A nano silver powder and its preparation method

Abstract

This disclosure provides a nano-silver powder and its preparation method, relating to the field of metal powder preparation technology. The preparation method of the nano-silver powder includes: dissolving a silver source in a first solvent to obtain a first solution with a concentration of 0.01M to 0.5M; dissolving a reducing agent, polyvinylpyrrolidone, and a polysaccharide-containing compound in a second solvent and adjusting the pH to 8 to 9 to obtain a second solution; adding the second solution dropwise to the first solution under stirring conditions at 15°C to 50°C, controlling the dropwise addition time between 30 min and 180 min to obtain a third solution; and sequentially subjecting the third solution to ultrasonic dispersion, centrifugal classification, washing, and drying to obtain the nano-silver powder. This disclosure can improve the quality of the nano-silver powder.

Description

Technical Field

[0001] This disclosure relates to the field of metal powder preparation technology, and more specifically, to a nano-silver powder and its preparation method. Background Technology

[0002] Nano silver powder plays an important role as a key raw material in numerous applications, including conductive pastes, printed electronics, circuit carriers, touch materials, electric heating films, and microelectronic interconnect materials.

[0003] Currently, the prepared nano-silver powder has the problem of poor quality.

[0004] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this disclosure is to provide a nano-silver powder and a method for preparing the same, thereby overcoming, at least to some extent, the problem of poor quality of nano-silver powder.

[0006] According to a first aspect of this disclosure, a method for preparing nano-silver powder is provided, comprising: dissolving a silver source in a first solvent to obtain a first solution with a concentration of 0.01M to 0.5M; dissolving a reducing agent, polyvinylpyrrolidone, and a polysaccharide-containing compound in a second solvent and adjusting the pH value to 8 to 9 to obtain a second solution; adding the second solution dropwise to the first solution under stirring conditions at 15°C to 50°C, controlling the dropwise addition time to be between 30 min and 180 min to obtain a third solution; and sequentially subjecting the third solution to ultrasonic dispersion, centrifugal classification, washing, and drying to obtain nano-silver powder.

[0007] Optionally, the silver source is one or a combination of silver nitrate, silver acetate, silver chloride, and silver lactate.

[0008] Optionally, the compound containing polysaccharide groups is one or more of chitosan, sodium alginate, sodium hyaluronate, dextran, and sodium carboxymethyl cellulose.

[0009] Optionally, in the preparation of the second solution, the polysaccharide-containing compound is added to the solvent first, rather than polyvinylpyrrolidone.

[0010] Optionally, the reducing agent is one or a combination of ascorbic acid, glucose, sodium borohydride, and sodium citrate.

[0011] Optionally, the concentration of the reducing agent is 0.05M to 0.2M, the concentration of polyvinylpyrrolidone is 0.01M to 0.08M, and the concentration of the polysaccharide-containing compound is 0.001M to 0.03M.

[0012] Optionally, the dropping rate is 5 mL / min to 15 mL / min, the reaction temperature corresponding to the dropping operation is 25°C to 35°C, and the stirring speed is 600 rpm to 900 rpm.

[0013] Optionally, the ultrasonic dispersion treatment has a power of 200W to 800W, a frequency of 20kHz to 40kHz, and a time of 5min to 30min.

[0014] Optionally, the washing process includes an ethanol washing process and a deionized water washing process.

[0015] According to a second aspect of this disclosure, a nano-silver powder is provided, prepared using any of the above-described methods for preparing nano-silver powder.

[0016] In the exemplary embodiments of this disclosure, a hierarchical synergistic mechanism is constructed through pH and dropwise control, where polysaccharide-dominated nucleation and dispersion and polyvinylpyrrolidone-dominated growth control overcome the problem of uncontrollable product morphology and solve the defect of being unable to simultaneously achieve high dispersion and low residue, thus improving the quality of the prepared nanopowder. Furthermore, the silver nanopowder prepared using the method of this disclosure can simultaneously possess ultrafine particle size and extremely low resistivity, breaking the technical bias in the prior art where high dispersibility and low resistivity are difficult to achieve simultaneously, demonstrating extremely high application value.

[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0019] Figure 1 A flowchart illustrating the preparation method of nano-silver powder according to embodiments of the present disclosure is shown.

[0020] Figure 2 A comparison diagram of the particle size distribution of the silver nanoparticles prepared in Example 1 and Comparative Example 1 of this disclosure is shown.

