An apparatus and method for preparing nano-powders by microwave plasma

Abstract

This application relates to an apparatus and method for preparing nano-powders by microwave plasma. It includes: a conductor tube, which comprises a quartz tube and a powder feeding tube arranged inside the quartz tube. The quartz tube vertically penetrates through the plasma delivery pipeline, and both ends of the quartz tube are open. The space between the powder feeding tube and the quartz tube forms a gas channel. The powder feeding tube includes a powder feeding layer, a liquid inlet layer, and a liquid outlet layer arranged successively from the center outwards. The liquid inlet layer and the liquid outlet layer are connected at a position near the bottom of the powder feeding tube; a vaporization chamber, which is arranged below the quartz tube, and the lower ends of the quartz tube and the powder feeding tube are both located inside the vaporization chamber. The vaporization chamber includes a reaction chamber and a first liquid cooling layer arranged successively from the inside outwards. The reaction chamber includes a first conical tube, a first circular tube, a second conical tube, and a second circular tube connected successively from top to bottom. By designing a powder feeding tube with a three-layer structure, a vaporization chamber with a structure of first expanding and then converging, and a rapid cooling chamber including a delay layer, a second liquid cooling layer, and a gas cooling layer, this application can improve the powder preparation efficiency.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of additive manufacturing, and in particular, to an apparatus and method for preparing nano-powders by microwave plasma. Background Art

[0002] Nano-powders refer to powders with diameters in the range of 1 - 100 nm. At this scale, the physical and chemical properties of powder particles are quite different from those at the macroscopic scale, endowing them with characteristics such as surface effect, volume effect, and quantum size effect. Nano-powders have broad application prospects in many fields such as chemical catalysts, microporous materials, and conductive pastes. Microwave plasma uses microwaves as the heat source for generating plasma. Compared with DC and high-frequency plasmas, using microwaves has many unique advantages: (1) High energy efficiency. Microwave energy is directly coupled to gas molecules, with high energy utilization efficiency and rapid heating. (2) No electrode pollution. There is no internal electrode during microwave discharge, avoiding electrode material pollution and being suitable for the preparation and treatment of high-purity substances. (3) Mild reaction conditions. The electron temperature is high while the gas temperature is low, and it can operate at a lower gas pressure. (4) High safety. There is no high-voltage electrode, so the safety is relatively high. (5) Wide application range. It is not limited by electrode materials and frequencies and is applicable to various gases and reaction conditions. Based on the above advantages, microwave plasma has great potential and industrial application value in the application of material preparation, and thus has become a research hotspot at home and abroad.

[0003] In the related art, during the process of preparing nano-powders by microwave plasma, due to the too high position of the powder outlet of the powder feeding tube, when the raw material powder enters the gasification chamber from the powder feeding tube, it is easy to melt at the powder outlet position of the powder feeding tube and block the powder outlet; moreover, when the raw material powder enters the gasification chamber, due to the unreasonable structural design of the gasification chamber, the powder is not gasified sufficiently; when the powder is gasified, the gasified powder is not cooled thoroughly enough, thus affecting the efficiency of preparing nano-powders.

[0004] Therefore, it is necessary to improve one or more problems existing in the above-mentioned related technical solutions.

[0005] It should be noted that the information disclosed in the above background art section is only used to enhance the understanding of the background of the present application, and thus may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0006] The purpose of the embodiments of the present application is to provide an apparatus and method for preparing nano-powders by microwave plasma, which can overcome one or more problems caused by the limitations and defects of the related art to a certain extent.

[0007] According to the first aspect of the embodiments of the present application, there is provided an apparatus for preparing nano-powders by microwave plasma, including:

[0008] A plasma delivery pipe, one end of the plasma delivery pipe is open and the other end is blocked.

[0009] A conductor pipe, including a quartz pipe and a powder feeding pipe arranged inside the quartz pipe. The quartz pipe vertically penetrates the plasma delivery pipe. Both ends of the quartz pipe are open. The interval between the powder feeding pipe and the quartz pipe forms a gas passage. The powder feeding pipe includes a powder feeding layer, a liquid inlet layer, and a liquid outlet layer arranged in sequence from the center outwards. The liquid inlet layer and the liquid outlet layer are communicated at a position near the bottom of the powder feeding pipe. Wherein, a plurality of powder outlet openings are uniformly arranged on the bottom of the powder feeding pipe, and each powder outlet opening is communicated with the powder feeding layer.

[0010] A gasification chamber is arranged below the quartz pipe, and the lower end of the quartz pipe and the lower end of the powder feeding pipe are both located inside the gasification chamber. The gasification chamber includes a reaction chamber and a first liquid cooling layer arranged in sequence from the inside outwards. The reaction chamber includes a first conical pipe, a first circular pipe, a second conical pipe, and a second circular pipe connected in sequence from top to bottom. Wherein, the central axes of the first conical pipe, the first circular pipe, the second conical pipe, and the second circular pipe are collinear, and the diameter of the first circular pipe is larger than the diameter of the second circular pipe.

[0011] A quenching chamber is arranged below the gasification chamber. The quenching chamber is communicated with the gasification chamber. The quenching chamber includes a first cooling layer and a second cooling layer arranged in sequence from the outside inwards. The second cooling layer includes a delay layer, a second liquid cooling layer, and a gas cooling layer connected in sequence from top to bottom.

[0012] A separation collector is arranged below the quenching chamber and is communicated with the quenching chamber.

[0013] In an embodiment of the present application, the bottom of the powder feeding pipe is a spherical curved surface, and the opening direction of the powder outlet is the same as the radius direction of the spherical curved surface.

[0014] In an embodiment of the present application, the included angle between the conical surface of the first conical pipe and its central axis, and the included angle between the conical surface of the second conical pipe and its central axis are both 90±2°.

[0015] In an embodiment of the present application, the ratio of the diameter of the second circular pipe to the diameter of the first circular pipe is 2 / 7 - 1 / 3.

