Preparation method of sphere-like silver powder and sphere-like silver powder

Abstract

The invention provides a preparation method of sphere-like silver powder and the sphere-like silver powder. The preparation method comprises the steps that an oxidation solution with the pH value within a first pH range and a reduction solution with the pH value within a second pH range are prepared; dissolving an auxiliary agent with ethanol to prepare an auxiliary agent solution; dissolving a surfactant with ethanol to obtain an active agent solution; dropwise adding an auxiliary agent solution into the oxidation solution in a stirring state to obtain a first reaction solution; continuously stirring the first reaction solution for a first period of time, and adding a reducing solution into the first reaction solution for a second period of time to obtain a second reaction solution; and after the second reaction solution is controlled to react for a third time period, the active agent solution is dropwise added into the second reaction solution within a fourth time period to obtain a silver powder suspension, and the silver powder suspension is cleaned and dried to obtain the silver powder. According to the preparation method of the spheroidic silver powder, the spheroidic silver powder is prepared by adjusting the pH value of the oxidation solution and the pH value of the reduction solution and combining the auxiliaries, the preparation process is simple, and the shape of the silver powder is controllable.

Description

Technical Field

[0001] This application relates to the field of precious metal new material preparation technology, and in particular to a method for preparing spherical silver powder and spherical silver powder. Background Technology

[0002] Silver powder, due to its excellent electrical and thermal conductivity, has wide applications in the electronics industry, catalysts, antibacterial materials, conductive inks, and coatings. In the silver powder industry, flake-shaped and spherical silver powders are the two most common types. The unique properties of flake-shaped silver powder make it promising for applications in conductive materials, EMI shielding, thermal interfaces, microelectronic packaging, and photovoltaic cells. It provides a reliable material solution for various high-performance electronic products and industrial applications. Existing methods for preparing near-spherical silver powder involve complex processes and exhibit low stability in powder shape. Summary of the Invention

[0003] This application provides a method for preparing near-spherical silver powder and near-spherical silver powder, aiming to solve the problems of complex processes and low stability of silver powder shape in existing near-spherical silver powder preparation methods.

[0004] In a first aspect, this application provides a method for preparing spherical silver powder, the method comprising: An oxidizing solution with a pH value in the first pH range and a reducing solution with a pH value in the second pH range were prepared respectively. The auxiliary agent is dissolved in ethanol to prepare an auxiliary agent solution; The surfactant is dissolved in ethanol to obtain an surfactant solution; The auxiliary agent solution is added dropwise to the oxidizing liquid under stirring to obtain the first reaction solution; After continuously stirring the first reaction solution for a first time, the reducing solution is added to the first reaction solution during a second time to obtain the second reaction solution; After controlling the reaction of the second reaction solution for a third time, the activator solution is added dropwise to the second reaction solution for a fourth time to obtain a silver powder suspension. The silver powder suspension is then washed and dried to obtain the silver powder.

[0005] In some possible embodiments, the preparation of the oxidizing solution with a pH value in a first pH range and the reducing solution with a pH value in a second pH range includes: Dissolve silver nitrate in deionized water to prepare an initial silver nitrate solution; A pH control agent is added to the initial silver nitrate solution to adjust the pH value of the initial silver nitrate solution to a first pH range, thereby obtaining the oxidation solution, and the solution temperature of the oxidation solution is adjusted to a first temperature range. Dissolve the reducing agent in deionized water to prepare the initial reducing solution; A pH control agent is added to the initial reducing solution to adjust the pH value of the initial reducing solution to a second pH range, thereby obtaining the reducing solution, and the solution temperature of the reducing solution is adjusted to a second temperature range.

[0006] In some possible embodiments, the pH control agent is one or more of nitric acid, oxalic acid, dilute sulfuric acid, sodium hydroxide, triethanolamine, ethylenediamine, diethylamine, triethylamine, ammonia, and ethanolamine.

[0007] In some possible embodiments, the mass concentration of silver nitrate in the oxidizing solution is 5-25%, and the mass concentration of the reducing agent in the reducing solution is 3-15%.

