Micron-sized spherical silver-coated copper powder and preparation method thereof

Abstract

The invention provides micron-sized spherical silver-coated copper powder and a preparation method thereof, and belongs to the technical field of metal powder.The preparation method comprises the following steps that copper powder is pretreated, and pretreated copper powder is obtained; under the condition of constant temperature, a part of the silver complexing solution is dropwise added into the copper powder mixed solution to obtain a reaction solution, and then the remaining silver complexing solution and the reduction solution are dropwise added into the reaction solution at the same time; and after the reaction is finished, carrying out solid-liquid separation, washing and drying to obtain the micron-sized spherical silver-coated copper powder. According to the invention, a replacement and chemical reduction method silver plating process is realized through a continuous feeding method. The method comprises the following steps: adding a small amount of silver complexing solution to perform replacement reaction with copper powder to generate silver nanoparticles on the surface of the copper powder; and then the reducing solution and the silver complexing solution are added into the copper powder at the same time, generated silver particles can be evenly deposited along the silver nanoparticles on the surface of the copper powder under the action of the reducing agent, and the utilization rate of silver ions is high.

Description

Technical Field

[0001] This invention relates to the field of metal powder technology, specifically to a micron-sized spherical silver-coated copper powder and its preparation method. Background Technology

[0002] Micron-sized silver-coated copper powder is a composite metal powder formed by depositing a dense silver coating on the surface of metallic copper particles using advanced surface treatment technology. While metallic silver has excellent conductivity, it is expensive and prone to silver ion migration; copper is inexpensive, but it easily oxidizes, forming an insulating layer that drastically reduces conductivity. Silver-coated copper powder achieves synergistic advantages through its core-shell structure: the silver layer isolates the copper core from oxygen while providing conductive channels, thereby improving the oxidation resistance and conductivity of the copper powder, making it a key material in electronics, photovoltaics, and other fields. For example, in heterojunction solar cell pastes, using silver-coated copper powder can reduce the amount of silver used in the paste, effectively reducing the cost of conductive paste by more than 30%. Furthermore, it replaces traditional solders in conductive adhesives, MLCC electrodes, and other fields.

[0003] Currently, methods for preparing silver-coated copper powder include physical, chemical, and pyrolysis methods. Physical methods use mechanical force to spread and coat silver powder onto the surface of copper powder. While simple and suitable for mass production, this method consumes a large amount of silver, resulting in high costs. Furthermore, because a metallurgical bond is not formed at the silver-copper interface, the silver layer peeling rate during slurry processing is >15%, and the conductive network is prone to breakage. Spray pyrolysis involves atomizing silver nitrate / copper droplets, causing silver to preferentially precipitate and coat the copper core in an H2 / N2 atmosphere. This method achieves in-situ coating without oxidation and yields high purity. However, the equipment is extremely complex, and the production capacity is low (0.5 kg / h), hindering large-scale industrial production. Chemical plating remains the mainstream method in industry, especially the substitution + chemical reduction dual mechanism. The reducing agent thickens the silver layer on the substitution layer, allowing for controllable silver layer thickness (150~500 nm). However, its uniformity and adhesion remain problems that urgently need to be solved. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a micron-sized spherical silver-coated copper powder and its preparation method, aiming to solve the technical problems of poor uniformity and adhesion of silver-coated copper powder prepared by chemical plating.

[0005] In a first aspect, embodiments of this application provide a method for preparing micron-sized spherical silver-coated copper powder, comprising the following steps: S1. Pre-treat the copper powder to remove the organic coatings and oxides on the surface to obtain pre-treated copper powder; S2. Disperse the pretreated copper powder, dispersant and protective agent in water to obtain a copper powder mixture; Silver salt and complexing agent are dispersed in water to obtain a silver complex solution; The reducing agent is dispersed in water to obtain a reduced solution; S3. Under constant temperature conditions, first add a portion of the silver complex solution to the copper powder mixture to obtain a reaction solution, and then add the remaining silver complex solution and reducing solution to the reaction solution simultaneously. S4. After the reaction is complete, solid-liquid separation, washing and drying are performed to obtain micron-sized spherical silver-coated copper powder.

[0006] Secondly, embodiments of this application provide a micron-sized spherical silver-coated copper powder, which is prepared using the above-described method.