[0016] In an embodiment of the present application, the retardation layer includes a graphite ring. A circle of first air holes is arranged along the radial direction of the graphite ring inside the graphite ring, and an annular channel is arranged along the axial direction of the graphite ring on the peripheral wall of the graphite ring. A plurality of first air inlet holes are uniformly arranged on the first cooling layer; wherein, the central axis of the graphite ring coincides with the central axis of the second circular tube, each of the first air holes communicates with the annular channel, each of the first air holes communicates with the second circular tube, and the annular channel communicates with each of the first air inlet holes;

[0017] The second liquid cooling layer includes a guiding water jacket, and the upper surface of the guiding water jacket is a conical surface; wherein, the ratio of the diameter of the upper end of the upper surface of the guiding water jacket to the diameter of the lower end of the upper surface of the guiding water jacket is 1 / 3 - 1 / 2, and the ratio of the distance between the upper end and the lower end of the upper surface of the guiding water jacket to the diameter of the upper end of the upper surface of the guiding water jacket is greater than or equal to 1 / 2;

[0018] The air cooling layer includes a gas distribution ring, the gas distribution ring is uniformly provided with a plurality of second air holes, and the first cooling layer is uniformly provided with a plurality of second air inlet holes, and each of the second air inlet holes communicates with the second air holes.

[0019] In an embodiment of the present application, the included angle between the guiding water jacket and the horizontal direction is 80 ± 1°.

[0020] In an embodiment of the present application, the aperture of the second air holes is 2 - 3 mm.

[0021] In an embodiment of the present application, a plurality of third air inlet holes and a plurality of air outlet holes are arranged on the plasma delivery pipeline, and the diameters of both the third air inlet holes and the air outlet holes are less than 4 mm.

[0022] In an embodiment of the present application, the separation and collection device includes a separation chamber, a powder barrel and a vacuum system. The upper end of the separation chamber communicates with the rapid cooling chamber, the lower end of the separation chamber communicates with the powder barrel, and the separation chamber communicates with the vacuum system.

[0023] According to a second aspect of the embodiments of the present application, there is provided a method for preparing nano-powders by microwave plasma, including:

[0024] The plasma delivery pipeline conducts microwaves to the quartz tube of the conductor tube, and after being excited and coupled with the powder delivery tube in the quartz tube, a microwave torch is formed at the bottom of the powder delivery tube, and the microwave torch is ejected into the gasification chamber by the rotating gas in the gas channel;

[0025] The airflow carries the raw material powder into the powder feeding layer, and cools the powder outlet position at the bottom of the powder feeding pipe through the liquid inlet layer and the liquid outlet layer, so that the raw material powder can be smoothly ejected from the powder outlet and enter the gasification chamber;

[0026] When the raw material powder enters the vaporization chamber, the first conical tube in the reaction chamber cooperates with the powder outlet, and the raw material powder diffuses and fills the first conical tube and the first circular tube, so that the raw material powder is fully vaporized under the action of the microwave torch. Then, the vaporized powder is gathered under the action of the second conical tube and sent to the second circular tube. The first liquid cooling layer cools the reaction chamber.

[0027] Afterwards, the vaporized powder in the second circular tube is sent into a quenching chamber, where the vaporized powder is acted upon by a delaying layer in the quenching chamber to delay its falling, and then the vaporized powder is pre-cooled by a second liquid cooling layer, and then sent into an air cooling layer for rapid cooling, so that the vaporized powder solidifies to form a nanopowder. In particular, while the delaying layer acts on the vaporized powder and the second liquid cooling layer pre-cools the vaporized powder, the first cooling layer simultaneously cools the vaporized powder entering the quenching chamber throughout the entire process.

[0028] The nano powder is collected by a separation collector to obtain the nano powder with different particle sizes.

[0029] The technical solutions provided by the embodiments of the present application may have the following beneficial effects:

[0030] In the embodiments of the present application, through the above-mentioned device, with the designed powder feeding pipe having a three-layer structure, raw material powder enters the powder feeding layer, and the powder outlet position at the bottom of the powder feeding pipe is cooled through the liquid inlet layer and the liquid outlet layer, which can prevent the raw material powder from melting at the powder outlet position due to excessive temperature at the powder outlet position, resulting in blockage of the powder outlet, thereby ensuring the smooth progress of powder feeding; through the designed reaction chamber with a structure of first expanding and then converging, when the raw material powder enters the gasification chamber, under the cooperation of the first conical tube and the powder outlet, the raw material powder fills the first conical tube and the first circular tube in a diffusive trend, so that the raw material powder is fully gasified under the action of the microwave torch, and then the gasified powder is converged under the action of the second conical tube and concentrated and sent to the second circular tube, facilitating rapid quenching in the rapid quenching chamber; through the designed rapid quenching chamber including a delay layer, a second liquid cooling layer and a gas cooling layer, when the gasified powder enters the rapid quenching chamber, the gasified powder is acted on by the delay layer in the rapid quenching chamber to delay the falling of the gasified powder, and then the gasified powder is pre-cooled by the second liquid cooling layer, and then sent to the gas cooling layer for rapid cooling, so that the gasified powder solidifies to form nano-powder. The present application can improve the powder making efficiency by designing a powder feeding pipe with a three-layer structure, a gasification chamber with a structure of first expanding and then converging, and a rapid quenching chamber including a delay layer, a second liquid cooling layer and a gas cooling layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings herein are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts.

[0032] Figure 1 Showing a schematic structural diagram of a device for preparing nano-powder by microwave plasma in an exemplary embodiment of the present application;

[0033] Figure 2 Showing a schematic diagram of the angle between the horizontal component of the rotating gas and the tangent direction of the pipe wall in an exemplary embodiment of the present application;

[0034] Figure 3 Showing a flowchart of the steps of a method for preparing nano-powder by microwave plasma in an exemplary embodiment of the present application;

[0035] Figure 4 Showing a transmission electron microscope image of nano-copper powder;

[0036] Figure 5 Showing a transmission electron microscope image of nano-silicon powder.

