A method for realizing dense coating of silver-coated copper powder at low silver content

Abstract

The application discloses a preparation method for realizing dense coating of silver-coated copper powder under low silver content, and comprises the following steps: after pretreatment of copper powder, the copper powder is mixed with water and a dispersing agent and stirred to obtain a copper precursor solution; a complexing agent A is added into the copper precursor solution and stirred, part of silver ammonia solution is slowly added into the copper precursor solution for reaction, and part of silver element is uniformly replaced on the surface of copper; the complexing agent B is mixed with the remaining silver ammonia solution, and then the mixture is added into the reaction solution, the temperature is increased for continuous reaction, and after the reaction is completed, solid-liquid separation, washing and drying are carried out to obtain the silver-coated copper powder. Through step-by-step replacement and weak reduction, uniform single-layer silver seed particles are first grown on the surface of copper under low silver ion concentration, and then under the induction and catalysis of the complexing agent, the silver crystals are used to form uniform and dense silver coating on the surface of the copper powder, so that the silver-coated copper powder has good oxidation resistance and high conductivity; the process is simple, convenient for large-scale production, the silver utilization rate is high, and the cost is saved.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of metal composite powder, in particular to a preparation method of realizing dense coating of silver-coated copper powder under low silver content. BACKGROUND

[0002] As conductive paste, its application has been limited by the high cost of silver powder, and it is urgent to be replaced by other powders. Copper is low in price and easy to process, and its electrical conductivity is only second to silver, but the surface of copper powder is highly chemically active and easily oxidized in air to form copper oxide on the surface, which makes its electrical conductivity poor. How to keep the copper powder from being oxidized during preparation and maintain its excellent electrical conductivity and long-term weather resistance is the key problem of the application of copper powder in conductive paste. Silver-coated copper powder is a composite powder in which a layer of silver particles is deposited on the surface of copper powder, forming a composite powder with a silver coating on the outside and a copper core inside. Under the protection of the outermost silver coating, the internal copper powder is not easy to be oxidized by contacting with air. At the same time, it can also improve the problem that silver is easy to migrate under the action of external environment under direct current voltage. Silver-coated copper powder with dense and high coating rate can have good electrical conductivity, significant oxidation resistance and low cost, and is expected to replace silver powder in conductive paste.

[0003] Chemical plating method is the most suitable method for widely producing silver-coated copper powder at present, which principle is to use oxidation-reduction reaction to promote metal ions to convert into metal elements and uniformly coat on the surface. It includes displacement method, reduction method and displacement-reduction method. Displacement method is that copper directly displaces silver ions due to high potential difference and fast reaction speed, which is easy to get loose and discontinuous silver layer. Reduction method uses reducing agent to reduce silver ions to silver elements and deposit on the surface of copper. Its coating rate is not high, and silver self-nucleation produces free silver particles. Displacement-reduction method combines the two, slows down the direct displacement of copper and silver ions, and the silver plating reaction is more stable, but the coating is not uniform. Solving the above problems is the key to preparing silver-coated copper powder with thin and dense silver coating.

[0004] Patent CN116550974A discloses a preparation method of silver-coated copper powder with core-shell structure and low silver content. The patent uses a reduction mechanism to prepare silver-coated copper powder, in which the complexing agent tannic acid mainly plays a reduction role. However, the silver-coated copper powder prepared mainly by reduction mechanism is easy to grow silver balls on the surface of copper powder, resulting in uneven coating.

[0005] Silver-coated copper powder with low silver content and high coating rate, and synergistic low cost, good long-term weather resistance and significant electrical conductivity, is the key development trend of silver-coated copper powder. SUMMARY

[0006] Invention purposes: The purpose of the present application is to provide a preparation method for realizing dense coating of silver-coated copper powder with low silver content and high silver ion utilization and uniform coating.

