Preparation method of silver powder

Abstract

The invention belongs to the technical field of preparation of silver-coated copper powder, and particularly relates to a preparation method of silver powder, which is characterized by comprising the following steps: (1) solution preparation: preparing a strain solution, a solution A, a solution B and a solution C; (2) silver powder synthesis is conducted, specifically, silver powder seed crystals are added into the solution C, the solution B is added after uniform stirring, then the solution A is dropwise added under the stirring condition, and a reaction is conducted for 15 min at the temperature of 10-30 DEG C; (3) silver powder surface treatment is conducted, specifically, a surface treating agent is added into the reaction mixed solution obtained in the step (2), a pH regulator is added to adjust the pH value to 6-7, and stirring is conducted for 10-15 min; and (4) silver powder post-treatment is conducted, specifically, after the reaction mixed solution in the step (3) is subjected to sedimentation and drainage, ethyl alcohol washing and drying are conducted, and the silver powder is obtained. The silver paste has the beneficial effects that the viscosity of the silver paste prepared from the silver powder is small, the viscosity increase is not obvious under high-speed stirring, and the thixotropy is good, so that the printing performance of the silver paste prepared from the silver powder is good.

Description

Technical Field

[0001] The invention belongs to the technical field of silver powder preparation, and particularly relates to a method for preparing silver powder. Background Art

[0002] There are three main methods for the production of silver powder: physical method, chemical method and microbial method. The chemical method has simple equipment and process, high production efficiency and is suitable for industrial production. Most silver powder manufacturers use chemical synthesis. Commonly used chemical methods include high temperature decomposition method, chemical transition method, electrochemical method, chemical reduction method and microemulsion method. Among them, chemical reduction method is a commonly used preparation method. Silver powder of different particle sizes can be prepared by controlling the reaction conditions. For example, in the chemical reduction method, the reaction temperature, reaction time, amount of reducing agent, etc. will affect the particle size of the silver powder. Therefore, choosing a suitable preparation method and controlling the reaction conditions are the key to controlling the particle size of the silver powder.

[0003] Among them, the type and amount of dispersant are also one of the factors affecting the particle size of silver powder. Dispersants can reduce the surface tension between silver powder and other substances, prevent silver powder from agglomerating, and improve the dispersibility of silver powder. Commonly used dispersants include surfactants, polymers, etc. Studies have shown that the type and amount of dispersants will affect the particle size and dispersibility of silver powder. For example, surfactants can reduce the interfacial tension between silver powder and other substances and improve the dispersibility of silver powder. Polymers can be adsorbed on the surface of silver powder to prevent silver powder from agglomerating. However, the amount of dispersant should also be properly controlled. Excessive use of dispersants will not only increase corporate costs and environmental pollution, but also affect subsequent purification processes. Therefore, a method for preparing silver powder that can reduce the amount of dispersant, has good dispersibility of silver powder, has good printing performance of the prepared silver paste, and has good conductive properties for battery cells is particularly important. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems and provide a method for preparing silver powder.

[0005] The present invention relates to a method for preparing silver powder, comprising the following steps: (1) Solution preparation: 100 mL of bacterial solution was filtered, washed twice with deionized water, and then resuspended in a phosphate buffer solution with a pH value of 7. The resuspended bacterial solution was ultrasonically disrupted for 30 minutes, and then centrifuged at 8000 r / min for 6 minutes. The supernatant was filtered three times with a 0.22 µm filter membrane, and the protein concentration was determined using Coomassie Brilliant Blue. Deionized water was added to control the protein concentration to 200 mg / mL, and the culture was carried out in a shaker at 30°C and 150 r / min in the dark to obtain a bacterial solution. Silver nitrate is prepared into a 1 mol / L silver nitrate solution, and a pH adjuster is added to adjust the pH value to 4, thereby obtaining solution A; The reducing agent is prepared into a 1.5 mol / L reducing agent solution, and a pH adjuster is added to adjust the pH value to 7, thereby obtaining solution B; Prepare a solution of polyvinyl pyrrolidone with a concentration of 250 g / L, and then add the bacterial solution to obtain solution C; (2) Silver powder synthesis: Add silver powder seeds to solution C, stir evenly, then add solution B, then drop solution A under stirring, and react at 10-30°C for 15 minutes; (3) Silver powder surface treatment: Add a surface treatment agent to the reaction mixture of step (2), and add a pH adjuster to adjust the pH value to 6-7, and stir for 10-15 minutes; (4) Post-processing of silver powder: The reaction mixture in step (3) is subjected to sedimentation and drainage, and then washed with ethanol and dried to obtain silver powder.

