Preparation method of silver-coated copper powder

Abstract

The invention provides a preparation method of silver-coated copper powder, and relates to the technical field of metal powder preparation. According to the preparation method, a copper core is directly prepared by adopting a chemical reduction method, then a silver layer is grown on the surface of the copper core by adopting a chemical plating method, and finally, the powder compactness is improved by adopting a jet mill polishing mode. The reducing agents with different reducing effects are added twice to reduce copper sulfate, so that the initial reaction rate is reduced, the whole reaction is stable, and the sphericity degree of copper crystal nucleus is improved; meanwhile, sulfate radicals in the reaction system and silver ions in the subsequent reaction can form silver sulfate precipitates, the reduction speed of silver-ammonia complex ions is further reduced, and the silver layer grows compactly; and meanwhile, the incompletely reacted glucose remained in the reaction system can be used for continuously reducing silver-ammonia complex ions when the silver-ammonia solution is subsequently dropwise added. By strictly controlling the growth speed of the silver powder from the seed crystal to the particles, the structure defects caused by rapid growth are reduced, and the performance of the final product is improved.

Description

Technical Field

[0001] The invention relates to the technical field of metal powder preparation, and in particular to a method for preparing silver-coated copper powder. Background Art

[0002] Copper powder has excellent electrical conductivity similar to that of silver (the volume resistivity of silver is 1.59×10 -6 Ω·cm, the volume resistivity of copper is 1.72×10 -6 Ω·cm), and the price of copper is only 1 / 20 of that of silver. In many cases, its application is limited not by its conductivity but by its oxidation resistance. Silver-coated copper powder is a core-shell structure powder with copper powder as the core and silver as the coating layer. When the coating layer is dense and complete, it has all the excellent properties of pure silver powder and has a great cost advantage over pure silver powder. It has extremely broad application prospects in the fields of microelectronics, photovoltaics, etc.

[0003] Since the low-temperature sintering process of heterojunction cells can avoid many performance defects caused by silver migration at high temperatures, silver-coated copper powder is particularly suitable for use in silver paste for low-temperature sintered heterojunction solar cells. Using silver-coated copper powder instead of pure silver powder can significantly reduce the non-silicon cost of the cell, which is of great significance for promoting the cost reduction and efficiency increase of heterojunction cells, and therefore has become the focus of current industry attention.

[0004] The existing methods for preparing silver-coated copper powder mainly include vapor deposition method, mechanical mixing method, chemical method, etc. The vapor deposition method has a complex process flow and high production cost. The mechanical method has many influencing factors and unstable product quality. The chemical method has simple process, controllable coating thickness, and low production cost, but the silver-coated copper powder prepared by the existing chemical method still has problems such as insufficient density of the silver plating layer and incomplete coating layer. The exposed copper powder is very easy to oxidize, resulting in the loss of overall conductivity, which affects the use effect of the silver-coated copper powder.

[0005] Therefore, improving the density and integrity of the silver coating of silver-coated copper powder is of great significance to the production technology of silver-coated copper powder and the development of the photovoltaic industry. Summary of the invention

[0006] In view of the defects of the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing a silver-coated copper powder with good compactness and integrity of the silver-plated layer. The method adopts a chemical reduction method to directly prepare a copper core, then uses a chemical plating method to grow a silver layer on its surface, and finally uses an air flow grinding method to improve the density of the powder. The growth rate of the silver powder from the seed to the particle is strictly controlled to reduce the structural defects caused by rapid growth, and the surface of the powder is further optimized through physical action, and finally a dense and uniformly coated silver-coated copper powder product is obtained. To achieve the above object, the present invention provides a method for preparing silver-coated copper powder, comprising the following steps: S1, adding a dispersant to a copper sulfate solution, and stirring to obtain a copper sulfate dispersion; S2, adding a first reducing agent, glucose solution, to the copper sulfate dispersion obtained in step S1, and performing a first reaction for 0.5-1.5 hours; then adding a second reducing agent, ascorbic acid, and performing a second reaction for 0.5-1.5 hours to obtain a copper core solution; S3, adding dispersant polyvinyl pyrrolidone to the silver nitrate solution, adding sodium hydroxide after the silver nitrate solution is fully dissolved, and then adding ammonia water dropwise until the solution is clear, thereby obtaining a silver ammonia solution; S4, under the condition of constant temperature of 50-60°C and mechanical stirring, the silver ammonia solution prepared in step S3 is added dropwise to the copper core solution at a speed of 2-5 ml / min, the speed of mechanical stirring is 300-350 rpm / min, and after 0.5-2 min, a glucose solution with a concentration of 150-175 g / L is added dropwise to the copper core solution at a speed of 2-5 ml / min, and after the addition is completed, the solution is filtered and washed; S5, dispersing the washed silver-coated copper powder in an ethanol solution of an organic acid with a mass concentration of 0.3-0.5%, filtering and drying, and then jet milling for 0.2-0.5h to obtain the silver-coated copper powder.

