A method for preparing micron-sized flaky silver powder

Abstract

The present invention discloses a method for preparing micron-sized flaky silver powder, comprising the steps of adding a reducing agent and a particle size control agent to a soluble silver salt aqueous solution to perform a liquid-phase reduction reaction, filtering after completion of the reaction, collecting the solid phase, and then washing and drying to obtain micron-sized flaky silver powder; the reducing agent is FeSO4, the particle size control agent is Fe2(SO4)3, and the molar ratio of FeSO4 to Fe2(SO4)3 is (1.0-30.0):1. The method for preparing micron-sized flaky silver powder of the present invention can effectively adjust the particle size distribution of the flaky silver powder by adjusting the molar ratio of FeSO4 to Fe2(SO4)3. The particle size of the flaky silver powder can be adjusted within a short time of 10-15 minutes, and the particle size of the flaky silver powder can be controlled within a wide range of 1-50 μm.

Description

Technical Field

[0001] The invention belongs to the field of metal powder processing, and in particular relates to a method for preparing silver powder. Background Art

[0002] Silver has excellent thermal and electrical conductivity. In the photovoltaic and electronics industries, silver powder is used as a conductive phase in electronic pastes. Among them, flake silver powder is widely used in conductive adhesives, flexible circuits, solar cell electrodes and other fields due to its better conductivity and reliability.

[0003] Flake silver powder generally has a larger specific surface area than silver powders of other morphologies. Since flake silver powder is generally connected by surface contact, while other non-flake silver powders are generally linked by point contact, flake silver powder can provide a larger contact area in the electronic paste, forming a better conductive network, thereby improving the conductive performance of the electronic paste. In addition, due to its unique two-dimensional structure, flake silver powder is easier to obtain a flat, highly adherent conductive pattern during the circuit printing process, thereby enhancing the stability of electronic components. Generally, electronic pastes require the particle size of flake silver powder to be in the micron range, and diameter (particle size) and thickness are the main shape parameters of flake silver powder. The smaller the diameter-to-thickness ratio, the closer the flake silver powder is to a cylindrical or square shape, and the higher the tap density, which is suitable for the preparation of conductive silver paste with a high silver content. Flake silver powder with a large diameter-to-thickness ratio generally has a lower tap density and is suitable for the preparation of conductive silver paste with a low silver content. Therefore, for different conductive silver paste application scenarios, it is urgent to establish an efficient flake silver powder particle size control technology to obtain nano silver powder of different particle sizes.

[0004] Numerous methods exist for preparing flaky silver powder, including electrochemical methods, liquid-phase reduction methods, mechanical ball milling methods, and photoinduction methods. Liquid-phase reduction methods, mechanical ball milling methods, or a combination of these methods are suitable for producing micron-sized flaky silver powder, which can meet the silver powder requirements for electronic pastes. However, these methods still have shortcomings in particle size control. For example, patent CN110465671A discloses a method for preparing flaky silver powder, comprising the following steps: adding a solvent and a coating agent to a raw silver powder; coating the silver powder with carbon dioxide; ball milling the silver powder for 0.5-1.0 h; and sintering, washing, and drying the milled silver powder to obtain flaky silver powder. While this method can produce flaky silver powder, the ball milling process consumes a lot of energy and has a relatively long reaction time. Furthermore, the particle size adjustment range is limited to 0.9-3.2 μm. For example, patent CN108555312A discloses a method for preparing flaky silver powder, comprising the following steps: mixing a silver nitrate solution with a reducing agent to conduct a liquid-phase reduction reaction; obtaining spherical silver powder through sedimentation, filtration, and drying; and ball-milling the spherical silver powder, separating, filtering, drying, and sieving to obtain flaky silver powder. This method has a lengthy process flow, with ball milling times as long as 8-15 hours, resulting in low production efficiency and a particle size distribution of 4-6 μm, with a narrow adjustable particle size range. For example, patent CN102756131A discloses a method for preparing flaky silver powder, comprising the following steps: preparing a silver nitrate solution; preparing an ascorbic acid solution; preparing an inducer solution; adding the ascorbic acid solution and the inducer solution to the silver nitrate solution to conduct a liquid-phase reduction reaction; and, after the reaction is complete, washing and drying to obtain flaky silver powder. Although this method can produce micron-sized flaky silver powder with a width-to-thickness ratio ≥ 10, the SEM image shows that there are some nano-sized spherical silver powders around the flaky silver powders, and the particle size adjustment range is 10-25 μm, which is a relatively small adjustable range.

