Method for green preparation of high-dispersity silver powder based on free aldehyde group-free sugar and application

Abstract

The invention provides a green method for preparing high-dispersity silver powder based on free aldehyde group-free sugar, which comprises the following steps of: dissolving silver salt in deionized water, and adding a dispersing agent to obtain silver salt dispersion liquid; the preparation method comprises the following steps: dissolving sugar without free aldehyde groups in deionized water, adding a catalyst, hydrolyzing to obtain a reducing solution, dropwise adding a silver salt dispersion liquid, adjusting the pH value, treating in an ultrasonic field, carrying out magnetic stirring reaction to obtain a silver powder suspension, centrifuging, washing, curing and freeze-drying the precipitate to obtain the high-dispersity silver powder. The used free aldehyde group-free sugar is cane sugar, and also can be cellulose, starch and the like. The invention further provides application, and the prepared high-dispersity silver powder is used for printing. The prepared high-dispersity silver powder is uniform in particle size distribution, good in dispersity and excellent in conductivity, high-temperature and high-pressure equipment is not needed, reaction conditions are mild, aftertreatment steps are simple and convenient, industrial large-scale production is easy to achieve, and the process is simple and easy to implement.

Description

Technical Field

[0001] This invention belongs to the field of silver powder preparation technology, specifically relating to a method and application for the green preparation of highly dispersible silver powder based on free aldehyde sugars. Background Technology

[0002] Silver powder, as an important functional material, is widely used in electronic pastes, conductive inks, catalysts, and other fields due to its excellent conductivity and chemical stability. Traditional silver powder preparation often uses aldehyde-containing compounds such as formaldehyde and acetaldehyde as reducing agents. While this method offers high reaction efficiency, it suffers from problems such as high toxicity, volatility, and severe environmental pollution. In recent years, the application of green reducing agents (such as glucose and ascorbic acid) has gradually gained attention; however, these substances often contain aldehyde groups or easily oxidized components, and still exhibit drawbacks such as poor storage stability and complex reaction byproducts. Summary of the Invention

[0003] The technical problem this invention aims to solve is to address the shortcomings of the prior art by providing a method and application for preparing highly dispersible silver powder based on a green process using free aldehyde sugars. The highly dispersible silver powder prepared by this method exhibits uniform particle size distribution, excellent dispersibility, and superior electrical conductivity. The entire preparation process requires no high-temperature or high-pressure equipment, operates under mild reaction conditions, and has simple post-processing steps, making it easy to scale up for industrial production. The process is characterized by its simplicity and ease of implementation. The prepared highly dispersible silver powder can be used in printing.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing highly dispersible silver powder based on free aldehyde sugar in a green manner, the method being as follows: S1. Dissolve silver salt in deionized water to obtain silver salt aqueous solution, then add dispersant and stir to dissolve to obtain silver salt dispersion; S2. Dissolve the sugar without free aldehydes in deionized water, add a catalyst, and carry out a hydrolysis reaction to obtain a reduced solution; The free aldehyde sugar (such as sucrose) in this invention is a natural carbohydrate with advantages such as wide availability, low price and non-toxicity. Its hydrolysis products can reduce silver ions through the polyhydroxy structure. S3. Add the silver salt dispersion obtained in S1 dropwise to the reducing solution obtained in S2, adjust the pH value to 8.0-8.5, and perform ultrasonic treatment at room temperature, a frequency of 20kHz-40kHz, and an ultrasonic power density of 0.3W / cm³. 2 ~0.8W / cm 2 The mixture was treated in an ultrasonic field for 10 to 20 minutes, and then magnetically stirred at a temperature of 45°C to 50°C for 45 to 60 minutes to obtain a silver powder suspension. This invention employs a hybrid mode combining ultrasonic-assisted dispersion and magnetic stirring. It leverages the breaking down of agglomerates and the improvement of mass transfer efficiency through ultrasound, while maintaining the stability of the reaction system through stirring, resulting in a narrower particle size distribution of silver powder. When magnetic stirring is used alone, the system relies on mechanical force to drive the mixing of materials. During the reduction, nucleation and growth of silver ions, particles are prone to form agglomerates due to local concentration differences, exhibiting a "quasi-agglomerate" distribution. In this invention, when ultrasonic assistance is used, the micro-jets and shock waves generated by the ultrasonic cavitation effect can effectively break up the already formed agglomerated particles, while enhancing the mass transfer efficiency between silver ions and the reducing solution, promoting more uniform nucleation, and resulting in smaller product particle size and better dispersibility. S4. Centrifuge the silver powder suspension obtained in S3, and wash the precipitate with deionized water and anhydrous ethanol in sequence until the conductivity of the washing solution is <50μS / cm to obtain the initial silver powder product. S5. The silver powder initial product obtained in S4 is aged at a temperature of 30℃~35℃ for 4d~5d, and then freeze-dried to obtain highly dispersible silver powder.

