Preparation method of high-sphericity superfine precious metal silver powder and silver-copper alloy powder

Abstract

The invention discloses a preparation method of high-sphericity superfine precious metal silver powder and silver-copper alloy powder, and belongs to the technical field of metal materials. The method comprises the following steps: melting pure Ag or AgCu alloy in a vacuum induction melting furnace, overheating the pure Ag or AgCu alloy at 100-200 DEG C, and preparing powder by adopting a vacuum (the vacuum degree is less than 3 * 10 <-3 > Pa), high-purity argon (the purity is greater than 99.999%) and high-pressure gas (the pressure is 1.5-3.0 MPa) atomization technology. The sphericity degree of the obtained powder is greater than 95%, the particle size distribution is as follows:-150 meshes account for 90%,-200 meshes account for 80%,-300 meshes account for 50%,-400 meshes account for 40%, and the unsieved particle size deviation accounts for less than 5%. The method is simple in process, low in cost, high in efficiency and suitable for large-scale production, can be widely applied to the fields of powder metallurgy electric contact materials, electronic paste, 3D printing and the like, and has the advantages of being high in fine powder rate, high in sphericity degree, low in oxygen content and the like.

Description

Technical Field

[0001] This invention relates to a method for preparing high-sphericity ultrafine precious metal silver powder and silver-copper alloy powder, belonging to the field of metal materials technology. Background Technology

[0002] High sphericity ultrafine powder materials are the basic raw materials for manufacturing powder metallurgy electrical contact materials, adhesive solder paste brazing materials, 3D printing materials, electronic pastes, etc., and their performance and quality directly determine the quality of parts. The methods currently used mainly include: (1) centrifugal atomization; (2) water atomization; (3) rotating electrode atomization; (4) consumable electrode atomization; (5) gas atomization, etc. The powder products mainly include Al alloy powder, Cu alloy powder, Ni alloy powder, Ti alloy powder, stainless steel powder, etc., but in terms of powder particle size composition and distribution, they all fail to meet the technical requirements of high sphericity ultrafine powder, that is, the powder sphericity is greater than 95%, the powder particle size distribution is -150 mesh (particle size <98μm) accounts for 90%, -200 mesh (particle size <74μm) accounts for 80%, -300 mesh (particle size <50μm) accounts for 50%, and -400 mesh (particle size <38μm) accounts for 40%. Although China has made some progress in the preparation of spherical ultrafine powders of non-ferrous metals, it still relies on imports for high-sphericity ultrafine pure Ag powder and AgCu alloy powder of precious metals. Furthermore, China's technical capabilities in vacuum gas atomization processes and powder preparation equipment are relatively weak, and it cannot meet the requirement of vacuum levels <3×10⁻⁶. -3 The atomization technical specifications require a purity of >99.999% for high-purity argon gas and a pressure of 1.5-3.0 MPa. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of existing ordinary atomization technologies in preparing high-sphericity ultrafine silver powder and silver-copper alloy powder, and to provide a new technology and process for vacuum melting and high-purity argon atomization powder preparation that can prepare high-sphericity ultrafine precious metal silver powder and silver-copper alloy powder. To achieve the above objective, this invention provides the following technical solution: (1) Raw material preparation: The purity of Ag raw material and Cu raw material is >99.95%.

[0004] (2) Vacuum induction melting: First, the vacuum induction melting equipment is evacuated to a vacuum degree of <3×10 -3 Pa; Melting pure Ag or AgCu alloy in a vacuum induction melting furnace with a power of 100KW.

[0005] (3) Atomization powder preparation: High-purity argon gas (purity >99.999%) is used as the atomization medium to prepare pure Ag powder and AgCu alloy powder by atomization.

[0006] (4) Pure Ag powder and AgCu alloy powder were subjected to ultrasonic vibration (power 400W, frequency 50KHZ) sieving and classification. The powder particle size classification was -150 mesh, -200 mesh, -300 mesh and -400 mesh. After sieving, the powder particle size distribution was -150 mesh (particle size <98μm) accounted for more than 90%, -200 mesh (particle size <74μm) accounted for more than 80%, -300 mesh (particle size <50μm) accounted for more than 50%, and -400 mesh (particle size <38μm) accounted for more than 40%. The proportion of unscreened powder particle size deviation was less than 5%.