[0007] The advantages of this application, which differ from existing technical solutions, include: 1. This invention achieves a silver plating process using a continuous feeding method, combining displacement and chemical reduction. First, a small amount of silver complexing solution is added to react with copper powder, generating silver nanoparticles on the copper powder surface. Then, a reducing solution and a silver complexing solution are simultaneously added to the copper powder. Under the action of the reducing agent, the generated silver particles can be uniformly deposited along the silver nanoparticles on the copper powder surface, resulting in high silver ion utilization.

[0008] 2. The silver-coated copper powder prepared by this invention has high sphericity, good dispersibility, complete and uniform silver coating, achieving a dense coating effect, and has good antioxidant capacity and electrical conductivity.

[0009] 3. The process of this invention is simple, can be continuously prepared, does not require the introduction of pollutants such as heavy metal ions, has high silver utilization, saves costs, and is suitable for industrial production.

[0010] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0011] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0012] Figure 1 This is a SEM image of the micron-sized spherical silver-coated copper powder prepared in Example 1.

[0013] Figure 2 This is a SEM image of the micron-sized spherical silver-coated copper powder prepared in Example 2.

[0014] Figure 3 This is a SEM image of the micron-sized spherical silver-coated copper powder prepared in Example 3. Detailed Implementation

[0015] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0017] Chemical plating remains the mainstream industrial method, especially the dual mechanism of displacement + chemical reduction. The reducing agent thickens the silver layer on the displacement layer, allowing for controllable silver layer thickness (150~500nm). However, uniformity and adhesion remain unresolved issues. Currently, the industrialization of photovoltaic heterojunction solar cells is driving rapid iteration of silver-coated copper technology towards lower silver content and higher environmental stability. Therefore, there is a need to provide a low-silver-content silver-coated copper powder with a dense, defect-free silver layer, high conductivity, and oxidation resistance.

[0018] To address the technical problems of poor uniformity and adhesion in the preparation of silver-coated copper powder by electroless plating, this application provides a micron-sized spherical silver-coated copper powder and its preparation method. A continuous feeding method is used to achieve a silver plating process combining displacement and chemical reduction. First, a small amount of silver complexing solution is added to the copper powder to undergo a displacement reaction, generating silver nanoparticles on the copper powder surface. Then, a reducing solution and a silver complexing solution are simultaneously added to the copper powder. Under the action of the reducing agent, the generated silver particles can be uniformly deposited along the silver nanoparticles on the copper powder surface, resulting in high silver ion utilization.

[0019] In a first aspect, embodiments of this application provide a method for preparing micron-sized spherical silver-coated copper powder, comprising the following steps: S1. Pre-treat the copper powder to remove the organic coatings and oxides on the surface to obtain pre-treated copper powder; S2. Mix the pretreated copper powder, dispersant and protective agent, and mix them evenly under ultrasonic conditions using mechanical stirring to obtain a copper powder mixture. Silver salt and complexing agent are dispersed in water to obtain a silver complex solution; The reducing agent is dispersed in water to obtain a reduced solution; S3. Place the silver complexing solution and the reducing solution in a water bath and heat them to a constant temperature. First, add a portion of the silver complexing solution dropwise to the copper powder mixture to obtain the reaction solution. Then, add the remaining silver complexing solution and the reducing solution dropwise to the reaction solution simultaneously. S4. After the reaction is complete, the solid product is obtained by vacuum filtration. The solid product is washed with deionized water and ethanol until the conductivity of the filtrate is less than or equal to 20 uS / cm. Then, it is placed in a vacuum drying oven for drying at 60℃ for 6 hours to obtain micron-sized spherical silver-coated copper powder.

[0020] In the technical solution of this application embodiment, the present invention first adds a portion of the silver complex solution to the copper powder mixture to cause a displacement reaction, thereby displacing some silver nanoparticles from the surface of the copper powder. Then, the reducing solution and the silver complex solution are added to the reaction solution at the same time. Under the action of the reducing agent, the generated silver particles can be uniformly deposited along the silver nanoparticles on the surface of the copper powder, resulting in high silver ion utilization.

[0021] If all the silver complex solution is added first, the Ag in the silver complex solution... + The copper powder will undergo a displacement reaction, and when a reducing agent is added subsequently, there will be no excess anions reacting with the reducing agent. In contrast, the silver complex solution directly reacts with the copper powder, failing to form a uniform and dense coating layer.

[0022] Furthermore, the reducing solution and the silver complexing solution in this invention are added in a combined process, which allows for simultaneous adjustment of the rates at which the reducing solution and the silver complexing solution are added, thereby enabling better control of the uniformity and density of the silver plating layer.