[0005] Preferably, the silver salt in S1 is silver nitrate; the concentration of the aqueous solution of the silver salt is 0.5 mol / L to 1.0 mol / L; and the dispersant is polyvinylpyrrolidone.

[0006] Preferably, the ratio of silver salt to dispersant in S1 is (0.05-0.1) mol: (5-10) g.

[0007] Preferably, the free aldehyde sugar in S2 is sucrose; the catalyst is a hydrochloric acid solution or a nitric acid solution, and the concentration of the catalyst is 0.2 mol / L to 0.3 mol / L.

[0008] Preferably, the ratio of the amount of the free aldehyde sugar, deionized water and catalyst in S2 is (17.1-34.2) g: 100 mL: (40-50) mL.

[0009] Preferably, the hydrolysis reaction in S2 is carried out at a temperature of 65°C to 70°C for a time of 90 min to 120 min.

[0010] Preferably, the volume ratio of the reducing solution and the silver salt dispersion in S3 is 1:2; the dropping rate is 4 mL / min; and the magnetic stirring reaction rate is 400 rpm to 500 rpm.

[0011] Preferably, in S4, the centrifugation speed is 10000 rpm to 12000 rpm, and the centrifugation time is 6 min to 8 min; in S5, the freeze-drying conditions are -50℃ to -45℃, and the freeze-drying time is 12 h to 14 h.

[0012] Preferably, the average particle size of the highly dispersible silver powder in S5 is 300 nm to 2 μm, and the tap density is 2.0 g / cm³. 3 ~5.4g / cm 3 The resistivity is 2.6 × 10⁻⁶ -6 Ω∙cm~3×10 -6 Ω∙cm.

[0013] The present invention also provides the application of the highly dispersible silver powder prepared by the above method, wherein the highly dispersible silver powder is used for printing.

[0014] Compared with the prior art, the present invention has the following advantages: This invention uses aldehyde-free sugars as reducing agents, replacing the toxic aldehyde-containing substances used in traditional processes. The byproducts of the reaction are biodegradable carbohydrate derivatives, effectively reducing environmental impact and demonstrating significant advantages in green and environmentally friendly practices. The selected aldehyde-free sugars (such as sucrose) are food-grade raw materials, costing only 1 / 3 to 1 / 2 the price of glucose, and exhibit good storage stability, making them suitable for large-scale production and providing a significant advantage in terms of raw materials. Through precise control of hydrolysis conditions and dispersant dosage, the prepared highly dispersible silver powder has a uniform particle size distribution, excellent dispersibility, and superior electrical conductivity, resulting in excellent product performance. The entire preparation process does not require high-temperature and high-pressure equipment, the reaction conditions are mild, and the post-processing steps are simple, making it easy to achieve industrial-scale production. The highly dispersible silver powder prepared by this invention exhibits good printing characteristics during printing and good co-firing compatibility with the dielectric layer during firing. Attached Figure Description

[0015] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0016] Figure 1 This is a scanning electron microscope (SEM) image of the highly dispersed silver powder prepared in Example 1 of this invention.

[0017] Figure 2 This is a scanning electron microscope (SEM) image of the highly dispersed silver powder prepared in Example 2 of this invention.

[0018] Figure 3 This is a scanning electron microscope (SEM) image of the silver powder prepared in Comparative Example 1 of this invention.

[0019] Figure 4 This is a scanning electron microscope (SEM) image of the silver powder prepared in Comparative Example 2 of this invention. Detailed Implementation

