Spherical silver powder preparation method based on plasma technology

Abstract

The invention discloses a spherical silver powder preparation method based on a plasma technology, and the preparation method comprises the following steps: S1, a reaction chamber is filled with inert gas, direct-current arc plasma is ignited between a silver anode and a high-temperature-resistant cathode, silver vapor is generated, and the silver anode is continuously fed to maintain the stability of the plasma; s2, pre-cooled mixed quenching gas is injected into the downstream of the plasma, so that the silver vapor is condensed, nucleated and grown into silver particles, and the silver particles are collected under the low-temperature condition; and S3, the collected silver particles are subjected to annealing treatment under the protective atmosphere, and the spherical silver powder is obtained. According to the preparation method, through a combined strategy of plasma instantaneous gasification, controllable gas phase condensation and downstream in-situ coating, nucleation is accurately controlled, particle aggregation is inhibited, and the preparation process of the spherical silver powder is comprehensively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanometer metal materials, in particular to a method for preparing spherical silver powder based on plasma technology. BACKGROUND

[0002] Silver powder has irreplaceable role in high-end electronics and optics due to its excellent electrical conductivity and optical reflectivity. As a classic process for preparing silver powder, the traditional physical evaporation condensation method evaporates metallic silver into atomic state in a high-temperature vacuum environment, and then the powder is formed by cooling in a condensation chamber. This method has been dominating silver powder production for a long time due to its simple process principle and no risk of chemical impurities residue in the product.

[0003] However, this process has multiple technical bottlenecks and has been difficult to meet the stringent requirements of high-end fields for silver powder performance. In terms of particle size control, the condensation rate of traditional equipment is uneven, resulting in wide particle size distribution of silver powder and making it impossible to stably prepare nanoscale silver powder with a particle size of 10-50 nm. High-end electronic paste requires nanoscale silver powder to achieve low resistance conduction, and uneven particle size will directly lead to fluctuations in the conductive performance of the paste. In terms of purity control, the crucible material is prone to release impurity ions during evaporation, and the condensation chamber is difficult to achieve absolute vacuum, which easily introduces oxygen, carbon and other impurities, making it difficult to break through 99.99% purity of silver powder. This will significantly reduce the light transmittance and reflection uniformity of the film layer for optical coating.

[0004] Energy consumption and large-scale production bottlenecks are also prominent. This process requires maintaining a high temperature of 1200℃ and a high vacuum environment, with energy consumption being 3-5 times that of chemical methods. Moreover, the production capacity of a single device is low (usually <5 kg per day), and there are large differences in powder morphology (such as sphericity and dispersibility) between batches, which cannot meet the demand for silver powder in high-end fields. In addition, the traditional process cannot accurately control the morphology of silver powder, and the irregularly shaped silver powder prepared is prone to agglomeration in the paste, further restricting its application in flexible electronics and high-precision optical devices, becoming a key technical obstacle for high-end silver powder preparation. SUMMARY

[0005] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes a method for preparing spherical silver powder based on plasma technology, which combines the strategies of "plasma instantaneous gasification + controllable gas phase condensation + downstream in-situ coating" to accurately control nucleation and inhibit particle agglomeration, and comprehensively improves the preparation process of spherical silver powder.

[0006] The present application also proposes the application of the above preparation method.

[0007] According to a first aspect of the present application, a method for preparing spherical silver powder based on plasma technology is proposed, which comprises the following steps: S1: filling the reaction chamber with inert gas, igniting direct current arc plasma between silver anode and high-temperature-resistant cathode to generate silver vapor, and continuously feeding the silver anode to maintain the stability of the plasma; S2: injecting pre-cooled mixed quenching gas downstream of the plasma to condense the silver vapor into nucleation and grow into silver particles, and collecting the silver particles under low-temperature conditions; S3: annealing the collected silver particles in a protective atmosphere to obtain spherical silver powder.

[0008] In some embodiments of the present application, the inert gas in step S1 includes argon, and the pressure in the reaction chamber is maintained at 1-5 kPa.

[0009] In some embodiments of the present application, the current of the cathode when igniting the direct current arc plasma in step S1 is 150-250 A.

[0010] In some embodiments of the present application, the silver anode in step S1 includes a silver rod with a purity of ≥99.99%.

[0011] In some embodiments of the present application, the high-temperature-resistant cathode in step S1 includes a tungsten rod with a purity of ≥99.5%.

[0012] In some embodiments of the present application, the silver anode in step S1 is continuously fed at a rate of 0.3-0.8 mm / s.

