Microwave plasma spheroidizing device and method

Abstract

The invention discloses a microwave plasma spheroidizing device and method. The microwave plasma spheroidizing device comprises a microwave source, a rectangular waveguide, a waveguide-to-coaxial structure, a coaxial transmission structure, a nozzle, an airflow blocking device and a powder feeding channel. The microwave source is connected with the rectangular waveguide, the waveguide-to-coaxial structure is arranged in the rectangular waveguide, one end of the coaxial transmission structure is vertically communicated with the middle of the rectangular waveguide, the other end of the coaxial transmission structure is connected with the nozzle, and an air inlet pipe is arranged on the coaxial transmission structure. A gas flow blocking device for preventing gas from entering is arranged in the coaxial transmission structure between the gas inlet pipe and the rectangular waveguide, the powder feeding channel, the rectangular waveguide, the waveguide-to-coaxial structure and the coaxial transmission structure are coaxially arranged, and the horizontal position of the tail end of the powder feeding channel is flush with the position of the top of the nozzle. According to the invention, axisymmetric, stable and controllable energy coupling of microwave transmission and discharge regions can be realized, so that an axisymmetric and high-energy-density stable plasma region is constructed, and the globe powder is more efficient and high in quality.

Description

Technical Field

[0001] This invention relates to the field of powder spheroidization technology, and in particular to a microwave plasma spheroidization apparatus and method. Background Technology

[0002] The principle of plasma spherical powder preparation technology is to use plasma as a heat source to heat the gas, and then send the raw material powder into the high-temperature plasma region through a carrier gas powder feeding device to melt it endothermally. Under the action of surface tension, spherical droplets are formed, and the droplets are then cooled and solidified into powder through a large temperature gradient. Due to its advantages such as high temperature and high hanerodynamics, plasma has been widely used in the preparation of high-melting-point metals and alloys. Traditional plasma spherical metal powder technology mostly uses radio frequency and DC arc plasma, but it suffers from problems such as low energy efficiency, high gas consumption, and electrode contamination. Microwave plasma technology, with its advantages of electrodeless discharge, high energy density, uniform plasma region, rapid start-up, and relatively simple device structure, demonstrates unique advantages in the field of high-quality spherical metal powder preparation.

[0003] However, traditional microwave plasma torch spheroidizing devices employ rectangular waveguide coupling (TE) 10 (Mode), driven by a 2.45GHz magnetron or solid-state source, with a quartz tube arranged across the microwave waveguide. This type of structure is extremely sensitive to electromagnetic boundary conditions within the waveguide and load impedance. For example... Figure 1 As shown, when used for spheroidizing metal powder, the high conductivity, mobility, and tendency to accumulate locally of the metal powder create a "dynamic electromagnetic load" in the strong electric field region of the waveguide, essentially introducing a moving metal boundary within the waveguide. This causes significant distortion and strong time-varying characteristics in the electric field distribution within the waveguide, preventing stable coupling of input energy to the plasma. Simultaneously, the plasma arc root exhibits irregular migration, arc skipping, and multi-point attachment on the inner wall or near-wall region of the quartz tube, transforming the discharge from a stable state to one of strong jitter. Furthermore, it becomes difficult to maintain coaxiality and stable matching between the heat source center and the powder's trajectory, turning the spheroidizing process from a controllable process into a highly random perturbation process. This severely affects the quality of different batches of powder, making it impossible to maintain optimal experimental conditions consistently. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a microwave plasma spheroidizing device and method.

[0005] The technical solution of the present invention is as follows: On the one hand, a microwave plasma spheroidizing device is provided, including a microwave source, a rectangular waveguide, a waveguide-to-coaxial structure, a coaxial transmission structure, a nozzle, a gas flow blocking device, and a powder feeding channel; The microwave source is connected to the rectangular waveguide. The waveguide-to-coaxial structure is disposed inside the rectangular waveguide. One end of the coaxial transmission structure is perpendicularly connected to the middle of the rectangular waveguide. The other end of the coaxial transmission structure is connected to the nozzle. An air inlet pipe is provided on the coaxial transmission structure. An airflow blocking device is provided inside the coaxial transmission structure between the air inlet pipe and the rectangular waveguide to prevent gas from entering. The powder feeding channel is coaxially arranged with the rectangular waveguide, the waveguide-to-coaxial structure, and the coaxial transmission structure, and the horizontal position of its end is flush with the top of the nozzle. The rectangular waveguide is used to input the microwaves output from the microwave source into the waveguide-to-coaxial structure in TE10 mode. The waveguide-to-coaxial structure is used to convert the TE10 mode into TEM mode. The coaxial transmission structure is used to transmit the microwave energy in TEM mode to the nozzle, so that the plasma gas entering through the inlet pipe forms a stable plasma flame at the nozzle.

