Micro silver powder with fluffy structure and preparation method thereof

Abstract

The invention provides micron silver powder with a fluffy structure and a preparation method of the micron silver powder, and belongs to the technical field of metal powder.The preparation method comprises the steps that a silver nitrate solution, an alkaline solution and a reducing agent solution are prepared; dropwise adding an alkaline solution into the silver nitrate solution in a constant-temperature stirring state to form a mixed solution; the mass ratio of the agent in the alkaline solution to silver nitrate in the silver nitrate solution is 1: (1-3); under the constant-temperature stirring state, the reducing agent solution is dropped into the mixed solution, a silver powder solution is obtained through reaction, and the mass ratio of a reducing agent in the reducing agent solution to silver nitrate in the silver nitrate solution is (3-5): 10; washing, carrying out solid-liquid separation, drying and screening to obtain micron silver powder with a fluffy structure; the tap density of the silver powder is 1.5-2.5 g / cm < 3 >. According to the preparation method, the fluffy-structure silver powder with low tap density, high plasticity and high sintering activity is successfully prepared through a two-step chemical reaction, so that the fluffy-structure silver powder becomes an ideal choice of a high-performance electronic functional material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal powder, in particular to a kind of structure fluffy micron silver powder and preparation method thereof. BACKGROUND

[0002] With the rapid evolution of electronic components to miniaturization, high integration and high frequency, the performance requirements of electronic functional materials such as conductive adhesive, thermal conductive adhesive and electromagnetic shielding material are continuously improved. Silver powder has become an indispensable key functional material in modern electronic industry because of its good electrical conductivity and thermal conductivity, as well as excellent chemical stability and sinterability. It is usually used as a conductive filler to mix with organic carriers, glass powder and other materials to make conductive paste, conductive adhesive or sintering paste, and is widely used in semiconductor packaging, thick film printed circuit, electronic component electrode and electromagnetic shielding.

[0003] Although the conventional spherical micron silver powder has good fluidity and printability, its tap density is high, it is tightly packed in the paste, the volume shrinks greatly during sintering, internal stress is easily generated, and the settling speed is fast, which leads to stratification of the paste, poor stability, and affects the consistency and reliability of printing.

[0004] Therefore, it is necessary to design a structure fluffy micron silver powder and preparation method thereof to solve the above problems. SUMMARY

[0005] In view of the technical problems in the background art, the present application provides a structure fluffy micron silver powder and preparation method thereof, which aims to solve the technical problems that the conventional spherical micron silver powder has high tap density and is tightly packed, which leads to large sintering shrinkage, easy generation of internal stress, easy stratification and poor stability in the paste, and further affects the consistency and reliability of printing.

[0006] In a first aspect, the present application provides a preparation method of a structure fluffy micron silver powder, comprising the following steps: S1. preparing silver nitrate solution, alkaline solution and reducing agent solution; S2. under constant temperature stirring, the alkaline solution is added dropwise into the silver nitrate solution to form a mixed solution; the mass ratio of the reagent in the alkaline solution to the silver nitrate in the silver nitrate solution is 1: (1-3); S3. under constant temperature stirring, the reducing agent solution is added dropwise into the mixed solution to obtain a silver powder solution after reaction; the mass ratio of the reducing agent in the reducing agent solution to the silver nitrate in the silver nitrate solution is (3-5): 10; then, after washing, solid-liquid separation and drying and screening, a structure fluffy micron silver powder is obtained; the tap density of the structure fluffy micron silver powder is 1.5-2.5 g / cm 3 .

[0007] As a further improvement of the present application, in step S1, the medicament in the alkaline solution is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, sodium sulfide, sodium phosphate, aniline.

[0008] As a further improvement of the present application, in step S1, the reducing agent in the reducing agent solution is one or more of sodium borohydride, triethanolamine, hydrazine hydrate, hydroquinone, hydroxylamine, ascorbic acid, sodium citrate, hydrogen peroxide, hydrazine sulfate, glucose, formaldehyde, potassium iodide.

[0009] As a further improvement of the present application, in steps S2 and S3, the constant temperature is 25-45℃.

