Submicron silver powder and preparation method thereof

Abstract

The invention relates to the technical field of metal powder, in particular to submicron silver powder and a preparation method thereof.The preparation method of the submicron silver powder comprises the steps that S1, a silver source solution, a reduction solution, a dispersion solution and a modification solution are prepared; s2, adding a reducing solution into the dispersion liquid, uniformly mixing, and adding an acid solution to form a base solution with the pH value of 1.0-4.8; s3, adding a silver source solution into the base solution, uniformly mixing, and adding an alkaline solution to form a reaction solution with the pH value of 6.5-11.0; s4, a modified solution is added into the reaction liquid, and silver powder dispersion liquid is prepared; and S5, the silver powder dispersion liquid is treated, and the submicron silver powder is prepared. The formed submicron silver powder is more regular in morphology, is circular, and is smaller in specific surface area compared with a flaky or approximately hexagonal silver powder, so that the dispersity of the silver powder in silver paste is improved, the silver paste has better flowability, and the printing uniformity is guaranteed. And the particle size of the formed submicron silver powder is uniform. And the tap density of the formed submicron silver powder is higher.

Description

Technical Field

[0001] This application relates to the field of metal powder technology, and in particular to a submicron-sized silver powder and its preparation method. Background Art

[0002] With societal development, electronic products are trending towards miniaturization in size and weight, leading to a gradual increase in demand for ultrafine metal powders. Simultaneously, higher requirements are being placed on the properties of these ultrafine metal powders. Silver powder, as an excellent material, is widely used in optical materials, electronic pastes, medicine, and catalysis due to its superior electrical and thermal conductivity, high plasticity, low-temperature sintering ability, and oxidation resistance. In the preparation of conductive silver paste for solar cells, silver powder accounts for 70%–90% of the total mass. The positive grid lines of solar cells are very narrow; if the silver powder particle size is too large, it cannot pass through the screen during printing, affecting the cell's electrical performance. If the silver powder particle size is too small, it is difficult to ensure the silver content in the paste, and it is not easily wetted by organic carriers, resulting in decreased printing performance, a larger shrinkage rate after sintering, and poor density. Therefore, the silver powder used in the front-side silver paste for solar cells is micron / submicron grade silver powder.

[0003] Currently, the chemical reduction method is widely used to prepare silver powder. Compared with other methods, it is simple to operate, low in cost, easy to control, and causes less environmental pollution. This method uses a reducing agent to reduce silver particles from silver salts or silver complex systems, encompassing the nucleation and growth processes of silver.

[0004] The existing technical solutions mentioned above have the following drawbacks: when preparing submicron silver powder by chemical reduction, the morphology is not very regular, the particle size is not very uniform, and the specific surface area is relatively large. Summary of the Invention

[0005] In order to make the morphology of submicron silver powder more regular, the particle size more uniform, and the specific surface area smaller, this application provides a submicron silver powder and its preparation method.

[0006] The primary objective of this application is to provide a method for preparing submicron-sized silver powder, employing the following technical solution: A method for preparing submicron-sized silver powder, comprising: S1. Prepare silver source solution, reducing solution, dispersion and modified solution; S2. Add the reducing solution to the dispersion, mix well, and then add an acidic solution to form a bottom solution with a pH of 1.0-4.8; S3. Add silver source solution to the base solution, mix well, and then add alkaline solution to form a reaction solution with pH 6.5-11.0; S4. Add the modified solution to the reaction solution to obtain a silver powder dispersion; S5. The silver powder dispersion is treated to obtain submicron-sized silver powder.