[0021] Figure 3 The images show a comparison of the SEM (Scanning Electron Microscope) images of the silver nanoparticles prepared in Example 1 and Comparative Example 1 of this disclosure.

[0022] Figure 4 The XRD (X-Ray Diffraction) patterns of the silver nanopowder prepared in Examples 1 to 3 and Comparative Example 1 of this disclosure are shown.

[0023] Figure 5 The diagram shows a comparison of the organic residue content of the nano-silver powder prepared in Examples 1 to 3 and Comparative Example 1 of this disclosure.

[0024] Figure 6 The sheet resistance comparison diagrams of the nano-silver powders prepared in Examples 1 to 3 and Comparative Example 1 of this disclosure are shown. Detailed Implementation

[0025] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this disclosure more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced with one or more of these specific details omitted, or other methods, processes, steps, etc., can be employed. In other instances, well-known technical solutions are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0026] Furthermore, the accompanying drawings are merely illustrative of this disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. The flowcharts shown in the drawings are merely exemplary illustrations and do not necessarily include all steps. For example, some steps may be broken down, while others may be combined or partially combined; therefore, the actual order of execution may change depending on the actual situation. Additionally, all terms such as "first," "second," and "third" below are for distinguishing purposes only and should not be construed as limiting the content of this disclosure.

[0027] In some methods, polyvinylpyrrolidone (PVP) or polysaccharides can be used alone as stabilizers to prepare silver nanoparticles. While using PVP alone can achieve low organic residue, its electrostatic stabilization effect in the early nucleation stage is insufficient, leading to severe initial silver nucleus aggregation, resulting in large final particle sizes (e.g., D50 ≥ 100 nm) and wide particle distribution, making sintering densification difficult and resulting in high sheet resistance (e.g., ≥ 1.0 mΩ). Using polysaccharide compounds alone, although providing strong electrostatic-steric barrier during nucleation, results in excessively strong and uncontrollable adsorption to the silver surface, easily forming a dense, difficult-to-eliminate organic coating layer. This leads to high organic residue after sintering, severely affecting the conductive pathways between particles, similarly resulting in substandard final sheet resistance.

[0028] This disclosure provides a simple and industrially scalable method for preparing nano-silver powder. The resulting silver powder exhibits both high dispersibility (concentrated particle size and low agglomeration) and low resistivity (sheet resistance ≤ 0.5 mΩ). It should be noted that all raw materials used in this disclosure are of analytical grade or higher purity.

[0029] Figure 1 A flowchart illustrating a method for preparing nano-silver powder according to an embodiment of this disclosure is shown schematically. (Reference) Figure 1 The method for preparing nano-silver powder according to the present disclosure may include the following steps:

[0030] S12. Dissolve the silver source in the first solvent to obtain a first solution with a concentration of 0.01M to 0.5M.

[0031] In an exemplary embodiment of this disclosure, the silver source is one or a combination of silver nitrate, silver acetate, silver chloride, and silver lactate. The first solvent may be deionized water, ethanol, or other alcohol solvents.

[0032] S14. Dissolve the reducing agent, polyvinylpyrrolidone, and polysaccharide-containing compound in a second solvent and adjust the pH to 8 to 9 to obtain a second solution.

[0033] In exemplary embodiments of this disclosure, the reducing agent may be one or more combinations of ascorbic acid, glucose, sodium borohydride, and sodium citrate. The polysaccharide-containing compound may be one or more combinations of chitosan, sodium alginate, sodium hyaluronate, dextran, and sodium carboxymethyl cellulose. The second solvent may be deionized water, ethanol, or other alcohol solvents. For example, both the second solvent and the first solvent may be deionized water.

[0034] According to some embodiments of this disclosure, in the preparation of the second solution, the polysaccharide-containing compound is added to the solvent first, compared to polyvinylpyrrolidone, to ensure that the polysaccharide molecules preferentially establish electrostatic or steric barrier structures in the system.

[0035] The reducing agent used in this disclosure has a concentration of 0.05M to 0.2M, the polyvinylpyrrolidone has a concentration of 0.01M to 0.08M (based on monomer units), and the polysaccharide-containing compound has a concentration of 0.001M to 0.03M.

[0036] S16. Under stirring conditions at 15℃ to 50℃, the second solution is added dropwise to the first solution, and the addition time is controlled between 30 min and 180 min to obtain the third solution.

