A method for preparing silver powder with ultrasound assistance, the silver powder obtained and its applications

Abstract

This invention provides a method for preparing silver powder with ultrasound assistance. The method includes the following steps: S1, solution preparation: preparing a reaction base solution, an oxidant solution, and a coating solution; S2, reaction process: under ultrasound and high-speed stirring, the reaction base solution is placed in a reaction vessel, and the oxidant solution is added within 1-90 seconds to start the reaction. After reacting for 0-10 minutes, the coating solution is added and the reaction continues for 1-5 minutes to obtain silver powder; S3, post-powder processing: the obtained silver powder is subjected to solid-liquid separation, washing, drying, and pulverization to obtain silver powder. The method provided by this invention, under the conditions of ultrasound assistance and stirring, and by increasing the amount of reducing agent and rapidly adding the oxidant, produces silver powder with high specific surface area, controllable particle size, good dispersibility, and high sintering activity. The entire reaction process is simple, low-cost, and suitable for mass production.

Description

Technical Field

[0001] This invention relates to the field of metal powder preparation technology, specifically to a method for preparing silver powder with ultrasonic assistance, the resulting silver powder, and its applications. Background Technology

[0002] In recent years, the rapid development of the microelectronics and new energy industries has greatly expanded the breadth and depth of applications for electronic pastes. Silver powder, with its excellent conductivity, has become an important component of electronic pastes and a key material in the electronics industry. It can be used as a conductive printing material for printed circuits, and also in the manufacture of main and sub-grids for photovoltaic solar cells or in the preparation of electromagnetic shielding silver paste. The specific surface area, particle size and distribution, tap density, and burn-off rate of silver powder are all interrelated and significantly influence its application. Currently, industrial silver powder is commonly synthesized using chemical reduction methods, often employing seed crystal methods combined with dispersants and coating agents to prepare wet silver powder, which is then dried and pulverized before use. However, current industrial silver powder production still suffers from uneven particle size distribution and large particle size, making it difficult to fully meet industry applications. To better meet current requirements, incorporating ultrasound into silver powder synthesis is a method that facilitates powder dispersion. For example, patent CN105855562A uses ultrasonic treatment to obtain nano-silver paste, resulting in silver powder with a size of 30-60nm; patent CN110576190B uses ultrasonic spray to prepare nano-silver powder, and the ultrasonic spray feeding method can prepare silver powder with a size of 10-16nm; patent CN111451521B uses ultrasonic modification to improve the powder dispersibility and tap density of the obtained silver powder; patent CN114939668A obtains silver powder by chemical reaction during ultrasonic stirring, and high power is beneficial for obtaining fine silver powder.

[0003] Although the above provides silver powder prepared by ultrasonic dispersion and chemical reduction, it still has the drawbacks of ultrasonication not playing an obvious role in its reaction and post-processing, resulting in silver powder with a small specific surface area and a long reaction time. Summary of the Invention

[0004] In view of this, the present invention provides a method for preparing silver powder with ultrasonic assistance. The silver powder obtained by this method has a high specific surface area, controllable particle size, good dispersibility, and high sintering activity. The entire reaction process is simple, efficient, and low in cost, making it suitable for mass production. Furthermore, the presence of voids on the surface of the powder after it is prepared into a slurry can achieve effective coating, making it less prone to secondary agglomeration during the printing process. It also maintains a certain degree of dispersibility in high-viscosity slurries, thus making it suitable for precision printing.

[0005] To address the above problems, the first aspect of the present invention provides a method for preparing silver powder with ultrasound assistance, the method comprising the following steps:

[0006] S1. Solution preparation: Prepare the reaction base solution, oxidant solution and coating solution;

[0007] S2. Reaction process: Under ultrasound and stirring, the oxidant solution is added to the reaction base liquid within 1-90s to start the reaction. After the reaction ends, 0-10min, the coating solution is added and the treatment continues for 1-5min to obtain porous silver powder.

[0008] S3. Powder post-processing: The silver powder obtained in step S2 is subjected to solid-liquid separation, washing, drying and pulverizing to obtain silver powder.

[0009] Furthermore, the reaction substrate in step S1 contains a dispersant, a reducing agent, and a surfactant, and the oxidizing agent solution is an oxidizing agent solution containing silver salt.

