Submicron hollow silver powder and preparation method and application thereof

Abstract

The invention belongs to the technical field of conductive materials. According to the preparation method of the submicron hollow silver powder, bubbles are generated in reaction liquid by adopting a nanometer bubble generating device. A spiral submicro-channel reactor is adopted to form a super-gravity field to control reaction liquid in the reactor, so that directional deposition and crystallization of high-density silver on the surface of spherical or sphere-like bubbles are realized, and the crystal structure, morphology, density and granularity of the hollow silver powder are regulated and controlled. The submicron hollow silver powder with high sintering activity and excellent conductivity is prepared by optimizing a chemical deposition process, accurately controlling nucleation and crystallization processes and improving dispersity, and the conversion efficiency of a photovoltaic cell is remarkably improved.

Description

Technical Field

[0001] The invention relates to silver powder and a preparation method and application thereof, and in particular to hollow silver powder and a preparation method and application thereof; and belongs to the technical field of conductive material preparation. Background Art

[0002] In the entire photovoltaic industry chain, front silver paste is one of the key factors that determine the conversion efficiency of solar cells. As the component with the highest content in silver paste, silver powder has become one of the key factors for the high conversion efficiency of silver paste.

[0003] Silver powder is divided into physical method and chemical method according to the powder making process, among which physical method includes physical grinding method, atomization method, laser ablation method, etc. Chemical preparation method includes liquid phase reduction method, chemical deposition method, spray thermal decomposition method (SP method), ultrasonic electrolysis method and other synthesis methods. Due to the lack of research foundation on the nucleation and crystallization control of photovoltaic silver paste silver powder, material morphology and particle size control, high dispersibility, surface and interface component regulation, slurry processing rheology and matching, the slurry produced using domestic silver materials has poor printing processing rheology, low sintering activity, and low battery conversion efficiency and fast attenuation under the conditions of equal wet weight of slurry and silver powder solid content. Most domestic silver powders are solid silver powders. Compared with hollow silver powders, their sintering activity is lower and the printing line shape is poor. Correspondingly, the submicron hollow silver powder of Japan's DOWA company has outstanding advantages such as silver dosage, specific surface area control, slurry sedimentation stability, surface sintering activity, sintering shrinkage and "bite" between silver powders. However, the hollow structure silver powder in the existing technology has high crystallinity, tap density and morphology and particle size distribution that are difficult to control, the preparation conditions are harsh, the reaction control conditions are sensitive, the output efficiency is low, etc., and there are high technical barriers. The large-scale industrial preparation of hollow structure silver powder is still an industry technical problem in my country.

[0004] The morphology, particle size and dispersibility of silver powder have a significant impact on the performance of silver paste. Hollow structure silver powder has obvious advantages in conductivity and sintering activity, but its preparation process is complicated and requires precise control of reaction conditions, optimization of nucleation and crystallization processes, and improvement of dispersibility to meet the photovoltaic industry's demand for high-performance silver paste. Summary of the invention

[0005] In view of the deficiencies in the comprehensive performance of silver powder in the prior art, the present invention provides a method for preparing submicron hollow silver powder, which optimizes the chemical deposition process, accurately controls the nucleation and crystallization process, improves the dispersibility, and prepares submicron hollow silver powder with high sintering activity and excellent conductivity, significantly improving the conversion efficiency of photovoltaic cells. This method not only solves the problem of high crystallinity and tap density control, but also realizes the precise control of morphology and particle size distribution, greatly improves the output efficiency, and lays a solid foundation for the independent research and development and industrial application of high-performance silver paste in my country's photovoltaic industry.

[0006] According to a first embodiment of the present invention, a method for preparing submicron hollow silver powder is provided, which comprises the steps of preparing a precursor solution, chemical deposition reaction, washing, drying and heat treatment.

