Sub-micron scale polycrystalline metal powders and methods of making same

Abstract

The embodiment of the present application provides a kind of sub-micron scale polycrystalline metal powder and its preparation method, wherein the preparation method of sub-micron scale polycrystalline metal powder includes the following steps: under stirring condition, precipitant solution is added dropwise into silver source solution, and nanometer scale silver hydroxide is generated by precipitation reaction;Coating agent is added to the reaction system in which nanometer scale silver hydroxide is generated, the reaction temperature is increased and aging reaction is carried out to obtain nanometer scale silver oxide;The obtained silver oxide is pretreated to obtain nanometer silver oxide precursor;Nanometer silver oxide precursor is uniformly dispersed in dispersant solution to obtain bottom liquid, and reducing agent solution is added to the bottom liquid, and reduction reaction is carried out to obtain sub-micron scale polycrystalline silver powder.The sub-micron scale polycrystalline metal powder and its preparation method provided by the present application effectively inhibit the agglomeration phenomenon, improve the sintering activity and dispersion stability in conductive paste, reduce the waste liquid generation in the preparation process, and reduce the environmental protection treatment cost.

Description

Technical Field

[0001] This application belongs to the field of conductive materials technology, and in particular relates to a submicron-scale polycrystalline metal powder and its preparation method. Background Technology

[0002] Nanoscale silver powder possesses excellent high conductivity and high sintering activity, enabling low-temperature sintering interconnection below 200℃. It is suitable for high-temperature-sensitive electronic processing scenarios such as flexible substrates and thermistor devices, and is widely used in conductive silver pastes, flexible electronics, and microcircuit packaging. It is a key core material in low-temperature printed electronics and electronic packaging. Compared to traditional micron-sized silver powder, its low-temperature processing advantages are significant, effectively avoiding problems such as substrate deformation, device damage, and high energy consumption caused by high-temperature processes, making it extremely valuable for industrial applications.

[0003] However, existing processes for preparing and applying nanoscale silver powder have significant technical shortcomings. Nanoscale silver powder has a small particle size and high surface energy, making it extremely prone to particle agglomeration. This not only reduces its own sintering activity, leading to poor uniformity and density of the sintered conductive layer, but also causes uneven dispersion in silver paste, seriously affecting the performance of the paste and the quality and stability of the finished electronic devices.

[0004] The current mainstream silver nitrate-vitamin C liquid-phase reduction preparation process has environmental drawbacks. To control the particle size accuracy of the powder, low-concentration reaction solutions are required, generating a large amount of production waste liquid. This waste liquid has a complex composition and contains a large amount of nitrate ions and organic byproducts generated from the oxidation of vitamin C, making pollutant treatment difficult and significantly increasing production, environmental protection, and operation and maintenance costs. This hinders the low-cost, large-scale, green industrial production of nanoscale silver powder. In summary, there is an urgent need to develop new nanoscale silver powder preparation processes to address the industry pain points of easy powder agglomeration and high waste liquid treatment costs. Summary of the Invention

[0005] The purpose of this application is to provide a submicron-scale polycrystalline metal powder and its preparation method, which effectively suppresses the agglomeration of nanoscale silver powder, improves its sintering activity and dispersion stability in conductive paste; at the same time, it reduces the generation of waste liquid during the preparation process and lowers the environmental treatment cost.

[0006] In a first aspect, embodiments of this application provide a method for preparing submicron-scale polycrystalline metal powder, the technical solution of which is as follows: A method for preparing submicron-scale polycrystalline silver powder includes the following steps: We provide silver source solutions, precipitant solutions, dispersant solutions, and reducing agent solutions; Under stirring conditions, the precipitant solution is added dropwise to the silver source solution, and a precipitation reaction occurs to generate nanoscale silver hydroxide. A coating agent was added to the reaction system for generating nanoscale silver hydroxide, the reaction temperature was increased, and an aging reaction was carried out to obtain nanoscale silver oxide. The obtained silver oxide was pretreated to obtain a nano-silver oxide precursor. The nano-silver oxide precursor was uniformly dispersed in a dispersant solution to obtain a base liquid, and a reducing agent solution was added to the base liquid to carry out a reduction reaction to obtain submicron-scale polycrystalline metal powder.

[0007] In some embodiments, the concentration ratio of the silver source in the silver source solution to the concentration ratio of the precipitant in the precipitant solution is 1:(1~1.1).

[0008] In some embodiments, the ratio of the concentration of the reducing agent in the reducing agent solution to the concentration of the silver source in the silver source solution is (1.05~1.2):1.

[0009] In some embodiments, the precipitant solution is added dropwise to the silver source solution at a rate of 15-25 mL / min, and the stirring speed is 300-400 rpm.

[0010] In some embodiments, the aging reaction conditions include raising the reaction temperature from room temperature to 40-80°C and reacting for 60-120 minutes.

[0011] In some embodiments, the reduction reaction conditions include stirring the reaction at room temperature for 30 to 60 minutes.

[0012] In some embodiments, the pretreatment of silver oxide includes filtration, washing, drying, and crushing.

[0013] In some embodiments, after the reduction reaction is completed, the process further includes centrifugal filtration, multiple washing, and vacuum drying to obtain submicron-scale polycrystalline silver powder.

[0014] In some embodiments, the silver source solution includes a silver nitrate solution; in other embodiments, the silver source solution also includes gum arabic powder.

[0015] In some embodiments, the precipitant in the precipitant solution includes one of sodium hydroxide, sodium carbonate, sodium oxalate, and potassium hydroxide.

[0016] In some embodiments, the dispersant in the dispersant solution includes one of PVP, gum arabic, gelatin, PVA, and PEG.