[0037] In the figure: 100, plasma delivery pipeline; 110, blanking plate; 200, conductor tube; 210, quartz tube; 220, powder feeding tube; 221, powder feeding layer; 222, liquid inlet layer; 223, liquid outlet layer; 224, powder outlet; 300, gasification chamber; 310, reaction chamber; 311, first conical tube; 312, first round tube; 313, second conical tube; 314, second round tube; 320, first liquid cooling layer; 400, rapid cooling chamber; 410, first cooling layer; 411, first air inlet hole; 412, second air inlet hole; 420, second cooling layer; 421, graphite ring; 422, annular channel; 423, first air hole; 430, guiding water jacket; 440, air cooling layer; 441, air distribution ring; 442, second air hole; 500, separation and collection device; 510, separation chamber; 520, powder bucket; 530, vacuum system; 600, first flange; 700, second flange; 800, third flange; 900, fourth flange; 1000, fifth flange; 1100, sixth flange; 1200, seventh flange; 1300, eighth flange; 1400, ninth flange; 1500, first sealing ring; 1600, second sealing ring; 1700, third sealing ring; 1800, fourth sealing ring; 1900, fifth sealing ring. Detailed implementation manners

[0038] Example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments can be implemented in various forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this application will be more complete and comprehensive, and will fully convey the concept of the example embodiments to those skilled in the art. The features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments.

[0039] In addition, the drawings are only schematic illustrations of the embodiments of the present application and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and thus their repeated description will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0040] In this example embodiment, a device for preparing nano-powders by microwave plasma is first provided. Refer to Figure 1As shown in the figure, the device may include: a plasma delivery pipe 100, a conductor pipe 200, a gasification chamber 300, a quenching chamber 400, and a separation and collection device 500. Among them, one end of the plasma delivery pipe 100 is open, and the other end is blocked; the conductor pipe 200 includes a quartz pipe 210 and a powder feeding pipe 220 disposed inside the quartz pipe 210. The quartz pipe 210 vertically penetrates the plasma delivery pipe 100. Both ends of the quartz pipe 210 are open. The space between the powder feeding pipe 220 and the quartz pipe 210 forms a gas passage. The powder feeding pipe 220 includes a powder feeding layer 221, a liquid inlet layer 222, and a liquid outlet layer 223 arranged in sequence from the center to the outside. The liquid inlet layer 222 and the liquid outlet layer 223 are connected at a position close to the bottom of the powder feeding pipe 220; among them, a plurality of powder outlets 224 are evenly arranged on the bottom of the powder feeding pipe 220, and each powder outlet 224 is connected to the powder feeding layer 221; the gasification chamber 300 is disposed below the quartz pipe 210, and the lower ends of the quartz pipe 210 and the powder feeding pipe 220 are both located inside the gasification chamber 300. The gasification chamber 300 includes a reaction chamber 310 and a first liquid cooling layer 320 arranged in sequence from the inside to the outside. The reaction chamber 310 includes a first conical pipe 311, a first circular pipe 312, a second conical pipe 313, and a second circular pipe 314 connected in sequence from top to bottom; among them, the central axes of the first conical pipe 311, the first circular pipe 312, the second conical pipe 313, and the second circular pipe 314 are collinear, and the diameter of the first circular pipe 312 is greater than the diameter of the second circular pipe 314; the quenching chamber 400 is disposed below the gasification chamber 300, and the quenching chamber 400 is connected to the gasification chamber 300. The quenching chamber 400 includes a first cooling layer 410 and a second cooling layer 420 arranged in sequence from the outside to the inside. The second cooling layer 420 includes a delay layer, a second liquid cooling layer, and a gas cooling layer 440 connected in sequence from top to bottom; the separation and collection device 500 is disposed below the quenching chamber 400 and is connected to the quenching chamber 400.

[0041] It can be understood that the plasma delivery pipe 100 is a hollow cavity for the transmission of microwaves. One end of the plasma delivery pipe 100 is open, and a first flange 600 is welded to the open end. The other end of the plasma delivery pipe 100 is blocked, specifically by using a plug plate 110 for blocking. The plug plate 110 is connected to the other end of the plasma delivery pipe 100 through a second flange 700. The plug plate 110 is used to limit the divergence direction of microwaves. Among them, the first flange 600 and the second flange 700 are coaxially and oppositely arranged, with the inner holes concentric and the inner diameters equal. The microwaves are generated by a plasma generator. The process of generating microwaves by the plasma generator can be understood with reference to the prior art, and this application will not elaborate on it.

[0042] The inner duct is used to couple with microwaves to generate a microwave torch. Specifically, when microwaves are conducted through the plasma delivery pipe 100 to the quartz tube 210 of the conductor tube 200, they are coupled with the powder delivery tube 220 in the quartz tube 210 after excitation, and a microwave torch is formed at the bottom of the powder delivery tube 220. The microwave torch is ejected into the gasification chamber 300 by the rotating gas in the gas passage. Among them, the gas passage is formed by the gap between the powder delivery tube 220 and the quartz tube 210. Three-way rotating gas cutting the wall downward is configured at the top of the gas passage. The air inlets of the three-way rotating gas are evenly arranged on the circumference of the top of the quartz tube 210. The rotating gas makes a spiral movement downward along the arc surface of the tube wall, as Figure 2 shown. The component of the rotating gas in the horizontal direction has an angle with the tangent direction of the tube wall, and this angle can be 30 - 60°. Setting this angle within the range of 30 - 60° can maintain a positive pressure inside the quartz tube 210 and prevent the gas in the quartz tube 210 from turbulent flow and backflow. In addition to ejecting the microwave torch into the gasification chamber 300, the rotating gas can also cool the quartz tube 210 to prevent the temperature of the quartz tube 210 from being too high. Moreover, the rotating gas can also form a gas wall to prevent the raw material powder from sticking to the wall and affecting the transmission of microwaves. It should be noted that the tube wall here refers to the wall of the quartz tube 210.

