Flaky self-assembled spherical silver powder and preparation method thereof
By controlling the reaction conditions of sulfate and silver nitrate solutions, sheet-like self-assembled spherical silver powder with large specific surface area and low tap density was prepared, solving the problems of low-temperature sintering and flowability, and realizing the multifunctional application of silver powder.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NINGXIA CNMC NEW MATERIAL CO LTD
- Filing Date
- 2023-11-21
- Publication Date
- 2026-05-12
AI Technical Summary
Existing technologies make it difficult to prepare silver powder that possesses both low-temperature sintering properties and excellent flowability.
A two-step reaction method was adopted to prepare sheet-like self-assembled spherical silver powder by controlling the volume ratio of sulfate solution and silver nitrate solution, temperature and dropping rate, ensuring that the silver powder grows in situ at the submicron level, forming a large specific surface area and low tap density.
A sheet-like self-assembled spherical silver powder with large specific surface area, low tap density, and high sphericity was prepared. It is suitable for low-temperature sintering slurry and combines the advantages of both spherical and sheet-like powders.
Abstract
Description
Technical Field
[0001] This invention belongs to the field of conductive filler technology, and particularly relates to a sheet-like self-assembled spherical silver powder and its preparation method. Background Technology
[0002] Silver powder, as an excellent conductive filler, is widely used in energy, microelectronics, and other fields. As a major component of electronic pastes, the morphology, particle size distribution, dispersibility, and tap density of silver powder all significantly influence the performance of the paste. Different technical specifications of silver powder have different applications; for example, high-tap-density spherical silver powder is often used in the preparation of high-silver-content silver pastes, while low-bulk-density flake silver powder is often used in the preparation of low-silver-content thin-film pastes.
[0003] Compared to flake silver powder, spherical silver powder has better fluidity in pastes, giving the paste better printability. Flake silver powder, on the other hand, has a larger specific surface area than spherical silver powder, allowing it to be sintered at lower temperatures to form a dense silver layer. Therefore, how to prepare a silver powder that possesses both low-temperature sintering characteristics and excellent fluidity is a pressing technical challenge that needs to be solved. Summary of the Invention
[0004] One of the objectives of this invention is to provide a method for preparing sheet-like self-assembled spherical silver powder. This method can obtain sheet-like self-assembled spherical silver powder with large specific surface area, low tap density and high sphericity, and is suitable for low-temperature sintering slurry.
[0005] The second objective of this invention is to provide a sheet-like self-assembled spherical silver powder.
[0006] To achieve one of the above objectives, the present invention employs the following technical solution:
[0007] A method for preparing sheet-like self-assembled spherical silver powder, the method comprising the following steps:
[0008] Step S1: Prepare a 0.65–1.5 mol / L sulfate solution and a 1.70–2.70 mol / L silver nitrate solution; the volume ratio of the sulfate solution to the silver nitrate solution is 2–6:1.
[0009] Step S2: Add 60-70% by volume of sulfate solution to the reaction vessel, stir and maintain at 25-100°C, then add 45-55% by volume of silver nitrate solution, and react for 3-7 minutes;
[0010] Step S3: While stirring, add the remaining 30-40% volume of sulfate solution and 45-55% volume of silver nitrate solution dropwise into the reaction vessel, continue stirring, and then separate, wash and dry in sequence to obtain sheet-like self-assembled spherical silver powder.
[0011] This invention employs a two-step reaction. The first step, a one-time pouring reaction (i.e., the reaction between the sulfate solution and the silver nitrate solution in step S2), rapidly yields monodisperse submicron-sized, sheet-like self-assembled spherical silver powder. The second step (i.e., the reaction between the sulfate solution and the silver nitrate solution in step S3) involves a change in the simultaneous dropwise addition method. This ensures that the reaction product between the sulfate solution and the silver nitrate solution in step S3 can grow in situ on the surface of the submicron silver powder already generated in step S2, gradually growing towards sheet-like growth. This guarantees a large specific surface area and a low sintering temperature for the resulting sheet-like self-assembled spherical silver powder. It avoids the problem of a single pouring reaction where, as the silver nitrate concentration decreases, the reaction kinetics weaken, and subsequent silver atoms deposit and grow in a direction that lowers the surface energy of the silver powder, resulting in dense spherical silver powder instead of sheet-like self-assembled spherical silver powder. Furthermore, in step S1, the volume ratio of the sulfate solution to the silver nitrate solution is 3–4:1.
