EP0524887B1 - Process and apparatus for the production of powders, in particular metal powders by atomisation - Google Patents

Description

The present invention relates to a method and a device for producing powders and in particular metal powders by atomization.

There are already installations for the production of metallic powders, in which atomization techniques are used (see for example FR-A-2 629 573). According to these known techniques, molten metal is poured onto a horizontal disc driven in rotation by a spindle rotating around a vertical axis. The metal is then projected towards the outside of the disc under the effect of centrifugal force and is divided into fine metal droplets which solidify on contact with a fluid or a cold wall.

However, whatever the current techniques, the main drawbacks are, on the one hand, the problem of powder pollution during melting, atomization, quenching and collection operations, on the other hand, the difficulties encountered to atomize a liquid of perfectly homogeneous material.

The present invention aims to overcome these technical problems and in particular to be able to disperse a sufficiently hot metallic liquid, without there being any chemical interaction between the dispersing means and the liquid, to create a quenching zone eliminating any possibility of pollution of the atomized metal, and to provide a "cold chain" allowing the powders obtained to be used without polluting them before manufacturing the final solid product, after compaction and sintering.

This object is achieved according to the invention by means of a device for producing powders and in particular of metallic powders by atomization comprising means for melting the material to be atomized, an atomization enclosure in which is arranged a dispersion head rotating at high speed for diffusing the molten material in atomized form, means for cooling the atomized material and the head and means for collecting the cooled powder material thus obtained, said melting means comprising at least one vertical inductive plasma furnace producing a gas envelope plasmagens containing the upper face of the dispersion head and said cooling means comprising a first series of members for distributing a cooling fluid disposed in the upper part of the atomization enclosure to create a cold zone at the periphery of the casing and a second series of members for circulating a cooling fluid arranged in the lower part of the enclosure to create a cold zone on the underside of the head, characterized in that said first series of organs for distributing a cooling fluid consists of a ramp of nozzles producing jets of fluid tangential to the surface of said envelope so as to create a quenching zone formed by a vortex around the plasma, and of nozzles producing a tangential wash to the enclosure.

According to another characteristic of the invention, said envelope of plasma gas consists of a cylindrical tube whose vertical axis is parallel to the vertical axis of the rotary head, and preferably the axis of the cylindrical tube is coincident with the 'axis of the head.

According to yet another characteristic, said vertical inductive plasma furnace is disposed above the upper face of the rotary head.

Another object of the invention is a method for manufacturing powders and in particular metallic powders by atomization, comprising the continuous melting of the material to be atomized flowing vertically and coaxially above a dispersing head rotating at great speed. speed intended for dispersing the molten material in atomized form, in a casing of plasma-producing gases by friction on the upper face of the rotary head, then quenching the atomized material and collecting the cooled powder material thus obtained, characterized in that quenching is carried out by passing said atomized material through a cooling vortex situated at the periphery of the envelope of plasma gas.

The invention allows the manufacture of ultra pure metallic powders using the above process.

Thanks to the cooled dispersion head rotating with a speed of up to 125,000 rpm, the device of the invention can absorb a large flow of heat produced by a plasma torch and onto which the liquid material falls. The atomized material then enters a quenching zone at the periphery of the head formed by a cylindrical tube of plasma gas moving parallel to the vertical axis of the head and enveloped in cold fluid. Finally, the powders obtained are recovered in a collection zone comprising at least one chamber containing a neutral gas in the gaseous, liquid or solid state, before their use in formed or shaped products.

The powders obtained by the process of the invention with very rapid cooling are ultra pure and have a very fine particle size.

The invention will be better understood on reading the description which follows and relating to the accompanying drawings.

Figure 1 is a schematic representation of the atomizing device of the present invention.

FIG. 2 is an enlarged view of the central part of the device in FIG. 1.

FIG. 3 represents the quenching zone with the members for distributing the cooling fluid.

