Preparation method of silver crystal powder and application thereof

Abstract

The present application relates to the field of metal particle preparation, in particular to a preparation method of silver crystal powder and application thereof. The present application provides a preparation method of silver crystal powder, which comprises adding silver sulfate and a reducing agent into an acid solution of a protective agent, and performing a reduction reaction under heating and stirring to obtain silver crystal powder. The present application provides a silver crystal powder, wherein the intensity ratio I (111) / I (200) of the silver crystal in (111) and (200) directions is greater than 4. The present application also provides a silver paste and a preparation method of the silver paste. The silver crystal powder provided by the present application has excellent shrinkage and crystallization properties, and the silver paste prepared by using the silver crystal powder has excellent high-temperature resistance and conductivity, and has a good prospect in application of electrode paste on the surface of electronic device electrodes.

Description

Technical Field

[0001] This invention relates to the field of metal particle preparation, and more particularly to a method for preparing silver crystal powder and its application. Background Technology

[0002] Silver powder, due to its good metallic luster, conductivity, and stability, has wide applications in the electronics, energy, anti-corrosion coatings, and decorative industries, particularly in cosmetics. Currently, silver powder preparation methods include physical and chemical methods. Physical methods include laser ablation, high-energy ball milling, and atomization. Chemical methods include liquid-phase reduction, microemulsion, and liquid-phase precipitation conversion. Among these, liquid-phase reduction is relatively simple and effective, and is widely used. It involves adding a reducing agent to a silver salt solution and controlling the reduction reaction conditions to reduce silver ions to elemental silver. Furthermore, to prepare ultrafine silver powder, dispersants or protective agents are often added to the reduction system to reduce silver particle aggregation.

[0003] Patent JP2000129318A (invalid) Silver Powder and its Production discloses a method of mixing an aqueous reaction system containing silver salts with an aqueous solution containing a reducing agent to reduce and precipitate silver particles, thereby obtaining silver powder.

[0004] Patent JP2006063414A (expired) discloses silver powder containing spherical high-roughness silver particles, silver powder containing flake-shaped high-roughness silver particles, a mixture of the above two types of silver powder, a method for manufacturing such silver powder, silver ink and silver paste containing such silver powder, and a method for manufacturing such silver powder by grinding such silver powder. It also discloses that silver powder is prepared using silver nitrate, a complexing agent, and a reducing agent.

[0005] Patent JP2007239077A (valid) discloses a method for manufacturing micro-silver particles and the micro-silver particles obtained by the method, which involves mixing a silver salt solution containing silver salt, chelating agent and gelatin with a reducing agent solution to produce micro-silver particles.

[0006] Patent JP2009120940A (failed) discloses a method for manufacturing metal nanoparticles that prepares silver particles using a silver precursor and a nonpolar solution.

[0007] Because silver nitrate has better solubility and reactivity, it is better suited for the chemical reduction process of silver powder and allows for better control of the particle size and morphology of the silver powder. Therefore, the aforementioned patents all use silver nitrate as the silver source for preparing silver powder. However, although the silver powder prepared by the above methods has certain advantages in some aspects, components such as electronic devices also require silver powder with better shrinkage and crystallinity properties. The silver powder prepared by the above methods also has the problem of insufficient shrinkage and crystallinity properties. The purpose of this invention is to provide a new method for preparing silver powder. Summary of the Invention

[0008] The purpose of this invention is to provide a novel method for preparing silver powder. This method uses silver sulfate as the silver source, adds specific reducing agents and protective agents, and controls the reaction conditions. The resulting silver powder exhibits good shrinkage and crystallization properties, showing promising application prospects. The specific technical solution of this invention is as follows:

[0009] In a first aspect, the present invention provides a method for preparing silver crystal powder, the method comprising:

[0010] Silver sulfate and a reducing agent are added to an acidic solution of a protective agent, and a reduction reaction is carried out under heating and stirring conditions to obtain silver crystal powder.

[0011] In any embodiment, the protective agent is at least one of gum arabic, propyl cellulose, ethyl cellulose, and polyvinylpyrrolidone;

[0012] Preferably, the protective agent is gum arabic.

