Submicron silver powder, its preparation method and use

Abstract

The application discloses submicron silver powder and a preparation method and application thereof, and belongs to the technical field of metal conductive powder.The preparation raw material of the submicron silver powder comprises an oxidizing agent, a reducing agent, a dispersing agent, a coating and settling agent and a twin crystal inhibitor; the oxidizing agent comprises at least one of silver nitrate, silver nitrite, silver carbonate and silver oxalate; the reducing agent comprises at least one of ascorbic acid, glucose, sodium borohydride, hydrazine hydrate and formaldehyde; the coating and settling agent comprises at least one of lauric acid, myristic acid, palmitic acid and stearic acid; and the twin crystal inhibitor comprises at least one of N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, hexamethylphosphorus triamide and dimethylacetamide; while effectively improving the dispersibility of the submicron silver powder, the twin crystal inhibitor restrains the growth of the eutectic face of the silver powder crystal, reduces the amount of the organic dispersing agent and improves the use performance of the silver powder at the slurry end.

Description

Technical Field

[0001] This invention belongs to the field of metal conductive powder technology, specifically, it relates to a submicron silver powder, its preparation method and application. Background Technology

[0002] In the modern photovoltaic and electronics industries, silver powder, as a key material, plays an irreplaceable role in many applications due to its excellent conductivity and chemical stability. Especially in electronic pastes, particularly the front-side silver paste for solar cells, silver powder, as the conductive phase, has a decisive influence on the overall performance of the conductive paste. Currently, there are various techniques for preparing submicron silver powder, including chemical liquid-phase reduction, plasma atomization, and high-temperature pyrolysis. Among these, chemical liquid-phase reduction has become the mainstream preparation process due to its advantages such as easy control of product characteristic parameters, lower equipment investment, and ease of large-scale production.

[0003] However, existing liquid-phase reduction methods for preparing ultrafine silver powder generally suffer from several problems that urgently need to be addressed. For example, the existing ultrafine silver powder synthesis process is more complex than that for micron-sized silver powder, often requiring multiple reduction reactions, making industrial-scale production difficult. One study disclosed a method for preparing nanoscale silver powder, which involves mixing a first silver salt, a first ammonia solution, a first reducing agent, and water to obtain a silver core solution; mixing the silver core solution, a first dispersant, and a first solvent to obtain a first reaction solution; mixing a second silver salt, a second ammonia solution, a surfactant, and a second solvent to obtain a second reaction solution; mixing a second reducing agent, a second dispersant, and a third solvent to obtain a third reaction solution; adding the second and third reaction solutions to the first reaction solution at the same rate to obtain a reaction mixture; and sequentially filtering, washing, and drying the reaction mixture to obtain silver powder. This process is complex, requiring the preparation of numerous reagents and multiple controlled reduction reactions, making industrial-scale production of the reagents difficult.

[0004] On the other hand, while existing relatively simple micron-scale silver powder preparation processes are straightforward, they do not address the problem of bare ultrafine silver particles easily agglomerating due to their high surface activity and being difficult to disperse after agglomeration. Therefore, in addition to surfactants, submicron powder preparation processes typically employ high-molecular-weight organic polymers with steric hindrance effects as dispersants. This residue of the high-molecular-weight organic polymer dispersant on the surface of the ultrafine silver powder has a highly adverse effect on the low-temperature sintering activity of the low-temperature silver paste. Consequently, the resistivity of the thick film formed after low-temperature heating and curing is difficult to reduce to the ideal level, and the bonding force between the thick film and the substrate is also negatively affected.

[0005] Therefore, it is urgent to propose a simple preparation method for submicron / nano silver powder to produce submicron / nano silver powder with low organic content and high dispersion. Summary of the Invention

[0006] The present invention aims to solve the aforementioned technical problems existing in the prior art. To this end, the present invention proposes a submicron silver powder, its preparation method, and its application, which effectively improves the dispersibility of submicron silver powder, inhibits the growth of the eutectic plane of silver powder crystals, reduces the amount of organic dispersant used, and improves the performance of silver powder in slurry applications.

[0007] The present invention also proposes a method for preparing submicron silver powder.

[0008] This invention also proposes the application of submicron silver powder in the photovoltaic field.

[0009] According to one aspect of the present invention, a submicron silver powder is provided, wherein the raw materials for preparing the submicron silver powder include: an oxidant, a reducing agent, a dispersant, a coating sedimentation agent, and a twinning inhibitor;

[0010] The oxidizing agent includes at least one of silver nitrate, silver nitrite, silver carbonate, and silver oxalate;

[0011] The reducing agent includes at least one of ascorbic acid, glucose, sodium borohydride, hydrazine hydrate, and formaldehyde;

[0012] The coating settling agent includes at least one of lauric acid, myristic acid, palmitic acid and stearic acid;

[0013] The twinning inhibitor includes at least one of N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, hexamethylphosphoric triamine, and dimethylacetamide.

