Microcrystalline silver powder, its preparation method and application

Abstract

The present application relates to a kind of microcrystalline silver powder and its preparation method and application, it is related to new material technical field.The preparation method includes the following steps: preparation of silver nitrate solution with concentration ≥2.0g / mL, dispersant solution, silver nitrate solution, dispersant solution is mixed, adjusting agent is added, stirring, obtain silver nitrate mixed solution;Preparation of reducing agent solution, reaction accelerator solution, reducing agent solution, reaction accelerator solution is mixed, and reduction mixed solution is obtained;Silver nitrate mixed solution is added dropwise into reduction mixed solution, and dropwise stirring is carried out, washing, solid-liquid separation, take precipitate, surface treatment is carried out by adding surface treatment agent, drying, powder, screening, and obtain microcrystalline silver powder.The preparation method is based on liquid phase reduction method, and the microcrystalline silver powder prepared has small particle size, high tap density, has monodispersity and narrow particle size distribution, strong adhesion.The preparation method process is simple and easy batch production, good stability, and raw material is non-toxic.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, and in particular to a microcrystalline silver powder, its preparation method, and its application. Background Technology

[0002] In today's information society, the rapid development of electronic products is changing people's living environment and lifestyles. The photovoltaic industry, in particular, has accelerated the development of electronic pastes in recent years, both domestically and internationally. Ultrafine silver powder is widely used in the electronics industry, becoming a fundamental functional material in conductive electronic pastes. However, with the rapid development of the photovoltaic and electronics industries, the demand for silver powder has also increased significantly. Therefore, how to prepare high-performance ultrafine silver powder has become a hot topic in the current electronics industry.

[0003] In conductive pastes, the conductive functional phase determines the electrical properties of the paste and affects the mechanical and physical properties of the sintered film. In conductive pastes, the functional phase is generally selected from precious metals with good electrical conductivity, such as gold, silver, copper, and palladium. Compared to other precious metals, silver is favored by the industry due to its excellent electrical and thermal conductivity and low price. Silver is a primary material for the conductive phase in electronic pastes because of its good electrical conductivity and physical and mechanical properties. Therefore, silver powder is used as the conductive phase in the photovoltaic and electronics industries.

[0004] Currently, the liquid-phase chemical reduction method is used to produce silver powder. This method has a simple process and low requirements for reaction equipment, making it suitable for both small-scale experiments and large-scale production. It can mass-produce most commercially available silver powder morphologies, and particle size can be well controlled. However, the preparation of ultrafine silver powder using the liquid-phase chemical reduction method differs from the preparation of spherical silver powder. Spherical silver powder, with its larger particle size, is easier to control and its dispersibility can be improved. Ultrafine silver powder, on the other hand, has very strong adhesion, making dispersibility difficult to control during mass production. This results in low surface cleanliness, leading to difficulty in controlling particle size and specific surface area, low tap density, and high corrosivity. Currently, the two main indicators for evaluating the performance of ultrafine silver powder are dispersibility and tap density. Ultrafine silver powder with better dispersibility and higher tap density produces conductive pastes with characteristics such as non-stickiness, low shrinkage, easy screen removal during printing, and dense sintering. Therefore, there is an urgent need to develop a method that has a simple process flow and can produce silver powder with high dispersibility, high tap density, high sintering activity and easy industrialization, so as to solve the problems of poor sintering activity, high shrinkage rate and high corrosivity, and improve electrical conductivity and photoelectric conversion ability. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for preparing microcrystalline silver powder. This method is based on liquid-phase reduction and yields microcrystalline silver powder with small particle size, high tap density, monodispersity, narrow particle size distribution, and strong adhesion. The preparation method is simple, suitable for mass production, exhibits good stability, and uses non-toxic raw materials, providing strong protection for production staff.

[0006] To achieve the above objectives, the present invention provides a method for preparing microcrystalline silver powder, comprising the following steps: preparing a silver nitrate solution using silver nitrate, preparing a dispersant solution, mixing the silver nitrate solution and the dispersant solution, adding a regulator, and stirring to obtain a mixed silver nitrate solution; preparing a reducing agent solution and a reaction promoter solution, mixing the reducing agent solution and the reaction promoter solution to obtain a reduced mixed solution; adding the mixed silver nitrate solution dropwise to the reduced mixed solution, stirring during the dropwise addition, washing, separating the solid and liquid, taking the precipitate, adding a surface treatment agent for surface treatment, drying, grinding into powder, and sieving to obtain microcrystalline silver powder;

[0007] The concentration of silver nitrate in the silver nitrate solution is ≥2.0 g / mL.