[0005] In summary, the main problems of the existing flaky silver powder preparation technology are the small controllable range of particle size and the long preparation process of flaky silver powder. It is urgent to establish a short-process preparation technology that can effectively control the particle size of micron-level flaky silver powder. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings and defects mentioned in the above background technology and provide a method for preparing micron-sized flaky silver powder that can achieve effective control in a short process. To solve the above technical problem, the technical solution proposed by the present invention is as follows:

[0007] A method for preparing micron-sized flaky silver powder comprises the following steps:

[0008] A reducing agent and a particle size control agent are added to a soluble silver salt aqueous solution to carry out a liquid phase reduction reaction. After the reaction is completed, the solid phase is filtered, collected, and then washed and dried to obtain micron-sized flaky silver powder.

[0009] The reducing agent is FeSO4, the particle size control agent is Fe2(SO4)3, and the molar ratio of FeSO4 to Fe2(SO4)3 is (1.0-30.0): 1. More preferably, the molar ratio of FeSO4 to Fe2(SO4)3 is (4.0-23.0): 1.

[0010] In the present invention, the molar ratio of FeSO4 to Fe2(SO4)3 is a key parameter for controlling the particle size of the flaky silver powder. The smaller the molar ratio of FeSO4 to Fe2(SO4)3, the larger the particle size of the flaky silver powder. The larger the molar ratio of FeSO4 to Fe2(SO4)3, the smaller the particle size of the flaky silver powder. 2+ Reduction of Ag + During the process, Fe 3+ Can change Fe 3+ / Fe 2+ Relative to Ag + / Ag redox potential difference, the redox potential difference is a key parameter affecting the particle size of the micron-sized flaky silver powder in the present invention. By controlling different molar ratios of FeSO4 and Fe2(SO4)3, the preparation of silver powders of different particle sizes can be achieved.

[0011] In the above preparation method, the molar ratio of FeSO4 to soluble silver salt is preferably (1-2):1. More preferably, the molar ratio of FeSO4 to soluble silver salt is (1.3-1.8):1. If the molar ratio of FeSO4 to silver salt is too low, the silver powder is incompletely reduced. If the molar ratio of FeSO4 to silver salt is too high, the cost increases.

[0012] In the above preparation method, preferably, FeSO4 and Fe2(SO4)3 are added to a soluble silver salt aqueous solution in the form of a mixed aqueous solution at a rate of 100-200ml / min, the concentration of the FeSO4 is 10-200g / L, the soluble silver salt aqueous solution is an AgNO3 aqueous solution, the mass concentration of the AgNO3 aqueous solution is 5-100g / L, and the volume of the mixed aqueous solution of FeSO4 and Fe2(SO4)3 is 0.5-2.0 times the volume of the soluble silver salt aqueous solution. More preferably, FeSO4 and Fe2(SO4)3 are added to a soluble silver salt aqueous solution in the form of a mixed aqueous solution at a rate of 120-180ml / min, the concentration of the FeSO4 is 30-180g / L, and the mass concentration of the AgNO3 aqueous solution is 10-80g / L.

[0013] When the concentration of FeSO4 is too low, the reduction rate is too slow and the production efficiency is reduced. When the concentration of FeSO4 is too high, it is easy to be quickly reduced to form spherical or quasi-spherical silver powder. When the concentration of AgNO3 aqueous solution is too low, the amount of flaky silver powder prepared in a single batch is small. When the concentration of AgNO3 aqueous solution is too high, it is easy to increase the nucleation and growth rate, resulting in the formation of spherical or quasi-spherical silver powder. When the addition rate of the mixed aqueous solution of FeSO4 and Fe2(SO4)3 is low, the reaction takes a long time and the preparation efficiency is reduced. When the addition rate is too high, AgNO3 is too high. + It is easy to be quickly reduced to form spherical or quasi-spherical silver powder. If the volume of the mixed aqueous solution of FeSO4 and Fe2(SO4)3 is too large, it is easy to produce a large amount of waste liquid. The total liquid volume of the reaction should be controlled within an appropriate range.