[0013] In some embodiments of the present application, the mixed quenching gas in step S2 includes a main gas and a reactive gas, the main gas includes helium and argon, and the reactive gas includes methane or acetylene.

[0014] The above-mentioned reactive gas can be decomposed in the high-activity environment generated by the plasma, and the carbon atoms generated will be deposited in situ on the surface of the newly formed silver nanoparticles to form an extremely thin amorphous carbon shell.

[0015] In some embodiments of the present application, the volume ratio of helium to argon in the main gas is (3-5):1.

[0016] In some embodiments of the present application, the flow rate of the reactive gas accounts for 3-5% of the total flow rate of the mixed quenching gas.

[0017] In some embodiments of the present application, the main gas is pre-cooled to below -150°C before being injected into the reaction chamber.

[0018] The above-mentioned main gas is cooled using a large amount of liquid nitrogen before being injected, which serves to rapidly reduce the temperature of the silver vapor, create extremely high supersaturation, and promote uniform nucleation.

[0019] In some embodiments of the present invention, the total flow rate of the mixed quenching gas in step S2 is 4000~5000 sccm.

[0020] In some embodiments of the present invention, the cryogenic conditions described in step S2 include a cryogenic environment cooled by liquid nitrogen.

[0021] In some embodiments of the present invention, the silver particles collected in step S2 are collected in a low-temperature environment using a polytetrafluoroethylene filter bag with a pore size ≤0.1 μm.

[0022] In some embodiments of the present invention, the mixed quenching gas described in step S2 is injected through a nozzle downstream of the plasma and at the front end of the condensation section.

[0023] During the collection of silver particles, the "core-shell structure" silver@carbon nanoparticles formed by condensation are collected in a low-temperature bag filter by airflow. Due to the presence of the carbon shell, direct metal contact between particles is blocked, thus solving the problem of hard agglomeration at the source of synthesis.

[0024] In some embodiments of the present invention, the annealing temperature in step S3 is 250°C to 350°C, and the annealing time is 30 to 90 minutes.

[0025] The purpose of the above annealing treatment is to partially or completely burn off the amorphous carbon shell on the surface, forming particles with a clean silver surface. This eliminates lattice defects within the particles and improves crystallinity. The annealed powder only needs to be cooled under an inert atmosphere; complex centrifugal washing is unnecessary.

[0026] In terms of mechanism: Plasma technology uses a plasma source to provide extremely high energy, which can completely vaporize the silver source within milliseconds, achieving efficient and uniform precursor supply. The temperature of the plasma arc reaches thousands to tens of thousands of degrees Celsius, which can instantly melt and vaporize the tip of the silver rod, producing high-density silver atom vapor.

[0027] Vapor-phase condensation, through vapor-phase condensation and in-situ compaction under ultra-high vacuum, involves evaporating metallic materials and then agglomerating them into ultrafine powder via collision with an inert gas, followed by pressurization and densification. This process allows for nanoscale control of material structure and is suitable for pure metals and their oxide systems; however, it is prone to compositional inhomogeneity issues when preparing alloys. This invention precisely controls nucleation and growth by precisely controlling condensation conditions (temperature, pressure, atmosphere).

[0028] To prevent the high-temperature region of the plasma from completely decomposing the carbon source gas into free carbon, the injection point of the reactive gas is set downstream of the plasma arc, at the beginning of the condensation channel. Hydrocarbons undergo controlled heterogeneous decomposition in this temperature region, and the resulting carbon atoms selectively deposit on the surface of silver nanoparticles, forming an extremely thin, continuous amorphous carbon shell of approximately 1–2 nm. This carbon shell acts as a "physical barrier," effectively preventing sintering and hard agglomeration of the particles during their movement and collection.

[0029] The present invention has at least the following beneficial effects: This invention proposes a method for preparing spherical silver powder based on plasma technology. This method employs a combined strategy of "instantaneous plasma vaporization + controllable gas-phase condensation + downstream in-situ coating" to precisely control nucleation, suppress particle agglomeration, and comprehensively improve the preparation process of spherical silver powder. Plasma vaporization has high efficiency and extremely fast quenching speed, with the nucleation process much faster than the growth process, enabling the preparation of spherical silver powder with extremely low average particle size and a very narrow particle size distribution. The in-situ formed carbon shell acts as a "physical barrier" during synthesis, preventing the sintering and agglomeration of the metal nuclei. Even after annealing to remove part of the carbon shell, the particles are fixed during formation, resulting in extremely loose and easily dispersed nano-silver powder. The annealed spherical silver powder has a clean surface and low interparticle contact resistance during tableting or sintering; its tablet resistivity is expected to approach the theoretical bulk resistivity of silver, superior to most powders prepared by wet chemical methods. DC arc plasma has high power density and a fast vaporization rate, enabling continuous production. The production capacity of a single unit is far higher than that of laboratory-level wet chemical methods. The entire process is solvent-free and free of complex ionic byproducts, resulting in extremely high product purity.