[0008] In the above preparation method, after silver nitrate is prepared into a high-concentration silver ion solution, a pH adjuster solid is directly added, along with a reaction promoter to rapidly nucleate the silver powder. Simultaneously, a dispersant is added to inhibit nucleation and crystal growth, controlling the silver powder particle size between 1.0 and 1.5 mm to increase the tap density. The silver powder obtained by this method is microcrystalline silver powder with small particle size and high tap density, suitable for use in crystalline silicon solar cells and various conductive silver pastes. Higher tap density of the silver powder results in a greater content of active conductive material within the monomer volume, better film density, and consequently, lower volume resistivity and contact resistance between the paste made from this microcrystalline silver powder and the conductive oxide after solidification, thus improving the photoelectric conversion efficiency of the solar cell. This preparation method is based on a liquid-phase oxidation-reduction method, is simple, uses a low-dispersant content, is non-toxic, has high production efficiency, is easy to mass-produce, exhibits good stability, and uses non-toxic raw materials, providing strong protection for production staff.

[0009] In one embodiment, the dispersant includes at least one of tannin, guar gum, and guar gum, and the mass of the dispersant is 0.15-1.5% of the mass of the silver nitrate.

[0010] The aforementioned raw materials, acting as dispersants, effectively control silver powder nucleation and inhibit the nucleation and growth process, thereby keeping the silver powder particle size within a smaller range and increasing the tap density. This preparation method uses a relatively small amount of dispersant that is easy to clean, improving dispersibility while simplifying cleaning. Applied at the downstream end of the slurry, silver, as a conductive phase, ultimately aims to reduce the resistance of the series circuit, resulting in low resistivity and ensuring the conductivity of silver.

[0011] In one embodiment, the reaction promoter includes at least one of triphenylphosphine and urea, and the mass of the reaction promoter is 0.05-0.2% of the mass of the silver nitrate.

[0012] The above-mentioned reaction promoters and their dosages, when combined with the dispersant, can enable silver powder to nucleate rapidly without causing excessive growth of nuclei crystals.

[0013] In one embodiment, the regulator includes at least one of sodium carbonate, ammonia, sodium hydroxide, and potassium hydroxide, and the mass of the regulator is 8-20% of the mass of the silver nitrate.

[0014] The above-mentioned regulators are used to adjust the pH value.

[0015] In one embodiment, the reducing agent includes at least one of ascorbic acid, glycerol, triethanolamine, and glucose, and the amount of the reducing agent is 0.35-1.0 times the silver content in the silver nitrate.

[0016] In one embodiment, the surface treatment agent includes at least one of oleic acid, dodecanoic acid, tetradecanoic acid, and boric acid, and the mass of the surface treatment agent is 0.25-1.0% of the mass of the silver nitrate.

[0017] In one embodiment, the temperature for preparing the silver nitrate solution is 20-40°C, the temperature for preparing the reducing agent solution is 35-45°C, the dropping time is 0.5-1.5 h, the stirring speed is 150-300 rp / min, the stirring temperature is 35-45°C, and the stirring time is 60-120 min.

[0018] The temperature range of silver nitrate solution and reducing agent solution is also an important factor to consider in experimental design. Different temperatures, combined with the type and amount of dispersant, will affect the physical parameters of silver powder, such as tap density and dispersibility, as well as sintering activity.

[0019] In one embodiment, the cleaning includes: cleaning the product obtained after dropwise addition and stirring until the conductivity is below 20 μs / cm; the solid-liquid separation is achieved by natural sedimentation; and the drying temperature is 65-85°C.

[0020] The present invention also provides microcrystalline silver powder obtained by the aforementioned preparation method. This microcrystalline silver powder has a high tap density of 4.5-6.0 g / ml, a particle size D50 of 0.8-2.0 μm, and a specific surface area of ​​1.0-2.0 m². 2 / g.

[0021] The aforementioned microcrystalline silver powder has small particle size, high tap density, and uniform morphology. It exhibits monodispersity, narrow particle size distribution, and strong adhesion, making it an ultrafine microcrystalline silver powder. Compared to conventional microcrystalline silver powder, it has higher activity and higher photoelectric conversion efficiency. Electrodes prepared using this microcrystalline silver powder can reduce contact attenuation, provide strong electrode connection capabilities, and exhibit strong drought resistance.

[0022] The present invention also provides the application of the microcrystalline silver powder in the preparation of electrodes and conductive pastes.