[0006] Preferably, the waveguide-to-coaxial structure is a frustum structure, which enables the equivalent impedance between the rectangular waveguide end and the coaxial transmission structure and discharge load to be matched.

[0007] Preferably, the coaxial transmission structure includes a coaxial outer conductor and a coaxial inner conductor arranged coaxially, and the powder feeding channel is disposed within the coaxial inner conductor.

[0008] Preferably, the coaxial inner conductor is integrated with the powder feeding channel.

[0009] Preferably, the coaxial inner conductor is a straight tube or has a pointed tip.

[0010] Preferably, the air intake pipe adopts a tangential rotating air intake structure.

[0011] Preferably, multiple air intake pipes are provided.

[0012] Preferably, the multiple air intake pipes are arranged on the same horizontal plane and are evenly distributed around the coaxial transmission structure.

[0013] On the other hand, a microwave plasma spheroidizing method is also provided, which uses the microwave plasma spheroidizing device described in any one of the above-mentioned methods for spheroidizing.

[0014] Preferably, the method includes the following steps: S1: Microwaves are input into the rectangular waveguide through the microwave source, and the microwaves are input to the waveguide-to-coaxial structure in TE10 mode via the rectangular waveguide. S2: The waveguide-to-coaxial structure converts the microwave energy in TE10 mode into microwave energy in TEM mode. The microwave energy in TEM mode is then transmitted to the nozzle via the coaxial transmission structure and forms an electric field enhancement region. S3: Powder is delivered to the nozzle through the powder feeding channel, and plasma gas is input into the waveguide-to-coaxial structure through the air inlet pipe. The plasma gas forms a stable plasma flame in the electric field enhancement region and causes the powder to absorb heat and melt to form spherical droplets. S4: The spherical droplets are output from the nozzle and cooled and solidified to obtain spherical powder.

[0015] The beneficial effects of this invention are: 1. Enhanced electromagnetic field axisymmetry and disturbance resistance: By setting up a waveguide-to-coaxial structure and utilizing the natural axisymmetry of the coaxial waveguide TEM mode, the electric field distribution in the discharge region is transformed from the original non-axisymmetric form that is sensitive to boundary conditions to an axisymmetric form. This reduces the asymmetric disturbance to the electric field after the introduction of metal powder, weakens the random drift of standing wave nodes / antinodes, and thus improves the stability of the electromagnetic field distribution.

[0016] 2. Controlled plasma arc root and improved discharge stability: The coaxial nozzle makes the electric field, airflow and powder transport coaxial. Furthermore, the tangential rotating air intake structure can promote the plasma to form a stable arc column on the axis first, suppressing instability phenomena such as arc root deviation, arc jumping, multi-point adhesion and wall discharge, thereby reducing the risk of local overheating and parasitic discharge in the discharge channel and improving the stability of continuous operation.

[0017] 3. Constructing a high-energy-density plasma region and more controllable heat source location: Through the coaxial arrangement of each component, the coaxial structure helps to concentrate electromagnetic energy in space near the nozzle outlet, forming an axisymmetric, high-energy-density plasma region. The heat source center position is stable, which is conducive to achieving stronger, more concentrated and more stable heating capabilities.

[0018] 4. Improved matching degree between powder trajectory and heat source, and enhanced repeatability of heating history: Since the powder is introduced coaxially through the powder feeding channel and passes through the high-temperature core area of ​​the plasma, the powder trajectory is coaxially matched with the center of the heat source, reducing the "edge-grabbing" or deviation of particles from the high-temperature area, while reducing the uneven heating history of particles caused by fluctuations in operating conditions, and improving the consistency of powder quality between different batches.

