Simple preparation method of silver-coated nickel-coated copper powder with low resistance and high oxidation resistance

Abstract

The invention discloses a simple and convenient preparation method of low-resistance and high-oxidation-resistance silver-coated and nickel-coated copper powder. The simple and convenient preparation method comprises the following steps: firstly, carrying out surface pretreatment on copper powder; mixing the pretreated copper powder with a dispersing agent, a sodium citrate complexing agent and a nickel salt solution to obtain a copper powder precursor solution; the method comprises the following steps: slowly dripping a reducing agent hydrazine hydrate into a copper powder precursor solution for reaction to obtain a nickel-coated copper solution; mixing the silver salt solution with a complexing agent, and dropwise adding the mixture into the nickel-coated copper solution; and washing and drying the obtained solid product to obtain the silver-coated nickel-coated copper powder. The silver-coated and nickel-coated copper powder is prepared by adopting a one-pot method, and the operation process is simple; in the silver layer forming process, the complexing agent L-histidine plays a role in integrating stable complexing, fast transfer and slow reduction, complexing silver ions alleviate the reduction rate and are directionally transferred and adsorbed to the nickel-coated copper surface, and therefore the prepared silver-coated nickel-coated copper powder has excellent conductivity and oxidation resistance.

Description

Technical Field

[0001] The invention relates to a method for preparing metal composite material powder, in particular to a simple method for preparing silver-coated nickel-coated copper powder with low resistance and high oxidation resistance. Background Art

[0002] Electronic pastes with gold, silver, copper, nickel and other metal powders as the main materials are increasingly used in the electronics industry, solar energy and other fields. Silver powder is widely used because of its good conductivity and thermal stability, but the high price of silver limits its application. Metallic copper powder has excellent conductivity and can meet the needs of electronic paste, but copper powder is highly active and easily oxidized in the air, causing its conductivity to decrease rapidly. The formation of copper oxide not only increases the sintering temperature, limits the formation of the conductive film, but also reduces the conductive performance. In order to reduce the oxidation of copper powder, the researchers proposed to coat the surface of the copper powder with a silver layer to prepare a core-shell structured silver-coated copper powder, which avoids the problem of silver migration and greatly reduces the production cost.

[0003] Chinese patent CN117943552A uses two-step reduction to coat the surface of copper powder in liquid phase with a silver layer with good morphology, density and uniformity under the conditions of constant temperature and stirring at 0°C, and can be applied to low-temperature curing slurry and conductive adhesive coatings. This method requires synthesis under low temperature environment, has strict temperature requirements, and has high energy consumption in the production process, which is not conducive to product process amplification and industrialization, and the product has a relatively single use.

[0004] Chinese patent CN118060535A uses physical vapor deposition technology to sputter a layer of silver on the surface of copper powder, which can reduce the replacement reaction of copper powder and reduce the loss of copper powder. The plating solution can be recycled and there is basically no wastewater discharge. The process is environmentally friendly but the process conditions are relatively complex. For example, during the vapor deposition process, the copper powder is placed in a vacuum vapor deposition chamber, and then the air pressure in the vacuum chamber is evacuated and argon gas is introduced for sputtering treatment. The operation is difficult, uniformity cannot be guaranteed, and it is difficult to apply it in large-scale industry. In addition, the bonding strength of the coating by physical electroplating is generally lower than that of chemical plating, and the long-term stability of the powder produced by physical electroplating is difficult to guarantee.

[0005] In the current electronic paste field, silver-coated copper powder cannot completely replace pure silver powder and is only used at low temperatures. This is mainly because the prepared silver-coated copper powder is not resistant to high temperatures. The copper powder in the core is easily oxidized when used at medium and high temperatures, so its application range is greatly limited. Chinese patent CN105598467B proposes a method for preparing silver-coated nickel-coated copper powder that can withstand high temperatures, which broadens the application range of the powder. However, the copper surface is coated three times during the preparation process, and filtered, washed and dissolved many times, with many process steps and cumbersome operation procedures.

[0006] At present, there have been many studies on silver-coated copper powder, but the high-temperature oxidation resistance of the prepared silver-coated copper powder still has great defects, and can only meet the performance requirements of high temperature resistance and high conductivity at around 250°C, which greatly limits its wider application; and the powder used for reflow soldering needs to be resistant to high temperatures up to 280°C, and the sintering conductive paste used for high-temperature insulating substrates such as ceramics and glass has a sintering temperature of about 500°C when sintering into a film. At present, pure silver-coated copper powder is difficult to meet its high temperature resistance requirements. Therefore, it is of great significance to simply prepare silver-coated nickel-coated copper powder with excellent high-temperature resistance and conductivity to achieve the replacement of precious metals with base metals and improve economic benefits, which is of great significance to promote the development and application of electronic pastes. Summary of the invention

[0007] Technical problem: The purpose of the present invention is to provide a simple method for preparing silver-coated nickel-coated copper powder with low resistance and high oxidation resistance. The method has a simple operation process, uniform coating effect, tight plating, high conductivity and oxidation resistance. The method is a method for preparing silver-coated nickel-coated copper powder with a core-shell structure, thereby broadening the application range of composite metal powders.

