Silver powder and its preparation method

Abstract

The present invention provides a silver powder and a preparation method thereof, belonging to the technical field of metal powder preparation. In the silver ammonia solution system of the present invention, by adjusting the pH of the solution before the reaction, the addition sequence and dosage of the dispersant, and synergistically controlling the addition method, addition sequence and rate of the reducing agent, a large number of nano silver crystal nuclei are generated in the early stage of the reaction system. The silver reduced in the middle and late stages of the reaction continues to grow incompletely and unevenly on the basis of the silver crystal nuclei, and finally a silver powder doped with large and small particles is formed. The present invention can obtain a mixed-state silver powder with large particles having a particle size of 0.8 - 1.2 μm and small particles having a particle size of 0.1 - 0.3 μm by using a one-step liquid-phase chemical reduction method. Among them, the large-particle silver powder forms the main conductive structure, and the small-particle nano silver powder fills the gaps between the silver powder and changes the contact state of the sub-micron silver powder, which can reduce the curing temperature and conduction resistance, thereby improving the sintering activity and conductivity of the silver powder, and can be widely applied to fields such as low-temperature curing photovoltaic cells and power semiconductor devices.

Description

Technical Field

[0001] The present invention relates to the technical field of metal powders and their preparation, and particularly to a silver powder and a method for preparing the same. Background Art

[0002] As a functional powder material, silver powder not only has excellent electrical and thermal conductivity, but also has unique powder characteristics in terms of microscopic morphology, surface properties, etc. It has become an essential raw material in electronic manufacturing and photovoltaic power generation. With the iterative upgrade of photovoltaic technology and the large-scale popularization and application of power semiconductor devices in new energy vehicles, the market demand has gradually shifted from traditional high-temperature sintered silver powder to low-temperature cured silver powder. Its composition is submicron silver powder with a particle size of about 1 μm and silver powder of two or three hundred nanometers. The presence of nanosilver powder can further reduce the sintering temperature and optimize the battery process window. In practical applications, usually two kinds of silver powders with different particle sizes are mixed and doped in a certain proportion, but the mixing effect is poor and the powder mixing is uneven. The silver powder with size doping generated by one-step reduction through chemical method can significantly improve the uniformity of the microscopic composition and sintering activity of the powder.

[0003] In the prior art, the patent with the publication number of CN118060552A discloses a method for preparing silver powder with high sintering activity. In this patent, sodium dodecylbenzenesulfonate is added during the preparation of the silver solution, and a buffer solution is prepared using sodium carbonate and acetic acid. During the reaction process, the buffer solution is added to the silver solution to regulate the pH of the whole reaction process, and formaldehyde is used to reduce silver carbonate precipitation to prepare small-particle silver powder, and then aging treatment is carried out. At the same time, sodium dodecylbenzenesulfonate is used to regulate the aging process of silver powder, so as to finally form silver powder in a state of size doping. Among them, the particle size of the large-particle silver powder is 2 - 8 μm, and the particle size of the small-particle silver powder is 0.2 - 0.6 μm. However, the reaction conditions mentioned in this patent are relatively harsh, the silver powder preparation process is long, and toxic and harmful formaldehyde is used as a reducing agent, so it cannot be mass-produced industrially, and its practical application value is relatively low. In addition, with the optimization and upgrade of solar cell technology, the silver powder with this particle size distribution can no longer meet the market demand of downstream slurries.

[0004] A patent with the publication number CN114042909A discloses a composite micro-nano silver powder and its preparation method. In this patent, under acidic conditions, a silver microcrystal suspension is first prepared by a liquid-phase chemical reduction method at a specified temperature; then, micron-sized silver powder is prepared by a one-step liquid-phase chemical reduction method at a specified temperature. During the growth of the micron-sized silver powder, the aforementioned silver microcrystal suspension is added, and by controlling the dosage distribution of the reducing agent before and after the addition of the silver microcrystal suspension, the size and mixing mass ratio of the nano-sized silver powder are adjusted; the obtained silver powder includes two sizes, and the ratio of the diameters of the two silver grains is 2 to 15. However, this method is an acidic reaction system, and the subsequent treatment of acidic waste liquid is difficult and costly. Moreover, this method requires two-step reduction preparation, the reaction process is complex, and the condition control is harsh. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present application provides a silver powder and its preparation method, aiming to solve the problems that the existing process for preparing silver powder is complex, the conditions are harsh, the raw materials are toxic and harmful, mass industrial production cannot be achieved, and the particle size distribution of the silver powder cannot meet the market demand of downstream slurries.

