Device and method for preparing nano dispersed composite powder based on plasma gasification

Abstract

The invention discloses a device and method for preparing nano dispersed composite powder based on plasma gasification, and belongs to the technical field of nano material preparation. A non-transferred arc plasma torch is adopted as a core, different metal raw materials are independently evaporated through a plurality of plasma gasification furnaces connected in parallel, and a primary cooler, a phase cooling mixing tower and a gas-solid separation system are matched for cooperative work; the method specifically comprises the following steps: a plasma gasification system generates high-temperature plasma (200-500 DEG C above the boiling point of metal) through a non-transferred arc plasma torch, and dynamically adjusts the height of a crucible to maintain the gasification rate; the primary cooler (1600-2100 DEG C) enables the metal vapor to be nucleated and crystallized into nano-particles, and agglomeration is inhibited; the phase cooling mixing tower realizes uniform compounding of multiple components by utilizing liquid nitrogen quenching and nitrogen flow stirring; the method has the advantages of continuous production, controllable components, good dispersity, high safety and the like, and is suitable for industrial preparation of the multi-element nano alloy powder.

Description

Technical Field

[0001] The present invention relates to an apparatus and method for preparing nano alloy powder, in particular to an apparatus and method for preparing nano-dispersed composite powder based on plasma. Technical Background

[0002] Nano materials are currently the most promising materials. Nano materials, namely ultra-fine crystal materials, are composed of single-phase, multi-phase crystals, quasi-crystals or amorphous-phase pure metals, multi-element alloys, intermetallic compounds, ceramics or composite materials. Their crystal size is 1-100 nm in one-dimensional scale. Due to their small crystal size, they have better ductility, superplasticity, strength, magnetism and optoelectronic properties than general static materials.

[0003] Currently, the main methods for preparing nano materials include mechanical pulverization method, evaporation condensation method, sol-gel method, chemical vapor deposition method, etc. The physical fragmentation method is a preparation method obtained by mechanical pulverization, electrospark explosion, etc. Its characteristics are simple operation and low cost, but the product purity is low, the particle size distribution is uneven, and there is a possibility of combustion and explosion during the pulverization process. The evaporation condensation method is to heat and evaporate the raw materials to make them into atoms or molecules, and then condense many atoms or molecules to generate fine nano particles. This preparation process generally does not involve chemical reactions such as combustion, and the whole process is a physical change process. Its characteristics are high purity, good crystal structure and controllable particle size. This process melts and vaporizes the material, requires a high heating temperature and high requirements for equipment. The sol-gel method is a preparation method in which metal compounds are solidified through solution, sol and gel, and then nano particles are generated through low-temperature heat treatment. This method is suitable for the preparation of oxides and II-VI group compounds and is not suitable for the preparation of simple substances; the chemical vapor deposition method is to synthesize nano powder by using chemical reactions between metal compound vapors. Its characteristics are high product purity and narrow particle size distribution, but it is difficult to collect.

[0004] In China, Patent ZL200410021190.1 and ZL 201410189518.4 respectively target the technology of mass-producing nano powders by DC transferred arc plasma. They adopt multi-electrodes to evaporate simultaneously to improve the evaporation efficiency, and adopt a multi-chamber multi-stage structure with separate evaporation, collection, screening, and passivation to ensure the coordinated progress of continuous evaporation and continuous automatic collection. However, they can only produce single-element nano powders, and the vacuum degree is not good, and the entry of air is likely to cause safety accidents. CN200960551Y discloses a device for preparing dispersed composite nano powders by a novel plasma multi-pole arc method. This technology pioneered the use of transferred arc plasma to prepare dispersed composite nano powders. However, due to the different electrical conductivities of different metals, it is very difficult to control the mass ratio between alloys, that is, it is very difficult to produce the required dispersed composite nano powders. CN117753978A also uses DC transferred arc plasma. Although it can only produce single-element metal nano powders, it solves the problem of vacuum sealing and ensures safe production. CN209733469U adopts a multi-chamber structure and can produce nano alloys, but still uses transferred arc plasma and cannot solve the problem of discontinuous feeding and supply of materials during the continuous feeding process. Summary of the Invention

[0005] In view of the deficiencies in the above technologies, the present invention provides a device and method for preparing nano alloys by using a non-transferred arc plasma torch to ionize gas to generate a high-temperature plasma with active particles. The device is flexible in operation, has simple equipment units, a large powder production capacity, and can continuously prepare various nano-dispersed composite powders.

