A method for preparing silver-coated metal core-shell powder

Abstract

The application discloses a preparation method of silver-coated metal core-shell powder and relates to the field of metal powder material preparation. The method comprises the following steps: uniformly dispersing inner core base material powder in a solvent, pre-activating the base metal powder, collecting the pre-activated powder, and washing the pre-activated powder until neutral; uniformly dispersing the pre-activated powder in a solvent, adjusting the system to be alkaline, adding a first part of silver precursor to carry out a replacement reaction in the presence of a complexing agent; continuously adding a second part of silver precursor and a reducing agent to obtain coated coarse powder; and sequentially performing surface passivation modification on the coated coarse powder to obtain silver-coated metal core-shell powder. The application initiates a reduction method for pre-activation and a one-pot replacement-reduction coating, and the silver plating layer is dense and complete; imidazole-quinone modification simultaneously improves acid resistance, oxidation resistance and conductivity, breaks through the bottleneck of insulating passivation, and meets the needs of electromagnetic shielding, conductive adhesive, low-temperature slurry and the like.

Description

Technical Field

[0001] This invention relates to the field of metal powder material preparation technology, specifically to a method for preparing silver-coated metal core-shell powder. Background Technology

[0002] With the rapid development of the photovoltaic, new energy vehicle, and electronic information industries, the demand for conductive silver paste, as a core functional material, continues to rise. In 2025, the global market size for photovoltaic conductive silver paste exceeded 220 billion yuan, with the domestic market accounting for over 70%. However, pure silver powder is expensive, and since 2023, silver prices have continued to surge, with the industrial silver price in 2026 increasing by over 400% compared to 2023, severely compressing the profit margins of downstream manufacturing industries. The industry generally uses silver-coated copper, nickel, and other metal powders as alternatives to pure silver powder, which can significantly reduce costs while maintaining conductivity, making it the recognized optimal solution in the era of high silver prices.

[0003] Currently, the industrial preparation of silver-coated metal core-shell powder generally adopts a multi-step process of "acid washing-alkali washing-sensitization-activation-displacement-reduction", which still suffers from the following difficult-to-overcome technical defects:

[0004] The pretreatment process is cumbersome and causes serious pollution from waste. The existing process requires multiple steps, including acid washing (to remove the oxide layer), alkali washing (to remove oil), sensitization (stannous chloride system), and activation (palladium chloride and other precious metal systems). Each step requires a large amount of pure water for washing, resulting in wastewater discharge of more than 50 tons per ton of product. The treatment cost of wastewater containing acids, alkalis, tin, palladium, and other heavy metals is extremely high. At the same time, the multi-step treatment process is prone to powder oxidation loss, and the product yield is usually only 80% to 85%.

[0005] The coating process is complex and inefficient. Existing technologies typically involve first preparing a preliminary coated powder through a displacement reaction, followed by solid-liquid separation, multiple washings, and then re-formulating the system for chemical reduction and repair. This process is lengthy, with a production cycle exceeding 10 hours. Repeated powder transfers can lead to oxidation and agglomeration, resulting in poor batch stability and making it unsuitable for large-scale applications in high-end scenarios.

[0006] Coating quality is difficult to control, resulting in significant product performance defects. Traditional sensitization and activation methods introduce tin and palladium impurities that are prone to remain, affecting conductivity. The silver layer formed by the displacement reaction is prone to defects such as pinholes and gaps, resulting in insufficient density and poor oxidation resistance of the powder. During high-temperature curing or storage, the matrix is ​​easily oxidized, leading to a significant decrease in conductivity. At the same time, the silver layer has weak adhesion to the matrix and is prone to falling off during high-speed stirring and rolling of the slurry, failing to meet the stringent requirements of high-end applications such as photovoltaic positive silver and automotive electronics.

[0007] High raw material costs and poor industrial adaptability. Sensitization requires a large amount of stannous chloride, and activation requires the use of the precious metal palladium chloride, which alone account for more than 15% of the raw material cost. Multiple processes lead to a significant increase in equipment investment, labor, and energy costs, making it difficult to meet the cost reduction requirements of large-scale industrial production.

[0008] To address the aforementioned issues, the industry has conducted extensive research on simplified processes in recent years. While patent CN118123016A simplifies the acid and alkali washing steps, it still requires stannous chloride sensitization. The easy oxidation of stannous ions leads to a deterioration in sensitization, and the wastewater pollution problem remains unresolved. Patent CN121755704A uses nickel chloride sensitization, but still requires palladium chloride activation, and the costs of precious metals and wastewater issues persist. Patent CN118477998A uses a one-step reduction process, but it cannot simultaneously complete depassivation, sensitization, and activation, resulting in uneven silver layer nucleation and insufficient coating density. Patent CN120961913A achieves rapid one-step preparation, but it relies on highly corrosive polyamines, resulting in high costs and easy residue buildup; the rapid growth of the silver layer makes it difficult to control density. Patent CN118218588A uses a two-step displacement-reduction method, but still requires intermediate separation and washing, leading to a long production cycle. The patent with publication number CN118060535A uses physical vapor deposition and electroplating technology, but the silver utilization rate is low, the silver-copper bonding force is not as good as the chemical method, and it lacks surface passivation modification treatment, resulting in insufficient antioxidant properties and slurry compatibility.

[0009] In summary, existing technologies have consistently failed to address systemic issues such as cumbersome pretreatment, heavy pollution from waste gas, wastewater, and solid waste, insufficient coating density, weak silver layer adhesion, high cost, and the conflict between conductivity and weather resistance in post-processing. Therefore, developing a simplified process for preparing silver-coated metal core-shell powders that produces dense silver layers, strong core-shell bonding, high conductivity and weather resistance, and is suitable for large-scale industrial production, has significant technological and industrial value. Summary of the Invention

[0010] The purpose of this invention is to provide a method for preparing silver-coated metal core-shell powder. This method removes the passivation layer on the metal surface using a reduction method, and performs a one-pot displacement-reduction reaction to coat metals such as copper and nickel with silver. This solves the problems of cumbersome pretreatment, heavy waste pollution, and insufficient coating density. Furthermore, by sequentially treating the coarse silver-coated powder with imidazole derivatives and quinone derivatives, the conflict between conductivity and weather resistance is resolved. Finally, annealing treatment addresses the failure issues of silver-coated powder under high-temperature conditions, such as silver-copper separation and core oxidation.

[0011] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0012] A method for preparing silver-coated metal core-shell powder includes the following steps:

[0013] S100. Disperse the core substrate powder evenly in a solvent, pre-activate the matrix metal powder, collect the pre-activated powder, and wash it until neutral.

[0014] S200. The above pre-activated powder is uniformly dispersed in a solvent, the system is adjusted to alkaline, and in the presence of a complexing agent, the first part of the silver precursor is added to carry out a displacement reaction; the second part of the silver precursor and the reducing agent are then added to obtain the coated coarse powder.

[0015] S300. The above-mentioned coated coarse powder is subjected to surface passivation modification in sequence to obtain silver-coated metal core-shell powder.

[0016] Step S100: Reduction sensitization pretreatment:

[0017] In alkaline or acidic control systems, reducing agents are used to treat the core substrate powder, achieving two objectives simultaneously: reducing and removing the natural oxide layer on the substrate surface (depassivation); at the same time, silver ion anchoring sites rich in hydrophilic active groups such as hydroxyl (-OH) and aldehyde (-CHO) are constructed in situ on the substrate surface, thereby completing surface sensitization and activation, and providing high-density nucleation sites for subsequent silver deposition.

