Preparation method of silver-coated copper powder

Abstract

The present invention provides a method for preparing silver-coated copper powder, which relates to the technical field of metal powder preparation. This preparation method directly prepares a copper core by chemical reduction method, then uses electroless plating method to grow a silver layer on its surface, and finally uses jet milling to improve the density of the powder. In the present invention, reducing agents with different reduction effects are added twice to reduce copper sulfate, which reduces the initial reaction rate, makes the whole reaction stable, and improves the sphericity of copper crystal nuclei. At the same time, sulfate radicals in the reaction system can form silver sulfate precipitation with silver ions in the subsequent reaction, further slowing down the reduction rate of silver ammonia complex ions and enabling the dense growth of the silver layer. At the same time, the unreacted completely glucose remaining in the reaction system can continue to reduce silver ammonia complex ions when silver ammonia solution is added dropwise later. By strictly controlling the growth rate of silver powder from crystal seeds to particles, the present invention reduces the structural defects caused by rapid growth and improves the performance of the final product.

Description

Technical Field

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

[0002] Copper metal powder has excellent electrical conductivity similar to that of silver (the volume resistivity of silver is 1.59×10 -6 Ω·cm, and 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, what restricts its application is not electrical conductivity, but oxidation resistance. Silver-coated copper powder is a powder with a core-shell structure with copper powder as the core and silver as the coating layer. In the state where the coating layer is dense and complete, it has all the excellent properties of pure silver powder, and at the same time has a great cost advantage compared with 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 batteries can avoid many performance defects caused by silver migration at high temperatures, silver-coated copper powder is particularly suitable for use in silver pastes 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 battery, which is of great significance for promoting the cost reduction and efficiency increase of heterojunction batteries, and thus has become the focus of current industry attention.

[0004] Existing methods for preparing silver-coated copper powder mainly include chemical vapor deposition method, mechanical mixing method, chemical method, etc. The chemical 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 the advantages of simple process, controllable coating layer 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 coating layer and incomplete coating layer. The exposed copper powder is extremely prone to oxidation, resulting in loss of overall electrical conductivity and affecting the use effect of silver-coated copper powder.

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

[0006] Aiming at the defects of the above-mentioned existing technologies, the purpose of the present invention is to provide a method for preparing silver-coated copper powder with good density and integrity of the silver coating layer. This method directly prepares a copper core by chemical reduction method, then uses electroless plating method to grow a silver layer on its surface, and finally uses air jet milling to improve the density of the powder. By strictly controlling the growth rate of silver powder from crystal seeds to particles, structural defects caused by rapid growth are reduced, and further, the surface of the powder is optimized by physical action, and finally a dense and uniformly coated silver-coated copper powder product is obtained.

[0007] To achieve the above object, the present invention provides a method for preparing silver-coated copper powder, comprising the following steps:

[0008] S1, adding a dispersant into a copper sulfate solution, and stirring evenly to obtain a copper sulfate dispersion;

[0009] S2, adding a first reducing agent glucose solution into the copper sulfate dispersion obtained in step S1, and carrying out a first reaction for 0.5 - 1.5 h; then adding a second reducing agent ascorbic acid to carry out a second reaction for 0.5 - 1.5 h to obtain a copper core solution;

[0010] S3, adding a dispersant polyvinylpyrrolidone into a silver nitrate solution, fully dissolving, adding sodium hydroxide, and then dropping ammonia water until the solution becomes clear to obtain a silver ammonia solution;

[0011] S4, under the conditions of constant temperature at 50 - 60 °C and mechanical stirring, dropping the silver ammonia solution prepared in step S3 into the copper core solution at a rate of 2 - 5 ml / min, the rotation speed of mechanical stirring is 300 - 350 rpm / min, and after 0.5 - 2 min, starting to drop a glucose solution with a concentration of 150 - 175 g / L into the copper core solution at a rate of 2 - 5 ml / min. After dropping, filter and wash;

[0012] 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 carrying out jet milling treatment for 0.2 - 0.5 h to obtain the silver-coated copper powder.

[0013] Further, the pH of the first reducing agent glucose solution is adjusted to 10 - 12 with sodium hydroxide before use.

[0014] Further, 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.

