A high tap density flake-like overlapping silver powder and its preparation method
High-density, overlapping, sheet-like silver powder was prepared by liquid-phase reduction, overcoming the shortcomings of mechanical ball milling and achieving high-density and high-yield silver powder production, suitable for medium- and low-temperature slurries.
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
- 2026-06-30
AI Technical Summary
In the existing technology, the production of high tap density flake silver powder has problems such as poor reproducibility, unstable product batches, grinding aid residue, and difficulty in separating grinding balls, which leads to a decrease in the purity of silver powder. Mechanical ball milling method has its shortcomings.
A liquid-phase reduction method was adopted, using sulfate solution as a reducing agent, a small amount of organic acid as a dispersant, and silver nitrate solution as an oxidant. By controlling the temperature and dropping rate and controlling the growth direction of silver crystal nuclei, high tap density sheet-like overlapping silver powder was prepared.
A high tap density (>5.0 g/cm3) and high yield (100%) of flake-like overlapping silver powder was achieved, which reduced the surface energy of the silver flakes and made it suitable for medium and low temperature slurries, avoiding the shortcomings of mechanical ball milling.
Abstract
Description
Technical Field
[0001] This invention belongs to the field of conductive silver paste technology, and particularly relates to a high tap density sheet-like overlapping silver powder and its preparation method. Background Technology
[0002] Flake silver powder, due to its unique two-dimensional structure and excellent conductivity, has wide applications in many fields such as photovoltaic industry, microelectronics technology, and flexible display technology. Conductive pastes made from flake silver powder, organic resin, and binders are often used in semiconductor chips and the back silver electrode of crystalline silicon solar cells. Silver powder, as a conductive component, directly affects the electrical performance of the paste. During the formation of the conductive coating in silver paste prepared from flake silver powder, the particles have both surface and line contacts, resulting in a larger contact area. Simultaneously, the repeated stacking of upper and lower silver flakes can form a denser conductive circuit. Currently, high-tap-density flake silver powder is generally produced using mechanical ball milling. However, ball milling has unavoidable shortcomings, such as poor reproducibility, inconsistent product batches, residual grinding aids in the silver powder reducing its purity, and incomplete separation of grinding balls damaging the mill. Therefore, how to prepare high-tap-density flake silver powder using a liquid-phase reduction method is a pressing technical challenge that needs to be addressed. Summary of the Invention
[0003] One of the objectives of this invention is to provide a method for preparing high-tap-density, overlapping sheet-like silver powder, which yields silver powder with high tap density and high yield.
[0004] The second objective of this invention is to provide a high tap density, sheet-like, overlapping silver powder.
[0005] To achieve one of the above objectives, the present invention employs the following technical solution:
[0006] A method for preparing high-tap-density, lamellar, overlapping silver powder, the method comprising the following steps:
[0007] Step S1: Prepare a 0.50–2.0 M sulfate solution and a 1.5–3.0 M silver nitrate solution;
[0008] The volume ratio of the sulfate solution to the silver nitrate solution is 1.5 to 6:1;
[0009] Step S2: After adding the first organic acid, the second organic acid, and 35-45% by volume of sulfate solution into the reaction vessel, start stirring and control the temperature at 5-30°C.
[0010] The mass ratio of the first organic acid, the second organic acid, and the silver nitrate solution is 0.05–0.2:0.1–0.5:100.
[0011] Step S3: While stirring, silver nitrate solution and 55-65% by volume sulfate solution are simultaneously added dropwise to the reaction vessel and stirring is continued for 10-15 minutes. Then, the mixture is separated, washed, and dried to obtain high tap density flake-like overlapping silver powder.
[0012] Furthermore, in step S1, the volume ratio of the sulfate solution to the silver nitrate solution is 2 to 4:1.
[0013] Furthermore, in step S1, the sulfate solution is either ferrous ammonium sulfate solution or ferrous sulfate solution.
[0014] Furthermore, in step S2, the first organic acid includes one or both of tartaric acid and citric acid;
[0015] The second organic acid includes one or both of succinic acid and ethylenediaminetetraacetic acid.
[0016] Furthermore, in step S2, the temperature is 10–20°C.
[0017] Furthermore, in step S3, the dropping rate of the silver nitrate solution is 80–140 ml / min;
[0018] The sulfate solution is added at a rate of 30–60 ml / min.
[0019] Furthermore, in step S3, the silver nitrate solution and the sulfate solution are added dropwise by means of a conduit along the wall of the reaction vessel and always kept above the liquid level.
[0020] To achieve the second objective mentioned above, the present invention employs the following technical solution:
[0021] A high-tap-density, lamellar, overlapping silver powder is prepared using the preparation method described above.