[0018] Step S200: One-pot displacement-reduction synergistic coating:

[0019] First, by utilizing the potential difference between the core substrate metal and silver ions, a first part of the silver source is added to the reaction system, resulting in a displacement reaction: silver ions are anchored and reduced to silver nanoparticles, which are uniformly deposited on the surface of the core substrate to form a continuous silver-coated main layer; at the same time, the in-situ generated silver nanoparticles can serve as catalytic active centers to guide the subsequent epitaxial growth of silver atoms, promote heterogeneous nucleation, and improve the utilization rate of silver.

[0020] After the displacement reaction is complete, without any solid-liquid separation or washing, the second silver source and a stoichiometric amount of reducing agent are directly added to the same reaction system to carry out a reduction reaction. This reduction process is specifically designed to repair any pinholes, gaps, and uncoated areas that may exist in the displacement silver layer, filling defects to obtain a dense, continuous, and complete silver plating layer. This one-pot synergistic coating strategy can effectively suppress the formation of free silver particles and prevent plating from peeling off.

[0021] Step S300: Surface Encapsulation Passivation Modification

[0022] The above-mentioned silver-coated coarse powder is subjected to surface modification treatment. Organic molecules form a dense passivation encapsulation layer on the surface of the silver layer, which significantly improves the oxidation resistance and weather resistance of the powder. At the same time, functional groups are introduced to improve the dispersibility of the powder in conductive slurry and its compatibility with organic carriers, ultimately achieving highly conductive and highly stable silver-coated metal core-shell powder.

[0023] The silver coating process of this invention exhibits good compatibility with the core substrate, adapting to various metal powder substrates such as copper powder. Specifically, through this process or methods derived from it, silver coating layers of varying thicknesses and properties can be formed on different metal powders by adjusting the silver coating ratio through two stages: displacement and reduction. This results in different silver-coated core-shell powder materials, achieving in-situ nucleation growth of the silver layer. This invention employs a synergistic coating process with displacement as the primary method and reduction as a secondary method. Material feeding can be tailored to coating requirements. SEM images show that the surface coating integrity rate of this invention is close to 100%, ensuring a tight bond between the silver layer and the substrate while precisely repairing pinhole defects through the reduction reaction, resulting in a continuous, dense, and defect-free complete silver coating layer.

[0024] Furthermore, the core substrate is selected from copper, nickel, aluminum, or a copper-nickel alloy, and the average particle size of the core substrate powder is 0.03 μm to 80 μm;

[0025] The amount of silver coating on the coarse powder is 0.5~50wt%.

[0026] Furthermore, in the first part of the silver precursor and the second part of the silver precursor, the mass of silver element undergoing the substitution reaction is not less than the mass of silver element undergoing the reduction reaction, and the mass of silver element in the first part of the silver precursor accounts for more than 50% of the total mass of silver element in the silver precursor.

[0027] Furthermore, in step S100, the pre-activation treatment method includes a reduction method or a phosphating solution treatment method;

[0028] Among them, the phosphating solution treatment method uses a phosphating system based on dihydrogen phosphate to treat the core substrate;

[0029] Phosphating systems based on dihydrogen phosphate include zinc dihydrogen phosphate and sodium hypophosphite;

[0030] The reduction method involves removing the passivation layer on the surface of the core substrate under alkaline conditions.

[0031] The reagents used in the reduction method are selected from one or more of glucose, fructose, maltose, formaldehyde, ascorbic acid, sodium ascorbate, isoascorbic acid, sodium isoascorbate, citric acid, sodium citrate, tartaric acid, sodium potassium tartrate, formic acid, sodium formate, hydrazine hydrate, sodium borohydride, and potassium borohydride.

[0032] Under weakly acidic conditions, a uniform, porous, nanoscale nickel phosphate conversion film is generated in situ on the surface of nickel powder using a phosphating system based on dihydrogen phosphate. This conversion film has two core functions: during the phosphating process, phosphoric acid gently dissolves the passivation layer on the nickel surface, while the phosphating film covers the nickel surface, completely preventing secondary passivation; the porous nickel phosphate film has a strong adsorption effect on silver ions, anchoring them to the nickel powder surface. Simultaneously, the phosphorus element in the phosphating film has reducing properties, preferentially reducing silver ions to silver atoms, forming nucleation sites within the film pores, and guiding the uniform growth of the silver layer.

[0033] The amount of the reagent added is 0.2% to 66.7% of the mass of the matrix metal powder.

[0034] Further, in step S200, the silver precursor is selected from silver nitrate or silver ammonia solution;

[0035] The complexing agent is selected from one or more of tetraethylenepentamine complexing agent, ammonia, ethanolamine, triethylamine, ethylenediamine, EDTA, disodium EDTA, citric acid, sodium citrate, and potassium sodium tartrate.

[0036] The molar ratio of the complexing agent to the silver element in the silver precursor is 1~10:1;

[0037] Further, in step S200, the reducing agent includes one or more of ascorbic acid, sodium ascorbate, isoascorbic acid, sodium isoascorbate, glucose, trisodium citrate, tartaric acid, sodium tartrate, potassium tartrate, potassium sodium tartrate, sodium hypophosphite, sodium borohydride, hydrazine hydrate, formaldehyde, or sodium formate.

[0038] The amount of reducing agent added is 1.0 to 5.0 times the molar amount of silver in the silver precursor in the second part;

[0039] Furthermore, in step S200,

[0040] The displacement reaction is carried out at a temperature of 5-40℃ for 15-25 minutes.

[0041] The reduction reaction is carried out at a temperature of 10~70℃ for 15~20 minutes.

[0042] Furthermore, the surface passivation modification method in step S300 includes the following: using higher fatty acids or higher fatty amines as surface modifiers;

[0043] The higher fatty acids include oleic acid or stearic acid;

[0044] The higher fatty amines include hexadecaneamine or octadecaneamine.

[0045] Furthermore, the surface passivation modification method in step S300 includes the following: sequentially treating the coated coarse powder with imidazole derivatives and quinone derivatives;

[0046] The amount of imidazole derivatives used is 0.5~6 wt% of the core substrate powder; the amount of quinone derivatives used is 0.5~6 wt% of the core substrate powder.

[0047] Surface modification utilizes electron donor / acceptor complexes to form electron transfer complexes on the powder surface, reducing the activation energy of electron migration. This provides excellent antioxidant protection without sacrificing or even improving conductivity, breaking through the technical bottleneck of conductivity degradation in traditional insulating passivators.

[0048] Further, in step S300, after surface passivation modification, annealing treatment can be performed; the annealing treatment includes the following: placing the surface-modified coated coarse powder in an inert atmosphere, maintaining the oxygen content ≤10ppm throughout the process, heating to 180~250℃, and holding at that temperature for 0.5~1.5h.

[0049] Annealing completes the alloying and metallurgical treatment of the core and shell at the interface: interface alloying heat treatment is performed in an inert atmosphere, improving the bonding strength between the core and shell materials, enhancing electrical conductivity, and improving high-temperature resistance, oxidation resistance, and corrosion resistance. Therefore, the SEM images of the silver-clad metal show no significant changes before and after annealing.

[0050] Compared with the prior art, the beneficial effects of the present invention are:

[0051] 1. This invention pioneers a reduction method for pre-activating metals such as copper and nickel, simplifying the traditional multi-step process of acid washing, alkali washing, sensitization (SnCl2), and activation (PdCl2) into a single-step reduction reaction. Combined with a one-pot displacement-reduction synergistic coating process, it significantly reduces equipment investment and wastewater discharge. The reducing agent used is green glucose or ascorbic acid, and the byproducts are N2, H2O, or harmless glycosides. Overall raw material costs are reduced by 30-50%, meeting the requirements of large-scale industrial green production.

