Preparation method of silver-coated copper powder

Abstract

The invention provides a preparation method of silver-coated copper powder, and belongs to the technical field of metal powder treatment. The used copper particle suspension contains a complexing agent, so that the activity of the copper particles can be reduced, the reaction rate of reduction coating can be reduced when a silver-ammonia complexing solution is added, and a compact silver layer slowly and uniformly grows on the surface of each copper particle; the reduction of the activity of the copper particles slows down the replacement reaction of silver ions and copper, and the situation that the coating surface is rough and loose due to the generation of overlarge silver particles is avoided; the silver grows slowly and compactly, so that the surface of the coated silver layer is smooth and compact on the basis of lower usage amount of the silver source; the preparation method is simple in process, low in silver content and low in production cost, and the coated silver layer is smooth and compact in surface.

Description

Technical Field

[0001] This invention belongs to the field of metal powder processing technology, and specifically relates to a method for preparing silver-coated copper powder. Background Technology

[0002] Silver possesses excellent electrical and thermal conductivity and catalytic properties. Silver powder is widely used in photovoltaics, electronics, catalysts, and pharmaceuticals, and there has long been a lack of alternative products. However, silver's high cost limits its large-scale application. Copper is cheaper and has excellent formability, machinability, electrical and thermal conductivity. However, it is prone to oxidation in humid environments as temperatures rise, forming a poorly conductive oxide film on its surface. Therefore, it cannot be used in products with high electrothermal requirements.

[0003] Silver-coated copper powder is produced by coating copper powder with silver powder, which retains the oxidation resistance and high conductivity of silver while reducing the amount of silver used and lowering costs. The main methods for preparing silver-coated copper powder include melt atomization, electroplating, vacuum plating, and electroless plating. Melt atomization can produce silver-coated copper powder with varying silver contents, but its process is complex and costly. Electroplating and vacuum plating require expensive equipment and necessitate external voltage guidance or vacuum pump operation, resulting in high energy consumption and lower cost-effectiveness. Electroless plating offers advantages such as simple operation, high deposition rate, and short coating time, but its coating is uneven and discontinuous. To improve coating quality, the silver layer thickness must be increased, thus increasing the amount of silver used. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing silver-coated copper powder. The preparation method provided by this invention is simple and can improve the density and uniformity of the coating even with low silver content.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing silver-coated copper powder, comprising:

[0007] A reducing agent solution and a silver ammonia complexing solution are simultaneously added to a copper particle suspension for reduction and coating to obtain silver-coated copper powder. The silver ammonia complexing solution includes silver nitrate, triethylenetetramine, and water. The copper particle suspension includes copper particles, a complexing agent, a dispersant, and water. The complexing agent is one or both of diethylenetriamine and triethylenetetramine. The mass of the complexing agent in the copper particle suspension is 5-20% of the mass of the copper particles.

[0008] Preferably, the mass of the complexing agent in the copper particle suspension is 10-15% of the mass of the copper particles.

[0009] Preferably, the copper particles in the copper particle suspension are spherical with a particle size of 1–5 μm.

[0010] Preferably, the dispersant in the copper particle suspension is one or two of polyvinylpyrrolidone, fatty alcohol polyoxyethylene ether, gelatin, and gum arabic.

[0011] Preferably, the mass of the dispersant in the copper particle suspension is 5-15% of the mass of the copper particles.

[0012] Preferably, the mass of silver nitrate in the silver ammonia complex solution is 15-35% of the mass of copper particles in the copper particle suspension, and the mass of triethylenetetramine in the silver ammonia complex solution is 67-70% of the mass of silver nitrate.

[0013] Preferably, the amount of reducing agent in the reducing agent solution is 0.5 to 0.85 times the amount of silver nitrate in the silver ammonia complex solution.

[0014] Preferably, the reducing agent solution is an aqueous solution of one or two of glucose, trisodium citrate and potassium sodium tartrate.

[0015] Preferably, the concentration of the reducing agent in the reducing agent solution is 100-200 g / L, and the concentration of silver nitrate in the silver ammonia complex solution is 30-100 g / L.

[0016] Preferably, the feeding rate of the reducing agent solution is 0.5 to 5.0 mL / min, and the feeding rate of the silver ammonia complex solution is 1.0 to 10.0 mL / min.

