Dendritic silver powder and method for producing the same

Abstract

The application provides dendritic silver powder and a preparation method thereof, and belongs to the technical field of metal powder preparation. First, a reducing agent solution is used as a bottom liquid, then the bottom liquid is heated and kept in a constant temperature state, at the same time, an ultrasonic device is started, then, under stirring, silver nitrate solution is quickly added to the bottom liquid by using a micro-pressure feeding mode, after the reaction is completed, a dispersing agent is directly added to the system, finally, after cleaning, drying and depolymerization processes, the target product dendritic silver powder is obtained. The preparation method has the advantages of simple process, fast reaction rate and low raw material cost, and can realize continuous production, and has good application prospect in the industrial field. The dendritic silver powder prepared by the application has small particle size and uniform dendritic structure, has good conductivity, sintering density and dispersibility, and meets the high-end requirements of flexible optoelectronic devices.

Description

Technical Field

[0001] This invention relates to the field of metal powder and its preparation technology, and in particular to a dendritic silver powder and its preparation method. Background Technology

[0002] Dendritic silver powder, as a core material for conductive functional phases, is widely used in high-end electronic fields such as flexible optoelectronic devices, thin-film solar cells, and touch screens. These devices place dual core requirements on electrode materials: in terms of electrical performance, they must possess both low surface resistivity and excellent vertical conductivity to achieve good ohmic contact with the transparent conductive film (TCF); in terms of mechanical performance, they must have high flexibility and bending resistance to ensure stable conductivity without fluctuations during device bending. Meanwhile, the printability, sintering density, and cost control of the electronic paste are also key considerations for industrial applications.

[0003] In the prior art, patent CN1369341A discloses a dendritic ultrafine silver powder and its preparation method. Although the silver powder obtained by this patent has excellent antibacterial properties and can be extended to some special conductive scenarios, it relies on copper powder replacement reaction for preparation, and the purity is difficult to guarantee. Moreover, the agglomeration size (1~10μm) does not match the dendrite size (40~300nm), resulting in insufficient continuity of the conductive network and failing to meet the requirements of high-end pastes for conductivity stability. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a dendritic silver powder and its preparation method, aiming to solve the problems of complex reaction conditions, low purity of silver powder and uneven dendritic structure in the preparation of existing dendritic silver powder.

[0005] In a first aspect, this application provides a method for preparing dendritic silver powder, comprising the following steps:

[0006] S1. Dissolve the reducing agent in deionized water to prepare the base solution;

[0007] S2. Dissolve silver nitrate in deionized water to prepare a silver nitrate solution;

[0008] S3. Heat the base liquid to a predetermined temperature and maintain it at a constant temperature. Under ultrasonic and stirring conditions, add silver nitrate solution by micro-pressure feeding. After the reaction is completed, add dispersant to obtain a silver powder mixed solution.

[0009] S4. Filter the silver powder mixture solution, wash, dry, and depolymerize to obtain the target silver powder.

[0010] In the technical solution of this application embodiment, a reducing agent solution is used as the base liquid. The base liquid is then heated and maintained at a constant temperature while an ultrasonic device is activated. Next, under stirring, a silver nitrate solution is added to the base liquid using a micro-pressure feeding method. After the reaction is complete, a dispersant is directly added to the system. Finally, after washing, drying, and depolymerization processes, the target product, dendritic silver powder, is obtained. This preparation method has the advantages of simple process, fast reaction rate, and low raw material cost, and can achieve continuous production, showing good application prospects in the industrial field.

[0011] In some embodiments, in step S1, the reducing agent is one or more of sodium citrate, sodium borohydride, formaldehyde, ascorbic acid, hydrazine hydrate, sodium gluconate, and sodium carbonate; the mass ratio of the reducing agent to silver nitrate is 2:1 to 1:2.

[0012] In this embodiment, silver powder with dendritic morphology and good dispersibility is obtained by adding a specific proportion of silver nitrate solution to the reducing agent solution.

[0013] In some embodiments, in step S3, the power of the ultrasound is 5~60W.

