Preparation method of silver powder with different surface microcrystalline structures

Abstract

The present invention relates to a method for preparing silver powder with different surface microcrystalline structures, specifically including the following steps: adding a dispersant and a neutralizing agent into a reducing agent solution to prepare solution A; dropping silver nitrate solution B into solution A during stirring to obtain a silver powder slurry; and obtaining the target silver powder after separation, washing, and drying. The silver powder prepared by the present invention has a particle size of 0.5 - 4.0 μm and a tapped density of more than 5.5 g / cm<supgt;3< / supgt>. It not only has good dispersibility and sphericity, but also can controllably adjust the surface microcrystalline structure of the silver powder through this method, enabling the silver powder to exhibit different activities and having broad application prospects in the field of photovoltaic silver paste.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of new precious metal materials, and particularly relates to a method for preparing silver powder with different surface microcrystalline structures. Background Art

[0002] With the increasing depletion of non-renewable energy sources such as petroleum and coal, the development of renewable energy has attracted more and more attention. As the most abundant and main clean energy, solar energy has received more attention. How to improve the efficiency of photovoltaic power generation has become the focus of research. Photovoltaic silver paste has become the main raw material for printing solar panels due to its excellent rheological properties and electrical conductivity. As the main conductive phase in solar cell silver paste, silver powder accounts for about 90% of the mass ratio in the silver paste, which plays a decisive role in the rheology and conductivity of the silver paste. With the development of different types of solar cells, different requirements are put forward for the performance of silver powder. Reasonably adjusting the activity of silver powder can optimize the contact resistance of solar cells and the sintering activity of the paste. Controllably preparing silver powder with different activities is an important research direction at present.

[0003] At present, there are mainly three ways to improve the activity of silver powder: one is to construct a hollow structure inside the silver powder to make the silver powder have higher activity without affecting the viscosity of the paste; the second is to reduce the crystallinity of the silver powder. The lower the degree of crystallization, the higher the corresponding sintering activity; the third is to increase the microcrystalline structure on the surface of the silver powder. Compared with the former two, constructing a microcrystalline structure on the surface of the silver powder has obvious advantages. On the one hand, while constructing the microcrystalline surface, it can ensure that the silver powder itself has high crystallinity and sphericity, which has great advantages in the paste printing process. On the other hand, this method does not need to change the original reaction system, the preparation process is relatively simple, and the reaction system is relatively stable. The more microcrystalline structures on the surface of the silver powder, the higher the activity of the silver powder, but at the same time, it will also cause the paste viscosity to be too high. When there are fewer microcrystalline structures on the surface of the silver powder, the activity of the silver powder is insufficient. Therefore, reasonably controlling the size of the microcrystals on the surface of the silver powder is an urgent problem to be solved at present.

[0004] Patent CN111922356A discloses a microcrystalline silver powder with a nano-silver surface structure and a preparation method thereof. This method uses the addition method to simultaneously add 70%-95% of the oxidant and all the reducing agent to the dispersant to prepare a silver suspension. First, adjust the pH of the suspension and add a surfactant to it, and then add the remaining silver nitrate solution to prepare microcrystalline silver powder with a nano-silver surface structure. The disadvantages of this method are that the sphericity of the prepared silver powder is poor, the preparation process is cumbersome, the batch stability is poor, and it is not suitable for large-scale production. At the same time, since the nano-silver is generated in the second step reaction and adsorbed on the surface of the micron-silver, the binding force between them is weak, and it is difficult to retain the nano-silver during the post-treatment process, and the post-treatment difficulty is large. Summary of the Invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the present invention discloses a method for preparing silver powder with different surface microcrystalline structures, which can effectively control the growth mode of silver particles and obtain spherical silver powder with microcrystals on the surface and controllable microcrystal size.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] The first aspect of the present invention provides a method for preparing silver powder with different surface microcrystalline structures, comprising the following steps:

[0008] (1) Adding a dispersant and a neutralizing agent to a reducing agent solution to prepare solution A;

[0009] (2) Dropwise adding silver nitrate solution B to solution A during stirring to obtain a silver powder slurry;

[0010] (3) Separating the silver powder in step (2), washing and drying it to obtain the target silver powder;

[0011] Further, the neutralizing agent in step (1) is selected from at least two of glucose, sodium borohydride, formaldehyde, ascorbic acid, hydrazine hydrate, alkanolamine, ammonia water, ammonium bicarbonate or sodium hydroxide; the neutralizing agent is 3-30% of the mass of silver nitrate.