[0052] 2. In this invention, the substitution reaction forms a silver master layer that is metallurgically bonded to the matrix, and the reduction reaction directionally repairs defects such as pinholes and gaps, resulting in a continuous and intact silver layer. The in-situ constructed zero-valent copper nanocrystal catalytic sites replace the precious metal palladium, which reduces costs while ensuring high bonding strength between the silver layer and the matrix, and prevents detachment and copper exposure after high-speed stirring, rolling, and high-temperature aging.

[0053] 3. The present invention sequentially treats and coats coarse powder with imidazole derivatives (electron donors) and quinone derivatives (electron acceptors) to form electron transfer complexes on the powder surface, thereby reducing the activation energy of electron migration. While improving acid resistance and oxidation resistance, it also effectively enhances conductivity, breaking through the technical bottleneck of traditional insulating passivators sacrificing conductivity.

[0054] 4. This invention uses interfacial alloying annealing to form an intermetallic compound or solid solution at the core-shell interface, which completely solves the failure problems of silver-copper separation and core oxidation of traditional silver-coated copper powder under high-temperature conditions, and expands the application field from low-temperature pastes to high-temperature sintered conductive pastes and power electronic devices.

[0055] 5. This invention is applicable to various substrates such as copper, nickel, aluminum, and copper-nickel alloys, as well as powders with different morphologies such as spherical, flake, and dendritic. By adjusting the ratio of replacement / reduction silver (replacement silver ≥ 50%), the thickness and performance of the silver layer can be precisely controlled within the range of 0.5% to 50.5% silver content, meeting the diverse needs of high-performance electromagnetic shielding electronic pastes, conductive adhesives, low-temperature conductive pastes, conductive filler additives, and other applications. Attached Figure Description

[0056] Figure 1 This is a field emission SEM image of the silver-coated copper powder after high-temperature annealing in Example 1 of the present invention.

[0057] Figure 2 This is a photograph of the silver-coated copper powder after high-temperature annealing in Example 1 of the present invention.

[0058] Figure 3 The TDG-DSC curve of the silver-coated copper powder sample annealed in Example 1 is shown.

[0059] Figure 4 The TDG-DSC curve of the sample from Example 1 that underwent only surface modification but not high-temperature annealing is shown.

[0060] Figure 5 This is a SEM image of a 25μm well-developed dendritic silver-coated copper structure from Example 2;

[0061] Figure 6 This is a 30μm underdeveloped dendritic silver-coated copper SEM image from Example 4;

[0062] Figure 7 Here is a SEM image of the product from Example 3;

[0063] Figure 8 Here is a photograph of the actual product from Example 3;

[0064] Figure 9 Here is a SEM image of the product from Example 8;

[0065] Figure 10 Here is a SEM image of the product from Example 9;

[0066] Figure 11 Here is a SEM image of the product from Example 10;

[0067] Figure 12Here is a photograph of the actual product from Example 10;

[0068] Figure 13 Here is a SEM image of the product from Example 13;

[0069] Figure 14 Here is a photograph of the actual product from Example 14;

[0070] Figure 15 SEM photos of product Comparison 1;

[0071] Figure 16 SEM photos of product 2 (for comparison).

[0072] Figure 17 SEM photos of product 3 (for comparison).

[0073] Figure 18 SEM photos of product 4 (for comparison);

[0074] Figure 19 SEM photos of product 5 (for comparison).

[0075] Figure 20 SEM photos of product 7 (for comparison);

[0076] Figure 21 SEM photos of product 8 for comparison;

[0077] Figure 22 Image of a single silver-coated copper particle in Example 1;

[0078] Figure 22 In the image, (a) is a single silver-coated copper particle (SEM image).

[0079] (b) is the EDS energy spectrum distribution of elemental (C,O,Cu,Ag,N) on the surface of a single silver-coated copper particle;

[0080] (c) is the EDS energy spectrum distribution of Ag on the surface of a single silver-coated copper particle;

[0081] (d) is the EDS energy spectrum distribution of Cu on the surface of a single silver-coated copper particle. Detailed Implementation

[0082] The method for determining / detecting the silver coating amount in this invention is as follows:

[0083] Titration (chemical precipitation / complexation reaction): GB / T 15072.2-2008 Chemical Analysis Methods for Noble Metal Alloys: Determination of Silver Content in Silver Alloys by Sodium Chloride Potentiometric Titration.

[0084] Example 1

[0085] S100. Disperse 220g of spherical copper powder with an average particle size of 5μm in 660g of deionized water (3 times the weight of the copper powder), stir and ultrasonically disperse for 15min. Add an aqueous solution containing 92g of sodium hydroxide (15wt%) while stirring, heat to 60℃ and keep stirring for 20min, then slowly add an aqueous solution containing 130g of glucose (25%), continue to slowly heat to 85℃ and keep stirring for 30min. Stop stirring and heating, allow to cool naturally, and use natural sedimentation to achieve solid-liquid separation and collect the copper powder. Wash the copper powder with deionized water until pH neutral, collect the sensitized copper powder, and proceed directly to the next step of silver coating without drying.

[0086] S200. First, displacement coating: Add the sensitized copper powder obtained in the previous step to deionized water with a weight of 4 times the copper powder, stir and ultrasonically disperse for 10 min, add an aqueous solution containing 8.8 g of PVP-K30 dispersant (concentration 5 wt%), and continue stirring and dispersing for 20 min; then add 45 g of tetraethylenepentamine complexing agent, and continue stirring and dispersing for 10 min; next, uniformly add an aqueous solution containing 34.5 g of silver nitrate (concentration 15 wt%) under vigorous stirring. The whole process is carried out at 23℃. After the addition is completed, keep stirring for 20 min.

[0087] Then, the "one-pot method" for reduction and repair was performed: A 10wt% aqueous solution containing 13g of isocyanate was added dropwise under vigorous stirring for 5 minutes; a 10wt% aqueous solution containing 3.5g of silver nitrate was then added dropwise under stirring for 15 minutes; stirring was stopped, and solid-liquid separation was achieved by natural sedimentation, collecting the crude silver-coated copper powder; the powder was washed with 100g of 2wt% glacial acetic acid aqueous solution until the washing liquid was no longer blue, and then washed with deionized water until the washing liquid was no longer blue and no copper ions were detected; then, the silver-coated copper powder was washed twice with 50g of anhydrous ethanol to remove moisture, with solid-liquid separation completed by Buchner funnel filtration after each anhydrous ethanol wash. The crude silver-coated copper powder was collected and proceeded directly to the next surface treatment step without drying.

[0088] S300. The crude silver-coated copper powder obtained in the previous step is dispersed in an appropriate amount of anhydrous ethanol (the amount used is 3 times the weight of the crude silver-coated copper powder) under stirring to obtain an ethanol dispersion of silver-coated copper powder. 2.2g of stearic acid is heated and dissolved in 20g of anhydrous ethanol, and then added to the above ethanol dispersion of the crude silver-coated copper powder under stirring. After rapid stirring and uniform dispersion, the temperature is raised to 60℃ and kept at this temperature while stirring for 15min. Then, stirring and heating are stopped, and the mixture is allowed to cool naturally to room temperature. Solid-liquid separation is achieved by Buchner funnel filtration. The silver-coated copper powder is collected, washed once with a small amount of ethanol (3 times the weight of the crude silver-coated copper powder) to remove as much residual excess ethanol and dispersant as possible. The powder is then vacuum dried at 50℃ for 2 hours and passed through a 600-mesh sieve to obtain the finished silver-coated copper powder. The silver content is determined to be 10.1wt% by titration.

