Semi-dry preparation process of superfine silver powder

Abstract

The invention discloses a preparation method of silver powder, which comprises the following steps: preparing a silver-containing stock solution in a silver-containing stock solution preparation tank, carrying out chemical reduction reaction in an atomization reaction kettle to form a silver powder precursor solution, conveying atomized feed to a spray drying tower through an electrostatic field generated by an electrode, and carrying out low-temperature electrostatic spray drying, and finally, collecting the silver powder by using a rotary particle collector. The silver powder prepared by the method has the advantages of uniform particles, high purity, high production efficiency and the like.

Description

Technical Field

[0001] The present invention belongs to the field of material preparation technology, and particularly relates to a method for preparing high-quality silver powder using innovative processes and advanced technical means. With the rapid development of modern science and technology, silver powder has shown its indispensable importance in many fields such as electronic circuits, photovoltaic energy, biomedicine, fine chemicals, etc. However, the existing silver powder preparation technology has gradually revealed its limitations in meeting the growing requirements of high performance, high precision and special applications.

[0002] The silver powder preparation field focused on by this invention aims to break through the bottleneck of traditional technology, open up a new preparation path, and achieve significant improvement in key performance indicators such as particle size, morphology, structure, dispersibility, purity, etc. of silver powder through unique process design and fine process control, and ensure an efficient, stable and large-scale mass production preparation process. This not only provides a higher quality material foundation for the widespread application of silver powder, but also will have a positive and far-reaching impact on the technological upgrading and innovative development of related industries. Background Art

[0003] In today's era of rapid technological development, silver powder, as a key functional material, plays a vital role in many cutting-edge fields such as high-performance electronic circuits, advanced photovoltaic energy conversion, precision biomedical applications, and fine chemical synthesis. However, traditional silver powder manufacturing methods, whether based on physical processes such as grinding, evaporation and condensation, or common chemical synthesis routes, face a series of challenges and limitations that are difficult to overcome. Traditional physical manufacturing methods, such as grinding, often lead to irregular shapes of silver powder particles, wide particle size distribution, and easy introduction of impurities during the production process, affecting the purity and performance of the silver powder. The evaporation and condensation method has the problems of complex equipment, high cost, and difficulty in large-scale production. In the field of chemical synthesis, common preparation methods are usually difficult to accurately control the particle size and morphology of silver powder, and agglomeration is prone to occur, resulting in poor dispersion of silver powder, which in turn affects its performance in applications. With the continuous advancement of science and technology, the performance requirements for silver powder are becoming more and more refined and stringent. In the electronics field, the development trend of miniaturization and high performance requires silver powder to have smaller particle size, more uniform particle size distribution and good conductivity; in the biomedicine field, specific application scenarios require silver powder to have high biocompatibility and precise size control; in the new energy field, efficient energy conversion depends on the high purity and excellent catalytic properties of silver powder.

[0004] Therefore, in order to meet these increasingly demanding and diversified demands, it is urgently necessary to develop an innovative silver powder preparation method that can achieve precise control of silver powder particles to ensure its excellent performance and stable quality, while having the advantages of high efficiency, scalable production and environmental friendliness, so as to promote the continuous innovation and development of related industries. Summary of the invention