[0020] Example 1 The method for preparing highly dispersible silver powder based on green preparation of free aldehyde sugars in this embodiment is as follows: S1. Dissolve 0.1 mol of silver salt (silver nitrate) in deionized water to obtain a silver salt aqueous solution with a concentration of 1.0 mol / L. Then add 10 g of dispersant (polyvinylpyrrolidone, molecular weight 58000) and stir to dissolve to obtain a silver salt dispersion. S2. Dissolve 34.2g of sucrose without free aldehydes in 100mL of deionized water, add 50mL of catalyst (0.2mol / L hydrochloric acid solution), and carry out hydrolysis reaction at 70℃ for 90min to obtain a reduced solution. S3. Add the silver salt dispersion obtained in S1 dropwise to the reducing solution obtained in S2 at a dropping rate of 4 mL / min. Adjust the pH to 8.5 with a 1 mol / L sodium hydroxide aqueous solution. Perform the ultrasonic treatment at room temperature, a frequency of 20 kHz, and an ultrasonic power density of 0.3 W / cm². 2 The solution was treated in an ultrasonic field for 20 minutes, and then magnetically stirred for 60 minutes at a temperature of 50°C and a speed of 400 rpm to obtain a silver powder suspension; the volume ratio of the reducing solution to the silver salt dispersion was 1:2. S4. Centrifuge the silver powder suspension obtained in S3 at 10000 rpm for 8 min. Wash the precipitate with deionized water 3 times and anhydrous ethanol 2 times. The conductivity of the washing solution is <50 μS / cm to obtain the initial silver powder product. S5. The silver powder initial product obtained in S4 is aged at 30℃ for 5 days and then freeze-dried at -50℃ for 12 hours to obtain highly dispersible silver powder.

[0021] The highly dispersed silver powder prepared in this embodiment has an average particle size of 2 μm and a tap density of 5.4 g / cm³. 3 The resistivity is 3.0 × 10⁻⁶. -6 Ω∙cm.

[0022] The highly dispersed silver powder prepared in this embodiment is shown in the SEM (Scanning Electron Microscopy) image. Figure 1 The silver powder particles are mostly spherical, with a regular and uniform appearance, and excellent overall dispersibility, with only a small amount of slight agglomeration. The particle size is also relatively uniform.

[0023] The highly dispersible silver powder prepared in this embodiment exhibits excellent printing characteristics during the printing process and demonstrates good co-firing compatibility with the dielectric layer during firing. The high dispersibility of the silver powder is a core factor in improving printing characteristics: fewer silver powder particles aggregate, resulting in more uniform dispersion in conductive pastes and more stable paste rheological properties. SEM (Scanning Electron Microscopy) revealed the presence of small silver particles. These particles have a large specific surface area and high surface free energy, providing ample thermodynamic driving force for sintering. They can more efficiently promote atomic transfer and sintering neck growth through surface diffusion and grain boundary diffusion. Simultaneously, the uniform size, near-spherical shape, and good dispersibility of the silver particles increase the number of contact points between particles and ensure a more synchronized and efficient mass transfer process, reducing localized under-sintering or over-sintering. Furthermore, the near-spherical morphology facilitates close packing, allowing pores to be more easily filled by atomic diffusion, reducing porosity defects. In addition, the lower sintering initiation temperature of the small silver particles makes it easier to match the sintering temperature window of the dielectric layer, alleviating shrinkage stress during co-firing. These multiple factors contribute to the sintering process, improving the density of the silver layer and the co-firing compatibility.

[0024] Example 2 The method for preparing highly dispersible silver powder based on green preparation of free aldehyde sugars in this embodiment is as follows: S1. Dissolve 0.05 mol of silver salt (silver nitrate) in deionized water to obtain a silver salt aqueous solution with a concentration of 0.5 mol / L. Then add 5 g of dispersant (polyvinylpyrrolidone, molecular weight 40000) and stir to dissolve to obtain a silver salt dispersion. S2. Dissolve 17.1g of sucrose without free aldehydes in 100mL of deionized water, add 40mL of catalyst (0.3 mol / L nitric acid solution), and carry out hydrolysis reaction at 65℃ for 120min to obtain a reduced solution. S3. Add the silver salt dispersion obtained in S1 dropwise to the reducing solution obtained in S2 at a dropping rate of 4 mL / min. Adjust the pH to 8.0 with a 1 mol / L sodium hydroxide aqueous solution. Perform the ultrasonic treatment at room temperature, a frequency of 40 kHz, and an ultrasonic power density of 0.8 W / cm³. 2 The solution was treated in an ultrasonic field for 10 min, and then magnetically stirred for 45 min at a temperature of 45℃ and a speed of 500 rpm to obtain a silver powder suspension; the volume ratio of the reducing solution to the silver salt dispersion was 1:2. S4. Centrifuge the silver powder suspension obtained in S3 at 12000 rpm for 6 min. Wash the precipitate with deionized water 3 times and anhydrous ethanol 2 times. The conductivity of the washing solution is <50 μS / cm to obtain the initial silver powder product. S5. The silver powder initial product obtained in S4 is aged at 35℃ for 4 days and then freeze-dried at -45℃ for 14 hours to obtain highly dispersible silver powder.