[0089] After surface modification, the silver-coated copper powder undergoes high-temperature annealing—interface alloying heat treatment—to improve the bonding strength between the silver and copper at the interface. The alloy interface facilitates electron diffusion and movement, reduces scattering, lowers the activation energy of electron movement, and further improves the conductivity of the powder. Specifically, the silver-coated copper powder from step three is placed in a tube furnace, and high-purity argon gas is introduced at a flow rate of 50 mL / min to replace the air in the furnace for 10 min, maintaining an oxygen content ≤10 ppm throughout the process. The temperature is then increased to 250℃ at a heating rate of 50℃ / min and held for 1.5 h, allowing an ultra-thin silver-copper solid solution alloying transition layer to form between the silver layer and the core substrate, achieving metallurgical bonding and simultaneously eliminating internal stress in the silver layer and increasing density. After holding, the powder is naturally cooled to room temperature under the protection of high-purity argon gas. After removal, it is immediately sealed and stored under nitrogen purging to obtain the final high-performance silver-coated copper core-shell conductive metal powder.

[0090] Field emission SEM image of silver-coated copper powder after high-temperature annealing is shown below. Figure 1 As shown, the actual product is as follows Figure 2 As shown.

[0091] The EDS energy dispersive spectrum of the surface elements of a single silver-coated copper particle in Example 1 more intuitively shows that the surface silver elements are in a uniform and dense distribution state. The actual product is as follows: Figure 22 As shown.

[0092] Thermogravimetric analysis (TGA) was performed on surface-treated and high-temperature annealed silver-coated copper powder samples for comparison, examining their initial oxidation temperature and oxidation growth under heating conditions. Using a TDG-DSC instrument in air, within a temperature range of 100–900 °C, at a heating rate of 10 °C / min, the oxidation resistance and high-temperature resistance of the samples were tested. The results are as follows: Figure 3 and Figure 4 As shown.

[0093] The results show that the annealed samples have better high-temperature resistance characteristics. Specifically, the initial oxidation temperature is 299℃, which is much higher than that of the samples after surface modification without high-temperature annealing. The samples after surface modification alone also reach a relatively high initial oxidation temperature of 266℃. In addition, the weight gain curve of the annealed silver-coated copper powder samples is slow throughout the heating process, with a weight gain of only 2.3% at 800℃, which is much smaller than the weight gain of the samples after surface modification without high-temperature annealing (6.9%).

[0094] Example 2

[0095] S100. Disperse 200g of well-developed dendritic electrolytic copper powder with an average particle size of 25μm in 800g of deionized water, stir and ultrasonically disperse for 10min, add an aqueous solution containing 15g of potassium hydroxide (concentration 20wt%) while stirring, heat to 50℃, slowly add an aqueous solution containing 40g of sodium isoascorbate (concentration 15wt%), continue to slowly heat to 80℃, stir and maintain for 25min; stop stirring and heating, allow to cool naturally, use filtration to achieve solid-liquid separation, collect the crude sensitized copper powder after the passivation layer is removed; wash the copper powder with deionized water until pH neutral, and proceed directly to the next step of silver coating without drying.

[0096] S200. First, displacement coating: Add the sensitized copper powder obtained in the previous step to 800g of deionized water, stir and ultrasonically disperse for 10min, add an aqueous solution containing 5g of gum arabic powder (concentration 5wt%), and continue stirring and dispersing for 20min; then add 25g of triethylenetetramine, and continue stirring and dispersing for 5min; next, uniformly add an aqueous solution containing 35.2g of silver nitrate (concentration 20wt%) under vigorous stirring. The whole process is carried out at 40℃, and stirring is maintained for 20min after the addition is completed.

[0097] Then, the "one-pot method" was used for reduction and repair: A 20wt% aqueous solution containing 10g of glucose was added dropwise while stirring for 5 minutes; a 25wt% silver ammonia solution containing 3.36g of silver nitrate was added dropwise while stirring, and the temperature was raised to 45℃ while stirring for 20 minutes; stirring was stopped and the mixture was cooled to room temperature. Solid-liquid separation was achieved by filtration, and the crude silver-coated copper powder was collected. After washing with deionized water until neutral, the crude silver-coated copper powder was washed with a 1% ascorbic acid aqueous solution for 20 minutes while stirring. The silver-coated copper powder was then filtered, and washed sequentially with deionized water and anhydrous ethanol to ensure neutrality and remove as much residual moisture as possible. The silver-coated copper powder was collected and, without drying, proceeded directly to the next surface treatment step; the washing process was the same as in Example 1.

[0098] S300. The crude silver-coated copper powder obtained in the previous step is dispersed in 200g of anhydrous ethanol under stirring to obtain an ethanol dispersion of silver-coated copper powder. Oleic acid is used as a surface modifier: specifically, 2g of oleic acid is dissolved in 20g of anhydrous ethanol, and then added to the above ethanol dispersion of silver-coated copper powder under stirring. After rapid stirring and uniform dispersion, the temperature is raised to 50℃ and kept at this temperature with rapid stirring for 10min. Then, stirring and heating are stopped, and the mixture is allowed to cool naturally to room temperature. Solid-liquid separation is achieved by natural sedimentation. The silver-coated copper powder is collected, washed once with 30g of ethanol to remove as much residual excess ethanol and oleic acid dispersant as possible. The powder is then dried in a forced-air dryer at 45℃ for 2 hours and passed through a 600-mesh sieve to obtain the finished silver-coated copper powder. The silver content is determined to be 11.2wt% by titration.

[0099] The surface-modified silver-coated powder was placed in a tube furnace, and high-purity nitrogen gas was introduced at a flow rate of 50 mL / min to replace the air in the furnace, maintaining an oxygen content ≤10 ppm throughout the process. The temperature was increased to 180℃ at a rate of 10℃ / min and held for 0.5 h to form an ultra-thin silver-copper or silver-nickel solid solution alloy transition layer at the interface between the silver layer and the core substrate, achieving metallurgical bonding and simultaneously eliminating internal stress in the silver layer and improving density. After holding, the powder was naturally cooled to room temperature under an inert atmosphere, removed, and immediately sealed and nitrogen-filled for storage, yielding the final high-performance silver-coated copper core-shell conductive metal powder, suitable for high-performance electromagnetic shielding electronic pastes. SEM images of the product are shown below. Figure 5 As shown.

[0100] Example 3

[0101] 150g of S100, flaky conductive copper powder with an average particle size of 10μm was dispersed in 600g of deionized water, stirred and ultrasonically dispersed for 15min, and an aqueous solution containing 65g of sodium hydroxide (concentration 30wt%) was added while stirring. The temperature was raised to 45℃, and an aqueous solution containing 100g of fructose (concentration 30wt%) was slowly added dropwise. The temperature was then slowly raised to 85℃ and stirred for 26min. Stirring and heating were stopped, and the mixture was allowed to cool naturally. Solid-liquid separation was achieved by filtration, and the crude sensitized copper powder after the passivation layer was removed was collected. The copper powder was washed with deionized water until the pH was neutral, and it was directly proceeded to the next step of silver coating without drying.

[0102] S200. First, displacement coating: Add the sensitized copper powder obtained in the previous step to 500g of deionized water, stir and ultrasonically disperse for 12min, add an aqueous solution containing 8g of gum arabic powder (concentration 6wt%), and continue stirring and dispersing for 15min; add an aqueous solution containing 60g of disodium oxalate dihydrate (EDTA·2Na·2H2O) (concentration 15wt%) dropwise, and continue stirring and dispersing for 8min; then, uniformly add a silver ammonia solution containing 35.1g of silver nitrate (concentration 23wt%) under vigorous stirring. The entire process is carried out at 5℃, and stirring is maintained for 23min after the addition is complete.