[0008] Technical solution: The simple preparation method of the silver-coated nickel-coated copper powder with low resistance and high oxidation resistance of the present invention comprises the following steps:

[0009] Step 1: Pre-treat the surface of the copper powder; remove organic impurities and oxides on the surface of the copper powder by ultrasonic treatment;

[0010] Step 2: mixing the pretreated copper powder with a dispersant, a complexing agent, and a nickel salt solution to obtain a copper powder precursor solution;

[0011] Step 3: slowly drop the reducing agent into the copper powder precursor solution, and after reaction, obtain a nickel-coated copper solution;

[0012] Step 4: Mix the silver salt solution and the complexing agent and slowly drip the mixture into the nickel-coated copper solution to obtain a reaction solution;

[0013] Step 5: The reaction solution is subjected to solid-liquid separation, and the obtained solid product is washed and dried to obtain the silver-coated nickel-coated copper powder.

[0014] in,

[0015] In step 2, the complexing agent is at least one of sodium citrate, ammonia water, aspartic acid, L-histidine, sodium tartrate, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, alanine, and aspartic acid.

[0016] In step 2, the dispersant is at least one of polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, gelatin and gum arabic.

[0017] In step 2, the mass ratio of the pretreated copper powder to the dispersant is 100:5-100:55, and the concentration of the copper powder precursor solution is 0.1 g / L-2 g / L.

[0018] In step 2, the mass ratio of copper powder to nickel salt is 1:1-20:1; the molar ratio of nickel salt to complexing agent is 1:1-1:10.

[0019] In step 3, the reducing agent is at least one of hydrazine hydrate, sodium borohydride, gum arabic, glucose, ascorbic acid, L-histidine, and glutamic acid.

[0020] The concentration of the reducing agent is 0.02 mol / L-0.2 mol / L.

[0021] In step 4, the molar concentration of the silver salt is 0.1 mol / L-1.5 mol / L.

[0022] In step 4, the complexing agent is at least one of ammonia water, sodium citrate, sodium tartrate, histidine, alanine, leucine, glycine, serine, valine, and proline.

[0023] In step 4, the mass ratio of the silver salt to the copper powder is 1:1-1:10; the molar ratio of the silver salt to the complexing agent is 1:1-1:40.

[0024] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0025] (1) Compared with single-layer materials formed by two metals, such as silver-coated copper and nickel-coated copper powder, silver grows on the copper surface to form a silver shell. At high temperatures, the tiny silver particles melt and produce holes, causing the copper powder in the core to be exposed and oxidized. Although nickel-coated copper has a good coating effect and improved antioxidant properties, its application range is limited due to the poor conductivity of nickel metal. Silver-coated nickel-coated copper not only retains the excellent resistivity of metallic silver, but also has the high antioxidant properties of metallic nickel.

[0026] (2) The preparation method of the present invention is a one-pot method for preparing powder, which has high raw material utilization rate and simple process. There is no need for filtering and re-dissolving in the middle. The overall process only requires continuous filling, which is simple to operate and easy to mass produce.

[0027] (3) The selection and addition form of the complexing agent in the present invention have a significant impact on the coating effect. The complexing agent selected in the preparation method plays an integrated role of stable complexation, fast migration, and slow reduction, which not only moderates the reduction rate of silver ions in the reaction system and avoids the aggregation of reduced silver; it can also directionally migrate silver ions to the nickel-coated copper surface for reduction, thereby achieving good coating. Therefore, the silver-coated nickel-coated copper powder prepared by this method has high sphericity, good dispersibility, dense and uniform coating, no obvious free silver, and good conductivity and oxidation resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the SEM image of the silver-coated nickel-coated copper powder in Example 1 (magnification is ×10k);

[0029] Figure 2 This is the SEM image of the silver-coated nickel-coated copper powder in Example 2 (magnification is ×10k);

[0030] Figure 3 This is the SEM image of the silver-coated nickel-coated copper powder in Example 3 (magnification is ×10k);

