Silver-coated copper powder based on fluidized bed chemical vapor deposition and preparation method thereof

Abstract

The invention relates to the technical field of metal composite material preparation, and particularly discloses silver-coated copper powder based on fluidized bed chemical vapor deposition and a preparation method thereof.The preparation method comprises the steps that in-situ reduction of the copper powder is conducted, specifically, in-situ reduction activation is conducted on the copper powder in a fluidized bed reactor, the oxygen content of the copper powder is reduced to 500 ppm or below, and a clean surface is obtained; and silver layer vapor deposition coating is conducted, specifically, the gaseous silver precursor is introduced into the fluidized bed reactor, and uniform and compact coating of silver is achieved on the surface of the copper powder in the fluidized state by controlling the deposition rate. The method is a full-gas-phase process, and generation of waste water is fundamentally eradicated. The prepared silver-coated copper powder has the characteristics of continuous and compact silver layer, clean interface and excellent oxidation resistance, is particularly suitable for preparing high-performance and low-cost photovoltaic conductive paste, and effectively promotes cost reduction and efficiency improvement of the photovoltaic industry.

Description

Technical Field

[0001] This invention belongs to the field of metal composite material preparation technology. More specifically, this invention relates to a silver-coated copper powder based on fluidized bed chemical vapor deposition and its preparation method. Background Technology

[0002] The rapid development of the photovoltaic industry has placed extreme demands on the cost control of conductive pastes. Silver powder, due to its irreplaceable conductivity and stability, is a key functional phase in conductive pastes; however, its high cost accounts for more than 50% of the non-silicon cost of solar cells, making it one of the main bottlenecks limiting photovoltaic prices. Against this backdrop, "silver-coated copper powder," which combines the low cost of copper with the excellent surface properties of silver, is considered the most promising solution for achieving "copper substitution for silver" and driving cost reduction and efficiency improvement in the industry.

[0003] However, the large-scale preparation of high-quality silver-coated copper powder faces significant challenges. Copper powder is chemically reactive and readily oxidizes to form a non-conductive oxide layer, rendering it unsuitable for direct application. Currently, the industry primarily relies on liquid-phase chemical methods for large-scale production, including chemical displacement and chemical reduction methods. While these methods are relatively mature, they suffer from the following inherent drawbacks: 1. Severe environmental pollution: The production process generates a large amount of wastewater containing heavy metal ions such as silver and copper, as well as organic complexes. The treatment cost is high, the environmental pressure is enormous, and it goes against the development trend of green manufacturing.

[0004] 2. Difficulty in controlling coating quality: The rapid reaction rate of the liquid phase makes it difficult to precisely control the nucleation and growth process, which can easily lead to uneven and non-dense silver coating, or even problems such as independent nucleation of silver particles or local exposure of copper nuclei, which seriously affect the conductivity, oxidation resistance and long-term reliability of the product.

[0005] 3. Complex process flow: In order to prevent abnormal silver deposition, various dispersants and protective agents are often required, and the subsequent steps are complicated. In addition, the precious silver in the waste liquid needs to be recovered by a complex process, which increases the overall cost and process complexity.

[0006] To avoid the pollution problems associated with liquid-phase methods, the industry has explored gas-phase technologies such as spray pyrolysis. However, these technologies typically suffer from low production capacity and extremely high requirements for controlling the atomization and decomposition processes of precursors, making it difficult to guarantee the uniformity of coating all particles and thus preventing large-scale industrial application. Summary of the Invention

[0007] The primary objective of this invention is to overcome the shortcomings of the prior art and provide a method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition. This method aims to eliminate wastewater pollution generated by traditional liquid-phase chemical methods at the source, and solve the technical problems of uneven and non-dense silver coating by precisely controlling in-situ gas-phase reduction activation and deposition kinetics, thereby achieving the clean, efficient and controllable preparation of high-quality silver-coated copper powder.