[0012] Further, the dispersant in step (1) is selected from at least one of polyethylene glycol, polyvinyl alcohol, gelatin, sodium dodecylbenzenesulfonate, Tween 80, polyvinylpyrrolidone or gum arabic; the dispersant is 10-40% of the mass of silver nitrate.

[0013] Further, the reducing agent in step (1) is selected from at least one of glucose, sodium borohydride, formaldehyde, ascorbic acid, hydrazine hydrate, hydroquinone, alkanolamine or hydrogen peroxide; the reducing agent is 5-60% of the mass of silver nitrate;

[0014] Further, the mass concentration of silver nitrate in solution B is 3-25%;

[0015] Further, the pH of the reducing agent solution is 1-5; the pH of solution A is 2-9; the pH of solution B is 2-6;

[0016] Further, the dropping time of silver nitrate solution B in step (2) is 1-20 min;

[0017] Preferably, the dropping time of silver nitrate solution B in step (2) is 2-15 min;

[0018] Further preferably, the lower limit of the time for adding the solution B is selected from 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, and the upper limit of the time for adding the solution B is selected from 9 min, 10 min, 11 min, 12 min, 13 min, 14 min;

[0019] Furthermore, the stirring speed of step (2) is 100-400 r / min, and the reaction temperature is 10-30° C.;

[0020] Furthermore, the drying temperature of step (3) is 50-90° C., and the drying time is 20-60 min;

[0021] Preferably, the drying temperature in step (3) is 55-80° C., and the drying time is 30-50 min.

[0022] The second aspect of the present invention provides a silver powder having different surface microcrystalline structures obtained by the above-mentioned preparation method, wherein the particle size of the silver powder is 0.5 to 4.0 μm and the tap density is 5.5 g / cm 3 As shown above, the surface of silver powder has microcrystals with different contents and sizes.

[0023] The beneficial effects of the present invention include but are not limited to:

[0024] (1) The present invention drips a solution B of appropriate concentration into a solution A at a certain speed, so that the silver element is rapidly precipitated and aggregated in the solution A. The silver powder prepared by the method has good activity and high sphericity;

[0025] (2) The present invention further adds a neutralizing agent of appropriate amount and type to solution A to increase the supersaturation of silver in the solution during the reaction process, accelerate the assembly rate of silver, and increase the content of microcrystals on the surface of the silver powder and increase the size of the microcrystals.

[0026] (3) The preparation method of the present invention can achieve the regulation of the size of the microcrystals on the surface of the silver powder by changing the type or content of the neutralizer. The spherical silver powder obtained has good dispersibility and high activity. The solar slurry after pulping has better plasticity and lower line resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a scanning electron microscope image of the spherical silver powder prepared in Example 1 of the present invention;

[0028] Figure 2 This is a scanning electron microscope image of the spherical silver powder prepared in Example 2 of the present invention;

[0029] Figure 3 This is a scanning electron microscope image of the spherical silver powder prepared in Example 3 of the present invention;

[0030] Figure 4 Scanning electron micrograph of the spherical silver powder prepared in Example 4 of the present invention;

[0031] Figure 5 Scanning electron micrograph of the spherical silver powder prepared in Comparative Example 1 of the present invention;

[0032] Figure 6 Scanning electron micrograph of the spherical silver powder prepared in Comparative Example 2 of the present invention. Detailed Description of the Invention

[0033] The present invention will be described below in conjunction with examples, but the present invention is not limited thereto. In the art, simple substitutions or improvements made to the present invention by those skilled in the art fall within the scope of the technical solutions protected by the present invention.

