DE2006075A1 - Method and device for the production of fine powders of a metal or an alloy - Google Patents

Description

Dr. Ing. E. BERKENFELD · Dipl.-Ing. H. BERKENFELD, patent attorneys, Cologne

Attachment file number

to enter - | Q. February 1970 Sch // ^{Name d Note} Shinku Yakin Kabushiki

Kaisha

Method and apparatus for producing fine powders of a metal or an alloy. "

The invention relates to a method and a device for producing fine powders of a metal or an alloy. For example, a size of less than 0.001 mm do not exhibit, by heating and evaporating and / or subliming the metal or alloy in an atmosphere active gases under a pressure that is below or above of atmospheric pressure. The invention relates in particular to a method and a device for generating fine powder of a metal or alloy by adding the metal or alloy is heated by energy beam heating or induction heating and vaporizes and / or sublimates is, as well as the vaporized and / or sublimed materials in the form of powder or particles of flowing Gas or gases entrained and introduced into a cooling device will.

It is known that extremely fine powders of a certain metal or alloy, for example having a powder size of less than 1,000 8, are of excellent quality when used as solid materials of a magnetic element, a superconductor, a chemical catalyst, an absorber for light or electromagnetic waves, as a raw material in powder metallurgy, as a semiconductor and the like. These extremely fine powders of a metal or alloy are currently in great demand to use them as a catalyst in the chemical industry, as a magnetic powder for a tape recording S 92/1 - ¹ "

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device and the like to use. In the case of the tape, when the powder size of the magnet powder is small, it becomes the Tape recorder possible for a long period of time to record at the slow speed of the tape so that tape manufacturers' demand for such is extremely high fine powders is great. However, it is difficult to obtain such fine powders of a metal or an alloy easily and in large size To produce quantities that are pure and of good quality.

A common method of producing such fine powders is in using a device provided with a tungsten resistance heater in a bell jar is. In this process, a heating device in the form of a knical winding of a tungsten wire with a diameter of 0.8 mm is used arranged in a bell jar which forms an airtight housing. About 50 mg of the metal or alloy will be used applied as a raw material for the fine powder to be produced on the winding of the heater. An outlet port is with connected to a discharge system and part of the connection between a bell jar part and a base part of the bell jar is hermetically sealed by a seal.

When producing fine powders using those described above Apparatus is first pumped out to a bell jar

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Maintain vacuum of about 10 torr. Inactive gas with a purity of about 99> 99 $ is then introduced into the bell jar in such a way that there is a pressure therein of 0.1 to 30 Torr for argon, 1 to 76O Torr for helium and 0.1 for xenon results in up to 10 Torr. The heating device is then suddenly heated by supplying an electric current of 100 W. At this time, the metal or alloy spreads in all directions in the bell jar in the form of a mist, is cooled on the inside of the bell jar, and adheres to the same in the form of a powder. The bell jar is then removed from a stationary position and the fine powder adhering to it is collected with a brush. In this way, about 10 mg of the fine powder is obtained in one operation. The size of the powder changes accordingly

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according to the type and pressure of the gas introduced, the degree of Heating, the dimensions of the bell jar and the spacing of the material from the heater and the inside of the bell jar. In the case of the production of fine iron powders, for example achieved the following results:

Type of gas Pressure in torr Powder size in Ä argon 3 200 argon 10 500 helium 30th 200 helium 500 500

When argon is used as the introduced gas, the powder size distribution obtained is better than when using helium. If helium is used And its pressure below 5 to £? Torr is held or when argon is used and its pressure is kept below 0.1 Torr, no mist is generated, but the same phenomenon as that of vacuum evaporation occurs. On the other hand, when argon is used and its pressure is more than 30 torr, no mist is generated unless the materials are considerably heated. According to this manufacturing method, an operation is _r in the yield of fine powder not more than 10 mg and the wire of the heating means is consumed after only zweinELiger use in the production of fine iron powder. For these reasons, the manufacturing process described above is only carried out on a trial scale. The deficiencies in this method are that the material of the resistance wire itself can evaporate and mix with the products, and that the yield of the fine powder is only a small amount.

