A flaky silver powder, a preparation method and application thereof

Abstract

This invention provides a flake-shaped silver powder, its preparation method, and its application. The method includes the following steps: mixing solution A and solution B and reacting them to prepare the flake-shaped silver powder; wherein solution A includes Ag. + The solution contains silver nanosheet seeds and ions with oxidizing properties, wherein the solution B contains ions with reducing properties, and the ions with oxidizing properties include Ce. 4+ or Fe 3+ At least one of the following. The preparation process of the flake silver powder of the present invention does not require the addition of polymeric dispersants or polymeric surfactants. The flake silver powder is prepared by a one-step reduction method. Under the combined action of oxidizing ions and silver nanosheet seeds in solution A, the degree of flake formation, surface smoothness and flatness of the prepared flake silver powder are improved, thereby improving the conductivity of the prepared flake silver powder.

Description

Technical Field

[0001] This invention belongs to the field of materials manufacturing technology, and relates to a flake-shaped silver powder, its preparation method, and its application. Background Technology

[0002] With the rapid development of the electronics and photovoltaic industries, research on low-temperature conductive silver paste has become a hot topic. The most important component of low-temperature conductive silver paste is silver powder. Compared to the point-to-point contact of non-flake silver powder, flake silver powder has a unique two-dimensional structure and a larger specific surface area. During the low-temperature curing of the conductive silver paste, it forms a conductive network through surface-to-surface and surface-to-line contacts, thereby achieving stronger conductivity. Currently, the main methods for synthesizing micron-sized flake silver powder are chemical reduction-mechanical ball milling and chemical reduction.

[0003] For example, CN104959625A discloses a method for preparing flake silver powder, comprising the following steps: dissolving silver nitrate and a first surfactant in water to prepare a silver solution; dissolving ascorbic acid and a second surfactant in water to prepare a reducing solution; dissolving an alkalinity regulator in water to prepare an alkaline aqueous solution; adding the silver solution and the alkaline aqueous solution to the reducing solution, and reacting to obtain silver powder; and ball milling the ball milling solvent, a third surfactant, and the silver powder in a ball mill jar to obtain the flake silver powder. For example, CN111872411A discloses a method for preparing nano-silver powder, comprising the following steps: dissolving a dispersant in water to prepare a dispersant solution, and adding a reducing agent to obtain a reducing solution; dissolving a silver source in water to obtain a silver source solution; adding the silver source solution dropwise to the reducing solution to obtain a silver powder slurry; centrifuging, washing, and drying the silver powder slurry to obtain the nano-silver powder, wherein the dispersant is preferably polyvinylpyrrolidone. For example, CN114367674A discloses a method for preparing silver powder, which mainly includes the following steps: (1) Take deionized water and silver nitrate, add a dispersant, stir until dissolved to obtain solution A; take deionized water and reducing agent, add a dispersant, stir until dissolved to obtain solution B; (2) Take solution B, add it to solution A, and after the reaction is complete, obtain suspension C; (3) Add alkali to suspension C, adjust pH to 9, add polyhydroxy polyamine chelating agent, continue to add alkali to adjust pH to 14, heat, keep warm and stir, and collect silver powder. The dispersant is any one or more of gelatin, gum arabic and polyvinylpyrrolidone.

[0004] The above process has the disadvantages of being relatively complex and unable to produce smooth and flat flake silver powder. Furthermore, the organic dispersant used tends to adhere to the surface of the flake silver powder, which greatly reduces the conductivity of the prepared flake silver powder. Summary of the Invention

[0005] In view of the above-mentioned problems existing in the prior art, the purpose of the present invention is to provide a method for preparing flake silver powder, flake silver powder, and the uses of flake silver powder.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing flake-shaped silver powder, the method comprising the following steps:

[0008] The flake-shaped silver powder was prepared by mixing solutions A and B and then reacting them.

[0009] The A solution contains Ag. + The solution B contains silver nanosheet seeds and ions with oxidizing properties, and the solution B contains ions with reducing properties.

[0010] The ions with oxidizing properties include Ce. 4+ or Fe 3+ At least one of them.

[0011] The preparation of the flake silver powder of this invention does not require the addition of polymeric dispersants or polymeric surfactants. Flake silver powder is prepared by a one-step reduction method. Under the combined action of oxidizing ions and silver nanosheet seeds in solution A, the degree of flake formation, surface smoothness and flatness of the prepared flake silver powder are improved, thereby improving the conductivity of the prepared flake silver powder.

