Silver powder with high crystallinity and narrow particle size distribution and preparation method thereof

Abstract

The invention provides silver powder with high crystallinity and narrow particle size distribution and a preparation method thereof, and belongs to the technical field of metal powder preparation. The preparation method comprises the following steps: preparing a silver nitrate solution, an ascorbic acid solution, a stabilizer solution, a dispersant solution, a seed crystal solution, a nitric acid solution and a surface modifier solution; adding the stabilizer solution and the nitric acid solution into the seed crystal solution, and mixing to obtain a solution A with specific PH; the dispersing agent solution is added into the silver nitrate solution for mixing, and a solution B is obtained; adding the solution B and an ascorbic acid solution into the solution A, fully reacting, and collecting a precipitate; and washing the precipitate, adding a surface modifier solution, fully stirring, drying, and dispersing to obtain the target silver powder. Different reaction mixed solutions are prepared step by step and then mixed according to a specific sequence, and the submicron silver powder with the high crystallinity and the large specific surface area is prepared through a simple and controllable method.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal powder and its preparation, in particular to a kind of high crystallinity and narrow particle size distribution silver powder and its preparation method. BACKGROUND

[0002] The application of silver powder ranges from macroscopic power transmission to microscopic electronic circuit, from daily antibacterial products to cutting-edge aerospace technology. The continuous expansion of its application field also continuously promotes the development of silver powder preparation technology towards more fine, functional and customized direction.

[0003] Silver powder is the core conductive material for preparing crystalline silicon solar cell metal electrode, and the morphology, particle size, tap density and other characteristics of silver powder directly determine the performance of the battery. Traditional silver powder is mostly micron-sized spherical and has wide particle size distribution. In recent years, in order to improve the rheological property of slurry and printing consistency, and to print finer and higher aspect ratio grid lines, silver powder with narrower particle size distribution, better dispersibility and higher crystallinity is required to adapt to new battery structure, improve printing performance and enhance printing precision.

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

[0005] In view of the technical problems in the background art, the present application provides a kind of high crystallinity and narrow particle size distribution silver powder and its preparation method, aims at solving the problems that the existing silver powder preparation process is difficult to prepare silver powder with high crystallinity, uniform particle size distribution and good sphericity.

[0006] In a first aspect, the present application provides a preparation method of a high crystallinity and narrow particle size distribution silver powder, comprising the following steps: S1. respectively prepare silver nitrate solution, ascorbic acid solution, stabilizer solution, dispersant solution, seed crystal solution, nitric acid solution and surface modifier solution; S2. under stirring, the stabilizer solution and the nitric acid solution are added to the seed crystal solution for mixing to obtain solution A, and the dispersant solution is added to the silver nitrate solution for mixing to obtain solution B; S3. the solution B and the ascorbic acid solution are simultaneously added to the solution A, after the reaction is completed, solid-liquid separation is carried out to obtain a precipitate; S4. the precipitate is washed, then the surface modifier solution is added, after sufficient stirring, drying and dispersion treatment, the target silver powder is obtained.

[0007] In the technical scheme of the embodiment of the present application, the seed crystal is treated by using a stabilizer and nitric acid in cooperation, and the stabilizer forms a protection and a specific pH, which makes the seed crystal have good stability and independence in the initial stage of the reaction, promotes the generation of silver powder with uniform particle size and high dispersion, and on this basis, the dispersant is added to the silver nitrate solution at a constant temperature, the effective groups of the dispersant form a steric hindrance, which further strengthens the uniformity and dispersion of the silver powder size, and the dispersant can control the growth rate of different crystal faces in the reaction process, and promote the generation of high-crystallinity silver powder particles with regular morphology, complete crystal lattice and few defects. Based on the cooperative treatment of the stabilizer and nitric acid on the seed crystal and the treatment of the dispersant on the silver nitrate at a constant temperature, the silver powder prepared by the present application has high crystallinity and narrow particle size distribution characteristics, and has a higher specific surface area than the traditional silver powder.

[0008] 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 cetyltrimethylammonium bromide; and the mass of the stabilizer accounts for 0.8-3.6% of the mass of silver nitrate in the silver nitrate solution.