[0037] According to some embodiments of this disclosure, the dropping rate is 5 mL / min to 15 mL / min, the reaction temperature corresponding to the dropping operation is, for example, 25°C to 35°C, and the stirring speed is 600 rpm to 900 rpm.

[0038] S18. The third solution is subjected to ultrasonic dispersion, centrifugal classification, washing and drying in sequence to obtain nano silver powder.

[0039] According to some embodiments of this disclosure, the ultrasonic dispersion treatment uses a power of 200W to 800W, a frequency of 20kHz to 40kHz, and a time of 5min to 30min. It should be noted that the purpose of centrifugation is to separate solids and liquids, and this disclosure does not limit the specific operation of this process. Washing treatment may include ethanol washing and deionized water washing.

[0040] The nano-silver powder prepared by the above process has the following particle size distribution: D10: 20nm to 35nm, D50: 20nm to 60nm, D90: 45nm to 65nm. The organic residue (TGA, 800℃) of the nano-silver powder is ≤3.0wt%, and the specific surface area is 5m². 2 / g to 15m 2 / g. Furthermore, the nano-silver powder exhibits a sheet resistance of ≤0.6mΩ under 10MPa compression conditions. The nano-silver powder particles are monodisperse spherical or near-spherical crystals.

[0041] In exemplary embodiments of this disclosure, on the one hand, polyvinylpyrrolidone and natural or modified polysaccharide compounds containing polysaccharide groups synergistically control nucleation and growth; on the other hand, adjusting the pH of the second solution to 8 to 9 improves the controllability of the reduction rate and reduces free radical side reactions; furthermore, the embodiments employ a syringe pump to add the second solution dropwise to the first solution at a rate of 5 mL / min to 15 mL / min to ensure gradual nucleation and uniform growth. Moreover, this disclosure reduces organic residues and achieves excellent flowability and tableting performance through ultrasonic dispersion, centrifugal fractionation, washing, and drying.

[0042] This disclosed method utilizes the molecular structural differences between polysaccharide-containing compounds and polyvinylpyrrolidone (PVP) to achieve functional segmentation during the reaction process. Under alkaline conditions obtained by controlling the pH, the polysaccharide component, due to its high pKa and high ionization in the solvent (e.g., aqueous solution), dominates the nucleation period, providing a strong electrostatic repulsion layer that inhibits nucleus quenching and initial aggregation, ensuring uniform nucleation. PPVP exhibits weaker complexation at this stage, but in the later stages of growth, its long-chain structure controls the crystal growth rate and morphology with moderate adsorption strength, ensuring controllable surface residues and facilitating sintering densification. This achieves precise synergy between polysaccharide-dominated dispersion and PPVP-controlled growth.

[0043] The solution controls the pH value between 8 and 9 to ensure that the polysaccharide component fully exerts its electrostatic stabilizing effect, while adjusting the reducing agent activity to a suitable critical point. Too high a pH will lead to uncontrollable, excessively rapid reduction, while too low a pH will result in insufficient electrostatic repulsion of the polysaccharides. In the example, a constant drip rate of 5 mL / min to 15 mL / min is used to ensure a slow, continuous, and batch-wise nucleation process, avoiding sudden, large-scale nucleation and subsequent disordered aggregation caused by a single feed. This is crucial for achieving an ultra-narrow particle size distribution.

[0044] To further illustrate the advantages of this disclosed solution, a comparison with some technologies is provided below.

[0045] In the preparation of nano silver powder, the choice of dispersant directly determines the performance of the final product.

[0046] Some approaches employ single-component systems, using either polyvinylpyrrolidone (PVP) or polysaccharide compounds alone. However, both methods have drawbacks. Specifically, while using PPVP alone results in low sintering residue, insufficient electrostatic protection during the initial nucleation stage easily leads to silver nucleus quenching and aggregation, making it difficult to achieve small particle sizes. On the other hand, while polysaccharides offer good nucleation and dispersion, their strong binding to the silver surface makes them difficult to wash off, resulting in high organic residue after sintering and severely deteriorating conductivity.

[0047] In other schemes, the two can be combined to form a two-component mixed system. However, the two-component approach in these schemes is a simple physical mixing without intervention in reaction kinetics. This leads to disordered competitive adsorption of the two stabilizers during the reaction, which not only fails to achieve complementary advantages but also results in the dual defects of agglomeration and high residue.

