Apparatus and method for spheroidizing powder

Abstract

An apparatus for spheroidizing a powder, the apparatus comprising a microwave chamber (20), a plasma chamber (35) having an inner wall and located in the microwave chamber, a confinement tube (3) connected to the plasma chamber, a container for a mixture of a process gas and a powder precursor, and a diverter (110) for diverting the powder precursor to the confinement tube (3), and a container (110) connected to the confinement tube to feed the mixture as an incoming gas stream to the plasma chamber so as to create a plasma torch in the plasma chamber by coupling the gas stream with microwave radiation, the diverter (110) being located within the confinement tube at the inlet of the plasma chamber, the diverter providing a wide channel (118) and a narrow channel (113), and separates the incoming airflow into a central airflow passing through the wide channel and a peripheral airflow passing through the narrow channel.

Description

[0001] This application claims priority to European Patent Application No. EP23382838.3, filed on 9 August 2023.

[0002] An apparatus for powder spheroidization via microwave-induced plasma is disclosed, comprising a microwave radiation generator, a plasma chamber, a confinement tube, and a container. The generator is used for the microwave chamber, the plasma chamber having an inner wall and located within the microwave chamber. The confinement tube is connected upstream and downstream of the plasma chamber. The container is used for a mixture of process gas and powder precursor, and is connected to the confinement tube to supply the mixture as an inlet gas flow to the plasma chamber to generate a plasma torch within the plasma chamber by coupling the gas flow with microwave radiation.

[0003] A method for preparing spherical bodies from powder precursors via microwave-induced plasma includes the following steps: forming a plasma torch in a plasma chamber by coupling an incoming flow of process gas with microwave radiation, and carrying the powder precursors into the plasma torch by using a process gas as a carrier gas to prepare spherical bodies from the powder precursors by in-flight melting. Background Technology

[0004] Different industrial sectors require spherical particles made from powders of various materials. The need for industrial processes to produce spherical powder particles stems from the search for the following benefits offered by spheroidization methods: - Improves powder flowability.

[0005] -Increase powder bulk density.

[0006] - Eliminates internal cavities and cracks in the powder, thereby improving the quality of parts made from this powder.

[0007] - Improves the surface morphology of particles.

[0008] Spheroidization is a process of in-flight melting and controlled solidification. Irregularly shaped (angular or non-uniform) powder precursors (typically from waste materials) are introduced into an inductively or microwave-induced plasma and immediately melted at the plasma's high temperature. The molten powder particles spherize under the influence of liquid surface tension. These droplets are cooled as they exit the plasma torch. The resulting spheroids are then collected as the spheroidization product.

[0009] Microwave-induced plasma is a type of plasma that emits high-frequency electromagnetic radiation in the GHz range. It can excite electrodeless gas discharge.

[0010] EP3996472A1 discloses an apparatus for powder spheroidization via microwave-induced plasma. The apparatus includes a microwave generator, a microwave cavity, a waveguide, a plasma chamber, a powder supply source, a gas supply source, and a compressed air supply source. The waveguide connects the microwave generator to the microwave cavity. The plasma chamber is located within the microwave cavity. The powder supply source is connected to the plasma chamber to supply a powder precursor stream. The gas supply source is connected to the plasma chamber to supply a process gas stream to form a plasma torch within the plasma chamber by coupling the process gas stream with microwave radiation. The compressed air supply source is used to cool the plasma chamber. The microwave cavity includes at least one opening for compressed air, allowing compressed air to cool the plasma chamber from the outside. The gas supply source is connected to the powder supply source so that the process gas carries the powder precursor into the plasma tube and thus into the plasma torch, whereby the powder precursor is spheroidized by in-flight melting.

[0011] Using the setup of EP3996472A1, some powder has been observed adhering to the inner wall of the plasma chamber. This is likely undesirable for several reasons: - The adhered powder can form a coating layer that can shield the chamber from the microwaves required to generate plasma; - Adhesive powder may be hotter than the melting point of the chamber wall and may damage the chamber wall; - Thermally adhered powder may impair the cooling of the plasma chamber. Summary of the Invention

[0012] The purpose of this disclosure is to provide an apparatus and method that overcomes or mitigates the shortcomings of the art.