[0022] Furthermore, the tap density of the high-tap-density lamellar overlapping silver powder is >5.0 g / cm³. 3 .
[0023] Furthermore, the high tap density flaky overlapping silver powder has an average particle size of 2.4–4.6 μm and a burn-off value of 0.07–0.12 °C at 530 °C.
[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, organic acids (including primary and secondary organic acids) in low quantities and with low decomposition temperatures as dispersants, and silver nitrate solution as an oxidizing agent, utilizing SO42-.2- The silver crystal nuclei exhibit strong bonding to the [1,1,0] crystal plane, and the small-molecule organic acid also exhibits strong bonding to the [1,1,1] crystal plane, causing the grains to grow along the two-dimensional plane, thus obtaining a sheet-like overlapping silver powder. Simultaneously, the amount of organic acid used is small, resulting in low residual amount in the silver sheet. Furthermore, the selected organic acids (such as binary, ternary, and tetracarboxylic acids) can all be decomposed at temperatures below 200℃, enabling the silver powder to be used in medium- and low-temperature slurries. The overlapping structure of this invention reduces the surface energy of the silver sheet, allowing for a continuous increase in sheet thickness. This provides a novel approach for preparing high-tap-density sheet-like silver powder using liquid-phase reduction instead of mechanical ball milling. The high-tap-density sheet-like overlapping silver powder prepared by this invention has a tap density > 5.0 g / cm³. 3 And the yield is as high as 100%. 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 1.0M ferrous ammonium sulfate solution and a 1.8M silver nitrate solution, wherein the volume ratio of the ferrous ammonium sulfate solution to the silver nitrate solution is 4:1.
[0029] S2. Tartaric acid, succinic acid, and 40% (by volume) ferrous ammonium sulfate solution are mixed and added to the reaction vessel as the base solution. Stirring is then started, and the temperature is raised and maintained at 30°C. The mass ratio of silver nitrate in the tartaric acid, succinic acid, and silver nitrate solution is 0.05:0.3:100.
[0030] S3. Under stirring, silver nitrate solution and the remaining 60% volume of ferrous ammonium sulfate solution are simultaneously added dropwise to the reaction vessel using a peristaltic pump, and stirring is continued for 10 minutes. Then, the mixture is separated, washed, and dried to obtain high tap density flake-like overlapping silver powder.
[0031] The silver nitrate solution was added at a rate of 100 ml / min, and the ferrous ammonium sulfate solution was added at a rate of 50 ml / min. Both solutions were added via a conduit along the wall of the reaction vessel, maintaining the liquid level above the target level at all times.
[0032] The high-tap-density, lamellar, overlapping silver powder in this embodiment has an average particle size of 2.4 μm and a tap density of 5.2 g / cm³.3 The burn loss at 530℃ was 0.07%, and the recovery rate was 99.9%.
[0033] Example 2:
[0034] S1. Prepare a 2.0M ferrous sulfate solution and a 3.0M silver nitrate solution, wherein the volume ratio of the ferrous sulfate solution to the silver nitrate solution is 2:1.
[0035] S2. A mixture of citric acid, ethylenediaminetetraacetic acid (EDTA), and 35% (by volume) ferrous sulfate solution is added to the reaction vessel as the base solution. Stirring is then started, and ice water is added to maintain the base solution temperature at 5°C. The mass ratio of silver nitrate in the citric acid, EDTA, and silver nitrate solution is 0.1:0.5:100.
[0036] S3. Under stirring, silver nitrate solution and the remaining 65% volume of ferrous sulfate solution are simultaneously added dropwise to the reaction vessel using a peristaltic pump, and stirring is continued for 15 minutes. Then, the mixture is separated, washed, and dried to obtain high tap density flake-like overlapping silver powder.
[0037] The silver nitrate solution was added at a rate of 130 ml / min, and the ferrous sulfate solution was added at a rate of 55 ml / min. Both solutions were added via a conduit along the wall of the reaction vessel, maintaining the solution level above the target level at all times.
[0038] The high-tap-density, lamellar, overlapping silver powder in this embodiment has an average particle size of 4.6 μm and a tap density of 5.1 g / cm³. 3 The burn loss at 530℃ was 0.12%, and the recovery rate was 99.8%.
[0039] Example 3:
[0040] S1. Prepare a 0.5M ferrous sulfate solution and a 1.5M silver nitrate solution, wherein the volume ratio of the ferrous sulfate solution to the silver nitrate solution is 6:1.
[0041] S2. A mixture of citric acid, succinic acid, and 45% (by volume) ferrous sulfate solution is added to the reaction vessel as the base solution. Stirring is then started, and ice water is added to maintain the temperature of the base solution at 10°C. The mass ratio of silver nitrate in the citric acid, succinic acid, and silver nitrate solution is 0.2:0.1:100.
