A method for preparing spherical copper powder in a two-stage reduction system

Abstract

The application discloses a method for preparing spherical copper powder in a two-stage reduction system and a two-step feeding device. 12 The method comprises the following steps: S1, preparing a dispersant; S2, preparing a copper salt aqueous solution, an NaOH aqueous solution, a C6H O6 aqueous solution and a PVP-BD aqueous solution; S3, carrying out two-step dropwise addition of hydrazine hydrate to obtain a copper powder suspension; and S4, performing centrifugation, cleaning and drying on the copper powder suspension. In the application, the step-by-step addition of hydrazine hydrate is reasonably selected, so that the nucleation and growth process of copper powder crystals can be effectively separated, and then the repeated growth of part of copper crystal nuclei is avoided, and the existence of large-size copper powder particles is reduced. The regulation means makes the number of crystal nuclei generated in the reaction appropriate, and the growth process of the crystal nuclei is slowly carried out, so that the ultrafine copper powder with very uniform particle size can be obtained. On the other hand, the prepared copolymer dispersant PVP-BD can resist the attraction between particles by virtue of the stereohindering effect of the appropriate vinylpyrrolidone groups, so that the dispersibility of the copper powder is improved.

Description

Technical Field

[0001] This invention relates to the field of copper powder preparation technology, and in particular to a method for preparing spherical copper powder using a two-stage reduction system. Background Technology

[0002] Ultrafine copper powder, due to its excellent conductivity and relatively low price, has great potential value in the electronics industry, including multilayer ceramic capacitors, printed circuit boards, and battery shielding. In the field of multilayer ceramic capacitors (MLCCs), ultrafine copper powder can be prepared into copper paste, serving as the internal and terminal electrodes of MLCCs, replacing the expensive silver paste which suffers from material migration issues. The copper powder used in MLCC electrodes requires good dispersibility and high tap density. Using copper powder with low tap density in MLCC manufacturing can lead to significant shrinkage of the copper powder layer. Methods for preparing ultrafine copper powder include electrolysis, atomization, physical evaporation-condensation, mechanical pulverization, and liquid-phase reduction. Liquid-phase reduction is currently the main method for preparing ultrafine copper powder due to its abundant and diverse raw materials, simple equipment, and ease of controlling copper powder particle size. The reducing agents used mainly include hydrazine hydrate, formaldehyde, and ascorbic acid. During the preparation process, dispersants such as polyvinylpyrrolidone, gelatin, and polyvinyl alcohol are often added to disperse the copper salt solution. Chinese patents CN101474678B and CN100544861C describe a two-step reduction method for preparing ultrafine copper powder using dispersants. In this method, divalent copper ions are first reduced to cuprous oxide using reducing agents such as hydrazine hydrate, formaldehyde, and ascorbic acid. Then, a second reduction is performed using hydrazine hydrate, formaldehyde, and ascorbic acid. By controlling the reduction conditions, ultrafine copper powders of different particle sizes are prepared. The main difficulties of this two-step copper powder reduction method are: (1) the rapid reduction rate of strong reducing agents such as hydrazine hydrate and formaldehyde, and how to precisely control the reaction process; and (2) how to select or prepare dispersants with significant effects.

[0003] In general, although there are many methods and processes for preparing ultrafine copper powder by liquid-phase reduction, most of them suffer from problems such as imprecise reaction control and unscientific selection of dispersants. It is necessary to develop new methods for preparing ultrafine copper powder with precise reaction control and good dispersant effect to address these problems. Therefore, this application provides a method for preparing spherical copper powder using a two-stage reduction system to meet the needs. Summary of the Invention

[0004] To address the shortcomings of the existing technologies, this invention proposes a simple and effective method for preparing spherical ultrafine copper powder based on a two-stage reduction system. The aim is to precisely control the morphology, particle size distribution, and dispersibility of the ultrafine copper powder by accurately controlling the reduction reaction and preparing an effective dispersant system.

[0005] To achieve the above objectives, this application provides the following technical solution: a method for preparing spherical copper powder using a two-stage reduction system.

[0006] S1. Preparation of dispersant: Add appropriate amounts of 1,4-butenediol, N-vinylpyrrolidone (NVP) and 0.5 wt% azobisisobutyronitrile (AIBN) to a glass ampoule. After three vacuum-nitrogen cycles, seal the ampoule under vacuum and then place it in an oil bath at 70-80°C for 24-48 hours. After the reaction, collect the residue and extract it with dichloromethane for 72-96 hours to leach out the reactants and homopolymers. After extraction, place the collected reactants in a vacuum drying oven at a constant temperature of 70-80°C until the product reaches a constant weight to completely remove volatile impurities. The final copolymer is named PVP-BD.

[0007] During the oil bath reaction, the temperature is controlled at 70-80 °C. The purpose of this temperature range is to ensure that the chemical reaction maintains a moderate rate, neither too fast nor too slow. Too fast a rate may lead to runaway reaction or unstable products, while too slow a rate may affect experimental efficiency and product yield. Simultaneously, most of the compounds involved in the reaction remain stable at this temperature, making them less prone to thermal decomposition or the generation of unnecessary byproducts. Similarly, the drying temperature is controlled at 70-80 °C. Within this temperature range, moisture in the substance can be effectively evaporated without compromising its thermal stability.