[0013] In a first aspect, an apparatus for powder spheroidization via microwave-induced plasma is provided, the apparatus comprising a microwave radiation generator, a microwave cavity, a plasma chamber, a confinement tube, a container, and a splitter, the plasma chamber having an inner wall and located within the microwave cavity, the confinement tube being connected upstream and downstream of the plasma chamber, the container being for a mixture of a process gas and a powder precursor, the container being connected to the confinement tube to supply the mixture as an inlet gas flow to the plasma chamber to generate a plasma torch within the plasma chamber by coupling the gas flow with microwave radiation, the splitter being located within the confinement tube at the inlet of the plasma chamber, the splitter providing a wide channel and a narrow channel such that the splitter separates the inlet gas flow into a central gas flow through the wide channel and a peripheral gas flow through the narrow channel.

[0014] In this way, the central airflow can be manipulated to generate a plasma torch in the plasma chamber, and the peripheral airflow can be manipulated to cool and clean the inner walls of the plasma chamber.

[0015] It should be understood that the term "wide channel" refers to a channel that is significantly wider than a channel called a "narrow channel," that is, the cross-section of a wide channel is clearly larger than the cross-section of a narrow channel.

[0016] In the example, the wide channel can be located in the central area of ​​the splitter. The wide channel can be included within the splitter.

[0017] In the example, the narrow channel may be located in or around the periphery of the shunt. The narrow channel may be included within the shunt, or the shunt may facilitate the formation of the narrow channel, for example, in combination with the inner wall of the plasma chamber.

[0018] In a second aspect, a method for preparing spherical bodies from powder precursors via microwave-induced plasma, the method comprising the steps of: forming a plasma torch in a plasma chamber by coupling an incoming flow of process gas with microwave radiation; carrying the powder precursors into the plasma torch by a process gas used as a carrier gas to prepare spherical bodies from the powder precursors by in-flight melting; and internally cooling the plasma tube by separating the incoming flow into a central flow and a peripheral flow, the central flow generating the plasma torch in the plasma chamber and the peripheral flow cooling the inner wall of the plasma tube. Attached Figure Description

[0019] Non-limiting examples of this disclosure will now be described with reference to the accompanying drawings, in which: Figure 1 This is a three-dimensional view of the components used to cool the inner wall of the plasma chamber; Figure 2 It is installed at the entrance of the plasma chamber. Figure 1 A three-dimensional cross-sectional view of the component; Figure 3 It is a 3D diagram of a perforated washer; Figure 4 It is installed at the entrance of the plasma chamber. Figure 3 A partial sectional perspective view of the washer; Figure 5 yes Figure 1 A cross-sectional elevation view of the components mounted upside down at the entrance of the plasma chamber; Figure 6 This is a perspective view of another component used to cool the inner wall of the plasma chamber; Figure 7 It is installed at the entrance of the plasma chamber. Figure 6 A cross-sectional elevation view of the component; Figure 8 This is a three-dimensional diagram of the component that centers the plasma torch within the plasma chamber; Figure 9It is installed at the plasma chamber outlet. Figure 8 A cross-sectional elevation view of the component; Figure 10 It is a three-dimensional view of the ring installed at the plasma chamber outlet; and Figure 11 This is a schematic diagram of equipment used for powder spheroidization. Detailed Implementation

[0020] Figure 11 An apparatus for powder spheroidization via microwave-induced plasma is schematically illustrated. This apparatus is similar to that disclosed in EP3996472A1, but it may or may not include the external cooling system described therein, and may include other features (such as those introduced in this specification) (see reference). Figures 1 to 10 For the sake of completeness, the contents of EP3996472A1 are incorporated herein by reference.

[0021] Figure 11 The equipment includes a container 1, a tank 2, a confinement tube 3, a microwave generator 4, a microwave circulator 5, a waveguide 6, a container 7, a filter 8, a waveguide short circuit 10, and a microwave cavity 20. The container 1 contains a compressed process gas 11, the tank 2 contains an irregular powder precursor, the container 7 is used for powder spherical bodies leaving the confinement tube, the filter 8 is used to intercept powder leaving the container 7, and the microwave cavity 20 is located between the waveguide 6 and the waveguide short circuit 10.