[0007] By employing the above technical solution and adjusting the pH environment in stages, the nucleation and growth of silver particles were separated and controlled. The acidic substrate slowed down the reduction rate of silver ions, preventing explosive nucleation and agglomeration, while the alkaline reaction solution accelerated the directional growth of silver particles, forming submicron-sized silver particles with high sphericity and good dispersibility. Combined with the subsequent coating of modifying agents, particle adhesion was further inhibited, tap density was increased, and specific surface area was reduced. The process is simple and cost-effective. The resulting submicron-sized silver powder has a more regular morphology and is spherical. Compared to flake-shaped or near-hexagonal submicron-sized silver powder, it has a smaller specific surface area, which is beneficial for improving the dispersibility of silver powder in silver paste, resulting in better fluidity and ensuring printing uniformity. The uniform particle size of the resulting submicron-sized silver powder allows for narrow grid lines to be printed using screen printing, avoiding clogging or shrinkage cracks. The higher tap density of the resulting submicron-sized silver powder leads to better density and improved conductivity of the sintered silver electrode.

[0008] This application further specifies that: in step S1, silver oxide is dissolved in deionized water to prepare a silver source solution with a concentration of 0.2-1.1 mol / L; a reducing agent is dissolved in deionized water to prepare a reducing solution with a concentration of 50-500 g / L; a dispersant containing 0.5-60% by mass of silver oxide is dissolved in deionized water to prepare a dispersion with a mass percentage concentration of 0.1-4 wt%; and a modifying agent is dissolved in anhydrous ethanol to prepare a modifying solution with a mass percentage concentration of 0.1-0.2 wt%.

[0009] By adopting the above technical solution, the modified solution can improve the dispersibility and stability of silver powder, coat the surface of silver powder to play an antioxidant role, enhance the conductivity of silver electrode, and improve the flowability of silver powder during the preparation process.

[0010] This application further specifies that: the silver oxide is one of silver nitrate, silver sulfate, silver carbonate and silver oxalate; the reducing agent is at least one of ascorbic acid, glucose, hydrazine hydrate, formaldehyde, hydrogen peroxide, glycerol, sodium hypochlorite, sodium borohydride, ferrous sulfate, thiourea dioxide, ethylene glycol sulfite and hydroquinone. The dispersant is at least one of the following: methylcellulose, carboxymethylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, gelatin, polyvinylpyrrolidone, gum arabic, gum guar, ethanol, Tween, polyethylene glycol, glycerol, methylpentanol, octylamine, polyethylamide, fatty acid polyethylene glycol ester, sodium tripolyphosphate, sodium hexametaphosphate, sodium pyrophosphate, glycolic acid, glyceric acid, malic acid, succinic acid, sodium citrate, potassium citrate, phthalic acid, isophthalic acid, terephthalic acid, triethylhexylphosphate, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate. The modifying agent is at least one of oleic acid, linoleic acid, linolenic acid, stearic acid, palmitic acid, arachidic acid, myristic acid, lauric acid, oleylamine, palmitic acid, monoethanolamine, diethanolamine, and triethanolamine.

[0011] By adopting the above technical solution, a synergistic effect of high efficiency reduction, excellent stability, environmental friendliness, cost savings, and wide applicability is achieved. This results in uniform silver particle size, precise reaction control, and high safety of the reaction system.

[0012] This application further specifies that: in step S1, when preparing the silver source solution, the reducing solution and the dispersion, the temperature is controlled at 20℃-40℃.

[0013] The present application further specifies that: in step S2, the stirring time is 3-5 min; in step S3, the stirring time is 2-5 min; and in step S4, the stirring reaction time is 15-25 min.

[0014] This application further specifies that the acidic solution is at least one selected from nitric acid, sulfuric acid, hydrochloric acid, oxalic acid, acetic acid, and benzenesulfonic acid; The alkaline solution is at least one of sodium hydroxide, ammonia, sodium carbonate, sodium citrate, potassium citrate, monoethanolamine, diethanolamine, triethanolamine, monoethylamine, diethylamine, triethylamine, formamide, acetamide, and propionamide.

[0015] This application further specifies that: in step S5, the silver powder dispersion is transferred to a filter press and repeatedly washed with deionized water until the conductivity is less than 20 μS / cm, and then dehydrated with anhydrous ethanol; the dehydrated silver powder is placed in a drying container for drying at a temperature of 50-80°C for 5-12 hours; the dried silver powder is then pulverized using a pulverizer to obtain submicron-sized silver powder.

