Preparation method of high-uniformity micrometer copper powder

Abstract

The application discloses a preparation method of high-uniformity micron copper powder, and comprises the following steps: 1, respectively preparing a copper salt solution, a mixed solution containing a surfactant and a reducing agent; 2, adding an organic ligand solution into the copper salt solution, stirring and reacting to obtain a suspension; 3, respectively performing first cooling on the mixed solution and the suspension, then mixing the cooled mixed solution and the suspension to obtain a reaction solution; 4, transferring the reaction solution into an environment with a temperature of 75-95 DEG C to perform a reduction reaction, and obtaining a product solution; 5, performing second cooling on the product solution to obtain the micron copper powder. The method provides a large number of uniform nucleation sites for copper atoms by using in-situ generated copper-based metal organic complexes as a self-sacrifice template, and the micron copper powder with high uniformity of particle size, regular morphology and good dispersibility is obtained by combining the dispersing effect of the surfactant, and the micron copper powder is suitable for the fields of multilayer ceramic capacitors, conductive paste, catalysts, heat exchange materials and powder metallurgy.

Description

Technical Field

[0001] This invention belongs to the field of metal powder preparation technology, and in particular relates to a method for preparing highly uniform micron-sized copper powder. Background Technology

[0002] Micron-sized copper powder is widely used in fields such as internal electrodes of multilayer ceramic capacitors, conductive pastes, catalysts, heat exchange materials, and powder metallurgy due to its excellent electrical and thermal conductivity and low cost. As electronic components develop towards miniaturization and high capacity, higher requirements are placed on the particle size uniformity, sphericity, dispersibility, and surface cleanliness of copper powder.

[0003] Currently, the main methods for preparing micron-sized copper powder include electrolysis, atomization, mechanical ball milling, and liquid-phase chemical reduction. Electrolysis produces copper powder with a distinct dendritic structure and a wide particle size distribution. Atomization involves large equipment investment and high energy consumption, and sphericity is difficult to control. Mechanical ball milling easily introduces impurities, resulting in irregular particle morphology and numerous surface defects. Liquid-phase chemical reduction has attracted much attention due to its mild conditions and controllable morphology; however, when traditional liquid-phase reduction directly reduces copper salts, the rapid reduction rate of copper ions and the difficulty in separating nucleation and growth processes easily lead to products with uneven particle size and severe agglomeration. Previous studies have attempted to improve dispersibility using large amounts of difficult-to-wash surfactants or template agents, but achieving high uniformity over a wide particle size range remains challenging. Furthermore, these high-molecular-weight surfactants or template agents adsorb onto the copper powder surface and are difficult to thoroughly clean, affecting subsequent conductivity.

[0004] In recent years, metal-organic complexes (especially metal-organic frameworks, MOFs) with high specific surface area and designable structures have often been used as sacrificial templates for the preparation of metal or metal oxide nanomaterials. However, while direct pyrolysis of metal-organic complexes can yield metallic products, these are usually limited to the nanoscale; and research on their use as ion-release precursors in liquid-phase reduction is still scarce. Therefore, developing a liquid-phase synthesis method that can utilize the template effect of metal-organic complexes and simultaneously achieve high uniformity and controllable particle size of micron-sized copper powder has significant industrial application value. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing highly uniform micron-sized copper powder. This method uses an in-situ generated copper-based organometallic complex as a self-sacrificing template to provide a large number of uniform nucleation sites for copper atoms. Combined with the dispersing effect of a surfactant, it yields micron-sized copper powder with highly uniform particle size, regular morphology, and good dispersibility, solving the problems of wide particle size distribution, poor uniformity, and uncontrollable morphology in copper powder prepared by existing technologies.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing highly uniform micron-sized copper powder, characterized in that the method includes the following steps: Step 1: Prepare copper salt solution and mixed solution containing surfactant and reducing agent respectively; Step 2: Add the organic ligand solution to the copper salt solution prepared in Step 1, and stir the reaction to obtain a suspension containing copper-based organometallic complex. Step 3: Cool the mixed solution prepared in Step 1 and the suspension obtained in Step 2 separately once, and then mix the cooled mixed solution and suspension to obtain the reaction solution; Step 4: Transfer the reaction solution obtained in Step 3 to an environment of 75℃~95℃ to carry out the reduction reaction and obtain the product solution; Step 5: Cool the product solution obtained in Step 4 a second time to obtain micron-sized copper powder.