[0008] S2. Prepare a certain amount of copper salt aqueous solution with a concentration of 1~4 mol / L, NaOH aqueous solution with a concentration of 3~12 mol / L, and 1.25~5 mol / L... Aqueous solution and 5% PVP-BD aqueous solution (copper salt by mass): First, place the copper salt aqueous solution in the first reactor vessel, and then place the first reactor vessel in a constant temperature water bath. Add NaOH aqueous solution dropwise under room temperature and stirring conditions, maintaining stirring for 20 minutes. Then, add PVP-BD aqueous solution and... The aqueous solution was heated to 50-60 °C and stirred rapidly until the reaction was complete. After standing, the supernatant was poured off and then centrifuged and washed to obtain cuprous oxide precipitate.

[0009] A 5% (by mass) PVP-BD aqueous solution of copper salt was selected. Insufficient dispersant will result in inadequate dispersion, failing to effectively inhibit grain growth. Excessive dispersant will remain in the reaction solution, compressing the electric double layer of the reacting ions and lowering the absolute value of the zeta potential, thus reducing the stabilizing effect of electrostatic repulsion. This will affect the stability of the reaction, and the viscosity of the reaction solution will also increase, leading to particle growth and agglomeration.

[0010] S3. The cuprous oxide precipitate obtained in step S2 above is added to an appropriate amount of deionized water to prepare a suspension, which is placed in a second reactor vessel. The second reactor vessel is placed in a constant temperature water bath. Under stirring, the PVP-BD aqueous solution prepared in the above step is added, and the temperature is rapidly raised to 50~60 ℃ and kept constant. 4~12 mL of hydrazine hydrate is added dropwise, and then the temperature is raised to 70~80 ℃. 8~24 mL of hydrazine hydrate is added dropwise, and the temperature is maintained until the reaction is completed to obtain a copper powder suspension.

[0011] Heating to 50-60℃ is considered the nucleation stage. Too high a temperature will involve the crystal growth stage, which is not conducive to the uniform growth of crystal nuclei. If the temperature is too low, there will be insufficient copper crystal nuclei, which will lead to the agglomeration and growth of copper grains with uneven particle size. Heating to 70-80℃ is considered the growth stage of copper crystal nuclei. Too low a temperature will result in incomplete reaction, while too high a temperature will result in too fast growth and uneven particle size distribution. Liquid is added dropwise, which allows for precise control of the addition rate of hydrazine hydrate, thus achieving the goal of accurately controlling the reaction process.

[0012] S4. After the copper powder suspension obtained in the above steps is allowed to stand, the supernatant is poured off. After centrifugation, copper powder is obtained. The copper powder is washed three times with deionized water and anhydrous ethanol in sequence, and then dried in a vacuum drying oven at 40 ℃~60 ℃ for 4 h~12 h to obtain ultrafine copper powder.

[0013] According to claim 1, a method for preparing spherical copper powder using a two-stage reduction system is characterized in that: in step S2, the copper salt is copper sulfate, copper nitrate, or copper chloride.

[0014] In a preferred embodiment of this example, in step S2, the copper salt is copper sulfate, copper nitrate, or copper chloride.

[0015] As a preferred embodiment of this example, it also includes an automatic feeding unit, an automatic dripping unit, and a storage tank for storing hydrazine hydrate solution;

[0016] Automatic feeding unit: When the water bath temperature in the water bath constant temperature pot is 50~60 ℃, the automatic feeding unit automatically adds a quantitative amount of hydrazine hydrate solution to the automatic dripping unit; when the water bath temperature in the water bath constant temperature pot is 70~80 ℃, the automatic feeding unit automatically adds a quantitative amount of hydrazine hydrate solution to the automatic dripping unit.

[0017] Automatic dripping unit: used to receive the hydrazine hydrate solution from the automatic feeding unit and automatically add the hydrazine hydrate solution in a quantitative manner.

[0018] In a preferred embodiment of this example, the liquid storage cylinder, the automatic feeding unit, and the automatic dripping unit are each provided in two sets. Each liquid storage cylinder, the automatic feeding unit, and the automatic dripping unit constitutes one set of automatic dripping units, and a total of two sets of automatic dripping units are provided.

[0019] When the water bath temperature in the water bath constant temperature pot is 50~60 ℃, one of the automatic feeding units automatically adds a quantitative amount of hydrazine hydrate solution to the automatic dripping unit.

[0020] When the water bath temperature in the water bath constant temperature pot is 70~80 ℃, another set of automatic feeding units automatically adds hydrazine hydrate solution to the automatic dripping unit in a quantitative manner.

[0021] As a preferred embodiment of this example, the upper and lower ends of the liquid storage cylinder 2 are respectively provided with an injection port and a drain pipe, and the inner cavity of the liquid storage cylinder 2 is equipped with a liquid discharge funnel 6.