[0007] Technical solutions: The preparation method for realizing dense coating of silver-coated copper powder with low silver content, comprises the following steps:

[0008] (1) The copper powder is pretreated to remove surface oxides and organic matter;

[0009] (2) The pretreated copper powder is mixed with water and a dispersing agent, and stirred to obtain a copper precursor solution;

[0010] (3) A complexing agent A is added to the copper precursor solution and stirred, and part of the silver ammonia solution is slowly added to the copper precursor solution for reaction, so that part of the silver element is uniformly replaced on the surface of the copper;

[0011] (4) The complexing agent B is mixed with the remaining silver ammonia solution, and then added to the reaction solution of step (3) and the temperature is raised for continuous reaction;

[0012] (5) After the reaction is completed, solid-liquid separation is performed, and the solid product is washed and dried to obtain silver-coated copper powder.

[0013] In step (1), the pretreatment of the copper powder is at least one of using a mixture of acetone, dilute sulfuric acid, NaOH, EDTA, ammonium sulfate and ammonia water, ethanol or deionized water.

[0014] In step (2), the dispersing agent is at least one of PEG600, PEG400, PVP and polyvinyl alcohol.

[0015] In step (2), the mass ratio of the copper powder to the dispersing agent is 100:5-100:20, and the concentration of the copper precursor solution is 0.1-0.5 mol / l.

[0016] In step (3), the complexing agent A is at least one of sodium tartrate, L-histidine, ethylenediaminetetraacetic acid and benzimidazole.

[0017] In step (3), the mass ratio of the pretreated copper powder to the silver in the total silver ammonia solution is 10:1-5:1, and the mass of the silver ammonia solution added in step (3) is 10%-15% of the total mass of the silver ammonia solution.

[0018] In step (3), the reaction temperature is 20-50℃, and the reaction time is 30-70 min.

[0019] In step (4), the complexing agent B is at least one of glutamic acid, disodium ethylenediaminetetraacetate, L-histidine, benzimidazole and ascorbic acid.

[0020] In step (4), the reaction temperature is 30-70℃, and the reaction time is 30-90 min; the reaction is carried out under mechanical stirring at a stirring speed of 400-600 r / min.

[0021] In steps (3) and (4), the mass ratio of the pretreated copper powder to the complexing agent A is 1:2-1:10, and the mass ratio of the complexing agent B to silver in the total silver-ammonia solution is 6:1-10:1. The silver-ammonia solution is prepared by adding 10%-15% dilute ammonia water dropwise into a silver nitrate solution until transparent, i.e., stop adding; wherein the concentration of the silver nitrate solution is 0.1 mol / L-0.5 mol / L. In step (3), the dropping speed of the silver-ammonia solution is 0.5 mL / min-2 mL / min.

[0022] In step (4), the dropping speed of the mixed solution of the silver-ammonia solution and the complexing agent B is 2 mL / min-10 mL / min.

[0023] In step (5), the solid-liquid separation is carried out by suction filtration to obtain a solid product, which is washed with ethanol and then dried in a vacuum drying oven for 8 h at a drying temperature of 50℃.

[0024] The present application adopts a step-by-step replacement method and a weak reduction mechanism to prepare the silver-coated copper powder, and the coating effect is better and the surface is more uniform. The significance of the step-by-step replacement method is that under a low silver ion concentration, a uniform single-layer silver seed particle is first grown on the surface of copper, and then silver crystals are induced by the complexing agent, thereby forming a uniform and dense coating. The present application uses double complexing agents for preparation, wherein the complexing agent B needs to have the characteristics of an amino acid compound with both amino and carboxylic acid groups, so as to be able to complex with silver ions and also to connect with metallic silver and copper.