[0031] Figure 4 This is the SEM image of the silver-coated nickel-coated copper powder in Example 4 (magnification is ×10k);

[0032] Figure 5 is a SEM image of the silver-coated nickel-coated copper powder in Example 5 (magnification is ×10k);

[0033] Figure 6 This is the SEM image of the silver-coated nickel-coated copper powder in Example 6 (magnification is ×10k);

[0034] Figure 7 This is the SEM image of the silver-coated nickel-coated copper powder in Comparative Example 1 (magnification is ×10k);

[0035] Figure 8 This is the SEM image of the silver-coated nickel-coated copper powder in Comparative Example 2 (magnification is ×10k);

[0036] Fig. 9 This is the thermogravimetric curve of the silver-coated nickel-coated copper powder in Example 1. DETAILED DESCRIPTION

[0037] The present invention is described in further detail below.

[0038] Example 1

[0039] A method for preparing a silver-coated nickel-coated copper powder with low resistance and high oxidation resistance comprises the following steps:

[0040] (1) Pretreatment of copper powder: 30 g of copper powder was placed in 150 mL of acetone solution and ultrasonically treated for 15 min; then the solid and liquid were separated, and the powder was dispersed in 150 mL of ethanol solution and ultrasonically treated for 15 min to separate the solid and liquid; then the powder was placed in 150 mL of ammonium mixed solution and ultrasonically treated for 15 min to remove organic impurities and oxides on the surface of the copper powder, wherein the ammonium mixed solution includes 0.5 mol / L ammonium sulfate and 1 mol / L ammonia water; then the solid and liquid were separated, and then the powder was placed in 150 mL of sodium hydroxide solution and ultrasonically treated for 15 min, wherein the concentration of the sodium hydroxide solution is 1 g / 100 ml; then the solid and liquid were separated, and then the copper powder was washed 3 times with deionized water and ethanol;

[0041] (2) Preparation of copper powder precursor: The pretreated copper powder was dispersed in deionized water, 6 g of nickel sulfate hexahydrate, 3 g of polyethylene glycol, and 5 g of sodium citrate were dissolved in 200 mL, 20 mL, and 200 mL of deionized water, respectively, and the four solutions were mixed and mechanically stirred at 500 rpm. The water bath temperature was set to 80° C. to obtain a copper powder precursor solution;

[0042] (3) Preparation of nickel-coated copper solution: 20 ml of 80% hydrazine hydrate solution and 60 ml of 2 mol / L sodium hydroxide solution were mixed to obtain a reducing agent solution, and the reducing agent solution was poured into the copper powder precursor solution to react for 1 hour to obtain a nickel-coated copper solution;

[0043] (4) Preparation of silver-coated nickel-coated copper powder: The pH of the nickel-coated copper solution was adjusted to 9 with 2 mol / L citric acid, and two 600 ml 0.3 mol / L L-histidine solutions were prepared. One was added to the nickel-coated copper solution, and the other was mixed with 300 mL 0.25 mol / L silver nitrate solution and then slowly dripped into the nickel-coated copper solution at 5 mL / min. This process was carried out under mechanical stirring at 500 r / min and the reaction temperature was 40°C.

[0044] (5) Cleaning and drying of silver-coated nickel-coated copper powder: The reaction solution was filtered to separate the solid and liquid; and the powder was cleaned with deionized water and ethanol for three times respectively; and then the cleaned silver-coated nickel-coated copper powder was placed in a vacuum drying oven at 50°C and dried for 6 hours.

[0045] Example 2

[0046] (1) Pretreatment of copper powder: 30 g of copper powder was placed in 150 mL of acetone solution and ultrasonically treated for 15 min; then the solid and liquid were separated, and the powder was dispersed in 150 mL of ethanol solution and ultrasonically treated for 15 min to separate the solid and liquid; then the powder was placed in 150 mL of ammonium mixed solution and ultrasonically treated for 15 min to remove organic impurities and oxides on the surface of the copper powder, wherein the ammonium mixed solution includes 0.5 mol / L ammonium sulfate and 1 mol / L ammonia water; then the solid and liquid were separated, and then the powder was placed in 150 mL of sodium hydroxide solution and ultrasonically treated for 15 min, wherein the concentration of the sodium hydroxide solution is 1 g / 100 ml; then the solid and liquid were separated, and then the copper powder was washed 3 times with deionized water and ethanol;

[0047] (2) Preparation of copper powder precursor: The pretreated copper powder was dispersed in deionized water, 6 g of nickel sulfate hexahydrate, 3 g of polyethylene glycol, and 5 g of sodium citrate were dissolved in 200 mL, 20 mL, and 200 mL of deionized water, respectively, and the four solutions were mixed and mechanically stirred at 500 rpm. The water bath temperature was set to 80° C. to obtain a copper powder precursor solution;

