Airflow heating / cooling integrated device for regulating powder particle size

Abstract

The application provides a gas flow heating / cooling integrated device for regulating powder particle size, and belongs to the technical field of submicron / nanometer powder preparation. The device is composed of a gas flow heating system and a gas flow cooling system. The front end of the gas flow heating system is connected with a plasma powder generation chamber, and the rear end of the gas flow heating system is connected with the gas flow cooling system. The powder particles carried by the carrier gas experience two stages of heating and cooling in sequence, so that the powder particle size uniformity is improved, and the quality of the powder product is improved. In the process of in-situ preparation of powder materials, through the heating / cooling integrated processing unit of flowing particles provided by the application, the regrowth of small-size particles and the inhibition of the aggregation and growth of large-size particles can be realized, the powder particle size uniformity is effectively improved, and the overall quality of the powder product is improved.

Description

An integrated airflow heating / cooling device for controlling powder particle size Technical Field

[0001] This invention belongs to the field of submicron / nano powder preparation technology. Specifically, it relates to an integrated device and method for further processing and controlling particles with a wide particle size distribution, and for reheating and cooling under carrier gas flow conditions, so as to obtain powder materials with uniform particle size. Background Technology

[0002] In microelectronic device manufacturing, submicron / nanometer-sized metal or alloy powder materials are the core components for forming conductive films or electrode layers. Extremely high requirements are placed on their average size, homogenization, crystallinity, microstructure, dispersion in the dielectric, sintering characteristics, and electrical properties. With the miniaturization of electronic components and wiring substrates, the spacing between conductive films and electrode layers continues to shrink. Therefore, it is desirable for the metal powder particles to be finer, more spherical, and have higher crystallinity. Taking multilayer ceramic chip capacitors (MLCCs) as an example, the metal electrode layers made using nickel powder electronic paste require nickel powder particles with a size between 100-300 nm. After subsequent sintering, a good conductive network is formed, which greatly improves the performance and quality of MLCCs.

[0003] Methods for preparing metal powder materials include physical vapor phase condensation (such as plasma heating evaporation, electron beam heating evaporation, and high-frequency induction heating evaporation), mechanical pulverization (high-energy ball milling, vibration ball milling, and stirring ball milling), chemical vapor phase decomposition, and chemical solution reduction. Among these, physical vapor phase methods, such as using high-temperature plasma to evaporate raw materials, forming a gaseous state, and obtaining microscale metal particles after nucleation and growth, are currently the most widely used preparation techniques. However, this preparation method has the drawback of a relatively wide particle size distribution, requiring further graded processing, which is one of the problems that urgently needs to be solved. Patents CN103128302A and CN104066537A provide a plasma device that can obtain a narrow particle size distribution of metal powder. It is equipped with cooling pipes and includes both direct cooling (direct contact between metal vapor and cooling medium) and indirect cooling (indirect contact between metal vapor and cooling medium), which improves the uniformity of powder particles to a certain extent. This method intervenes in the particle growth process through cooling, which can suppress the formation of large particles, but lacks necessary intervention measures for the regrowth of small particles. The device of this patent invention takes into account both the regrowth of small particles and the suppression of the formation of large particles, thereby improving the uniformity of powder particle size and realizing the possibility of particle size adjustment under flow conditions. Summary of the Invention

[0004] This invention provides an apparatus and method for controlling the size and distribution of powder particles. Addressing the shortcomings of current plasma evaporation methods for preparing metal powders, which suffer from wide particle size distribution, this invention designs an integrated device for reheating and cooling powder particles under carrier gas flow conditions. This device balances the regrowth of small particles with the suppression of large particle formation, thereby improving powder particle size uniformity and enhancing the quality of the powder product.

[0005] To achieve the above objectives, the details of the device of the present invention are as follows:

[0006] An integrated heating / cooling device for regulating the size and distribution of powder particles comprises two main parts: a gas flow heating system 1 and a gas flow cooling system 8. The front end of the gas flow heating system is connected to a plasma powder generation chamber, and the rear end of the gas flow heating system is connected to the gas flow cooling system. The powder particles carried by the carrier gas undergo two stages of sequential heating and cooling, thereby improving the uniformity of powder particle size and enhancing the quality of the powder product.

