A microfluidic continuous preparation method of surface micro-ridged spherical silver powder

Abstract

The application discloses a kind of micro-jet continuous preparation methods of micro-pleated spherical silver powder, to solve the problem that traditional stirring reaction method is difficult to continuously prepare high sphericity, high dispersibility and surface has regular micro-pleated structure silver powder using micro-jet mixing reaction mode.The method comprises: configuration and filtration silver precursor and reducing agent solution;Temperature is controlled to 15-35 DEG C respectively;Two solutions are pumped into Y type micro-jet reactor with flow ratio 1:1 by metering pump, and high-speed collision mixing is formed at a certain flow and angle at the reactor outlet, efficient mixing and reaction are realized;Add total addition amount is 1% of silver nitrate weight Gelatin and stearic acid as dispersion stabilizer to inhibit agglomeration and control wrinkle morphology;After suction filtration, washing and vacuum drying, the product is obtained.By using the above technical scheme, continuous, high-stability preparation of micro-pleated high-sphericity silver powder can be realized, and the process method is easy to expand production by modularization.

Description

Technical fields: This invention belongs to the field of precious metal powder preparation technology, specifically relating to a micro-jet continuous preparation method for surface-micro-wrinkled spherical silver powder. Background technology: Currently, against the backdrop of the rapid development of the electronics industry and new energy technologies, spherical silver powder serves as a core conductive filler in key areas such as conductive pastes, solar cell electrodes, flexible electronic devices, 5G high-frequency communication components, and advanced packaging materials. Its surface microstructure, particle size distribution, and specific surface area directly affect the rheological properties, printing accuracy, sintering density, conductive network connectivity efficiency, and lifespan of the conductive paste. Among these, micro-wrinkled spherical silver powder, as a special morphology material combining high specific surface area and good flowability, can significantly increase the sintering activity of particles while maintaining high filling density. This allows for more efficient construction of three-dimensional conductive pathways under low-temperature sintering conditions, reducing sintering temperature and energy consumption. Furthermore, the micro-wrinkled structure can enhance the interfacial anchoring effect between the silver powder and the organic carrier, improving the paste's storage stability and printing consistency. Therefore, achieving precise control over the high sphericity, narrow particle size distribution, and designable surface microstructures (such as micro-wrinkles and nanoscale roughness) of ultrafine silver powder particles has become a key technological bottleneck for improving the overall performance of high-end electronic materials.

[0001] In existing technologies, liquid-phase reduction is widely used for the synthesis of spherical silver powder. It typically employs traditional mechanical stirring or co-current dropping mixing processes, which may suffer from low mixing efficiency, uneven mass and heat transfer, and excessively large local concentration gradients. This results in poor uniformity of silver powder particle morphology, insufficient sphericity, and difficulty in forming a well-structured, highly reproducible micro-wrinkled surface. CN113226597B discloses a spherical silver powder and its manufacturing method, which prepares spherical silver powder containing numerous closed pores by controlling the reaction temperature. The preparation process is based on a conventional liquid-phase stirring and mixing reduction reaction. CN116809945B discloses a near-spherical silver powder and its preparation method, which uses a co-current dropping method to simultaneously add silver nitrate solution and reducing agent solution to a dispersant solution, preparing near-spherical silver powder with a narrow particle size distribution and high tap density. Some solutions attempt to introduce microchannel reactors or external field enhancement techniques to optimize the mixing and mass transfer process at the microscale and achieve rapid and uniform nucleation. However, solid particles are prone to deposition and aggregation within the microscale channels, frequently causing blockages and severely restricting continuous and large-scale production capabilities. Furthermore, existing processes generally rely on high concentrations of surfactants (such as polyvinylpyrrolidone (PVP) and sodium citrate) to control morphology and prevent aggregation. However, these organic additives tend to remain on the silver powder surface, increasing the difficulty of subsequent cleaning and potentially generating carbides or pores during sintering, degrading conductivity and affecting its application in high-reliability electronic devices.