[0023] The present invention also provides an electronic paste prepared using the aforementioned microcrystalline silver powder.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] This invention discloses a microcrystalline silver powder, its preparation method, and its application. The preparation method is based on a liquid-phase reduction method, resulting in microcrystalline silver powder with small particle size, high tap density, monodispersity, narrow particle size distribution, and strong adhesion. The preparation method is simple, suitable for mass production, exhibits good stability, and uses non-toxic raw materials, providing strong protection for production staff. The resulting silver powder is microcrystalline silver powder with small particle size, high tap density, uniform morphology, monodispersity, and narrow particle size distribution. It is an ultrafine microcrystalline silver powder with higher activity and photoelectric conversion efficiency compared to conventional microcrystalline silver powder. Attached Figure Description

[0026] Figure 1 The image shows the morphology of the microcrystalline silver powder prepared in Example 1.

[0027] Figure 2 The morphology of the microcrystalline silver powder prepared for Comparative Example 1 is shown in the figure.

[0028] Figure 3 The image shows the morphology of the microcrystalline silver powder prepared in Example 2.

[0029] Figure 4 The morphology of the microcrystalline silver powder prepared in Comparative Example 2 is shown in the figure.

[0030] Figure 5 The image shows the morphology of the microcrystalline silver powder prepared in Example 3.

[0031] Figure 6 The morphology of the microcrystalline silver powder prepared in Comparative Example 3 is shown in the figure.

[0032] Figure 7 The image shows the morphology of the microcrystalline silver powder prepared for Comparative Example 4. Detailed Implementation

[0033] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0035] source:

[0036] Unless otherwise specified, all reagents, materials, and equipment used in this embodiment are commercially available; unless otherwise specified, all test methods are conventional test methods in this field.

[0037] Example 1

[0038] (1) Dissolve 1 kg of silver nitrate in 5 L of deionized water in a mixing tank to prepare a silver nitrate solution (silver nitrate concentration is 0.2 g / mL) and control the solution temperature at 30 ± 2 °C.

[0039] (2) Weigh 1.5g of tannin (dispersant) and dissolve it in 20ml of deionized water to prepare a dispersant solution, and control the solution temperature at 30℃. In this embodiment, the mass of the dispersant is 0.15% of the mass of silver nitrate.

[0040] (3) Weigh 0.5g of triphenylphosphine (reaction promoter) and dissolve it in 20ml of deionized water to prepare a reaction promoter solution, and control the solution temperature at 30℃. In this embodiment, the mass of the reaction promoter is 0.05% of the mass of silver nitrate.

[0041] (4) Weigh 80g of sodium carbonate solid as the regulator. In this embodiment, the mass of the regulator is 8% of the mass of silver nitrate.

[0042] (5) Add the tannin solution (dispersant solution) to the silver nitrate solution and stir to obtain solution A.

[0043] (6) Add sodium carbonate solid to the A solution mixing vessel at once, start stirring at a speed of 350 rp / min to obtain B solution (silver nitrate mixed solution).

[0044] (7) Weigh 0.22 kg of glucose (reducing agent) into the reaction vessel, add water to dissolve and prepare 1 L of reducing agent solution, heat to 40 °C; add triphenylphosphine solution (reaction promoter solution), stir, and stir at a speed of 200 rp / min to obtain solution C (reducing mixed solution).

[0045] (8) Add solution B (silver nitrate mixed solution) dropwise to solution C (reducing mixed solution) to start the reaction. Stir the dropwise addition at a speed of 200 rpm for 1 hour, maintaining the temperature inside the reactor at 35-45°C. After the dropwise addition is complete, stir for 10 minutes until the reaction is complete. After the reaction is complete, wash the silver powder obtained from the reaction until the conductivity is below 20 μS / cm, and allow it to settle naturally for solid-liquid separation.

[0046] (9) After separation, the silver powder was treated with 5g of tetradecanoic acid (surface treatment agent), dried at 65℃ until constant weight, pulverized and sieved to obtain microcrystalline silver powder with high tap density. In this embodiment, the mass of the surface treatment agent was 0.5% of the mass of silver nitrate. Morphology (see...) Figure 1 Its specific surface area is 1.0-2.0 m². 2 / g.

[0047] Example 2

[0048] (1) Dissolve 1 kg of silver nitrate in 5 L of deionized water in a mixing tank to prepare a silver nitrate solution (silver nitrate concentration is 0.2 g / mL) and control the solution temperature at 30 ± 2 °C.