[0009] In this embodiment, by adding a stabilizer to the nitrate seed crystal and using the stabilizer to pretreat the nitrate seed crystal, a seed crystal solution with good dispersion, high stability and rich active sites can be obtained in advance, silver is preferentially deposited on the seed crystal during the reaction, and finally the obtained silver powder has the characteristics of narrow particle size distribution, good dispersion, regular morphology, high crystallinity and the like.

[0010] 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; and the mass of the dispersant accounts for 0.5-3.5% of the mass of silver nitrate in the silver nitrate solution.

[0011] In this embodiment, by premixing the dispersant solution and the silver nitrate solution to form a stable silver ion complex, the reaction speed is effectively controlled, the uniformity of the size is ensured, the steric hindrance isolation is established in advance, the silver powder is guided to grow regularly, and the regularity of the silver powder morphology is ensured.

[0012] In some embodiments, in step S1, the seed crystal in the seed crystal solution is one or more of nickel nitrate, magnesium nitrate, aluminum nitrate, copper nitrate, and zinc nitrate; and the mass of the seed crystal accounts for 0.1-0.5% of the mass of silver nitrate in the silver nitrate solution.

[0013] In the embodiment, the heterogeneous nucleation substrate can significantly reduce the energy required for nucleation, and a large number of fine particles can be formed after the nitrate is reduced, the reaction interface is increased, and the existing particles are used as the substrate to make the silver ions quickly and uniformly reduced and deposited on the surface of the particles; the nitrate seed can provide highly dispersed fixed deposition points, so that the silver preferentially grows on the particles formed by the respective independent nitrates, thereby effectively improving the dispersity of the silver powder particles; on the particle substrate formed by the nitrates, the particle and the silver lattice match well, the silver tends to crystallize and grow in a more ordered and denser manner, which is beneficial to the generation of silver powder particles with smooth surface and high crystallinity.

[0014] In some embodiments, 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.

[0015] In the embodiment, the addition of nitric acid can accurately adjust the pH value of the system, so that the seed maintains an appropriate hydrolysis state, the acidic environment can inhibit the excessive hydrolysis of the seed, maintain the uniformity and high active surface of the seed, and provide more effective sites for heterogeneous nucleation of silver; the acidic environment provided by the nitric acid can reduce the agglomeration of the seed, so that the seed is more uniformly distributed; the surface charge distribution of the nitrate seed in the acidic medium is more controllable, which is beneficial to the uniform growth of silver on the surface of the seed, and the formation of 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 the silver powder.

[0016] 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 0.2-3% of the mass of silver nitrate in the silver nitrate solution.

[0017] In the embodiment, the addition of the surface modifier improves the applicability of the silver powder in the slurry. The coating layer of the surface modifier can effectively improve the dispersity of the slurry, control the rheological property of the slurry, and make the slurry maintain better linearity after printing, thereby improving the aspect ratio of the electrode and the battery efficiency.

[0018] 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.

[0019] In the embodiment, the mixing of the oxidation solution and the reduction solution with specific concentration ratio can ensure that the oxidation-reduction reaction is fully carried out.

[0020] In some embodiments, in step S2, the pH value of the solution A is 0.5-6; and the temperature of the mixing is 20-50°C.

[0021] In this embodiment, under a specific pH value, i.e. acidic condition, the seed crystal is pretreated by heating and stirring with a stabilizer, which consolidates the dispersity, uniformity and abundance of the effective sites provided by the nitrate seed crystal in the reaction process, so that silver can be uniformly deposited in a heterogeneous phase; the pretreatment of the solution A by constant temperature stirring can reduce the randomness of nucleation and growth, so as to ensure the uniformity of the silver powder size and the regularity of the morphology during the deposition process.

[0022] In some embodiments, 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 temperature of the reaction is 20-50°C.

[0023] In this embodiment, by a specific and constant dropwise adding speed, the reactants are continuously provided at a balanced concentration, so that the silver powder growth is dominant, which is conducive to the generation of submicron silver powder with uniform size and regular morphology; by a specific reaction temperature, the silver powder is ensured to grow at a certain reaction rate, so as to control the morphology, size, crystallinity and other characteristics of the silver powder.