[0002] In summary, existing technologies still have significant shortcomings in areas such as precise control of micro-wrinkled particle morphology (including wrinkle density, depth, and periodicity), process stability (continuous operation capability, anti-clogging performance), product purity (low organic residue), and industrial applicability (scalability, cost-effectiveness). Therefore, there is an urgent need to develop a novel preparation method that integrates efficient mixing, precise process control, and green synthesis concepts to achieve high consistency, high purity, and high efficiency in the preparation of micro-wrinkled spherical silver powder, thereby meeting the stringent requirements of high-performance electronic materials for conductive fillers. Summary of the Invention: The purpose of this invention is to provide a microjet continuous preparation method for spherical silver powder with a surface micro-wrinkled structure. Utilizing the advantages of Y-type microjet mixing reaction technology, such as high mass and heat transfer efficiency, uniform material mixing, and ease of modular scaling, this method achieves high-speed jet impact mixing of the reaction solution at a certain angle at a specific point outside the microchannel. While achieving efficient mixing, it effectively avoids the risk of blockage caused by particle precipitates within the microchannel. This solves the problems of inaccurate particle morphology control, low continuous production efficiency, and insufficient microstructure optimization in existing spherical silver powder preparation technologies, enabling the efficient, continuous, and stable preparation of ultrafine silver powder with high sphericity, high dispersibility, and a regular micro-wrinkled surface structure.

[0003] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A continuous microjets preparation method for surface-wrinkled spherical silver powder includes the following specific steps: Step 1: Precise preparation and purification of silver precursor solution and reducing agent solution Analytical grade silver nitrate was dissolved in deionized water to prepare a silver precursor solution A with a concentration of 0.1-0.5 mol / L. Simultaneously, food-grade ascorbic acid was dissolved in deionized water of the same quality. One or two surface dispersants selected from gelatin, stearic acid, and PVP (weighing 0.5-1.0% by weight of silver nitrate) were dissolved in an appropriate amount of ethanol and added to the ascorbic acid solution. The mixture was stirred until homogeneous to prepare a reducing agent solution B with a concentration of 0.06-0.30 mol / L. After preparation, both solutions were vacuum filtered using a microporous membrane made of polytetrafluoroethylene (PTFE) to thoroughly remove insoluble particles, microorganisms, and colloidal impurities, ensuring the cleanliness of the reaction system. Furthermore, the pH of the silver precursor solution was adjusted to 2.0-5.0 by adding nitric acid, and the pH of the reducing agent solution was simultaneously adjusted to a similar range to optimize the reduction reaction kinetics and suppress side reactions (such as silver ion hydrolysis or ascorbic acid oxidative degradation).

[0004] Step 2: Solution preheating and high-precision temperature control The silver precursor solution A and reducing agent solution B prepared in step 1 are respectively introduced into two independent isothermal storage tanks. These tanks are made of 316L stainless steel with electrolytically polished inner walls, and have a volume of 5-10 liters, exhibiting good corrosion resistance and low metal ion leaching characteristics. The tanks employ a combination of a two-stage semiconductor cooling module and a precision electric heating wire for temperature control, along with a high-response PID controller, to precisely stabilize the solution temperature within the range of 15-35℃, with temperature fluctuations controlled within ±0.5℃. Before entering the reactor, the solution must be circulated at an isothermal state for at least 30 minutes to ensure a uniform overall temperature field and avoid inconsistent nucleation rates caused by localized temperature differences.

[0005] Step 3: High-speed collision and mixing reaction of microjets Two temperature-controlled solutions, A and B, are synchronously input into the two internal channels of the Y-type microjet reactor at a volumetric flow rate ratio of 1:1 via two high-precision metering pumps (single-channel flow control accuracy ±0.5%). This microjet mixing reaction module system is as follows: Figure 1 As shown, the Y-type microjet reactor is 3D printed using photosensitive resin, possessing excellent chemical inertness and pressure resistance. It contains two microchannels with an inner diameter of 0.5-1.0 mm, corresponding to inlet 1, inlet 2, and outlet 3, outlet 4, respectively. The two outlets are inclined inwards, with an outlet spacing d = 10-20 mm. The liquid streams ejected from outlets 3 and 4 collide and mix at a single point outside the Y-type microjet reactor, effectively preventing solid products from depositing and clogging inside the microchannels. When the two liquid streams are ejected at high speed from the nozzles and collide at the collision point, the instantaneous Reynolds number exceeds 4000, forming a highly turbulent vortex mixing zone. The mixing time is shortened to the millisecond level (<10 ms). While achieving instantaneous and uniform mixing of silver ions and reducing agent molecules, the vortex mixing effect may also help improve the sphericity of silver particles, giving their surface a tangled micro-wrinkled morphology.

[0006] Step 4: In-situ surface modification and dispersion stabilization One or two of the following surface dispersants—gelatin, stearic acid, and polyvinylpyrrolidone (PVP)—dissolved in an appropriate amount of ethanol are pre-added to the silver precursor solution or reducing agent solution as a dispersion stabilizer. The amount added is 0.1-2.0% (preferably 1.0%) of the weight of silver nitrate. The dispersion stabilizer forms a protective coating layer on the silver surface through coordination adsorption during the early stages of silver atom nucleation. This adsorption layer effectively suppresses van der Waals forces between particles through steric hindrance, preventing agglomeration; furthermore, it regulates the growth rate of the silver crystal facets, making the surface structure more regular and controllable.

[0007] Step 5: Product separation, washing and drying Solutions A and B rapidly mix upon jet collision, undergoing nucleation and growth reactions. This mixed solution flows vertically into a beaker containing 200-2000 mL of deionized water as the base solution. The base solution in the beaker is continuously stirred at different magnetic stirring speeds (0-400 r / min). After the reaction is complete, the solution gradually separates into precipitates. The supernatant is added to a 10% NaCl solution; no white flocculent precipitate is observed, indicating complete reduction of silver nitrate. The reaction solution is filtered, and the precipitate is washed 3-4 times with deionized water to fully remove the adsorbed dispersant stabilizer and reaction byproducts (such as dehydroascorbic acid and nitrate ions) until the conductivity of the wash water drops below 5 μS / cm. The filtered solid product is dried in a vacuum drying oven at 60℃ for 4-6 h to constant weight and then naturally cooled to room temperature, yielding loose, non-agglomerated, micro-wrinkled spherical silver powder.

[0008] The preferred embodiment further includes the following technical features: (1) The concentration of the silver precursor solution is preferably 0.1-0.2 mol / L. To ensure the reduction rate of silver ions, the experiment adopts an excess of ascorbic acid. The concentration of the reducing agent solution is preferably 0.06-0.12 mol / L to ensure complete reaction and minimal byproducts.

[0009] (2) The metering pump is uniformly controlled by a central synchronous controller, supporting a stable flow rate adjustment range of 0-1000ml / min, and adapting to different batches or process parameter switching.

[0010] (3) The Y-type microjet reactor is formed by photosensitive resin 3D printing, which has excellent chemical inertness and pressure resistance. It has two microchannels with an inner diameter of 0.5-1.0 mm, corresponding to inlet 1, inlet 2 and outlet 3, outlet 4 respectively. The two outlets are inclined inward, the jet angle between the two outlet channels is 2θ=60°, and the outlet spacing d=10-20 mm. The two liquid streams sprayed from outlet 3 and outlet 4 are mixed at a point outside the Y-type microjet reactor.

[0011] (4) The complete set of synthesis reaction equipment can be integrated in parallel by modularly replicating multiple sets of Y-type micro-jet reaction units. It can share the solution storage and supply system, temperature control unit, filtration and washing unit and drying unit. It can achieve continuous operation by using an integrated online monitoring and automatic control system.

[0012] (5) Thanks to the mixing and precipitation reaction of the two liquid streams outside the microchannel, the microchannel reaction system does not have the problem of scaling and blockage caused by particle precipitation in the microchannel. It does not require shutdown for cleaning and can significantly improve production efficiency and equipment utilization.

[0013] (6) The obtained micro-wrinkled spherical silver powder has excellent physicochemical properties: ① High sphericity, characterized by the particle's aspect ratio, i.e., the ratio of the particle's vertical diameter *a* to its horizontal diameter *b*, as shown in the attached figure. Figure 2 As shown, the closer the value is to 1, the higher the sphericity of the particles. In conductive silver paste, spherical silver powder with a higher void filling rate can be achieved. The aspect ratio of the spherical silver powder particles prepared in this invention is in the range of 1 ± 0.2. ② The spherical silver powder has a narrow particle size distribution, with an average particle size of Dav = 2-3 μm; the tap density reaches 6.1-6.2 g / cm³. 3 It is significantly superior to traditional spherical silver powder (typically <6.0 g / cm³). 3 ); ③ The silver powder product obtained by this invention has two advantages: First, the silver powder product has high sphericity, high dispersibility, and high tap density, which is beneficial to improving the silver powder solid content and sintering density of the conductive paste; Second, the surface of the obtained particles has a uniform and neat surface micro-wrinkle morphology, which will effectively increase the specific surface area of ​​the particles, improve the sintering activity of the particles, and make it easier to achieve sintering neck connection during the sintering process.

[0014] Compared with the prior art, the present invention has the following significant advantages: (1) The innovative use of Y-type microjet reactor to replace traditional batch reactor or microchannel reactor, and the realization of millisecond-level mixing through external high-speed collision, while significantly improving the mixing efficiency of reaction liquid, avoids the problem of blockage caused by particle deposition in microreactor channel, and ensures the stability of continuous production; (2) By precisely controlling the jet collision point, temperature, flow rate and surface modifier, the controllable preparation of the micro-wrinkled structure on the surface of spherical silver powder was achieved. This structure significantly improves the specific surface area and sintering activity while maintaining high sphericity. (3) The whole process is free of toxic reagents, low energy consumption and low residue, meets the requirements of green manufacturing, and is easy to scale up to industrial-grade capacity through modularization. It is suitable for the urgent demand for high-performance silver powder in fields such as high-end electronic packaging, photovoltaic conductive paste, and flexible electronic printing. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the Y-type microjet reactor module and the jet mixing process proposed in this invention; Figure 2 This is a scanning electron microscope image of the spherical silver powder with a surface micro-wrinkle morphology prepared in Example 1. Figure 3 A schematic diagram of the conventional stirring and mixing reaction process used in Comparative Example 1. Figure 4 Scanning electron microscope image of the micron-sized silver particles prepared in Comparative Example 1 Detailed implementation method: To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0016] Example 1 In the above-mentioned continuous microfluidic preparation method of micro-wrinkled spherical silver powder, according to the steps, firstly, a reactant solution is prepared. Under light-protected conditions, 17g of silver nitrate is dissolved in 1000mL of deionized water to prepare a 0.1mol / L solution. Then, 0.23mL of nitric acid (2.0% of the weight of silver nitrate) is added to the silver nitrate solution and stirred continuously under mechanical stirring to obtain reaction solution A, with a pH of approximately 2. Next, 10.56g of ascorbic acid is weighed and dissolved in 1000mL of deionized water to prepare a 0.06mol / L ascorbic acid solution. Then, 0.17g of surfactant (0.5% each of stearic acid and gelatin, with a total addition of 1% of the weight of silver nitrate) is weighed and dissolved in 5mL of ethanol. This is then added to the ascorbic acid solution and stirred continuously to obtain a reduction solution B, with a pH of 3.5. The temperature of reaction solution A and reduction solution B is maintained at 25℃ using an electrically heated constant-temperature water bath. After the two solutions are prepared, they must be vacuum filtered using a microporous membrane made of polytetrafluoroethylene to thoroughly remove insoluble particles, microorganisms and colloidal impurities, ensuring the cleanliness of the reaction system.

[0017] The prepared silver precursor solution (solution A) and reducing solution (solution B) were separately introduced into two independent 5L constant-temperature storage tanks and circulated under constant temperature for at least 30 minutes to ensure a uniform overall temperature field and avoid inconsistent nucleation rates caused by local temperature differences. This step, through high-precision temperature control and sufficient pre-circulation, eliminated the internal thermal gradient of the solution, ensuring that the two liquid streams entering the reactor had completely consistent thermodynamic states. Figure 1The microjets mixing reaction module shown controls the metering pump flow rate to 90 ml / min, inputting solutions A and B at the same flow rate into the two internal channels of the Y-type microjets reactor. The Y-type microjets reactor is 3D printed from photosensitive resin and contains two microchannels with an inner diameter of 0.75 mm, corresponding to inlet 1, inlet 2 and outlet 3, outlet 4. The two outlets are inclined inwards, with an outlet spacing d = 10 mm. The liquid streams ejected from outlets 3 and 4 converge at a point outside the Y-type microjets reactor, with an angle 2θ of 60° between the two jets at the mixing point. Solutions A and B are ejected from the nozzle at a specific angle and flow rate and mix at the collision point. During jet collision, they rapidly mix, forming a highly turbulent vortex mixing zone, achieving instantaneous and uniform mixing and growth reaction of silver ions and reducing agent molecules at the molecular scale. This step achieves instantaneous mixing at the molecular scale through an external high-speed collision mechanism, completely avoiding the clogging risk caused by particle deposition inside traditional microchannel reactors, while providing a highly uniform chemical environment for homogeneous nucleation.

[0018] The jet mixture was vertically poured into a beaker containing 200 mL of deionized water as the base solution. The magnetic stirring speed in the beaker was controlled at 200 r / min. After 1 minute of continuous stirring, the solution gradually separated into layers and precipitated. The supernatant was added to a 10% NaCl solution; no white flocculent precipitate was observed, indicating complete reduction of silver nitrate. After the reaction, the solution was filtered, and the precipitate was washed 3-4 times with deionized water until the conductivity of the wash water dropped below 5 μs / cm. The filtered solid product was dried in a vacuum drying oven at 60℃ for 4-6 hours until constant weight was achieved, yielding highly spherical silver particles with an average particle size of 2.69 μm, an aspect ratio of 0.98, and a tap density of 6.19 g / cm³, exhibiting surface micro-wrinkles. The scanning electron microscope image is shown below. Figure 2 As shown.

[0019] Example 2 Under light-protected conditions, 34 g of silver nitrate was dissolved in 1000 mL of deionized water to prepare a 0.2 mol / L solution. Then, 0.46 mL of nitric acid (2.0% of the silver nitrate weight) was added to the silver nitrate solution and stirred continuously under mechanical stirring to obtain reaction solution A, with a pH of approximately 2. 21.12 g of ascorbic acid was weighed and dissolved in 1000 mL of deionized water to prepare a 0.12 mol / L ascorbic acid solution. Then, 0.34 g of surfactant (0.5% each of stearic acid and gelatin, totaling 1% of the silver nitrate weight) was weighed and dissolved in 10 mL of ethanol. This surfactant was then added to the ascorbic acid solution and stirred continuously to obtain reduced solution B, with a pH of 3.5. Both solutions were vacuum filtered through a filter membrane and then injected into two 5 L constant-temperature storage tanks, circulated at a constant temperature of 25°C for at least 30 minutes. The reaction solution was then subjected to the following process: Figure 1 The microjet mixing reaction module shown controls the metering pump flow rate at 80 ml / min, inputting solutions A and B at the same flow rate into two microchannels with an inner diameter of 0.75 mm in the Y-type microjet reactor. The jet outlet spacing d = 10 mm, and the jet angle 2θ = 60°. After collision mixing, the solution falls vertically into a beaker containing 200 mL of deionized water as the base solution. The base solution in the beaker is magnetically stirred at a rate of 200 r / min. After continuous stirring for 1 min, the solution gradually separates and precipitates. The supernatant is added to a 10% NaCl solution, and no white flocculent precipitate is observed, indicating that the silver nitrate is completely reduced. After the reaction is complete, the solution is filtered and the precipitate is washed 3-4 times with deionized water until the conductivity of the wash water drops below 5 μs / cm. The filtered solid product is placed in a vacuum drying oven at 60℃ and dried for 4-6 h to constant weight, thus obtaining high sphericity silver particles with surface micro-wrinkles, having an average particle size of 2.61 μm, a particle aspect ratio of 1.02, and a tap density of 6.12 g / cm3.

