Preparation method of micro-nano spherical copper powder

Abstract

The invention discloses a preparation method of micro-nano spherical copper powder. The preparation method comprises the following steps: mixing a copper salt solution with a sodium citrate protective agent, adding a glucose reducing agent, adjusting the pH to an alkaline condition, reacting for 30 minutes at 60 DEG C under the protection of nitrogen, and carrying out centrifugal washing and freeze drying to obtain the spherical micro-nano copper powder. The method is simple in process, low in cost and easy for large-scale production, and the obtained copper powder has the advantages of being uniform in particle size, good in dispersity and high in oxidation resistance.

Description

Technical Field

[0001] This invention relates to the field of metal powder preparation technology, and more specifically to a method for preparing micro / nano spherical copper powder. Background Technology

[0002] Micro- and nano-copper powder, as a functional material with unique physicochemical properties, occupies an irreplaceable position in modern industry and high-tech fields due to its excellent electrical conductivity, superior thermal conductivity, and high catalytic activity. In the field of electronic packaging, with the rapid development of electronic devices towards miniaturization and high density, stringent requirements have been placed on the thermal and electrical conductivity and dimensional compatibility of packaging materials. Micro- and nano-copper powder, due to its small particle size and large specific surface area, can fill packaging gaps, forming highly efficient thermal and electrical conduction pathways, effectively solving the heat dissipation problem of electronic components during operation, improving device stability and lifespan, and has become a core component of high-end electronic packaging materials. In the field of conductive pastes, micro- and nano-copper powder replaces traditional precious metal powders (such as silver powder and gold powder) in the preparation of conductive pastes, which not only significantly reduces production costs but also maintains excellent conductivity. It is widely used in the manufacture of printed circuit boards, solar cell electrodes, flexible electronic devices, etc., promoting the low-cost and large-scale development of the electronics manufacturing industry.

[0003] Micro- and nano-sized copper powders possess excellent electrical, thermal, and catalytic properties, making them crucial in modern industry and high-tech fields. In electronic packaging, they fill gaps and solve heat dissipation problems, making them a core component of high-end packaging materials. In conductive pastes, they can replace precious metals to reduce costs and support the large-scale development of the electronics manufacturing industry. In catalysis, the high specific surface area of ​​micro- and nano-sized copper powders results in abundant surface active sites, exhibiting excellent catalytic activity and selectivity for many chemical reactions. In antibacterial materials, micro- and nano-sized copper powders release copper ions to disrupt bacterial cell membrane structures and inhibit bacterial metabolic processes, exhibiting broad-spectrum antibacterial properties and long-lasting effects. However, there is a significant contradiction between the widespread application demand for micro- and nano-sized copper powders and the limitations of existing preparation technologies.

[0004] Traditional methods for preparing micro / nano copper powder mainly include physical methods and early chemical methods. Physical methods, such as mechanical crushing, use mechanical force to break up bulk copper materials to obtain fine powder. However, this method consumes a lot of energy, produces copper powder with a very wide particle size distribution and irregular morphology, and easily introduces impurities during the crushing process, leading to reduced product purity. Early chemical methods, such as electrolysis, produce copper powder particles that are large, often dendritic or flaky, with poor dispersibility. Furthermore, electrolysis consumes a lot of energy and causes significant wastewater treatment stress. Currently, chemical reduction is one of the mainstream technologies for preparing micro / nano copper powder. It uses a reducing agent to reduce copper ions in a copper salt solution to elemental copper, followed by further processing to obtain micro / nano copper powder. Compared to traditional methods, it has certain advantages in particle size control. However, this method still faces several technical bottlenecks: On the one hand, to achieve preliminary control over the particle size and morphology of copper powder, complex process routes are often required, such as multi-stage reaction systems, precise dropwise processes, or special reaction atmosphere control. High-precision reaction equipment (such as high-pressure reactors and ultrasonic reactors) is also necessary, which not only increases equipment investment costs but also raises the difficulty of process operation and production energy consumption. On the other hand, existing chemical reduction methods struggle to simultaneously ensure the uniformity, dispersibility, and oxidation resistance of micro / nano copper powder. During the reduction reaction, copper particles are prone to agglomeration, leading to a wider particle size distribution, which is difficult to completely avoid even with the addition of dispersants. Furthermore, micro / nano copper powder has a large specific surface area and high chemical activity, making it easily oxidized by oxygen in the air during preparation and subsequent storage and use, forming an oxide layer that damages its core electrical and thermal properties, severely affecting the product's application performance.