[0007] A method for preparing submicron hollow silver powder, the method comprising the following steps: (1) Preparation of silver ammonia solution: prepare silver nitrate solution, then add ammonia water, stir evenly until the precipitate is dissolved, and obtain silver ammonia solution; then add dispersant, stir and mix evenly, and place in a nanobubble generating device; (2) Reduction: adding a reducing agent to the silver ammonia solution dispersion system, transferring the reaction mixture in step (1) from the nanobubble generating device into the spiral submicrochannel reactor, and subjecting the reaction mixture to a reduction reaction under spiral flow conditions; (3) Separation and purification: After the reduction reaction is completed, the mixed solution after the reaction is separated and washed to obtain a silver powder precipitate; (4) Drying: Drying the silver powder precipitate to obtain submicron hollow silver powder.

[0008] Preferably, the method further comprises the following steps: (5) The dried submicron hollow silver powder is subjected to surface coating treatment with a coating agent, and then further dried to obtain coated submicron hollow silver powder.

[0009] In the present invention, the dispersant in step (1) is one or more of oleic acid, alkylphenol polyoxyethylene ether, tristyrylphenol polyoxyethylene ether, phthalate (preferably tetra-n-butyl titanate), and polyvinyl pyrrolidone. Preferably, the dispersant is alkylphenol polyoxyethylene ether and / or tristyrylphenol polyoxyethylene ether. More preferably, the dispersant is a mixture of alkylphenol polyoxyethylene ether and tristyrylphenol polyoxyethylene ether. More preferably, the dispersant is a mixture of alkylphenol polyoxyethylene ether and tristyrylphenol polyoxyethylene ether in a weight ratio of 1:0.3-0.6.

[0010] Preferably, 2-30 g of dispersant is added per liter of silver ammonia solution, preferably 5-20 g of dispersant is added per liter of silver ammonia solution, and more preferably 8-16 g of dispersant is added per liter of silver ammonia solution.

[0011] In the present invention, the concentration of silver nitrate in the silver nitrate solution in step (1) is 3 to 5 mol / L.

[0012] In the present invention, the amount of ammonia water added is adjusted to a pH of the silver nitrate solution of 8-12. The mass concentration of the ammonia water is 5-20%.

[0013] In the present invention, the reducing agent in step (2) is one or more of ascorbic acid, citric acid, and glycerol.

[0014] Preferably, 120-300 g of reducing agent is added per liter of silver ammonia solution.

[0015] In the present invention, the coating agent is an isopropanol solution of stearic acid; wherein the concentration of stearic acid is 6% to 12%.

[0016] In the present invention, the rotation speed of the nano bubble generator is 400-700 r / min. The air intake of the nano bubble generator is 0.1-0.5 L / min. The reaction temperature is 25°C-40°C. The size of the bubbles generated by the nano bubble generator is 10-100 nm (average 50 nm ± 5 nm). The residence time of the silver nitrate solution in the nano bubble generator is 20-40 min.

[0017] In the present invention, the diameter of the spiral submicrochannel reactor is 0.5-2 mm, the length is 50-200 cm, the flow rate of the reaction mixture in the spiral submicrochannel reactor is 0.1-1 mL / min, and the reaction time of the reaction mixture in the spiral submicrochannel reactor is 0.5-2 hours.

[0018] Preferably, the separation in step (3) is suction filtration; the washing is performed 2-4 times with deionized water; and the temperature of the reduction reaction is 55°C-85°C.

[0019] In the present invention, the drying in step (4) and step (5) is performed by vacuum drying, the drying temperature is 65° C.-85° C., and the drying time is 2-12 hours.

[0020] According to a second embodiment provided by the present invention, a submicron hollow silver powder is provided.

[0021] A submicron hollow silver powder is prepared by the method described in the first embodiment.

[0022] According to a third embodiment provided by the present invention, a use of submicron hollow silver powder is provided.

[0023] The submicron hollow silver powder prepared by the method of the first embodiment is applied to the fields of conductive coatings, antibacterial materials and electromagnetic shielding, and is preferably used in conductive silver paste for solar cells.