[0007] Furthermore, the pH of the first reducing agent glucose solution is adjusted to 10-12 with sodium hydroxide before use.

[0008] Furthermore, the concentration of the first reducing agent is 5-7 mol / L, and the concentration of the second reducing agent is 1-2 mol / L.

[0009] Furthermore, the reaction temperatures of the first reaction and the second reaction are both 60-90°C.

[0010] Furthermore, the dispersant is polyvinyl pyrrolidone, and the amount of the dispersant is 0.5-1% of the mass of copper sulfate.

[0011] Furthermore, in step S5, the process conditions of the air jet mill treatment are: using a fluidized bed jet mill, and the grinding gas pressure is 0.2MPa-0.8MPa.

[0012] Furthermore, in step S5, the mass volume ratio of the silver-coated copper powder to the ethanol solution is (4-5) g: (90-100) ml.

[0013] Furthermore, in step S3, the concentration of the silver nitrate solution is 40-50 g / L, the amount of the dispersant is 0.1-1% of the mass of the silver nitrate, and the amount of the sodium hydroxide is 0.1-1% of the mass of the silver nitrate.

[0014] Furthermore, in step S1, the concentration of the copper sulfate solution is 0.3-0.6 mol / L.

[0015] Furthermore, in step S5, the organic acid is one or more of stearic acid, oleic acid, ricinoleic acid, palmitic acid, and elaeisoleic acid.

[0016] The beneficial effects of the present invention are: 1. The preparation method of the silver-coated copper powder provided by the present invention firstly adopts a chemical reduction method to directly prepare a copper core, then uses a chemical plating method to grow a silver layer on its surface, and finally adopts an air flow grinding method to improve the density of the powder. The present invention reduces the structural defects caused by rapid growth by strictly controlling the growth rate of the silver powder from the seed to the particle.

[0017] 2. In step S2, the present invention reduces copper sulfate by adding reducing agents with different reducing effects twice, which reduces the initial reaction rate, makes the whole reaction stable, and improves the sphericity of the copper nucleus; at the same time, the sulfate radical in the reaction system can form silver sulfate precipitation with the silver ions in the subsequent step S4 reaction, further slowing down the speed at which the silver ammonia complex ions are reduced, so that the silver layer grows densely; at the same time, the unreacted glucose retained in the reaction system can continue to reduce the silver ammonia complex ions when the silver ammonia solution is added dropwise in the subsequent step S4. Compared with the traditional seed crystal preparation process, the design of this reaction process avoids the cumbersome operation of seed crystal washing and purification, simplifies the preparation process, and makes the byproducts and unreacted products in the seed crystal preparation process reasonably utilized, thereby improving the performance of the final product.

[0018] 3. In step S4, the present invention adopts the operation of gradually adding silver ammonia solution. Because the addition of silver ammonia solution will gradually increase the alkalinity of the system, as the alkalinity increases, the reducing ability of glucose also gradually increases, so that the chemical silver plating reaction on the surface of the copper crystal core starts smoothly. This provides a reaction system that starts gradually and the process is stable, which also contributes to the dense structure of the final product.

[0019] 4. In step S5, the jet milling treatment can not only ensure that the surface of the powder is fully coated with organic matter, but also further improve the density and sphericity of the powder through mechanical grinding. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a scanning electron microscope image of the silver-coated copper powder prepared in Example 1.

[0021] Figure 2 This is a scanning electron microscope image of the silver-coated copper powder prepared in Example 2.

[0022] Figure 3 This is a scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 1.

[0023] Figure 4 This is a scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 3.

[0024] Figure 5 This is a scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 4.

[0025] Figure 6 This is a scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 5.

[0026] Figure 7 This is a scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 6. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0029] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0030] In the prior art, the preparation process of silver-coated copper powder is to first prepare copper powder and then plate silver on the surface of the copper powder. The process flow includes tedious washing and purification operations, and the process is complicated.