[0034] Example 1:

[0035] When a small amount of neutralizing agent is added, the content of microcrystals on the surface of silver powder 1# is small

[0036] Weigh 1.02 kg of silver nitrate solid and prepare a silver nitrate solution B with a mass fraction of 5%; weigh 0.55 kg of ascorbic acid as a reducing agent and prepare a reducing agent solution with a mass concentration of 6.5%. Weigh 0.22 kg of polyvinylpyrrolidone as a dispersant, 30 g of ammonia water and 36.5 g of hydrazine hydrate as neutralizing agents and add them to the reducing agent solution to prepare solution A.

[0037] Maintain the temperature of the reaction kettle at 15 °C and the stirring speed at 300 r / min, and add solution B dropwise to solution A over a period of 5 min.

[0038] Wash with deionized water and ethanol, filter the supernatant by suction, dry at 70 °C for 30 min, and sieve through a 500-mesh sieve to obtain silver powder. The actual particle size D50 of the obtained silver powder is 1.43 μm, and the tapped density is 6.10 g / m 3 , and the scanning electron micrograph is shown in Figure 1 , as Figure 1 shown, the silver powder has a concentrated particle size distribution, good dispersibility, and a small content of surface microcrystals.

[0039] Example 2:

[0040] Compared with Example 1, the amount of neutralizing agent is increased, and the content of microcrystals on the surface of silver powder 2# increases

[0041] Weigh 1.02 kg of silver nitrate solid and prepare a silver nitrate solution B with a mass fraction of 5%; weigh 0.55 kg of ascorbic acid as a reducing agent and prepare a reducing agent solution with a mass concentration of 6.5%. Weigh 0.22 kg of polyvinylpyrrolidone as a dispersant, 130 g of ammonia water and 36.5 g of hydrazine hydrate as neutralizing agents and add them to the reducing agent solution to prepare solution A.

[0042] Maintain the temperature of the reaction kettle at 15 °C and the stirring speed at 300 r / min. Add solution B dropwise to solution A, and the dropping time is 5 min.

[0043] Wash with deionized water and ethanol, filter the supernatant by suction, dry at 70 °C for 30 min, and sieve through a 500-mesh sieve to obtain silver powder. The actual particle size D50 of the obtained silver powder is 1.5 μm, and the tapped density is 6.08 g / m 3 , and the scanning electron micrograph is shown in Figure 2 , such as Figure 2 shown. The particle size distribution and size of the silver powder are basically the same as those in Example 1. A small amount of microcrystals appear on the surface of the silver powder, but the microcrystal size is small.

[0044] Example 3:

[0045] Compared with Example 2, the amount of neutralizing agent is further increased, and the content of microcrystals on the surface of silver powder 3# increases significantly

[0046] Weigh 1.02 kg of silver nitrate solid and prepare a silver nitrate solution B with a mass fraction of 5%; weigh 0.55 kg of ascorbic acid as a reducing agent and prepare a reducing agent solution with a mass concentration of 6.5%. Weigh 0.22 kg of polyvinylpyrrolidone as a dispersant, 130 g of ammonia water and 72.5 g of hydrazine hydrate as neutralizing agents and add them to the reducing agent solution to prepare solution A.

[0047] Maintain the temperature of the reaction kettle at 15 °C and the stirring speed at 300 r / min. Add solution B dropwise to solution A, and the dropping time is 5 min.

[0048] Wash with deionized water and ethanol, filter the supernatant by suction, dry at 70 °C for 30 min, and sieve through a 500-mesh sieve to obtain silver powder. The actual particle size D50 of the obtained silver powder is 1.45 μm, and the tapped density is 6.0 g / m 3 , and the scanning electron micrograph is shown in Figure 3 , such as Figure 3 shown. The particle size distribution and size of the silver powder are basically the same as those in Example 1. The content of surface microcrystals increases, and the microcrystal size does not change significantly.

[0049] Example 4:

[0050] Compared with Example 3, the amount of neutralizing agent is further increased, and silver powder 4# has a large number of microcrystals with larger sizes on its surface

[0051] Weigh 1.02 kg of silver nitrate solid and prepare a silver nitrate solution B with a mass fraction of 5%; weigh 0.55 kg of ascorbic acid as a reducing agent and prepare a reducing agent solution with a mass concentration of 6.5%. Weigh 0.22 kg of polyvinylpyrrolidone as a dispersant, 130 g of ammonia water and 91.2 g of hydrazine hydrate as neutralizing agents and add them to the reducing agent solution to prepare solution A.