[0024] In the technical solution provided by the present invention, a silver nitrate solution is first prepared, and then ammonia water is added to adjust the pH to 8-12. After the precipitate is completely dissolved, a silver ammonia solution ([Ag(NH3)2OH]) is obtained. Then a dispersant is added, and gas is introduced into the silver ammonia solution through a nano bubble generator to form uniform nano bubbles. The nano bubbles promote the uniform dispersion of the dispersant in the silver ammonia solution, and at the same time, some bubbles are retained in the silver ammonia solution to prevent the silver ammonia solution from agglomerating during the deposition process. Subsequently, a reducing agent is added to the above-mentioned mixed solution, and the reaction mixture is placed in a spiral submicrochannel reactor. Under the state of spiral flow, a reduction reaction is carried out at 55°C-85°C. During the reaction, the nano bubbles continue to act, effectively inhibiting the agglomeration of silver particles, and ensuring that the generated submicron hollow silver powder has a uniform structure and a consistent particle size. After the reaction is completed, the solid product is separated by suction filtration and washed 2-4 times with deionized water to remove residual impurities. Finally, the product is vacuum dried, the drying temperature is controlled at 65° C.-85° C., and the drying time is 2-12 hours to obtain high-purity submicron hollow silver powder.

[0025] As a preferred technical solution of the present invention, the prepared submicron hollow silver powder is further subjected to surface coating treatment with a coating agent, and after the coating treatment, the coated submicron hollow silver powder is obtained by drying. The coating treatment prevents oxidation of the submicron hollow silver powder, improves the stability of the submicron hollow silver powder, and also further improves the optical effect of the submicron hollow silver powder.

[0026] In the preferred technical scheme of the present invention, the inventor further experimentally studied and verified that the type and amount of the dispersant directly affect the hollow ratio, specific surface area, tap density, heat loss and particle size distribution of the submicron hollow silver powder. In the present invention, a single substance among oleic acid, alkylphenol polyoxyethylene ether, tristyrylphenol polyoxyethylene ether, phthalate, and polyvinyl pyrrolidone is used as a dispersant, or a mixture of oleic acid, alkylphenol polyoxyethylene ether, tristyrylphenol polyoxyethylene ether, phthalate, and polyvinyl pyrrolidone is used as a dispersant. Experimental studies have shown that when alkylphenol polyoxyethylene ether and tristyrylphenol polyoxyethylene ether are used as dispersants, the performance of the submicron hollow silver powder is better. The inventor further discovered through experiments that when a mixture of alkylphenol polyoxyethylene ether and tristyrylphenol polyoxyethylene ether is used, and the mixture of alkylphenol polyoxyethylene ether and tristyrylphenol polyoxyethylene ether is controlled to be 1:0.3-0.6 by weight as a dispersant, the hollow rate of the obtained submicron hollow silver powder is as high as more than 90%, the specific surface area is significantly improved, the tap density is uniform, the heat loss is reduced, the particle size distribution is more concentrated, and the overall performance reaches the optimal state. In addition, the experiment also shows that the dispersant combination can effectively regulate the growth direction of silver particles during the reaction process, ensure the integrity and stability of the hollow structure, and further enhance the application potential of submicron hollow silver powder in optics, electronics and other fields. By optimizing the dispersant combination and ratio, the experimental results confirm that the hollow structure of the submicron hollow silver powder is more regular, the surface smoothness is improved, and the optical reflection performance is enhanced. It is suitable for the manufacture of high-precision optical devices and broadens its application prospects in high-tech fields.

[0027] In the present invention, the nano bubble generating device (nano bubble generator) is a mature device in the prior art, which is also called a nano aerator and a micro-nano bubble generating device. The device generates nano-scale bubbles through high-frequency vibration, which effectively promotes the uniformity of the reaction. The nano bubble generating device is used in the preparation process of the present invention, and it is only necessary to control the process condition parameters of the nano bubble generating device. The scientific research-specific micro-nano bubble generator 1-100T produced by Hangzhou Guimou Technology Co., Ltd. and the ZJC-NM series small experimental micro-nano bubble generator produced by Shanghai Zhongmou Technology Co., Ltd. are both suitable for the present invention. In the process of preparing submicron hollow silver powder of the present invention, the rotation speed of the nano bubble generating device is controlled to be 400-700r / min; the air intake of the nano bubble generating device is 0.1-0.5L / min; the reaction temperature is 25℃-40℃; the size of the bubbles generated by the nano bubble generating device is 10-100nm; the residence time of the silver nitrate solution in the nano bubble generating device is 20-40min.