[0017] This invention provides a method for preparing silver-coated copper powder, comprising: simultaneously adding a reducing agent solution and a silver ammonia complexing solution to a copper particle suspension for reduction coating to obtain silver-coated copper powder; wherein the silver ammonia complexing solution comprises silver nitrate, triethylenetetramine, and water; wherein the copper particle suspension comprises copper particles, a complexing agent, a dispersant, and water; wherein the complexing agent is one or both of diethylenetriamine and triethylenetetramine; and wherein the mass of the complexing agent in the copper particle suspension is 5-20% of the mass of the copper particles. The copper particle suspension used in this invention contains a certain amount of complexing agent. By limiting the type and amount of complexing agent, the activity of the copper particles can be reduced. The addition of a silver ammonia complexing solution can slow down the reduction coating reaction rate, allowing a dense silver layer to grow slowly and uniformly on the surface of the copper particles. The reduced activity of the copper particles also slows down the substitution reaction between silver ions and copper, preventing the formation of excessively large silver particles that would result in a rough and porous coating surface. Because the silver grows slowly and densely, a smooth and dense silver layer surface is achieved with a relatively low silver source usage. The preparation method of this invention is simple, has a low silver content, low production cost, and produces a smooth and dense silver layer surface. The results of the examples show that using the preparation method provided by this invention, a smooth and dense silver-coated copper powder can be obtained with a silver content between 8% and 16% (mass fraction). Attached Figure Description

[0018] Figure 1 This is a SEM image of the silver-coated copper powder of Embodiment 1 of the present invention;

[0019] Figure 2 This is a SEM image of the silver-coated copper powder of Embodiment 2 of the present invention;

[0020] Figure 3 This is a SEM image of the silver-coated copper powder of Embodiment 3 of the present invention;

[0021] Figure 4 This is a SEM image of the silver-coated copper powder of Example 4 of the present invention;

[0022] Figure 5 This is a SEM image of the silver-coated copper powder of Example 5 of the present invention;

[0023] Figure 6 This is a SEM image of the silver-coated copper powder of Example 6 of the present invention;

[0024] Figure 7 This is a SEM image of the silver-coated copper powder of Comparative Example 1 of the present invention.

[0025] Figure 8 This is a SEM image of the silver-coated copper powder of Comparative Example 2 of the present invention;

[0026] Figure 9 This is a SEM image of the silver-coated copper powder of Comparative Example 3 of the present invention. Detailed Implementation

[0027] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0028] There are no particular restrictions on the purity of any of the raw materials used in this invention, but high-purity raw materials are preferred.

[0029] This invention provides a method for preparing silver-coated copper powder, comprising:

[0030] A reducing agent solution and a silver ammonia complexing solution are simultaneously added to a copper particle suspension for reduction and coating to obtain silver-coated copper powder. The silver ammonia complexing solution includes silver nitrate, triethylenetetramine, and water. The copper particle suspension includes copper particles, a complexing agent, a dispersant, and water. The complexing agent is one or both of diethylenetriamine and triethylenetetramine. The mass of the complexing agent in the copper particle suspension is 5-20% of the mass of the copper particles.

[0031] This invention involves simultaneously adding a reducing agent solution and a silver ammonia complex solution to a copper particle suspension for reduction and coating, thereby obtaining silver-coated copper powder.

[0032] In this invention, the copper particle suspension comprises copper particles, a complexing agent, a dispersant, and water.

[0033] In this invention, the copper particles are preferably spherical, with a particle size preferably of 1–5 μm, more preferably 2–4 μm. As one embodiment of this invention, the particle size of the copper particles can be 1 μm, 2 μm, 3 μm, 3.5 μm, 4 μm, or 5 μm. Spherical copper particles are beneficial for silver coating, and a particle size within the above-mentioned range is beneficial for further improving the density and uniformity of the coating.

[0034] In this invention, the complexing agent is one or both of diethylenetriamine and triethylenetetramine, preferably triethylenetetramine. As one embodiment of the invention, when two complexing agents are used, their proportions can be arbitrary. Using the aforementioned complexing agent can reduce the activity of copper particles. When the silver ammonia complexing solution is added, the reaction rate of the reduction coating can be reduced, resulting in the slow and uniform growth of a dense silver layer on the surface of the copper particles. The reduced activity of the copper particles also decreases the displacement reaction between silver ions and copper, avoiding the formation of excessively large silver particles that would lead to a rough and porous coating surface.