[0049] (2) Weigh 1.5g of tannin (dispersant) and dissolve it in 20ml of deionized water to prepare a dispersant solution, and control the solution temperature at 30℃. In this embodiment, the mass of the dispersant is 0.15% of the mass of silver nitrate.

[0050] (3) Weigh 0.5g of triphenylphosphine (reaction promoter) and dissolve it in 20ml of deionized water to prepare a reaction promoter solution, and control the solution temperature at 30℃. In this embodiment, the mass of the reaction promoter is 0.05% of the mass of silver nitrate.

[0051] (4) Weigh 80g of sodium hydroxide solid as the regulator. In this example, the mass of the regulator is 8% of the mass of silver nitrate.

[0052] (5) Add the tannin solution (dispersant solution) to the silver nitrate solution and stir to obtain solution A.

[0053] (6) Add the sodium hydroxide solid to the A solution mixing vessel at once, start stirring, and stir at a speed of 350 rp / min to obtain the B solution (silver nitrate mixed solution).

[0054] (7) Weigh 0.22 kg of glucose (reducing agent) into the reaction vessel, add water to dissolve and prepare 1 L of reducing agent solution, heat to 40 °C; add triphenylphosphine solution (reaction promoter solution), stir, and stir at a speed of 200 rp / min to obtain solution C (reducing mixed solution).

[0055] (8) Add solution B (silver nitrate mixed solution) dropwise to solution C (reducing mixed solution) to start the reaction. Stir the dropwise addition at a speed of 200 rpm for 1 hour, maintaining the temperature inside the reactor at 35-45°C. After the dropwise addition is complete, stir for 10 minutes until the reaction is complete. After the reaction is complete, wash the silver powder obtained from the reaction until the conductivity is below 20 μS / cm, and allow it to settle naturally for solid-liquid separation.

[0056] (9) After separation, the silver powder was treated with 5g of tetradecanoic acid (surface treatment agent), dried at 65℃ until constant weight, pulverized and sieved to obtain microcrystalline silver powder with high tap density. In this embodiment, the mass of the surface treatment agent was 0.5% of the mass of silver nitrate. Morphology (see...) Figure 3 Its specific surface area is 1.0-2.0 m². 2 / g.

[0057] Example 3

[0058] (1) Dissolve 1 kg of silver nitrate in 5 L of deionized water in a mixing tank to prepare a silver nitrate solution (silver nitrate concentration is 0.2 g / mL) and control the solution temperature at 30 ± 2 °C.

[0059] (2) Weigh 1.5g of tannin (dispersant) and dissolve it in 20ml of deionized water to prepare a dispersant solution, and control the solution temperature at 30℃. In this embodiment, the mass of the dispersant is 0.15% of the mass of silver nitrate.

[0060] (3) Weigh 0.5g of triphenylphosphine (reaction promoter) and dissolve it in 20ml of deionized water to prepare a reaction promoter solution, and control the solution temperature at 30℃. In this embodiment, the mass of the reaction promoter is 0.05% of the mass of silver nitrate.

[0061] (4) Weigh 80g of potassium hydroxide solid as the regulator. In this example, the mass of the regulator is 8% of the mass of silver nitrate.

[0062] (5) Add the tannin solution (dispersant solution) to the silver nitrate solution and stir to obtain solution A.

[0063] (6) Add potassium hydroxide solid to the A solution mixing tank at once, start stirring, and stir at a speed of 350 rp / min to obtain B solution (silver nitrate mixed solution).

[0064] (7) Weigh 0.22 kg of glucose (reducing agent) into the reaction vessel, add water to dissolve and prepare 1 L of reducing agent solution, heat to 40 °C; add triphenylphosphine solution (reaction promoter solution), stir, and stir at a speed of 200 rp / min to obtain solution C (reducing mixed solution).

[0065] (8) Add solution B (silver nitrate mixed solution) dropwise to solution C (reducing mixed solution) to start the reaction. Stir the dropwise addition at a speed of 200 rpm for 1 hour, maintaining the temperature inside the reactor at 35-45°C. After the dropwise addition is complete, stir for 10 minutes until the reaction is complete. After the reaction is complete, wash the silver powder obtained from the reaction until the conductivity is below 20 μS / cm, and allow it to settle naturally for solid-liquid separation.

[0066] (9) After separation, the silver powder was treated with 5g of tetradecanoic acid (surface treatment agent), dried at 65℃ until constant weight, pulverized and sieved to obtain microcrystalline silver powder with high tap density. In this embodiment, the mass of the surface treatment agent was 0.5% of the mass of silver nitrate. Morphology (see...) Figure 5 Its specific surface area is 1.0-2.0 m². 2 / g.