[0017] In some embodiments, the coating agent includes one of lauric acid, myristic acid, palmitic acid, and stearic acid, and the weight of the coating agent accounts for 5 to 20% of the dispersant in the dispersant solution.

[0018] In some embodiments, the reducing agent solution is a glucose solution.

[0019] Secondly, embodiments of this application provide a submicron-scale polycrystalline metal powder, which is prepared using the above-described preparation method.

[0020] In some embodiments, the average particle size of the submicron-scale polycrystalline silver powder is 200-300 nm, and the tap density is 3-5 g / cm³. 3 Furthermore, the surface of the submicron-scale polycrystalline silver powder has a polycrystalline structure.

[0021] By employing a process route of precipitation reaction to generate silver hydroxide, aging to obtain silver oxide, and then reduction, the particle size distribution and surface structure of nanoscale silver powder are effectively controlled, particle agglomeration is inhibited, and the concentration and conditions of the reaction system are optimized to reduce waste liquid generation. This effectively inhibits the agglomeration of nanoscale silver powder, improves its sintering activity and dispersion stability in conductive pastes, and at the same time reduces waste liquid generation during the preparation process, thereby lowering environmental treatment costs. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic flowchart of the method for preparing submicron-scale polycrystalline metal powder provided in the embodiments of this application; Figure 2 This is a scanning electron microscope image of the submicron-scale polycrystalline metal powder provided in Example 1 of this application; Figure 3 This is a scanning electron microscope image of the submicron-scale polycrystalline metal powder provided in Example 2 of this application; Figure 4 This is a scanning electron microscope image of the submicron-scale polycrystalline metal powder provided in Example 3 of this application; Figure 5 This is a scanning electron microscope image of the nanoscale metal powder provided in Comparative Example 1 of this application; Figure 6 This is a scanning electron microscope image of the submicron-scale polycrystalline metal powder provided in Comparative Example 2 of this application; Figure 7 This is a scanning electron microscope image of the submicron-scale polycrystalline metal powder provided in Comparative Example 3 of this application. Detailed Implementation

[0024] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that the embodiments of this application can also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the embodiments of this application with unnecessary detail.

[0025] It should also be understood that the term "and / or" as used in the specification of embodiments of this application and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0026] Furthermore, in the description of the embodiments and the appended claims of this application, the terms "first," "second," "third," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance.

[0027] In the description of embodiments in this application, references to "some embodiments" or "some embodiments" mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in some embodiments," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiments, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized. "A plurality" refers to two or more.

[0028] In traditional existing nanoscale silver powder preparation processes, due to the small particle size and high surface energy of nanoscale silver powder, particle agglomeration is a very significant problem. This reduces the uniformity and density of the sintered conductive layer and affects the dispersibility in the silver paste, resulting in damage to the paste's performance and the quality and stability of the finished electronic devices. Furthermore, in the existing silver nitrate-vitamin C liquid-phase reduction preparation process, a large amount of waste liquid containing nitrate ions and organic byproducts is generated, which increases the difficulty of pollutant treatment and raises environmental protection and operation and maintenance costs.

[0029] For example, in the flexible electronics manufacturing scenario, nanoscale silver powder is used to prepare conductive silver paste for printing electronic circuits. Due to particle agglomeration, the uniformity of the paste is destroyed during the coating process, and the continuity of the conductive circuit is interrupted after sintering, resulting in local open circuits or resistance fluctuations. At the same time, the production waste liquid contains high concentrations of nitrate and organic pollutants, which require special treatment facilities for disposal, leading to interruptions in the production process and the occupation of resources.

[0030] If the above problems are not solved, the reliability of electronic devices will continue to decline, the feasibility of large-scale production will be severely restricted, and the industrial application of nanoscale silver powder in low-temperature printed electronics and microcircuit packaging will be hindered.

[0031] In response, this application provides a method for preparing submicron-scale polycrystalline metal powder, which includes the following steps: S10. Provide silver source solution, precipitant solution, dispersant solution and reducing agent solution; S20. Under stirring conditions, the precipitant solution is added dropwise to the silver source solution, and a precipitation reaction occurs to generate nanoscale silver hydroxide. S30. Add a coating agent to the reaction system for generating nanoscale silver hydroxide, increase the reaction temperature and carry out an aging reaction to obtain nanoscale silver oxide. S40. The obtained silver oxide is pretreated to obtain a nano silver oxide precursor. S50. The nano-silver oxide precursor is uniformly dispersed in the dispersant solution to obtain the base liquid, and the reducing agent solution is added to the base liquid to carry out the reduction reaction to obtain submicron-scale polycrystalline metal powder.

[0032] The method for preparing submicron-scale polycrystalline metal powder provided in this application achieves effective control over the particle size and morphology of nanoscale silver powder through stepwise controlled precipitation, aging, and reduction processes. In existing technologies, nanoscale silver powder is prone to particle agglomeration, leading to reduced sintering activity and uneven slurry dispersion. This embodiment effectively inhibits particle agglomeration and excessive growth by introducing a coating agent during the conversion of silver hydroxide to silver oxide and utilizing a dispersant in the subsequent reduction step. The coating agent modifies the particle surface during the silver oxide formation stage, and the dispersant continuously stabilizes the silver particles during the reduction reaction, thereby obtaining nanoscale silver powder with good dispersibility and polycrystalline structure, which contrasts sharply with the agglomeration problem commonly found in existing technologies.

