A method for preparing low-oxygen-content copper powder based on in-situ reduction

Abstract

This invention provides a method for preparing low-oxygen copper powder based on in-situ reduction, comprising the following steps: Step 1: Melting electrolytic copper ingots in a smelting furnace, then adding copper-boron alloy ingots to melt, obtaining molten copper; Step 2: Plating nickel plating solution in a powder collection bin at the bottom of an atomization chamber, the nickel plating solution comprising nickel sulfate, sodium hypophosphite, buffer, complexing agent, and surfactant, with a pH of 3-6; Step 3: Atomizing the molten copper from Step 1 into powder; Step 4: Placing the powder from Step 3 into the nickel plating solution in the powder collection bin from Step 2, reacting for a certain time, then filtering, vacuum drying, and crushing to obtain nickel-plated copper powder; Step 5: Placing the nickel-plated copper powder from Step 4 into a vacuum atmosphere furnace, evacuating, and heat-treating; Step 6: Sieving the heat-treated powder from Step 5 to obtain copper powder with high sphericity and low oxygen content. The copper powder of this invention has high sphericity, good flowability, and an oxygen content ≤50ppm. After 10 days of storage, the oxygen content can still be maintained below 100ppm.

Description

Technical Field

[0001] This invention relates to the fields of powder metallurgy and additive manufacturing technology, and more specifically, to a method for preparing low-oxygen-content copper powder based on in-situ reduction. Background Technology

[0002] Copper and copper-based composite materials have ultra-high electrical and thermal conductivity and good ductility, and are widely used in aerospace, electronic packaging, thermal management, catalysts and other fields. Powder metallurgy and additive manufacturing are among the main preparation methods for copper and copper-based composite materials. With the rapid development of technology, more stringent requirements are being placed on the sphericity and oxygen content of copper powder.

[0003] Copper powder preparation mainly utilizes gas atomization, water atomization, and liquid-phase reduction methods, but these methods generally suffer from high oxygen content. High-oxygen-content copper powder easily forms copper oxide inclusions during powder metallurgy or 3D printing, leading to low density, significantly reduced electrical / thermal conductivity, and low yield. According to the national standard GB / T 41882, the oxygen content of oxygen-free copper powder for 3D printing must be ≤500ppm. For high electrical / thermal conductivity applications, such as high-conductivity oxygen-free copper and high-thermal-conductivity diamond copper, the oxygen content must be ≤100ppm.

[0004] Patent CN108360024A discloses a method for preparing copper powder for 3D printing. Copper salt is dissolved in an aqueous sulfuric acid solution, protected by a non-oxidizing gas, and then electrolyzed to obtain copper powder with a particle size of 3-5 μm and an oxygen content of 375 ppm. Patent CN113134614A discloses a method for preparing low-oxygen spherical injection molding copper powder. The method involves heating copper material to melt under an inert atmosphere, adding deoxidizing agent charcoal powder and calcium carbide to purify the copper liquid, and then atomizing and sieving the copper liquid to obtain spherical copper powder with a controllable median diameter of 25-60 μm and an oxygen content of less than 0.2%.

[0005] Furthermore, copper powder is prone to secondary oxidation during storage and transportation; nickel plating can improve its oxidation resistance. Patent CN1988973A discloses a nickel-plated copper powder preparation and its manufacturing method, which involves adding palladium salt to copper powder slurry, using hydrazine as a reducing agent to grow a palladium catalyst on the copper powder surface, and then adding a nickel plating solution to obtain nickel-plated copper powder. Patent CN101733401A discloses a method for preparing nickel-plated copper powder, which involves activating copper powder in hydrochloric acid solution and then chemically plating it in a nickel plating solution to obtain nickel-plated copper powder. Nickel plating on copper powder usually requires activation or sensitization treatment of the copper powder, which can lead to corrosion and contamination, increasing the oxygen content. Summary of the Invention

[0006] In view of this, the present invention aims to propose a method for preparing low-oxygen-content copper powder based on in-situ reduction. By introducing an in-situ reducing agent and coating with a nano-isolation layer, copper powder with high sphericity and low oxygen content is obtained, meeting the requirements of powder metallurgy and additive manufacturing. The low-oxygen-content copper powder based on in-situ reduction described in this invention has high sphericity, good flowability, and an oxygen content ≤50ppm. After standing for 10 days, the oxygen content can still be maintained below 100ppm, making it suitable for the powder metallurgy and additive manufacturing preparation of highly conductive oxygen-free copper and highly thermally conductive diamond copper.

