JPS59118803A - Production of ultrafine metallic particle - Google Patents

Abstract

PURPOSE:To obtain easily ultrafine particles of a high melting point metal with a small-sized device and with high efficiency without requiring much electric power by converging the arc column generated between the metallic material on an anode and a cathode onto the molten surface of the metallic material and producing the ultrafine metallic particles. CONSTITUTION:Arc discharge is generated between a cathode 2 and a metallic material 4 of the same polarity placed on an anode 3 when an arc voltage is impressed on a power source 5 after the inside of a vessel 1 is maintained in an inert gaseous atmosphere of Ar, He, etc. If, for example, gaseous H2 is blown to an arc column 6, the column 6 is made into the shape of an inverted triangle converged to the material 4 as shown in the figure and therefore ultrafine metallic particles are generated from around the column 6. The kind of the arc current, the range of the arc voltage, the kind and compsn. of the atmosphere gas in the vessel 1, the pressure in the vessel 1, etc. are the possible conditions for converging the column 6.

Description

DETAILED DESCRIPTION OF THE INVENTION This BA generates #1 using arc discharge. The present invention relates to a method for producing ultrafine metal particles that can produce ultrafine metal particles with well-uniformed diameters.

Conventionally, as a method for manufacturing ultrafine metal particles for magnetic recording media having a size of 1 μm or less, there are, for example, the following methods. One of these is reduction of a solid salt with a gas.fc is a chemical method for producing ultrafine metal particles by thermal decomposition. This method has the disadvantage that ultrafine metal particles obtained by reducing oxides, oxalates, etc. are formed into fine single crystals of 1 μm or less, but they tend to agglomerate into complex particle shapes.

The second is a chemical method in which chlorides such as iron and cobalt are precipitated from solution in a magnetic field using a highly reactive reducing agent such as NaB I H4 to produce ultrafine particles of metals and their compounds. It's a method. This method also tends to form aggregated particles. However, although this method can produce high-performance ultrafine alloy particles in the laboratory, it poses pollution problems when mass-produced, and is not suitable for lid production due to high cost. The third method is a physical method in which ultrafine metal particles are produced by heating and melting a metal or its alloy in a vacuum or low-pressure inert gas to evaporate it.

As shown in FIG. 1, this method involves heating and evaporating a metal material 4 provided inside a chamber 1 under low pressure by induction melting using a multi-frequency coil 7 in a low-pressure inert gas such as argon or helium. Let it coagulate and solidify. According to this method, ultrafine metal particles of metal or its alloy having a uniform particle size of 0.1 μm or less can be obtained. Moreover, in this method, by controlling the type and pressure of the atmospheric gas in the cha/par 1 and the evaporation temperature, the particle size can be controlled within the range of several tens of tens of thousands to several thousand. Accordingly, when a ferromagnetic metal or alloy is used as the metal material, its magnetic properties can be varied over a wide range. In addition to the above-mentioned high frequency heating, there are heating methods such as electron beam melting, plasma jet, arc discharge, and GO2 gas laser as means for melting metal. Furthermore, these evaporation methods have the advantage of being chemically stable compared to the above two methods.

On the other hand, this evaporation method simply uses the evaporation of the metal material by heating it, so it has the disadvantage of low production efficiency of metal fine particles. In addition, it is difficult to produce ultrafine metal particles of high-melting point metals, such as Nb and Ta.Furthermore, the production equipment becomes larger to increase the surface area of the molten metal, and a large amount of electricity is required, resulting in high costs. be.

The present invention has been made in view of the above points, and its purpose is to improve the production efficiency of ultrafine metal particles.
Moreover, it is an object of the present invention to provide a method for manufacturing ultrafine metal particles that is easy to manufacture even with high-melting-point metals, and that is inexpensive in that the manufacturing apparatus is small and does not necessarily require a large amount of electric power.

The outline of the present invention will be explained below with reference to FIGS. 2 to 5, together with a device S for one-person use.

