JPS6152306A - Production of pulverous metallic powder - Google Patents

Abstract

PURPOSE:To obtain pulverous metallic powder having high purity with good productivity by reducing a metallic chloride by plasma heating in the presence of gaseous hydrogen and capturing and refining the resulted product thereof under specific conditions. CONSTITUTION:The metallic chloride which is a raw material A is supplied to a heating furnace 1 and when said chloride is heated to a high temp. by a plasma arc in the presence of the gaseous hydrogen, the chloride is quickly reduced to a pulverous product B. The product B flows together with the gaseous hydrogen through a discharge port 3 and a valve 4 to a capturing device 5. The product B in the high-temp. state in the device 5 is quickly cooled and captured by water C. The suspension is discharged from the device 5 by a pump 11 and is subjected to a solid-liquid sepn. The separated solid component is indirectly heated in gaseous hydrogen flow so that the hydrate by the impurities sticking to the solid content is desorbed and evaporated. As a result the pulverous metallic powder having high purity is obtd. with a good yield.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing fine metal powder by plasma heating.

In recent years, fine metal powders have been used in large-capacity magnetic memories, sensors, solar heat-absorbing paints, and superconductors due to their magnetic, optical, electrical, chemical reactivity, and sintering properties, which are completely absent from metal lumps. New fields of use are rapidly developing, such as materials, high-efficiency catalysts, and new sintered bodies.

The present invention relates to a method for producing high-purity metal fine powder with good productivity in response to such new uses.

<Prior art and its problems> Conventionally, chemical methods and physical methods have been adopted as methods for producing fine metal powder. The former chemical method involves obtaining fine metal powder as a precipitate through a chemical reaction in a solution;
Alternatively, a metal compound with a higher vapor pressure and lower melting point than the metal, such as a metal chloride, is heated and evaporated and reduced with hydrogen to collect fine metal powder.According to these conventional methods, There is a problem that the particle size of the obtained metal fine powder is large, and the purity of the metal fine powder is low because it is unavoidable that the metal fine powder is contaminated with moisture, by-products, etc. The latter physical method, commonly known as the vacuum evaporation method, is a method in which metal is heated and evaporated in a low-pressure inert gas to collect fine metal powder, and is currently commonly used. According to this method, although particles with small particle size and high purity can be obtained, there are problems in that the evaporation rate is slow, resulting in low productivity and therefore high cost.

Recently, a method for producing fine metal powder (commonly known as evaporation in gas method) has been proposed, which utilizes the reactivity of plasma hydrogen gas to metal and heats the metal with plasma. Volume No. 8, pp. 72-74, 1983
Year). This is a method in which metal is plasma heated in a hydrogen gaff atmosphere, and the so-called metal smoke generated violently from the periphery of the molten metal is collected, but even with this method, the production of fine metal powder is still difficult. There are problems in terms of performance (for example, production rate and yield), and there are also problems such as large particles being mixed in due to the scattering of the melt that occurs during heating.

<Problems to be Solved by the Invention> The present invention solves the problems of the conventional method such as sloping. The present invention provides a method for producing high-purity fine metal powder with good productivity by collecting and refining under specific conditions.

Means for Solving the Problems> However, the present inventors have developed a method using plasma heating, which is relatively effective among conventional methods in satisfying the average particle size, purity, and productivity of the obtained metal fine powder. As a result of intensive research on the manufacturing method of fine metal powder, we found that even with this conventional method, the productivity and purity were still insufficient. In order to prevent the molten material from scattering, it is not possible to provide sufficient power for plasma heating, and when evaporating metal chlorides by heating, evaporation can be made sufficiently fast, but the so-called metal generated by plasma heating In cases where it is not possible to sufficiently remove chlorine, etc. by simply condensing and collecting smoke (metal vapor) in the gas phase, the identification of raw materials and heating sources and collection-related operations are detailed below. The present inventors have discovered that high-purity fine metal powder can be produced with good productivity if the process is carried out under the specific conditions described above, and have completed the present invention.

That is, the present invention reduces a metal chloride by plasma heating in the presence of hydrogen gas, and then converts the product into a high-temperature
I: A method for producing a fine metal powder, which is characterized by introducing the powder into water until it is trapped in the water, and then heating and refining the solid content separated from the water in the presence of a hydrogen gas.

Hereinafter, the configuration of the present invention will be explained in more detail based on the drawings. FIG. 1 is a systematic process diagram showing one implementation procedure of the present invention. In the present invention, the raw materials to be treated include ferrous chloride (FeCβ2) and nickel chloride/L/ (N1Cl2
), etc., are metal chlorides.

