Method for preparing silver powder through reduction of hydrazine hydrate with adjustable particle size

Abstract

The invention belongs to the technical field of metal powder preparation, and discloses a method for preparing silver powder through reduction of hydrazine hydrate with the adjustable particle size. The preparation method comprises the following steps that a first dispersing agent is dissolved in deionized water, a silver-ammonia solution and a hydrazine hydrate solution are sequentially added, stirring reaction is conducted, and nano-silver seed crystal sol is obtained; uniformly mixing the obtained nano-silver seed crystal sol with a hydrazine hydrate solution and a second dispersing agent to obtain a reducing base solution; adding a surface modifier into absolute ethyl alcohol, and uniformly dissolving to obtain a surface modification coating solution; preparing a silver-ammonia solution, adding the prepared silver-ammonia solution into the reducing base solution, then adding the surface modification coating solution, and stirring for reaction to obtain silver powder slurry liquid; and after solid-liquid separation, a solid phase is taken, washed and dried, and silver powder is obtained. The preparation method is simple in process, the particle size of the silver powder can be adjusted through the adding amount of the seed crystal, and the prepared silver powder particles are uniform in particle size distribution, high in dispersity and suitable for the fields of conductive silver paste, electronic packaging and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of metal powder preparation, and particularly relates to a method for preparing silver powder by reducing hydrazine hydrate with adjustable particle size. Background Art

[0002] Silver powder is the core key raw material of conductive silver paste, and its key performance parameters directly affect the printing and conductive properties of silver paste. Especially in recent years, the photovoltaic industry has developed rapidly, and higher requirements are placed on silver powder. For example, narrow particle size distribution, high dispersibility, high sphericity, etc. The conventional process is to use a liquid phase reduction method for synthesis while adding a large amount of polymer dispersant. The advantages of the liquid phase method are simple process flow, large output, controllable silver powder performance, and easy industrial mass production. At present, the liquid phase method is the most widely used method for preparing silver powder. The conventional preparation method controls the particle size and dispersibility of silver powder by adding a large amount of dispersant. The amount of wastewater is large and it is difficult to treat the wastewater because it contains a large amount of organic residues in the dispersant. In addition, there are more organic residues in the produced silver powder, which affects the subsequent application performance of the silver powder. Under this background, it is of certain positive significance to develop a new method for preparing silver powder.

[0003] Patent CN 114367674 A discloses a method for preparing silver powder, which uses a liquid phase reduction method, silver nitrate and a reducing agent, and adds a certain amount of aqueous dispersant or oily dispersant to obtain silver powder with certain dispersibility. Patent CN 116765415A discloses a method for preparing silver powder, which mixes a silver source solution with an aqueous hydrazine hydrate solution to obtain a reaction solution, wherein the silver source solution contains a silver source substance and an amino protective agent; the reaction solution is mixed with an organic dispersant to obtain a silver dispersion, wherein the organic dispersant contains an alkyl chain; and silver powder is separated from the dispersion. The amino group contained in the amino protective agent can be compatible with the silver core, and the branched molecular structure of the amino protective agent can provide steric hindrance to better fix the silver core. Therefore, by using a silver source solution containing a silver source substance and an amino protective agent, the agglomeration of silver particles in the silver source solution can be avoided. CN 1266761 A discloses a method for preparing nanometer-grade silver powder. The method comprises the following steps: dissolving silver nitrate in water, adding ammonia water to prepare a silver-ammonia solution, and then slowly adding a reducing agent solution composed of a reducing agent and a protecting agent. The reducing agent may be ascorbic acid (vitamin C), hydrazine hydrate or sodium borohydride, and the protecting agent may be polyvinylpyrrolidone (PVP), alkyl mercaptan (RSH), oleic acid or palmitic acid. The silver in the silver-ammonia solution is reduced to nanometer-grade silver powder. After filtering out the silver powder, the silver powder is immersed in oleic acid as a passivating agent, filtering to remove the oleic acid, and vacuum drying to obtain the nanometer-grade silver powder.

