Silver powder having high sintering activity and method for preparing the same

Abstract

The present application relates to a kind of silver powder with high sintering activity, the silver powder is spherical, its surface has loose porous structure, purity is above 99%, and particle size D50 is based on the change of reaction system formula and reaction condition in its preparation process and kept in 0.1~3.0 μm adjustable interval. Meanwhile, the preparation method of the silver powder is disclosed.The present application indirectly adds flocculent hydroxide as heterophase crystal nucleus in the synthesis process of silver powder, and the silver particles reduced around flocculent heterophase crystal nucleus grow uniformly, so that it has loose porous structure, is conducive to the conduction of hot air, so as to realize low-temperature sintering.

Description

Technical Field

[0001] This invention relates to the fields of metal powder metallurgy and powder material preparation, and particularly to a silver powder with high sintering activity and its preparation method. Background Technology

[0002] The electronics and information industry is developing rapidly. Low-temperature curing conductive silver paste, as a key functional material, is widely used in membrane switches, keyboards, touch screens and radio frequency identification by screen printing to produce conductive film layers.

[0003] Low-temperature curing silver paste is a type of silver paste that can be cured at temperatures below 300℃ to form a conductive film. It consists of a conductive phase (silver powder), a binder phase (resin and organic solvent), and additives. However, since the melting point of silver is 961.78℃, conventional silver powder is difficult to sinter below 300℃. Reducing the crystallinity and particle size of the silver powder is an effective method to improve sintering activity and lower the sintering temperature. CN114743716A describes a method where a solution of silver ions or silver ion complexes is stirred in an inert gas environment, and a reducing agent is added to carry out a reduction reaction, maintaining a temperature change of less than 5℃ throughout the reaction. After the reduction reaction is completed, the silver powder is washed, dried, and pulverized to obtain low-temperature sinterable silver powder. However, the inert atmosphere conditions required by this method are difficult to achieve in actual mass production. CN110842213B uses a low-concentration silver solution in the initial stage of the reaction, reducing 0.1%-5% of the total silver nitrate to small silver crystals, which are easily adsorbed by a dendritic polymer framework agent to form a "silver tree" containing silver crystal nuclei. Then, silver ions are added very slowly, allowing them to gradually grow into hollow silver powder particles on the crystal nuclei of the "silver tree" framework. This silver powder has the characteristics of large specific surface area, large pore size, and high catalytic efficiency. However, this patented silver powder is used as an industrial catalyst, and the sintering characteristics of the silver powder are not mentioned. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a silver powder with high sintering activity that can achieve low-temperature sintering.

[0005] The technical problem to be solved by the present invention is to provide a method for preparing silver powder with high sintering activity.

[0006] To address the aforementioned problems, the present invention provides a silver powder with high sintering activity, characterized in that: the silver powder is spherical, its surface has a loose and porous structure, its purity is above 99%, and its particle size D50 is adjustable between 0.1 and 3.0 μm based on the changes in the reaction system formulation and reaction conditions during its preparation.

[0007] The method for preparing silver powder with high sintering activity as described above is characterized by: using silver nitrate as raw material, firstly forming flocculent hydroxide by adding metal salt for hydrolysis; then using the aforementioned hydroxide as heterogeneous seed crystals for silver reduction, inducing uniform growth of silver seed crystals, and adjusting the degree of growth of silver seed crystals in all directions by adding dispersant, thereby obtaining loose and porous silver powder.

[0008] The method for preparing silver powder with high sintering activity as described above includes the following steps:

[0009] (1) Preparation of oxidizing solution:

[0010] After mixing silver nitrate, metal salt, and dispersant, pure water is added and stirred until homogeneous to obtain a mixed solution with a silver nitrate concentration of 0.01~2.00 mol / L, which is the oxidation solution.

[0011] (2) Formation of heterogeneous crystal nuclei:

[0012] Under stirring conditions, a sodium hydroxide solution with a mass concentration of 1-10% is added to the oxidation solution to adjust the pH value of the oxidation solution to 5-8, so that flocculent hydroxides appear uniformly in the oxidation solution;

[0013] (3) Preparation of reducing solution:

[0014] After mixing the dispersant and reducing agent, pure water is added and stirred until homogeneous to obtain a reducing solution with a reducing agent concentration of 0.01~2.00 mol / L; the molar ratio of dispersant to reducing agent is 0.001~0.0001.