For the production of fine powders of a metal or an alloy it was also proposed to use the arc discharge ^, by vaporizing the anode of a material itself and / or is sublimated. This method can only be used for Generating the powder from soot. or silicon carbide, to produce fine powder of a metal oxide by heating and evaporating and / or subliming various metals in an ordinary Atmosphere or for producing fine powders of a nitride in one

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Nitrogen atmosphere.

In one respect it is important that the arc discharge is carried out in an atmosphere of inactive gases to produce the pure fine powders of the metal or alloy. However, since the pressure of the gas and the shape of the electrode significantly affect the nature of the discharge, it really is extremely difficult to achieve a stable operating condition.

Furthermore, in order to increase the yield of fine powders in a gas atmosphere, For example, to increase argon or nitrogen, it is necessary to lower the voltage for the arc discharge. But when As the voltage decreases, the arc discharge extends over a larger area and therefore it cannot reach a high temperature be achieved. For these reasons, it is found that the method of producing fine powders by arc discharge is unsuitable for obtaining large amounts of fine powders of a metal or an alloy.

The object of the invention is therefore to eliminate the deficiencies indicated above and a method and a Apparatus for producing pure fine powders of a metal or an alloy in large quantities.

The method for producing fine powders of a metal or an alloy is, according to the invention, that materials for the fine powders of a metal or an alloy to be produced in an airtight container that a vacuum is established in the container so that inactive gas is introduced into the container for heating the materials, to vaporize and / or sublime the same in the form of a mist that the vaporized and / or sublimated materials are introduced into a cooling device and that the fine powder of the adhering to the inside of the cooling device Metal or alloy.

An apparatus for carrying out the method for producing fine powders of a metal or an alloy consists in accordance with of the invention from an airtight container with an Ah-3 92/1 -4-

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guide device is provided, from one arranged in the container Receiving device for the materials for the fine powders to be produced, consisting of a device for heating the materials, to vaporize and / or sublime them to form powders or particles from a gas flow generating device which vaporises and / or sublimates them powdery.Materials in the form of a mist in a cooling device introduces, which can cool the vaporized and / or sublimed powdery materials, so that the cooled Adhering materials to the inside of the cooling device, and from a device for collecting those adhering to the inside fine powder of metal or alloy.

The method and apparatus according to the invention will be described in more detail below in some exemplary embodiments with reference to the drawings, in which shows j

1 shows a schematic representation of a first embodiment the invention,

Fig. 2 is a schematic representation of a second embodiment and

3 shows a schematic representation of a third embodiment.

Figures 4, 5 and 6 show schematic representations of others Embodiments of the invention. ·

Fig. 7 shows a graph which appears

the Gäsmengen relates, the beam can be used to generate the plasma * and showing a relationship illustrate between the pressure of a gas in .- ". ■ ... einem'-Behäl.ter and the amount of the fine powder * under this Pressure is generated.

Fig. 8 shows a graph showing the change in powder size of fine iron powder corresponding to 3 92/1 - ■ ".; ■■ ^: , ^: " ■■ '. ■■' -5-

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according to the change in pressure of the gas, when a gas mixture of helium and hydrogen is used to generate the plasma jet.