Figures 4a and 4b schematically show embodiments of the means for melting and supplying molten metal to the atomization enclosure.

As shown in FIGS. 1 and 2, the material to be melted and to be atomized is introduced by supply means A into the apparatus, for example in the initial form of a cylindrical bar 1 whose diameter is related to the power of the melting means, notably consisting of a plasma oven B.

According to variants of implementation of the process, the material to be atomized is initially in the form of pieces of various sizes, powders, shots or else may be directly brought to the molten state in the device.

The bar 1 is placed vertically in the axis of the oven B, the valve V1 then being closed, maintaining the oven B and the enclosure C in a neutral atmosphere. After vacuuming and purging the bar supply chamber several times, valve V1 is open. The bar 1 is then lowered with a hydropneumatic or electromechanical cylinder regulated at the speed which corresponds to the desired flow rate. It is preheated in the preheating furnace 3 by the currents induced with one or more inducing turns 5 at a frequency between 10 and 30 kHz, depending on its diameter.

It is also possible to carry out the melting of the material to be atomized by means of a melting device by direct induction in a cold cage with electromagnetic confinement of the molten charge as described in French patent 88 04 460 (FR-A-2 629 573).

The bar then enters the inductive plasma oven 4. The plasma is ignited by creating an electric arc between the bar brought to high voltage and a retractable mobile electrode 8 located at ground. Depending on the more or less advanced position of the bar in the flame, during the casting, the vein or the liquid drops of molten materials pass more or less long over the hottest part of the plasma to, on the one hand, reach overheating and , on the other hand, pass through the most reactive area of the oven.

Preferably a cold cage 7 is used to protect the oven enclosure, and polished to increase the thermal efficiency of the plasma. The bar 1 is thus heated at its periphery by direct induction of the HF fields - skin effect -, and by thermal conduction and convection of the plasma gases. It melts in a cone, point directed downwards, at an angle, the opening of which depends on the nature of the plasma gases. There is thus a casting which is, depending on the power of the furnace and the penetration of the bar into the plasma, continuous or not and perfectly axial. As for the diameter of the liquid stream or of the drops, it depends on the flow of liquid and the opening of the cone.

Under these conditions, the material to be atomized is first received in fusion in a cold crucible (as in French patent 2,697,050) from which it flows by gravity passing through an electromagnetic and / or composite nozzle before enter the atomization enclosure as shown in Figures 4a and 4b. The electromagnetic and / or composite nozzle constitutes a means of feeding and regulating the flow of molten metal and optionally makes it possible to maintain the metal in the desired thermal state.

The device shown in FIGS. 4a and 4b comprises means B for melting the solid (metal) material M consisting for example of a plasma torch. The molten material then flows into a cold crucible 100 to form a bath of molten metal. The heat losses on the surface of the bath are optionally compensated for by additional heating means B ′. The molten material then flows vertically through the bottom of the crucible through an electromagnetic nozzle 101 (Figure 4a) or composite 102 (Figure 4b).

French Patent No. 87 00 866 (FR-A-2 609 914) already describes a composite nozzle 102 used for controlling a flow of liquid metal operating for example with a coil 102b at 450 kHz.

The electromagnetic nozzle 101 comprises a peripheral coil 101b inducing a high frequency field so as to create a constriction of the liquid stream thus causing a variation in the flow of molten material. The molten material then enters the atomization enclosure to come into contact with the dispersion head 9.