[0019] 5. Adapting to metal powder spheroidizing conditions and expanding the range of operable process parameters: Under typical operating conditions of high conductivity and high disturbance of metal powder, it can still maintain a relatively stable electromagnetic coupling and discharge mode, which enhances the adaptability of the device to powder type, powder feed fluctuations and short-term aggregation, thereby expanding the range of usable process parameters.

[0020] 6. Eliminate the risk of dielectric tube ablation and powder adhesion: The coaxial cavity generator, which is integrated with the coaxial inner conductor, replaces the quartz tube constraint, realizing microwave plasma discharge without physical dielectric tube constraint. This design fundamentally avoids the risk of quartz tube ablation.

[0021] In summary, this invention addresses the core problems of "electromagnetic field distortion, coupling mismatch, arc root deviation, and discharge instability" in the spheroidization of metal powders, enabling the construction of a more stable, axisymmetric, and high-energy-density microwave plasma region, thereby achieving more efficient and high-quality spheroidization of powders. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A schematic diagram showing the electric field distortion and strong plasma arc root jitter caused by introducing a dynamic electromagnetic load into the metal powder of an existing spheroidizing device. Figure 2 This is a schematic diagram of the structure of the microwave plasma spheroidizing device of the present invention; Figure 3 This is a schematic diagram illustrating microwave delivery efficiency under different power and flow rates in a specific embodiment. Figure 4 This is a simulation diagram of the electric field for different coaxial inner conductor shapes in a specific embodiment; Figure 5 This is a schematic diagram of the intake pipe in a specific embodiment; Figure 6 This is a simulation diagram of different intake structures in a specific embodiment; Figure 7 This is a schematic diagram of the spheroidization result using the microwave plasma spheroidization method of the present invention in a specific embodiment; Figure 8 In one specific embodiment, a conventional unmodified rectangular waveguide (TE) is used. 10 A schematic diagram of the spheroidization result achieved by coupling a microwave plasma torch with a modal. Figure 9 for Figure 8 A schematic diagram of the spheroidized quartz tube adhering to the wall. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and technical features described in this application can be combined with each other. It should also be pointed out that, unless otherwise indicated, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms "comprising" or "including" and similar words used in this invention refer to elements or objects preceding the word that encompass the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0025] like Figure 2 As shown, the present invention provides a microwave plasma spheroidizing device, including a microwave source, a rectangular waveguide, a waveguide-to-coaxial structure, a coaxial transmission structure, a nozzle, a gas flow blocking device, and a powder feeding channel; The microwave source is connected to the rectangular waveguide. The waveguide-to-coaxial structure is disposed inside the rectangular waveguide. One end of the coaxial transmission structure is perpendicularly connected to the middle of the rectangular waveguide. The other end of the coaxial transmission structure is connected to the nozzle. An air inlet pipe is provided on the coaxial transmission structure. An airflow blocking device is provided inside the coaxial transmission structure between the air inlet pipe and the rectangular waveguide to prevent gas from entering. The powder feeding channel is coaxially arranged with the rectangular waveguide, the waveguide-to-coaxial structure, and the coaxial transmission structure, and the horizontal position of its end is flush with the top of the nozzle. The rectangular waveguide is used to input the microwaves output from the microwave source into the waveguide-to-coaxial structure in TE10 mode. The waveguide-to-coaxial structure is used to convert the TE10 mode into TEM mode. The coaxial transmission structure is used to transmit the microwave energy in TEM mode to the nozzle, so that the plasma gas entering through the inlet pipe forms a stable plasma flame at the nozzle.

[0026] Existing rectangular waveguides (TE) 10 The electromagnetic field distribution of a (mode-coupled) microwave plasma torch during the spheroidization of metal powder is easily disturbed by the metal powder, the coupling state is prone to mismatch, arc root offset leads to unstable plasma operation, and powder adhesion to the wall affects microwave transmission. In this invention, by setting up a waveguide-to-coaxial structure, a coaxial transmission structure, and coaxial arrangement of all components, axisymmetric, stable, and controllable energy coupling between microwave transmission and the discharge region can be achieved, thereby constructing an axisymmetric, high-energy-density stable plasma region, thus solving the following problems: 1. Solving the problem of metal powder affecting TE in rectangular waveguides 10 The problem of strong perturbation in the electric field distribution is addressed by the fact that the electromagnetic field is geometrically axisymmetric. This reduces the asymmetric pulling and hot spot migration of the metal powder on the electric field in the discharge region, and suppresses the random drift of the standing wave nodes / antinodes.