[0006] On the one hand, an embodiment of the present application provides a method for preparing silver powder, including the following steps:

[0007] S1. Prepare a silver solution

[0008] Fully mix silver nitrate and deionized water, then add ammonia water until the solution changes from turbid to clear, control the pH of the solution to be 11 - 12, add sodium citrate, and stir until completely dissolved to obtain a silver solution; wherein, the ratio of deionized water, silver nitrate, and sodium citrate is 100 mL: 30 - 80 g: 1 - 5 g;

[0009] S2. Prepare a reducing solution

[0010] Add glucose to deionized water, and after mixing evenly, obtain a reducing solution;

[0011] S3. Oxidation-reduction reaction

[0012] Under mechanical stirring conditions, drop the reducing solution obtained in step S2 into the silver solution obtained in step S1 at a rate of 10 - 15 mL / min. After the dropping is completed, continue the reaction to obtain a silver powder material;

[0013] S4. Post-treatment of silver powder

[0014] Perform solid-liquid separation, washing, drying, and crushing on the silver powder material obtained in step S3 to obtain the target silver powder.

[0015] In the technical solution of the embodiment of the present application, in the silver ammonia solution system, by adjusting the pH of the solution before the reaction, the addition sequence and dosage of the dispersant, and synergistically controlling the addition method, addition sequence and rate of the reducing agent, a large number of nano silver crystal nuclei are generated in the early stage of the reaction system. The silver reduced in the middle and late stages of the reaction continues to grow non-uniformly on the basis of the silver crystal nuclei, and finally silver powder doped with large and small particles is formed.

[0016] In some embodiments, in step S2, the dosage of the glucose is 60% - 90% of the mass of the silver nitrate.

[0017] In this embodiment, glucose is used as a reducing agent to reduce silver in the silver solution.

[0018] In some embodiments, in step S3, the time for the continuous reaction is 1.5 - 2.5 h.

[0019] In this embodiment, after the addition of the reducing agent is completed, the reaction continues for a period of time to continuously reduce silver, and it grows non-uniformly on the basis of the silver crystal nuclei.

[0020] In some embodiments, in step S1, the mass concentration of the ammonia water is 23% - 27%.

[0021] In this embodiment, adding ammonia water with a certain concentration to silver nitrate can reduce silver ions to stable Ag(NH3)2 + , and at the same time, provide an alkaline environment for subsequent reactions.

[0022] In some embodiments, in step S3, the temperature during the dropping process and the reaction process is 30 - 60 °C; the rotation speed of the mechanical stirring is 450 - 550 rpm.

[0023] In this embodiment, under the conditions of specific temperature and stirring, the silver solution and the reducing agent can better contact and fully reduce silver.

[0024] In some embodiments, in step S4, the drying treatment is carried out using a forced-air oven, and the drying temperature is 45 - 55 °C; the crushing treatment is carried out using a fluidized-bed jet mill, and the pressure of the crushing treatment is 0.5 - 0.7 MPa.

[0025] In this embodiment, through drying and grinding treatments, the generated silver forms granular silver powder.

[0026] In a second aspect, the embodiment of the present application provides a kind of silver powder, which is prepared by using the above silver powder preparation method; the silver powder contains large-particle silver powder with a particle size of 0.8 - 1.2 μm and small-particle silver powder with a particle size of 0.1 - 0.3 μm.

[0027] In the technical solution of the embodiment of the present application, large-particle silver powder forms the main conductive structure, and small-particle nano silver powder fills the gaps between the silver powder and changes the contact state of the sub-micron silver powder, which can reduce the curing temperature and conduction resistance, thereby improving the sintering activity and conductivity of the silver powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solution of the present application, the drawings used in the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 SEM image of the silver powder prepared in Example 1.

[0030] Figure 2 SEM images of the silver powder prepared in Examples 2 to 5.

[0031] Figure 3 SEM images of the silver powder prepared in Comparative Examples 1 to 9. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The embodiments of the technical solution of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, so they are only examples and cannot be used to limit the protection scope of the present application.

[0033] Referring to "embodiment" in this article means that the specific features, structures or characteristics described in connection with the embodiment can be included in at least one embodiment of the present application. The appearance of this phrase in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0034] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the front and back associated objects.