[0043] It should also be noted that the plasma delivery pipe 100 is jointly restricted by the quartz tube 210 and the rotating gas in the gas passage to control the microwave torch to provide appropriate torch parameters (such as the diameter, length, and temperature of the microwave torch). The diameter of the microwave torch can be controlled by the quartz tube 210, and the length of the microwave torch can be adjusted by the flow rate and pressure of the rotating gas.

[0044] In this application, the inner duct includes the quartz tube 210 and the powder delivery tube 220 arranged inside the quartz tube 210. The powder delivery tube 220 has a three-layer structure including a powder delivery layer 221, a liquid inlet layer 222, and a liquid outlet layer 223 arranged in sequence from the center to the outside. Setting the powder delivery layer 221 in the middle position of the powder delivery tube 220 can ensure the maximum utilization of the energy of the microwave torch. The liquid inlet layer 222 and the liquid outlet layer 223 are connected at a position close to the bottom of the powder delivery tube 220, which can better cool the powder outlet 224 of the powder delivery tube 220 and prevent the temperature of the powder outlet 224 at the bottom of the powder delivery tube 220 from being too high, resulting in the melting of the raw material powder at the powder outlet 224 and blocking the powder outlet 224. The number of powder outlets 224 can be set according to the actual situation, and this application does not limit this.

[0045] It should be noted that the specific connection relationship between the quartz tube 210 and the plasma delivery pipe 100 is as follows:

[0046] The upper end of the quartz tube 210 is connected to the plasma delivery pipeline 100 through the third flange 800, and the lower end of the quartz tube 210 is connected to the plasma delivery pipeline 100 through the fourth flange 900, so as to enable the quartz tube 210 to vertically penetrate through the plasma delivery pipeline 100. Wherein, the wall thickness of the quartz tube 210 is 4 - 6 mm, and both the inner surface and the outer surface of the quartz tube 210 are smooth. The inner diameters of the third flange 800 and the fourth flange 900 are equal, and the outer diameter of the quartz tube 210 is slightly smaller than the inner diameter of the third flange 800, which is convenient for connecting the quartz tube 210 to the plasma delivery pipeline 100 through the third flange 800 and the fourth flange 900.

[0047] Furthermore, in order to ensure the sealed connection between the quartz tube 210 and the plasma delivery pipeline 100, when the upper end of the quartz tube 210 is connected to the plasma delivery pipeline 100 through the third flange 800 in this application, a first sealing ring 1500 is also provided to achieve the sealed connection between the upper end of the quartz tube 210 and the plasma delivery pipeline 100. When the lower end of the quartz tube 210 is connected to the plasma delivery pipeline 100 through the fourth flange 900, a second sealing ring 1600 is also provided to achieve the sealed connection between the lower end of the quartz tube 210 and the plasma delivery pipeline 100. Wherein, both the third flange 800 and the fourth flange 900 are provided with 45° internal chamfers for placing the corresponding sealing rings. Both the first sealing ring 1500 and the second sealing ring 1600 are O-ring seals, and the materials of the first sealing ring 1500 and the second sealing ring 1600 are both rubber.

[0048] In this application, the gasification chamber 300 is of a double-layer structure, and the gasification chamber 300 includes a reaction chamber 310 and a first liquid cooling layer 320. The reaction chamber 310 has a structure of first expanding and then converging, and the reaction chamber 310 is used to fully gasify the raw material powder entering the reaction chamber 310. Specifically, when the raw material powder enters the reaction chamber 310, with the cooperation of the first conical tube 311 and the powder outlet 224, and by designing the diameter of the first circular tube 312 to be larger than the diameter of the second circular tube 314, the raw material powder is filled in the first conical tube 311 and the first circular tube 312 in a diffusive trend, and is fully gasified under the action of the microwave torch, and then the gasified powder is converged under the action of the second conical tube 313 and sent to the second circular tube 314 in a concentrated manner, which is convenient for entering the rapid cooling chamber 400 for rapid quenching. Wherein, the first liquid cooling layer 320 is used to cool down the reaction chamber 310 to prevent the temperature in the reaction chamber 310 from being too high, which affects the gasification of the raw material powder.

[0049] It should be noted that the specific connection relationship between the gasification chamber 300 and the quartz tube 210 is as follows: The lower end of the quartz tube 210 is located inside the gasification chamber 300. The gasification chamber 300 is connected to the quartz tube 210 through the fifth flange 1000. At the same time, the fifth flange 1000 and the fourth flange 900 are connected by screws. The lower end of the gasification chamber 300 is provided with a sixth flange 1100. Among them, in order to ensure the sealed connection between the fifth flange 1000 and the fourth flange 900, a third sealing ring 1700 is also provided between the fifth flange 1000 and the fourth flange 900.

[0050] In this application, the quench chamber 400 is also a double-layer structure, including a first cooling layer 410 and a second cooling layer 420. The second cooling layer 420 includes a delay layer, a second liquid cooling layer, and a gas cooling layer 440 connected in sequence from top to bottom. Among them, the delay layer is used to act on the gasified powder to make the gasified powder fall slowly. The second liquid cooling layer is used to pre-cool the gasified powder that falls slowly. The gas cooling layer 440 is used to rapidly cool the pre-cooled gasified powder so that the gasified powder solidifies to form nano-powder. The first cooling layer 410 cools the gasified powder entering the quench chamber 400 throughout the process.