[0025] The highly dispersed silver powder prepared in this embodiment has an average particle size of 300 nm and a tap density of 2.0 g / cm³. 3 The resistivity is 2.6 × 10⁻⁶ -6 Ω∙cm.

[0026] The highly dispersed silver powder prepared in this embodiment is shown in the SEM (Scanning Electron Microscopy) image. Figure 2 It can be observed that the silver powder particles are mainly spherical or near-spherical in shape, with uniform dispersion between particles, no obvious agglomeration, and a relatively uniform particle size distribution. This characteristic of regular morphology, good dispersibility, and uniform particle size not only demonstrates the excellent dispersion effect of the prepared silver powder, but also benefits its subsequent applications.

[0027] The highly dispersible silver powder prepared in this embodiment has good printing characteristics during the printing process and good co-firing compatibility with the dielectric layer during the firing process.

[0028] Example 3 The method for preparing highly dispersible silver powder based on green preparation of free aldehyde sugars in this embodiment is as follows: S1. Dissolve 0.07 mol of silver salt (silver nitrate) in deionized water to obtain a 0.7 mol / L silver salt aqueous solution. Then add 7 g of dispersant (polyvinylpyrrolidone, molecular weight 50000) and stir to dissolve to obtain a silver salt dispersion with a concentration of . S2. Dissolve 25.6g of free aldehyde sugar in 100mL of deionized water, add 45mL of catalyst (0.25mol / L hydrochloric acid solution), and carry out hydrolysis reaction at 65℃ for 100min to obtain the reduced solution. S3. Add the silver salt dispersion obtained in S1 to the reducing solution (sucrose) obtained in S2 at a dropping rate of 4 mL / min, adjust the pH to 8.4, and perform ultrasonic treatment at room temperature, a frequency of 30 kHz, and an ultrasonic power density of 0.5 W / cm³. 2 The solution was treated in an ultrasonic field for 15 minutes, and then magnetically stirred at 48°C for 50 minutes to obtain a silver powder suspension; the volume ratio of the reducing solution to the silver salt dispersion was 1:2. S4. Centrifuge the silver powder suspension obtained in S3 at 12000 rpm for 8 min. Wash the precipitate with deionized water 3 times and anhydrous ethanol 2 times. The conductivity of the washing solution is <50 μS / cm to obtain the initial silver powder product. S5. The silver powder initial product obtained in S4 is aged at 30℃ for 5 days and then freeze-dried at -45℃ for 12 hours to obtain highly dispersible silver powder.

[0029] The highly dispersed silver powder prepared in this embodiment has an average particle size of 1.1 μm and a tap density of 3.7 g / cm³. 3 The resistivity is 2.8 × 10⁻⁶. -6 Ω∙cm.

[0030] The highly dispersible silver powder prepared in this embodiment exhibits typical spherical characteristics in morphology, with rounded and regular particle outlines, no obvious sharp edges or irregular protrusions, and a high degree of surface smoothness. This silver powder demonstrates excellent monodispersity properties, with no obvious agglomeration between particles.

[0031] The highly dispersible silver powder prepared in this embodiment is used for printing. Its spherical structure can reduce the viscosity of the ink system and improve the fluidity and spreadability during the printing process. The uniform particle size distribution can ensure the consistency of the printed coating thickness and reduce surface unevenness caused by particle size differences. The excellent dispersibility can avoid clogging of the printing screen, ensure the fineness and continuity of the pattern lines, and ultimately improve the conductivity and stability of the printed conductive layer.

[0032] Comparative Example 1 The method for preparing silver powder in this comparative example is the same as in Example 2, except that polyvinylpyrrolidone in step S1 is replaced with gum arabic. The SEM scanning electron microscope results of the prepared silver powder are shown below. Figure 3 The silver powder particles were significantly refined, and the agglomeration was extremely severe, with blurred particle boundaries and a chaotic morphology. These results indicate that the type of dispersant has a crucial impact on the morphology, particle size, and dispersibility of silver powder. Gum arabic's dispersing control ability is far weaker than that of polyvinylpyrrolidone (PVP), leading to the agglomeration and refinement of the silver powder particles.