[0016] The second objective of this application is to provide a submicron-sized silver powder, employing the following technical solution: A submicron-sized silver powder was prepared using the above-described method.

[0017] This application further specifies that the submicron silver powder is spherical, with a D50 of 0.8-1.6 μm and a tap density greater than 5.0 g / cm³. 3 Specific surface area less than 0.4 m² 2 / g.

[0018] In summary, the beneficial technical effects of this application are as follows: 1. By adjusting the pH environment in stages, the nucleation and growth of silver particles were separated and controlled. The acidic substrate slowed down the reduction rate of silver ions, preventing explosive nucleation and agglomeration, while the alkaline reaction solution accelerated the directional growth of silver particles, forming submicron-sized silver particles with high sphericity and good dispersibility. Combined with the subsequent coating of modifying agents, particle adhesion was further inhibited, tap density was increased, and specific surface area was reduced. The process is simple and cost-effective. The resulting submicron-sized silver powder has a more regular morphology and is spherical. Compared to flake-shaped or near-hexagonal submicron-sized silver powder, it has a smaller specific surface area, which is beneficial for improving the dispersibility of silver powder in silver paste, resulting in better fluidity and ensuring printing uniformity. The uniform particle size of the resulting submicron-sized silver powder allows for narrow grid lines to be printed using screen printing, avoiding clogging or shrinkage cracks. The higher tap density of the resulting submicron-sized silver powder leads to better density and improved conductivity of the sintered silver electrode.

[0019] 2. The modified solution can improve the dispersibility and stability of silver powder, coat the surface of silver powder to play an antioxidant role, enhance the conductivity of silver electrode, and improve the flowability of silver powder during the preparation process. Attached Figure Description

[0020] Figure 1 This is a flowchart of a method for preparing submicron-sized silver powder; Figure 2 This is an electron microscope image of the submicron-sized silver powder prepared in Example 1; Figure 3 This is an electron microscope image of the submicron-sized silver powder prepared in Example 2; Figure 4 This is an electron microscope image of the submicron-sized silver powder prepared in Example 3; Figure 5 This is an electron microscope image of the submicron-sized silver powder prepared in Example 4; Figure 6 This is an electron microscope image of the submicron-sized silver powder prepared in Example 5; Figure 7 This is an electron microscope image of the submicron-sized silver powder prepared in Example 6; Figure 8 This is an electron microscope image of the submicron-sized silver powder prepared in Example 7; Figure 9 This is an electron microscope image of the submicron silver powder prepared in Example 8; Figure 10This is an electron microscope image of the submicron silver powder prepared in Comparative Example 1. Figure 11 This is an electron microscope image of the submicron-sized silver powder prepared in Comparative Example 2.

[0021] Figure 12 This is an electron microscope image of the submicron-sized silver powder prepared in Comparative Example 3. DETAILED DESCRIPTION

[0022] The following is in conjunction with the appendix Figure 1-12 This application will be described in further detail.

[0023] Reference Figure 1 This application discloses a method for preparing submicron-sized silver powder, comprising: S1. Prepare silver source solution, reducing solution, dispersion and modified solution.

[0024] The embodiments of this application do not particularly limit the preparation steps of the silver source solution, reducing solution, dispersion, and modified solution. Any known preparation steps can be used in this application without departing from the concept of this application. These are merely illustrative examples and not limitations on the scope of protection. For example, silver oxide can be dissolved in deionized water to prepare silver source solutions with concentrations of 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, or 1.1 mol / L. Similarly, a reducing agent can be dissolved in deionized water to prepare reducing solutions with concentrations of 50 g / L, 100 g / L, 150 g / L, 200 g / L, 250 g / L, 300 g / L, 350 g / L, 400 g / L, 450 g / L, or 500 g / L. For example, dissolve 0.5%, 2%, 10%, 20%, 30%, 40%, 50%, or 60% (by mass) of a dispersant containing silver oxide in deionized water to prepare dispersions with mass percentage concentrations of 0.1 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, or 4 wt%. Alternatively, dissolve the modifying agent in anhydrous ethanol to prepare modified solutions with mass percentage concentrations of 0.1 wt%, 0.11 wt%, 0.12 wt%, 0.13 wt%, 0.14 wt%, 0.15 wt%, 0.16 wt%, 0.17 wt%, 0.18 wt%, 0.19 wt%, or 0.2 wt%.