[0006] A device for preparing nano-dispersed composite powders based on plasma gasification comprises multiple sets of plasma gasification systems, a nano-dispersed composite mixing, crystallization, and forming system, and a gas-solid separation system. The plasma gasification system comprises plasma gasification furnaces (4A, 4B, 4C, 4D, and 4E), non-transferred arc plasma torches (3A, 3B, 3C, 3D, and 3E), a refrigerating machine (1), and a deionized water circulation pump (2). The refrigerating machine (1) is used to cool the anode and cathode of the non-transferred arc plasma torch to prevent the evaporation of the anode and cathode by the high temperature of the plasma, and has the effect of cold-wall constricting the plasma. The nano alloy mixing, crystallization, and forming system is composed of primary coolers (5A, 5B, 5C, 5D, and 5E) and a phase-cooling mixing tower (6). The gas-solid separation system mainly consists of a bag filter (7) and a vacuum pump (8).

[0007] Further, the number of plasma gasification systems is determined according to the types of nano-dispersed composite powders to be prepared. For example, if preparing heat-resistant dispersed composite nano-powder PM2515, two sets of plasma gasification systems are required; if preparing dispersed composite nano-powder PM504 for cold work tool steel, 4 sets of plasma gasification systems are needed; if preparing heat-resistant dispersed composite nano-powder PM2905, 7 sets of plasma gasification systems are required. The cooling systems of the plasma torches can share one set of refrigerating machine and deionized water circulation water pump, or can be configured one-to-one according to the cooling capacity, or N-to-one. The primary cooler in the nano-dispersed composite evaporation system needs to be correspondingly configured with the plasma gasification system, while the rest of the systems share one set.

[0008] Further, the plasma gasification system is characterized in that a metal material feed inlet is provided on the plasma gasification chamber, and two sealed cut-off valves are provided at the feed inlet. The purpose of the two sealed cut-off valves is to ensure the vacuum degree in the plasma gasification chamber during the feeding process, and the gauge pressure of the plasma gasification chamber is maintained at -5000 Pa to -50 Pa.

[0009] Further, one or more plasma torches can be provided at the top of the plasma gasification chamber. The multiple plasma torches are arranged equidistantly in the circumferential direction, and the central circle diameter of the plasma flame flows of the multiple plasma torches is 50 mm to 200 mm, and they are arranged tangentially. The plasma torches are determined according to the material quantity.

[0010] Further, the average temperature of the plasma gasification furnace is controlled 10 - 100 °C higher than the melting point of the metal, the heating center temperature formed by the plasma torch is controlled 200 - 500 °C higher than the boiling point of the metal, and the height of the liquid metal borne by the crucible (4-2) in the plasma gasification furnace is maintained at 50 - 500 mm. As the metal molten liquid evaporates, the solution volume in the crucible (4-2) gradually decreases. In order to ensure a stable metal gasification rate formed by the plasma torch flame flow in the metal, the pneumatic lifting device (4-3) under the crucible (4-2) in the gasification furnace is started to lift the crucible (4-2) upward, keeping the contact position between the molten liquid in the crucible (4-2) and the flame flow of the plasma torch unchanged and keeping the metal gasification temperature unchanged. The output of the alloy can be adjusted according to the power of the plasma torch to ensure that the required time for the gasification of multiple metals to produce the required amount is the same.

[0011] Further, the metal gas (composed of electrons and metal particles) and the plasma high-temperature gas generated by the plasma gasification furnace enter the primary cooler (5) through a pipeline. The metal gasification gas nucleates, crystallizes, and grows in the primary cooler to form nano-materials, and the temperature in the primary cooler is maintained between 1600 - 2100 °C.

[0012] Furthermore, at high temperatures, the movement of nanomaterials speeds up, overcoming molecular attraction and preventing the agglomeration of nanomaterials. The primary cooler is cooled by circulating cooling water, and the amount of cooling water is adjusted adaptively according to the output of the metal gasification gas.

[0013] Furthermore, several single-element nanometals enter the phase-cooling mixing tower through pipelines carried by a plasma gas stream (nitrogen or argon) for mixing. The phase-cooling mixing tower uses liquid nitrogen for cooling. The liquid nitrogen transfers the cooling capacity to each nanopowder through phase change. The nanopowders are rapidly cooled and formed, and are fully mixed under the action of pneumatic stirring of the nitrogen gas stream to form nanoalloy powders.

[0014] Furthermore, the uniformly mixed nanoalloy powders enter the bag filter (7) under the suction of the vacuum pump (8) for gas-solid separation. The separated nitrogen can be directly discharged or filled into cylinders for external sale.

