High crystallinity and narrow particle size distribution silver powder and method of making same

Abstract

The application provides a kind of high crystallinity and narrow particle size distribution silver powder and its preparation method, belongs to metal powder preparation technical field.The application is prepared by preparing silver nitrate solution, ascorbic acid solution, stabilizer solution, dispersant solution, seed solution, nitric acid solution and surface modifier solution;Stabilizer solution and nitric acid solution are mixed into seed solution to obtain solution A with specific PH;Dispersant solution is added into silver nitrate solution to mix, and solution B is obtained;Solution B and ascorbic acid solution are added into solution A, and the precipitate is collected after sufficient reaction;After washing treatment to the precipitate, surface modifier solution is added again, and after sufficient stirring, the target silver powder is obtained by drying and dispersing treatment.The submicron silver powder with high crystallinity and large specific surface area is prepared by step-by-step preparation of different reaction mixed solutions and then mixing in a specific order in a simple and controllable method.

Description

Technical Field

[0001] This invention relates to the field of metal powder and its preparation technology, and in particular to a silver powder with high crystallinity and narrow particle size distribution and its preparation method. Background Technology

[0002] The applications of silver powder range from macroscopic power transmission to microscopic electronic circuits, from everyday antibacterial products to cutting-edge aerospace technology. This continuous expansion of its applications is also driving silver powder preparation technology towards greater refinement, functionality, and customization.

[0003] Silver powder is a core conductive material for preparing the metal electrodes of crystalline silicon solar cells. The morphology, particle size, and tap density of silver powder directly determine the performance of the cell. Traditional silver powder is mostly micron-sized spherical with a wide particle size distribution. In recent years, in order to improve the rheology of the paste and printing consistency, efforts have been made to print finer grid lines with higher aspect ratios. This requires silver powder to have a narrower particle size distribution, better dispersibility, and higher crystallinity to adapt to the new cell structure, improve printing performance, and enhance printing accuracy.

[0004] Therefore, it is necessary to develop a submicron silver powder with higher crystallinity, narrower particle size distribution, and higher sphericity. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a silver powder with high crystallinity and narrow particle size distribution and its preparation method, aiming to solve the problem that existing silver powder preparation processes are difficult to obtain silver powder that simultaneously achieves high crystallinity, uniform particle size distribution and good sphericity.

[0006] In a first aspect, this application provides a method for preparing silver powder with high crystallinity and narrow particle size distribution, comprising the following steps:

[0007] S1. Prepare silver nitrate solution, ascorbic acid solution, stabilizer solution, dispersant solution, seed crystal solution, nitric acid solution and surface modifier solution respectively;

[0008] S2. Under stirring conditions, the stabilizer solution and the nitric acid solution are added to the seed crystal solution and mixed to obtain solution A; the dispersant solution is added to the silver nitrate solution and mixed to obtain solution B.

[0009] S3. Add the solution B and the ascorbic acid solution to the solution A at the same time. After the reaction is completed, perform solid-liquid separation to obtain the precipitate.

[0010] S4. The precipitate is washed, then a surface modifier solution is added, and after thorough stirring, it is dried and dispersed to obtain the target silver powder.

[0011] In the technical solution of this application embodiment, the synergistic treatment of seed crystals by stabilizers and nitric acid, with the protection of stabilizer formation and a specific pH, ensures good stability and independence of the seed crystals in the early stage of the reaction, promoting the formation of silver powder with uniform particle size and high dispersion. Furthermore, by adding a dispersant to the silver nitrate solution at a constant temperature, the effective groups of the dispersant form spatial barriers, further enhancing the uniformity and dispersibility of the silver powder size. The dispersant can also regulate the growth rate of different crystal faces during the reaction, promoting the formation of highly crystalline silver powder particles with regular morphology, complete crystal lattice, and few defects. Based on the synergistic treatment of seed crystals by stabilizers and nitric acid, and the treatment of silver nitrate by dispersants at a constant temperature, the silver powder obtained by this invention exhibits high crystallinity and narrow particle size distribution characteristics, and has a higher specific surface area compared to traditional silver powder.

[0012] In some embodiments, in step S1, the stabilizer in the stabilizer solution is one or more of sodium citrate, sodium dodecyl sulfate, 1-dodecyl mercaptan, mercaptoacetic acid, and hexadecyltrimethylammonium bromide; the mass of the stabilizer accounts for 0.8 to 3.6% of the mass of silver nitrate in the silver nitrate solution.