In FIGS. 1 and 2, the molten material flows into the atomization enclosure C at the center of the upper face of a dispersion or atomization head driven in rotation by the spindle 10 at a speed of up to '' at 125,000 rpm. The shape of the dispersion head 9 is determined according to the optimal thermal mapping and advantageously, it is produced in the form of a cylinder whose dimensions are determined by the nature of the constituent material and the temperature sought on the upper side coming into contact with the molten material depending on the particle size sought for the powders. The upper face of the head is preferably situated in a substantially horizontal plane and is crossed vertically by a heat flux generated by the plasma gases heated by induction by the inductor 6. The plasma zone consists of an envelope of plasma gas in cylindrical tube shape whose vertical axis is parallel, being close to or coincident with the vertical axis of said head 9. The underside of the cylindrical head 9 and the spindle 10 are cooled by axial circulation 11 of a fluid cooling which can be either water for the most important thermal fluxes, or a gas or a liquid gas such as argon or helium for example, in the case where a surface temperature of the head is desired more high.

The atomizing cylindrical head 9 is either made of copper, or of tungsten, or of a refractory alloy or not depending on the surface temperature which must be reached.

The underside of the cylinder constituting said head 9 is advantageously provided with a hemispherical cavity licked by the cooling fluid 11 circulating axially. The cooling of the underside of the head 9 creates a temperature gradient in the mass thereof which is included for copper between 60 and 180 ° C / cm and between 200 and 500 ° C / cm for tungsten.

The supply of heat by the plasma to the liquid metal up to the very surface of the head and the thermal resistance between the liquid material and said head make the dispersed material remain liquid (despite the heat extracted through the head).

To increase the thermal resistance and, on the one hand to have a dispersion head as cold as possible having regard to its mechanical properties, on the other hand, to have a liquid to be dispersed sufficiently hot to remain homogeneous, atomization is carried out by "erosion", the "erosion" consisting in diffusing and dispersing the liquid by friction and thus avoiding its "wetting" with the upper side of the head.

• a. fondre le matériau dans des conditions géométriques et thermocinétiques optimales, pour obtenir une coulée parfaitement axiale et stable ;
• b. surchauffer la veine liquide pour obtenir un liquide homogène ;
• c. créer un flux thermique à travers la face supérieure de la tête d'atomisation 9 et assurer une cartographie thermique compatible avec la tenue mécanique de ladite tête ;
• d. maintenir la pureté des produits lors de l'atomisation jusqu'à la trempe.

The use of the plasma "torch" allows to:

• at. melt the material under optimal geometrical and thermokinetic conditions, to obtain a perfectly axial and stable casting;
• b. overheating the liquid stream to obtain a homogeneous liquid;
• vs. create a heat flow through the upper face of the atomization head 9 and provide thermal mapping compatible with the mechanical strength of said head;
• d. maintain the purity of the products during atomization until quenching.

After atomization, the liquid particles pass directly from the plasma zone 12 which envelops the head, to a quench zone 13 consisting of a cooling medium, two-phase or not, forming a vortex around the plasma. To this end, a series of nozzles 15 placed on a circular ramp 14 at the top of the atomization enclosure C, sends the cooling fluid tangentially to the plasma gas tube 12.

According to an advantageous embodiment as shown in FIG. 3, there is a ramp of eighteen nozzles 15 distributing a total flow of liquid argon sufficient to obtain complete cooling of the powders. The nozzle ejection axis X 15 is inclined relative to the plane of the upper face of the head 9 with a jet width determined so as to obtain rapid cooling and a rotation effect of opposite direction (counter-rotating) to that of the head 9 in order to brake the movement of powders.

The nozzle ejection orifice 15 is located above the powder ejection triangle.

The passage from the plasma zone consisting of the envelope of plasma gases 12 at high temperature, to the quenching zone 13 at low temperature, on the one hand, eliminates the chemical reactions which occur between 1500 ° C and 200 ° C and very particularly those of oxidation in the case of metals and alloys and, on the other hand, avoids the formation of phases intermediates which do not allow microcrystalline and even amorphous structures to be obtained.

The refrigerant vortex 13 thus formed entrains the liquid and then solid particles in spiral trajectories, thus avoiding, on the one hand, direct impacts with the walls of the enclosure C, on the other hand, gas turbulence towards the top of the device, turbulence which could disturb the plasma and atomization.