[0033] Comparative Example 2 The preparation method of the silver powder in this comparative example is the same as that in Example 2, except that ultrasonic field treatment is not performed in step S3, only magnetic stirring is performed. The SEM scanning electron microscope image of the prepared silver powder is shown below. Figure 4 The silver powder exhibits significant particle agglomeration, with irregular morphology and numerous aggregates of varying sizes, resulting in poor particle dispersion. The particle size distribution is wide, ranging from tens to hundreds of nanometers, with a median particle size (D...)... 50 The particles are too large, resulting in poor overall particle uniformity.

[0034] In step S3 of this comparative example, no ultrasonic treatment was performed. When only magnetic stirring was used, the system relied on mechanical force to drive the material mixing. During the reduction and nucleation of silver ions and the growth process, the particles were prone to form agglomerates due to local concentration differences, exhibiting a "quasi-agglomerate" distribution.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing highly dispersible silver powder in a green manner based on free aldehyde sugars, characterized in that, The method is as follows: S1. Dissolve silver salt in deionized water to obtain silver salt aqueous solution, then add dispersant and stir to dissolve to obtain silver salt dispersion; S2. Dissolve the sugar without free aldehydes in deionized water, add a catalyst, and carry out a hydrolysis reaction to obtain a reduced solution; S3. Add the silver salt dispersion obtained in S1 dropwise to the reducing solution obtained in S2, adjust the pH value to 8.0-8.5, and perform ultrasonic treatment at room temperature, a frequency of 20kHz-40kHz, and an ultrasonic power density of 0.3W / cm³. 2 ~0.8W / cm 2 The mixture was treated in an ultrasonic field for 10 to 20 minutes, and then magnetically stirred at a temperature of 45°C to 50°C for 45 to 60 minutes to obtain a silver powder suspension. S4. Centrifuge the silver powder suspension obtained in S3, and wash the precipitate with deionized water and anhydrous ethanol in sequence until the conductivity of the washing solution is <50μS / cm to obtain the initial silver powder product. S5. The silver powder initial product obtained in S4 is aged at a temperature of 30℃~35℃ for 4d~5d, and then freeze-dried to obtain highly dispersible silver powder.

2. The method for preparing highly dispersible silver powder based on free aldehyde sugars according to claim 1, characterized in that, The silver salt in S1 is silver nitrate; the concentration of the aqueous solution of the silver salt is 0.5 mol / L to 1.0 mol / L; and the dispersant is polyvinylpyrrolidone.

3. The method for preparing highly dispersible silver powder based on free aldehyde sugars according to claim 1, characterized in that, The ratio of silver salt to dispersant in S1 is (0.05-0.1) mol: (5-10) g.

4. The method for preparing highly dispersible silver powder based on free aldehyde sugars according to claim 1, characterized in that, The free aldehyde sugar in S2 is sucrose; the catalyst is a hydrochloric acid solution or a nitric acid solution, and the concentration of the catalyst is 0.2 mol / L to 0.3 mol / L.

5. The method for preparing highly dispersible silver powder based on free aldehyde sugars according to claim 1, characterized in that, The ratio of the amount of free aldehyde sugar, deionized water and catalyst in S2 is (17.1-34.2) g: 100 mL: (40-50) mL.

6. The method for preparing highly dispersible silver powder based on free aldehyde sugars according to claim 1, characterized in that, The hydrolysis reaction described in S2 is carried out at a temperature of 65℃~70℃ for a time of 90min~120min.

7. The method for preparing highly dispersible silver powder based on free aldehyde sugars according to claim 1, characterized in that, The volume ratio of the reducing solution to the silver salt dispersion in S3 is 1:2; the dropping rate is 4 mL / min; and the magnetic stirring reaction rate is 400 rpm to 500 rpm.

8. The method for preparing highly dispersible silver powder based on free aldehyde sugars according to claim 1, characterized in that, In S4, the centrifugation speed is 10000rpm~12000rpm, and the centrifugation time is 6min~8min; in S5, the freeze-drying conditions are -50℃~-45℃, and the freeze-drying time is 12h~14h.

9. The method for preparing highly dispersible silver powder based on free aldehyde sugars according to claim 1, characterized in that, The highly dispersible silver powder described in S5 has an average particle size of 300 nm to 2 μm and a tap density of 2.0 g / cm³. 3 ~5.4g / cm 3 The resistivity is 2.6 × 10⁻⁶ -6 Ω∙cm~3×10 -6 Ω∙cm.

10. An application of a highly dispersible silver powder prepared by the method of any one of claims 1-9, wherein the highly dispersible silver powder is used for printing.

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