[0012] In this invention, Ag in solution A + A redox reaction occurs with reducing ions in solution B, using silver nanosheet seeds as nuclei to prepare sheet-like silver powder. The oxidizing ions in solution A can dissolve the unstable non-sheet-like silver nuclei in the reaction system. Furthermore, due to the oxidizing etching effect of the oxidizing ions in solution A, defects will be generated on the surface of the silver nanosheet seeds. The generation of these defects is conducive to promoting the growth of sheet-like silver powder, thus ensuring that the silver powder finally prepared is a relatively stable sheet-like structure.

[0013] In this invention, due to the presence of silver nanosheet seeds, when solutions A and B are mixed, the reduced Ag atoms are deposited on the silver nanosheet seeds to continue growing, avoiding the simultaneous occurrence of crystal nucleation and growth processes, thereby playing a role in regulating the size, shape, and uniformity of the silver powder.

[0014] This invention relates to Ag + The source is not limited, but includes, for example, at least one of silver nitrate or silver sulfate.

[0015] Preferably, the Ag in solution A +The concentration is 0.05-2 mol / L, for example 0.05 mol / L, 0.1 mol / L, 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 or 1 mol / L.

[0016] In this invention, when Ag in solution A + When the concentration of Ag in solution A is high, the proportion of spherical silver powder in the prepared silver powder will increase; when the concentration of Ag in solution A is high... + When the concentration is low, the efficiency of forming flake silver powder will be low.

[0017] In this invention, the types of silver nanosheet seed crystals include, but are not limited to, silver nanosheet colloids.

[0018] Preferably, the mass of the silver nanosheet seed crystals is equal to the mass of Ag in solution A. + 0.001% to 0.05% of the mass, for example, 0.001%, 0.005%, 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, or 0.05%.

[0019] In this invention, when the amount of silver nanosheet seed crystals added is small, it is impossible to prepare flake-shaped silver powder; when the amount of silver nanosheet seed crystals added is large, it increases the preparation cost of flake-shaped silver powder.

[0020] Preferably, the concentration of the oxidizing ion is 0.015-1.0 mol / L, for example 0.015 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.1 mol / L, 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, or 1.0 mol / L, and more preferably 0.06-0.3 mol / L.

[0021] In this invention, due to the presence of Ag in solution A + The concentration of ions with reducing properties is higher than that of ions with oxidizing properties in solution A. Therefore, when solutions A and B are mixed, the ions with reducing properties in solution B will preferentially react with the Ag ions in solution A. + reaction.

[0022] For example, the Ce 4+ Derived from soluble cerium salts, the present invention does not limit the types of soluble cerium salts, but includes, by way of example, at least one of cerium sulfate, cerium ammonium nitrate, or cerium(IV) nitrate.

[0023] In this invention, the Fe 3+ Derived from soluble iron salts, this invention does not limit the types of soluble iron salts, but includes, for example, at least one of ferric chloride, ferric nitrate or ferric sulfate.

[0024] In this invention, when the concentration of oxidizing ions in solution A is high, it will dissolve the silver nanosheet seeds in solution A and increase the amount of reducing agent. When the concentration of oxidizing ions in solution A is low, it cannot perform the functions of oxidation etching and eliminating non-sheet silver nanosheet seeds.

[0025] Preferably, the pH of solution A is ≤1, for example, 0.2, 0.4, 0.6, 0.8 or 1.

[0026] Preferably, the reducing ions include Fe. 2+ .

[0027] For example, the Fe 2+ Derived from soluble ferrous salts, this invention does not limit the type of soluble ferrous salts, but includes, for example, at least one of ferrous chloride, ferrous nitrate or ferrous sulfate.

[0028] Preferably, the concentration of the reducing ion is 0.1-2 mol / L, for example 0.1 mol / L, 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 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, or 2.0 mol / L, and more preferably 1-2 mol / L.

[0029] In this invention, when the concentration of reducing ions in solution B is high, the reduction rate is fast, which makes it difficult to synthesize flake silver powder. When the concentration of reducing ions in solution B is low, the yield of flake silver powder will be low.