[0028] In the present invention, the reduction reaction is carried out using a spiral submicrochannel reactor, preferably a double-spiral submicrochannel reactor. The reactor optimizes the fluid dynamics to ensure that the reactants are fully mixed and the reaction efficiency is improved. Experimental results show that in the spiral submicrochannel reactor, the generation rate of submicron hollow silver powder is increased by 30%, and the particle size distribution is more uniform, further enhancing its application reliability in the field of high-performance materials. The spiral submicrochannel reactor is a mature device in the prior art, which is also called a spiral continuous flow microchannel reactor or a spiral submicrochannel reactor. Chinese Patent CN112827440A discloses its specific structure. The spiral submicrochannel reactors produced by NYC-YN-2X (8D) of Changzhou Namou Technology Co., Ltd. and H-Flow-S50 of Oumou Technology Co., Ltd. are both suitable for the present invention. The present invention selects a spiral submicrochannel reactor with a diameter of 0.5-20mm and a length of 50-2000cm, the flow rate of the reaction mixture in the spiral submicrochannel reactor is 0.1-1mL / min, and the reaction time of the reaction mixture in the spiral submicrochannel reactor is 0.5-2 hours.

[0029] The submicron hollow silver powder prepared by the present invention not only has excellent optical properties but also exhibits excellent chemical stability through a specific process and the selection of specific additives. The submicron hollow silver powder prepared by the present invention contains more than 60% of the silver powder and has a specific surface area of ​​0.25 to 0.6 m 2 / g, tap density 5~7g / cm 3 , heat loss (538℃) 0.1~0.9%, particle size distribution D10≤1.0μm, D50≤3.0μm, D90≤5.0μm. It has high sintering activity (sintering temperature is 5-10 degrees lower than the reference), photoelectric conversion efficiency is 0.03~0.07% higher than the reference, and has good printing processability, low wire breakage rate, and good grid line aspect ratio. It is used for photovoltaic conductive silver paste with high quality and stability.

[0030] Compared with the prior art, the technical solution provided by the present invention has the following friendly technical effects: 1. Introduce nanobubble generating device, which can effectively inhibit the continuous growth of silver particles, control the growth rate of crystal nuclei and the particle size of silver powder products. Use nanobubbles as crystal nuclei to prepare submicron hollow silver powder.

[0031] 2. Use a spiral submicrochannel reactor to form a supergravity field, control the reaction liquid in the reactor to achieve high-density silver directional deposition and crystallization on the surface of spherical or quasi-spherical bubbles, and regulate the crystal structure, morphology, density and particle size of hollow silver powder.

[0032] 3. In the preferred technical solution of the present invention, a suitable dispersant is selected to effectively prevent the agglomeration of silver particles and ensure the uniform dispersion of silver powder. By precisely controlling the reaction conditions, the obtained submicron hollow silver powder has excellent sphericity and porosity, and improves the conductivity and antibacterial effect. It is suitable for high-performance solar cell conductive silver paste and significantly improves the photoelectric conversion efficiency.

[0033] 4. The submicron hollow silver powder prepared by the present invention has significantly improved conductivity, antibacterial properties and electromagnetic shielding performance, especially its application in the conductive silver paste of solar cells, which significantly improves the efficiency and stability of the cells. The prepared submicron hollow silver powder has high sintering activity, and its photoelectric conversion efficiency is 0.03-0.07% higher than that of domestic silver powder, and it has good printing processability and a wire breakage rate reduced by more than 20%. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Scanning electron microscope image (10,000 times) of submicron hollow silver powder prepared in Example 1 of the present application; Figure 2 Scanning electron microscope image (10,000 times) of submicron hollow silver powder prepared in Example 3 of the present application; Figure 3 FIB-SEM-5μm cross-sectional image of submicron hollow silver powder prepared in Example 11 of the present application; Figure 4 This is a FIB-SEM-1 μm cross-sectional image of the submicron hollow silver powder prepared in Example 11 of the present application. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is illustrated below by way of example, and the scope of protection requested by the present invention includes but is not limited to the following embodiments. Example 1