[0005] In summary, existing preparation technologies are insufficient to meet the comprehensive requirements of high-end applications for micro / nano copper powders that exhibit uniform morphology, good dispersibility, excellent oxidation resistance, high purity, low cost, and mass production capability. Therefore, developing a new method that is simple, convenient, low-cost, and capable of stably preparing high-purity spherical micro / nano copper powders is not only of significant academic research value but also breaks through existing technological bottlenecks, promoting the in-depth expansion of micro / nano copper powder applications across various fields and yielding significant economic and social benefits. Summary of the Invention

[0006] This invention provides a method for preparing micro / nano spherical copper powder, which is simple to operate, low in cost, and can be prepared in batches. This method obtains spherical copper powder with uniform particle size, good dispersibility, and excellent antioxidant properties by precisely controlling reaction conditions and introducing a protective agent.

[0007] This invention provides a method for preparing micro / nano spherical copper powder, comprising:

[0008] Add a protective agent to an aqueous solution of copper salt with a concentration of 0.1 mol / L to 0.3 mol / L and stir to dissolve, thus obtaining a copper salt-protective agent mixed solution;

[0009] A reducing agent with a concentration of 0.3 mol / L to 0.6 mol / L and a sodium hydroxide aqueous solution with a concentration of 1 mol / L to 5 mol / L are added sequentially to the copper salt-protecting agent mixed solution until the pH value of the copper salt-protecting agent mixed solution is alkaline.

[0010] An alkaline copper salt-protectant mixed solution was placed in a three-necked flask. Under nitrogen protection, the three-necked flask was heated and reacted using a magnetic stirring heating mantle. When the solution in the three-necked flask turned reddish-brown, the reaction was quenched in an ice-water bath.

[0011] When the temperature of the three-necked flask is at room temperature, centrifugation, washing, and drying are performed to obtain micro-nano copper powder.

[0012] Preferably, the copper salt is any one of copper chloride, copper sulfate, and copper nitrate.

[0013] Preferably, under the nitrogen protection conditions, the nitrogen flow rate is 50-100 mL / min.

[0014] Preferably, the reducing agent is a glucose solution.

[0015] Preferably, the pH value is in the range of 10-12.

[0016] Preferably, the process of centrifugation, washing, and drying to obtain micro / nano copper powder while the three-necked flask is at room temperature specifically includes:

[0017] When the temperature of the three-necked flask is at room temperature, centrifugation is performed, and the flask is washed alternately with anhydrous ethanol and deionized water until the solution in the three-necked flask is neutral. After drying, the micro-nano copper powder is obtained.

[0018] The centrifugation speed for centrifugal separation is 5000rpm-10000rpm;

[0019] The drying process is either vacuum drying at 80°C for 3 hours or freeze drying for 24 hours.

[0020] Preferably, the heating reaction of the three-necked flask under nitrogen protection using a magnetic stirring heating mantle, wherein the solution in the three-necked flask turns reddish-brown, specifically includes:

[0021] Under nitrogen protection, the alkaline copper salt-protectant mixed solution in the three-necked flask is heated to 60°C and reacted for 30 minutes using a magnetic stirring heating jacket. The colors of the alkaline copper salt-protectant mixed solution are, in sequence: milky white, green, blue, orange, brown, and reddish-brown.