[0014] In the above preparation method, preferably, a complexing agent and a dispersing agent are further added to the soluble silver salt aqueous solution, wherein the complexing agent includes at least one of ethylenediaminetetraacetic acid, citric acid and tartaric acid, and the concentration of the complexing agent is 1-10 g / L, and the dispersing agent includes at least one of polyvinyl pyrrolidone, gelatin and gum arabic, and the concentration of the dispersing agent is 0.1-1 g / L. More preferably, the concentration of the complexing agent is 3-8 g / L, and the concentration of the dispersing agent is 0.2-0.7 g / L. When the concentration of the complexing agent is too low, the complexing strength is low, and the Ag + It is easily and rapidly reduced to form spherical or quasi-spherical silver powder. When the complexing agent concentration is too high, the complexing strength is too strong, resulting in the silver complex being unable to be reduced to silver powder. When the dispersant concentration is too low, it is easy to cause silver powder to agglomerate. When the dispersant concentration is too high, an excessively thick coating will form on the silver powder surface, resulting in a decrease in the conductive properties of the silver powder.

[0015] In the above preparation method, preferably, during the liquid phase reduction reaction, the reaction is carried out at 10-80°C with stirring for 5-20 minutes; during the cleaning and drying, the solid phase is washed with ultrapure water and anhydrous ethanol until the pH of the washing liquid is neutral, and then the obtained solid phase is placed at 30-65°C and vacuum dried for 2-5 hours. More preferably, during the liquid phase reduction reaction, the reaction is carried out at 20-65°C with stirring for 10-15 minutes; during the cleaning and drying, the obtained solid phase is placed at 35-55°C and vacuum dried for 3-4 hours. During the liquid phase reduction reaction, when the reaction temperature is low, the liquid phase reduction time is prolonged. When the reaction temperature is too high, the energy consumption increases, and the accuracy of particle size control will be affected to a certain extent. When the reaction time is too short, the liquid phase reduction is incomplete, and the generated powder does not reach the desired particle size. When the reaction time is too long, the preparation efficiency decreases.

[0016] Compared with the prior art, the advantages of the present invention are:

[0017] The preparation method of the micron-sized flaky silver powder of the present invention can effectively adjust the particle size distribution of the flaky silver powder by adjusting the molar ratio of FeSO4 to Fe2(SO4)3, can adjust the particle size of the flaky silver powder within a short time of 10-15 minutes, and can regulate the particle size of the flaky silver powder within a large range of 1-50 μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 This is a scanning electron microscope image of the flaky silver powder prepared in Example 1.

[0020] Figure 2 This is a scanning electron microscope image of the flaky silver powder prepared in Example 2.

[0021] Figure 3 This is a scanning electron microscope image of the flaky silver powder prepared in Example 3.

[0022] Figure 4 This is a scanning electron microscope image of the flaky silver powder prepared in Example 4.

[0023] Figure 5 This is a scanning electron microscope image of the flaky silver powder prepared in Example 5. DETAILED DESCRIPTION

[0024] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0025] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0026] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0027] Example 1:

[0028] A method for preparing micron-sized flaky silver powder comprises the following steps:

[0029] (1) Preparation of AgNO3 aqueous solution: a certain mass of solid AgNO3 was dissolved in a certain volume of ultrapure water to prepare an AgNO3 aqueous solution with a mass concentration of 10 g / L; citric acid was added to the AgNO3 aqueous solution as a complexing agent with a concentration of 1.5 g / L; gelatin was added to the AgNO3 aqueous solution as a dispersant with a concentration of 0.2 g / L.