[0051] It should be noted that the specific connection relationship between the quench chamber 400 and the gasification chamber 300 is as follows:

[0052] The quench chamber 400 is connected to the gasification chamber 300 through the seventh flange 1200. At the same time, the seventh flange 1200 and the sixth flange 1100 are connected by screws. Among them, in order to ensure the sealed connection between the seventh flange 1200 and the sixth flange 1100, a fourth sealing ring 1800 is also provided between the seventh flange 1200 and the sixth flange 1100.

[0053] In this application, the separation and collection device 500 is located below the quench chamber 400 and is connected to the quench chamber 400, and is used to collect the nano-powder to obtain nano-powders with different particle sizes.

[0054] It should be noted that the specific connection relationship between the separation and collection device 500 and the quench chamber 400 is as follows:

[0055] The lower end of the quench chamber 400 is provided with an eighth flange 1300. The separation and collection device 500 is connected to the quench chamber 400 through the ninth flange 1400. At the same time, the ninth flange 1400 and the eighth flange 1300 are connected by screws. Among them, in order to ensure the sealed connection between the ninth flange 1400 and the eighth flange 1300, a fifth sealing ring 1900 is also provided between the ninth flange 1400 and the eighth flange 1300.

[0056] In the embodiments of the present application, through the above-mentioned device, with the designed powder feeding pipe 220 having a three-layer structure, the raw material powder enters the powder feeding layer 221, and the powder outlet 224 at the bottom of the powder feeding pipe 220 is cooled through the liquid inlet layer 222 and the liquid outlet layer 223, which can prevent the raw material powder from melting at the position of the powder outlet 224 due to excessive temperature at the powder outlet 224, resulting in blockage of the powder outlet 224, thereby ensuring the smooth progress of powder feeding; through the designed reaction chamber 310 with a structure of first expanding and then converging, when the raw material powder enters the gasification chamber 300, under the cooperation of the first conical tube 311 and the powder outlet 224, the raw material powder fills the first conical tube 311 and the first circular tube 312 in a diffused trend, so that the raw material powder is fully gasified under the action of the microwave torch, and then the gasified powder is converged under the action of the second conical tube 313 and concentratedly sent to the second circular tube 314, facilitating rapid quenching in the rapid quenching chamber 400; through the designed rapid quenching chamber 400 including a delaying layer, a second liquid cooling layer and a gas cooling layer 440, when the gasified powder enters the rapid quenching chamber 400, the delaying layer in the rapid quenching chamber 400 acts on the gasified powder to delay the falling of the gasified powder, and then the gasified powder is pre-cooled by the second liquid cooling layer, and then sent to the gas cooling layer 440 for rapid cooling, so that the gasified powder solidifies to form nano-powder. The design of the present application through the powder feeding pipe 220 with a three-layer structure, the gasification chamber 300 with a structure of first expanding and then converging, and the rapid quenching chamber 400 including a delaying layer, a second liquid cooling layer and a gas cooling layer 440 can improve the powder making efficiency.

[0057] Next, reference will be made to Figure 1 to describe each part of the above-mentioned device for preparing nano-powder by microwave plasma in the present exemplary embodiment in more detail.

[0058] In one embodiment, the bottom of the powder feeding pipe 220 is a spherical curved surface, and the opening direction of the powder outlet 224 is consistent with the radius direction of the spherical curved surface.

[0059] It can be understood that the opening direction of the powder outlet 224 being consistent with the radius direction of the spherical curved surface can achieve the full dispersion of the raw material powder and the rapid synchronous powder feeding of multiple powder outlets 224, so as to maximize the utilization of the microwave torch energy.

[0060] In one embodiment, the angle between the conical surface of the first conical tube 311 and its central axis, and the angle between the conical surface of the second conical tube 313 and its central axis are both 90±2°.

[0061] It can be understood that if the included angle between the conical surface of the first conical tube 311 and its central axis is too small, it is not conducive to the diffusion of the raw material powder. If the included angle between the conical surface of the first conical tube 311 and its central axis is too large, the pressure of the gas entering the reaction chamber 310 from the powder feeding tube 220 will be weakened, which is not conducive to the movement of the raw material powder towards the middle first circular tube 312. Therefore, in this application, the included angle between the conical surface of the first conical tube 311 and its central axis is set to 90±2°, which can enable the gas and the raw material powder coming out of the powder outlet 224 at the bottom of the powder feeding tube 220 to diffuse quickly for sufficient gasification.

[0062] The included angle between the conical surface of the second conical tube 313 and its central axis is 90±2°, which can quickly gather the gasified powder obtained after sufficient gasification in the middle first circular tube 312, facilitating subsequent entry into the quenching chamber 400. If the included angle between the conical surface of the second conical tube 313 and its central axis is too large, it is easy for the gasified powder to accumulate on the conical surface of the second conical tube 313.

[0063] In one embodiment, the ratio of the diameter of the second circular tube 314 to the diameter of the first circular tube 312 is 2 / 7 - 1 / 3.

[0064] It can be understood that by designing the ratio of the diameter of the second circular tube 314 to the diameter of the first circular tube 312 to be 2 / 7 - 1 / 3, it can ensure that the gas in the quenching chamber 400 does not flow back into the gasification chamber 300.

[0065] In one embodiment, the retardation layer includes a graphite ring 421. A circle of first air holes 423 is arranged along the radial direction of the graphite ring 421 inside the graphite ring 421, and an annular channel 422 is arranged along the axial direction of the graphite ring 421 on the peripheral wall of the graphite ring 421. A number of first air inlet holes 411 are evenly arranged on the first cooling layer 410; wherein, the central axis of the graphite ring 421 is collinear with the central axis of the second circular tube 314, each first air hole 423 is communicated with the annular channel 422, each first air hole 423 is communicated with the second circular tube 314, and the annular channel 422 is communicated with each first air inlet hole 411;

[0066] The second liquid cooling layer includes a guiding water jacket 430, and the upper surface of the guiding water jacket 430 is a conical surface; wherein, the ratio of the diameter of the upper end of the upper surface of the guiding water jacket 430 to the diameter of the lower end of the upper surface of the guiding water jacket 430 is 1 / 3 - 1 / 2, and the ratio of the distance between the upper end and the lower end of the upper surface of the guiding water jacket 430 to the diameter of the upper end of the upper surface of the guiding water jacket 430 is greater than or equal to 1 / 2;

[0067] The air-cooling layer 440 includes a gas distribution ring 441. A number of second air holes 442 are evenly arranged on the gas distribution ring 441. A number of second air inlets 412 are evenly arranged on the first cooling layer 410. Each second air inlet 412 communicates with a second air hole 442.