[0027] 2. To address the issues of easy mismatch in coupling conditions and large fluctuations in reflected power, a waveguide-to-coaxial mode conversion coupling structure is adopted. This allows microwave energy to be stably transmitted in TEM mode within the coaxial section, and enables repeatable discharge excitation and energy deposition at the coaxial nozzle. This reduces abrupt changes in reflected power and discharge morphology caused by transient powder distribution, thereby improving the stable operating window of the discharge.

[0028] 3. To solve the problems of arc root offset, wall-attached discharge and discharge mode instability, the discharge electric field, airflow channel and powder delivery channel are arranged coaxially by the coaxial nozzle structure. The central inner conductor also serves as the powder delivery channel, so that the powder introduction path is aligned with the high field region, which promotes the plasma to form a stable column on the axis and avoids the irregular adhesion of the arc root to the tube wall.

[0029] 4. To solve the problem of difficulty in matching plasma heat source and powder trajectory, the high energy density plasma region formed by axisymmetric TEM field and coaxial nozzle is used to make the heat source center and powder stream spatially stable and coaxial, reduce the time fluctuation of temperature field and effective heating zone, and improve the repeatability and controllability of powder heating history.

[0030] 5. Completely eliminates the quartz tube-confined plasma mode, solving the problem of microwave transmission failure caused by quartz tube ablation and powder adhesion to the wall.

[0031] In one specific embodiment, the waveguide-to-coaxial structure is a frustum structure, which enables the equivalent impedance matching between the rectangular waveguide end and the coaxial transmission structure and discharge load. Optionally, the matching effect satisfies S11 (representing the input reflection coefficient (input return loss)) being less than -10dB and S21 (representing the forward transmission coefficient (gain)) being close to 0.

[0032] It should be noted that the key to the waveguide-to-coaxial structure lies in impedance matching: by adjusting the height H and bottom radius R of the frustum, the reflected power of the structure is minimized during operation, thereby reducing standing waves, increasing ignition success rate, and improving discharge stability. This matching effect can be verified through reflected power / VSWR or S-parameter tests.

[0033] In one specific embodiment, the frustum structure has a bottom radius of 40mm and a height of 54.6mm, and nitrogen is used for ignition testing. Figure 3 As shown, the microwave delivery efficiency is >98% under different power and flow rates. It should be noted that the frustum structure described may not be as... Figure 2 The top is directly connected to the powder feeding channel. It can have a platform, but the platform should not cause abrupt changes in the geometry inside the transition cavity. At the same time, the matching needs to be verified by the reflected power (or S11).

[0034] In one specific embodiment, the coaxial transmission structure includes a coaxial outer conductor and a coaxial inner conductor arranged coaxially, and the powder feeding channel is disposed within the coaxial inner conductor.

[0035] In the above embodiments, the coaxial outer conductor and the coaxial inner conductor are generally made of metal materials with good conductivity and heat and corrosion resistance (such as copper / stainless steel). The length and the size of the annular gap between the inner and outer conductors need to be matched with microwave transmission and discharge stability. The length of the outer conductor is usually taken on the order of one wavelength to reduce the influence of end reflection. The size of the annular gap forms a stable swirling flow field while ensuring low reflection energy transfer and avoiding breakdown and blockage. Finally, the size is determined by the reflection power and discharge / spheroidization stability.

[0036] In one specific embodiment, the coaxial inner conductor is integrated with the powder feeding channel. In this embodiment, the coaxial inner conductor may be lined with an insulating layer.

[0037] In one specific embodiment, the coaxial inner conductor is a straight tube or a tapered shape. In one specific embodiment, the electric field simulation using a straight tube or a tapered tube as the coaxial inner conductor is as follows: Figure 4 As shown. From Figure 4 It can be seen that regardless of whether a straight tube or a tube with a tapered tip is used as the coaxial inner conductor, a strong electric field can be generated at the tip. The straight tube offers lower powder feeding resistance, but the electric field concentration is weaker, and its stability depends on airflow and operating conditions. The tapered tip provides better ignition, stronger flame stability, and more concentrated spheroidization, but it is more demanding on particle size and powder feeding rate, and it is necessary to avoid excessively small tips that could cause powder blockage. The appropriate coaxial inner conductor can be selected based on the type of powder being processed.