[0013] In this embodiment, by adding a stabilizer to the nitrate seed crystals and pretreating the nitrate seed crystals with the stabilizer, a seed crystal solution with good dispersibility, high stability and abundant active sites can be obtained in advance. During the reaction process, silver preferentially undergoes heterogeneous deposition on the seed crystals, and the resulting silver powder has the characteristics of narrow particle size distribution, good dispersibility, regular morphology and high crystallinity.

[0014] In some embodiments, in step S1, the dispersant in the dispersant solution is one or more of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, sodium polyacrylate, gelatin, and gum arabic; the mass of the dispersant accounts for 0.5 to 3.5% of the mass of silver nitrate in the silver nitrate solution.

[0015] In this embodiment, the dispersant solution and silver nitrate solution are premixed to form a stable silver ion complex, which effectively controls the reaction rate, ensures the uniformity of size, establishes steric hindrance in advance, guides the regular growth of silver powder, and ensures the regularity of silver powder morphology.

[0016] In some embodiments, in step S1, the seed crystals in the seed solution are one or more of nickel nitrate, magnesium nitrate, aluminum nitrate, copper nitrate, and zinc nitrate; the mass of the seed crystals accounts for 0.1 to 0.5% of the mass of silver nitrate in the silver nitrate solution.

[0017] In this embodiment, the heterogeneous nucleation substrate can significantly reduce the energy required for nucleation. After the nitrate is reduced, it can form a large number of fine particles, increasing the reaction interface. Using the existing particles as a substrate, silver ions can be rapidly and uniformly reduced and deposited on its surface. The nitrate seed crystals can provide highly dispersed fixed deposition points, allowing silver to preferentially grow on the particles formed by the independent nitrates, thereby effectively improving the dispersibility of silver powder particles. On the nitrate-formed particle substrate, due to the good lattice matching between the particles and silver, silver tends to crystallize and grow in a more ordered and dense manner, which is conducive to generating silver powder particles with smooth surfaces and high crystallinity.

[0018] In some embodiments, in step S1, the mass of nitric acid in the nitric acid solution accounts for 0.5 to 4.2% of the mass of silver nitrate.

[0019] In this embodiment, the addition of nitric acid can precisely adjust the pH value of the system, keeping the seed crystals in a suitable hydrolytic state. The acidic environment can inhibit excessive hydrolysis of the seed crystals, maintain the uniformity and highly active surface of the seed crystals, and provide more effective sites for heterogeneous nucleation of silver. The acidic environment provided by nitric acid can reduce seed crystal agglomeration and make the seed crystals more uniformly distributed. The surface charge distribution of nitrate seed crystals in acidic media is more controllable, which is conducive to the uniform growth of silver on the seed crystal surface, forming silver powder with uniform particle size and regular morphology. The anisotropic growth of silver under acidic conditions is inhibited, which strengthens the regularity of the silver powder morphology.

[0020] In some embodiments, in step S1, the surface modifier in the surface modifier solution is one or more of saturated fatty acids, unsaturated organic acids, silane coupling agents, titanate coupling agents, and aluminate coupling agents; the mass of the surface modifier accounts for 0.2 to 3% of the mass of silver nitrate in the silver nitrate solution.

[0021] In this embodiment, the applicability of silver powder in the paste is improved by adding a surface modifier. The coating layer of the surface modifier can effectively improve the dispersibility of the paste and regulate its rheology, allowing it to maintain better linearity after printing, thereby improving the aspect ratio of the electrode and the battery efficiency.

[0022] In some embodiments, in step S1, the mass concentration of the silver nitrate solution is 100~350g / L, and the mass concentration of the ascorbic acid solution is 80~280g / L; the mass ratio of the ascorbic acid in the ascorbic acid solution to the silver nitrate in the silver nitrate solution is 1:1~1:2.5.

[0023] In this embodiment, mixing the oxidizing solution and the reducing solution with a specific concentration ratio ensures that the redox reaction proceeds fully.

[0024] In some embodiments, in step S2, the pH value of solution A is 0.5~6; and the mixing temperature is 20~50°C.

[0025] In this embodiment, under specific pH conditions, i.e. acidic conditions, a pretreatment of the seed crystals by heating and stirring with a stabilizer is used to consolidate the dispersion, uniformity, and abundance of effective sites provided by the nitrate seed crystals during the reaction process, so that silver can be deposited uniformly in a heterogeneous phase. The constant temperature stirring pretreatment of solution A can reduce the randomness of nucleation and growth, so that the silver powder size is uniform and the morphology is more regular during the deposition process.