[0030] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description. Detailed Implementation

[0031] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0032] Unless otherwise specified in the following examples and comparative examples, all instruments and reagents are commercially available and can be purchased through conventional channels.

[0033] Example 1 This embodiment provides a method for preparing spherical silver powder based on plasma technology, and the specific steps are as follows: 1) Setup of the reaction chamber and plasma generation: Anode: A high-purity (≥99.99%) silver rod is used as the consumable anode (silver source) with a diameter of 8 mm.

[0034] Cathode: High-temperature resistant tungsten rod (≥99.5%) with a diameter of 3 mm is used.

[0035] The reaction chamber is made of water-cooled stainless steel or quartz tubes and is equipped with at least two viewing windows (for observation and optical monitoring). It has a pressure resistance range of at least vacuum to 10 kPa. The reaction chamber is filled with high-purity argon gas (≥99.999%) until the pressure stabilizes at 3 kPa. The cooling water circulation system is activated to ensure adequate cooling of the electrodes and reaction chamber walls. A DC voltage is applied between the electrodes to ignite the DC arc plasma; the cathode current is 200 A. During energization, the silver rod is fed at a feed rate of 0.5 mm / s to maintain a stable arc and a continuous supply of silver vapor.

[0036] 2) Downstream in-situ coating and condensation channel: After the plasma stabilizes, a mixed quenching gas is injected downstream of the plasma and at the front of the condensation section through a precision nozzle. The total flow rate is 4500 sccm. The mixed quenching gas includes the main gas and the reactive gas, with the flow rate of the reactive gas accounting for 3% of the flow rate of the mixed quenching gas.

[0037] Main gas: The helium / argon mixture is precooled to -196°C using liquid nitrogen, wherein the volume ratio of helium to argon is 4:1.

[0038] Reactive gas: High-purity methane (≥99.99%).

[0039] 3) Particle collection system: A cryogenic bag filter made of polytetrafluoroethylene (PTFE) with a pore size ≤0.1 μm was used. The entire synthesis process lasted 30–60 minutes. The entire collector was placed in a liquid nitrogen-cooled jacket to ensure that the particles were collected at low temperatures, preventing premature decomposition of the carbon shell or sintering of the particles.

[0040] 4) Post-processing: The collected powder was subjected to low-temperature annealing for 60 min (at a constant temperature of 300°C) in an argon-filled tube furnace. The purpose of this step was to partially or completely burn off the amorphous carbon shell on the surface, forming particles with a clean silver surface. This also eliminated lattice defects within the particles and improved crystallinity. The annealed powder only needed to be naturally cooled under argon to obtain spherical silver powder.

[0041] Example 2 This embodiment provides a method for preparing spherical silver powder based on plasma technology, and the specific steps are as follows: 1) Setup of the reaction chamber and plasma generation: Anode: A high-purity (≥99.99%) silver rod is used as the consumable anode (silver source) with a diameter of 8 mm.

[0042] Cathode: High-temperature resistant tungsten rod (≥99.5%) with a diameter of 3 mm is used.

[0043] The reaction chamber is made of water-cooled stainless steel or quartz tubes and is equipped with at least two viewing windows (for observation and optical monitoring). It has a pressure resistance range of at least vacuum to 10 kPa. The reaction chamber is filled with high-purity argon gas (≥99.999%) until the pressure stabilizes at 3 kPa. The cooling water circulation system is activated to ensure adequate cooling of the electrodes and reaction chamber walls. A DC voltage is applied between the electrodes to ignite the DC arc plasma; the cathode current is 160 A. During energization, the silver rod is fed at a feed rate of 0.5 mm / s to maintain a stable arc and a continuous supply of silver vapor.

[0044] 2) Downstream in-situ coating and condensation channel: After the plasma stabilizes, a mixed quenching gas is injected downstream of the plasma and at the front of the condensation section through a precision nozzle. The total flow rate is 4000 sccm. The mixed quenching gas includes the main gas and the reactive gas, with the flow rate of the reactive gas accounting for 3% of the flow rate of the mixed quenching gas.