[0008] In some possible embodiments, the mass of the auxiliary agent is 1-10% of the mass of the silver nitrate, and the mass of the surfactant is 0.1-10% of the mass of the silver nitrate.

[0009] In some possible embodiments, the first pH range is 1-3, and the second pH range is 2-8.

[0010] In some possible embodiments, the surfactant is one or more of the following: ethylene glycol monostearate, zinc stearate, aluminum monostearate, ethylene glycol distearate, glyceryl tristearate, polyethylene glycol monostearate, dodecyl stearate, methyl stearate, 12-hydroxystearic acid, sorbitan stearate, stearic acid, lauric acid, and oleic acid.

[0011] In some possible embodiments, the second duration is 1-10 seconds.

[0012] In some possible embodiments, the third duration is 1-10 min, and the fourth duration is 0-5 min.

[0013] Secondly, this application provides a quasi-spherical silver powder, which is prepared according to the quasi-spherical silver powder preparation method described in any of the preceding claims.

[0014] This application provides a method for preparing near-spherical silver powder and the near-spherical silver powder itself, comprising: preparing an oxidizing solution with a pH value in a first pH range and a reducing solution with a pH value in a second pH range; dissolving an auxiliary agent in ethanol to obtain an auxiliary agent solution; dissolving a surfactant in ethanol to obtain an surfactant solution; adding the auxiliary agent solution dropwise to the oxidizing solution under stirring to obtain a first reaction solution; after continuously stirring the first reaction solution for a first time, adding the reducing solution to the first reaction solution for a second time to obtain a second reaction solution; controlling the reaction of the second reaction solution for a third time, adding the surfactant solution dropwise to the second reaction solution for a fourth time to obtain a silver powder suspension; and washing and drying the silver powder suspension to obtain silver powder. The near-spherical silver powder preparation method provided by this application, by adjusting the pH values ​​of the oxidizing and reducing solutions and combining with auxiliary agents, prepares near-spherical silver powder. The preparation process is simple and the shape of the silver powder is controllable. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic flowchart of an embodiment of the method for preparing spherical silver powder provided in this application; Figure 2 This is a scanning electron microscope image of silver powder from Embodiment 1 of this application; Figure 3 This is a scanning electron microscope image of silver powder from Embodiment 2 of this application; Figure 4 This is a scanning electron microscope image of silver powder from Embodiment 3 of this application; Figure 5 This is a scanning electron microscope image of silver powder from Embodiment 4 of this application. Detailed Implementation

[0017] 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 a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0018] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0019] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0020] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0021] The following disclosure provides many different embodiments or examples for implementing different structures of this application. To simplify the disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the scope of this application. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, various specific examples of processes and materials are provided in this application, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0022] like Figure 1 The diagram shown is a flowchart of an embodiment of the method for preparing spherical silver powder provided in this application, which may include the following steps: 10. Prepare an oxidizing solution with a pH value in the first pH range and a reducing solution with a pH value in the second pH range.

[0023] This application primarily utilizes an oxidizing solution and a reducing solution to prepare silver powder via a redox reaction. Therefore, it is necessary to prepare the oxidizing solution and the reducing solution separately. Specifically, silver nitrate can be dissolved in deionized water to prepare an initial silver nitrate solution, and a reducing agent can be dissolved in deionized water to prepare an initial reducing solution. The method for preparing near-spherical silver powder provided in this application can control the size of the near-spherical silver powder, mainly by adjusting the pH values ​​of the oxidizing and reducing solutions. Therefore, it is also necessary to add a pH control agent to the initial silver nitrate solution to adjust its pH value to a first pH range to obtain the oxidizing solution, and to add a pH control agent to the initial reducing solution to adjust its pH value to a second pH range to obtain the reducing solution.

