Silver powder and method for producing the same

Abstract

The application provides silver powder and a preparation method thereof, and belongs to the technical field of metal powder preparation. The application obtains large flaky silver powder by using silver powder micro-morphology control agent and small particle silver powder directional growth inducer in combination, and by synergistically controlling solution pH, temperature and adding mode of the reaction, so that the small particle thick flaky silver powder is directionally arranged and grown. The oxidizing agent and reducing agent solution are simultaneously added into the base solution, the sodium citrate in the base solution controls the generation of the small particle thick flaky silver powder, and the alkaline inducer adjusts the solution pH while promoting the directional growth of the silver powder particles, thereby obtaining the target silver powder. On the other hand, in the alkaline reaction system, the prepared silver powder has a fast settling rate, a good solid-liquid separation effect and a low waste liquid treatment cost. Compared with the dendritic or traditional single flaky silver powder, the flaky silver powder prepared by the application has a low sintering shrinkage rate of the powder slurry, a better contact effect between the silver powder particles, a good sintering activity and conductivity, and a good market application prospect.

Description

Technical Field

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

[0002] With the rapid development of information technology and intelligent technology, the market demand for electronic devices such as touch screens and IC cards is increasing day by day, and silver powder has become a key conductive powder material in the electronics field. At present, spherical silver powder has poor conductivity due to its regular particle shape and few contact points between particles, making it unusable in conductive adhesives and other products. Therefore, more research has been conducted on silver powder products with special morphologies such as flake silver powder and dendritic silver powder.

[0003] In the prior art, patent CN117600482A discloses a method for preparing high tap density flake silver powder. This patent prepares spherical silver powder by chemical reduction, and then obtains flake silver powder with uniform particle size by shaping and sand milling. However, the surface of the silver powder is flat and regular, and the morphology is uniform, resulting in poor overlap between powder particles. As a result, the sintering activity and conductivity in downstream slurry applications are not good. It needs to be mixed with small-particle nano and submicron silver powder to improve its application performance. In addition, patent CN110935888A discloses a method for preparing dendritic silver powder. The method involves first preparing a silver nitrate solution and a reducing agent solution, and then adding the silver nitrate solution dropwise to the reducing agent solution under certain reaction conditions to carry out a chemical reduction reaction, thereby obtaining dendritic silver powder with an average length of 5~15μm. When this silver powder is used as a conductive filler in conductive adhesives and other products, under certain filling conditions, it can increase the contact area and contact probability between powder particles, which is conducive to the formation of conductive networks and thus reduces the through-current threshold. However, this preparation method requires strict control of the reaction process, and the silver powder product is prone to agglomeration due to its high surface energy, and the paste has poor printability and high sintering shrinkage rate. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a silver powder and its preparation method, aiming to solve the problems of high contact resistance and sintering yield of existing silver powder in electronic pastes, and the difficulty of industrial production.

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

[0006] S1. Dissolve silver nitrate in deionized water to prepare an oxidizing solution;

[0007] S2. Dissolve ascorbic acid in deionized water to prepare a reducing solution;

[0008] S3. Dissolve sodium citrate in deionized water, and then adjust the pH value to 11-12 with an alkaline inducer to obtain the base solution;

[0009] S4. Under stirring conditions, the oxidizing liquid and the reducing liquid are simultaneously added to the bottom liquid. After the reaction is completed, solid-liquid separation, washing, and drying are performed to obtain the target silver powder.

[0010] In the technical solution of this application embodiment, by using a combination of a silver powder microstructure control agent (sodium citrate) and a small-particle silver powder directional growth agent (alkaline inducer), and by synergistically controlling the pH, temperature and addition method of the reaction solution, large-scale silver powder with directional arrangement of small-particle thick-sheet silver powder is obtained; and by using an alkaline reaction system, the prepared silver powder has a fast sedimentation rate, good solid-liquid separation effect, and low waste liquid treatment cost, making it suitable for industrial production.

[0011] In some embodiments, in step S4, the addition is performed by dripping at a rate of 10 mL / min.

[0012] In this embodiment, the growth rate of the nano-silver crystal nuclei in the early stage of the reaction is controlled by using a drop-feeding method, so that they can be stably formed into small granular flake silver powder, and then directionally connected into flakes in the later stage of the reaction.

