Device and method for preparing micro-nano silver powder based on micro-droplets

Abstract

The invention provides a device and a method for preparing micro-nano silver powder based on micro-droplets. The preparation device comprises a siphon mixing system, a reaction kettle and a detection system, the siphon mixing system is used for sucking a silver source solution and a reducing agent solution into a high-pressure gas pipeline by providing high-pressure inert gas and utilizing the siphon effect of the high-pressure inert gas, and meanwhile, reaction liquid is formed through rapid mixing; the reaction liquid is sprayed into the reaction kettle through an atomizing nozzle to form a plurality of micro-droplets; the detection system comprises a detection bent pipe which is wound out of the reaction kettle, and a micro-nano silver particle detection device is mounted in the detection bent pipe and is used for monitoring the change process of micro-droplets in the detection bent pipe in real time. Therefore, according to the preparation method provided by the invention, the real-time monitoring and adjustment of the micro-nano silver powder preparation process and the accurate regulation and control of the particle size and the morphology of the micro-nano silver powder are realized, the improvement of the consistency and the quality of the micro-nano silver powder product is facilitated, the exploration of the silver powder synthesis process is facilitated, and the exploration research and development period is shortened.

Description

Technical Field

[0001] This invention relates to the field of silver powder production technology, specifically to an apparatus and method for preparing micro-nano silver powder based on microdroplets. Background Technology

[0002] Silver powder, as an important functional material, has wide applications in electronics, photovoltaics, catalysts, and biomedicine. With technological advancements and changing market demands, the requirements for the particle size, morphology, purity, and dispersibility of silver powder are becoming increasingly stringent. However, traditional silver powder preparation methods, especially those based on mechanical stirring in chemical reactors or magnetic stirring in laboratories, face numerous challenges.

[0003] I. The synthesis process is cumbersome and inefficient: Traditional chemical reactor preparation of nano-silver powder typically involves multiple steps, including mixing reactants, heating, cooling, washing, separation, and drying. These steps are not only cumbersome, but each step can also introduce impurities, affecting the purity of the final product. Chemical laboratory preparation usually requires the preparation of multiple solutions and the reaction according to a preset mixing ratio, which cannot accurately obtain product quality. Only by completing the entire process can the morphology and particle size of the silver powder under this process be accurately known.

[0004] Second, real-time control is difficult: Once a reaction begins in a chemical reactor, it is very difficult to adjust the reaction conditions in real time. This means that if the initial conditions are not set properly or an accident occurs during the reaction, the entire batch of silver powder may be unusable, resulting in a waste of raw materials and energy. Although control is possible in the laboratory, it still requires a long period of time and multiple batches of trial and error to obtain the optimal process.

[0005] III. High-Temperature-Induced Grain Growth: While high temperatures can accelerate chemical reactions and increase the nucleation rate, excessively high temperatures can lead to rapid grain growth, which is particularly detrimental to nano-silver powders requiring fine particle size control. Furthermore, high temperatures can trigger agglomeration, further affecting the dispersibility and application performance of the silver powder. During mass production, the exothermic reaction caused by the reduction reaction makes the reaction even more difficult to control.

[0006] IV. Long Process Selection Cycle: In the early stages of process condition testing, the concentration changes significantly due to the continuous reaction between the silver source and reducing agent during mixing and stirring. The resulting nano-silver powder particle size also varies due to changes in solution concentration. Only through long-term, repeated experiments to obtain a wider process window can the optimal preparation process be achieved. However, process selection typically involves controlled variable methods, and only single-factor experiments can be conducted at a time. The final result is only known after synthesis and testing. But for silver powder synthesis, numerous factors influence the final morphology and particle size, including the type and concentration of the silver source solution, the type and concentration of the reducing agent, the type and concentration of the dispersant, reaction temperature, feeding rate, stirring speed, pH control, and reaction time. Furthermore, since gradient experiments (e.g., concentration intervals, feeding rate intervals, temperature intervals) are generally used during exploration, continuous adjustment is not possible, leading to a risk of trial and error and omissions. Accurate morphology and particle size trends can only be obtained by continuously refining the interval range, resulting in significant time and material costs, severely hindering the development of silver powder preparation processes.

[0007] To address the aforementioned problems, researchers have conducted extensive exploration and improvements. For example, they have improved the design of reaction vessels to enhance mixing efficiency and reaction uniformity; employed new reducing agents and stabilizers to improve the dispersibility and stability of silver powder; and utilized physical methods such as ultrasound and microwaves to accelerate the reaction and improve product quality. Orthogonal methods have been used to reduce the number of experiments, but the selection of factors and levels in orthogonal experiments still relies on trial and error based on experience. Therefore, these improvements mostly only alleviate the problems to a certain extent and cannot fundamentally solve the limitations of traditional preparation methods, especially in the initial screening of the silver powder synthesis process conditions during the experimental phase, where they are particularly hampered. Summary of the Invention

[0008] In view of this, based on the microdroplet reaction, this invention designs a device and method for preparing micro / nano silver powder, which can cause the silver source and reducing agent to react in microdroplets, realizing rapid mixing and uniform reaction of reactants in microdroplets, thereby improving synthesis efficiency; at the same time, it also realizes real-time monitoring and adjustment of the micro / nano silver powder preparation process, which is conducive to exploring the silver powder synthesis process and shortening the research and development cycle in the early laboratory stage.

[0009] Specifically, the present invention provides the following technical solutions: An apparatus for preparing micro / nano silver powder based on microdroplets, comprising: A siphon mixing system includes a gas supply unit for providing high-pressure inert gas, a high-pressure gas pipeline connected to the gas supply unit, a silver source solution storage unit, a reducing agent solution storage unit, a silver source solution supply pipeline connecting the silver source solution storage unit and the high-pressure gas pipeline, a reducing agent solution supply pipeline connecting the reducing agent solution storage unit and the high-pressure gas pipeline, and an atomizing nozzle installed at the end of the high-pressure gas pipeline. The silver source solution storage unit stores the silver source solution, and the reducing agent solution storage unit stores the reducing agent solution. Under the siphoning action of the high-pressure inert gas, the silver source solution and the reducing agent solution are respectively siphoned from the silver source solution storage unit and the reducing agent solution storage unit into the high-pressure gas pipeline and mixed to form a reaction liquid. The reaction vessel includes a main component for synthesizing silver powder. The atomizing nozzle is disposed inside the reaction vessel to atomize the reaction liquid and form multiple micro-droplets inside the reaction vessel. Most of the micro-droplets react directly inside the reaction vessel to synthesize micro- and nano-silver particles, which then naturally settle to the bottom of the reaction vessel. The detection system includes a detection bend installed on the reaction vessel. Both ends of the detection bend are located inside the reaction vessel, with one end positioned near the atomizing nozzle, allowing a portion of the microdroplets to fall into the detection bend. The micro- and nano-silver particles synthesized within the microdroplets fall from the other end of the detection bend to the bottom of the reaction vessel. The detection bend also includes a transparent bend extending out of the reaction vessel, in which a micro- and nano-silver particle detection device is installed to monitor the changes in the microdroplets in real time.

[0010] Furthermore, the gas supply unit includes a low-temperature gas supply unit and a heating unit installed on the high-pressure gas pipeline. The low-temperature gas supply unit provides low-temperature inert gas, which expands and becomes the high-pressure inert gas after being heated by the heating unit. In this way, the silver source solution and the reducing agent solution are carried out and mixed by the siphon principle. The low-temperature inert gas expands and atomizes when heated, which promptly removes the heat of the oxidation-reduction reaction and helps to prevent the growth of silver grains caused by high temperature.

[0011] Furthermore, the reactor is a double-layer reactor, including an inner reactor for silver powder reaction and an outer reactor equipped with a cooling unit. The atomizing nozzle sprays the micro-droplets into the inner reactor. This configuration can keep the inner reactor at a low temperature, preventing the silver crystals generated by the reaction of the silver source and reducing agent from growing or agglomerating, which is beneficial for precise control of the morphology and particle size of the silver powder.

[0012] Furthermore, the preparation apparatus also includes an optical system, which can be used to control the crystallinity and morphology of micro / nano silver powder. The optical system includes a light source installed above the reactor. This allows for further study of the influence of the light source on the crystallinity and morphology of silver powder grains, thus broadening the applicability of the preparation apparatus.

[0013] Furthermore, the preparation apparatus also includes a computer-integrated integrated control system that controls the siphon mixing system, reaction vessel, detection system, and optical system. This integrated control system can adjust the process parameters for the synthesis of micro / nano silver powder based on the real-time feedback results of each controlled object.

[0014] A method for preparing micro / nano silver powder based on microdroplets, the method using the above-mentioned preparation apparatus to prepare silver powder, comprising: The gas supply unit is activated to provide high-pressure inert gas. The high-pressure inert gas uses a siphon effect to draw the silver source solution and reducing agent solution into the high-pressure gas pipeline, where they are mixed to form a reaction solution. The reaction liquid is atomized by the atomizing nozzle to form multiple micro-droplets sprayed into the reaction vessel. Most of the micro-droplets are synthesized into micro-nano silver particles in the reaction vessel and naturally settle to the bottom of the reaction vessel; another part of the micro-droplets fall into the detection bend tube, and the micro-nano silver particle detection device monitors the change process of the micro-droplets in real time. Based on the real-time monitoring results of the micro / nano silver particle detection device, the synthesis process parameters of micro / nano silver powder are adjusted in real time.

[0015] Furthermore, the step of forming the reaction liquid includes: first, introducing a low-temperature inert gas into a high-pressure gas pipeline, then heating the low-temperature inert gas to cause it to expand violently due to heat, forming a high-pressure inert gas in the high-pressure gas pipeline, which is then sprayed out through an atomizing nozzle; after the high-pressure inert gas is sprayed out, a negative pressure is formed in the high-pressure gas pipeline, which rapidly draws the silver source solution and reducing agent solution into the high-pressure gas pipeline through a siphon effect, and they mix to form the reaction liquid.

[0016] Furthermore, the above preparation method also includes: activating the light system to irradiate the microdroplets formed in the reaction vessel by atomization through the atomizing nozzle, so as to regulate the morphology and crystallinity of the micro-nano silver powder.

[0017] Furthermore, the step of adjusting the synthesis process parameters of micro / nano silver powder in real time includes: adjusting the heating temperature of the heating unit to control the particle size of the micro / nano silver powder; and / or The morphology of the micro / nano silver powder is synergistically controlled by the pH value of the reaction solution and the light source in the optical system.

[0018] Furthermore, the above preparation method also includes: after all the silver source solution and reducing agent solution have completely reacted, the temperature inside the reaction vessel is kept below 5°C by the cooling system; in order to avoid grain growth, and finally obtain silver powder with the target particle size and morphology.

[0019] Therefore, the above-mentioned apparatus and method for preparing micro / nano silver powder based on microdroplets provided by the present invention have the following characteristics: 1) Energy-saving and efficient: Through high-pressure gas rapid heating and siphon mixing, the liquid gas expands when heated, atomizing the mixture into tiny droplets, which react rapidly within the droplets. Compared with the traditional reaction stirring paddle synthesis for preparing nanopowder, this significantly shortens the reaction time and improves production efficiency.

[0020] 2) Flexible and Adjustable: An integrated control system is used to control the various functional systems in the above-mentioned preparation device. Process parameters can be adjusted in real time based on feedback data from each system, improving product consistency and quality. Especially when exploring the influence of various factors on the morphology and particle size of silver powder under synthesis conditions, continuous adjustment can be achieved. The law of influence on the morphology of silver powder under certain conditions can be quickly obtained in a single realization. This provides sufficient basis for exploring process windows and raw material selection, and scale-up of silver powder synthesis processes, shortening the exploration and research cycle.

[0021] 3) Avoiding Agglomeration: Traditional reaction vessels rely on mixing and stirring. Due to the continuous changes in solution concentration and the exothermic redox reaction, silver powder synthesis is prone to twinning and agglomeration. The preparation device and method provided by this invention utilize rapid mixing and reaction in the form of microdroplets. The reactant concentration within the microdroplets is relatively stable, thus facilitating the formation of better nanocrystals. Simultaneously, the low-temperature inert gas expansion absorbs heat, promptly removing the reaction heat and helping to prevent grain growth caused by high temperatures. Furthermore, the double-layer reaction vessel lowers the overall ambient temperature, and low-temperature control effectively prevents grain growth, making it particularly suitable for the preparation of nano-silver powder.

[0022] 4) Precise control: By combining light modulation and real-time detection systems, precise control of the particle size and morphology of silver powder can be achieved. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the usage state of the device for preparing micro- and nano-silver powder based on microdroplets provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the control relationships of each system in the apparatus for preparing micro- and nano-silver powder based on microdroplets provided in Embodiment 1 of the present invention. The component symbols in each diagram are as follows: 001-High-pressure gas pipeline; 002-Heating resistance wire; 031-Silver source solution supply pipeline; 032-Reducing agent solution supply pipeline; 004-Atomizing nozzle; 005-Reaction vessel; 006-Light source; 007-Microdroplets; 008-Waste liquid discharge port; 009-Precipitated silver powder; 010-Detection bend; A01-Low-temperature gas supply unit; A02-Heating unit; A03-Optical system; A04-Cooling system; A05-Detection system. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0025] All terms used in this invention are common terms in the relevant field. Unless otherwise specified, the raw materials, equipment, preparation processes, testing methods, etc., used are all prior art in the relevant field. The "inert gas" mentioned in this invention refers to a gas that does not undergo a chemical reaction with reaction liquids such as silver source solution or reducing agent solution.

[0026] In view of the many shortcomings of traditional silver powder preparation methods, this invention proposes a device and method for preparing micro / nano silver powder based on microdroplets. This device and method mainly utilizes low-temperature gas high-pressure expansion combined with siphon principle rapid atomization technology to form microdroplets containing a mixed silver source solution and a reducing agent solution. The silver source and reducing agent react within the microdroplets, unlike traditional microemulsion methods, achieving reaction within the same solvent. Furthermore, due to minimal concentration changes, rapid mixing and uniform reaction of the reactants are achieved. Simultaneously, real-time control of the optical system module and low-temperature control of the double-layer reactor effectively solve the problems of grain growth and agglomeration caused by high temperatures. In addition, combined with a detection system, and with the entire system controlled by an integrated control system, precise monitoring and real-time adjustment of the silver powder preparation process are achieved, thereby greatly improving the quality and production efficiency of the silver powder; especially, it can significantly shorten the research and development cycle in the laboratory stage. The specific implementation scheme provided by this invention is as follows.

[0027] Example 1 See Figure 1 and Figure 2 This invention provides an apparatus for preparing micro- and nano-silver powder based on microdroplets, including a siphon mixing system for mixing reactants to form a reaction solution, a reaction vessel 005 mainly used for synthesizing silver powder, and a detection system A05 for detecting the particle size and / or morphology of silver powder.

[0028] The siphon mixing system includes a gas supply unit, a high-pressure gas pipeline 001, a silver source solution supply pipeline 031, a reducing agent solution supply pipeline 032, a silver source solution storage unit 033, a reducing agent solution storage unit 034, and an atomizing nozzle 004. The gas supply unit primarily provides high-pressure inert gas capable of generating microdroplets. The front end of the high-pressure gas pipeline 001 is connected to the gas supply unit, and the atomizing nozzle 004 is installed at its end. The silver source solution storage unit 033 stores the silver source solution and is connected to the high-pressure gas pipeline 001 via the silver source solution supply pipeline 031. The reducing agent solution storage unit 034 stores the reducing agent solution and is connected to the high-pressure gas pipeline 001 via the reducing agent solution supply pipeline 032. The high-pressure inert gas in the high-pressure gas pipeline 001 uses a siphon principle to draw the silver source solution and reducing agent solution from the silver source solution storage unit 033 and the reducing agent solution storage unit 034 respectively into the high-pressure gas pipeline 001 for mixing, forming a reaction liquid.

[0029] In this embodiment, the gas supply unit includes a cryogenic gas supply unit A01 and a heating unit A02 installed on the high-pressure gas pipeline 001. The cryogenic gas supply unit A01 introduces cryogenic inert gas into the high-pressure gas pipeline 001. After being heated by the heating unit 001, the cryogenic inert gas expands and becomes the high-pressure inert gas. The high-pressure inert gas uses the siphon principle to draw out the silver source solution and reducing agent solution and mix them in the high-pressure gas pipeline 001. The cryogenic inert gas expands and atomizes upon heating, promptly carrying away some of the heat generated by the reaction of the reactants in the reaction liquid in the high-pressure gas pipeline 001, which helps prevent the growth of silver grains due to high temperature. The cryogenic inert gas is an inert gas such as liquid nitrogen or dry ice. The heating unit can be an electric heating unit, a microwave heating unit, an induction heating unit, etc., capable of quickly receiving control signals and adjusting in real time. Preferably, the heating unit is an electric heating unit. In this embodiment, the cryogenic inert gas is liquid nitrogen, and the heating unit is an electric heating unit, including an electric heating resistance wire 002 wound around the high-pressure gas pipeline 001.

[0030] The atomizing nozzle 004 is installed inside the reaction vessel 005 to rapidly mix and atomize the reaction liquid, forming multiple microdroplets 007. In each microdroplet 007, the silver source and reducing agent react to generate micro / nano silver particles. Most of the microdroplets 007 react directly within the reaction vessel to synthesize micro / nano silver particles and naturally settle to the bottom of the vessel; the remaining microdroplets 007 enter the detection system A05 to detect the particle size and morphology of the silver particles. The reaction of the silver source and reducing agent within the microdroplets achieves a reaction within the same solvent, and the small concentration change enables rapid mixing and uniform reaction of the reactants, which is beneficial for improving the quality of silver powder and production efficiency.

[0031] In this embodiment, the reactor 005 is a double-layer reactor, comprising an inner reactor layer for silver powder reaction and an outer reactor layer equipped with a cooling system A04. The microdroplets are mainly sprayed into the inner reactor layer. The cooling system A04 in reactor 005 keeps the inner reactor layer at a low temperature, preventing the silver crystals generated by the reaction of the silver source and reducing agent from growing or agglomerating, which is beneficial for precise control of the morphology and particle size of the silver powder. A waste liquid discharge port 008 is also provided at the bottom of the reactor for discharging the upper mixed clear liquid formed by natural sedimentation after the reaction is completed in the reactor.

[0032] The detection system A05 includes a detection bend 010 installed on the reaction vessel 005. A portion of the detection bend 010 extends beyond the reaction vessel 005, with both ends positioned within the inner layer of the reaction vessel. One end is positioned near the atomizing nozzle 004, allowing some microdroplets to fall naturally into the detection bend. The micro-nano silver particles synthesized within the microdroplets react in the detection bend and exit the reaction vessel, naturally settling to the bottom of the reaction vessel from the other end of the detection bend. A transparent bend is provided in the portion of the detection bend that extends beyond the reaction vessel and is exposed outside the reaction vessel. A micro-nano silver particle detection device is installed in the transparent bend to monitor the changes in the microdroplets passing through it in real time. Due to the extremely fast reaction rate of silver source reduction, not only the size of the microdroplets can be detected in the transparent bend, but also the particle size and morphology of the silver powder particles. Preferably, the micro-nano silver particle detection device includes at least one of an online particle size detection device and a photomicrograph. In this embodiment, the micro / nano silver particle detection device includes an online particle size detection device and a photomicrograph capture device, which can monitor the particle size of microdroplets, the particle size of micro / nano silver particles and their morphology in real time as they pass through a transparent curved tube.

[0033] The detection bend 010 can be S-shaped, U-shaped, or arc-shaped. In this embodiment, the detection bend 010 is an S-shaped transparent glass tube, which is beneficial for collecting microdroplets and minimizes the impact of the detection bend on the reaction inside the microdroplets; it also does not affect the influence of the light source on the growth of silver powder grains in the microdroplets.

[0034] In one specific embodiment, the apparatus for preparing micro / nano silver powder further includes an optical system A03 controlled by the integrated control system. The optical system A03 can be used to regulate the crystallinity and morphology of the silver powder particles, thereby further studying the influence of light on the growth and morphology of silver powder grains and broadening the applicability of the preparation apparatus. In this embodiment, the optical system A03 includes a lamp source 006 installed above the reactor. By controlling the wavelength and intensity of the light source, the morphology and particle size of the micro / nano silver powder are controlled. The lamp source 006 can be a xenon lamp, sodium lamp, etc. In this embodiment, the lamp source 006 is a xenon lamp with an emission power of 0–300 W.

[0035] Furthermore, the preparation apparatus also includes a computer-integrated integrated control system that controls the siphon mixing system, reaction vessel, detection system, and optical system. This integrated control system can adjust the synthesis process parameters of the micro / nano silver powder based on real-time feedback from each controlled object. Specifically, the particle size and morphology of the micro / nano silver powder are controlled by adjusting the concentrations of the silver source solution and reducing agent solution; the particle size and dispersibility of the micro / nano silver powder are controlled by adjusting the supply pressure of the high-pressure inert gas, thereby controlling the siphon reaction rate of the silver source solution and reducing agent solution and the size of the microdroplets; and the morphology of the micro / nano silver powder is controlled by adjusting the pH value of the reaction solution and the wavelength and intensity of the light source. Thus, the preparation apparatus can achieve continuous adjustment of conditions such as mixing speed, microdroplet size, reaction solution pH, and raw material concentration, optimizing the preparation process of the micro / nano silver powder.

[0036] It should be noted that the number of storage units or their connected supply pipes in the above-mentioned preparation device is at least two, but not limited to two; that is, it is not limited to silver source solution storage unit 033, reducing agent solution storage unit 034, silver source solution supply pipe 031, and reducing agent solution supply pipe 032. The specific number of storage units or their connected supply pipes is determined based on whether the composition of the silver source solution and the reducing agent solution includes all the raw materials required for silver powder synthesis. When the solute of the silver source solution is only silver source and the solute of the reducing agent solution is only reducing agent, the above-mentioned preparation device also needs to further provide storage units or their supply pipes for raw materials such as dispersant solution, pH adjuster solution, and additive solution required for silver powder synthesis, which are connected to high-pressure gas pipe 001. When the silver source solution and the reducing agent solution contain all the raw materials required for silver powder synthesis, the number of storage units or their connected supply pipes in the preparation device is two.

[0037] Example 2 Based on the preparation apparatus provided in Example 1, this example provides a method for preparing micro / nano silver powder based on microdroplets, including the following steps: The cryogenic gas supply unit A01 is activated to introduce cryogenic inert gas into the high-pressure gas pipeline 001; at the same time, the heating unit A02 is turned on, and the electric heating wire 002 heats the cryogenic inert gas in the pipeline. The cryogenic inert gas expands violently when heated to form high-pressure inert gas, which is then sprayed out through the atomizing nozzle 004. After the high-pressure inert gas is introduced, a negative pressure is created in the high-pressure gas pipeline 001. Through the siphon effect, the silver source solution and reducing agent solution connected to the high-pressure gas pipeline 001 are rapidly drawn into the high-pressure gas pipeline 001, mixed to form a reaction liquid, and then atomized through the atomizing nozzle 004 to form multiple micro-droplets 007 sprayed into the reaction vessel. The silver source and reducing agent in the micro-droplets 007 react to synthesize micro-nano silver particles; at the same time, the cooling system A04 of the reaction vessel is started to adjust the temperature inside the reaction vessel. Most of the microdroplets 007 are synthesized into micro / nano silver particles in the reactor and naturally settle to the bottom of the reactor to form micro / nano silver powder products; another part of the microdroplets fall into the detection bend 010, and the micro / nano silver particle detection device is used to monitor the particle size and morphology of the micro / nano silver particles that have passed through the transparent bend outside the reactor in real time; wherein, according to actual needs, if necessary, the light system A03 is activated and the lamp source 006 is adjusted to irradiate the microdroplets formed in the reactor; The integrated control system adjusts the parameters of each system in real time based on the detection data to optimize the preparation process of micro-nano silver powder products. After all the silver source and reducing agent have reacted, the low-temperature gas supply unit A01, the atomizing nozzle 004, and the micro / nano silver particle detection device are turned off, while the cooling system A04 is kept on continuously, so that the reaction vessel 005 is kept at a low temperature not higher than 5°C. Preferably, the temperature inside the reaction vessel does not exceed 0°C, to avoid the growth of micro / nano silver crystals, and finally obtain silver powder with the target particle size and morphology. This achieves precise control of the silver powder particle size and morphology, and also improves the accuracy of screening and optimizing process parameters using this method.

[0038] In one specific embodiment, to further explore the influence of various factors in the synthesis process conditions on the morphology and particle size of silver powder, the synthesis process parameters of the micro-nano silver powder are adjusted and repeated experiments are conducted based on the monitoring results of the micro-nano silver particle detection device until the synthesis process parameters of the micro-nano silver powder are finally determined. Specifically, the step of adjusting the synthesis process parameters of the micro-nano silver powder in real time includes: adjusting the heating temperature of the heating unit to control the particle size of the micro-nano silver powder; and / or controlling the morphology of the micro-nano silver powder in a coordinated manner by adjusting the pH value of the reaction solution and the wavelength and intensity of the light source.

[0039] Based on the feedback from the optical system to the integrated control system, when the particle size of the micro / nano silver powder is small, the heating temperature of the control heating unit is reduced, narrowing the temperature difference from liquid nitrogen to vaporization, and decreasing the gas expansion pressure, resulting in a larger micro-droplet size after spraying, thus increasing the particle size of the micro / nano silver powder. Conversely, when the particle size of the micro / nano silver powder is large, the heating temperature of the control heating unit is increased, widening the temperature difference from liquid nitrogen to vaporization, and increasing the gas expansion pressure, resulting in a smaller micro-droplet size after spraying, thus reducing the particle size of the micro / nano silver powder. The sphericity of the micro / nano silver powder can be achieved by adjusting the pH value of the reaction solution; for example, when the sphericity of the micro / nano silver powder is low, increasing the pH value of the reaction solution can obtain better sphericity; when the crystallinity of the micro / nano silver powder is low, decreasing the pH value of the reaction solution can increase the crystallinity of the silver powder. The wavelength and intensity (power) of the light source are adjusted to synergistically regulate the crystallinity and morphology of the silver powder grains. For example, when the micro / nano silver powder has a flake-like morphology, under the same power conditions, increasing the wavelength of the light source increases the size of the micro / nano silver flakes; decreasing the wavelength decreases the size. At the same wavelength, increasing the power increases the nucleation rate, resulting in smaller nanosheets; decreasing the power decreases the nucleation rate, resulting in larger nanosheets. When the micro / nano silver powder has a dendritic morphology, the pH of the reaction solution and the rate of addition of the silver source solution are adjusted.

[0040] Therefore, the method provided by this invention optimizes the preparation process of micro / nano silver powder by adjusting the parameters of each system in real time and enabling continuous adjustment of conditions such as mixing speed and microdroplet size control. This achieves several advantages: firstly, it allows for precise control of the particle size and morphology of the silver powder product, improving its consistency and quality; secondly, it enables continuous adjustment of the process parameters of each system, allowing for rapid determination of the influence of these conditions on the particle size and morphology of the silver powder in a single implementation, providing ample evidence for exploring process windows, selecting raw materials, and scaling up the silver powder synthesis process; and thirdly, it significantly shortens the research and development cycle in the laboratory stage.

[0041] The silver source solution and reducing agent solution described in this invention are both existing technologies, including a silver source, reducing agent, dispersant, pH adjuster, and additives. The silver source solution may include a silver source and a dispersant, and the reducing agent solution includes a reducing agent. The silver source can be silver nitrate, silver ammonia, or other substances. The dispersant can be polyvinylpyrrolidone (PVP-K15), PVP-K30, gum arabic, citric acid, hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, polyvinyl alcohol, gelatin, or other substances. The reducing agent can be ascorbic acid, formaldehyde, sodium borohydride, or other substances. The pH adjuster can be nitric acid, sodium hydroxide, sodium carbonate, sodium bicarbonate, sulfuric acid, or other substances used to adjust the pH value of the silver source solution and / or the reducing agent solution. The additives are mainly catalysts, and their addition is determined based on process requirements. Specifically, the composition and concentration of each component of the silver source solution and reducing agent solution can be determined based on process requirements and the number of raw material storage units in the aforementioned preparation apparatus.

[0042] In summary, the apparatus and method for preparing micro- and nano-silver powder based on microdroplets provided in this invention achieve rapid mixing and uniform reaction of reactants within microdroplets, thereby improving the efficiency of silver powder synthesis. Simultaneously, it enables real-time monitoring and adjustment of the micro- and nano-silver powder preparation process, achieving precise control over the particle size and morphology of the micro- and nano-silver powder. This is beneficial for improving the consistency and quality of silver powder products, and also facilitates the exploration of silver powder synthesis processes, shortening the research and development cycle in the early laboratory stage.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A device for preparing micro / nano silver powder based on microdroplets, characterized in that, include: A siphon mixing system includes a gas supply unit for providing high-pressure inert gas, a high-pressure gas pipeline connected to the gas supply unit, a silver source solution storage unit, a reducing agent solution storage unit, a silver source solution supply pipeline connecting the silver source solution storage unit and the high-pressure gas pipeline, a reducing agent solution supply pipeline connecting the reducing agent solution storage unit and the high-pressure gas pipeline, and an atomizing nozzle installed at the end of the high-pressure gas pipeline. The silver source solution storage unit stores the silver source solution, and the reducing agent solution storage unit stores the reducing agent solution. Under the siphoning action of the high-pressure inert gas, the silver source solution and the reducing agent solution are respectively siphoned from the silver source solution storage unit and the reducing agent solution storage unit into the high-pressure gas pipeline and mixed to form a reaction liquid. The reaction vessel includes a main component for synthesizing silver powder. The atomizing nozzle is disposed inside the reaction vessel to atomize the reaction liquid and form multiple micro-droplets inside the reaction vessel. Most of the micro-droplets react directly inside the reaction vessel to synthesize micro- and nano-silver particles, which then naturally settle to the bottom of the reaction vessel. The detection system includes a detection bend installed on the reaction vessel. Both ends of the detection bend are located inside the reaction vessel, with one end positioned near the atomizing nozzle, allowing a portion of the microdroplets to fall into the detection bend. The micro- and nano-silver particles synthesized within the microdroplets fall from the other end of the detection bend to the bottom of the reaction vessel. The detection bend also includes a transparent bend extending out of the reaction vessel, in which a micro- and nano-silver particle detection device is installed to monitor the changes in the microdroplets in real time.

2. The preparation apparatus according to claim 1, characterized in that, The gas supply unit includes a cryogenic gas supply unit and a heating unit installed on the high-pressure gas pipeline. The cryogenic gas supply unit provides cryogenic inert gas, which expands into the high-pressure inert gas after being heated by the heating unit.

3. The preparation apparatus according to claim 1, characterized in that, The reactor is a double-layer reactor, including an inner reactor for silver powder reaction and an outer reactor equipped with a cooling unit. The atomizing nozzle sprays the micro-droplets into the inner reactor.

4. The preparation apparatus according to any one of claims 1-3, characterized in that, The preparation apparatus further includes an optical system that can be used to control the crystallinity and morphology of micro / nano silver powder, the optical system including a light source installed above the inside of the reaction vessel.

5. The preparation apparatus according to claim 4, characterized in that, The preparation apparatus also includes an integrated control system, which is computer-integrated and can control the siphon mixing system, the reaction vessel, the detection system and the optical system. This integrated control system can adjust the process parameters for the synthesis of micro-nano silver powder based on the real-time feedback results of each controlled object.

6. A method for preparing micro- and nano-silver powder based on microdroplets, comprising the following steps: (The method describes the preparation apparatus according to any one of claims 1-5.) The gas supply unit is activated to provide high-pressure inert gas. The high-pressure inert gas uses a siphon effect to draw the silver source solution and reducing agent solution into the high-pressure gas pipeline, where they are mixed to form a reaction solution. The reaction liquid is atomized by the atomizing nozzle to form multiple micro-droplets sprayed into the reaction vessel. Most of the micro-droplets are synthesized into micro-nano silver particles in the reaction vessel and naturally settle to the bottom of the reaction vessel; another part of the micro-droplets fall into the detection bend tube, and the micro-nano silver particle detection device monitors the change process of the micro-droplets in real time. Based on the real-time monitoring results of the micro / nano silver particle detection device, the synthesis process parameters of micro / nano silver powder are adjusted in real time.

7. The preparation method according to claim 6, characterized in that, The steps for forming the reaction liquid include: first, introducing a low-temperature inert gas into a high-pressure gas pipeline, then heating the low-temperature inert gas to cause it to expand violently due to heat, forming a high-pressure inert gas in the high-pressure gas pipeline, which is then sprayed out through an atomizing nozzle; after the high-pressure inert gas is sprayed out, a negative pressure is formed in the high-pressure gas pipeline, which rapidly draws the silver source solution and reducing agent solution into the high-pressure gas pipeline through a siphon effect, and they mix to form the reaction liquid.

8. The preparation method according to claim 6 or 7, characterized in that, It also includes the step of: activating the light system to irradiate the microdroplets formed in the reaction vessel by atomization through the atomizing nozzle.

9. The preparation method according to claim 8, characterized in that, The steps of adjusting the synthesis process parameters of micro / nano silver powder in real time include: adjusting the heating temperature of the heating unit to control the particle size of the micro / nano silver powder; and / or The morphology of the micro / nano silver powder is synergistically controlled by the pH value of the reaction solution and the light source in the optical system.

10. The preparation method according to claim 6, 7, or 9, characterized in that, The process also includes the following steps: after all the silver source solution and reducing agent solution have completely reacted, the temperature inside the reactor is maintained at no more than 5°C by the cooling system until the waste liquid in the reactor is completely discharged.

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