[0035] In this invention, the mass of the complexing agent in the copper particle suspension is 5-20% of the mass of the copper particles, preferably 10-15%. As one embodiment of this invention, the mass of the complexing agent in the copper particle suspension can be 5%, 8%, 10%, 12%, 15%, 18%, or 20% of the mass of the copper particles. When the relationship between the mass of the complexing agent and the mass of the copper particles in the copper particle suspension is within the above range, the density and uniformity of the silver-coated copper powder coating can be improved.

[0036] In this invention, the dispersant in the copper particle suspension is preferably one or two of polyvinylpyrrolidone, fatty alcohol polyoxyethylene ether, gelatin, and gum arabic; as one embodiment of this invention, when two dispersants are used, their dosage ratio can be arbitrary. The above-mentioned types of dispersants are beneficial for further improving the dispersibility of copper particles in the copper particle suspension.

[0037] In this invention, the mass of the dispersant in the copper particle suspension is preferably 5-15% of the mass of the copper particles, more preferably 8-12%. As one embodiment of this invention, the mass of the dispersant in the copper particle suspension can be 5%, 7%, 9%, 10%, 11%, 12%, or 14% of the mass of the copper particles. Having the mass of the dispersant in the copper particle suspension within the above-mentioned range is beneficial for further improving the dispersibility of the copper particles in the suspension.

[0038] In one embodiment of the present invention, the mass concentration of copper particles in the copper particle suspension can be 5 to 100 g / L.

[0039] As one embodiment of the present invention, the method for preparing the copper particle suspension is as follows: copper particles are mixed with deionized water, then a dispersant and a complexing agent are added, and ultrasonic stirring is performed to obtain a copper particle suspension; the stirring rate can be 600-1000 r / min; the ultrasonic frequency can be 40 kHz and the power can be 300 W; the ultrasonic stirring time can be 20 min.

[0040] In one embodiment of the present invention, the copper particles can be pretreated before use; the pretreatment is as follows: the copper particles are ultrasonically cleaned in an alkaline solution for 10-30 minutes, filtered, and rinsed three times with distilled water; then the copper particles are ultrasonically cleaned in a dilute acid for 10-30 minutes, filtered, and rinsed three times with distilled water; the alkaline solution can be a sodium hydroxide solution or a potassium hydroxide solution, and the concentration of the alkaline solution can be 0.05-0.25 mol / L; the dilute acid can be sulfuric acid or nitric acid, and the concentration of the dilute acid can be 0.5-1.0 mol / L; the ultrasonic cleaning frequency can be 40 kHz, and the power can be 300 W.

[0041] In this invention, the silver ammonia complex solution comprises silver nitrate, triethylenetetramine, and water. Preferably, the mass of silver nitrate in the silver ammonia complex solution is 15-35% of the mass of the copper particles in the copper particle suspension, more preferably 20-30%. As one embodiment of this invention, the mass of silver nitrate can be 15%, 18%, 20%, 21.5%, 25%, 30%, or 35% of the mass of the copper particles. Higher amounts of silver nitrate are more beneficial for silver coating, but significantly increase costs. This invention limits the amount of silver nitrate within the above range, balancing coating quality and cost.

[0042] In this invention, the mass of triethylenetetramine in the silver ammonia complex solution is preferably 67-70% of the mass of silver nitrate, more preferably 68-69%. Triethylenetetramine can form a stable complex with silver ions, thereby controlling the rate of reduction coating. The relationship between the mass of triethylenetetramine and the mass of silver nitrate in the silver ammonia complex solution is within the above range, which is beneficial to further improve the density and uniformity of the coating.

[0043] In this invention, the concentration of silver nitrate in the silver ammonia complex solution is preferably 30–100 g / L, more preferably 50–80 g / L. As one embodiment of this invention, the concentration of silver nitrate in the silver ammonia complex solution can be 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 71.7 g / L, 80 g / L, 90 g / L, or 100 g / L. A concentration of silver nitrate in the silver ammonia complex solution within the above range is beneficial for controlling the reduction coating rate and further improving the density and uniformity of the coating.

[0044] In this invention, the reducing agent solution is preferably an aqueous solution of one or two of glucose, trisodium citrate, and potassium sodium tartrate. Using the above-mentioned reducing agent helps control the reduction coating rate, further improving the density and uniformity of the coating.

[0045] In this invention, the amount of reducing agent in the reducing agent solution is preferably 0.5 to 0.85 times the amount of silver nitrate in the silver ammonia complex solution, more preferably 0.6 to 0.7 times. Maintaining the relationship between the amount of reducing agent and silver nitrate within the above range is beneficial for improving the utilization rate of silver nitrate and further reducing costs.