[0013] In any embodiment, the reducing agent is selected from at least one of ascorbic acid, hydrazine, hydroquinone, phenylhydrazine, and formalin;

[0014] Preferably, the reducing agent is ascorbic acid.

[0015] In any embodiment, the heating temperature is 30-80°C and the reaction time is 5-1h.

[0016] In any embodiment, silver sulfate is added in the form of a silver sulfate dispersion at a concentration of 0.01 mol / dm³. 3 -1mol / dm 3 ;

[0017] In any embodiment, the concentration of the protective agent in the acidic solution is 1 g / L-20 g / L;

[0018] In any embodiment, the mass ratio of added silver sulfate to the protective agent is (0.01-0.2):1;

[0019] In any embodiment, the molar ratio of the added reducing agent to silver sulfate is 0.5-2.

[0020] In any embodiment, the solvent of the acidic solution and the solvent of the silver sulfate dispersion are both selected from water or organic solvents.

[0021] In any embodiment, the pH of the acidic solution is below 2;

[0022] In any embodiment, the pH of the solution is adjusted to below 2 by adding sulfuric acid.

[0023] In any embodiment, the organic solvent is free of hydroxyl groups; the hydroxyl-free organic solvent includes, but is not limited to, acetone.

[0024] Secondly, the present invention provides a silver crystal powder, wherein the intensity ratio I of the silver crystals in the (111) and (200) directions is I. (111) / I (200) Greater than 4.

[0025] Thirdly, the present invention provides a silver paste comprising silver crystal powder prepared by the method described in the first aspect.

[0026] In any embodiment, the silver paste is sintered to have a porous structure.

[0027] Fourthly, the present invention provides a method for preparing silver paste, comprising:

[0028] Ethyl cellulose, butyl carbitol acetate, and silver crystal powder prepared by the method of the first aspect or silver crystal powder provided by the second aspect are mixed and the viscosity is adjusted to obtain silver paste.

[0029] In any embodiment, the silver crystal powder, ethyl cellulose, and butyl carbitol acetate constitute 70-90 wt%, 1-10 wt%, and 9-20 wt% of the silver paste, respectively.

[0030] Fifthly, the present invention provides a silver paste provided in the third or fourth aspect for application on the electrode surface.

[0031] The method of applying silver paste to the electrode surface according to the present invention includes, but is not limited to, coating the electrode surface with silver paste and then curing it, which can improve the reliability of the corresponding electronic components.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. This invention uses silver sulfate instead of the more commonly used silver nitrate. Since silver sulfate has relatively low solubility and high stability in solution, the release rate of silver ions can be better controlled, making it easier to control the reaction rate and the size and morphology of the generated silver particles, resulting in more uniform silver particles.

[0034] 2. The silver crystal powder provided by the method of the present invention has good shrinkage characteristics, which can achieve tight packaging, thereby improving the reliability and stability of electronic components prepared using it. In addition, the good shrinkage performance is also conducive to the formation of conductive networks and improves conductivity.

[0035] 3. The silver crystal powder (111) provided by the method of the present invention has a high orientation, which can reduce scattering and obstruction and form a conductive network, which is more conducive to the transport of electrons in the crystal, thereby improving the conductivity of the silver powder;

[0036] 4. The silver paste provided by the present invention uses silver crystal powder with high orientation (111) and has a porous structure. These porous structures give the silver paste good flexibility, stress resistance and heat dissipation performance. In addition, the porous structure makes it contain a large number of pores. These pores can provide a certain buffer space when the material is subjected to external force or thermal stress, so that the silver paste can better adapt to stress changes caused by factors such as the difference in thermal expansion coefficient between different components, and avoid cracks, breakage and other problems, thereby improving the reliability and durability of the encapsulation connection. In addition, the high specific surface area brought by the porous structure can enhance the adhesion between the silver paste and the substrate.