[0052] Maintain the temperature of the reaction kettle at 15 °C and the stirring speed at 300 r / min. Add solution B dropwise to solution A over a period of 5 min.

[0053] Wash with deionized water and ethanol, filter the supernatant by suction, dry at 70 °C for 30 min, and sieve through a 500-mesh sieve to obtain silver powder. The actual particle size D50 of the obtained silver powder is 1.5 μm, and the tapped density is 6.30 g / m 3 , and the scanning electron micrograph is shown in Figure 4 , as Figure 4 shown. The particle size distribution and size of the silver powder are basically the same as those in Example 1, the number of surface microcrystals increases significantly, and the microcrystal size grows significantly.

[0054] Comparative Example 1:

[0055] The preparation method of silver powder D1# in the comparative example is basically the same as that in Example 1, except that no neutralizing agent is used

[0056] Weigh 1.02 kg of silver nitrate solid and prepare a silver nitrate solution B with a mass fraction of 5%; weigh 0.55 kg of ascorbic acid as a reducing agent and prepare a reducing agent solution with a mass concentration of 6.5%. Weigh 0.22 kg of polyvinylpyrrolidone as a dispersant and add it to the reducing agent solution to prepare solution A.

[0057] Maintain the temperature of the reaction kettle at 15 °C and the stirring speed at 300 r / min. Add solution B dropwise to solution A over a period of 5 min.

[0058] Wash with deionized water and ethanol, filter the supernatant by suction, dry at 70 °C for 30 min, and sieve through a 500-mesh sieve to obtain silver powder. The actual particle size D50 of the obtained silver powder is 1.39 μm, and the tapped density is 6.18 g / m 3 , and the scanning electron micrograph is shown in Figure 5 , as Figure 5 shown. When the neutralizing agent is not added, the dispersibility of the silver powder is acceptable, but the particle size distribution range is relatively wide, the sphericity is poor, the crystallinity is low, and there are almost no microcrystals on the surface.

[0059] Comparative Example 2:

[0060] The preparation method of silver powder D2# in the comparative example is basically the same as that in Example 1, except that only ammonia water is used as the neutralizing agent

[0061] Weigh 1.02 kg of silver nitrate solid and prepare a silver nitrate solution B with a mass fraction of 5%; weigh 0.55 kg of ascorbic acid as a reducing agent and prepare a reducing agent solution with a mass concentration of 6.5%. Weigh 0.22 kg of polyvinylpyrrolidone as a dispersant and 130 g of ammonia water as a neutralizing agent, and add them to the reducing agent solution to prepare solution A.

[0062] Maintain the temperature of the reaction kettle at 15 °C and the stirring speed at 300 r / min. Add solution B dropwise to solution A over a period of 5 min.

[0063] The mixture was washed with deionized water and ethanol, the supernatant was filtered, dried at 70°C for 30 min, and passed through a 500-mesh sieve to obtain silver powder. The actual particle size D50 of the obtained silver powder was 1.43 μm, and the tap density was 6.05 g / m 3 , SEM images are shown in Figure 6 ,like Figure 6 As shown, when ammonia water is used as a neutralizer, the silver powder has a good dispersion, a high content of microcrystals on the surface of the silver powder, and a small size of microcrystals, but the microcrystal morphology between particles varies greatly and the stability is poor.

[0064] Test example:

[0065] The performance parameters of the silver powder obtained in each embodiment and comparative example are shown in Table 1:

[0066] Table 1

[0067]

[0068]

[0069] It can be seen from the results in Table 1 that, since no neutralizer is added to Comparative Example 1, on the one hand, the reaction rate is low, resulting in a slow precipitation process of silver atoms, a long nucleation process, and a wide particle size distribution; on the other hand, the slow reaction rate leads to a low supersaturation of silver atoms, and silver atoms tend to grow in situ, the silver powder has high crystallinity, low surface roughness, and poor activity of the silver powder. In Comparative Example 2, only ammonia water is used as a neutralizer, and the reaction rate of the silver powder is too fast. Although the initial nucleation process is short and the silver powder size is uniform, the growth process of the silver powder is too fast, resulting in unstable silver powder morphology. In specific Examples 1 to 4, by regulating the type and amount of the neutralizer, the content of microcrystals on the surface of the silver powder increases, the size of the microcrystals increases, and the specific surface area of ​​the silver powder increases; the silver powder prepared by this regulation method has good stability, and the surface microcrystal morphology and size are controllable, which proves that under this system, precise regulation of the microcrystals on the surface of the silver powder is achieved.