[0015] Further, the reaction temperature of both the first reaction and the second reaction is 60 - 90 °C.

[0016] Further, the dispersant is polyvinylpyrrolidone, and the dosage of the dispersant is 0.5 - 1% of the mass of copper sulfate.

[0017] Further, in step S5, the process conditions of jet milling treatment are: using a fluidized bed opposed jet mill, and the crushing gas pressure is 0.2 MPa - 0.8 MPa.

[0018] Further, in step S5, the mass - volume ratio of the silver-coated copper powder to the ethanol solution is (4 - 5) g : (90 - 100) ml.

[0019] Further, in step S3, the concentration of the silver nitrate solution is 40 - 50 g / L, the dosage of the dispersant is 0.1 - 1% of the mass of silver nitrate, and the dosage of sodium hydroxide is 0.1 - 1% of the mass of silver nitrate.

[0020] Further, in step S1, the concentration of the copper sulfate solution is 0.3 - 0.6 mol / L.

[0021] Further, in step S5, the organic acid is one or more of stearic acid, oleic acid, ricinoleic acid, palmitic acid, and lacceroic acid.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. The preparation method of silver-coated copper powder provided by the present invention first directly prepares a copper core by a chemical reduction method, then uses an electroless plating method to grow a silver layer on its surface, and finally uses a jet mill to polish to improve the density of the powder. By strictly controlling the growth rate of silver powder from crystal seeds to particles, the present invention reduces the structural defects caused by rapid growth.

[0024] 2. In step S2, the present invention reduces the initial reaction rate by adding reducing agents with different reduction effects twice to reduce copper sulfate, making the whole reaction stable and improving the sphericity of copper crystal nuclei; at the same time, sulfate radicals in the reaction system can form silver sulfate precipitation with silver ions in the subsequent step S4 reaction, further slowing down the reduction rate of silver ammonia complex ions and enabling the silver layer to grow densely; at the same time, the unreacted completely glucose remaining in the reaction system can continue to reduce silver ammonia complex ions when adding silver ammonia solution in the subsequent step S4. This design of the reaction process, compared with the traditional crystal seed preparation process, not only avoids the cumbersome operations of crystal seed washing and purification, simplifies the preparation process, but also makes reasonable use of by-products and unreacted substances in the crystal seed preparation process, improving the performance of the final product.

[0025] 3. In step S4, the present invention adopts the operation of gradually adding silver ammonia solution. Since the addition of silver ammonia solution will gradually increase the alkalinity of the system, and with the increase of alkalinity, the reduction ability of glucose also gradually increases, making the reaction of electroless plating silver on the surface of copper crystal nuclei start smoothly. This provides a reaction system that starts gradually and has a stable process, which also helps the dense structure of the final product.

[0026] 4. In step S5, the jet mill 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 polishing. Description of the Drawings

[0027] Figure 1 It is a scanning electron microscope image of the silver-coated copper powder prepared in Example 1.

[0028] Figure 2 Scanning electron microscope image of the silver-coated copper powder prepared in Example 2.

[0029] Figure 3 Scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 1.

[0030] Figure 4 Scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 3.

[0031] Figure 5 Scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 4.

[0032] Figure 6 Scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 5.

[0033] Figure 7 Scanning electron microscope image of the silver-coated copper powder prepared in Comparative Example 6. Detailed implementation manners

[0034] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Here, it should also be noted that in order to avoid obscuring the present invention due to unnecessary details, only the structures and / or processing steps closely related to the solution of the present invention are shown in the drawings, while other details less related to the present invention are omitted.

[0036] In addition, it should also be noted that the term "comprising", "including", or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or device.

[0037] In the prior art, the preparation process of silver-coated copper powder is mostly to first prepare copper powder and then deposit silver on the surface of the copper powder. There are cumbersome operations of washing and purification in the process flow, and the process is complex.

[0038] The present invention provides a method for preparing silver-coated copper powder, which directly prepares a copper core by a chemical reduction method, then uses an electroless plating method to grow a silver layer on its surface, and finally uses a jet mill to polish to improve the powder density. The present invention reduces the structural defects caused by rapid growth by strictly controlling the growth rate of silver powder from the seed crystal to the particle.