[0025] Compared with single complexing agent replacement, the step-by-step replacement method using double complexing agents ensures a low silver content, a high coating rate, and good density and smooth and uniform coating surface. In the first step, a small amount of silver-ammonia solution is slowly added to the mixture of copper powder and complexing agent A, and a layer of "silver seeds" is formed on the surface of the copper powder; in the second step, the remaining silver-ammonia solution is mixed with the complexing agent B and then added to the reaction solution, and the "silver seeds" on the surface of the copper induce silver ions to deposit on the surface after replacement in the second step, thereby ensuring uniform distribution of the silver layer. The complexing agent B not only has a replacement effect but also has a certain reducing property. When subsequent silver ions cannot be replaced, the complexing agent B can continue to reduce the remaining silver ions, so as to ensure that as much silver ions as possible are converted into elemental silver, and the utilization rate of silver ions is extremely high.

[0026] Advantages: Compared with the prior art, the present application has the following remarkable effects:

[0027] (1) The present application uses a double complexing agent and a step-by-step replacement method. Complexing agent A helps the copper powder to grow a layer of "silver seeds", and then complexing agent B is used for secondary coating. The presence of "silver seeds" induces the subsequent silver element to be replaced and then more uniformly grown on the surface. In addition, the reducing property of complexing agent B also helps the reduction of silver ions, and the utilization rate of silver ions is extremely high. (2) The silver-coated copper powder prepared by the present application has complete coating, smooth coating surface, uniform silver layer distribution, and achieves the effect of dense coating, and has good oxidation resistance and high conductivity. (3) The process of the present application is simple and convenient for large-scale production, and the utilization rate of silver is high, saving cost. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 SEM image of silver-coated copper powder in Example 1;

[0029] Figure 2 SEM image of silver-coated copper powder in Comparative Example 1;

[0030] Figure 3 SEM image of silver-coated copper powder in Comparative Example 2;

[0031] Figure 4 SEM image of silver-coated copper powder in Comparative Example 3;

[0032] Figure 5 SEM image of silver-coated copper powder in Comparative Example 4;

[0033] Figure 6 SEM image of silver-coated copper powder in Comparative Example 5;

[0034] Figure 7 SEM image of silver-coated copper powder in Comparative Example 6;

[0035] Figure 8 SEM image of silver-coated copper powder in Comparative Example 7;

[0036] Figure 9 Thermogravimetric curve of silver-coated copper powder in Example 1. DETAILED DESCRIPTION

[0037] The present application will be further described in detail below.

[0038] Example 1

[0039] S1: First, take 5g of copper powder, add 50mL of acetone to remove organic matter, ultrasonic oscillation for 30min, suction filtration; then add 50mL of 0.5mol / L ammonium sulfate and 1mol / L ammonia water mixed solution to the copper powder to remove the surface organic matter, ultrasonic oscillation for 30min, suction filtration; then, add 50mL of ethanol to the copper powder, ultrasonic oscillation for 30min, suction filtration, finally, repeatedly wash the copper powder with water several times, suction filtration.

[0040] S2: Dissolve 5g of the cleaned copper powder in 500mL of deionized water, add 0.5g of PEG600 to it, weigh 17.5g of sodium tartrate and dissolve it in 200ml of deionized water, then add it to the copper solution to obtain a copper precursor solution, and mechanically stir it at a speed of 500r / min, with a reaction temperature of 30℃.

[0041] S3: Prepare a silver ammonia solution, weigh 0.8g of silver nitrate and dissolve it in 20ml of water, then add diluted ammonia water dropwise until it is clear and transparent, wherein the volume ratio of ammonia water to deionized water is 1:2.

[0042] S4: Take 3ml of the above prepared silver ammonia solution and add it dropwise to the copper precursor solution at a rate of 0.5mL / min, and after the addition is complete, react for 30min.

[0043] S5: After the reaction is completed, adjust the reaction temperature to 40℃, weigh 4.5g of L-histidine and dissolve it in 120ml of deionized water, then add the remaining silver ammonia solution to the L-histidine solution and stir for 3min. Then add it dropwise to the reaction system at a rate of 5mL / min, and react for 60min.

[0044] S6: After the reaction is completed, wash it with ethanol and deionized water several times, suction filter, and then place it in a vacuum drying oven at 50℃ for 8h.