[0004] Although the above methods can obtain silver powder with good dispersibility, there is still a problem of large amount of dispersant used, and the above existing technologies do not disclose the particle size control mechanism in the silver powder preparation process. Summary of the invention

[0005] In view of the shortcomings and deficiencies of the above prior art, the object of the present invention is to provide a method for preparing silver powder by hydrazine hydrate reduction with adjustable particle size. The method of the present invention can stably produce submicron and micron-level highly dispersed and highly tapped spherical silver powder.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing silver powder by reducing hydrazine hydrate with adjustable particle size comprises the following preparation steps:

[0008] (1) Seed preparation:

[0009] The first dispersant is dissolved in deionized water as a seed to prepare a base solution, a silver ammonia solution is added and stirred evenly, and then a hydrazine hydrate solution is added and stirred to react to obtain a nano silver seed sol;

[0010] (2) Preparation of reducing base solution:

[0011] The nano silver seed sol obtained in step (1) is mixed evenly with the hydrazine hydrate solution and the second dispersant to obtain a reduced base solution;

[0012] (3) Preparation of surface modification coating solution:

[0013] Adding the surface modifier into anhydrous ethanol and dissolving it evenly to obtain a surface modification coating solution;

[0014] (4) Preparation of silver powder:

[0015] Prepare a silver ammonia solution and add it to the reducing base solution of step (2), then add the surface modification coating solution of step (3) and stir to react to obtain a silver powder slurry liquid; after solid-liquid separation, take the solid phase and wash and dry to obtain silver powder.

[0016] Furthermore, in step (1), the first dispersant is selected from one or more of gelatin, polyvinyl pyrrolidone, gum arabic, polyvinyl alcohol, polyethylene glycol, Tween, sodium citrate, triethanolamine, etc.; preferably one or more of gelatin, polyvinyl pyrrolidone, gum arabic, polyethylene glycol.

[0017] Furthermore, the concentration of the first dispersant in the seed crystal preparation base solution in step (1) is 10 to 200 g / L.

[0018] Furthermore, the silver ammonia solution in steps (1) and (4) has a molar ratio of ammonia to silver of 2 to 6:1, and is prepared by the following method: adding ammonia water to a silver nitrate solution having a silver concentration of 0.1 to 2 mol / L and mixing well to obtain a silver ammonia solution.

[0019] Furthermore, the concentration of the hydrazine hydrate solution in steps (1) and (2) is 0.1 to 0.6 mol / L.

[0020] Furthermore, the stirring reaction temperature in step (1) is 20 to 50°C, preferably 25 to 30°C.

[0021] Furthermore, the particle size of the nanosilver in the nanosilver seed sol in step (1) is 20-40 nm, and the concentration of the nanosilver is 0.1-10 g / L.

[0022] Furthermore, the amount of the nano silver seed sol added in step (2) is 1% to 100% of the mass of the silver nitrate used to prepare the silver ammonia solution in the silver powder preparation stage of step (4); preferably, the amount of the nano silver seed sol added is 25% to 70% of the mass of the silver nitrate.

[0023] Furthermore, in step (2), the second dispersant is polyethyleneimine, polyimide, polyetherimide, polysuccinimide, octenylsuccinic anhydride, succinic acid, palmitic acid, etc.

[0024] Furthermore, the amount of the second dispersant added in step (2) is 0.01% to 2% of the mass of the silver powder prepared in step (4).

[0025] Furthermore, the surface modifier in step (3) is one or more of oleic acid, caprylic acid, stearic acid, lauric acid, oleylamine, and palmitic acid.

[0026] Furthermore, the amount of the surface modifier used in step (3) is 0.1% to 2% of the mass of the silver powder prepared in step (4).

[0027] Furthermore, the silver ammonia solution in step (4) is added quickly by pouring.

[0028] The preparation method of the present invention involves the following reactions:

[0029] a) AgNO 3 +2NH 3 ·H 2 O——Ag(NH 3 ) 2 NO 3 +2H 2 O;

[0030] b) 4Ag(NH 3 ) 2 NO 3 +N 2 H 4 ·H 2 O——4Ag↓+N 2 ↑+4NH 4NO 3 +4NH 3 ↑+H 2 O.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The preparation method of the present invention has a simple process, a small amount of dispersant is used, and the synthesis time is short, and it is easy to industrialize production; the prepared silver powder particles have uniform particle size distribution and high dispersibility, and are suitable for conductive silver paste, electronic packaging and other fields.

[0033] (2) The present invention prepares the nano silver seed sol in advance, and the particle size of the silver powder can be adjusted by the amount of seed added, which has the advantage of convenient particle size adjustment.