[0024] The first pH range is 1-3, such as 1, 1.5, 2.0, 2.5, 3.0, etc.; the second pH range is 2-8, such as 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, etc. Adjusting the pH of different solutions affects the solubility of substances in the solution, thus influencing the final product. In the method for preparing spherical silver powder provided in this application, after preparing the initial oxidation solution, the pH of the initial oxidation solution is first adjusted to the first pH range. When the auxiliary agent solution is subsequently added to the pH-adjusted oxidation solution, the solubility of the auxiliary agent in the oxidation solution can be changed, thereby altering the properties of the silver powder obtained from the subsequent redox reaction. For the oxidation solution, when the pH fluctuates within the first pH range, the lower the pH of the oxidation solution, the higher the solubility of the auxiliary agent in the oxidation solution, which is beneficial for the formation of silver powder. In some embodiments, the pH control agent may be one or more selected from nitric acid, oxalic acid, dilute sulfuric acid, sodium hydroxide, triethanolamine, ethylenediamine, diethylamine, triethylamine, ammonia, and ethanolamine. The reducing agent used to prepare the reducing solution may be one or more selected from glucose, sodium borohydride, formaldehyde, and ascorbic acid.

[0025] In the above embodiments, after preparing the oxidizing solution and the reducing solution respectively, it is necessary to adjust the solution temperature of the oxidizing solution within a first temperature range and the solution temperature of the reducing solution within a second temperature range. This is because the solution temperature also affects the solubility of the solvent in the solution, thereby affecting the subsequent reaction process. Therefore, it is necessary to adjust the solution temperature of the oxidizing solution to 5-25℃, that is, the first solution temperature range is 5-25℃; for example, the first solution temperature is 5℃, 10℃, 15℃, 20℃, 25℃, etc. The solution temperature of the reducing solution is also adjusted to the range of 5-25℃, that is, the second solution temperature range is also 5-25℃; for example, the second solution temperature is 5℃, 10℃, 15℃, 20℃, 25℃, etc. For the oxidizing solution, since the silver powder preparation method provided in this application also prepares an auxiliary agent solution, and the auxiliary agent needs to be added dropwise to the oxidizing solution; when the temperature of the oxidizing solution fluctuates within the first temperature range, the higher the solution temperature of the oxidizing solution, the higher the solubility of the auxiliary agent in the oxidizing solution, which is beneficial to the formation of silver powder.

[0026] 20. Dissolve the auxiliary agent in ethanol to prepare an auxiliary agent solution.

[0027] The silver powder preparation method of this application also requires the addition of an auxiliary agent solution to help control the size and shape of the silver powder. This is because the auxiliary agent can combine with silver ions and form microemulsions of different sizes under the action of surface energy, thereby obtaining initial silver microcrystals of different sizes in the subsequent redox reaction. Therefore, the auxiliary agent can be dissolved in ethanol solution to prepare an auxiliary agent solution; the auxiliary agent solution will change the size and shape of the silver powder. The specific process of the auxiliary agent solution participating in the redox reaction is described in detail in the subsequent embodiments and is not limited here. It should be noted that in this application, an excess of auxiliary agent solution is usually added to the oxidizing solution to ensure that the auxiliary agent combines with as many silver ions as possible. The auxiliary agent will combine with the silver ions in the oxidizing solution under the action of surface energy to obtain microemulsions of different sizes. When the auxiliary agent solution is in excess, the microemulsion will partially separate and remain suspended in the oxidizing solution.

[0028] In some embodiments, the additive can be one or more of benzoic acid, phenylpropionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, lauric acid, stearic acid, oleic acid, and trisodium hypotriacetate. The mass of the additive in this application can be 1-10% of the mass of silver nitrate; for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, etc. For the additives provided in this application, the longer the carbon chain of the additive, the larger the size of the microemulsion formed. Therefore, additives with different carbon chain lengths can be selected according to actual needs to obtain microemulsions of different sizes, thereby obtaining silver powder of different sizes. Simultaneously, combined with the method of controlling the silver powder size by adjusting the solution temperature of the oxidation solution and the pH value of the oxidation and reduction solutions in the foregoing embodiments, this application can simultaneously adjust the solution temperature of the oxidation solution, adjust the pH value of the oxidation and reduction solutions, and select different additives to adjust the final silver powder size and shape.

[0029] 30. Dissolve the surfactant in ethanol to obtain an surfactant solution.