1 is a heat-resistant sealed container, 2 is a cathode electrode inserted into the container 1, and the cathode electrode 2 is made of a material such as tungsten. Reference numeral 3 denotes an anode made of hearth copper, for example, constituting the bottom of the container 1, and a metal material 4 from which ultrafine metal particles are to be produced is placed on this anode, facing the cathode.

5 is a power source, and when heavy pressure is applied to this power source 5, an arc column 6 is created between the cathode electrode 2 and the metal material 4 which can be used as an anode.
is formed.

Then, when the inside of the container 1 is surrounded by an inert gas such as argon, helium, neon, etc., and arc pressure is applied to the power source 5,
Arc discharge is performed between the metal material 4 of the same polarity placed on the upper surface of the cathode electrode 2 and the anode electrode 3. Apart from this, when hydrogen gas is sprayed onto the arc column 6, for example, the shape of the arc column 6 becomes a shape squeezed into the metal material 4 as shown in FIG. is generated. Inert gases such as argon, helium, and neon are used because they are stable and do not easily react with other elements. The production efficiency of the ultrafine metal particles 4 is remarkable, and ultrafine metal particles with a small average particle size and a good particle size distribution can be produced. As a result of blowing the gas onto the arc column 6, the arc column 6 becomes constricted in shape, resulting in large heat loss, so the arc column 6 is designed to minimize this loss. This is because the cross section self-shrinks. This is called a thermal pinch effect. Another factor that narrows down the arc column 6 is the magnetic pinch effect. This is because the electrons and ions (electron flow elements) of the metal material 3 in the arc column 6 flow approximately 11 parallel to the center line of the arc column 6, but these electrons and ions are affected by the magnetic field generated by it. Therefore, mutual absorption force is generated, and the arc column 6
This is because the cross section of This magnetic pinch effect is proportional to the arc current and becomes most noticeable at mperθ of 80 mm or more. Due to these thermal pinching effects and magnetic pinching effects, the arc column 6 self-contracts, and the anode 3
The arc column 6 is concentrated at one point with respect to the metal material 4 above. As a result, the vicinity has very high temperatures, e.g.
~10,000 K'', a part of the molten metal of the metal material 4 is in an atomic state and is introduced into the arc column 6.The ionization voltage is Fe17, 13V.

Co 8.5 V, Ni 7.6 V, Hz 13.
5V, Ar15.9V Since the resistance of metal is lower than that of surrounding gases such as argon, once metal atoms begin to be generated from the molten metal, the concentration of the iiL flow increases, and the arc column 6
The molten metal shrinks further near the anode. In this way, due to the combination of causes and effects, the shape of the arc column 6 is squeezed into a substantially inverted triangular shape with respect to the surface of the metal material 4, as shown in FIG. As a result, the metal material 4Fi becomes atomic and continues to enter the arc column 6 in large quantities. Then, the ionized metal atoms are diffused as they travel along the arc column 6 in the direction of the cathode 2 and are neutralized by electrons, so that they return to the state of metal atoms and scatter outside the arc column 6. This metal atom is II! It collides with the surrounding inert gas or hydrogen gas and condenses and solidifies into ultrafine metal particles.

As another means of generating a thermal pinch effect, an inert gas introduced into the container 1, such as argon, helium, neon, etc., may be used. A thermal pinch effect can also be obtained. This is because hydrogen is a lighter element than argon, has a higher particle velocity, and has a greater ability to absorb heat. In other words, since the cooling effect is strong, the arc column 6 self-contracts in the same way as when gas is blown onto the arc column 6. Even when hydrogen is used as the atmospheric gas in this way, the arc column 6 is connected to the metal material 1.
-) You can squeeze the whistle as shown in Figure 3 for 4.