[0068] It can be understood that a circle of first air holes 423 is arranged along the radial direction of the inside of the graphite ring 421. The height position of the first air holes 423 is in the middle of the graphite ring 421. When preparing the nano powder, an inert gas is introduced from the outside to the inside through the first air inlets 411 on the first cooling layer 410. The inert gas enters the annular channel 422 and then enters the second air holes 442 distributed along the radial direction to form an air wall, which cooperates with the heat preservation effect of the graphite ring 421 to delay the falling of the vaporized powder and enhance the vaporization effect. The vaporized powder enters the area where the guiding water jacket 430 is located, and the guiding water jacket 430 pre-cools the vaporized powder. Among them, the inert gas is nitrogen or argon. The number of the first air inlets 411 and the number of the second air holes 442 can both be set according to the actual situation, and the present application does not limit this.

[0069] Furthermore, the number of the first air inlets 411 can be 4. The 4 first air inlets 411 are evenly distributed along the peripheral wall of the first cooling layer 410. Each first air inlet 411 communicates with the annular channel 422. The inner diameter of the first air inlet 411 is 16 mm.

[0070] At the same time, since the upper surface of the guiding water jacket 430 is a conical surface, and the ratio of the diameter of the upper end of the upper surface of the guiding water jacket 430 to the diameter of the lower end of the upper surface of the guiding water jacket 430 is 1 / 3 - 1 / 2, and the ratio of the distance between the upper end and the lower end of the upper surface of the guiding water jacket 430 to the diameter of the upper end of the upper surface of the guiding water jacket 430 is greater than or equal to 1 / 2. Designing the guiding water jacket 430 in this way can make the guiding water jacket 430 restrict the reduction of its diameter and facilitate better pre-cooling of the vaporized powder.

[0071] After the pre-cooling is completed, the pre-cooled vaporized powder enters the gas distribution ring 441. At the same time, a large flow of cooling gas is introduced into the area where the gas distribution ring 441 is located through the second air inlets 412 and the second air holes 442 evenly distributed on the gas distribution ring 441 to rapidly cool the pre-cooled vaporized powder and solidify it to form nano powder.

[0072] In one embodiment, the included angle between the guiding water jacket 430 and the horizontal direction is 80 ± 1°.

[0073] It can be understood that in order for the guiding water jacket 430 to restrict the reduction of its diameter and better pre-cool the vaporized powder, the included angle between the guiding water jacket 430 and the horizontal direction is designed to be 80 ± 1°.

[0074] In one embodiment, the aperture diameter of the second air hole 442 is 2 - 3 mm.

[0075] It can be understood that designing the aperture diameter of the second air hole 442 to be 2 - 3 mm facilitates the introduction of cooling gas into the area where the gas distribution ring 441 is located. The aperture diameter of the second air hole 442 can be 2 mm, 2.3 mm, 2.5 mm, 2.7 mm, 3 mm, etc., and can be specifically set according to the actual situation, and this application does not limit this.

[0076] In one embodiment, a plurality of third air inlet holes are provided on the plasma delivery pipe 100, and a plurality of air outlet holes are provided on the plasma delivery pipe 100. The diameters of both the third air inlet holes and the air outlet holes are less than 4 mm.

[0077] It can be understood that the third air inlet holes are used to introduce cooling gas to cool the plasma delivery pipe 100, and the air outlet holes are used for the outflow of the cooling gas after cooling the plasma delivery pipe 100. Among them, since microwaves cannot pass through holes with a diameter less than 4 mm, in order to prevent microwave leakage while cooling the plasma delivery pipe 100, this application designs the diameters of both the third air inlet holes and the air outlet holes to be less than 4 mm. The number of the third air inlet holes and the number of the air outlet holes can be set according to the actual situation, and this application does not limit this.

[0078] In one embodiment, the separation and collection device 500 includes a separation chamber 510, a powder barrel 520, and a vacuum system 530. The upper end of the separation chamber 510 is communicated with the rapid cooling chamber 400, the lower end of the separation chamber 510 is communicated with the powder barrel 520, and the separation chamber 510 is communicated with the vacuum system 530.

[0079] It can be understood that the number of the powder barrels 520 can be set according to the actual situation, and this application does not limit this. The separation chamber 510 and the vacuum system 530 are used to collect nano - powders with different particle sizes into the corresponding powder barrels 520.

[0080] In this exemplary embodiment, a method for preparing nano - powders by microwave plasma is also provided. Using the device for preparing nano - powders by microwave plasma in any of the above - mentioned embodiments for powder preparation, refer to Figures 1 to 3 , this method includes: step S101 to step S105.

[0081] Among them, step S101: The plasma delivery pipe 100 conducts microwaves to the quartz tube 210 of the conductor tube 200. After being excited and coupled with the powder delivery tube 220 in the quartz tube 210, a microwave torch is formed at the bottom of the powder delivery tube 220, and the microwave torch is ejected into the gasification chamber 300 by the rotating gas in the gas channel.

[0082] Step S102: The airflow entrains the raw material powder into the powder feeding layer 221, and the powder outlet 224 position on the bottom of the powder feeding pipe 220 is cooled by the liquid inlet layer 222 and the liquid outlet layer 223, so that the raw material powder can be smoothly ejected from the powder outlet 224 and enter the gasification chamber 300.