Even if these contain water of crystallization (for example, NtC4.6H
20) Or it may be an anhydride, and its form may be a powder or a pellet shape, but from the viewpoint of stability of plasma heating, etc., which will be described later, it is preferable to dehydrate and dry it, including crystal water. is preferred. These raw materials A are supplied to the heating furnace 1. The heating furnace 1 is equipped with a plasma torch 2, from which a plasma arc (plasma jet) using hydrogen gas and an inert gas (hereinafter referred to as argon gas) as working gas is injected. . The raw material A supplied to the heating furnace 1 is plasma heated and reduced in the presence of hydrogen gas, and the product B is carried out from the discharge port 3 as if riding on the jet stream of the plasma arc. When heating raw materials with plasma, there are means for supplying the raw materials to the heating furnace, such as dropping the raw materials under their own weight or transporting the raw materials with an airflow of hydrogen gas and/or argon gas, and sources of plasma arc and heating. The type and shape of the furnace, the content of the working gas for the plasma arc, etc. can be appropriately selected depending on the type and form of the raw material and other conditions.

The product B carried out from the discharge port 3 is in a considerably high temperature state, but this product B passes through the valve 4 and reaches the collector 5, where water is collected as it is. In the case of the drawing, the collector 5 has a drain valve 6 at the bottom, a discharge lower of the drain valve above the side, and an outlet 8 for taking out the collected suspended matter on the slope below the side. Each tank 9 is filled with water C,
This water C is constantly being replenished at the valve 4.
A guide tube 10 for product B connected to is positioned with its tip opening in water C. Therefore, the product B is collected by being put into the water C, but the water collection in the present invention is not limited to this. It's okay. In any case, the important point is that product B is introduced into the water while still at high temperature and is captured.

A considerable portion of product B is suspended in water C by water collection. This suspension is extracted from the collector 5 with the pump 11,
For example, the solid and liquid are separated by filtration or the like, and the solid content obtained by separation is then purified to obtain a desired product, ie, a fine metal powder.

The solid content thus obtained is purified by heating the solid content in the presence of hydrogen gas. In view of the purpose of the present invention, this purification is preferably carried out in a manner that prevents contamination with impurities and exposure to the atmosphere.

Therefore, for example, the receiver with which the solid content comes into contact during refining is preferably made of the same metal or ceramic as raw material A, and it is also preferable to heat it indirectly in a complete hydrogen gas flow. It is. FIG. 2 is a schematic diagram illustrating a test apparatus used for such purification, and this test apparatus was used for tests such as Examples described later. heating wire 1
A quartz tube 14 is surrounded on the outer circumferential surface of the electric furnace 13 in which the quartz tube 2 is buried, and a ceramic port 15 filled with the above-mentioned solids is inserted and placed inside the quartz tube 14. The inlet and outlet sides are each sealed with Silicon Camp 16 and 17. The silicone cap 16 on the inlet side has a thermometer 18 and a hydrogen gas supply pipe 19, and the silicone cap 17 on the outlet side has a hydrogen gas exhaust pipe 20, both of which lead to the inside of the quartz pipework 4. Once installed, the tip of the discharge pipe 20 is sealed with water. The solid fraction is heated at a predetermined temperature under a stream of hydrogen gas that is continuously supplied, and the gas generated at this time is carried out as hydrogen gas, while the solid fraction is reduced and purified.

Function> Next, the function of the present invention will be explained based on FIGS. 1 and 2. When raw material A is supplied to heating furnace 1 and heated at high temperature with a plasma arc in the presence of hydrogen scum, raw material A has a significantly higher vapor pressure than its constituent metals, and the plasma arc reaches as high as 10,000°C. Since it has an extremely high temperature, it evaporates rapidly and immediately reacts with hydrogen gas or hydrogen ions activated by the high temperature of the plasma arc, and is rapidly reduced to become a fine powder product B. This product B has an extremely small particle size because the production reaction is carried out in the gas phase or in an ionized state at extremely high temperatures and is obtained through a reaction between particles such as atoms and molecules.

Generally, when metal chloride is vaporized and reduced with hydrogen, the product contains, in addition to so-called metal smoke (metal vapor), unreacted raw material A (metal chloride), oxygen, free chlorine, etc. included. However, in the case of plasma heating as in the present invention,
Because the reaction is extremely high temperature, the content of unreacted substances is small, and the way oxygen and free chlorine are attached is special.
It can be easily removed by a combination of water collection and hydrogen purification. This product B is carried along with the hydrogen gas and argon gas used as working gases, as if riding on the jet flow of plasma jet from the plasma torch 2, and passes through the discharge port 3 and the pulp 4 in sequence. and reaches the collector 5. In this collector 5, the product B in a high temperature state is rapidly cooled and collected by water C, while hydrogen gas and argon gas are exhausted from the discharge lower,
Provided for reuse as necessary.