[0046] In this invention, the concentration of the reducing agent in the reducing agent solution is preferably 100–200 g / L, more preferably 150–180 g / L; as one embodiment of this invention, the concentration of the reducing agent in the reducing agent solution can be 100 g / L, 120 g / L, 150 g / L, 180 g / L, or 200 g / L. A reducing agent concentration within the above range is beneficial for controlling the rate of reduction coating, further improving the density and uniformity of the coating.

[0047] In this invention, the addition rate of the reducing agent solution is preferably 0.5–5.0 mL / min, more preferably 2–4 mL / min; as one embodiment of this invention, the addition rate of the reducing agent solution can be 1 mL / min, 2 mL / min, 2.5 mL / min, 3 mL / min, 4 mL / min, or 5 mL / min. Adding the reducing agent solution within the above range is beneficial for controlling the rate of reduction coating, further improving the density and uniformity of the coating.

[0048] In this invention, the preferred feeding rate of the silver ammonia complex solution is 1.0–10.0 mL / min, more preferably 4–8 mL / min. As one embodiment of this invention, the feeding rate of the reducing agent solution can be 2 mL / min, 3 mL / min, 5 mL / min, 6 mL / min, 7 mL / min, or 9 mL / min. Feeding rates of the silver ammonia complex solution within the above ranges are beneficial for controlling the reduction and coating rate, further improving the density and uniformity of the coating.

[0049] In one embodiment of the present invention, the reducing agent solution and the silver ammonia complex solution are added to the copper particle suspension by simultaneously adding the reducing agent solution and the silver ammonia complex solution to the copper particle suspension under ultrasonic stirring conditions; the frequency of the ultrasonication can be 40 kHz and the power can be 300 W; the stirring rate can be 600-1000 r / min.

[0050] In one embodiment of the present invention, after the reducing agent solution and the silver ammonia complex solution are added to the copper particle suspension, the mixture is stirred ultrasonically for 15 minutes, filtered and separated, and the resulting solid phase is washed in deionized water until the conductivity of the washing solution is <10μS / cm. After drying, silver-coated copper powder is obtained.

[0051] The copper particle suspension used in this invention contains a complexing agent, which can reduce the activity of the copper particles. When a silver ammonia complex solution is added, the reaction rate of reduction coating can be reduced, resulting in the slow and uniform growth of a dense silver layer on the surface of the copper particles. The reduction in the activity of the copper particles also reduces the occurrence of the substitution reaction between silver ions and copper, avoiding the formation of excessively large silver particles that would lead to a rough and loose coating surface. Due to the slow and dense growth of silver, a smooth and dense silver layer surface is achieved with a low amount of silver source used. The preparation method of this invention is simple, has a low silver content, low production cost, and produces a smooth and dense silver layer surface.

[0052] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0053] Example 1

[0054] A method for preparing silver-coated copper powder, the specific steps of which are as follows:

[0055] (1) Place 100g of 3.5μm copper particles in 1L of 0.075mol / L sodium hydroxide solution and clean them by ultrasonication (40kHz, 300W) for 10min. Filter and wash with deionized water 3 times. Place them in 1L of 0.5mol / L sulfuric acid solution and clean them by ultrasonication (40kHz, 300W) for 30min. Filter and wash with deionized water 3 times to remove copper ions from the surface of the copper particles.

[0056] (2) Place the cleaned copper particles in 1L of deionized water, add 10g of polyvinylpyrrolidone and 10g of triethylenetetramine, and sonicate (40kHz, 300W) for 20min at a stirring rate of 1000r / min to obtain a copper particle suspension.

[0057] (3) Turn on ultrasonic stirring (40kHz, 300W), and simultaneously add reducing agent solution and silver ammonia complex solution to the copper particle suspension obtained in step (2) for reduction and coating. The stirring rate is 1000r / min, the dropping rate of reducing agent solution is 2.5mL / min, and the dropping rate of silver ammonia complex solution is 5mL / min. After the addition is complete, continue ultrasonic stirring for 15min, filter and separate, place the precipitate in deionized water to wash until the conductivity of the washing solution is <10μS / cm, dry, and obtain silver-coated copper powder with a silver mass content of 12%.