[0023] Furthermore, in some embodiments, in step S3, the silver complex solution is first added dropwise to the copper powder mixture over a period of 2 minutes, using a peristaltic pump at a rate of 5-30 mL / min. Then, add the remaining silver complex solution and reducing solution dropwise to the reaction solution simultaneously over a period of 25-30 minutes using a peristaltic pump at a rate of 5-30 mL / min.

[0024] Furthermore, in some embodiments, the copper powder is spherical copper powder with a particle size of 1~10μm.

[0025] In the technical solution of this application embodiment, copper powder is prepared by aerosol method.

[0026] Furthermore, in some embodiments, the pretreatment step in step S1 includes ultrasonic cleaning using an acidic cleaning solution and / or an alkaline cleaning solution; Acidic cleaning solutions include at least one of dilute sulfuric acid and dilute hydrochloric acid; Alkaline cleaning solutions include at least one of sodium hydroxide solution, potassium hydroxide solution, ammonium sulfate solution, and ammonia water.

[0027] Furthermore, in some embodiments, the dispersant includes at least one of PEG, PVA, PVP, gelatin, sodium dodecyl sulfate, and sodium stearate, and the mass ratio of copper powder to dispersant is 100:(0.5~10); And / or, the protective agent includes at least one of benzotriazole, methylbenzotriazole, methylbenzotriazole, and benzimidazole, and the mass ratio of copper powder to protective agent is 100:(0.1~1).

[0028] In the technical solution of this application embodiment, the protective agent serves to protect the copper powder particles from corrosion and oxidation, and to improve the coating quality of the silver plating layer.

[0029] In the liquid-phase reaction environment for preparing silver-coated copper powder, the copper powder is easily oxidized. The protective agent can undergo chemical adsorption and coordination reactions with the copper atoms on the surface of the copper powder to form a dense protective film on the surface of the copper powder, which is usually only a few molecular layers thick.

[0030] Meanwhile, without a protective agent, the reaction rate would be extremely rapid during the displacement reaction. Silver ions would quickly be reduced at the active sites on the copper powder surface, forming coarse, loose silver particles instead of a dense, continuous coating. The protective film formed on the copper surface by the protective agent acts as a "buffer layer" or "regulator," slowing down the rate at which silver ions contact the copper surface. This makes the reduction and deposition process of silver more gentle and controllable, helping to form a uniform, dense, and continuous silver coating.

[0031] Furthermore, in some embodiments, the concentration of silver salt in the silver complexing solution is 0.1~1.5 mol / L, and the concentration of complexing agent is 0.1~1.5 mol / L.

[0032] The mass ratio of silver in copper powder to silver salt is (4~10):1.

[0033] Furthermore, in some embodiments, the complexing agent includes at least one of ethylenediaminetetraacetic acid, tetraethylenepentamine, triethylenetetraamine, ammonia, sodium tartrate, L-histidine, glutamic acid, and thiourea.

[0034] In the technical solution of this application embodiment, the core function of the complexing agent is to transform free silver ions into silver complex ions, and to obtain a dense, uniform, and bright silver coating layer by controlling its release rate.

[0035] Without a complexing agent, the reducing solution will instantly remove a large number of free silver ions (Ag). + ) reduced to silver atoms (Ag) 0In this reaction, silver atoms rapidly aggregate in the solution, forming numerous tiny silver particles. These silver nuclei do not coat the copper powder but remain as free silver powder, resulting in waste and contamination. Simultaneously, some silver particles also deposit on the surface of the copper powder, but due to the rapid reaction, the deposited layer is rough and loose. The resulting mixture is a mixture of silver-coated copper powder and free silver powder, with poor coating quality.

[0036] Complexing agents will react with Ag + The formation of stable silver complex ions greatly reduces the free Ag + At a certain concentration, the reducing agent can only reduce free Ag. + When free Ag + After being consumed, the complexed Ag + The silver ions will slowly dissociate to replenish themselves. The reduction rate of silver ions is controlled by the dissociation rate of the complexing agent, making the reaction mild and controllable, ultimately resulting in a high-quality coated silver layer.

[0037] Furthermore, in some embodiments, the reducing agent includes at least one of ascorbic acid, glucose, formaldehyde, sodium borohydride, and hydrazine hydrate; The concentration of reducing agent in the reducing solution is 0.1 mol / L-1.0 mol / L; The molar ratio of reducing agent to silver salt is (1.1~1.5):1.

[0038] Furthermore, in some embodiments, the isothermal condition in step S3 is 25~70°C.