[0035] To solve the problems that the existing process for preparing silver powder is complex, the conditions are harsh, the raw materials are toxic and harmful, it is impossible to carry out batch industrial production, and the particle size distribution of silver powder cannot meet the market demand of downstream slurries, the present application provides a method for preparing silver powder. In a silver ammonia solution system, by adjusting the pH of the solution before the reaction, the addition sequence and dosage of the dispersant, and synergistically controlling the addition method, addition sequence and rate of the reducing agent, a large number of nano silver crystal nuclei are generated in the early stage of the reaction system. The silver reduced in the middle and late stages of the reaction continues to grow unevenly on the basis of the silver crystal nuclei, and finally silver powder doped with large and small particles is formed. The present invention can obtain a mixed state of silver powder with large particles having a particle size of 0.8 - 1.2 μm and small particles having a particle size of 0.1 - 0.3 μm by a one-step liquid-phase chemical reduction method. The large particle silver powder forms the main conductive structure, and the small particle nano silver powder fills the gaps between the silver powder and changes the contact state of the submicron silver powder, which can reduce the curing temperature and conduction resistance, thereby improving the sintering activity and conductivity of the silver powder. The preparation method of the present invention is simple and easy to implement, has low cost, and the generated silver powder has good sintering activity and conductivity, and can be widely applied to fields such as low-temperature curing photovoltaic cells and power semiconductor devices.

[0036] The present invention provides a method for preparing silver powder, comprising the following steps:

[0037] S1. Prepare a silver solution

[0038] Fully mix silver nitrate with deionized water, then add ammonia water until the solution changes from turbid to clear, control the pH of the solution to be 11 - 12, add sodium citrate, and stir until completely dissolved to obtain a silver solution; wherein, the ratio of deionized water, silver nitrate and sodium citrate is 100 mL: 30 - 80 g: 1 - 5 g;

[0039] S2. Prepare a reducing solution

[0040] Add glucose to deionized water, and after mixing evenly, obtain a reducing solution;

[0041] S3. Oxidation-reduction reaction

[0042] Under the condition of mechanical stirring, add the reducing solution obtained in step S2 dropwise to the silver solution obtained in step S1 at a rate of 10 - 15 mL / min. After the dropping is completed, continue the reaction to obtain a silver powder material;

[0043] S4. Post-treatment of silver powder

[0044] Perform solid-liquid separation, washing, drying and crushing on the silver powder material obtained in step S3 to obtain the target silver powder.

[0045] In the technical solution of the embodiment of the present application, in the silver ammonia solution system, by adjusting the pH of the solution before the reaction, the addition sequence and dosage of the dispersant, and synergistically controlling the addition method, addition sequence and rate of the reducing agent, a large number of nano silver crystal nuclei are generated in the early stage of the reaction system, and the silver reduced in the middle and late stages of the reaction continues to grow incompletely and unevenly on the basis of the silver crystal nuclei, and finally silver powder doped with large and small particles is formed.

[0046] Further, in some embodiments, in step S2, the dosage of the glucose is 60% - 90% of the mass of the silver nitrate.

[0047] In the technical solution of the embodiment of the present application, glucose is used as a reducing agent to reduce silver in the silver solution.

[0048] Further, in some embodiments, in step S3, the time for the continuous reaction is 1.5 - 2.5 h.

[0049] In the technical solution of the embodiment of the present application, after the addition of the reducing agent is completed, the reaction continues for a period of time to enable silver to be continuously reduced and grow incompletely and unevenly on the basis of the silver crystal nuclei.

[0050] Further, in some embodiments, in step S1, the mass concentration of the ammonia water is 23% - 27%.

[0051] In the technical solution of the embodiment of the present application, adding ammonia water with a certain concentration to silver nitrate can reduce silver ions to stable Ag(NH3)2 + , and at the same time, provide an alkaline environment for the subsequent reaction.

[0052] Further, in some embodiments, in step S3, the temperature of the dropping process and the reaction process is 30 - 60 °C; the rotation speed of the mechanical stirring is 450 - 550 rpm.

[0053] In the technical solution of the embodiment of the present application, under the conditions of a specific temperature and stirring, the silver solution and the reducing agent can better contact and fully reduce silver.

[0054] Further, in some embodiments, in step S4, the drying treatment is carried out using a blast drying oven, and the drying temperature is 45 - 55 °C; the crushing treatment is carried out using a fluidized bed jet mill, and the pressure of the crushing treatment is 0.5 - 0.7 MPa.

[0055] In the technical solution of the embodiment of the present application, through drying and grinding treatments, the generated silver is formed into granular silver powder.