[0024] In a second aspect, the application provides a high-crystallinity and narrow-particle-size-distribution silver powder, which is prepared by the above-mentioned method for preparing high-crystallinity and narrow-particle-size-distribution silver powder, 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.

[0025] In the technical scheme of the embodiments of the application, the silver powder has uniform and extremely small particle size, large specific surface area and high crystallinity, can be adapted to new battery structures, improve printing performance and enhance printing precision. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The SEM image of the silver powder prepared in Example 1 of the application.

[0027] Figure 2 The SEM image of the silver powder prepared in Examples 2-3 and Comparative Examples 1-2 of the application.

[0028] Figure 3 The SEM image of the silver powder prepared in Comparative Examples 3-4 of the application.

[0029] Figure 4 The SEM image of the silver powder prepared in Comparative Example 5 of the application. DETAILED DESCRIPTION

[0030] The embodiments of the technical solutions of the present application are described in detail below. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0031] Reference to "embodiments" herein means that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily mutually exclusive of other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0032] In order to solve the problem that it is difficult to prepare silver powder with high crystallinity, uniform particle size distribution and good sphericity by using the existing silver powder preparation process, the present application provides a high-crystallinity and narrow-particle-size-distribution silver powder and a preparation method thereof. By step-by-step preparation of different reaction mixed solutions and then mixing according to specific conditions, sub-micron silver powder with high crystallinity, narrow particle size distribution and large specific surface area is prepared by a simple and controllable method.

[0033] Using the seed solution as a heterogeneous nucleation substrate can significantly reduce the energy required for nucleation. After the nitrate is reduced, a large number of fine particles are formed, increasing the reaction interface. Using the existing particles as a substrate, silver ions are quickly and uniformly reduced and deposited on the surface thereof. The nitrate seed can also provide highly dispersed fixed deposition points, so that silver preferentially grows on the particles formed by the nitrate, thereby effectively improving the dispersibility of the silver powder particles. On the particle substrate formed by the nitrate, the lattice matching between the particles and silver is good, and silver tends to crystallize and grow in a more ordered and denser manner, which is conducive to the formation of silver powder particles with smooth surfaces and high crystallinity.

[0034] The synergistic treatment of the seed crystal with the stabilizer and nitric acid has the protection formed by the stabilizer and the specific pH, which makes the seed crystal have good stability and independence in the initial stage of the reaction, promotes the generation of silver powder with uniform particle size and high dispersion, and the like; by adding the stabilizer to the nitrate seed crystal and using the stabilizer to pretreat the nitrate seed crystal, a seed crystal solution with good dispersion, high stability and rich active sites can be obtained in advance, the silver preferentially deposits on the seed crystal in the reaction process, and finally the obtained silver powder has the characteristics of narrow particle size distribution, good dispersion, regular morphology, high crystallinity and the like; the addition of nitric acid can accurately adjust the pH value of the system, so that the seed crystal maintains an appropriate hydrolysis state, the acidic environment can inhibit the excessive hydrolysis of the seed crystal, and the uniformity and high active surface of the seed crystal are maintained, so as to provide more effective sites for heterogeneous nucleation of silver; the acidic environment provided by the nitric acid can reduce the agglomeration of the seed crystal, so that the seed crystal is more uniformly distributed; the surface charge distribution of the nitrate seed crystal in the acidic medium is more controllable, which is beneficial to the uniform growth of silver on the surface of the seed crystal, and the formation of 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 the silver powder.

[0035] On this basis, by adding a dispersant to the silver nitrate solution at a constant temperature, the uniformity and dispersion of the silver powder size are further strengthened by the space barrier formed by the effective groups of the dispersant, and the dispersant can regulate the growth rate of different crystal faces in the reaction process, so as to promote the generation of high-crystallinity silver powder particles with regular morphology, complete crystal lattice and few defects.

[0036] Based on the synergistic treatment of the seed crystal with the stabilizer and nitric acid as the base solution, the silver nitrate solution treated with the dispersant at a constant temperature and the reducing agent solution (ascorbic acid solution) are simultaneously added to the base solution, so as to prepare silver powder with high crystallinity and narrow particle size distribution characteristics, which has a higher specific surface area than traditional silver powder.