[0030] The surfactant solution provided in this application can control the coating of surfactant molecules on the surface of silver powder particles generated by the redox reaction during silver powder preparation, preventing excessive particle growth and thus controlling the size and shape of the silver powder. Simultaneously, the surfactant molecules present on the surface of the silver powder can impart a certain degree of hydrophobicity, facilitating subsequent preparation of photovoltaic silver paste.

[0031] 40. Add the auxiliary agent solution dropwise to the oxidizing liquid under stirring to obtain the first reaction solution.

[0032] 50. After continuously stirring the first reaction solution for a first time, add the reducing solution to the first reaction solution during a second time to obtain the second reaction solution.

[0033] In this application, the additive solution needs to be added to the oxidizing liquid first to ensure that the additive is fully dissolved in the oxidizing liquid before the subsequent redox reaction. Therefore, the additive solution needs to be added dropwise to the oxidizing liquid under stirring to obtain the first reaction solution. The first reaction solution also needs to be continuously stirred for a first time to ensure that the additive solution and the oxidizing liquid are fully mixed and to improve the solubility of the additive in the oxidizing liquid. For this application, the additive solution can be added to the oxidizing liquid dropwise, thus improving the solubility of the additive in the oxidizing liquid and ensuring that the additive and the oxidizing liquid are fully mixed.

[0034] After continuously stirring the first reaction solution for a first time, a reducing solution can be added to the first reaction solution to obtain a second reaction solution. The oxidizing and reducing solutions in the second reaction solution will undergo a redox reaction to produce silver powder. At this time, the additives dissolved in the second reaction solution will regulate the morphology of the generated silver powder. Specifically, after the oxidizing and reducing solutions undergo a redox reaction to obtain silver particles, the additives can combine with silver ions and form microemulsions of different sizes under the action of surface energy. When subsequent redox reactions are carried out, they actually undergo redox reactions with the silver ions in the microemulsions to obtain initial silver microcrystals of different sizes. When the initial silver microcrystals reach a certain concentration, they will aggregate to form submicron-sized silver powder. Therefore, silver powder of different sizes can be obtained using an additive solution.

[0035] In this application, the reducing solution is typically added to the first reaction solution within a second time period, which is usually 1-10 seconds, such as 1 second, 2 seconds, 3 seconds, 4 seconds, 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds, 10 seconds, etc. For this application, it is generally necessary to rapidly add the reducing solution to the first reaction solution within a short time to increase the reaction rate and ensure the size and shape of the silver powder.

[0036] 60. After controlling the reaction time of the second reaction solution for a third time, the activator solution is added dropwise to the second reaction solution during the fourth time to obtain a silver powder suspension. The silver powder suspension is then washed and dried to obtain silver powder.

[0037] In the aforementioned embodiments, the reducing solution is added to the first reaction solution during a second time interval to obtain a second reaction solution. A redox reaction then occurs in the second reaction solution to produce silver powder. After the second reaction solution continues to react for a third time interval, a silver powder suspension containing the desired silver powder is obtained. At this point, the silver powder is dispersed and suspended in the second reaction solution after the reaction. It is necessary to separate the silver powder from this suspension to obtain the final spherical silver powder. Therefore, the second reaction solution can be rotated at a speed of 400 r / min-600 r / min, and the surfactant solution can be added to the second reaction solution after the reaction for a fourth time interval to disperse the generated silver powder. Specifically, adding the surfactant solution to the second reaction solution allows surfactant molecules to coat the surface of the silver powder particles, preventing excessive particle growth. After obtaining the silver powder suspension, it needs to be washed and dried to obtain the final silver powder. In some embodiments, the second reaction solution can be rotated at speeds of 400 r / min, 450 r / min, 500 r / min, 550 r / min, 600 r / min, etc. In some embodiments, the third duration can be 1-10 minutes, such as 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, etc. In some embodiments, the fourth duration can be 0-5 minutes, such as 0.5 minutes, or 1 minute, or 1.5 minutes, or 2 minutes, or 2.5 minutes, or 3 minutes, or 3.5 minutes, or 4 minutes, or 4.5 minutes, or 5 minutes, etc.