[0037] 5. The preparation method of this invention uses low-temperature sintering, which is simple and has low energy consumption and cost. Attached Figure Description

[0038] Figure 1 This is a concept diagram of the reaction of this invention;

[0039] Figure 2 Here is a SEM image of the silver crystal powder synthesized in Example 1;

[0040] Figure 3 This is a particle size distribution diagram of the silver crystal powder synthesized in Example 1;

[0041] Figure 4 This is a graph showing the relationship between the concentration of gum arabic added in this invention and the D50 of silver powder;

[0042] Figure 5 These are the X-ray diffraction patterns of silver crystal powder in Example 1 and Comparative Example 1;

[0043] Figure 6 These are the differential thermogravimetric curves of silver crystal powder in Example 1 and Comparative Example 1;

[0044] Figure 7 These are the shrinkage curves of the silver paste prepared from silver powder in Example 4 and Comparative Example 2;

[0045] Figure 8 This is the relationship between the firing temperature and resistivity of the silver paste prepared from silver powder in Example 4;

[0046] Figure 9 These are SEM images of the silver paste sintered structures prepared from silver powder in Example 4 and Comparative Example 2. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0048] This application provides a method for preparing silver crystal powder, the method being:

[0049] Silver sulfate and a reducing agent are added to an acidic solution of a protective agent, and a reduction reaction is carried out under heating and stirring conditions to obtain silver crystal powder. This method can solve the problems of insufficient shrinkage and crystallization properties of silver powder prepared by existing methods.

[0050] This invention uses silver sulfate instead of the more commonly used silver nitrate. Since silver sulfate has relatively low solubility and high stability in solution, the release rate of silver ions can be better controlled, making it easier to control the reaction rate and the size and morphology of the generated silver particles, resulting in more uniform silver particles.

[0051] In any embodiment, the protective agent is at least one of gum arabic, propyl cellulose, ethyl cellulose, and polyvinylpyrrolidone;

[0052] The protective agent of this invention adsorbs onto the surface of the generated silver particles, which helps to prevent the silver particles from agglomerating, control the growth of silver particles, and ultimately affect the morphology, particle size and properties of silver powder.

[0053] Preferably, the protective agent is gum arabic;

[0054] Gum arabic exhibits excellent dispersibility, effectively dispersing silver particles in solution and preventing particle aggregation and precipitation. This helps control the size of silver particles and improves the uniformity and stability of silver powder, ensuring product quality. Furthermore, gum arabic displays stable chemical properties in acidic solutions, resisting decomposition or deterioration, which helps maintain the stability of the reaction system, reduces side reactions, and improves product purity and yield. Additionally, compared to some other chemically synthesized protective agents, gum arabic has a smaller environmental impact and higher safety. Using gum arabic as a protective agent can also improve the tap density and monodispersity of silver powder.

[0055] As an example, when gum arabic is chosen as the protective agent in this invention, and the concentration ratio of reducing agent (R) and silver sulfate (M) is maintained at a constant level, the particle size variation of the prepared silver crystal powder is as follows: Figure 4 .Depend on Figure 4It can be seen that if R / M = 1, increasing the gum arabic concentration will change the D50 from 1,300 nm to 500 nm, indicating that the gum arabic concentration has a significant effect on the particle size of the prepared silver crystal powder.

[0056] In any embodiment, the reducing agent is selected from at least one of ascorbic acid, hydrazine, hydroquinone, phenylhydrazine, and formalin;

[0057] Preferably, the reducing agent is ascorbic acid; ascorbic acid has suitable reducing properties, which helps to better control the reaction rate and product quality during the preparation process. In addition, when ascorbic acid is used as a reducing agent, the reaction process is relatively easy to control, which is beneficial to producing silver powder particles with uniform particle size distribution and regular shape; ascorbic acid has less impact on the environment and poses less health risk to operators.

[0058] In any embodiment, the heating temperature is 30-80°C, and the reaction time is 1-5 hours;

[0059] The reaction process of this invention employs low-temperature sintering. During low-temperature sintering, the organic components in the porous silver paste are more easily volatilized and decomposed, allowing the silver particles to better connect and fuse together, forming a dense conductive structure. The lower sintering temperature can reduce thermal damage to sensitive components such as chips, reduce energy consumption during the packaging process, and facilitate large-scale and automated production.

[0060] In any embodiment, the stirring is performed using a stirrer. The type of stirrer is not limited here, but examples include magnetic stirrers or bladed mixers. The intensity of the stirring is also not limited, as long as it is sufficient to thoroughly mix the solution without it spilling out of the container.