[0010] This invention provides a method for preparing silver powder with ultrasound assistance. Ultrasound is introduced into a reaction vessel, and a redox reaction is carried out under high-speed stirring to generate silver powder. The cavitation effect of ultrasound and the mechanical shear force generated by the surfactant under high-speed stirring break down a large number of bubbles into smaller bubbles. The presence of numerous small bubbles acts as nuclei in the reaction system, which is beneficial for the formation of smaller silver grains. Under the influence of surface energy, the grains aggregate into porous, spherical silver powder. To prevent secondary agglomeration of the generated powder, a coating liquid is added. Combined with a short feeding rate and a high molar ratio of electron transfer in the reducing agent, the system's reducing power is enhanced, further ensuring rapid nucleation. This utilizes micro- and nano-bubbles to form particles with smaller diameters. Due to the spontaneous decrease in surface energy, many of the synthesized small particles aggregate to form spherical shapes. During aggregation, lattice mismatch between particles results in a certain degree of porosity in the final powder, resulting in micron-sized particles. However, the powder exhibits a high specific surface area, controllable particle size, good dispersibility, and high sintering activity. The entire reaction process is simple, low-cost, and suitable for mass production.

[0011] Further, the specific steps of the reaction process in step S2 are as follows: the reaction base liquid is placed in the reaction vessel, and after stirring for 10-30 minutes under ultrasonication at 50-900W and stirring at a stirring rate of 400-1500r, the oxidant solution is added at a constant flow within 1-30 seconds to start the reaction. After the addition is completed and the reaction is completed for 0-10 minutes, the coating solution is added and the treatment is continued for 1-5 minutes to obtain silver powder.

[0012] In this invention, the reaction substrate is treated with ultrasound and stirring for 10-30 minutes before the reaction to form a sufficient number of micro / nano bubbles. Then, the oxidant is added to the reaction substrate within a short time, utilizing the existing micro / nano bubbles for explosive nucleation, which inhibits subsequent grain growth and forms small-sized powder. In this invention, the coating solution is added 0-10 minutes after the reaction is complete. This means that the coating solution can be added immediately after the oxidant solution is added, or it can be added within 10 minutes after the reaction.

[0013] Further, the silver salt is silver nitrate, and the concentration of silver ions in the oxidant solution is 0.1–5.0 mol / L, preferably 0.1–1.0 mol / L.

[0014] Further, in step S1, the reducing agent is one or more of glucose, hydrazine hydrate, sodium borohydride, potassium borohydride, ascorbic acid, urea, formaldehyde, and isoascorbic acid, and the concentration of the reducing agent in the reaction substrate is 0.2–2.0 mol / L.

[0015] Furthermore, the molar ratio of the reducing agent to silver ions in the redox process is (1.5–4):1, preferably (1.5–2.5):1.

[0016] In this invention, to ensure rapid nucleation in the presence of a large number of bubbles, the method of increasing the molar number of reducing agent is used, that is, the concentration of reducing agent is increased accordingly. The excess of reducing agent and the rapid addition of oxidizing agent in the oxidation reaction are conducive to explosive nucleation and inhibit the subsequent grain growth process, thereby obtaining powder with smaller particle size. The accelerated aggregation of small-diameter powder under surface energy forms spherical powder with internal pores. The presence of internal pores makes the silver powder exhibit a higher specific surface area at the same size level.

[0017] Further, the specific steps of step S3 are as follows: after the silver powder obtained in step S2 is centrifuged, filtered and washed multiple times, it is then sieved, dried and pulverized to obtain spherical silver powder; in this invention, in order to accelerate the drying of the powder, the specific drying conditions are: using a lower alcohol or polyol to replace the water in the silver powder, or placing the silver powder in a circulating atmospheric dryer or vacuum dryer at 50°C for 10 hours.

[0018] Further, the dispersant is one or more of PVP, maleic acid, cyclodextrin, fumaric acid, gelatin, malic acid, gum arabic, and oleic acid, and the amount of the dispersant is 5% to 35% of the mass of the silver salt, preferably 1% to 5%.