[0030] Preferably, the B solution also contains ions that have a morphology guiding effect.

[0031] Preferably, the ions with morphology guiding effect include SO4. 2- Or at least one of citrate.

[0032] In this invention, the SO4 2-The sulfate is derived from sulfuric acid or soluble sulfate. This invention does not limit the type of soluble sulfate, but includes, for example, at least one of FeSO4, (NH4)2SO4, K2SO4 or Na2SO4.

[0033] In this invention, the citrate ion is derived from at least one of citric acid or soluble citrate. This invention does not limit the type of soluble citrate, but includes, for example, at least one of sodium citrate, ammonium citrate, potassium citrate, or ferrous citrate.

[0034] Preferably, the concentration of the morphology-guiding ions in solution B is 0.1-6 mol / L, for example, 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 0.7 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, or 6.0 mol / L, and more preferably 1-2 mol / L.

[0035] In this invention, when the concentration of morphology-guiding ions in solution B is high, Ag in solution A will be indiscriminately adsorbed on the (111), (100) and (110) crystal planes of the silver nanosheet seed crystals, resulting in isotropic growth of silver grains and the formation of spherical silver powder. When the concentration of morphology-guiding ions in solution B is low, the morphology-guiding ions are insufficient to cover the preferential adsorption crystal plane (111) in the silver nanosheet seed crystals, which also leads to the formation of spherical silver powder.

[0036] For example, the morphology-guiding ions and reducing ions in solution B can be provided by one substance or by two substances. For instance, adding FeSO4 to the solution provides both morphology-guiding SO4 and reducing ions. 2- It also provides Fe with reducing properties. 2+ This simplifies the preparation process.

[0037] Preferably, solution A and solution B are mixed in the following manner:

[0038] While stirring, add solution A to solution B.

[0039] In this invention, the reason for adding solution A to solution B while stirring is to ensure that the prepared silver powder has better uniformity.

[0040] Preferably, the reaction temperature is 25-40°C, for example 25°C, 30°C, 35°C or 40°C.

[0041] Preferably, the reaction time is 0.5-2 hours, for example 0.5 hours, 1 hour, 1.5 hours or 2 hours.

[0042] Preferably, after the reaction of solution A and solution B, solid-liquid separation is performed, and the separated solid is washed and dried to obtain the flake silver powder; the filtrate, after reduction treatment, can be returned to prepare solution B, thus achieving recycling.

[0043] In this invention, the solid-liquid separation method includes, but is not limited to, filtration or vacuum filtration.

[0044] The present invention does not limit the method of reduction treatment. For example, the method of reduction treatment includes, but is not limited to, electroreduction or chemical reduction.

[0045] In one embodiment of the present invention, Fe is used as the reducing ion in solution B. 2+ For example, let's explain Fe 2 + The role and recovery method of Fe in the preparation process of flake silver powder: In the preparation process of flake silver powder, Fe in solution B... 2+ Ag + Oxidized to Fe 3+ The Fe in the filtrate is removed by electroreduction. 3+ Converted to Fe 2+ Thus, recycling is achieved. The electroreduction method includes the following steps:

[0046] The resulting filtrate was placed in a diaphragm electrolysis apparatus, wherein the anode was an iron plate, the cathode was a stainless steel plate, the diaphragm was an anion exchange membrane, the electrolysis temperature was 50℃, the electrolysis time was 60 min, and the electrolysis current density was 250 A / m³. 2 The power consumption in this process is 1.5 kWh / kg Fe.

[0047] During electrolysis, a reduction reaction occurs at the cathode: Fe 3+ +e - →Fe 2+ Oxidation reaction occurs at the anode: Fe - 2e - →Fe 2+ This will remove the Fe from the filtrate. 3+ It was converted to Fe 2+ .

[0048] In another embodiment of the present invention, Fe is used as the reducing ion in solution B. 2+ For example, let's explain Fe2+ The role and recovery method of Fe in the preparation process of flake silver powder: In the preparation process of flake silver powder, Fe in solution B... 2+ Ag + Oxidized to Fe 3+ The Fe in the filtrate is removed by chemical reduction. 3+ Converted to Fe 2+ Thus, recycling is achieved. The chemical reduction method includes the following steps:

[0049] The resulting filtrate was mixed with a reducing agent, and after stirring and reacting, the Fe in the filtrate was removed. 3+ It was converted to Fe 2+ The filtrate after oxidation-reduction can be added back to solution B.

