A preparation method of silver-coated copper powder

Abstract

The present invention discloses a method for preparing silver-coated copper powder, comprising the following steps: (1) depositing a silver deposition layer having a porous structure on the surface of copper powder by a displacement method to obtain a silver-coated copper powder precursor; (2) adding the silver-coated copper powder precursor to a metal salt solution that is easily decomposed by heat, so that the silver deposition layer of the silver-coated copper powder precursor fully absorbs the metal salt solution that is easily decomposed by heat due to capillary phenomenon, and then filtering, washing, and drying to obtain the silver-coated copper powder precursor loaded with the metal salt that is easily decomposed by heat; (3) placing the silver-coated copper powder precursor loaded with the metal salt that is easily decomposed by heat together with a carbon-containing reducing agent in a closed environment for heat treatment, thereby obtaining silver-coated copper powder, wherein the pore structure of the silver deposition layer of the silver-coated copper powder is filled with a metal element. The pores of the silver plating layer on the surface of the silver-coated copper powder prepared by the preparation method of the present invention are filled with a metal element, thereby improving the antioxidant performance and density of the silver-coated copper powder.

Description

Technical Field

[0001] The invention belongs to the field of conductive materials, and in particular relates to a method for preparing conductive copper powder. Background Art

[0002] Due to the rapid development of the information, electronics, and communications industries, demand for electronic paste, a fundamental functional material integrating materials, electronic technology, and chemical engineering, has increased significantly. Currently, conductive pastes primarily use silver as a conductive filler. Silver pastes offer high precision, reliability, and conductivity. However, the high price of silver significantly increases the production cost of these pastes, and silver migration can affect their effectiveness.

[0003] Copper and silver have similar electrical conductivity and are low-cost, but their oxidation resistance is poor. Many studies have attempted to reduce costs and improve the oxidation resistance of copper powder by coating it with a layer of silver. Common methods for preparing silver-coated copper powder include electrodeposition, photoinduction, displacement, and displacement-reduction. While the displacement method is particularly convenient for preparing silver-coated copper powder, the resulting silver-coated copper powder has numerous pores on its surface, resulting in poor coating density and low coating coverage, which in turn reduces the powder's oxidation resistance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology and provide a method for preparing silver-coated copper powder with good coating density and high coverage rate.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0006] A method for preparing silver-coated copper powder comprises the following steps:

[0007] (1) depositing a silver deposition layer having a porous structure on the surface of the copper powder by a replacement method to obtain a silver-coated copper powder precursor;

[0008] (2) adding the silver-coated copper powder precursor to a metal salt solution that is easily decomposed by heat, allowing the silver deposition layer of the silver-coated copper powder precursor to fully absorb the metal salt solution that is easily decomposed by heat due to capillary phenomenon, and then filtering, washing, and drying to obtain the silver-coated copper powder precursor loaded with the metal salt that is easily decomposed by heat;

[0009] (3) placing the silver-coated copper powder precursor loaded with a metal salt that is easily decomposed by heat and a carbon-containing reducing agent in a closed environment for heat treatment to obtain silver-coated copper powder, wherein the pore structure of the silver deposition layer of the silver-coated copper powder is filled with a metal element.

[0010] In the above preparation method, preferably, depositing a silver deposition layer with a porous structure on the surface of the copper powder by a replacement method includes the following steps: mixing the copper powder with a dispersant and a complexing agent, heating and stirring, and then slowly adding a silver nitrate solution to carry out a replacement reaction, and the reaction product is washed, sonicated, filtered, and dried to obtain a silver-coated copper powder precursor.

[0011] In the above preparation method, preferably, the amount of silver nitrate in the silver nitrate solution is 50-100% of the mass of the copper powder.

[0012] In the above preparation method, preferably, the silver nitrate solution is added at a rate of 2-10 mL / min.

[0013] The present invention utilizes a large amount of silver nitrate solution and a slow addition rate, which facilitates the deposition of more silver on the copper powder surface. Furthermore, the silver is present on the copper powder surface in a porous structure with a relatively small pore size. When subsequently placed in a metal salt solution that readily decomposes upon heating, the metal salt solution penetrates into the pore structure due to capillary action, subsequently decomposing and oxidizing to form a single metal, thereby improving the oxidation performance of the silver-coated copper powder. However, if the amount of silver nitrate used is small and the addition rate is fast, the silver content on the copper powder surface may be low and uneven, potentially resulting in incomplete coating.