[0031] The present invention provides a method for preparing silver-coated copper powder, wherein a copper core is directly prepared by chemical reduction, a silver layer is grown on its surface by chemical plating, and finally the powder is polished by air flow grinding to improve the density. The present invention reduces structural defects caused by rapid growth by strictly controlling the growth rate of silver powder from seed to particle.

[0032] Specifically, the present invention reduces copper sulfate by adding reducing agents with different reducing effects twice, thereby reducing the initial reaction rate, making the entire reaction stable, and improving the sphericity of the copper crystal nucleus; at the same time, the sulfate radicals in the reaction system can form silver sulfate precipitation with the silver ions in the subsequent reaction, further slowing down the speed at which the silver ammonia complex ions are reduced, so that the silver layer grows densely; at the same time, the unreacted glucose remaining in the reaction system can continue to reduce the silver ammonia complex ions when the silver ammonia solution is subsequently added. Compared with the traditional seed crystal preparation process, the design of this reaction process avoids the cumbersome operation of seed crystal washing and purification, simplifies the preparation process, and also makes reasonable use of byproducts and unreacted materials in the seed crystal preparation process, thereby improving the performance of the final product.

[0033] The present invention provides a method for preparing silver-coated copper powder, comprising the following steps: S1, adding a dispersant polyvinyl pyrrolidone to a copper sulfate solution, and stirring the solution to obtain a copper sulfate dispersion; The dosage of the dispersant is 0.5-1% of the mass of copper sulfate; the concentration of the copper sulfate solution is 0.3-0.6 mol / L.

[0034] S2, adding the first reducing agent glucose solution to the copper sulfate dispersion obtained in step S1, and carrying out a first reaction for 0.5-1.5 hours; then adding the second reducing agent ascorbic acid to carry out a second reaction for 0.5-1.5 hours to obtain a copper core solution; the reaction temperature of the first reaction and the second reaction are both 60-90°C.

[0035] The pH of the first reducing agent glucose solution is adjusted to 10-12 with sodium hydroxide before use.

[0036] The concentration of the first reducing agent is 5-7 mol / L, and the concentration of the second reducing agent is 1-2 mol / L.

[0037] S3, adding dispersant polyvinyl pyrrolidone to the silver nitrate solution, adding sodium hydroxide after the silver nitrate solution is fully dissolved, and then adding ammonia water dropwise until the solution is clear, thereby obtaining a silver ammonia solution; The concentration of the silver nitrate solution is 40-50 g / L, the amount of the dispersant is 0.1-1% of the mass of the silver nitrate, and the amount of the sodium hydroxide is 0.1-1% of the mass of the silver nitrate.

[0038] S4, under the condition of constant temperature of 50-60°C and mechanical stirring, the silver ammonia solution prepared in step S3 is added dropwise to the copper core solution at a speed of 2-5 ml / min, the speed of mechanical stirring is 300-350 rpm / min, and after 0.5-2 min, a glucose solution with a concentration of 150-175 g / L is added dropwise to the copper core solution at a speed of 2-5 ml / min, and after the addition is completed, the solution is filtered and washed; In step S4, the operation of gradually adding silver ammonia solution is adopted. Because the addition of silver ammonia solution will gradually increase the alkalinity of the system, as the alkalinity increases, the reducing ability of glucose also gradually increases, so that the chemical silver plating reaction on the surface of the copper crystal core starts smoothly. This provides a reaction system that starts gradually and the process is stable. It also contributes to the dense structure of the final product.

[0039] S5, dispersing the washed silver-coated copper powder in an ethanol solution of an organic acid with a mass concentration of 0.3-0.5%, filtering and drying, and then jet milling for 0.2-0.5h to obtain the silver-coated copper powder.

[0040] The mass volume ratio of silver-coated copper powder to ethanol solution is (4-5) g: (90-100) ml.

[0041] The process conditions of the air flow mill treatment are as follows: a fluidized bed jet-type air flow mill is used, and the crushing gas pressure is 0.2MPa-0.8MPa.

[0042] Wherein, the organic acid is one or more of stearic acid, oleic acid, ricinoleic acid, palmitic acid and elaeisoleic acid.

[0043] In step S5, the jet milling treatment can not only ensure that the surface of the powder is fully coated with organic matter, but also further improve the density and sphericity of the powder through mechanical grinding.

[0044] The preparation method of the silver-coated copper powder provided by the present invention is described below in conjunction with specific examples. Unless otherwise specified, the raw materials and reagents in the examples of the present application are purchased through commercial channels.