[0008] Another objective of this invention is to provide a high-performance silver-coated copper powder prepared by the above method, which has the characteristics of continuous and dense silver layer, clean interface and strong bonding force, and excellent anti-oxidation performance.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition includes the following steps: S1. In-situ reduction of copper powder: Pretreated copper powder with an average particle size D50 of 0.5-5 μm is introduced into a fluidized bed reactor. The air in the fluidized bed reactor is replaced with a carrier gas. The copper powder is in a fluidized state in the carrier gas atmosphere. The fluidized bed reactor is then heated to 300℃-500℃. A mixture of reducing gas and carrier gas is then introduced to carry out the reduction reaction. The oxygen content in the copper powder is reduced to below 500 ppm, and the reduction reaction is then terminated. S2. Silver vapor deposition coating: After S1, the copper powder continues to be fluidized in the carrier gas atmosphere. The temperature of the fluidized bed reactor is adjusted to 90-190°C, and gaseous silver precursor is introduced into the fluidized bed reactor to react with the fluidized copper powder. Then, the supply of gaseous silver precursor is stopped, and the temperature of the fluidized bed reactor is raised to 250-350°C. The fluidized state is maintained for 30-60 minutes in the carrier gas atmosphere to deposit a silver layer on the surface of the copper powder, finally forming silver-coated copper powder.

[0010] Furthermore, in the aforementioned method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition, the gaseous silver precursor is any one of vaporized trimethylphosphonoacetate silver, (1,5-cyclooctadiene) (hexafluoroacetylacetone) silver, or β-diketone silver complex; the gaseous silver precursor is mixed with a carrier gas and transported together, and during the transport process, the transport environment temperature of the gaseous silver precursor is the same as the vaporization temperature, and the volumetric flow rate ratio between the carrier gas and the gaseous silver precursor is 1:20 to 1:2; the carrier gas is any one of nitrogen, argon, or helium.

[0011] Furthermore, in the aforementioned method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition, the volume percentage of the reducing gas in the mixture of reducing gas and carrier gas is not less than 10%, and the reducing gas is any one of hydrogen, carbon monoxide, hydrogen sulfide, methane, and sulfur monoxide.

[0012] Furthermore, in the aforementioned method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition, in S1, the gas velocity of the mixture of reducing gas and carrier gas is 0.2–3 μmf; in S2, the deposition rate of the gaseous silver precursor is 2.0–10 nm / min.

[0013] Furthermore, in the aforementioned method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition, after S2, the formed silver-coated copper powder is in a fluidized state in a carrier gas atmosphere, the isothermal time is not less than 30 minutes, and the gas velocity is 0.2 to 0.5 Ut.

[0014] Furthermore, in the aforementioned method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition, the copper powder in S1 is pretreated by organic acid cleaning and vacuum drying. The pretreatment steps are as follows: 1) Take spherical or near-spherical copper powder with an average particle size D50 of 0.5-5 μm and a purity ≥99.9%; 2) Clean the copper powder obtained in step 1) with a 1%-5% concentration of dilute organic acid solution, then wash with deionized water, and finally perform vacuum drying; the dilute organic acid solution is any one of acetic acid, formic acid, oxalic acid, and citric acid.

[0015] The silver-coated copper powder prepared by the above-mentioned method of preparing silver-coated copper powder based on fluidized bed chemical vapor deposition includes a copper core and a silver layer coated on the copper core. The average thickness of the silver layer is between 50 and 500 nm. After the silver-coated copper powder is subjected to an accelerated aging test of 1000 hours at 85°C and 85% relative humidity, its surface resistivity decay rate is less than 10%.

[0016] Furthermore, in the aforementioned silver-coated copper powder, the tap density of the silver-coated copper powder is not less than 40% of its theoretical density, and its specific surface area increases by no more than 15% compared to the specific surface area of ​​the uncoated copper core.

[0017] Compared with the prior art, the present invention has the following significant advantages: 1. Innovation at the source, achieving green manufacturing: This invention adopts a full gas phase process, completely eliminating water and liquid chemical reagents, and fundamentally solving the problem of heavy metal wastewater pollution generated by traditional liquid phase methods, resulting in huge environmental benefits.