[0022] The automatic feeding unit 5 includes an L-shaped air guide pipe 51 mounted on the mounting frame 3. The lower end of the L-shaped air guide pipe 51 extends into the heating water of the water bath constant temperature pot 1. A liquid storage ball 52 with an internal liquid storage chamber is installed at the lower end of the L-shaped air guide pipe 51. The liquid storage chamber is filled with a low-boiling-point liquid. A movable rod 53 is slidably arranged inside the air chamber of the L-shaped air guide pipe 51, and the end of the movable rod 53 away from the L-shaped air guide pipe 51 slides through the corresponding liquid storage cylinder 2. A sealing ring is provided at the connection between the liquid storage cylinder 2 and the L-shaped air guide pipe 51. The end of the moving rod 53 has multiple racks 54 arranged in a straight line, and the racks 54 mesh with the drive gear 57. The drive gear 57 is fixedly sleeved on the rotating shaft 55. The rotating shaft 55 is rotatably mounted on the mounting bracket 3. The lower end of the rotating shaft 55 is fixed with a sealing plate 56 for blocking and sealing the outlet of the drain pipe. The part of the moving rod 53 located in the inner cavity of the liquid storage cylinder 2 is provided with a groove, and an elastic sealing gasket 58 is fixed on the bottom plane of the groove. Both the groove and the corresponding elastic sealing gasket 58 are provided with leakage holes 59.

[0023] The automatic dripping unit 4 includes a conical liquid receiving trough 41 fixedly installed at the lower end of the corresponding liquid storage cylinder 2. The conical liquid receiving trough 41 is located below the drain pipe. A U-shaped hollow tube 42 is fixed in the inner cavity of the conical liquid receiving trough 41, and one end of the U-shaped hollow tube 42 is located in the conical liquid receiving trough 41. The other end of the U-shaped hollow tube 42 passes through the conical liquid receiving trough 41. A U-shaped capillary fiber strip 43 is provided in the inner cavity of the U-shaped hollow tube 42.

[0024] The two liquid storage spheres 52 are each filled with low-boiling-point liquids with different boiling points.

[0025] In a preferred embodiment of this invention, the upper and lower ends of the sealing plate 56 are respectively provided with a first inclined surface 561 and a second inclined surface 562, and the inclination directions of the first inclined surface 561 and the second inclined surface 562 are opposite.

[0026] In a preferred embodiment of this invention, a hollow tube 7 communicating with the inner cavity of the liquid storage cylinder 2 is provided on the outer wall of the liquid storage cylinder 2, and a waterproof and breathable layer 8 is provided in the inner cavity of the hollow tube 7.

[0027] In summary, the technical effects and advantages of this invention are as follows:

[0028] 1. The present invention has a reasonable structure. On the one hand, conventional reduction with hydrazine hydrate involves adding the hydrazine hydrate all at once, which is equivalent to a non-stepwise reaction. This fails to separate the nucleation and growth processes of copper powder particles, resulting in a very wide particle size distribution and irregular particle shapes due to repeated multi-directional growth of large particles. The present invention rationally selects to add hydrazine hydrate in steps, which can effectively separate the nucleation and growth processes of copper powder crystals, thereby avoiding the repeated growth of some copper crystal nuclei and reducing the presence of large-diameter copper powder particles. This control method ensures that the number of crystal nuclei generated by the reaction is appropriate, and the growth process of the crystal nuclei can proceed slowly, resulting in ultrafine copper powder with very uniform particle size. On the other hand, the copolymer dispersant PVP-BD prepared in the present invention contains an appropriate amount of vinylpyrrolidone groups, which can act as a steric hindrance to resist the attraction between particles, thereby improving the dispersibility of copper powder. Furthermore, the ester groups formed by the copolymerization of some 1,4-butenediol create a strong adsorption effect with the copper powder particles. At this point, the strong electrostatic repulsion between the vinylpyrrolidone groups attached to these groups effectively separates the copper particles, generating a strong steric hindrance effect. This increases the attraction barrier between particles, reducing the probability of contact between particles and preventing further aggregation of copper crystal nuclei, thus improving dispersibility. This treated dispersant can effectively prevent the agglomeration of copper powder particles, thereby obtaining ultrafine copper powder particles with uniform particle size.

[0029] 2. In this invention, the two-step feeding device can automatically and quantitatively add hydrazine hydrate solution in two separate steps. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application 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 this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a SEM image of the ultrafine copper powder obtained by the present invention;

[0032] Figure 2 for Figure 1 First-view high-magnification scanning electron microscope image of the SEM image;

[0033] Figure 3 for Figure 1 Second-view high-magnification scanning electron microscope image of the SEM image;

[0034] Figure 4 This is a schematic diagram of a two-step feeding device;

[0035] Figure 5 for Figure 4 Schematic diagram of the automatic feeding unit in the middle;

[0036] Figure 6 for Figure 5 Schematic diagram of the cross-sectional structure of the conical liquid receiving tank;

[0037] Figure 7 for Figure 4 Schematic diagram of the cross-sectional structure of the middle liquid storage tank.