[0050] In the above methods, the reducing agent includes, but is not limited to, at least one of thiourea, elemental iron, elemental copper, elemental zinc, sulfide, sulfite, or ascorbic acid.

[0051] In this invention, the detergent used for washing the separated solids includes, but is not limited to, at least one of water or ethanol.

[0052] In a second aspect, a silver powder prepared by the method described in the first aspect of the present invention is provided, wherein the mass percentage of flake silver powder in the silver powder is greater than 95%.

[0053] In this invention, the silver powder has a high degree of flake formation and a relatively smooth and flat surface, which is beneficial to improving the conductivity of the silver powder.

[0054] Preferably, the D50 of the silver powder is 2-3 μm, for example 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm or 3 μm.

[0055] Preferably, the D90 of the silver powder is 5-6 μm, for example 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm or 6 μm.

[0056] A third method provides the application of the silver powder described in the second aspect of the present invention in the preparation of conductive silver paste.

[0057] The silver powder in this invention has good conductivity. When used to prepare conductive silver paste, it can greatly improve the conductivity of the conductive silver paste, especially the conductivity of low-temperature conductive silver paste.

[0058] Compared with existing technologies, the present invention has the following beneficial effects:

[0059] (1) The flake silver powder of this invention does not require the addition of polymeric dispersants or polymeric surfactants during preparation. Flake silver powder is prepared via a one-step reduction method. Under the combined action of oxidizing ions and silver nanosheet seeds in solution A, the degree of flake formation, surface smoothness, and flatness of the prepared flake silver powder are improved, thereby enhancing its electrical conductivity. Furthermore, this invention enables the reuse of solution B through a simple electroreduction or chemical reduction method, offering advantages of being green, efficient, and low-cost.

[0060] (2) The silver powder in this invention has a high degree of flake formation and good conductivity. When it is used to fill conductive silver paste, it will significantly improve the conductivity of conductive silver paste, especially the conductivity of low temperature conductive silver paste. Attached Figure Description

[0061] Figure 1 This is a flowchart illustrating the preparation of flake-shaped silver powder in one embodiment of the present invention;

[0062] Figure 2 This is a scanning electron microscope (SEM) image of the silver powder in Example 1;

[0063] Figure 3 This is a particle size distribution diagram of the silver powder in Example 1;

[0064] Figure 4 The images show SEM images of the silver powder and the commercially available flake silver powder prepared by ball milling in Example 2.

[0065] Figure 5 The image shows the X-ray diffraction (XRD) pattern of the silver powder in Example 2.

[0066] Figure 6 Here is a SEM image of the silver powder in Example 3;

[0067] Figure 7 SEM images of the silver powder in Examples 4-7;

[0068] Figure 8 SEM images of the silver powder in Examples 8-11;

[0069] Figure 9 SEM images of the silver powder in Examples 12-14;

[0070] Figure 10 Here is a SEM image of the silver powder in Example 15;

[0071] Figure 11 SEM images of silver powder in Comparative Examples 1-5;

[0072] Figure 12 SEM image of silver powder in Comparative Example 6;

[0073] Figure 13 The volume resistivity test results of conductive silver paste filled with commercial flake silver powder prepared by ball milling in Example 2. Detailed Implementation

[0074] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0075] In this embodiment of the invention, "room temperature" is defined as 25°C.

[0076] One embodiment of the present invention provides a method for preparing flake-shaped silver powder, such as... Figure 1 As shown, Figure 1 The flowchart for preparing flake silver powder in one embodiment of the present invention specifically includes the following steps: adding solution A to solution B to carry out a reduction reaction, filtering after the reaction to obtain micron-sized flake silver powder; in addition, the filtrate obtained by filtration can be reintroduced into solution B by electroreduction or chemical reduction, thereby realizing the recycling of the filtrate.

[0077] Example 1

[0078] This embodiment provides a method for preparing flake-shaped silver powder, including the following steps:

[0079] (1) Preparation of solution A: Weigh silver nitrate and cerium ammonium nitrate, dissolve them in deionized water, add 100 mL of silver nanosheet colloid with a concentration of 10 mg / L, and dilute with water to 1 L. The concentration of Ag in solution A is... + The concentration was 0.3 mol / L, Ce 4+ The concentration was 0.06 mol / L, and the mass of the silver nanosheet colloid was Ag. + The mass of solution A is 0.003%, and the pH value of solution A is 0.5.

