Spherical submicron silver powder and method for preparing the same

Abstract

The application discloses a kind of spherical sub-micron silver powder and its preparation method.The method is under the condition of magnetic field, silver salt solution is mixed with ammonia water and the system pH is adjusted to alkaline range, to obtain silver ammonia solution, then the silver ammonia solution is sequentially added with the solution containing surfactant and reducing agent to carry out reduction reaction, and the silver powder is obtained.The method can adjust the morphology size of sub-micron spherical silver powder, and the size and morphology of the prepared silver powder are more uniform, which can be used for the preparation of solar cells, flexible circuit electronic paste.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of silver powder, specifically relates to a kind of spherical submicron silver powder, and also relates to its preparation method, belongs to nanometer material preparation technical field. BACKGROUND

[0002] With the further optimization of energy structure, solar cell industry develops rapidly, which puts forward higher requirements for solar cell grid line. Fine grid line with high conductivity is beneficial to increase light receiving area and improve photoelectric conversion efficiency. As the conductive phase of cell grid line silver paste, the uniformity of size and morphology of silver powder is beneficial to improve the tap density of silver powder and the conductivity of silver paste. At the same time, the uniformity of size and morphology of silver powder is also the premise of the stability of silver paste process. Therefore, it is of great significance to control the uniformity of size and morphology of silver powder.

[0003] At present, the preparation methods of micro-nano silver powder mainly include liquid phase chemical reduction method, electrochemical reduction method and photochemical reduction method. Liquid phase chemical reduction method is an important technology for preparing nano-sized particles with small particle size and narrow particle size distribution. The basic principle is to use a reducing agent to deposit silver from its salt or complex aqueous solution or organic system in powder form to obtain silver nano product. The advantages of this method are relatively simple equipment and process, high yield of silver nanoparticles, and therefore better application in industrial production. For example, Fan Xin et al. (Chemical reduction method for preparing nano silver particles and its characterization, Functional Materials [J.], 2007(06):996-999.) reduced AgNO3 with NaBH4, used polyvinylpyrrolidone (PVP) as a dispersion protective agent, and prepared nano silver by ultrasonic oscillation and vigorous stirring. However, the conventional liquid phase chemical reduction reaction method has the problem that the size of silver particles is difficult to accurately control, and the complexity of the reaction system is involved, which is often controlled by multiple reaction steps and solution conditions.

[0004] Photochemical reduction method is a method for preparing metal elements by using free radicals generated by light radiation to reduce metal cations. For example, Zhong Fuxin et al. (Photochemical preparation of nano silver colloid and research on its resonance scattering spectrum, Spectroscopy and Spectral Analysis [J.], 2000, 20(5):3.) used ultraviolet light to irradiate a solution containing Ag + When the solution is irradiated with ultraviolet light, free radicals with reducing properties are generated in the solution, and the free radicals can further reduce Ag + into Ag. Although stable silver particles of different sizes are prepared, the reaction requires a specific light source, the efficiency and yield of photochemical reduction reaction are affected by the intensity and wavelength of the light source, and sufficient irradiation time is required.

[0005] Zhu J, Liu S, Palchik O et al. ("Shape-controlled synthesis of silver nanoparticles by pulse sonoelectrochemical methods" Langmuir [J]., 2000, 16(16): 231-236.) used different content PEG as dispersant, and prepared spherical nanoparticles, nanowires and curved nanorods and other various morphologies of silver nanomaterials by electrochemical reduction method. The electrochemical reduction method is based on that free electrons can be generated in the metal ions in the solution in a certain electrochemical system, so that the metal ions in high valence state can be reduced to zero-valent metal elements, and the shape of the product can be controlled by controlling the related electrical parameters in the deposition process. The electrochemical reduction method needs an external power supply to provide current to drive the reaction. Especially in the process of industrial production, the shape and size of the electrode need to be carefully optimized and designed. In addition, the selection, maintenance and replacement of electrode materials and electrolyte will increase the cost and operation difficulty.