[0009] The present invention aims to provide a new method for preparing silver powder, the principle of which is based on the combination of chemical reduction reaction and low-temperature electrostatic spray drying technology. Chemical reduction reaction can effectively convert silver-containing compounds into silver element, while low-temperature electrostatic spray drying technology can ensure that the silver element is dried into silver powder to form a finer particle size and stable quality, and realize rapid drying and precise control of particle morphology. In the preparation process, the silver-containing stock solution preparation tank can ensure the uniform distribution of silver ions in the stock solution through a carefully designed stirring and liquid discharge mechanism, laying the foundation for the consistency and stability of subsequent reactions. In the atomization reactor, the fine atomized particles formed by the two-fluid nozzle increase the contact area of ​​the reactants and improve the reaction efficiency. The electrostatic field generated by the electrode prompts the silver monomer solution with a perfect reaction to form an aerosol and stably suspend, and the particle size of the final product is controlled by adjusting the particle size and electric field load of the two-fluid nozzle. In order to verify the effectiveness of the present invention, we conducted a series of empirical studies and compared them with traditional silver powder preparation methods. Traditional methods such as physical grinding often result in irregular shapes of silver powder particles and wide particle size distribution, and impurities are easily introduced during the production process, affecting the purity and performance of the silver powder. Chemical precipitation methods are usually difficult to accurately control the particle size and morphology of silver powder, and agglomeration is prone to occur, resulting in poor dispersibility of silver powder. The physical atomization method has large equipment investment, high energy consumption, low yield and high cost, and is difficult to prepare silver powder below the micron level. The experimental results of the present invention show that by controlling the parameters of the two-fluid nozzle, such as injection pressure and flow rate, the size of the atomized particles can be accurately adjusted, thereby significantly affecting the particle size of the final silver powder. By adjusting the conditions of the chemical reduction reaction, including reaction temperature, time and reactant concentration, the effective regulation of the particle size of the silver powder is successfully achieved. The wind speed and temperature distribution of the low-temperature hot air circulation in the spray drying tower, as well as the intensity of the low-temperature electrostatic field, are optimized, so that the silver powder particles grow and solidify uniformly during the drying process, avoiding the agglomeration and adhesion of the particles. Compared with the traditional method, the silver powder prepared by the present invention has significant advantages such as uniform particles, controllable particle size, high purity and good dispersibility.

[0010] The basic technical solution of the present invention comprises the following steps: (See the attached drawing of the specification for the preparation process overview) Figure 1 )

[0011] Prepare the stock solution of the silver compound in the silver stock solution preparation tank. Mix silver nitrate with deionized water under experimental conditions. Under working conditions, choose a suitable silver-containing compound as the silver source according to local conditions. Common ones are silver nitrate, silver chloride, etc. The silver-containing stock solution is mixed with deionized water or other suitable solvents in the preparation tank to form a uniform mixed solution. After being discharged from the discharge port, it is charged by the electrode to form a charged silver-containing stock solution. (See the attached figure of the specification for the diagram of the silver stock solution preparation tank Figure 2 ).

[0012] Prepare the corresponding reducing agent according to the type of silver-containing stock solution, such as ascorbic acid (vitamin C), hydrazine hydrate, formaldehyde, sodium borohydride, etc. The reducing agent, additive and silver-containing stock solution are sprayed into the atomization reactor through a dual-fluid nozzle to form fine atomized particles according to the required chemical reaction ratio for chemical reduction reaction. The dual-fluid nozzle forms a silver powder precursor solution. In this process, the electrostatic field generated by the electrode causes the liquid particles that have completed the reaction to be affected by the charge, breaking through the surface tension, tearing the large droplets into small droplets, and forming finer liquid mist particles, so that the silver monomer droplets that have been reacted are easier to form aerosols suspended above, reducing the adhesion of silver single particles. (For the diagram of the atomization reactor, please refer to the attached figure of the instruction manual Figure 3 ).

[0013] The aerosol silver powder precursor solution is transported through an aerosol pipeline, sprayed downward from the top of the spray drying tower through a conical air nozzle, and transported to the spray drying tower at a uniform speed. In the spray drying tower, low-temperature electrostatic spray drying is performed using a low-temperature hot air cycle. The air supply volume, inlet temperature and outlet temperature of the spray drying tower are set to evaporate the moisture without being destructive to the silver powder, and finally form silver powder particles. In order to protect the silver powder from oxidation, the air supply gas in the spray drying tower is generally an inert protective gas, and nitrogen is generally selected due to cost reasons. Finally, a rotating particle collector is used to collect the silver powder. There are multiple layers of grid-type partitions in the middle of the rotating particle collector, which are loaded with static electricity to adsorb silver single-substance particles that meet the specifications. After escaping from the escape port, larger particles are gathered at the recovery port at the bottom of the spray drying tower, which does not affect the quality of the silver powder in the rotating particle collector. (For a diagram of the spray drying tower, please refer to the attached figure of the specification. Figure 4 )