[0007] This invention employs a liquid-phase chemical reduction method to prepare highly uniform micron-sized copper powder. An organic ligand reacts with copper ions to generate a copper-based organometallic complex precursor, which serves as a "self-sacrificing template," providing numerous uniform nucleation sites for subsequent copper atom growth. This avoids excessively wide particle size distribution caused by multi-stage nucleation and effectively slows down the reduction reaction rate. Simultaneously, the dispersing effect of the surfactant promotes uniform growth of the micron-sized copper powder. Furthermore, by mixing a solution containing surfactant and reducing agent with a suspension containing the copper-based organometallic complex after a first cooling step, premature copper nucleus formation during mixing is prevented. This ensures that the reduction reaction for copper nucleus formation only initiates after the reduction reaction in the reaction solution, guaranteeing high uniformity of the micron-sized copper powder. Additionally, by pre-setting the ambient temperature to the target temperature, the heating rate of the reaction solution is increased, ensuring that the ambient temperature remains at the target temperature for most of the copper nucleus formation and growth process, further guaranteeing high uniformity of the micron-sized copper powder. Finally, a second cooling step cools the product solution and allows the micron-sized copper powder to settle sufficiently.

[0008] The above-mentioned method for preparing highly uniform micron-sized copper powder is characterized in that, in step one, the copper salt is one or more of copper sulfate, copper chloride, and copper nitrate, and the concentration of the copper salt solution is 100g / L to 300g / L; the reducing agent is ascorbic acid and / or sodium ascorbate; the surfactant is polyvinylpyrrolidone and / or polyethylene glycol; and each liter of the mixed solution contains 100g to 500g of reducing agent.

[0009] The copper salts used in this invention are all readily soluble in water and inexpensive, while the reducing agent and surfactant are both non-toxic, harmless, and readily soluble in water.

[0010] The above-mentioned method for preparing highly uniform micron-sized copper powder is characterized in that the mass ratio of the reducing agent to the surfactant in step one is (50~200):1.

[0011] This invention controls the amount of surfactant used to minimize surfactant residue on the surface of micron-sized copper powder.

[0012] The method for preparing highly uniform micron-sized copper powder described above is characterized in that the mass ratio of copper salt to reducing agent in step one is 1:(1.5~2).

[0013] The above-mentioned method for preparing highly uniform micron-sized copper powder is characterized in that the organic ligand in step two is dimethylimidazole and / or sodium 3-carboxybenzenesulfonate, and the concentration of the organic ligand solution is 100 g / L to 250 g / L.

[0014] The method for preparing highly uniform micron-sized copper powder described above is characterized in that the mass ratio of the copper salt in step one to the organic ligand in step two is (2~4):1.

[0015] The above-mentioned method for preparing highly uniform micron-sized copper powder is characterized in that the temperature of the first cooling in step three is below 5°C, and the method of the first cooling is an ice-water bath.

[0016] This invention slows down the reduction reaction rate of the mixed solution and suspension containing surfactants during the mixing process, thereby avoiding the formation of copper nuclei and providing favorable conditions for the uniform nucleation and growth of copper powder.

[0017] The above-mentioned method for preparing highly uniform micron-sized copper powder is characterized in that the specific method of the reduction reaction in step four is as follows: the reaction solution is transferred to a constant temperature oil bath or water bath preheated to 75℃~95℃ for a reduction reaction for 3h~6h, while stirring is performed at a stirring rate of 400rpm~600rpm.