[0015] (4) Control of the reduction process:

[0016] The temperature of the oxidizing solution obtained in step (2) and the reducing solution obtained in step (3) is controlled at 10~20℃. The oxidizing solution and the reducing solution of the same volume are rapidly mixed under stirring conditions, and the temperature rise of the system at the end of the reduction process is controlled to not exceed 5℃. After the reduction reaction is completed, silver powder is obtained by solid-liquid separation.

[0017] (5) The silver powder obtained in step (4) is washed, dried and crushed to obtain highly active sintered silver powder with a loose and porous structure.

[0018] The metal salt is a soluble salt of a group VIII, IB, IIB, or IIIA metal, and the molar ratio of the metal salt to silver nitrate is 0.001 to 0.0001.

[0019] The dispersant is one of PVP, PEG, gelatin, gum arabic, sodium citrate, sodium dodecylbenzenesulfonate, Tween, and lauric acid; the molar ratio of the dispersant to silver nitrate is 0.001 to 0.0001.

[0020] The reducing agent is one of hydrazine hydrate, formaldehyde, ascorbic acid, glycerol, triethanolamine, and glucose.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. In the process of silver powder synthesis, the present invention indirectly adds flocculent hydroxide as heterogeneous crystal nuclei. The reduced silver particles grow uniformly around the flocculent heterogeneous crystal nuclei, giving it a loose and porous structure, which is conducive to the conduction of hot air, thereby achieving low-temperature sintering.

[0023] 2. The silver powder obtained by this invention was sintered at 300℃. SEM images showed that the silver powder particles could be fully sintered at 300℃ (see...). Figure 4 ). Attached Figure Description

[0024] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0025] Figure 1 SEM image (4000x) of silver powder prepared in Example 1 of this invention.

[0026] Figure 2 SEM image (4000x) of silver powder prepared in Example 2 of this invention.

[0027] Figure 3 SEM image (4000x) of silver powder prepared for Comparative Example 1.

[0028] Figure 4 The image shows a 10,000x SEM image of the silver powder obtained in Example 1 of this invention after sintering at 300°C. Detailed Implementation

[0029] A silver powder with high sintering activity is spherical with a loose and porous structure on its surface. The purity is above 99%, and the particle size D50 is adjustable between 0.1 and 3.0 μm based on the changes in the reaction system formulation and reaction conditions during its preparation.

[0030] The preparation method of the silver powder with high sintering activity is as follows: silver nitrate is used as raw material, and flocculent hydroxide is first formed by adding metal salt and hydrolyzing it; then the aforementioned hydroxide is used as a heterogeneous seed crystal for silver reduction, inducing the uniform growth of silver seed crystals, and the degree of growth of silver seed crystals in all directions is adjusted by adding a dispersant, thereby obtaining loose and porous silver powder.

[0031] The specific preparation method includes the following steps:

[0032] (1) Preparation of oxidizing solution:

[0033] After mixing silver nitrate, metal salt, and dispersant, pure water is added and stirred until homogeneous to obtain a mixed solution with a silver nitrate concentration of 0.01~2.00 mol / L, which is the oxidation solution.

[0034] Wherein: the metal salt is a soluble salt of a metal from Group VIII, IB, IIB, or IIIA, and the preferred soluble salt is a nitrate; the molar ratio of the metal salt to silver nitrate is 0.001 to 0.0001.

[0035] The dispersant is one of PVP, PEG, gelatin, gum arabic, sodium citrate, sodium dodecylbenzene sulfonate, Tween, and lauric acid; the molar ratio of the dispersant to silver nitrate is 0.001~0.0001.

[0036] (2) Formation of heterogeneous crystal nuclei:

[0037] Under stirring conditions, a sodium hydroxide solution with a mass concentration of 1-10% is added to the oxidation solution to adjust the pH value of the oxidation solution to 5-8, so that flocculent hydroxides appear uniformly in the oxidation solution.

[0038] (3) Preparation of reducing solution:

[0039] After mixing the dispersant and reducing agent, pure water is added and stirred evenly to obtain a reducing solution with a reducing agent concentration of 0.01~2.00mol / L; the molar ratio of dispersant to reducing agent is 0.001~0.0001.