[0014] In this embodiment, ultrasonic treatment is used to enhance the mass transfer efficiency of the reaction system, ensuring reaction uniformity and the formation of dendritic silver powder.

[0015] In some embodiments, in step S3, the pressure during micro-pressure feeding is 0.1~5MPa.

[0016] In this embodiment, the addition rate of silver nitrate solution can be precisely controlled by micro-pressure feeding, avoiding abnormal product morphology caused by excessively high local concentrations. In addition, micro-pressure is a type of spraying, delivering only nanoliter-microliter levels of silver nitrate solution to the base liquid per unit time. This results in a discrete point contact state between the silver nitrate solution and the reaction base liquid. This contact form can maximize the reduction of the diffusion gradient of silver nitrate in the base liquid, ensuring that silver ions are evenly distributed in the base liquid and grow in a directional manner according to the thermodynamic laws of dendrite growth, thereby ensuring the stable formation and morphological uniformity of the dendritic structure.

[0017] In some embodiments, in step S3, the predetermined temperature is 20~40°C.

[0018] In this embodiment, the temperature range can match the diffusion rate and reduction reaction rate of silver ions under micro-pressure injection feeding, further helping to maintain the regularity of the dendritic structure.

[0019] In some embodiments, in step S3, the dispersant is one or more of polyvinylpyrrolidone, arachidic acid, potassium stearate, stearic acid, oleic acid, potassium oleate, ricinoleate, palmitic acid, and glycerol; the mass ratio of the dispersant to silver nitrate is 0.0005:1 to 0.005:1.

[0020] In this embodiment, by selecting the above-mentioned specific type of dispersant and limiting its mass ratio with silver nitrate, the growth process of dendritic silver powder can be precisely controlled.

[0021] Secondly, this application provides a dendritic silver powder, which is prepared by the above-mentioned method for preparing dendritic silver powder, wherein the particle size of the dendritic silver powder is 1~20μm and the dendrite length is <5μm.

[0022] In the technical solution of this application embodiment, the silver powder obtained has a small particle size and low sintering shrinkage rate; the dendritic structure and agglomeration size are matched and uniform, the contact effect between silver powder particles is good, and the sintering activity and conductivity are good. Attached Figure Description

[0023] Figure 1 This is a SEM image of the silver powder prepared in Example 1 of this application.

[0024] Figure 2 This is a SEM image of the silver powder prepared in Comparative Example 7 of this application. Detailed Implementation

[0025] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0026] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0027] To address the problems of complex reaction conditions, low purity, and uneven dendritic structure in existing silver powder preparation methods, this application provides a dendritic silver powder and its preparation method. A reducing agent solution is used as the base liquid. The base liquid is then heated and maintained at a constant temperature while an ultrasonic device is activated. Next, under stirring, a silver nitrate solution is added to the base liquid using a micro-pressure feeding method. After the reaction is complete, a dispersant is directly added to the system. Finally, after washing, drying, and depolymerization processes, the target product, dendritic silver powder, is obtained. This invention employs a dual process combining ultrasonic assistance and micro-pressure feeding during the reaction. A micro-pressure jetting device injects silver nitrate solution into the reducing agent substrate in a micron-level jet stream, injecting only nanoliters to microliters of solution per unit time. This creates a discrete point-contact reaction interface, precisely controlling the silver ion release rate and preventing excessively high local concentrations, thus initially generating uniform small-particle silver powder. Stirring facilitates rapid detachment of the silver powder from the reaction interface, preventing localized accumulation. Furthermore, the energy provided by ultrasound accelerates the uniform dispersion of small-particle silver powder within the system through micro-turbulence generated by cavitation, eliminating concentration differences caused by sedimentation. Simultaneously, it regulates the silver ion deposition kinetics, guiding the small-particle silver powder to grow directionally according to dendritic patterns. This results in small-particle dendritic silver powder with uniform dendrite morphology. The particle size of the silver powder aggregates matches the length of individual dendrites. This structure exhibits a higher overlap rate between dendritic silver powder particles compared to other dendritic structures, forming a dense conductive network with excellent conductivity, sintering density, and dispersibility, meeting the high-end requirements of flexible optoelectronic devices. Meanwhile, the selection of raw materials avoids complex components, using only simple and readily available basic raw materials. Furthermore, the entire synthesis process does not involve high-molecular-weight organic compounds, simplifying the reaction system and reducing the difficulty of subsequent cleaning processes and the risk of impurity residue. In addition, a dispersant is added directly after the reaction, which effectively inhibits the agglomeration of powder particles through steric hindrance, ensuring product dispersibility. It also modifies the surface of the silver powder, enhancing its surface activity and laying a good foundation for subsequent applications. This preparation method has the advantages of simple process, fast reaction rate, and low raw material cost, and can achieve continuous industrial production, showing promising application prospects in the industrial field.