[0045] Example 2

[0046] S1: First, take 5g of copper powder, add 50mL of acetone to remove organic matter, ultrasonic oscillation for 30min, suction filtration; then add 50mL of 0.5mol / L ammonium sulfate and 1mol / L ammonia water mixed solution to the copper powder to remove the surface organic matter, ultrasonic oscillation for 30min, suction filtration; then, add 50mL of ethanol to the copper powder, ultrasonic oscillation for 30min, suction filtration, finally, repeatedly wash the copper powder with water several times, suction filtration.

[0047] S2: Dissolve 5g of the cleaned copper powder in 500mL of deionized water, add 0.5g of PEG600 to it, weigh 17.5g of sodium tartrate and dissolve it in 200ml of deionized water, then add it to the copper solution to obtain a copper precursor solution, and mechanically stir it at a speed of 500r / min, with a reaction temperature of 30℃.

[0048] S3: Prepare silver-ammonia solution, take 0.8g silver nitrate, dissolve in 20ml water, add diluted ammonia water dropwise until clear and transparent, wherein the volume ratio of ammonia water to deionized water is 1:2.

[0049] S4: Take 6ml of the above prepared silver-ammonia solution, and add it dropwise to the copper precursor solution at a rate of 1mL / min, after the dropwise addition is completed, react for 30min.

[0050] S5: After the reaction is completed, adjust the reaction temperature to 40℃, take 2.2g L-histidine, dissolve in 100ml deionized water, add the remaining silver-ammonia solution to the histidine solution, stir for 3min, then add it dropwise to the reaction system at a rate of 3mL / min, after the dropwise addition is completed, react for 60min.

[0051] S6: After the reaction is completed, wash with ethanol and deionized water several times, then perform suction filtration, and place it in a vacuum drying oven, dry at 50℃ for 8h.

[0052] Example 3

[0053] S1: First, take 5g of copper powder, add 50mL of acetone to remove organic matter, ultrasonic oscillation for 30min, suction filtration; then add 50mL of a mixed solution of 0.5mol / L ammonium sulfate and 1mol / L ammonia water to the copper powder to remove surface organic matter, ultrasonic oscillation for 30min, suction filtration; then add 50mL of ethanol to the copper powder, ultrasonic oscillation for 30min, suction filtration, and finally, repeatedly wash the copper powder with water several times, and perform suction filtration.

[0054] S2: Dissolve the washed copper powder 5g in 500mL of deionized water, add 0.5g of PEG600 to it, take 17.5g of sodium tartrate, dissolve in 200ml of deionized water, after dissolution, add it to the copper solution to obtain a copper precursor solution, and perform mechanical stirring at a speed of 500r / min, and the reaction temperature is 30℃.

[0055] S3: Prepare silver-ammonia solution, take 0.8g silver nitrate, dissolve in 10ml water, add diluted ammonia water dropwise until clear and transparent, wherein the volume ratio of ammonia water to deionized water is 1:2.

[0056] S4: Take 3ml of the above prepared silver-ammonia solution, and add it dropwise to the copper precursor solution at a rate of 1mL / min, after the dropwise addition is completed, react for 30min.

[0057] S5: After the reaction is completed, adjust the reaction temperature to 40℃, take 4.5g L-histidine, dissolve in 120ml deionized water, add the remaining silver-ammonia solution to the histidine solution, stir for 3min, then add it dropwise to the reaction system at a rate of 6mL / min, after the dropwise addition is completed, react for 45min.

[0058] S6: After the reaction, clean with ethanol and deionized water for several times, then filter and dry in vacuum drying oven at 50℃ for 8h.

[0059] Example 4

[0060] S1: First, take 5g copper powder, add 50mL acetone to remove organic matter, ultrasonic oscillation for 30min, filter; then add 50mL mixed solution of 0.5mol / L ammonium sulfate and 1mol / L ammonia water to the copper powder to remove surface organic matter, ultrasonic oscillation for 30min, filter; then add 50mL ethanol to the copper powder, ultrasonic oscillation for 30min, filter, finally, repeatedly clean the copper powder with water for several times, filter.