[0080] (2) Preparation of solution B: Weigh ferrous sulfate and dissolve it in deionized water, then dilute to 900 mL. The Fe... 2+ The concentration is 1 mol / L, SO4 2- The concentration is 1 mol / L;

[0081] (3) At 30°C, solution A is quickly poured into solution B while stirring. The reaction is carried out for 30 min. After filtration, the resulting solid is washed with water and ethanol and dried at 60°C to obtain the flake silver powder.

[0082] Example 2

[0083] This embodiment provides a method for preparing flake-shaped silver powder, including the following steps:

[0084] (1) Preparation of solution A: Weigh silver nitrate and cerium ammonium nitrate, dissolve them in deionized water, add 300 mL of silver nanosheet colloid with a concentration of 40 mg / L, and dilute with water to 1 L. The concentration of Ag in solution A is... + The concentration is 1 mol / L, Ce 4+ The concentration was 0.13 mol / L, and the mass of the silver nanosheet colloid was Ag. + At 0.01% by mass, solution A has a pH of 0.6.

[0085] (2) Preparation of solution B: Weigh ferrous sulfate and sodium sulfate, dissolve them in deionized water, and dilute to 2L. Fe... 2+ The concentration was 1.2 mol / L, SO4 2- The concentration is 2 mol / L;

[0086] (3) At 30°C, solution A is quickly poured into solution B while stirring. The reaction is carried out for 40 min. After filtration, the resulting solid is washed with water and ethanol and dried at 50°C to obtain the flake silver powder.

[0087] Example 3

[0088] This embodiment provides a method for preparing flake-shaped silver powder, including the following steps:

[0089] (1) Preparation of solution A: Weigh silver nitrate and ferric nitrate, dissolve them in deionized water, add 500 mL of silver nanosheet colloid with a concentration of 40 mg / L, and dilute with water to 1 L. The concentration of Ag in solution A is... + The concentration was 1.5 mol / L, Fe 3+ The concentration was 0.3 mol / L, and the mass of the silver nano crystals was Ag. + The mass fraction is 0.012%, and the pH value of solution A is 0.4.

[0090] (2) Preparation of solution B: Weigh ferrous chloride and citric acid, dissolve them in deionized water, and dilute to 1.5 L. Fe... 2+ The concentration of is 1.5 mol / L, and the concentration of citrate is 2.0 mol / L;

[0091] (3) At 30°C, solution A is quickly poured into solution B while stirring. The reaction is carried out for 30 min. After filtration, the resulting solid is washed with water and ethanol and dried at 60°C to obtain the flake silver powder.

[0092] Example 4

[0093] The only difference from Example 2 is that solution B contains Fe 2+ The concentration is 0.5 mol / L, SO4 2-The concentration is 0.5 mol / L.

[0094] Example 5

[0095] The only difference from Example 2 is that solution B contains Fe 2+ The concentration is 1 mol / L, SO4 2- The concentration is 1 mol / L.

[0096] Example 6

[0097] The only difference from Example 2 is that solution B contains Fe 2+ The concentration is 1.5 mol / L, SO4 2- The concentration is 1.5 mol / L.

[0098] Example 7

[0099] The only difference from Example 2 is that solution B contains Fe 2+ The concentration is 2 mol / L, SO4 2- The concentration is 2 mol / L.

[0100] Example 8

[0101] The only difference from Example 1 is that 50 mL of silver nanosheet colloid with a concentration of 20 mg / L was added to solution A.

[0102] Example 9

[0103] The only difference from Example 1 is that 100 mL of silver nanosheet colloid with a concentration of 20 mg / L is added to solution A.

[0104] Example 10

[0105] The only difference from Example 1 is that 150 mL of silver nanosheet colloid with a concentration of 20 mg / L was added to solution A.

[0106] Example 11

[0107] The only difference from Example 1 is that 200 mL of silver nanosheet colloid with a concentration of 20 mg / L was added to solution A.

[0108] Example 12

[0109] The only difference from Example 2 is that Ce in solution A... 4+ The concentration is 0.01 mol / L.