[0006] In summary, the conventional chemical reduction method is controlled by multiple reaction steps and solution conditions, and the complexity of the reaction increases the technical cost of its industrialization. In addition, by adjusting the solution concentration conditions to control the size of the prepared silver powder, the silver powder often needs to realize its size uniformity through "burst nucleation" in a short time, so it is affected by the solution mixing process. SUMMARY

[0007] In view of the deficiencies of the prior art, the first object of the present application is to provide a spherical sub-micron silver powder. The surface of the silver powder is smooth, and the size and morphology are more uniform.

[0008] The second object of the present application is to provide a preparation method of a spherical sub-micron silver powder. The method is simple and low in cost, and can effectively solve the problem of uneven particle size distribution of the silver powder prepared by the traditional liquid phase chemical reduction method.

[0009] In order to achieve the above technical purposes, the present application provides a preparation method of a spherical sub-micron silver powder, which comprises the following steps: mixing a silver salt solution with ammonia water under the condition of a magnetic field, adjusting the pH of the system to the alkaline range to obtain a silver-ammonia solution, and then adding a solution containing a surfactant and a reducing agent into the silver-ammonia solution in sequence to carry out a reduction reaction.

[0010] The present application can prepare sub-micron silver powder with different particle sizes and uniform morphology by magnetic field regulation, wherein (1) the external magnetic field has a great promoting effect on the growth of silver nanoparticles along the <111> direction, but weakens the growth of the trunk along the <311> direction, so that the trunk can be assembled and arranged along a specific direction; (2) the addition of the magnetic field can affect the particle size of the generated silver nanoparticles, because the existence of the magnetic field affects the diffusion of the crystal grains and suppresses the convection, so that the growth of the crystal grains is limited and the organization is refined; (3) because the magnetic field and the reactants are not in direct contact, the formation of special structures can be controlled while avoiding the introduction of defects and the generation of silver powder with different morphologies, thereby ensuring the consistency of the morphology of the silver powder.

[0011] As a preferred scheme, the magnetic field is in the horizontal or vertical direction, and the magnetic field size is 18-180 mT, and is further preferably 18.07-49.27 mT. With the increase of the central magnetic field strength, the particle size of the sub-micron spherical silver powder gradually decreases, and with the increase of the external magnetic field strength, the particle size distribution is more uniform, the particle size deviation is reduced, and the sub-micron spherical silver powder with smooth surface and uniform size can be obtained, but too strong magnetic field may cause magnetic interaction between silver particles or impurities and silver particles in the solution, reducing its uniformity or purity.

[0012] As a preferred scheme, the silver salt includes at least one of silver chloride, silver oxide and silver nitrate.

[0013] As a preferred scheme, the silver salt is silver nitrate.

[0014] As a preferred scheme, the molar concentration of the silver nitrate solution is 16-19 mM.

[0015] As a preferred scheme, the volume-mass ratio of the ammonia water to the silver salt is 34.25-41.67 mL:1 g. The mass concentration of the ammonia water is 25-28%.

[0016] As a preferred scheme, the pH is adjusted to 8-11.

[0017] As a preferred scheme, the pH adjuster is sodium hydroxide.

[0018] As a preferred scheme, the surfactant includes at least one of benzotriazole, gum arabic, succinic acid and stearic acid.

[0019] As a preferred scheme, the mass of the surfactant is 0.005-0.5 times the mass of the silver salt.

[0020] As a preferred scheme, the mass ratio of the surfactant to the solvent in the solution containing the surfactant is 0.8-1.2:100, and is further preferably 1:100.

[0021] As a preferred scheme, the reducing agent comprises at least one of formaldehyde solution, acetaldehyde solution, glucose solution and hydrazine hydrate.

[0022] As a preferred scheme, the reducing agent is formaldehyde solution. The mass concentration of the formaldehyde solution is 37%.