[0019] The dispersant used in this invention is to prevent the silver powder from agglomerating during the formation process, thereby affecting its morphology. The amount of the dispersant is 5% to 35% of the mass of the silver salt, preferably 1% to 5%. If the amount is too small, it will not have a dispersing effect, and if the amount is too large, the powder surface will be coated with a large amount of dispersant, which will be difficult to clean and will affect the activity of the powder.

[0020] Further, the surfactant in step S1 is one or more of Tween 80, Span 80, sodium dodecylbenzene sulfonate, sodium dodecyl sulfonate, polyvinyl alcohol, and polyethylene glycol, and the amount of surfactant used is 0.1% to 10% of the mass of the silver salt, preferably 1% to 5%.

[0021] In this invention, the surfactant emulsifies under ultrasonic stirring to form micro-nano bubbles as crystal nuclei. The amount of surfactant is adjusted according to the number of micro-nano bubbles, which affects the number of crystal nuclei in the reaction system. In order to obtain an appropriate amount of micro-nano bubbles, the amount of surfactant in this invention is 0.1% to 10% of the mass of the silver salt, preferably 1% to 5%.

[0022] Further, the coating solution in step S1 is obtained by dissolving a coating agent in a solvent. The coating agent is at least one selected from lauric acid, sodium laurate, silane coupling agent, oleic acid, lauric acid, stearic acid, palmitic acid, and benzotriazole. The amount of coating agent used is 0.01% to 5% of the mass of the silver salt, preferably 0.02% to 0.5%. The solvent is either ethanol or deionized water, preferably ethanol. The mass fraction of the coating agent in the coating solution is 0.2% to 2.0%.

[0023] A second aspect of the present invention provides a silver powder prepared by the above method, which has many pores on its surface and a large specific surface area.

[0024] A third aspect of the present invention provides an application of the silver powder obtained by the above method in the preparation of high-precision conductive line printing paste. Specifically, it can be used in the preparation of silver paste for the main grid and sub-grid of photovoltaic solar cells, the preparation of silver paste for paper-based RFID printing circuits, and the preparation of electromagnetic shielding silver paste.

[0025] The beneficial effects of this invention are as follows:

[0026] This invention provides a method for preparing silver powder with ultrasound assistance. Ultrasound is introduced into a reaction vessel, and the ultrasonic cavitation and emulsification of surfactants generate micro-nano bubbles as seed crystals for silver powder synthesis. At the same time, ultrasonic cavitation and mechanical shearing prevent the bubbles from growing too large, thus serving as seed crystals for explosive nucleation during the reaction. The addition of a coating liquid prevents secondary agglomeration of the generated powder. Combined with a short feeding rate and a high ratio of electron transfer molar ratio of reducing agent, the system's reducing power is enhanced, and rapid nucleation is further ensured, thereby forming small-sized particles using micro-nano bubbles. Because the surface energy of the system tends to decrease spontaneously, many small particles synthesized aggregate to form spherical shapes. During the aggregation process, the lattice mismatch between particles results in certain porosity in the final powder, which has a micron-sized particle size. However, the powder exhibits a high specific surface area, controllable particle size, good dispersibility, and high sintering activity. The entire reaction process is simple, low-cost, and suitable for mass production. Furthermore, the presence of surface pores in the powder after being formulated into a slurry can achieve effective coating, making it less prone to secondary agglomeration during printing. It also maintains a certain degree of dispersibility in high-viscosity slurries, thus making it suitable for precision printing. Attached Figure Description

[0027] Figure 1 This is a SEM image of the powder from Example 2;

[0028] Figure 2 This is a particle size distribution diagram of the powder in Example 2;

[0029] Figure 3 This is a SEM image of the powder from Example 4;

[0030] Figure 4 This is a SEM image of the powder from Example 5;

[0031] Figure 5 This is a particle size distribution diagram of the powder in Example 5;

[0032] Figure 6 This is a SEM image of the powder from Example 6;

[0033] Figure 7 This is a SEM image of the powder from Example 7;

[0034] Figure 8 This is a SEM image of the powder from Example 8;

[0035] Figure 9 SEM images of powders in Comparative Example 1

[0036] Figure 10 This is a particle size distribution diagram of the powder in Comparative Example 1;

[0037] Figure 11 This is the SEM image of the powder in Comparative Example 2;

[0038] Figure 12 This is a particle size distribution diagram of the powder in Comparative Example 2;

[0039] Figure 13 This is a SEM image of the powder from Comparative Example 3. Detailed Implementation

[0040] The present invention will be further described below with reference to specific embodiments. It should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and the present invention is not limited to these examples.