[0048] A detailed comparison of the embodiments disclosed herein with the above-described solutions is shown in Table 1:

[0049] Table 1

[0050]

[0051] As can be seen, the present invention successfully decouples the advantages of PVP and polysaccharides by precisely controlling the pH and the kinetics of the dropwise addition, and applies them to different reduction stages, achieving a technical effect of reducing sheet resistance by at least 40% compared to other solutions.

[0052] In summary, the embodiments disclosed herein overcome the shortcomings of single-component systems. By utilizing the strong electrostatic interaction of polysaccharides during the nucleation stage, the problems of easy aggregation and large particle size in single PVP systems are solved. Simultaneously, by utilizing the easy desorption properties of PVP during the growth stage, the problems of high organic residue and poor conductivity in single polysaccharide systems are addressed. This unique synergistic mechanism of the present disclosure results in the prepared silver nanoparticles possessing ultrafine particle size and extremely low resistivity, exhibiting excellent quality performance.

[0053] The scheme of Embodiment 1 of this disclosure will be described below.

[0054] First, 1.699 g of silver nitrate (molar mass 169.87 g / mol) was dissolved in 100 mL of deionized water to obtain a 0.1 M first solution.

[0055] In addition, add 100 mL of deionized water to a 250 mL beaker, dissolve 0.1 M ascorbic acid (0.176 g dissolved in 100 mL), add 0.02 M PVP (K30) (approximately 0.730 g), add 0.01 M chitosan (calculated as aminoglycosides to ensure the molar count range), stir until completely dissolved, and adjust the pH to 8.5 with ammonia water to obtain the second solution.

[0056] Next, the second solution was placed in a syringe pump and added dropwise to the first solution at a rate of 10 mL / min. The first solution was placed in a 30°C water bath and stirred at 800 rpm. After the addition was complete, the reaction continued for 1.5 h, observing the solution color gradually change from colorless to pale yellow and then to brownish-yellow, yielding the third solution, indicating the formation of nano-silver.

[0057] Subsequently, the third solution was subjected to ultrasonic dispersion to deagglomerate the micro-agglomerates. The parameters for ultrasonic dispersion included: power 500W, frequency 20kHz, and time 15min.

[0058] Then, the solid and supernatant were separated by high-speed centrifugation, and the supernatant was discarded. The centrifugation speed was 10,000 rpm and the time was 15 min.

[0059] Finally, the sample was washed and dried to obtain a dry powder sample. Specifically, it was washed three times with 50 mL of ethanol each time, followed by two washes with deionized water. For drying, the wet powder was placed in a vacuum drying oven at 50°C for 12 hours.

[0060] The powder obtained in Example 1 was tested. The test results include:

[0061] Particle size was statistically analyzed using dynamic light scattering (DLS), with D10 = 28 nm, D50 = 37 nm, and D90 = 52 nm. The average particle size was 38.1 ± 4.6 nm.

[0062] The morphology of the powder was observed using a scanning electron microscope. It was found that the prepared powder was spherical, monodisperse, with a particle diameter of 25 nm to 48 nm, which was consistent with the results of the DLS above.

[0063] XRD was used to identify its crystal phase. The results showed that the diffraction peak positions were consistent with the face-centered cubic (fcc) silver phase, and the 111, 200 and 220 peaks were obvious.

[0064] The specific surface area of ​​the obtained powder is 9.8 m². 2 / g.

[0065] Thermogravimetric analysis (TGA) results showed that the organic residue was ≤2.2wt% at 800℃.

[0066] The sheet resistance measured by the sheet resistance tester was 0.46±0.04mΩ, with the pressing condition being 10MPa.

[0067] In the scheme of Example 1 of this disclosure, the polyhydroxy / amino side chains of chitosan work together with the hydration layer in the solvent to provide good solvation and electrostatic / steric barrier effects during the nucleation period, inhibiting agglomeration. PVP weakly complexes the silver nucleus surface through its pyrrolidone groups, controlling the growth rate and leaving a controllable organic layer on the final surface. This allows the particle surface to maintain a certain degree of sinterability while being protected. The synergy of these two factors leads to concentrated particle size and low organic residue, thereby achieving low sheet resistance. It should be noted that the above TGA data were measured under inert nitrogen protection (≤2.2wt%). However, under the air sintering atmosphere (oxygen atmosphere) of actual conductive paste applications, PVP and polysaccharide components are more prone to oxidative decomposition. Therefore, the actual organic residue after sintering will be significantly lower than the measured value, better reflecting the high densification and low residue advantages of this disclosure.