[0038] In a specific embodiment, such as Figure 5 As shown, the air intake pipe adopts a tangential rotating air intake structure. The tangential rotating air intake structure is tangential to the coaxial outer conductor in the top view direction, forming tangential air intake; in the side view direction, the angle between the air intake pipe and the coaxial axis is 1-90°.

[0039] In the above embodiments, the tangential rotating air intake structure can form a more stable swirling flow field between the coaxial inner and outer conductors, making the plasma flame more axisymmetric and less prone to oscillation, while making it less likely for powder to hit the wall surface, thereby improving spheroidization uniformity and reducing wall adhesion loss.

[0040] In one specific embodiment, multiple intake pipes are provided. Optionally, the multiple intake pipes are arranged on the same horizontal plane and are evenly distributed around the coaxial transmission structure.

[0041] In this invention, the airflow blocking device is mainly used to prevent gas from flowing back into the rectangular waveguide, thus providing protection and heat insulation. In a specific embodiment, the airflow blocking device is made of quartz.

[0042] In one specific embodiment, simulation experiments were conducted using different air intake structures, and the results are as follows: Figure 6 As shown. From Figure 6 It can be seen that tangential air intake can significantly establish a stable swirling flow; on this basis, adding a blocking structure can further suppress the upper backflow and strengthen the downward swirling column, making the flow field more axisymmetric and more stable, which is more conducive to stabilizing the flame and improving the consistency of powder spheroidization.

[0043] It should be noted that, in this invention, the length of the nozzle can be set according to process requirements. The nozzle has a constraining and shaping effect on the flame; appropriately increasing the nozzle length can increase the effective action length of the powder in the high-temperature zone, thereby benefiting the spheroidization and stabilization of the processing window.

[0044] This device can be used for the spheroidization preparation of high-melting-point metals, high-melting-point alloys and high-melting-point oxide powders, including but not limited to copper and copper alloys, iron and iron alloys, titanium and titanium alloys, cobalt and cobalt alloys, tungsten and tungsten alloys, nickel and nickel alloys, ceramic powders, etc.

[0045] On the other hand, the present invention also provides a microwave plasma spheroidizing method, wherein spheroidizing is performed using any one of the microwave plasma spheroidizing devices described above.

[0046] Preferably, the method includes the following steps: S1: Microwaves are input into the rectangular waveguide through the microwave source, and the microwaves are input to the waveguide-to-coaxial structure in TE10 mode via the rectangular waveguide. S2: The waveguide-to-coaxial structure converts the microwave energy in TE10 mode into microwave energy in TEM mode. The microwave energy in TEM mode is then transmitted to the nozzle via the coaxial transmission structure and forms an electric field enhancement region. S3: Powder is delivered to the nozzle through the powder feeding channel, and plasma gas is input into the waveguide-to-coaxial structure through the air inlet pipe. The plasma gas forms a stable plasma flame in the electric field enhancement region and causes the powder to absorb heat and melt to form spherical droplets. S4: The spherical droplets are output from the nozzle and cooled and solidified to obtain spherical powder.

[0047] In a specific embodiment, copper powder was used as an example, and the microwave plasma spheroidization method described in this invention was employed for spheroidization treatment. In this embodiment (the waveguide-to-coaxial frustum dimensions are a bottom radius of 40mm and a height of 54.6mm. Additionally, the straight section of the coaxial outer conductor is 120mm long, the constricted section of the coaxial outer conductor is 60mm high and 61.41mm long; the coaxial inner conductor is a straight tube with a length of 180mm, an inner diameter of 6mm, and a wall thickness of 2mm. The rectangular waveguide section uses BJ22), the microwave input power was 500W, the plasma gas was 25L / min nitrogen, with two tangential gas inlets (90° inlet), and the powder carrier gas was 2L / min argon. The powder was axially fed into the coaxial inner conductor through a hollow channel. The product was observed using a UMT103i microscope, and the results are as follows... Figure 7 As shown. From Figure 7 It can be seen that the spheroidizing effect of the present invention is significant, and the spheroidizing rate error is small when different batches are tested with the same parameters.