[0038] In the diagram: 1. Water bath constant temperature pot; 2. Liquid storage cylinder; 3. Mounting bracket; 4. Automatic dripping unit; 41. Conical liquid receiving trough; 42. U-shaped hollow tube; 43. Capillary fiber strip; 5. Automatic feeding unit; 51. L-shaped air guide tube; 52. Liquid storage ball; 53. Movable rod; 54. Rack; 55. Rotating shaft; 56. Sealing plate; 561. First inclined surface; 562. Second inclined surface; 57. Drive gear; 58. Elastic sealing gasket; 59. Leakage hole; 6. Liquid discharge funnel; 7. Hollow column; 8. Waterproof and breathable layer. Detailed Implementation

[0039] 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.

[0040] Example 1

[0041] A process for preparing ultrafine copper powder includes the following steps:

[0042] S1. Preparation of dispersant: 5g of 1,4-butenediol, 5.8g of N-vinylpyrrolidone (NVP) and 0.5wt% of azobisisobutyronitrile (AIBN) of NVP were added to a glass ampoule. After three vacuum-nitrogen cycles, the ampoule was vacuum sealed and then placed in an oil bath at 70°C for 24 hours. After the reaction, the residue was collected and extracted with dichloromethane for 72 hours to leach out the reactants and homopolymers. After extraction, the collected reactants were placed in a vacuum drying oven at a constant temperature of 60°C until the product reached a constant weight to completely remove volatile impurities. The final copolymer was named PVP-BD.

[0043] S2. Prepare a 1 mol / L copper salt aqueous solution, a 3 mol / L NaOH aqueous solution, and a 1.25 mol / L... Aqueous solution, and 5% PVP-BD aqueous solution by mass of copper salt.

[0044] S3. First, take 300 mL of the copper salt aqueous solution prepared in step 2 and place it in a two-step feeding device. Under room temperature and stirring conditions, add 250 mL of the NaOH aqueous solution prepared in step 2 dropwise. After stirring for 20 minutes, add 10 mL of the dispersant (PVP-BD aqueous solution) prepared in step 2, and then continue to add the dispersant prepared in step 2. The aqueous solution was heated to 50 °C and stirred rapidly until the reaction was complete. After standing, the supernatant was poured off, and then the solution was centrifuged and washed to obtain cuprous oxide precipitate.

[0045] S4. Add the cuprous oxide precipitate obtained in the above steps to 500 mL of deionized water to prepare a suspension, and place it in a two-step feeding device. Under stirring, add 10 mL of the dispersant (PVP-BD aqueous solution) prepared in the above steps, and at the same time rapidly raise the temperature to 50 °C, add 4 mL of hydrazine hydrate dropwise, then raise the temperature to 70 °C, and add another 8 mL of hydrazine hydrate dropwise, while maintaining the temperature until the reaction is completed, to obtain a copper powder suspension.

[0046] Step 5: After the copper powder suspension obtained in Step 4 is allowed to stand, the supernatant is poured off. After centrifugation, copper powder is obtained. The powder is then washed three times with deionized water and anhydrous ethanol in sequence, and then dried in a vacuum drying oven at 40 ℃ for 12 h to finally obtain the target product, ultrafine copper powder.

[0047] Example 2

[0048] A process for preparing ultrafine copper powder includes the following steps:

[0049] S1. Preparation of dispersant: 5g of 1,4-butenediol, 5.8g of N-vinylpyrrolidone (NVP) and 0.5wt% of azobisisobutyronitrile (AIBN) of NVP were added to a glass ampoule. After three vacuum-nitrogen cycles, the ampoule was vacuum sealed and then placed in an oil bath at 70°C for 24 hours. After the reaction, the residue was collected and extracted with dichloromethane for 72 hours to leach out the reactants and homopolymers. After extraction, the collected reactants were placed in a vacuum drying oven at a constant temperature of 60°C until the product reached a constant weight to completely remove volatile impurities. The final copolymer was named PVP-BD.

[0050] S2. Prepare a 2 mol / L copper salt aqueous solution, a 6 mol / L NaOH aqueous solution, and a 2.5 mol / L... Aqueous solution, and 5% PVP-BD aqueous solution by mass of copper salt.

[0051] S3. First, take 300 mL of the copper salt aqueous solution prepared in step 2 and place it in... Two-step feeding device In the process, under room temperature and stirring conditions, add 250 mL of the NaOH aqueous solution prepared in step 2, stir for 20 minutes, then add 10 mL of the dispersant (PVP-BD aqueous solution) prepared in step 2, and then continue to add the dispersant prepared in step 2. The aqueous solution was heated to 50 °C and stirred rapidly until the reaction was complete. After standing, the supernatant was poured off, and then the solution was centrifuged and washed to obtain cuprous oxide precipitate.

[0052] S4. Add the cuprous oxide precipitate obtained in the above steps to 500 mL of deionized water to prepare a suspension, and place it in a two-step feeding device. Under stirring, add 10 mL of the dispersant (PVP-BD aqueous solution) prepared in the above steps, and at the same time rapidly raise the temperature to 50 °C, add 8 mL of hydrazine hydrate dropwise, then raise the temperature to 70 °C, and add another 16 mL of hydrazine hydrate dropwise, while maintaining the temperature until the reaction is completed, to obtain a copper powder suspension.

