tend to get entangled with the spiral discharge electrode 27 and the needle discharge electrode 31 . As a result, the resistance between the discharge electrodes 27, 31 and the metal fiber 60 becomes lower, and the arc discharge generation efficiency is improved.

If impurities adhere to the surface of the metal fiber 60, the electrical resistance increases. When the aggregate of the metal fibers 60 is filled in the discharge vessel 11 and a high voltage is applied to the discharge electrodes 27 and 31, the portion of the metal fibers 60 with increased electrical resistance becomes non-energized, and the metal fibers 60 do not melt and evaporate. There is a risk that it will remain in the form of
In this example, by applying a high voltage for a predetermined time, most of the aggregates are melted and evaporated, and when the application of the high voltage is finished, a low voltage and large current is applied to melt and evaporate the metal fibers. 60 can be melt evaporated.

FIG. 8 shows the main part of an ultrafine particle manufacturing apparatus 10A used in the ultrafine particle manufacturing method according to the second embodiment. A central shaft 33 is attached to the upper end of the spiral discharge electrode 32 . The central shaft 33 is supported by a bearing 35 provided in the center of the upper lid 34 and protrudes from the upper lid 34 . A sprocket 36 is attached to the projecting end of the central shaft 33 . On the other hand, a motor 37 is fixed to the upper lid 34, and a sprocket 38 is attached to the drive shaft of the motor 37. As shown in FIG. A sprocket 36 of the central shaft 33 and a sprocket 38 of the motor 37 are connected by a chain 39 . Since a high voltage is applied to the upper lid 34, the motor 37 and its wiring are insulated from the upper lid 34 by ceramics. A ceramic chain 39 is used to insulate between the sprocket 36 of the central shaft 33 and the sprocket 38 of the motor 37 .

Three metal rods 32a are welded to the spiral discharge electrode 32 at equal angular intervals so that the pitch of the spiral does not change and the electrode does not wobble.
The other configuration of the ultrafine particle manufacturing apparatus 10A according to the second embodiment is the same as that of the ultrafine particle manufacturing apparatus 10 according to the first embodiment. do.

In the ultrafine particle production apparatus 10A according to the present embodiment, after removing the upper lid 34 and filling the main body 13 of the discharge vessel 11 with the metal fibers 60, when the main body 13 is covered with the upper lid 34, the spiral shape according to the first embodiment is formed. Similar to the discharge electrode 27 , a spiral discharge electrode 32 is incorporated so as to be in contact with the inner peripheral surface of the main body 13 . After generating ultrafine particles by applying voltage to the discharge electrode 32 and the discharge electrode 31, when the motor 37 is operated, the spiral discharge electrode 32 slides on the inner peripheral surface of the main body and rotates around the needle discharge electrode 31 as the center of rotation. Rotate. As a result, the ultrafine particles adhering to the inner peripheral surface of the main body 13 are scraped off by the spiral discharge electrode 32 and accumulated on the lower lid 15, so that the lower lid 15 is removed and collected.

According to this embodiment, the spiral discharge electrode 32 can be rotated around the needle-shaped discharge electrode 31 , and the needle-shaped discharge electrode 31 does not interfere with the rotation of the spiral discharge electrode 32 . Therefore, the spiral discharge electrode 32 can be continuously rotated in one direction, and the ultrafine particles adhering to the inner wall surface of the discharge vessel 11 can be efficiently scraped off and collected by the rotation of the spiral discharge electrode 32. .
Although aluminum fibers are used as the metal fibers 60 in this embodiment, the method for producing ultrafine particles according to the present invention is not limited to this, and can be applied to stainless steel fibers and fibers of various alloys.

DESCRIPTION OF SYMBOLS 10, 10A...Ultrafine particle manufacturing apparatus 11...Discharge vessel 12...Power supply part 13...Main body 14...Upper lid 15...Lower lid 16...Upper cylindrical body 17...Clamp 18...Lower cylindrical body 19...Clamp 20...Frame 21...Bracket 22 Insulator 23 Wing nut 24 Positive current-carrying wire 25 Pressure gauge 26 Safety valve 27 Spiral discharge electrode 29 Negative current-carrying wire 31 Needle-shaped discharge electrode 32 Spiral discharge electrode 33 Center Shaft 34 Upper lid 35 Bearing 36 Sprocket 37 Motor 38 Sprocket 39 Chain 40 Power supply circuit 50 Operation panel circuit 60 Metal fiber (aluminum fiber)
C1... Capacitor C2... Capacitor

Claims (1)

Using an ultrafine particle production apparatus comprising a discharge vessel, a plurality of discharge electrodes arranged inside the discharge vessel, and a power supply unit for supplying power to the discharge electrodes, the metal material placed in the discharge vessel and the plurality of discharge electrodes are separated. A method for producing ultrafine particles by generating an arc discharge between and generating plasma in a discharge vessel to generate ultrafine particles from a metal material,
The discharge vessel comprises a vertical cylindrical main body and an upper lid that covers the upper opening of the main body,
1. A method for producing ultrafine particles, comprising filling a discharge vessel with an aggregate of metal fibers having a wire diameter of 20 μm to 50 μm and a wire length of 50 mm to 200 mm as a metal material through a top opening.

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