[0083] Step S103: When the raw material powder enters the gasification chamber 300, under the cooperation of the first conical tube 311 and the powder outlet 224 in the reaction chamber 310, the raw material powder fills the first conical tube 311 and the first circular tube 312 in a diffusion trend, so that the raw material powder is fully gasified under the action of the microwave torch, and then the gasified powder is converged under the action of the second conical tube 313 and concentrated and sent to the second circular tube 314; wherein, the first liquid cooling layer 320 cools the reaction chamber 310.

[0084] Step S104: After that, the gasified powder in the second circular tube 314 is sent into the quenching chamber 400, and the gasified powder is acted on by the delaying layer in the quenching chamber 400 to delay the falling of the gasified powder, and then the gasified powder is pre-cooled by the second liquid cooling layer, and then sent into the air cooling layer 440 for rapid cooling, so that the gasified powder solidifies to form nano-powder; wherein, during the process of the delaying layer acting on the gasified powder and during the process of the second liquid cooling layer pre-cooling the gasified powder, the first cooling layer 410 simultaneously cools the gasified powder entering the quenching chamber 400 throughout the process.

[0085] Step S105: The nano-powder is collected by the separation collector 500 to obtain nano-powders with different particle sizes.

[0086] It should be noted that the method for preparing nano-powder by microwave plasma in this application has been described in the above-mentioned equipment for preparing nano-powder by microwave plasma, and this application will not elaborate on it.

[0087] The following further elaborates on this application through the following embodiments.

[0088] Example 1

[0089] Start the vacuum system 530, evacuate the closed chamber composed of the reaction chamber 310, the quenching chamber 400, and the separation collector 500 to 1.0×10 -2 Pa, and then fill the closed chamber with high-purity nitrogen until the pressure in the closed chamber reaches 8×10 4 Pa;

[0090] Set the power of the plasma generator to 12 kW, generate a microwave torch at the middle position of the reaction chamber 310, set the diameter of the microwave torch to 75 - 80 mm, and the length of the microwave torch to 300 - 330 mm;

[0091] At the top of the starting gas channel, three-way tangential downward-rotating gas, with a single gas flow rate of 200 - 300 L / min, an inlet gas pressure of 4 - 5 Bar, and a gas temperature of 10 - 15 °C.

[0092] Irregular copper powder with a diameter of 20 - 30 μm is fed. A total of 5 powder outlets 224 with a diameter of 3 mm each are provided at the bottom of the powder feeding pipe 220, and the powder feeding amount of a single powder outlet 224 is 1 - 2 g / min.

[0093] Start the graphite ring 421 in the quench chamber 400 to form a gas wall with a gas diameter of 80 mm and a thickness of 2 mm, so that the gasified copper powder stays in the high-temperature zone for 0.5 - 1.0 s.

[0094] Start the second air holes 442 of the gas distribution ring 441 in the quench chamber 400, and control the intake air volume of the cooling gas at 500 - 600 L / min.

[0095] Collect nano-copper powder with a particle size of 10 - 50 nm at the bottom of the powder bucket 520.

[0096] Figure 4 This is the transmission electron microscope image of the nano-copper powder. It can be seen from it that the sphericity of the nano-copper powder is improved, the yield of the nano-copper powder is higher, and the particle size is smaller.

[0097] Example 2

[0098] Start the vacuum system 530 to evacuate the closed chamber composed of the reaction chamber 310, the quench chamber 400, and the separation and collection device 500 to 1.0×10 -2 Pa, and then fill the closed chamber with high-purity nitrogen until the pressure of the closed chamber reaches 8×10 4 Pa;

[0099] Set the power of the plasma generator to 12 kW to generate a microwave torch at the middle position of the reaction chamber 310. Set the diameter of the microwave torch to 75 - 80 mm and the length of the microwave torch to 350 - 400 mm;

[0100] At the top of the starting gas channel, three-way tangential downward-rotating gas, with a single gas flow rate of 300 - 350 L / min, an inlet gas pressure of 4 - 5 Bar, and a gas temperature of 10 - 15 °C.

[0101] Irregular silicon powder with a diameter of 1 - 10 μm is fed. A total of 7 powder outlets 224 with a diameter of 4 mm each are provided at the bottom of the powder feeding pipe 220, and the powder feeding amount of a single powder outlet 224 is 0.5 - 1.0 g / min.

[0102] Start the graphite ring 421 in the quench chamber 400 to form a gas wall with a gas volume diameter of 80 mm and a thickness of 2 mm, so that the gasified silicon powder stays in the high-temperature zone for 1 - 1.5 s.

[0103] Start the second air hole 442 of the gas distribution ring 441 in the quench chamber 400, and control the intake air volume of the cooling gas at 650 - 700 L / min.

[0104] Collect nano-silicon powder with a particle size of 10 - 30 nm at the bottom of the powder barrel 520.

[0105] Figure 5 This is a transmission electron microscope image of nano-silicon powder. It can be seen from it that the sphericity of the nano-silicon powder is improved, the yield of the nano-silicon powder is higher, and the particle size is smaller.

[0106] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of this application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0107] Those skilled in the art will readily think of other implementation schemes of this application after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of this application, and these variations, uses or adaptations follow the general principles of this application and include the common general knowledge or conventional technical means in the technical field not disclosed in this application.