[0018] This invention improves the uniformity of copper powder growth by stirring during the reduction reaction, which facilitates heat and mass transfer in the reaction system.

[0019] The method for preparing highly uniform micron-sized copper powder described above is characterized in that the temperature of the secondary cooling in step five is 8°C to 12°C.

[0020] The above-mentioned method for preparing highly uniform micron-sized copper powder is characterized in that, after secondary cooling in step five, separation, washing and drying are performed, wherein the washing is performed by alternating washing with deionized water and anhydrous ethanol, and the drying is performed by drying in a vacuum drying oven at a temperature not exceeding 40°C for 24h~48h.

[0021] This invention employs vacuum low-temperature drying to prevent the oxidation of copper powder.

[0022] Compared with the prior art, the present invention has the following advantages: 1. This invention uses in-situ generated copper-based organometallic complexes as self-sacrificing templates to reduce copper ions in situ on the template surface, avoiding the uneven particle size caused by the random formation of copper nuclei in the liquid phase. At the same time, it controls the release rate of copper ions. Combined with the dispersing effect of surfactants, the micron-sized copper powder has a highly uniform particle size, regular morphology, and good dispersibility.

[0023] 2. By adjusting the type and concentration of organic ligands, the reduction reaction temperature and the reaction time, this invention can achieve flexible control of the average particle size of micron-sized copper powder, meeting the differentiated requirements of copper powder particle size for different application scenarios such as electronic pastes, catalysts, and conductive inks.

[0024] 3. This invention uses a liquid-phase reduction method to prepare copper powder by controlling the reaction temperature at 75℃~95℃, without the need for high-temperature and high-pressure equipment; moreover, the liquid-phase reduction reaction time is short and the post-processing is simple, which is conducive to industrial-scale production.

[0025] 4. The preparation method of this invention can obtain high-purity micron-sized copper powder, which can be used in the fields of multilayer ceramic capacitors and conductive pastes without further surface treatment.

[0026] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0027] Figure 1 This is a SEM image of the micron-sized copper powder obtained in Example 1 of the present invention.

[0028] Figure 2 This is a SEM image of the micron-sized copper powder obtained in Example 2 of the present invention.

[0029] Figure 3 This is a SEM image of the micron-sized copper powder obtained in Example 3 of the present invention.

[0030] Figure 4 This is a SEM image of the micron-sized copper powder obtained in Example 4 of the present invention.

[0031] Figure 5 The image shows the XRD pattern of the micron-sized copper powder obtained in Example 4 of this invention.

[0032] Figure 6 This is a SEM image of the micron-sized copper powder obtained in Example 5 of the present invention.

[0033] Figure 7 This is a SEM image of the micron-sized copper powder obtained in Comparative Example 1 of this invention. Detailed Implementation

[0034] Example 1 The preparation method of this embodiment includes the following steps: Step 1: Dissolve 100g of copper sulfate in deionized water to prepare 1L of copper salt solution with a concentration of 100g / L. Dissolve 200g of ascorbic acid and 1g of polyvinylpyrrolidone (PVP, average molecular weight 58000g / mol) in deionized water to prepare 2L of mixed solution. Step 2: Prepare a 0.2L organic ligand solution of dimethylimidazole with a concentration of 250g / L, and add it to the copper salt solution prepared in Step 1. Stir and react for 0.5h to obtain a suspension containing copper-based organometallic complex. Step 3: Cool the mixed solution prepared in Step 1 and the suspension obtained in Step 2 in an ice-water bath for 0.5 h. Then mix the mixed solution and suspension, which have been cooled to 4 °C, evenly to obtain the reaction solution. Step 4: Transfer the reaction solution obtained in Step 3 to a constant temperature water bath at 75°C for a reduction reaction for 3 hours, while stirring at a rate of 400 rpm to obtain a product solution containing micron-sized copper powder. Step 5: Transfer the product solution obtained in Step 4 to a refrigerator at 8°C for secondary cooling, so that the product solution is cooled and the micron copper powder settles completely. Then remove the supernatant and wash the precipitate alternately with deionized water and anhydrous ethanol for a total of 5 times. Then dry it in a vacuum drying oven at 40°C for 24 hours to obtain micron copper powder.