[0039] Specifically, in the present invention, copper sulfate is reduced by adding reducing agents with different reduction effects twice, which reduces the initial reaction rate, makes the whole reaction stable, and improves the sphericity of copper crystal nuclei. At the same time, sulfate radicals in the reaction system can form silver sulfate precipitate with silver ions in the subsequent reaction, further slowing down the reduction rate of silver ammonia complex ions and enabling the dense growth of the silver layer. At the same time, the unreacted glucose remaining in the reaction system can continue to reduce silver ammonia complex ions when the silver ammonia solution is added dropwise later. The design of this reaction process, compared with the traditional seed preparation process, not only avoids the cumbersome operations of seed washing and purification, simplifies the preparation process, but also enables the rational utilization of by-products and unreacted substances during the seed preparation process, improving the performance of the final product.

[0040] The present invention provides a method for preparing silver-coated copper powder, comprising the following steps:

[0041] S1, adding the dispersant polyvinylpyrrolidone into the copper sulfate solution and stirring evenly to obtain a copper sulfate dispersion;

[0042] Wherein, 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.

[0043] S2, adding the first reducing agent glucose solution to the copper sulfate dispersion obtained in step S1, carrying out the first reaction for 0.5-1.5 h; then adding the second reducing agent ascorbic acid to carry out the second reaction for 0.5-1.5 h to obtain a copper core solution; the reaction temperatures of both the first reaction and the second reaction are 60-90 °C.

[0044] Wherein, the pH of the first reducing agent glucose solution is adjusted to 10-12 with sodium hydroxide before use.

[0045] 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.

[0046] S3, adding the dispersant polyvinylpyrrolidone into the silver nitrate solution, fully dissolving it, adding sodium hydroxide, and then dropping ammonia water until the solution becomes clear to obtain a silver ammonia solution;

[0047] Wherein, the concentration of the silver nitrate solution is 40-50 g / L, the dosage of the dispersant is 0.1-1% of the mass of silver nitrate, and the dosage of sodium hydroxide is 0.1-1% of the mass of silver nitrate.

[0048] S4. Under the conditions of constant temperature at 50 - 60 °C and mechanical stirring, the silver ammonia solution prepared in step S3 is added dropwise into the copper core solution at a rate of 2 - 5 ml / min. The rotation speed of the mechanical stirring is 300 - 350 rpm / min. After 0.5 - 2 min, a glucose solution with a concentration of 150 - 175 g / L is added dropwise into the copper core solution at a rate of 2 - 5 ml / min. After the addition is completed, filtration and washing are carried out.

[0049] In step S4, the operation of adding the silver ammonia solution drop by drop is adopted. Because the addition of the silver ammonia solution will gradually increase the alkalinity of the system. As the alkalinity increases, the reducing ability of glucose also gradually increases, enabling the reaction of electroless silver plating on the surface of the copper crystal nuclei to start smoothly. This provides a reaction system that starts gradually and has a stable process. It also contributes to the dense structure of the final product.

[0050] S5. The washed silver-coated copper powder is dispersed in an ethanol solution of an organic acid with a mass concentration of 0.3 - 0.5%. After filtration, it is dried, and then subjected to air flow milling for 0.2 - 0.5 h to obtain the silver-coated copper powder.

[0051] The mass-volume ratio of the silver-coated copper powder to the ethanol solution is (4 - 5) g : (90 - 100) ml.

[0052] Among them, the process conditions of the air flow milling are as follows: using a fluidized bed opposed jet air flow mill, and the crushing gas pressure is 0.2 MPa - 0.8 MPa.

[0053] Among them, the organic acid is one or more of stearic acid, oleic acid, ricinoleic acid, palmitic acid, and laccaic acid.

[0054] In step S5, the air flow milling 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.

[0055] Next, the preparation method of the silver-coated copper powder provided by the present invention will be described in combination with specific examples. Unless otherwise specified, the raw materials and reagents in the examples of this application are all purchased through commercial channels.

[0056] Example 1

[0057] This example provides a preparation method of silver-coated copper powder, which specifically includes the following steps:

[0058] S1. Prepare 1 L of 0.5 mol / L copper sulfate solution (79.81 g of copper sulfate), and then add 0.48 g of polyvinylpyrrolidone (K30), and stir evenly to obtain a copper sulfate dispersion.