[0015] The working principle of the present invention is based on the sequential collaborative work of three subsystems:

[0016] 1. Plasma gasification system: A non-transferred arc plasma torch (using nitrogen or argon as the working medium) is used to generate high-temperature plasma (the temperature can reach 200 - 500 °C above the boiling point of the metal). Different metal raw materials are independently evaporated through multiple parallel gasification furnaces. Each furnace is equipped with a crucible to load metals (such as Mo, Co, etc.). The height of the crucible is dynamically adjusted through a pneumatic lifting device to ensure stable contact between the plasma flame and the molten metal surface and maintain a constant gasification rate. The refrigerator and deionized water circulation pump cool the anode and cathode of the plasma torch to prevent damage caused by high temperature. At the same time, the cold-wall constriction technology restricts the shape of the plasma to improve energy efficiency. The vacuum seal (-5000~-50 Pa) and the double-channel seal valve feeding system avoid oxidation and air leakage to ensure safety.

[0017] 2. Nano-dispersion composite mixing and crystallization system: The metal vapor enters the primary cooler (1600 - 2100 °C) and is rapidly cooled by circulating cooling water, prompting atoms to collide and nucleate and crystallize into nanoparticles. The high-temperature environment inhibits agglomeration; subsequently, multi-component nanopowders are rapidly cooled by liquid nitrogen in the phase-cooling mixing tower (the tower temperature is about 40 °C). The liquid nitrogen releases the cooling capacity through phase change to instantaneously solidify the particles. At the same time, the nitrogen gas stream forms turbulent stirring to achieve uniform dispersion and composite of different metal nanopowders and lock the alloy composition ratio.

[0018] 3. Gas-solid separation system: The mixed gas-solid flow is drawn into the bag filter by the vacuum pump. The nanopowders are efficiently captured by the filter bags, and the remaining nitrogen can be recycled or sold externally. By hierarchically regulating the parameters of each subsystem (such as the power of the plasma torch, the cooling rate, and the vacuum degree), the high-purity, composition-controllable, and continuous production of nano-dispersion composite powders is ultimately achieved, solving the problems of alloy ratio fluctuation, particle agglomeration, and production interruption in traditional technologies.

[0019] The present invention has the following advantages compared with the prior art devices:

[0020] (1) By using a non-transferred arc plasma torch, the disadvantage of easy arc breakage of the transferred arc plasma torch is avoided, ensuring the continuous stability of production;

[0021] (2) Multiple non-transferred plasma torches can be used in the gasifier, improving production efficiency;

[0022] (3) By connecting multiple plasma gasifiers in series, various different dispersed composite nanopowders can be produced;

[0023] (4) By using a non-transferred plasma torch with adjustable power, the power of the plasma torch is controlled to control the gasification amount of the metal, ensuring the proportion stability of the metal alloy powder;

[0024] (5) This device can produce a large amount of nano-dispersed composite powder with stable quality;

[0025] (6) This device can fully disperse and mix the composite nanopowders in the gaseous state, with good results. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic process flow diagram of the present invention;

[0027] Figure 2 is a schematic structural diagram of the plasma gasifier;

[0028] Figure 3 is a schematic structural diagram A of the plasma torch;

[0029] Figure 4 is a schematic structural diagram B of the plasma torch;

[0030] Figure 5 is a scanning electron microscope image of the wear-resistant and heat-resistant composite nanopowder PM2515SME (the dark color is Mo, the light color is Co; Mo:Co = 3:5);

[0031] Figure 6 is a scanning electron microscope image of the wear-resistant and heat-resistant composite nanopowder PM504SME.

[0032] In the figure: 1 - Refrigerator; 2 - Deionized water circulation pump; 3 - Plasma gasification chamber group; 3A - Plasma torch No. 3A; 3B - Plasma torch No. 3B; 3C - Plasma torch No. 3C; 3D - Plasma torch No. 3D; 3E - Plasma torch No. 3E; 4A - Liquid metal No. 4A; 4B - Liquid metal No. 4B; 4C - Liquid metal No. 4C; 4D - Liquid metal No. 4D; 4E - Liquid metal No. 4E; 5A - Primary cooler No. 5A; 5B - Primary cooler No. 5B; 5C - Primary cooler No. 5C; 5D - Primary cooler No. 5D; 5E - Primary cooler No. 5E; 6 - Liquid nitrogen tank; 7 - Bag filter; 8 - Vacuum pump; 4-1 - Plasma gasification furnace;

[0033] 4-2 - Crucible; 4-3 - Pneumatic lifting device; 4-4 - Metal vaporization outlet; 4-5 - Plasma torch; 3-1

[0034] —Plasma cathode; 3-2 - Plasma anode; 3-3 - Working gas inlet; 3-4 - Cooling water outlet;

[0035] 3-5 - Plasma torch housing; 3-6 - Cooling water outlet.