[0036] A method for preparing submicron hollow silver powder comprises the following steps: (1) Preparation of silver ammonia solution: prepare 6L of 4mol / L silver nitrate solution, then add 10% dilute ammonia water until no precipitation is generated, stir evenly until the precipitation is completely dissolved, and adjust the pH to 9. Then add 60g of oleic acid, stir and mix evenly, and place in the nanobubble generating device; adjust the temperature in the nanobubble generating device to 30℃; the size of the bubbles generated by the nanobubble generating device is 50nm±5nm; the residence time of the silver nitrate solution in the nanobubble generating device is 30min; (2) Add 900 g of ascorbic acid to the silver ammonia solution dispersion; (3) The reaction mixture in step (2) is transferred from the nanobubble generating device into the spiral submicrochannel reactor, the temperature of the device is set to 70°C, the flow rate of the reaction mixture in the spiral submicrochannel reactor is 0.05 mL / min, and the residence time of the reaction mixture in the spiral submicrochannel reactor is 1 hour. The reactor can form a supergravity field, control the reaction liquid in the reactor to achieve high-density silver directional deposition crystallization on the surface of spherical or quasi-spherical bubbles, and regulate the crystal structure and morphology, density, and particle size of the hollow silver powder; (4) After the reduction reaction is fully completed, the mixed solution after the reaction is filtered to obtain a silver powder precipitate, which is then washed twice with deionized water and filtered to obtain a solid; (5) Drying and sieving: The silver powder precipitate is dried in a vacuum drying oven at a temperature of 75°C for 6 hours. It is then sieved with a 400-mesh sieve to obtain submicron hollow silver powder. Example 2

[0037] A method for preparing submicron hollow silver powder comprises the following steps: (1) Preparation of silver ammonia solution: prepare 6L of 4mol / L silver nitrate solution, then add 10% dilute ammonia water until no precipitation is generated, stir evenly until the precipitation is completely dissolved, and adjust the pH to 10. Then add 60g of alkylphenol polyvinyl ether, stir and mix evenly, and place in the nanobubble generating device; adjust the temperature in the nanobubble generating device to 30℃; the size of the bubbles generated by the nanobubble generating device is 50nm±5nm; the residence time of the silver nitrate solution in the nanobubble generating device is 30min; (2) Add 1000 g of citric acid to the silver ammonia solution dispersion system; (3) The reaction mixture in step (2) is transferred from the nanobubble generating device into the spiral submicrochannel reactor, the temperature of the device is set to 70°C, the flow rate of the reaction mixture in the spiral submicrochannel reactor is 0.05 mL / min, and the residence time of the reaction mixture in the spiral submicrochannel reactor is 1 hour. The reactor can form a supergravity field, control the reaction liquid in the reactor to achieve high-density silver directional deposition crystallization on the surface of spherical or quasi-spherical bubbles, and regulate the crystal structure and morphology, density, and particle size of the hollow silver powder; (4) After the reduction reaction is fully completed, the mixed solution after the reaction is filtered to obtain a silver powder precipitate, which is then washed twice with deionized water and filtered to obtain a solid; (5) Drying and sieving: The silver powder precipitate is dried in a vacuum drying oven at a temperature of 75°C for 6 hours. It is then sieved with a 400-mesh sieve to obtain submicron hollow silver powder. Example 3