[0035] In this embodiment, copper sulfate can be replaced with copper chloride and / or copper nitrate, ascorbic acid can be replaced with sodium ascorbate, or a combination of ascorbic acid and sodium ascorbate, and polyvinylpyrrolidone can be replaced with polyethylene glycol, or a combination of polyvinylpyrrolidone and polyethylene glycol.

[0036] The microstructure of the micron-sized copper powder obtained in this embodiment is as follows: Figure 1 As shown, the micron-sized copper powder has a particle size of 0.6µm to 1.4µm, with an average particle size of 1µm. It is spherical, uniform in size, and free from agglomeration.

[0037] Example 2 The preparation method of this embodiment includes the following steps: Step 1: Dissolve 200g of copper chloride in deionized water to prepare 1L of copper salt solution with a concentration of 200g / L. Dissolve 300g of sodium ascorbate and 3g of polyethylene glycol (PEG, average molecular weight 4000g / mol) in deionized water to prepare 1L of mixed solution. Step 2: Prepare a 0.5L organic ligand solution of dimethylimidazole with a concentration of 200g / L, and add it to the copper salt solution prepared in Step 1. Stir and react for 0.7h to obtain a suspension containing copper-based organometallic complex. Step 3: Cool the mixed solution prepared in Step 1 and the suspension obtained in Step 2 in an ice-water bath for 0.7 h. Then mix the mixed solution and suspension, which have been cooled to 3 °C, evenly to obtain the reaction solution. Step 4: Transfer the reaction solution obtained in Step 3 to a constant temperature water bath at 85°C for a reduction reaction for 4 hours, while stirring at a rate of 500 rpm, to obtain a product solution containing micron-sized copper powder. Step 5: Transfer the product solution obtained in Step 4 to a 12°C refrigerator for secondary cooling, so that the product solution cools and the micron copper powder settles completely. Then remove the supernatant and wash the precipitate with deionized water and anhydrous ethanol alternately for a total of 6 times. Then dry it in a vacuum drying oven at 35°C for 30 hours to obtain micron copper powder.

[0038] The microstructure of the micron-sized copper powder obtained in this embodiment is as follows: Figure 2 As shown, the micron-sized copper powder has a particle size of 1.8µm to 2.2µm, with an average particle size of 2µm. It is spherical, uniform in size, and free from agglomeration.

[0039] Example 3 The preparation method of this embodiment includes the following steps: Step 1: Dissolve 320g of copper chloride in deionized water to prepare a 2L copper salt solution with a concentration of 160g / L. Dissolve 500g of sodium ascorbate and 6.25g of polyvinylpyrrolidone (PVP, average molecular weight 58000g / mol) in deionized water to prepare a 1L mixed solution. Step 2: Prepare a 0.8L solution of 3-carboxybenzenesulfonate with an organic ligand concentration of 100g / L, and add it to the copper salt solution prepared in Step 1. Stir and react for 1 hour to obtain a suspension containing a copper-based organometallic complex. Step 3: Cool the mixed solution prepared in Step 1 and the suspension obtained in Step 2 in an ice-water bath for 1 hour. Then mix the mixed solution and suspension, which have been cooled to 3°C, evenly to obtain the reaction solution. Step 4: Transfer the reaction solution obtained in Step 3 to a constant temperature water bath at 90°C for a reduction reaction for 4.5 hours, while stirring at a rate of 500 rpm to obtain a product solution containing micron-sized copper powder. Step 5: Transfer the product solution obtained in Step 4 to a 10°C refrigerator for secondary cooling, so that the product solution cools and the micron copper powder settles completely. Then remove the supernatant and wash the precipitate alternately with deionized water and anhydrous ethanol for a total of 7 times. Then dry it in a vacuum drying oven at 35°C for 48 hours to obtain micron copper powder.