[0061] S2: Dissolve the cleaned copper powder 5g in 500mL deionized water, add 0.5g PEG600, weigh 17.5g sodium tartrate and dissolve in 150ml deionized water, then add to the copper solution, get copper precursor solution, mechanical stirring at 600r / min, reaction temperature 30℃.

[0062] S3: Prepare silver ammonia solution, weigh 0.8g silver nitrate, dissolve in 20ml water, add diluted ammonia water dropwise until clear and transparent, wherein the volume ratio of ammonia water to deionized water is 1:2.

[0063] S4: Take 6ml of the above prepared silver ammonia solution, add to the copper precursor solution at a rate of 2mL / min, after adding, react for 30min.

[0064] S5: After the reaction, adjust the reaction temperature to 40℃, weigh 4.5g L-histidine, dissolve in 120ml deionized water, add the remaining silver ammonia solution to the histidine solution, stir for 3min, then add to the reaction system at a rate of 5mL / min, react for 60min.

[0065] S6: After the reaction, clean with ethanol and deionized water for several times, then filter and dry in vacuum drying oven at 50℃ for 8h.

[0066] Example 5

[0067] S1: First, take 5g copper powder, add 50mL acetone to remove organic matter, ultrasonic oscillation for 30min, filter; then add 50mL mixed solution of 0.5mol / L ammonium sulfate and 1mol / L ammonia water to the copper powder to remove surface organic matter, ultrasonic oscillation for 30min, filter; then add 50mL ethanol to the copper powder, ultrasonic oscillation for 30min, filter, finally, repeatedly clean the copper powder with water for several times, filter.

[0068] S2: 5 g of the cleaned copper powder was dissolved in 500 mL of deionized water, 0.5 g of polyvinyl alcohol was added thereto, 11.6 g of sodium tartrate was weighed and dissolved in 150 mL of deionized water, and after dissolution, the solution was added to the copper solution to obtain a copper precursor solution, and mechanical stirring was performed at a speed of 600 r / min, and the reaction temperature was 20°C.

[0069] S3: A silver-ammonia solution was prepared, 0.8 g of silver nitrate was weighed and dissolved in 20 mL of water, and diluted ammonia water was added dropwise until it was clear and transparent, wherein the volume ratio of ammonia water to deionized water was 1:2.

[0070] S4: 3 mL of the above prepared silver-ammonia solution was added dropwise to the copper precursor solution at a rate of 0.5 mL / min, and after the dropwise addition was completed, the reaction was performed for 70 min.

[0071] S5: After the reaction was completed, the reaction temperature was adjusted to 40°C, 4.5 g of L-histidine was weighed and dissolved in 120 mL of deionized water, the remaining silver-ammonia solution was added to the histidine solution, and stirring was performed for 3 min. Then, the solution was added dropwise to the reaction system at a rate of 5 mL / min, and the reaction was performed for 30 min.

[0072] S6: After the reaction was completed, the product was washed with ethanol and deionized water several times, suction filtered, and placed in a vacuum drying oven, and dried at 50°C for 8 h.

[0073] Example 6

[0074] S1: First, 5 g of copper powder was added to 50 mL of acetone to remove organic matter, and ultrasonic oscillation was performed for 30 min, and suction filtration was performed. Then, 50 mL of a mixed solution of 0.5 mol / L of ammonium sulfate and 1 mol / L of ammonia water was added to the copper powder to remove surface organic matter, and ultrasonic oscillation was performed for 30 min, and suction filtration was performed. Then, 50 mL of ethanol was added to the copper powder, and ultrasonic oscillation was performed for 30 min, and suction filtration was performed. Finally, the copper powder was repeatedly washed with water several times, and suction filtration was performed.