[0038] After the activator solution is completely added to the second reaction solution and the two are thoroughly mixed, the silver powder suspension is subjected to processes such as sedimentation, washing, filtration, drying, and grinding to obtain submicron silver powder. The submicron silver powder typically has a spherical structure. Specific methods for sedimentation, washing, filtration, drying, and grinding of the silver powder can be found in existing technologies and will not be elaborated in this application.

[0039] The method for preparing spherical silver powder provided in this application has a simple process, high production efficiency, and good stability, which is conducive to the stable batch production of submicron silver powder in industrial production. It also avoids the addition of macromolecular dispersants, reduces the chemical oxygen demand in wastewater, and lowers wastewater treatment costs. At the same time, the initial microcrystals of the silver powder are small, the melting point is low, and the conductivity is good. The submicron silver powder preparation method provided by this invention has controllable morphology, producing spherical or spherical shapes, with no hard agglomerates and good dispersion.

[0040] The method for preparing spherical silver powder provided in this application will be described in detail below with reference to specific embodiments.

[0041] Example 1: Weigh 1.6 kg of silver nitrate solid and mix it with deionized water to prepare an initial silver nitrate solution with a mass fraction of 8%. Add nitric acid to the initial silver nitrate solution to obtain a silver nitrate solution with a pH of 2; simultaneously, control the temperature of the silver nitrate solution at 15°C. Weigh 0.86 kg of ascorbic acid as a reducing agent and mix it with deionized water to prepare an initial reducing solution with a mass concentration of 4.5%. Adjust the pH of the initial reducing solution to 2 to obtain the reducing solution; simultaneously, control the temperature of the reducing solution at 15°C. Weigh 0.05 kg of butyric acid as an auxiliary agent, dissolve it in ethanol, and prepare an auxiliary agent solution with a mass concentration of 2.5%. Weigh lauric acid as a surfactant, dissolve it in ethanol, and prepare a lauric acid-ethanol solution.

[0042] Add the auxiliary agent solution to the silver nitrate solution to obtain the first reaction solution. Maintain the temperature of the first reaction solution at 15°C and the stirring speed at 500 rpm. Quickly add the reducing solution to the oxidizing solution to obtain the second reaction solution; control the addition time to 2 seconds. After the addition is complete, continue the reaction for 2 minutes, then add a 1.6% (w / w) lauric acid-ethanol solution to the second reaction solution. After reacting for 10 min, the mixture was washed with deionized water and ethanol, and the supernatant was filtered. The filtered silver powder was dried at 60℃ for 30 min, and then passed through a 500-mesh sieve to obtain the final silver powder. The actual particle size D50 of the obtained silver powder was 1.5 μm, and the specific surface area was 0.50 m² / g. Scanning electron microscopy images are shown below. Figure 2 .

[0043] Example 2: Weigh 1.6 kg of silver nitrate solid and mix it with deionized water to prepare an initial silver nitrate solution with a mass fraction of 8%. Add nitric acid to the initial silver nitrate solution to obtain a silver nitrate solution with a pH of 2; simultaneously, control the temperature of the silver nitrate solution at 15°C. Weigh 0.86 kg of ascorbic acid as a reducing agent and mix it with deionized water to prepare an initial reducing solution with a mass concentration of 4.5%. Adjust the pH of the initial reducing solution to 2 to obtain the reducing solution; simultaneously, control the temperature of the reducing solution at 15°C. Weigh 0.05 kg of octanoic acid as an auxiliary agent, dissolve it in ethanol, and prepare an auxiliary agent solution with a mass concentration of 2.5%. Weigh lauric acid as a surfactant, dissolve it in ethanol, and prepare a lauric acid-ethanol solution.