[0010] As a further improvement of the present application, in step S2, the dropping speed is 0.1-3 L / min.

[0011] As a further improvement of the present application, in step S3, the dropping speed is 0.1-2 L / min.

[0012] As a further improvement of the present application, in step S3, the drying and screening is performed by drying at 70-110℃ and then screening with a mesh screen of 10-400 mesh.

[0013] In a second aspect, the present application provides a micro-silver powder with a fluffy structure, which is prepared by the method of the first aspect.

[0014] The present application has the following beneficial effects: The present application provides a micro-silver powder with a fluffy structure and a preparation method thereof. The silver nitrate solution, the alkaline solution and the reducing agent solution are prepared. The alkaline solution is dropped into the silver nitrate solution under constant temperature and stirring to form a mixed solution. The mass ratio of the medicament in the alkaline solution to the silver nitrate in the silver nitrate solution is 1:(1-3). The reducing agent solution is dropped into the mixed solution under constant temperature and stirring to obtain a silver powder solution. The mass ratio of the reducing agent in the reducing agent solution to the silver nitrate in the silver nitrate solution is (3-5):10. Then, the silver powder solution is washed, solid-liquid separated, dried and screened to obtain the micro-silver powder with a fluffy structure. The tap density of the silver powder is 1.5-2.5 g / cm 3 The present application successfully prepares the silver powder with a fluffy structure, low tap density, high plasticity and high sintering activity by a two-step chemical reaction, which makes it an ideal choice for high-performance electronic functional materials. The raw materials of the present application are easy to obtain, the process is simple to operate, the reaction conditions are mild, and no complex equipment or harsh environment is needed. The parameters such as dropping speed, reaction temperature and stirring rate can be controlled to effectively regulate the morphology of the silver powder. The production cost is low, and it is suitable for large-scale industrial production.

[0015] The present application adopts a two-step method to prepare silver powder. First, a basic solution is added to a silver nitrate solution under constant temperature stirring to obtain a mixed solution, and then a reducing agent solution is added to the above mixed solution to obtain a silver powder solution. The intermediate obtained in the first step plays a crucial role in controlling the morphology of the final synthesized silver powder, and the intermediate also decomposes in the subsequent reaction, resulting in a fluffy silver powder with low tap density and strong plasticity. This fluffy silver powder is an ideal material for preparing high-performance conductive silver paste, thermal paste and catalyst, as it is easier to form a dense conductive / thermal network and has higher sintering activity. In addition, the method of the present application can precisely control the particle size of the silver powder by adjusting the amount of the basic solution added, to meet the needs of different application scenarios.

[0016] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application, the following specific embodiments of the present application can be implemented according to the content of the specification, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application will be described in detail. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0018] Figure 1 The electron microscope image of the micron silver powder prepared in Example 1 of the present application; Figure 2 The electron microscope image of the micron silver powder prepared in Example 2 of the present application; Figure 3 The electron microscope image of the micron silver powder prepared in Example 4 of the present application; Figure 4 The electron microscope image of the micron silver powder prepared in Example 5 of the present application; Figure 5 The electron microscope image of the micron silver powder prepared in Comparative Example 1. DETAILED DESCRIPTION

[0019] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following examples are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, but cannot limit the protection scope of the present application.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application; the use of the terms "including," "comprising," "having" and "with" in the specification and claims herein are used to mean "including but not limited to" or "comprising but not limited to" or "having but not limited to" or "with but not limited to," and are not used to mean "consisting only of" or "consisting only of."

[0021] In the description of the embodiments of the present application, the technical terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0022] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The occurrence of the phrase "in one embodiment" in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessary that every embodiment include every feature that is described in connection with that or any other embodiment. It will be explicitly understood by those of ordinary skill in the art that the embodiments described herein can be combined with other embodiments.

[0023] In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0024] Although the conventional spherical micron silver powder has good fluidity and printability, its tap density is high, it is packed tightly in the slurry, the volume shrinks greatly during sintering, internal stress is easily generated, and the settling speed is fast, which leads to poor stability of the slurry, affecting the consistency and reliability of printing.