[0059] S2. Prepare 100 ml of 6 mol / L glucose solution (the first reducing agent, 108.11 g of glucose), adjust the pH to 12 with sodium hydroxide, then add it to the copper sulfate dispersion obtained in step S1, react at 60 °C for 1 h, and then add 100 ml of 1.5 mol / L ascorbic acid solution (the second reducing agent, 26.42 g of ascorbic acid) and continue to react for 0.5 h to obtain the copper core solution.

[0060] S3. Preparation of silver ammonia solution

[0061] Under the condition of mechanical stirring, add 10 g of silver nitrate (the concentration of silver nitrate solution is 50 g / L) to 200 ml of deionized water. After mixing thoroughly, add 0.1 g of polyvinylpyrrolidone. After complete dissolution, add 0.1 g of sodium hydroxide, and then dropwise add ammonia water until the solution becomes clear.

[0062] S4. Preparation of glucose solution: Under the condition of mechanical stirring, add 35 g of glucose (the concentration of glucose solution is 175 g / L) to 200 ml of deionized water and stir until completely dissolved.

[0063] Redox reaction: Under the conditions of constant temperature at 60 °C and mechanical stirring, dropwise add the silver ammonia solution into the copper core solution at a rate of 2 ml / min, keep the rotation speed of mechanical stirring at 300 rpm / min, and start to dropwise add the glucose solution into the copper core solution at the same rate after 1 min. After the dropping is completed, filter and wash.

[0064] S5. Product surface treatment

[0065] Filter the washed silver-coated copper powder, disperse it in an ethanol solution of stearic acid with a mass concentration of 0.5%, filter and then dry it, and then carry out air flow grinding treatment for 0.5 h with a crushing gas pressure of 0.6 MPa to obtain the product silver-coated copper powder. Among them, the mass-volume ratio of silver-coated copper powder to ethanol solution is 4 g:100 ml.

[0066] Example 2

[0067] Example 2 provides a preparation method of 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 elaborated here.

[0068] Comparison of main parameters between Example 2 and Example 1

[0069]

[0070] Figure 1 、 Figure 2 They are the scanning electron microscope images (SEM) of the silver-coated copper powder prepared in Example 1 and Example 2 respectively.

[0071] It can be seen that the obtained silver-coated copper powder grows densely, has a high sphericity, and has no obvious structural defects.

[0072] Comparative Example 1

[0073] Comparative Example 1 provides a method for preparing silver-coated copper powder. Compared with Example 1, the difference lies in that step S5 is not carried out. The rest is roughly the same as in Example 1 and will not be elaborated here.

[0074] Figure 3 It 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 carried out, the appearance of the silver-coated copper powder is relatively irregular.

[0075] Comparative Example 2

[0076] Comparative Example 2 provides a method for preparing silver-coated copper powder. Compared with Example 1, the difference lies in that in step S2, the second reducing agent ascorbic acid is not used. The rest is roughly the same as in Example 1 and will not be elaborated here.

[0077] It can be known from experiments that when the second reducing agent ascorbic acid is not used, the reducing property of the glucose reducing agent is insufficient, and only relying on glucose as a reducing agent cannot completely reduce all copper ions in this reaction system, and the yield of copper powder in the copper core solution is very low, resulting in the subsequent steps being meaningless.

[0078] Comparative Example 3

[0079] Comparative Example 3 provides a method for preparing silver-coated copper powder. Compared with Example 1, the difference lies in that in step S2, the first reducing agent glucose is not used. The rest is roughly the same as in Example 1 and will not be elaborated here.

[0080] Figure 4 It 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 reducing property of the ascorbic acid reducing agent is stronger than that of glucose, and it cannot make the reaction start smoothly at a slow speed. Therefore, the generated copper is relatively irregular and has a low sphericity, affecting the subsequent growth of the silver layer.

[0081] Comparative Example 4

[0082] Comparative Example 4 provides a method for preparing silver-coated copper powder. Compared with Example 1, the difference lies 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 in Example 1 and will not be elaborated here.

