JPS60228604A - Production of ultrafine particles - Google Patents

Abstract

PURPOSE:To produce efficiently ultrafine metallic particles in the stage of generating an arc between a base metal for evaporation and an electrode to form the ultrafine particles by making the current value to be passed as arc current smaller than the specific current value. CONSTITUTION:The base metal is evaporated in gaseous hydrogen or non- oxidizing hydrogen-contg. compd. or the gaseous mixture composed thereof or the gaseous mixture composed of such gas and inert gas and the arc is generated between the base metal and the electrode, by which the ultrafine particles are produced. The current smaller than the current value at which the arc begins to change from the shape diverging from the electrode to the base metal to the shape concentrating to the local part on the base metal as designated as IA is passed as the arc current. The current value IA in this case is IA=aL+b and L is the distance between the base metal and the electrode (mm.), (a), (b) are the values which vary mainly with the compsn. of the gaseous atmosphere, the compsn. of the base metal, the compsn., shape and diameter of the electrode, the flow rate of a shielding gas, atmospheric pressure, etc. and are the values within a 30A/mm.>=a>=2A/mm., 200A/mm.>=b>=0 range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for efficiently producing ultrafine particles, particularly ultrafine metal particles having a particle size of 1 μm or less.

[Background of the invention]

Regarding the manufacturing method of ultrafine particles, see Japanese Patent Publication No. 55-4412.
3, Special Publication No. 57-44725, Special Publication No. 58-541
Methods such as No. 66 are known. These methods are called in-gas evaporation method and hydrogen arc heating method, and are effective methods for producing ultrafine particles. However, since the in-gas evaporation method requires large-scale production equipment, it is difficult to economically produce ultrafine particles. On the other hand, although the hydrogen arc heating method has a higher production efficiency (2) than the evaporation method in gas, it does not utilize a more efficient method that takes advantage of the hydrogen arc's characteristic of arc concentration.

[Purpose of the invention]

In view of the above, an object of the present invention is to provide a method for producing ultrafine particles with unprecedented efficiency.

[Summary of the invention]

The present invention provides a method for evaporating between a base material to be evaporated and an electrode in hydrogen gas, non-oxidizing hydrogen-containing compound gas (CH4, NH, etc.), a mixture of both, or a mixture of these gases and an inert gas. In the method for producing ultrafine particles that generates an arc, if the current value at which the arc starts to change from a shape that spreads from the electrode onto the base material to a shape that concentrates locally on the base material is 8, then IA=aL+b However, L: Distance between the base material and the electrode (mu) a, b: Values that vary mainly depending on the gas composition of the atmosphere, the composition of the base material, the composition of the electrode, the shape/diameter, the shielding gas flow rate, the atmospheric pressure, etc. (3) 30A/nw++≧a≧2 A/mm200A/n
A value in the range o≧b≧0.

This is characterized in that a current value smaller than the current value (6) shown by is caused to flow as an arc current.

The present invention has been made based on the discovery of the following new phenomenon.

In hydrogen gas, a non-oxidizing hydrogen-containing compound gas, a mixture of both, or a mixture of these gases and an inert gas, a tungsten electrode for discharging is used as a cathode, and a base material such as a metal on a water-cooled copper crucible is used as an anode, When producing ultrafine particles by generating an arc between two poles and heating and evaporating metal with the arc, the shape of the arc changes after a certain current value, and as this change occurs, the production efficiency of ultrafine particles increases significantly. I discovered a phenomenon. This change in the shape of the arc is a change in which the arc spreading from the tungsten electrode to the base becomes concentrated in a localized area on the metal surface in the water-cooled copper crucible after a certain current value is reached.

(4) This phenomenon is different from the dissolution and release reaction of hydrogen in molten metal described in the above-mentioned publications (Japanese Patent Publication No. 57-44725, Japanese Patent Publication No. 58-54165).

This phenomenon is explained as follows.