[0012] Furthermore, in step S1, the sulfate in the sulfate solution is one or a mixture of two or more of ferrous ammonium sulfate, ferrous sulfate, or hydroxylamine sulfate.
[0013] Furthermore, in step S2, the temperature is 50–75°C.
[0014] Furthermore, in step S3, the dropping rate of the silver nitrate solution is greater than or equal to the dropping rate of the sulfate solution.
[0015] This invention controls the dropping rates of silver nitrate solution and sulfate solution to ensure rapid addition of high-concentration silver nitrate, thereby reducing the Ag content in the base solution. + It can maintain a certain concentration, thereby enabling the submicron sheet-like self-assembled spherical silver powder to grow in situ, allowing the small sheets to grow along the two-dimensional plane.
[0016] Furthermore, in step S3, the dropping rate of the silver nitrate solution is 50-80 ml / min;
[0017] The sulfate solution is added at a rate of 50–70 ml / min.
[0018] Furthermore, in step S3, the stirring reaction time is 7 to 12 minutes.
[0019] Furthermore, in step S3, the silver nitrate solution is added by inserting a conduit along the wall of the reaction vessel below the liquid level.
[0020] The sulfate solution is added dropwise by maintaining the liquid level above the liquid level along the wall of the reaction vessel using a conduit.
[0021] To achieve the second objective mentioned above, the present invention employs the following technical solution:
[0022] A sheet-like self-assembled spherical silver powder, wherein the sheet-like self-assembled spherical silver powder is prepared by the preparation method described above.
[0023] Furthermore, the specific surface area of the sheet-like self-assembled spherical silver powder is >11 m². 2 / g, tap density <1.2g / cm³ 3 The average particle size is 1.88–2.53 μm, and the loose packing density is 0.55–0.64 g / cm³. 3 The burn loss value at 530℃ is 0.05% to 0.07%.
[0024] In summary, the technical solution of the present invention has the following beneficial effects:
[0025] This invention uses sulfate solution as a reducing agent, utilizing the SO4 in the sulfate solution. 2- The strong binding ability of the silver crystal nucleus [1,1,0] crystal plane acts as a stabilizer and protectant in the nucleation-growth-aggregation process of silver particles. Monodisperse spherical silver powder can be prepared without introducing other additives, ensuring low residue of impurities during silver powder synthesis and significantly reducing washing difficulty, making it suitable for industrial production. The specific surface area of the sheet-like self-assembled spherical silver powder prepared by this invention is >11 m². 2 / g, tap density <1.2g / cm³ 3 It exhibits high sphericity, with an average particle size of 1.88–2.53 μm and a loose packing density of 0.55–0.64 g / cm³. 3 With a burn-off value of 0.05-0.07% at 530℃, it can combine the advantages of spherical powder and flake powder after being prepared into a slurry, making it suitable for low-temperature sintering slurries. Detailed Implementation
[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0027] Example 1:
[0028] S1. Prepare a 0.90 mol / L ferrous ammonium sulfate solution as a reducing agent and a 2.00 mol / L silver nitrate solution as an oxidizing agent. The volume ratio of the ferrous ammonium sulfate solution to the silver nitrate solution is 3:1.
[0029] S2. Take out a 66% ferrous ammonium sulfate solution by volume and add it to the reaction vessel as the reaction base liquid. Start stirring and maintain the temperature at 25°C. Then take out a 50% silver nitrate solution by volume and add it to the reaction vessel. React for 3 minutes.
[0030] S3. Under stirring, the remaining 34% volume of ferrous ammonium sulfate solution and 50% volume of silver nitrate solution are simultaneously added dropwise into the reactor using a peristaltic pump. Stirring continues for 7 minutes, followed by separation, washing, and drying to obtain sheet-like self-assembled spherical silver powder.
[0031] The dropping rate of both the silver nitrate solution and the ferrous ammonium sulfate solution was controlled at 50 ml / min. The silver nitrate solution was added by inserting a conduit along the reactor wall below the liquid level, while the ferrous ammonium sulfate solution was added by maintaining the conduit above the liquid level along the reactor wall.