[0045] Example 1 This embodiment provides a method for preparing silver-coated copper powder, which specifically comprises the following steps: S1, prepare 1L 0.5mol / L copper sulfate solution (79.81g copper sulfate), add 0.48g polyvinyl pyrrolidone (K30), and stir evenly to obtain a copper sulfate dispersion; S2, prepare 100 ml of 6 mol / L glucose solution (first reducing agent, 108.11 g glucose), adjust the pH to 12 with sodium hydroxide, then add it to the copper sulfate dispersion obtained in step S1 and react at 60°C for 1 h, then add 100 ml of 1.5 mol / L ascorbic acid solution (second reducing agent, 26.42 g ascorbic acid) and continue to react for 0.5 h to obtain a copper core solution.

[0046] S3, Preparation of silver ammonia solution Under mechanical stirring, add 10g of silver nitrate (the concentration of silver nitrate solution is 50g / L) to 200ml of deionized water, mix well, add 0.1g of polyvinyl pyrrolidone, add 0.1g of sodium hydroxide after it is fully dissolved, and then add ammonia water dropwise until the solution is clear.

[0047] S4, preparation of glucose solution: under mechanical stirring, add 35g glucose (the concentration of glucose solution is 175g / L) into 200ml deionized water and stir until completely dissolved.

[0048] Redox reaction: under the condition of constant temperature of 60℃ and mechanical stirring, add silver ammonia solution to the copper core solution at a rate of 2 ml / min, maintain the mechanical stirring speed at 300 rpm / min, and start to add glucose solution to the copper core solution at the same rate after 1 minute. After the addition is completed, filter and wash.

[0049] S5, product surface treatment The washed silver-coated copper powder was filtered, dispersed in an ethanol solution of stearic acid with a mass concentration of 0.5%, filtered and dried, and then subjected to a jet mill treatment for 0.5 h at a crushing gas pressure of 0.6 MPa to obtain the product silver-coated copper powder, wherein the mass volume ratio of the silver-coated copper powder to the ethanol solution was 4 g:100 ml.

[0050] Example 2 Example 2 provides a method for preparing silver-coated copper powder, and its main parameter changes compared with Example 1 are shown in the following table; the rest are roughly the same as Example 1 and will not be repeated here.

[0051] Comparison of main parameters between Example 2 and Example 1 Figure 1 , Figure 2 The scanning electron microscope images (SEM) of the silver-coated copper powder prepared in Example 1 and Example 2 are shown respectively.

[0052] It can be seen that the obtained silver-coated copper powder grows relatively densely, has high sphericity, and has no obvious structural defects.

[0053] Comparative Example 1 Comparative Example 1 provides a method for preparing silver-coated copper powder, which is different from Example 1 in that step S5 is not performed. The rest is substantially the same as Example 1 and will not be described in detail.

[0054] Figure 3 This is a scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 1. It can be seen that when the airflow milling treatment is not performed, the appearance of the silver-coated copper powder is relatively irregular.

[0055] Comparative Example 2 Comparative Example 2 provides a method for preparing silver-coated copper powder, which is different from Example 1 in that: in step S2, the second reducing agent ascorbic acid is not used. The rest is substantially the same as Example 1 and will not be described again.

[0056] Experiments show that when ascorbic acid, the second reducing agent, is not used, the reducing property of the glucose reducing agent is not enough, and glucose alone cannot reduce all copper ions in this reaction system. The yield of copper powder in the copper core solution is very low, making the subsequent steps meaningless.

[0057] Comparative Example 3 Comparative Example 3 provides a method for preparing silver-coated copper powder, which is different from Example 1 in that: in step S2, the first reducing agent glucose is not used. The rest is substantially the same as Example 1 and will not be described again.

[0058] Figure 4 This is a scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 3. It can be seen that the silver-coated copper powder generated by the reaction is very irregular. The reason is that the ascorbic acid reducing agent has a stronger reducing property than glucose, and the reaction cannot start slowly and steadily. Therefore, the generated copper is relatively irregular and has a low sphericity, which affects the subsequent growth of the silver layer.

[0059] Comparative Example 4 Comparative Example 4 provides a method for preparing silver-coated copper powder, which is different from Example 1 in that: in step S2, sodium hydroxide is not used to adjust the pH of the glucose solution. The rest is roughly the same as Example 1 and will not be repeated here.

[0060] Figure 5 This is a scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 4. It can be seen that the silver-coated copper powder generated by the reaction is very irregular. The reason is that the reducing property of glucose will increase with the increase of alkalinity in the system. If the pH is not adjusted, the reducing property of glucose is too weak to guide the reaction to start, and it will not work.