[0014] The strongly polar aprotic solvents, such as the twinning inhibitors in this invention, can form strong complexes with silver ions, effectively slowing down the reduction rate of silver ions and preventing rapid nucleation and disordered growth. Simultaneously, they allow the nano-silver crystal nuclei formed in the early stages of the reaction to be uniformly dispersed in a polar environment. Furthermore, they can synergistically interact with polyvinylpyrrolidone, adsorbing onto the surface of silver crystals and promoting crystal growth towards more regular spherical or cubic structures, reducing the formation of elongated twinned structures.

[0015] The addition of twinning inhibitors during the preparation process effectively improves the dispersibility of submicron silver powder while inhibiting the growth of eutectic planes of silver powder crystals, reducing the amount of organic dispersant used, thereby enhancing the performance of silver powder in slurry and simplifying the existing preparation process of submicron / nano silver powder. It eliminates the need for multiple reduction reactions and has strong industrialization conversion capabilities.

[0016] The role of coating and settling agents in improving the dispersibility of silver powder mainly includes two aspects. First, the coating and settling agent combines with the surface of silver particles through chemical or physical adsorption to form a monolayer coating. Second, the long carbon chains (C12) extend outward to form a physical barrier, preventing van der Waals forces between particles and inhibiting agglomeration. Adsorption and steric hindrance enable the formation of a stable coating layer on the surface of submicron silver powder, preventing the submicron silver powder from agglomerating and caking during drying and storage.

[0017] In some embodiments of the present invention, the dispersant includes at least one selected from polyvinylpyrrolidone K10, polyvinylpyrrolidone K30, polyvinylpyrrolidone K90, polyethylene glycol, polyacrylic acid, polyvinyl alcohol, gelatin, and gum arabic.

[0018] In some embodiments of the present invention, the dispersant includes polyvinylpyrrolidone K30.

[0019] In some embodiments of the present invention, the coating agent is lauric acid.

[0020] In some embodiments of the present invention, the submicron silver powder has a D10 particle size of 100-200 nm, a D50 particle size of 300-500 nm, and a D90 particle size of 700-1000 nm.

[0021] The tap density of the submicron silver powder is 5–7 g / cm³. 3 ;

[0022] The burn-off rate of the submicron silver powder is 0.5-0.7%.

[0023] The burn-off of the submicron silver powder refers to the percentage of mass loss due to the volatilization of moisture, adsorbates, or residual organic matter after heating the silver powder sample to approximately 600°C in air and holding it therefore for about 1 hour. This value indicates that the silver powder has good purity and thermal stability.

[0024] According to two aspects of the present invention, a method for preparing the aforementioned submicron silver powder is provided, comprising:

[0025] S1. The dispersant solution and the twinning inhibitor are mixed to obtain a reaction solution, and the pH of the reaction solution is adjusted to 7.5-9.5;

[0026] S2. Mix the reducing agent solution, the oxidizing agent solution, and the reaction solution to obtain a silver powder suspension;

[0027] S3. The silver powder suspension and the coating sedimentation agent are mixed and reacted to obtain submicron silver powder.

[0028] In some embodiments of the present invention, the solvent in the solution of the reducing agent includes water.

[0029] In some embodiments of the present invention, the solvent in the solution of the oxidant includes water.

[0030] In some embodiments of the present invention, the solvent in the solution of the dispersant includes water.

[0031] In some embodiments of the present invention, the molar ratio of the twinning inhibitor to the oxidant is 0.005 to 0.04:1.

[0032] First, this ratio range ensures that the strongly polar aprotic solvent forms a moderate complex with silver ions. Under the preferred ratio, the twinning inhibitor works through the following synergistic mechanism: (1) polar groups such as carbonyl groups in the molecule react with Ag. + (1) Forming dynamic coordination bonds to control the reduction reaction rate within the ideal range; (2) Generating intermolecular forces with the dispersant to form a composite adsorption layer on the surface of the silver crystal nucleus, selectively inhibiting the excessive growth of the eutectic plane and promoting the crystal to develop in an isotropic direction.

[0033] In some embodiments of the present invention, the concentration of the oxidant solution is 0.5-2 mol / L, and the amount used is 1-20 L;

[0034] The concentration of the reducing agent solution is 0.6–1.2 mol / L, and the amount used is 0.3–15 L;

[0035] The concentration of the dispersant solution is 1×10⁻⁶. -4 ~5×10 -4 mol / L, dosage is 1-40L.