Pig. 1 shows schematically a first embodiment of the invention. A container 1 consists of a generally cylindrical drum 2. A front lid 3 and a rear lid 4 are detachably attached to both ends of the drum 2. In a lower part of the drum 2 and near the front cover 3 a crucible 5 is arranged which can be cooled and which contains the metal or alloy to be evaporated and / or sublimated 6 records. On the front cover 3, a plasma gun 7 is attached, the axis of which obliquely from above onto the metal or the Alloy 6 is directed to act on a plasma jet 8 ' to bring that vaporizes and / or sublimates the same, being a The nozzle 9 of the gun 7 is open towards the inside of the container 1. A plasma generating device is known. -Not Active gas for generating the plasma jet 8, such as argon, helium or nitrogen, is fed into the plasma gun 7 from a pressure vessel 10 introduced. The amount of gas flow is measured with a flow meter 11 and a manometer 12, while the The flow rate is regulated by a valve 15. Like Fig. 1 shows, the plasma gun 7 and the crucible 5 are connected to a direct current source, which can also be fed with alternating current of 200 V, for example. When the plasma gun 7 is energized by the electric power source 14, the gas in the gun 7 is ionized and in the form of the plasma jet 8 blown out of the nozzle 9 onto the metal or alloy 6 to strike the same or the same bombard, keeping the metal or alloy at a positive potential. In Fig. 1, 15 is an electrical Sbrom regulator and 16 denotes a starter.

The interior of the container 1 is pumped out with an air pump 17 *, for example a centrifugal pump, to a pressure lying below atmospheric pressure (which is, for example, less than 10 ^- ^ Torr) and this pressure is measured with a Geisler tube 18. A cooling device 19 arranged in the vicinity of the crucible 5 has a conical shape and is provided with openings S 92/1 -6- at both ends.

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20 and 21 provided. The front opening 20 is open against the flow of the vaporized and / or sublimed metal or alloy, while the rear opening 21 was used to insert a scraper 22 which carries brushes 25, which can strip off the fine powder adhering to the inside of the cooling device. A funnel 24 is provided which serves to receive the fine powder stripped off by the brushes 23 and which allows it to fall into an airtight container 25. This airtight container 25 prevents the "fine" powder produced from coming into contact with the open air and is particularly necessary for obtaining fine powders for experimental or "scientific research". In Fig. 1, 2.Ü- denotes a gas line which connects the pressure vessel 10 with the plasma gun 7. With 27, 28 cooling water lines are designated for the plasma gun 7, while with 29 and J> 0 cooling water lines for the crucible 5 and the cooling device 19 are designated. ·

The inventive method for producing fine powders is using the device described above such as follows, executed:.

First, the container 1 is set to the predetermined pressure (below 10 torr) and then becomes plasma generating Gas into the container through the plasma gun 7 from the pressure vessel 10 introduced to the pressure in the container to the pressure which is suitable for producing fine powders of the metal or alloy of "desired powder size. The characterizing feature of the illustrated embodiment of the invention ^ consists in using a mixture of helium and hydrogen. When the plasma gun 7 is a current of 700 V is applied in the plasma gun Plasma generated from the nozzle 9 in the container 1 in the form of the plasma jet or the plasma gas flow 8 is thrown and applied obliquely to the metal or alloy 6 in the crucible 5 to heat the same or to vaporize and / or sublime. In this case, the plasma jet or the gas flow 8, which is inclined towards the surface of the metal or the alloy 3 92 / i. > -γ-

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is brought into action, reflected, the angle of reflection is determined by the angle of incidence. The vaporized and / or sublimed materials are in the reflected plasma beam or the gas flow 8 and form fine powder in the form of solid, liquid or vapor particles, which move backwards in the cooling device I9. After the same are cooled in this device, they solidify and form fine grains, which on the inside of the cooling device 19 cling. The adhering cold powders of the metal or the alloy are wiped off by means of the brushes 23. The scraper 22 is arranged so that it can move back and forth, as well as up and down. The stripped fine powder of the metal or alloy slide down along the inclined bottom surface of the cooler I9 and are over the Hopper 24 received in the airtight container 25.

The embodiment of the invention shown in FIG. 2 is essentially similar to the first embodiment according to FIG. 1 with the exception of the following points: The crucible 5 of FIG. 1 is replaced by a crucible 31 ^with induction heating and the plasma gun 7 of FIG. 1 is replaced by a hot gas generating device 32. The parts corresponding to the device according to FIG. 1 are denoted by the same reference numerals.