[0040] The reducing agent is one of the following: hydrazine hydrate, formaldehyde, ascorbic acid, glycerol, triethanolamine, or glucose.

[0041] The dispersant is the same as in step (1).

[0042] (4) Control of the reduction process:

[0043] The temperature of the oxidizing solution obtained in step (2) and the reducing solution obtained in step (3) is controlled to be 10~20℃. The same volume of the oxidizing solution and the reducing solution are rapidly mixed under stirring conditions, and the temperature rise of the system is controlled to be no more than 5℃ after the reduction process is completed. After the reduction reaction is completed, silver powder is obtained by solid-liquid separation.

[0044] (5) The silver powder obtained in step (4) is washed, dried and crushed to obtain highly active sintered silver powder with a loose and porous structure.

[0045] Example 1: A method for preparing silver powder with high sintering activity, comprising the following steps:

[0046] (1) Preparation of oxidizing solution:

[0047] Silver nitrate, copper nitrate, and sodium citrate dispersant are mixed and then pure water is added. After stirring evenly, a mixed solution with a silver nitrate concentration of 1.00 mol / L is obtained, which is the oxidation solution.

[0048] The molar ratio of copper nitrate to silver nitrate is 0.0001; the molar ratio of sodium citrate to silver nitrate is 0.005.

[0049] (2) Formation of heterogeneous crystal nuclei:

[0050] Under stirring conditions, a 1% sodium hydroxide solution was added to the oxidation solution to adjust the pH to 6, so that flocculent hydroxides would appear uniformly in the oxidation solution.

[0051] (3) Preparation of reducing solution:

[0052] Sodium citrate, a dispersant, and ascorbic acid, a reducing agent, are mixed and then pure water is added. After stirring evenly, a reducing solution with a reducing agent concentration of 1.00 mol / L is obtained.

[0053] The molar ratio of sodium citrate to ascorbic acid is 0.005.

[0054] (4) Control of the reduction process:

[0055] The temperature of the oxidizing and reducing solutions obtained in step (2) is controlled at 20°C. The same volume of the oxidizing and reducing solutions obtained in step (2) is rapidly mixed under stirring conditions, and the system temperature is controlled to rise by 3°C at the end of the reduction process. After the reduction reaction is completed, silver powder is obtained by solid-liquid separation.

[0056] (5) The silver powder obtained in step (4) is washed, dried and crushed to obtain highly active sintered silver powder with a loose and porous structure.

[0057] The silver powder has a purity of 99.7% and a particle size D50 of 1.0 μm. SEM results are shown below. Figure 1 The surface of the particles has a loose and porous structure.

[0058] Example 2 A method for preparing silver powder with high sintering activity, comprising the following steps:

[0059] (1) Preparation of oxidizing solution:

[0060] Silver nitrate, aluminum nitrate, and dispersant Tween 80 are mixed and then pure water is added. After stirring evenly, a mixed solution with a silver nitrate concentration of 2.00 mol / L is obtained, which is the oxidation solution.

[0061] The molar ratio of aluminum nitrate to silver nitrate is 0.001; the molar ratio of dispersant Tween 80 to silver nitrate is 0.008.

[0062] (2) Formation of heterogeneous crystal nuclei:

[0063] Under stirring conditions, a 10% sodium hydroxide solution was added to the oxidation solution to adjust the pH to 8, so that flocculent hydroxides would appear uniformly in the oxidation solution.

[0064] (3) Preparation of reducing solution:

[0065] After mixing the dispersant Tween 80 and the reducing agent glycerol, pure water was added and stirred evenly to obtain a reducing solution with a reducing agent concentration of 2.00 mol / L.

[0066] The molar ratio of dispersant Tween 80 to glycerol is 0.003.

[0067] (4) Control of the reduction process:

[0068] The temperature of the oxidizing and reducing solutions obtained in step (2) is controlled at 10°C. The same volume of the oxidizing and reducing solutions obtained in step (2) is rapidly mixed under stirring conditions, and the system temperature is controlled to rise by 2°C at the end of the reduction process. After the reduction reaction is completed, silver powder is obtained by solid-liquid separation.

[0069] (5) The silver powder obtained in step (4) is washed, dried and crushed to obtain highly active sintered silver powder with a loose and porous structure.

