High-sphericity superfine silver powder and preparation method and application thereof

Abstract

According to the high-sphericity superfine silver powder and the preparation method and application thereof, when the superfine silver powder is prepared through a chemical reduction method, a hydrothermal method is added for assistance, the crystal nucleus growth process of the silver powder is accurately controlled by adjusting parameters such as temperature and reaction time through the hydrothermal method, and the high-sphericity superfine silver powder is obtained. According to the method, the particle size and morphology are regulated and controlled, the superfine silver powder which is excellent in performance, uniform in particle size and high in sphericity degree and is used for preparing the conductive paste is prepared, and then the conductive paste prepared from the superfine silver powder with the high sphericity degree has excellent conductive performance.

Description

Technical Field

[0001] The invention relates to the technical field of precious metal powder materials, and in particular to an ultrafine silver powder with high sphericity, a preparation method and application thereof. Background Art

[0002] With the global energy transition and the surge in demand for clean energy, the photovoltaic industry is expanding rapidly around the world. In order to meet this demand, major photovoltaic manufacturers are constantly seeking ways to improve battery efficiency and reduce costs, and silver powder, as a key material for positive electrode silver paste, has also become one of the core optimization targets. Ultrafine silver powder with high sphericity is an important component of photovoltaic positive silver. The physical form and particle size characteristics of this silver powder will directly affect the performance, production cost and overall market competitiveness of photovoltaic cells by affecting the performance of positive electrode silver paste. This plays an important role in improving the efficiency of photovoltaic cells, reducing production costs and achieving material optimization.

[0003] At present, in the industrial production process, liquid phase chemical reduction is the main method for preparing spherical silver powder, which has the advantages of low production cost and relatively simple process route; however, in the actual preparation process of ultrafine silver powder, it is very difficult to strictly control the particle size and particle size distribution, and it is easy to have uneven particle size or particle agglomeration, and the sphericity of silver powder is difficult to ensure. Therefore, there is an urgent need for a high-sphericity ultrafine silver powder and its preparation method and application to meet the application needs of clients. Summary of the invention

[0004] The purpose of the present invention is to solve the technical problems in the existing silver powder preparation process that the sphericity is difficult to ensure and the particle size is difficult to control.

[0005] In order to solve the above technical problems, the present invention first provides a method for preparing ultrafine silver powder with high sphericity, comprising: S1, mixing a silver nitrate solution, a dispersant, a buffer, a coating agent, a reducing agent and a solvent to obtain a reaction suspension; S2, heating and heat-insulating the reaction suspension, and obtaining a solid-liquid mixture after cooling; wherein the heating temperature of the heating and heat-insulating treatment is 100-200° C., and the heat-insulating time is 2h-5h; S3, subjecting the solid-liquid mixture to sedimentation to obtain a precipitate, and then washing and drying the precipitate to obtain ultrafine silver powder with high sphericity.

[0006] Preferably, the reaction suspension in step S1 comprises the following components in parts by mass: 20 to 30 parts of silver nitrate solution, 1 to 10 parts of dispersant, 1 to 5 parts of buffer, 0.5 to 5 parts of coating agent, 5 to 20 parts of reducing agent, and 300 to 600 parts of solvent.

[0007] Preferably, step S1 specifically includes: S11, mixing the reducing agent with a portion of the solvent and stirring until dissolved to obtain a first mixed solution; S12, mixing the buffer, the dispersant and another portion of the solvent and stirring until dissolved to obtain a second mixed solution; S13, adding the silver nitrate solution, the coating agent and the first mixed solution into the second mixed solution in sequence and stirring at a uniform speed to obtain a reaction suspension.

[0008] Preferably, in step S11: the reducing agent is at least one of ascorbic acid, formaldehyde, glucose, ethylene glycol and hydrazine hydrate.

[0009] Preferably, in step S12: the buffer is at least one of acetic acid, sodium acetate, sodium citrate, phosphoric acid, boric acid, sodium borate and sodium bicarbonate; the dispersant is at least one of polyvinyl pyrrolidone, polyethylene glycol, sodium dodecyl sulfate, sodium polyacrylate and Tween.

[0010] Preferably, in step S13: the coating agent is at least one of oleic acid, lauric acid, a silane coupling agent and stearic acid.