[0025] In order to solve the technical problems that the conventional spherical micron silver powder has high tap density and is packed tightly, which leads to large sintering shrinkage, easy generation of internal stress, and fast settling speed in the slurry, which easily causes layering, thereby affecting the consistency and reliability of printing, the present application provides a micron silver powder with a fluffy structure and a preparation method thereof, wherein by adopting a unique two-step liquid phase reduction method, first, a basic solution is added to a silver nitrate solution under constant temperature stirring to form a key intermediate, and then a reducing agent solution is added to the intermediate system for reduction and decomposition, so that the micron silver powder with a fluffy structure, low tap density and high sintering activity can be prepared.

[0026] In a first aspect, the embodiments of the present application provide a preparation method of a micron silver powder with a fluffy structure, comprising the following steps: S1. Preparing a silver nitrate solution, a basic solution and a reducing agent solution; S2. The alkaline solution is added dropwise into the silver nitrate solution under constant temperature stirring to form a mixed solution; the mass ratio of the reagent in the alkaline solution to the silver nitrate in the silver nitrate solution is 1:(1-3); S3. The reducing agent solution is added dropwise into the mixed solution under constant temperature stirring, and a silver powder solution is obtained after reaction; the mass ratio of the reducing agent in the reducing agent solution to the silver nitrate in the silver nitrate solution is (3-5):10; then, the structure-puffed micron silver powder is obtained through washing, solid-liquid separation, and drying and screening; the tap density of the structure-puffed micron silver powder is 1.5-2.5 g / cm 3 .

[0027] The silver powder is prepared by a two-step method in the application. First, the alkaline solution is added into the silver nitrate solution under constant temperature stirring, and an intermediate is generated by the reaction of the alkaline solution and the silver nitrate; then, the reducing agent solution is added to reduce and decompose the intermediate in situ. This process makes the newly generated silver atoms deposit and grow on the original loose framework of the intermediate, so that the micron silver powder with a puffed structure, strong plasticity, and excellent slurry stability is obtained. When applied in the field of electronic paste, the silver powder can be sintered under mild conditions to form a sintered body with high density, high thermal conductivity, high electrical conductivity, and high reliability, which is an ideal material to meet the needs of the next generation of high-performance electronic packaging and circuit manufacturing.

[0028] Further, in some embodiments, in step S1, the reagent in the alkaline solution is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, sodium sulfide, sodium phosphate, and aniline.

[0029] In the technical scheme of the embodiments of the application, the alkaline reagent provides anions to form different types of insoluble silver salt precipitates or soluble complex intermediate with silver ions. The crystal structures and solubilities of different silver salts are different, and the intermediate framework with different initial morphologies can be formed. Suitable alkaline reagents can control the amount of intermediate generated, the pH value of the reaction system, and the reduction kinetics, which is conducive to the formation of silver powder with a puffed structure and low tap density.

[0030] Further, in some embodiments, in step S1, the reducing agent in the reducing agent solution is one or more of sodium borohydride, triethanolamine, hydrazine hydrate, hydroquinone, hydroxylamine, ascorbic acid, sodium citrate, hydrogen peroxide, hydrazine sulfate, glucose, formaldehyde, and potassium iodide.

[0031] In the technical scheme of the embodiments of the present application, the reducing agent can decompose and reduce the intermediate to generate an aggregate with fluffy structure, and at the same time, the silver atoms are deposited on the skeleton of the intermediate in an orderly manner, which is beneficial to form fluffy silver powder with more uniform particle size and relatively regular structure; by selecting different types or combinations of reducing agents, the particle size, fluffiness and surface state of the silver powder can be accurately controlled; by adjusting the relative amount of the reducing agent, the reduction rate and degree of the intermediate can be controlled, and gradient control of the silver powder from high activity, super-fluffiness to relatively compact and stable structure is realized, so as to meet the differentiated requirements of different electronic pastes on sintering activity and paste stability.

[0032] Further, in some embodiments, in steps S2 and S3, the constant temperature is 25-45℃.