[0110] Example 13

[0111] The only difference from Example 2 is that Ce in solution A... 4+ The concentration is 0.03 mol / L.

[0112] Example 14

[0113] The only difference from Example 2 is that Ce in solution A... 4+ The concentration is 0.05 mol / L.

[0114] Example 15

[0115] The only difference from Example 2 is that the SO4 in solution B is different. 2- The concentration is 0.5 mol / L.

[0116] Comparative Example 1

[0117] The only difference from Example 2 is that no silver nanosheet seeds were added to solution A, and no cerium peroxide was added to solution B.

[0118] Comparative Example 2

[0119] The only difference from Example 2 is that no silver nanosheet seeds were added to solution A, while an equimolar amount of Ce was added to solution B. 3+ .

[0120] Comparative Example 3

[0121] The only difference from Example 2 is that no silver nanosheet seeds were added to solution A.

[0122] Comparative Example 4

[0123] The only difference from Example 2 is that no cerium nitrate was added to solution B.

[0124] Comparative Example 5

[0125] The only difference from Example 2 is that an equimolar amount of Ce was added to solution B. 3+ .

[0126] Comparative Example 6

[0127] The only difference from Example 2 is that the oxidizing ions in solution A are equimolar amounts of hypochlorite.

[0128] Figure 2 Here is a SEM image of the silver powder in Example 1, where Figure 2 b in Figure 2 A magnified view of part 'a' in the image. Figure 2 As can be seen from the above, the silver powder prepared in Example 1 is flake-shaped silver powder with an average particle size of 3.0 μm and an average thickness of 0.2 μm, and the particle size of the flake-shaped silver powder is relatively uniform.

[0129] Figure 3 This is a particle size distribution diagram of the silver powder in Example 1, from... Figure 3As can be seen from the data, the silver powder in Example 1 has a narrower particle size distribution, indicating that the silver powder in Example 1 has a more uniform particle size distribution. Furthermore, from... Figure 3 As can be seen from the data, the D50 (particle size at which the cumulative distribution of particles is 50%, also known as the average particle size or median diameter) of the silver powder in Example 1 is 2.83 μm.

[0130] Figure 4 The images show SEM images of the silver powder and the commercially available flake silver powder (GY-1, Hunan Guoyin New Materials Co., Ltd.) prepared by ball milling in Example 2. Figure 4 In the image, 'a' is the SEM image of the silver powder from Example 2. Figure 4 In the image, b represents a SEM image of commercially available flake silver powder prepared by ball milling. Figure 4 As can be seen from a in Example 2, the silver powder prepared in Example 2 has a flake structure and is hexagonal. The average particle size of the silver powder is 5.4 μm and the average thickness is 0.4 μm. The dispersibility and uniformity of the silver powder prepared in Example 2 are better than those of commercial flake silver powder prepared by ball milling. Furthermore, the surface of the silver powder prepared in Example 2 is smoother and flatter, which is beneficial to increasing the contact area between the flake silver powders, thereby improving the conductivity of the flake silver powder.

[0131] Figure 5 The image shows the XRD pattern of the silver powder in Example 2. Figure 5 As can be seen from the XRD pattern, the peaks of the silver powder prepared in Example 2 are relatively sharp and the half-width of the XRD peaks is relatively narrow, indicating that the silver powder prepared in Example 2 is elemental silver with good crystallinity.

[0132] Figure 6 Here is a SEM image of the silver powder in Example 3. Figure 6 As can be seen, the silver powder in Example 3 is also a highly flake-like silver powder, and the surface of the silver powder is relatively smooth and flat.

[0133] Figure 7 The images shown are SEM images of the silver powder in Examples 4-7. Figure 7 In the image, 'a' is the SEM image of the silver powder in Example 4. Figure 7 In the image, b is the SEM image of the silver powder in Example 5. Figure 7 In the image, d represents the SEM image of the silver powder in Example 6. Figure 7 In the image, 'e' represents the SEM image of the silver powder in Example 7. Figure 7 It can be seen from this that when Fe in solution B... 2+ and SO4 2- When the concentration is low, it is impossible to prepare silver powder with a high degree of flake formation and a smooth and flat surface.