[0007] The airflow heating system 1, as shown in Figure 1, includes an input port 2, a powder conveying pipe 3, a primary heating circuit 4, a secondary heating circuit 5, a magnetic field shielding plate 6, and an output port 7. The carrier gas carries the powder particles already formed in the plasma powder generation chamber through a flow circulation, entering the powder conveying pipe 3 from the input port 2. At this point, the powder contains a large number of small particles with a wide particle size distribution. The heating stage begins. The primary heating circuit 4 uses induction heating, a low-temperature heating method; while the secondary heating circuit 5 uses resistance heating, a high-temperature heating method. The primary induction heating (low-temperature heating) process aims to enhance the aggregation and bonding of small particles. The induced magnetic field distribution along the axial direction of the powder conveying pipe 3 is particularly beneficial for the aggregation and growth of magnetic powder particles (such as nickel powder). The secondary resistance heating (high-temperature heating) stage aims to promote the further growth of particles already agglomerated in the primary heating stage, strengthen the sintering and metallurgical bonding between particle surfaces, improve particle crystallinity, and achieve effective growth of small particles. During the induction heating stage, the induced magnetic field promotes the magnetization of weakly magnetic particles. The magnetized particles are then interconnected through magnetic coupling, providing favorable conditions for subsequent high-temperature heating. To reduce the influence of the magnetic field during the high-temperature stage, a magnetic field shielding plate 6 is installed between the primary heating circuit 4 and the secondary heating circuit 5 to minimize the impact of the induced magnetic field during the high-temperature heating stage and reduce magnetic coupling between large particles. During the high-temperature heating stage, if the temperature exceeds the Curie temperature of the ferromagnetic powder, the particles will transform into a paramagnetic state or undergo thermal demagnetization. The magnetic coupling between particles weakens or disappears, inhibiting the aggregation and growth of large particles. After heat treatment, the powder particles circulate with the carrier gas and enter the cooling stage.

[0008] Furthermore, the primary heating circuit 4 is set with a temperature range of 100 to 300°C; the secondary heating circuit 5 is set with a temperature range of 400 to 1000°C.

[0009] Furthermore, the primary heating circuit 4 includes an electromagnetic induction heating coil wound around a heating tube, a heat insulation layer wrapped around it, and a temperature control device. It is a location where small particles gather and combine under the influence of an induced magnetic field.

[0010] Furthermore, the secondary heating circuit 5 includes a resistive layer surrounding the heating tube, a heat insulation layer covering the outer layer, and a temperature control device. This is a location for the regeneration and growth of small-sized particles.

[0011] Furthermore, the magnetic field shielding plate 6 is a composite material circular plate with good electromagnetic shielding effect.

[0012] The airflow cooling system 8, as shown in Figure 2, is a heat exchange site, including an input port 9, an output port 10, a condenser wall 11, a cooling medium inlet 12, a cooling medium outlet 13, a condenser pipe 14, a condenser cylinder 15, a valve 16, a powder collection container 17, a condenser top cover 18, a condenser pipe inlet 19, a condenser pipe outlet 20, and a condenser cylinder inlet and outlet 21. The input port 9 is located below the condenser wall 11, and the output port 10 is located above it on the opposite side. A valve 16 is located between the bottom of the condenser wall 11 and the powder collection container 17. A condenser cylinder 15 is located inside the condenser wall 11, with the condenser pipe 14 wrapped around its outer circumference. The condenser pipe 14 is connected to the condenser pipe inlet 19 and condenser pipe outlet on the condenser top cover 18, and the condenser cylinder 15 is connected to the condenser cylinder inlet and outlet 21 on the condenser top cover 18. After high-temperature heating, the small particles in the powder have grown sufficiently, and the continued high temperature will lead to the continued growth of larger particles. Therefore, thorough cooling is achieved in the airflow cooling system 8. After being heated by the airflow heating system 1, the powder particles flow with the carrier gas and enter through the input port 9 at the bottom of the airflow cooling system 8. They are thoroughly cooled by passing through the low-temperature sections of the condensation chamber wall 11, condensation pipe 14, condensation cylinder 15, and condensation chamber top cover 18, before entering the next processing unit from the top output port 10. The condensation section is designed with pipe and cylinder walls to maximize the heat exchange area and improve cooling efficiency. After passing through the airflow cooling system, the powder reaches room temperature, and the uniformity of powder particle size is significantly improved.

[0013] Furthermore, a cooling medium can be filled inside the condensation chamber wall 11, flowing in the opposite direction to the carrier gas flow. This medium enters the airflow cooling system 8 through the cooling medium inlet 12 and exits through the cooling medium outlet 13, improving the heat transport and transfer rate, thereby increasing the cooling efficiency of the powder. The cooling medium inlet 12 is located below the output port 10, and the cooling medium outlet 13 is located above the input port 9.

[0014] Furthermore, the cooling medium is deionized water.

[0015] Furthermore, two sets of condenser tubes 6 are wound around the condenser cylinder 7, both of which are made of copper or aluminum, which have high thermal conductivity.

[0016] The innovations of this invention are as follows: First, the two-stage heating system of low temperature and high temperature promotes the agglomeration and growth of small-sized particles in the powder, which is particularly suitable for the secondary growth of weakly magnetic particles; second, the integrated heating / cooling design of the flowing particles effectively reduces the regrowth of large-sized particles, thereby improving the uniformity of powder particle size.