[0025] In the embodiments of this application, the silver oxide contained is one of silver nitrate, silver sulfate, silver carbonate, and silver oxalate. The reducing agent is at least one of ascorbic acid, glucose, hydrazine hydrate, formaldehyde, hydrogen peroxide, glycerol, sodium hypochlorite, sodium borohydride, ferrous sulfate, thiourea dioxide, ethylene glycol sulfite, and hydroquinone. The dispersant is methylcellulose, carboxymethylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, gelatin, polyvinylpyrrolidone, gum arabic, gulp, ethanol, Tween, polyethylene glycol, glycerol, methylpentanol, octylamine, polyethylamide, fatty acid polyethylene glycol ester, sodium tripolyphosphate, sodium hexametaphosphate, sodium pyrophosphate, glycolic acid, glyceric acid, malic acid, succinic acid, sodium citrate, potassium citrate, phthalic acid, isophthalic acid, terephthalic acid, triethylhexylphosphonic acid, and triethylhexylphosphonic acid. At least one of sodium dodecyl sulfate and sodium dodecylbenzene sulfonate. The modifying agent is at least one of oleic acid, linoleic acid, linolenic acid, stearic acid, palmitic acid, arachidic acid, myristic acid, lauric acid, oleylamine, palmitic acid, monoethanolamine, diethanolamine, and triethanolamine.

[0026] It should be noted that when preparing silver source solutions, reducing solutions, and dispersions, the temperature should be controlled at 20℃, 25℃, 30℃, 35℃, or 40℃.

[0027] S2. Add the reducing solution to the dispersion, mix well, and then add an acidic solution to form a bottom solution with a pH of 1.0-4.8.

[0028] In this embodiment, after adding the reducing solution to the dispersion, the mixture is stirred for 2 min, 2.5 min, or 3 min to ensure uniform mixing of the dispersion and the reducing solution. Then, an acidic solution is added dropwise to the mixture to adjust the pH of the base solution to 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 4.8, and stirring continues for 1 min, 1.5 min, or 2 min.

[0029] The acidic solution in this application embodiment is at least one of nitric acid, sulfuric acid, hydrochloric acid, oxalic acid, acetic acid, and benzenesulfonic acid.

[0030] S3. Add silver source solution to the base solution, mix well, and then add alkaline solution to form a reaction solution with pH 6.5-11.0.

[0031] In this embodiment, the silver source solution is poured into the base solution all at once, and stirred for 1 min, 1.5 min, 2 min, 2.5 min or 3 min. Then, an alkaline solution is added dropwise to the mixed solution to adjust the pH of the reaction solution to 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5 or 11.0, and then stirring is continued for 1 min, 1.5 min or 2 min.

[0032] The alkaline solution in this application embodiment is at least one selected from sodium hydroxide, ammonia, sodium carbonate, sodium citrate, potassium citrate, monoethanolamine, diethanolamine, triethanolamine, monoethylamine, diethylamine, triethylamine, formamide, acetamide, and propionamide.

[0033] S4. Add the modified solution to the reaction solution to obtain a silver powder dispersion.

[0034] In this embodiment, after adding the modified solution to the reaction solution, the mixture is stirred continuously for 15 min, 18 min, 20 min, 22 min, or 25 min to allow for a complete reaction.

[0035] S5. The silver powder dispersion is treated to obtain submicron-sized silver powder.

[0036] In this embodiment, the silver powder dispersion is first transferred to a filter press and repeatedly washed with deionized water until the conductivity is below 20 μS / cm, 15 μS / cm, or 10 μS / cm, and then dehydrated with anhydrous ethanol. The dehydrated silver powder is then placed in a drying container for drying at temperatures of 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C for durations of 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours. Afterward, the dried silver powder is pulverized using a pulverizer to obtain submicron-sized silver powder.