[0011] Preferably, the solvent is water; and the stirring rates in step S11, step S12 and step S13 are all 300-500 r / min.

[0012] Preferably, step S3 specifically includes: S31, performing sedimentation treatment on the solid-liquid mixture, and removing the supernatant to obtain a precipitate; S32, mixing the precipitate with ethanol and performing a first centrifugal treatment; then mixing the precipitate with deionized water and performing a second centrifugal treatment, until the precipitate is washed to a conductivity of less than 20 μS / m, to obtain wet silver powder; S33, drying the wet silver powder at 60° C. and passing it through a 300-mesh sieve to finally obtain ultrafine silver powder with high sphericity.

[0013] Accordingly, the present invention also provides a high sphericity ultrafine silver powder, which is prepared by the preparation method of high sphericity ultrafine silver powder as described above; wherein the particle size of the high sphericity ultrafine silver powder is 0.82 μm to 3.53 μm, and the tap density is 6.24 g / cm 3 , with a specific surface area of ​​0.32m 2 / g.

[0014] Correspondingly, the present invention further provides a use of the above-mentioned high sphericity ultrafine silver powder in the preparation of conductive silver paste.

[0015] The beneficial effects of the present invention are as follows: Different from the prior art, the present invention provides an ultrafine silver powder with high sphericity, a preparation method thereof and an application thereof. The preparation method of the ultrafine silver powder with high sphericity adds a hydrothermal method to assist while preparing the ultrafine silver powder by a chemical reduction method. The temperature, reaction time and other parameters are adjusted by the hydrothermal method to accurately control the crystal nucleus growth process of the silver powder, thereby achieving the regulation of the particle size and morphology, and preparing an ultrafine silver powder with uniform particle size and high sphericity for preparing a conductive paste with excellent performance, thereby making the conductive paste prepared by the ultrafine silver powder with high sphericity in the present invention have excellent conductive properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A flow chart of a method for preparing ultrafine silver powder with high sphericity provided by an embodiment of the present invention; Figure 2 This is an electron microscope image of the high sphericity ultrafine silver powder provided in Example 1 of the present invention; Figure 3 This is an electron microscope image of the high sphericity ultrafine silver powder provided in Comparative Example 1. DETAILED DESCRIPTION

[0017] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] Aiming at the problem that the uneven crystal growth in the current production process of ultrafine silver powder leads to the diversification of particle morphology, the generation of irregular particles, the local supersaturation of chemical reaction or the uneven reduction conditions will lead to the irregular morphology of silver powder, the present invention provides a method for preparing ultrafine silver powder with high sphericity, the prepared spherical silver powder has high sphericity, high dispersibility, good particle size distribution and uniformity, and the surface of the silver powder has a certain roughness. The sample after printing with the conductive silver paste configured by the method has low volume resistivity and excellent conductive performance, and the synthesis process of the silver powder in the present invention has the characteristics of simple operation and non-toxicity, and is suitable for large-scale production.

[0019] In order to achieve the above technical objectives, this application adopts the following technical solutions: In a first aspect, the present invention first provides a method for preparing ultrafine silver powder with high sphericity.

[0020] See also Figure 1 , Figure 1 A flow chart of a method for preparing ultrafine silver powder with high sphericity provided by an embodiment of the present invention; wherein the above-mentioned preparation method specifically comprises: S1, mixing a silver nitrate solution, a dispersant, a buffer, a coating agent, a reducing agent and a solvent to obtain a reaction suspension.

[0021] Specifically, step S1 includes: S11, mixing the reducing agent with a portion of the solvent and stirring until dissolved to obtain a first mixed solution; S12, mixing the buffer, the dispersant and another portion of the solvent and stirring until dissolved to obtain a second mixed solution; S13, adding the silver nitrate solution, the coating agent and the first mixed solution into the second mixed solution in sequence and stirring at a uniform speed to obtain a reaction suspension.

[0022] Furthermore, the solvent in step S11 and step S12 is water; and the stirring rate in step S11, step S12 and step S13 is set to 300-500 r / min.