The nozzles 16 oriented towards the walls of the enclosure, projecting onto them an argon mist which flows along the walls, thus driving the powders down and thus ensuring a tangential washing to the enclosure.

The mixture of liquid and powder is deposited at the bottom of enclosure C.

The powder obtained is therefore deposited at the bottom of the enclosure C and is recovered in the container 17.

The cooling and the collection of the powder are thus carried out using a neutral gas in the gaseous, liquid or solidified state after immersion of the collected powder in the liquid phase.

The invention also provides the possibility of combining in the same unit several atomization devices arranged around the energy sources: medium frequency preheating generator (MF) and plasma torch generator (HF).

The description which follows illustrates an example of the operating mode of the method of the invention with reference to the device illustrated in FIG. 1.

Example

Elaboration in the device of the invention, of 10 kg of alloy powder with two bars of 24 mm in diameter.

The operation is semi-continuous, in sequence of 2 bars.

We will start with the loading operation of the bar n ° 1 then by that of preheating by the Medium Frequency oven of 10 kHz of 30 kW, followed by those of fusion by the plasma torch of 100 kW, of centrifugal dispersion and of cooling by of liquid argon in gaseous helium, finally by that of recovery of the powder in a collector cooled by liquid nitrogen.

In the following, D denotes a flow, P a pressure, T a temperature, V a valve, B a flange.

PRELIMINARY Operations:

• Degassing at room temperature with the PV1 pump, then with the PV2 molecular pump to obtain in the enclosure the collector, the disperser or rotary head, the argon pipes and the liquid argon accumulator, a static vacuum of 10 -5 torr;
• Argon U sweep at 1 bar;
• Closing of valve V1
• Empty at 10-3 torr;
• Filling with helium by the valve V4 via a pressure regulation device (MKS) to maintain at 2 bars;
• Opening of valve VA9 of the disperser gas bearing, with PA9 = 2 bars;
• Rotation of the disperser at low speed, at around 5,000 rpm;
• Introduction of cooling water from the head, at a flow rate DE1 = 10 g / s;
• Cooling of the enclosure and the collector with liquid nitrogen at 3 bars;
• Cooling of the accumulator to 2 bars;
• Filling the accumulator by condensing argon U
• Introduction of argon gas into the cold cage of the plasma torch by the valve VA2 at a flow DA2 = 0.3 l / s;
• Pressurization, PA6 = 3 bars, of the argon accumulator (not shown) and opening of the valves VA3, VA4 and VA5 for degassing of the liquid argon pipes and priming of the pumps cryogenic;
• Filling the liquid nitrogen expansion tanks (not shown) up to the "ni" levels respectively at pressures PNi = 2 bars, for i = 1 to 6.

Operations A: LOADING DURATION seconds A1 Introduction and fixing of bar n ° 1 20 A2 Closing of flanges B1 and B2 and of valve V8 10 A3 Starting the PV1 vacuum pump A4 V7 valve opening: vacuum <0.01 torr 30 AT 5 Closing of valve V7 and opening of valve VA1, Filling the airlock at 3 bars, closing of valve VA1 10 A6 Purging: opening of the V7 valve for vacuum within 0.1 torr A7 Closing of V7 and stopping of the vacuum pump PV1 AT 8 Opening of the enclosure-airlock valve V1 for filling the airlock with helium via valve V4 of the pressure regulator device (MKS) at 2 bars 40