[0022] In summary, this invention provides a method for preparing micro / nano spherical copper powder, comprising: adding a protective agent to a copper salt aqueous solution with a concentration of 0.1 mol / L-0.3 mol / L and stirring to dissolve, thereby obtaining a copper salt-protective agent mixed solution; sequentially adding a reducing agent with a concentration of 0.3 mol / L-0.6 mol / L and a sodium hydroxide aqueous solution with a concentration of 1 mol / L-5 mol / L to the copper salt-protective agent mixed solution until the pH of the copper salt-protective agent mixed solution is alkaline; placing the alkaline copper salt-protective agent mixed solution in a three-necked flask, and heating the three-necked flask under nitrogen protection using a magnetic stirring heating mantle; when the color of the alkaline copper salt-protective agent mixed solution in the three-necked flask turns reddish-brown, quenching the reaction in an ice-water bath; and centrifuging, washing, and drying the three-necked flask at room temperature to obtain micro / nano copper powder. This method uses sodium citrate as a protective agent to effectively control the growth direction of copper grains and form a regular spherical morphology. Through the synergistic effect of glucose reducing agent and alkaline conditions, a mild and controllable reduction process is achieved. In the heating reaction, nitrogen protection can effectively prevent the oxidation of copper powder and ensure the purity of the product. This method has a simple process, mild reaction conditions, and low equipment requirements, making it suitable for large-scale production. The copper powder obtained by this method has a particle size distribution between 0.5μm and 1μm, good sphericity, good dispersibility, and strong antioxidant capacity. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of a method for preparing micro / nano spherical copper powder according to an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of a scanning electron microscope image of copper powder in Embodiment 1 of the present invention;

[0026] Figure 3 This is a schematic diagram of a scanning electron microscope image of copper powder in Embodiment 2 of the present invention;

[0027] Figure 4 This is a schematic scanning electron microscope image of the copper powder in Example 3 of the present invention. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The following is in conjunction with the appendix Figure 1 The present invention will be further described in detail below with reference to specific embodiments. Figure 1 As shown in the embodiment of the present invention, a method for preparing micro / nano spherical copper powder mainly includes the following steps:

[0030] Step 101: Add a protective agent to a copper salt aqueous solution with a concentration of 0.1 mol / L-0.3 mol / L and stir to dissolve, to obtain a copper salt-protective agent mixed solution;

[0031] Step 102: Add a reducing agent with a concentration of 0.3 mol / L to 0.6 mol / L and a sodium hydroxide aqueous solution with a concentration of 1 mol / L to 5 mol / L to the copper salt-protecting agent mixed solution in sequence until the pH value of the copper salt-protecting agent mixed solution is alkaline;

[0032] Step 103: Place the alkaline copper salt-protectant mixed solution in a three-necked flask, and heat the three-necked flask under nitrogen protection using a magnetic stirring heating mantle. When the solution in the three-necked flask turns reddish-brown, quench the reaction in an ice-water bath.

[0033] Step 104: When the temperature of the three-necked flask is at room temperature, centrifugation, washing and drying are performed to obtain micro-nano copper powder.

[0034] In step 101, the copper salt solution is prepared by preparing an aqueous solution of copper salt with a concentration of 0.1 mol / L to 0.3 mol / L under magnetic stirring. Then, the protective agent is added to the solution and stirred until completely dissolved to obtain a copper salt-protective agent mixed solution. It should be noted that the copper salt here can be any one of copper chloride, copper sulfate, or copper nitrate; the protective agent here is sodium citrate.

[0035] Further, the glucose was prepared into a 0.3 mol / L-0.6 mol / L glucose aqueous solution and stirred until completely dissolved.

[0036] In step 102, a glucose aqueous solution is added to the copper salt-protectant mixed solution, and then a freshly prepared 1 mol / L-5 mol / L sodium hydroxide aqueous solution is added. The pH value of the copper salt-protectant mixed solution is adjusted based on the added sodium hydroxide aqueous solution. In this embodiment of the invention, the pH value of the copper salt-protectant mixed solution is between 10 and 12, that is, the copper salt-protectant mixed solution is adjusted to alkaline.

[0037] In step 103, the alkaline copper salt-protectant mixed solution is placed in a three-necked flask. Under the condition of continuous nitrogen protection, the three-necked flask is heated and reacted using a magnetic stirring heating mantle. When the temperature rises to 60°C, the reaction is carried out for 30 minutes. The color change of the alkaline copper salt-protectant mixed solution in the three-necked flask is observed. When the color of the alkaline copper salt-protectant mixed solution in the three-necked flask turns reddish-brown, the reaction is quenched in an ice-water bath.

[0038] It should be noted that in practical applications, under nitrogen protection conditions, the flow rate of nitrogen is 50-100 mL / min; when the alkaline copper salt-protectant mixed solution in the three-necked flask is heated to 60℃ and reacted for 30 min, the color of the alkaline copper salt-protectant mixed solution first turns milky white, then turns green, blue, orange, brown, and finally reddish brown.