[0037] This application discloses a submicron-sized silver powder, prepared using the aforementioned method for preparing submicron-sized silver powder. The submicron-sized silver powder has a D50 of 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, or 1.6 μm, and a tap density of 5.0 g / cm³. 3 6.0g / cm 3 7.0g / cm 3 8.0g / cm 3 9.0g / cm 3 Or 10.0g / cm 3 The above has a specific surface area of ​​0.4 m². 2 / g, 0.3m 2 / g, 0.2m 2 / g or 0.1m 2 / g or less. Example

[0038] Example 1 This embodiment provides a method for preparing submicron-sized silver powder, including: S1. Dissolve 34g of silver nitrate in 1L of deionized water at 20℃ to form a silver source solution. Dissolve 11.8g of thiourea dioxide in 240g of deionized water at 20℃ to form a reducing solution. Dissolve 20g of carboxymethyl cellulose in 5L of deionized water at 20℃ to form a dispersion. Dissolve 0.1g of palmitic acid and 0.1g of stearic acid in 50ml of anhydrous ethanol to form a modified solution.

[0039] S2. Add the reducing solution to the dispersion, stir for 2 minutes, then add nitric acid dropwise to adjust the pH of the bottom solution to 3.5, and stir for another 1 minute.

[0040] S3. Pour the silver source solution directly into the base solution, then add ammonia dropwise to adjust the pH of the reaction solution to 6.8. After adjustment, continue stirring for 2 minutes.

[0041] S4. Add the modified solution to the reaction solution and continue stirring for 20 minutes to obtain a silver powder dispersion.

[0042] S5. Transfer the silver powder dispersion to a filter press and wash repeatedly with deionized water until the conductivity is less than 20 μS / cm, then dehydrate with anhydrous ethanol. Place the dehydrated silver powder in a drying container and dry at 70°C for 8 hours. Then, pulverize the dried silver powder using a pulverizer to obtain submicron-sized silver powder with a spherical morphology.

[0043] Example 2 The difference from Example 1 is that the pH of the base solution was adjusted to 4.0 before adding the silver source solution to the base solution. After adding the silver source solution to the base solution, the pH of the reaction solution was adjusted to 6.8.

[0044] Example 3 The difference from Example 1 is that the pH of the base solution was adjusted to 4.3 before adding the silver source solution to the base solution. After adding the silver source solution to the base solution, the pH of the reaction solution was adjusted to 6.8.

[0045] Example 4 The difference from Example 1 is that the pH of the base solution was adjusted to 4.8 before adding the silver source solution to the base solution. After adding the silver source solution to the base solution, the pH of the reaction solution was adjusted to 6.8.

[0046] Example 5 The difference from Example 1 is that 85g of silver nitrate was dissolved in 1L of deionized water at a controlled temperature of 20°C to form a silver source solution. 29.5g of thiourea dioxide was dissolved in 240g of deionized water at a controlled temperature of 20°C to form a reducing solution. 100g of carboxymethyl cellulose was dissolved in 5L of deionized water at a controlled temperature of 20°C to form a dispersion.

[0047] Example 6 The difference from Example 1 is that 340g of silver nitrate was dissolved in 1L of deionized water at a controlled temperature of 20°C to form a silver source solution. 118g of thiourea dioxide was dissolved in 240g of deionized water at a controlled temperature of 20°C to form a reducing solution. 200g of carboxymethyl cellulose was dissolved in 5L of deionized water at a controlled temperature of 20°C to form a dispersion.

[0048] Example 7 The difference from Example 1 is that 18.8g of ascorbic acid was dissolved in 240g of deionized water and the temperature was controlled at 20°C to form a reducing solution.

[0049] Example 8 The difference from Example 1 is that 13.6g of polyvinylpyrrolidone was dissolved in 5L of deionized water and the temperature was controlled at 20°C to form a dispersion.

[0050] Comparative Example Comparative Example 1 The difference from Example 1 is that the pH value is not adjusted before or after adding the silver source solution to the substrate.