[0018] 2. Excellent coating quality and reliable performance: The antioxidant properties of the prepared silver-coated copper powder are close to those of pure silver powder, indicating that the silver layer is continuous and intact. Oxygen cannot directly contact the copper core at the bottom layer through physical channels. Therefore, the copper core is effectively isolated from the oxidation environment. Moreover, the silver layer will not fall off the copper core under thermal stress, resulting in gaps that expose the copper core. This indicates that the silver layer has high density and that the interface between the silver layer and the copper core is strong and clean.

[0019] 3. Strong process controllability and easy scale-up: This invention establishes precise control windows for key parameters such as reduction temperature / atmosphere, deposition rate, and precursor concentration, resulting in good process repeatability and stable product quality, laying a solid foundation for large-scale industrial production. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of a method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition, as described in this invention.

[0021] Figure 2 This is a schematic diagram of the reaction system used to prepare silver-coated copper powder. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] When implementing the preparation method of silver-coated copper powder based on fluidized bed chemical vapor deposition described in this invention, a corresponding reaction system is required, such as... Figure 2 As shown, the system includes: a fluidized bed reactor 1, an evaporator 2, a reducing gas storage tank 3, a carrier gas storage tank 4, and a tail gas treatment device 5. Each of the evaporator 2, reducing gas storage tank 3, and carrier gas storage tank 4 is equipped with an independently controlled mass flow meter and valve. The carrier gas storage tank 4 is connected to the evaporator 2. The evaporator 2, reducing gas storage tank 3, and carrier gas storage tank 4 are connected to a main pipe 6, which extends to the bottom of the fluidized bed reactor 1. A heating tape (not shown in the diagram) is installed on the main pipe 6 located outside the fluidized bed reactor 1. The heating cable ensures that the temperature of the main pipe 6 located outside the fluidized bed reactor 1 is the same as or close to the temperature of the evaporator 2. An electric heating furnace 11 and thermocouples 12 are spaced apart and arranged around the outside of the fluidized bed reactor 1. The exhaust gas treatment device 5 includes a cooler 51, a filter 52, a buffer tank 53, and a liquid seal tank 54 connected in sequence. An electric incinerator 55 is connected after the liquid seal tank 54. The exhaust gas treatment device 5 filters the exhaust gas generated during the preparation process before discharging it, reducing air pollution. In use, opening the top cover of the fluidized bed reactor 1 allows copper powder to be poured into it. Then, the carrier gas storage tank 4 introduces carrier gas into the fluidized bed reactor 1 for displacement, keeping the copper powder in a fluidized state.

[0024] The gaseous silver precursor produced by evaporator 2 is any one of vaporized trimethylphosphonoacetate silver, (1,5-cyclooctadiene) (hexafluoroacetylacetone) silver, or β-diketone silver complex. The reducing gas provided by reducing gas storage tank 3 is any one of hydrogen, carbon monoxide, hydrogen sulfide, methane, or sulfur monoxide. In this embodiment, hydrogen is preferred. The carrier gas provided by carrier gas storage tank 4 is any one of nitrogen, argon, or helium. In this embodiment, nitrogen is preferred.