[0041] Example 1:

[0042] This embodiment provides a method for preparing silver powder with ultrasound assistance, the method comprising the following steps:

[0043] S1. Solution preparation: Dissolve 425g of silver nitrate in 5000ml of deionized water to obtain an oxidizing agent solution; dissolve 440g of ascorbic acid, 50g of maleic acid as dispersants, and 20g of Tween 80 as surfactants in 10000ml of deionized water to obtain a reaction base solution containing a reducing agent; dissolve 2g of lauric acid in 1000ml of ethanol and stir thoroughly to obtain a coating solution for later use.

[0044] S2. Reaction process: The reaction base liquid is placed in the reaction vessel and stirred for 10 minutes under 50W ultrasound and a stirring rate of 400r. Then, the oxidant solution is added at a constant flow within 10 seconds to start the reaction. After the addition is complete, the reaction is carried out for 5 minutes. Then, the coating liquid is added and the treatment is continued for 1 minute before stopping, resulting in porous silver powder.

[0045] S3. Powder post-processing: After centrifugation to clean the surface of the obtained silver powder, it is filtered and dried in a vacuum drying oven at 50°C for 10 hours. The silver powder is then pulverized and sieved to obtain silver powder.

[0046] Example 2

[0047] This embodiment provides a method for preparing silver powder with ultrasound assistance, the method comprising the following steps:

[0048] S1. Solution preparation: Dissolve 425g of silver nitrate in 5000ml of deionized water to obtain an oxidizing agent solution; dissolve 440g of ascorbic acid (reducing agent), 50g of maleic acid (dispersant), and 20g of Tween 80 surfactant in 10000ml of deionized water to obtain a reaction base solution containing the reducing agent; dissolve 2g of lauric acid in 100ml of ethanol and stir thoroughly to obtain a coating solution for later use.

[0049] S2. Reaction process: The reaction base liquid is placed in the reaction vessel and stirred for 10 minutes under 200W ultrasound and a stirring rate of 500r. Then, the oxidant solution is added at a constant flow within 30 seconds to start the reaction. After the addition is complete, the reaction is carried out for 5 minutes. Then, the coating liquid is added and the treatment is continued for 5 minutes before stopping, resulting in porous silver powder.

[0050] S3. Powder post-processing: Same as in Example 1.

[0051] Example 3

[0052] S1. Solution preparation: Dissolve 425g of silver nitrate in 5000ml of deionized water to obtain an oxidizing agent solution; dissolve 440g of ascorbic acid, 30g of maleic acid, and 20g of PVP-K30 as dispersants and 20g of sodium dodecyl sulfonate as a surfactant in 10000ml of deionized water to obtain a reaction base solution containing the reducing agent; dissolve 2g of lauric acid in 1000ml of ethanol and stir thoroughly to obtain a coating solution for later use.

[0053] S2. Reaction process: The reaction base liquid is placed in the reaction vessel, the stirring speed is set to 600r, the ultrasonic power is set to 400W, and the reaction base liquid is treated under stirring and ultrasonication for 15min. Then, the oxidant solution is added at a constant flow within 30s to start the reaction. After 5min of reaction, the coating liquid is added and the treatment is continued for another 5min before stopping, to obtain porous silver powder.

[0054] S3. Powder post-processing: Same as in Example 1.

[0055] Example 4

[0056] This embodiment provides a method for preparing silver powder with ultrasound assistance, the method comprising the following steps:

[0057] S1. Solution preparation: Dissolve 425g of silver nitrate in 5000ml of deionized water to obtain an oxidizing agent solution; dissolve 440g of ascorbic acid (reducing agent), 50g of maleic acid (dispersant), and 20g of Tween 80 (surfactant) in 10000ml of deionized water to obtain a reaction base solution containing the reducing agent; dissolve 2g of lauric acid in 1000ml of ethanol and stir thoroughly to obtain a coating solution for later use.