[0033] The preparation path employed in this embodiment involves generating silver hydroxide through a silver source solution and a precipitant solution, which is then converted into a silver oxide precursor and finally reduced to silver powder. This provides an alternative to the traditional silver nitrate-vitamin C liquid-phase reduction process. Existing silver nitrate-vitamin C processes suffer from the generation of large amounts of complex waste liquid, significant challenges in environmental treatment, and high costs. The preparation method in this embodiment avoids directly using vitamin C as a reducing agent, potentially leading to different byproduct systems. This provides new possibilities for waste liquid treatment, helps reduce environmental and operational costs, and promotes the green industrial production of nanoscale silver powder. Through this multi-step conversion path, this method allows for more precise control of the reaction process, resulting in high-quality submicron-scale polycrystalline silver powder, while also demonstrating potential advantages in environmental protection.

[0034] In summary, the preparation method of this embodiment effectively solves the problems of easy agglomeration of nanoscale silver powder and high environmental protection costs of traditional preparation processes by introducing coating agents and dispersants and adopting a unique intermediate product conversion pathway. It provides an innovative and practical technical solution for preparing high-performance, environmentally friendly submicron-scale polycrystalline silver powder.

[0035] For ease of understanding, the following explains some key terms in this embodiment: Silver source solution refers to a solution containing soluble silver salts, which serves as the source of silver ions and is the starting reactant for preparing nanoscale silver powder. The concentration and composition of this solution affect the morphology and size of the subsequent reaction products.

[0036] In this embodiment, the silver source solution is a silver nitrate solution. By specifying silver nitrate as the silver source solution, the high purity and good stability of the initial silver ions in solution can be ensured. This provides a pure and stable reaction environment for the subsequent precipitation reaction, effectively avoiding side reactions or product contamination that may be caused by the introduction of impurities. At the same time, a stable supply of silver ions helps to precisely control the nucleation and growth process of nanoscale silver hydroxide, thereby ensuring the morphology and uniformity of the intermediate product, silver oxide.

[0037] In other embodiments, the silver source solution also includes gum arabic powder. That is, the silver source solution includes silver nitrate solution and gum arabic. Gum arabic can prevent the reduction of silver ions / agglomeration of silver particles; if tiny silver crystal nuclei are formed in the silver nitrate solution, they easily aggregate and precipitate. Gum arabic is a high-molecular-weight hydrophilic colloid; its molecular chains can adsorb onto the surface of newly formed silver particles, forming a steric barrier that prevents particle adhesion and aggregation, keeping the system homogeneous and stable. When the high-molecular-weight colloid dissolves in water, it forms a viscous aqueous phase, increasing the solution viscosity, slowing down the movement and collision of silver ions / silver particles, and improving the compatibility of each component, allowing silver nitrate to be dispersed more evenly in water. Silver nitrate aqueous solutions are prone to hydrolysis upon prolonged storage and precipitate silver oxide turbidity upon exposure to light. The colloidal environment of gum arabic can buffer the system, encapsulate silver ions, reduce decomposition caused by hydrolysis and light exposure, and extend the storage time of the silver source solution.

[0038] A precipitant solution is a solution containing a substance that can react with silver ions to form a precipitate. By controlling the method of addition and concentration of this solution, the rate of precipitation reaction and the initial particle size of the product can be controlled.

[0039] Dispersant solutions are solutions containing dispersants. Their main function is to help nanoparticles disperse uniformly in subsequent steps, prevent agglomeration, and may modify the particle surface.

[0040] A reducing agent solution is a solution containing a substance capable of reducing silver ions or silver compounds to elemental silver. The reducing power of this solution and the method of its addition are key factors in controlling the final morphology and crystallinity of the silver powder.

[0041] A coating agent is a substance added to a reaction system that can form a protective film or adsorption layer on the surface of nanoparticles to inhibit particle growth, prevent agglomeration, and may affect the surface properties of the particles.

[0042] Aging reaction refers to the process of placing precipitates or particles in a solution at a certain temperature for a period of time to promote crystal growth, morphological evolution, or surface modification of the particles.

[0043] In this application, by employing a nano-silver oxide precursor and with the aid of a dispersant, submicron-scale polycrystalline silver powder with an average particle size of 200-300 nm is generated. The single-crystal structure has a size of approximately 50-100 nm, exhibiting high sintering activity, and the resulting submicron-scale polycrystalline silver powder possesses excellent dispersibility.

[0044] Furthermore, the wastewater can be divided into two parts: one part is high-salt (nitrate) wastewater, and the other part is high-glucose oxidation product wastewater. The high-concentration organic wastewater from glucose oxidation and the washing wastewater containing sodium nitrate are treated separately to avoid the high salt content inhibiting biochemical activity and organic matter contaminating sodium nitrate. Simultaneously, the residual sludge or effluent from the aerobic stage of glucose oxidation wastewater treatment is introduced as a carbon source into the denitrification stage of sodium nitrate wastewater treatment, achieving waste-to-waste treatment, eliminating the need for external commercial carbon sources, and reducing overall treatment costs.

[0045] In the application, step S10 provides a silver source solution, a precipitant solution, a dispersant solution, and a reducing agent solution. The silver source solution can be a variety of soluble silver salt solutions, such as silver nitrate solution, silver acetate solution, or silver chloride complex solution, and its concentration can be adjusted according to the requirements of the target product. The precipitant solution can be an alkaline solution that can react with silver ions to form silver hydroxide precipitate, such as sodium hydroxide solution, potassium hydroxide solution, or ammonia. The dispersant solution can be a solution containing a polymer or surfactant, such as polyvinylpyrrolidone solution, polyvinyl alcohol solution, or gum arabic solution. The reducing agent solution can be a variety of reducing compound solutions, such as glucose solution, ascorbic acid solution, or hydrazine hydrate solution.