[0007] (5) The obtained pure Ag powder and AgCu alloy powder are packaged under vacuum conditions to obtain pure Ag and AgCu alloy highly spherical ultrafine powder.

[0008] Preferably, in step (2), the superheating temperature is 100℃-200℃ and the refining time is 5-10min.

[0009] Preferably, in step (3), the gas atomizing nozzle is an annular slit spray disc, the atomizing gas pressure is 1.5-3.0MPa, the liquid flow diameter is Φ3.0mm-Φ6.0mm, and the annular slit width is 0.2-1.0mm.

[0010] The particle size distribution and particle size deviation technical indicators for preparing high sphericity ultrafine precious metal silver powder and silver-copper alloy powder by the method of the present invention are as follows: the particle size classification in step (4) is -150 mesh, -200 mesh, -300 mesh, and -400 mesh; the particle size distribution is -150 mesh (particle size <98μm) accounts for more than 90%, -200 mesh (particle size <74μm) accounts for more than 80%, -300 mesh (particle size <50μm) accounts for more than 50%, and -400 mesh (particle size <38μm) accounts for more than 40%, and the proportion of unsieved powder particle size deviation is less than 5%.

[0011] The high sphericity ultrafine precious metal silver powder and silver-copper alloy powder prepared by the method of the present invention must meet the following requirements for powder appearance and sphericity: the overall appearance of pure Ag powder and AgCu alloy powder samples is spherical, and the powder sphericity is greater than 95%.

[0012] This invention reduces metal oxidation and slag formation through vacuum induction melting, and then uses high-pressure, high-purity argon gas atomization to rapidly cool the molten metal and form spherical droplets. The annular nozzle design and high gas pressure improve atomization efficiency and ensure uniform cooling and solidification of the droplets, thereby obtaining powder with high sphericity and narrow particle size distribution. High-purity argon gas, as an inert medium, prevents oxidation and improves powder purity.

[0013] The beneficial effects of this invention are: (1) The present invention uses an annular slit gas atomizing nozzle as a spray plate. The atomizing gas pressure is high and the diameter of the molten metal is small, which improves the cooling speed of the molten metal, avoids the segregation of the alloy, and improves the atomization efficiency of the molten metal. By controlling the impurity elements and superheat of the molten metal in the powder making process, the preparation of precious metal ultrafine powder is realized. After sieving, the particle size distribution is more than 90% of -150 mesh (particle size <98μm), more than 80% of -200 mesh (particle size <74μm), more than 50% of -300 mesh (particle size <50μm), and more than 40% of -400 mesh (particle size <38μm). The particle size deviation of the powder that has not been sieved is less than 5%.

[0014] (2) The present invention uses vacuum melting of pure Ag or AgCu alloy, which reduces metal oxidation and slag formation; and uses high-purity argon (purity >99.999%) as atomizing medium, which increases the surface adhesion of metal droplets and improves the sphericity of powder. The sphericity of powder is greater than 95% and the oxygen content is <300ppm.

[0015] (3) The precious metal pure Ag powder and AgCu alloy powder of the present invention have stable quality, simple preparation technology, high production efficiency and low cost; AgCu alloy powder has uniform structure and no segregation; the technology is suitable for large-scale production, and the high sphericity ultrafine precious metal powder can meet the requirements of powder raw materials for industries such as powder metallurgy electrical contact materials, adhesive solder paste brazing materials, 3D printing materials, and electronic pastes. Attached Figure Description

[0016] Figure 1 The scanning electron microscope morphology of Ag powder in Example 1 of this invention; Figure 2 The scanning electron microscope morphology of Ag powder in Example 2 of this invention; Figure 3 The scanning electron microscope morphology of AgCu28 alloy powder in Example 3 of this invention; Figure 4 The scanning electron microscope (SEM) morphology of AgCu28 alloy powder in Example 4 of this invention is shown. Detailed Implementation

[0017] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0018] Example 1 A method for preparing highly spherical ultrafine precious metal silver powder and silver-copper alloy powder specifically includes the following steps: (1) Pure Ag is used as raw material, with a purity of >99.95%.