[0023] Furthermore, in step S13, the silver nitrate solution should be added first, and then the first mixed solution should be added. The addition time of the first mixed solution is 10 to 20 seconds, and the stirring time is 15 minutes. Among them, silver nitrate may play a key initiating role in the system. Adding the silver nitrate solution first can make it fully dispersed in the system and gradually react with other components added later, so that the start and progress of the reaction can be better controlled. If the first mixed solution is added first, the reducing agent therein may react with other substances in the system prematurely, making the reaction difficult to control and affecting the quality and performance of the product.

[0024] In step S11: the reducing agent is at least one of ascorbic acid, formaldehyde, glucose, ethylene glycol and hydrazine hydrate; wherein the silver nitrate solution and the reducing agent undergo a redox reaction, so that the silver ions in the solution are reduced to silver powder; the amount of the reducing agent should exceed the theoretical value of the stoichiometric ratio by 5% to 10% to achieve the effect of completely reducing the silver ions in the solution.

[0025] In step S12: the buffer is at least one of acetic acid, sodium acetate, sodium citrate, phosphoric acid, boric acid, sodium borate and sodium bicarbonate; wherein the buffer is used to adjust and stabilize the pH value to ensure that the reduction process of silver ions is carried out within a controllable range. It can not only regulate the reduction rate, avoid particle agglomeration and side reactions, but also affect the morphology and particle size distribution of the silver powder, thereby improving the quality and performance of the silver powder.

[0026] In step S12: the dispersant is at least one of polyvinyl pyrrolidone, polyethylene glycol, sodium dodecyl sulfate, sodium polyacrylate and Tween; wherein the role of the dispersant is mainly reflected in preventing the silver powder particles from agglomerating, improving the particle dispersibility, controlling the particle morphology and stabilizing the solution system. By selecting a suitable dispersant, the quality, uniformity and processing performance of the silver powder can be significantly improved, thereby optimizing its application effect in the fields of photovoltaics, electronics, etc.

[0027] In step S13: the coating agent is at least one of oleic acid, lauric acid, silane coupling agent and stearic acid; wherein the coating agent mainly forms a protective layer on the surface of the particles to prevent oxidation, control particle growth, avoid agglomeration, improve dispersibility and sintering performance. An appropriate coating agent can not only improve the quality of the silver powder, but also improve its performance in storage, transportation and subsequent applications.

[0028] In step S1, the reaction suspension includes the following components in parts by mass: 20 to 30 parts of silver nitrate solution, 1 to 10 parts of dispersant, 1 to 5 parts of buffer, 0.5 to 5 parts of coating agent, 5 to 20 parts of reducing agent, and 300 to 600 parts of solvent.

[0029] Specifically, the amount of silver nitrate solution used is 20 to 30 parts, which not only ensures that there are enough silver ions to participate in the reaction to obtain the required amount of product, but also avoids waste or unnecessary side reactions caused by excessive dosage.

[0030] Specifically, the amount of dispersant used in an amount of 1 to 10 parts can effectively prevent the agglomeration of silver powder particles, and through electrostatic repulsion or steric hindrance effect, the particles maintain good dispersion, and obtain uniformly distributed ultrafine silver powder; when the amount of dispersant is insufficient, the agglomeration of particles cannot be effectively inhibited, resulting in mutual adsorption between silver powder particles, and eventually forming large particles or agglomeration, affecting the particle size distribution and performance of the product; when the amount of dispersant is excessive, a too thick molecular layer will be formed on the surface of the particles, resulting in excessive repulsion between particles, making it difficult for particles to approach, which may affect sintering and conductivity. In addition, excessive dispersant residues may also affect the purity of the silver powder.

[0031] Specifically, a usage range of 1 to 5 parts of the buffer can effectively adjust the pH value of the entire system while avoiding adverse effects on the reaction due to excessive usage of the buffer.

[0032] Specifically, the coating agent in an amount of 0.5 to 5 parts can effectively exert its coating effect, while too much coating agent may affect the performance of the silver particles or increase the cost.

[0033] Specifically, the amount of the reducing agent, which is 5 to 20 parts, needs to match the amount of the silver nitrate solution to ensure that the silver ions can be fully reduced. At the same time, the amount of the reducing agent should not be too much to avoid side reactions or affect the quality of the product.

[0034] Specifically, the amount of solvent used is 300 to 600 parts to ensure that other reactants are fully dissolved and dispersed to form a uniform reaction system. At the same time, the amount of solvent used should not be too much, so as not to affect the concentration and efficiency of the reaction.