[0058] The reducing agent solution is prepared by weighing 30g of trisodium citrate and adding water to make a 150mL solution; the silver ammonia complex solution is prepared by weighing 21.5g of silver nitrate, dissolving it in 200mL of water, adding 15g of triethylenetetramine to form a complex, and finally adding water to make a 300mL silver ammonia complex solution.

[0059] Example 2

[0060] A method for preparing silver-coated copper powder, the specific steps of which are as follows:

[0061] (1) Place 100g of 3.5μm copper particles in 1L of 0.075mol / L sodium hydroxide solution and clean them by ultrasonication (40kHz, 300W) for 10min. Filter and wash with deionized water 3 times. Place them in 1L of 0.5mol / L sulfuric acid solution and clean them by ultrasonication (40kHz, 300W) for 30min. Filter and wash with deionized water 3 times to remove copper ions from the surface of the copper particles.

[0062] (2) Place the cleaned copper particles in 1L of deionized water, add 10g of gelatin and 15g of triethylenetetramine, and sonicate (40kHz, 300W) for 20min at a stirring rate of 1000r / min to obtain a copper particle suspension.

[0063] (3) Turn on ultrasonic stirring (40kHz, 300W), and simultaneously add reducing agent solution and silver ammonia complex solution to the copper particle suspension obtained in step (2) for reduction and coating. The stirring rate is 1000r / min, the dropping rate of reducing agent solution is 2.5mL / min, and the dropping rate of silver ammonia complex solution is 5mL / min. After the addition is complete, continue ultrasonic stirring for 15min, filter and separate, place the precipitate in deionized water to wash until the conductivity of the washing solution is <10μS / cm, dry, and obtain silver-coated copper powder with a silver mass content of 12%.

[0064] The reducing agent solution is prepared by weighing 30g of trisodium citrate and adding water to make a 150mL solution; the silver ammonia complex solution is prepared by weighing 21.5g of silver nitrate, dissolving it in 200mL of water, adding 15g of triethylenetetramine to form a complex, and finally adding water to make a 300mL silver ammonia complex solution.

[0065] Example 3

[0066] A method for preparing silver-coated copper powder, the specific steps of which are as follows:

[0067] (1) Place 100g of 1μm copper particles in 1L of 0.075mol / L sodium hydroxide solution and clean them by ultrasonication (40kHz, 300W) for 10min. Filter the solution and clean them three times with deionized water. Place the copper particles in 1L of 0.5mol / L sulfuric acid solution and clean them by ultrasonication (40kHz, 300W) for 30min. Filter the solution and clean them three times with deionized water to remove copper ions from the surface of the copper particles.

[0068] (2) Place the cleaned copper particles in 1L of deionized water, add 10g of polyvinylpyrrolidone and 5g of triethylenetetramine, and sonicate (40kHz, 300W) for 20min at a stirring rate of 1000r / min to obtain a copper particle suspension.

[0069] (3) Turn on ultrasonic stirring (40kHz, 300W), and simultaneously add reducing agent solution and silver ammonia complex solution to the copper particle suspension obtained in step (2) for reduction and coating. The stirring rate is 1000r / min, the dropping rate of reducing agent solution is 2.5mL / min, and the dropping rate of silver ammonia complex solution is 5mL / min. After the addition is complete, continue ultrasonic stirring for 15min, filter and separate, place the precipitate in deionized water to wash until the conductivity of the washing solution is <10μS / cm, dry, and obtain silver-coated copper powder with a silver mass content of 12%.

[0070] The reducing agent solution is prepared by weighing 30g of trisodium citrate and adding water to make a 150mL solution; the silver ammonia complex solution is prepared by weighing 21.5g of silver nitrate, dissolving it in 200mL of water, adding 15g of triethylenetetramine to form a complex, and finally adding water to make a 300mL silver ammonia complex solution.

[0071] Example 4

[0072] A method for preparing silver-coated copper powder, the specific steps of which are as follows:

[0073] (1) Place 100g of 1μm copper particles in 1L of 0.075mol / L sodium hydroxide solution and clean them by ultrasonication (40kHz, 300W) for 10min. Filter the solution and clean them three times with deionized water. Place the copper particles in 1L of 0.5mol / L sulfuric acid solution and clean them by ultrasonication (40kHz, 300W) for 30min. Filter the solution and clean them three times with deionized water to remove copper ions from the surface of the copper particles.