[0048] (3) Preparation of nickel-coated copper solution: 20 ml of 80% hydrazine hydrate solution and 60 ml of 2 mol / L sodium hydroxide solution were mixed to obtain a reducing agent solution, and the reducing agent solution was poured into the copper powder precursor solution to react for 1 hour to obtain a nickel-coated copper solution;

[0049] (4) Preparation of silver-coated nickel-coated copper powder: prepare two 600 ml 0.3 mol / L L-histidine solutions, add one to the nickel-coated copper solution, and mix the other with 300 mL 0.25 mol / L silver nitrate solution and then slowly drip into the nickel-coated copper solution at 5 mL / min. This process is carried out under mechanical stirring at 500 r / min and the reaction temperature is 40°C.

[0050] (5) Cleaning and drying of silver-coated nickel-coated copper powder: The reaction solution was filtered to separate the solid and liquid; and the powder was cleaned with deionized water and ethanol for three times respectively; and then the cleaned silver-coated nickel-coated copper powder was placed in a vacuum drying oven at 50°C and dried for 6 hours.

[0051] Example 3

[0052] (1) Pretreatment of copper powder: 30 g of copper powder was placed in 150 mL of acetone solution and ultrasonically treated for 15 min; then the solid and liquid were separated, and the powder was dispersed in 150 mL of ethanol solution and ultrasonically treated for 15 min to separate the solid and liquid; then the powder was placed in 150 mL of ammonium mixed solution and ultrasonically treated for 15 min to remove organic impurities and oxides on the surface of the copper powder, wherein the ammonium mixed solution includes 0.5 mol / L ammonium sulfate and 1 mol / L ammonia water; then the solid and liquid were separated, and then the powder was placed in 150 mL of sodium hydroxide solution and ultrasonically treated for 15 min, wherein the concentration of the sodium hydroxide solution is 1 g / 100 ml; then the solid and liquid were separated, and then the copper powder was washed 3 times with deionized water and ethanol;

[0053] (2) Preparation of copper powder precursor: The pretreated copper powder was dispersed in deionized water, 6 g of nickel sulfate hexahydrate, 3 g of polyethylene glycol, and 5 g of sodium citrate were dissolved in 200 mL, 20 mL, and 200 mL of deionized water, respectively, and the four solutions were mixed and mechanically stirred at 500 rpm. The water bath temperature was set to 80° C. to obtain a copper powder precursor solution;

[0054] (3) Preparation of nickel-coated copper solution: 20 ml of 80% hydrazine hydrate solution and 60 ml of 2 mol / L sodium hydroxide solution were mixed to obtain a reducing agent solution, and the reducing agent solution was poured into the copper powder precursor solution to react for 1 hour to obtain a nickel-coated copper solution;

[0055] (4) Preparation of silver-coated nickel-coated copper powder: The pH of the nickel-coated copper solution was adjusted to 9 with 2 mol / L citric acid, 1200 ml of 0.3 mol / L L-histidine solution was prepared and added to the nickel-coated copper solution; 300 mL of 0.25 mol / L silver nitrate solution was prepared and slowly dripped into the nickel-coated copper solution at 5 mL / min. This process was carried out under mechanical stirring at 500 r / min and the reaction temperature was 40°C;

[0056] (5) Cleaning and drying of silver-coated nickel-coated copper powder: The reaction solution was filtered to separate the solid and liquid; and the powder was cleaned with deionized water and ethanol for three times respectively; and then the cleaned silver-coated nickel-coated copper powder was placed in a vacuum drying oven at 50°C and dried for 6 hours.

[0057] Example 4

[0058] (1) Pretreatment of copper powder: 30 g of copper powder was placed in 150 mL of acetone solution and ultrasonically treated for 15 min; then the solid and liquid were separated, and the powder was dispersed in 150 mL of ethanol solution and ultrasonically treated for 15 min to separate the solid and liquid; then the powder was placed in 150 mL of ammonium mixed solution and ultrasonically treated for 15 min to remove organic impurities and oxides on the surface of the copper powder, wherein the ammonium mixed solution includes 0.5 mol / L ammonium sulfate and 1 mol / L ammonia water; then the solid and liquid were separated, and then the powder was placed in 150 mL of sodium hydroxide solution and ultrasonically treated for 15 min, wherein the concentration of the sodium hydroxide solution is 1 g / 100 ml; then the solid and liquid were separated, and then the copper powder was washed 3 times with deionized water and ethanol;