[0058] S2. Reaction process: The reaction base liquid is placed in the reaction vessel and stirred for 15 minutes under 900W ultrasound and a stirring rate of 1500r. Then, the oxidant solution is added at a constant flow within 30 seconds to start the reaction. After the addition is complete, the reaction is carried out for 15 minutes. Then, the coating liquid is added and the treatment is continued for 5 minutes before stopping, resulting in porous silver powder.

[0059] S3. Powder post-processing: Same as in Example 1.

[0060] Example 5

[0061] Referring to Example 2, the difference from Example 2 is that the amount of Tween 80, as a surfactant, is increased to 40g.

[0062] Example 6

[0063] Referring to Example 3, the difference from Example 3 is that the amount of sodium dodecyl sulfonate as a surfactant is increased to 40g.

[0064] Example 7

[0065] S1. Solution preparation: Dissolve 425g of silver nitrate in 5000ml of deionized water to obtain an oxidizing agent solution; dissolve 440g of ascorbic acid, 30g of maleic acid, and 20g of PVP-K30 as dispersants and 20g of sodium dodecyl sulfate as a surfactant in 10000ml of deionized water to obtain a reaction base solution containing the reducing agent; dissolve 2g of palmitic acid in 1000ml of ethanol and stir thoroughly to obtain a coating solution for later use.

[0066] S2. Reaction process: The reaction base liquid is placed in the reaction vessel, the stirring speed is set to 800r, the ultrasonic power is set to 200W, and the reaction base liquid is treated under stirring and ultrasonication for 15min. Then, the oxidant solution is added at a constant flow within 30s to start the reaction. After reacting for 10min, the coating liquid is added and the treatment is continued for 5min before stopping, resulting in porous silver powder.

[0067] S3. Powder post-processing: Same as in Example 1.

[0068] Example 8

[0069] Referring to Example 7, the difference is that 50g of fumaric acid was used as a dispersant and 20g of Tween 80 was used as a surfactant.

[0070] Comparative Example 1

[0071] Referring to Example 2, the difference from Example 2 is that no surfactant is added to the reaction base liquid, the reaction process is the same as in Example 2, and no ultrasound is added to the reaction vessel. Other conditions are the same as in Example 1.

[0072] Comparative Example 2

[0073] Referring to Example 2, the difference is that the reducing agent 440g of ascorbic acid was replaced with 220g, and ultrasound was not added during the reaction. Other conditions were the same as in Example 2.

[0074] Comparative Example 3

[0075] Referring to Example 2, the difference is that the oxidant solution was added at a constant flow for 120 seconds to obtain silver powder.

[0076] Comparative Example 4

[0077] Referring to Example 2, without using the coating liquid, all other conditions are the same as in Example 2.

[0078] Test case

[0079] The silver powders prepared in Examples 2, 4-8 and Comparative Examples 1-3 were scanned using a field emission scanning electron microscope, and the particle size of the products prepared in Examples 2 and 3, as well as Comparative Examples 1, 2 and 4, was measured using a laser particle size analyzer. The results are shown in Table 1 below.

[0080] Table 1. Particle size values ​​of various silver powders

[0081] Test Project D10(um) D50(um) D90(um) Micromorphology Example 2 0.744 1.363 2.743 spherical Example 5 0.729 1.338 2.743 spherical Comparative Example 1 1.637 2.619 4.357 coarse strip Comparative Example 2 0.955 2.214 4.792 polyhedral Comparative Example 4 1.267 2.031 3.543 /

[0082] As shown in Table 1, the silver powder prepared by the present invention has a small particle size. According to the scanning electron microscope, the microstructure of the silver powder prepared by the present invention is a porous sphere.

[0083] Comparing the data from Example 2 and Comparative Example 1, it can be seen that the silver powder prepared without the addition of surfactant and without ultrasonic assistance has a much larger particle size than the silver powder prepared in Example 2. Furthermore, scanning electron microscopy reveals that the powder prepared in Comparative Example 1 exhibits a coarse, strip-like surface (see...). Figure 9 The result indicates that the initially formed structure was relatively large, and it subsequently aggregated into even larger silver particles.