[0019] (2) A ring-slit spray disc is used as the atomizing gas nozzle, and the ring slit width is 0.2 mm.

[0020] (3) Place pure Ag into a vacuum induction melting furnace, and then evacuate the furnace to a vacuum degree of <3×10. -3 Pa, start increasing power and temperature, melt pure Ag in vacuum induction melting furnace, power is 100KW, superheat temperature is 100℃, refining time is 5min.

[0021] (4) High-purity argon gas (purity > 99.999%) was used as the atomizing medium. The high-pressure gas pressure was 1.5 MPa. 5 kg of pure Ag powder was prepared by one atomization.

[0022] (5) The pure Ag powder was classified by ultrasonic vibration sieving, and the particle size was classified as -150 mesh, -200 mesh, -300 mesh and -400 mesh.

[0023] (6) After testing and analysis, the overall appearance of pure Ag powder is spherical, with a sphericity of 97%. After sieving, the particle size distribution is as follows: -150 mesh (particle size <98μm) 92%, -200 mesh (particle size <74μm) 85%, -300 mesh (particle size <50μm) 53%, -400 mesh (particle size <38μm) 41%, and the particle size deviation of unsieved powder is 4.3%.

[0024] (7) The precious metal pure Ag powder is encapsulated under vacuum conditions to obtain pure Ag high spherical ultrafine powder.

[0025] Figure 1 This is the SEM morphology of the spherical ultrafine Ag powder prepared in this embodiment, from... Figure 1 As can be seen, the Ag powder prepared in this embodiment has high sphericity and fine particle size; the pure silver powder prepared in this embodiment has a sphericity of up to 97%, fine particle size and concentrated particle size distribution, with excellent results. The reason is that the small annular gap width (0.2 mm) and the relatively low atomizing gas pressure (1.5 MPa) are matched to form a high-speed but extremely fine and concentrated airflow field. This airflow can efficiently and uniformly shear the liquid flow of Φ3.0 mm-Φ6.0 mm, so that the broken silver droplets are of uniform size. At the same time, the moderate superheat (100 °C) not only ensures the good fluidity of the molten metal, but also avoids the volatilization, excessive splashing or satellite ball formation of the molten metal due to excessive temperature. This provides the best conditions for the droplets to be fully spherical under the action of surface tension, thereby obtaining extremely high sphericity and ideal particle size distribution.

[0026] Example 2 A method for preparing highly spherical ultrafine precious metal silver powder and silver-copper alloy powder specifically includes the following steps: (1) Pure Ag is used as raw material, with a purity of >99.95%.

[0027] (2) A ring-slit spray disc is used as the atomizing gas nozzle, with a ring slit width of 0.5 mm.

[0028] (3) Place pure Ag into a vacuum induction melting furnace, and then evacuate the furnace to a vacuum degree of <3×10. -3 Pa, start increasing power and temperature, melt pure Ag in vacuum induction melting furnace, power is 100KW, superheat temperature is 150℃, refining time is 7min.

[0029] (4) High-purity argon gas (purity > 99.999%) was used as the atomizing medium. The high-pressure gas pressure was 2.5 MPa. 5 kg of pure Ag powder was prepared by one atomization.

[0030] (5) The pure Ag powder was classified by ultrasonic vibration sieving, and the powder particle size was classified as -150 mesh, -200 mesh, -300 mesh and -400 mesh.

[0031] (6) After testing and analysis, the overall appearance of pure Ag powder is spherical, with a sphericity of 98%. After sieving, the particle size distribution is as follows: -150 mesh (particle size <98μm) 93%, -200 mesh (particle size <74μm) 87%, -300 mesh (particle size <50μm) 55%, -400 mesh (particle size <38μm) 44%, and the particle size deviation of powder that has not been sieved is 4.1%.

[0032] (7) The precious metal pure Ag powder is encapsulated under vacuum conditions to obtain pure Ag high spherical ultrafine powder.