[0022] The powder precursor and process gas are mixed in container 2, and the resulting gas mixture 21 is transported as a gas flow to confinement tube 3.

[0023] Circulator 5 protects microwave generator 4. Waveguide 6 and waveguide short circuit 10 transmit microwave radiation to microwave cavity 20, which is passed through confinement tube 3.

[0024] Figure 2 A plasma chamber 35 passing through the microwave cavity 20 is shown, which is formed as part of the confinement tube 3. The confinement tube 3 includes the plasma chamber 35 and can be made as a single unit. However, it may be convenient for the plasma chamber 35 to be a separate component, in which case the portion of the confinement tube is located upstream of the plasma chamber and can be connected to the plasma chamber via mechanical connections 30, 34, 32 (e.g., cover plate 30, gasket 34, and clamp 32).

[0025] A plasma torch is generated in a plasma chamber 35 by coupling a process gas flow 21 (carrying a powder precursor) with microwave radiation resonating in a microwave cavity. The walls of the plasma chamber 35 can be made of quartz, which is invisible to microwave radiation and resistant to high temperatures, but can also be made of other materials with these properties, such as sapphire, mica, boron nitrides, and alumina.

[0026] Container 7 collects a mixture 31 of gas and powder spheres exiting plasma chamber 35. The powder spheres are left in container 7 to cool, and the gas exits the container as a mixture 71 still containing some small powder particles. Filter 8 intercepts these small powder particles and provides clean gas 81 to be reused as process gas.

[0027] Advantageously, the process gas flow is laminar or near-laminar in order to keep powder particles along a given path. The goal is not perfect laminar flow, but flow without turbulence, as turbulence would harm the plasma.

[0028] Figure 1 A first tubular element 110 is shown to be installed at the inlet of plasma chamber 35. The first tubular element 110 includes a central portion 115, two end portions 114 and 116, and an axial channel 118, wherein the two end portions 114 and 116 are wider than the central portion 115. The first tubular element 110 also includes a ring 112 surrounding the end portions 114. A series of slots 113 exist between the ring 112 and the end portions 114. The channel 118 may be cylindrical.

[0029] continue Figure 2 It further illustrates a first tubular element 110 installed at the inlet of plasma chamber 35 within the confinement tube 3. A clamp 32 holds the confinement tube 3 to the plasma chamber 35, and for airtightness, a gasket 34 is located between the cover plate 30 and the plasma chamber 35. Most of the gas mixture 21 passes through channel 118, but some of the gas mixture 21 enters this portion of the confinement tube 3 through slit 113. This arrangement separates the gas mixture 21 into two airflows: a central airflow (through channel 118) and a peripheral airflow (through slit 113).

[0030] The central airflow becomes the plasma torch within the plasma chamber 35. The peripheral airflow is faster than the central airflow because it passes through a narrow channel: first through slit 113, and then through a section 119 left between the inner wall of the confinement tube 3 and the relatively wide end portion 116 of the first tubular element 110. This rapid peripheral flow achieves two important results in the plasma chamber 35: it cools the walls of the plasma chamber, and it drags away powder deposited on or adhered to the walls.

[0031] Figure 3A perforated washer 120 is shown, which has a large central hole 124 and a plurality of small axial perforations 122 distributed around the central hole 124. Figure 4 A perforated gasket 120 is shown installed at the inlet of the plasma chamber 35, between the connecting cover plate 30 and the gasket 34. Most of the gas mixture 21 passes through the hole 124, but some of the gas mixture 21 enters the plasma chamber 35 through the perforation 122. Similarly, this arrangement separates the gas mixture 21 into a central flow and a peripheral flow, achieving the aforementioned effects at least to a sufficient degree. Furthermore, this arrangement is more... Figure 2 The layout is simpler.