[0036] The above concentration range ensures a sufficient and stable supply of silver ions, maintains a moderate ion concentration gradient, stabilizes the crystal growth rate, avoids explosive nucleation caused by local oversaturation, and ensures uniform particle size distribution.

[0037] In some embodiments of the present invention, the oxidant includes silver nitrate.

[0038] In some embodiments of the present invention, the solution concentration of the oxidant is specifically controlled to include about 0.8 mol / L, 1.2 mol / L, 1.5 mol / L or 1.8 mol / L.

[0039] In some embodiments of the present invention, the concentration of the reducing agent solution is 0.6 to 1.2 mol / L.

[0040] The above concentration range ensures complete reduction of silver ions and maintains pH stability in the reaction system.

[0041] In some embodiments of the present invention, the solution concentration of the reducing agent specifically includes about 0.7 mol / L, 0.9 mol / L or 1.1 mol / L.

[0042] In some embodiments of the present invention, the concentration of the dispersant solution is 1 × 10⁻⁶. -4 ~5×10 -4 mol / L.

[0043] At the above dispersant concentration, a complete adsorption layer is formed on the surface of silver particles, so that molecules are uniformly anchored on the silver crystal surface, and the anisotropy index of crystal growth is controlled in synergy with the twinning inhibitor.

[0044] In some embodiments of the present invention, the solution concentration of the dispersant specifically includes about 2 × 10⁻⁶. -4 mol / L, 3×10 -4 mol / L or 4×10 -4 mol / L.

[0045] In some embodiments of the present invention, the ratio of the coating settling agent to the oxidant is 0.001 to 0.01:1 according to a molar ratio.

[0046] In some embodiments of the present invention, the ratio of the coating settling agent to the oxidant is 0.002:1, 0.005:1, or 0.008:1, measured by molar ratio.

[0047] In some embodiments of the present invention, the molar ratio of the coating settling agent to the oxidant is 0.001 to 0.01:1.

[0048] In some embodiments of the present invention, step S1 further includes adding a pH adjuster to adjust the pH of the reaction solution to 7.5 to 9.5.

[0049] Under the above conditions, the pH adjuster forms a stable complex with silver ions, which reduces the reduction reaction rate and effectively avoids the common explosive nucleation phenomenon.

[0050] In some embodiments of the present invention, the pH adjuster includes at least one of ammonia, sodium hydroxide, nitric acid, and formic acid.

[0051] In some embodiments of the present invention, step S2 includes: adding a solution of reducing agent, a solution of oxidizing agent, and a solution of dispersant to a reaction solution and mixing them to obtain a silver powder suspension.

[0052] In some embodiments of the present invention, in step S2, the feeding rate of the reducing agent solution is 40%-60% / min of the reaction liquid volume;

[0053] In step S2, the feeding rate of the oxidant solution is 40%-60% / min of the reaction liquid volume.

[0054] In some embodiments of the present invention, in step S2, the feeding time of the reducing agent solution, the oxidizing agent solution, and the dispersant solution is 1 to 10 minutes.

[0055] In some embodiments of the present invention, step S3 includes the following post-processing steps: sedimentation, filtration, washing, drying and crushing.

[0056] According to three aspects of the present invention, the application of the aforementioned submicron silver powder in the photovoltaic field is proposed. Attached Figure Description

[0057] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0058] Figure 1 This is a SEM image of the silver powder morphology from Example 1;

[0059] Figure 2 This is a SEM image of the silver powder morphology from Example 2;

[0060] Figure 3 This is a SEM image of the silver powder morphology in Example 3;

[0061] Figure 4 The image shows the SEM image of the silver powder morphology in Comparative Example 1.

[0062] Figure 5 The image shows the SEM image of the silver powder morphology in Comparative Example 2.

[0063] Figure 6 This is a SEM image of the silver powder morphology in Comparative Example 3.

[0064] Figure 7 This is a SEM image of the silver powder morphology in Comparative Example 4.

[0065] Figure 8 This is a SEM image of the silver powder morphology in Comparative Example 5. Detailed Implementation

[0066] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0067] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0068] Example 1

[0069] This embodiment provides a submicron silver powder, and the specific steps are as follows:

[0070] Dissolve 200g of silver nitrate in 1L of pure water and control the solution temperature at 20℃ to obtain an oxidizing agent solution;

[0071] Dissolve 120g of ascorbic acid in 1L of pure water and control the solution temperature at 20℃ to obtain a reducing agent solution.