[0070] The performance parameters of the silver powder obtained in each embodiment and comparative example after further pulping are shown in Table 2:

[0071] Table 2

[0072] Sample Fineness VIS High Width Ratio Silver powder 1# in the example 4 190 / 90 / 39 12.50 30.36 0.412 Silver powder 2# in the example 3 200 / 98 / 42 12.51 29.36 0.426 Silver powder 3# in the example 3 230 / 105 / 40 11.80 27.36 0.431 Silver powder 4# in the example 3 244 / 110 / 55 12.71 26.30 0.483 Silver powder D1# in the comparative example 3 200 / 75 / 40 12.35 32.50 0.380 Silver powder D2# in the comparative example 6 210 / 120 / 60 12.15 25.21 0.482

[0073] As can be seen from the results in Table 2, the silver powder D1# of the comparative example has a high crystallinity and a relatively smooth surface. Therefore, the viscosity after pulping is low, the line width after sintering is large, and the aspect ratio is small, which proves that the activity of the silver powder is low. The silver powder D2# of the comparative example has poor dispersibility and a large fineness after pulping. And because the content of microcrystals on the surface of the silver powder is high, the line width after sintering is small, and the silver powder shows higher sintering activity. The silver powder 4# of the example has good dispersibility and high sphericity, and there are a large number of microcrystals on the surface of the silver powder. Therefore, the fineness of the slurry is small, the sintering line width is narrow, the silver powder has better plasticity and higher activity, and the comprehensive performance is better. By comparison, the present invention discloses a preparation method of silver powder with different surface microcrystal structures. The silver powder prepared by this method not only has good dispersibility and sphericity, but also can controllably adjust the surface microcrystal structure of the silver powder, so that the silver powder shows different activities, and has broad application prospects in the field of photovoltaic silver paste.

[0074] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A preparation method of silver powder with different surface microcrystalline structures, characterized in that, It includes the following steps: (1) Adding a dispersant and a neutralizing agent into a reducing agent solution to prepare solution A; the neutralizing agent in step (1) is selected from hydrazine hydrate and ammonia water; the neutralizing agent is 3-30% of the mass of silver nitrate; the dispersant is 10-40% of the mass of silver nitrate; the reducing agent is 5-60% of the mass of silver nitrate; the pH of the reducing agent solution is 1-5; (2) While stirring, dropping silver nitrate solution B into solution A to obtain a silver powder slurry; the mass concentration of silver nitrate in solution B is 3-25%; the pH of solution A is 2-9; the pH of solution B is 2-6; (3)Separate the silver powder in step (2), wash and dry it to obtain the target silver powder; the particle size of the silver powder is 0.5 to 4.0 μm, and the tapped density is 5.5 g / cm 3 or more, and the silver powder surface has microcrystals with different contents and sizes.

2. The preparation method according to claim 1, wherein The dispersant in step (1) is selected from at least one of polyethylene glycol, polyvinyl alcohol, gelatin, sodium dodecylbenzenesulfonate, Tween 80, polyvinylpyrrolidone or gum arabic.

3. The preparation method according to claim 1, characterized in that, The reducing agent in step (1) is selected from at least one of glucose, sodium borohydride, formaldehyde, ascorbic acid, hydrazine hydrate, hydroquinone, alkanolamine or hydrogen peroxide.

4. The preparation method according to claim 1, characterized in that, The dropping time of silver nitrate solution B in step (2) is 1-20 min.

5. The preparation method according to claim 1, wherein The stirring speed in step (2) is 100-400 r / min, and the reaction temperature is 10-30 °C.

6. The preparation method according to claim 1, wherein The drying temperature in step (3) is 50-90 °C, and the drying time is 20-60 min.

7. Silver powder with different surface microcrystalline structures prepared by the preparation method according to any one of claims 1-6.

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