[0074] (2) Place the cleaned copper particles in 1L of deionized water, add 10g gum arabic and 20g triethylenetetramine, and sonicate (40kHz, 300W) for 20min at a stirring rate of 1000r / min to obtain a copper particle suspension.

[0075] (3) Turn on ultrasonic stirring (40kHz, 300W), and simultaneously add reducing agent solution and silver ammonia complex solution to the copper particle suspension obtained in step (2) for reduction and coating. The stirring rate is 1000r / min, the dropping rate of reducing agent solution is 2.5mL / min, and the dropping rate of silver ammonia complex solution is 5mL / min. After the addition is complete, continue ultrasonic stirring for 15min, filter and separate, place the precipitate in deionized water to wash until the conductivity of the washing solution is <10μS / cm, dry, and obtain silver-coated copper powder with a silver mass content of 12%.

[0076] The reducing agent solution is prepared by weighing 30g of trisodium citrate and adding water to make a 150mL solution; the silver ammonia complex solution is prepared by weighing 21.5g of silver nitrate, dissolving it in 200mL of water, adding 15g of triethylenetetramine to form a complex, and finally adding water to make a 300mL silver ammonia complex solution.

[0077] Example 5

[0078] A method for preparing silver-coated copper powder, the specific steps of which are as follows:

[0079] (1) Place 100g of 3.5μm copper particles in 1L of 0.075mol / L sodium hydroxide solution and clean them by ultrasonication (40kHz, 300W) for 10min. Filter and wash with deionized water 3 times. Place them in 1L of 0.5mol / L sulfuric acid solution and clean them by ultrasonication (40kHz, 300W) for 30min. Filter and wash with deionized water 3 times to remove copper ions from the surface of the copper particles.

[0080] (2) Place the cleaned copper particles in 1L of deionized water, add 10g of polyvinylpyrrolidone and 10g of triethylenetetramine, and sonicate (40kHz, 300W) for 20min at a stirring rate of 1000r / min to obtain a copper particle suspension.

[0081] (3) Turn on ultrasonic stirring (40kHz, 300W), and simultaneously add reducing agent solution and silver ammonia complex solution to the copper particle suspension obtained in step (2) for reduction and coating. The stirring rate is 1000r / min, the dropping rate of reducing agent solution is 2.5mL / min, and the dropping rate of silver ammonia complex solution is 5mL / min. After the addition is complete, continue ultrasonic stirring for 15min, filter and separate, place the precipitate in deionized water to wash until the conductivity of the washing solution is <10μS / cm, dry, and obtain silver-coated copper powder with a silver mass content of 16%.

[0082] The reducing agent solution is prepared by weighing 30g of trisodium citrate and adding water to make a 150mL solution; the silver ammonia complex solution is prepared by weighing 30g of silver nitrate, dissolving it in 200mL of water, adding 20.9g of triethylenetetramine to form a complex, and finally adding water to make a 300mL silver ammonia complex solution.

[0083] Example 6

[0084] A method for preparing silver-coated copper powder, the specific steps of which are as follows:

[0085] (1) Place 100g of 3.5μm copper particles in 1L of 0.075mol / L sodium hydroxide solution and clean them by ultrasonication (40kHz, 300W) for 10min. Filter and wash with deionized water 3 times. Place them in 1L of 0.5mol / L sulfuric acid solution and clean them by ultrasonication (40kHz, 300W) for 30min. Filter and wash with deionized water 3 times to remove copper ions from the surface of the copper particles.

[0086] (2) Place the cleaned copper particles in 1L of deionized water, add 10g of gelatin and 10g of triethylenetetramine, and sonicate (40kHz, 300W) for 20min at a stirring rate of 1000r / min to obtain a copper particle suspension.

[0087] (3) Turn on ultrasonic stirring (40kHz, 300W), and simultaneously add reducing agent solution and silver ammonia complex solution to the copper particle suspension obtained in step (2) for reduction and coating. The stirring rate is 1000r / min, the dropping rate of reducing agent solution is 2.5mL / min, and the dropping rate of silver ammonia complex solution is 5mL / min. After the addition is complete, continue ultrasonic stirring for 15min, filter and separate, place the precipitate in deionized water to wash until the conductivity of the washing solution is <10μS / cm, dry, and obtain silver-coated copper powder with a silver mass content of 8%.

[0088] The reducing agent solution is prepared by weighing 30g of trisodium citrate and adding water to make a 150mL solution; the silver ammonia complex solution is prepared by weighing 13.7g of silver nitrate, dissolving it in 200mL of water, adding 15g of triethylenetetramine to form a complex, and finally adding water to make a 300mL silver ammonia complex solution.