[0039] Secondly, embodiments of this application provide a micron-sized spherical silver-coated copper powder, which is prepared using the above-described method.

[0040] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0041] I. Preparation Method Example 1 A method for preparing micron-sized spherical silver-coated copper powder includes the following steps: S1: Weigh 85g of copper powder and add it to 1000mL of 1mol / L sodium hydroxide solution. Stir ultrasonically for 20min and filter. Then add 1000mL of 0.5mol / L dilute sulfuric acid to the copper powder to remove surface oxides. Stir ultrasonically for 20min and filter. Wash with deionized water several times.

[0042] S2: Dissolve the cleaned copper powder in 1000mL of deionized water, then add 2g PVP and 0.5g benzotriazole, and mechanically stir under ultrasonic conditions to obtain a copper powder mixture.

[0043] S3: Weigh 25g silver nitrate, 15g disodium ethylenediaminetetraacetate and 20g tetraethylenepentamine and dissolve them in 500mL of water to prepare a silver complex solution; add 30g ascorbic acid to 500mL of deionized water to obtain a reducing solution; put both solutions into a water bath and heat to 40℃ and keep warm. S4: Under constant temperature conditions, the silver complex solution is slowly added dropwise to the copper powder mixture, with the dropping rate controlled at 10 ml / min, so that some silver is displaced from the surface of the copper powder. After 5 min, the reducing solution and the remaining silver complex solution are added dropwise to the reaction system at the same time, with the dropping rate controlled at 10 ml / min. S5: After the feeding is completed, continue the reaction for 10 minutes. After the reaction is completed, perform solid-liquid separation, wash with deionized water and ethanol several times, and then dry to obtain micron-sized spherical silver-coated copper powder.

[0044] Example 2 A method for preparing micron-sized spherical silver-coated copper powder includes the following steps: S1: Weigh 85g of copper powder and add it to 1000mL of 1mol / L sodium hydroxide solution. Stir ultrasonically for 20min and filter. Then add 1000mL of 0.5mol / L dilute sulfuric acid to the copper powder to remove surface oxides. Stir ultrasonically for 20min and filter. Wash with deionized water several times.

[0045] S2: Dissolve the cleaned copper powder in 1000mL of deionized water, then add 2g PVP and 0.5g benzotriazole, and mechanically stir under ultrasonic conditions to obtain a copper powder mixture.

[0046] S3: Weigh 25g silver nitrate, 15g disodium ethylenediaminetetraacetate and 20g tetraethylenepentamine and dissolve them in 500mL of water to prepare a silver complex solution; add 30g ascorbic acid to 500mL of deionized water to obtain a reducing solution; put both solutions into a water bath and heat to 60℃ and keep warm. S4: Under constant temperature conditions, the silver complex solution is slowly added dropwise to the copper powder mixture, with the dropping rate controlled at 10 ml / min, so that some silver is displaced from the surface of the copper powder. After 5 min, the reducing solution and the remaining silver complex solution are added dropwise to the reaction system at the same time, with the dropping rate controlled at 10 ml / min. S5: After the feeding is completed, continue the reaction for 10 minutes. After the reaction is completed, perform solid-liquid separation, wash with deionized water and ethanol several times, and then dry to obtain micron-sized spherical silver-coated copper powder.

[0047] Example 3 A method for preparing micron-sized spherical silver-coated copper powder includes the following steps: S1: Weigh 85g of copper powder and add it to 1000mL of 1mol / L sodium hydroxide solution. Stir ultrasonically for 20min and filter. Then add 1000mL of 0.5mol / L dilute sulfuric acid to the copper powder to remove surface oxides. Stir ultrasonically for 20min and filter. Wash with deionized water several times.

[0048] S2: Dissolve the cleaned copper powder in 1000mL of deionized water, then add 2g PVP and 0.5g benzotriazole, and mechanically stir under ultrasonic conditions to obtain a copper powder mixture.

[0049] S3: Weigh 25g silver nitrate, 15g disodium ethylenediaminetetraacetate and 20g tetraethylenepentamine and dissolve them in 500mL of water to prepare a silver complex solution; add 30g ascorbic acid to 500mL of deionized water to obtain a reducing solution; put both solutions into a water bath and heat to 60℃ and keep warm. S4: Under constant temperature conditions, the silver complex solution is slowly added dropwise to the copper powder mixture, with the dropping rate controlled at 20 ml / min, so that some silver is displaced from the surface of the copper powder. After 5 min, the reducing solution and the remaining silver nitrate solution are added dropwise to the reaction system at the same time, with the dropping rate controlled at 20 ml / min. S5: After the feeding is completed, continue the reaction for 10 minutes. After the reaction is completed, perform solid-liquid separation, wash with deionized water and ethanol several times, and then dry to obtain micron-sized spherical silver-coated copper powder.