[0007] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0008] A method for preparing low-oxygen-content copper powder based on in-situ reduction includes the following steps:

[0009] Step 1: Heat and melt the electrolytic copper ingot in a smelting furnace, then add copper-boron alloy ingot and melt to obtain molten copper;

[0010] Step 2: Fill the powder collection bucket at the bottom of the atomization chamber with nickel plating solution. The nickel plating solution includes nickel sulfate, sodium hypophosphite, buffer, complexing agent, and surfactant. The pH of the nickel plating solution is 3~6.

[0011] Step 3: Atomize the molten copper from Step 1 into powder;

[0012] Step 4: Drop the powder from Step 3 into the nickel plating solution in the powder collection bucket from Step 2. After reacting for a certain period of time, filter, vacuum dry, and crush to obtain nickel-plated copper powder.

[0013] Step 5: Place the nickel-plated copper powder from Step 4 into a vacuum atmosphere furnace, evacuate the vacuum, and perform heat treatment.

[0014] Step 6: Sieve the powder after heat treatment in step 5 to obtain copper powder with high sphericity and low oxygen content.

[0015] Furthermore, in step one, the boron content in the copper-boron alloy is 1-10%.

[0016] Furthermore, in step one, the melting vacuum degree is ≤50Pa, and the melting temperature is 1200~1500℃.

[0017] Furthermore, in step one, before smelting the electrolytic copper ingots and copper-boron alloy ingots, the electrolytic copper ingots and copper-boron alloy ingots need to be pickled, cleaned, and dried.

[0018] Furthermore, the pickling process uses a sulfuric acid solution with a concentration of 0.5~1.5M, and the pickling time is 3~6 hours.

[0019] Furthermore, in step one, the amount of copper-boron alloy added is determined according to the amount of boron added to the copper powder being 0.005~0.1%.

[0020] Furthermore, in step two, the buffer is one or more of acetic acid-sodium acetate, citric acid-sodium citrate, and potassium hydrogen phthalate.

[0021] Furthermore, in step two, the complexing agent is one or more of boric acid, citric acid, malic acid, succinic acid, and salicylic acid.

[0022] Furthermore, in step two, the surfactant is one or more of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, and ammonium polyacrylate.

[0023] Further, in step two, the concentration of nickel sulfate is 0.01~0.8 mol / L, the concentration of sodium hypophosphite is 0.01~1.5 mol / L, the concentration of buffer is 0.1~1 mol / L, the concentration of complexing agent is 0.1~1 mol / L, and the amount of surfactant is 0.1~5 wt%.

[0024] Furthermore, in step three, the specific steps are as follows: a heating and ultrasonic device is installed at the bottom of the powder collection tank to heat the nickel plating solution to 80~100℃, the ultrasonic device is turned on, and at the same time, the copper liquid in step one is guided to the atomizing nozzle, and low-temperature nitrogen gas is used to impact and break it, atomizing it into fine droplets and solidifying it into powder.

[0025] Furthermore, in step five, the vacuum degree is ≤100Pa, the heat treatment temperature is 300~900℃, and the heat treatment time is 1~10h.

[0026] Compared with existing technologies, the present invention provides a method for preparing low-oxygen copper powder based on in-situ reduction. This method, through a synergistic process of boron doping, in-situ nickel plating, and heat treatment, overcomes the technical bottlenecks of easy oxidation, high oxygen content, poor storage stability, and insufficient conductivity in traditional copper powder preparation processes, and has the following advantages:

[0027] 1) This invention enables precise control of internal oxygen composition, achieving the preparation of copper powder with low oxygen content. This invention constructs a dual internal and external oxygen control system, fundamentally solving the problem of copper powder oxidation. On one hand, boron is introduced into the powder, which reacts with and solidifies oxygen components such as free and adsorbed oxygen within the copper matrix, completely eliminating the oxygen source inside the powder and creating a stable low-oxygen state. On the other hand, a nickel plating layer is constructed on the surface to prevent the intrusion of external oxygen media. After process optimization, the oxygen content of the prepared copper powder is ≤50ppm, effectively avoiding the negative impact of oxygen on the physicochemical properties of copper powder.