[0013] In some embodiments, in step S4, the temperature of the reaction is 20~40°C.

[0014] In this embodiment, silver powder with a specific particle size can be obtained by controlling the growth rate of silver powder particles at a specific temperature.

[0015] In some embodiments, in step S4, the stirring speed is 500 rpm.

[0016] In this embodiment, stirring can improve the uniformity of the reaction solution mixing, thereby controlling the consistency of the silver powder particle size distribution.

[0017] In some embodiments, in step S1, the concentration of silver nitrate in the oxidizing solution is 100 g / L; the concentration of ascorbic acid in the reducing solution is 60 g / L; and the mass of ascorbic acid in the reducing solution is 0.6 to 0.8 times the mass of silver nitrate in the oxidizing solution.

[0018] In this embodiment, the reaction rate can be controlled and the complete reaction can be ensured by configuring specific concentrations of oxidizing and reducing solutions.

[0019] In some embodiments, in step S3, the sodium citrate is 10% of the mass of silver nitrate and has a concentration of 0.01 g / mL in the base solution.

[0020] In this embodiment, sodium citrate acts as both a reducing agent and a dispersant. On the one hand, by controlling the concentration of sodium citrate in the base solution, the nucleation rate of nano-silver crystals in the early stage of the reaction is accelerated, resulting in small silver powder particles of a specific size. On the other hand, sodium citrate controls the microstructure of the silver powder particles to be flake-like and to what extent through selective adsorption on different crystal faces of the silver powder.

[0021] In some embodiments, the alkaline inducer is one or more of triethylamine, ethanolamine, acetamide, and diethylamine.

[0022] In this embodiment, while adjusting the pH of the solution with an alkaline inducer to control the reaction rate, it can also promote the directional growth of small, thick, flake-like silver powder into flakes.

[0023] Secondly, this application provides a silver powder prepared by the above-mentioned silver powder preparation method. The morphology of the silver powder is a large sheet-like silver powder formed by the directional growth of thick sheet-like small silver powder particles; the particle size of the thick sheet-like small silver powder particles is 1~3μm, and the thickness-to-diameter ratio is 5:1; the diameter of the large sheet-like silver powder is 5~30μm.

[0024] In the technical solution of this application embodiment, the sintering shrinkage rate of silver powder is low, and the contact effect between silver powder particles is good, with good sintering activity and conductivity, which can be widely used in electronic fields such as electronic touch screens and IC cards. Attached Figure Description

[0025] Figure 1 This is a SEM image of the silver powder prepared in Example 1.

[0026] Figure 2 SEM images of the silver powder prepared in Example 2 and Comparative Example 1.

[0027] Figure 3 SEM images of the silver powders prepared in Example 3 and Comparative Examples 2-3.

[0028] Figure 4 The images are SEM images of the silver powder prepared in Comparative Examples 4 and 5.

[0029] Figure 5 This is a SEM image of the silver powder prepared in Comparative Example 6. Detailed Implementation

[0030] 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.

[0031] 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.

[0032] To address the problems of high contact resistance and sintering yield of existing silver powder in electronic pastes, and the difficulty of industrial production, this application provides a silver powder and its preparation method. By combining a silver powder microstructure control agent (sodium citrate) and a small-particle silver powder directional growth agent (alkaline inducer), and synergistically controlling the pH, temperature, and addition method of the reaction solution, large-scale flake silver powder with directional growth of small-particle thick flakes was obtained. Oxidizing and reducing agent solutions were simultaneously added to the base solution. Sodium citrate in the base solution acted as both a reducing agent and a dispersant. On the one hand, controlling the concentration of sodium citrate in the base solution accelerated the nucleation rate of nano-silver crystals in the initial stage of the reaction, resulting in small-particle silver powder of a specific size. On the other hand, sodium citrate selectively adsorbed different crystal faces of the silver powder, controlling the microstructure of the silver powder particles to be flake-like and the degree of flake formation. The alkaline inducer, while adjusting the solution pH to control the reaction rate, also promoted the directional growth of small-particle thick flake silver powder into flakes. Furthermore, the alkaline reaction system resulted in a fast sedimentation rate, good solid-liquid separation, and low wastewater treatment cost, making it suitable for industrial production. Furthermore, compared with dendritic silver powder or traditional single thin sheet silver powder, the flake silver powder prepared by this invention has a lower sintering shrinkage rate in the powder slurry, better contact effect between silver powder particles, better sintering activity and conductivity, and can be widely used in electronic fields such as electronic touch screens and IC cards, with good market application prospects.