$\overline{\text{110}}$

Operations B and C: PREHEATING, MELTING AND CENTRIGUGAL DISPERSION DURATION seconds B1 Starting the 30 kW MF generator 5 B2 Lowering the bar: at a speed Vb of 5 cm / s to the HF I2 inductor (2) 10 C2 Introduction of gases into the head of the plasma torch: opening of the valve VA2, the valve VH2 being closed Argon U: DA = 0.3 l / s; Hydrogen: DH2 = 0 LN2 (LN2 = liquid nitrogen) Nitrogen pressure in the cover of the disperser: PN5 = 6 bars C3 Plasma ignition at 18 kW by 6 kV HF electric arc between the rod and a movable electrode to ground, then, ascent from the rod to the MF inductor, I1 (1) 20 C4 Rise to 50% of the maximum plasma power C5 Increase in argon flow at DA2 = 0.5 l / s and introduction of hydrogen-opening of VH2- with DH2 = 0.0025 l / s 5 LN2 Lower temperatures and therefore nitrogen pressures in - the upper jacket of the enclosure: PN1 = 1 bar, - the lower jacket of the enclosure: PN2 = 1.6 bar, - the accumulator jacket ......: PN4 = 1.6 bar, - the jacket of the argon pipes: PN6 = 1 bar C6 Opening of the high pressure liquid argon valve VA3: DA3 = 0.075 l / s (PA3 = 10 bars) 10 B3 Rise in power of the MF generator, PMo, to obtain Tb 5 B4 When the temperature of the bar is at Tb fixed, lowering of the bar at the speed Vb = 0.27 cm / s (10 g / s) adjust the power PMo to keep Tb at the parade; 100 C7 Same as C4 at 100% and C5 with flow rates: DH2 = 0.005 l / s, DA2 = 1 l / s Speed increase of the rotary head: Vrd = 1000 r / s 10 C8 Liquid argon from the cooling nozzles: DA = 0.15 l / s; PA3 = 20 bars C9 Stroke of the 125 cm bar in the plasma at Vb = 0.27 cm / s 455 C10 Preheating stop C11 10 cm stroke of the rod in the plasma at Vb = 0.27 cm / s 40 D1 Rise of the bar (140 cm) at speed Vb = 20 m / s D2 Closure of the enclosure-airlock separation valve, V1 C12 Decrease of the plasma generator to 18% of the maximum power DH2 = 0 and DA2 = 0.3 l / s, Reduction of the head speed Vrd = 80 rpm LN2 PN1 = 1.6 bar, PN2 = 2 bar, PN3 = 2 bar, DA5 = 10 g / s, PN6 = 2 bar Duration of the merger $\overline{\text{660}}$

Operations E, D and A: WASHING, UNLOADING, LOADING DURATION seconds D3 Airlock depressurization: opening of valve V8 D4 Cooling of the bar; opening of valve VA1 E1 Opening of VA4, VA7 being closed for washing the bottom of the enclosure, flow DA4 = 1 l / s 20 E2 2 seconds after opening VA4 and for 5 seconds opening VA5, flow DA5 = 1 l / s E5 Partial sedimentation of the powder (greater than 30 µm) 50 D5 B2 flange opening D6 Closing of valve VA1 D7 Opening of door B1 D8 Unpinning and extraction of the "butt" from the bar $\overline{\text{70}}$

E6 There are two possibilities - total sedimentation of the powder greater than 5 µm 1200 - replenishment of the accumulator with liquid argon: 60 During this time, operations A, from A1 to A7, are carried out for bar n ° 2. A8 Opening of valve VA1 to fill the airlock at 2 bars $\overline{\text{1260}}$