In this embodiment, the same as in the first embodiment the container 1 is initially pumped out through an outlet opening 33 by means of a vacuum pump, whereupon gas, such as helium, Argon or the like is introduced into the container. Before starting the device, alternating current is applied to the windings 3 4 of the crucible 31 brought into action with induction heating, the frequency of the electric current being high or low, if desired, so that the metal or alloy 6 is heated and melted in the crucible. Then the hot gas generating device 32 is actuated by heating a gas flow 35 through the heating coils 36, the gas flow then exits through the nozzles of a nozzle plate 37. That evaporated and / or sublimated metal or alloy is brought into the form of a mist by the heated gas flow, i. in the form of solid, liquid or vaporous particles, 3 92/1 -8-

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which are carried along in the cooling device 19. The process will then be used in conjunction with Pig. 1 described way continued.

According to this embodiment, the heating of the metal or the alloy 6 and the movement of the vaporized and / or sublimated metal or the alloy in the form of a mist are carried out by different devices, so that these two processes can be controlled independently of one another. The shape, number and position of the devices, as well as the temperature and the amount of gas flow are controlled in the desired manner and can be adapted to the best conditions for the movement of the fine powders. When using a crucible bit induction heating, the source supplying the heating current can also be stationary and very easily regulated. The device according to this second embodiment can easily be manufactured on a large scale. The crucible 31 with induction heating shown in FIG. 2 is suitable for heating a metal or an alloy which does not react with the material of the crucible. The use of the crucible with induction heating is therefore preferred in that the crucible can, for example, receive a metal or an alloy and heat it if a metal or an alloy is used which reacts with the material of the crucible.

In the embodiment described above, it is possible to make the heating coils> 4 ineffective and instead of gas use high temperature gas with normal temperature * Furthermore, if in the hot gas generating device 32 KÜhleinriöh « arranged, - is it possible to use cold gas » If normal temperature gas or cold gas is used wIM, are the evaporated and / or sublimed materials during their conveyance precooled and completely cooled in the cooling device 19 »

After all, all or part of the gas can come from reducing Gas or oxidizing gas. The reducing oil is not only intended to oxidize the metal or alloy prevent * Even if the metal or alloy is in

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The form of the mist of the oxidized metal or alloy can get fine powders of the pure metal or alloy can be obtained because they are reduced. By oxidizing gas, fine grains of the oxidized metal become or the alloy.

When two or more kinds of gases are used as the heating gas, For example, the gases from each source thereof are introduced into the inlet of the hot gas generating device 32 and mix while passing through it. A variety of gas generating devices can also be placed and within them Different gases can be introduced into different devices.

It is possible with any other different metal organisms and the like which are mixed in the gas flow before the gas is discharged from the gas generating device 32 exit. It is also possible to have a large number of crucibles with induction heating along those emerging from the nozzle plate 37 Arrange gas flow and fill each of the crucibles with a different metal or alloy. In this case fine powders of a mixture of two or more kinds of metals or alloys can be obtained.

Reference will now be made to the third embodiment of the invention on Fig. 3 described. This embodiment is in essentially similar to the second embodiment according to FIG. 2, but differs from the latter in that it is used as a heating device a heat source 38 is arranged. From this a high energy emitting heating beam 39 * such as an electron beam, a laser beam (low amplification through stimulated emission of radiation) or a maser beam (microwave amplification by excited emission of radiation) directed directly at the metal or alloy 6 in crucible 3I, wobdi this crucible of course no heating windings 3 ^ as shown in FIG. The design and the effects of this embodiment are essentially similar that of the second embodiment except those mentioned above Points, so that an exact description can be omitted.

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In place of the heating from the resistor windings J4 is it is possible to use electrical discharge heating. In Fig. 4 this embodiment is shown schematically, at which the electrode 40 negative voltage "and the Electrode 41 is supplied with positive voltage. The electric Discharge takes place between the two electrodes 4-0 and 41. The gas flow introduced into the space between the two electrodes is ionized and heated directly, whereupon the same emerges from a nozzle 42. The gas, which ions or an excited atom (Molecule), contains, is against the metal or alloy 6 g ^ read. If - as mentioned above - two or more types of When gases are used, a different kind of gas can be introduced through a hole 4j provided in the electrode 41 will. If the diameter of the nozzle 42 is small, this can Gas can be thrown out of the nozzle 42 and spread evenly if no nozzle plate is provided.