[0059] (2) Preparation of copper powder precursor: The pretreated copper powder was dispersed in deionized water, 6 g of nickel sulfate hexahydrate, 3 g of polyethylene glycol, and 5 g of sodium citrate were dissolved in 200 mL, 20 mL, and 200 mL of deionized water, respectively, and the four solutions were mixed and mechanically stirred at 500 rpm. The water bath temperature was set to 80° C. to obtain a copper powder precursor solution;

[0060] (3) Preparation of nickel-coated copper solution: 20 ml of 80% hydrazine hydrate solution and 60 ml of 2 mol / L sodium hydroxide solution were mixed to obtain a reducing agent solution, and the reducing agent solution was poured into the copper powder precursor solution to react for 1 hour to obtain a nickel-coated copper solution;

[0061] (4) Preparation of silver-coated nickel-coated copper powder: The pH of the nickel-coated copper solution was adjusted to 9 with 2 mol / L citric acid, 1200 ml of 0.3 mol / L L-histidine solution was mixed with 300 mL of 0.25 mol / L silver nitrate solution, and then slowly dripped into the nickel-coated copper solution at 5 mL / min. This process was carried out under mechanical stirring at 500 r / min and the reaction temperature was 40°C.

[0062] (5) Cleaning and drying of silver-coated nickel-coated copper powder: The reaction solution was filtered to separate the solid and liquid; and the powder was cleaned with deionized water and ethanol for three times respectively; and then the cleaned silver-coated nickel-coated copper powder was placed in a vacuum drying oven at 50°C and dried for 6 hours.

[0063] Example 5

[0064] (1) Pretreatment of copper powder: 30 g of copper powder was placed in 150 mL of acetone solution and ultrasonically treated for 15 min; then the solid and liquid were separated, and the powder was dispersed in 150 mL of ethanol solution and ultrasonically treated for 15 min to separate the solid and liquid; then the powder was placed in 150 mL of ammonium mixed solution and ultrasonically treated for 15 min to remove organic impurities and oxides on the surface of the copper powder, wherein the ammonium mixed solution includes 0.5 mol / L ammonium sulfate and 1 mol / L ammonia water; then the solid and liquid were separated, and then the powder was placed in 150 mL of sodium hydroxide solution and ultrasonically treated for 15 min, wherein the concentration of the sodium hydroxide solution is 1 g / 100 ml; then the solid and liquid were separated, and then the copper powder was washed 3 times with deionized water and ethanol;

[0065] (2) Preparation of copper powder precursor: The pretreated copper powder was dispersed in deionized water, 6 g of nickel sulfate hexahydrate, 3 g of polyethylene glycol, and 5 g of sodium citrate were dissolved in 200 mL, 20 mL, and 200 mL of deionized water, respectively, and the four solutions were mixed and mechanically stirred at 500 rpm. The water bath temperature was set to 80° C. to obtain a copper powder precursor solution;

[0066] (3) Preparation of nickel-coated copper solution: 20 ml of 80% hydrazine hydrate solution and 60 ml of 2 mol / L sodium hydroxide solution were mixed to obtain a reducing agent solution, and the reducing agent solution was poured into the copper powder precursor solution to react for 1 hour to obtain a nickel-coated copper solution;

[0067] (4) Preparation of silver-coated nickel-coated copper powder: The pH of the nickel-coated copper solution was adjusted to 9 with 2 mol / L citric acid, and two 600 ml 0.24 mol / L L-histidine solutions were prepared. One was added to the nickel-coated copper solution, and the other was mixed with 300 mL 0.25 mol / L silver nitrate solution and then slowly dripped into the nickel-coated copper solution at 5 mL / min. This process was carried out under mechanical stirring at 500 r / min and the reaction temperature was 40°C.

[0068] (5) Cleaning and drying of silver-coated nickel-coated copper powder: The reaction solution was filtered to separate the solid and liquid; and the powder was cleaned with deionized water and ethanol for three times respectively; and then the cleaned silver-coated nickel-coated copper powder was placed in a vacuum drying oven at 50°C and dried for 6 hours.