[0048] In addition, a traditional, unmodified rectangular waveguide (TE) was also used. 10 A microwave plasma torch coupled to a mode (or similar) was used to spheroidize copper powder. Under the same microwave input power of 500W, the spheroidization results of different batches were as follows: Figure 8 As shown. The phenomenon of powder sticking to the wall of the quartz tube after spheroidization treatment is as follows. Figure 9 As shown. From Figure 8 and Figure 9 It can be seen that due to the instability of the discharge and spheroidization processes in traditional rectangular waveguides, the quality of spheroidized powder varies greatly under the same process conditions; at the same time, there is a phenomenon of powder sticking to the wall, which seriously affects microwave transmission, and simply adjusting the gas flow rate cannot solve the problem of wall sticking.

[0049] In summary, this invention enables the construction of more stable, axisymmetric, and high-energy-density microwave plasma regions, and more efficient and high-quality geochemical powders. Compared with existing technologies, this invention represents a significant advancement.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A microwave plasma spheroidizing device, characterized in that, It includes a microwave source, a rectangular waveguide, a waveguide-to-coaxial structure, a coaxial transmission structure, a nozzle, an airflow blocking device, and a powder feeding channel; The microwave source is connected to the rectangular waveguide. The waveguide-to-coaxial structure is disposed inside the rectangular waveguide. One end of the coaxial transmission structure is perpendicularly connected to the middle of the rectangular waveguide. The other end of the coaxial transmission structure is connected to the nozzle. An air inlet pipe is provided on the coaxial transmission structure. An airflow blocking device is provided inside the coaxial transmission structure between the air inlet pipe and the rectangular waveguide to prevent gas from entering. The powder feeding channel is coaxially arranged with the rectangular waveguide, the waveguide-to-coaxial structure, and the coaxial transmission structure, and the horizontal position of its end is flush with the top of the nozzle. The rectangular waveguide is used to convert the microwaves output from the microwave source into TE. 10 The mode input is fed to the waveguide-to-coaxial structure, which is used to transmit the TE signal. 10 The mode is switched to TEM mode, and the coaxial transmission structure is used to transmit the microwave energy of TEM mode to the nozzle, so that the plasma gas entering through the air inlet pipe forms a stable plasma flame at the nozzle.

2. The microwave plasma spheroidizing device according to claim 1, characterized in that, The waveguide-to-coaxial structure is a frustum structure, which enables the equivalent impedance between the rectangular waveguide end and the coaxial transmission structure and discharge load to be matched.

3. The microwave plasma spheroidizing device according to claim 1, characterized in that, The coaxial transmission structure includes a coaxial outer conductor and a coaxial inner conductor, and the powder feeding channel is disposed within the coaxial inner conductor.

4. The microwave plasma spheroidizing device according to claim 3, characterized in that, The coaxial inner conductor is integrated with the powder feeding channel.

5. The microwave plasma spheroidizing device according to claim 3, characterized in that, The coaxial inner conductor is a straight tube or has a pointed tip.

6. The microwave plasma spheroidizing device according to any one of claims 1-5, characterized in that, The air intake pipe adopts a tangential rotating air intake structure.

7. The microwave plasma spheroidizing device according to claim 6, characterized in that, The air intake pipe is provided in multiple parts.

8. The microwave plasma spheroidizing device according to claim 7, characterized in that, Multiple intake pipes are arranged on the same horizontal plane and are evenly distributed around the coaxial transmission structure.

9. A microwave plasma spheroidization method, characterized in that, Spheroidization is performed using the microwave plasma spheroidizing apparatus described in any one of claims 1-8.

10. The microwave plasma spheroidization method according to claim 9, characterized in that, Includes the following steps: S1: Microwaves are input into the rectangular waveguide through the microwave source, and the microwaves are transmitted through the rectangular waveguide at a TE... 10 The mode input is fed into the waveguide-to-coaxial structure; S2: The waveguide-to-coaxial structure enables TE 10 The microwave energy of the TEM mode is converted into microwave energy of the TEM mode, and the microwave energy of the TEM mode is transported to the nozzle through the coaxial transmission structure to form an electric field enhancement region. S3: Powder is delivered to the nozzle through the powder feeding channel, and plasma gas is input into the waveguide-to-coaxial structure through the air inlet pipe. The plasma gas forms a stable plasma flame in the electric field enhancement region and causes the powder to absorb heat and melt to form spherical droplets. S4: The spherical droplets are output from the nozzle and cooled and solidified to obtain spherical powder.

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