[0045] Main gas: The helium / argon mixture is precooled to -196°C using liquid nitrogen, wherein the volume ratio of helium to argon is 4:1.

[0046] Reactive gas: High-purity acetylene (≥99.99%).

[0047] 3) Particle collection system: A cryogenic bag filter made of polytetrafluoroethylene (PTFE) with a pore size ≤0.1 μm was used. The entire synthesis process lasted 30–60 minutes. The entire collector was placed in a liquid nitrogen-cooled jacket to ensure that the particles were collected at low temperatures, preventing premature decomposition of the carbon shell or sintering of the particles.

[0048] 4) Post-processing: The collected powder was subjected to low-temperature annealing for 60 min (at a constant temperature of 250°C) in an argon-filled tube furnace. The purpose of this step was to partially or completely burn off the amorphous carbon shell on the surface, forming particles with a clean silver surface. This also eliminated lattice defects within the particles and improved crystallinity. The annealed powder only needed to be naturally cooled under argon to obtain spherical silver powder.

[0049] Example 3 This embodiment provides a method for preparing spherical silver powder based on plasma technology, and the specific steps are as follows: 1) Setup of the reaction chamber and plasma generation: Anode: A high-purity (≥99.99%) silver rod is used as the consumable anode (silver source) with a diameter of 8 mm.

[0050] Cathode: High-temperature resistant tungsten rod (≥99.5%) with a diameter of 3 mm is used.

[0051] The reaction chamber is made of water-cooled stainless steel or quartz tubes and is equipped with at least two viewing windows (for observation and optical monitoring). It has a pressure resistance range of at least vacuum to 10 kPa. The reaction chamber is filled with high-purity argon gas (≥99.999%) until the pressure stabilizes at 3 kPa. The cooling water circulation system is activated to ensure adequate cooling of the electrodes and reaction chamber walls. A DC voltage is applied between the electrodes to ignite the DC arc plasma; the cathode current is 220 A. During energization, the silver rod is fed at a feed rate of 0.5 mm / s to maintain a stable arc and a continuous supply of silver vapor.

[0052] 2) Downstream in-situ coating and condensation channel: After the plasma stabilizes, a mixed quenching gas is injected downstream of the plasma and at the front of the condensation section through a precision nozzle. The total flow rate is 5000 sccm. The mixed quenching gas includes the main gas and the reactive gas, with the flow rate of the reactive gas accounting for 5% of the flow rate of the mixed quenching gas.

[0053] Main gas: The helium / argon mixture is precooled to -196°C using liquid nitrogen, wherein the volume ratio of helium to argon is 4:1.

[0054] Reactive gas: High-purity methane (≥99.99%).

[0055] 3) Particle collection system: A cryogenic bag filter made of polytetrafluoroethylene (PTFE) with a pore size ≤0.1 μm was used. The entire synthesis process lasted 30–60 minutes. The entire collector was placed in a liquid nitrogen-cooled jacket to ensure that the particles were collected at low temperatures, preventing premature decomposition of the carbon shell or sintering of the particles.

[0056] 4) Post-processing: The collected powder was subjected to low-temperature annealing for 60 min (at a constant temperature of 350°C) in an argon-filled tube furnace. The purpose of this step was to partially or completely burn off the amorphous carbon shell on the surface, forming particles with a clean silver surface. This also eliminated lattice defects within the particles and improved crystallinity. The annealed powder only needed to be naturally cooled under argon to obtain spherical silver powder.

[0057] Comparative Example 1 This comparative example provides a method for preparing spherical silver powder based on plasma technology. The only difference between this method and Example 1 is that the cathode voltage is adjusted to 100 A, while the other steps remain the same as in Example 1.

[0058] Comparative Example 2 This comparative example provides a method for preparing spherical silver powder based on plasma technology. The only difference between this method and Example 1 is that the total flow rate of the mixed quenching gas is adjusted to 3000 sccm, while the rest of the steps are the same as in Example 1.

[0059] Comparative Example 3 This comparative example provides a method for preparing spherical silver powder based on plasma technology. The only difference between this method and Example 1 is that the proportion of reactive gas in the mixed quenching gas is adjusted to 1%, while the other steps remain the same as in Example 1.