[0053] Step 5: After the copper powder suspension obtained in Step 4 is allowed to stand, the supernatant is poured off. After centrifugation, copper powder is obtained. The powder is then washed three times with deionized water and anhydrous ethanol in sequence, and then dried in a vacuum drying oven at 40 ℃ for 12 h to finally obtain the target product, ultrafine copper powder.

[0054] Example 3

[0055] A process for preparing ultrafine copper powder includes the following steps:

[0056] S1. Preparation of dispersant: 5g of 1,4-butenediol, 5.8g of N-vinylpyrrolidone (NVP) and 0.5wt% of azobisisobutyronitrile (AIBN) of NVP were added to a glass ampoule. After three vacuum-nitrogen cycles, the ampoule was vacuum sealed and then placed in an oil bath at 70°C for 24 hours. After the reaction, the residue was collected and extracted with dichloromethane for 72 hours to leach out the reactants and homopolymers. After extraction, the collected reactants were placed in a vacuum drying oven at a constant temperature of 60°C until the product reached a constant weight to completely remove volatile impurities. The final copolymer was named PVP-BD.

[0057] S2. Prepare a 3 mol / L copper salt aqueous solution, a 9 mol / L NaOH aqueous solution, and a 3.75 mol / L... Aqueous solution, and 5% PVP-BD aqueous solution by mass of copper salt.

[0058] S3. First, take 300 mL of the copper salt aqueous solution prepared in step 2 and place it in a two-step feeding device. Under room temperature and stirring conditions, add 250 mL of the NaOH aqueous solution prepared in step 2. After stirring for 20 minutes, add 10 mL of the dispersant (PVP-BD aqueous solution) prepared in step 2, and then continue to add the dispersant prepared in step 2. The aqueous solution was heated to 50 °C and stirred rapidly until the reaction was complete. After standing, the supernatant was poured off, and then the solution was centrifuged and washed to obtain cuprous oxide precipitate.

[0059] S4. Add the cuprous oxide precipitate obtained in the above steps to 500 mL of deionized water to prepare a suspension, and place it in a two-step feeding device. Under stirring, add 10 mL of the dispersant (PVP-BD aqueous solution) prepared in the above steps, and at the same time rapidly raise the temperature to 50 °C, add 12 mL of hydrazine hydrate dropwise, then raise the temperature to 70 °C, and add another 24 mL of hydrazine hydrate dropwise, while maintaining the temperature until the reaction is completed, to obtain a copper powder suspension.

[0060] S5. After the copper powder suspension obtained in step 4 is allowed to stand, the supernatant is poured off. After centrifugation, copper powder is obtained. The powder is then washed three times with deionized water and anhydrous ethanol in sequence, and then dried in a vacuum drying oven at 40 ℃ for 12 h to finally obtain the target product, ultrafine copper powder.

[0061] Comparative Example 1

[0062] The preparation process of the ultrafine copper powder provided in this embodiment is roughly the same as that in Example 1. The main difference is that in this embodiment, an equal mass of polyvinylpyrrolidone is used instead of a dispersant.

[0063] Comparative Example 2

[0064] The preparation process of the ultrafine copper powder provided in this embodiment is roughly the same as that in Example 2. The main difference is that sodium dodecylbenzenesulfonate of equal mass is used instead of dispersant in this embodiment.

[0065] Comparative Example 3

[0066] The preparation process of the ultrafine copper powder provided in this embodiment is roughly the same as that in Example 3. The main difference is that in this embodiment, an equal mass of gum arabic is used instead of the reaction additive.

[0067] Sample testing

[0068] The nano-copper oxide powder samples prepared in Examples 1-3 and Comparative Examples 1-3 were tested respectively, and the test data are recorded in the table below:

[0069]

[0070] In this invention, the stepwise addition of hydrazine hydrate effectively separates the nucleation and growth processes of copper powder crystals, thus avoiding the repeated growth of some copper crystal nuclei and reducing the presence of large-diameter copper powder particles. This control method ensures an appropriate number of crystal nuclei are generated, allowing the growth process to proceed slowly, resulting in ultrafine copper powder with relatively uniform particle size. Furthermore, the treated dispersant exhibits excellent performance, effectively preventing the agglomeration of copper powder particles, thereby obtaining ultrafine copper powder particles with uniform particle size and a tendency to form near-spherical shapes. Therefore, the ultrafine copper powder preparation process provided by this invention has broader market prospects and greater commercial value.

[0071] A two-step feeding device, reference Figure 4 It includes a water bath constant temperature pot 1, an automatic feeding unit 5, an automatic dripping unit 4, and a storage cylinder 2 for storing hydrazine hydrate solution;

[0072] Automatic feeding unit 5: When the water bath temperature in the water bath constant temperature pot 1 is 50~60 ℃, it automatically adds a quantitative amount of hydrazine hydrate solution to the automatic dripping unit 4; when the water bath temperature in the water bath constant temperature pot 1 is 70~80 ℃, it automatically adds a quantitative amount of hydrazine hydrate solution to the automatic dripping unit 4.