[0034] (3) The present invention can significantly improve the morphology of silver powder and enhance its dispersibility by adding a second dispersant to the reducing base liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figures 1 to 7 They are electron microscope images of the silver powder products obtained in Examples 1 to 7 respectively;

[0036] Figures 8-9 They are electron microscope images of the silver powder products obtained in Comparative Examples 1 and 2 respectively. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0038] Example 1

[0039] (1) Weigh 30 g of the first dispersant polyvinyl pyrrolidone, add it to 500 mL of deionized water to dissolve as a seed crystal to prepare a base solution, add the prepared silver ammonia solution (weigh 5 g of silver nitrate and dissolve it in 10 mL of deionized water, weigh 6 g of ammonia water and add it to the above silver nitrate solution to prepare a silver ammonia solution) and stir evenly, then quickly add the prepared hydrazine hydrate solution (weigh 8 g of hydrazine hydrate and dilute it with 15 mL of deionized water), stir and react at room temperature for 10 minutes to obtain a nano silver seed sol with a particle size of 20 to 40 nm.

[0040] (2) Weigh 12 g of hydrazine hydrate and add it to 400 mL of deionized water, add 30 g of the nano silver seed sol prepared in step (1), add 0.1 g of the second dispersant polyethyleneimine, control the temperature of the feed liquid to 30±1° C. and mix well to obtain a reduced base liquid.

[0041] (3) Weigh 0.3 g of oleic acid and add it to 100 mL of anhydrous ethanol and stir evenly to obtain a surface modification coating solution.

[0042] (4) Add the reducing base solution of step (2) to a 5L glass beaker, then quickly pour in the prepared silver ammonia solution (weigh 65g of silver nitrate and dissolve it in 300mL of deionized water, weigh 70g of ammonia water and add it to the above silver nitrate solution at a uniform rate while stirring, and control the liquid temperature to 30±1°C). After adding the silver ammonia solution, add the surface modification coating solution prepared in step (3) and stir to react. After the reaction is completed, stop stirring, perform solid-liquid separation, wash the separated silver powder with deionized water three times, put the washed silver powder into an oven and dry it at 50°C to obtain an average particle size of 400-600nm and a tap density of 4.83g / cm 3 , a silver powder product with good dispersibility. The electron microscope image of the obtained silver powder product is as follows Figure 1 shown.

[0043] Example 2

[0044] Compared with Example 1, the amount of the nano silver seed sol added in step (2) is reduced to 15 g, and the rest is the same.

[0045] The electron microscope image of the silver powder product obtained in this embodiment is as follows Figure 2 The obtained silver powder product has uniform particle size, with an average particle size of 1.7 μm and a tap density of 6.03 g / cm 3 , which is suitable for silver powder used in solar front silver paste.

[0046] Example 3

[0047] Compared with Example 1, the amount of the nano silver seed sol added in step (2) is reduced to 5 g, and the rest is the same.

[0048] The electron microscope image of the silver powder product obtained in this embodiment is as follows Figure 3 As shown in the figure, due to the greatly reduced amount of seed crystals added, the silver powder particles grow significantly, but the particle size distribution is wide and the particle size is uneven.

[0049] Example 4

[0050] Compared with Example 1, the amount of the nano silver seed sol added in step (2) is increased to 45 g, and the rest is the same.

[0051] The electron microscope image of the silver powder product obtained in this embodiment is as follows Figure 4 The obtained silver powder product has uniform particle size, with an average particle size of 0.9 μm and a tap density of 5.3 g / cm 3 .

[0052] Example 5

[0053] Compared with Example 1, the amount of the nano silver seed sol added in step (2) is increased to 60 g, and the rest is the same.

[0054] The electron microscope image of the silver powder product obtained in this embodiment is as follows Figure 5 Although the particle size of the obtained silver powder product can be further reduced to 100-300 nm, there are obvious agglomerates.

[0055] Example 6

[0056] Compared with Example 1, in step (4), the silver ammonia solution is added dropwise to the hydrazine hydrate reduction base solution at a rate of 20 ml / min, and the rest is the same.

[0057] The electron microscope image of the silver powder product obtained in this embodiment is as follows Figure 6 Although the silver powder particles can grow by dripping, they are seriously aggregated under the strong reducing property of hydrazine hydrate.

[0058] Example 7

[0059] Compared with Example 1, the second dispersant in step (2) uses succinic acid instead of polyethyleneimine, and the rest is the same.

[0060] The electron microscope image of the silver powder product obtained in this embodiment is as follows Figure 7 The obtained silver powder product has uniform particle size, with an average particle size of 300-600nm and a tap density of 4.61g / cm 3 .