[0060] Comparative Example 4 This comparative example provides a method for preparing spherical silver powder based on plasma technology. The only difference between this method and Example 1 is that the proportion of reactive gas in the mixed quenching gas is adjusted to 7%, while the other steps remain the same as in Example 1.

[0061] Comparative Example 5 This comparative example provides a method for preparing spherical silver powder based on plasma technology. The only difference between this method and Example 1 is that the annealing temperature in the post-processing is adjusted to 200°C, while the other steps remain the same as in Example 1.

[0062] Comparative Example 6 This comparative example provides a method for preparing spherical silver powder based on plasma technology. The only difference between this method and Example 1 is that the annealing temperature in the post-processing is adjusted to 400°C, while the other steps remain the same as in Example 1.

[0063] Test case This experiment prepared spherical silver powder samples based on the methods provided in Examples 1-3 and Comparative Examples 1-6. The main differences between Examples 1-3 and Comparative Examples 1-6 are shown in Table 1. Performance tests were conducted on the above samples, and the specific experimental methods and results are as follows: Table 1. Key Difference Parameters between Examples 1-3 and Comparative Examples 1-6

[0064] 1. Particle size detection The particle size of the spherical silver powder sample was measured using a laser particle size analyzer (Mastersizer3000), and the results are shown in Table 2.

[0065] 2. Morphological assessment The morphology of the spherical silver powder samples was evaluated using a KYKY-2800 scanning electron microscope (SEM), and the results are shown in Table 2.

[0066] 3. Dispersion detection The dispersibility of the spherical silver powder samples was detected using a KYKY-2800 scanning electron microscope (SEM), and the results are shown in Table 2.

[0067] 4. Conductivity testing The conductivity of spherical silver powder samples was tested using a Shanghai Huayan SX1934 digital four-probe tester. The spherical silver powder samples were pressed into circular sheets at 50 MPa, and the resistivity of the pressed sheets was measured using the four-probe tester. The results are shown in Table 2.

[0068] Table 2 Test Results

[0069] The results in Table 2 show that: 1) Comparative Example 1 showed a significant decrease in overall performance compared to Example 1 due to the reduction in cathode current. This may be because the low current resulted in a low plasma temperature, which prevented the silver raw material from fully vaporizing. Some silver droplets condensed before complete evaporation, forming a wide distribution of micron-sized and nano-sized particles. The low-energy plasma could not provide sufficient surface tension to spherize the silver droplets, resulting in ellipsoidal, dumbbell-shaped, or dendritic particles with reduced tap density, affecting subsequent conductivity. The low-temperature plasma could not provide sufficient energy to promote the orderly arrangement of silver atoms, leading to numerous dislocations and stacking faults within the particles. These structural defects reduce the oxidation resistance and long-term stability of the silver powder.

[0070] 2) Comparative Example 2 showed a significant deterioration in overall performance due to the reduction in the total flow rate of the mixed quenching gas. This may be because the cooling rate was insufficient after the flow rate of the mixed quenching gas was reduced. The low flow rate of gas could not quickly remove the heat from the silver vapor, resulting in a longer residence time of the silver droplets in the high-temperature zone, causing secondary collisions and fusion, which in turn led to uneven particle size distribution and agglomeration. Furthermore, the low cooling rate also caused the silver atoms to be unable to arrange themselves in a sufficiently orderly manner, resulting in structural defects.

[0071] 3) Comparative Example 3 showed a significant deterioration in overall performance due to the reduction in the flow rate of reactive gas methane. This may be because the methane injected downstream of the plasma arc would normally undergo controlled heterogeneous pyrolysis in this temperature range, and the resulting carbon atoms would selectively deposit on the surface of silver nanoparticles to form an extremely thin, continuous amorphous carbon shell. This carbon shell, as a physical barrier, effectively prevents sintering and hard agglomeration of particles during movement and collection. However, when the methane supply is insufficient, the coating layer is not fully formed, leading to "hard agglomeration" of the silver particles.