[0014] In the above preparation method, preferably, the dispersant includes one or more of polyvinyl pyrrolidone, polyethylene glycol, polyacrylic acid, and polypropylene alcohol, and the concentration of the dispersant is 0.001-0.5 mol / L; the complexing agent includes one or more of EDTA, EDTA-2Na, EDTA-4Na, ammonia water, ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine, and the concentration of the complexing agent is 0.01-1 mol / L. Too low a dispersant concentration will result in poor dispersion and easy powder agglomeration, while too high a concentration will increase the solution viscosity, poor fluidity, and increase costs. Too low a complexing agent concentration will result in poor complexing ability, while too high a concentration will result in a slow reaction rate and increased costs.

[0015] In the above preparation method, preferably, the reaction temperature during the replacement reaction is controlled at 30-80° C. In the present invention, the reaction temperature is preferably controlled at 30-80° C. Too low a temperature will result in a slow reaction rate and incomplete reaction, while too high a temperature will result in an overly intense reaction that is difficult to control.

[0016] In the above preparation method, preferably, the copper powder has a particle size of 1-4 microns. Too small a particle size of the copper powder will cause the powder to agglomerate easily, while too large a particle size will cause uneven silver coating.

[0017] In the above preparation method, preferably, the metal salt solution that is easily decomposed by heat comprises one or more of a basic nickel carbonate solution, a bismuth subnitrate solution, and a nickel nitrite solution, and the concentration of the metal salt solution that is easily decomposed by heat is 0.1-10 g / L. To maximize the concentration of the metal salt solution in the metal salt solution that is easily decomposed by heat, the solution may be heated during dissolution, for example, by stirring and dissolving in a water bath at 50°C.

[0018] In the above preparation method, preferably, before depositing the porous silver layer on the copper powder surface by displacement, the copper powder is first mixed evenly with a sulfuric acid solution, stirred for reaction, filtered, and dried. The sulfuric acid has a mass concentration of 5-20%. The first acid wash can reduce the oxide layer on the copper surface and remove impurities on the copper surface, which is conducive to depositing a larger amount of silver.

[0019] In the above preparation method, preferably, the heat treatment temperature is 60-80°C and the heat treatment time is 2-6 hours. Low heat treatment temperature and short heat treatment time will cause incomplete decomposition and reduction, while high heat treatment temperature will affect the stability of silver-coated copper powder.

[0020] The principle of the present invention is as follows Figure 1 As shown, taking nickel salt as an example, the present invention utilizes a displacement method to prepare silver-coated copper powder. After pre-treating the copper powder, it is mixed with a dispersant and a complexing agent. Then, a large amount of a high-concentration silver nitrate solution is slowly added to the mixed solution. A displacement reaction occurs within the system, and the copper powder replaces the silver, causing the silver to be deposited on the surface of the copper powder to obtain the silver-coated copper powder. The silver-coated copper powder prepared by this method is simple to prepare, has a high silver conversion rate, and a relatively thick silver deposition layer with relatively many pores. However, the silver-coated copper powder prepared by this simple method has many pores on the surface, which reduces its antioxidant performance. Therefore, the present invention uses the impregnation method to fill the pores of the silver-coated copper powder. The prepared silver-coated copper powder precursor is placed in a nickel salt solution that is easily decomposed by heat, stirred and mixed evenly, and the nickel salt solution that is easily decomposed by heat enters the pores of the silver-coated copper powder. The surface nickel salt is filtered and washed (due to the capillary phenomenon, the nickel salt solution in the pores is not easy to be washed away, and the nickel salt on the surface is easier to wash away. A relatively gentle water flow is used for washing; at the same time, the presence of nickel on the surface will reduce its oxidation resistance, so it is necessary to ensure that the nickel salt solution on the surface of the silver-coated copper powder precursor is washed away), and then dried. The silver-coated copper powder precursor is placed in a closed environment together with a carbon-containing reducing agent (such as charcoal) and dried. The nickel salt solution, which is easily decomposed by heat, is unstable and decomposes into nickel oxide. The charcoal can slowly react with oxygen in the air to generate carbon monoxide. The carbon monoxide reduces the nickel oxide to metallic nickel, which fills the pores of the silver-coated copper powder. The pores of the silver-plated layer on the surface of the silver-coated copper powder prepared in this way are filled with metallic nickel to improve the oxidation resistance. The nickel is basically only present in the pores and is almost not contained on the surface. The product has high density, excellent oxidation resistance and good conductivity.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] 1. The preparation method of the silver-coated copper powder of the present invention adopts the replacement method to prepare the silver-coated copper powder. This method is simple and easy to perform. No additional reducing agent is required to prepare the silver-coated copper powder. Compared with the traditional reduction method, the experimental steps are reduced and the formation of silver element in the solution is avoided. The silver content on the surface of the silver-coated copper powder is high.