[0006] Preferably, in step (1), the bacterial species in the bacterial solution include Escherichia coli and Bacillus subtilis.

[0007] Preferably, in step (1), the ratio of Escherichia coli to Bacillus subtilis is 4:6.

[0008] Preferably, in step (1), the reducing agent is at least one of hydrazine hydrate, lithium aluminum tetrahydride, ascorbic acid and hydrogen peroxide.

[0009] Preferably, in step (1), the polyvinyl pyrrolidone is 15% to 25% of the mass of silver in silver nitrate, and the bacterial solution is 0.2% of the mass of silver in silver nitrate.

[0010] Preferably, in step (2), the molar ratio of silver nitrate to reducing agent is 1:1 to 1.3.

[0011] Preferably, in step (2), the dropping speed of solution A is 11 to 140 ml / min.

[0012] Preferably, in the step (2), after the solution A is added dropwise, the pH value of the reaction mixture is 5 to 6.5.

[0013] Preferably, in steps (1) and (3), the pH adjuster is at least one of aqueous ammonia, sodium hydroxide and sodium carbonate.

[0014] Preferably, in step (3), the surface treatment agent is oleylamine, and the amount of the surface treatment agent used is 3% of the mass of the corresponding silver in the silver nitrate.

[0015] Compared with the prior art, the advantages and positive effects of the present invention are: Compared with the prior art, the preparation method of the silver powder of the present invention is (1) The silver powder prepared by the silver powder preparation method of the present invention has high dispersibility, concentrated particle size, large specific surface area and tap density, and low burning loss; (2) Although the silver paste prepared by the silver powder has a low viscosity, the viscosity does not increase significantly under high-speed stirring, and the thixotropy is good, indicating that the silver paste prepared by the silver powder of the present invention has good printing performance; (3) The silver paste prepared by the silver powder is printed on the battery cell. After printing and sintering, the aspect ratio of the grid line is large, the series resistance of the battery cell is low, and the grid line breakage phenomenon is less when the silver paste is printed on the battery cell. The silver powder prepared by the silver powder preparation method of the present invention improves the conversion efficiency of the battery and is more conducive to the conductivity of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solution of the embodiment of the present invention, the following briefly introduces the drawings required for describing the embodiment. Figure 1 This is a scanning electron microscope image of the silver powder provided in Example 1; Figure 2 This is a scanning electron microscope image of the silver powder provided in Example 2; Figure 3 The scanning electron microscope image of the silver powder provided for Comparative Example 1; Figure 4 The scanning electron microscope image of the silver powder provided for Comparative Example 2; Figure 5 This is a printing effect diagram of the silver paste prepared from the silver powder provided in Example 1; Figure 6 This is a printing effect diagram of the silver paste prepared from the silver powder provided in Example 2; Figure 7 This is a printing effect diagram of the silver paste prepared from the silver powder provided in Comparative Example 1; Figure 8 This is a printing effect diagram of the silver paste prepared with the silver powder provided in Comparative Example 2. DETAILED DESCRIPTION

[0017] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described below with reference to the accompanying drawings and embodiments.

[0018] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments of the following disclosure.

[0019] Example 1 A method for preparing silver powder comprises the following steps: (1) Solution preparation: 100 mL of bacterial solution was filtered, washed twice with deionized water, and resuspended in a phosphate buffer solution with a pH value of 7.0. The resuspended bacterial solution was ultrasonically disrupted for 30 minutes, and then centrifuged at 8000 r / min for 6 minutes. The supernatant was filtered three times with a 0.22 µm filter membrane, and the protein concentration was determined using Coomassie Brilliant Blue. Deionized water was added to control the protein concentration to 200 mg / mL, and the culture was incubated in a shaker at 30°C and 150 r / min in the dark to obtain a bacterial solution.

[0020] 3.16 kg of silver nitrate was prepared into a 1 mol / L silver nitrate solution, and ammonia water was added to adjust the pH value to 4 to obtain solution A.

[0021] 3.5 kg of ascorbic acid was prepared into a 1.5 mol / L reducing agent solution, and ammonia water was added to adjust the pH value to 7 to obtain solution B.

[0022] Prepare a solution with a concentration of 250 g / L by adding 3.1 kg of polyvinyl pyrrolidone and then add 200 ml of bacterial solution to obtain solution C.

[0023] 2) Silver powder synthesis 95 g of silver powder seeds with a particle size of 100 nm were added to solution C, and solution B was added after stirring. Then solution A was added dropwise under stirring. The pH value of the reaction mixture was 6.5 after the addition was completed. The mixture was reacted at 30°C for 15 min.