[0038] A method for preparing submicron hollow silver powder comprises the following steps: (1) Preparation of silver ammonia solution: prepare 6L of 4mol / L silver nitrate solution, then add 10% dilute ammonia water until no precipitation is generated, stir evenly until the precipitation is completely dissolved, and adjust the pH to 11. Then add 60g of polyvinyl pyrrolidone, stir and mix evenly, and place in a nanobubble generating device; adjust the temperature in the nanobubble generating device to 30℃; the size of the bubbles generated by the nanobubble generating device is 50nm±5nm; the residence time of the silver nitrate solution in the nanobubble generating device is 30min; (2) Add 1200 g of propylene glycol to the silver ammonia solution dispersion; (3) The reaction mixture in step (2) is transferred from the nanobubble generating device into the spiral submicrochannel reactor, the temperature of the device is set to 70°C, the flow rate of the reaction mixture in the spiral submicrochannel reactor is 0.05 mL / min, and the residence time of the reaction mixture in the spiral submicrochannel reactor is 1 hour. The reactor can form a supergravity field, control the reaction liquid in the reactor to achieve high-density silver directional deposition crystallization on the surface of spherical or quasi-spherical bubbles, and regulate the crystal structure and morphology, density, and particle size of the hollow silver powder; (4) After the reduction reaction is fully completed, the mixed solution after the reaction is filtered to obtain a silver powder precipitate, which is then washed twice with deionized water and filtered to obtain a solid; (5) Drying and sieving: The silver powder precipitate is dried in a vacuum drying oven at a temperature of 75°C for 6 hours. It is then sieved with a 400-mesh sieve to obtain submicron hollow silver powder. Example 4

[0039] A method for preparing submicron hollow silver powder comprises the following steps: (1) Preparation of silver ammonia solution: prepare 6L of 4mol / L silver nitrate solution, then add 10% dilute ammonia water until no precipitation is generated, stir evenly until the precipitation is completely dissolved, and adjust the pH to 12. Then add 60g of tetra-n-butyl titanate, stir and mix evenly, and place in a nanobubble generating device; adjust the temperature in the nanobubble generating device to 30℃; the size of the bubbles generated by the nanobubble generating device is 50nm±5nm; the residence time of the silver nitrate solution in the nanobubble generating device is 30min; (2) Add 1500 g of ascorbic acid to the silver ammonia solution dispersion; (3) The reaction mixture in step (2) is transferred from the nanobubble generating device into the spiral submicrochannel reactor, the temperature of the device is set to 70°C, the flow rate of the reaction mixture in the spiral submicrochannel reactor is 0.05 mL / min, and the residence time of the reaction mixture in the spiral submicrochannel reactor is 1 hour. The reactor can form a supergravity field, control the reaction liquid in the reactor to achieve high-density silver directional deposition crystallization on the surface of spherical or quasi-spherical bubbles, and regulate the crystal structure and morphology, density, and particle size of the hollow silver powder; (4) After the reduction reaction is fully completed, the mixed solution after the reaction is filtered to obtain a silver powder precipitate, which is then washed twice with deionized water and filtered to obtain a solid; (5) Drying and sieving: The silver powder precipitate is dried in a vacuum drying oven at a temperature of 75°C for 6 hours. It is then sieved with a 400-mesh sieve to obtain submicron hollow silver powder. Example 5

[0040] A method for preparing submicron hollow silver powder comprises the following steps: (1) Preparation of silver ammonia solution: prepare 6L of 4mol / L silver nitrate solution, then add 10% dilute ammonia water until no precipitation is generated, stir evenly until the precipitation is completely dissolved, and adjust the pH to 10. Then add 60g of tristyrylphenol polyoxyethylene ether, stir and mix evenly, and place in a nanobubble generating device; adjust the temperature in the nanobubble generating device to 30℃; the size of the bubbles generated by the nanobubble generating device is 50nm±5nm; the residence time of the silver nitrate solution in the nanobubble generating device is 30min; (2) Add 1000 g of citric acid to the silver ammonia solution dispersion system; (3) The reaction mixture in step (2) is transferred from the nanobubble generating device into the spiral submicrochannel reactor, the temperature of the device is set to 70°C, the flow rate of the reaction mixture in the spiral submicrochannel reactor is 0.05 mL / min, and the residence time of the reaction mixture in the spiral submicrochannel reactor is 1 hour. The reactor can form a supergravity field, control the reaction liquid in the reactor to achieve high-density silver directional deposition crystallization on the surface of spherical or quasi-spherical bubbles, and regulate the crystal structure and morphology, density, and particle size of the hollow silver powder; (4) After the reduction reaction is fully completed, the mixed solution after the reaction is filtered to obtain a silver powder precipitate, which is then washed twice with deionized water and filtered to obtain a solid; (5) Drying and sieving: The silver powder precipitate is dried in a vacuum drying oven at a temperature of 75°C for 6 hours. It is then sieved with a 400-mesh sieve to obtain submicron hollow silver powder. Example 6

[0041] Example 1 was repeated, except that the prepared micron hollow silver powder was further treated in step (6); (6) The dried silver powder is subjected to surface coating treatment, wherein the coating agent is an isopropanol solution of stearic acid, and the concentration of stearic acid is 8%. After the treatment is completed, the powder is dried in a vacuum drying oven at 75°C for 6 hours and sieved through a 400-mesh sieve to obtain coated submicron hollow silver powder.