[0023] 2. The pores of the silver-plated layer on the surface of the silver-coated copper powder prepared by the preparation method of the present invention are filled with metal elements to improve the oxidation resistance, high density, excellent oxidation resistance and good conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 The present invention is a process flow chart of the preparation method of the silver-coated copper powder.

[0026] Figure 2 This is a thermogravimetric analysis (TG) curve of the silver-coated copper powder prepared in Example 1.

[0027] Figure 3 This is a thermogravimetric analysis (TG) curve of the silver-coated copper powder prepared in Example 2.

[0028] Figure 4 This is a thermogravimetric analysis (TG) curve of the silver-coated copper powder prepared in Comparative Example 1. DETAILED DESCRIPTION

[0029] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0030] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0031] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0032] Example 1:

[0033] As Figure 1 shown, a method for preparing silver-coated copper powder includes the following steps:

[0034] (1) Pretreatment of copper powder: Weigh 3 g of copper powder with a particle size of 2.5 μm and mix it evenly with 50 ml of sulfuric acid solution with a mass fraction of 10%. Stir and react for a period of time, then filter and dry to obtain pretreated copper powder;

[0035] (2) Preparation of mixed solution: Weigh 0.65 g of PVP and 4.38 g of EDTA-2Na, add them to 400 mL of deionized water and stir to dissolve. Flush the pretreated copper powder into this solution with 50 mL of deionized water, and heat and stir;

[0036] (3) Preparation of silver solution: Weigh 3 g of silver nitrate, add 200 mL of deionized water, and prepare a silver nitrate solution;

[0037] (4) Preparation of silver-coated copper powder precursor: When the temperature of the mixed solution where the copper powder is located rises to 50 °C, use a peristaltic pump to drip the silver nitrate solution into it at a speed of 5 mL / min. After the dripping is completed, react for 20 min, and obtain the silver-coated copper powder precursor through washing, ultrasonic treatment, filtration, and drying;

[0038] (5) Preparation of nickel carbonate solution: Weigh 1 g of basic nickel carbonate, add 200 ml of deionized water, stir and dissolve it in a water bath at 50 °C for 10 min, and filter to obtain a nickel carbonate solution;

[0039] (6) Add the prepared silver-coated copper powder precursor to the nickel carbonate solution, mix and stir for 30 min, filter, wash, and dry to obtain a silver-coated copper powder precursor with nickel carbonate inhaled in the pores;

[0040] (7) Weigh 3 g of activated carbon powder (400 mesh, powdery) and the silver-coated copper powder precursor prepared in step (6), place them in a closed container, and dry them in an oven at 80 °C for 3 h to obtain silver-coated copper powder, and the silver deposition layer of this silver-coated copper powder is filled with elemental nickel.

[0041] Example 2:

[0042] As Figure 1 shown, a method for preparing silver-coated copper powder includes the following steps:

[0043] (1) Pretreatment of copper powder: Weigh 3 g of copper powder with a particle size of 2.5 μm and mix it evenly with 50 ml of sulfuric acid solution with a mass fraction of 10%. Stir and react for a period of time, then filter and dry to obtain pretreated copper powder;

[0044] (2) Prepare the mixed solution: Weigh 0.65 g of PVP and 4.38 g of EDTA-2Na, add them to 400 mL of deionized water and stir to dissolve. Flush the pretreated copper powder into this solution with 50 mL of deionized water, and heat up and stir;

[0045] (3) Prepare the silver solution: Weigh 3 g of silver nitrate, add 200 mL of deionized water to prepare the silver nitrate solution;

[0046] (4) Prepare the silver-coated copper powder precursor: When the mixed solution where the copper powder is located is heated to 50 °C, use a peristaltic pump to drip the silver nitrate solution into it at a speed of 5 mL / min. After the dripping is completed, react for 20 min, and obtain the silver-coated copper powder precursor through washing, ultrasonic treatment, filtration, and drying;