[0051] Comparative Example 2 This comparative example provides a method for preparing submicron-sized silver powder, including: (1) Mix ultrapure water and glycerol in a mass ratio of 1:1 as solvents to prepare 0.2 L of 2 mol / L silver nitrate solution, 1.5 L of 0.2 mol / L ascorbic acid solution, and 1 L of 0.6 mol / L benzotriazole solution at room temperature.

[0052] (2) At room temperature, add benzotriazole solution to silver nitrate solution, stir and mix well, then add 0.2 mol / L nitric acid aqueous solution dropwise to adjust the pH of the system to 2.8. Then add ascorbic acid solution, control the reaction temperature at 35℃, and nucleation reaction for 6 min.

[0053] (3) Add 2 mol / L sodium hydroxide aqueous solution to the reaction product of step (2), adjust the pH value of the system to 11, maintain the reaction temperature at 35℃, and react for 1 hour to obtain silver powder dispersion.

[0054] (4) The silver powder dispersion was centrifuged to obtain silver colloid. The silver colloid was washed three times with ethanol and once with ultrapure water, and then vacuum dried at 55°C for 3 hours to obtain submicron silver powder with a flake-like morphology.

[0055] Comparative Example 3 This comparative example provides a method for preparing submicron-sized silver powder, including: (1) Weigh 1 kg of silver nitrate and place it in 3 L of deionized water. After stirring, dissolve the nitrate, add 20 g of polyvinylpyrrolidone and mix well. Then store the mixture in a storage container at a low temperature of 20 °C.

[0056] (2) Weigh 0.1 kg of glucose and 0.5 kg of vitamin C and place them in 3 L of deionized water. Dissolve them by stirring. Then store them in a storage container at a low temperature of 20 °C.

[0057] (3) Weigh 250g of polyvinylpyrrolidone, 1g of gelatin, 1g of Tween 40, and 1g of Tween 80 as dispersants and dissolve them in 4L of water, and add 2.5g of lysine. After preparation, use it as the base liquid and put it into the reaction vessel.

[0058] (4) Dissolve 15g of silver nitrate in 89.85ml (100g) of ethylene glycol, then add 9g of gluconic acid and 9g of glucose for aging to obtain a seed solution. Dilute the obtained solution with deionized water at a mass ratio of 1:99 to obtain a seed dilution solution. Add polyvinyl alcohol and Tween 80 to the seed dilution solution as dispersants, and mix them evenly with concentrations of 0.03g / L and 0.01g / L respectively. The solution is then detected by ultraviolet-visible spectrophotometry. The detection results are as follows: the absorption characteristic peak of the seed solution is 460.1mm and the absorption peak intensity is 0.7. The crystal size of the nano-silver in the seed solution is 20-80nm and the concentration is 2ppm, which meets the standard and can be used as a seed solution.

[0059] (5) The cold water circulation pump was turned on to control the temperature of the reaction tank to 20°C. At the same time, the valves of the pump pipes on both sides were opened to pump the silver salt solution and reducing solution from the storage tank into the reaction tank. First, the pump of the reducing solution was turned on to control the flow rate of the reducing solution to 0.1 L / min. 5% of the total amount of reducing solution was pumped into the reaction tank to mix with the bottom liquid. Then, the pump of the silver salt solution was turned on to control the flow rate of the silver salt solution to 0.11 L / min. At the same time, the speed of the impeller of the reactor was kept at 400 r / min.

[0060] (6) At this time, the third variety solution is added by spraying, and the spraying rate is similar to that of the silver salt solution. When the reaction solution turns black, the flow rate of the silver salt solution is adjusted to 0.05 L / min within 10 seconds. At this time, the flow rate of the silver salt solution is lower than that of the remaining reducing solution, and the difference between the two is 0.05 L / min.

[0061] (7) After 30-35 mins of feeding, the reaction ends. At this time, add 2g and 1g of the prepared flocculant (lauric acid and stearic acid) to the reaction tank by pouring. At the same time, adjust the temperature of the reaction system in the reaction tank to 40℃, increase the speed of the impeller in the reaction tank to 800r / min, and continue to maintain it for 10 mins to complete the silver powder flocculation and sedimentation.