[0072] S1. Dissolve 20g of polyvinylpyrrolidone K30 in 1.25L of pure water, control the solution temperature at 20℃, add 2g of nitric acid, 3g of ammonia water, and 3.4g of N,N-dimethylformamide to obtain the reaction solution;

[0073] S2. While the reaction solution is continuously stirred at a speed of 440 rpm / min, the reducing agent solution and the oxidizing agent solution are added to the reaction solution at a rate of 60% / min of solution volume. After the addition is completed, a silver powder suspension is obtained.

[0074] S3. Dissolve 0.5g of lauric acid in 20ml of ethanol, add silver powder suspension, and collect the solid phase after continuous stirring. Wash with pure water and ethanol respectively, dry and gas mill to obtain the final product silver powder.

[0075] The SEM image of the silver powder prepared in this embodiment is shown below. Figure 1 As shown:

[0076] Figure 1 The silver particles exhibit a highly monodisperse spherical / cubic structure, with a D50 particle size consistently within the 300-500 nm range, and a smooth surface free of twinning defects. This morphology confirms that the synergistic effect of N,N-dimethylformamide and polyvinylpyrrolidone effectively inhibits eutectic plane growth, while the lauric acid coating layer prevents particle agglomeration, consistent with a tap density of 5-7 g / cm³. 3 Specific surface area: 1.7-2.2 m² 2 / g index requirements.

[0077] Example 2

[0078] The difference between this embodiment and Example 1 is that the amount of N,N-dimethylformamide used is 0.4g, and the reducing agent solution and oxidizing agent solution are added to the reaction solution simultaneously at a rate of 40% / min of solution volume.

[0079] Figure 2 The image shown is a SEM image of the silver powder morphology from Example 2, corresponding to a 50% reduction in the amount of N,N-dimethylformamide. The particle dispersion remains good, although some particles show a slight tendency towards angularity, indicating that crystal growth orientation begins to emerge when the amount of twinning inhibitor is insufficient. This result confirms the linear regulatory effect of N,N-dimethylformamide concentration on silver crystal face growth; an addition of more than 1% is required to achieve optimal morphology control.

[0080] Example 3

[0081] The difference between this embodiment and Example 1 is that 3.4g of N,N-dimethylformamide is replaced with 2g of dimethylacetamide, and the reducing agent solution and the oxidizing agent solution are added to the reaction solution simultaneously at a rate of 50% / min of solution volume.

[0082] Figure 3 This is a SEM image of the silver powder morphology in Example 3, a comparative experiment using dimethylacetamide instead of N,N-dimethylformamide. The particles still maintain a regular geometric shape, but the particle size distribution is slightly wider.

[0083] Comparative Example 1

[0084] This comparative example provides a submicron silver powder, which differs from Example 1 in that the amount of N,N-dimethylformamide used is 0.1g.

[0085] Comparative Example 1 above exhibits typical twinning defects: insufficient twinning inhibitors lead to the formation of elongated flocculent twins, and hard agglomeration exists between particles, resulting in disordered stacking of silver atoms along the crystal plane, which affects the conductivity of the slurry.

[0086] Comparative Example 2

[0087] This comparative example provides a submicron silver powder, which differs from Example 1 in that the amount of N,N-dimethylformamide used is 8g.

[0088] In this comparative example, the addition of N,N-dimethylformamide exceeded the limit, resulting in a lamellar anomalous structure. Excessive N,N-dimethylformamide excessively passivates the active sites on the crystal planes, leading to predominantly two-dimensional directional growth. This structure significantly reduces the tap density.

[0089] Comparative Example 3:

[0090] This comparative example provides a submicron silver powder, which differs from Example 1 in that it does not contain lauric acid and is treated only with ethanol.

[0091] In this comparative example, the absence of lauric acid coating resulted in the formation of a dense, plate-like structure between particles due to van der Waals forces, verifying the dual function of the coating flocculant: its long chains not only prevent aggregation through steric hindrance but also promote rapid solid-liquid separation.

[0092] Comparative Example 4

[0093] This comparative example strictly maintains all raw material formulations and process parameters of Example 1, only changing the feeding rate: the reducing agent solution and the oxidizing agent solution are added to the reaction solution simultaneously at a rate of 20% / min of solution volume.

[0094] The feeding in this comparative ratio was too slow, resulting in an excessively long crystal nucleus growth time. The twinning inhibitor had limited effect, and the silver powder showed a polycrystalline growth trend with agglomeration.

[0095] Comparative Example 5

[0096] This comparative example strictly maintains all raw material formulations and process parameters of Example 1, only changing the feeding rate: the reducing agent solution and the oxidizing agent solution are added to the reaction solution simultaneously at a rate of 70% / min of solution volume.