[0044] Add the auxiliary agent solution to the silver nitrate solution to obtain the first reaction solution. Maintain the temperature of the first reaction solution at 15°C and the stirring speed at 500 rpm. Quickly add the reducing solution to the oxidizing solution to obtain the second reaction solution; control the addition time to 2 seconds. After the addition is complete, continue the reaction for 2 minutes, then add a 1.6% (w / w) lauric acid-ethanol solution to the second reaction solution. After reacting for 10 minutes, the mixture was washed with deionized water and ethanol, and the supernatant was filtered. The filtered silver powder was dried at 60°C for 30 minutes, and then passed through a 500-mesh sieve to obtain the final silver powder. Example 2 was prepared using essentially the same method as Example 1, the main difference being the use of octanoic acid as an auxiliary agent. The actual particle size D50 of the obtained silver powder was 2.6 μm, and the specific surface area was 0.36 m² / g. The scanning electron microscope image is shown below. Figure 3 .

[0045] Example 3: Weigh 1.6 kg of silver nitrate solid and mix it with deionized water to prepare an initial silver nitrate solution with a mass fraction of 8%. Add nitric acid to the initial silver nitrate solution to obtain a silver nitrate solution with a pH of 2; simultaneously, control the temperature of the silver nitrate solution at 15°C. Weigh 0.86 kg of ascorbic acid as a reducing agent and mix it with deionized water to prepare an initial reducing solution with a mass concentration of 4.5%. Adjust the pH of the initial reducing solution to 2 to obtain the reducing solution; simultaneously, control the temperature of the reducing solution at 15°C. Weigh 0.05 kg of butyric acid as an auxiliary agent, dissolve it in ethanol, and prepare an auxiliary agent solution with a mass concentration of 2.5%. Weigh lauric acid as a surfactant, dissolve it in ethanol, and prepare a lauric acid-ethanol solution.

[0046] Add the auxiliary agent solution to the silver nitrate solution to obtain the first reaction solution. Maintain the temperature of the first reaction solution at 15°C and the stirring speed at 500 rpm. Quickly add the reducing solution to the oxidizing solution to obtain the second reaction solution; control the addition time to 2 seconds. After the addition is complete, continue the reaction for 2 minutes, then add a 1.6% (w / w) lauric acid-ethanol solution to the second reaction solution. After reacting for 10 minutes, the mixture was washed with deionized water and ethanol, and the supernatant was filtered. The filtered silver powder was dried at 60°C for 30 minutes, and then passed through a 500-mesh sieve to obtain the final silver powder. Example 3 was prepared using a method basically the same as Example 1, the main difference being the use of lauric acid as an additive. The actual particle size D50 of the obtained silver powder was 2.5 μm, and the specific surface area was 0.28 m² / g. The scanning electron microscope image is shown below. Figure 4 .

[0047] Example 4: Weigh 1.6 kg of silver nitrate solid and mix it with deionized water to prepare an initial silver nitrate solution with a mass fraction of 8%. Add nitric acid to the initial silver nitrate solution to obtain a silver nitrate solution with a pH of 2; simultaneously, control the temperature of the silver nitrate solution at 15°C. Weigh 0.86 kg of ascorbic acid as a reducing agent and mix it with deionized water to prepare an initial reducing solution with a mass concentration of 4.5%. Adjust the pH of the initial reducing solution to 2 to obtain the reducing solution; simultaneously, control the temperature of the reducing solution at 15°C. Weigh 0.05 kg of butyric acid as an auxiliary agent, dissolve it in ethanol, and prepare an auxiliary agent solution with a mass concentration of 2.5%. Weigh lauric acid as a surfactant, dissolve it in ethanol, and prepare a lauric acid-ethanol solution.

[0048] Add the auxiliary agent solution to the silver nitrate solution to obtain the first reaction solution. Maintain the temperature of the first reaction solution at 15°C and the stirring speed at 500 rpm. Quickly add the reducing solution to the oxidizing solution to obtain the second reaction solution; control the addition time to 2 seconds. After the addition is complete, continue the reaction for 2 minutes, then add a 1.6% (w / w) lauric acid-ethanol solution to the second reaction solution. After reacting for 10 minutes, the mixture was washed with deionized water and ethanol, and the supernatant was filtered. The filtered silver powder was dried at 60°C for 30 minutes, and then passed through a 500-mesh sieve to obtain the final silver powder. Example 4 was prepared using a method basically the same as Example 2, the main difference being the use of an oxidizing solution with a pH of 1. The actual particle size D50 of the obtained silver powder was 1.45 μm, and the specific surface area was 0.43 m² / g. The scanning electron microscope image is shown below. Figure 5 .