[0026] In some embodiments, in step S3, the addition is done by dropwise addition, the addition rate of solution B is 50~150 mL / min, the addition rate of ascorbic acid solution is 50~150 mL / min, and the reaction temperature is 20~50℃.

[0027] In this embodiment, a specific and constant dropping rate is used to continuously provide a balanced concentration of reactants, which allows silver powder growth to dominate and is conducive to generating submicron silver powder with uniform size and regular morphology. A specific reaction temperature is used to ensure that the silver powder grows at a certain reaction rate, thereby controlling the morphology, size, crystallinity and other properties of the silver powder.

[0028] Secondly, this application provides a silver powder with high crystallinity and narrow particle size distribution, characterized in that it is prepared by the above-mentioned method for preparing silver powder with high crystallinity and narrow particle size distribution, and the specific surface area of ​​the silver powder with high crystallinity and narrow particle size distribution is 0.4~1.1m². 2 / g, particle size D50 is 0.5~0.9μm, tap density is 3.5~6.5g / mL.

[0029] In the technical solution of this application embodiment, the silver powder has a uniform and extremely small particle size, a large specific surface area and a high degree of crystallinity, which can be adapted to new battery structures, improve printing performance and enhance printing accuracy. Attached Figure Description

[0030] Figure 1 This is a SEM image of the silver powder prepared in Example 1 of this application.

[0031] Figure 2 The images are SEM images of the silver powders prepared in Examples 2-3 and Comparative Examples 1-2 of this application.

[0032] Figure 3 The images shown are SEM images of the silver powder prepared in Comparative Examples 3-4 of this application.

[0033] Figure 4 This is a SEM image of the silver powder prepared in Comparative Example 5 of this application. Detailed Implementation

[0034] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] To address the challenges of existing silver powder preparation processes in simultaneously achieving high crystallinity, uniform particle size distribution, and excellent sphericity, this application provides a silver powder with high crystallinity and narrow particle size distribution, along with its preparation method. By preparing different reaction mixtures stepwise and then mixing them under specific conditions, a simple and controllable method is used to prepare submicron silver powder with high crystallinity, narrow particle size distribution, and a large specific surface area.

[0037] Using seed solution as a heterogeneous nucleation substrate can significantly reduce the energy required for nucleation. After nitrate is reduced, it can form a large number of fine particles, increasing the reaction interface. With the existing particles as the substrate, silver ions can be rapidly and uniformly reduced and deposited on its surface. Nitrate seed crystals can also provide highly dispersed fixed deposition points, allowing silver to preferentially grow on the particles formed by their own independent nitrates, thereby effectively improving the dispersibility of silver powder particles. On the nitrate-formed particle substrate, due to the good lattice matching between the particles and silver, silver tends to crystallize and grow in a more ordered and dense manner, which is conducive to the generation of silver powder particles with smooth surfaces and high crystallinity.

[0038] The synergistic treatment of seed crystals using stabilizers and nitric acid provides protection against stabilizer formation and a specific pH, resulting in good stability and independence of the seed crystals in the early stages of the reaction. This promotes the formation of silver powder with uniform particle size and high dispersion. By adding stabilizers to nitrate seed crystals for pretreatment, a seed crystal solution with good dispersibility, high stability, and abundant active sites can be obtained in advance. During the reaction, silver preferentially undergoes heterogeneous deposition on the seed crystals, ultimately resulting in silver powder with narrow particle size distribution, good dispersibility, regular morphology, and high crystallinity. Advanced features: The addition of nitric acid can precisely adjust the pH value of the system, keeping the seed crystals in a suitable hydrolytic state. The acidic environment can inhibit excessive hydrolysis of the seed crystals, maintain the uniformity and highly active surface of the seed crystals, and provide more effective sites for heterogeneous nucleation of silver. The acidic environment provided by nitric acid can reduce seed crystal agglomeration and make the seed crystals more uniformly distributed. The surface charge distribution of nitrate seed crystals in acidic media is more controllable, which is conducive to the uniform growth of silver on the seed crystal surface, forming silver powder with uniform particle size and regular morphology. The anisotropic growth of silver under acidic conditions is inhibited, which strengthens the regularity of the silver powder morphology.