[0025] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0026] Example 1: A basic process embodiment of the preparation method of silver-coated copper powder based on fluidized bed chemical vapor deposition according to the present invention. S1. Raw Materials and Pretreatment: S1.1 Selection of copper powder: Spherical copper powder with an average particle size D50 of 1.5μm and a purity ≥99.9%; S1.2 Pretreatment: Take 100g of the above copper powder, soak and wash it in 2% dilute acetic acid solution for 10 minutes, wash it with deionized water until neutral, and then vacuum dry it at 100℃ for 3 hours. S2. Equipment and Core Processes: A fluidized bed reactor with a height-to-diameter ratio (H / D) of 5:1 is used, such as... Figure 1 As shown; S2.1 In-situ reduction of copper powder: The pretreated copper powder is loaded into a fluidized bed reactor, and the air in the fluidized bed reactor is replaced with nitrogen until the oxygen content in the fluidized bed reactor is <10ppm. The copper powder is in a fluidized state in a nitrogen atmosphere. Then, the temperature is raised to 400℃ at a heating rate of 10℃ / min. A mixture of nitrogen and hydrogen with a hydrogen integral of 30% is introduced and the gas velocity is controlled at 0.25Umf. Under these conditions, fluidization reduction is carried out for 90 minutes. After reduction, a sample is taken for rapid testing. The oxygen content in the copper powder is reduced to below 280ppm. S2.2 Silver vapor deposition coating: After the reduction reaction is completed, the temperature of fluidized bed reactor 1 is reduced to 180℃, and the fluidizing gas is switched to a mixture of nitrogen and hydrogen with a hydrogen gas integral of 10%, and the gas velocity is increased to 0.5Ut. Trimethylphosphonoacetic acid silver is placed in evaporator 2 and heated to 180℃ for vaporization. The temperature of main pipe 6 is controlled at 180℃. The gaseous trimethylphosphonoacetic acid silver is mixed with nitrogen and then introduced into fluidized bed reactor 1 for deposition. The silver layer deposition rate is 2.0nm / min, and the reaction lasts for 60 minutes. Then the supply of gaseous trimethylphosphonoacetic acid silver is stopped, and the temperature of fluidized bed reactor 1 is raised to 300℃. The fluidization state is maintained for 30-60 minutes under a nitrogen atmosphere. At high temperature, the gaseous trimethylphosphonoacetic acid silver coated on copper powder decomposes and deposits a silver layer on the surface of copper powder, finally forming silver-coated copper powder. The mass ratio of copper to silver is controlled at 5:1, that is, 100g of copper powder requires 20g of silver. The silver content in each gram of trimethylphosphonoacetate can be calculated based on the molecular formula of trimethylphosphonoacetate and the atomic weight of silver. The volume concentration of gaseous trimethylphosphonoacetate in the mixture of gaseous trimethylphosphonoacetate and nitrogen is 0.8%. The vaporization temperature of trimethylphosphonoacetate is between 160℃ and 190℃. During the transportation of the mixture of gaseous trimethylphosphonoacetate and nitrogen, the temperature of the main pipe 6 is controlled at 180℃. The gaseous trimethylphosphonoacetate can enter the fluidized bed reactor 1 under the transportation environment of 180℃. This can prevent the gaseous trimethylphosphonoacetate from condensing and solidifying at low temperature and blocking the pipeline due to excessively low temperature, and also prevent the gaseous trimethylphosphonoacetate from decomposing at high temperature and blocking the pipeline due to excessively high temperature. S3. Post-processing of the product: After the reaction is completed, the supply of gaseous trimethylphosphonosilver acetate is stopped. The silver-coated copper powder formed continues to be fluidized in a nitrogen atmosphere for 30 minutes. During this period, the temperature of fluidized bed reactor 1 remains unchanged. Finally, it is cooled to room temperature under nitrogen protection and the product is collected and recorded as sample A.

[0027] Example 2: The preparation method of silver-coated copper powder based on fluidized bed chemical vapor deposition described in this invention is used in a low-temperature, low-speed deposition example. This embodiment aims to explore the feasibility of obtaining high-quality silver layers at lower temperatures and deposition rates.

[0028] S1. Raw materials and pretreatment: Same as in Example 1; S2. Equipment and core processes: Same as in Example 1; S2.1 In-situ reduction of copper powder: The process is the same as in Example 1, and the oxygen content in the copper powder after reduction is 310 ppm; S2.2 Silver vapor deposition coating: After the reduction reaction, the temperature of the fluidized bed reactor was lowered to 110℃; the fluidizing gas was switched to a mixture of nitrogen and hydrogen with a hydrogen volume concentration of 5% and a gas velocity of 0.45 Ut. The β-diketone silver complex was placed in evaporator 2 and vaporized at 110℃. The temperature of the main pipe 6 was controlled at 110℃. The gaseous β-diketone silver complex was mixed with nitrogen and then introduced into the fluidized bed reactor 1 for deposition. The silver layer deposition rate was 1.0 nm / min, and the reaction lasted for 120 minutes. The supply of gaseous β-diketone silver complex was stopped, and the fluidized bed reactor 1 was heated to 300℃. The fluidization process was maintained for 30–60 min under a nitrogen atmosphere. At this high temperature, the gaseous β-diketone silver complex coated on the copper powder decomposed, depositing a silver layer on the copper powder surface, ultimately forming silver-coated copper powder. The mass ratio of copper to silver was controlled at 5:1, and the volume concentration of the gaseous β-diketone silver complex in the mixture of gaseous β-diketone silver complex and nitrogen was 0.4%. The vaporization temperature of the β-diketone silver complex was between 100℃ and 120℃. S3. Post-processing of the product: Same as in Example 1, collect the product and record it as sample B.