[0033] In a first aspect, this application provides a method for preparing silver powder, comprising the following steps:

[0034] S1. Dissolve silver nitrate in deionized water to prepare an oxidizing solution;

[0035] S2. Dissolve ascorbic acid in deionized water to prepare a reducing solution;

[0036] S3. Dissolve sodium citrate in deionized water, and then adjust the pH value to 11-12 with an alkaline inducer to obtain the base solution;

[0037] S4. Under stirring conditions, the oxidizing liquid and the reducing liquid are simultaneously added to the bottom liquid. After the reaction is completed, solid-liquid separation, washing, and drying are performed to obtain the target silver powder.

[0038] In the technical solution of this application embodiment, by using a combination of a silver powder microstructure control agent (sodium citrate) and a small-particle silver powder directional growth agent (alkaline inducer), and by synergistically controlling the pH, temperature and addition method of the reaction solution, large-scale silver powder with directional arrangement of small-particle thick-sheet silver powder is obtained; and by using an alkaline reaction system, the prepared silver powder has a fast sedimentation rate, good solid-liquid separation effect, and low waste liquid treatment cost, making it suitable for industrial production.

[0039] Furthermore, in some embodiments, in step S4, the addition is carried out by dripping at a rate of 10 mL / min.

[0040] In the technical solution of this application embodiment, the growth rate of nano-silver crystal nuclei in the early stage of the reaction is controlled by using a drop-feeding method, so that they can be stably formed into small particle-shaped silver powder, and then directionally connected into sheets in the later stage of the reaction.

[0041] Furthermore, in some embodiments, the reaction temperature in step S4 is 20~40°C.

[0042] In the technical solution of this application embodiment, silver powder with a specific particle size can be obtained by controlling the growth rate of silver powder particles at a specific temperature.

[0043] Furthermore, in some embodiments, in step S4, the stirring speed is 500 rpm.

[0044] In the technical solution of this application embodiment, stirring can improve the uniformity of the reaction solution mixing, thereby controlling the consistency of the silver powder particle size distribution.

[0045] Furthermore, in some embodiments, in step S1, the concentration of silver nitrate in the oxidizing solution is 100 g / L; the concentration of ascorbic acid in the reducing solution is 60 g / L; and the mass of ascorbic acid in the reducing solution is 0.6 to 0.8 times the mass of silver nitrate in the oxidizing solution.

[0046] In the technical solution of this application embodiment, the reaction rate can be controlled and the complete reaction can be ensured by configuring oxidizing and reducing solutions of specific concentrations.

[0047] Furthermore, in some embodiments, in step S3, the sodium citrate is 10% of the mass of silver nitrate, and its concentration in the substrate is 0.01 g / mL.

[0048] In the technical solution of this application embodiment, sodium citrate acts as both a reducing agent and a dispersant. On the one hand, by controlling the concentration of sodium citrate in the base solution, the nucleation rate of nano-silver crystals in the early stage of the reaction is accelerated, and small-particle silver powder of a specific size is obtained. On the other hand, sodium citrate controls the micromorphology of silver powder particles to be flake-like and the degree of flake formation by selectively adsorbing different crystal planes of silver powder.

[0049] Furthermore, in some embodiments, the alkaline inducer is one or more of triethylamine, ethanolamine, acetamide, and diethylamine.

[0050] In the technical solution of this application embodiment, while adjusting the pH of the solution with an alkaline inducer to control the reaction rate, it can also promote the directional growth of small-particle thick-sheet silver powder into sheets.

[0051] Furthermore, in some embodiments, in step S4, the drying temperature is 50°C and the time is 10 hours.

[0052] Secondly, this application provides a silver powder prepared by the above-mentioned silver powder preparation method. The morphology of the silver powder is a large sheet-like silver powder formed by the directional growth of thick sheet-like small silver powder particles; the particle size of the thick sheet-like small silver powder particles is 1~3μm, and the thickness-to-diameter ratio is 5:1; the diameter of the large sheet-like silver powder is 5~30μm.