[0040] The microstructure of the micron-sized copper powder obtained in this embodiment is as follows: Figure 3 As shown, the particle size of this micron-sized copper powder is 3.5µm~4.5µm, with an average particle size of 4µm. It is spherical, uniform in size, and free from agglomeration.

[0041] Example 4 The preparation method of this embodiment includes the following steps: Step 1: Dissolve 300g of copper sulfate in deionized water to prepare 1L of copper salt solution with a concentration of 300g / L. Dissolve 600g of sodium ascorbate and 12g of polyethylene glycol (PEG, average molecular weight 8000g / mol) in deionized water to prepare 1.2L of mixed solution. Step 2: Prepare 1L of dimethylimidazole into an organic ligand solution with a concentration of 100g / L, and add it to the copper salt solution prepared in Step 1. Stir and react for 1 hour to obtain a suspension containing a copper-based organometallic complex. Step 3: Cool the mixed solution prepared in Step 1 and the suspension obtained in Step 2 in an ice-water bath for 0.8 h. Then mix the mixed solution and suspension, which have been cooled to 3 °C, evenly to obtain the reaction solution. Step 4: Transfer the reaction solution obtained in Step 3 to a constant temperature water bath at 85°C for a reduction reaction for 5 hours, while stirring at a rate of 600 rpm, to obtain a product solution containing micron-sized copper powder. Step 5: Transfer the product solution obtained in Step 4 to a 10°C refrigerator for secondary cooling, so that the product solution cools and the micron copper powder settles completely. Then remove the supernatant and wash the precipitate with deionized water and anhydrous ethanol alternately for a total of 6 times. Then dry it in a vacuum drying oven at 35°C for 36 hours to obtain micron copper powder.

[0042] The microstructure of the micron-sized copper powder obtained in this embodiment is as follows: Figure 4 As shown, the micron-sized copper powder has a particle size of 9µm~11µm, with an average particle size of 10µm. It exhibits a near-spherical shape, uniform particle size, and no agglomeration. The XRD pattern of this micron-sized copper powder is shown in the figure. Figure 5 As shown, the XRD diffraction peaks are strong and their positions coincide with the standard XRD diffraction peaks of elemental copper, with no other impurity diffraction peaks.

[0043] Example 5 The preparation method of this embodiment includes the following steps: Step 1: Dissolve 200g of copper chloride in deionized water to prepare 2L of copper salt solution with a concentration of 100g / L. Dissolve 400g of ascorbic acid and 8g of polyvinylpyrrolidone (PVP, average molecular weight 58000g / mol) in deionized water to prepare 2L of mixed solution. Step 2: Prepare a 0.8 L solution of dimethylimidazole with an organic ligand concentration of 120 g / L, and add it to the copper salt solution prepared in Step 1. Stir and react for 0.8 h to obtain a suspension containing a copper-based organometallic complex. Step 3: Cool the mixed solution prepared in Step 1 and the suspension obtained in Step 2 in an ice-water bath for 1 hour. Then mix the mixed solution and suspension, which have been cooled to 3°C, evenly to obtain the reaction solution. Step 4: Transfer the reaction solution obtained in Step 3 to a constant temperature oil bath at 95°C for reduction reaction for 6 hours, while stirring at a rate of 550 rpm to obtain a product solution containing micron-sized copper powder. Step 5: Transfer the product solution obtained in Step 4 to a 10°C refrigerator for secondary cooling, so that the product solution cools and the micron copper powder settles completely. Then remove the supernatant and wash the precipitate alternately with deionized water and anhydrous ethanol for a total of 7 times. Then dry it in a vacuum drying oven at 35°C for 48 hours to obtain micron copper powder.

[0044] The microstructure of the micron-sized copper powder obtained in this embodiment is as follows: Figure 6 As shown, the micron-sized copper powder has a particle size of 12µm~18µm, with an average particle size of 15µm. It is spherical, uniform in size, and free from agglomeration.