[0084] By comparing the SMT diagram of Example 2 (see...) Figure 1 ) and the SMT diagram of Comparative Example 2 (see Figure 11 As can be seen from Table 1, the microstructure of the powder surface is a polyhedral structure. Furthermore, as can be seen from Table 1, by reducing the amount of reducing agent and not adding ultrasound during the reaction, the particle size of the silver powder prepared in Comparative Example 2 is much larger than that of the silver powder prepared in Example 2.

[0085] Compare the SMT diagram of Example 2 (see) Figure 1 ) and the SMT diagram of Comparative Example 3 (see Figure 13 It can be seen that increasing the feeding time of the oxidizing liquid, that is, adding the oxidizing agent solution at a constant flow for a period of more than 90 seconds, results in silver powder exhibiting more crystalline morphology. Even in a reaction system where there is excess oxidizing agent, ultrasonic cavitation and emulsification at the same time, increasing the feeding time will cause the small particles formed to grow further, thus growing into a polyhedral structure in the form of crystals. Under the same particle size, its specific surface area is much smaller than that of silver powder with a porous structure.

[0086] Comparing the data of Example 2 and Comparative Example 4, it can be seen that in Comparative Example 4, no coating agent was used to coat the obtained silver powder. After the silver powder was dried, the particle size was found to be larger when tested with a laser particle size analyzer. Without the effect of the coating agent, the silver powder underwent secondary agglomeration after synthesis, which affected the fineness value during the silver paste preparation process.

[0087] Specific surface area was obtained using a V-sorb4800S specific surface area analyzer from Guoyin Precision Measurement. The powder was pretreated at 150℃ for 30 min before adsorption and desorption, and the data were fitted using the BET multi-point method. See Table 2 below:

[0088] Table 2 Specific surface area values ​​of various silver powders

[0089]

[0090] Comparing the specific surface area values ​​of the silver powder prepared in Example 2 and Comparative Example 1, it can be seen that without adding surfactant to the base liquid and without adding ultrasound during the reaction process, the specific surface area of ​​the silver powder obtained is about 2.5 times smaller than that of the silver powder prepared in Example 2.

[0091] Comparing the specific surface area values ​​of the silver powder prepared in Example 2 and Comparative Example 1, it can be seen that the specific surface area of ​​the silver powder obtained by reducing the amount of reducing agent is more than 1.5 times smaller than that of the silver powder prepared in Example 2.

[0092] Comparing the specific surface area values ​​of the silver powder prepared in Example 2 and Comparative Example 1, it can be seen that extending the time of adding the oxidant solution results in a specific surface area of ​​silver powder that is more than 2.4 times smaller than that of the silver powder prepared in Example 2.

[0093] Comparing the specific surface area values ​​of the silver powder prepared in Example 2 and Comparative Example 4, it can be seen that the specific surface area of ​​the prepared silver powder is smaller than that of the silver powder prepared in Example 2.

[0094] In the preparation of silver powder in this invention, micro-nano bubbles are created as crystal nuclei by adding ultrasonic cavitation and emulsification of surfactants. The porous spherical silver powder is obtained by rapidly adding excess reducing agent and oxidizing agent, which exhibits high specific surface area performance under the same particle size.

[0095] Application Example 1

[0096] 25g of resin and 16g of solvent were mixed and stirred to dissolve. Then, 55g of silver powder obtained in Example 2 was added and stirred until homogeneous. The mixture was further stirred using a homogenizer, and then ground twice using a three-roll mill. 1g of curing agent and 3g of additives were added, and the mixture was finely ground three times. After standing and degassing, a conductive silver paste for RFID was obtained. The resin consisted of 90% trichloroethylene resin and 10% acrylic resin. The solvents included 15% DBE solvent, 10% isophorone, 82% 783 solvent, and 3% additives. The obtained silver paste was used to print flexible electronic tags on paper / PET substrates. The tags exhibited excellent sensing performance. The printed 7015 (70mm long, 15mm wide antenna) UHF RFID tags had a reading distance of 8-10m.