[0032] Figure 5 It shows Figure 2 A variation of the example. Figure 5 Components and Figure 2 The components are basically the same, but in Figure 5 In the middle, the first tubular element 110 relative to its in Figure 2 The central position is installed in an inverted position, i.e., upside down. This arrangement is intended for situations where the gas in the central flow differs from the gas in the peripheral flow. In this case, the gas in the central flow flows downstream through the confining pipe 3, and the gas in the peripheral flow can enter laterally, for example, from a different pipe 38.

[0033] Figure 6 A second tubular element 130 is shown, which is a variation of the first tubular element 110. Figure 6 In the text, the second tubular element 130 is indicated relative to... Figure 1 The first tubular element 110 is in an inverted position. The second tubular element 130 includes two end portions 134 and 136, a central portion 135, and a channel 138, the central portion 135 being narrower than the end portions 134 and 136. The second tubular element 130 also includes a retainer 132 to support the second tubular element 130 through its central portion 135. The channel 118 may be cylindrical.

[0034] Figure 7 A second tubular element 130, installed within the confinement tube 3 at the inlet of the plasma chamber 35, is shown. A gasket 139, located between the cover plate 30 and the end portion 136, ensures airtightness at the connection between the confinement tube 3 and the plasma chamber 35. Figure 7 The arrangement shown is similar to Figure 5 The arrangement is similar, and is intended for situations where the gas in the center flow differs from the gas in the peripheral flow. In this case, the gas in the center flow flows downstream through the confinement pipe 3, and the gas in the peripheral flow can enter the confinement pipe 3 laterally from different pipes 38.

[0035] exist Figure 7 In the example, the peripheral flow enters the plasma chamber 35 through a section 137 left between the inner wall of the confinement tube 3 and the relatively wide end portion 134 of the second tubular element 130, at the entrance of the plasma chamber.

[0036] 120 perforated washers can be used Figure 7 The device is installed between the end portion 134 and the liner 34, and is held at the entrance of the plasma chamber 35 by clamp 32. This arrangement can enhance the separation of the gas mixture into a central flow and a peripheral flow.

[0037] Figure 9 A conical exhaust port 140 is shown installed at the outlet of plasma chamber 35. Figure 8 The conical outlet 140 itself is shown. The conical outlet 140 includes a flange 142 and a cone 144. A clamp 33 attaches the flange 142 to the plasma chamber 35, and its airtightness is ensured by a gasket 36 located between the plasma chamber and the outlet 140. The flange 142 includes a plurality of holes 146 for attaching it to the clamp 33 (e.g., by bolts).

[0038] The portion of the confinement tube 3 located downstream of the plasma chamber 35 can be connected to the plasma chamber 35 via mechanical connections 33, 36, 142 (i.e., clamp 33, gasket 36, and flange 142).

[0039] The cone 144 causes mixing of the central and peripheral airflows downstream of the plasma torch and increases the velocity of the generated flow, thereby helping to keep the plasma torch axially centered within the plasma chamber 35 and preventing powder deposition on the inner wall of the plasma chamber 35.

[0040] Figure 10 A ring 150 is shown, having a first central hole 154 and a second central hole 153, at least two side holes 152, and a plurality of axial holes 156. The second central hole 153 is narrower than the first central hole 154 and is located downstream of the first central hole 154. The axial holes 156 may be distributed corresponding to the holes 146 of a tapered outlet 140. The ring 150 can be mounted around a cone 144 by bolts between the holes 146. Figure 9 The settings.

[0041] Another gas can be introduced through the orifice 152 of the ring 150 and formed to flow around the cone 144 to cool the cone 144. If this gas flows at a high speed, it will mix the gas with the powder spheres 31 (see...). Figure 11The plasma chamber 35 is drawn out, thereby accelerating the gas flow 31 (the velocity of the gas flow 31 is also increased by the tapering of the cone 144). The annular region between the cone 144 and the second central hole 153 can be narrow, thereby increasing the velocity of the gas introduced through the hole 152.

[0042] Pads 34, 36 and 139 can be made of graphite.

[0043] The external cooling disclosed in EP3996472A1 can be combined with the internal cooling described herein.