[0032] The average particle size of the sheet-like self-assembled spherical silver powder in this embodiment is 1.88 μm, and the tap density is 1.02 g / cm³. 3 The loose bulk density is 0.55 g / cm³. 3 Specific surface area 12m² 2 / g, burn loss at 530℃: 0.05%.
[0033] Example 2:
[0034] S1. Prepare a 0.67 mol / L ferrous sulfate solution as a reducing agent and a 2.64 mol / L silver nitrate solution as an oxidizing agent. The volume ratio of the ferrous sulfate solution to the silver nitrate solution is 4:1.
[0035] S2. Take out 60% ferrous sulfate solution by volume and add it to the reaction vessel as the base liquid. Start stirring and maintain the temperature at 30°C. Then take out 55% silver nitrate solution by volume and add it to the reaction vessel. React for 7 minutes.
[0036] S3. While stirring, the remaining 40% volume of ferrous sulfate solution and 45% volume of silver nitrate solution are simultaneously added dropwise into the reactor using a peristaltic pump. Stirring continues for 10 minutes, followed by separation, washing, and drying to obtain sheet-like self-assembled spherical silver powder.
[0037] The dropping rate of silver nitrate solution was controlled at 65 ml / min, and the dropping rate of ferrous sulfate solution was controlled at 55 ml / min. The silver nitrate solution was added by inserting a conduit along the reactor wall below the liquid level, while the ferrous sulfate solution was added by keeping the conduit above the liquid level along the reactor wall.
[0038] The average particle size of the sheet-like self-assembled spherical silver powder in this embodiment is 2.07 μm, the tap density is 1.10 g / cm³, and the loose density is 0.61 g / cm³. 3 Specific surface area 11.6 m² 2 / g, burn loss at 530℃: 0.07%.
[0039] Example 3:
[0040] S1. Prepare a 1.5 mol / L hydroxylamine sulfate solution as a reducing agent and a 1.76 mol / L silver nitrate solution as an oxidizing agent. The volume ratio of the hydroxylamine sulfate solution to the silver nitrate solution is 2:1.
[0041] S2. Take out 70% of the hydroxylamine sulfate solution by volume and add it to the reaction vessel as the base liquid. Turn on the stirring and maintain the temperature at 100°C. Then take out 45% of the silver nitrate solution by volume and add it to the reaction vessel. React for 5 minutes.
[0042] S3. Under stirring, the remaining 30% volume of hydroxylamine sulfate solution and 55% volume of silver nitrate solution are simultaneously added dropwise into the reactor using a peristaltic pump. Stirring continues for 12 minutes, followed by separation, washing, and drying to obtain sheet-like self-assembled spherical silver powder.
[0043] The dropping rate of silver nitrate solution was controlled at 80 ml / min, and the dropping rate of hydroxylamine sulfate solution was controlled at 70 ml / min. The silver nitrate solution was added by inserting a conduit along the reactor wall below the liquid level, while the ferrous sulfate solution was added by keeping the conduit above the liquid level along the reactor wall.
[0044] The average particle size of the sheet-like self-assembled spherical silver powder in this embodiment is 2.53 μm, and the tap density is 1.19 g / cm³. 3 The loose bulk density is 0.64 g / cm³. 3 Specific surface area 11.2 m² 2 / g, burn loss at 530℃: 0.07%.
[0045] Example 4:
[0046] S1. Prepare a 0.65 mol / L ferrous ammonium sulfate solution as a reducing agent and a 2.50 mol / L silver nitrate solution as an oxidizing agent. The volume ratio of the ferrous ammonium sulfate solution to the silver nitrate solution is 2:1.
[0047] S2. Take out a 65% ferrous ammonium sulfate solution by volume and add it to the reaction vessel as the reaction base liquid. Start stirring and maintain the temperature at 50℃. Then take out a 48% silver nitrate solution by volume and add it to the reaction vessel. React for 4 minutes.
[0048] S3. Under stirring, the remaining 35% volume of ferrous ammonium sulfate solution and 52% volume of silver nitrate solution are simultaneously added dropwise into the reactor using a peristaltic pump. Stirring continues for 8 minutes, followed by separation, washing, and drying to obtain sheet-like self-assembled spherical silver powder.
[0049] The dropping rate of silver nitrate solution was controlled at 70 ml / min, and the dropping rate of ferrous ammonium sulfate solution was controlled at 60 ml / min. The silver nitrate solution was added by inserting a conduit along the reactor wall below the liquid level, while the ferrous ammonium sulfate solution was added by keeping the conduit along the reactor wall above the liquid level.