[0061] Comparative Example 1

[0062] Compared with Example 1, the second dispersant polyethyleneimine was not added in step (2), and the rest was the same.

[0063] The electron microscope image of the silver powder product obtained in this comparative example is as follows Figure 8 As shown in the figure, since no second dispersant was added to the base liquid, the agglomeration phenomenon was serious.

[0064] Comparative Example 2

[0065] Compared with Example 1, this comparative example does not add a surface modification coating solution in step (4), and the rest is the same.

[0066] The electron microscope image of the silver powder product obtained in this comparative example is as follows Fig. 9 As shown in the figure, the silver powder product obtained has serious agglomeration phenomenon because no surface modifier is added.

[0067] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing silver powder by reducing hydrazine hydrate with adjustable particle size, characterized in that: The method comprises the following preparation steps: (1) Seed preparation: The first dispersant is dissolved in deionized water as a seed to prepare a base solution, a silver ammonia solution is added and stirred evenly, and then a hydrazine hydrate solution is added and stirred to react to obtain a nano silver seed sol; (2) Preparation of reducing base solution: The nano silver seed sol obtained in step (1) is mixed evenly with the hydrazine hydrate solution and the second dispersant to obtain a reduced base solution; (3) Preparation of surface modification coating solution: Adding the surface modifier into anhydrous ethanol and dissolving it evenly to obtain a surface modification coating solution; (4) Preparation of silver powder: Prepare a silver ammonia solution and add it to the reducing base solution of step (2), then add the surface modification coating solution of step (3) and stir to react to obtain a silver powder slurry solution; After solid-liquid separation, the solid phase is washed and dried to obtain silver powder.

2. The method for preparing silver powder by reducing hydrazine hydrate with adjustable particle size according to claim 1, characterized in that: In step (1), the first dispersant is selected from one or more of gelatin, polyvinyl pyrrolidone, gum arabic, polyvinyl alcohol, polyethylene glycol, Tween, sodium citrate, and triethanolamine; and the concentration of the first dispersant in the seed preparation base solution is 10 to 200 g / L.

3. The method for preparing silver powder by reducing hydrazine hydrate with adjustable particle size according to claim 1, characterized in that: The silver ammonia solution in steps (1) and (4) has a molar ratio of ammonia to silver of 2 to 6:1, and is prepared by the following method: adding ammonia water to a silver nitrate solution having a silver concentration of 0.1 to 2 mol / L and mixing well to obtain a silver ammonia solution.

4. The method for preparing silver powder by reducing hydrazine hydrate with adjustable particle size according to claim 1, characterized in that: The concentration of the hydrazine hydrate solution in steps (1) and (2) is 0.1 to 0.6 mol / L.

5. The method for preparing silver powder by reducing hydrazine hydrate with adjustable particle size according to claim 1, characterized in that: The stirring reaction temperature in step (1) is 20-50° C.; the particle size of the nanosilver in the nanosilver seed sol is 20-40 nm, and the concentration of the nanosilver is 0.1-10 g / L.

6. The method for preparing silver powder by reducing hydrazine hydrate with adjustable particle size according to claim 3, characterized in that: The amount of the nano silver seed sol added in step (2) is 1% to 100% of the mass of the silver nitrate used to prepare the silver ammonia solution in the silver powder preparation stage of step (4); preferably, the amount of the nano silver seed sol added is 25% to 70% of the mass of the silver nitrate.

7. The method for preparing silver powder by reducing hydrazine hydrate with adjustable particle size according to claim 1, characterized in that: In step (2), the second dispersant is one or more of polyethyleneimine, polyimide, polyetherimide, polysuccinimide, octenylsuccinic anhydride, succinic acid, and palmitic acid; the amount of the second dispersant added is 0.01% to 2% of the mass of the silver powder prepared in step (4).

8. The method for preparing silver powder by reducing hydrazine hydrate with adjustable particle size according to claim 1, characterized in that: The surface modifier in step (3) is one or more of oleic acid, caprylic acid, stearic acid, lauric acid, oleylamine, and palmitic acid; the amount of the surface modifier is 0.1% to 2% of the mass of the silver powder prepared in step (4).

9. The method for preparing silver powder by reducing hydrazine hydrate with adjustable particle size according to claim 1, characterized in that: The silver ammonia solution in step (4) is added quickly by pouring.

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