When product B in a high temperature state is rapidly cooled and collected by water C, unreacted raw material A (metal chloride, e.g. Ni
C#2) ij: It dissolves in water C to form an aqueous solution, and similarly, oxygen and free chlorine in product B become a kind of hydrate-like substance (hereinafter referred to as hydrate) when quenched with water C. form,
This hydrate is attached to the generated fine metal powder with a weak bonding force, and such fine metal powder is suspended in the water C. The form in which the hydrate is weakly attached to the fine metal powder is characteristic. It looks like something fluffy like algae is attached to the surface of fine metal powder. Such a characteristic morphology cannot be obtained by collecting the product B by condensing it in the gas phase as in the conventional method. The difference between the two is even more obvious when you look at the attached reference photos taken with an electron microscope of the collected solids (Photo 1 shows the case where the collected solids were quenched with water, and Photo 2 shows the case where the collected solids were collected in the gas phase without using water. When condensed and collected, both are 50,000 times larger).

Next, the suspension is extracted from the collector 5 using the pump 11,
Separate solid and liquid. The separated solids are of the characteristic form described above and are subsequently heated indirectly in a hydrogen stream as shown in FIG. 2 below. The heating temperature varies depending on the type of metal and the particle size of the fine powder produced.
The temperature must be lower than the sintering starting temperature of the metal, but usually about 300°C is sufficient. By this heating, the hydrates caused by the impurities mentioned above, which are precipitated and weakly attached to the metal fine powder in the solid fraction, easily react with hydrogen and are separated from the fine powder and vaporized. carried outside,
As a result, highly pure metal fine powder can be obtained in good yield. Regarding the metal fine powder according to the present invention produced in this way, a reference photograph (photograph 3.50000 times) taken by an electron microscope similar to the above case is attached.

<Effects of the Invention> As explained above, the present invention is capable of producing high-purity fine metal powder with good productivity, and has a qualitative advantage in new uses of fine metal powder, which are rapidly developing. and has an effect that can be sufficiently applied in terms of quantity.

<Example> The experiment was carried out according to FIGS. 1 and 2. First, commercially available anhydrous nickel chloride (purity: 99.4% by weight) was pelletized into a disk shape with a diameter of 16 mm and a thickness of iow.

Then, the pellets were continuously fed into a heating furnace under a hydrogen and argon gas atmosphere at a rate of 10 kg/hour by falling under their own weight.
In the heating furnace equipped with a plasma torch, a plasma arc (plasma jet) using hydrogen and argon gas as working gas was injected into the beam (hydrogen gas consumption: 2 tNm'/hour, plasma torch output: 84 KW).
). Next, the high-temperature product discharged from the heating furnace was quenched and collected with water to obtain a suspension. This suspension was separated into solid and liquid by filtration, and the separated solid content was filled into a ceramic boat and heated under a sufficient flow of hydrogen gas for 30 minutes.
The mixture was indirectly heated at 0° C. for 2 hours/100 g of solid content to produce fine metal powder. The produced fine metal powder was an ultra-fine powder with an average particle size of about 700 grains, and the contents of the fine metal powder are shown in Table 1 along with the solid content. The results in the table are the sum total of 20 repeated tests. In the example, fine metal powder was manufactured using the above method, and in the comparative example, the test was conducted under the same conditions as the example. This is the case where the product is condensed and collected in the gas phase without any subsequent treatment such as quenching collection with water and solid-liquid separation as in the example 0 Table 1 The results of Table 1 also show that the effects of the present invention are is clearly obvious 0

[Brief explanation of drawings]

FIG. 1 is a systematic process diagram showing one implementation procedure of the present invention, and FIG. 2 is a schematic diagram illustrating a test apparatus used for purification in the present invention. 1... Heating furnace, 2... Plasma torch,
3.7...Discharge port, 4...Pulp, 5...
Collector, 6. Drainage pulp, 8. Outlet port, 9. Tank, 10.-Guiding pipe,
11...Pump, 12...Heating wire,
13... Electric furnace, 14... Quartz tube, 15... Ceramic hoard, 16, 17... Silicon cap, 18... Thermometer, 19... Supply pipe, 20... Discharge pipe, A ...Raw material, B...Product, C...Water,
D...Solid content, Figure 1 Figure 2

Claims (1)

[Claims] 1. After reducing metal chloride by plasma heating in the presence of hydrogen gas, the product is collected in a high temperature state and water is collected,
A method for producing fine metal powder, which comprises then heating and refining the solid content separated from water in the presence of hydrogen gas.