Fig. 5 shows another embodiment in which the hot gas generating device 37, the crucible 31 and the heat source 3Ö are provided in pairs. In this embodiment in the cooler 19, fine powders of two kinds of metals or alloys.

Fig. 6 shows a further embodiment of the invention in which a lens or lenses for electrons (or a lens or lenses for charged particles) are arranged in the gas flow. The lens 44 is arranged between the hot gas generating device 32 or the crucible 3I and the heat source 38. The lens 44 can be referred to as an electromagnetic lens which can focus the flow of ionized gas and direct it against the metal or alloy in crucible J51. As FIG. 6 shows, the lens can also be designed as a deflecting lens which deflects the gas flow. The lens 45 is arranged between the crucible 31 and the heat source 38 or the cooling device 19 and can deflect the gas flow. If such deflecting lenses are used, the positions of the elements I9, 3I and Jb can be chosen relatively freely. The electromagnetic. Lens 45 can be a deflecting lens that reduces the flow of gas against the surface of the cooling

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facility distracts.

In Pig. 1 shown first embodiment of the invention, the amount of fine powder produced is larger when the pressure in the container 1 is lower when a smaller amount of the flow of the plasma generating gas is introduced into the plasma gun 7 and when the electric current in the plasma gun 7 is stronger. However, there is a lower limit to the value of the Pressure in the container and the amount of gas flow in the plasma gun 7 in order to obtain a stable discharge. This limit is variable according to the type of gas. The results of experiments with four types of gases, namely Ar, Ar + 15 $ Hp, He and He + 15 $ HL (^ expressed in moles) are as follows:

Ar Ar + 15Jg H ₂ He He +

Pressure (Torr) 250 6Ö 250 10

Flow rate 2 0.5 3 1 (f / sec)

When the flow rate of the above gas is kept at the lower limit and the pressure in the container is changed, the amount of the generated fine iron powder (as an example) is shown in Fig. 7. As this graph shows, the amounts of the products decrease in the order of He + 15 # H ₂ , He, Ar + 15% Hg, Ar and the amount of fine powders generated in the atmosphere of He + 15 $ H " is considerably different from the amount of fine powders generated in the atmosphere of Ar. The graph also shows that the amount of fine powders produced does not change even if the pressure in the container is increased in the case of the atmosphere of He + 15 # H _p and He, but that the amount of fine powders produced suddenly decreases, when the pressure reaches a certain value in the case of the atmosphere of Ar + 15 # H _p and Ar. It can also be seen from the graph that the amount of the products increases more in the case of He + 15% H ₂ or Ar + 15 # H ₂ than in the case of He or Ar used alone.

In the above experiments, the reason why the amount of He or Ar to be added is limited to $ 15 is due to the construct

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tion of the plasma gun as described below will. The invention is not limited to this value.

The advantages of adding H ₂ are as follows:

a) The plasma jet is easier to detect;

b) the temperature of the plasma jet becomes higher, so the amount of evaporated metal increases and

c) The fine powders produced can be prevented from oxidizing will.

One of the distinguishing features of the invention also exists in that in the case of using the mixture of helium gas and hydrogen gas, the amount of the products does not change as in the case of using helium gas alone when the pressure of the gas changes over a wide range, e.g. 10-800 torr.

According to the construction of the plasma gun, the amount of Hp to be changed. The state of stability of the plasma jet; is caused by the construction of the plasma gun. Therefore the best condition for the stability of the plasma jet To achieve this, it is necessary to regulate the amount of Hg added. For this reason was at; found in the above experiments, that the correct value of the amount of Hp addition is $ 15.