[0023] As a preferred scheme, the molar amount of formaldehyde in the formaldehyde solution is 1.5-3 times of the silver element in the silver salt.

[0024] As a preferred scheme, the condition of the reduction reaction is that the reaction is stirred at room temperature for 0.5-3 h.

[0025] The application further provides a spherical sub-micron silver powder prepared by the above method.

[0026] As a preferred scheme, the particle size of the silver powder is 0.27-0.49 μm.

[0027] Compared with the prior art, the application has the following advantages:

[0028] (1) The spherical sub-micron silver powder prepared has a smooth surface, and the size and morphology are more uniform;

[0029] (2) The size and morphology of the spherical sub-micron silver powder are controlled by using an external magnetic field, and since the magnetic field is not directly contacted with the reactants, the introduction of defects can be avoided during the preparation of the silver powder, the generation of silver powder with different morphologies is avoided, and the consistency of the morphology of the silver powder is ensured;

[0030] (3) The method is simple, low in cost, strong in controllability, and does not produce environmental pollution. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The figure is a schematic diagram of the application of a magnetic field for preparing sub-micron silver powder from a solution.

[0032] Figure 2 The figure is a schematic diagram of the application of a magnetic field for preparing sub-micron silver powder from a silicon single wafer.

[0033] Figure 3 The figure is a schematic diagram of the process of the preparation of spherical sub-micron silver powder by the application of an external magnetic field chemical reduction.

[0034] Figure 4 The figure is a SEM image of the sub-micron silver powder prepared in Example 1, wherein (a)-(e) correspond to samples 1-5, respectively.

[0035] Figure 5 The figure is a particle size statistical distribution diagram of the sub-micron silver powder prepared in Example 1, wherein (a)-(e) correspond to samples 1-5, respectively.

[0036] Figure 6 The infrared spectrum of the 1-5 sub-micron silver powder samples prepared in Example 1.

[0037] Figure 7 The XPS 3d region spectrum of Ag of the silver nanoparticles of the 5 sample in Example 1.

[0038] Figure 8 The DSC test result graph of the 2-5 sub-micron silver powder samples prepared in Example 1.

[0039] Figure 9 The SEM graph of the sub-micron silver powder prepared in Example 2, wherein (a)-(d) correspond to the 6-9 samples, respectively.

[0040] Figure 10 The SEM graph of the sub-micron silver powder prepared in Example 3, wherein (a)-(d) correspond to the 10-13 samples, respectively.

[0041] Figure 11 The SEM graph of the sub-micron silver powder prepared in Example 4. DETAILED DESCRIPTION

[0042] The following examples are intended to further illustrate the present application, but not to limit the present application.

[0043] Example 1

[0044] This example is a preparation method of spherical sub-micron silver powder, and the specific steps are as follows:

[0045] (1) Preparation of precursor silver ammonia solution: 1.08 g of silver nitrate was weighed and added to 360 ml of deionized water to prepare a solution, which was stirred uniformly at a speed of 500 rpm by using a JJ-1B 200W constant speed electric stirrer. The solution was marked as No. 1-5 samples, respectively. Except for No. 1 sample, no magnetic field was added, and for No. 2-5 samples, an external magnetic field was added in the horizontal direction, wherein the magnetic field strength of No. 2 sample was 18.07 mT, that of No. 3 sample was 28.65 mT, that of No. 4 sample was 38.71 mT, and that of No. 5 sample was 49.27 mT. Then, 45 ml of ammonia water (ammonia water reagent mass concentration was 25-28%) was added into the above silver nitrate solution, and then 0.75 g of NaOH was added to adjust the pH value of the solution to 10.

[0046] (2) Preparation of surfactant solution: 0.054 g of stearic acid was weighed and dissolved in 5.4 g of anhydrous ethanol, respectively.

[0047] (3) Solution mixing: 5 portions of the above stearic acid solution were injected into the 5 groups of silver ammine solution obtained in step (1), and 1.08 ml of formaldehyde solution (purity 37 wt.%) was added respectively, and the injection time was within 1 min.