Operations B and C: PREHEATING, MELTING AND CENTRIFUGAL DISPERSION DURATION seconds A9 Opening of the airlock valve, V1 5 C4 Rise to 50% of the maximum plasma power C5 DA2 = 0.5 l / s and introduction of hydrogen, DH2 = 0.0025 l / s 5 LN2 Lower temperatures and therefore nitrogen pressures in - the upper jacket of the enclosure: PN1 = 1 bar, - the lower jacket of the enclosure: PN2 = 1.6 bar, - the accumulator jacket ......: PN4 = 1.6 bar, - the jacket of the argon pipes: PN6 = 1 bar C6 Opening of the high pressure liquid argon valve VA3: DA3 = 0.075 l / s (PA3 = 10 bars) 10 B3 Rise in power of the MF generator, PMo, to obtain Tb; 5 B4 When the temperature of the bar is at Tb fixed, lowering of the bar 25 cm at the speed Vb = 0.27 cm / s (10 g / s) 100 C7 Same as C4 at 100% and C5 with flow rates: DH2 = 0.0051 l / s, Head speed increase: Vrd = 1000 rpm 10 C8 Liquid argon from the cooling nozzles: DA3 = 0.15 l / s; PA3 = 20 bars C9 125 cm stroke of the bar in the plasma at Vb = 0.27 cm / s 455 C10 Preheating stop C11 10 cm stroke of the rod in the plasma at Vb = 0.27 cm / s 40 C12 Stopping or lowering the plasma generator to 18% of maximum power with stopping H2 and lowering the argon at DA2 = 0.3 l / s, Decreasing the speed of the head Vrd = 80 r / s LN2 PN1 = 1.6 bar, PN2 = 2 bar, PN3 = 2 bar, DA5 = 10 g / s, PN6 = 2 bar Duration of the merger: $\overline{\text{630}}$

Operations E, D, A and G: WASHING, UNLOADING, LOADING, HEAD DURATION seconds D1, D2, D3, D4, E1, D2, E5, D5, D6, D7, D8, E6 Sedimentation of the powder Operations A: A1, A2, A3, A4, A5, A6, A7, A8; Change of dispersion head if necessary: Operation G G1 Closure of the hood head by the capsule electrode G2 Closure of valves VE1 and VN5, Draining of water and nitrogen 1200 $\overline{\text{1200}}$

G3 Stopping then extracting the engine G4 Change of dispersion head or Polishing of the head G5 Replacing the disperser G6 Degassing and re-pressure of the disperser chamber Operations F: DEPOSIT DURATION seconds F1 Emptying of the bottom of the tank by opening the VA6 valve (Use of an annex cryogenic accumulator tank) 30 F2 Closure of valves VA6 and V9 20 F3 Extraction of the manifold and replacement with a ^2nd 60 F4 Reheat ¹ collector drain liquid nitrogen and hot air passing through the jacket, degassing by the vacuum of the ^2nd collector, open VA10 120 F6 by cooling the liquid nitrogen ^2nd collector $\overline{\text{230}}$

• 1 h 8 min en décantant entre 2 barreaux ou
• 48 min en remplissant l'accumulateur d'argon liquide avec de l'argon liquide en réserve.

To obtain 10 kg of alloy powder in a collector,

• 1 h 8 min by decanting between 2 bars or
• 48 min by filling the accumulator with liquid argon with liquid argon in reserve.

The method and the device of the invention make it possible to manufacture powders from various families of materials and in particular superalloys based on nickel, titanium and titanium alloys, aluminum, Niobium alloys, etc.

Claims (19)

1. Apparatus for producing powders, and in particular metal powders by atomizing, the apparatus comprising

   - an atomizing enclosure (C) in which a dispersion head (9) is disposed rotating at high speed to scatter the molten material in atomized form,

   - melting means (B) for melting the material to be atomized (1) comprising at least one vertical inductive plasma furnace (4) producing an envelope of plasma-generating gases (12) containing the top face of the dispersion head,

   - cooling means for cooling the atomized material and the dispersion head (9) constituted by a first series of members (15,16) for dispensing a cooling fluid disposed in the top portion of the atomizing enclosure to create a cold zone (13) at the periphery of the envelope (12), and by a second series of members (11) for circulating a cooling fluid, said series being disposed in the bottom portion of the enclosure (C) to create a cold zone at the bottom face of the head (9), and