[0061] In any embodiment, the molar ratio of the reducing agent to silver sulfate is 0.5-2;

[0062] The reducing agent of this invention reduces silver ions to metallic silver. The amount of reducing agent affects the rate and efficiency of the reduction reaction, and thus the purity and yield of the silver powder. Excessive reducing agent will broaden the particle size distribution of the silver powder, affecting its uniformity and consistency, and may also trigger side reactions, generating unnecessary impurities or byproducts. These impurities may reduce the purity and conductivity of the silver powder. Insufficient reducing agent will lead to incomplete reaction, thereby reducing the yield and recovery rate of silver powder. Furthermore, due to incomplete reaction, the generated silver particles may have irregular shapes and larger particle sizes, affecting the physical and chemical properties of the silver powder. However, depending on the reaction volume or the concentration of silver sulfate, when the size of the reaction vessel and the concentration of silver sulfate are appropriate, the molar ratio can also be below 0.5 or above 2.0.

[0063] In any embodiment, the concentration of the added silver sulfate dispersion is 0.01–1 mol / dm³. 3 ;

[0064] In this invention, silver sulfate is used as a source of silver ions. The amount added affects the concentration of silver ions in the reaction system. The concentration of silver sulfate in the dispersion is controlled to be 0.01–1 mol / dm³. 3 This ensures the smooth progress of the reaction, while values ​​greater or less than this may affect the yield and purity of the silver powder.

[0065] In any embodiment, the concentration of the added protective agent is 1 g / L to 20 g / L;

[0066] In any embodiment, the mass ratio of added silver sulfate to protective agent is (0.01-0.2):1.

[0067] The protective agent of this invention plays a role in stabilizing silver particles and preventing agglomeration during the reaction. By controlling the concentration and amount of the protective agent, the particle size and morphology of silver powder can be effectively controlled, thereby improving the dispersibility and stability of silver powder.

[0068] In any embodiment, the organic solvent does not contain hydroxyl groups, and there is no specific limitation; for example, acetone is given.

[0069] The present invention does not use organic solvents containing hydroxyl groups because solvents containing hydroxyl groups will cause sulfates to hydrolyze.

[0070] In any embodiment, the solvent in the acidic solution and the silver sulfate dispersion is selected from water or an organic solvent; and the pH of the acidic solution and the silver sulfate dispersion is controlled to be below 2; the present invention adjusts the pH to be below 2 by adding sulfuric acid;

[0071] Preferably, the pH of the acidic solution and the silver sulfate dispersion is below 1;

[0072] See Figure 1 When the pH is below 1, the solubility of the solution becomes very high, resulting in a uniform state of metal ions in the early stages of nucleation, while the precipitation rate generally decreases. If the precipitation rate decreases, there are fewer crystal nuclei, and the crystallinity of the silver particles increases as they grow.

[0073]

[0074] In equation (1), V is the rate of precipitation, S is the solubility of the precipitate, Q is the amount of precipitate in the solution, and K is a constant.

[0075] According to the above formula, the precipitation rate depends on the supersaturation. The greater the supersaturation or the lower the solubility of the precipitate, the greater the precipitation rate. As a result, the number of crystal nuclei increases and the particles become smaller.

[0076] This invention improves the solubility of silver sulfate by controlling the acidity of the acidic solution, thereby slowing down the precipitation rate, reducing the size of the crystal nuclei, promoting subsequent particle growth, and generating highly crystalline silver particles.

[0077] Secondly, the present invention provides a silver crystal powder prepared by the method described above.

[0078] In any embodiment, the intensity ratio I of the silver crystal in the (111) and (200) directions is... (111) / I (200) Greater than 4.

[0079] Thirdly, the present invention provides a silver paste comprising silver crystal powder prepared by the method described in the first aspect.

[0080] In any embodiment, the silver paste has a porous structure.

[0081] Fourthly, the present invention provides a method for preparing silver paste, comprising:

[0082] Ethyl cellulose, butyl carbitol acetate, and the silver crystal powder prepared by the first aspect of the above method or the silver crystal powder provided by the second aspect are mixed, and the viscosity is adjusted to obtain silver paste.