Here, the relationship between the powder size of the fine metal powders and the pressure in the container will be described. When the pressure in the container is higher, the powder size of the fine powders produced is larger. When He + 15 ^ H _{2 is} used as the gas and the pressure in the container is changed, the mean diameter is 8 of the powder size of the fine iron powders produced (as an example) in fl. 8 shown. When the pressure in the container is low such as 200 torr, the mean diameter of the powder size is 200 8, and when the pressure in the container is high such as 800 torr, the diameter is about 1000 % and the powder size changes linearly the pressure. When the pressure is high, or in other words, the density of the gas molecules

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becomes large, the free mobility of the gas is low. This creates the opportunity for the gas molecules to move accordingly combine their collision with each other before they reach the inside of the container, which gives the powder size of the products results. It is therefore possible to base fine powders of the metal or alloy with the desired powder size of the experimental value as shown in FIG.

To cool and solidify the evaporated and / or sublimated Metal or alloy, it is advantageous to determine the angle of incidence of the plasma jet on the vaporized material (the angle between the plasma jet and the surface of the metal or alloy) small, because then the transition path of the reflected gas jet to the surface of the cooling device becomes long.

As already mentioned, according to the embodiment of the invention, which _{provides for the use of a gas mixture of He and H 2} as a plasma-generating gas, in order to heat the metal by the plasma jet, or to vaporize and / or sublime it, and to cool it down, large amounts of fine powders of the metal or alloy and the desired sizes of the fine powders can be obtained.

Claims

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Claims (7)

Dr. Ing. E. BERKENFELD Dip 1.-1 ng. H. BERKENFELD, Patentanwälte, Cologne Attachment file number for the entry from ίο., February 1970 Sch // Natne d · Ann- Shinku Yakin Kabusniki Kalsha P a te η t ans ρ r ü c h e 1. A method for producing fine powders of a metal or an alloy, characterized in that the metal or the alloy is heated or evaporated and / or by radiant heating in an atmosphere of a non-aktiventäses under a pressure which is below or above atmospheric pressure is sublimated that the vaporized and / or sublimed materials are conveyed by a gas flow into a cooling device and that the materials are cooled on an inner surface of the cooling device and solidified in powder form. " 2. The method according to claim 1, characterized in that that a gas mixture of 10-80 $ helium and hydrogen as plasma Generating gas is used to direct a plasma jet from a plasma gun in an oblique direction at the metal or to blow the alloy. J. Method according to claim 1 or 2, characterized in that that by changing the pressure in a container the desired size of the fine powder of the metal or alloy is obtained. 4. Apparatus for carrying out the method according to claim 1, characterized by an airtight container (1), which can be maintained under a pressure that is below or above the atmospheric pressure, through a crucible (5), which takes up the metal or alloy (6) to be vaporized and / or sublimated, by a plasma generating one Device (Y), from which a plasma jet (8) in oblique s 92/1 ■ -15- 009836/1394 Λ 2Ü06U75 Direction is blown against the metal or alloy, and by a cooling device (19)> which the evaporated and / or sublimed materials can cool and solidify. 5 · Device for carrying out the method according to claim 1, characterized by an airtight container (1) which can be kept under a pressure which is below or above of atmospheric pressure, through a crucible (3I) with induction heating, which takes up the metal to be vaporized and / or sublimated or the alloy (6), and through a hot gas generating device (32) with or without heating device (36), which the vaporized and / or sublimed materials introduced into a cooling device (I9), the cooling device cooling and solidifying the materials. 6. Apparatus for carrying out the method according to claim 1, characterized by an airtight container (1), which can be maintained at a pressure below or above atmospheric pressure by a crucible (31) which can be cooled and which is to be evaporated and / or to be sublimated metal or the alloy (6) absorbs, by a heating device (38), which a beam of high Energy emitted to vaporize and / or sublime the metal or alloy and through a hot gas generating device (32), which introduces the vaporized and / or sublimed materials into a cooling device (I9), the Cooling device cools and solidifies the materials. 7. Device according to claims 4-6, characterized in that the crucible can be cooled. 3 §2 / 1 -16- 009836/1394