[0046] In step S20, under stirring conditions, the precipitant solution is added dropwise to the silver source solution, resulting in a precipitation reaction to form nanoscale silver hydroxide. The dropwise addition process can be achieved using equipment such as a peristaltic pump, a constant flow pump, or a dropping funnel to control the dropping rate. Stirring conditions can be provided using equipment such as a magnetic stirrer, a mechanical stirrer, or an ultrasonic stirrer to ensure thorough mixing of the reactants and promote uniform precipitation. For example, a lower dropping rate combined with moderate stirring can be used to facilitate the formation of smaller silver hydroxide precipitates. Alternatively, a faster dropping rate combined with stronger stirring can be used to improve reaction efficiency.

[0047] In step S30, a coating agent is added to the reaction system for generating nanoscale silver hydroxide, the reaction temperature is increased, and an aging reaction is carried out to obtain nanoscale silver oxide. The coating agent can be a variety of organic acids or surfactants, such as lauric acid, oleic acid, or sodium dodecylbenzenesulfonate, and its amount can be adjusted according to the amount of silver hydroxide. Increasing the reaction temperature can be achieved by water bath heating, oil bath heating, or an electric heating mantle to accelerate the conversion of silver hydroxide to silver oxide. The aging time can be adjusted according to the desired silver oxide particle size and morphology; for example, aging can be carried out for a longer time at room temperature or for a shorter time at a higher temperature.

[0048] In step S40, the obtained silver oxide is pretreated to obtain a nano-silver oxide precursor. The pretreatment step may include various operations, such as separating the silver oxide solid from the solution by centrifugation or filtration. The separated solid can be washed multiple times to remove residual impurity ions. The washed solid can be dried, for example, at low temperature in a vacuum oven to remove moisture. The dried solid can also be subjected to simple crushing or grinding to obtain a more uniform powder state.

[0049] In step S50, the nano-silver oxide precursor is uniformly dispersed in a dispersant solution to obtain a base liquid. A reducing agent solution is then added to the base liquid to initiate a reduction reaction, yielding submicron-scale polycrystalline silver powder. The dispersion of the nano-silver oxide precursor can be achieved through ultrasonic dispersion, mechanical stirring, or high-speed shearing to ensure a stable suspension in the dispersant solution. The reducing agent solution can be added dropwise, all at once, or in batches. The reduction reaction can be carried out at room temperature or under heating conditions, and the reaction time can be adjusted according to the type and concentration of the reducing agent.

[0050] In some embodiments, the concentration ratio of the silver source in the silver source solution to the concentration ratio of the precipitant in the precipitant solution is 1:(1~1.1). Specifically, the concentration ratio of the silver source in the silver source solution to the concentration ratio of the precipitant in the precipitant solution is 1:1, 1:1.05, 1:1.08, 1:1.1, etc., to optimize the morphology and particle size of the precipitate while ensuring complete reaction. The scheme of this application ensures that the stoichiometric relationship between silver ions and precipitant is optimized during the precipitation reaction by precisely controlling the concentration ratio of the silver source in the silver source solution to the concentration ratio of the precipitant in the precipitant solution within the range of 1:(1~1.1). This precise concentration ratio allows the precipitant to exist in a slightly excess state, thereby effectively promoting the full conversion of silver ions into nanoscale silver hydroxide precipitate, while inhibiting the rapid and disordered crystal nucleus growth caused by local supersaturation. By controlling the reactant concentration, the precipitation rate and nucleation process can be effectively adjusted, resulting in silver hydroxide particles with smaller average particle size and narrower particle size distribution, and reducing the tendency of particle aggregation.

[0051] In some embodiments, the concentration ratio of the reducing agent in the reducing agent solution to the silver source concentration in the silver source solution is (1.05~1.2):1. The scheme of this application ensures the full conduct of the reduction reaction by precisely controlling the concentration ratio of the reducing agent in the reducing agent solution to the silver source concentration in the silver source solution within the range of (1.05~1.2):1. In the preparation process of submicron-scale polycrystalline silver powder, the reduction reaction is a key step in converting silver ions into silver atoms. By setting a slightly excess of reducing agent, the problem of incomplete reduction due to insufficient reducing agent can be effectively avoided, thereby improving the conversion rate of silver ions and the yield of the final product. At the same time, this moderate excess avoids the overuse of reducing agent, reduces reagent waste, and lowers production costs.

[0052] In some embodiments, the precipitant solution is added to the silver source solution at a rate of 15-25 mL / min, and the stirring speed is 300-400 rpm. Specifically, the precipitant solution is added to the silver source solution at rates of 15 mL / min, 20 mL / min, 25 mL / min, etc., and the stirring speed is 300 rpm, 320 rpm, 350 rpm, 400 rpm, etc. The scheme of this application optimizes the key precipitation reaction step in the preparation method of submicron-scale polycrystalline silver powder by precisely controlling the dropping rate of the precipitant solution and the stirring speed of the reaction system. In the process of adding the precipitant solution dropwise to the silver source solution to generate nanoscale silver hydroxide, controlling the dropping rate of the precipitant solution within the specific range of 15-25 mL / min ensures that the precipitant is slowly introduced into the reaction system in a controlled manner, avoiding the "nucleation explosion" phenomenon caused by instantaneous local high concentration, thereby facilitating the formation of a moderate number and uniformly sized initial crystal nuclei. Meanwhile, maintaining the stirring speed within a specific range of 300-400 rpm ensures thorough mixing and efficient mass transfer of the liquid within the reaction system. This allows the newly introduced precipitant to disperse rapidly and uniformly throughout the silver source solution, preventing the formation of localized supersaturated regions and effectively inhibiting the aggregation of existing silver hydroxide particles. This synergistic control mechanism enables precise regulation of the nucleation and growth process of silver hydroxide particles, resulting in nanoscale silver hydroxide intermediates with narrower size distribution, more regular morphology, and better dispersibility. High-quality nanoscale silver hydroxide serves as a precursor for subsequent silver oxide and the final submicron-scale polycrystalline silver powder, laying the foundation for their superior final performance.