[0134] Figure 8 The images shown are SEM images of the silver powder in Examples 8-11. Figure 8In the image, 'a' is the SEM image of the silver powder in Example 8. Figure 8 In the image, b is the SEM image of the silver powder in Example 9. Figure 8 In the image, d represents the SEM image of the silver powder in Example 10. Figure 8 In the image, 'e' represents the SEM image of the silver powder in Example 11. Figure 8 As can be seen, when the amount of silver nanosheet seed crystals added to solution A reaches a certain proportion, the prepared silver powder is flake-shaped silver powder.

[0135] Figure 9 The images shown are SEM images of the silver powder in Examples 12-14. Figure 9 In the image, 'a' is the SEM image of the silver powder in Example 12. Figure 9 In the image, b is the SEM image of the silver powder in Example 13. Figure 9 In the image, 'c' represents the SEM image of the silver powder from Example 14. Figure 9 As can be seen, the silver powder prepared in Example 12 is spherical, the silver powder prepared in Example 13 is a mixture of spherical and flake-shaped silver powder, and the silver powder prepared in Example 14 is also a mixture of spherical and flake-shaped silver powder. Moreover, the proportion of flake-shaped silver powder in the silver powder in Example 14 is greater than that in Example 13.

[0136] Figure 10 This is a SEM image of the silver powder in Example 15. The image shows that SO42-, which has a morphology-guiding effect, is present in solution B. 2- When the concentration of silver powder decreases, the content of flake silver powder in the prepared silver powder will also decrease accordingly.

[0137] Figure 11 The images show SEM images of silver powder in Comparative Examples 1-5. Figure 11 In the image, 'a' is the SEM image of the silver powder in Comparative Example 1. Figure 11 In the image, b is the SEM image of the silver powder in Comparative Example 2. Figure 11 In the image, c represents the SEM image of the silver powder in Comparative Example 3. Figure 11 In the image, d represents the SEM image of the silver powder in Comparative Example 4. Figure 11 In the image, 'e' represents the SEM image of the silver powder in Comparative Example 5. Figure 11 As can be seen, the silver powder prepared in Comparative Examples 1 and 2 is spherical, meaning that if silver nanosheet seeds and Ce are not added to the reaction system... 4+ Therefore, it is impossible to prepare flake-shaped silver powder. The silver powder prepared in Comparative Example 3 is a mixture of flake-shaped and spherical silver powder, indicating that Ce... 4+ The addition of precipitate is beneficial to the preparation of flake-shaped silver powder to some extent, but without the combined action of silver nanosheet seeds, it is impossible to prepare silver powder with a high degree of flake formation. The silver powders prepared in Comparative Examples 4 and 5 are granular with small particle size, indicating that simply adding silver nanosheet seeds or silver nanosheet seeds combined with Ce 3+Using them together cannot produce flake-shaped silver powder.

[0138] Figure 12 The image shows a SEM image of the silver powder in Comparative Example 6. It can be seen from the image that adding Ce... 4+ When the hypochlorite ion, which also has oxidizing properties, is replaced, the prepared silver powder is spherical, indicating that not all ions with oxidizing properties can be used to prepare the flake-shaped silver powder in this application.

[0139] Performance testing:

[0140] The conductivity of the conductive silver paste filled with commercially available flake silver powder prepared in Example 2 and by ball milling was tested. Preparation of the conductive silver paste:

[0141] Silver powder and an active carrier are mixed in a ratio of 80:20 to obtain conductive silver paste. The composition and mass ratio of the active carrier are: divalent ester (dicarboxylic acid ester): saturated resin (polyethylene): polyamide wax = 77:2:1.

[0142] Conductivity test of conductive silver paste:

[0143] The prepared conductive silver paste was screen-printed onto a polyethylene terephthalate (PET) film to form a thin-film circuit (10mm × 100mm). The circuit was then placed in an oven and cured at 160℃ for 30 minutes. After cooling to room temperature, the volume resistivity was measured. The results are as follows: Figure 13 As shown, where, Figure 13 The illustrations in the text are physical diagrams of thin-film circuits. Figure 13 The "homemade flake silver powder" in the text refers to the conductive silver paste filled with silver powder prepared in Example 2. Figure 13 The term "commercial flake silver powder" refers to conductive silver paste filled with commercially available flake silver powder prepared by ball milling. Figure 13 As can be seen, under the premise of the same silver powder content, the bulk resistivity of the conductive silver paste filled with silver powder prepared in Example 2 of the present invention is 1.2 × 10⁻⁶. -5 Ω·cm, which is much lower than the bulk resistivity of conductive silver paste filled with commercially available flake silver powder prepared by ball milling (8×10). -5 The results above indicate that the conductive silver paste filled with silver powder prepared in this invention has superior conductivity (Ω·cm).