[0036] Specific embodiments

[0037] The subject matter described herein will now be discussed with reference to example embodiments. It should be understood that discussing these embodiments is only to enable those skilled in the art to better understand and thus implement the subject matter described herein, and the functions and arrangements of the elements discussed can be changed without departing from the scope of protection of the content of this specification. Each example can omit, substitute, or add various processes or components as needed. Additionally, the features described relative to some examples can also be combined in other examples.

[0038] As Figure 1-4 shown, the overall process of the system is presented: Plasma gasification system (multiple parallel gasification furnaces) → Primary cooler → Phase-cooling mixing tower → Bag filter. The internal structure of a single plasma gasification furnace is depicted in detail, including a crucible (4-2), a lifting mechanism (4-3), and a plasma torch (4-5); the plasma torch (corresponding to Figure 3 、 Figure 4 ) is installed on the top of the gasification furnace and forms a high-temperature plasma (2000 - 2500 °C) through the ionization of the working gas (argon / nitrogen) to melt and vaporize the metal in the crucible. The lifting mechanism adjusts the height of the crucible through air pressure to ensure stable contact between the molten liquid surface and the plasma flame flow and maintain continuous gasification. The vaporized metal vapor enters the primary cooler ( Figure 1 such as 5A, 5B in

[0039] ) through the metal vaporization outlet (4-4).The primary cooler (such as 5A, 5B, etc.) rapidly cools the metal vapor through circulating cooling water (temperature 1600–2100 °C), promoting atomic nucleation and forming nanoparticles (particle size 50–100 nm). The high-temperature environment inhibits particle agglomeration and ensures dispersibility. Subsequently, the multi-component nanopowder contacts liquid nitrogen (flow rate 5–10 kg / min) in the phase-cooling mixing tower (6), and the cold quantity is released through the phase change of liquid nitrogen (tower temperature 40 °C), instantaneously solidifying the particles and locking the composition ratio. The nitrogen gas flow (flow velocity 10–15 m / s) forms turbulent stirring to achieve uniform mixing. Finally, the gas-solid mixture flows through the bag filter (7) for separation, the nanopowder is captured, and the nitrogen gas is recycled or sold externally. Each subsystem maintains a negative pressure (-5000–-50 Pa) through a vacuum pump (8) to ensure the continuity and safety of the process.

[0040] As Figure 3-4 shown, the details of the non-transferred arc plasma torch are respectively presented, including the cathode (3-1), anode (3-2), working gas inlet (3-3), and cooling water channels (3-4, 3-6). When the plasma torch operates, the working gas enters from the inlet (3-3), forms a high-temperature plasma jet through arc ionization, and directly acts on the metal liquid surface. The cooling water circulates through the channels ( Figure 3 3-4 and 3-6 in), preventing the electrodes from overheating. Multiple plasma torches are circumferentially and equidistantly arranged at the top of the gasifier, and their tangential plasma flame flows (diameter 50–200 mm) form a vortex effect, enhancing the gasification efficiency. The power of the plasma torch (such as 30–90 kW) controls the metal gasification rate by adjusting the arc intensity to ensure the precise ratio of the multi-component alloy.

[0041] Example 1

[0042] Prepare the wear-resistant and heat-resistant composite powder PM2515. Two plasma gasifiers (i.e., the Mo plasma gasifier and the Co plasma gasifier) are used to prepare this alloy powder. The Mo plasma gasifier is charged with 15 Kg of Mo, and the Co plasma gasifier is charged with 25 Kg of Co. The power of the torch of the Mo plasma furnace is 40 KW, and the torch of the Co plasma furnace is 65 KW. The average temperature of the Mo plasma torch gasifier is controlled at 1900 °C, the average temperature of the Co plasma torch gasifier is controlled at 1900 °C, the temperature of the primary cooler connected to each is controlled at 1600 °C, the vacuum degree of the plasma gasifier is controlled at -3500 Pa, and the average tower temperature of the phase-cooling mixing tower is controlled at 40 °C. The obtained dispersed composite nanopowder SME is as shown in Figure 5:

[0043] Example 2

[0044] Prepare wear-resistant and heat-resistant composite powder PM504. Four plasma gasification furnaces (i.e., C plasma gasification furnace, Mo plasma gasification furnace, Cr plasma gasification furnace, and V plasma gasification furnace) are used to prepare this alloy powder. The C plasma gasification furnace is charged with 14 Kg of C, the Mo plasma gasification furnace is charged with 35 Kg of Mo, the Cr plasma gasification furnace is charged with 47 Kg of Cr, and the V plasma gasification furnace is charged with 37 Kg of V. The power of the torch of the C plasma furnace is 30 KW for one, the torches of the Mo and V plasma furnaces are 30 KW for three, and the torch of the Cr plasma gasification furnace is 30 KW for four. The average temperature of the C plasma torch gasification furnace is controlled at 2100 °C, the average temperature of the Co plasma torch gasification furnace is controlled at 1600 °C, the average temperature of the Cr plasma torch gasification furnace is controlled at 2100 °C, the average temperature of the V plasma torch gasification furnace is controlled at 1950 °C, the temperature of the primary cooler connected to each is controlled at 1600 °C, the vacuum degree of the plasma gasification furnace is controlled at -4500 Pa, and the average tower temperature of the phase-cooling mixing tower is controlled at 40 °C. The obtained dispersed composite nanopowder SME is as shown in Figure 6.

[0045] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A device for preparing nano-dispersed composite powder based on plasma gasification, characterized in that: include: The plasma gasification system is composed of a plurality of plasma gasification furnaces (4A, 4B, 4C...) connected in parallel, each gasification furnace is equipped with a non-transferred arc plasma torch (3A, 3B, 3C...), a crucible (4-2) and a gas pressure lifting mechanism (4-3); the plasma torch uses nitrogen or argon as a working gas, and its power is adjustable to control the metal gasification rate; the crucible dynamically adjusts the liquid level through the lifting mechanism to keep the contact position between the plasma flame flow and the molten metal constant; The nano-dispersed composite mixed crystallization system comprises a primary cooler (5A, 5B, 5C...) corresponding to the plasma gasification furnace and a phase cooling mixing tower (6); the primary cooler rapidly cools the metal vapor to 1600-2100° C. by circulating cooling water to form nano-particles; the phase cooling mixing tower adopts liquid nitrogen quenching and nitrogen flow stirring to achieve uniform mixing of multi-component nano-powders; The gas-solid separation system is composed of a bag filter (7) and a vacuum pump (8) and is used to separate nano powder and gas.

2. The device for preparing nano-dispersed composite powder by plasma gasification according to claim 1, characterized in that: The plasma gasification system also includes a refrigerator (1) and a deionized water circulation pump (2) for cooling the cathode and anode of the plasma torch; a double-channel sealing cut-off valve for maintaining the vacuum degree of the gasification chamber at -5000Pa to -50Pa; and multiple plasma torches are arranged tangentially and equidistantly in the circumferential direction, and the diameter of the center circle of the plasma flame flow is 50-200mm.

3. The device for preparing nano-dispersed composite powder by plasma gasification according to claim 2, characterized in that The cooling water flow of the primary cooler (5A, 5B, 5C...) is adaptively adjusted according to the metal vaporization amount to inhibit the agglomeration of nanoparticles; the liquid nitrogen flow of the phase-cooled mixing tower (6) is 5-10 kg / min, the nitrogen flow rate is 10-15 m / s, and the tower temperature is controlled below 40°C.

4. The method for preparing nano-dispersed composite powder by plasma gasification according to claim 1, characterized in that , including the following steps: (1) Different metal raw materials are loaded into the crucibles of multiple plasma gasifiers respectively, and a non-transferred arc plasma torch is used to generate high-temperature plasma (temperature is 200-500°C higher than the boiling point of the metal) to evaporate the metal to form atomic vapor; (2) The metal vapor enters the primary cooler (1600-2100°C) and is rapidly cooled, nucleating and crystallizing into nanoparticles; (3) The multi-component nanopowders are solidified by rapid cooling with liquid nitrogen in a phase cooling mixing tower and stirred and mixed by a nitrogen flow; (4) The mixed gas-solid flow is separated by a bag filter to obtain nano-dispersed composite powder, and the remaining gas is recovered or sold.

5. A method for preparing nano-dispersed composite powder by plasma gasification according to claim 4, characterized in that: The gasification rate of each metal is controlled by adjusting the power of the plasma torch, so that the gasification time of multiple components is synchronized and the alloy component ratio deviation is ≤3%; the average particle size of the nano powder is 50-100nm and the agglomeration index is ≤5%.

6. The method according to claim 4 or 5, characterized in that: The vacuum degree of the plasma gasification furnace is maintained at -5000Pa to -50Pa, and the tower temperature is ≤40°C during liquid nitrogen quenching.

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