[0073] Automatic dripping unit 4: Used to receive hydrazine hydrate solution from automatic feeding unit 5 and automatically add hydrazine hydrate solution in a quantitative manner.

[0074] As a preferred embodiment of this example, Figure 1 As shown, there are two sets of liquid storage cylinder 2, automatic feeding unit 5 and automatic dripping unit 4. Each liquid storage cylinder 2, automatic feeding unit 5 and automatic dripping unit 4 constitutes one set of automatic dripping unit, and a total of two sets of automatic dripping units are provided.

[0075] When the water bath temperature in the water bath constant temperature pot 1 is 50~60 ℃, one of the automatic feeding units 5 automatically adds a quantitative amount of hydrazine hydrate solution to the automatic dripping unit 4.

[0076] When the water bath temperature in the water bath constant temperature pot 1 is 70~80 ℃, another set of automatic feeding units 5 automatically adds hydrazine hydrate solution to the automatic dripping unit 4 in a quantitative manner.

[0077] Setting up two sets of automatic dripping units to perform automatic liquid injection operations at different temperature ranges facilitates the orderly conduct of the operation.

[0078] As a preferred embodiment of this example, Figure 4-7 As a preferred embodiment of this example, the upper and lower ends of the liquid storage cylinder 2 are respectively provided with an injection port and a drain pipe, and the inner cavity of the liquid storage cylinder 2 is equipped with a drain funnel 6.

[0079] The automatic feeding unit 5 includes an L-shaped air guide pipe 51 mounted on the mounting frame 3. The lower end of the L-shaped air guide pipe 51 extends into the heating water of the water bath constant temperature pot 1. A liquid storage ball 52 with an internal liquid storage chamber is installed at the lower end of the L-shaped air guide pipe 51. The liquid storage chamber is filled with a low-boiling-point liquid. A movable rod 53 is slidably arranged inside the air chamber of the L-shaped air guide pipe 51, and the end of the movable rod 53 away from the L-shaped air guide pipe 51 slides through the corresponding liquid storage cylinder 2. A sealing ring is provided at the connection between the liquid storage cylinder 2 and the L-shaped air guide pipe 51. The end of the moving rod 53 has multiple racks 54 arranged in a straight line, and the racks 54 mesh with the drive gear 57. The drive gear 57 is fixedly sleeved on the rotating shaft 55. The rotating shaft 55 is rotatably mounted on the mounting bracket 3. The lower end of the rotating shaft 55 is fixed with a sealing plate 56 for blocking and sealing the outlet of the drain pipe. The part of the moving rod 53 located in the inner cavity of the liquid storage cylinder 2 is provided with a groove, and an elastic sealing gasket 58 is fixed on the bottom plane of the groove. Both the groove and the corresponding elastic sealing gasket 58 are provided with leakage holes 59.

[0080] The automatic dripping unit 4 includes a conical liquid receiving trough 41 fixedly installed at the lower end of the corresponding liquid storage cylinder 2. The conical liquid receiving trough 41 is located below the drain pipe. A U-shaped hollow tube 42 is fixed in the inner cavity of the conical liquid receiving trough 41, and one end of the U-shaped hollow tube 42 is located in the conical liquid receiving trough 41. The other end of the U-shaped hollow tube 42 passes through the conical liquid receiving trough 41. A U-shaped capillary fiber strip 43 is provided in the inner cavity of the U-shaped hollow tube 42.

[0081] The two liquid storage spheres 52 are each filled with low-boiling-point liquids with different boiling points.

[0082] When the temperature in the water bath constant temperature pot 1 reaches 50~60 ℃, the boiling point of the low-boiling point liquid in one of the liquid storage balls 52 is within this range. At this time, the low-boiling point liquid vaporizes, causing the gas pressure in the L-shaped gas guide tube 51 to increase, which will push the movable rod 53 to move outward. During this process, when the leakage hole 59 moves away from below the liquid outlet of the liquid funnel 6 (that is, the liquid outlet of the liquid funnel 6 is blocked by the elastic sealing gasket 58), the rack 54 will engage with the drive gear 57. The drive gear 57 will drive the sealing plate 56 to rotate, releasing the obstruction of the liquid outlet of the liquid storage cylinder 2. The hydrazine hydrate solution below the liquid funnel 6 enters the conical liquid receiving tank 41 through this liquid outlet. Through the capillary effect of the capillary fiber strip 43, the hydrazine hydrate solution in the conical liquid receiving tank 41 is transported from the liquid outlet end of the capillary fiber strip 43 to the liquid discharge end and finally drips downward, performing a quantitative liquid addition operation. After the liquid addition is completed, heating continues. When the temperature rises to 70℃... At ~80℃, the boiling point of the low-boiling-point liquid in the other liquid storage ball 52 is within this range. At this time, the low-boiling-point liquid vaporizes, the movable rod 53 moves outward, and the sealing plate 56 releases its obstruction of the liquid outlet of the other liquid storage cylinder 2. The hydrazine hydrate solution below the lower liquid funnel 6 enters the conical receiving tank 41 through this liquid outlet and is automatically and quantitatively added by the capillary fiber strip 43. After the reaction is completed, the temperature drops, the low-boiling-point gas liquefies, the gas pressure in the L-shaped gas guide tube 51 decreases, the movable rod 53 returns to its original position, and at the same time, the sealing plate 56 seals and blocks the liquid outlet of the liquid storage cylinder 2 (at this time, the liquid outlet of the lower liquid funnel 6 is aligned with the leakage hole 59, and the solution above the lower liquid funnel 6 enters the lower part for later use). Using the capillary fiber strip 43 for dripping can make the dripping speed consistent and avoid the impact on the quality of the copper powder product caused by the continuous change of the dripping speed due to other factors.