[0039] Based on this, by adding a dispersant to the silver nitrate solution at a constant temperature, the effective groups of the dispersant form a spatial barrier, which further enhances the uniformity and dispersibility of the silver powder size. In addition, the dispersant can regulate the growth rate of different crystal planes during the reaction process, promoting the formation of highly crystalline silver powder particles with regular morphology, complete crystal lattice and few defects.

[0040] Based on the synergistic treatment of seed crystals by stabilizer and nitric acid as the base liquid, silver nitrate solution treated with dispersant at constant temperature and reducing agent solution (ascorbic acid solution) are simultaneously added to the base liquid to obtain silver powder with high crystallinity and narrow particle size distribution characteristics, which has a higher specific surface area than traditional silver powder.

[0041] In a first aspect, this application provides a method for preparing silver powder with high crystallinity and narrow particle size distribution, comprising the following steps:

[0042] S1. Prepare silver nitrate solution, ascorbic acid solution, stabilizer solution, dispersant solution, seed crystal solution, nitric acid solution and surface modifier solution respectively;

[0043] S2. Under stirring conditions, the stabilizer solution and the nitric acid solution are added to the seed crystal solution and mixed to obtain solution A; the dispersant solution is added to the silver nitrate solution and mixed to obtain solution B.

[0044] S3. Add the solution B and the ascorbic acid solution to the solution A at the same time. After the reaction is completed, perform solid-liquid separation to obtain the precipitate.

[0045] S4. The precipitate is washed, then a surface modifier solution is added, and after thorough stirring, it is dried and dispersed to obtain the target silver powder.

[0046] In the technical solution of this application embodiment, the synergistic treatment of seed crystals by stabilizers and nitric acid, with the protection of stabilizer formation and a specific pH, ensures good stability and independence of the seed crystals in the early stage of the reaction, promoting the formation of silver powder with uniform particle size and high dispersion. Furthermore, by adding a dispersant to the silver nitrate solution at a constant temperature, the effective groups of the dispersant form spatial barriers, further enhancing the uniformity and dispersibility of the silver powder size. The dispersant can also regulate the growth rate of different crystal faces during the reaction, promoting the formation of highly crystalline silver powder particles with regular morphology, complete crystal lattice, and few defects. Based on the synergistic treatment of seed crystals by stabilizers and nitric acid, and the treatment of silver nitrate by dispersants at a constant temperature, the silver powder obtained by this invention exhibits high crystallinity and narrow particle size distribution characteristics, and has a higher specific surface area compared to traditional silver powder.

[0047] Furthermore, in some embodiments, in step S1, the stabilizer in the stabilizer solution is one or more of sodium citrate, sodium dodecyl sulfate, 1-dodecyl mercaptan, mercaptoacetic acid, and hexadecyltrimethylammonium bromide; the mass of the stabilizer accounts for 0.8 to 3.6% of the mass of silver nitrate in the silver nitrate solution.

[0048] In the technical solution of this application embodiment, by adding a stabilizer to the nitrate seed crystals and pretreating the nitrate seed crystals with the stabilizer, a seed crystal solution with good dispersibility, high stability and abundant active sites can be obtained in advance. During the reaction process, silver preferentially undergoes heterogeneous deposition on the seed crystals, and the resulting silver powder has the characteristics of narrow particle size distribution, good dispersibility, regular morphology and high crystallinity.

[0049] Furthermore, in some embodiments, in step S1, the dispersant in the dispersant solution is one or more of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, sodium polyacrylate, gelatin, and gum arabic; the mass of the dispersant accounts for 0.5 to 3.5% of the mass of silver nitrate in the silver nitrate solution.

[0050] In the technical solution of this application embodiment, the dispersant solution and silver nitrate solution are premixed to form a stable silver ion complex, which effectively controls the reaction rate, ensures the uniformity of size, establishes steric hindrance isolation in advance, guides the regular growth of silver powder, and ensures the regularity of silver powder morphology.

[0051] Furthermore, in some embodiments, in step S1, the seed crystals in the seed solution are one or more of nickel nitrate, magnesium nitrate, aluminum nitrate, copper nitrate, and zinc nitrate; the mass of the seed crystals accounts for 0.1 to 0.5% of the mass of silver nitrate in the silver nitrate solution.