[0042] The method described in Example 2 was adopted, and the different process conditions were followed according to the following different dispersant types and amounts. The other process conditions were the same as those in Example 2. Tests were conducted to detect the properties of the submicron hollow silver powders prepared in each example. The results are shown in the following table.

[0043]

[0044] In the present invention, the specific surface area and tap density are tested according to the provisions of GB / T 1774-2009, the heat loss is tested according to GB / T 5150, the particle size distribution is tested according to GB / T 19077-2016, and the hollow ratio is calculated by scanning electron microscopy. The data of each embodiment show that the type and amount of dispersant have a significant effect on the performance of submicron hollow silver powder. Through comparative analysis, it is found that the composite use of alkylphenol polyoxyethylene ether and tristyrylphenol polyoxyethylene ether can significantly improve the hollow ratio and specific surface area, optimize the tap density, and reduce heat loss at a specific ratio, which provides an important reference for the preparation of high-performance submicron hollow silver powder. Further experimental verification shows that the optimal ratio is 1:0.4. Under this ratio, the hollow structure of silver powder is more stable, the thermal stability is improved, and the application prospect is broad. In addition, the ratio has shown excellent repeatability and stability in multiple experiments, providing a reliable basis for industrial production. In the future, the process parameters can be further optimized on this basis, in order to achieve wide application in more fields. The study also found that this ratio significantly improves the conductivity and oxidation resistance of silver powder, and is expected to play an important role in the electronics, medical and other industries. Experimental data show that the particle size distribution of silver powder is more uniform under this ratio, further improving its application performance. In addition, the stability of this ratio in high temperature environment has also been verified, providing a new solution for high temperature application scenarios.

[0045] In the embodiments of the present invention, some of the materials are from the following sources: oleic acid was purchased from Shanghai Lisen Chemical, with a purity of 99.5%. Alkylphenol polyvinyl ether (CAS: 9036-19-5) was purchased from Taizhou Jiayin Chemical Co., Ltd. (NP-10), with a turbidity point (1% aqueous solution) of 68-78°C, hydroxyl 87±5mgKNH / g, moisture less than or equal to 1.0%, pH (1% aqueous solution) 5.0-7.0, HLB value 13.3-14, and purity 98.8%. Tristyrylphenol polyoxyethylene ether (CAS: 99734-09-5) was provided by Jiangsu Hai'an Petrochemical, with a turbidity point (1% aqueous solution) of 90-100°C, HLB value 12-16, and purity 98.6% (model: concentrated milk 603). Ascorbic acid was purchased from Hebei Kelongduo Biotechnology Co., Ltd. with a purity of 99.2%. Stearic acid was provided by Guangzhou Gongxin Chemical with a purity of 98.8%. Isopropanol was purchased from Shandong Qilu Chemical Industry with a purity of 99.7%. The experimental water was deionized water with a purity of 99.9%. Citric acid was purchased from Jiangsu Suhua Group with a purity of 99.5%. Polyvinylpyrrolidone (CAS: 9003-39-8) was purchased from Gongbik New Materials Technology Co., Ltd., PVP-K25, number average molecular weight 32000, resin content (wt%) > 95, viscosity (mps.s-25℃ / 5%ap) 1.7-2.1, pH 3.0-7.0, K value 22.4-27.0, purity 99.3%. Propylene glycol was purchased from Suzhou Minghua Sugar Alcohol Co., Ltd. with a purity of 99.8%. Tetrabutyl titanate (CAS: 5593-70-4) was purchased from Shandong Oriental Riqi New Materials Co., Ltd. All raw materials have undergone strict quality inspection to ensure the accuracy and reliability of the experimental results.