[0035] S2, heating and heat-insulating the reaction suspension, and obtaining a solid-liquid mixture after cooling; wherein the heating temperature of the heating and heat-insulating treatment is 100-200° C., and the heat-insulating time is 2h-5h.

[0036] Specifically, step S2 also includes: First, the reaction suspension is transferred to a high-pressure reactor for heating and insulation treatment. The heating temperature is 100-200°C and the insulation time is 2h-5h. In this temperature range, the thermal motion of the molecules is intensified and the collision frequency between the reactants is increased, which is beneficial to the reaction. At the same time, a higher temperature can also reduce the activation energy of the reaction, making the reaction easier to occur. At the same time, by controlling the insulation time, the degree of the reaction can be adjusted to avoid excessive or insufficient reaction.

[0037] Afterwards, after the reaction kettle is cooled, the solid-liquid mixture in the kettle is poured out.

[0038] S3, subjecting the solid-liquid mixture to sedimentation to obtain a precipitate, and then washing and drying the precipitate to obtain ultrafine silver powder with high sphericity.

[0039] Specifically, step S3 also includes: S31, performing sedimentation treatment on the solid-liquid mixture, and removing the supernatant to obtain a precipitate; S32, mixing the precipitate with ethanol and performing a first centrifugal treatment; then mixing the precipitate with deionized water and performing a second centrifugal treatment, until the precipitate is washed to a conductivity of less than 20 μS / m, to obtain wet silver powder; wherein, washing the precipitate to a conductivity of less than 20 μS / m indicates that the ion impurity content in the precipitate is very low, and meets a high purity requirement; S33, drying the wet silver powder at 60° C. and passing it through a 300-mesh sieve to finally obtain ultrafine silver powder with high sphericity; wherein, the sieving treatment can remove large particles of impurities and agglomerates in the silver powder to obtain ultrafine silver powder with high sphericity and relatively uniform particle size; the 300-mesh sieve has a small aperture and can effectively screen out silver powder particles that meet the requirements, thereby improving the quality and performance of the product.

[0040] Accordingly, the present invention also provides a high sphericity ultrafine silver powder, which is prepared by the preparation method of high sphericity ultrafine silver powder as described above; wherein the particle size of the high sphericity ultrafine silver powder is 0.82 μm to 3.53 μm, and the tap density is 6.24 g / cm 3 , with a specific surface area of ​​0.32m 2 / g.

[0041] Specifically, the high sphericity ultrafine silver powder provided by the present invention has a uniform particle size distribution, a certain degree of surface roughness, and no agglomeration phenomenon occurs, thereby making the conductive paste prepared by the high sphericity ultrafine silver powder in the present invention have excellent conductive properties.

[0042] Correspondingly, the present invention further provides a use of the above-mentioned high sphericity ultrafine silver powder in the preparation of conductive silver paste.

[0043] The technical solution of the present invention is now further described in conjunction with specific embodiments.

[0044] Embodiment 1: This embodiment 1 provides a high sphericity ultrafine silver powder and a preparation method thereof, the preparation method comprising the following steps: Step 1, liquid preparation: Solution A: Take 500 ml of ethylene glycol, add 500 ml of deionized water, and stir evenly to obtain solution A; Solution B: Take 160g of silver nitrate and add it to a beaker. Add it to 500ml of deionized water and stir to dissolve to obtain Solution B. Solution C: Take 10g of polyvinyl pyrrolidone and add it to a beaker, dissolve it in 500ml of deionized water, stir and dissolve it, then add 3g of sodium citrate and 11.5g of sodium acetate, stir and dissolve it to obtain solution C; Solution D: Take 0.5 g of oleic acid and add it into a beaker. Add 10 ml of anhydrous ethanol and stir to dissolve to obtain solution D. Step 2: Preparation of silver powder: Add solution B to solution C and start stirring. Set the stirring rate to 500 rpm. Then add solution A to solution C. The time from the beginning of adding solution A to the end should be controlled within 10-20 seconds. Set the stirring time to 5 minutes. After the stirring is finished, add solution D and continue stirring for 10 minutes. The reaction is finished. After the reaction, the obtained reaction suspension was transferred to a high pressure reactor, heated to 180°C, and kept warm for 3 hours; After the heat preservation is completed and the reactor is cooled, the reaction suspension is subjected to sedimentation treatment, and the supernatant is poured out to obtain a reaction precipitate; The silver powder was cleaned and stirred with anhydrous ethanol at a rate of 800 rpm and a stirring time of 10 min. After the stirring was completed, the anhydrous ethanol and the silver powder were separated by centrifugation, and then cleaned and stirred with deionized water at a rate of 800 rpm and a stirring time of 10 min. The above operation was repeated until the conductivity of the washing liquid was less than 20 μS / m, and the preparation of the wet silver powder was completed. The wet silver powder was dried at 60°C for 12 hours. After drying, it was sieved through a 300-mesh sieve to obtain ultrafine silver powder with high sphericity. Figure 2 shown.