[0056] Second aspect, embodiments of the present application provide a silver powder prepared by using the silver powder preparation method described above; the silver powder contains large particle silver powder with a particle size of 0.8 - 1.2 μm and small particle silver powder with a particle size of 0.1 - 0.3 μm.

[0057] In the technical solution of the embodiments of the present application, the large particle silver powder forms the main conductive structure, and the small particle nano - silver powder fills the gaps between the silver powder and changes the contact state of the sub - micron silver powder, which can reduce the curing temperature and conduction resistance, thereby improving the sintering activity and conductivity of the silver powder.

[0058] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those without specific technologies or conditions indicated in the embodiments, the technologies or conditions described in the literature in the field or according to the product specifications are followed. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0059] Example 1

[0060] This embodiment provides a method for preparing silver powder, which includes the following steps:

[0061] S1. Completely dissolve 50 g of silver nitrate in 100 mL of deionized water, then add ammonia water with a mass concentration of 25% until the solution changes from turbid to clear. When controlling the pH value of the solution to be 11, add 3.5 g of sodium citrate and stir until completely dissolved to obtain a silver solution;

[0062] S2. Weigh 35 g of glucose, add it to 100 mL of deionized water, and stir to mix evenly to obtain a reducing solution;

[0063] S3. Under the conditions of a stirring speed of 500 rpm and a temperature of 40 °C, add the reducing solution to the silver solution at a dropping rate of 10 mL / min. After all of it is added, continue to react fully for 2 h to obtain silver powder material;

[0064] S4. Filter and wash the silver powder material, dry it in a blast drying oven at 50 °C, and then perform crushing treatment in a fluidized bed air mill at 0.6 MPa to obtain the target silver powder product.

[0065] The SEM image of the silver powder prepared in this embodiment is as Figure 1 shown.

[0066] From Figure 1 it can be seen that the silver powder prepared in this embodiment has good dispersibility and crystallinity, the large particle size is 0.8 - 1.2 μm, and the small particle size is 0.1 - 0.3 μm.

[0067] Example 2 and Comparative Examples 1 - 2

[0068] Example 2 and Comparative Examples 1-2 respectively provide a method for preparing silver powder. Compared with Example 1, the difference lies in that the pH of the solution is controlled differently in step S1, as shown in Table 1 specifically. The other steps are substantially the same as those in Example 1 and will not be elaborated here.

[0069] Table 1 pH values in Example 2 and Comparative Examples 1-2

[0070]

[0071] Examples 3-4 and Comparative Examples 3-4

[0072] Examples 3-4 and Comparative Examples 3-4 respectively provide a method for preparing silver powder. Compared with Example 1, the difference lies in that the dosage of sodium citrate is different in step S1, as shown in Table 2 specifically. The other steps are substantially the same as those in Example 1 and will not be elaborated here.

[0073] Table 2 Dosage of sodium citrate in Examples 3-4 and Comparative Examples 3-4

[0074]

[0075] Example 5 and Comparative Examples 5-6

[0076] Example 5 and Comparative Examples 5-6 respectively provide a method for preparing silver powder. Compared with Example 1, the difference lies in that the dropping rate of the reducing solution is different in step S3, as shown in Table 3 specifically. The other steps are substantially the same as those in Example 1 and will not be elaborated here.

[0077] Table 3 Dropping rate of the reducing solution in Example 5 and Comparative Examples 5-6

[0078]

[0079] Comparative Example 7

[0080] This comparative example provides a method for preparing silver powder. Compared with Example 1, the difference lies in that the adding method of the reducing solution is different in step S3, and it is added by the way of one-time pouring. The other steps are substantially the same as those in Example 1 and will not be elaborated here.

[0081] Comparative Example 8

[0082] This comparative example provides a method for preparing silver powder. Compared with Example 1, the difference lies in that sodium citrate is not added in step S1, but is added to the reducing solution in step S2. The other steps are substantially the same as those in Example 1 and will not be elaborated here.

[0083] Comparative Example 9

[0084] This comparative example provides a method for preparing silver powder. Compared with Example 1, the difference is that in step S3, the order of adding the silver solution and the reducing solution is opposite, and the silver solution is added to the reducing solution at a dropping rate of 10 mL / min. The other steps are substantially the same as those in Example 1 and will not be repeated here.

[0085] The SEM images of the silver powders prepared in Examples 2 to 5 and Comparative Examples 1 to 9 are as follows: Figure 2 , 3 shown.