[0037] In a first aspect, the application provides a preparation method of silver powder with high crystallinity and narrow particle size distribution, which comprises the following steps: S1. Prepare silver nitrate solution, ascorbic acid solution, stabilizer solution, dispersant solution, seed crystal solution, nitric acid solution and surface modifier solution, respectively; S2. Under stirring conditions, the stabilizer solution and the nitric acid solution are added to the seed crystal solution for mixing to obtain solution A, and the dispersant solution is added to the silver nitrate solution for mixing to obtain solution B; S3. The solution B and the ascorbic acid solution are simultaneously added to the solution A, and after the reaction is completed, solid-liquid separation is performed to obtain a precipitate; S4. The precipitate is washed, then the surface modifier solution is added, and after sufficient stirring, drying and dispersion treatment are performed to obtain the target silver powder.

[0038] In the technical scheme of the embodiment of the application, the seed crystal is treated by the stabilizer and nitric acid in cooperation, and the stabilizer forms a protection and a specific PH, so that the seed crystal has good stability and independence in the initial stage of the reaction, and the silver powder with uniform particle size and high dispersion is generated; on this basis, the dispersant is added to the silver nitrate solution at a constant temperature, the space barrier is formed by the effective groups of the dispersant, the uniformity and dispersion of the silver powder size are further strengthened, and the dispersant can control the growth rate of different crystal faces in the reaction process, so that the silver powder particles with regular morphology, complete crystal lattice and few defects are generated. Based on the cooperative treatment of the stabilizer and nitric acid on the seed crystal and the treatment of the dispersant on the silver nitrate at a constant temperature, the silver powder prepared by the application has high crystallinity and narrow particle size distribution characteristics, and has a higher specific surface area than the traditional silver powder.

[0039] Further, 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, mercapto acetic 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.

[0040] In the technical scheme of the embodiment of the application, the stabilizer is added to the nitrate seed crystal, and the stabilizer is used to pretreat the nitrate seed crystal, so that a seed crystal solution with good dispersion, high stability and rich active sites can be obtained in advance, silver is preferentially deposited on the seed crystal during the reaction process, and finally the obtained silver powder has the characteristics of narrow particle size distribution, good dispersion, regular morphology, high crystallinity and the like.

[0041] Further, 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 0.5-3.5% of the mass of silver nitrate in the silver nitrate solution.

[0042] In the technical scheme of the embodiment of the application, the dispersant solution and the silver nitrate solution are premixed to form a stable silver ion complex, so as to effectively control the reaction speed, ensure the uniformity of the size, pre-establish a space barrier isolation, guide the regular growth of the silver powder, and ensure the regularity of the silver powder morphology.

[0043] Further, in some embodiments, in step S1, the seed crystal in the seed crystal solution is one or more of nickel nitrate, magnesium nitrate, aluminum nitrate, copper nitrate and zinc nitrate; the mass of the seed crystal accounts for 0.1-0.5% of the mass of silver nitrate in the silver nitrate solution.

[0044] The heterogeneous nucleation substrate can significantly reduce the energy required for nucleation, and a large number of fine particles can be formed after the nitrate is reduced, the reaction interface is increased, and the existing particles are used as a substrate to enable the silver ions to be quickly and uniformly reduced and deposited on the surface thereof; the nitrate seed crystal can provide a highly dispersed fixed deposition point, so that the silver preferentially grows on the particles formed by the respective independent nitrates, thereby effectively improving the dispersity of the silver powder particles; on the particle substrate formed by the nitrates, the particle and the silver lattice are well matched, the silver tends to crystallize and grow in a more ordered and denser manner, and the silver powder particles with a smooth surface and high crystallinity can be favorably generated.

[0045] Further, in some embodiments, in step S1, the mass of the nitric acid in the nitric acid solution accounts for 0.5-4.2% of the mass of the silver nitrate.