[0048] (4) Solution reaction and separation: under the stirring speed of 500 rpm, the silver powder was fully ripened by stirring for 2 h, after the reaction was completed, the solution was filtered by SHZ-D circulating water type vacuum pump, and the silver powder was separated respectively, and the silver powder was ultrasonically cleaned twice with anhydrous ethanol using a KQ-3200E ultrasonic cleaner.

[0049] (5) Silver powder drying: the above silver powder after anhydrous ethanol ultrasonic cleaning was placed in a culture dish, and then put into a DZE type vacuum drying oven to dry at a temperature rising speed of 10 ℃ / min to 60 ℃, and the drying time was 5 h.

[0050] The size, morphology and particle surface condition of the sub-micron spherical silver powder prepared in this embodiment were detected by a scanning electron microscope (SEM), infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS) and DSC testing, etc.

[0051] Scanning electron microscope (SEM) instrument: NovaNanoSEM230 type scanning electron microscope produced by FEI Czech Republic s.r.o, test method: prepare the ethanol dispersion solution of sub-micron silver particles, drop a few drops on the conductive glue, dry with a hair dryer, and then put into the instrument to observe under vacuum. Test conditions: acceleration voltage 5kv. The scanning electron microscope mainly characterizes the surface micro-morphology of the silver particles.

[0052] Infrared spectroscopy (IR) instrument: Nicolet iS50 type Fourier transform infrared spectroscopy analyzer produced by Thermo, test method: mix the sample (about 1 mg) and dry KBr (about 200 mg) uniformly in an agate mortar, grind thoroughly, then put the mixture uniformly between the top and bottom dies of a solid pressing mold, then put the mold into a pressing machine under a pressure of 8T / cm 2 around for 1-2 minutes to obtain a transparent sample sheet. Take out the sample sheet and load it into a solid sample test holder for testing. When the molecules of a substance are exposed to infrared light of different wavelengths, some specific wavelengths of infrared light will be absorbed, resulting in the generation of the infrared absorption spectrum of the molecules, and the structure of the molecules can be analyzed and identified by infrared spectroscopy.

[0053] X-ray photoelectron spectroscopy (XPS) instrument: ESCALAB 250Xi X-ray photoelectron spectrometer produced by Thermo Fisher Scientific, test method: about 2mg of powder sample is adhered to double-sided carbon conductive adhesive or ordinary double-sided adhesive for testing. X-ray photoelectron spectroscopy is a technology that uses an electron spectrometer to measure the energy distribution of photoelectrons and Auger electrons of the sample surface irradiated by X-ray photons, to realize element analysis.

[0054] Differential scanning calorimetry (DSC) analysis: Perkinelmer TG8000-FTIR-GCMS-ATD thermal gravimetric infrared gas chromatograph produced by PerkinElmer, test method: a few milligrams of sample is taken with a spoon and spread on the bottom of the crucible, covered with a lid and placed in the instrument for testing. It is a method for measuring the physical properties of a substance as a function of temperature under programmed temperature control. The physical and chemical processes with thermal effects during the heating process of the substance are characterized by measuring the thermal physical properties of the sample itself and the relationship between temperature or time.

[0055] According to the sample preparation process in the Figure 3 , and applying a magnetic field in the manner shown in the Figure 1 , taking the stirring injection reaction method and after filtration and washing, the nano-silver particle sample is obtained. After collecting the prepared sample, SEM detection is first performed. From the recorded experimental results, in the microscopic layer, from the SEM images of the sample particles presented in the Figure 4 , it can be observed that in the Figure 4 a. Under the condition of no magnetic field, the surface of the silver nano-particles of the sample is rough and uneven, and some particles with extremely small particle size are scattered at the edge; in the Figure 4 b. After adding a horizontal magnetic field H=18.07mT, the surface of the silver nano-particles obtained by agglomeration becomes smooth, and there are no obvious uneven grooves, and no particles with too small particle size are observed in the field of view; observing the Figure 4 a-e and the Figure 5 , it can be seen that when the magnetic field becomes larger, the particle size of the prepared sample particles gradually decreases, and the distribution of the powder particle size is more concentrated.