[0086] Depend on Figure 2 It can be seen that the appearance and particle size of the silver powder prepared in Examples 2 to 6 are similar to those in Example 1, indicating that during the preparation of the silver solution, the dispersant sodium citrate is added when the pH value is controlled at 11 to 12; the ratio of the addition amount of sodium citrate to deionized water and silver nitrate is 1 to 5 g: 100 mL: 30 to 80 g; in the redox reaction, when the drop rate of the reducing solution is 10 to 15 mL / min, the prepared silver powder has stable dispersibility and size distribution. Figure 3 It can be seen that in Comparative Examples 2, 6 to 9, since the pH of the silver solution in the early stage of the reaction is too high, changing the method of adding the reducing solution and the dispersant or increasing the dropping rate of the reducing solution will lead to too fast a silver reduction rate in the early stage of the reaction, resulting in poor crystal shape and small particles of the generated silver particles; and in Comparative Example 4, due to excessive use of the dispersant, the silver crystal nuclei generated in the early stage of the reaction are completely coated and cannot continue to grow in the later stage; and in Comparative Examples 1, 3 and 5, due to the incomplete formation of the silver precursor, the amount of the dispersant is too small and the dropping rate is too slow, resulting in serious agglomeration of the formed silver particles and poor dispersibility.

[0087] In summary, the present invention adjusts the pH of the solution before the reaction and the order and amount of the dispersant added in the silver ammonia solution system, and coordinately controls the addition method, order and rate of the reducing agent, so that a large number of nano silver nuclei are generated in the early stage of the reaction system, and the silver reduced in the middle and late stages of the reaction continues to grow unevenly on the basis of the silver nuclei, and finally forms a silver powder doped with large and small particles. The present invention adopts a liquid phase chemical reduction method to obtain a large particle with a particle size of 0.8~1.2μm and a small particle mixed silver powder with a particle size of 0.1~0.3μm, and the process route is simple and the production cost is low. In addition, the large and small particle doped silver powder prepared by the present invention forms a main conductive structure with large particle silver powder, and the small particle nano silver powder fills the gap between the silver powder and changes the contact state of the submicron silver powder, thereby reducing the curing temperature and on-resistance, and improving the sintering activity and conductivity of the silver powder, which can be widely used in the fields of low-temperature curing photovoltaic cells and power semiconductor devices.

[0088] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing silver powder, characterized in that: The steps include: S1. Prepare silver solution Fully mix silver nitrate and deionized water, then add ammonia water to make the solution clear from turbid, and control the pH of the solution to 11-12, add sodium citrate, and stir until completely dissolved to obtain a silver solution; wherein the ratio of deionized water, silver nitrate and sodium citrate is 100mL:30-80g:1-5g; S2. Prepare the restore solution Add glucose into deionized water and mix well to obtain a reducing solution; S3. Redox reaction Under mechanical stirring conditions, the reducing solution obtained in step S2 is added dropwise to the silver solution obtained in step S1 at a rate of 10-15 mL / min. After the addition is completed, the reaction is continued to obtain a silver powder material; S4. Silver powder post-treatment The silver powder material obtained in step S3 is subjected to solid-liquid separation, washing, drying and crushing to obtain the target silver powder; The reaction time is 1.5-2.5 hours; the target silver powder contains large silver particles with a particle size of 0.8-1.2 μm and small silver particles with a particle size of 0.1-0.3 μm.

2. The method for preparing silver powder according to claim 1, characterized in that: In step S2, the amount of glucose used is 60% to 90% of the mass of the silver nitrate.

3. The method for preparing silver powder according to claim 1, characterized in that: In step S1, the mass concentration of the ammonia water is 23-27%.

4. The method for preparing silver powder according to claim 1, characterized in that: In step S3, the temperature of the dropping process and the reaction process is 30-60°C.

5. The method for preparing silver powder according to claim 1, characterized in that: In step S3, the rotation speed of the mechanical stirring is 450-550 rpm.

6. The method for preparing silver powder according to claim 1, characterized in that: In step S4, the drying process is carried out in a blast oven, and the drying temperature is 45-55°C.

7. The method for preparing silver powder according to claim 1, characterized in that: In step S4, the crushing process adopts a fluidized bed jet mill, and the pressure of the crushing process is 0.5-0.7 MPa.

8. A silver powder, characterized in that: The silver powder is prepared by the method for preparing the silver powder according to any one of claims 1 to 7.

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