[0050] II. Analysis of Test Results for Each Embodiment and Comparative Example Figures 1-3 SEM images of the silver-coated copper powders prepared in Examples 1-3 of this invention are shown below. The silver content in the silver-coated copper powders prepared in different examples is around 15.0%, indicating high silver ion utilization. The SEM images show that the silver-coated copper powder prepared in Example 1 has a uniform and dense silver coating, complete coverage, no free silver nanoparticles, good dispersibility, and no obvious agglomeration. Although the silver coating in Examples 2 and 3 is complete, the surface of the silver-coated copper powder is relatively rough, with protruding silver particles, indicating that the conditions in Example 1 achieve the best results.

[0051] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing micron-sized spherical silver-coated copper powder, characterized in that, Includes the following steps: S1. Pre-treat the copper powder to remove the organic coatings and oxides on the surface to obtain pre-treated copper powder; S2. Disperse the pretreated copper powder, dispersant and protective agent in water to obtain a copper powder mixture; Silver salt and complexing agent are dispersed in water to obtain a silver complex solution; The reducing agent is dispersed in water to obtain a reduced solution; S3. Under constant temperature conditions, a portion of the silver complex solution is first added dropwise to the copper powder mixture to obtain a reaction solution, and then the remaining silver complex solution and the reducing solution are simultaneously added dropwise to the reaction solution. S4. After the reaction is complete, solid-liquid separation, washing and drying are performed to obtain micron-sized spherical silver-coated copper powder.

2. The method for preparing micron-sized spherical silver-coated copper powder according to claim 1, characterized in that, In step S3, the silver complex solution is first added dropwise to the copper powder mixture for 2-5 minutes at a rate of 5-30 mL / min. Then, the remaining silver complex solution and the reducing solution are simultaneously added dropwise to the reaction solution over a period of 25-30 minutes at a rate of 5-30 mL / min.

3. The method for preparing micron-sized spherical silver-coated copper powder according to claim 1, characterized in that, The copper powder is spherical with a particle size of 1~10μm.

4. The method for preparing micron-sized spherical silver-coated copper powder according to claim 1, characterized in that, The pretreatment step in step S1 includes ultrasonic cleaning using an acidic cleaning solution and / or an alkaline cleaning solution; The acidic cleaning solution includes at least one of dilute sulfuric acid and dilute hydrochloric acid; The alkaline cleaning solution includes at least one of sodium hydroxide solution, potassium hydroxide solution, ammonium sulfate solution, and ammonia water.

5. The method for preparing micron-sized spherical silver-coated copper powder according to claim 1, characterized in that, The dispersant includes at least one of PEG, PVA, PVP, gelatin, sodium dodecyl sulfate, and sodium stearate, and the mass ratio of copper powder to dispersant is 100:(0.5~10). And / or, the protective agent includes at least one of benzotriazole, methylbenzotriazole, methylbenzotriazole, and benzimidazole, and the mass ratio of copper powder to protective agent is 100:(0.1~1).

6. The method for preparing micron-sized spherical silver-coated copper powder according to claim 1, characterized in that, The concentration of silver salt in the silver complexing solution is 0.1~1.5 mol / L, and the concentration of complexing agent is 0.1~1.5 mol / L; The mass ratio of copper powder to silver in silver salt is (4~10):

1.

7. The method for preparing micron-sized spherical silver-coated copper powder according to claim 1, characterized in that, The complexing agent includes at least one of ethylenediaminetetraacetic acid, tetraethylenepentamine, triethylenetetraamine, ammonia, sodium tartrate, L-histidine, glutamic acid, and thiourea.

8. The method for preparing micron-sized spherical silver-coated copper powder according to claim 1, characterized in that, The reducing agent includes at least one of ascorbic acid, glucose, formaldehyde, sodium borohydride, and hydrazine hydrate. The concentration of the reducing agent in the reducing solution is 0.1~1.0 mol / L; The molar ratio of the reducing agent to the silver salt is (1.1~1.5):

1.

9. The method for preparing micron-sized spherical silver-coated copper powder according to claim 1, characterized in that, The constant temperature conditions described in step S3 are 25~70℃.

10. A micron-sized spherical silver-coated copper powder, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 9.

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