[0033] Figure 2 This is the SEM morphology of the spherical ultrafine Ag powder prepared in this embodiment, from... Figure 2 As can be seen, the Ag powder prepared in this embodiment has high sphericity and fine particle size. Based on Example 1, this embodiment further improves the sphericity of the silver powder to 98%, and the proportion of each particle size range is also higher, resulting in the best effect. This is because the moderate annular gap width (0.5 mm) and the high atomizing gas pressure (2.5 MPa) form the best synergistic atomization effect. The wider air gap and higher pressure provide stronger atomization kinetic energy and a larger airflow coverage, which can more thoroughly break up the molten metal flow, thereby producing finer powder and optimizing the particle size distribution. At the same time, the higher superheat (150°C) further reduces the viscosity of the molten metal and enhances its sphericity. The precise combination of these three parameters achieves a perfect balance between atomization efficiency and sphericity quality, thus achieving the best overall effect.

[0034] Example 3 A method for preparing highly spherical ultrafine precious metal silver powder and silver-copper alloy powder specifically includes the following steps: (1) AgCu28 alloy was designed and prepared using Ag and Cu raw materials, with a purity of >99.95%.

[0035] (2) A ring-slit spray disc is used as the atomizing gas nozzle, with a ring slit width of 0.7 mm.

[0036] (3) Place pure Ag and pure Cu into a vacuum induction melting furnace, and then evacuate the furnace to a vacuum degree of <3×10. -3 Pa, start increasing power and temperature, melt pure Ag and pure Cu in vacuum induction melting furnace, power is 100KW, superheat temperature is 170℃, refining time is 8min.

[0037] (4) High-purity argon gas (purity > 99.999%) was used as the atomizing medium, and the high-pressure gas pressure was 2.6 MPa. 5 kg of AgCu28 alloy powder was prepared by atomization in one step.

[0038] (5) The pure AgCu28 alloy powder was classified by ultrasonic vibration sieving, and the powder particle size was classified as -150 mesh, -200 mesh, -300 mesh and -400 mesh.

[0039] (6) After testing and analysis, the overall appearance of AgCu28 alloy powder is spherical, with a sphericity of 96%. After sieving, the particle size distribution is as follows: -150 mesh (particle size <98μm) 94%, -200 mesh (particle size <74μm) 88%, -300 mesh (particle size <50μm) 59%, -400 mesh (particle size <38μm) 48%, and the particle size deviation of unsieved powder is 4.0%.

[0040] (7) The precious metal AgCu28 alloy powder is encapsulated under vacuum conditions to obtain AgCu28 highly spherical ultrafine powder.

[0041] Figure 3 This is the SEM morphology of the spherical ultrafine AgCu28 alloy powder prepared in this embodiment, from... Figure 3 As can be seen, the AgCu28 alloy powder prepared in this embodiment exhibits high sphericity and fine particle size. This embodiment successfully prepared AgCu28 alloy powder with 96% sphericity and a uniform microstructure without segregation, solving the problem of easy segregation in alloy powders. For AgCu alloys, preventing copper segregation is crucial. A wider annular gap (0.7 mm) and a higher atomizing gas pressure (2.6 MPa) ensure that the alloy liquid flow is instantly and fully broken into fine droplets, achieving an extremely high cooling rate and greatly suppressing the diffusion and segregation tendency of copper. A higher superheat (170 °C) ensures that the Ag and Cu components are fully miscible and have excellent fluidity, being "frozen" under rapid solidification conditions to form a uniform microstructure. This set of parameters is specifically optimized for the alloy system, focusing on achieving uniformity of the alloy microstructure while ensuring high sphericity.

[0042] Example 4 A method for preparing highly spherical ultrafine precious metal silver powder and silver-copper alloy powder specifically includes the following steps: (1) AgCu28 alloy was designed and prepared using Ag and Cu raw materials, with a purity of >99.95%.

[0043] (2) A ring-slit spray disc is used as the atomizing gas nozzle, with a ring slit width of 1.0 mm.

[0044] (3) Place pure Ag and pure Cu into a vacuum induction melting furnace, and then evacuate the furnace to a vacuum degree of <3×10. -3 Pa, start increasing power and temperature, melt pure Ag and pure Cu in vacuum induction melting furnace, power is 100KW, superheat temperature is 200℃, refining time is 10min.

[0045] (4) High-purity argon gas (purity > 99.999%) was used as the atomizing medium, and the high-pressure gas pressure was 3.0 MPa. 5 kg of AgCu28 alloy powder was prepared by atomization in one step.