[0062] (8) The solution containing silver powder was centrifuged to separate the solid and liquid phases. After being washed twice with ethanol, the solution was filtered through a filter screen to obtain wet powder. The wet powder was placed in a vacuum oven and dried at low temperature to obtain submicron silver powder with a near-hexagonal morphology.

[0063] Performance testing Test 1: The tap density of submicron silver powder in each example and comparative example was determined according to GB / T 5162-2020 "Determination of tap density of metal powder".

[0064] Test 2: The particle size D50 of submicron silver powder in each example and comparative example was determined using a laser particle size analyzer according to ISO 13320 standard.

[0065] Test 3: The specific surface area of ​​submicron silver powder in each example and comparative example was determined by gas adsorption BET method according to GB / T 19587-2016.

[0066] The test results are shown in Table 1. Electron micrographs of the submicron silver powders prepared in Examples 1-8 and Comparative Examples 1-3 are shown in Table 1. Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 , Figure 10 , Figure 11 and Figure 12 .

[0067] Table 1 Performance Test Results Refer to Table 1. Figure 2 , Figure 11 and Figure 12 Compared to Comparative Examples 1-3, the submicron-sized silver powder prepared in Examples 1-8 is spherical, with a smaller specific surface area compared to flake-shaped or near-hexagonal submicron-sized silver powder. This improves the dispersibility of the silver powder in the silver paste, resulting in better fluidity and ensuring printing uniformity. The formed submicron-sized silver powder has a more uniform and higher particle size. Furthermore, the formed submicron-sized silver powder has a higher tap density, leading to better compactness and improved conductivity of the sintered silver electrode.

[0068] As can be seen from Comparative Example 1 and Examples 1-8, by adjusting the pH value of the system before and after adding the silver source solution to the base liquid, the tap density and particle size D50 of the submicron silver powder can be significantly increased, and the specific surface area of ​​the submicron silver powder can be significantly reduced.

[0069] As can be seen from Examples 1-4, the higher the pH of the base solution is adjusted before adding the silver source solution, the higher the tap density and particle size D50 of the resulting submicron silver powder, and the lower the specific surface area.

[0070] As can be seen from Examples 1 and 6, as the concentrations of the silver source solution, reducing solution and dispersion are increased simultaneously, the tap density and specific surface area do not change, but the particle size D50 increases significantly.

[0071] As can be seen from Examples 1 and 7, replacing the reducing agent with ascorbic acid instead of thiourea dioxide can improve the tap density and particle size D50.

[0072] The implementation principle of this embodiment is as follows: by adjusting the pH environment in stages, the nucleation and growth of silver particles are separated and controlled. The acidic substrate slows down the reduction rate of silver ions, preventing explosive nucleation and agglomeration, while the alkaline reaction solution accelerates the directional growth of silver particles, forming submicron-sized silver particles with high sphericity and good dispersibility. Combined with the subsequent coating of modifying agents, particle adhesion is further inhibited, tap density is increased, and specific surface area is reduced. The process is simple and cost-controllable. The resulting submicron-sized silver powder has a more regular morphology and is spherical. Compared to flake-shaped or near-hexagonal submicron-sized silver powder, it has a smaller specific surface area (less than 0.4 m² / g), which is beneficial for improving the dispersibility of silver powder in silver paste, giving the silver paste better fluidity and ensuring printing uniformity. The resulting submicron-sized silver powder has a uniform particle size (D50 of 0.8-1.6 μm), allowing for narrow grid lines to be printed using screen printing, avoiding clogging or shrinkage cracks. The resulting submicron-sized silver powder has a higher tap density (greater than 5.0 g / cm3), and the silver electrode has good density and improved conductivity after sintering.