[0039] In step 104, after the reaction is quenched in an ice-water bath in the three-necked flask, when the temperature of the three-necked flask is at room temperature, the three-necked flask can be centrifuged and then washed alternately with anhydrous ethanol and deionized water until the reddish-brown solution in the three-necked flask is neutral. Further, the neutral solution is dried to finally obtain micro-nano copper powder.

[0040] It should be noted that the centrifugation speed during this process is 5000rpm-10000rpm. For drying the neutral solution, vacuum drying can be used at 80℃ for 3 hours; alternatively, freeze drying can be used for 24 hours.

[0041] To more clearly illustrate the method for recycling silver electrodes from waste crystalline silicon photovoltaic modules provided by the embodiments of the present invention, several embodiments related to this method are described below.

[0042] Example 1: Preparation of micro / nano copper powder using copper chloride as copper salt

[0043] 1.1 Raw material preparation

[0044] Copper salt: Copper chloride (CuCl2, analytical grade), 2g, dissolved in 25mL of deionized water;

[0045] Protectant: Sodium citrate (analytical grade), dosage 2g;

[0046] Reducing agent: glucose (analytical grade), prepare a 2 mol / L glucose aqueous solution (the amount should be adjusted according to the reaction system to ensure that copper ions are fully reduced);

[0047] Alkaline solution: Sodium hydroxide (analytical grade), prepare a 2 mol / L sodium hydroxide aqueous solution (the amount used is determined according to the pH adjustment requirements);

[0048] Protective gas: High-purity nitrogen (purity ≥ 99.99%);

[0049] Washing reagents: anhydrous ethanol (analytical grade), deionized water;

[0050] Reaction vessel: 250mL three-necked flask.

[0051] 1.2 Experimental Procedure

[0052] Preparation of copper salt-protectant mixed solution: Add 25 mL of deionized water to a 250 mL three-necked flask, then add 2 g of copper chloride, turn on magnetic stirring (stirring speed set to 500 rpm), and stir until the copper chloride is completely dissolved; then add 2 g of sodium citrate, and continue stirring at the same stirring speed for 20 min to obtain a homogeneous and transparent copper salt-protectant mixed solution.

[0053] Reaction system adjustment: Slowly pour 2 mol / L glucose aqueous solution into the above mixed solution (pouring rate controlled at 3 mL / min), and continue stirring for 10 min after pouring. Then add 2 mol / L sodium hydroxide aqueous solution dropwise, while monitoring the pH value of the solution in real time with a pH meter until the pH stabilizes at 11.5. Keep the magnetic stirring rate constant during the process.

[0054] Heating reduction reaction: Install a magnetic stirrer in the middle opening of a three-necked flask, connect a nitrogen gas delivery tube to the left opening (inserted below the solution surface), and install a thermometer in the right opening. Open the nitrogen valve and control the nitrogen flow rate at 80 mL / min, continuously ventilating for 15 min to remove air from the system; start the magnetic stirring heating mantle, maintain a stirring speed of 500 rpm, and heat the solution to 60°C, holding the temperature for 30 min. During the reaction, the solution color successively changes from milky white to green to blue to orange to brown, finally turning reddish-brown. Immediately transfer the three-necked flask to an ice-water bath to quench the reaction, and continue stirring until the system temperature drops to room temperature.

[0055] Post-processing: The cooled reaction solution was transferred to centrifuge tubes and centrifuged at 5000 rpm for 15 min, discarding the supernatant. The precipitate was washed alternately with anhydrous ethanol and deionized water, centrifuged at the same speed after each wash, and the operation was repeated 3 times until the pH of the washing solution reached 7.0 (neutral). The washed precipitate was placed in a freeze dryer and freeze-dried for 24 hours. After removal, it was ground through a 200-mesh sieve to obtain reddish-brown micro-nano spherical copper powder.

[0056] like Figure 2 As shown, the micro-nano spherical copper powder obtained by this method was observed by scanning electron microscopy (SEM). The SEM characterization showed that the copper powder particles were regularly spherical with an average particle size of 600 nm, uniform particle size distribution, and no agglomeration.