[0033] In the technical scheme of the embodiments of the present application, the appropriate temperature range provides an optimal kinetic environment for the two key processes of skeleton construction and skeleton transformation. In the process of generating the intermediate by the reaction of the alkaline solution and silver nitrate, the temperature of 25-45℃ provides a mild nucleation environment, which can promote the uniform formation of a large number of small crystal nuclei and limit their excessive growth, so as to construct an ideal fluffy skeleton with high specific surface area which is formed by the loose accumulation of numerous small primary particles; if the temperature is too low, the nucleation rate is slow, which may lead to large and uneven intermediate particles, and if the temperature is too high, it will cause explosive nucleation and rapid growth, which is easy to form compact hard agglomerates. When the reducing agent is dropped into the above-mentioned skeleton suspension, if the temperature is too high, the reduction reaction will be too violent, and the newly generated silver atoms may not have time to deposit on the original skeleton in an orderly manner, but occur homogeneous nucleation in the solution to generate new and compact silver particles, thereby destroying or diluting the original fluffy structure. In the temperature range of 25-45℃, the secondary agglomeration or Ostwald ripening of the newly generated micron silver powder with high surface energy can be effectively inhibited, so as to prepare high-performance micron silver powder with fluffy structure.

[0034] Further, in some embodiments, in step S2, the dropping speed is 0.1-3 L / min. In step S3, the dropping speed is 0.1-2 L / min.

[0035] In the technical scheme of the embodiment of the present application, in step S2, by controlling the adding speed of the alkaline solution, an ideal fluffy skeleton is built in the system, but too fast speed can cause uneven mixing due to local violent reaction, the generated intermediate structure is not uniform, which affects the stability of the final product; if the dropping speed is too slow, the intermediate can grow excessively, and the structure is coarse, and the bulkiness and specific surface area of the silver powder reduced from the coarse skeleton will be much lower than expected. In step S3, by controlling the adding speed of the reducing agent solution, the intermediate is reduced in situ into silver powder without destroying the skeleton, so that high-quality and high-stability fluffy silver powder is obtained; if the dropping speed is too fast, the concentration of the reducing agent will be too high instantaneously, which can cause free silver ions to be reduced to generate new and dense silver particles, and the fluffy intermediate skeleton is filled and wrapped by the rapidly generated silver, so that the bulkiness of the finally obtained silver powder is greatly reduced and the tap density is increased; if the dropping speed is too slow, the intermediate skeleton can be decomposed or phase changed, and the silver powder particles generated first are always suspended in the reaction solution in the subsequent long-time dropping process, which can cause irreversible secondary agglomeration and destroy the fluffy structure.

[0036] Further, in some embodiments, in step S3, the drying and screening is performed as follows: after drying at 70-110℃, the product is screened by using a sieve with a mesh size of 10-400.

[0037] In the technical scheme of the embodiment of the present application, by drying at a suitable temperature, the water is completely removed, and at the same time, the structure of the silver powder particles is effectively protected from being damaged due to low-temperature sintering, and the fluffy morphology formed in the previous steps is protected; by screening, the large-particle impurities are removed and the maximum particle size of the product is controlled, so that the particle size distribution of the silver powder is standardized and customized.

[0038] In a second aspect, the embodiment of the present application provides a fluffy micro-silver powder, which is prepared by the preparation method of the first aspect.

[0039] In the present application, a two-step chemical reaction is adopted, by accurately controlling the proportion of reagents, reaction temperature and dropping speed, a fluffy micro-silver powder with strong plasticity and excellent slurry stability is obtained, the tap density of the micro-silver powder is 1.5-2.5 g / cm 3 , the specific surface area is greater than 0.3 m 2 / g, and the particle size distribution D50 is 5-20 μm.