Claims

1. A method for preparing submicron hollow silver powder, characterized in that: The steps include: (1) Preparation of silver ammonia solution: prepare silver nitrate solution, then add ammonia water, stir evenly until the precipitate is dissolved, and obtain silver ammonia solution; then add dispersant, stir and mix evenly, and place in a nanobubble generating device; (2) Reduction: adding a reducing agent to the silver ammonia solution dispersion system, transferring the reaction mixture in step (1) from the nanobubble generating device into the spiral submicrochannel reactor, and subjecting the reaction mixture to a reduction reaction under spiral flow conditions; (3) Separation and purification: After the reduction reaction is completed, the mixed solution after the reaction is separated and washed to obtain a silver powder precipitate; (4) Drying: Drying the silver powder precipitate to obtain submicron hollow silver powder.

2. The preparation method according to claim 1, characterized in that: The method further comprises the following steps: (5) The dried submicron hollow silver powder is subjected to surface coating treatment with a coating agent, and then further dried to obtain coated submicron hollow silver powder.

3. The preparation method according to claim 1 or 2, characterized in that: The dispersant in step (1) is one or more of oleic acid, alkylphenol polyoxyethylene ether, tristyrylphenol polyoxyethylene ether, phthalate, and polyvinyl pyrrolidone; preferably, the dispersant is alkylphenol polyoxyethylene ether and / or tristyrylphenol polyoxyethylene ether; further preferably, the dispersant is a mixture of alkylphenol polyoxyethylene ether and tristyrylphenol polyoxyethylene ether, and more preferably, the dispersant is a mixture of alkylphenol polyoxyethylene ether and tristyrylphenol polyoxyethylene ether in a weight ratio of 1:0.3-0.6; Preferably, 2-30 g of dispersant is added per liter of silver ammonia solution, preferably 5-20 g of dispersant is added per liter of silver ammonia solution, and more preferably 8-16 g of dispersant is added per liter of silver ammonia solution.

4. The preparation method according to claim 1 or 2, characterized in that: The concentration of silver nitrate in the silver nitrate solution in step (1) is 3 to 5 mol / L; and / or The amount of ammonia water added is adjusted to a pH of the silver nitrate solution of 8-12; the mass concentration of the ammonia water is 5-20%.

5. The preparation method according to claim 1 or 2, characterized in that: The reducing agent in step (2) is one or more of ascorbic acid, citric acid, and glycerol; Preferably, 120-300 g of reducing agent is added per liter of silver ammonia solution.

6. The preparation method according to claim 2, characterized in that: The coating agent is an isopropanol solution of stearic acid; wherein the concentration of the stearic acid is 6% to 12%.

7. The preparation method according to claim 1 or 2, characterized in that: The rotation speed of the nano bubble generating device is 400-700r / min; the air intake volume of the nano bubble generating device is 0.1-0.5L / min; the reaction temperature is 25°C-40°C; the size of the bubbles generated by the nano bubble generating device is 10-100nm; the residence time of the silver nitrate solution in the nano bubble generating device is 20-40min; and / or The diameter of the spiral submicrochannel reactor is 0.5-20 mm, the length is 50-2000 cm, the flow rate of the reaction mixture in the spiral submicrochannel reactor is 0.1-1 mL / min, and the reaction time of the reaction mixture in the spiral submicrochannel reactor is 0.5-2 hours.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The separation in step (3) is suction filtration; the washing is performed 2-4 times with deionized water; the temperature of the reduction reaction is 55°C-85°C; and / or The drying in step (4) and step (5) is performed by vacuum drying, the drying temperature is 65° C.-85° C., and the drying time is 2-12 hours.

9. A submicron hollow silver powder, characterized in that: The submicron hollow silver powder is prepared according to the method according to any one of claims 1-8.

10. Use of the submicron hollow silver powder prepared by the method according to any one of claims 1 to 8, characterized in that: The submicron hollow silver powder is applied to the fields of conductive coatings, antibacterial materials and electromagnetic shielding, and is preferably used in conductive silver paste for solar cells.

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