[0050] The average particle size of the sheet-like self-assembled spherical silver powder in this embodiment is 2.03 μm, and the tap density is 1.12 g / cm³. 3 The loose bulk density is 0.60 g / cm³. 3 Specific surface area 11.5 m² 2 / g, burn loss at 530℃: 0.06%.
[0051] Example 5:
[0052] S1. Prepare a 1.2 mol / L ferrous sulfate solution as a reducing agent and a 2.70 mol / L silver nitrate solution as an oxidizing agent. The volume ratio of the ferrous sulfate solution to the silver nitrate solution is 6:1.
[0053] S2. Take out a 68% ferrous sulfate solution by volume and add it to the reaction vessel as the base liquid. Start stirring and maintain the temperature at 75°C. Then take out a 52% silver nitrate solution by volume and add it to the reaction vessel. React for 6 minutes.
[0054] S3. Under stirring, the remaining 32% volume of ferrous sulfate solution and 48% volume of silver nitrate solution are simultaneously added dropwise into the reactor using a peristaltic pump. Stirring continues for 11 minutes, followed by separation, washing, and drying to obtain sheet-like self-assembled spherical silver powder.
[0055] The dropping rate of silver nitrate solution was controlled at 65 ml / min, and the dropping rate of ferrous sulfate solution was controlled at 55 ml / min. The silver nitrate solution was added by inserting a conduit along the reactor wall below the liquid level, while the ferrous sulfate solution was added by keeping the conduit above the liquid level along the reactor wall.
[0056] The average particle size of the sheet-like self-assembled spherical silver powder in this embodiment is 2.15 μm, and the tap density is 1.01 g / cm³. 3 The loose bulk density is 0.57 g / cm³. 3 Specific surface area 11.3 m² 2 / g, burn loss at 530℃: 0.05%.
[0057] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.
Claims
1. A method for preparing sheet-like self-assembled spherical silver powder, characterized in that, The preparation method includes the following steps: Step S1: Prepare a 0.65–1.5 mol / L sulfate solution and a 1.70–2.70 mol / L silver nitrate solution; The volume ratio of the sulfate solution to the silver nitrate solution is 2~6:1; In step S1, the sulfate in the sulfate solution is ferrous ammonium sulfate, ferrous sulfate, or a mixture of one or more of hydroxylamine sulfate. Step S2: Add 60-70% volume of sulfate solution to the reaction vessel, stir and maintain at 25-100℃, then add 45-55% volume of silver nitrate solution and react for 3-7 minutes. Step S3: While stirring, add the remaining 30-40% volume of sulfate solution and 45-55% volume of silver nitrate solution dropwise into the reaction vessel, continue stirring, and then separate, wash and dry in sequence to obtain sheet-like self-assembled spherical silver powder. In step S3, the dropping rate of the silver nitrate solution is greater than or equal to the dropping rate of the sulfate solution; In step S3, the silver nitrate solution is added by inserting a conduit along the wall of the reaction vessel below the liquid level. The sulfate solution is added dropwise by maintaining the liquid level above the liquid level along the wall of the reaction vessel using a conduit.
2. The preparation method according to claim 1, characterized in that, In step S1, the volume ratio of the sulfate solution to the silver nitrate solution is 3-4:
1.
3. The preparation method according to claim 2, characterized in that, In step S2, the temperature is 50~75℃.
4. The preparation method according to claim 3, characterized in that, In step S3, the dropping rate of the silver nitrate solution is 50-80 ml / min; The sulfate solution is added at a rate of 50–70 ml / min.
5. The preparation method according to claim 4, characterized in that, In step S3, the stirring reaction time is 7 to 12 minutes.
6. A sheet-like self-assembled spherical silver powder, characterized in that, The sheet-like self-assembled spherical silver powder is prepared using the preparation method described in any one of claims 1 to 5.
7. The sheet-like self-assembled spherical silver powder according to claim 6, characterized in that, The specific surface area of the sheet-like self-assembled spherical silver powder is >11m². 2 / g, tap density <1.2g / cm³ 3 The average particle size is 1.88~2.53μm, and the loose packing density is 0.55~0.64g / cm³. 3 The burn loss value at 530℃ is 0.05~0.07%.