[0067] Comparative Example 1

[0068] A silver powder is prepared in a manner that is basically the same as in Example 1, except that the temperature of the silver nitrate solution in step (1) is 60°C.

[0069] Various irregular mixed silver powders were prepared in this comparative example, and their morphologies are shown in (see...). Figure 2 ).

[0070] Comparative Example 2

[0071] A silver powder, the preparation method of which is basically the same as that in Example 1, the difference being that no reaction promoter is added.

[0072] In this comparative example, relatively cohesive spherical silver powder was prepared, with the morphology shown in (see...). Figure 4 ).

[0073] Comparative Example 3

[0074] A silver powder, the preparation method of which is basically the same as that of Example 1, except that in step (4), the regulator is prepared into a solution.

[0075] In this comparative example, relatively large crystalline silver powder was prepared, and its morphology (see...) Figure 6 ).

[0076] Comparative Example 4

[0077] A silver powder is prepared in a manner that is basically the same as in Example 1, except that in step (2), the dispersant is replaced with a common rosin dispersant.

[0078] The comparative example yielded silver powder with very small particle size, poor dispersibility, and low tapping density. Its morphology is shown in (see...). Figure 7 ).

[0079] Experimental Example

[0080] The silver powders of the examples and comparative examples were tested as follows:

[0081] (1) The particle size of silver powder was determined by using a Malvern laser particle size analyzer and anhydrous ethanol as solvent, and ultrasonically dispersing for 10 minutes.

[0082] (2) The tap density of silver powder is measured using a tap density meter.

[0083] (3) The conventional micro powder A in Table 1 below is C-01 of Guangdong Lingguang New Materials Co., Ltd., which is prepared by the method of reducing silver oxide with triethanolamine.

[0084] The test results are shown in Table 1:

[0085] Table 1. Particle size and tap density of each embodiment and comparative example.

[0086]

[0087] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0088] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing microcrystalline silver powder, characterized in that, Includes the following steps: A silver nitrate solution is prepared using silver nitrate, wherein the concentration of silver nitrate in the silver nitrate solution is ≥2.0 g / mL. A dispersant solution is prepared by mixing the silver nitrate solution and the dispersant solution, adding a regulator, and stirring to obtain a mixed silver nitrate solution. A reducing agent solution and a reaction accelerator solution are prepared by mixing the reducing agent solution and the reaction accelerator solution to obtain a reducing mixed solution. The mixed silver nitrate solution is added dropwise to the reducing mixed solution, and the mixture is stirred, washed, and subjected to solid-liquid separation. The precipitate is collected, surface-treated with a surface treatment agent, dried, pulverized, and sieved to obtain microcrystalline silver powder. The dispersant includes at least one of tannin, guar gum, and guar gum, and the mass of the dispersant is 0.15-1.5% of the mass of the silver nitrate; the reaction promoter includes at least one of triphenylphosphine and urea, and the mass of the reaction promoter is 0.05-0.2% of the mass of the silver nitrate; the regulator includes at least one of sodium carbonate, ammonia, sodium hydroxide, and potassium hydroxide, and the mass of the regulator is 8-20% of the mass of the silver nitrate; the surface treatment agent includes at least one of oleic acid, dodecanoic acid, tetradecanoic acid, and boric acid, and the mass of the surface treatment agent is 0.25-1.0% of the mass of the silver nitrate. The temperature for preparing the silver nitrate solution is 20-40℃, and the temperature for preparing the reducing agent solution is 35-45℃; the dropping time is 0.5-1.5h, the stirring speed is 150-300 rp / min, the stirring temperature is 35-45℃, and the stirring time is 60-120min.

2. The preparation method according to claim 1, characterized in that, The reducing agent includes at least one of ascorbic acid, glycerol, triethanolamine, and glucose, and the amount of the reducing agent is 0.35-1.0 times the silver content in the silver nitrate.

3. The microcrystalline silver powder obtained by the preparation method according to any one of claims 1-2, characterized in that, This microcrystalline silver powder is a high-tap-density microcrystalline silver powder, with a tap density of 4.5-6.0 g / ml, a particle size D50 of 0.8-2.0 μm, and a specific surface area of ​​1.0-2.0 m². 2 / g.

4. The application of the microcrystalline silver powder according to claim 3 in the preparation of electrodes and conductive pastes.

5. A conductive paste, characterized in that, It was prepared using the microcrystalline silver powder described in claim 3.

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