[0049] As can be seen from the foregoing embodiments, by adjusting the pH value of the oxidation solution and the type of additives, spherical silver powders of different sizes can be obtained in this application. The additives include, but are not limited to, one or more of benzoic acid, phenylpropionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, lauric acid, stearic acid, oleic acid, and trisodium hypotriacetate, but rather refer to various organic carboxylic acids, organic carboxylate salts, or organic amines. The ethanol used in preparing the additive solution and activator solution is not specifically ethanol; it can also be other water-soluble organic solvents.

[0050] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0051] The foregoing has provided a detailed description of a method for preparing spherical silver powder and the spherical silver powder itself, as provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing near-spherical silver powder, characterized in that, The method includes: An oxidizing solution with a pH value in the first pH range and a reducing solution with a pH value in the second pH range were prepared respectively. The auxiliary agent is dissolved in ethanol to prepare an auxiliary agent solution; The surfactant is dissolved in ethanol to obtain an surfactant solution; The auxiliary agent solution is added dropwise to the oxidizing liquid under stirring to obtain the first reaction solution; After continuously stirring the first reaction solution for a first time, the reducing solution is added to the first reaction solution during a second time to obtain the second reaction solution; After controlling the reaction of the second reaction solution for a third time, the activator solution is added dropwise to the second reaction solution for a fourth time to obtain a silver powder suspension. The silver powder suspension is then washed and dried to obtain the silver powder.

2. The method for preparing near-spherical silver powder according to claim 1, characterized in that, The preparation of the oxidizing solution with a pH value in a first pH range and the reducing solution with a pH value in a second pH range includes: Dissolve silver nitrate in deionized water to prepare an initial silver nitrate solution; A pH control agent is added to the initial silver nitrate solution to adjust the pH value of the initial silver nitrate solution to a first pH range, thereby obtaining the oxidation solution, and the solution temperature of the oxidation solution is adjusted to a first temperature range. Dissolve the reducing agent in deionized water to prepare the initial reducing solution; A pH control agent is added to the initial reducing solution to adjust the pH value of the initial reducing solution to a second pH range, thereby obtaining the reducing solution, and the solution temperature of the reducing solution is adjusted to a second temperature range.

3. The method for preparing near-spherical silver powder according to claim 2, characterized in that, The pH control agent is one or more of the following: nitric acid, oxalic acid, dilute sulfuric acid, sodium hydroxide, triethanolamine, ethylenediamine, diethylamine, triethylamine, ammonia, and ethanolamine.

4. The method for preparing near-spherical silver powder according to claim 2, characterized in that, The oxidation solution contains 5-25% silver nitrate by mass, and the reducing solution contains 3-15% reducing agent by mass.

5. The method for preparing near-spherical silver powder according to claim 1, characterized in that, The mass of the auxiliary agent is 1-10% of the mass of the silver nitrate, and the mass of the surfactant is 0.1-10% of the mass of the silver nitrate.

6. The method for preparing near-spherical silver powder according to claim 1, characterized in that, The first pH range is 1-3, and the second pH range is 2-8.

7. The method for preparing near-spherical silver powder according to claim 1, characterized in that, The surfactant is one or more of the following: ethylene glycol monostearate, zinc stearate, aluminum monostearate, ethylene glycol distearate, glyceryl tristearate, polyethylene glycol monostearate, dodecyl stearate, methyl stearate, 12-hydroxystearic acid, sorbitan stearate, stearic acid, lauric acid, and oleic acid.

8. The method for preparing near-spherical silver powder according to claim 1, characterized in that, The second duration is 1-10 seconds.

9. The method for preparing near-spherical silver powder according to claim 1, characterized in that, The third duration is 1-10 minutes, and the fourth duration is 0-5 minutes.

10. A type of spherical silver powder, characterized in that, The spherical silver powder is prepared according to the method for preparing spherical silver powder according to any one of claims 1-9.

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