[0103] Then, the "one-pot method" was used for reduction and repair: A 21wt% aqueous solution containing 10.6g of ascorbic acid was added dropwise under vigorous stirring, and stirring was maintained for 3 minutes; a 23wt% silver ammonia solution containing 5.1g of silver nitrate was then added dropwise under stirring, and stirring was maintained at room temperature for 15 minutes; stirring was stopped, and solid-liquid separation was achieved by filtration, collecting the crude silver-coated copper powder; after washing with deionized water until neutral, the crude silver-coated copper powder was washed with 300g of 1.5% ascorbic acid aqueous solution for 25 minutes with stirring; then, the silver-coated copper powder was collected by suction filtration using a Buchner funnel, and then washed sequentially with deionized water and anhydrous ethanol to ensure the silver-coated copper powder was neutral and to remove as much residual moisture as possible. The collected silver-coated copper powder was not dried and proceeded directly to the next surface treatment step (washing process as in Example 1).

[0104] S300. The crude silver-coated copper powder obtained in the previous step is dispersed in 250g of anhydrous ethanol under stirring to obtain an ethanol dispersion of silver-coated copper powder. Oleic acid is used as a surface modifier: specifically, 1.8g of stearamine (octadecylamine) is dissolved in 28g of anhydrous ethanol, and then added to the above ethanol dispersion of silver-coated copper powder under stirring. After rapid stirring and uniform dispersion, the temperature is raised to 55℃ and kept at this temperature with rapid stirring for 15min. Then, stirring and heating are stopped, and the mixture is allowed to cool naturally to room temperature. Solid-liquid separation is achieved by suction filtration using a Buchner funnel. The silver-coated copper powder is collected, washed once with 100g of ethanol to remove as much residual excess ethanol and stearamine dispersant as possible. The powder is then dried at 55℃ for 2 hours and passed through a 320-mesh sieve to obtain the finished silver-coated copper powder. The silver content is determined to be 15.1% by titration.

[0105] The modified silver-coated powder was placed in a tube furnace, and high-purity nitrogen gas was introduced at a flow rate of 80 mL / min to replace the air in the furnace, maintaining an oxygen content ≤10 ppm throughout the process. The temperature was increased to 180℃ at a rate of 8℃ / min and held for 1.0 h to form an ultra-thin silver-copper or silver-nickel solid solution alloying transition layer at the interface between the silver layer and the core substrate, achieving metallurgical bonding and simultaneously eliminating internal stress in the silver layer and improving density. After holding, the powder was naturally cooled to room temperature under an inert atmosphere, removed, and immediately sealed and nitrogen-filled for storage, yielding the final high-performance silver-coated copper core-shell conductive metal powder. Product SEM images are shown below. Figure 7 As shown in the photos, the actual product is as follows. Figure 8 As shown. The product is suitable for high-performance electromagnetic shielding electronic pastes and conductive adhesives, as well as low-temperature conductive pastes.

[0106] Example 4

[0107] The substrate copper powder is 30μm underdeveloped dendritic electrolytic copper powder. Steps S100, S200, and the annealing process are the same as in Example 2. The oleic acid modification method is replaced by an electron donor / acceptor complex treatment method, as detailed below:

[0108] The crude silver-coated copper powder obtained in the previous step was dispersed in 200g of ethanol solution containing 1.0g of 2-[(2,4-dichlorophenyl)methyl]-1H-benzimidazole (0.5wt% of copper powder substrate) and stirred at 35~40℃ for 25min. After solid-liquid separation, the copper powder was collected and air-dried at room temperature. Then, at room temperature, the copper powder was added to 150g of anhydrous ethanol solution containing 1.0g of tetramethylp-quinone dimethylane (0.5wt% of copper powder substrate) under stirring, and stirred and soaked for 25min to complete solid-liquid separation and collect the silver-coated copper powder. The silver-coated copper powder was replaced and washed twice with a small amount of anhydrous ethanol, and solid-liquid separation was achieved by natural sedimentation. The silver-coated copper powder was collected and washed once with 30g of ethanol to remove as much residual excess ethanol and treatment agent as possible. After drying in a forced-air oven at 50℃ for 2.5 hours, the finished silver-coated copper powder was obtained by passing it through a 600-mesh sieve. It also achieves a complete, uniform, and dense coating, with a silver coating content of 11.2% as determined by titration, making it suitable for high-performance electromagnetic shielding electronic pastes. Product SEM images are shown below. Figure 6 As shown.

[0109] Example 5

[0110] Steps S100, S200, and the annealing process are the same as in Example 2. The oleic acid modification method is replaced by an electron donor / acceptor complex treatment method, as detailed below:

[0111] The crude silver-coated copper powder obtained in the previous step was dispersed in 200g of ethanol solution containing 6.0g of 2-[(2,4-dichlorophenyl)methyl]-1H-benzimidazole (3wt% of copper powder substrate) and stirred at 35~40℃ for 25min. After solid-liquid separation, the copper powder was collected and air-dried at room temperature. Then, at room temperature, the copper powder was added to 150g of anhydrous ethanol solution containing 6.0g of tetramethylp-quinone dimethylane (3wt% of copper powder substrate) with stirring and stirred for 25min to complete solid-liquid separation and collect the silver-coated copper powder. The silver-coated copper powder was replaced and washed twice with a small amount of anhydrous ethanol, and solid-liquid separation was achieved by natural sedimentation. The silver-coated copper powder was collected and washed once with 30g of ethanol to remove excess ethanol and treatment agent. After drying at 50℃ for 2.5 hours, the silver-coated copper powder was passed through a 200-mesh sieve to obtain the finished silver-coated copper powder. The silver content was determined to be 11.1wt% by titration.

[0112] Example 6

[0113] Steps S100, S200, and the annealing process are the same as in Example 2. The oleic acid modification method is replaced by an electron donor / acceptor complex treatment method, as detailed below:

[0114] The crude silver-coated copper powder obtained in the previous step was dispersed in 250g of ethanol solution containing 9.0g of 2-[(2,4-dichlorophenyl)methyl]-1H-benzimidazole (6wt% of copper powder substrate) and stirred at 35~40℃ for 30min. After solid-liquid separation, the copper powder was collected and air-dried at room temperature. Then, at room temperature, the copper powder was added to 250g of anhydrous ethanol solution containing 9.0g of tetramethylp-quinone dimethylane (6wt% of copper powder substrate) with stirring, and stirred and soaked for 30min to complete solid-liquid separation and collect the silver-coated copper powder. The silver-coated copper powder was replaced and washed three times with a small amount of anhydrous ethanol, and solid-liquid separation was achieved by centrifugation sedimentation. The flake-like silver-coated copper powder was collected, and washed twice with 60g of ethanol to remove as much residual excess ethanol and treatment agent as possible. After drying in a forced-air oven at 50℃ for 2.5 hours, the silver-coated copper powder was obtained by passing through a 300-mesh sieve. The silver coating content was determined to be 11.2wt% by titration.

[0115] Example 7

[0116] According to the formulation and operation of Example 1, 150g of granular copper powder (average particle size 20μm) was used as the base material. Following the formulation and operation of Example 1, the material was added at a designed silver coating amount of 8.2wt% (18.8g of silver nitrate for displacement silver coating and 1.9g of silver nitrate for reduction repair silver coating). The stoichiometry of each material was calculated proportionally according to Example 1. This silver-coated copper powder exhibits complete silver coating and excellent high-temperature resistance, with an initial oxidation temperature of 291℃ and a weight gain of only 2.8% at 800℃. Even under low silver coating conditions, it effectively improves oxidation resistance. The silver coating amount was determined to be 8.1wt% by titration.