[0014] After the preparation is completed, the rotating particle collector is pulled out of the spray drying tower under the protection of inert gas. After the static electricity effect is eliminated, the silver powder falls off naturally. Effective control of particle size:

[0015] Select appropriate atomizing nozzles and spray rods, and control the hydraulic pressure, air pressure, and flow parameters of the dual-fluid nozzle to adjust the size of the atomized particles, thereby affecting the final particle size of the silver powder.

[0016] Adjusting the conditions of the chemical reduction reaction, including reaction pH, temperature, time and reactant concentration, etc., can affect the generation rate and aggregation state of the silver monomer and achieve regulation of the particle size of the silver powder.

[0017] According to the material input and particle size monitoring, the voltage and frequency of the electrode are adjusted in time, and the particles of the cracked liquid mist are adsorbed by electric charge to make the particles more uniform.

[0018] Optimize the inert gas wind speed and temperature distribution of the low-temperature hot air circulation in the spray drying tower, as well as the electrostatic strength of the rotating particle collector to ensure the uniform growth and solidification of the silver powder particles during the drying process, so as to achieve the purpose of controlling the particle size. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is an overview of the entire preparation process. Figure 2 This is a schematic diagram of the structure of a silver-containing raw solution preparation tank. Depending on the working conditions, preparation quantity, raw materials, etc., the shape, material and structure of the preparation tank will be different. Figure 3 This is a schematic diagram of the structure of the atomizing reactor. Depending on the working conditions, preparation amount, reducing agent, etc., the shape, material, sensing element and structure of the atomizing reactor will be different. Figure 4 The diagram is a schematic diagram of the structure of a spray drying tower and a partial diagram of the structure of a rotating particle collector. Depending on the working conditions, preparation volume, reducing agent, etc., the shape, material, fan position and structure of the spray drying tower will be different.

Claims

1. A method for preparing silver powder, characterized in that: The following steps are involved: preparing a stock solution of a silver compound in a silver-containing stock solution preparation tank; The reducing agent, additive and silver-containing stock solution are mixed in a certain proportion, and formed into fine atomized particles through a dual-fluid nozzle, and then added into an atomizing reactor to undergo a chemical reduction reaction to form a silver powder precursor solution. The electrostatic field generated by the electrode makes it easier for the silver monomer solution that has been fully reacted to form an aerosol suspended above. The silver powder precursor solution of the atomized feed is sprayed uniformly through an air nozzle and transported to a spray drying tower; In the spray drying tower, low-temperature hot air circulation is used to perform low-temperature electrostatic spray drying to form silver powder particles; The silver powder was collected using a rotating particle collector.

2. The method for preparing silver powder according to claim 1, characterized in that: In the silver-containing stock solution preparation tank, the bottom stirring nozzle and the middle liquid outlet are coordinated to achieve a relatively uniform and stable liquid concentration.

3. The method for preparing silver powder according to claim 1, characterized in that: The atomization reactor generates aerosol through atomization, and uses the top electrode plate to attract and make it easier for the particles after the reaction to suspend. The material is fed into the spray drying tower only after sufficient reaction.

4. The method for preparing silver powder according to claim 1, characterized in that: The low-temperature hot air circulation system in the spray drying tower works synergistically with the low-temperature electrostatic field to ensure that the silver powder particles are dried quickly and in a uniform shape, and are not prone to sticking.

5. The method for preparing silver powder according to claim 1, characterized in that: The particle size of the silver powder can be effectively controlled by controlling the parameters of the dual-fluid nozzle, the chemical reduction reaction conditions and the working parameters of the spray drying tower.

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