[0028] In a first aspect, this application provides a method for preparing dendritic silver powder, comprising the following steps:

[0029] S1. Dissolve the reducing agent in deionized water to prepare the base solution;

[0030] S2. Dissolve silver nitrate in deionized water to prepare a silver nitrate solution;

[0031] S3. Heat the base liquid to a predetermined temperature and maintain it at a constant temperature. Under ultrasonic and stirring conditions, add silver nitrate solution by micro-pressure feeding. After the reaction is completed, add dispersant to obtain a silver powder mixed solution.

[0032] S4. Filter the silver powder mixture solution, wash, dry, and depolymerize to obtain the target silver powder.

[0033] In the technical solution of this application embodiment, a reducing agent solution is used as the base liquid. The base liquid is then heated and maintained at a constant temperature while an ultrasonic device is activated. Next, under stirring, a silver nitrate solution is added to the base liquid using a micro-pressure feeding method. After the reaction is complete, a dispersant is directly added to the system. Finally, after washing, drying, and depolymerization processes, the target product, dendritic silver powder, is obtained. This preparation method has the advantages of simple process, fast reaction rate, and low raw material cost, and can achieve continuous production, showing good application prospects in the industrial field.

[0034] Furthermore, in some embodiments, in step S1, the reducing agent is one or more of sodium citrate, sodium borohydride, formaldehyde, ascorbic acid, hydrazine hydrate, sodium gluconate, and sodium carbonate; the mass ratio of the reducing agent to silver nitrate is 2:1 to 1:2.

[0035] In the technical solution of this application embodiment, silver powder with dendritic morphology and good dispersibility is obtained by adding a specific proportion of silver nitrate solution to a reducing agent solution.

[0036] Furthermore, in some embodiments, in step S3, the power of the ultrasound is 5~60W.

[0037] In the technical solution of this application embodiment, ultrasonic treatment is used to enhance the mass transfer efficiency of the reaction system, ensuring reaction uniformity and the formation of dendritic silver powder.

[0038] Furthermore, in some embodiments, in step S3, the pressure during the micro-pressure feeding is 0.1~5MPa.

[0039] In the technical solution of this application embodiment, the addition rate of silver nitrate solution can be precisely controlled by micro-pressure feeding, avoiding abnormal product morphology caused by excessively high local concentrations. Furthermore, micro-pressure is a type of injection, delivering only nanoliter-microliter levels of silver nitrate solution to the base solution per unit time, resulting in a discrete point contact state between the silver nitrate solution and the reaction base solution. This contact form can maximize the reduction of the diffusion gradient of silver nitrate in the base solution, ensuring that silver ions are uniformly distributed in the base solution and grow in a directional manner according to the thermodynamic laws of dendrite growth, thereby guaranteeing the stable formation and morphological uniformity of the dendritic structure.

[0040] Furthermore, in some embodiments, in step S3, the predetermined temperature is 20~40°C.

[0041] In the technical solution of this application embodiment, the temperature range can match the diffusion rate and reduction reaction rate of silver ions under the micro-pressure injection feeding method, further helping to maintain the regularity of the dendritic structure.

[0042] Further, in some embodiments, in step S3, the dispersant is one or more of polyvinylpyrrolidone, arachidic acid, potassium stearate, stearic acid, oleic acid, potassium oleate, ricinoleate, palmitic acid, and glycerol; the mass ratio of the dispersant to silver nitrate is 0.0005:1 to 0.005:1.