[0097] The addition of feed in this comparative example was too slow, resulting in excessively rapid reduction of silver nitrate and rapid nucleation. The silver powder particle size was within 0.3 μm (visually estimated, without particle size measurement), and there was localized agglomeration, leading to the failure of the experiment.

[0098] Table 1. Performance Testing

[0099] D10(nm) D50(nm) D90(nm) Zhenshi Comparison Table burn damage Example 1 112 310 845 6.3 2.10 0.68 Example 2 152 376 823 6.8 1.95 0.55 Example 3 195 487 850 6.9 1.87 0.57 Comparative Example 1 293 674 1012 / / Comparative Example 2 / / / / / Comparative Example 3 / / / / /

[0100] Table 1 analyzes the test data of the examples and comparative examples: The submicron silver powders prepared in Examples 1-3 exhibit excellent performance indicators. Among them, the D50 particle size of Example 1 is 310 nm, the D10-D90 distribution is 112-845 nm, and the tap density reaches 6.3 g / cm³. 3 The specific surface area is 2.10 m². 2 / g, with a burn loss of only 0.68%, and all parameters met the technical requirements. In contrast, Comparative Example 1, due to insufficient N,N-dimethylformamide (0.1g), resulted in an increased D50 particle size of 674nm, and obvious twinning defects and particle agglomeration were visible in the SEM image; In Comparative Example 2, excessive addition of N,N-dimethylformamide (8g) caused a lamellar abnormal structure, making it impossible to obtain effective measurement data; Comparative Example 3, without the addition of lauric acid, resulted in severe particle agglomeration, verifying the key role of the coating sedimentation agent in preventing silver powder agglomeration.

[0101] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A submicron silver powder, characterized in that, The raw materials for preparing the submicron silver powder are: oxidant, reducing agent, dispersant, coating and settling agent, and twinning inhibitor; The oxidizing agent includes at least one of silver nitrate, silver nitrite, silver carbonate, and silver oxalate; The reducing agent includes at least one of ascorbic acid, glucose, sodium borohydride, hydrazine hydrate, and formaldehyde; The coating settling agent includes at least one of lauric acid, myristic acid, palmitic acid and stearic acid; The twinning inhibitor includes at least one of N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, hexamethylphosphoric triamine, and dimethylacetamide; The dispersant includes at least one of polyvinylpyrrolidone K10, polyvinylpyrrolidone K30, polyvinylpyrrolidone K90, polyethylene glycol, polyacrylic acid, polyvinyl alcohol, gelatin, and gum arabic; The burn-off rate of the submicron silver powder is 0.5-0.7%; The submicron silver powder is prepared by the following method: S1. Mix the dispersant solution and the twinning inhibitor to obtain a reaction solution, and adjust the pH of the reaction solution to 7.5~9.5; S2. Mix the reducing agent solution, the oxidizing agent solution, and the reaction solution to obtain a silver powder suspension; S3. The silver powder suspension and the coating sedimentation agent are mixed and reacted, and then post-treated to obtain submicron silver powder.

2. The submicron silver powder according to claim 1, characterized in that, The submicron silver powder has a D10 particle size of 100-200 nm, a D50 particle size of 300-500 nm, and a D90 particle size of 700-1000 nm. The tap density of the submicron silver powder is 5~7 g / cm³. 3 .

3. The submicron silver powder according to claim 1, characterized in that, The molar ratio of the twinning inhibitor to the oxidant is 0.005~0.04:

1.

4. The submicron silver powder according to claim 1, characterized in that, The concentration of the oxidant solution is 0.5~2 mol / L, and the amount used is 1-20L; The concentration of the reducing agent solution is 0.6~1.2 mol / L, and the amount used is 0.3-15L; The concentration of the dispersant solution is 1×10⁻⁶. -4 ~ 5×10 -4 mol / L, dosage is 1-40L.

5. The submicron silver powder according to claim 1, characterized in that, In step S2, the feeding rate of the reducing agent solution is 40%-60% / min of the reaction liquid volume; In step S2, the feeding rate of the oxidant solution is 40%-60% / min of the reaction liquid volume.

6. The submicron silver powder according to claim 1, characterized in that, In step S2, the feeding time of the reducing agent solution, the oxidizing agent solution, and the dispersant solution is 1~10 min.

7. The submicron silver powder according to claim 1, characterized in that, The molar ratio of the coating settling agent to the oxidant is 0.001~0.01:

1.

8. An application of submicron silver powder as described in any one of claims 1 to 7 in the photovoltaic field.

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