[0024] (3) Silver powder surface treatment: Add the surface treatment agent to the reaction mixture of step (2), and add ammonia water to adjust the pH value to 6, and stir for 10 minutes.

[0025] (4) Post-processing of silver powder: The reaction mixture in step (3) is subjected to sedimentation and drainage, and then washed with ethanol and dried to obtain 1.3 μm silver powder.

[0026] Example 2 A method for preparing silver powder comprises the following steps: (1) Solution preparation: 100 mL of bacterial solution was filtered, washed twice with deionized water, and resuspended in a phosphate buffer solution with a pH value of 7.0. The resuspended bacterial solution was ultrasonically disrupted for 30 minutes, and then centrifuged at 8000 r / min for 6 minutes. The supernatant was filtered three times with a 0.22 µm filter membrane, and the protein concentration was determined using Coomassie Brilliant Blue. Deionized water was added to control the protein concentration to 200 mg / mL, and the culture was incubated in a shaker at 30°C and 150 r / min in the dark to obtain a bacterial solution.

[0027] 3.16 kg of silver nitrate was prepared into a 1 mol / L silver nitrate solution, and ammonia water was added to adjust the pH value to 4 to obtain solution A.

[0028] 0.93 kg of hydrazine hydrate was prepared into a 1.5 mol / L reducing agent solution, and ammonia water was added to adjust the pH value to 7 to obtain solution B.

[0029] Prepare a solution with a concentration of 250 g / L by adding 4.9 kg of polyvinyl pyrrolidone and then add 200 ml of bacterial solution to obtain solution C.

[0030] 2) Silver powder synthesis 68 g of silver powder seeds with a particle size of 100 nm were added to solution C, and solution B was added after stirring. Then solution A was added dropwise under stirring. After the addition was completed, the pH value of the reaction mixture was 5. The mixture was reacted at 15°C for 15 minutes.

[0031] (3) Silver powder surface treatment: Add oleylamine to the reaction mixture of step (2), and add aqueous ammonia to adjust the pH value to 7, and stir for 15 minutes.

[0032] (4) Post-processing of silver powder: The reaction mixture in step (3) is subjected to sedimentation and drainage, and then washed with ethanol and dried to obtain 1.6 μm silver powder.

[0033] Comparative Example 1 The difference between this embodiment and embodiment 1 is that no bacterial solution is added to solution C.

[0034] Comparative Example 2 The difference between this embodiment and embodiment 2 is that after the dropwise addition of solution A is completed, the pH value of the reaction mixture is adjusted to 7 with a pH regulator.

[0035] Performance Testing (1) The particle size, specific surface area, tap density and ignition loss of the silver powder prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were measured. The results are shown in Table 1. The silver powder prepared in Examples 1 and 2 and Comparative Examples 1 and 2 was observed by scanning electron microscope. The results are shown in Table 1. Figure 1-4 shown.

[0036] Table 1 It can be seen from Table 1 that the particle size distribution of the silver powder in Example 1 is more uniform, the specific surface area is larger, the tap density is larger, and the ignition loss is lower than that in Comparative Example 1; at the same time, the particle size distribution of the silver powder in Example 2 is more uniform, the specific surface area is larger, the tap density is larger, and the ignition loss is lower than that in Comparative Example 2.

[0037] from Figure 1-4 It is concluded that: compared with comparative example 1, the silver powder in Example 1 has better dispersibility; compared with comparative example 2, the silver powder in Example 2 also has better dispersibility, indicating that the silver powder of the present invention has good dispersibility.

[0038] (2) The silver powders of Examples 1 and 2 and Comparative Examples 1 and 2 were respectively prepared into silver pastes; the silver pastes were subjected to silver paste viscosity test and rheological test, and the results are shown in Table 2; the silver pastes were printed on the cells by screen printing process, and solar cell samples were prepared by fast firing process, and the aspect ratio of the grid lines after printing and sintering was tested, and the series resistance of the cell samples was tested by a solar cell test system, and the results are shown in Table 3; the cell was subjected to electroluminescence detection, and the detection image was as shown in Table 3. Figure 5-8 shown.

[0039] The preparation method of silver paste is as follows: 92% by weight of silver powder is evenly mixed with 6% of carrier and 2% of glass powder, and the silver paste is obtained after three-roll rolling, wherein the carrier formula is as follows: 5% by weight of ethyl cellulose, 10% by weight of JH180 thixotropic agent, 20% by weight of dibutyl phthalate, 20% by weight of diethylene glycol butyl ether acetate, 20% by weight of diethylene glycol butyl ether, 15% by weight of pinene alcohol, and 10 parts by weight of dodecanol.