[0045] Comparative Example 1 The difference between this comparative example and Example 4 is that step two was not performed. Instead, the copper salt solution and the mixed solution prepared in step one were directly mixed after a first cooling in step three, followed by a reduction reaction, a second cooling, washing, and drying.

[0046] The microstructure of the micron-sized copper powder obtained in this comparative example is as follows: Figure 7 As shown, the micron-sized copper powder is extremely non-uniform in size, with particle sizes ranging from 5 μm to 20 μm, and contains a large number of irregular blocky and chain-like agglomerates. Compared with the micron-sized copper powder obtained in Example 4, the product of this comparative example exhibits severe particle size inhomogeneity and agglomeration. This result clearly shows that without the intermediate step of copper-based metal-organic complex, direct reduction of copper ions cannot achieve uniform nucleation and growth, resulting in a wide particle size distribution and severe agglomeration. This further confirms the key role of pre-forming a copper-based metal-organic complex structure in improving the uniformity of micron-sized copper powder in this invention.

[0047] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing highly uniform micron-sized copper powder, characterized in that, The method includes the following steps: Step 1: Prepare copper salt solution and mixed solution containing surfactant and reducing agent respectively; Step 2: Add the organic ligand solution to the copper salt solution prepared in Step 1, and stir the reaction to obtain a suspension containing copper-based organometallic complex. Step 3: Cool the mixed solution prepared in Step 1 and the suspension obtained in Step 2 separately once, and then mix the cooled mixed solution and suspension to obtain the reaction solution; Step 4: Transfer the reaction solution obtained in Step 3 to an environment of 75℃~95℃ to carry out the reduction reaction and obtain the product solution; Step 5: Cool the product solution obtained in Step 4 a second time to obtain micron-sized copper powder.

2. The method for preparing highly uniform micron-sized copper powder according to claim 1, characterized in that, The copper salt mentioned in step one is one or more of copper sulfate, copper chloride and copper nitrate, and the concentration of the copper salt solution is 100g / L to 300g / L; the reducing agent is ascorbic acid and / or sodium ascorbate, and the surfactant is polyvinylpyrrolidone and / or polyethylene glycol, and each liter of the mixed solution contains 100g to 500g of reducing agent.

3. The method for preparing highly uniform micron-sized copper powder according to claim 1, characterized in that, The mass ratio of the reducing agent to the surfactant in step one is (50~200):

1.

4. The method for preparing highly uniform micron-sized copper powder according to claim 1, characterized in that, The mass ratio of copper salt to reducing agent in step one is 1:(1.5~2).

5. The method for preparing highly uniform micron-sized copper powder according to claim 1, characterized in that, The organic ligands in step two are dimethylimidazole and / or sodium 3-carboxybenzenesulfonate, and the concentration of the organic ligand solution is 100 g / L to 250 g / L.

6. The method for preparing highly uniform micron-sized copper powder according to claim 1, characterized in that, The mass ratio of the copper salt in step one to the organic ligand in step two is (2~4):

1.

7. The method for preparing highly uniform micron-sized copper powder according to claim 1, characterized in that, The temperature of the first cooling step in step three is below 5°C, and the method of the first cooling step is an ice-water bath.

8. The method for preparing highly uniform micron-sized copper powder according to claim 1, characterized in that, The specific method for the reduction reaction described in step four is as follows: the reaction solution is transferred to a constant temperature oil bath or water bath preheated to 75℃~95℃ for a reduction reaction for 3h~6h, while stirring at a stirring rate of 400rpm~600rpm.

9. The method for preparing highly uniform micron-sized copper powder according to claim 1, characterized in that, The temperature for the secondary cooling in step five is 8℃~12℃.

10. The method for preparing highly uniform micron-sized copper powder according to claim 1, characterized in that, After the secondary cooling in step five, the parts are separated, washed, and dried. The washing is performed by alternating between deionized water and anhydrous ethanol, and the drying is performed by drying in a vacuum drying oven at a temperature not exceeding 40°C for 24 to 48 hours.

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