[0069] Example 6

[0070] (1) Pretreatment of copper powder: 30 g of copper powder was placed in 150 mL of acetone solution and ultrasonically treated for 15 min; then the solid and liquid were separated, and the powder was dispersed in 150 mL of ethanol solution and ultrasonically treated for 15 min to separate the solid and liquid; then the powder was placed in 150 mL of ammonium mixed solution and ultrasonically treated for 15 min to remove organic impurities and oxides on the surface of the copper powder, wherein the ammonium mixed solution includes 0.5 mol / L ammonium sulfate and 1 mol / L ammonia water; then the solid and liquid were separated, and then the powder was placed in 150 mL of sodium hydroxide solution and ultrasonically treated for 15 min, wherein the concentration of the sodium hydroxide solution is 1 g / 100 ml; then the solid and liquid were separated, and then the copper powder was washed 3 times with deionized water and ethanol;

[0071] (2) Preparation of copper powder precursor: The pretreated copper powder was dispersed in deionized water, 6 g of nickel sulfate hexahydrate, 3 g of polyethylene glycol, and 5 g of sodium citrate were dissolved in 200 mL, 20 mL, and 200 mL of deionized water, respectively, and the four solutions were mixed and mechanically stirred at 500 rpm. The water bath temperature was set to 80° C. to obtain a copper powder precursor solution;

[0072] (3) Preparation of nickel-coated copper solution: 20 ml of 80% hydrazine hydrate solution and 60 ml of 2 mol / L sodium hydroxide solution were mixed to obtain a reducing agent solution, and the reducing agent solution was poured into the copper powder precursor solution to react for 1 hour to obtain a nickel-coated copper solution;

[0073] (4) Preparation of silver-coated nickel-coated copper powder: The pH of the nickel-coated copper solution was adjusted to 9 with 2 mol / L citric acid, and two 600 ml 0.36 mol / L L-histidine solutions were prepared. One was added to the nickel-coated copper solution, and the other was mixed with 300 mL 0.25 mol / L silver nitrate solution and then slowly dripped into the nickel-coated copper solution at 5 mL / min. This process was carried out under mechanical stirring at 500 r / min and the reaction temperature was 40°C.

[0074] (5) Cleaning and drying of silver-coated nickel-coated copper powder: The reaction solution was filtered to separate the solid and liquid; and the powder was cleaned with deionized water and ethanol for three times respectively; and then the cleaned silver-coated nickel-coated copper powder was placed in a vacuum drying oven at 50°C and dried for 6 hours.

[0075] Comparative Example 1

[0076] (1) Pretreatment of copper powder: 30 g of copper powder was placed in 150 mL of acetone solution and ultrasonically treated for 15 min; then the solid and liquid were separated, and the powder was dispersed in 150 mL of ethanol solution and ultrasonically treated for 15 min to separate the solid and liquid; then the powder was placed in 150 mL of ammonium mixed solution and ultrasonically treated for 15 min to remove organic impurities and oxides on the surface of the copper powder, wherein the ammonium mixed solution includes 0.5 mol / L ammonium sulfate and 1 mol / L ammonia water; then the solid and liquid were separated, and then the powder was placed in 150 mL of sodium hydroxide solution and ultrasonically treated for 15 min, wherein the concentration of the sodium hydroxide solution is 1 g / 100 ml; then the solid and liquid were separated, and then the copper powder was washed 3 times with deionized water and ethanol;

[0077] (2) Preparation of copper powder precursor: The pretreated copper powder was dispersed in deionized water, 6 g of nickel sulfate hexahydrate, 3 g of polyethylene glycol, and 5 g of sodium citrate were dissolved in 200 mL, 20 mL, and 200 mL of deionized water, respectively, and the four solutions were mixed and mechanically stirred at 500 rpm. The water bath temperature was set to 80° C. to obtain a copper powder precursor solution;

[0078] (3) Preparation of nickel-coated copper solution: 20 ml of 80% hydrazine hydrate solution and 60 ml of 2 mol / L sodium hydroxide solution were mixed to obtain a reducing agent solution, and the reducing agent solution was poured into the copper powder precursor solution to react for 1 hour to obtain a nickel-coated copper solution;

[0079] (4) Preparation of silver-coated nickel-coated copper powder: The pH of the nickel-coated copper solution was adjusted to 9 with 2 mol / L citric acid, and two 600 ml 0.20 mol / L disodium ethylenediaminetetraacetic acid solutions were prepared. One was added to the nickel-coated copper solution, and the other was mixed with 300 mL 0.25 mol / L silver nitrate solution and then slowly dripped into the nickel-coated copper solution at 5 mL / min. This process was carried out under mechanical stirring at 500 r / min and the reaction temperature was 40°C.

[0080] (5) Cleaning and drying of silver-coated nickel-coated copper powder: The reaction solution was filtered to separate the solid and liquid; and the powder was cleaned with deionized water and ethanol for three times respectively; and then the cleaned silver-coated nickel-coated copper powder was placed in a vacuum drying oven at 50°C and dried for 6 hours.