[0044] Although only a few examples are disclosed herein, other alternatives, modifications, uses, and / or equivalents are possible. Furthermore, all possible combinations of the described examples are covered. Therefore, the scope of this disclosure should not be limited to any particular example but should be determined solely through a fair reading of the appended claims. If reference numerals relating to the drawings are placed in parentheses within the claims, they are used only to attempt to increase the comprehensibility of the claims and should not be construed as limiting the scope of the claims.

Claims

1. An apparatus for powder spheroidization via microwave-induced plasma, the apparatus comprising a microwave radiation generator (4), a plasma chamber (35), a confinement tube (3), and a container (2), the generator (4) being used for a microwave cavity (20), the plasma chamber (35) having an inner wall and located within the microwave cavity, the confinement tube (3) being connected upstream and downstream of the plasma chamber, and the container (2) being used for a mixture of a process gas and a powder precursor, the container being connected to the confinement tube to supply the mixture as an inlet gas flow (21) to the plasma chamber to generate a plasma torch in the plasma chamber by coupling the gas flow with microwave radiation, characterized in that, It also includes a splitter (110; 120; 130) located within the confinement tube at the entrance of the plasma chamber, the splitter providing a wide channel (118; 124; 138) and a narrow channel (113, 119; 122; 137) such that the splitter separates the incoming airflow (21) into a central airflow through the wide channel and a peripheral airflow through the narrow channel.

2. The device according to claim 1, wherein, The diverter includes tubular elements (110; 130), and the wide channels (118; 138) are channels of the tubular elements.

3. The device according to claim 2, wherein, The tubular element (110; 130) includes a central portion (115; 135) and two end portions (114, 116; 134, 136), the two end portions (114, 116; 134, 136) being wider than the central portion.

4. The device according to claim 3, wherein, The tubular element (110) includes a ring (112) surrounding one of the end portions (114) and provides a plurality of slits (113) between the ring and the end portion, the slits being portions of the narrow channel.

5. The device according to claim 4, wherein, The tubular element (110) is placed axially inside the confinement tube (3), wherein the ring (112) is located at the end portion (114) of the tubular element furthest from the plasma chamber (35).

6. The device according to claim 4, wherein, The tubular element (110) is placed axially inside the confinement tube (3), wherein the ring (112) is located at the end portion (114) of the tubular element closest to the plasma chamber (35).

7. The device according to claim 3, wherein, One of the end portions (136) of the tubular element (130) is wider than the other end portion (134).

8. The device according to claim 7, wherein, The tubular element (130) is placed axially inside the confinement tube (3), wherein the widest end portion (136) is located at the end of the tubular element furthest from the plasma chamber (35).

9. The device according to any one of claims 2 to 8, wherein, The tubular element (110; 130) is axially placed inside the confinement tube (3), and the narrow channel is formed at least partially in an annular section (119; 137) between the inner wall of the confinement tube (3) and the end portion (116; 134) of the tubular element (110; 130) closest to the plasma chamber (35).

10. The device according to claim 1, wherein, The diverter includes a perforated washer (120) having a central hole (124) and a plurality of small axial perforations (122), the central hole (124) serving as the wide channel and the plurality of small axial perforations (122) serving as the narrow channel.

11. The device according to claims 8 and 10, wherein, The perforated gasket (120) is placed downstream of the tubular element (130).

12. The device according to any one of the preceding claims, the device comprising an outlet (140) located at the outlet of the plasma chamber (35), the outlet comprising a conical cone (144).

13. The device according to any one of the preceding claims, the device comprising a ring (150) located downstream of the plasma chamber (35), the ring comprising a plurality of side holes (152).

14. The device according to claims 12 and 13, wherein, The ring (150) is placed around the conical cone (144).

15. A method for preparing spherical bodies from powder precursors by microwave-induced plasma, the method comprising the step of forming a plasma torch in a plasma chamber by coupling an inlet flow of process gas with microwave radiation, characterized in that, It also includes the following steps: - The powder precursor is carried into the plasma torch by a process gas used as a carrier gas so that the powder precursor can be formed into spheres by melting in flight; - The plasma tube is cooled from the inside by separating the incoming airflow into a central airflow and a peripheral airflow, the central airflow generating the plasma torch in the plasma chamber, and the peripheral airflow cooling the inner wall of the plasma chamber.

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