[0052] In the technical solution of this application embodiment, the heterogeneous nucleation substrate can significantly reduce the energy required for nucleation. After the nitrate is reduced, it can form a large number of fine particles, increasing the reaction interface. Using the existing particles as a substrate, silver ions can be rapidly and uniformly reduced and deposited on its surface. The nitrate seed crystals can provide highly dispersed fixed deposition points, allowing silver to preferentially grow on the particles formed by the independent nitrates, thereby effectively improving the dispersibility of silver powder particles. On the nitrate-formed particle substrate, since the particle and silver lattice match well, silver tends to crystallize and grow in a more ordered and dense manner, which is conducive to generating silver powder particles with smooth surfaces and high crystallinity.

[0053] Furthermore, in some embodiments, in step S1, the mass of nitric acid in the nitric acid solution accounts for 0.5 to 4.2% of the mass of silver nitrate.

[0054] In the technical solution of this application embodiment, the addition of nitric acid can precisely adjust the pH value of the system, so that the seed crystals are kept in a suitable hydrolysis state. The acidic environment can inhibit the excessive hydrolysis of the seed crystals, maintain the uniformity and highly active surface of the seed crystals, and provide more effective sites for the heterogeneous nucleation of silver. The acidic environment provided by nitric acid can reduce the agglomeration of seed crystals and make the seed crystals more uniformly distributed. The surface charge distribution of nitrate seed crystals in acidic medium is more controllable, which is conducive to the uniform growth of silver on the seed crystal surface, forming silver powder with uniform particle size and regular morphology. The anisotropic growth of silver under acidic conditions is inhibited, which strengthens the regularity of the morphology of silver powder.

[0055] Further, in some embodiments, in step S1, the surface modifier in the surface modifier solution is one or more of saturated fatty acids, unsaturated organic acids, silane coupling agents, titanate coupling agents, and aluminate coupling agents; the mass of the surface modifier accounts for 0.2 to 3% of the mass of silver nitrate in the silver nitrate solution.

[0056] In the technical solution of this application embodiment, the applicability of silver powder in the paste is improved by adding a surface modifier. The coating layer of the surface modifier can effectively improve the dispersibility of the paste and regulate its rheology, so that it maintains better linearity after printing, thereby improving the aspect ratio of the electrode and the battery efficiency.

[0057] Furthermore, in some embodiments, in step S1, the mass concentration of the silver nitrate solution is 100~350 g / L, and the mass concentration of the ascorbic acid solution is 80~280 g / L; the mass ratio of ascorbic acid in the ascorbic acid solution to silver nitrate in the silver nitrate solution is 1:1~1:2.5.

[0058] In the technical solution of this application embodiment, the oxidation-reduction reaction can be fully carried out by mixing an oxidizing solution and a reducing solution with a specific concentration ratio.

[0059] Furthermore, in some embodiments, in step S2, the pH value of solution A is 0.5~6; the mixing temperature is 20~50℃; the mixing time of solution A is 1~20min; and the mixing time of solution B is 0.5~20min.

[0060] In the technical solution of this application embodiment, under a specific pH value, i.e. acidic conditions, a pretreatment of the seed crystals by heating and stirring with a stabilizer is used to consolidate the dispersion, uniformity, and abundance of effective sites provided by the nitrate seed crystals during the reaction process, so that silver can be deposited uniformly in a heterogeneous phase; the constant temperature stirring pretreatment of solution A can reduce the randomness of nucleation and growth, so that the silver powder size is uniform and the morphology is more regular during the deposition process.

[0061] Furthermore, in some embodiments, in step S3, the addition is carried out by dropwise addition, the addition rate of solution B is 50~150 mL / min, the addition rate of ascorbic acid solution is 50~150 mL / min, and the reaction temperature is 20~50℃.

[0062] In the technical solution of this application embodiment, a specific and constant dropping rate is used to continuously provide reactants of a balanced concentration, so that the growth of silver powder becomes dominant, which is beneficial to the generation of submicron silver powder with uniform size and regular morphology; a specific reaction temperature is used to ensure that the silver powder grows at a certain reaction rate, thereby controlling the morphology, size, crystallinity and other characteristics of the silver powder.

[0063] Furthermore, in some embodiments, step S4 specifically includes the following steps:

[0064] First, the precipitate is washed with deionized water until the conductivity is <20μS / cm. Then, the supernatant is removed to obtain the first precipitate. The water content of the first precipitate is ≤20%. Then, the first precipitate is washed with ethanol to remove the supernatant, thus completing the washing process.

[0065] Furthermore, in some embodiments, in step S4, the dispersion process is performed by grinding dispersion.