[0061] Comparative Example 5 Comparative Example 5 provides a method for preparing silver-coated copper powder, which is different from Example 1 in that the copper sulfate in step S1 is replaced by copper nitrate. The rest is substantially the same as Example 1 and will not be described again.

[0062] Figure 6 This is a scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 5. It can be seen that the growth of the silver layer is relatively irregular compared with Example 1. The reason may be that there is a lack of sulfate in the reaction system, and the silver ions in the subsequent step S4 reaction cannot form precipitation, thereby slowing down the speed at which the silver ammine ions are reduced, so the growth of the silver layer is relatively irregular.

[0063] Comparative Example 6 Comparative Example 6 provides a method for preparing silver-coated copper powder, which is different from Example 1 in that: in step S5, the process conditions of the air flow mill treatment are: the crushing gas pressure is 0.1 MPa, and the treatment time is 0.3 h. The rest is roughly the same as Example 1 and will not be repeated here.

[0064] Figure 7 This is a scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 6. It can be seen that when the pulverizing gas pressure of the jet mill is less than 0.2 MPa, the strength is insufficient and the sphericity of the obtained silver-coated copper powder deteriorates.

[0065] It should be noted that the organic acid may also be one or more of ricinoleic acid, palmitic acid, and elaeisoleic acid.

[0066] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing silver-coated copper powder, characterized in that: The steps include: S1, adding a dispersant to a copper sulfate solution, and stirring to obtain a copper sulfate dispersion; S2, adding a first reducing agent, glucose solution, to the copper sulfate dispersion obtained in step S1, and performing a first reaction for 0.5-1.5 hours; then adding a second reducing agent, ascorbic acid, and performing a second reaction for 0.5-1.5 hours to obtain a copper core solution; S3, adding dispersant polyvinyl pyrrolidone to the silver nitrate solution, adding sodium hydroxide after the silver nitrate solution is fully dissolved, and then adding ammonia water dropwise until the solution is clear, thereby obtaining a silver ammonia solution; S4, under the condition of constant temperature of 50-60°C and mechanical stirring, the silver ammonia solution prepared in step S3 is added dropwise to the copper core solution at a speed of 2-5 ml / min, the speed of mechanical stirring is 300-350 rpm / min, and after 0.5-2 min, a glucose solution with a concentration of 150-175 g / L is added dropwise to the copper core solution at a speed of 2-5 ml / min, and after the addition is completed, the solution is filtered and washed; S5, dispersing the washed silver-coated copper powder in an ethanol solution of an organic acid with a mass concentration of 0.3-0.5%, filtering and drying, and then jet milling for 0.2-0.5h to obtain the silver-coated copper powder.

2. The method for preparing silver-coated copper powder according to claim 1, characterized in that: In step S2, the pH of the first reducing agent glucose solution is adjusted to 10-12 with sodium hydroxide before use.

3. The method for preparing silver-coated copper powder according to claim 1, characterized in that: In step S2, the concentration of the first reducing agent is 5-7 mol / L, and the concentration of the second reducing agent is 1-2 mol / L.

4. The method for preparing silver-coated copper powder according to claim 1, characterized in that: In step S2, the reaction temperatures of the first reaction and the second reaction are both 60-90°C.

5. The method for preparing silver-coated copper powder according to claim 1, characterized in that: In step S1, the dispersant is polyvinyl pyrrolidone, and the amount of the dispersant is 0.5-1% of the mass of copper sulfate.

6. The method for preparing silver-coated copper powder according to claim 1, characterized in that: In step S5, the process conditions of the jet mill treatment are: using a fluidized bed jet mill with a grinding gas pressure of 0.2 MPa-0.8 MPa.

7. The method for preparing silver-coated copper powder according to claim 1, characterized in that: In step S5, the mass volume ratio of the silver-coated copper powder to the ethanol solution is (4-5) g: (90-100) ml.

8. The method for preparing silver-coated copper powder according to claim 1, characterized in that: In step S3, the concentration of the silver nitrate solution is 40-50 g / L, the amount of the dispersant is 0.1-1% of the mass of the silver nitrate, and the amount of the sodium hydroxide is 0.1-1% of the mass of the silver nitrate.

9. The method for preparing silver-coated copper powder according to claim 1, characterized in that: In step S1, the concentration of the copper sulfate solution is 0.3-0.6 mol / L.

10. The method for preparing silver-coated copper powder according to claim 1, characterized in that: In step S5, the organic acid is one or more of stearic acid, oleic acid, ricinoleic acid, palmitic acid, and elaeisoleic acid.

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