[0057] Example 2: Preparation of micro / nano copper powder using copper chloride as copper salt

[0058] 2.1 Raw material preparation

[0059] Copper salt: Copper chloride (CuCl2, analytical grade), 2g, dissolved in 25mL of deionized water;

[0060] Protectant: Sodium citrate (analytical grade), dosage 2g;

[0061] Reducing agent: glucose (analytical grade), prepare a 2 mol / L glucose aqueous solution (the amount should be adjusted according to the reaction system to ensure that copper ions are fully reduced);

[0062] Alkaline solution: Sodium hydroxide (analytical grade), prepare a 2 mol / L sodium hydroxide aqueous solution (the amount used is determined according to the pH adjustment requirements);

[0063] Protective gas: High-purity nitrogen (purity ≥ 99.99%);

[0064] Washing reagents: anhydrous ethanol (analytical grade), deionized water;

[0065] Reaction vessel: 250mL three-necked flask.

[0066] 2.2 Experimental Procedure

[0067] Preparation of copper salt-protectant mixed solution: Add 25 mL of deionized water to a 250 mL three-necked flask, then add 2 g of copper chloride, turn on magnetic stirring (stirring speed set to 500 rpm), and stir until the copper chloride is completely dissolved; then add 2 g of sodium citrate, and continue stirring at the same stirring speed for 20 min to obtain a homogeneous and transparent copper salt-protectant mixed solution.

[0068] Reaction system adjustment: Slowly pour 2 mol / L glucose aqueous solution into the above mixed solution (pouring rate controlled at 3 mL / min), and continue stirring for 10 min after pouring. Then add 2 mol / L sodium hydroxide aqueous solution dropwise, while monitoring the pH value of the solution in real time with a pH meter until the pH stabilizes at 10.0. Keep the magnetic stirring rate constant during the process.

[0069] Heating reduction reaction: Install a magnetic stirrer in the middle opening of a three-necked flask, connect a nitrogen gas delivery tube to the left opening (inserted below the solution surface), and install a thermometer in the right opening. Open the nitrogen valve and control the nitrogen flow rate at 80 mL / min, continuously ventilating for 15 min to remove air from the system; start the magnetic stirring heating mantle, maintain a stirring speed of 500 rpm, and heat the solution to 60°C, holding the temperature for 30 min. During the reaction, the solution color successively changes from milky white to green to blue to orange to brown, finally turning reddish-brown. Immediately transfer the three-necked flask to an ice-water bath to quench the reaction, and continue stirring until the system temperature drops to room temperature.

[0070] Post-processing: The cooled reaction solution was transferred to centrifuge tubes and centrifuged at 5000 rpm for 15 min, discarding the supernatant. The precipitate was washed alternately with anhydrous ethanol and deionized water, centrifuged at the same speed after each wash, and the operation was repeated 3 times until the pH of the washing solution reached 7.0 (neutral). The washed precipitate was placed in a freeze dryer and freeze-dried for 24 hours. After removal, it was ground through a 200-mesh sieve to obtain reddish-brown micro-nano spherical copper powder.

[0071] like Figure 3 As shown, the micro-nano spherical copper powder obtained by this method was observed by scanning electron microscopy (SEM). The SEM characterization showed that the copper powder was a regular sphere with an average particle size of 800 nm, uniform particle size distribution, and no agglomeration.

[0072] Example 3: Preparation of micro / nano copper powder using copper chloride as copper salt

[0073] 3.1 Raw material preparation

[0074] Copper salt: Copper chloride (CuCl2, analytical grade), 2g, dissolved in 25mL of deionized water;

[0075] Protectant: Sodium citrate (analytical grade), dosage 2g;

[0076] Reducing agent: glucose (analytical grade), prepare a 2 mol / L glucose aqueous solution (add as needed to ensure sufficient reaction with the copper salt system);

[0077] Alkaline solution: Sodium hydroxide (analytical grade), prepare a 2 mol / L sodium hydroxide aqueous solution (the amount used is determined according to the requirement of adjusting the pH to 10.0);

[0078] Protective gas: High-purity nitrogen (purity ≥99.99%), with a controlled flow rate of 80 mL / min;

[0079] Washing reagents: anhydrous ethanol (analytical grade), deionized water;

[0080] Reaction vessel: 250mL three-necked flask;

[0081] Separation equipment: centrifuge (set speed 5000 rpm), freeze dryer (set drying time 24 hours).