[0046] (5) The pure AgCu28 alloy powder was classified by ultrasonic vibration sieving, and the powder particle size was classified as -150 mesh, -200 mesh, -300 mesh and -400 mesh.

[0047] (6) After testing and analysis, the overall appearance of AgCu28 alloy powder is spherical, with a sphericity of 98%. After sieving, the particle size distribution is as follows: -150 mesh (particle size <98μm) 96%, -200 mesh (particle size <74μm) 90%, -300 mesh (particle size <50μm) 62%, -400 mesh (particle size <38μm) 50%, and the particle size deviation of powder that has not been sieved is 3.8%.

[0048] (7) The precious metal AgCu28 alloy powder is encapsulated under vacuum conditions to obtain AgCu28 highly spherical ultrafine powder.

[0049] Figure 4 This is the SEM morphology of the spherical ultrafine AgCu28 alloy powder prepared in this embodiment, from... Figure 4As can be seen, the AgCu28 alloy powder prepared in this embodiment exhibits high sphericity and fine particle size. This embodiment yielded AgCu28 alloy powder with a sphericity as high as 98% and the finest particle size (50% of which is -400 mesh), demonstrating the ability of this process to produce top-grade alloy powder. This embodiment employed the extreme settings within the parameter range of this invention—the widest annular gap (1.0 mm) and the highest atomizing gas pressure (3.0 MPa). This generated the most energetic and abundant atomizing gas flow field, maximizing the breaking ability of the molten metal flow, thus producing the finest powder particle size and the highest proportion of each particle size range. The highest superheat (200°C) ensured that even with high copper content, the alloy liquid maintained optimal fluidity and uniformity. Coupled with the extremely high cooling rate brought about by the extreme atomization parameters, near-perfect AgCu28 alloy powder with high sphericity, ultrafine particle size, and no segregation was prepared.

[0050] As can be seen from Examples 1-4, this invention, through precise design and coordinated control of key parameters such as vacuum degree, atomization pressure, annular gap width, and superheat, can flexibly optimize the process for different materials (pure silver or silver-copper alloys), and stably produce high-quality powders far exceeding existing atomization powder production technologies. Whether it is a pure metal pursuing ultimate sphericity and particle size distribution, or an alloy requiring uniform composition without segregation, this invention can provide targeted solutions through adjustments to process parameters.

Claims

1. A method for preparing high-sphericity ultrafine precious metal silver powder and silver-copper alloy powder, characterized in that: The method mainly comprises the following steps: (1) raw material preparation: silver and copper raw materials with purity of not less than 99.95% are adopted; (2) vacuum melting: the raw materials are placed in a vacuum induction melting furnace, and are heated, melted and refined; (3) high-pressure gas atomization: a ring-slit type spray disc is adopted for a gas atomization nozzle, and inert gas is used as atomization medium to atomize the metal liquid stream, so that metal powder is prepared; (4) screening treatment: the powder obtained by atomization is subjected to ultrasonic vibration screening and grading, so that powder products with target particle size distribution are obtained; (5) vacuum packaging: the screened powder is packaged under vacuum condition.

2. The method of claim 1, wherein the high-sphericity ultrafine noble metal silver powder, silver-copper alloy powder is characterized in that: The vacuum melting process of step (2) is carried out at a power of 100 KW and a superheating temperature of 100-200℃.

3. The method of claim 1, wherein the high-sphericity ultrafine noble metal silver powder, silver-copper alloy powder is characterized in that: The refining time in step (2) is 5-10 min.

4. The method of claim 1, wherein the high-sphericity ultrafine noble metal silver powder, silver-copper alloy powder is characterized in that: The inert gas in step (3) is high-purity argon with purity of >99.999%.

5. The method of claim 1, wherein the high-sphericity ultrafine noble metal silver powder, silver-copper alloy powder is characterized in that: The atomization gas pressure in step (3) is 1.5-3.0 MPa, and the liquid stream diameter is Φ3.0-Φ6.0 mm.

6. The method of claim 1, wherein the high-sphericity ultrafine noble metal silver powder, silver-copper alloy powder is characterized in that: The ring-slit width in step (3) is 0.2-1.0 mm.

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