In a high humidity arc, hydrogen is dissociated into atoms due to thermal dissociation, and the heat of dissociation causes the bare arc to be squeezed into 100% inert gas.

Further, the atomically dissociated hydrogen recombines on the surface of the molten metal and releases energy corresponding to the dissociation energy (4.4 eV/one molecule of hydrogen), promoting the evaporation of the metal.

Generally, metal vapor requires less energy for ionization than an inert gas or a mixed gas of an inert gas and another gas. Therefore, the electrons emitted from the cathode (tungsten electrode in this case) concentrate in the area where the metal vapor is present.
The resulting high current density requires high heat losses to balance this, promoting metal evaporation.

This evaporation of metal further concentrates the arc. Due to this cause and effect, the concentration of the arc is stabilized, a high temperature region (5) is formed, and the metal is efficiently evaporated.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 11.

First, the apparatus will be explained with reference to FIG. 1 is a vacuum chamber, 2 is a torch, and 3 is a tungsten electrode, which is cooled by cooling water W1.

4 is a water-cooled copper crucible, which is cooled by cooling water W2. 5 is a base material, and 6 is a gas nozzle.

7 is a gas passage, 8 is a suction cover, and 9 is a suction nozzle. 10 is an insulating cover for insulating the water-cooled copper crucible 4. 11 is a crucible elevator, which controls the distance between the electrodes. 12 is a filter, which captures ultrafine particles carried by the carrier gas G1. 13 to 1.5 are gate valves. A circulation pump 16 circulates the gas inside the chamber 1. 17 is a vacuum pump, and 18 is a gas cylinder.

First, the inside of the vacuum chamber 1 is evacuated by the vacuum pump 15, and then an atmosphere of argon gas or argon gas or argon gas or argon (6) hydrogen is created. After the gate valve 15 is closed, the gas in the chamber 1 is circulated by the circulation pump 16. Thereafter, an arc is generated between the tungsten electrode 3 and the base material 5. The generated ultrafine particles are sent from the gas nozzle 6, ride on the carrier gas G1 that is blown up around the water-cooled copper crucible 4 through the gas passage 7, and are passed through the suction cover 8.
．． It is carried through the suction nozzle 9 and captured by the filter 12. The gas passage 7 and the suction force cover 8 greatly increase the collection rate of ultrafine particles.

After the ultrafine particles are captured by the filter 12, the gas Gl is used again by the circulation pump 16 as the shield gas G2 and the carrier gas G1.

Figure 2 shows the arc (
The shape of the high-efficiency arc (hereinafter referred to as high-efficiency arc) is shown below. For comparison, the shape of an arc generated in a conventional method (hereinafter referred to as a general arc) is shown.

Note that all arcs were observed using an ND filter (Nα9).

Figures 2 and 3 show the i! Distance between poles L and 10
+no+ Shows the arc shape when closed. Figure 2 shows I =
1.0 OA, FIG. 3 shows I=20 OA.

The region A shown in the figure shows the red color characteristic of a hydrogen atmosphere, and the region B shows the blue-green color characteristic of iron. Note that even when nickel or copper is used as the base material, the region A shows a color similar to that of iron, and in the case of titanium, it shows white.

The general arc (1=20OA) in FIG. 3 shows a shape that spreads out from the tungsten electrode, and the illegal high-efficiency arc in FIG. 2 shows a shape in which the arc is concentrated locally in the base metal, as described above.

Comparing the amount of ultrafine particles produced by both arcs, the high-efficiency arc (I = 100A) is better than the general arc (1 =
20OA>, about 3 times as much. In this way, the existence range of a highly efficient arc that is excellent for producing ultrafine particles is determined by the arc current value, the distance between the electrodes, the shape, diameter, and composition of the electrodes.
It changes depending on the composition and pressure of the atmospheric gas, the type of base material, the shielding gas flow rate, etc.