[0083] It is important to note the following: First, the capillary fiber strip 43 is made of polyethylene material, which has excellent corrosion resistance and water absorption. The diameter of the capillary fiber strip 43 is set to 60 to 85 μm, allowing the fibers to maintain sufficient flexibility and surface area, which helps increase the contact area with the liquid, thereby improving water absorption. The porosity (i.e., the spacing between capillary fibers) is 35 to 45 μm, which facilitates the smooth entry and adsorption of liquid, while also preventing the liquid from passing through too quickly due to excessively large gaps, thus preventing sufficient adsorption. Second, multiple sets of capillary fiber strips 43 can be set as needed. Third, the leakage hole 59 will not move outside the liquid storage cylinder during the entire operation. Fourth, the height of the lower liquid funnel 6 in the two liquid storage cylinders 2 can be designed as needed (if the heights are inconsistent, the amount of hydrazine hydrate solution below the lower liquid funnel 6 will be inconsistent to accommodate the needs of two additions). Fifth, the boiling point of one low-boiling liquid is controlled at 50~60 ℃, and the boiling point of the other low-boiling liquid is controlled at 70~80 ℃. ℃; Sixth, throughout the entire process, the rack 54 and the drive gear 57 do not separate.

[0084] As a preferred embodiment of this example, Figure 5 As shown, the upper and lower ends of the sealing plate 56 are respectively provided with a first inclined surface 561 and a second inclined surface 562, and the inclination directions of the first inclined surface 561 and the second inclined surface 562 are opposite.

[0085] The first inclined surface 561 and the second inclined surface 562 can prevent the solution adhering to the sealing plate 5 from spreading on the sealing plate 56, and facilitate the solution on the sealing plate 6 to drip into the water bath constant temperature pot 1.

[0086] As a preferred embodiment of this example, Figure 7 As shown, a hollow tube 7 communicating with the inner cavity of the liquid storage cylinder 2 is provided on the outer wall of the liquid storage cylinder 2, and a waterproof and breathable layer 8 is provided in the inner cavity of the hollow tube 7.

[0087] Maintaining consistent atmospheric pressure inside and outside the liquid storage cylinder 2 facilitates rapid drainage of liquid from the liquid storage cylinder 2 into the conical receiving tank.

[0088] It should be noted that the waterproof and breathable layer 8 is made of polytetrafluoroethylene, which has excellent corrosion resistance and can be prevented from being corroded by hydrazine hydrate solution.

[0089] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing spherical copper powder using a two-stage reduction system, characterized in that: S1. Preparation of dispersant: Add appropriate amounts of 1,4-butenediol, N-vinylpyrrolidone (NVP) and 0.5 wt% azobisisobutyronitrile (AIBN) to a glass ampoule. After three vacuum-nitrogen cycles, seal the ampoule under vacuum and then place it in an oil bath at 70-80 °C for 24-48 hours. After the reaction, collect the residue and extract it with dichloromethane for 72-96 hours to leach out the reactants and homopolymers. After extraction, place the collected reactants in a vacuum drying oven at a constant temperature of 70-80 °C until the product reaches a constant weight to completely remove volatile impurities. The final copolymer is named PVP-BD. S2. Prepare a certain amount of copper salt aqueous solution with a concentration of 1~4 mol / L, NaOH aqueous solution with a concentration of 3~12 mol / L, and C6H4O2 aqueous solution with a concentration of 1.25~5 mol / L. 12 O6 aqueous solution and 5% PVP-BD aqueous solution (copper salt by mass): First, place the copper salt aqueous solution in the first reactor vessel, and place the first reactor vessel in a water bath constant temperature pot. Under room temperature and stirring conditions, add NaOH aqueous solution dropwise, keeping stirring for 20 min. Then, add PVP-BD aqueous solution and... The aqueous solution was heated to 50-60°C and stirred rapidly until the reaction was complete. After standing, the supernatant was poured off and then centrifuged and washed to obtain cuprous oxide precipitate. S3. The cuprous oxide precipitate obtained in step S2 above is added to an appropriate amount of deionized water to prepare a suspension, which is placed in a second reactor vessel. The second reactor vessel is placed in a water bath constant temperature pot. Under stirring, the PVP-BD aqueous solution prepared in the above step is added, and the temperature is rapidly raised to 50~60 ℃ and kept constant. 4~12 mL of hydrazine hydrate is added dropwise, and then the temperature is raised to 70~80 ℃, and 8~24 mL of hydrazine hydrate is added dropwise. The temperature is maintained until the reaction is completed to obtain a copper powder suspension. S4. After the copper powder suspension obtained in the above steps is allowed to stand, the supernatant is poured off. After centrifugation, copper powder is obtained. The copper powder is washed three times with deionized water and anhydrous ethanol in sequence, and then dried in a vacuum drying oven at 40 ℃~60 ℃ for 4 h~12 h to obtain ultrafine copper powder.