[0097] Application Example 2

[0098] 8.2 g of silver powder obtained in Example 1, along with 0.9 g of glass powder, 0.41 g of acrylic resin (20%) and vinyl chloride resin (80%), and 0.9 g of organic solvents butyl carbitol and carbitol acetate, were mixed and stirred. Then, 0.1 g of organic additives were added, and the mixture was mixed and degassed using a rotary vacuum degassing machine. The mixture was then dispersed and ground using a three-roll mill to obtain silver paste. Lines of 1×100 mm were obtained using a screen printing machine, dried at 650°C for 15 min, and its resistivity was measured to be 4.78×10⁻⁶. -8 Ω·m. For lines 20µm wide, printing with this high-viscosity paste results in a line width of 35µm and a height of 20µm after curing. The lines exhibit good reproducibility and a large aspect ratio, making it suitable for fine grid printing in photovoltaic solar cells.

[0099] The above descriptions are merely embodiments of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. For those skilled in the art, the scope of protection of this invention should be understood to include substitutions and modifications that do not depart from the invention, and are covered by the rights of this patent application.

Claims

1. A method for preparing silver powder with ultrasonic assistance, characterized in that, The method includes the following steps: S1. Solution preparation: Prepare the reaction base solution, oxidant solution and coating solution, wherein the reaction base solution contains a dispersant, a reducing agent and a surfactant, and the oxidant solution is an oxidant solution containing silver salt; S2. Reaction process: The reaction base liquid is placed in the reaction vessel and stirred for 10-15 minutes under ultrasonic treatment of 50-900W and stirring speed of 400-1500r. Then, the oxidant solution is added at a constant flow within 1-30 seconds to start the reaction. After the addition is completed, the reaction is carried out for 0-10 minutes. Then, the coating liquid is added and the treatment is continued for 1-5 minutes to obtain porous silver powder. S3. Powder post-processing: The obtained silver powder is obtained by solid-liquid separation, washing, drying and pulverizing. In step S1, the molar ratio of the reducing agent to the number of electrons transferred in the redox process is (1.5-4):

1. In step S1, the dispersant is one or more of PVP, maleic acid, cyclodextrin, fumaric acid, gelatin, malic acid, gum arabic, and oleic acid, and the surfactant is one or more of Tween 80, Span 80, sodium dodecylbenzene sulfonate, sodium dodecyl sulfonate, polyvinyl alcohol, and polyethylene glycol.

2. The method for preparing silver powder with ultrasound assistance according to claim 1, characterized in that, The silver salt is silver nitrate, and the concentration of silver ions in the oxidant solution is 0.1–5.0 mol / L.

3. The method for preparing silver powder with ultrasound assistance according to claim 2, characterized in that, In step S1, the reducing agent is one or more of glucose, hydrazine hydrate, sodium borohydride, potassium borohydride, ascorbic acid, urea, formaldehyde, and isoascorbic acid, and the concentration of the reducing agent in the reaction substrate is 0.2–2.0 mol / L.

4. The method for preparing silver powder with ultrasonic assistance according to claim 1, characterized in that the specific steps of step S3 are as follows: after the silver powder obtained in step S2 is centrifuged, filtered and washed multiple times, it is then sieved, dried and pulverized to obtain spherical silver powder; the specific drying conditions are as follows: the silver powder is placed in a circulating atmospheric dryer or vacuum dryer at 50°C for 10 hours.

5. The method for preparing silver powder with ultrasound assistance according to claim 1, characterized in that, The amount of the dispersant used is 5% to 35% of the mass of the silver salt; The amount of surfactant used is 0.1% to 10% of the mass of the silver salt.

6. The method for preparing silver powder with ultrasound assistance according to claim 1, characterized in that, The coating solution in step S1 is obtained by dissolving a coating agent in a solvent. The coating agent is at least one selected from lauric acid, sodium laurate, silane coupling agent, oleic acid, lauric acid, stearic acid, palmitic acid, and benzotriazole. The amount of coating agent used is 0.01% to 5% of the mass of the silver salt. The solvent is either ethanol or deionized water. The mass fraction of the solvent in the coating solution is 0.2% to 2.0%.

7. A silver powder prepared by the method according to any one of claims 1 to 6.

8. The application of silver powder prepared by the method according to any one of claims 1 to 6 in the preparation of high-precision conductive line printing paste.

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