[0075] S2: 5 g of the cleaned copper powder was dissolved in 500 mL of deionized water, 2 g of PEG600 was added thereto, 11.6 g of sodium tartrate was weighed and dissolved in 150 mL of deionized water, and after dissolution, the solution was added to the copper solution to obtain a copper precursor solution, and mechanical stirring was performed at a speed of 600 r / min, and the reaction temperature was 20°C.

[0076] S3: A silver-ammonia solution was prepared, 0.8 g of silver nitrate was weighed and dissolved in 20 mL of water, and diluted ammonia water was added dropwise until it was clear and transparent, wherein the volume ratio of ammonia water to deionized water was 1:2.

[0077] S4: 3 mL of the above prepared silver-ammonia solution was added dropwise to the copper precursor solution at a rate of 0.5 mL / min, and after the dropwise addition was completed, the reaction was performed for 30 min.

[0078] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, 4.5 g of L-histidine is weighed, dissolved in 120 ml of deionized water, and the remaining silver amine solution is added to the histidine solution, and stirred for 3 min. Then, it is added dropwise to the reaction system at a rate of 2 mL / min, and the reaction is performed for 90 min.

[0079] S6: After the reaction is completed, it is washed with ethanol and deionized water for multiple times, filtered, and placed in a vacuum drying box, and dried at 50°C for 8 h.

[0080] Example 7

[0081] S1: First, 5 g of copper powder is added to 50 ml of sodium hydroxide to remove organic matter, and ultrasonic oscillation is performed for 30 min, and then filtered; then, 50 ml of a mixed solution of 0.5 mol / L of ammonium sulfate and 1 mol / L of ammonia water is added to the copper powder to remove surface organic matter, and ultrasonic oscillation is performed for 30 min, and then filtered; then, 50 ml of ethanol is added to the copper powder, and ultrasonic oscillation is performed for 30 min, and then filtered; finally, the copper powder is repeatedly washed with water multiple times, and then filtered.

[0082] S2: The cleaned copper powder 5 g is dissolved in 500 ml of deionized water, 0.25 g of PVP is added thereto, 11.6 g of sodium tartrate is weighed and dissolved in 150 ml of deionized water, and after dissolution, it is added to the copper solution to obtain a copper precursor solution, and mechanical stirring is performed at a speed of 600 r / min, and the reaction temperature is 50°C.

[0083] S3: A silver amine solution is prepared, 0.8 g of silver nitrate is weighed and dissolved in 30 ml of water, and then diluted ammonia water is added dropwise until it is clear and transparent, and the volume ratio of ammonia water to deionized water is 1:2.

[0084] S4: 3 ml of the above prepared silver amine solution is added dropwise to the copper precursor solution at a rate of 0.5 mL / min, and after the dropwise addition is completed, the reaction is performed for 30 min.

[0085] S5: After the reaction is completed, the reaction temperature is adjusted to 40°C, 4.5 g of L-histidine is weighed, dissolved in 120 ml of deionized water, and the remaining silver amine solution is added to the histidine solution, and stirred for 3 min. Then, it is added dropwise to the reaction system at a rate of 10 mL / min, and the reaction is performed for 45 min.

[0086] S6: After the reaction is completed, it is washed with ethanol and deionized water for multiple times, filtered, and placed in a vacuum drying box, and dried at 50°C for 8 h.

[0087] Example 8

[0088] S1: First, 5 g of copper powder was taken, 50 mL of acetone was added to remove organic matter, ultrasonic oscillation was performed for 30 min, and suction filtration was performed; then, 50 mL of 3% dilute sulfuric acid solution was added to the copper powder to remove surface oxides, ultrasonic oscillation was performed for 30 min, and suction filtration was performed; then, 50 mL of ethanol was added to the copper powder, ultrasonic oscillation was performed for 30 min, and suction filtration was performed; finally, the copper powder was repeatedly washed with water for multiple times, and suction filtration was performed.

[0089] S2: 5 g of the cleaned copper powder was dissolved in 500 mL of deionized water, 0.25 g of PVP was added, 33.4 g of sodium tartrate was weighed and dissolved in 250 mL of deionized water, and after dissolution, the copper solution was obtained, and mechanical stirring was performed at a speed of 400 r / min, and the reaction temperature was 50℃.