[0047] (5) Prepare the bismuth subnitrate solution: Weigh 1 g of bismuth subnitrate, add 200 ml of deionized water, stir and dissolve it for 10 min under the condition of a water bath at 50 °C, and filter to obtain the bismuth subnitrate solution;

[0048] (6) Add the prepared silver-coated copper powder precursor to the bismuth subnitrate solution, mix and stir for 30 min, filter, wash, and dry to obtain the silver-coated copper powder precursor with bismuth subnitrate inhaled in the pores;

[0049] (7) Weigh 3 g of activated carbon powder (400 mesh, powdery) and the silver-coated copper powder precursor prepared in step (6), place them in a closed container, and dry them in an oven at 80 °C for 3 h to obtain the silver-coated copper powder, and the silver deposition layer of the silver-coated copper powder is filled with elemental bismuth.

[0050] Example 3:

[0051] As Figure 1 shown, a method for preparing silver-coated copper powder includes the following steps:

[0052] (1) Pretreat the copper powder: Weigh 3 g of copper powder with a particle size of 2.5 um and mix it evenly with 50 ml of sulfuric acid solution with a mass fraction of 10%, stir and react for a period of time, filter and dry to obtain the pretreated copper powder;

[0053] (2) Prepare the mixed solution: Weigh 0.65 g of PVP and 4.38 g of EDTA-2Na, add them to 400 mL of deionized water and stir to dissolve. Flush the pretreated copper powder into this solution with 50 mL of deionized water, and heat up and stir;

[0054] (3) Prepare the silver solution: Weigh 1.5 g of silver nitrate, add 200 mL of deionized water to prepare the silver nitrate solution;

[0055] (4) Preparation of silver-coated copper powder precursor: When the mixed solution containing copper powder is heated to 50 °C, the silver nitrate solution is added dropwise thereto at a rate of 5 mL / min using a peristaltic pump. After the addition is complete, the reaction is carried out for 20 min, and then it is washed, ultrasonically treated, filtered, and dried to obtain the silver-coated copper powder precursor;

[0056] (5) Preparation of bismuth subnitrate solution: Weigh 1 g of bismuth subnitrate, add 200 ml of deionized water, stir and dissolve it in a water bath at 50 °C for 10 min, and filter to obtain the bismuth subnitrate solution;

[0057] (6) Add the prepared silver-coated copper powder precursor to the bismuth subnitrate solution, mix and stir for 30 min, filter, wash, and dry to obtain the silver-coated copper powder precursor with bismuth subnitrate inhaled in the pores;

[0058] (7) Weigh 3 g of activated carbon powder (400 mesh, powdery) and the silver-coated copper powder precursor prepared in step (6), place them in a closed container, and dry them in an oven at 80 °C for 3 h to obtain the silver-coated copper powder. The silver deposition layer of the silver-coated copper powder is filled with elemental bismuth.

[0059] Comparative Example 1:

[0060] A method for preparing silver-coated copper powder, comprising the following steps:

[0061] (1) Pretreatment of copper powder: Weigh 3 g of copper powder with a particle size of 2.5 μm and mix it evenly with 50 ml of sulfuric acid solution with a mass fraction of 10%. Stir and react for a period of time, filter, and dry to obtain the pretreated copper powder;

[0062] (2) Preparation of mixed solution: Weigh 0.65 g of PVP and 4.38 g of EDTA-2Na, add them to 400 mL of deionized water, stir and dissolve, and flush the pretreated copper powder into this solution with 50 mL of deionized water, then heat and stir;

[0063] (3) Preparation of silver solution: Weigh 3 g of silver nitrate, add 200 mL of deionized water, and prepare the silver nitrate solution;

[0064] (4) Preparation of silver-coated copper powder precursor: When the mixed solution containing copper powder is heated to 50 °C, the silver nitrate solution is added dropwise thereto at a rate of 5 mL / min using a peristaltic pump. After the addition is complete, the reaction is carried out for 20 min, and then it is washed, ultrasonically treated, filtered, and dried to obtain the silver-coated copper powder.

[0065] The antioxidant properties of the silver-coated copper powder in Examples 1-3 and Comparative Example 1 were detected. The silver-coated copper powder after treatment in each example and comparative example was tested by thermogravimetric analysis (150 mg sample), and the respective weight gain ratios were statistically calculated. The results are shown in the following table and Figures 2-4 as follows.