[0043] In the technical solution of this application embodiment, by selecting the above-mentioned specific type of dispersant and limiting its mass ratio with silver nitrate, the growth process of dendritic silver powder can be precisely controlled.

[0044] Furthermore, in some embodiments, in step S3, the stirring speed is 200~400 rpm.

[0045] Secondly, this application provides a dendritic silver powder, characterized in that it is prepared by the above-mentioned method for preparing dendritic silver powder, wherein the particle size of the dendritic silver powder is 1~20μm and the dendrite length is <5μm.

[0046] In the technical solution of this application embodiment, the silver powder obtained has a small particle size and low sintering shrinkage rate; the dendritic structure and agglomeration size are matched and uniform, the contact effect between silver powder particles is good, and the sintering activity and conductivity are good.

[0047] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0048] Example 1

[0049] This embodiment provides a method for preparing dendritic silver powder, including the following steps:

[0050] S1. Dissolve 100g of ascorbic acid in 500mL of deionized water to prepare the base solution.

[0051] S2. Dissolve 100g of silver nitrate in 200mL of deionized water to prepare a silver nitrate solution.

[0052] S3. Heat the base liquid to 25°C and maintain a constant temperature. Turn on the ultrasonic device (power 5W). Under stirring conditions of 350rpm, add silver nitrate solution to the base liquid through a micro-pressure feeding device (pressure 5MPa). After the reaction is complete, add 0.1g of stearic acid to obtain a silver powder mixed solution.

[0053] S4. Filter the silver powder mixture solution, wash, dry, and depolymerize to obtain the target silver powder.

[0054] The SEM image of the target silver powder obtained in this embodiment is as follows: Figure 1 As shown.

[0055] Depend on Figure 1 It can be seen that the obtained target silver powder has obvious dendritic morphology, uniform particle size and high dispersion.

[0056] Examples 2-3 and Comparative Examples 1-2

[0057] Examples 2-3 and Comparative Examples 1-2 each provide a method for preparing dendritic silver powder. Compared with Example 1, the difference lies in the different mass ratio of reducing agent to silver nitrate in the base solution, as shown in Table 1. The other steps are roughly the same as in Example 1, and will not be repeated here.

[0058] Table 1. Mass ratio of ascorbic acid to silver nitrate and morphology of silver powder in Examples 2-3 and Comparative Examples 1-2.

[0059]

[0060] As shown in Table 1, the morphology of the silver powder obtained in Examples 2-3 is similar to that in Example 1; in Comparative Example 1, the proportion of dendrite morphology is reduced and the proportion of plate morphology is increased; in Comparative Example 2, the silver powder is mostly spiky.

[0061] Examples 4-5 and Comparative Examples 3-6

[0062] Examples 4-5 and Comparative Examples 3-6 respectively provide a method for preparing dendritic silver powder. Compared with Example 1, the difference lies in the ultrasonic power and the pressure of micro-pressure feeding, as shown in Table 2. The other steps are roughly the same as in Example 1, and will not be repeated here.

[0063] Table 2 shows the ultrasonic power, micro-pressure feeding pressure, and silver powder morphology in Examples 4-5 and Comparative Examples 3-6.

[0064]

[0065] As shown in Table 2, the appearance and particle size of the silver powder prepared in Examples 4 and 5 are similar to those in Example 1; in Comparative Example 3, the silver powder is spherical with many protrusions on the surface; in Comparative Example 4, the feeding pressure is too high, and the silver powder is irregularly shaped at the submicron level and cannot exhibit dendritic structure; in Comparative Example 5, the ultrasonic power is too low, and the silver powder is irregularly shaped with a wide particle size distribution; in Comparative Example 6, the ultrasonic power is too high, and the silver powder exhibits agglomeration.

[0066] Comparative Example 7

[0067] Comparative Example 7 provides a method for preparing dendritic silver powder. Compared with Example 1, the difference is that in step (3), the base liquid is added to the silver nitrate solution. The other steps are roughly the same as in Example 1, and will not be repeated here.