[0090] S3: The silver ammonia solution was prepared, 0.8 g of silver nitrate was weighed and dissolved in 30 mL of water, and dilute ammonia water was added dropwise until it was clear and transparent, wherein the volume ratio of ammonia water to deionized water was 1:2.

[0091] S4: 3 mL of the above prepared silver ammonia solution was taken and added dropwise to the copper precursor solution at a rate of 0.5 mL / min, and after the dropwise addition was completed, the reaction was performed for 30 min.

[0092] S5: After the reaction was completed, the reaction temperature was adjusted to 40℃, 4.5 g of L-histidine was weighed and dissolved in 120 mL of deionized water, the remaining silver ammonia solution was added to the histidine solution, and stirring was performed for 3 min. Then, it was added dropwise to the reaction system at a rate of 5 mL / min, and the reaction was performed for 45 min.

[0093] S6: After the reaction was completed, the product was repeatedly washed with ethanol and deionized water for multiple times, suction filtration was performed, and the product was placed in a vacuum drying oven and dried at 50℃ for 8 h.

[0094] Comparative Example 1

[0095] On the basis of Example 1, different from Example 1 is that in step S5, L-histidine is replaced by tryptophan.

[0096] Comparative Example 2

[0097] On the basis of Example 1, different from Example 1 is that in step S2, sodium tartrate is replaced by 2 g of disodium ethylenediaminetetraacetate.

[0098] Comparative Example 3

[0099] On the basis of Example 1, different from Example 1 is that only a single complexing agent, sodium tartrate, is used, and the silver ammonia solution is prepared and added dropwise to the copper precursor solution at a rate of 0.5 mL / min, and after the dropwise addition is completed, the reaction is performed for 60 min, and the reaction is completed.

[0100] Comparative Example 4

[0101] On the basis of Example 1, different from Example 1, only single complexing agent L-histidine is used, all the silver ammine solution is added to the histidine solution, stirring for 3 min. Then it is added dropwise to the reaction system at a rate of 5 mL / min, and the reaction is carried out for 60 min, and the reaction is completed.

[0102] Comparative Example 5

[0103] On the basis of Example 1, different from Example 1, the order of the double complexing agents is exchanged. In step S2, 4.5 g of L-histidine is weighed and dissolved in 120 mL of deionized water; in step S5, 17.5 g of sodium tartrate is weighed and dissolved in 200 mL of deionized water, and the remaining silver ammine solution is added to the sodium tartrate solution.

[0104] Comparative Example 6

[0105] On the basis of Example 1, different from Example 1, in step S4, 6 mL of the above prepared silver ammine solution is taken.

[0106] Comparative Example 7

[0107] On the basis of Example 1, different from Example 1, in step S2, 11.6 g of sodium tartrate is weighed and dissolved in 150 mL of deionized water; in step S5, 2.3 g of L-histidine is weighed and dissolved in 90 mL of deionized water.

[0108] The silver-coated copper powders of the above-mentioned Example 1 and Comparative Examples 1-7 are subjected to scanning electron microscope testing, as shown in Table 1. Figures 1-8 Comparing Example 1 with Comparative Examples 1-4, in Example 1, the prepared silver-coated copper powder has complete coating and smooth surface, the silver layer is uniformly distributed, the coating effect is good, and the actual measured silver content on the surface of the silver-copper powder is 14.5%, realizing the dense coating of silver-coated copper at low silver content. Comparing Example 1 with Comparative Examples 1 and 2, in Comparative Example 1, the copper powder is corroded, the silver coating is not complete, and the coating surface is rough; in Comparative Example 2, the copper powder is severely corroded, and the coating is not complete; it can be seen that replacing one of the two complexing agents for step-by-step replacement method has a great influence on the coating effect, and the selection of the two complexing agents is very important, and sodium tartrate and L-histidine are the best in the coating effect.