[0083] In any embodiment, the silver crystal powder, ethyl cellulose, and butyl carbitol acetate constitute 70-90 wt%, 1-10 wt%, and 9-20 wt% of the silver paste, respectively.

[0084] The present invention will be described below through specific embodiments.

[0085] Unless otherwise specified, the reagents used in the embodiments and comparative examples of this invention are all conventionally procured, and there are no special requirements regarding the manufacturer or model. Furthermore, the preparation methods of the acidic solutions of the protective agents in the following embodiments and comparative examples are all conventional methods. Specifically, the protective agent is added to the solvent, the pH of the solution is measured, and then the pH value of the solution is adjusted by using sulfuric acid with a mass fraction of 70% to make the acidity or alkalinity meet the set requirements. The pH value of the silver sulfate dispersion is also adjusted by using sulfuric acid with a mass fraction of 70% to make the acidity or alkalinity meet the set requirements.

[0086] Example 1

[0087] This embodiment provides an example of the preparation of silver crystal powder:

[0088] Add 0.05 mol / dm³ to an acidic aqueous solution of 10 g / L gum arabic (pH 1). 3A dispersion of silver sulfate (pH 1) and ascorbic acid were mixed, with the molar ratio of ascorbic acid to silver sulfate being 1 and the mass ratio of silver sulfate to protective agent being 0.05. The mixture was stirred at 500 rpm for 1 hour at 50°C. A 48% sodium hydroxide aqueous solution was added, and the mixture was washed at 80°C for 2 hours. Ammonium nitrate was added for neutralization. The supernatant was removed from the powder that had settled naturally by decantation. The supernatant was then replaced with acetone as a solvent, and the mixture was dried at 35°C for 1 day to obtain silver crystalline powder.

[0089] Comparative Example 1

[0090] This comparative example provides an example of the preparation of silver crystal powder:

[0091] Add 0.05 mol / dm³ to an acidic aqueous solution containing gum arabic (pH 1). 3 A dispersion of silver nitrate (pH 1) and ascorbic acid were mixed, with the molar ratio of ascorbic acid to silver nitrate being 1 and the mass ratio of silver sulfate to protective agent being 0.05. The mixture was stirred at 500 rpm for 1 hour at 50°C. A 48% sodium hydroxide aqueous solution was added, and the mixture was washed at 80°C for 2 hours. Ammonium nitrate was then added for neutralization. The supernatant was removed from the powder that had settled naturally by decantation. The supernatant was then replaced with acetone as a solvent, and the mixture was dried at 35°C for 1 day to obtain silver crystalline powder.

[0092] Figure 2 This is a SEM image of the silver crystal powder prepared in Example 1. (From...) Figure 2 It can be seen that the silver powder prepared in this embodiment is spherical and dispersed in a monodisperse state;

[0093] Figure 3 Example 1 shows the particle size distribution of silver powder as determined by a laser diffractometer. The median particle size (D50) based on volume is 610 nm.

[0094] Figure 5 These are X-ray diffraction patterns of silver crystal powders obtained in Example 1 and Comparative Example 1, determined by powder X-ray diffraction. (a) is the X-ray diffraction pattern of silver powder obtained from sulfate in Example 1, and (b) is the X-ray diffraction pattern of silver powder obtained from silver nitrate in Comparative Example 1. Figure 5 It can be seen that, under the same conditions, using silver sulfate as the silver source, the intensity in the (111) and (200) directions is greater than that in I. (111) / I (200) The value is 4.19; using silver nitrate as the silver source, the intensity ratio in the (111) and (200) directions is higher than that in I. (111) / I (200) The value is 3.87; therefore, the silver powder obtained when silver sulfate is used as the silver source has a high crystal orientation.

[0095] Figure 6(a) and (b) are the differential thermal analysis (DTA) and thermogravimetric (TG) curves of the silver crystal powders in Example 1 and Comparative Example 1, respectively, measured using a differential thermal gravimetric analyzer. According to the DTA, exothermic peaks accompanied by a decrease in TG are observed at 320°C in (a) and at 260°C in (b). This indicates that the silver crystal powder prepared using silver sulfate as a raw material has better heat resistance.