[0029] Example 3: The preparation method of silver-coated copper powder based on fluidized bed chemical vapor deposition described in this invention is used for coating highly active ultrafine powders. This embodiment demonstrates the adaptability of the method to ultrafine copper powder, which is more difficult to coat.

[0030] S1. Raw materials and pretreatment: Ultrafine spherical copper powder with an average particle size D50 of 0.8 μm, pretreated in the same way as in Example 1; S2. Equipment and core processes: Fluidized bed reactor 1 with a height-to-diameter ratio (H / D) of 8:1 is used to improve fluidization quality; S2.1 In-situ reduction of copper powder: The reduction temperature is increased to 450℃, the volume concentration of hydrogen in the mixed gas of hydrogen and nitrogen is increased to 50%, the reduction time is extended to 120 minutes, and the oxygen content in the copper powder after reduction is reduced to 150ppm. S2.2 Silver vapor deposition coating: The deposition temperature was 90℃. (1,5-cyclooctadiene)(hexafluoroacetylacetone) silver was used as the silver precursor, vaporized at 90℃, with a deposition rate stabilized at 1.5 nm / min. The reaction was carried out for 80 minutes, after which the supply of gaseous (1,5-cyclooctadiene)(hexafluoroacetylacetone) silver was stopped, and the fluidized bed reactor 1 was heated to 300℃. The fluidization state was maintained for 30–60 minutes under a nitrogen atmosphere. At this high temperature, the coating was applied to copper... The gaseous (1,5-cyclooctadiene)(hexafluoroacetylacetone) silver on the powder decomposes and deposits a silver layer on the surface of the copper powder, eventually forming silver-coated copper powder; the mass ratio of copper to silver is controlled at 5:1, the volume concentration of gaseous (1,5-cyclooctadiene)(hexafluoroacetylacetone) silver in the mixture of gaseous (1,5-cyclooctadiene)(hexafluoroacetylacetone) silver and nitrogen is 0.6%; the vaporization temperature of (1,5-cyclooctadiene)(hexafluoroacetylacetone) silver is between 90℃ and 120℃; S3. Post-processing of the product: Same as in Example 1, collect the product and record it as sample C.

[0031] The tap density of the silver-coated copper powder produced in Examples 1-3 is no less than 40% of its theoretical density (the theoretical density is the density of a fully dense material calculated based on the silver and copper composition ratio and an ideal crystal structure), and the specific surface area of ​​the silver-coated copper powder prepared in the three examples increases by no more than 15% compared to the specific surface area of ​​the uncoated copper core. By controlling the increase in tap density and specific surface area, the following advantages can be obtained: (1) Ensure processing performance: Sufficient tap density means good powder flowability and high filling capacity, which facilitates automated production; The specific surface area is not increased excessively (i.e., not exceeding 15%), which avoids the powder from agglomerating severely due to excessively high surface energy, affecting dispersibility and slurry stability.

[0032] (2) Controlling the coating quality: The tapped density meets the standard, the silver layer is not too thick or forms loose adhesion, and the coating layer is dense; The increase in specific surface area is small, the silver layer is uniform and complete, and there is no surface roughening caused by non-uniform deposition or corrosion.