[0056] From the infrared spectrum test results in the Figure 6 , it can be seen that the five samples prepared in the experiment all have smaller peaks near 3450cm -1 and 1650cm -1 , which is caused by the presence of some free water in the sample powder to be tested. No other functional group peaks are found, indicating that the silver powder obtained after filtration and two alcohol washes is relatively pure, and there is no organic matter attached to the surface.

[0057] From the infrared spectrum test results in theFigure 7 The XPS test results show that, compared to the standard Ag3d 3 / 2 Image spectrum comparison: In the Ag 3d spectrum image of sample 5 in Example 1, Ag3d... 3 / 2 The energy spectrum peaks increased and shifted towards higher binding energies, indicating that the formation environment of nano-silver under the above reaction system changed. As the outer electron cloud density decreased, its shielding effect on the inner electrons was significantly reduced, and the binding energy of the inner electrons increased significantly.

[0058] From the appendix Figure 8 The DSC test results show that the curves obtained under different horizontal magnetic fields are roughly the same. Samples in groups 2-5 all showed only one exothermic peak, occurring at 963.55℃, 962.92℃, 962.33℃, and 962.42℃, respectively. Since the melting point of silver is 961.93℃, it can be determined that the silver nanoparticles prepared in these four experiments have high purity.

[0059] Example 2

[0060] This embodiment describes a method for preparing spherical submicron silver powder, which involves applying a magnetic field of 50–180 mT in the vertical direction. The specific steps are as follows:

[0061] (1) Preparation of precursor silver ammonia solution: Weigh 1.08g of silver nitrate and add 360ml of deionized water to prepare a solution. Stir evenly with a JJ-1B 200W constant speed electric stirrer at 500rpm. Label the samples as 10 to 13. Apply an external magnetic field to the horizontal direction of the samples 10 to 13. The magnetic field strength of sample 10 is 63.06mT; sample 11 is 114.21mT; sample 12 is 157.04mT; and sample 13 is 180.78mT. Add 45ml of ammonia water (mass concentration of 25-28%) to the above silver nitrate solution. Then add 0.75g of NaOH to adjust the pH of the solution to 10.

[0062] (2) Preparation of surfactant solution: Weigh 0.054g of stearic acid into 4 portions and dissolve each portion in 5.4g of anhydrous ethanol.

[0063] (3) Solution mixing: Inject the above 4 portions of stearic acid solution into the 4 groups of silver ammonia solution obtained in step (1), and then add 1.08 ml of formaldehyde solution (purity of 37 wt.%) to each group. The injection time is within 1 min.

[0064] (4) Solution reaction and separation: the silver powder was fully matured under stirring at a stirring speed of 500 rpm for 2 h, and after the reaction was completed, the solution was filtered by a SHZ-D circulating water vacuum pump, and the silver powder was separated, and the silver powder was ultrasonically cleaned twice with anhydrous ethanol by using a KQ-3200E ultrasonic cleaner.

[0065] (5) Silver powder drying: the silver powder after the ultrasonic cleaning with anhydrous ethanol was placed in a culture dish, and then was placed in a DZE vacuum drying oven to be dried at a temperature rising speed of 10 ℃ / min to 60 ℃, and the drying time was 5 h.

[0066] The sub-micron spherical silver powder prepared in the example was detected by SEM. From the attached Figure 10 It can be observed that the particle size of the spherical silver powder prepared by applying a magnetic field in the vertical direction is in the range of 0.39-0.31 μm, which is similar to the particle size distribution and morphology of the silver powder prepared by applying a magnetic field in the horizontal direction in Example 1.