[0053] In some embodiments, the aging reaction conditions include raising the reaction temperature from room temperature to 40-80°C and reacting for 60-120 minutes. Specifically, the reaction temperature can be 40°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc. The reaction time can be 60 minutes, 70 minutes, 75 minutes, 80 minutes, 90 minutes, 100 minutes, 105 minutes, 110 minutes, 120 minutes, etc. Specifically, a moderately increased temperature can effectively increase the kinetic energy of molecules in the reaction system, accelerate the conversion rate of nanoscale silver hydroxide to nanoscale silver oxide, and promote the crystal growth and maturation process of silver oxide particles. At the same time, limiting the reaction time to 60-120 minutes ensures that the particles have sufficient time to mature, thereby obtaining nanoscale silver oxide particles with uniform size and regular morphology, and effectively inhibiting excessive growth and agglomeration of particles. This controlled aging process provides a high-quality nano-silver oxide precursor for the subsequent reduction reaction, resulting in submicron-scale polycrystalline silver powder with superior particle size distribution and crystal structure.

[0054] In some embodiments, the reduction reaction conditions include stirring at room temperature for 30–60 minutes. Specifically, the reaction time can be 30 min, 35 min, 40 min, 45 min, 50 min, 60 min, etc. Using room temperature conditions in the reduction reaction typically means conducting the reaction at ambient temperature, for example, within the temperature range of 15°C to 30°C. This temperature condition helps reduce energy consumption, simplifies equipment requirements, and effectively avoids rapid growth and aggregation of nanoparticles caused by high temperatures, thereby contributing to obtaining nanoscale silver powder with uniform particle size distribution and controllable morphology. The purpose of stirring the reaction is to ensure that the nano-silver oxide precursor, dispersant solution, and reducing agent solution in the reaction system are fully mixed, thereby ensuring the uniformity of the reduction reaction. Stirring can promote mass transfer between reactants, prevent the precipitation of the nano-silver oxide precursor, and help maintain the homogeneity of the system, avoiding uneven nucleation and growth caused by excessively high local concentrations. The reaction time is set at 30-60 minutes to ensure the reduction reaction proceeds fully, reducing most of the nano-silver oxide precursor to nano-sized silver powder. This avoids excessive growth or agglomeration of nano-sized silver particles that might occur with prolonged reactions, thus facilitating the acquisition of submicron-scale polycrystalline silver powder with specific particle size and morphology. For example, the stirring speed can be controlled between 200-500 rpm to ensure thorough mixing without introducing excessive shear force.

[0055] In some embodiments, the pretreatment of silver oxide includes filtration, washing, drying, and crushing.

[0056] Through the pretreatment steps of filtration, washing, drying, and crushing of silver oxide described above, this application can effectively remove impurities from nanoscale silver oxide, preventing them from affecting product purity in subsequent steps. Simultaneously, drying and crushing effectively prevent the agglomeration of silver oxide particles, ensuring good dispersibility and uniform particle size distribution of the nanoscale silver oxide precursor. This allows the nanoscale silver oxide precursor to form a stable and uniform substrate in the dispersant solution, providing high-quality reactants for the subsequent reduction reaction. This significantly improves the efficiency of the reduction reaction and the uniformity of the product, ultimately yielding submicron-scale polycrystalline silver powder with higher purity, more regular morphology, and a more concentrated particle size distribution.

[0057] In some embodiments, after the reduction reaction is completed, the process further includes centrifugal filtration, multiple washing, and vacuum drying to obtain the submicron-scale polycrystalline silver powder. This significantly improves the purity of the prepared submicron-scale polycrystalline silver powder, ensures the stability of its morphology and particle size, and thus enables it to exhibit superior conductivity and stability in subsequent applications such as conductive pastes.

[0058] The proposed method involves first centrifuging and filtering after the reduction reaction to efficiently separate the solid submicron-scale polycrystalline silver powder from the liquid reaction medium. Centrifugal force causes the denser nanoscale silver powder to settle rapidly, achieving initial solid-liquid separation and removing most liquid impurities. Subsequently, to further remove soluble ions, organic residues, or unreacted reagents adsorbed on the surface of the nanoscale silver powder, multiple washing steps are employed. By repeatedly adding detergent (such as deionized water or ethanol) and centrifuging and filtering again, these impurities can be effectively dissolved and removed, ensuring the purity of the nanoscale silver powder. Finally, to thoroughly remove the solvent introduced during the washing process and avoid potential oxidation or agglomeration of the nanoscale silver powder at high temperatures, vacuum drying is used. In a vacuum environment, the boiling point of the solvent is lowered, allowing for rapid evaporation at a lower temperature, resulting in dry and pure submicron-scale polycrystalline silver powder. This series of post-processing steps works synergistically to ensure that the prepared submicron-scale polycrystalline silver powder has high purity, good dispersibility, and a stable nanostructure, thus solving the problem of insufficient purity of the product after the reduction reaction.

[0059] In some embodiments, the precipitant in the precipitant solution includes one of sodium hydroxide, sodium carbonate, sodium oxalate, and potassium hydroxide. The precipitant in the precipitant solution is a key component for reacting with silver ions in the silver source solution to generate nanoscale silver hydroxide. Its selection directly affects the efficiency of the precipitation reaction, the purity of the product, and subsequent conversion processes. This application, by limiting the precipitant in the precipitant solution to one of sodium hydroxide, sodium carbonate, sodium oxalate, and potassium hydroxide in the method for preparing submicron-scale polycrystalline silver powder, ensures that silver ions in the silver source solution can be efficiently and controllably converted into nanoscale silver hydroxide. These specific precipitants have good reactivity and selectivity, effectively promoting the precipitation of silver ions while avoiding the introduction of excessive impurities.