[0030] (2) Prepare a mixed solution of FeSO4 and Fe2(SO4)3: dissolve solid FeSO4 in ultrapure water, with a molar ratio of FeSO4 to AgNO3 of 1.2 and a FeSO4 concentration of 40 g / L; add solid Fe2(SO4)3 to the FeSO4 aqueous solution, with a molar ratio of FeSO4 to Fe2(SO4)3 of 4.37.

[0031] (3) Add a mixed solution of FeSO4 and Fe2(SO4)3 to the AgNO3 aqueous solution through a separatory funnel at a rate of 150 ml / min.

[0032] (4) Liquid phase reduction reaction, filtration separation of solid and liquid: At 30°C and under stirring, add an appropriate volume of FeSO4 and Fe2(SO4)3 mixed solution to an appropriate volume of AgNO3 solution. After reacting for 15 minutes, stop stirring, filter and separate the solid and liquid to obtain a solid product; the volume of the FeSO4 and Fe2(SO4)3 mixed solution is 1.3 times the volume of the AgNO3 solution.

[0033] (5) Cleaning and drying of the solid product: The solid product obtained in step (4) was cleaned with ultrapure water and anhydrous ethanol respectively until the pH of the washing solution was neutral, and then the solid product was vacuum dried at 40°C for 2 hours to obtain a flaky silver powder product with a particle size of 52 μm. The scanning electron microscope image thereof is shown in FIG. Figure 1 shown.

[0034] Example 2:

[0035] A method for preparing micron-sized flaky silver powder comprises the following steps:

[0036] (1) Preparation of AgNO3 aqueous solution: a certain mass of solid AgNO3 was dissolved in a certain volume of ultrapure water to prepare an AgNO3 aqueous solution with a mass concentration of 70 g / L; tartaric acid was added to the AgNO3 aqueous solution as a complexing agent with a concentration of 6 g / L; gelatin was added to the AgNO3 aqueous solution as a dispersant with a concentration of 0.3 g / L.

[0037] (2) Prepare a mixed solution of FeSO4 and Fe2(SO4)3: dissolve solid FeSO4 in ultrapure water, with a molar ratio of FeSO4 to AgNO3 of 1.7 and a FeSO4 concentration of 40 g / L; add solid Fe2(SO4)3 to the FeSO4 aqueous solution, with a molar ratio of FeSO4 to Fe2(SO4)3 of 7.62.

[0038] (3) Add a mixed solution of FeSO4 and Fe2(SO4)3 to the AgNO3 aqueous solution at a rate of 110 ml / min using a peristaltic pump.

[0039] (4) Liquid phase reduction reaction, filtering and separating the solid and liquid: at 50°C and under stirring, add an appropriate volume of a mixed solution of FeSO4 and Fe2(SO4)3 to an appropriate volume of an AgNO3 solution, react for 20 minutes, stop stirring, filter and separate the solid and liquid to obtain a solid product; the volume of the mixed solution of FeSO4 and Fe2(SO4)3 is 1.7 times that of the AgNO3 solution.

[0040] (5) Cleaning and drying of the solid product: The solid product obtained in step (4) was cleaned with ultrapure water and anhydrous ethanol respectively until the pH of the washing solution was neutral, and then the solid product was vacuum dried at 40°C for 3 hours to obtain a flaky silver powder product with a particle size of 44 μm. The scanning electron microscope image of the product is shown in FIG. Figure 2 shown.

[0041] Example 3:

[0042] A method for preparing micron-sized flaky silver powder comprises the following steps:

[0043] (1) Preparation of AgNO3 aqueous solution: a certain mass of solid AgNO3 is dissolved in a certain volume of ultrapure water to prepare an AgNO3 aqueous solution with a mass concentration of 55 g / L; tartaric acid is added to the AgNO3 aqueous solution as a complexing agent with a concentration of 7 g / L; polyvinylpyrrolidone is added to the AgNO3 aqueous solution as a dispersant with a concentration of 0.3 g / L.

[0044] (2) Preparation of a mixed solution of FeSO4 and Fe2(SO4)3: Dissolve solid FeSO4 in ultrapure water, with a molar ratio of FeSO4 to AgNO3 of 1.3 and a FeSO4 concentration of 40 g / L; add solid Fe2(SO4)3 to the FeSO4 aqueous solution, with a molar ratio of FeSO4 to Fe2(SO4)3 of 12.74.