[0066] Secondly, this application provides a silver powder with high crystallinity and narrow particle size distribution, characterized in that it is prepared by the above-mentioned method for preparing silver powder with high crystallinity and narrow particle size distribution, and the specific surface area of ​​the silver powder with high crystallinity and narrow particle size distribution is 0.4~1.1m². 2 / g, particle size D50 is 0.5~0.9μm, tap density is 3.5~6.5g / mL.

[0067] In the technical solution of this application embodiment, the silver powder has a uniform and extremely small particle size, a large specific surface area and a high degree of crystallinity, which can be adapted to new battery structures, improve printing performance and enhance printing accuracy.

[0068] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0069] Example 1

[0070] This embodiment provides a method for preparing silver powder with high crystallinity and narrow particle size distribution, including the following steps:

[0071] S1. Prepare silver nitrate solution, ascorbic acid solution, sodium citrate solution, gelatin solution, seed crystal solution, nickel nitrate solution, nitric acid solution, and a mixed solution of palmitic acid / arachidic acid, respectively;

[0072] The concentrations of the following solutions are as follows: silver nitrate solution: 180 g / L; ascorbic acid solution: 150 g / L, with a mass ratio of ascorbic acid to silver nitrate of 1:2; sodium citrate solution: 10 g / L, where sodium citrate accounts for 1.1% of the mass of silver nitrate; gelatin solution: 1.6 g / L, where gelatin accounts for 0.5% of the mass of silver nitrate; nickel nitrate solution: 5 g / L, where nickel nitrate accounts for 0.15% of the mass of silver nitrate; nitric acid solution: 2 mol / L, where nitric acid accounts for 0.5% of the mass of silver nitrate; and palmitic acid / arachidic acid mixed solution: 6 g / L, where the total mass of palmitic acid / arachidic acid accounts for 0.2% of the mass of silver nitrate.

[0073] S2. Under stirring conditions at 30℃, sodium citrate solution and nitric acid solution were added to nickel nitrate solution and stirred for 5 min to obtain solution A with a pH of 5.5; under constant temperature stirring conditions at 30℃, gelatin solution was added to silver nitrate solution and stirred for 3 min to obtain solution B.

[0074] S3. Under the stirring conditions of a water bath at 35℃, solution B is added to solution A at a dropping rate of 50 mL / min. At the same time, ascorbic acid solution is added to solution A at a dropping rate of 75 mL / min. After the addition is completed, stirring is continued for 5 min. Solid-liquid separation is performed to obtain the precipitate.

[0075] S4. Washing the precipitate: First, wash the precipitate repeatedly with deionized water until the conductivity is <20μS / cm, then remove the supernatant to obtain a first precipitate with a water content of 15%; then wash the first precipitate twice with ethanol to remove the supernatant and obtain a second precipitate; add a mixed solution of palmitic acid / arachidic acid to the second precipitate, stir for 10 min, dry at a constant temperature of 40℃ to constant weight, and then grind and disperse to obtain the target silver powder.

[0076] The SEM image of the silver powder prepared in this embodiment is shown below. Figure 1 As shown.

[0077] Depend on Figure 1 It can be seen that the obtained silver powder is a regular spherical powder with a particle size concentrated in the range of 0.4 to 0.8 μm, and has high crystallinity and large specific surface area.

[0078] Examples 2-3 and Comparative Examples 1-2

[0079] Examples 2-3 and Comparative Examples 1-2 respectively provide a method for preparing silver powder with high crystallinity and narrow particle size distribution. The difference from Example 1 is that the amount of sodium citrate is different, as shown in Table 1. The other steps are roughly the same as in Example 1, and will not be repeated here.

[0080] The SEM images of the silver powders prepared in Examples 2-3 and Comparative Examples 1-2 are shown below. Figure 2 As shown.

[0081] Table 1. Mass percentage of sodium citrate and morphology of silver powder in Examples 1-3 and Comparative Examples 1-2

[0082]

[0083] The appearance and particle size of the silver powder prepared in Examples 2 and 3 are similar to those in Example 1. Compared with the silver powder prepared in Example 1, the silver powder in Comparative Example 1 has an irregular morphology and a wider size distribution. The insufficient amount of stabilizer leads to a decrease in the stability of the seed crystals, which act as heterogeneous nuclei in the subsequent growth stage, causing small particles to dissolve and large particles to grow, ultimately resulting in a wider particle size distribution of the silver powder. The silver powder particles formed in Comparative Example 2 are small in size and agglomerate. Excessive stabilizer inhibits the activity of the seed crystals, reduces the reaction rate of silver, and excessive inhibition of growth leads to new, uncontrolled secondary nucleation, resulting in the generation of a large number of small silver powder particles. The uneven growth rate leads to increased agglomeration.