[0096] Example 2

[0097] This embodiment provides an example of the preparation of silver crystal powder:

[0098] Add 0.01 mol / dm³ to an acidic aqueous solution of 1 g / L propyl cellulose (pH 1.8). 3 A dispersion of silver sulfate (pH 1.8) and hydrazine were mixed to achieve a molar ratio of ascorbic acid to silver sulfate of 0.5 and a mass ratio of silver sulfate to propyl cellulose of 0.01. The mixture was stirred at 700 rpm for 5 hours at 30°C. A 48% sodium hydroxide aqueous solution was added, and the mixture was washed at 80°C for 2 hours. Ammonium nitrate was added for neutralization. The supernatant was removed from the naturally settled powder by decantation. The supernatant was then replaced with acetone as a solvent, and the powder was dried at 35°C for 1 day to obtain silver crystalline powder.

[0099] Upon testing, the silver crystal powder I obtained in this embodiment... (111) / I (200) It is 4.01;

[0100] Example 3

[0101] This embodiment provides an example of the preparation of silver crystal powder:

[0102] Add 1 mol / dm³ to an acidic aqueous solution of 1 g / L polyvinylpyrrolidone (pH 2.0). 3 A dispersion of silver sulfate (pH 2.0) and hydroquinone were mixed, with the molar ratio of ascorbic acid to silver sulfate being 2 and the mass ratio of silver sulfate to polyvinylpyrrolidone being 0.2. The mixture was stirred at 80°C and 800 rpm for 2 hours. A 48% sodium hydroxide aqueous solution was added, and the mixture was washed at 80°C for 2 hours. Ammonium nitrate was then added for neutralization. The supernatant was removed from the naturally settled powder by decantation, and the solution was replaced with acetone. The powder was dried at 35°C for 1 day to obtain silver crystalline powder.

[0103] Upon testing, the silver crystal powder I obtained in this embodiment... (111) / I (200) It is 4.05.

[0104] Example 4 and Comparative Example 2

[0105] This embodiment provides an example of the preparation of silver paste:

[0106] Silver crystal powder, ethyl cellulose, and butyl carbitol acetate were mixed in a weight ratio of 85 wt%: 2 wt%: 13 wt%. The viscosity of the paste was adjusted to approximately 200 Pa·s to obtain a silver paste. The silver paste was then coated onto a PET film with a thickness of approximately 250 μm using a doctor blade and dried at 100°C for 2 hours. In Example 4, the silver crystal powder used was the silver crystal powder prepared in Example 1, and in Comparative Example 2, the silver crystal powder used was the silver crystal powder prepared in Comparative Example 1.

[0107] Figure 7 (a) and (b) are the shrinkage curves of the silver paste in Example 4 and Comparative Example 2, respectively, measured by a thermomechanical analysis apparatus (TMA). The test results show that (a) has a shrinkage rate of 6% at 600°C, and (b) has a shrinkage rate of 15%, indicating that it has a strength ratio of I. (111) / I (200) Silver crystal powder with an orientation of 4 or higher has superior heat resistance, which also shows that the technical solution of the present invention improves the shrinkage characteristics of existing silver crystal powder.

[0108] Figure 8 The resistivity value is obtained by firing the silver paste in Example 4 of this invention at 400℃~900℃ for 10 minutes. Figure 8 The resistivity of the silver paste in Example 4 at 400°C is shown to be 4.16 × 10⁻⁶. -6 (·cm), while the resistivity at 900℃ decreases to 2.3×10⁻⁶. -6 (·cm). This indicates that the silver paste prepared in Example 4 has good thermal stability and excellent high-temperature electrical conductivity.

[0109] Furthermore, the SEM observation results of the sintered bodies obtained by firing the silver paste obtained in Example 4 and Comparative Example 2 at 900°C for 10 minutes are respectively referred to [reference needed]. Figure 9 (a) and (b). Figure 9 (a) shows that the silver paste sintered body of Example 4 has many pores and is a porous body; Figure 9 (b) shows that the sintered silver paste of Comparative Example 2 has a dense structure, which indicates that the porous material of the silver paste prepared by the method of the present invention improves the adhesion to the ceramic substrate and exhibits the characteristic of being difficult to crack.