[0082] 3.2 Experimental Procedure

[0083] Preparation of copper salt-protectant mixed solution: Add 25 mL of deionized water to a 250 mL three-necked flask, then add 2 g of copper chloride, turn on magnetic stirring (set the stirring speed as needed to ensure uniform dissolution), and stir until the copper chloride is completely dissolved; then add 2 g of sodium citrate, and continue stirring for 20 minutes while maintaining magnetic stirring to form a homogeneous and transparent copper salt-protectant mixed solution.

[0084] Reaction system adjustment: Slowly pour a 2 mol / L glucose aqueous solution into the above copper salt-protectant mixed solution (the pouring rate should be controlled as needed to avoid violent local reactions); after the glucose aqueous solution has been poured, continue to stir magnetically; then add a 2 mol / L sodium hydroxide solution dropwise, while monitoring the pH value of the solution in real time with a pH meter until the pH of the solution stabilizes at 10.0, and continue to stir magnetically throughout the process.

[0085] Heating reduction reaction: Connect a nitrogen protection device to the three-necked flask, open the nitrogen valve, and control the nitrogen flow rate at 80 mL / min to continuously purge air from the system; start the heating device and heat the solution in the three-necked flask to 60°C, and maintain the temperature at 60°C for 30 min. During the reaction, observe the color change of the solution in real time, which will successively change from milky white to green to blue to orange to brown, and finally turn reddish-brown; when the solution turns reddish-brown, immediately transfer the reaction flask to an ice-water bath for quenching, and continue stirring until the temperature of the solution in the reaction flask cools to room temperature.

[0086] Post-processing: The reaction solution cooled to room temperature was transferred to centrifuge tubes, and the centrifuge speed was set to 5000 rpm for centrifugation. After centrifugation, the supernatant was discarded, and the precipitate was washed alternately with anhydrous ethanol and deionized water, repeating the washing operation 3 times. Finally, the washed precipitate was transferred to a freeze dryer and freeze-dried for 24 hours to obtain reddish-brown micro-nano spherical copper powder.

[0087] like Figure 4 As shown, the micro-nano spherical copper powder obtained by this method was observed by scanning electron microscopy (SEM). The SEM characterization showed that the copper powder was a regular sphere with an average particle size of 800 nm, uniform particle size distribution, and no agglomeration.

[0088] Example 4: Preparation of micro / nano copper powder using copper sulfate as copper salt

[0089] 4.1 Raw material preparation

[0090] Copper salt: Copper sulfate (CuSO4, analytical grade), 1.8 g, dissolved in 25 mL of deionized water;

[0091] Protectant: Sodium citrate (analytical grade), dosage 2g;

[0092] Reducing agent: glucose (analytical grade), prepare a 2 mol / L glucose aqueous solution (add as needed to ensure sufficient reaction with the copper salt system);

[0093] Alkaline solution: Sodium hydroxide (analytical grade), prepare a 2 mol / L sodium hydroxide aqueous solution (the amount used is determined according to the requirement of adjusting the pH to 10.0);

[0094] Protective gas: High-purity nitrogen (purity ≥99.99%), with a controlled flow rate of 80 mL / min;

[0095] Washing reagents: anhydrous ethanol (analytical grade), deionized water;

[0096] Reaction vessel: 250mL three-necked flask;

[0097] Separation equipment: centrifuge (set speed 5000 rpm), freeze dryer (set drying time 24 hours).

[0098] 4.2 Experimental Procedure

[0099] Preparation of copper salt-protectant mixed solution: Add 25 mL of deionized water to a 250 mL three-necked flask, then add 1.8 g of copper sulfate, turn on magnetic stirring (set the stirring speed as needed to ensure uniform dissolution), and stir until the copper sulfate is completely dissolved; then add 2 g of sodium citrate, and continue stirring with magnetic stirring for 20 minutes to form a homogeneous and transparent copper salt-protectant mixed solution.

[0100] Reaction system adjustment: Slowly pour a 2 mol / L glucose aqueous solution into the above copper salt-protectant mixed solution (the pouring rate should be controlled as needed to avoid violent local reactions); after the glucose aqueous solution has been poured, continue to stir magnetically; then add a 2 mol / L sodium hydroxide solution dropwise, while monitoring the pH value of the solution in real time with a pH meter until the pH of the solution stabilizes at 10.0, and continue to stir magnetically throughout the process.