[0040] Table 2 It can be concluded from Table 2 that compared with Comparative Examples 1 and 2, although the silver paste prepared by the silver powder of Examples 1 and 2 has a lower viscosity, the viscosity does not increase significantly under high-speed stirring, and the thixotropy of the silver paste is better, indicating that the silver paste prepared by the silver powder of the present invention has good printing performance.

[0041] Table 3 It can be concluded from Table 3 that the series resistance of the battery cells in Examples 1 and 2 is lower than that in Comparative Examples 1 and 2, respectively, which is more conducive to battery conductivity, and the aspect ratio after silver powder printing and sintering is larger, which further proves that the silver powder of the present invention reduces the viscosity of the slurry, but the conversion efficiency of the battery is still high.

[0042] from Figure 5-8 It is concluded that the breakage of the grid lines after printing and sintering in Examples 1 and 2 is less than that in Comparative Examples 1 and 2, respectively, which proves that the silver paste prepared by the silver powder of the present invention has a better printing effect.

[0043] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes for application in other fields. However, any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing silver powder, characterized in that: The following steps are involved: (1) Solution preparation: 100 mL of bacterial solution was filtered, washed twice with deionized water, and then resuspended in a phosphate buffer solution with a pH value of 7. The resuspended bacterial solution was ultrasonically disrupted for 30 minutes, and then centrifuged at 8000 r / min for 6 minutes. The supernatant was filtered three times with a 0.22 µm filter membrane, and the protein concentration was determined using Coomassie Brilliant Blue. Deionized water was added to control the protein concentration to 200 mg / mL, and the culture was carried out in a shaker at 30°C and 150 r / min in the dark to obtain a bacterial solution. Silver nitrate is prepared into a 1 mol / L silver nitrate solution, and a pH adjuster is added to adjust the pH value to 4, thereby obtaining solution A; The reducing agent is prepared into a 1.5 mol / L reducing agent solution, and a pH adjuster is added to adjust the pH value to 7, thereby obtaining solution B; Prepare a solution of polyvinyl pyrrolidone with a concentration of 250 g / L, and then add the bacterial solution to obtain solution C; (2) Silver powder synthesis: Add silver powder seeds to solution C, stir evenly, then add solution B, then drop solution A under stirring, and react at 10-30°C for 15 minutes; (3) Silver powder surface treatment: Add a surface treatment agent to the reaction mixture of step (2), and add a pH adjuster to adjust the pH value to 6-7, and stir for 10-15 minutes; (4) Post-processing of silver powder: The reaction mixture in step (3) is subjected to sedimentation and drainage, and then washed with ethanol and dried to obtain silver powder.

2. The method for preparing silver powder according to claim 1, characterized in that: In the step (1), the bacterial species in the bacterial solution include Escherichia coli and Bacillus subtilis.

3. The method for preparing silver powder according to claim 2, characterized in that: In the step (1), the ratio of the Escherichia coli to the oceanic Bacillus is 4:

6.

4. The method for preparing silver powder according to claim 3, characterized in that: In the step (1), the reducing agent is at least one of hydrazine hydrate, lithium aluminum tetrahydride, ascorbic acid and hydrogen peroxide.

5. The method for preparing silver powder according to claim 4, characterized in that: In the step (1), the polyvinyl pyrrolidone is 15% to 25% of the mass of silver in silver nitrate, and the bacterial solution is 0.2% of the mass of silver in silver nitrate.

6. The method for preparing silver powder according to claim 5, characterized in that: In the step (2), the molar ratio of the silver nitrate to the reducing agent is 1:1 to 1.

3.

7. The method for preparing silver powder according to claim 6, characterized in that: In the step (2), the dropwise addition rate of the solution A is 11 to 140 ml / min.

8. The method for preparing silver powder according to claim 7, characterized in that: In the step (2), after the solution A is added dropwise, the pH value of the reaction mixture is 5 to 6.

5.

9. The method for preparing silver powder according to claim 8, characterized in that: In the steps (1) and (3), the pH adjuster is at least one of ammonia water, sodium hydroxide and sodium carbonate.

10. The method for preparing silver powder according to claim 9, characterized in that: In the step (3), the surface treatment agent is oleylamine, and the amount of the surface treatment agent used is 3% of the mass of the corresponding silver in the silver nitrate.

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