[0067] Example 3

[0068] This example is to supplement the mechanism of the adjustment of the magnetic field on the silver powder, by adjusting the external magnetic field, to adjust the relationship between the magnetic interaction between the particles and the van der Waals force between the particles, and finally realize the assembly of the silver nanoparticles in a specific direction. The silver powder prepared by the chemical reduction method on a single crystal silicon wafer with an external magnetic field in this example was carried out according to the following steps:

[0069] (1) Preparation of silver ammonia solution: 1.08 g of silver nitrate was weighed, and 360 ml of deionized water was added to prepare a 6-9 number four-group sample solution, 45 ml of ammonia water (mass concentration of 25-28%) was added to each group of silver nitrate solution, and then 0.75 g of NaOH was added to adjust the pH value of the solution to 10.

[0070] (2) Preparation of surfactant solution: 4 portions of 0.054 g of stearic acid were respectively dissolved with 5.4 g of anhydrous ethanol.

[0071] (3) Solution mixing: the four portions of stearic acid solution were respectively added to the 6-9 number silver ammonia solution obtained in step (1), and the whole process was mixed by using a JJ-1B 200W constant speed electric stirrer under stirring at a stirring speed of 500 rpm, and after the mixing was completed, it was stored in a refrigerator for subsequent experiments.

[0072] (4) The silicon single crystal wafer was cut to a suitable size, and 1.08 ml of formaldehyde (purity 37 wt.%) and the prepared mixed solution were dropped on the single crystal wafer by using a pipette to make the silver nanoparticles directly deposit on the silicon single crystal wafer. Except for the sample No. 6, no magnetic field was added, and for the samples No. 7 to No. 9, an external magnetic field was added in the horizontal direction, wherein the sample No. 7 was 18.07 mT, the sample No. 8 was 28.65 mT, and the sample No. 9 was 49.27 mT. The silicon single crystal wafer was collected after 2 h.

[0073] (5) Silver powder drying: The collected silver powder on the single crystal silicon wafer was respectively cleaned by using anhydrous ethanol in a KQ-3200E ultrasonic cleaner, and then was placed in a culture dish and was put into a DZE vacuum drying oven to be dried at a temperature of 60 °C with a temperature rising speed of 10 °C / min. The drying time was 5 h.

[0074] The size, morphology and particle surface condition of the sub-micron spherical silver powder samples No. 6 to No. 9 prepared in this embodiment were tested and analyzed by SEM.

[0075] From the attached Figure 9The micro-morphology of four samples is observed, and the arrangement morphology of the assembled Ag nanoparticles ranges from scattered island, relatively dispersed linear to closely arranged linear. The main interaction between the silver nanoparticles includes the generally existing van der Waals force and the interaction force of magnetic dipoles. The van der Waals force generally exists between all individuals, and generally shows the attraction between individuals, so that the objects are close to each other. For our spherical silver nanoparticles, if only the van der Waals force exists, the final structure will be a dense packing structure rather than a structure with a special orientation. The special self-assembly morphology of Ag particles under the magnetic field shows that there is an interaction between the magnetic dipoles of the silver nanoparticles. Through the analysis of the experimental results, the reason why the external magnetic field can control the preparation of silver powder is that: (1) it is found that the arrangement morphology of the assembled Ag nanoparticles on the single crystal silicon wafer ranges from scattered island, relatively dispersed linear to closely arranged linear, which is due to the main interaction between the silver nanoparticles including the generally existing van der Waals force and the interaction force of magnetic dipoles. The external magnetic field has a great promoting effect on the growth of the silver nanoparticles along the <111> direction, but has a weakening effect on the growth of the trunk along the <311> direction, so that the trunk can be assembled and arranged along a specific direction; (2) the addition of the magnetic field has a certain influence on the particle size of the generated silver nanoparticles. Within the range of the magnetic field added in the experiment, with the increase of the magnetic field, the particle size of the prepared sample gradually decreases, and the distribution of the powder particle size is more concentrated. The main reason is that the existence of the magnetic field affects the diffusion of the crystal grains, restrains the convection, limits the growth of the crystal grains, and refines the structure; (3) the powder surface is smooth and the particle size distribution is relatively average after the external magnetic field is added, which may be because the magnetic field and the reactants are not in direct contact, so that the formation of the special structure can be controlled and the introduction of defects can be avoided.