(8) The current value that starts to change from a general arc to a high-efficiency arc■
4 varies depending on various factors as described above. As a result of measuring this current value IA by changing the distance between wires #i, T, =
It was found that it is expressed as aL+b. a and b vary depending on the other factors mentioned above, gas composition, electrode shape, composition, diameter, base material composition, atmospheric pressure, shielding gas flow rate, etc. From the results of a wide range of experiments including various base materials, electrodes, gas compositions, and pressures, it was confirmed that a was in the range of 2A/1rxn to 30A/me, and b was in the range of o to 200A/mo+.

The results of measuring the current value (■6) when the base material is nickel or iron are shown in Section 4.5.6@.

In Figure 4, the base material is nickel and the atmospheric gas is Ar-50.
%H2, pressure 1 atm, cathode is tungsten electrode (diameter 3.
2mm, 2% Doria), shielding gas flow rate 15Q
The relationship between arc current, interelectrode distance, and arc shape when /win is shown.

Of the two straight lines shown in FIG. 4, straight line 1 (high current side) is the current value IA at which the general arc shape begins to change to a high efficiency arc. Straight line 2 (9) (low current side) is the current value indicating the end of the change from the general arc to the high efficiency arc. The regions divided by these two straight lines 1.2 will be hereinafter referred to as the -crotch region, transition region, and high efficiency region from the high current side.

5 shows the case where the base material is iron and other conditions are the same as in FIG. 4, and FIG. 6 shows the case where the atmospheric gas composition is Ar-36%H2 and the other conditions are the same as in FIG. 5. Compared to FIG. 5, the transition and high efficiency regions have shifted to the low current side. Generally, when the hydrogen concentration is lowered, the transition and high efficiency regions shift to the lower current side, and the amount of ultrafine particles produced decreases accordingly.

Conversely, when the hydrogen concentration is increased, the current shifts to a higher current side and the amount of ultrafine particles produced also increases.

Comparing the amount of ultrafine particles produced in the general area and the high efficiency area, the amount in the high efficiency area is much higher.

This is because the arc in the high-efficiency region (high-efficiency arc) concentrates locally on the base material, so that the base material can be efficiently evaporated. - In the crotch region, only a portion of the base material (approximately 40 g of iron or nickel) is melted, whereas in the high efficiency region, only a portion of the base metal (approximately 40 g of iron or nickel) is melted, where the arc is concentrated. As a result, less heat is used for purposes other than metal evaporation, resulting in higher efficiency. -Specific numerical values for the amount of ultrafine particles produced in the crotch region and high efficiency region are shown in Section 7.
Shown in Figure 8.9.

In Figure 7, the base material is nickel, Ar -50% H2 atmosphere, pressure is 1 atm, distance between electrodes L = 10~12cm, shielding gas flow rate is 151/m, and curve 1 is made of tungsten with a diameter of 3.2 cm as the cathode. Electrode (contains 2% Doria), curve 2 shows cathode diameter 6
．． This is the amount of ultrafine nickel particles produced when using a 4 m tungsten electrode (containing 2% doria).

By changing the diameter and shape of the electrode, the high efficiency region shifts and the seventh
As seen in the figure, the amount of production in the -crotch area is approximately 6 times (approximately 4
0g/h). This phenomenon, in which changes in the diameter, shape, and composition of the electrode shift the high efficiency region to the high current side and generate ultrafine particles more efficiently, has also been confirmed with other metals.

The amount of ultrafine particles generated when the base material is changed to iron or titanium is shown in Section 8.
, shown in Figure 9. In addition, in Figures 8 and 9, the diameter of the cathode is 3.2W.
A ++ tungsten electrode (containing 2% doria (11)) was used, and the other conditions were the same as in FIG.

FIG. 8 shows the amount of ultrafine particles produced when the base material is iron, and FIG. 8 shows the amount of ultrafine particles produced when the base material is titanium. As shown in the example of nickel in FIG. 7, even in the case of iron and titanium, the production amount in the high efficiency range is much higher than that in the general range.