[0017] The beneficial effects of this invention are as follows: In the process of preparing powder materials in situ, the integrated heating / cooling treatment unit for flowing particles enables the regrowth of small-sized particles and inhibits the aggregation and growth of large-sized particles, effectively improving the uniformity of powder particle size and enhancing the overall quality of the powder product. Attached Figure Description

[0018] Figure 1 is a schematic diagram of the airflow heating device of the present invention; Figure 2 is a schematic diagram of the airflow cooling device of the present invention;

[0019] As shown in Figure 1: 1 airflow heating system, 2 input port, 3 powder conveying pipe, 4 primary heating circuit, 5 secondary heating circuit, 6 magnetic field shielding plate, 7 input port.

[0020] As shown in Figure 2: 8 airflow cooling system, 9 input port, 10 output port, 11 condenser wall, 12 cooling medium inlet, 13 cooling medium outlet, 14 condenser tube, 15 condenser cylinder, 16 valve, 17 powder collection container, 18 condenser top cover, 19 condenser tube inlet, 20 condenser tube outlet, 21 condenser cylinder inlet and outlet.

[0021] Figure 3 is a schematic diagram of the overall device of the present invention. Detailed Implementation

[0022] The above-described contents of the present invention will be further described in detail below with reference to specific embodiments, but the scope of the present invention is not limited to the following examples.

[0023] An integrated heating / cooling device for regulating powder particle size and distribution comprises two main parts: a gas flow heating system 1 and a gas flow cooling system 8. The front end of the gas flow heating system is connected to a plasma powder generation chamber, and the rear end is connected to the gas flow cooling system. Powder particles carried by a carrier gas undergo two sequential stages of heating and cooling, improving powder particle size uniformity and enhancing the quality of the powder product. The gas flow heating system 1, as shown in Figure 1, includes an input port 2, a powder conveying pipe 3, a primary heating circuit 4, a secondary heating circuit 5, a magnetic field shielding plate 6, and an output port 7. The carrier gas carries the powder particles already formed in the plasma powder generation chamber through a flow circulation, entering the powder conveying pipe 3 from the input port 2. The heating stage begins, where the primary heating circuit 4 uses induction heating (low-temperature heating), and the secondary heating circuit 5 uses resistance heating (high-temperature heating). A magnetic field shielding plate 6 is installed between the primary heating circuit 4 and the secondary heating circuit 5.

[0024] In this embodiment, submicron-sized metallic nickel powder is prepared by DC arc plasma evaporation. The powder prepared in situ is formed in the generation chamber and flows sequentially through the airflow heating system and airflow cooling system of this invention with the carrier gas. The powder sample is then collected in the collection chamber.

[0025] First, open the top cover of the arc generation chamber of the electric arc equipment, add an appropriate amount of metallic nickel ball raw material to the crucible, install the graphite electrode, and then close the top cover. Add an appropriate amount of metallic nickel ball raw material to the primary feeding hopper of the feeding system (this raw material is used as a supplementary material after the raw material in the crucible is lost). The entire equipment system is heated to 1 Pa, including the airflow heating system and airflow cooling system of this invention, and filled with a mixed gas of hydrogen and argon at a pressure of 80 kPa. The arc current is set to 200 A, and the arc is ignited, forming a stable arc between the cathode carbon rod and the raw material. The nickel ball raw material in the crucible melts into a liquid state (this process lasts for 5-10 minutes). The electrode position is adjusted vertically to make the distance between the cathode and the molten liquid surface 5 cm, resulting in metallic fumes and the formation of in-situ prepared powder. The circulating fan is turned on to circulate the airflow throughout the equipment, carrying the powder generated in-situ in the generation chamber into the heating / cooling device of this invention.

[0026] Secondly, the flowing powder is heated at a low temperature (300℃) in the primary induction heating circuit 4 of the airflow heating system 1. The powder flow rate is determined by the speed of the circulating fan. Afterward, the flowing powder enters the secondary resistance heating circuit 5 for high-temperature heating (800℃, higher than the Curie temperature of nickel, 358℃). After completing the primary and secondary heating stages, the hot flowing powder enters the airflow cooling system 8.

[0027] Finally, in the airflow cooling system 8, deionized water is used as the cooling medium, with the temperature set at 20°C. The flow rate of the cooling medium is set to 20 L / min for the condensation chamber wall, 30 L / min for the condensation copper tube, and 50 L / min for the condensation cylinder. The flowing powder then enters the subsequent collection chamber.