[0053] In the technical solution of this application embodiment, the sintering shrinkage rate of silver powder is low, and the contact effect between silver powder particles is good, with good sintering activity and conductivity, which can be widely used in electronic fields such as electronic touch screens and IC cards.

[0054] 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.

[0055] Example 1

[0056] This embodiment provides a method for preparing silver powder, including the following steps:

[0057] S1. An oxidizing solution was prepared by dissolving 5g of silver nitrate in 50mL of deionized water.

[0058] S2. Dissolve 3g of ascorbic acid in 50mL of deionized water to prepare a reducing solution.

[0059] S3. Dissolve 0.5g of sodium citrate in 50mL of deionized water, and then gradually add triethylamine to adjust the pH of the solution to 11 to obtain the base solution.

[0060] S4. Under stirring conditions of 40℃ and 500rpm, the above oxidizing solution and reducing solution are simultaneously added dropwise to the bottom liquid at a rate of 10mL / min. After all the solution has been added, the reaction continues for 10min. After solid-liquid separation and washing, the solution is dried at 50℃ for 10h to obtain the target silver powder.

[0061] The SEM image of the silver powder prepared in this embodiment is shown below. Figure 1 As shown.

[0062] Depend on Figure 1 It can be seen that the obtained silver powder is a large sheet-like silver powder with an average particle size of about 15 μm, formed by the directional growth of thick sheet-like small silver particles, among which the particle size of the thick sheet-like small silver particles is 1~3 μm.

[0063] Example 2 and Comparative Example 1

[0064] Example 2 and Comparative Example 1 respectively provide a method for preparing silver powder. Compared with Example 1, the difference is that in Example 2, triethylamine is replaced with polyvinylacetamide, and in Comparative Example 1, it is replaced with sodium hydroxide. The other steps are roughly the same as in Example 1, and will not be repeated here.

[0065] SEM images of the silver powder prepared in Example 2 and Comparative Example 1 are shown below. Figure 2 As shown.

[0066] Depend on Figure 2 It can be seen that the morphology of the silver powder obtained in Example 2 is similar to that in Example 1; although thick flake-shaped small silver powder can be generated in Comparative Example 1 under the combined action of sodium citrate and sodium hydroxide, it cannot continue to grow and connect into large flake-shaped silver powder due to the lack of triethylamine induction, and the microscopic arrangement of the powder particles becomes disordered.

[0067] Example 3 and Comparative Examples 2-3

[0068] Example 3 and Comparative Examples 2-3 each provide a method for preparing silver powder. Compared with Example 1, the difference lies in the pH value of the base solution (the amount of triethylamine added is different), as shown in Table 1. The other steps are roughly the same as in Example 1, and will not be repeated here.

[0069] The SEM images of the silver powders prepared in Example 3 and Comparative Examples 2-3 are shown below. Figure 3 As shown.

[0070] Table 1. pH value and silver powder morphology of the base solution in Example 3 and Comparative Examples 2-3

[0071]

[0072] The appearance and particle size of the silver powder prepared in Example 3 were similar to those in Example 1. Compared with the silver powder prepared in Example 3, the amount of triethylamine added in Comparative Example 2 was relatively small, which slowed down the reaction rate and resulted in larger particle size of the thick flake silver powder. In addition, the small silver powder particles lacked effective directional growth induction, and the microstructure became disordered. In contrast, the pH of the bottom solution in Comparative Example 3 was too high, which led to a faster nucleation rate of silver powder in the early stage of the reaction, and finally obtained small silver powder particles with an average particle size of about 200 nm.

[0073] Comparative Examples 4-5

[0074] Comparative Examples 4 and 5 each provide a method for preparing silver powder. The difference between them and Example 1 is the amount of sodium citrate added, as shown in Table 2. The other steps are roughly the same as in Example 1 and will not be repeated here.

[0075] Table 2. Amount of sodium citrate added and morphology of silver powder in Comparative Examples 4-5

[0076]

[0077] SEM images of the silver powder prepared in Comparative Examples 4 and 5 are shown below. Figure 4 As shown.

[0078] Depend on Figure 4 It is known that when the amount of sodium citrate added is too small, the reaction rate is slow and the specific crystal faces of the silver particles cannot be effectively adsorbed. Different silver crystal faces cannot grow differentially, and the final product is silver powder particles with a spherical morphology and a particle size >2μm. When the amount of sodium citrate added is too large, the specific crystal faces of the silver particles generated in the entire reaction process will be densely adsorbed, resulting in the prepared silver powder with a high degree of flake formation, excessive thickness and flat surface, poor slurry formation and high viscosity in downstream slurry applications.