   - means (17) for collecting the cooled powder material obtained in this way, characterized in that said first series of members for dispensing a cooling fluid is constituted by a ring of nozzles (15) producing jets of fluid that are tangential to the surface of said envelope (12) so as to create a quenching zone (13) formed of a vortex around the plasma, and nozzles (16) producing a washing that is tangential to the enclosure.
2. The apparatus according to claim 1, characterized in that said nozzles (15) of the first series are placed above the powder ejection triangle and possess ejection axes X that slope relative to the plane of the top face of the dispersion head (9).
3. The apparatus according to one of the preceding claims, characterized in that said envelope (12) of plasma-generating gases is constituted by a cylindrical tube whose vertical axis is parallel to the vertical axis of the rotary head (9).
4. The apparatus according to claim 3, characterized in that the vertical axis of the cylindrical tube is close to or coincides with the vertical axis of the head.
5. The apparatus according to one of the preceding claims, characterized in that said vertical inductive plasma furnace (4) is disposed above the top face of the rotary head (9).
6. The apparatus according to one of the preceding claims, characterized in that said dispersion head (9) is cylindrical and its top face is disposed in a plane that is substantially horizontal.
7. The apparatus according to one of the preceding claims, characterized in that said inductive plasma furnace (4) is associated with an induced current preheating furnace (3).
8. The apparatus according to one of the preceding claims, characterized in that it further comprises a cold crucible (100) disposed beneath the melting means (A) to receive the material to be atomized in the molten state, and a nozzle (101, 102) for adjusting the flow rate of said molten material for feeding the atomizing enclosure (C).
9. A method of manufacturing powders, and in particular metal powders, by atomization, the method comprising continuously melting the material to be atomized which flows vertically and coaxially above a dispersion head (9) rotating at high speed for the purpose of dispersing the molten material in atomized form into an envelope of plasma-generating gases by friction on the top face of the rotary head (9), and then quenching the atomized material and collecting the cooled powder material obtained in this way, characterized in that said atomized material is quenched by passing through a cooling vortex situated at the periphery of the envelope of plasma-generating gases.
10. The method according to claim 9, characterized in that the powders are collected under an inert gas in the gaseous, liquid, or solid state.
11. The method according to one of claims 9 or 10, characterized in that atomization is performed at pressures greater than atmospheric pressure.
12. The method according to claims 9 to 11, characterized in that the plasma is lit by striking a high tension electric arc between the material to be atomized (1) and an electrode placed on the axis of the furnace (4).
13. The method according to one of claims 9 to 12, characterized in that the atomized material is quenched by being brought into contact with a cold, gaseous, liquid, or two-phase fluid, thereby enabling monocrystalline or amorphous structures to be obtained.
14. The method according to one of claims 9 to 13, characterized in that the gases produced during quenching are liquefied in a condenser and the powders are recovered with a fraction of the liquefied gases in at least one container enabling the mixture to be maintained in the liquid or solid state.
15. The method according to one of claims 9 to 14, characterized in that the dispersion head (9) is rotated at a speed lying in the range 30,000 rpm to 125,000 rpm.
16. The method according to one of claims 9 to 15, characterized in that a temperature gradient is established in the dispersion head (9) of 60°C/cm to 180°C/cm for a head made of copper and of 200°C/cm to 500°C/cm for a head made of tungsten.
17. The method according to one of claims 9 to 16, characterized in that the atomized material is quenched by means of nozzles (15) dispensing a total flow rate of liquid argon that is sufficient to cool the powder completely; the ejection axes of said nozzles being inclined relative to the plane of the top face of said dispersion head (9), and the width of the jets being determined so as to produce a contra-rotating effect thereof relative to said head (9) so as to brake the motion of the powders.
18. The method according to one of claims 9 to 17, characterized in that the material to be atomized is initially in the form of a cylindrical rod (1).
19. The method according to one of claims 9 to 18, characterized in that the material to be atomized is initially received in the molten state in a cold crucible (100) from which it flows through a flow adjustment nozzle (101, 102) towards the atomizing enclosure (C).

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