[0117] Example 8

[0118] Preparation of phosphating solution (phosphide mainly composed of dihydrogen phosphate): Add the following reagents sequentially to 100 mL of deionized water, stir until completely dissolved, and adjust the pH to 3.0~3.5 with dilute phosphoric acid:

[0119] Main film-forming agent: zinc dihydrogen phosphate 8g (80g / L); reducing agent: sodium hypophosphite 2g (20g / L); accelerator: sodium nitrate 0.5g (5g / L); stabilizer: citric acid 0.3g (3g / L);

[0120] 15g of spherical copper-nickel alloy powder (average particle size 5μm) was mechanically washed with 5% dilute sulfuric acid at room temperature for 20min, followed by washing with deionized water until neutral. The spherical copper-nickel alloy powder substrate, after acid pickling to remove the passivation layer, was then added to 50mL of the above phosphating solution. The mixture was mechanically stirred and heated to above 50℃, maintaining the stirring temperature for 30min. The substrate precipitate was collected by natural sedimentation. The supernatant was discarded, and the substrate was washed with deionized water until neutral. No baking was required; the substrate proceeded directly to the next step of activation and reduction silver plating.

[0121] 15g of the sensitized copper-nickel alloy powder substrate was added to 45g of a 4wt% aqueous solution of PVP-K30 and dispersed by rapid mechanical stirring for 15min. Then, an aqueous solution containing 5g of EDTA·2Na·2H2O (5wt%) and an aqueous solution containing 2.5g of glucose (20wt%) were added. The mixture was heated to above 60℃ and mechanically stirred for 60min. Next, a silver ammonia solution containing 4.0g of silver nitrate (20wt%) was added dropwise. After maintaining the temperature for 15min, an aqueous solution containing 3g of isoascorbic acid (10wt%) was added dropwise. After the addition was complete, heating was stopped and stirring continued for 20min. Solid-liquid separation was achieved by centrifugation. The silver-coated copper powder was collected, washed with deionized water until neutral, and finally washed once with 30g of anhydrous ethanol to remove residual ethanol and dispersant. The powder was then vacuum dried at 50℃ for 2 hours. After passing through a 600-mesh sieve, the silver-coated copper-nickel was obtained. The silver content was determined to be 14.8wt% by titration. SEM images of the product are shown below. Figure 9 As shown.

[0122] Example 9

[0123] The substrate was copper nanowires (20-30 nm in diameter, 15-30 μm in length), with a silver coating of 50 wt%. The stoichiometry of all materials was calculated proportionally according to Example 1. The collection of the silver-coated copper nanowires was performed by centrifugation at 4500 rpm for 15 min. The surface treatment agent was stearic acid or octadecylamine; the fourth high-temperature heat treatment was omitted. Other steps were the same as in Example 1. The silver coating was determined to be 49.9 wt% by titration. SEM images of the product are shown below. Figure 10 As shown, the prepared silver-coated copper nanowires exhibit good dispersibility, a uniform and dense silver plating layer, and strong oxidation resistance and conductivity. Silver utilization is high, with only a small amount of free silver nanoparticles. These silver-coated copper nanowires can be well integrated into slurry systems as conductive filler additives, reducing the amount of conductive filler required, lowering costs, and improving conductivity simultaneously.

[0124] Example 10

[0125] The copper powder substrate in Example 1 was replaced with spherical nickel powder particles (average particle size 3μm), and the fourth step of high-temperature heat treatment was omitted, while other ingredients and operations remained unchanged. The silver coating content was determined to be 10.1wt% by titration. SEM images of the product are shown below. Figure 11 As shown in the picture, the actual product is as follows. Figure 12 As shown. By Figure 11 and 12 It can be seen that a complete, uniform and dense coating can also be obtained. Compared with the silver-coated copper powder in Example 1, the surface coating is complete, but it is rougher, has a stronger granular feel, and contains a small number of nickel particles that are not coated with silver.

[0126] Example 11

[0127] The copper powder substrate in Example 1 was replaced with spherical aluminum powder particles (average particle size 42 μm), and the fourth step of high-temperature heat treatment was omitted. Furthermore, step S100 of Example 1 was modified to an acid washing process of the aluminum powder substrate, specifically as follows: the aluminum powder substrate was washed with a 10% glacial acetic acid ethanol solution, and the aluminum powder was dispersed by stirring and ultrasonication (300 W) for 20 min; then stirring and ultrasonication were stopped, and solid-liquid separation was achieved by sedimentation to collect the aluminum powder; the aluminum powder was washed with deionized water until pH neutral, and without drying, it proceeded directly to step S200 of Example 1, with the rest being the same as in Example 1. The silver coating amount was determined to be 10.0 wt% by titration. The results also showed a complete silver coating effect, with a slightly rough coating surface morphology, and a small number of incompletely silvered aluminum powder particles and free nano-silver particles were observed. However, the oxidation resistance of this silver-coated aluminum powder was significantly improved compared to pure aluminum powder: the initial oxidation temperature exceeded 560℃, but the resistance was as high as 1.6 Ω or more, and the conductivity was far inferior to the silver-coated copper powder of Example 1.

[0128] Example 12

[0129] The copper powder substrate in Example 1 was replaced with spherical reduced iron powder (average particle size 50 μm), and the fourth high-temperature heat treatment was omitted, while other ingredients and operations remained unchanged. The silver coating amount was determined to be 10.1 wt% by titration. A complete silver coating effect was still achieved, but the coated surface morphology was rough, with a strong granular feel, and some uncoated or incompletely silvered iron powder particles and free nano-silver particles remained, indicating that the silver source utilization rate needs further improvement. However, the oxidation resistance of this silver-coated iron powder was significantly improved compared to pure reduced iron powder: the initial oxidation temperature exceeded 472℃, but the resistivity was as high as 1.5 Ω, and the conductivity was lower than that of the silver-coated copper powder in Example 1.

[0130] Example 13

[0131] Following the formulation and procedure of Example 1, 150g of near-spherical granular copper powder (average particle size 1.5μm) was used as the base material. According to the formulation and procedure of Example 1, the material was added at a designed silver coating weight of 15.1wt% (35.1g of silver nitrate for displacement silver coating and 5.0g of silver nitrate for reduction repair silver coating). The stoichiometry of each material was calculated proportionally according to Example 1, and the procedure remained unchanged. The silver coating weight was determined to be 15.0wt% by titration. SEM images of the product are shown below. Figure 13 As shown in the picture, the actual product is as follows. Figure 14 As shown. By Figure 13 and 14 It can be seen that a complete, uniform and dense coating can also be obtained, and the properties of the powder are similar to those in Example 1, making it suitable for a variety of low-temperature conductive adhesives and conductive pastes.

[0132] Example 14

[0133] According to the formulation and operation of Example 1, 100g of spherical granular copper powder (average particle size 80μm) was used as the base material. Following the formulation and operation of Example 1, the material was added at a designed silver coating weight of 0.51wt% (0.7g of silver nitrate for displacement silver coating and 0.1g of silver nitrate for reduction repair silver coating). The stoichiometry of each material was calculated proportionally according to Example 1, and the operation remained unchanged. The silver coating weight was determined to be 0.5wt% by titration. This method can obtain a complete and uniform silver plating layer with a thickness of approximately 2nm.