The conditions for narrowing down the arc pillar 6 in this way are as follows:
The type of arc current, the range of arc voltage, the type and composition of atmospheric gas in the container 1, the pressure in the container 1, etc. can be considered. When producing ultrafine metal particles of Fe-Ni alloy, arc? I! ,MU100~600
600 mre, 7-re voltage 15-160 Volt,
When conducting an experiment using argon as an inert gas with a length of 5 to 15 mm, the relationship between the hydrogen ions introduced into the argon (overlapping percentage) and the atmospheric pressure in the container 1 is shown in Figure 4. A straight line t was obtained as shown below. In other words, when producing ultrafine metal particles of Fe-Ni alloy, the fourth
As can be seen from the figure, in the area above the straight line t, ultrafine Fe--Ni alloy metal particles can be produced that have a small average particle size, a good particle size distribution, and a high production rate. The flow diameter distribution in this case is shown in FIG. Incidentally, the pressure inside container 1 is 80 Torr.
Under the pressure of , arc current is 200 μm, arc tEE is 25
When arc discharge is performed below the V,7 length of 8 m, the arc column 6 is in the most narrowed state.

Next, some embodiments of the present invention will be described.

Example 1 Fe-Ni alloy (Fe:Ni ratio: i 00 : 9 m view percent) was used as the metal material 4, and hydrogen gas was added to the argon gas in an argon cage as the inert gas. 90% m, arc current 200 mpθre, arc voltage 25v.

When arc discharge is performed for about 120 minutes with an arc length of 7%, the manufacturing efficiency is 1.2 (Ii/win), the average grain size is 3ooa), and the saturated magnetization σS is 150 (emu/, 9).
, coercive force Ha 1400 (Os), squareness ratio Br/Bs
0.55+7) ultrafine metal particles of Fa-Ni alloy were obtained.

Example 2 Fa-Go gold alloy (Fe:Co ratio: 100:38) was used as the metal material 4, argon was used as the inert gas, and 90% by weight of hydrogen gas was mixed in the argon. , Arc Nt & 200 A
mpere, when arc voltage is 25V and arc discharge is performed under the 7-length 1 fin for about 120 minutes, W overmotion 54
1.2 (N/min), average particle size 200-(&),
Saturation a σs160 (6mu/y), coercive force Ha
Ultrafine metal particles of Fe-GO alloy having characteristics of 14'00 (Oe) and a squareness ratio Br/Bs of 0.58 were obtained.

As a result, the Fe-Ni alloy and Fe-Go gold alloy metal ultrafine particles packed in Examples 1 and 2 have particle sizes corresponding to single domain particles of iron-based ferromagnetic alloys, and the particle size distribution also increases. A chain-like ultrafine particle powder consisting of sharp, spherical fine particles is obtained, and is suitable for high-density recording media.

As in Kamiro, the present invention changes the shape of the shear arc column by thermal pinching action and magnetic pinching action by blowing gas onto the arc pillar or by making the arc discharge atmosphere in the container surrounded by gas buds with different density. Since it can be self-shrinked and squeezed onto the molten surface of the metal material, the production efficiency is tens to hundreds of times higher than conventional evaporation methods, even for melting point metals, and the average particle size and particle size distribution are also small. It has excellent characteristics such as sharpness, and because the equipment is small and requires low power, ultrafine metal particles can be obtained at low cost.

Also, the type of gas introduced into the container and the pressure inside the container.

By selecting the type and composition of the metal material, the particle size, magnetic properties, etc. of the ultrafine metal particles to be produced can be appropriately controlled.

[Brief explanation of the drawing]

Figure 1 is a cross section 1 showing the conventional evaporation method using high frequency heating.
2 is a sectional view showing an example of the apparatus used in the present invention, FIG. FIG. 5 is a characteristic diagram showing the production efficiency of ultrafine metal particles in relation to the hydrogen ion concentration fed into the container and the internal pressure inside each vessel, and FIG. 5 is a curve diagram showing the particle size distribution. 1... Container, 2... Cathode, 3... Anode, 4...
Metal material, 6... arc pillar. Patent applicant: Pioneer Co., Ltd., 4-2610 Hanazono, Tokorozawa City, Pioneer Co., Ltd. Tokorozawa Factory (η) Inventor: Gogo Fukutake, 4-2610 Hanazono, Tokorozawa City, Pioneer Co., Ltd. Tokorozawa Factory

Claims (1)

[Claims] 7. A method for producing ultrafine metal particles by generating arc pillars between a metal material placed on an anode and the anode, the shape of the arc pillar being squeezed onto the molten surface of the metal material. A method for producing ultrafine metal particles characterized by: