High-dispersion metal powder preparation method and high-dispersion metal powder preparation device

Abstract

A high-dispersion metal powder preparation method, comprising: step (1) adding a base liquid into a synthetic reaction kettle (10), and performing internal and external circulation of the synthetic reaction kettle (10) by means of an external circulation dispersion device (20) connected to the synthetic reaction kettle (10) to achieve stable circulation; step (2) when the stable circulation meets preset requirements, continuously adding an oxidation liquid and a reduction liquid into the synthetic reaction kettle (10) to be mixed with the base liquid to form a reaction liquid, continuously forcedly dispersing the reaction liquid by means of the external circulation dispersion device (20), and feeding the dispersed reaction liquid into the synthetic reaction kettle (10); step (3) performing sampling analysis and testing in the synthesis reaction process, and when the particle size of metal powder generated in the synthesis reaction meets the requirements, stopping adding the oxidation liquid and the reduction liquid so as to stop the synthesis reaction; and step (4) discharging the reaction liquid from the synthetic reaction kettle (10), and then performing solid-liquid separation, cleaning, post-treatment and drying to obtain high-dispersion metal powder. The method can ensure that particles in the synthesis reaction kettle (10) are always in a monodispersed state for uniform growth, and the metal powder with high dispersion, narrow particle size distribution and high uniformity is obtained. Also involved is a high-dispersion metal powder preparation device (100).

Description

Highly dispersed metal powder preparation method and highly dispersed metal powder preparation device Technical Field

[0001] The disclosure of the present application relates to the technical field of synthetic metal powder, and in particular to a method for preparing highly dispersed metal powder and a device for preparing highly dispersed metal powder. Background Art

[0002] The dispersibility, particle size distribution, and uniformity of metal powders synthesized by chemical reduction have a decisive impact on their performance. The production equipment and synthesis process for metal powders influence the powder's morphology, dispersibility, and parameters such as particle size distribution and width, ultimately impacting its application performance. High-performance metal powders used in the photovoltaic industry must exhibit excellent dispersion, a concentrated particle size distribution, and high sphericity.

[0003] At present, the method for synthesizing and preparing metal powder by existing methods is to add an oxidizing solution, a reducing solution, a dispersing solution and other additives to a synthesis reactor under certain control conditions to carry out an oxidation-reduction reaction. During the reaction process, the uniformity of the reaction system is generally ensured by an agitator and / or other enhanced disperser on the synthesis reactor, but these stirring methods cannot completely guarantee the uniformity of the reaction solution, and the powder particle clusters that appear in the reaction system cannot be depolymerized in time. This results in the produced metal particles having poor dispersibility, low sphericity, excessive irregular powder, and a wide particle size distribution. Directly using the slurry prepared by this powder can easily cause problems such as poor printability, uneven lines, and poor electrical properties during the printing process. Various powder post-treatments need to be performed on this powder to achieve better application performance. Summary of the Invention

[0004] In order to solve the above-mentioned existing technical problems or part of them, the purpose of the present invention is to provide a method for preparing highly dispersed metal powder and a device for preparing highly dispersed metal powder, which controls the synthesis of highly dispersed, narrow particle size dispersion and highly uniform metal powder through a forced external circulation dispersion device with high dispersion function.

[0005] According to one aspect of the present invention, a method for preparing highly dispersed metal powder is provided, the method comprising the following steps:

[0006] Step (1) adding the bottom liquid into the synthesis reactor, and performing internal and external circulation of the synthesis reactor through an external circulation dispersion device connected to the synthesis reactor to achieve stable circulation;

[0007] Step (2) After the stable circulation meets the predetermined requirements, the oxidizing liquid and the reducing liquid are continuously added to the synthesis reaction kettle to mix with the bottom liquid to form a reaction liquid, and a synthesis reaction is carried out. During the synthesis reaction, the reaction liquid is continuously forced to disperse through the external circulation dispersion device and is fed into the synthesis reaction kettle;

[0008] Step (3) sampling, analyzing and testing during the synthesis reaction; when the particle size of the metal powder generated by the synthesis reaction meets the requirements, stopping the addition of the oxidizing solution and the reducing solution to stop the synthesis reaction;

[0009] Step (4) After the reaction liquid is discharged from the synthesis reactor, it is subjected to solid-liquid separation, cleaning, post-treatment, and drying to obtain highly dispersed metal powder.

[0010] According to another aspect of the present invention, there is provided a device for preparing highly dispersed metal powder using the above-mentioned method for preparing highly dispersed metal powder, comprising:

[0011] Synthesis reactor;

[0012] An external circulation dispersing device is connected to the pipeline of the synthesis reactor, and the bottom liquid or the reaction liquid is forcibly dispersed in the external circulation dispersing device;

[0013] The circulation device is connected to the synthesis reactor and the external circulation dispersion device pipeline respectively, so that the bottom liquid or the reaction liquid is continuously circulated in the highly dispersed metal powder preparation device.

[0014] The method and apparatus for preparing highly dispersed metal powder according to the embodiments of the present invention have at least one of the following advantages or part of one of the advantages:

[0015] 1. The present invention utilizes a method in which the reaction liquid is continuously fed into an external circulation dispersing device outside the synthesis reactor for efficient dispersion during the synthesis reaction. This allows metal powder that may have agglomerated in the synthesis reactor to be promptly dispersed, thereby resolving the drawback of ineffective and timely dispersion caused by using only the agitator of the synthesis reactor. The present invention ensures that the particles throughout the synthesis reactor remain in a monodispersed state and grow uniformly, thereby resolving the problem of uniform dispersion of the metal powder.

[0016] 2. While the oxidizing solution, reducing solution, and dispersing solution are added to the synthesis reactor for synthesis, the reaction solution is fed into an external circulation disperser equipped with an ultrasonic device and / or a shear disperser for high-dispersion performance, where it undergoes cyclic shear dispersion to complete the synthesis of highly dispersed and uniform metal powder. This method has good repeatability and strong operability. The metal powder produced by this method has the advantages of high dispersion, narrow particle size distribution, and high uniformity, overcoming the shortcomings of existing metal powders such as poor dispersibility, wide particle size distribution, and poor uniformity. It is suitable for use in conductive slurries, conductive adhesives, and other fields where high requirements are placed on the dispersibility, particle size distribution, and uniformity of metal powders.

[0017] 3. By utilizing the characteristics of the external circulation disperser, which is small in size and does not have dead corners during stirring, the agglomerated powder that is inevitably formed during the synthesis process in the large-scale synthesis reactor used for production due to the existence of dead corners in stirring is continuously and completely dispersed. In the present invention, the particles forcibly dispersed by the small external circulation disperser are continuously returned to the large-scale synthesis reactor to continue participating in the reaction until the particle size of the silver particles meets the requirements. During the reaction process, various reaction liquid parameters can be conveniently adjusted in the large-scale synthesis reactor.

[0018] 4. The silver particles formed after the mixed reaction of the oxidizing solution and the reducing solution will continue to participate in the next cycle of synthesis reaction as seeds. The newly generated silver particles will grow and adjust the microcrystalline morphology on the original silver particles. This cycle is repeated until the particle size of the silver powder reaches the required level. Using this method, in addition to controlling the silver powder particle size by adjusting the parameters of the oxidizing solution and the reducing solution during the synthesis of silver powder, the particle size and morphology of the silver powder can also be controlled by controlling the amount of silver source during the reaction cycle.

[0019] 5. In the present invention, a small disperser is used in conjunction with a large synthesis reactor to achieve large-scale production while reducing the amplification effect of production. The use of a small disperser is mainly to fully ensure the dispersion and particle size uniformity of the silver powder by utilizing its small size and the absence of a stirring dead angle.

[0020] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] These and / or other aspects and advantages of the present invention will become apparent and readily understood from the following description of the preferred embodiments taken in conjunction with the accompanying drawings, in which:

[0022] FIG1 is a flow chart of a method for preparing highly dispersed metal powder according to one embodiment of the present invention;

[0023] FIG2 is a schematic structural diagram of a device for preparing highly dispersed metal powder according to another embodiment of the present invention;

[0024] Figures 3 to 7 are scanning electron microscope images of silver powder prepared according to the method shown in Examples 1 to 5 of the present invention;

[0025] 8-9 are scanning electron microscope images of the silver powder prepared according to the method shown in Comparative Examples 1-2 of the present invention. DETAILED DESCRIPTION

[0026] The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall concept of the present invention and should not be construed as limiting the present invention.

[0027] 1 , which shows a flow chart of a method for preparing highly dispersed metal powder according to an embodiment of the present invention, as shown in the figure, the preparation method mainly includes the following four steps.

[0028] Specifically, the method for preparing highly dispersed metal powder comprises the following steps:

[0029] Step (1) adding the bottom liquid into the synthesis reactor, and performing internal and external circulation of the synthesis reactor through an external circulation dispersion device connected to the synthesis reactor to achieve stable circulation;

[0030] Step (2) After the stable circulation meets the predetermined requirements, the oxidizing liquid and the reducing liquid are continuously added to the synthesis reaction kettle to mix with the bottom liquid to form a reaction liquid, and a synthesis reaction is carried out. During the synthesis reaction, the reaction liquid is continuously forced to disperse through the external circulation dispersion device and is fed into the synthesis reaction kettle;

[0031] Step (3) sampling, analyzing and testing during the synthesis reaction; when the particle size of the metal powder generated by the synthesis reaction meets the requirements, stopping the addition of the oxidizing solution and the reducing solution to stop the synthesis reaction;

[0032] Step (4) After the reaction liquid is discharged from the synthesis reactor, it is subjected to solid-liquid separation, cleaning, post-treatment, and drying to obtain highly dispersed metal powder.

[0033] The term "high dispersion" as used herein refers to either of the following: one is that, when observed using a scanning electron microscope, there are essentially no more than two silver powder particles adhering together, and the silver powder particle size distribution is uniform; the other is measured by the particle size distribution width, which is measured by measuring the particle size D10, D50, and D90 on a laser diffraction particle size analyzer and then calculated as follows: Particle size distribution width = (D90-D10) / D50. A value below 1 indicates that the silver powder is essentially free of agglomeration, the silver powder particle size is uniform, and the silver powder dispersion is high, which is considered high dispersion. A value between 1 and 1.2 indicates relatively high dispersion, while a value greater than 1.2 indicates poor dispersion, uneven silver powder particle size, wide distribution, or severe silver powder agglomeration.

[0034] As discussed in the background of this invention, to at least partially address the technical problems identified, embodiments of the present invention utilize a method in which the reaction liquid is continuously fed into an external circulation dispersion device outside the synthesis reactor during the synthesis reaction for efficient dispersion. This allows metal powder that may have agglomerated within the synthesis reactor to be promptly dispersed, thereby addressing the drawbacks of using only the reactor's agitator. The technical solution of the present invention ensures that the particles throughout the synthesis reactor remain monodispersed and grow uniformly, thereby addressing the issue of uniform metal powder dispersion.

[0035] First, I will introduce the preparation of the base liquid (or dispersion liquid), oxidizing liquid, and reducing liquid, and will not introduce them in detail later.

[0036] 1. Preparation of the oxidizing solution: Add a certain amount or a predetermined amount of metal salt to a certain amount of pure water, stir and dissolve, and keep the temperature at 15°C-45°C. The metal salt in the oxidizing solution includes any one of oxalates, carbonates, sulfates, citrates, nitrates, metal oxides, and metal ammonia complexes, or any combination thereof. The concentration of the metal salt is 30g / L-300g / L, preferably 120g / L-240g / L. In one example, when preparing the oxidizing solution with silver nitrate, ammonia water can also be added to prepare it into a silver ammonia complex solution for use.

[0037] 2. Preparation of the reducing solution: Add a predetermined amount of reducing agent to a predetermined amount of pure water, stir to dissolve, and maintain the temperature at 15°C-45°C. The reducing agent in the reducing solution may include any one of hydrazine hydrate, formaldehyde, formic acid, ammonium formate, ascorbic acid, hydrogen peroxide, triethanolamine, glycerol, glucose, and hydroxylamine, or any combination thereof. The reducing agent concentration is 20g / L-200g / L, preferably 50g / L-150g / L.

[0038] 3. Preparation of the dispersion: Add a predetermined amount of dispersant to a predetermined amount of pure water, stir to dissolve, and maintain the temperature at 15°C-45°C. The dispersant in the dispersion can include one or any combination of polyvinyl alcohol, guar gum, arabic resin, polyvinyl pyrrolidone, fatty acid, copper nitrate, and magnesium nitrate. The concentration of the dispersant is 0g / L-500g / L, preferably 10g / L-100g / L.

[0039] The "post-treatment" mentioned here refers to coating the surface of the silver powder with a layer of organic matter to modify the surface of the powder. The organic matter can be one or a mixture of fatty acid salts, fatty acid amides, organic acids, fatty amines, fatty enamines, surfactants, and organosilicon compounds.

[0040] 2 , which shows a schematic structural diagram of a device for preparing highly dispersed metal powder according to an embodiment of the present invention.

[0041] The highly dispersed metal powder production apparatus 100 includes a synthesis reactor 10, an external circulation dispersion device 20, and a circulation device 30. The external circulation dispersion device 20 is connected to the synthesis reactor 10 through a pipeline, and forcibly disperses the base liquid or reaction liquid within the external circulation dispersion device 20. The circulation device 30 is connected to the synthesis reactor 10 and the external circulation dispersion device 20 through pipelines, respectively, to continuously circulate the base liquid or reaction liquid within the highly dispersed metal powder production apparatus 100. In one example, the circulation device 30 may be a circulation pump, etc.

[0042] As shown in FIG2 , the outlet of the synthesis reactor 10 is connected to a first pipeline 51 , which branches into two flow paths. The first flow path 52 of the two flow paths passes through a first valve 53 , a circulation device 30 , a second valve 54 , an external circulation dispersion device 20 in sequence and is connected to an inlet 55 of the synthesis reactor 10 via a second pipeline 59 .

[0043] A third valve 57 is provided on the second flow path 56 of the two flow paths to discharge the reaction liquid after the synthesis reaction is stopped from the synthesis reactor 10 to form the final product.

[0044] In one example, the external circulation dispersion device 20 includes at least one external circulation disperser 20, for example, one external circulation disperser 20 or multiple external circulation dispersers 20 connected in series. That is, in embodiments of the present invention, multiple external circulation dispersers 20 can be installed on the external piping of a synthesis reactor 10 to achieve a complete circulation of the reaction liquid in the synthesis reactor 10 within 1-10 minutes, that is, to achieve stable circulation.

[0045] To ensure adequate dispersion of the metal powder, at least one external circulation disperser 20 is connected in series outside the synthesis reactor 10. This external circulation disperser 20 provides adequate and efficient dispersion of the reaction liquid, allowing the metal powder in the reaction liquid to be promptly dispersed and deagglomerated, ensuring that the particles in the synthesis reactor grow in a monodisperse state.

[0046] The characteristic of the external circulation device 20 is to forcibly disperse the agglomerated powder in the reaction liquid in the device, mainly to disperse the agglomerated powder generated during the reaction to form a single particle state to participate in the next reaction.

[0047] The volume of the external circulation dispersing device 20 is smaller than the synthesis reactor 10. Usually, the volume of each external circulation disperser 20 is 2L-50L, preferably 5L-20L. The volume of the external circulation dispersing device 20 needs to be controlled within a certain range. If the volume of the external circulation dispersing device 20 is too large or too small, the reaction liquid will not achieve the ideal dispersion effect when passing through the external circulation dispersing device 20 due to its too large or too small volume, causing the metal powder to easily agglomerate. The volume ratio of the external circulation dispersing device 20 to the synthesis reactor 10 is 1:2000, preferably 1:500. Of course, those skilled in the art can also make a choice according to actual needs. In one embodiment, an ultrasonic device 40 is provided on the outer wall or inside of at least one external circulation disperser 20 of the external circulation dispersing device 20. Of course, a shearing disperser 40 can also be provided inside it.

[0048] When an ultrasonic device 40 or a shearing disperser 40 is provided, the bottom liquid is forcibly dispersed by the ultrasonic device 40 or the shearing disperser 40 on the external circulation disperser 20 and then returns to the reaction liquid system along the tangential direction of the inner wall of the synthesis reactor 10 through the outlet of the external circulation disperser 20.

[0049] It should be noted that the at least one external circulation disperser 20 can be a device that performs forced dispersion using any principle, without limitation. The ultrasonic device 40 can be configured as an ultrasonic dispersion rod, and the at least one external circulation disperser 20 with the shearing disperser 40 can be configured as a high-speed homogenizer. For example, the ultrasonic device 40 or the shearing disperser 40 can be configured as an integrated or separate unit and positioned at the center of the at least one external circulation disperser 20.

[0050] In order to further enhance the dispersion of the metal powder in the reaction solution in the at least one external circulation disperser 20, an ultrasonic device 40 is installed on the at least one external circulation disperser 20. When, for example, an ultrasonic vibration rod and / or a high-speed dispersion homogenizer is installed inside the at least one external circulation disperser 20, the distance d from the outer wall of the ultrasonic vibration rod and / or the high-speed dispersion homogenizer to the inner wall of the corresponding external circulation disperser 20 is 1-30 cm, preferably 2-10 cm.

[0051] In one example, the ultrasonic device 40 installed inside the at least one external circulation disperser 20 is in an elongated shape, such as an ultrasonic rod, and has an ultrasonic frequency of 20 kHz to 100 kHz, preferably 40 kHz to 80 kHz.

[0052] In addition, a high-speed dispersing homogenizer may be installed inside at least one external circulation disperser 20 , and the rotation speed of the high-speed dispersing homogenizer is 3000 rpm-5000 rpm.

[0053] When performing forced external circulation, a combination of ultrasonic waves and high-speed dispersing homogenizers can be used simultaneously to further achieve high dispersion of metal powder and concentrated distribution of particle size.

[0054] In one example, in order to ensure that the reaction solution is fully dispersed in at least one external circulation dispersing device 20, the shape of the external circulation disperser 20 or the dispersing device 20 is very important. The external circulation disperser 20 itself cannot have a dead angle, and its joints should be connected at a certain curvature to ensure that the reaction solution flows from bottom to top through the external circulation disperser in a piston-like manner without reflux. Therefore, the structure of the external circulation disperser 20 in the present invention is set to a (slender) cylindrical shape with a radian end cap at both ends and a polished interior, and is connected to the synthesis reactor 10 through a joint with a radian.

[0055] In the present invention, the metal powder has a spherical or quasi-spherical morphology. By adding an external circulation dispersion device 20, the forced dispersion effect ensures that the prepared metal powder has high dispersibility and uniformity. Furthermore, the metal powder prepared in the present invention has a narrow distribution width, with the particle size distribution width (D90 - D10 / D50) of the metal powder being less than 1.0. The metal powder includes powders of any one of silver, copper, tin, and nickel, or any combination thereof.

[0056] Characterization method of particle size distribution width: Test the particle size D10, D50, and D90 on a laser diffraction particle size analyzer, and then calculate according to the following formula:

[0057] Particle size distribution width = (D90-D10) / D50;

[0058] The smaller the particle size distribution width value, the better the dispersion and uniformity of the metal powder (such as silver powder); the larger the value, the worse the dispersion and uniformity of the silver powder.

[0059] Returning to the method for preparing highly dispersed metal powder of the present invention, after the above operations reach the required stability, the oxidizing liquid and the reducing liquid are added to the synthesis reactor 10 for the synthesis reaction. During the entire synthesis reaction, the reaction liquid is continuously fed into the external circulation disperser 20 by the circulation pump 30 at the bottom of the synthesis reactor 10 for strong dispersion without dead angles and without distinction, and then fed back into the synthesis reactor 10 for the synthesis reaction. Sampling, analysis and testing are carried out during the reaction. When the particle size of the metal powder meets the requirements, the addition of the oxidizing liquid and the reducing liquid is stopped to stop the synthesis reaction. Finally, after the synthesis reaction liquid is discharged from the synthesis reactor 10, it undergoes solid-liquid separation, cleaning, post-treatment, drying and other processes to obtain a highly dispersed metal powder.

[0060] It should be noted that the reaction liquid is also fed into the external circulation disperser 20 in a plug flow state for forced dispersion.

[0061] The method and apparatus for preparing highly dispersed metal powder of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0062] Example 1

[0063] 1. Add 800g of silver nitrate to 5000g of pure water at 15℃-45℃, stir and dissolve to prepare the oxidizing solution;

[0064] 2. Add 600 g of ascorbic acid to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a reducing solution;

[0065] 3. Add 100 g of polyvinyl pyrrolidone to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a dispersion.

[0066] 4. Add the dispersion as the reaction liquid (base liquid) into the synthesis reactor 10 and start the agitator 11 in the synthesis reactor 10.

[0067] 5. The reaction solution was forced through the external circulation disperser 20 by a circulation pump 30 for internal and external circulation. The external circulation disperser 20 had a capacity of 5 L. An ultrasonic vibrating rod 40 was installed in the external circulation disperser 20. The frequency of the ultrasonic vibrating rod 40 was adjusted to 20 kHz and the power was 2000 W. The distance d between the ultrasonic vibrating rod 40 and the inner wall of the external circulation disperser 20 was 3 cm. The flow rate was adjusted so that the base liquid flowed from bottom to top in the external circulation disperser 20 in a plug flow state and completed one cycle within 2 minutes.

[0068] 6. The oxidizing and reducing liquids are dropwise added to the synthesis reactor 10 for a synthesis reaction. The oxidizing and reducing liquids are continuously fed into the external circulation disperser 20 in a plug flow state for forced dispersion, and then recirculated back into the synthesis reactor 10 for reaction. Sampling, analysis, and testing are performed during the reaction. When the metal powder particle size reaches the required level, the dropwise addition is stopped. Stirring and circulation are continued for 10 minutes, and the reaction is terminated. The resulting reaction liquid is subjected to solid-liquid separation, cleaning, post-treatment, and drying to obtain a highly dispersed, narrowly distributed, and uniform silver powder with a D50 of 1.48 μm and a silver powder distribution width of 0.73.

[0069] The particle size and particle size distribution of the silver powder prepared in Example 1 are shown in Table 1.

[0070] The scanning electron microscope image of the silver powder prepared in Example 1 is shown in FIG3 . The silver powder is substantially spherical in shape and has the characteristics of uniform morphology, excellent dispersibility, and high crystallinity.

[0071] Example 2

[0072] 1. Add 800g of silver nitrate to 5000g of pure water at 15℃-45℃, stir and dissolve to prepare an oxidizing solution;

[0073] 2. Add 600 g of ascorbic acid to 5000 g of pure water at 15-45 ° C, stir and dissolve to obtain a reducing solution;

[0074] 3. Add 50 g of polyvinyl alcohol and 50 g of fatty acid salt to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a dispersion.

[0075] 4. The subsequent reaction steps are the same as those in Example 1. Example 2 The frequency of the ultrasonic vibration rod 40 is adjusted to 40 kHz.

[0076] 5. The D50 of the prepared silver powder is 1.46 μm and the distribution width of the silver powder is 0.88, so it is a highly dispersed, narrowly distributed and uniform silver powder.

[0077] The particle size and particle size distribution of the silver powder prepared in Example 2 of the present invention are shown in Table 1.

[0078] The scanning electron microscope image of the silver powder prepared in Example 2 of the present invention is shown in FIG4 . The silver powder is spherical, has a uniform morphology, good dispersion, no agglomeration, and high crystallinity.

[0079] Example 3

[0080] 1. Add 1000g of silver nitrate to 5000g of pure water at 15℃-45℃, stir and dissolve to prepare the oxidizing solution;

[0081] 2. Add 700g of ammonium formate to 5000g of pure water at 15℃-45℃, stir and dissolve to obtain a reducing solution;

[0082] 3. Add 150 g of polyvinyl pyrrolidone to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a dispersion.

[0083] 4. The subsequent reaction steps are the same as those in Example 1, except that the base liquid completes one cycle in 2 minutes through the circulating disperser 20, and the frequency of the ultrasonic vibrating rod 40 is adjusted to 60 kHz.

[0084] 5. The D50 of the prepared silver powder is 1.58um, and the distribution width of the silver powder is 0.91.

[0085] The particle size and particle size distribution of the silver powder prepared in Example 3 of the present invention are shown in Table 1.

[0086] The scanning electron microscope image of the silver powder prepared in Example 3 of the present invention is shown in FIG5 . The silver powder is spherical in shape and has the characteristics of relatively uniform morphology, excellent dispersibility, no agglomeration, and high crystallinity.

[0087] Example 4

[0088] 1. Add 2.4 kg of silver nitrate to 15 kg of pure water at 15-45 ° C, stir and dissolve to prepare an oxidizing solution;

[0089] 2. Add 15 kg of hydrazine hydrate to 15 kg of pure water at 15°C-45°C, stir and dissolve to obtain a reducing solution;

[0090] 3. Add 150g of PVPK30 to 5kg of pure water at 15℃-45℃ and stir to dissolve to obtain a dispersion.

[0091] 4. Subsequent reaction steps were the same as in Example 1. The external circulation disperser 20 was replaced with a high-speed homogenizer. The distance d between the outer edge of the high-speed homogenizer's dispersing head and the inner wall of the external circulation disperser was 5 cm, and the high-speed homogenizer speed was 4000 rpm. The base liquid completed one cycle through the external circulation disperser 20 within 2 minutes.

[0092] 5. The D50 of the prepared silver powder is 1.56 μm, and the distribution width of the silver powder is 0.88.

[0093] The particle size and particle size distribution of the silver powder prepared in Example 4 of the present invention are shown in Table 1.

[0094] The scanning electron microscope image of the silver powder prepared in Example 4 of the present invention is shown in FIG6 . The silver powder is spherical, has a relatively uniform morphology, good dispersion, no agglomeration, and high crystallinity.

[0095] Example 5

[0096] 1. Add 800g of silver nitrate to 5000g of pure water at 15℃-45℃, stir and dissolve to prepare an oxidizing solution;

[0097] 2. Add 500 g of ascorbic acid to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a reducing solution;

[0098] 3. Add 100 g of polyvinyl pyrrolidone to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a dispersion.

[0099] 4. The subsequent reaction steps were the same as in Example 1. The external circulation disperser 20 was replaced with a high-speed homogenizer. The distance d between the outer edge of the high-speed homogenizer's dispersing head and the inner wall of the external circulation disperser container was 3 cm. The high-speed homogenizer's speed was 3500 rpm. The base liquid completed one cycle through the external circulation disperser 20 in 1 minute.

[0100] 5. The D50 of the prepared silver powder is 1.57 μm and the distribution width of the silver powder is 0.9.

[0101] The particle size and particle size distribution of the silver powder prepared in Example 5 of the present invention are shown in Table 1.

[0102] The scanning electron microscope image of the silver powder prepared in Example 5 of the present invention is shown in FIG7 . The silver powder is spherical, has a relatively uniform morphology, good dispersion, no agglomeration, and high crystallinity.

[0103] Comparative Example 1

[0104] 1. Add 800g of silver nitrate to 5000g of pure water at 15℃-45℃, stir and dissolve to prepare the oxidizing solution;

[0105] 2. Add 600 g of ascorbic acid to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a reducing solution;

[0106] 3. Add 100 g of polyvinyl alcohol to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a dispersion.

[0107] 4. Close valves 53 and 57 and do not perform forced external circulation. While stirring, add the dispersion to the synthesis reactor 10, then add the oxidizing solution and reducing solution. After the reaction is complete, stop adding the oxidizing solution and reducing solution. Finally, after the synthesis reaction liquid undergoes solid-liquid separation, cleaning, post-treatment, and drying, a D50 of 1.61 μm is obtained. The distribution width of the silver powder is calculated as 1.11 using the formula (D90-D10) / D50, indicating poor dispersion and a wide particle size distribution of silver powder.

[0108] The particle size and particle size distribution of the silver powder prepared in Comparative Example 1 are shown in Table 1.

[0109] The scanning electron microscope image of the silver powder prepared in Comparative Example 1 is shown in FIG8 . The silver powder has irregular and spherical morphologies, poor dispersibility, and severe agglomeration.

[0110] Comparative Example 2

[0111] 1. Add 800g of silver nitrate to 5000g of pure water at 15℃-45℃, stir and dissolve to prepare the oxidizing solution;

[0112] 2. Add 300 g of hydrazine hydrate to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a reducing solution;

[0113] 3. Add 200 g of polyvinyl pyrrolidone to 5000 g of pure water at 15°C-45°C, stir and dissolve to obtain a dispersion.

[0114] 4. Close valves 53 and 57 and do not perform forced external circulation. While stirring, add the dispersion to the synthesis reaction kettle, then add the oxidizing solution and reducing solution. After the reaction is complete, stop adding the oxidizing solution and reducing solution. Finally, after the synthesis reaction liquid undergoes solid-liquid separation, cleaning, post-treatment, and drying, a D50 of 1.45 μm is obtained. The distribution width of the silver powder is calculated as 1.08 using the formula (D90-D10) / D50, indicating poor dispersion and a wide particle size distribution of silver powder.

[0115] The particle size and particle size distribution of the silver powder prepared in Comparative Example 2 are shown in Table 1.

[0116] The scanning electron microscope image of the silver powder prepared in Comparative Example 2 is shown in FIG9 . The silver powder has an irregular, spherical shape, poor dispersibility, and severe agglomeration.

[0117] Table 1 Comparison of the results of Examples 1-5 and Comparative Examples 1-2

[0118] The silver powders of Examples 1-5 and Comparative Examples 1 and 2 were prepared into slurries using the same method and tested using the same method. The results are shown in Table 2. The data show that the silver powders of Examples 1-5, due to the forced dispersion of the silver powder into the reaction solution without blind spots or discrimination during the synthesis process, broke up the soft agglomerated silver powder produced during the synthesis process. The resulting silver powders were well-dispersed and had a narrow particle size distribution. The slurries prepared from the silver powders had low viscosity and excellent resistivity, generally around 2.8 Ω.cm. In contrast, the slurries prepared from silver powders synthesized without the forced external circulation dispersion device had relatively high viscosity and a resistivity exceeding 3.5 Ω.cm, representing a resistivity increase of approximately 30% compared to the silver powders prepared using the forced external circulation dispersion device.

[0119] Table 2 Comparison of slurry performance data of implementation results

[0120] The method and apparatus for preparing highly dispersed metal powder according to the embodiments of the present invention have at least one of the following advantages or part of one of the advantages:

[0121] 1. The present invention utilizes a method in which the reaction liquid is continuously fed into an external circulation dispersing device outside the synthesis reactor for efficient dispersion during the synthesis reaction. This allows metal powder that may have agglomerated in the synthesis reactor to be promptly dispersed, thereby resolving the problem of inability to effectively and timely achieve dispersion using only the agitator of the synthesis reactor. The present invention ensures that the particles throughout the synthesis reactor remain in a monodispersed state and grow uniformly, thereby resolving the problem of uniform dispersion of the metal powder.

[0122] 2. While the oxidizing solution, reducing solution, and dispersing solution are added to the synthesis reactor for synthesis, the reaction solution is fed into an external circulation disperser equipped with an ultrasonic device and / or a shear disperser for high-dispersion function, where it undergoes cyclic shear dispersion to complete the synthesis of highly dispersed and uniform metal powder. This method has good repeatability and strong operability. The metal powder produced by this method has the advantages of high dispersion, narrow particle size distribution, and high uniformity, overcoming the shortcomings of existing metal powders such as poor dispersibility, wide particle size distribution, and poor uniformity. It is suitable for use in conductive slurries, conductive adhesives, and other fields where high requirements are placed on the dispersibility, particle size distribution, and uniformity of metal powders.

[0123] 3. By utilizing the characteristics of the external circulation disperser, which is small in size and does not have dead corners during stirring, the agglomerated powder that is inevitably formed during the synthesis process in the large-scale synthesis reactor used for production due to the existence of dead corners in stirring is continuously and completely dispersed. In the present invention, the particles forcibly dispersed by the small external circulation disperser are continuously returned to the large-scale synthesis reactor to continue participating in the reaction until the particle size of the silver particles meets the requirements. During the reaction process, various reaction liquid parameters can be conveniently adjusted in the large-scale synthesis reactor.

[0124] 4. The silver particles formed after the mixed reaction of the oxidizing solution and the reducing solution will continue to participate in the next cycle of synthesis reaction as seeds. The newly generated silver particles will grow and adjust the microcrystalline morphology on the original silver particles. This cycle is repeated until the particle size of the silver powder reaches the required level. Using this method, in addition to controlling the silver powder particle size by adjusting the parameters of the oxidizing solution and the reducing solution during the synthesis of silver powder, the particle size and morphology of the silver powder can also be controlled by controlling the amount of silver source during the reaction cycle.

[0125] 5. In the present invention, a small disperser is used in conjunction with a large synthesis reactor to achieve large-scale production while reducing the amplification effect of production. The use of a small disperser is mainly to fully ensure the dispersion and particle size uniformity of the silver powder by utilizing its small size and the absence of a stirring dead angle.

[0126] The foregoing description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the foregoing embodiment. Persons skilled in the art will appreciate that modifications may be made to these embodiments without departing from the principles and spirit of the overall concept of the present invention, and such modifications should be considered to fall within the scope of protection of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing highly dispersed metal powder, comprising the following steps: Step (1) adding a bottom liquid into a synthesis reactor, and performing internal and external circulation of the synthesis reactor through an external circulation dispersion device connected to the synthesis reactor to achieve a stable circulation, wherein the bottom liquid enters the external circulation dispersion device from bottom to top in a plug flow state, is forcibly dispersed by the external circulation dispersion device, and then flows into the synthesis reactor along a tangential direction of the reactor wall of the synthesis reactor to achieve a stable circulation; Step (2) After the stable circulation meets the predetermined requirements, the oxidizing liquid and the reducing liquid are continuously added to the synthesis reactor to mix with the bottom liquid to form a reaction liquid, and a synthesis reaction is carried out. During the synthesis reaction, the reaction liquid is continuously forced to disperse through the external circulation dispersion device and fed into the synthesis reactor, wherein an ultrasonic device is provided on the outer wall or inside of at least one external circulation disperser in the external circulation dispersion device and / or a shear disperser is provided inside of at least one external circulation disperser in the external circulation dispersion device. The volume ratio of the external circulation dispersion device to the synthesis reactor is 1:2000-1:500, and the external circulation dispersion device ensures that the reaction liquid flows from bottom to top through the external circulation disperser in a piston-like manner without backflow. Step (3) sampling, analyzing and testing during the synthesis reaction; when the particle size of the metal powder generated by the synthesis reaction meets the requirements, stopping the addition of the oxidizing solution and the reducing solution to stop the synthesis reaction; Step (4) After the reaction liquid is discharged from the synthesis reactor, it is subjected to solid-liquid separation, cleaning, post-treatment, and drying to obtain highly dispersed metal powder.

2. The method for preparing highly dispersed metal powder according to claim 1, wherein: The bottom liquid continuously circulates between the synthesis reactor and the external circulation dispersion device and completes one cycle within a period of 1-10 minutes to achieve stable circulation.

3. The method for preparing highly dispersed metal powder according to claim 2, wherein: The external circulation dispersion device and the synthesis reactor are connected in series via a pipeline; The volume of the at least one external circulation disperser is 2-50L.

4. The method for preparing highly dispersed metal powder according to claim 3, characterized in that: The at least one external circulation disperser is cylindrical with curved ends at both ends and a polished interior, and is connected to the synthesis reactor pipeline via a curved joint.

5. The method for preparing highly dispersed metal powder according to claim 4, characterized in that: When the ultrasonic device is arranged in the at least one external circulation disperser, the distance from the outer wall of the ultrasonic device to the inner wall of the at least one external circulation disperser is in the range of 1-30 cm, and the ultrasonic frequency of the ultrasonic device is in the range of 20-100 kHz.

6. The method for preparing highly dispersed metal powder according to claim 4, characterized in that: When the shearing disperser is arranged in the at least one external circulation disperser, the distance from the outer wall of the shearing disperser to the inner wall of the at least one external circulation disperser is in the range of 1-30 cm.

7. The method for preparing highly dispersed metal powder according to claim 5 or 6, characterized in that: The distance between the outer wall of the ultrasonic device or the shear disperser and the inner wall of the at least one external circulation disperser is in the range of 2-10 cm; The ultrasonic frequency of the ultrasonic device is in the range of 40-80kHz; The rotation speed of the shearing disperser ranges from 3000 to 5000 rpm.

8. The method for preparing highly dispersed metal powder according to claim 7, characterized in that: The metal powder has a spherical or quasi-spherical shape; The particle size distribution width of the metal powder is less than 1.0; The metal powder includes powder of any one of silver, copper, tin and nickel or any combination thereof.

9. The method for preparing highly dispersed metal powder according to claim 1, wherein: The base liquid is pure water or a dispersion liquid, the dispersion liquid is an aqueous solution containing any one of polyvinyl alcohol, guar gum, arabic resin, polyvinyl pyrrolidone, fatty acid, copper nitrate, magnesium nitrate, or any combination thereof, and the concentration of the dispersion liquid is 10-100 g / L; Preparation of the oxidizing solution: add the metal salt into pure water, stir and dissolve, and keep the temperature at 15℃-45℃. The metal salt in the oxidizing solution includes any one of oxalate, carbonate, sulfate, citrate, nitrate, metal oxide, and metal ammonia complex, or any combination thereof, and the concentration of the metal salt is 30-300 g / L. When the metal salt is silver nitrate, the oxidizing solution is a silver ammonia complex solution prepared by adding ammonia water to silver nitrate. The reducing solution is prepared by adding a reducing agent into pure water, stirring and dissolving the reducing agent, and maintaining the temperature at 15° C.-45° C. The reducing agent includes any one of hydrazine hydrate, formaldehyde, formic acid, ammonium formate, ascorbic acid, hydrogen peroxide, triethanolamine, glycerol, glucose, and hydroxylamine, or any combination thereof, and the concentration of the reducing agent is 20-200 g / L.

10. A device for preparing highly dispersed metal powder using the method for preparing highly dispersed metal powder according to any one of claims 1 to 9, comprising: Synthesis reactor; An external circulation dispersing device, the external circulation dispersing device is connected to the synthesis reactor pipeline, the bottom liquid or the reaction liquid is forcibly dispersed in the external circulation dispersing device, and the volume ratio of the external circulation dispersing device to the synthesis reactor is 1:2000-1:500; A circulation device, the circulation device being connected to the synthesis reactor and the external circulation dispersion device pipeline respectively, so that the bottom liquid or the reaction liquid is continuously circulated in the highly dispersed metal powder preparation device; The external circulation dispersion device includes at least one external circulation disperser, an ultrasonic device or a shearing disperser is arranged inside the at least one external circulation disperser, the distance from the outer wall of the ultrasonic device or the shearing disperser to the inner wall of the at least one external circulation disperser is in the range of 1-30 cm, the ultrasonic frequency of the ultrasonic device is in the range of 40-80 kHz, and the rotation speed of the shearing disperser is in the range of 3000-5000 rpm.

11. The device for preparing highly dispersed metal powder according to claim 10, characterized in that: The at least one external circulation disperser is cylindrical with curved ends at both ends and a polished interior, and is connected to the synthesis reactor pipeline via a curved joint.

12. The device for preparing highly dispersed metal powder according to claim 11, characterized in that: The outlet of the synthesis reactor is connected to a first pipeline, the first pipeline is branched into two flow paths, the first flow path of the two flow paths passes through a first valve, a circulation device, a second valve, the external circulation dispersion device in sequence and is connected to the inlet of the synthesis reactor; A third valve is provided on the second flow path of the two flow paths to discharge the reaction liquid after the synthesis reaction is stopped.

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