[0045] Embodiment 2: Step 1, liquid preparation: Solution A: Take 86.4 g of ascorbic acid, add 500 ml of deionized water, and stir evenly to obtain solution A; Solution B: Take 160g of silver nitrate and add it to a beaker. Add it to 500ml of deionized water and stir to dissolve to obtain Solution B. Solution C: Take 10g of polyvinyl pyrrolidone and add it to a beaker, dissolve it in 500ml of deionized water, stir and dissolve it, then add 3g of boric acid and 11.5g of sodium borate, stir and dissolve it to obtain solution C; Solution D: Take 0.5 g of oleic acid and add it into a beaker. Add 10 ml of anhydrous ethanol and stir to dissolve to obtain solution D.

[0046] Step 2: Preparation of silver powder: Add solution B to solution C and start stirring. Set the stirring rate to 500 rpm. Then add solution A to solution C. The time from the beginning of adding solution A to the end should be controlled within 10-20 seconds. Set the stirring time to 5 minutes. After the stirring is finished, add solution D and continue stirring for 10 minutes. The reaction is finished. After the reaction, the obtained reaction suspension was transferred to a high pressure reactor, heated to 180°C, and kept warm for 3 hours; After the heat preservation is completed and the reactor is cooled, the reaction suspension is subjected to sedimentation treatment, and the supernatant is poured out to obtain a reaction precipitate; The silver powder was cleaned and stirred with anhydrous ethanol at a rate of 800 rpm and a stirring time of 10 min. After the stirring was completed, the anhydrous ethanol and the silver powder were separated by centrifugation, and then cleaned and stirred with deionized water at a rate of 800 rpm and a stirring time of 10 min. The above operation was repeated until the conductivity of the washing liquid was less than 20 μS / m, and the preparation of the wet silver powder was completed. The wet silver powder was dried at 60°C for 12 h. After drying, it was sieved through a 300-mesh sieve to obtain ultrafine silver powder with high sphericity.

[0047] Embodiment 3: Step 1, liquid preparation: Solution A: Take 86.4g of glucose, add 500ml of deionized water, and stir evenly to obtain Solution A; Solution B: Take 160g of silver nitrate and add it to a beaker. Add it to 500ml of deionized water and stir to dissolve to obtain Solution B. Solution C: Take 10g of polyethylene glycol and add it to a beaker, dissolve it in 500ml of deionized water, stir and dissolve it, then add 3g of sodium citrate and 11.5g of sodium acetate, stir and dissolve it to obtain solution C; Solution D: Take 0.5 g of lauric acid and add it into a beaker. Add 10 ml of anhydrous ethanol and stir to dissolve to obtain solution D. Step 2: Preparation of silver powder: Add solution B to solution C and start stirring. Set the stirring rate to 500 rpm. Then add solution A to solution C. The time from the beginning of adding solution A to the end should be controlled within 10-20 seconds. Set the stirring time to 5 minutes. After the stirring is finished, add solution D and continue stirring for 10 minutes. The reaction is finished. After the reaction, the obtained reaction suspension was transferred to a high pressure reactor, heated to 180°C, and kept warm for 3 hours; After the heat preservation is completed and the reactor is cooled, the reaction suspension is subjected to sedimentation treatment, and the supernatant is poured out to obtain a reaction precipitate; The silver powder was cleaned and stirred with anhydrous ethanol at a rate of 800 rpm and a stirring time of 10 min. After the stirring was completed, the anhydrous ethanol and the silver powder were separated by centrifugation, and then cleaned and stirred with deionized water at a rate of 800 rpm and a stirring time of 10 min. The above operation was repeated until the conductivity of the washing liquid was less than 20 μS / m, and the preparation of the wet silver powder was completed. The wet silver powder was dried at 60°C for 12 h. After drying, it was sieved through a 300-mesh sieve to obtain ultrafine silver powder with high sphericity.