[0109] Comparing Example 1 with Comparative Examples 3 and 4, in Comparative Example 3, the coating is not complete, the coating surface is not smooth, silver grows rapidly in one place, and the coating layer cannot be dense; in Comparative Example 4, the coating surface is not smooth, there are silver islands, and there are a large number of silver balls. It can be seen that the effect of single complexing agent is not good.

[0110] Comparing Example 1 with Comparative Example 5, in which a large number of silver balls are present on the surface of the silver layer, silver ion complex deposition is uneven; in the step-by-step displacement method, the order of the complexing agents has a great influence on the coating effect. The best result of silver-coated copper is obtained by first using sodium tartrate for displacement and then using L-histidine for the second step of coating.

[0111] Comparing Example 1 with Comparative Example 6, in which the amount of silver ammonia solution added in the first step of the reaction is doubled, the surface of the silver-coated copper powder in Comparative Example 6 is severely corroded, and the coating surface is also incomplete.

[0112] Comparing Example 1 with Comparative Example 7, in which the amount of complexing agent is reduced, it can be observed that the surface of the silver layer is rough, the density of the silver layer is not high, and the silver layer is loose. Therefore, in the step-by-step displacement method, the amount of silver ammonia added in the first step and the amount of double complexing agents have a great influence on the dense coating of silver-coated copper. In Example 1, the amount of silver ammonia added in the first step and the amount of double complexing agents achieve dense coating of silver-coated copper at a low silver content.

[0113] By Figure 9 From the thermogravimetric curve, it can be observed that the silver-coated copper powder in Example 1 starts to gain weight at 270°C, and has good oxidation resistance.

Claims

1. A method for achieving dense coating of silver-coated copper powder at low silver content, characterized by, The method comprises the following steps: (1) pretreating the copper powder to remove surface oxides and organic substances; (2) mixing the pretreated copper powder with water and a dispersing agent, and stirring to obtain a copper precursor solution; (3) adding a complexing agent A to the copper precursor solution and stirring, slowly adding part of silver ammonia solution to the copper precursor solution to carry out a reaction, and allowing part of elemental silver to uniformly replace the copper surface; the complexing agent A is sodium tartrate; the mass ratio of the pretreated copper powder to silver in the total silver ammonia solution is 10:1-5:1; the mass of the added silver ammonia solution is 10%-15% of the mass of the total silver ammonia solution; and the mass ratio of the pretreated copper powder to the complexing agent A is 1:2-1:10; (4) mixing a complexing agent B with the remaining silver ammonia solution, and then adding the mixture to the reaction solution in step (3) and continuing the reaction by increasing the temperature; the complexing agent B is L-histidine; and the mass ratio of the complexing agent B to silver in the total silver ammonia solution is 6:1-10:1; (5) carrying out solid-liquid separation after the reaction, washing and drying the solid product, and obtaining silver-coated copper powder.

2. The preparation method for achieving dense coating of silver-coated copper powder with low silver content according to claim 1, characterized in that, The reaction temperature in step (3) is 20-50℃, and the reaction time is 30-70 min; the reaction temperature in step (4) is 30-70℃, and the reaction time is 30-90 min.

3. The method of claim 1, wherein the silver-coated copper powder is densified by a process comprising the steps of: In step (3), the dropping speed of the silver ammonia solution is 0.5 mL / min-2 mL / min. The concentration of silver nitrate used for preparing the total silver ammonia solution is 0.1 mol / L-0.5 mol / L.

4. The preparation method for achieving dense coating of silver-coated copper powder with low silver content according to claim 1, characterized in that, In step (4), the dropping speed of the mixed solution of the silver ammonia solution and the complexing agent B is 2 mL / min-10 mL / min.

5. The preparation method for achieving dense coating of silver-coated copper powder with low silver content according to claim 1, characterized in that, In step (2), the mass ratio of the copper powder to the dispersing agent is 100:5-100:20.

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