[0081] Comparative Example 2

[0082] (1) Pretreatment of copper powder: 30 g of copper powder was placed in 150 mL of acetone solution and ultrasonically treated for 15 min; then the solid and liquid were separated, and the powder was dispersed in 150 mL of ethanol solution and ultrasonically treated for 15 min to separate the solid and liquid; then the powder was placed in 150 mL of ammonium mixed solution and ultrasonically treated for 15 min to remove organic impurities and oxides on the surface of the copper powder, wherein the ammonium mixed solution includes 0.5 mol / L ammonium sulfate and 1 mol / L ammonia water; then the solid and liquid were separated, and then the powder was placed in 150 mL of sodium hydroxide solution and ultrasonically treated for 15 min, wherein the concentration of the sodium hydroxide solution is 1 g / 100 ml; then the solid and liquid were separated, and then the copper powder was washed 3 times with deionized water and ethanol;

[0083] (2) Preparation of copper powder precursor: The pretreated copper powder was dispersed in deionized water, 6 g of nickel sulfate hexahydrate, 3 g of polyethylene glycol, and 5 g of sodium citrate were dissolved in 200 mL, 20 mL, and 200 mL of deionized water, respectively, and the four solutions were mixed and mechanically stirred at 500 rpm. The water bath temperature was set to 80° C. to obtain a copper powder precursor solution;

[0084] (3) Preparation of nickel-coated copper solution: 20 ml of 80% hydrazine hydrate solution and 60 ml of 2 mol / L sodium hydroxide solution were mixed to obtain a reducing agent solution, and the reducing agent solution was poured into the copper powder precursor solution to react for 1 hour to obtain a nickel-coated copper solution;

[0085] (4) Preparation of silver-coated nickel-coated copper powder: The pH of the nickel-coated copper solution was adjusted to 9 with 2 mol / L citric acid, 300 mL of 0.25 mol / L silver nitrate solution was prepared, 20% wt ammonia water was added to the silver nitrate solution until the solution was clear, and then the solution was slowly added to the nickel-coated copper solution at a rate of 5 mL / min. This process was carried out under mechanical stirring at 500 r / min and the reaction temperature was 40° C.

[0086] (5) Cleaning and drying of silver-coated nickel-coated copper powder: The reaction solution was filtered to separate the solid and liquid; and the powder was cleaned with deionized water and ethanol for three times respectively; and then the cleaned silver-coated nickel-coated copper powder was placed in a vacuum drying oven at 50°C and dried for 6 hours.

[0087] The silver-coated nickel-coated copper powders of the above-mentioned Examples 1-6 were tested by scanning electron microscopy. By comparing Example 1 with Example 2, it can be clearly observed that there are more free growth of silver particles in Example 2, and the coating effect in Example 2 is not ideal. The silver particles are relatively concentrated and prominent, and part of the powder is corroded. In Example 1, the silver layer grows evenly on the powder surface, no free silver particles appear, and the dispersion is good, and there is no obvious corrosion phenomenon. This is closely related to pH, indicating that when the pH is 9, the silver reduction reaction is relatively mild, while in an overly alkaline environment, the reduction rate of hydrazine hydrate is too fast, resulting in uneven coating effect and the generation of a large amount of free silver. Fig. 9 The thermogravimetric curve of the powder shows that the weight of the powder starts to increase from 450°C, indicating that the silver-coated nickel-coated copper powder prepared in Example 1 has excellent antioxidant properties. Figure 3 As shown, it can be observed that most of the silver in the silver-coated nickel-coated copper powder in Example 3 is reduced on the surface of the nickel-coated copper powder, but the silver is too concentrated in clusters and the surface is not uniform, which indicates that the complexing agent L-histidine has a certain adsorption effect on the nickel-coated copper powder; Figure 4 As shown in the figure, most of the silver in the silver-coated nickel-coated copper powder in Example 4 grows disorderly, mostly free silver, and cannot achieve uniform coating of the silver layer on the nickel-coated copper surface. The two illustrate that the addition form of the complexing agent has a significant impact on the coating effect. Example 1 combines two addition forms. In the process of reducing silver, half of the silver ions are complexed with the complexing agent L-histidine, which slows down the reduction rate. At the same time, the other half of the complexing agent mainly plays a role in directional transfer and adsorption to the nickel-coated copper surface, achieving uniform coating of the silver layer and effectively reducing the generation of free silver. Comparing Example 1 with Example 5 and Example 6, as shown in the figure, Figure 5 As shown, it can be observed that the silver-coated nickel-coated copper powder in Example 5 has more free growth of silver particles, and the free silver clusters are concentrated, the surface of the nickel-coated copper is not completely coated with silver, and the utilization rate of silver is not high, indicating that a small amount of complexing agent cannot slow down the reduction rate of the reaction, and the effect of slow reduction cannot be achieved. In addition, due to the small amount of complexing agent, the transfer adsorption effect is significantly reduced, and the effect of fast migration cannot be achieved. Comparing Example 1 with Example 6, as shown in FIG. Figure 6 As shown, it can be observed that the corrosion phenomenon of the silver-coated nickel-coated copper powder in Example 6 is more serious, the silver particles are larger, and the surface coating is incomplete, indicating that the experiment needs to be controlled within the range of an appropriate amount of complexing agent. Example 1 can achieve uniform coating of the silver layer without corrosion within the range of an appropriate amount of complexing agent. Comparing Example 1 with Comparative Example 1 and Comparative Example 2, as shown in FIG. Figure 7 , 8 As shown, the reduced silver is reduced in the system in a free form, and is not coated on the nickel-coated copper surface, and the role of the complexing agent double-sided tape is not played, indicating that the selection of the complexing agent is crucial, and the complexing agent silver layer coating effect selected in Example 1 is ideal, and less free silver is generated, which reflects the role of the complexing agent L-histidine in stable complexation, fast migration, and slow reduction.