[0068] The scheme of Embodiment 2 of this disclosure will be described below.

[0069] Compared to Example 1, Example 2 scales up the raw materials in a 2L beaker, replacing chitosan with sodium alginate while maintaining the same molar concentration and consistent stirring kinetics. The result is a particle size and dispersibility similar to those of Example 1.

[0070] The powder obtained in Example 2 was tested. The test results include:

[0071] Particle size was statistically analyzed using dynamic light scattering, with D10=30nm, D50=40nm, and D90=55nm.

[0072] The morphology of the powder was observed using a scanning electron microscope. It was found that the prepared powder consisted of nearly spherical particles with slight chain-like connections, which was caused by bridging formed by sodium alginate.

[0073] Thermogravimetric analysis results showed that the organic residue was approximately 2.4 wt% at 800 °C.

[0074] The sheet resistance measured by the sheet resistance tester was 0.52±0.06mΩ, with the pressing condition being 10MPa.

[0075] In the scheme of Embodiment 2 of this disclosure, by adjusting the dosage and flow rate of sodium alginate, the degree of bridging can be controlled during the scale-up process, ensuring that the conductivity remains at a level of ≤0.6 mΩ, which is suitable for large-scale production. It is worth noting that in scale-up production, it is necessary to maintain similar dimensionless numbers (such as Reynolds numbers) or keep the feeding time per unit volume constant.

[0076] The scheme of Embodiment 3 of this disclosure will be described below.

[0077] Compared to Example 1, the difference in Example 3 lies in the raw material formulation. Specifically, Example 3 uses 0.01M sodium carboxymethyl cellulose (CMC-Na) to replace chitosan, which has a medium molecular weight and a degree of substitution of 0.7.

[0078] The powder obtained in Example 3 was tested. The test results include:

[0079] Particle size was statistically analyzed using dynamic light scattering, with D10=26nm, D50=35nm, and D90=48nm.

[0080] Thermogravimetric analysis results showed that the organic residue was approximately 1.8 wt% at 800 °C.

[0081] The sheet resistance measured by the sheet resistance tester was 0.42±0.03mΩ, with the pressing condition being 10MPa.

[0082] In the scheme of Embodiment 3 of this disclosure, sodium carboxymethyl cellulose has high hydrophilicity and is easily replaced during the washing stage, resulting in less organic residue after sintering, thus obtaining lower sheet resistance, which is a preferred solution for high-performance applications.

[0083] The scheme of Embodiment 4 of this disclosure will be described below.

[0084] The raw material formulation of Example 4 includes: silver acetate (analytical grade, molar mass 166.91 g / mol), D-glucose (analytical grade), polyvinylpyrrolidone K30, sodium carboxymethyl cellulose, ammonia (for pH adjustment), ethanol and deionized water.

[0085] First, prepare a 0.1M silver acetate solution.

[0086] Next, dissolve glucose (0.15M concentration) in 100mL of deionized water, add 0.025M polyvinylpyrrolidone and 0.01M polyvinylpyrrolidone, stir to dissolve, and then adjust the pH to 8.8 with ammonia.

[0087] Subsequently, the solution obtained above was placed in a syringe pump and added dropwise to the silver acetate solution at a constant rate of 12 mL / min. The reaction temperature was 35 °C and the stirring speed was 750 rpm.

[0088] The subsequent sonication, centrifugation, washing, and drying were the same as in Example 1.

[0089] The powder obtained in Example 4 was tested. The test results include:

[0090] Particle size was statistically analyzed using dynamic light scattering, with D10=28nm, D50=45nm, and D90=82nm.

[0091] Thermogravimetric analysis results showed that the organic residue was approximately 2.1 wt% at 800 °C.

[0092] The sheet resistance measured by the sheet resistance tester was 0.49±0.05mΩ, with the pressing condition being 10MPa.

[0093] In the scheme of Example 4 of this disclosure, a system using silver acetate as the silver source and glucose as the reducing agent, combined with the composite stabilizer system and specific dropping process of this disclosure, can still obtain high-quality nano-silver powder with narrow particle size distribution, low organic residue, and sheet resistance ≤0.5mΩ. This indicates that the method of this disclosure has good raw material compatibility and process versatility.