[0068] The microstructure of the silver powder prepared in this comparative example is as follows: Figure 2 As shown.

[0069] Depend on Figure 2 It can be seen that when the base solution is added to silver nitrate, the local reaction rate of the reaction system is high. As the base solution diffuses in the silver nitrate solution, the overall reaction rate decreases rapidly, resulting in uneven concentration of reduced elemental silver particles in the system, which directly leads to a wide particle size distribution and agglomeration of silver powder.

[0070] In summary, this application provides a dendritic silver powder and its preparation method. A reducing agent solution is used as the base liquid. The base liquid is then heated and maintained at a constant temperature while an ultrasonic device is activated. Next, under stirring, a silver nitrate solution is added to the base liquid using a micro-pressure feeding method. After the reaction is complete, a dispersant is directly added to the system. Finally, after washing, drying, and depolymerization processes, the target product, dendritic silver powder, is obtained. This invention employs a dual process combining ultrasonic assistance and micro-pressure feeding during the reaction. A micro-pressure jetting device injects silver nitrate solution into the reducing agent substrate in a micron-level jet stream, injecting only nanoliters to microliters of solution per unit time. This creates a discrete point-contact reaction interface, precisely controlling the silver ion release rate and preventing excessively high local concentrations, thus initially generating uniform small-particle silver powder. Stirring facilitates rapid detachment of the silver powder from the reaction interface, preventing localized accumulation. Furthermore, the energy provided by ultrasound accelerates the uniform dispersion of small-particle silver powder within the system through micro-turbulence generated by cavitation, eliminating concentration differences caused by sedimentation. Simultaneously, it regulates the silver ion deposition kinetics, guiding the small-particle silver powder to grow directionally according to dendritic patterns. This results in small-particle dendritic silver powder with uniform dendritic morphology, and the particle size of the silver powder aggregates matches the length of the individual dendrites. This structure exhibits a higher overlap rate between dendritic silver powder particles compared to other dendritic structures, forming a dense conductive network with excellent conductivity, sintering density, and dispersibility, meeting the high-end requirements of flexible optoelectronic devices. Meanwhile, the selection of raw materials avoids complex components, using only simple and readily available basic raw materials. Furthermore, the entire synthesis process does not involve high-molecular-weight organic compounds, simplifying the reaction system and reducing the difficulty of subsequent cleaning processes and the risk of impurity residue. In addition, a dispersant is added directly after the reaction, which effectively inhibits the agglomeration of powder particles through steric hindrance, ensuring product dispersibility. It also modifies the surface of the silver powder, enhancing its surface activity and laying a good foundation for subsequent applications. This preparation method has the advantages of simple process, fast reaction rate, and low raw material cost, and can achieve continuous industrial production, showing promising application prospects in the industrial field.

[0071] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for producing dendritic silver powder, characterized by, The method comprises the following steps: S1. dissolving a reducing agent in deionized water to prepare a base solution, wherein the reducing agent is ascorbic acid; S2. dissolving silver nitrate in deionized water to prepare a silver nitrate solution, wherein the mass ratio of the reducing agent to the silver nitrate is 2:1-1:2; S3. heating the base solution to a predetermined temperature and maintaining the temperature, adding the silver nitrate solution in a micro-pressure feeding mode under ultrasonic and stirring conditions, adding a dispersing agent after the reaction is completed to obtain a silver powder mixed solution, wherein the power of the ultrasonic is 5-60 W, the pressure in the micro-pressure feeding is 0.1-5 MPa, the predetermined temperature is 20-40 DEG C, the dispersing agent is stearic acid, and the mass ratio of the dispersing agent to the silver nitrate is 0.0005:1-0.005:1; S4. filtering, washing, drying and depolymerizing the silver powder mixed solution to obtain a target silver powder.

2. A dendritic silver powder, characterized by, The dendritic silver powder is prepared by the method of claim 1, wherein the particle size of the dendritic silver powder is 1-20 mu m, and the dendrite length is less than 5 mu m.

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