[0060] In some embodiments, the dispersant in the dispersant solution includes one of polyvinylpyrrolidone (PVP), gum arabic, gelatin, polyvinyl alcohol (PVA), and polyethylene glycol (PEG). By selecting these specific types of dispersants, they can be effectively adsorbed onto the surface of the nano-silver oxide precursor. This adsorption establishes a physical barrier (steric hindrance) or provides electrostatic repulsion between the nanoparticles, thereby significantly inhibiting the aggregation and sedimentation of the nano-silver oxide precursor in the dispersant solution.

[0061] In applications, polyvinylpyrrolidone (PVP), a water-soluble polymer, contains hydrophilic groups in its molecular chain, enabling it to adsorb onto the surface of nanoparticles through steric hindrance or electrostatic repulsion, effectively preventing particle aggregation. Gum arabic, a natural polysaccharide, possesses excellent water solubility and surface activity, allowing it to adsorb onto the nanoparticle surface to form a protective layer and improve the stability of the dispersion system. Gelatin, an amphoteric electrolyte protein, has a molecular structure that can form an adsorption layer on the nanoparticle surface, providing steric hindrance and electrostatic repulsion for stable nanoparticle dispersion. Polyvinyl alcohol, a water-soluble synthetic polymer, exhibits excellent film-forming and dispersing properties, and can adsorb onto the nanoparticle surface through hydrogen bonding, providing effective steric hindrance. Polyethylene glycol, a water-soluble polyether, forms an adsorption layer on the nanoparticle surface through its polymer chains, generating a steric hindrance effect and preventing nanoparticle aggregation.

[0062] In some embodiments, the coating agent includes one of lauric acid, myristic acid, palmitic acid, and stearic acid, and the weight of the coating agent accounts for 5-20% of the dispersant in the dispersant solution. The 5-20% weight of the coating agent ensures that it adequately covers the surface of the silver oxide nanoparticles, providing sufficient steric hindrance or electrostatic repulsion, while avoiding the introduction of excessive organic impurities or adverse effects on subsequent reactions due to excessive coating agent.

[0063] The present application describes a method that involves introducing a specific type of coating agent, namely one of lauric acid, myristic acid, palmitic acid, or stearic acid, during the aging reaction stage of the conversion of nanoscale silver hydroxide to nanoscale silver oxide. This is done under strictly controlled conditions (i.e., the weight of the coating agent accounts for 5-20% of the dispersant in the dispersant solution). These fatty acids can effectively adsorb onto the surface of the silver oxide nanoparticles, forming a dense organic protective layer. This protective layer provides effective steric hindrance, significantly inhibiting the aggregation and disordered growth of nanoparticles during high-temperature aging, thereby ensuring that the obtained nanoscale silver oxide has a more uniform particle size distribution and a more stable dispersion.

[0064] In some embodiments, the reducing agent solution is a glucose solution. A glucose solution is an aqueous solution with glucose as the solute. Glucose, as a naturally occurring aldose, contains an aldehyde group and multiple hydroxyl groups in its molecular structure, giving it excellent reducing properties. In the preparation method of this application, the glucose solution acts as a reducing agent, reducing silver ions in the nanoscale silver oxide precursor to metallic silver atoms, thereby promoting the formation of submicron-scale polycrystalline silver powder. The mild reducing properties of glucose help to precisely control the nucleation and growth process of silver nanoparticles, which is beneficial for obtaining submicron-scale polycrystalline silver powder with uniform particle size distribution and controllable morphology, thus improving the performance and application potential of the final product.

[0065] Secondly, this application proposes a submicron-scale polycrystalline silver powder, which is prepared using the above-described method.

[0066] The submicron-scale polycrystalline silver powder provided in this embodiment effectively suppresses the agglomeration problem of nanoscale silver powder by combining a coating agent and a dispersant in a specific ratio and employing a multi-step conversion path of silver hydroxide-silver oxide-silver powder. This avoids the complex waste liquid generated by traditional vitamin C reduction processes, achieving the dual effect of improving the sintering activity of nanoscale silver powder and reducing production and environmental protection costs. Specifically, the preparation method first involves adding a precipitant solution dropwise to a silver source solution under stirring to generate nanoscale silver hydroxide. Then, a coating agent is added to the reaction system, and the temperature is increased for aging to obtain nanoscale silver oxide. After pretreatment, a nanoscale silver oxide precursor is obtained. Finally, this precursor is uniformly dispersed in a dispersant solution to form a base liquid, and a reducing agent solution is added for a reduction reaction. During this process, the coating agent forms a protective layer on the particle surface, and the dispersant maintains the uniform dispersion of the particles. The synergistic effect of the two significantly reduces the van der Waals forces between particles, effectively preventing agglomeration.

[0067] Meanwhile, this process abandons the highly polluting vitamin C reduction system and instead uses environmentally friendly reducing agents such as glucose, significantly reducing the content of nitrate ions and organic byproducts in the waste liquid and simplifying the waste liquid treatment process. Through the above technical solution, the obtained submicron-scale polycrystalline silver powder not only possesses excellent low-temperature sintering performance, adapting to the processing requirements of flexible substrates and thermistor components, but also achieves a green and environmentally friendly production process, providing reliable technical support for the low-cost, large-scale industrialization of nanoscale silver powder.