[0046] In the technical scheme of the embodiments of the present application, the addition of nitric acid can accurately adjust the pH value of the system, so that the seed crystal maintains an appropriate hydrolysis state, the acidic environment can inhibit the excessive hydrolysis of the seed crystal, the uniformity and high active surface of the seed crystal are maintained, and more effective sites are provided for the heterogeneous nucleation of silver; the acidic environment provided by the nitric acid can reduce the agglomeration of the seed crystal, so that the seed crystal is more uniformly distributed; the surface charge distribution of the nitrate seed crystal in the acidic medium is more controllable, which is conducive to the uniform growth of silver on the surface of the seed crystal, and the formation of 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 the silver powder.

[0047] Further, in some embodiments, in step S1, the surface modifier in the surface modifier solution is one or more of a saturated fatty acid, an unsaturated organic acid, a silane coupling agent, a titanate coupling agent, and an aluminate coupling agent; the mass of the surface modifier accounts for 0.2-3% of the mass of the silver nitrate in the silver nitrate solution.

[0048] In the technical scheme of the embodiments of the present application, the addition of the surface modifier improves the applicability of the silver powder in the slurry. The coating layer of the surface modifier can effectively improve the dispersity of the slurry, control the rheological property of the slurry, and enable the slurry to maintain a better linearity after printing, thereby improving the aspect ratio of the electrode and the battery efficiency.

[0049] Further, 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.

[0050] In the technical scheme of the embodiments of the present application, the mixing of the oxidation solution and the reduction solution with specific concentration ratios can ensure that the oxidation-reduction reaction proceeds sufficiently.

[0051] Further, in some embodiments, in step S2, the pH value of the solution A is 0.5-6; the temperature of the mixing is 20-50℃; the mixing time of the solution A is 1-20 min, and the mixing time of the solution B is 0.5-20 min.

[0052] In the technical scheme of the embodiments of the present application, under a specific pH value, i.e. an acidic condition, the seed crystal is pretreated by heating and stirring with a stabilizer, which consolidates the dispersity, uniformity and richness of the effective sites provided by the nitrate seed crystal in the reaction process, so that the silver can be uniformly deposited in a heterogeneous phase; the constant temperature stirring pretreatment of the solution A can reduce the randomness of nucleation and growth, so as to ensure the uniformity of the silver powder size and the more regular morphology in the deposition process.

[0053] Further, in some embodiments, 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℃.

[0054] In the technical scheme of the embodiments of the present application, by using a specific and constant dropwise adding speed, the reactants with balanced concentration are continuously provided, so that the silver powder growth is dominant, which is conducive to generating submicron silver powder with uniform size and regular morphology; by using a specific reaction temperature, the silver powder is ensured to grow at a certain reaction rate, so as to control the morphology, size, crystallinity and other characteristics of the silver powder.

[0055] Further, in some embodiments, in step S4, the washing specifically includes the following steps: First, the precipitate is washed with deionized water until the conductivity is less than 20 μS / cm, and then the supernatant is removed to obtain a first precipitate; the water content of the first precipitate is less than or equal to 20%; and then the first precipitate is washed with ethanol, and the supernatant is removed, thereby completing the washing.

[0056] Further, in some embodiments, in step S4, the dispersion treatment is grinding and dispersion.

[0057] In a second aspect, the present application provides a high-crystallinity and narrow-particle-size-distribution silver powder, which is prepared by the above-mentioned method for preparing high-crystallinity and narrow-particle-size-distribution silver powder, 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.

[0058] In the technical scheme of the embodiments of the present application, the silver powder has uniform and extremely small particle size, large specific surface area and high crystallinity, which can be adapted to the new battery structure, improve the printing performance and enhance the printing precision.

[0059] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are used to explain the present application, and should not be construed as limiting the present application. If a specific technique or condition is not specified in the examples, the technique or condition described in the literature in the art or according to the product manual is used. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be obtained on the market.