[0094] The scheme of Comparative Example 1 of this disclosure is described below.

[0095] In Comparative Example 1, no polysaccharide-containing compounds were added, the polyvinylpyrrolidone concentration was 0.03M, and the rest was the same as in Example 1.

[0096] The test results include:

[0097] Particle size statistics were performed using dynamic light scattering, with D10=80nm, D50=140nm, and D90=180nm. Figure 2A comparison diagram of the particle size distribution of the silver nanoparticles prepared in Example 1 and Comparative Example 1 of this disclosure is shown.

[0098] Its morphology was observed using a scanning electron microscope, revealing obvious aggregation and irregular morphology. Figure 3 The SEM images of the silver nanopowder prepared in Example 1 and Comparative Example 1 of this disclosure are shown.

[0099] Its crystal phase was identified by XRD, and the results showed that its diffraction peak positions were consistent with those of face-centered cubic (fcc) silver phase. Figure 4 XRD patterns of the silver nanopowder prepared in Examples 1 to 3 and Comparative Example 1 of this disclosure are shown.

[0100] Thermogravimetric analysis results showed that the organic residue was approximately 4.8 wt% at 800℃. Figure 5 The diagram shows a comparison of the organic residue content of the nano-silver powder prepared in Examples 1 to 3 and Comparative Example 1 of this disclosure.

[0101] The sheet resistance measured by the sheet resistance tester was 1.50±0.12mΩ, with the pressing condition being 10MPa. Figure 6 The sheet resistance comparison diagrams of the nano-silver powders prepared in Examples 1 to 3 and Comparative Example 1 of this disclosure are shown.

[0102] The above comparison demonstrates the inherent defects of the single PVP stabilizer system. In a weakly alkaline environment (pH 8.5), the reduction rate is relatively high, but PVP's initial complexation and steric hindrance effects on silver nuclei are insufficient. The lack of a strong electrostatic repulsion layer provided by polysaccharide molecules leads to rapid and disordered aggregation (quenching) of newly formed silver nuclei in the early stages of nucleation. This aggregation reduces the number of crystal nuclei and forms initially large aggregates. During subsequent growth, these aggregates continue to grow, ultimately resulting in large-sized silver nanoparticles with extremely wide particle size distribution and irregular morphology. This, in turn, affects the densification during tableting and sintering, failing to meet the requirements of high-performance conductive applications. These results strongly support the introduction of polysaccharide components in the embodiments of this disclosure, precisely compensating for the insufficient stability of PVP during the nucleation period and achieving the excellent technical effect of synergistic high dispersibility and low resistivity.

[0103] The scheme of Comparative Example 2 of this disclosure is described below.

[0104] In Comparative Example 2, polyvinylpyrrolidone was not added, and the remaining steps were the same as in Example 1.

[0105] The test results include:

[0106] Particle size was statistically analyzed using dynamic light scattering, with D10=40nm, D50=55nm, and D90=90nm.

[0107] Its morphology was observed using a scanning electron microscope, revealing partial aggregation.

[0108] Thermogravimetric analysis results showed that the organic residue was approximately 3.6 wt% at 800℃.

[0109] The sheet resistance measured by the sheet resistance tester was 1.80±0.16mΩ, with a pressing condition of 10MPa.

[0110] It is evident that while using polysaccharides alone helps suppress aggregation and achieve smaller particle sizes, the strong binding forces of the hydroxyl and amino groups on the polysaccharide molecules to the silver surface make complete desorption or substitution difficult during subsequent washing and drying, resulting in a thick organic coating layer. This coating layer acts as a high-resistivity barrier during tableting, severely hindering contact between silver particles and the formation of conductive pathways, leading to a final sheet resistance far exceeding that of the silver powder prepared in this invention. The addition of PVP successfully optimized the properties of the final organic layer, reduced residue, and thus achieved the goal of low sheet resistance.

[0111] The scheme of Comparative Example 3 of this disclosure will be explained below.

[0112] In Comparative Example 3, instead of adding dropwise, the second solution was added to the first solution in one rapid dropwise motion, and the remaining steps were the same as in Example 1.

[0113] The test results include:

[0114] Particle size was statistically analyzed using dynamic light scattering, with D10=60nm, D50=85nm, and D90=130nm.

[0115] Its morphology was observed using a scanning electron microscope, revealing obvious aggregation and irregular shapes.