[0083] Figure 5SEM image of the silver-coated copper powder prepared in Comparative Example 4. It can be seen that the silver-coated copper powder formed by the reaction is very irregular. The reason is that the reducibility of glucose increases with the increase of alkalinity in the system. Without pH adjustment, the reducibility of glucose is too weak to initiate the reaction and thus fails to play a role.

[0084] Comparative Example 5

[0085] Comparative Example 5 provides a method for preparing silver-coated copper powder. Compared with Example 1, the difference lies in that copper sulfate in Step S1 is replaced by copper nitrate. The rest is substantially the same as in Example 1 and will not be elaborated here.

[0086] Figure 6 SEM image of the silver-coated copper powder prepared in Comparative Example 5. It can be seen that, compared with Example 1, the growth of the silver layer is relatively irregular. The reason may be the lack of sulfate in the reaction system, so that silver ions in the subsequent reaction of Step S4 cannot form precipitates, thereby slowing down the reduction rate of silver ammonia complex ions, and thus the growth of the silver layer is relatively irregular.

[0087] Comparative Example 6

[0088] Comparative Example 6 provides a method for preparing silver-coated copper powder. Compared with Example 1, the difference lies in that in Step S5, the process conditions of jet milling treatment are: the pressure of the pulverizing gas is 0.1 MPa, and the treatment time is 0.3 h. The rest is substantially the same as in Example 1 and will not be elaborated here.

[0089] Figure 7 SEM image of the silver-coated copper powder prepared in Comparative Example 6. It can be seen that when the pressure of the pulverizing gas for jet milling treatment is less than 0.2 MPa, the strength is insufficient, and the sphericity of the obtained silver-coated copper powder becomes poor.

[0090] It should be noted that the organic acid can also be one or more of ricinoleic acid, palmitic acid, and laccolic acid.

[0091] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing silver-coated copper powder, characterized in that, It includes the following steps: S1. Add a dispersant into a copper sulfate solution and stir evenly to obtain a copper sulfate dispersion; S2. Add a first reducing agent, a glucose solution, into the copper sulfate dispersion obtained in step S1 and carry out a first reaction for 0.5 - 1.5 h; then add a second reducing agent, ascorbic acid, and carry out a second reaction for 0.5 - 1.5 h to obtain a copper core solution; wherein, the pH of the first reducing agent glucose solution is 10 - 12; S3. Add a dispersant, polyvinylpyrrolidone, into a silver nitrate solution, fully dissolve it, add sodium hydroxide, and then dropwise add ammonia water until the solution becomes clear to obtain a silver ammonia solution; S4. Under the conditions of constant temperature at 50 - 60 °C and mechanical stirring, dropwise add the silver ammonia solution prepared in step S3 into the copper core solution at a rate of 2 - 5 ml / min, and the rotation speed of the mechanical stirring is 300 - 350 rpm / min. After 0.5 - 2 min, start to dropwise add a glucose solution with a concentration of 150 - 175 g / L into the copper core solution at a rate of 2 - 5 ml / min. After the addition is completed, filter and wash; sulfate radicals in the reaction system form silver sulfate precipitation with silver ions in the reaction in step S4, further slowing down the reduction rate of silver ammonia complex ions and enabling the silver layer to grow densely; S5. Disperse the washed silver-coated copper powder in an ethanol solution of an organic acid with a mass concentration of 0.3 - 0.5%, filter and dry it, and then carry out jet milling treatment for 0.2 - 0.5 h to obtain silver-coated copper powder.

2. The preparation method of the copper-coated silver powder according to claim 1, wherein: In step S2, adjust the pH of the first reducing agent glucose solution with sodium hydroxide.

3. The preparation method of the copper-coated silver powder according to claim 1, wherein: 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 preparation method of the copper-coated silver 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 preparation method of the copper-coated silver powder according to claim 1, characterized in that: In step S1, the dispersant is polyvinylpyrrolidone, and the dosage of the dispersant is 0.5 - 1% of the mass of copper sulfate.

6. The preparation method of the copper-coated silver powder according to claim 1, wherein: In step S5, the process conditions of the jet milling treatment are: use a fluidized bed opposed jet mill, and the crushing gas pressure is 0.2 MPa - 0.8 MPa.

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

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

10. The preparation method of the copper-coated silver 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 laccaic acid.

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