[0144] analyze:

[0145] As can be seen from the data in Examples 1-3, the preparation method in the embodiments of the present invention can prepare micron-sized flake silver powder, and the surface of the prepared flake silver powder is relatively smooth and flat, with good dispersibility and uniformity.

[0146] The data from Examples 2 and 4-7 show that when the concentrations of morphology-guiding ions and reducing ions in solution B are low, it is impossible to prepare silver powder with a smooth and flat surface, and the degree of flake formation of the prepared silver powder is low.

[0147] The data from Examples 1 and 8-11 show that silver powder with a high degree of flake formation can be prepared as long as the concentration of silver nanosheet colloid in solution A is within a certain range.

[0148] The data from Examples 2 and 12-14 show that Ce in solution A 4+ The concentration of Ce has a significant impact on the prepared silver powder. When the concentration of Ce in solution A is high... 4+ When the concentration is low, it is impossible to prepare silver powder with a smooth and flat surface, and the degree of flake formation of the prepared silver powder is low.

[0149] The data from Examples 2 and 15 show that the concentration of morphology-guiding ions in solution B has a significant impact on the preparation of silver powder. When the concentration of morphology-guiding ions is low, silver powder with a high degree of flake formation cannot be prepared.

[0150] The data from Example 2 and Comparative Examples 1-5 show that silver powder with a high degree of flake formation can only be prepared with the cooperation of silver nanosheet seeds and ions with oxidizing effect. Simply adding silver nanosheet seeds or simply adding ions with oxidizing effect cannot prepare silver powder with a high degree of flake formation.

[0151] The data from Example 2 and Comparative Example 6 show that not all ions with oxidizing properties can be used to prepare silver powder with a smooth, flat surface and a high degree of flake formation.

[0152] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing flake-shaped silver powder, characterized in that, The method includes the following steps: The flake-shaped silver powder was prepared by mixing solutions A and B and then reacting them. Wherein, the A solution includes Ag + , silver nanosheet seeds and ions with oxidizing effect, the B solution includes ions with reducing effect; The ions with oxidizing properties include Ce. 4+ or Fe 3+ At least one of them; Ag in solution A + The concentration is 0.05-2 mol / L; The mass of the silver nanosheet seed crystals is Ag in solution A. + 0.001%-0.05% of the mass; The concentration of the oxidizing ions is 0.015-1.0 mol / L; The pH of solution A is ≤1; The reducing ions include Fe. 2+ ; The concentration of the reducing ions is 0.1-2 mol / L; the B solution also contains ions that guide morphology. The ions with morphology-guiding function include SO4. 2- ; The concentration of morphology-guiding ions in solution B is 0.1-6 mol / L.

2. The method according to claim 1, characterized in that, The concentration of the oxidizing ions is 0.06-0.3 mol / L.

3. The method according to claim 1, characterized in that, The concentration of the reducing ions is 1-2 mol / L.

4. The method according to claim 1, characterized in that, The concentration of morphology-guiding ions in solution B is 1-2 mol / L.

5. The method according to claim 1, characterized in that, Mix solution A and solution B as follows: While stirring, add solution A to solution B.

6. The method according to claim 1, characterized in that, The reaction temperature is 25-40℃.

7. The method according to claim 1, characterized in that, The reaction time is 0.5-2 hours.

8. The method according to claim 1, characterized in that, After the reaction of solutions A and B, solid-liquid separation is performed. The separated solid is washed and dried to obtain the flake silver powder. The filtrate is reduced and then returned to prepare solution B, thus achieving recycling.

9. A silver powder prepared by the method according to any one of claims 1-8, characterized in that, The mass percentage of flake silver powder in the silver powder is greater than 95%.

10. The silver powder according to claim 9, characterized in that, The D50 of the silver powder is 2-3 μm.

11. The silver powder according to claim 9, characterized in that, The D90 of the silver powder is 5-6 μm.

12. The use of silver powder as described in any one of claims 9-11 in the preparation of conductive silver paste.

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