[0089] Comparative Example 1

[0090] A method for preparing silver-coated copper powder, the specific steps of which are as follows:

[0091] (1) Place 100g of 1μm copper particles in 1L of 0.075mol / L sodium hydroxide solution and clean them by ultrasonication (40kHz, 300W) for 10min. Filter the solution and clean them three times with deionized water. Place the copper particles in 1L of 0.5mol / L sulfuric acid solution and clean them by ultrasonication (40kHz, 300W) for 30min. Filter the solution and clean them three times with deionized water to remove copper ions from the surface of the copper particles.

[0092] (2) Place the cleaned copper particles in 1L of deionized water, add 10g of polyvinylpyrrolidone, and sonicate (40kHz, 300W) for 20min at a stirring rate of 1000r / min to obtain a copper particle suspension.

[0093] (3) Turn on ultrasonic stirring (40kHz, 300W), and simultaneously add reducing agent solution and silver ammonia complex solution to the copper particle suspension obtained in step (2) for reduction and coating. The stirring rate is 1000r / min, the dropping rate of reducing agent solution is 2.5mL / min, and the dropping rate of silver ammonia complex solution is 5mL / min. After the addition is complete, continue ultrasonic stirring for 15min, filter and separate, place the precipitate in deionized water to wash until the conductivity of the washing solution is <10μS / cm, dry, and obtain silver-coated copper powder;

[0094] The reducing agent solution is prepared by weighing 30g of trisodium citrate and adding water to make a 150mL solution; the silver ammonia complex solution is prepared by weighing 21.5g of silver nitrate, dissolving it in 200mL of water, adding 15g of triethylenetetramine to form a complex, and finally adding water to make a 300mL silver ammonia complex solution.

[0095] Comparative Example 2

[0096] A method for preparing silver-coated copper powder, the specific steps of which are as follows:

[0097] (1) Place 100g of 3.5μm copper particles in 1L of 0.075mol / L sodium hydroxide solution and clean them by ultrasonication (40kHz, 300W) for 10min. Filter and wash with deionized water 3 times. Place them in 1L of 0.5mol / L sulfuric acid solution and clean them by ultrasonication (40kHz, 300W) for 30min. Filter and wash with deionized water 3 times to remove copper ions from the surface of the copper powder.

[0098] (2) Place the cleaned copper particles in 1L of deionized water, add 10g of polyvinylpyrrolidone and 5g of triethylenetetramine, and sonicate (40kHz, 300W) for 20min at a stirring rate of 1000r / min to obtain a copper particle suspension.

[0099] (3) Turn on ultrasonic stirring (40kHz, 300W), add silver ammonia complex solution dropwise to the copper particle suspension obtained in step (2) for reduction and coating, stirring rate 1000r / min, dropping rate 5mL / min, after the addition is complete, continue ultrasonic stirring for 15min, filter and separate, place the precipitate in deionized water to wash until the conductivity of the washing solution is <10μS / cm, dry, and obtain silver-coated copper powder;

[0100] The silver ammonia complex solution is prepared by weighing 21.5g of silver nitrate, dissolving it in 200mL of water, adding 15g of triethylenetetramine to form a complex, and finally adding water to prepare a 300mL silver ammonia complex solution.

[0101] Comparative Example 3

[0102] A method for preparing silver-coated copper powder, the specific steps of which are as follows:

[0103] (1) Place 100g of 1μm copper particles in 1L of 0.075mol / L sodium hydroxide solution and clean them by ultrasonication (40kHz, 300W) for 10min. Filter the solution and wash the particles three times with deionized water. Place the particles in 1L of 0.5mol / L sulfuric acid solution and clean them by ultrasonication (40kHz, 300W) for 30min. Filter the solution and wash the particles three times with deionized water to remove copper ions from the surface of the copper powder.

[0104] (2) Place the cleaned copper particles in 1L of deionized water, add 10g of gelatin, and sonicate (40kHz, 300W) for 20min at a stirring rate of 1000r / min to obtain a copper particle suspension.