[0084] Examples 4-5, Comparative Examples 3-4

[0085] Examples 4-5 and Comparative Examples 3-4 respectively provide a method for preparing silver powder with high crystallinity and narrow particle size distribution. Compared with Example 1, the difference is the amount of nitric acid used, as shown in Table 2. The other steps are roughly the same as in Example 1, and will not be repeated here.

[0086] Table 2 shows the mass percentage of nitric acid, pH value of solution A, and morphology of silver powder in Examples 1, 4-5, and Comparative Examples 3-4.

[0087]

[0088] SEM images of the silver powder prepared in Comparative Examples 3 and 4 are shown below. Figure 3 As shown.

[0089] Depend on Figure 3 It is known that when the amount of nitric acid is too small and the pH value is too high, a large number of fine and irregular silver powder particles will be generated and agglomeration will occur, resulting in a wider particle size distribution and lower crystallinity of silver powder. When the amount of nitric acid is too large and the pH value is too low, the silver powder will have a rough and irregular morphology. Excessive nitric acid will affect the spatial barrier effect of the dispersant, resulting in polarization of silver powder particle size and a wider particle size distribution.

[0090] Comparative Example 5

[0091] This comparative example provides a method for preparing silver powder with high crystallinity and narrow particle size distribution. Compared with Example 1, the difference is that in step (2), gelatin solution (dispersant solution) is added to solution A as the base liquid, and in step (3), silver nitrate solution and ascorbic acid solution are added to the base liquid at the same time. Other steps are roughly the same as in Example 1, and will not be repeated here.

[0092] The microstructure of the silver powder prepared in this comparative example is as follows: Figure 4 As shown.

[0093] Depend on Figure 4 It can be seen that when the dispersant is added to solution A as the base liquid, the resulting silver powder exhibits severe agglomeration and irregular morphology, leading to a wider particle size distribution and reduced crystallinity.

[0094] In summary, this application provides a silver powder with high crystallinity and narrow particle size distribution, and a method for preparing the same. By preparing different reaction mixtures stepwise and then mixing them under specific conditions, submicron silver powder with high crystallinity, narrow particle size distribution, and large specific surface area can be prepared in a simple and controllable manner.

[0095] Using seed solution as a heterogeneous nucleation substrate can significantly reduce the energy required for nucleation. After nitrate is reduced, it can form a large number of fine particles, increasing the reaction interface. With the existing particles as the substrate, silver ions can be rapidly and uniformly reduced and deposited on its surface. Nitrate seed crystals can also provide highly dispersed fixed deposition points, allowing silver to preferentially grow on the particles formed by their own independent nitrates, thereby effectively improving the dispersibility of silver powder particles. On the nitrate-formed particle substrate, due to the good lattice matching between the particles and silver, silver tends to crystallize and grow in a more ordered and dense manner, which is conducive to the generation of silver powder particles with smooth surfaces and high crystallinity.

[0096] The synergistic treatment of seed crystals using stabilizers and nitric acid provides protection against stabilizer formation and a specific pH, resulting in good stability and independence of the seed crystals in the early stages of the reaction. This promotes the formation of silver powder with uniform particle size and high dispersion. By adding stabilizers to nitrate seed crystals for pretreatment, a seed crystal solution with good dispersibility, high stability, and abundant active sites can be obtained in advance. During the reaction, silver preferentially undergoes heterogeneous deposition on the seed crystals, ultimately resulting in silver powder with narrow particle size distribution, good dispersibility, regular morphology, and high crystallinity. Advanced features: The addition of nitric acid can precisely adjust the pH value of the system, keeping the seed crystals in a suitable hydrolytic state. The acidic environment can inhibit excessive hydrolysis of the seed crystals, maintain the uniformity and highly active surface of the seed crystals, and provide more effective sites for heterogeneous nucleation of silver. The acidic environment provided by nitric acid can reduce seed crystal agglomeration and make the seed crystals more uniformly distributed. The surface charge distribution of nitrate seed crystals in acidic media is more controllable, which is conducive to the uniform growth of silver on the seed crystal surface, forming silver powder with uniform particle size and regular morphology. The anisotropic growth of silver under acidic conditions is inhibited, which strengthens the regularity of the silver powder morphology.