[0068] In some embodiments, the average particle size of the submicron-scale polycrystalline silver powder is 200-300 nm, and the tap density is 3-5 g / cm³. 3 Furthermore, the surface of the submicron-scale polycrystalline silver powder exhibits a polycrystalline structure. Specifically, controlling the average particle size within the range of 200–300 nm ensures good dispersibility of the nanoscale silver powder in the dispersant solution, preventing agglomeration and providing a suitable size basis for the subsequent sintering process. Based on this, by optimizing particle morphology and packing properties, the tap density of the nanoscale silver powder reaches 3–5 g / cm³, meaning that the powder particles can be packed more tightly, effectively reducing the porosity of the powder packing. More importantly, by precisely controlling the conditions of the reduction reaction, a polycrystalline structure is formed on the surface of the nanoscale silver powder. This polycrystalline structure increases the surface active sites and grain boundaries of the nanoscale silver powder, which promotes the connection and densification between silver particles during subsequent application in conductive pastes and sintering, forming a more stable and efficient conductive pathway.

[0069] The average particle size refers to the statistical average size of silver powder particles at the nanoscale, reflecting the overall fineness of the powder. This particle size range helps ensure good dispersibility and filling properties of nanoscale silver powder in conductive pastes, while avoiding excessively high sintering temperatures due to excessively small particle sizes or decreased conductivity due to excessively large particle sizes.

[0070] Tap density refers to the density of powder when it reaches its maximum compactness under specific vibration conditions. It is an important indicator for measuring the packing performance of powder. A higher tap density means that the powder particles are packed tightly together and have low porosity. This is crucial for increasing the solid content of conductive slurries, reducing sintering shrinkage, and improving the density of conductive films.

[0071] The polycrystalline structure of submicron-scale polycrystalline silver powder refers to the fact that nanoscale silver powder particles are composed of multiple grains arranged in different crystal orientations and interconnected. This polycrystalline structure provides more grain boundaries, thereby increasing the active surface area of ​​the nanoscale silver powder, which is beneficial for forming a denser conductive network during sintering and improving conductivity. In addition, the polycrystalline structure may also endow nanoscale silver powder with better mechanical stability and oxidation resistance.

[0072] Example Example 1 This application provides a submicron-scale polycrystalline metal powder and its preparation method, wherein the preparation method includes the following steps: S10. Provide silver source solution, precipitant solution, dispersant solution and reducing agent solution; Prepare the silver source solution: Dissolve 17g of silver nitrate and 1.2g of gum arabic powder in 400mL of ultrapure water at room temperature. Once dissolved, use the solution as the silver source solution. Prepare the precipitant solution: Dissolve 4.2g of sodium hydroxide in 400mL at room temperature to prepare the precipitant solution. Prepare the reducing agent solution: Dissolve 19g of glucose and 4.2g of sodium hydroxide in 400mL of ultrapure water at room temperature. The solution is then used as the reducing agent solution. Prepare the dispersant solution: Dissolve 0.6g of polyacrylic acid in 200mL of ultrapure water. Once dissolved, use the solution as a dispersant. S20. Under the condition of stirring speed of 360 rpm, the precipitant solution is added dropwise to the silver source solution, and the dropping rate is controlled at 20 mL / min. The precipitation of nanoscale silver hydroxide begins. S30. After the addition is complete, add 0.12g of lauric acid, raise the reaction temperature to 60℃, and continue aging the reaction for 60min to obtain nanoscale silver oxide. S40 nanoscale silver oxide can be obtained as a nano silver oxide precursor by filtration, washing, drying and crushing. S50. The above silver oxide precursor is uniformly dispersed in a polyacrylic acid solution to obtain a base liquid. The reducing agent solution is directly poured into the base liquid, the reaction temperature is increased to 60°C, and the reaction is stirred for 30 min. After the reaction is completed, the nanoscale silver powder is centrifuged and filtered, washed with pure water, and finally washed and filtered with anhydrous ethanol. Then, it is placed in a vacuum drying oven at 30°C and dried for 24 h to obtain submicron-scale polycrystalline silver powder.

[0073] The technical specifications of the submicron-scale polycrystalline silver powder obtained in Example 1 are as follows: average particle size of 200-300 nm, tap density of 4.2 g / cm³. 3 The surface has a polycrystalline structure, with a single crystal size of approximately 50 nm, such as Figure 2 As shown.

[0074] Example 2 The process is basically the same as in Example 1, except that the precipitant solution is added dropwise to the silver source solution at a rate of 40 mL / min to induce precipitation and form nanoscale silver hydroxide.

[0075] The technical specifications of the submicron-scale polycrystalline silver powder obtained in Example 2 are as follows: average particle size of 200-300 nm, tap density of 3.8 g / cm³. 3 The surface has a polycrystalline structure, with a single crystal size of approximately 100 nm, such as Figure 3 As shown.

[0076] Example 3 The process is basically the same as in Example 1, except that the silver oxide precursor is uniformly dispersed in a polyacrylic acid solution and the reducing agent solution is added dropwise to the base solution at a rate of 20 mL / min.

[0077] The technical specifications of the submicron-scale polycrystalline silver powder obtained in Example 2 are as follows: average particle size of 200-300 nm, tap density of 3.8 g / cm³. 3 The surface has a polycrystalline structure, and the single crystal size distribution is uneven, ranging from 50 to 150 nm. Figure 4 As shown.

[0078] Comparative Example Comparative Example 1 It is basically the same as Example 1, except that Comparative Example 1 does not undergo an aging reaction, but directly proceeds to the washing and drying steps.

[0079] like Figure 5 As shown, the nanoscale silver powder obtained in Comparative Example 1 has an uneven particle size distribution, making it impossible to determine whether it is polycrystalline or monocrystalline. Due to the lack of a coating agent and aging process, the generated silver oxide is in an amorphous structure, and the generated silver powder exhibits a random morphology.