[0079] Comparative Example 6

[0080] This comparative example provides a method for preparing silver powder. The difference from Example 1 is that the oxidizing and reducing solutions are added in a single pouring manner. The other steps are roughly the same as in Example 1 and will not be repeated here.

[0081] The microstructure of the silver powder prepared in this comparative example is as follows: Figure 5 As shown.

[0082] Depend on Figure 5 It is known that the one-time pouring method cannot control the mixing uniformity and reaction rate of the reaction solution, resulting in the final formation of silver powder with mixed particles of different sizes and agglomerated spherical sheets.

[0083] In summary, this application provides a silver powder and its preparation method. By combining a silver powder microstructure control agent (sodium citrate) and a small-particle silver powder directional growth agent (alkaline inducer), and synergistically controlling the pH, temperature, and addition method of the reaction solution, large-scale flake silver powder with directional growth of small-particle thick flakes is obtained. Oxidizing and reducing agent solutions are simultaneously added to the base solution. Sodium citrate in the base solution acts as both a reducing agent and a dispersant. On the one hand, controlling the concentration of sodium citrate in the base solution accelerates the nucleation rate of nano-silver crystals in the initial stage of the reaction, resulting in small-particle silver powder of a specific size. On the other hand, sodium citrate selectively adsorbs different crystal planes of the silver powder, controlling the microstructure of the silver powder particles to be flake-like and the degree of flake formation. The alkaline inducer, while adjusting the solution pH to control the reaction rate, also promotes the directional growth of small-particle thick flake silver powder into flakes. Furthermore, the alkaline reaction system results in a fast sedimentation rate, good solid-liquid separation, and low waste liquid treatment cost, making it suitable for industrial production. Furthermore, compared with dendritic silver powder or traditional single thin sheet silver powder, the flake silver powder prepared by this invention has a lower sintering shrinkage rate in the powder slurry, better contact effect between silver powder particles, better sintering activity and conductivity, and can be widely used in electronic fields such as electronic touch screens and IC cards, with good market application prospects.

[0084] 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 silver powder, characterized by, The method comprises the following steps: S1. dissolving silver nitrate in deionized water to prepare an oxidizing solution; S2. dissolving ascorbic acid in deionized water to prepare a reducing solution; S3. dissolving sodium citrate in deionized water, and then adding a basic inducing agent to adjust the pH value to 11-12 to prepare a bottom solution; S4. under stirring, the oxidizing solution and the reducing solution are simultaneously added to the bottom solution, after the reaction is completed, solid-liquid separation, washing, and drying are performed to obtain the target silver powder; In step S4, the adding mode is dropwise adding, the dropwise adding rate is 10 mL / min, the reaction temperature is 20-40℃, and the stirring speed is 500 rpm; In step S1, the concentration of silver nitrate in the oxidizing solution is 100 g / L; The concentration of ascorbic acid in the reducing solution is 60 g / L; The mass of ascorbic acid in the reducing solution is 0.6-0.8 times the mass of silver nitrate in the oxidizing solution; In step S3, the sodium citrate is 10% of the mass of silver nitrate, and the concentration in the bottom solution is 0.01 g / mL; The basic inducing agent is one or more of triethylamine, ethanolamine, acetamide, and diethylamine; the basic inducing agent can adjust the pH of the solution to control the reaction rate, and can also promote the directional growth of small particle flaky silver powder into flakes; The sodium citrate simultaneously acts as a reducing agent and a dispersing agent; Through the combined use of the silver powder micro-morphology control agent sodium citrate and the small particle silver powder directional growth agent basic inducing agent, and the synergistic control of the pH, temperature, and adding mode of the solution of the reaction, large flaky silver powder with small particle flaky silver powder directional arrangement growth is obtained.

2. A silver powder characterized in that, The silver powder is prepared by the preparation method of claim 1, the morphology of the silver powder is large flaky silver powder with small particle flaky silver powder directional arrangement growth, the particle size of the small particle flaky silver powder is 1-3 μm, the thickness-diameter ratio is 5:1, and the diameter of the large flaky silver powder is 5-30 μm.

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