[0097] Based on this, by adding a dispersant to the silver nitrate solution at a constant temperature, the effective groups of the dispersant form a spatial barrier, which further enhances the uniformity and dispersibility of the silver powder size. In addition, the dispersant can regulate the growth rate of different crystal planes during the reaction process, promoting the formation of highly crystalline silver powder particles with regular morphology, complete crystal lattice and few defects.

[0098] Based on the synergistic treatment of seed crystals by stabilizer and nitric acid as the base liquid, silver nitrate solution treated with dispersant at constant temperature and reducing agent solution (ascorbic acid solution) are simultaneously added to the base liquid to obtain silver powder with high crystallinity and narrow particle size distribution characteristics, which has a higher specific surface area than traditional silver powder.

[0099] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for producing a silver powder having a high crystallinity and a narrow particle size distribution, characterized by, The method comprises the following steps: S1. Prepare silver nitrate solution, ascorbic acid solution, stabilizer solution, dispersant solution, seed solution, nitric acid solution and surface modifier solution respectively; S2. Under stirring, mix the stabilizer solution and the nitric acid solution with the seed solution to obtain solution A, and mix the dispersant solution with the silver nitrate solution to obtain solution B; S3. Add the solution B and the ascorbic acid solution into the solution A at the same time, and after the reaction is completed, perform solid-liquid separation to obtain a precipitate; S4. Wash the precipitate, then add the surface modifier solution, fully stir, and then dry and disperse to obtain the target silver powder.

2. The method of claim 1, wherein the silver powder has a crystallinity of 80% or more and a particle size distribution of 0.5 or less. In step S1, the stabilizer in the stabilizer solution is one or more of sodium citrate, sodium dodecyl sulfate, 1-dodecyl mercaptan, mercaptoacetic acid, and cetyltrimethylammonium bromide; the mass of the stabilizer accounts for 0.8-3.6% of the mass of silver nitrate in the silver nitrate solution.

3. The method of claim 1, wherein the silver powder has a crystallinity of 80% or more and a narrow particle size distribution. In step S1, the dispersant in the dispersant solution is one or more of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, sodium polyacrylate, gelatin, and gum arabic; the mass of the dispersant accounts for 0.5-3.5% of the mass of silver nitrate in the silver nitrate solution.

4. The method of claim 1, wherein the silver powder has a crystallinity of 90% or more and a particle size distribution of 0.5 or less. In step S1, the seed in the seed solution is one or more of nickel nitrate, magnesium nitrate, aluminum nitrate, copper nitrate, and zinc nitrate; the mass of the seed accounts for 0.1-0.5% of the mass of silver nitrate in the silver nitrate solution.

5. The method of claim 1, wherein the silver powder has a crystallinity of 90% or more and a narrow particle size distribution. In step S1, the mass of nitric acid in the nitric acid solution accounts for 0.5-4.2% of the mass of silver nitrate.

6. The method of claim 1, wherein the silver powder has a crystallinity of at least 90% and a narrow particle size distribution. In step S1, the surface modifier in the surface modifier solution is one or more of saturated fatty acid, unsaturated organic acid, silane coupling agent, titanate coupling agent, and aluminate coupling agent; the mass of the surface modifier accounts for 0.2-3% of the mass of silver nitrate in the silver nitrate solution.

7. The method of claim 1, wherein the silver powder has a crystallinity of at least 90% and a narrow particle size distribution. In step S1, the mass concentration of the silver nitrate solution is 100-350 g / L, and the mass concentration of the ascorbic acid solution is 80-280 g / L; the mass ratio of ascorbic acid in the ascorbic acid solution to silver nitrate in the silver nitrate solution is 1:1-1:2.

5.

8. The method of claim 1, wherein the silver powder has a crystallinity of at least 90% and a narrow particle size distribution. In step S2, the pH value of the solution A is 0.5-6; and the mixing temperature is 20-50℃.

9. The method of claim 1, wherein the silver powder has a crystallinity of at least 90% and a narrow particle size distribution. In step S3, the adding mode is dropwise adding, the adding rate of the solution B is 50-150 mL / min, the adding rate of the ascorbic acid solution is 50-150 mL / min; and the reaction temperature is 20-50℃.

10. A high crystallinity and narrow particle size distribution silver powder, characterized by, The high-crystallinity and narrow-size-distribution silver powder is prepared by the method of any one of claims 1-9, and has a specific surface area of 0.4-1.1 m 2 / g, a particle size D50 of 0.5-0.9 μm, and a tap density of 3.5-6.5 g / mL.

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