[0076] The application introduces an external magnetic field in the horizontal or vertical direction of the reaction container. The existence of the magnetic field can affect the diffusion of the crystal grains and restrain the convection. With the increase of the central magnetic field strength, the particle size of the sub-micron spherical silver powder gradually decreases, and with the increase of the external magnetic field strength, the particle size distribution is more uniform, the particle size deviation is reduced, and the sub-micron spherical silver powder with smooth surface and uniform size can be obtained. The magnetic field and the reactants are not in direct contact, so that the introduction of defects can be avoided when preparing the silver powder, the generation of silver powder with different morphologies can be avoided, the consistency of the silver powder morphology can be ensured, and in addition, most of the chemical reagents in the traditional chemical reduction method are toxic, so that the influence on the environment can be reduced by controlling the particle size distribution.

[0077] Example 4

[0078] The spherical sub-micron silver powder is prepared by the method of Example 1, except that a 300 mT magnetic field is applied in the horizontal direction.

[0079] The sub-micron spherical silver powder prepared in the embodiment is detected by SEM.

[0080] From the attached Figure 11 It can be observed that the uniformity of the size of the obtained silver powder is obviously reduced, which is due to the magnetic interaction between the silver particles in the solution under the action of the strong magnetic field, reducing the uniformity.

Claims

1. A method for preparing spherical submicron silver powder, characterized in that: Under magnetic field conditions, a silver salt solution is mixed with ammonia water and the pH of the system is adjusted to the alkaline range to obtain a silver ammonia solution. Then, a solution containing a surfactant and a reducing agent are added to the silver ammonia solution in sequence to carry out a reduction reaction, thereby obtaining silver powder with a particle size of 0.27~0.49μm. The magnetic field is horizontal or vertical, and the magnitude of the magnetic field is 50~180mT. As the magnetic field strength increases, the particle size of the spherical submicron silver powder particles gradually decreases, and the particle size distribution becomes more uniform.

2. The method for preparing spherical submicron silver powder according to claim 1, characterized in that: The silver salt includes at least one of silver chloride, silver oxide, and silver nitrate; The volume-to-mass ratio of ammonia to silver salt is 34.25~41.67 mL:1 g; the mass concentration of ammonia is 25~28%.

3. The method for preparing spherical submicron silver powder according to claim 1, characterized in that: The pH is adjusted to 8-11.

4. The method for preparing spherical submicron silver powder according to claim 1, characterized in that: The surfactant includes at least one of benzotriazole, gum arabic, succinic acid, and stearic acid; The mass of the surfactant is 0.005 to 0.5 times that of the silver salt.

5. The method for preparing spherical submicron silver powder according to claim 1, characterized in that: The reducing agent includes at least one of formaldehyde solution, acetaldehyde solution, glucose solution, and hydrazine hydrate.

6. The method for preparing spherical submicron silver powder according to claim 5, characterized in that: The reducing agent is a formaldehyde solution; the molar amount of formaldehyde in the formaldehyde solution is 1.5 to 3 times that of silver in the silver salt.

7. A method for preparing spherical submicron silver powder according to claim 1, 4, 5 or 6, characterized in that: The conditions for the reduction reaction are: stirring at room temperature for 0.5 to 3 hours.

8. A spherical submicron silver powder, characterized in that: It is prepared by the method described in any one of claims 1 to 7.

9. The spherical submicron silver powder according to claim 8, characterized in that: The silver powder has a particle size of 0.27~0.49μm.

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