[0040] 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 cannot be understood as limiting the present application. If the specific technology or condition is not specified in the examples, the technology or condition described in the literature in the art or according to the product manual is used. If the reagent or instrument is not specified by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0041] Example 1 The present example provides a method for preparing a micro-silver powder with a fluffy structure, comprising the following steps: S1. Take 10 kg of silver nitrate and add it to 50 L of water, stir at 30°C until dissolved to obtain a silver nitrate solution; Take 5 kg of sodium carbonate and add it to 15 L of water, stir at 30°C until dissolved to obtain a basic solution; Take 4 kg of formaldehyde and dilute it with 6 kg of deionized water to obtain a reducing agent solution; S2. Under the condition of constant temperature at 30°C and stirring at 200 rpm, add the basic solution to the silver nitrate solution at a feeding speed of 1 L / min to form a mixed solution; S3. Under the condition of constant temperature at 30°C and stirring at 200 rpm, add the reducing agent solution to the mixed solution at a feeding speed of 0.8 L / min, and after the feeding is completed, obtain a silver powder solution, then wash, separate the solid and liquid, dry at 85°C, and screen using a 100 mesh screen to obtain a micro-silver powder with a fluffy structure, the scanning electron microscope image of which is shown in Figure 1 .

[0042] Example 2 The present example provides a method for preparing a micro-silver powder with a fluffy structure, which is different from Example 1 only in that 3.3 kg of sodium carbonate is taken and added to 10 L of water, stirred at 30°C until dissolved, i.e. the mass ratio of reagent to silver nitrate is 1:3, and other experimental parameters and conditions are basically the same as those of Example 1, which will not be repeated here. The scanning electron microscope image of the obtained micro-silver powder is shown in Figure 2 , it can be seen that due to the reduction of the amount of sodium carbonate, the particle size of the silver powder becomes larger.

[0043] Example 3 The present example provides a method for preparing a micro-silver powder with a fluffy structure, which is different from Example 1 only in that 10 kg of sodium carbonate is taken and added to 30 L of water, stirred at 30°C until dissolved, i.e. the mass ratio of reagent to silver nitrate is 1:1, and other experimental parameters and conditions are basically the same as those of Example 1, which will not be repeated here.

[0044] Example 4 The present example provides a method for preparing a micro-silver powder with a fluffy structure, which is different from Example 1 only in that in steps S2 and S3, the constant temperature is 25°C, and other experimental parameters and conditions are basically the same as those of Example 1, which will not be repeated here. The scanning electron microscope image of the obtained micro-silver powder is shown in Figure 3 .

[0045] Example 5 The embodiment provides a preparation method of the micro-silver powder with a fluffy structure. Compared with the embodiment 1, the only difference is that the constant temperature is 45 DEG C in steps S2 and S3, and other experimental parameters and conditions are basically the same as those of the embodiment 1, which will not be repeated here. The scanning electron microscope (SEM) image of the obtained micro-silver powder is shown in the figure. Figure 4 As can be seen from the figure, the suitable reaction temperature is helpful to the uniform formation of the crystal nucleus and limits the excessive growth of the crystal nucleus, so that the micro-silver powder with a high-performance fluffy structure is prepared. Figures 3-4

[0046] Comparative example 1 The comparative example 1 provides a preparation method of the micro-silver powder with a fluffy structure, which comprises the following steps. S1. 100 ml of the nano-silver solution is measured, and the molar concentration of the nano-silver is 5 10 -7 mol / L; S2. 200 g of polyvinylpyrrolidone K30 is weighed, 100 g of ascorbic acid is weighed, and 50 L of water is added to dissolve, so as to obtain a mixed solution; S3. The nano-silver solution is poured into the mixed solution under the condition of 25 DEG C constant temperature and 200 rpm stirring, so as to obtain a bottom solution; S4. 5 kg of silver nitrate is weighed and dissolved in 20 L of water, and 2.5 kg of ascorbic acid is weighed and dissolved in 20 L of pure water; S5. The silver nitrate solution prepared in step S4 and the ascorbic acid solution are synchronously added into the bottom solution prepared in step S3 under the condition of 25 DEG C constant temperature and stirring, the feeding speed is 3 L / min, after the feeding is completed, a silver powder solution is obtained, and finally, spherical silver powder is obtained through washing, solid-liquid separation and drying and shaping, and the scanning electron microscope (SEM) image of the spherical silver powder is shown in the figure. Figure 5 As can be seen from the figure, the silver powder is a large-size spherical silver powder with a compact structure and regular morphology.