[0042] S3. Under stirring, silver nitrate solution and the remaining 55% volume of ferrous sulfate solution are simultaneously added dropwise to the reaction vessel using a peristaltic pump, and stirring is continued for 12 minutes. Then, the mixture is separated, washed, and dried to obtain high tap density flake-like overlapping silver powder.
[0043] The silver nitrate solution was added at a rate of 80 ml / min, and the ferrous sulfate solution was added at a rate of 30 ml / min. Both solutions were added via a conduit along the wall of the reaction vessel, maintaining the solution level above the target level at all times.
[0044] The high-tap-density, lamellar, overlapping silver powder in this embodiment has an average particle size of 4.2 μm and a tap density of 5.23 g / cm³. 3 The burn loss at 530℃ was 0.10%, and the recovery rate was 99.85%.
[0045] Example 4:
[0046] S1. Prepare a 1.5M ferrous ammonium sulfate solution and a 2.5M silver nitrate solution, wherein the volume ratio of the ferrous ammonium sulfate solution to the silver nitrate solution is 1.5:1.
[0047] S2. Tartaric acid, ethylenediaminetetraacetic acid, and 42% (by volume) ferrous ammonium sulfate solution are mixed and added to the reaction vessel as the base solution. Stirring is then started, and the temperature is raised and maintained at 20°C. The mass ratio of silver nitrate in the tartaric acid, ethylenediaminetetraacetic acid, and silver nitrate solution is 0.15:0.4:100.
[0048] S3. Under stirring, silver nitrate solution and the remaining 58% volume of ferrous ammonium sulfate solution are simultaneously added dropwise to the reaction vessel using a peristaltic pump, and stirring is continued for 14 minutes. Then, the mixture is separated, washed, and dried to obtain high tap density flake-like overlapping silver powder.
[0049] The silver nitrate solution was added at a rate of 140 ml / min, and the ferrous ammonium sulfate solution was added at a rate of 60 ml / min. Both solutions were added via a conduit along the wall of the reaction vessel, maintaining the liquid level above the target level at all times.
[0050] The high-tap-density, lamellar, overlapping silver powder in this embodiment has an average particle size of 3.5 μm and a tap density of 5.16 g / cm³. 3 The burn loss at 530℃ was 0.09%, and the recovery rate was 99.5%.
[0051] 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 producing a high tap density flaky overlapped silver powder, characterized by, The preparation method includes the following steps: Step S1: Prepare a 0.50–2.0 M sulfate solution and a 1.5–3.0 M silver nitrate solution; The volume ratio of the sulfate solution to the silver nitrate solution is 1.5~6:1; In step S1, the sulfate solution is either ferrous ammonium sulfate solution or ferrous sulfate solution; Step S2: Add the first organic acid, the second organic acid, and 35-45% by volume of sulfate solution to the reaction vessel, then start stirring and control the temperature at 5-30℃. In step S2, the first organic acid includes one or both of tartaric acid and citric acid; The second organic acid includes one or both of succinic acid and ethylenediaminetetraacetic acid; The mass ratio of the first organic acid, the second organic acid, and the silver nitrate solution is 0.05–0.2:0.1–0.5:
100. Step S3: While stirring, silver nitrate solution and 55-65% volume sulfate solution are simultaneously added dropwise to the reaction vessel and stirred for 10-15 minutes. Then, the mixture is separated, washed, and dried to obtain high tap density flake-like overlapping silver powder. In step S3, the dropping rate of the silver nitrate solution is 80–140 ml / min; The dropping rate of the sulfate solution is 30–60 ml / min; In step S3, the silver nitrate solution and the sulfate solution are added dropwise by means of a conduit along the wall of the reaction vessel and always kept above the liquid level.
2. The production method according to claim 1, characterized by, In step S1, the volume ratio of the sulfate solution to the silver nitrate solution is 2 to 4:
1.
3. The preparation method according to claim 2, characterized in that, In step S2, the temperature is 10~20℃.
4. A high tap density, sheet-like, overlapping silver powder, characterized in that, The high tap density flake-like overlapping silver powder is prepared using the preparation method described in any one of claims 1 to 3.
5. The high tap density flake-like overlapping silver powder according to claim 4, characterized in that, The high tap density flaky overlapping silver powder has a tap density > 5.0 g / cm 3 .
6. The high tap density flake-like overlapping silver powder according to claim 5, characterized in that, The high tap density flaky overlapping silver powder has an average particle size of 2.4~4.6μm and a burn-off value of 0.07~0.12℃ at 530℃.