[0110] Examples 5-6

[0111] Silver crystal powder, ethyl cellulose, and butyl carbitol acetate were mixed in a weight ratio of 73 wt%: 6 wt%: 11 wt%. The viscosity of the paste was adjusted to approximately 200 Pa·s to obtain a silver paste. The silver paste was then coated onto a PET film with a thickness of approximately 250 μm using a doctor blade and dried at 100°C for 2 hours. In Example 5, the silver crystal powder used was the silver crystal powder prepared in Example 2, and in Example 6, the silver crystal powder used was the silver crystal powder prepared in Example 3.

[0112] The silver pastes prepared in Examples 5 and 6 also exhibited a porous structure after sintering at 900°C. Furthermore, the properties of the silver pastes obtained in Examples 5 and 6 were tested, and their resistivity at 400°C was 4.3 × 10⁻⁶. -6 W·cm and 4.4×10 - 6 The resistivity at 900℃ is 2.4 × 10 W·cm. -6 The shrinkage curve of the silver paste was determined by a thermomechanical analysis device (TMA) at W·cm. The test results showed that the shrinkage rate of the silver paste in Examples 5 and 6 at 600°C was about 6%.

[0113] In summary, the silver nanoparticles prepared by the method of this invention have uniform particle size and good thermal shrinkage and crystallization properties. The silver paste prepared using these nanoparticles has a porous structure and good electrical conductivity and heat resistance, showing promising application prospects.

[0114] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing silver crystal powder, characterized in that, include: Silver sulfate and a reducing agent are added to an acidic solution of a protective agent, wherein the pH of the acidic solution is ≤2. A reduction reaction is carried out under heating and stirring conditions at 30~80℃ to obtain silver crystal powder. The ratio of the X-ray diffraction intensity of the silver crystal powder in the (111) and (200) directions is I. （111） / I （200） >4; The solvent for the acidic solution is water or an organic solvent that does not contain hydroxyl groups.

2. The method for preparing silver crystal powder according to claim 1, characterized in that, The protective agent is at least one of gum arabic, propyl cellulose, ethyl cellulose, and polyvinylpyrrolidone.

3. The method for preparing silver crystal powder according to claim 1, characterized in that, The reducing agent is selected from at least one of ascorbic acid, hydrazine, hydroquinone, phenylhydrazine, and formalin.

4. The method for preparing silver crystal powder according to claim 1, characterized in that, Silver sulfate was added in the form of a silver sulfate dispersion with a concentration of 0.01 mol / dm³. 3 -1mol / dm 3 .

5. The method for preparing silver crystal powder according to claim 1, characterized in that, The pH of the acidic solution is ≤1, and is adjusted by adding sulfuric acid.

6. The method for preparing silver crystal powder according to claim 1, characterized in that, The concentration of the protective agent in the acidic solution is 1 g / L-20 g / L, and the mass ratio of silver sulfate to the protective agent is (0.01-0.2):

1.

7. The method for preparing silver crystal powder according to claim 1, characterized in that, The organic solvent is acetone.

8. The method for preparing silver crystal powder according to claim 1, characterized in that, The reaction time is 1-5 hours, and the stirring speed is 500, 700, or 800 rpm.

9. The method for preparing silver crystal powder according to claim 8, characterized in that, The molar ratio of the reducing agent to silver sulfate is 0.5-2:

1.

10. A silver crystal powder, characterized in that, The silver crystal powder prepared by the method according to any one of claims 1-9 has an X-ray diffraction intensity ratio I in the (111) and (200) directions. （111） / I （200） >4.

11. A silver paste, characterized in that, The mixture includes silver crystal powder prepared by the method according to any one of claims 1-9, ethyl cellulose, and butyl carbitol acetate, wherein the silver crystal powder accounts for 70-90 wt% by mass.

12. The silver paste according to claim 11, characterized in that, The silver paste has a porous structure after sintering.

13. A method for preparing silver paste, characterized in that, include: Ethyl cellulose, butyl carbitol acetate, and the silver crystal powder according to claim 10 are mixed and the viscosity is adjusted to obtain silver paste.

14. A silver paste according to claim 12, characterized in that, It is applied to the electrode surface.

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