[0134] Comparative Example 1

[0135] After replacement and covering, no restoration or repair is performed. Details are as follows:

[0136] S100, Step 1: Disperse 25g of spherical copper powder with an average particle size of 5μm in 50g of deionized water, stir and ultrasonically disperse for 15min, add an aqueous solution containing 12g of sodium hydroxide (concentration 25wt%) while stirring, heat to 50℃, slowly add an aqueous solution containing 20g of glucose (concentration 15%), continue to slowly heat to 80℃, stir and maintain for 30min; stop stirring and heating, allow to cool naturally, use natural sedimentation to achieve solid-liquid separation, collect the crude sensitized copper powder; wash the copper powder with deionized water until pH neutral, collect the crude sensitized copper powder, and proceed directly to the next step of silver coating without drying.

[0137] S200, Full Replacement Coating: Add the activated copper powder obtained in the previous step to 75g of deionized water, stir and ultrasonically disperse for 5min, add an aqueous solution containing 1g of PVP-K60 dispersant (concentration 4wt%), and continue stirring and dispersing for 20min; then add 5g of tetraethylenepentamine complexing agent, and continue stirring and dispersing for 10min; next, uniformly add an aqueous solution containing 4.3g of silver nitrate (concentration 15wt%) under vigorous stirring. The whole process is carried out at room temperature (10~25℃), and stirring is maintained for 20min after the addition is completed.

[0138] Stop stirring and use centrifugal filtration to achieve solid-liquid separation, collecting the silver-coated copper powder. Wash the silver-coated copper powder with deionized water until the washing liquid is no longer blue and no copper ions are detected. Then, wash the silver-coated copper powder with anhydrous ethanol to remove as much residual moisture as possible: wash three times with anhydrous ethanol, using 20g of anhydrous ethanol each time. Collect the crude silver-coated copper powder, do not dry it, and proceed directly to the next surface treatment step.

[0139] S300. The crude silver-coated copper powder obtained in the previous step is dispersed in 60g of anhydrous ethanol under stirring to obtain an ethanol dispersion of silver-coated copper powder. Stearic acid is used as a surface modifier: specifically, 0.5g of stearic acid is dispersed in 15g of anhydrous ethanol, and then added to the above ethanol dispersion of silver-coated copper powder under stirring. After rapid stirring and uniform dispersion, the temperature is raised to 55℃ and maintained at this temperature with stirring for 22min. Then, stirring and heating are stopped, and the mixture is allowed to cool naturally to room temperature. Solid-liquid separation is achieved by sedimentation or filtration. The silver-coated copper powder is collected, washed once with a small amount of ethanol to remove as much residual excess ethanol and dispersant as possible, and then vacuum dried at 50℃ for 2 hours. Surface modification is then performed. After surface modification, high-temperature annealing treatment—interface alloying heat treatment—is performed on the silver-coated copper powder, with the specific operation the same as in Example 1. After high-temperature annealing, the silver-coated copper powder is passed through a 600-mesh sieve to obtain the finished silver-coated copper powder. The silver content is determined by titration to be 10.1wt%. SEM images of the product are shown below. Figure 15 As shown, there are obviously a few pinhole defects, a few areas on the surface that are not well covered, and the integrity and density of the silver plating layer are not good.

[0140] Comparative Example 2

[0141] The difference from Comparative Example 1 is that the amount of silver nitrate used in both the replacement-coated silver and reduction-remediation methods was 19.2g, while the amount of isoascorbic acid used was changed to 19.2g. Product SEM photos are shown below. Figure 16 As shown, when the proportion of silver nitrate in the replacement portion decreases and the proportion of silver nitrate in the reduction portion increases, although the total silver coating amount remains unchanged (silver content determined by titration is 10.1 wt%), the silver source utilization rate decreases. A large number of nano-silver particles appear outside the copper particles and fail to participate in the formation of the silver plating layer, leading to a deterioration in coating density. This indicates that to obtain a denser silver coating and improve silver source utilization, the proportion of silver nitrate in the replacement portion should be higher than that in the reduction and repair portion, and increasing the silver source proportion in the replacement portion helps to improve silver source utilization.

[0142] Comparative Example 3

[0143] Based on Example 1, the following adjustments were made: the reducing agent glucose for the sensitized copper powder was halved / the sodium hydroxide was halved. Product SEM photos are shown below. Figure 17 As shown, the silver plating layer is loose and porous with poor density, and the powder exhibits poor conductivity, oxidation resistance, and water and oxygen resistance. Some of the nano-silver particles are loosely attached to the surface of the copper substrate particles and do not participate in the formation of a dense coating of the silver plating layer. The silver content was determined to be 10.1 wt% by titration.

[0144] Comparative Example 4

[0145] Based on Example 1, the following adjustments were made: The amount of silver nitrate used for silver replacement coating was 3.8g, and the amount of silver nitrate used for silver reduction and repair coating was 34.9g. The silver coating content was determined by titration to be 10.0%. The product SEM image is shown below. Figure 18 As shown, because the proportion of silver-coated material that is reduced and repaired is much higher than that that that is replaced, a large number of free silver nanoclusters are formed. Not only is the coating integrity poor, but the silver source utilization rate is low and the dispersion is poor.

[0146] Comparative Example 5

[0147] The silver coating amount in Example 1 was adjusted: the amount of silver nitrate used for displacement coating was increased to 0.37 g. Everything else remained unchanged. The powder morphology and properties are as follows:

[0148] Only a few scattered silver nanoparticles were found on the surface of the powder particles. EDS spectroscopy showed that the surface area of ​​the copper powder particles was basically uncovered by silver. Figure 19 As shown.

[0149] The initial oxidation temperature was 184.04℃, much lower than that of Basic Example 1 and other examples with silver plating; the weight gain at 800℃ was 12.447%, much higher than that of Basic Example 1 and other examples with silver plating. The silver content was determined to be 0.1 wt% by titration.

[0150] Comparative Example 6

[0151] Before step S100 in Example 1, an acid washing process for the copper powder substrate is added, specifically as follows: the copper powder substrate is washed with a 25% aqueous solution of glacial acetic acid, and the copper powder is dispersed by stirring and ultrasonication at 400W for 30 minutes; then stirring and ultrasonication are stopped, and solid-liquid separation is achieved by sedimentation or filtration to collect the copper powder; the copper powder is washed with deionized water until the pH is neutral, and it proceeds directly to step S100 without drying, the rest being the same as in Example 1. The silver content was determined to be 10.1 wt% by titration.

[0152] Comparative Example 7

[0153] Step S100 was replaced with acid washing of the copper powder substrate using the method of Comparative Example 6, followed by copper powder collection; the remaining operations were the same as in Example 1. The silver coating content was determined to be 10.0 wt% by titration. The silver-coated copper core-shell conductive powder prepared in this comparative example exhibited significantly inferior performance, particularly its oxidation resistance, compared to Example 1. SEM images of the product are shown below. Figure 20 As shown, the appearance and SEM images are significantly different from those of Example 1. The powder surface is rough and the color is yellowish-beige. The silver plating layer of some particles is incomplete, and the density is not as good as that of Example 1. The proportion of free nano-silver particles that are not involved in the coating is relatively high, the silver source utilization rate is not high, and the initial oxidation temperature is 239°C, which is much lower than that of Example 1.