[0073] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing submicron-sized silver powder, characterized in that, include: S1. Prepare silver source solution, reducing solution, dispersion and modified solution; S2. Add the reducing solution to the dispersion, mix well, and then add an acidic solution to form a bottom solution with a pH of 1.0-4.8; S3. Add the silver source solution to the base solution, mix well, and then add an alkaline solution to form a reaction solution with a pH of 6.5-11.0; S4. Add the modified solution to the reaction solution to obtain a silver powder dispersion; S5. The silver powder dispersion is processed to obtain submicron-sized silver powder.

2. The method for preparing submicron-sized silver powder according to claim 1, characterized in that, In step S1, the silver oxide is dissolved in deionized water to prepare the silver source solution with a concentration of 0.2-1.1 mol / L; The reducing agent is dissolved in deionized water to prepare a reducing solution with a concentration of 50-500 g / L; the dispersant containing 0.5-60% by mass of silver oxide is dissolved in deionized water to prepare a dispersion with a mass percentage concentration of 0.1-4 wt%; the modifying agent is dissolved in anhydrous ethanol to prepare a modifying solution with a mass percentage concentration of 0.1-0.2 wt%.

3. The method for preparing submicron-sized silver powder according to claim 2, characterized in that, The silver oxide is one of silver nitrate, silver sulfate, silver carbonate, and silver oxalate; The reducing agent is at least one of ascorbic acid, glucose, hydrazine hydrate, formaldehyde, hydrogen peroxide, glycerol, sodium hypochlorite, sodium borohydride, ferrous sulfate, thiourea dioxide, ethylene glycol sulfite, and hydroquinone. The dispersant is at least one selected from methylcellulose, carboxymethylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, gelatin, polyvinylpyrrolidone, gum arabic, gum guar, ethanol, Tween, polyethylene glycol, glycerol, methylpentanol, octylamine, polyethylamide, fatty acid polyethylene glycol ester, sodium tripolyphosphate, sodium hexametaphosphate, sodium pyrophosphate, glycolic acid, glyceric acid, malic acid, succinic acid, sodium citrate, potassium citrate, phthalic acid, isophthalic acid, terephthalic acid, triethylhexylphosphate, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate. The modifying agent is at least one selected from oleic acid, linoleic acid, linolenic acid, stearic acid, palmitic acid, arachidic acid, myristic acid, lauric acid, oleylamine, palmitic acid, monoethanolamine, diethanolamine, and triethanolamine.

4. The method for preparing submicron-sized silver powder according to claim 1, characterized in that, In step S1, the temperature is controlled between 20°C and 40°C when preparing the silver source solution, the reducing solution, and the dispersion.

5. The method for preparing submicron-sized silver powder according to claim 1, characterized in that, In step S2, the stirring time is 3-5 min; in step S3, the stirring time is 2-5 min; in step S4, the stirring reaction time is 15-25 min.

6. The method for preparing submicron-sized silver powder according to claim 1, characterized in that, The acidic solution is at least one of nitric acid, sulfuric acid, hydrochloric acid, oxalic acid, acetic acid, and benzenesulfonic acid; The alkaline solution is at least one of sodium hydroxide, ammonia, sodium carbonate, sodium citrate, potassium citrate, monoethanolamine, diethanolamine, triethanolamine, monoethylamine, diethylamine, triethylamine, formamide, acetamide, and propionamide.

7. The method for preparing submicron-sized silver powder according to claim 1, characterized in that, In step S5, the silver powder dispersion is transferred to a filter press and repeatedly washed with deionized water until the conductivity is less than 20 μS / cm, and then dehydrated with anhydrous ethanol. The dehydrated silver powder is placed in a drying container for drying at a temperature of 50-80°C for 5-12 hours. The dried silver powder is then pulverized using a pulverizer to obtain the submicron-sized silver powder.

8. A submicron-sized silver powder, characterized in that, It is prepared using the method for preparing submicron silver powder according to any one of claims 1 to 7.

9. The submicron-sized silver powder according to claim 1, characterized in that, The submicron-sized silver powder is spherical with a D50 of 0.8-1.6 μm and a tap density greater than 5.0 g / cm³. 3 Specific surface area less than 0.4 m² 2 / g.

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