[0033] (3) Optimize material properties: In the electronics field (such as conductive adhesives and electromagnetic shielding coatings), a uniform silver layer can ensure excellent conductivity and oxidation resistance. During the sintering process, appropriate powder density and surface properties help to form a dense and electrically conductive final product.

[0034] (4) Process monitoring standards: Tap density and specific surface area increase can be used as quality control parameters in the production process.

[0035] Comparative Example 1: Traditional Chemical Displacement Method Preparation process: Take 100g of copper powder of the same specifications as in Example 1, disperse it in 2000L of deionized water, add 1kg of polyvinylpyrrolidone, and mechanically stir under nitrogen protection. Add silver nitrate solution and reducing agent solution dropwise in parallel, control the reaction temperature at 50℃ and pH=4.5, and react for 1 hour. After the reaction is completed, filter, wash five times, and vacuum dry at 80℃ for 12 hours to obtain the product, which is denoted as sample D.

[0036] Comparative Example 2: FBCVD process without in-situ reduction Preparation process: Except for omitting the in-situ reduction and activation step, the other process parameters are exactly the same as in Example 1. That is, after copper powder pretreatment, the temperature is directly raised to 300°C under nitrogen protection, and then gaseous trimethylphosphonosilver acetate is introduced for deposition to obtain the product, which is denoted as sample E.

[0037] Performance Testing and Comparative Analysis The products obtained from the embodiments and comparative examples of the present invention were systematically tested, and the results are as follows:

[0038] Average silver layer thickness test: Selection of silver dissolving solution: Use a chemical solution that dissolves only the surface plating (silver layer) but does not corrode the underlying substrate (copper powder). In this embodiment, a nitric acid-sulfuric acid mixture is preferred. The nitric acid-sulfuric acid mixture can quickly dissolve the silver layer, while the corrosion of the copper powder is relatively slow. By controlling the concentration, temperature and soaking time, the corrosion of the copper substrate can be minimized. Then, the mass of the silver layer is calculated by the mass difference before and after dissolution, and the thickness is then calculated.

[0039] Experimental steps: Weigh the initial mass of the sample, m1; prepare the concentration of the silver dissolving solution; immerse the sample in the silver dissolving solution, controlling the time to avoid corroding the copper powder; after cleaning and drying, weigh to obtain the remaining mass, m2; finally, calculate the average thickness: δ=(m1-m2) / (ρ·A). ρ is the density of pure silver, approximately 10.49 g / cm³ (at 20°C). Note: The actual density of the electroplated silver layer may be slightly lower than the theoretical value (due to impurities or porosity), but for general quality control, the theoretical value is sufficiently accurate. A is the total area of ​​the sample surface covered by the silver layer. The concentration of the silver dissolving solution and the immersion time of the sample are within the range of fine-tuning based on conventional knowledge by those skilled in the art when applying this invention.

[0040] The test of tap density of silver-coated copper powder mainly follows the national standard GB / T 5162-2006 "Determination of tap density of metal powder".

[0041] The preparation method of silver-coated copper powder based on fluidized bed chemical vapor deposition described in this invention has the following beneficial effects: 1. Coating quality: The antioxidant properties of the products (A, B, C) in the embodiments of the present invention are close to those of pure silver powder, indicating that the silver layer is continuous and intact. Oxygen cannot directly contact the copper core in the bottom layer through physical channels. Therefore, the copper core is effectively isolated from the oxidation environment. Moreover, the silver layer will not fall off the copper core under thermal stress, resulting in gaps that expose the copper core. This indicates that the silver layer has high density and the interface between the silver layer and the copper core is strong and clean.

[0042] 2. Interface and stability: The interface of the product of this invention is clean and free of oxidation, which is in stark contrast to Comparative Example 2 (E), directly resulting in its extremely excellent antioxidant stability (attenuation rate after aging <8%), which is far superior to Comparative Example 1 (D, 45%) and Comparative Example 2 (E, 68%).

[0043] 3. Environmental protection and efficiency: The method of this invention completely achieves zero wastewater discharge, and the process flow is compact, and the production cycle is greatly shortened.