[0154] Comparative Example 8

[0155] In Example 1 (classic example), the silver source was entirely modified to undergo reduction coating, without any coating replacement step. Specifically: S200, Reduction Coating: The sensitized copper powder obtained in the previous step was added to deionized water at 4 times its weight in copper powder. The mixture was stirred and ultrasonically dispersed for 10 minutes. An aqueous solution containing 8.8g of PVP-K30 dispersant (5wt%) was added, and the mixture was stirred and dispersed for another 20 minutes. Then, 45g of tetraethylenepentamine complexing agent was added dropwise, and the mixture was stirred and dispersed for another 10 minutes. Next, an aqueous solution containing 29.6g of antioxidant acid (10wt%) was added dropwise under vigorous stirring, while maintaining stirring. 5 min; then, using a peristaltic pump, uniformly add a silver ammonia solution (concentration 10wt%) containing 38.0 g of silver nitrate, stirring for 25 min after the addition is complete; stop stirring and use natural sedimentation to achieve solid-liquid separation, collecting the crude silver-coated copper powder; wash the powder twice with 400 g of 2wt% glacial acetic acid aqueous solution until the washing liquid is no longer blue, then wash the silver-coated copper powder with deionized water until the washing liquid is no longer blue and no copper ions are detected, and the pH is neutral; then wash the silver-coated copper powder twice with 100 g of anhydrous ethanol to remove moisture from the powder, completing solid-liquid separation by Buchner funnel filtration after each anhydrous ethanol wash. Collect the crude silver-coated copper powder, do not dry it, and proceed directly to the next surface treatment step. S100, S300, and S400 are the same as in Example 1. The silver coating content was determined to be 9.86 wt% by titration. SEM photos of the product are shown below. Figure 21 As shown, the performance of the silver-coated copper core-shell type conductive metal powder prepared in Comparative Example 8 is not as good as that in Example 1. Although the appearance and SEM images are similar to those of Example 1, the surface morphology of the powder is rougher and the color is more pale yellow, indicating that the density of the silver plating layer is not as good as that of Example 1. In addition, free nano-silver particles are present, which leads to a decrease in the utilization rate of the silver source and an initial oxidation temperature of 278°C, which is lower than that of Example 1.

[0156] Comparative Example 9

[0157] The difference from Example 1 is that no surface passivation modification is performed. Everything else is the same as in Example 1.

[0158] The performance of the products from Examples 1-6 and Comparative Example 9 was tested, and the results are shown in Table 1.

[0159] Test method:

[0160] Acid resistance: Immersion in 100% acetic acid until a visible blue color appears;

[0161] Initial oxidation temperature: using a TDG-DSC tester, in an air atmosphere, within the range of 100~900℃, with a heating rate of 10℃ / min;

[0162] Weight gain at 800℃: Using a TDG-DSC tester, in an air atmosphere, within the range of 100~900℃, the heating rate is 10℃ / min.

[0163] Table 1 shows the performance test results of the products from Examples 1-6 and Comparative Example 9.

[0164]

[0165] As shown in Table 1, Comparative Example 9, without surface treatment, has a resistivity of 0.596Ω, an acid resistance of 3.5 minutes, an initial oxidation temperature of 257℃, and a weight gain of 6.9% at 800℃.

[0166] Examples 1-3 of this invention use higher fatty acids or higher fatty amines as surface modifiers, with a resistivity of 0.682-0.975Ω, acid resistance of 5-7 minutes, initial oxidation temperature of 285-302℃, and weight gain of 2.1-2.9% at 800℃. Acid resistance and oxidation resistance are significantly improved, but electrical conductivity is reduced.

[0167] Examples 4-6 involved treating the coated coarse powder with imidazole derivatives and quinone derivatives sequentially. The resistivity was 0.249-0.384 Ω, the acid resistance was 12-18 minutes, the initial oxidation temperature was 315-337℃, and the weight gain at 800℃ was 1.1-1.8%. Compared with Comparative Example 9 and Examples 1-3, Examples 4-6 showed significantly improved conductivity, acid resistance, and oxidation resistance.

Claims

1. A method for preparing silver-coated metal core-shell powder, characterized in that, Includes the following steps: S100. Disperse the core substrate powder evenly in a solvent, pre-activate the matrix metal powder, collect the pre-activated powder, and wash it until neutral. S200. The above pre-activated powder is uniformly dispersed in a solvent, the system is adjusted to alkaline, and in the presence of a complexing agent, the first part of the silver precursor is added to carry out a displacement reaction; the second part of the silver precursor and the reducing agent are then added to obtain the coated coarse powder. S300. The above-mentioned coated coarse powder is subjected to surface passivation modification in sequence to obtain silver-coated metal core-shell powder.

2. The preparation method according to claim 1, characterized in that, The core substrate is selected from copper, nickel, aluminum, iron, or copper-nickel alloy, and the average particle size of the core substrate powder is 0.03μm~80μm; The amount of silver coating on the coarse powder is 0.5~50wt%.

3. The preparation method according to claim 1, characterized in that, In the first part of the silver precursor and the second part of the silver precursor, the mass of silver element undergoing the substitution reaction is not less than the mass of silver element undergoing the reduction reaction, and the mass of silver element in the first part of the silver precursor accounts for more than 50% of the total mass of silver element in the silver precursor.

4. The preparation method according to claim 1, characterized in that, In step S100, the pre-activation treatment method includes reduction or phosphating solution treatment. Among them, the phosphating solution treatment method uses a phosphating system based on dihydrogen phosphate to treat the core substrate; Phosphating systems based on dihydrogen phosphate include zinc dihydrogen phosphate and sodium hypophosphite; The reduction method involves removing the passivation layer on the surface of the core substrate under alkaline conditions. The reagents used in the reduction method are selected from one or more of glucose, fructose, maltose, formaldehyde, ascorbic acid, sodium ascorbate, isoascorbic acid, sodium isoascorbate, citric acid, sodium citrate, tartaric acid, sodium potassium tartrate, formic acid, sodium formate, hydrazine hydrate, sodium borohydride, and potassium borohydride. The amount of the reagent added is 0.2% to 66.7% of the mass of the matrix metal powder.

5. The preparation method according to claim 1, characterized in that, In step S200, the silver precursor is selected from silver nitrate or silver ammonia solution; The complexing agent is selected from one or more of tetraethylenepentamine complexing agent, ammonia, ethanolamine, triethylamine, ethylenediamine, EDTA, disodium EDTA, citric acid, sodium citrate, and sodium potassium tartrate. The molar ratio of the complexing agent to the silver element in the silver precursor is 1~10:

1.

6. The preparation method according to claim 1, characterized in that, In step S200, the reducing agent includes one or more of the following: ascorbic acid, sodium ascorbate, isoascorbic acid, sodium isoascorbate, glucose, trisodium citrate, tartaric acid, sodium tartrate, potassium tartrate, potassium sodium tartrate, sodium hypophosphite, sodium borohydride, hydrazine hydrate, formaldehyde, or sodium formate. The amount of the reducing agent added is 1.0 to 5.0 times the molar amount of silver in the silver precursor in the second part.

7. The preparation method according to claim 1, characterized in that, In step S200, The displacement reaction is carried out at a temperature of 5-40℃ for 15-25 minutes. The reduction reaction is carried out at a temperature of 10~70℃ for 15~20 minutes.

8. The preparation method according to claim 1, characterized in that, The surface passivation modification method in step S300 includes the following: using higher fatty acids or higher fatty amines as surface modifiers; The higher fatty acids include oleic acid or stearic acid; The higher fatty amines include hexadecaneamine or octadecaneamine.

9. The preparation method according to claim 1, characterized in that, The surface passivation modification method in step S300 includes the following: sequentially treating the coated coarse powder with imidazole derivatives and quinone derivatives; The amount of imidazole derivatives used is 0.5~6 wt% of the core substrate powder; the amount of quinone derivatives used is 0.5~6 wt% of the core substrate powder.

10. The preparation method according to claim 1, characterized in that, In step S300, after surface passivation modification, annealing treatment can be performed; the annealing treatment includes the following: placing the surface-modified coated coarse powder in an inert atmosphere, maintaining the oxygen content ≤10ppm throughout the process, heating to 180~250℃, and holding at that temperature for 0.5~1.5h.

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