[0070] The silver powder has a purity of 99.5% and a particle size D50 of 0.5 μm. SEM results are shown below. Figure 2 The surface of the particles has a loose and porous structure.

[0071] Comparative Example 1

[0072] (1) Preparation of oxidizing solution:

[0073] After mixing silver nitrate and dispersant PVP (k30), pure water is added and stirred until homogeneous to obtain a mixed solution with a silver nitrate concentration of 1.0 mol / L, which is the oxidation solution.

[0074] The molar ratio of dispersant to silver nitrate is 0.001.

[0075] (2) Preparation of reducing solution:

[0076] After mixing the dispersant PVP and the reducing agent hydrazine hydrate, pure water was added and stirred evenly to obtain a reducing solution with a reducing agent concentration of 2.00 mol / L.

[0077] The molar ratio of dispersant to reducing agent is 0.001.

[0078] (3) Control of the reduction process:

[0079] The temperatures of the oxidizing and reducing solutions were controlled at 30°C. Equal volumes of oxidizing and reducing solutions were rapidly mixed under stirring. After the reduction process was complete, the system temperature rose by 5°C. Following solid-liquid separation, silver powder was obtained.

[0080] (4) The silver powder obtained in step (3) is washed, dried and crushed to obtain the product silver powder.

[0081] The silver powder has a purity of 99.1% and a particle size D50 of 3.5 μm. SEM results are shown below. Figure 3 The surface of the particles has a dense structure.

Claims

1. A silver powder having high sintering activity, characterized by: The silver powder is spherical with a loose and porous structure on its surface. Its purity is above 99%, and the particle size D50 is adjustable between 0.1 and 3.0 μm based on variations in the reaction system formulation and conditions during preparation. The preparation method is as follows: using silver nitrate as a raw material, a flocculent hydroxide is first formed by adding a metal salt and hydrolyzing it. Then, the aforementioned hydroxide is used as a heterogeneous seed crystal for silver reduction, inducing uniform growth of the silver seed crystals. The degree of growth of the silver seed crystals in all directions is adjusted by adding a dispersant, thereby obtaining a loose and porous silver powder. The metal salt is a soluble salt of a Group VIII, IB, IIB, or IIIA metal, and the molar ratio of the metal salt to silver nitrate is 0.001 to 0.0001.

2. A method for preparing silver powder with high sintering activity as described in claim 1, comprising the following steps: (1) Preparation of oxidizing solution: After mixing silver nitrate, metal salt, and dispersant, pure water is added and stirred until homogeneous to obtain a mixed solution with a silver nitrate concentration of 0.01~2.00 mol / L, which is the oxidation solution. (2) Formation of heterogeneous crystal nuclei: Under stirring conditions, a sodium hydroxide solution with a mass concentration of 1-10% is added to the oxidation solution to adjust the pH value of the oxidation solution to 5-8, so that flocculent hydroxides appear uniformly in the oxidation solution; (3) Preparation of reducing solution: After mixing the dispersant and reducing agent, pure water is added and stirred until homogeneous to obtain a reducing solution with a reducing agent concentration of 0.01~2.00 mol / L; the molar ratio of dispersant to reducing agent is 0.001~0.0001. (4) Control of the reduction process: The temperature of the oxidizing solution obtained in step (2) and the reducing solution obtained in step (3) is controlled at 10~20℃. The oxidizing solution and the reducing solution of the same volume are rapidly mixed under stirring conditions, and the temperature rise of the system at the end of the reduction process is controlled to not exceed 5℃. After the reduction reaction is completed, silver powder is obtained by solid-liquid separation. (5) The silver powder obtained in step (4) is washed, dried and crushed to obtain highly active sintered silver powder with a loose and porous structure.

3. The method for preparing silver powder with high sintering activity as described in claim 2, characterized in that: The dispersant is one of PVP, PEG, gelatin, gum arabic, sodium citrate, sodium dodecylbenzenesulfonate, Tween, and lauric acid; the molar ratio of the dispersant to silver nitrate is 0.001 to 0.0001.

4. The method of claim 2, wherein the silver powder having high sinterability is prepared by adding a dispersant to a silver salt solution, and then reducing the silver salt solution. The reducing agent is one of hydrazine hydrate, formaldehyde, ascorbic acid, glycerol, triethanolamine, and glucose.

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