Claims

1. An apparatus for preparing nano-powders by microwave plasma, characterized in that, Comprising: A plasma delivery pipe, one end of the plasma delivery pipe is open and the other end is blocked; A conductor pipe, including a quartz pipe and a powder feeding pipe arranged inside the quartz pipe. The quartz pipe vertically penetrates the plasma delivery pipe. Both ends of the quartz pipe are open. The space between the powder feeding pipe and the quartz pipe forms a gas channel. The powder feeding pipe includes a powder feeding layer, a liquid inlet layer, and a liquid outlet layer arranged in sequence from the center outwards. The liquid inlet layer and the liquid outlet layer are communicated at a position close to the bottom of the powder feeding pipe. Wherein, a plurality of powder outlet openings are uniformly arranged on the bottom of the powder feeding pipe, and each powder outlet opening is communicated with the powder feeding layer; A gasification chamber, arranged below the quartz pipe, and the lower ends of the quartz pipe and the powder feeding pipe are both located inside the gasification chamber. The gasification chamber includes a reaction chamber and a first liquid cooling layer arranged in sequence from the inside outwards. The reaction chamber includes a first conical pipe, a first circular pipe, a second conical pipe, and a second circular pipe connected in sequence from top to bottom. Wherein, the central axes of the first conical pipe, the first circular pipe, the second conical pipe, and the second circular pipe are collinear, and the diameter of the first circular pipe is larger than the diameter of the second circular pipe; A quenching chamber, arranged below the gasification chamber. The quenching chamber is communicated with the gasification chamber. The quenching chamber includes a first cooling layer and a second cooling layer arranged in sequence from the outside inwards. The second cooling layer includes a delay layer, a second liquid cooling layer, and a gas cooling layer connected in sequence from top to bottom; A separation and collector, arranged below the quenching chamber and communicated with the quenching chamber.

2. The apparatus for preparing nano-powders by microwave plasma according to claim 1, wherein, The bottom of the powder feeding pipe is a spherical curved surface, and the opening direction of the powder outlet opening is consistent with the radius direction of the spherical curved surface.

3. The device for preparing nanopowder by microwave plasma according to claim 1, characterized in that: The included angle between the conical surface of the first conical pipe and its central axis, and the included angle between the conical surface of the second conical pipe and its central axis are both 90±2°.

4. The device for preparing nanopowder by microwave plasma according to claim 1, characterized in that: The ratio of the diameter of the second circular pipe to the diameter of the first circular pipe is 2 / 7 - 1 / 3.

5. The apparatus for preparing nano-powders by microwave plasma according to claim 1, characterized in that, The delay layer includes a graphite ring. A circle of first air holes is arranged radially inside the graphite ring along the graphite ring. An annular channel is arranged axially on the peripheral wall of the graphite ring along the graphite ring. A plurality of first air inlet holes are uniformly arranged on the first cooling layer. Wherein, the central axis of the graphite ring is collinear with the central axis of the second circular pipe. Each first air hole is communicated with the annular channel, each first air hole is communicated with the second circular pipe, and the annular channel is communicated with each first air inlet hole; The second liquid cooling layer includes a guiding water jacket, and the upper surface of the guiding water jacket is a conical surface. Wherein, the ratio of the diameter of the upper end of the upper surface of the guiding water jacket to the diameter of the lower end of the upper surface of the guiding water jacket is 1 / 3 - 1 / 2, and the ratio of the distance between the upper end and the lower end of the upper surface of the guiding water jacket to the diameter of the upper end of the upper surface of the guiding water jacket is greater than or equal to 1 / 2; The gas cooling layer includes a gas distribution ring. The gas distribution ring is uniformly provided with a plurality of second air holes. A plurality of second air inlet holes are uniformly arranged on the first cooling layer, and each second air inlet hole is communicated with the second air hole.

6. The apparatus for preparing nano-powders by microwave plasma according to claim 5, characterized in that, The included angle between the guide water jacket and the horizontal direction is 80±1°.

7. The device for preparing nanopowder by microwave plasma according to claim 6, characterized in that: The diameter of the second pores is 2-3 mm.

8. The device for preparing nano-powders by microwave plasma according to claim 1, characterized in that, A plurality of third air inlet holes are provided on the plasma delivery pipe, and a plurality of air outlet holes are provided on the plasma delivery pipe. The diameters of the third air inlet holes and the air outlet holes are both less than 4 mm.

9. The apparatus for preparing nano-powders by microwave plasma according to claim 1, wherein, The separation collector includes a separation chamber, a powder barrel and a vacuum system. The upper end of the separation chamber is communicated with the quenching chamber, the lower end of the separation chamber is communicated with the powder barrel, and the separation chamber is communicated with the vacuum system.

10. A method for preparing nano-powders by microwave plasma, characterized in that, The device for preparing nanopowder using microwave plasma according to any one of claims 1 to 9 is used for powder preparation, comprising: The plasma delivery pipe transmits the microwave to the quartz tube of the conductor tube, which is excited and coupled with the powder delivery tube in the quartz tube, forming a microwave torch at the bottom of the powder delivery tube. The rotating gas in the gas channel sprays the microwave torch into the gasification chamber. The airflow carries the raw material powder into the powder feeding layer, and cools the powder outlet position at the bottom of the powder feeding pipe through the liquid inlet layer and the liquid outlet layer, so that the raw material powder can be smoothly ejected from the powder outlet and enter the gasification chamber; When the raw material powder enters the vaporization chamber, the first conical tube in the reaction chamber cooperates with the powder outlet, and the raw material powder diffuses and fills the first conical tube and the first circular tube, so that the raw material powder is fully vaporized under the action of the microwave torch. Then, the vaporized powder is gathered under the action of the second conical tube and sent to the second circular tube. The first liquid cooling layer cools the reaction chamber. Afterwards, the vaporized powder in the second circular tube is sent into a quenching chamber, where the vaporized powder is acted upon by a delaying layer in the quenching chamber to delay its falling, and then the vaporized powder is pre-cooled by a second liquid cooling layer, and then sent into an air cooling layer for rapid cooling, so that the vaporized powder solidifies to form a nanopowder. In particular, while the delaying layer acts on the vaporized powder and the second liquid cooling layer pre-cools the vaporized powder, the first cooling layer simultaneously cools the vaporized powder entering the quenching chamber throughout the entire process. The nano powder is collected by a separation collector to obtain the nano powder with different particle sizes.

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