[0060] Example 1 The present embodiment provides a method for preparing silver powder with high crystallinity and narrow particle size distribution, comprising the following steps: S1. Prepare silver nitrate solution, ascorbic acid solution, sodium citrate solution, gelatin solution, seed solution, nickel nitrate solution, nitric acid solution and mixed solution of palmitic acid / peanut acid, respectively. The mass concentration of the silver nitrate solution is 180 g / L; the mass concentration of the ascorbic acid solution is 150 g / L, and the mass ratio of ascorbic acid to silver nitrate is 1:2; the mass concentration of the sodium citrate solution is 10 g / L, and the mass of the sodium citrate solution accounts for 1.1% of the mass of the silver nitrate; the mass concentration of the gelatin solution is 1.6 g / L, and the mass of the gelatin accounts for 0.5% of the mass of the silver nitrate; the mass concentration of the nickel nitrate solution is 5 g / L, and the mass of the nickel nitrate accounts for 0.15% of the mass of the silver nitrate; the amount-of-substance concentration of the nitric acid solution is 2 moL / L, and the mass of the nitric acid accounts for 0.5% of the mass of the silver nitrate; the mass concentration of the mixed solution of palmitic acid / peanut acid is 6 g / L, and the total mass of the palmitic acid / peanut acid accounts for 0.2% of the mass of the silver nitrate.

[0061] S2. Under stirring at 30°C, the sodium citrate solution and the nitric acid solution are added to the nickel nitrate solution, and stirred for 5 min to obtain solution A with a pH value of 5.5; under constant temperature stirring at 30°C, the gelatin solution is added to the silver nitrate solution and stirred for 3 min to obtain solution B.

[0062] S3. Under stirring in a water bath at 35°C, solution B is added to solution A at a dropping speed of 50 mL / min, and at the same time, the ascorbic acid solution is added to solution A at a dropping speed of 75 mL / min; after the dropping is completed, the stirring is continued for 5 min, and the solid-liquid separation is performed to obtain a precipitate.

[0063] S4. Washing the precipitate: repeatedly washing the precipitate with deionized water until the conductivity is < 20 μS / cm, removing the supernatant, and obtaining a first precipitate with a water content of 15%; then washing the first precipitate twice with ethanol, removing the supernatant, and obtaining a second precipitate; adding a mixed solution of palmitic acid / peanut acid to the second precipitate, stirring for 10 min, drying at a constant temperature of 40 °C until the weight is constant, and then polishing and dispersing to obtain the target silver powder.

[0064] The SEM image of the silver powder prepared in this example is shown in FIG. 1. Figure 1

[0065] As can be seen from FIG. 1, the obtained silver powder is a regular spherical powder, the particle size is concentrated in 0.4-0.8 μm, and the silver powder has high crystallinity and large specific surface area. Figure 1 Examples 2-3 and Comparative Examples 1-2

[0066] Examples 2-3 and Comparative Examples 1-2 each provide a method for preparing a silver powder with high crystallinity and narrow particle size distribution, and the difference from Example 1 is that the amount of sodium citrate is different, as shown in Table 1, and the other steps are substantially the same as those of Example 1, which will not be described here. The SEM images of the silver powder prepared in Examples 2-3 and Comparative Examples 1-2 are shown in FIGS. 2-4, respectively.

[0067] Figure 2

[0068] Table 1: Mass ratio of sodium citrate and silver powder morphology in Examples 1-3 and Comparative Examples 1-2 The appearance and particle size of the silver powder prepared in Examples 2-3 are similar to those of Example 1; compared with the silver powder prepared in Example 1, the silver powder in Comparative Example 1 has irregular morphology and wide size distribution, and the low amount of stabilizer leads to reduced stability of the crystal seeds, which acts as a heterogeneous core in the subsequent growth stage, leading to dissolution of small particles and growth of large particles, and ultimately leading to wide particle size distribution of the silver powder; in Comparative Example 2, the silver powder has small particle size and agglomeration, the excessive amount of stabilizer inhibits the activity of the crystal seeds, reduces the reaction rate of silver, and excessive inhibition of growth leads to uncontrolled secondary nucleation, resulting in a large amount of small particle silver powder, and uneven growth rate leads to increased agglomeration.

[0069] Examples 4-5 and Comparative Examples 3-4 Examples 4-5 and Comparative Examples 3-4 each provide a method for preparing a silver powder with high crystallinity and narrow particle size distribution, and the difference from Example 1 is that the amount of nitric acid is different, as shown in Table 2, and the other steps are substantially the same as those of Example 1, which will not be described here.