2. The method for preparing spherical copper powder using a two-stage reduction system according to claim 1, characterized in that: In step S2, the copper salt is copper sulfate, copper nitrate, or copper chloride.

3. The method for preparing spherical copper powder using a two-stage reduction system according to claim 1, characterized in that: The S3 is prepared using a two-step feeding device, which includes a water bath constant temperature pot (1), an automatic feeding unit (5), an automatic dripping unit (4), and a storage cylinder (2) for storing hydrazine hydrate solution. Automatic feeding unit (5): When the water bath temperature in the water bath constant temperature pot (1) is 50~60 ℃, it automatically adds a quantitative amount of hydrazine hydrate solution to the automatic dripping unit (4); when the water bath temperature in the water bath constant temperature pot (1) is 70~80 ℃, it automatically adds a quantitative amount of hydrazine hydrate solution to the automatic dripping unit (4). Automatic dripping unit (4): used to receive the hydrazine hydrate solution from the automatic feeding unit (5) and automatically add the hydrazine hydrate solution in a quantitative manner.

4. The method for preparing spherical copper powder using a two-stage reduction system according to claim 3, characterized in that: The liquid storage cylinder (2), the automatic feeding unit (5) and the automatic dripping unit (4) are each provided in two sets. Each liquid storage cylinder (2), the automatic feeding unit (5) and the automatic dripping unit (4) constitutes one set of automatic dripping units, and a total of two sets of automatic dripping units are provided. When the water bath temperature in the water bath constant temperature pot (1) is 50~60 ℃, one of the automatic feeding units (5) automatically adds hydrazine hydrate solution to the automatic dripping unit (4) in a quantitative manner. When the water bath temperature in the water bath constant temperature pot (1) is 70~80 ℃, another set of automatic feeding units (5) automatically adds hydrazine hydrate solution to the automatic dripping unit (4) in a quantitative manner.

5. The method for preparing spherical copper powder using a two-stage reduction system according to claim 4, characterized in that: The liquid storage cylinder (2) is provided with an injection port and a drain pipe at its upper and lower ends, respectively, and a liquid discharge funnel (6) is installed in the inner cavity of the liquid storage cylinder (2). The automatic feeding unit (5) includes an L-shaped air guide pipe (51) mounted on a mounting frame (3). The lower end of the L-shaped air guide pipe (51) extends into the heating water of the water bath constant temperature pot (1). A liquid storage ball (52) with an internal liquid storage chamber is installed at the lower end of the L-shaped air guide pipe (51). The liquid storage chamber is filled with a low-boiling-point liquid. A movable rod (53) is slidably arranged in the air chamber of the L-shaped air guide pipe (51). The end of the movable rod (53) away from the L-shaped air guide pipe (51) slides through the corresponding liquid storage cylinder (2). A sealing ring is provided at the connection between the liquid storage cylinder (2) and the L-shaped air guide pipe (51). The end of the moving rod (53) has multiple racks (54) arranged in a straight line, and the racks (54) mesh with the drive gear (57). The drive gear (57) is fixedly sleeved on the rotating shaft (55). The rotating shaft (55) is rotatably mounted on the mounting bracket (3). The lower end of the rotating shaft (55) is fixed with a sealing plate (56) for blocking and sealing the outlet of the drain pipe. The moving rod (53) is provided with a groove in the part of the inner cavity of the storage cylinder (2), and an elastic sealing gasket (58) is fixed on the bottom plane of the groove. Both the groove and the corresponding elastic sealing gasket (58) are provided with leakage holes (59). The automatic dripping unit (4) includes a conical liquid receiving groove (41) fixedly installed at the lower end of the corresponding liquid storage cylinder (2). The conical liquid receiving groove (41) is located below the drain pipe. A U-shaped hollow tube (42) is fixed in the inner cavity of the conical liquid receiving groove (41). One end of the U-shaped hollow tube (42) is located in the conical liquid receiving groove (41), and the other end of the U-shaped hollow tube (42) passes through the conical liquid receiving groove (41). The inner cavity of the U-shaped hollow tube (42) is provided with a U-shaped capillary fiber strip (43). The two liquid storage balls (52) are each filled with low-boiling-point liquids with different boiling points.

6. The method for preparing spherical copper powder using a two-stage reduction system according to claim 5, characterized in that: The sealing plate (56) has a first inclined surface (561) and a second inclined surface (562) respectively at its upper and lower ends. The first inclined surface (561) and the second inclined surface (562) have opposite inclination directions.

7. The method for preparing spherical copper powder using a two-stage reduction system according to claim 5, characterized in that: The outer wall of the liquid storage cylinder (2) is provided with a hollow column (7) that communicates with the inner cavity of the liquid storage cylinder (2), and the inner cavity of the hollow column (7) is provided with a waterproof and breathable layer (8).

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