[0047] Comparative example 2 The comparative example 2 provides a preparation method of the micro-silver powder with a fluffy structure. Compared with the embodiment 1, the only difference is that 2 kg of sodium carbonate is weighed and added into 6 L of water, and the mixture is stirred to dissolve at 30 DEG C constant temperature, that is, the mass ratio of the reagent to silver nitrate is 1:5, and other experimental parameters and conditions are basically the same as those of the embodiment 1, which will not be repeated here. In the experiment, due to the small amount of sodium carbonate, only a small amount of silver nitrate participates in the reaction to generate an intermediate, and most of the silver nitrate still exists in the form of silver nitrate, so that the micro-silver powder with a fluffy structure cannot be finally obtained.

[0048] Comparative example 3 ​Comparative Example 3 provides a method for preparing a micro-silver powder with fluffy structure, which is different from Example 1 only in that the constant temperature is 60°C in steps S2 and S3, and other experimental parameters and conditions are basically the same as those of Example 1, which will not be repeated here. Due to the excessively high reaction temperature, the Cannizzaro reaction occurs, and the disproportionation occurs under high-temperature alkaline conditions to generate methanol and formic acid, which consumes the reducing agent, resulting in insufficient amount of reducing agent to completely reduce the intermediate, and finally the micro-silver powder with fluffy structure cannot be obtained.

[0049] The detection results of the silver powder obtained in the examples and comparative examples are shown in Table 1.

[0050] Table 1: Detection results of the parameters of the silver powder obtained in the examples and comparative examples As can be seen from Table 1, the tap density of the silver powder prepared in the examples of the present application is smaller, and the specific surface area is larger than that of Comparative Example 1, indicating that the silver powder synthesized in the examples of the present application has a fluffy structure, which helps the silver powder to stably exist in the slurry, and has good slurry dispersibility and stability.

[0051] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, other ways constructed by combining part of the constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing micron-sized silver powder with a porous structure, characterized in that, Includes the following steps: S1. Prepare silver nitrate solution, alkaline solution, and reducing agent solution; S2. Under constant temperature and stirring conditions, the alkaline solution is added dropwise to the silver nitrate solution to form a mixed solution; The mass ratio of the reagent in the alkaline solution to the silver nitrate in the silver nitrate solution is 1:(1~3). S3. Under constant temperature stirring, the reducing agent solution is added dropwise to the mixed solution, and a silver powder solution is obtained through reaction. The mass ratio of the reducing agent in the reducing agent solution to the silver nitrate in the silver nitrate solution is (3~5):

10. Subsequently, after washing, solid-liquid separation, drying, and sieving, a porous micron-sized silver powder was obtained; the tap density of the porous micron-sized silver powder was 1.5~2.5 g / cm³. 3 .

2. The method for preparing the porous micron-sized silver powder according to claim 1, characterized in that, In step S1, the reagent in the alkaline solution is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, sodium sulfide, sodium phosphate, and aniline.

3. The method for preparing the porous micron-sized silver powder according to claim 1, characterized in that, In step S1, the reducing agent in the reducing agent solution is one or more of the following: sodium borohydride, triethanolamine, hydrazine hydrate, hydroquinone, hydroxylamine, ascorbic acid, sodium citrate, hydrogen peroxide, hydrazine sulfate, glucose, formaldehyde, and potassium iodide.

4. The method for preparing the porous micron-sized silver powder according to claim 1, characterized in that, In steps S2 and S3, the constant temperature is 25~45℃.

5. The method for preparing the porous micron-sized silver powder according to claim 1, characterized in that, In step S2, the dripping rate is 0.1~3 L / min.

6. The method for preparing the porous micron-sized silver powder according to claim 1, characterized in that, In step S3, the dripping rate is 0.1~2 L / min.

7. The method for preparing the porous micron-sized silver powder according to claim 1, characterized in that, In step S3, the drying and sieving method is as follows: after drying at 70~110℃, sieving is performed using a 10~400 mesh sieve.

8. A micron-sized silver powder with a loose structure, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

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