[0070] ​​​Table 2 Mass ratio of nitric acid, pH value of solution A and morphology of silver powder in Example 1, 4-5 and Comparative Examples 3-4 The SEM images of the silver powder prepared in Comparative Examples 3-4 are shown in Figure 3

[0071] As can be seen from Figure 3 , when the amount of nitric acid is too small and the pH value is too high, a large amount of fine and irregularly shaped silver powder particles are generated, and agglomeration occurs, resulting in a wide particle size distribution and low crystallinity of the silver powder; when the amount of nitric acid is too large and the pH value is too low, the silver powder has a rough and irregular morphology, and the excess nitric acid affects the steric hindrance of the dispersant, resulting in a two-pole differentiation of the silver particle size and a wide particle size distribution.

[0072] Comparative Example 5 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), the gelatin solution (dispersant solution) is added to solution A as a bottom solution, and in step (3), the silver nitrate solution and ascorbic acid solution are simultaneously added to the bottom solution. The other steps are substantially the same as those of Example 1, and will not be described here.

[0073] The microscopic morphology of the silver powder prepared in this comparative example is shown in Figure 4

[0074] As can be seen from Figure 4 , adding the dispersant to solution A as a bottom solution results in severe agglomeration of the final silver powder, irregular morphology, wide particle size distribution, and low crystallinity.

[0075] In summary, the present application provides a method for preparing silver powder with high crystallinity and narrow particle size distribution. By preparing different reaction mixed solutions step by step 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.

[0076] Using a seed solution as a heterogeneous nucleation substrate can significantly reduce the energy required for nucleation. After reduction of the nitrate salt, a large number of fine particles are formed, increasing the reaction interface. Using existing particles as a substrate allows silver ions to be rapidly and uniformly reduced and deposited on their surface. The nitrate salt seed also provides highly dispersed and fixed deposition points, allowing silver to preferentially grow on the particles formed by the nitrate salt, thereby effectively improving the dispersibility of the silver powder particles. On the particle substrate formed by the nitrate salt, the lattice matching between the particles and silver is good, and silver tends to crystallize and grow in a more ordered and denser manner, which is beneficial to the generation of silver powder particles with smooth surfaces and high crystallinity.

[0077] ​​The synergic treatment of the seed crystal with the stabilizer and nitric acid has the protection formed by the stabilizer and the specific PH, which makes the seed crystal have good stability and independence in the initial stage of the reaction, promotes the generation of silver powder with uniform particle size and high dispersion; by adding the stabilizer into the nitrate seed crystal and using the stabilizer to pretreat the nitrate seed crystal, the seed crystal solution with good dispersion, high stability and rich active sites can be obtained in advance, the silver preferentially deposits on the seed crystal in the reaction process, and finally the obtained silver powder has the characteristics of narrow particle size distribution, good dispersion, regular morphology, high crystallinity and the like; the addition of nitric acid can accurately adjust the pH value of the system, so that the seed crystal maintains the appropriate hydrolysis state, the acidic environment can inhibit the excessive hydrolysis of the seed crystal, maintains the uniformity and high active surface of the seed crystal, and provides more effective sites for the heterogeneous nucleation of silver; the acidic environment provided by the nitric acid can reduce the agglomeration of the seed crystal, so that the seed crystal is more uniformly distributed; the surface charge distribution of the nitrate seed crystal in the acidic medium is more controllable, which is beneficial to the uniform growth of silver on the surface of the seed crystal, and the formation of 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 the silver powder.

[0078] On this basis, by adding a dispersant to the silver nitrate solution at a constant temperature, the uniformity and dispersion of the silver powder size are further strengthened by the space barrier formed by the effective groups of the dispersant, and the dispersant can regulate the growth rate of different crystal faces in the reaction process, promote the formation of high-crystallinity silver powder particles with regular morphology, complete lattice and few defects.

[0079] Based on the synergic treatment of the seed crystal with the stabilizer and nitric acid as the base solution, the silver nitrate solution treated with the dispersant at a constant temperature and the reducing agent solution (ascorbic acid solution) are simultaneously added into the base solution to prepare silver powder with high crystallinity and narrow particle size distribution characteristics, which has a higher specific surface area than the traditional silver powder.

[0080] The above examples are only used to illustrate the technical solutions of the present application and not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the present application.

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 at least 90% 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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