[0028] After the entire preparation equipment has been running continuously for several hours, and the evaporation loss and supply of nickel metal raw materials have stabilized, and the temperature readings at various detection points have become stable, establishing a stable temperature field, powder is collected from the sampling container at the junction of the generation chamber and the heating pipe, and from the powder collection vessel 17 at the bottom of the cooling system, for powder particle size and distribution testing. In this invention, adjustable parameters include airflow rate, primary heating temperature setting, secondary heating temperature setting, cooling medium selection, cooling chamber wall temperature setting, condenser tube temperature setting, and condenser cylinder wall temperature setting. By selecting and setting these heating and cooling conditions, the purpose of controlling powder particle size and its distribution can be well achieved.

[0029] The above specific embodiments are merely one implementation of the present invention, but should not be construed as limiting the scope of the present invention. In the device of the present invention, the control technology for the size and distribution of submicron / nano-scale powder particles can be modified by those skilled in the art without departing from the concept of the present invention, and these modifications are all within the protection scope of the present invention.

Claims

1. An integrated airflow heating / cooling device for controlling powder particle size, characterized in that, The integrated device comprises two main parts: a gas flow heating system (1) and a gas flow cooling system (8). The front end of the gas flow heating system is connected to the plasma powder generation chamber, and the rear end of the gas flow heating system is connected to the gas flow cooling system. The powder particles formed in the plasma powder generation chamber are carried by the carrier gas through two stages of heating and cooling, thereby improving the uniformity of powder particle size and improving the quality of powder products. The gas flow heating system (1) includes a first input port (2), a powder conveying pipe (3), a primary heating circuit (4), a secondary heating circuit (5), a magnetic field shielding partition (6), and a first output port (7). The carrier gas carries the powder particles in a flow circulation, entering the powder conveying pipe (3) from the first input port (2), and sequentially entering the primary heating and secondary heating stages in the powder conveying pipe (3), before flowing into the gas flow cooling system from the first output port (7). System (8); The primary heating circuit (4) adopts induction heating, which is low-temperature heating, and the secondary heating circuit (5) adopts resistance heating, which is high-temperature heating; A magnetic field shielding plate (6) is installed between the primary heating circuit (4) and the secondary heating circuit (5); The primary heating circuit (4) is set with a temperature range of 100~300℃; The secondary heating circuit (5) is set with a temperature range of 400~1000℃; The primary heating circuit (4) includes an electromagnetic induction heating coil wound around the heating tube, a heat insulation layer wrapped on the outer layer, and a temperature control device; Under the action of the induced magnetic field, the primary heating circuit is a place where small-sized particles gather and combine; The secondary heating circuit (5) includes a resistance layer wrapped around the heating tube, a heat insulation layer wrapped on the outer layer, and a temperature control device; The secondary heating circuit is a place where small-sized particles regenerate and grow.

2. The integrated airflow heating / cooling device for controlling powder particle size according to claim 1, characterized in that, The magnetic field shielding plate (6) is a composite material circular plate with good electromagnetic shielding effect.

3. The integrated airflow heating / cooling device for controlling powder particle size according to claim 1, characterized in that, The airflow cooling system (8) is a heat exchange site, including a second input port (9), a second output port (10), a condenser wall (11), a condenser tube (14), a condenser cylinder (15), a powder collection vessel (17), and a condenser top cover (18). The second input port (9) is located below the condenser wall (11), and the second output port (10) is located above the opposite side of the second input port (9). The powder collection vessel (17) is located at the bottom of the condenser wall (11). The condenser cylinder (15) is located inside the condenser wall (11), and its outer periphery is wrapped with... The condenser tube (14) is connected to the condenser tube inlet and outlet on the top cover (18) of the condenser chamber, and the condenser cylinder (15) is connected to the condenser cylinder inlet and outlet on the top cover (18) of the condenser chamber. After being heated by the airflow heating system (1), the powder particles flow with the carrier gas and enter through the second input port (9) at the bottom of the airflow cooling system (8). After being fully cooled by the low-temperature parts of the condenser chamber wall (11), condenser tube (14), condenser cylinder (15), and condenser chamber top cover (18), they enter the next processing unit from the second output port (10) at the top.

4. The integrated airflow heating / cooling device for regulating powder particle size according to claim 3, characterized in that, The cooling medium is filled inside the condensation chamber wall (11) and flows in the opposite direction to the carrier gas flow. It enters the airflow cooling system (8) from the cooling medium inlet (12) and flows out from the cooling medium outlet (13), thereby improving the heat transport and transfer rate and thus improving the cooling efficiency of the powder. The cooling medium inlet (12) is located below the second output port (10) and the cooling medium outlet (13) is located above the second input port (9).

5. The integrated airflow heating / cooling device for regulating powder particle size according to claim 4, characterized in that, The cooling medium is deionized water.

6. The integrated airflow heating / cooling device for regulating powder particle size according to claim 3, characterized in that, The condenser cylinder (15) is wound with two sets of condenser tubes (14), both of which are made of copper or aluminum.

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