Figure 10.11 shows transmission electron micrographs of ultrafine iron and nickel particles obtained in the high efficiency region.

Both metals have a uniform particle size of 0.01 to 0.1 μm.

Note that high-efficiency arcs are generated not only in cases where iron, nickel, and titanium are used as base materials, but also in various metal alloys and other substances such as chromium, cobalt, iron alloys, nickel alloys, and titanium alloys.

The amount of the above-mentioned ultrafine metal particles with a particle size of 1 μm or less produced was compared with the general range and is summarized in Table 1.

(12) Table 1 Furthermore, the power required for producing ultrafine particles is also much smaller in the high efficiency range than in the general range.

Table 2 shows the production efficiency obtained by dividing the amount of ultrafine particles produced in the general region and high efficiency region shown in Table 1 by the input power.

Table 2 As mentioned above, ultrafine particles can be produced economically because large-scale production equipment is not required like in-gas evaporation method, and compared to the conventional hydrogen arc heating method. It can be manufactured with extremely high efficiency.

〔Effect of the invention〕

As explained above, according to the present invention, ultrafine particles of iron, nickel, titanium, alloys thereof, various metals such as chromium, cobalt, alloys, and other substances, especially particles with a particle size of 1
It has become possible to produce ultrafine metal particles of μm or less with high efficiency and low power consumption.

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram of the manufacturing equipment used in the manufacturing method of the present invention, Fig. 2 is a schematic explanatory diagram of the arc (IS with an ND filter) generated in the manufacturing method of the present invention, and Fig. 3 is a schematic explanatory diagram of the manufacturing equipment used in the manufacturing method of the present invention. Figure 4.5.6 is an explanatory diagram showing the arc generated in the method, and shows the arc current and interelectrode distance in the conventional manufacturing method (-crotch region) and the manufacturing method of the present invention (transition region, high efficiency region). The relationship diagram, Figure 7.8.9 is the relationship diagram between arc current and ultrafine particle generation amount, and Figure 10.11 is (14
) This is a transmission electron micrograph (magnification i: 100,000 times) of ultrafine particles obtained by the production method of the present invention. ■...Chamber, 2...Torch, 3...Tungsten electrode, 4...Water-cooled copper crucible, 5...Base material, 6
...Gas nozzle, 7...Gas passage, 8...Suction cover, 9...Suction nozzle, 10...Insulation cover, 1
1... Crucible elevator, 12... Filter, 13, 1
4, 15...Gate valve, 16...Circulation pump,
17... Vacuum pump, 18... Gas cylinder, 19.
...Tungsten electrode, 20...Base material, G1...Carrier gas, G2...Shield gas, Wl, W2...
・Cooling gas. Agent Patent attorney Akio Takahashi (15) -J 6 Fig. θ Z4 tθ Distance between electric power source L (plain air) No 7 m Ar7 electric washing L (A) Fig. 3 - Rechargeable enemy 1 (A) Fig. q Arc chamber N L T- (Aji 1θ Figure 11 Figure 41-

Claims (1)

[Claims] 1. Generating an arc between the base material to be evaporated and the electrode in hydrogen gas, non-oxidizing hydrogen-containing compound gas, a mixture of both, or a mixture of these gases and an inert gas. In the method of manufacturing ultrafine particles by causing the arc to spread from the electrode to the base material, if the current value starts to change from a shape that spreads from the electrode to the base material to a shape that concentrates locally on the base material, L: Distance between base material and electrode (m,) a, b: Value that changes mainly depending on the gas composition of the atmosphere, composition of the base material, composition of the electrode, shape/diameter, shielding gas flow rate, atmospheric pressure, etc. A method for producing ultrafine particles (1), characterized in that a current value smaller than the current value IA shown by is passed as an arc current. 2, a, b to 30 A/m≧a≧2AA/+am200A/+m
The method for producing ultrafine particles according to claim 1, characterized in that ≧b≧0.