[0044] 4. Technical universality: Examples 1 to 3 demonstrate that this method can be adapted to copper powders of different particle sizes by adjusting parameters, and has good process universality and scalability.

[0045] The method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition described in this invention successfully solves the pollution and quality bottlenecks of traditional methods. It is a green, efficient, and high-performance silver-coated copper powder preparation technology with great prospects for industrial application.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition, characterized in that, Includes the following steps: S1. In-situ reduction of copper powder: Pretreated copper powder with an average particle size D50 of 0.5-5 μm is introduced into a fluidized bed reactor. The air in the fluidized bed reactor is replaced with a carrier gas. The copper powder is in a fluidized state in the carrier gas atmosphere. The fluidized bed reactor is then heated to 300℃-500℃. A mixture of reducing gas and carrier gas is then introduced to carry out the reduction reaction. The oxygen content in the copper powder is reduced to below 500 ppm, and the reduction reaction is then terminated. S2. Silver vapor deposition coating: After S1, the copper powder continues to be fluidized in the carrier gas atmosphere. The temperature of the fluidized bed reactor is adjusted to 90-190°C, and gaseous silver precursor is introduced into the fluidized bed reactor to react with the fluidized copper powder. Then, the supply of gaseous silver precursor is stopped, and the temperature of the fluidized bed reactor is raised to 250-350°C. The fluidized state is maintained for 30-60 minutes in the carrier gas atmosphere to deposit a silver layer on the surface of the copper powder, finally forming silver-coated copper powder.

2. The method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition according to claim 1, characterized in that, The gaseous silver precursor is any one of vaporized trimethylphosphonoacetate silver, (1,5-cyclooctadiene)(hexafluoroacetylacetone) silver, or β-diketone silver complex; the gaseous silver precursor is mixed with a carrier gas and transported together, and during the transport process, the transport environment temperature of the gaseous silver precursor is the same as the vaporization temperature, and the volumetric flow rate ratio between the carrier gas and the gaseous silver precursor is 1:20 to 1:2; the carrier gas is any one of nitrogen, argon, or helium.

3. The method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition according to claim 2, characterized in that, In the mixture of reducing gas and carrier gas, the volume percentage of reducing gas is not less than 10%, and the reducing gas is any one of hydrogen, carbon monoxide, hydrogen sulfide, methane, and sulfur monoxide.

4. The method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition according to claim 1, characterized in that, In S1, the gas velocity of the mixture of reducing gas and carrier gas is 0.2–3 Umf; in S2, the deposition rate of gaseous silver precursor is 2.0–10 nm / min.

5. The method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition according to claim 1, characterized in that, After S2, the formed silver-coated copper powder is in a fluidized state in the carrier gas atmosphere, with a constant temperature time of not less than 30 minutes and a gas velocity of 0.2 to 0.5 Ut.

6. The method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition according to claim 1, characterized in that, The copper powder in S1 is pretreated by organic acid cleaning and vacuum drying. The pretreatment steps are as follows: 1) Take spherical or near-spherical copper powder with an average particle size D50 of 0.5-5 μm and a purity ≥99.9%; 2) Clean the copper powder in step 1) with a 1%-5% concentration of dilute organic acid solution, then wash with deionized water, and finally vacuum dry; the dilute organic acid solution is any one of acetic acid, formic acid, oxalic acid, and citric acid.

7. The silver-coated copper powder prepared by the method for preparing silver-coated copper powder based on fluidized bed chemical vapor deposition according to any one of claims 1 to 6, characterized in that, It includes a copper core and a silver layer covering the copper core, the thickness of which is 50-500 nm; at the interface between the silver layer and the copper core, the copper element exists in the form of elemental copper; after the silver-coated copper powder is subjected to an accelerated aging test of 1000 hours at 85°C and 85% relative humidity, its surface resistivity decay rate is less than 10%.

8. The silver-coated copper powder according to claim 7, characterized in that, The tap density of the silver-coated copper powder is not less than 40% of its theoretical density, and its specific surface area increases by no more than 15% compared to the specific surface area of ​​the uncoated copper core.

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