[0116] Thermogravimetric analysis results showed that the organic residue was approximately 3.0 wt% at 800℃.

[0117] The sheet resistance measured by the sheet resistance tester was 1.05±0.12mΩ, with the pressing condition being 10MPa.

[0118] As can be seen, when a reducing agent / stabilizer mixture is added rapidly and in one go, the silver ions and reducing agent in the system instantly reach a high local supersaturation, leading to explosive and massive nucleation. Although the stabilizer is present, it cannot timely and uniformly coat all the newly formed nuclei, causing severe disordered aggregation and agglomeration. Subsequently, the crystals grow rapidly in an uncontrolled state, ultimately resulting in a significant increase in particle size and an extremely wide particle size distribution. This result strongly demonstrates that the constant-rate dropping method defined in this invention is a key technical feature for achieving stepwise and uniform nucleation of nano-silver, thereby obtaining high dispersion, narrow distribution, and ultimately ensuring low sheet resistance.

[0119] Table 2 shows the test results of the above embodiments and comparative examples of this disclosure.

[0120] Table 2

[0121]

[0122] When applying this disclosed solution to industrial applications, on the one hand, the linear velocity and Reynolds number of the agitator should be matched to maintain kinetic similarity. On the other hand, fractional centrifugation or membrane separation processes can be employed to improve efficiency and repeatability. Furthermore, the solvent and washing liquid can be recycled to save costs.

[0123] Furthermore, the silver nitrate used in this embodiment is corrosive and photosensitizing, so skin contact should be avoided and it should be stored in the dark. Silver ions in the waste liquid can be precipitated and recovered to avoid environmental pollution.

[0124] Furthermore, this disclosure also provides a nano-silver powder, which can be prepared using the above-described method for preparing nano-silver powder.

[0125] It should be noted that although the steps of the method in this disclosure are described in a specific order in the accompanying drawings, this does not require or imply that the steps must be performed in that specific order, or that all the steps shown must be performed to achieve the desired result. Additional or alternative steps may be omitted, multiple steps may be combined into one step, and / or a step may be broken down into multiple steps.

[0126] Furthermore, the above figures are merely illustrative of the processes included in the method according to exemplary embodiments of this disclosure and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0127] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0128] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A method for preparing nano-silver powder, characterized in that, include: The silver source is dissolved in a first solvent to obtain a first solution with a concentration of 0.01 M to 0.5 M; The first solvent is deionized water or an alcohol solvent; A reducing agent, polyvinylpyrrolidone, and a polysaccharide-containing compound are dissolved in a second solvent, and the pH is adjusted to 8 to 9 to obtain a second solution. In the preparation of the second solution, the polysaccharide-containing compound is added to the solvent first, before the polyvinylpyrrolidone. The concentration of the reducing agent is 0.05 M to 0.2 M, the concentration of the polyvinylpyrrolidone is 0.01 M to 0.08 M, and the concentration of the polysaccharide-containing compound is 0.001 M to 0.03 M. Under stirring conditions, the second solution is added dropwise to the first solution, and the dropping time is controlled between 30 min and 180 min to obtain the third solution; wherein the dropping rate is 5 mL / min to 15 mL / min, the reaction temperature corresponding to the dropping operation is 25℃ to 35℃, and the stirring speed is 600 rpm to 900 rpm; The third solution was subjected to ultrasonic dispersion, centrifugal classification, washing, and drying in sequence to obtain nano-silver powder.

2. The preparation method according to claim 1, characterized in that, The silver source is one or a combination of silver nitrate, silver acetate, silver chloride, and silver lactate.

3. The preparation method according to claim 1, characterized in that, The compound containing polysaccharide groups is one or more of chitosan, sodium alginate, sodium hyaluronate, dextran, and sodium carboxymethyl cellulose.

4. The preparation method according to claim 1, characterized in that, The reducing agent is one or a combination of ascorbic acid, glucose, sodium borohydride, and sodium citrate.

5. The preparation method according to claim 1, characterized in that, The ultrasonic dispersion treatment has a power of 200W to 800W, a frequency of 20kHz to 40kHz, and a time of 5min to 30min.

6. The preparation method according to claim 1, characterized in that, The washing process includes ethanol washing and deionized water washing.

7. A nano-silver powder, characterized in that, The nano-silver powder was prepared using the preparation method described in any one of claims 1 to 6.

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