[0020] Example 3 Under light-protected conditions, 34 g of silver nitrate was dissolved in 1000 mL of deionized water to prepare a 0.2 mol / L solution. Then, 0.46 mL of nitric acid (2.0% of the silver nitrate weight) was added to the silver nitrate solution and stirred continuously under mechanical stirring to obtain reaction solution A, with a pH of approximately 2. 21.12 g of ascorbic acid was weighed and dissolved in 1000 mL of deionized water to prepare a 0.12 mol / L ascorbic acid solution. Then, 0.34 g of surfactant (0.5% each of stearic acid and gelatin, totaling 1% of the silver nitrate weight) was weighed and dissolved in 10 mL of ethanol. This surfactant was then added to the ascorbic acid solution and stirred continuously to obtain reduced solution B, with a pH of 3.5. Both solutions were vacuum filtered through a filter membrane and then injected into two 5 L constant-temperature storage tanks, circulated at a constant temperature of 25°C for at least 30 minutes. The reaction solution was then subjected to the following process: Figure 1The microjet mixing reaction module shown controls the metering pump flow rate at 100 ml / min, inputting solutions A and B at the same flow rate into two microchannels with an inner diameter of 0.75 mm in the Y-type microjet reactor. The jet outlet spacing d = 10 mm, and the jet angle 2θ = 60°. After collision mixing, the solution falls vertically into a beaker containing 200 mL of deionized water as the base solution. The base solution in the beaker is magnetically stirred at a rate of 200 r / min. After continuous stirring for 1 min, the solution gradually separates and precipitates. The supernatant is added to a 10% NaCl solution, and no white flocculent precipitate is observed, indicating that the silver nitrate is completely reduced. After the reaction is complete, the solution is filtered and the precipitate is washed 3-4 times with deionized water until the conductivity of the wash water drops below 5 μs / cm. The filtered solid product is placed in a vacuum drying oven at 60℃ and dried for 4-6 h to constant weight, thus obtaining high sphericity silver particles with surface micro-wrinkles, having an average particle size of 2.50 μm, a particle aspect ratio of 0.97, and a tap density of 6.15 g / cm3.

[0021] Comparative Example 1 Adopting such Figure 3 The conventional stirring and mixing reaction process shown is used to prepare micron-sized silver particles using a conventional uniform addition method. First, the reactant solution is prepared. Under light-protected conditions, 17g of silver nitrate is dissolved in 1000mL of deionized water to prepare a 0.1mol / L solution. Then, 0.23mL of nitric acid (2.0% of the weight of silver nitrate) is added to the silver nitrate solution and stirred continuously under mechanical stirring to obtain reaction solution A, with a pH of approximately 2. Next, 10.56g of ascorbic acid is weighed and dissolved in 1000mL of deionized water to prepare a 0.06mol / L ascorbic acid solution. Then, 0.17g of surfactant is weighed and dissolved in 5mL of ethanol (surfactants are either gelatin alone or a combination of 0.5% stearic acid and 0.5% gelatin, with a total addition amount of 1% of the weight of silver nitrate). The ascorbic acid solution is then added and stirred continuously to obtain reduced solution B, with a pH of 3.5. An electrically heated constant-temperature water bath is used to maintain the temperature of reaction solution A and reduced solution B at 25℃. After the two solutions are prepared, they must be vacuum filtered using a microporous membrane made of polytetrafluoroethylene to thoroughly remove insoluble particles, microorganisms and colloidal impurities, ensuring the cleanliness of the reaction system.