[0072] 4) Comparative Example 4 showed a significant deterioration in overall performance due to the increased flow rate of the reactive gas methane. This may be because excess methane decomposes at high temperatures, producing a large number of carbon atoms, C2, C3, and other carbon clusters. These carbon clusters can act as independent gas-phase nucleation centers, forming numerous, very fine amorphous carbon nanoparticles. These carbon nanoparticles compete with silver vapor for the heat of the quenching gas, reducing the overall quenching rate. A slower cooling rate means that silver vapor has a longer "time window" for atomic migration and particle growth, resulting in larger silver particles in the early stages of nucleation. Excessive methane levels also lead to the formation of a thicker amorphous carbon shell on the surface of each silver nucleus. While this thick shell prevents "hard agglomeration" (metal-metal contact), it cannot prevent a phenomenon called "soft agglomeration." Multiple silver particles encased in thick carbon shells may attract each other through van der Waals forces on the carbon shell surface in the gas flow, colliding and temporarily adhering together to form a loose, "grape bunch"-like agglomerate composed of multiple core-shell particles. This "soft agglomeration" ultimately leads to an increase in the particle size of the spherical silver powder, a decrease in its dispersion, and a reduction in its conductivity.

[0073] 5) In Comparative Example 5, the annealing temperature was lowered. While the increase in particle size was not particularly significant, the conductivity was greatly affected. This may be because the excessively low annealing temperature resulted in incomplete removal of the carbon shell, leaving a layer of carbon on the surface of the finished silver powder. This carbon layer is an insulator and severely degrades the conductivity of the silver powder. Even if the particles themselves are spherical, the presence of residual carbon will lead to extremely high resistivity when making conductive pastes. Furthermore, the particles formed by rapid plasma condensation contain numerous lattice defects such as vacancies and dislocations. Low-temperature annealing cannot provide sufficient energy for atoms to move to their equilibrium positions. At this point, the resistivity of the powder remains high, and the internal stress within the particles is not released, potentially leading to instability during long-term storage or use.

[0074] 6) Comparative Example 6 showed a significant deterioration in overall performance after increasing the annealing temperature. This may be because the excessively high annealing temperature led to particle sintering and coarsening, as well as excessive reaction of the carbon shell, resulting in damage to the silver particles. The particles were connected by forming "necks," causing hard agglomeration and eventually fusing into larger, irregular porous particles. This completely destroyed the original spherical morphology and monodispersity, leading to a decrease in specific surface area.

[0075] Based on the above results, it can be seen that the present invention provides a method for preparing spherical silver powder based on plasma technology. Through a combination strategy of "instantaneous plasma vaporization + controllable gas phase condensation + downstream in-situ coating", nucleation is precisely controlled and particle agglomeration is suppressed, thus comprehensively improving the preparation process of spherical silver powder.

[0076] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

Claims

1. A method for preparing spherical silver powder based on plasma technology, characterized in that, The preparation method includes the following steps: S1: The reaction chamber is filled with inert gas, and a DC arc plasma is ignited between the silver anode and the high-temperature resistant cathode to generate silver vapor, which is continuously fed to the silver anode to maintain plasma stability. S2: A pre-cooled mixed quenching gas is injected downstream of the plasma to cause silver vapor to condense into nuclei and grow into silver particles, which are then collected under low-temperature conditions. S3: The collected silver particles are annealed under a protective atmosphere to obtain spherical silver powder.

2. The method for preparing spherical silver powder based on plasma technology according to claim 1, characterized in that, The inert gas mentioned in step S1 includes argon, and its pressure in the reaction chamber is maintained at 1~5 kPa.

3. The method for preparing spherical silver powder based on plasma technology according to claim 1, characterized in that, In step S1, the current of the cathode when igniting the DC arc plasma is 150~250 A.

4. The method for preparing spherical silver powder based on plasma technology according to claim 1, characterized in that, The mixed quenching gas in step S2 includes a host gas and a reactive gas. The host gas includes helium and argon, and the reactive gas includes methane or acetylene.

5. The method for preparing spherical silver powder based on plasma technology according to claim 3, characterized in that, The volume ratio of helium to argon in the main gas is (3~5):

1.

6. The method for preparing spherical silver powder based on plasma technology according to claim 3, characterized in that, The flow rate of the reactive gas accounts for 3% to 5% of the total flow rate of the mixed quenching gas.

7. The method for preparing spherical silver powder based on plasma technology according to claim 1, characterized in that, The total flow rate of the mixed quenching gas in step S2 is 4000~5000 sccm.

8. The method for preparing spherical silver powder based on plasma technology according to claim 1, characterized in that, The low-temperature conditions mentioned in step S2 include a low-temperature environment cooled by liquid nitrogen.

9. The method for preparing spherical silver powder based on plasma technology according to claim 1, characterized in that, The annealing temperature in step S3 is 250℃~350℃, and the annealing time is 30~90 min.

10. The application of the plasma-based spherical silver powder preparation method according to any one of claims 1 to 9 in the preparation of spherical silver powder.

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