Claims

1. A simple method for preparing silver-coated nickel-coated copper powder with low resistance and high oxidation resistance, characterized in that: The following steps are involved: Step 1: Pre-treat the surface of copper powder; Ultrasonic treatment is used to remove organic impurities and oxides on the surface of copper powder; Step 2: mixing the pretreated copper powder with a dispersant, a complexing agent, and a nickel salt solution to obtain a copper powder precursor solution; Step 3: slowly drop the reducing agent into the copper powder precursor solution, and after reaction, obtain a nickel-coated copper solution; Step 4: Mix the silver salt solution and the complexing agent and slowly drip the mixture into the nickel-coated copper solution to obtain a reaction solution; Step 5: The reaction solution is subjected to solid-liquid separation, and the obtained solid product is washed and dried to obtain the silver-coated nickel-coated copper powder.

2. The method for preparing the silver-coated nickel-coated copper powder with low resistance and high oxidation resistance according to claim 1, characterized in that: In step 2, the complexing agent is at least one of sodium citrate, ammonia water, aspartic acid, L-histidine, sodium tartrate, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, alanine, and aspartic acid.

3. The simple preparation method of the silver-coated nickel-coated copper powder with low resistance and high oxidation resistance according to claim 1, characterized in that: In step 2, the dispersant is at least one of polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, gelatin and gum arabic.

4. The simple preparation method of the silver-coated nickel-coated copper powder with low resistance and high oxidation resistance according to claim 1, characterized in that: In step 2, the mass ratio of the pretreated copper powder to the dispersant is 100:5-100:55, and the concentration of the copper powder precursor solution is 0.1 g / L-2 g / L.

5. The simple preparation method of the silver-coated nickel-coated copper powder with low resistance and high oxidation resistance according to claim 1, characterized in that: In step 2, the mass ratio of copper powder to nickel salt is 1:1-20:1; the molar ratio of nickel salt to complexing agent is 1:1-1:

10.

6. The simple preparation method of the silver-coated nickel-coated copper powder with low resistance and high oxidation resistance according to claim 1, characterized in that: In step 3, the reducing agent is at least one of hydrazine hydrate, sodium borohydride, gum arabic, glucose, ascorbic acid, L-histidine, and glutamic acid.

7. The method for preparing the silver-coated nickel-coated copper powder with low resistance and high oxidation resistance according to claim 6, characterized in that: The concentration of the reducing agent is 0.02 mol / L-0.2 mol / L.

8. The simple preparation method of the silver-coated nickel-coated copper powder with low resistance and high oxidation resistance according to claim 1, characterized in that: In step 4, the molar concentration of the silver salt is 0.1 mol / L-1.5 mol / L.

9. The simple preparation method of the silver-coated nickel-coated copper powder with low resistance and high oxidation resistance according to claim 1, characterized in that: In step 4, the complexing agent is at least one of ammonia water, sodium citrate, sodium tartrate, histidine, alanine, leucine, glycine, serine, valine, and proline.

10. The simple preparation method of the silver-coated nickel-coated copper powder with low resistance and high oxidation resistance according to claim 1, characterized in that: In step 4, the mass ratio of the silver salt to the copper powder is 1:1-1:10; the molar ratio of the silver salt to the complexing agent is 1:1-1:40.

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