[0022] 200 mL of solution A was placed in a 1 L beaker, and the magnetic stirring speed was set to 200 r / min. 200 mL of solution B was taken and added dropwise to silver nitrate solution A at a uniform rate over 1 min. The reaction was continued with stirring for another 1 min. The supernatant of the mixed solution was then added dropwise to a 10% NaCl solution for testing. No white precipitate was formed, indicating complete reduction of the silver nitrate. The silver particles were filtered and washed, and the solid particles were washed 3-4 times with deionized water until the conductivity of the wash water decreased to below 5 μs / cm. The filtered solid product was dried in a vacuum drying oven at 60℃ for 4-6 h until constant weight was obtained, yielding micron-sized near-spherical silver particles. The scanning electron microscope (SEM) image shows... Figure 4 As shown. Among them, Figure 4 (a) Gelatin was used alone as a surfactant, with a single particle size of approximately 3-5 μm. Figure 4 (b) Using gelatin and stearic acid as surfactants, the single particle size is approximately 1-3 μm. Although the silver particles obtained under the two comparative conditions have different particle sizes, neither yielded the spherical silver particles with surface micro-wrinkles prepared by the method of this invention, and some formed large particles with disordered agglomeration.

[0023] As can be seen from the comparison of the embodiments and the comparative examples, the microjet mixing reaction method used in the present invention can prepare silver powder particles with high sphericity and surface micro-wrinkle structure, which is significantly better than the traditional stirring reaction method of the comparative examples.

[0024] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A continuous microjets preparation method for micro-wrinkled spherical silver powder, characterized in that: The specific steps include the following: Step 1: Prepare a silver precursor solution and a reducing agent solution of a certain concentration. Filter both solutions to remove impurities and control the temperature within the range of 15-35℃. Step 2: Establish a microjet mixing reaction system including two independent liquid inlet pipelines, a Y-type microjet mixing reactor device and an open bulk reaction vessel. The two liquid streams converge precisely at a certain angle at a specific point outside the microchannel nozzle outlet through the two outlets of the Y-type microjet mixing device. Step 3: Implement the microjets mixing reaction process. The temperature-controlled silver precursor solution and reducing agent solution are simultaneously pumped into the Y-type microjets reactor at a volume flow ratio of 1:1 using a metering pump. Two high-speed colliding liquid flows are formed at the reactor inlet, and uniform vortex mixing is generated. Step 4: The mixed solution is allowed to fall freely into an open bulk reaction vessel containing deionized water and the reaction continues for 1 minute. The solid product is then washed with deionized water and dried under vacuum at 60°C for 4-6 hours until constant weight is achieved, resulting in loose, non-agglomerated micro-wrinkled spherical silver powder.

2. The micro-jet continuous preparation method of micro-wrinkled spherical silver powder according to claim 1, characterized in that: The concentration of the silver precursor solution is 0.1-0.5 mol / L, the concentration of the reducing agent solution is 0.06-0.30 mol / L, and the pH of both solutions is adjusted to the range of 2.0-5.

0.

3. The microjets continuously preparing micro-wrinkled spherical silver powder according to claim 1, characterized in that: The constant temperature storage tank is made of 316L stainless steel and has a volume of 5-10 liters. The external circulation heat exchange system adopts a two-stage semiconductor refrigeration and electric heating combination temperature control method, with a temperature control accuracy of ±0.5℃.

4. The microjets continuously preparing micro-wrinkled spherical silver powder according to claim 1, characterized in that: The Y-shaped microjet mixing device is manufactured using 3D printing of polyester material. The angle between the axes of the two microchannel outlets is 60-90°, the inner diameter of the nozzle outlet is 0.5-1.0 mm, and the intersection point is precisely set at a distance of 5-10 mm from the nozzle outlet outside the microchannel.

5. The microjets continuously preparing micro-wrinkled spherical silver powder according to claim 1, characterized in that: The total flow rate of the solution is controlled within the range of 50-200 ml / min.

6. The microjets continuously preparing micro-wrinkled spherical silver powder according to claim 1, characterized in that: Adding one or two of the following surface dispersants—gelatin, stearic acid, and polyvinylpyrrolidone (PVP)—to the reducing agent solution in advance can effectively inhibit particle aggregation and regulate the depth and density of microfolds.

7. The microjets continuously preparing micro-wrinkled spherical silver powder according to claim 1, characterized in that: The method is suitable for continuous production. By connecting multiple Y-shaped microjet mixers in parallel to form a mixing array, it avoids the clogging problem caused by the deposition and growth of solid particles in the microchannels, and significantly improves the stability and runtime of continuous production. The process has a high degree of modularity, is easy to scale up and integrate, and is suitable for industrial continuous production.

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