[0045] (3) Add a mixed solution of FeSO4 and Fe2(SO4)3 to the AgNO3 aqueous solution through a separatory funnel at a rate of 180 ml / min.

[0046] (4) Liquid phase reduction reaction, filtering and separating the solid and liquid: at 50°C and under stirring, add an appropriate volume of a mixed solution of FeSO4 and Fe2(SO4)3 to an appropriate volume of an AgNO3 solution, react for 20 minutes, stop stirring, filter and separate the solid and liquid to obtain a solid product; the volume of the mixed solution of FeSO4 and Fe2(SO4)3 is 1.6 times that of the AgNO3 solution.

[0047] (5) Cleaning and drying of the solid product: The solid product obtained in step (4) was cleaned with ultrapure water and anhydrous ethanol respectively until the pH of the washing solution was neutral, and then the obtained solid product was placed in a vacuum dryer at 45°C for 2 hours to obtain a flaky silver powder product with a particle size of 25 μm, the scanning electron microscope image of which is as follows: Figure 3 shown.

[0048] Example 4:

[0049] A method for preparing micron-sized flaky silver powder comprises the following steps:

[0050] (1) Preparation of AgNO3 aqueous solution: a certain mass of solid AgNO3 is dissolved in a certain volume of ultrapure water to prepare an AgNO3 aqueous solution with a mass concentration of 30 g / L; citric acid is added to the AgNO3 aqueous solution as a complexing agent with a concentration of 5 g / L; polyvinylpyrrolidone is added to the AgNO3 aqueous solution as a dispersant with a concentration of 0.6 g / L.

[0051] (2) Prepare a mixed solution of FeSO4 and Fe2(SO4)3: dissolve solid FeSO4 in ultrapure water, with a molar ratio of FeSO4 to AgNO3 of 1.5 and a FeSO4 concentration of 40 g / L; add solid Fe2(SO4)3 to the FeSO4 aqueous solution, with a molar ratio of FeSO4 to Fe2(SO4)3 of 15.12.

[0052] (3) Add a mixed solution of FeSO4 and Fe2(SO4)3 to the AgNO3 aqueous solution at a rate of 100 ml / min using a peristaltic pump.

[0053] (4) Liquid phase reduction reaction, filtering and separating the solid and liquid: Add an appropriate volume of a mixed solution of FeSO4 and Fe2(SO4)3 to an appropriate volume of an AgNO3 solution at 60°C with stirring, react for 15 minutes, stop stirring, filter and separate the solid and liquid to obtain a solid product; the volume of the mixed solution of FeSO4 and Fe2(SO4)3 is 1.4 times that of the AgNO3 solution.

[0054] (5) Cleaning and drying of the solid product: The solid product obtained in step (4) was cleaned with ultrapure water and anhydrous ethanol respectively until the pH of the washing solution was neutral, and then the solid product was placed in a vacuum dryer at 50°C for 4 hours to obtain a flaky silver powder product with a particle size of 13 μm. The scanning electron microscope image thereof is shown in FIG. Figure 4 shown.

[0055] Example 5:

[0056] A method for preparing micron-sized flaky silver powder comprises the following steps:

[0057] (1) Preparation of AgNO3 aqueous solution: a certain mass of solid AgNO3 was dissolved in a certain volume of ultrapure water to prepare an AgNO3 aqueous solution with a mass concentration of 45 g / L; ethylenediaminetetraacetic acid was added to the AgNO3 aqueous solution as a complexing agent with a concentration of 3 g / L; and gum arabic was added to the AgNO3 aqueous solution as a dispersant with a concentration of 0.4 g / L.

[0058] (2) Preparation of a mixed solution of FeSO4 and Fe2(SO4)3: dissolve solid FeSO4 in ultrapure water, with a molar ratio of FeSO4 to AgNO3 of 1.3 and a FeSO4 concentration of 40 g / L; add solid Fe2(SO4)3 to the FeSO4 aqueous solution, with a molar ratio of FeSO4 to Fe2(SO4)3 of 22.77.