[0048] Comparative Example 1: Step 1, liquid preparation: Solution A: Take 500 ml of ethylene glycol, add 500 ml of deionized water, and stir evenly to obtain solution A; Solution B: Take 160g of silver nitrate and add it to a beaker. Add it to 500ml of deionized water and stir to dissolve to obtain Solution B. Solution C: Take 10g of polyvinyl pyrrolidone and add it to a beaker, dissolve it in 500ml of deionized water, stir and dissolve it, then add 3g of sodium citrate and 11.5g of sodium acetate, stir and dissolve it to obtain solution C; Solution D: Take 0.5 g of oleic acid and add it into a beaker. Add 10 ml of anhydrous ethanol and stir to dissolve to obtain solution D. Step 2: Preparation of silver powder: Add solution B to solution C and start stirring. Set the stirring rate to 500 rpm. Then add solution A to solution C. The time from the beginning of adding solution A to the end should be controlled within 10-20 seconds. Set the stirring time to 5 minutes. After the stirring is finished, add solution D and continue stirring for 10 minutes. The reaction is finished. The silver powder was cleaned and stirred with anhydrous ethanol, the stirring rate was set to 800 rpm, and the stirring time was set to 10 min; after the stirring was completed, the anhydrous ethanol and the silver powder were separated by centrifugation; Then, the mixture was washed and stirred with deionized water, the stirring rate was set to 800 rpm, and the stirring time was set to 10 min; the above operation was repeated until the conductivity of the washing liquid was less than 20 μS / m, and the preparation of wet silver powder was completed; The wet silver powder was dried at 60°C for 12 hours. After drying, it was sieved through a 300-mesh sieve to obtain ultrafine silver powder with high sphericity. Figure 3 shown.

[0049] The performance of the silver powder prepared in the above Examples 1 to 3 and Comparative Example 1 was tested, and the test results are shown in Table 1: Table 1 Performance indicators of Examples 1 to 3 and Comparative Example 1

[0050] Specifically, in contrast to Examples 1 to 3, Comparative Example 1 did not undergo hydrothermal autoclave heating and heat preservation treatment. Examples 1 to 3 all used a hydrothermal method to assist in the preparation of silver powder, which has many advantages in the preparation of silver powder, including controllable particle size and morphology, good dispersibility, high purity, mild reaction conditions, etc. These advantages make the hydrothermal method unique in the preparation of high-quality ultrafine silver powder, and it is suitable for fields such as conductive silver paste and conductive ink that have high requirements for silver powder performance.

[0051] As shown in Table 1, the high sphericity ultrafine silver powder prepared in Example 1 has a smaller particle size than that of Example 2, Example 3 and Comparative Example 1, with D100 kept below 3.53 μm, a relatively uniform particle size distribution, and a bulk density of 4.28 g / cm 3 , has a higher tap density, its tap density reaches 6.24g / cm 3 Compared with the comparative example 1 without hydrothermal auxiliary preparation, the performance of the ultrafine silver powder prepared in example 1 is greatly improved.

[0052] The present invention discloses a high sphericity ultrafine silver powder and a preparation method and application thereof, belonging to the field of precious metal powder materials. The ultrafine silver powder obtained by the method has high sphericity and a well-controlled particle size. The ultrafine silver powder obtained by the above preparation method has a particle size of 0.82 μm to 3.53 μm and a tap density of 6.24 g / cm 3 , with a specific surface area of ​​0.32m 2 / g. The spherical silver powder prepared by the present invention has high sphericity, high dispersibility, good particle size distribution and uniformity, and the surface of the silver powder has a certain degree of roughness. The sample after printing with the conductive silver paste configured by the present invention has low volume resistivity and excellent conductive performance, and the synthesis process of the silver powder in the present invention has the characteristics of simple operation and non-toxicity.