[0101] Heating reduction reaction: Connect a nitrogen protection device to the three-necked flask, open the nitrogen valve, and control the nitrogen flow rate at 80 mL / min to continuously purge air from the system; start the heating device and heat the solution in the three-necked flask to 60°C, and maintain the temperature at 60°C for 30 min. During the reaction, observe the color change of the solution in real time, which will successively change from milky white to green to blue to orange to brown, and finally turn reddish-brown; when the solution turns reddish-brown, immediately transfer the reaction flask to an ice-water bath for quenching, and continue stirring until the temperature of the solution in the reaction flask cools to room temperature.

[0102] Post-processing: The reaction solution cooled to room temperature was transferred to centrifuge tubes, and the centrifuge speed was set to 5000 rpm for centrifugation. After centrifugation, the supernatant was discarded, and the precipitate was washed alternately with anhydrous ethanol and deionized water, repeating the washing operation 3 times. Finally, the washed precipitate was transferred to a freeze dryer and freeze-dried for 24 hours to obtain reddish-brown micro-nano spherical copper powder.

[0103] Scanning electron microscopy revealed that the obtained copper powder was a regular spherical shape with an average particle size of 600 nm, uniform particle size distribution, and no agglomeration.

[0104] Example 5: Preparation of micro / nano copper powder using copper sulfate as copper salt

[0105] 5.1 Raw material preparation

[0106] Copper salt: Copper sulfate (CuSO4, analytical grade), 1.8 g, dissolved in 25 mL of deionized water;

[0107] Protectant: Sodium citrate (analytical grade), dosage 2g;

[0108] Reducing agent: glucose (analytical grade), prepare a 2 mol / L glucose aqueous solution (add as needed to ensure sufficient reaction with the copper salt system);

[0109] Alkaline solution: Sodium hydroxide (analytical grade), prepare a 2 mol / L sodium hydroxide aqueous solution (the amount used is determined according to the requirement of adjusting the pH to 10.0);

[0110] Protective gas: High-purity nitrogen (purity ≥99.99%), with a controlled flow rate of 80 mL / min;

[0111] Washing reagents: anhydrous ethanol (analytical grade), deionized water;

[0112] Reaction vessel: 250mL three-necked flask;

[0113] Separation equipment: centrifuge (set speed 5000 rpm), freeze dryer (set drying time 24 hours).

[0114] 5.2 Experimental Procedure

[0115] Preparation of copper salt-protectant mixed solution: Add 25 mL of deionized water to a 250 mL three-necked flask, then add 1.8 g of copper sulfate, turn on magnetic stirring (set the stirring speed as needed to ensure uniform dissolution), and stir until the copper sulfate is completely dissolved; then add 2 g of sodium citrate, and continue stirring with magnetic stirring for 20 minutes to form a homogeneous and transparent copper salt-protectant mixed solution.

[0116] Reaction system adjustment: Slowly pour a 2 mol / L glucose aqueous solution into the above copper salt-protectant mixed solution (the pouring rate should be controlled as needed to avoid violent local reactions); after the glucose aqueous solution has been poured, continue to stir magnetically; then add a 2 mol / L sodium hydroxide solution dropwise, while monitoring the pH value of the solution in real time with a pH meter until the pH of the solution stabilizes at 10.0, and continue to stir magnetically throughout the process.

[0117] Heating reduction reaction: Connect a nitrogen protection device to the three-necked flask, open the nitrogen valve, and control the nitrogen flow rate at 80 mL / min to continuously purge air from the system; start the heating device and heat the solution in the three-necked flask to 60°C, and maintain the temperature at 60°C for 30 min. During the reaction, observe the color change of the solution in real time, which will successively change from milky white to green to blue to orange to brown, and finally turn reddish-brown; when the solution turns reddish-brown, immediately transfer the reaction flask to an ice-water bath for quenching, and continue stirring until the temperature of the solution in the reaction flask cools to room temperature.

[0118] Post-processing: The reaction solution cooled to room temperature was transferred to centrifuge tubes, and the centrifuge speed was set to 5000 rpm for centrifugation. After centrifugation, the supernatant was discarded, and the precipitate was washed alternately with anhydrous ethanol and deionized water, repeating the washing operation 3 times. Finally, the washed precipitate was transferred to a freeze dryer and freeze-dried for 24 hours to obtain reddish-brown micro-nano spherical copper powder.