[0059] (3) Add a mixed solution of FeSO4 and Fe2(SO4)3 to the AgNO3 aqueous solution through a separatory funnel at a rate of 200 ml / min.

[0060] (4) Liquid phase reduction reaction, filtering and separating the solid and liquid: at 40°C and under stirring, add an appropriate volume of a mixed solution of FeSO4 and Fe2(SO4)3 to an appropriate volume of an AgNO3 solution, react for 5 minutes, stop stirring, filter and separate the solid and liquid to obtain a solid product; the volume of the mixed solution of FeSO4 and Fe2(SO4)3 is 1.6 times that of the AgNO3 solution.

[0061] (5) Cleaning and drying of the solid product: The solid product obtained in step (4) was cleaned with ultrapure water and anhydrous ethanol respectively until the pH of the washing solution was neutral, and then the obtained solid product was placed in a vacuum dryer at 40°C for 4 hours to obtain a flaky silver powder product with a particle size of 1.8 μm, the scanning electron microscope image of which is as follows: Figure 5 shown.

Claims

1. A method for preparing micron-sized flaky silver powder, characterized in that: The following steps are involved: A reducing agent and a particle size control agent are added to a soluble silver salt aqueous solution to carry out a liquid phase reduction reaction. After the reaction is completed, the solid phase is filtered, collected, and then washed and dried to obtain micron-sized flaky silver powder. The reducing agent is FeSO4, the particle size control agent is Fe2(SO4)3, and the molar ratio of FeSO4 to Fe2(SO4)3 is (1.0-30.0):1; FeSO4 and Fe2(SO4)3 are added to a soluble silver salt aqueous solution in the form of a mixed aqueous solution at a rate of 100-200 ml / min, wherein the concentration of the FeSO4 is 10-200 g / L, the soluble silver salt aqueous solution is an AgNO3 aqueous solution, the mass concentration of the AgNO3 aqueous solution is 5-100 g / L, and the volume of the mixed aqueous solution of FeSO4 and Fe2(SO4)3 is 0.5-2.0 times the volume of the soluble silver salt aqueous solution; A complexing agent and a dispersant are further added to the soluble silver salt aqueous solution, wherein the complexing agent includes at least one of ethylenediaminetetraacetic acid, citric acid, and tartaric acid, and the concentration of the complexing agent is 1-10 g / L; the dispersant includes at least one of polyvinyl pyrrolidone, gelatin, and gum arabic, and the concentration of the dispersant is 0.1-1 g / L; During the liquid phase reduction reaction, the reaction is carried out at 10-80°C with stirring for 5-20 minutes.

2. The preparation method according to claim 1, characterized in that The molar ratio of FeSO4 to Fe2(SO4)3 is (4.0-23.0):

1.

3. The preparation method according to claim 1, characterized in that The molar ratio of FeSO4 to soluble silver salt is (1-2):

1.

4. The preparation method according to claim 3, characterized in that The molar ratio of FeSO4 to soluble silver salt is (1.3-1.8):

1.

5. The preparation method according to claim 1, characterized in that FeSO4 and Fe2(SO4)3 are added to a soluble silver salt aqueous solution in the form of a mixed aqueous solution at a rate of 120-180 ml / min, the concentration of the FeSO4 is 30-180 g / L, and the mass concentration of the AgNO3 aqueous solution is 10-80 g / L.

6. The preparation method according to claim 1, characterized in that The concentration of the complexing agent is 3-8 g / L, and the concentration of the dispersant is 0.2-0.7 g / L.

7. The preparation method according to any one of claims 1 to 5, characterized in that During cleaning and drying, the solid phase is washed with ultrapure water and anhydrous ethanol until the pH of the washing solution is neutral, and then the obtained solid phase is placed in a vacuum dryer at 30-65° C. for 2-5 hours.

8. The preparation method according to claim 7, characterized in that During the liquid phase reduction reaction, the reaction is carried out at 20-65° C. with stirring for 10-15 minutes. During the washing and drying, the obtained solid phase is placed at 35-55° C. and vacuum dried for 3-4 hours.

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