[0105] (3) Turn on ultrasonic stirring (40kHz, 300W), and simultaneously add reducing agent solution and silver ammonia complex solution to the copper particle suspension obtained in step (2) for reduction and coating. The stirring rate is 1000r / min, the dropping rate of reducing agent solution is 2.5mL / min, and the dropping rate of silver ammonia complex solution is 5mL / min. After the addition is complete, continue ultrasonic stirring for 15min, filter and separate, place the precipitate in deionized water to wash until the conductivity of the washing solution is <10μS / cm, dry, and obtain silver-coated copper powder;

[0106] The reducing agent solution is prepared by weighing 30g of trisodium citrate and adding water to make a 150mL solution; the silver ammonia complex solution is prepared by weighing 21.5g of silver nitrate, dissolving it in 200mL of water, adding 15g of triethylenetetramine to form a complex, and finally adding water to make a 300mL silver ammonia complex solution.

[0107] Test case

[0108] The silver-coated copper powders prepared in Examples 1-6 and Comparative Examples 1-3 were observed using a scanning electron microscope (SEM), and SEM images were obtained, as shown below. Figures 1-9 As shown.

[0109] from Figure 1 , Figure 2 It can be seen that the silver-coated copper powder in Examples 1 and 2 has a smooth and dense surface; Figure 3 , Figure 4 Compared to Figure 1 , Figure 2 The surface is slightly rough, mainly because 5% (relative to the mass of copper particles) of triethylenetetramine was added to the copper particle suspension in Example 3, and 20% of triethylenetetramine was added to the copper particle suspension in Example 4. Compared with 10% in Example 1 and 15% in Example 2, the coating quality decreased, indicating that the amount of complexing agent should be in the range of 5-20%. Too much or too little will reduce the surface quality of the silver-coated copper powder.

[0110] By comparison Figure 1 , Figure 2 and Figure 5 , Figure 6 It can be seen that the preparation method of the present invention has a good coating effect in the range of silver content of 8-16%.

[0111] from Figure 7 , Figure 9 It can be seen that without the addition of a complexing agent, the surface of the silver-coated copper powder contains free silver microcrystals, has numerous pores, and is rough; from Figure 8 It can be seen that no reducing agent was added during the reduction coating process, resulting in a rough surface of the silver-coated copper powder.

[0112] contrast Figures 1-6 and Figure 7 , Figure 9 As can be seen, by adding a complexing agent to the copper particle suspension, the present invention can make the surface of silver-coated copper powder smooth and dense.

[0113] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing silver-coated copper powder, comprising: A reducing agent solution and a silver ammonia complex solution were simultaneously added to a copper particle suspension for reduction and coating to obtain silver-coated copper powder. The silver ammonia complex solution comprises silver nitrate, triethylenetetramine, and water; the copper particle suspension comprises copper particles, a complexing agent, a dispersant, and water; the complexing agent is one or both of diethylenetriamine and triethylenetetramine; the mass of the complexing agent in the copper particle suspension is 5-20% of the mass of the copper particles.

2. The preparation method according to claim 1, characterized in that, The mass of the complexing agent in the copper particle suspension is 10-15% of the mass of the copper particles.

3. The preparation method according to claim 1, characterized in that, The copper particles in the copper particle suspension are spherical with a particle size of 1–5 μm.

4. The preparation method according to claim 1, characterized in that, The dispersant in the copper particle suspension is one or two of polyvinylpyrrolidone, fatty alcohol polyoxyethylene ether, gelatin, and gum arabic.

5. The preparation method according to claim 4, characterized in that, The mass of the dispersant in the copper particle suspension is 5-15% of the mass of the copper particles.

6. The preparation method according to claim 1, characterized in that, The mass of silver nitrate in the silver ammonia complex solution is 15-35% of the mass of copper particles in the copper particle suspension, and the mass of triethylenetetramine in the silver ammonia complex solution is 67-70% of the mass of silver nitrate.

7. The preparation method according to claim 1, characterized in that, The reducing agent solution is an aqueous solution of one or two of glucose, trisodium citrate, and potassium sodium tartrate.

8. The preparation method according to claim 7, characterized in that, The amount of reducing agent in the reducing agent solution is 0.5 to 0.85 times the amount of silver nitrate in the silver ammonia complex solution.

9. The preparation method according to claim 8, characterized in that, The concentration of the reducing agent in the reducing agent solution is 100-200 g / L, and the concentration of silver nitrate in the silver ammonia complex solution is 30-100 g / L.

10. The preparation method according to claim 9, characterized in that, The feeding rate of the reducing agent solution is 0.5–5.0 mL / min, and the feeding rate of the silver ammonia complex solution is 1.0–10.0 mL / min.

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