[0080] Comparative Example 2 The process is basically the same as in Example 1, except that the obtained nano-silver oxide precursor is not subjected to crushing.

[0081] like Figure 6 As shown, the technical specifications of the submicron-scale polycrystalline silver powder obtained in Comparative Example 2 are as follows: average particle size is 500-800 nm, with severe particle adhesion, and tap density is 3 g / cm³. 3 , with a polycrystalline surface structure.

[0082] Comparative Example 3 This comparative example provides a submicron-scale polycrystalline metal powder and its preparation method, wherein the preparation method includes the following steps: S10. Provide silver source solution, precipitant solution, dispersant solution and reducing agent solution; Prepare the silver source solution: At room temperature, dissolve 51g of silver nitrate and 3.6g of gum arabic powder in 400mL of ultrapure water. Once dissolved, use the solution as the silver source solution. Prepare the precipitant solution: Dissolve 12.6g of sodium hydroxide in 400mL at room temperature to prepare the precipitant solution. Prepare the reducing agent solution: Dissolve 57g of glucose and 12.6g of sodium hydroxide in 400mL of ultrapure water at room temperature. Once dissolved, use the solution as the reducing agent. Prepare the dispersant solution: Dissolve 0.6g of polyacrylic acid in 200mL of ultrapure water. Once dissolved, use the solution as a dispersant. S20. Under the condition of stirring speed of 360 rpm, the precipitant solution is added dropwise to the silver source solution, and the dropping rate is controlled at 20 mL / min. Micron-sized silver hydroxide begins to precipitate. S30. After the addition is complete, add 0.12g of lauric acid, raise the reaction temperature to 60℃, and continue aging the reaction for 60min to obtain micron-sized silver oxide. S40 nanoscale silver oxide can be obtained as a nano silver oxide precursor by filtration, washing, drying and crushing. S50. The above silver oxide precursor is uniformly dispersed in a polyacrylic acid solution to obtain a base liquid. The reducing agent solution is directly poured into the base liquid, the reaction temperature is increased to 60°C, and the reaction is stirred for 30 min. After the reaction is completed, the nanoscale silver powder is centrifuged and filtered, washed with pure water, and finally washed and filtered with anhydrous ethanol. Then, it is placed in a vacuum drying oven at 30°C and dried for 24 h to obtain submicron-scale polycrystalline silver powder.

[0083] Technical specifications of the submicron-scale polycrystalline silver powder obtained in Comparative Example 3: average particle size of 700-900 nm, tap density of 4.8 g / cm³. 3 The surface has a polycrystalline structure, with single crystal sizes of approximately 100~200nm, such as... Figure 7 As shown.

[0084] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0085] The above-described embodiments are only used to illustrate the technical solutions of the embodiments of this application, and are not intended to limit them. Although the embodiments of this application have been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of the embodiments of this application.

Claims

1. A method for preparing submicron-scale polycrystalline metal powder, characterized in that, Includes the following steps: We provide silver source solutions, precipitant solutions, dispersant solutions, and reducing agent solutions; Under stirring conditions, the precipitant solution is added dropwise to the silver source solution, and a precipitation reaction occurs to generate nanoscale silver hydroxide; A coating agent was added to the reaction system for generating nanoscale silver hydroxide, the reaction temperature was increased, and an aging reaction was carried out to obtain nanoscale silver oxide. The obtained silver oxide was pretreated to obtain a nano-silver oxide precursor. The nano-silver oxide precursor is uniformly dispersed in the dispersant solution to obtain a base liquid, and the reducing agent solution is added to the base liquid to carry out a reduction reaction to obtain submicron-scale polycrystalline metal powder.

2. The preparation method according to claim 1, characterized in that, The ratio of the concentration of the silver source in the silver source solution to the concentration of the precipitant in the precipitant solution is 1:(1~1.1).

3. The preparation method according to claim 1, characterized in that, The ratio of the concentration of the reducing agent in the reducing agent solution to the concentration of the silver source in the silver source solution is (1.05~1.2):

1.

4. The preparation method according to claim 1, characterized in that, The precipitant solution is added dropwise to the silver source solution at a rate of 15-25 mL / min, and the stirring speed is 300-400 rpm.

5. The preparation method according to claim 1, characterized in that, The aging reaction conditions include raising the reaction temperature from room temperature to 40-80°C and reacting for 60-120 minutes; and / or, The conditions for the reduction reaction include stirring at room temperature for 30-60 minutes.

6. The preparation method according to claim 1, characterized in that, The pretreatment of the silver oxide includes filtration, washing, drying, and crushing; and / or, After the reduction reaction is completed, the process includes centrifugation and filtration, multiple washing, and vacuum drying to obtain the submicron-scale polycrystalline silver powder.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The silver source solution includes silver nitrate solution, and the silver source solution also includes gum arabic powder; and / or, The precipitant in the precipitant solution includes one of sodium hydroxide, sodium carbonate, sodium oxalate, and potassium hydroxide; and / or, The dispersant in the dispersant solution includes one of PVP, gum arabic, gelatin, PVA, and PEG.

8. The preparation method according to any one of claims 1 to 6, characterized in that, The coating agent includes one of lauric acid, myristic acid, palmitic acid, and stearic acid, and the weight of the coating agent accounts for 5-20% of the dispersant in the dispersant solution; and / or, The reducing agent solution is a glucose solution.

9. A submicron-scale polycrystalline metal powder, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 8.

10. The submicron-scale polycrystalline metal powder as described in claim 9, characterized in that, The submicron-scale polycrystalline metal powder has an average particle size of 200-300 nm and a tap density of 3-5 g / cm³. 3 Furthermore, the surface of the submicron-scale polycrystalline metal powder has a polycrystalline structure.

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