[0053] The present invention prepares ultrafine silver powder by chemical reduction method and adds hydrothermal method to assist, thereby providing a novel method for preparing silver powder. By adjusting parameters such as temperature and reaction time by hydrothermal method, the crystal nucleus growth process of silver powder is accurately controlled, thereby achieving regulation of particle size and morphology, and preparing an ultrafine silver powder with excellent performance, uniform particle size and high sphericity for preparing conductive paste.

[0054] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For matters that are not described in detail in some embodiments, reference may be made to the description in other embodiments.

[0055] The above embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing ultrafine silver powder with high sphericity, characterized in that: The steps include: S1, mixing a silver nitrate solution, a dispersant, a buffer, a coating agent, a reducing agent and a solvent to obtain a reaction suspension; S2, heating and heat-insulating the reaction suspension, and obtaining a solid-liquid mixture after cooling; wherein the heating temperature of the heating and heat-insulating treatment is 100-200° C., and the heat-insulating time is 2h-5h; S3, subjecting the solid-liquid mixture to sedimentation to obtain a precipitate, and then washing and drying the precipitate to obtain ultrafine silver powder with high sphericity.

2. The method for preparing ultrafine silver powder with high sphericity according to claim 1, characterized in that: The reaction suspension in the step S1 comprises the following components in parts by mass: 20 to 30 parts of silver nitrate solution, 1 to 10 parts of the dispersant, 1 to 5 parts of the buffer, 0.5 to 5 parts of the coating agent, 5 to 20 parts of the reducing agent, and 300 to 600 parts of the solvent.

3. The method for preparing high sphericity ultrafine silver powder according to claim 1, characterized in that: The S1 step specifically includes: S11, mixing the reducing agent with a portion of the solvent and stirring until dissolved to obtain a first mixed solution; S12, mixing the buffer, the dispersant and another portion of the solvent and stirring until dissolved to obtain a second mixed solution; S13, adding the silver nitrate solution, the coating agent and the first mixed solution into the second mixed solution in sequence and stirring at a uniform speed to obtain the reaction suspension.

4. The method for preparing high sphericity ultrafine silver powder according to claim 3, characterized in that: In the step S11: the reducing agent is at least one of ascorbic acid, formaldehyde, glucose, ethylene glycol and hydrazine hydrate.

5. The method for preparing ultrafine silver powder with high sphericity according to claim 3, characterized in that: In the step S12: the buffer is at least one of acetic acid, sodium acetate, sodium citrate, phosphoric acid, boric acid, sodium borate and sodium bicarbonate; the dispersant is at least one of polyvinyl pyrrolidone, polyethylene glycol, sodium dodecyl sulfate, sodium polyacrylate and Tween.

6. The method for preparing high sphericity ultrafine silver powder according to claim 3, characterized in that: In the step S13: the coating agent is at least one of oleic acid, lauric acid, a silane coupling agent and stearic acid.

7. The method for preparing ultrafine silver powder with high sphericity according to claim 3, characterized in that: The solvent is water; the stirring rates in the step S11, the step S12 and the step S13 are all 300-500 r / min.

8. The method for preparing ultrafine silver powder with high sphericity according to claim 1, characterized in that: The S3 step specifically includes: S31, performing sedimentation treatment on the solid-liquid mixture, and removing the supernatant to obtain the precipitate; S32, mixing the precipitate with ethanol and performing a first centrifugal treatment; then mixing the precipitate with deionized water and performing a second centrifugal treatment, until the precipitate is washed to a conductivity of less than 20 μS / m, to obtain wet silver powder; S33, drying the wet silver powder at 60° C. and passing it through a 300-mesh sieve to finally obtain the high-sphericity ultrafine silver powder.

9. A high sphericity ultrafine silver powder, characterized in that: The method for preparing high sphericity ultrafine silver powder according to any one of claims 1 to 8 is prepared; wherein the particle size of the high sphericity ultrafine silver powder is 0.82 μm to 3.53 μm, and the tap density is 6.24 g / cm 3 , with a specific surface area of ​​0.32m 2 / g.

10. Use of the high sphericity ultrafine silver powder according to claim 9 in preparing conductive silver paste.

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