[0066] Table 1: Data Sheet for Testing the Antioxidant Properties of Examples 1-3 and Comparative Example 1

[0067] Weight gain ratio (%) Example 1 12.75 Example 2 10.53 Example 3 10.88 Comparative Example 1 12.83

[0068] As can be seen from Table 1 and Figures 2-4 it can be seen that 150 mg samples of silver-coated copper powder treated in each example and comparative example were taken for thermogravimetric analysis. In Example 1, 2 and Comparative Example 1, silver nitrate was used in an amount of 3 g and the dropping rate was 5 ml / min. Silver-coated copper powder was prepared without using metal salts with nickel salt and bismuth salt respectively. The result was that the weight gain of the sample in Comparative Example 1 was the highest at 12.83%, while the weight gains of the samples in the two examples were less, 12.75% and 10.53% respectively. In Example 3, silver nitrate was used in an amount of 1.5 g and the dropping rate was 5 ml / min. Silver-coated copper powder was prepared with bismuth salt. The result was that the weight gain of the sample in Example 3 was 10.88%, more than that in Example 2, indicating that a large amount of silver nitrate is beneficial to improving the antioxidant property. By comparing the weight gain data of the examples and the comparative examples, it was found that the weight gain of the silver-coated copper powder prepared by treating with metal salts was relatively low, which indicated that the silver-coated copper powder treated with metal salts achieved the effect of plugging pores and improved its antioxidant property.

Claims

1. A method for preparing silver-coated copper powder, characterized in that, The following steps are involved: (1) depositing a silver deposition layer having a porous structure on the surface of the copper powder by a replacement method to obtain a silver-coated copper powder precursor; (2) adding the silver-coated copper powder precursor to a metal salt solution that is easily decomposed by heat, allowing the silver deposition layer of the silver-coated copper powder precursor to fully absorb the metal salt solution that is easily decomposed by heat due to capillary phenomenon, and then filtering, washing, and drying to obtain the silver-coated copper powder precursor loaded with the metal salt that is easily decomposed by heat; (3) placing the silver-coated copper powder precursor loaded with a metal salt that is easily decomposed by heat and a carbon-containing reducing agent in a closed environment for heat treatment to obtain silver-coated copper powder, wherein the pore structure of the silver deposition layer of the silver-coated copper powder is filled with a metal element.

2. The preparation method according to claim 1, characterized in that, The method comprises the following steps: mixing the copper powder with a dispersant and a complexing agent, heating and stirring, slowly adding a silver nitrate solution to carry out a replacement reaction, and washing, ultrasonicating, filtering and drying the reaction product to obtain a silver-coated copper powder precursor.

3. The preparation method according to claim 2, characterized in that, The amount of silver nitrate in the silver nitrate solution is 50-100% of the mass of the copper powder.

4. The preparation method according to claim 2, wherein The silver nitrate solution is added at a rate of 2-10 mL / min.

5. The preparation method according to claim 2, characterized in that, The dispersant includes one or more of polyvinyl pyrrolidone, polyethylene glycol, polyacrylic acid and polypropylene alcohol, and the concentration of the dispersant is 0.001-0.5 mol / L; the complexing agent includes one or more of EDTA, EDTA-2Na, EDTA-4Na, ammonia water, ethylenediamine, diethylenetriamine, triethylenetetramine and tetraethylenepentamine, and the concentration of the complexing agent is 0.01-1 mol / L.

6. The preparation method according to claim 2, characterized in that, During the replacement reaction, the reaction temperature is controlled at 30-80°C.

7. The preparation method according to any one of claims 1-6, characterized in that, The particle size of the copper powder is 1-4 microns.

8. The preparation method according to any one of claims 1-6, characterized in that, The metal salt solution that is easily decomposed by heat includes one or more of basic nickel carbonate solution, bismuth subnitrate solution and nickel nitrite solution. The concentration of the metal salt solution that is easily decomposed by heat is 0.1-10 g / L.

9. The preparation method according to any one of claims 1-6, characterized in that, Before depositing a silver deposition layer with a porous structure on the surface of copper powder by using a replacement method, the copper powder is firstly mixed with a sulfuric acid solution, stirred for reaction, filtered and dried. The mass concentration of the sulfuric acid is 5-20%.

10. The preparation method according to any one of claims 1-6, characterized in that, The heat treatment temperature is 60-80° C., and the heat treatment time is 2-6 hours.

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