[0119] Scanning electron microscopy revealed that the obtained copper powder was a regular spherical shape with an average particle size of 800 nm, uniform particle size distribution, and no agglomeration.

[0120] In summary, this invention provides a method for preparing micro / nano spherical copper powder, comprising: adding a protective agent to a copper salt aqueous solution with a concentration of 0.1 mol / L-0.3 mol / L and stirring to dissolve, thereby obtaining a copper salt-protective agent mixed solution; sequentially adding a reducing agent with a concentration of 0.3 mol / L-0.6 mol / L and a sodium hydroxide aqueous solution with a concentration of 1 mol / L-5 mol / L to the copper salt-protective agent mixed solution until the pH of the copper salt-protective agent mixed solution is alkaline; placing the alkaline copper salt-protective agent mixed solution in a three-necked flask, and heating the three-necked flask under nitrogen protection using a magnetic stirring heating mantle; when the color of the alkaline copper salt-protective agent mixed solution in the three-necked flask turns reddish-brown, quenching the reaction in an ice-water bath; and centrifuging, washing, and drying the three-necked flask at room temperature to obtain micro / nano copper powder. This method uses sodium citrate as a protective agent to effectively control the growth direction of copper grains and form a regular spherical morphology. Through the synergistic effect of glucose reducing agent and alkaline conditions, a mild and controllable reduction process is achieved. In the heating reaction, nitrogen protection can effectively prevent the oxidation of copper powder and ensure the purity of the product. This method has a simple process, mild reaction conditions, and low equipment requirements, making it suitable for large-scale production. The copper powder obtained by this method has a particle size distribution between 0.5μm and 1μm, good sphericity, good dispersibility, and strong antioxidant capacity.

[0121] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing micro / nano spherical copper powder, characterized in that, include: Add a protective agent to an aqueous solution of copper salt with a concentration of 0.1 mol / L to 0.3 mol / L and stir to dissolve, thus obtaining a copper salt-protective agent mixed solution; A reducing agent with a concentration of 0.3 mol / L to 0.6 mol / L and a sodium hydroxide aqueous solution with a concentration of 1 mol / L to 5 mol / L are added sequentially to the copper salt-protecting agent mixed solution until the pH value of the copper salt-protecting agent mixed solution is alkaline. An alkaline copper salt-protectant mixed solution was placed in a three-necked flask. Under nitrogen protection, the three-necked flask was heated and reacted using a magnetic stirring heating mantle. When the color of the alkaline copper salt-protectant mixed solution in the three-necked flask turned reddish-brown, the reaction was quenched in an ice-water bath. When the temperature of the three-necked flask is at room temperature, centrifugation, washing, and drying are performed to obtain micro-nano copper powder.

2. The method as described in claim 1, characterized in that, The copper salt is any one of copper chloride, copper sulfate, and copper nitrate.

3. The method as described in claim 1, characterized in that, Under the nitrogen protection conditions, the nitrogen flow rate is 50-100 mL / min.

4. The method as described in claim 1, characterized in that, The reducing agent is a glucose solution.

5. The method as described in claim 1, characterized in that, The pH value ranges from 10 to 12.

6. The method as described in claim 1, characterized in that, The process of centrifugation, washing, and drying at room temperature in the three-necked flask to obtain micro / nano copper powder specifically includes: When the temperature of the three-necked flask is at room temperature, centrifugation is performed, and the flask is washed alternately with anhydrous ethanol and deionized water until the solution in the three-necked flask is neutral. After drying, the micro-nano copper powder is obtained. The centrifugation speed is 5000rpm-10000rpm; the drying is vacuum drying at 80℃ for 3 hours; or freeze drying for 24 hours.

7. The method as described in claim 1, characterized in that, The process of heating the three-necked flask under nitrogen protection using a magnetic stirring heating mantle, specifically including the reaction when the solution in the three-necked flask turns reddish-brown, includes: Under nitrogen protection, the alkaline copper salt-protectant mixed solution in the three-necked flask is heated to 60°C and reacted for 30 minutes using a magnetic stirring heating jacket. The colors of the alkaline copper salt-protectant mixed solution are, in sequence: milky white, green, blue, orange, brown, and reddish-brown.

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