[0028] 2) This invention significantly improves the oxidation resistance of powder, enhances stability, and extends service life. Through vacuum or hydrogen atmosphere heat treatment, this invention increases the density of the nickel plating layer on the copper powder surface, effectively sealing easily oxidized sites such as pores and defects on the powder surface, and isolating the copper substrate from external corrosive media such as air and moisture, thus significantly improving the powder's oxidation resistance. After 10 days of storage under normal conditions, the oxygen content of the copper powder can still be stably controlled below 100 ppm, with a small increase in oxygen content and weak performance degradation. This solves the problem of easy secondary oxidation and performance degradation during conventional low-oxygen copper powder storage, greatly improving the product's storage and usage stability.

[0029] 3) The process of this invention has strong synergy, resulting in good consistency in product structure and performance. This invention performs in-situ nickel plating on fresh powder during gas atomization, eliminating the need for activation and sensitization pretreatment processes. This avoids problems such as copper powder agglomeration and oxidation caused by excessive processes, and is more conducive to achieving low oxygen content in the copper powder. Combined with subsequent heat treatment, the final prepared copper powder particles have stable structure and excellent performance consistency. Attached Figure Description

[0030] Figure 1 Scanning electron microscope image of copper powder prepared in Example 1 of the present invention;

[0031] Figure 2 This is a flowchart illustrating the in-situ reduction process for forming low-oxygen-content copper powder according to the present invention. Detailed Implementation

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0033] This invention addresses the technical shortcomings of traditional copper powder, such as high oxygen content, susceptibility to secondary oxidation, and poor powder stability. It innovatively designs an integrated preparation process combining boron doping in-situ reduction, gas atomization in-situ nickel plating, and heat treatment densification. First, boron doping is used to perform in-situ reduction within the copper powder, achieving precise control of oxygen content. This invention achieves boron doping during the alloy smelting stage. Boron acts as an oxygen absorber, reacting with various oxygen components within the copper powder, including adsorbed and free oxygen, at high temperatures to fix the oxygen element, thus fundamentally deoxidizing and controlling oxygen levels and solving the problem of excessive oxygen content within the copper powder. Second, in-situ nickel plating is performed during gas atomization, avoiding secondary oxidation. This invention overcomes the drawbacks of traditional copper powder processes that involve first preparing the powder, then activating it, and finally plating it. Utilizing the high surface activity of the fresh powder during gas atomization, the powder falls into the nickel plating solution, completing in-situ nickel plating. This process eliminates the need for activation, sensitization, and other pretreatments, avoiding secondary oxidation of the powder. Third, a dual oxygen control mechanism is constructed, synergistically integrating internal and external processes. This invention establishes a two-way oxygen control system: internal boron deoxidation and oxygen fixation combined with external nickel plating for barrier protection. Internally, the deoxidizing and solidifying effect of boron completely eliminates oxygen components within the copper powder. Externally, the nickel plating layer isolates the powder from external oxidizing media such as air and moisture, improving its oxidation resistance and solving the technical problem of high initial oxygen content and easy secondary oxidation during storage and transportation of traditional copper powder. Finally, through heat treatment, this invention effectively increases the density of the nickel plating layer, sealing micropores in the powder and enhancing its oxidation resistance and structural stability. Furthermore, it further promotes the full reaction of boron with oxygen components in the matrix, completely deoxidizing and reducing the overall oxygen content of the powder. The process flow of this invention is coherent and highly synergistic, effectively reducing the oxygen content in copper powder and improving its oxidation resistance.

[0034] Specifically, such as Figures 1-2 As shown, this invention provides a method for preparing low-oxygen-content copper powder based on in-situ reduction, comprising the following steps:

[0035] Step 1: Pickle the high-purity electrolytic copper ingot and copper-boron alloy ingot, clean and dry them, then put the electrolytic copper ingot into the melting furnace of the gas atomization powder making equipment, draw a vacuum, heat until the copper ingot is completely melted, and then add the copper-boron alloy ingot and melt it completely to obtain molten copper.

[0036] Step 2: Fill the powder collection bin at the bottom of the atomization chamber with nickel plating solution. The nickel plating solution contains nickel sulfate, sodium hypophosphite, buffer, complexing agent, and surfactant. The pH of the nickel plating solution is 3-6.

[0037] Step 3: Install heating and ultrasonic devices at the bottom of the powder collection tank, heat the nickel plating solution to 80~100℃, turn on the ultrasonic device, and at the same time, introduce the copper liquid from Step 1 into the intermediate ladle, guide it to the atomizing nozzle, and use low-temperature nitrogen to impact and break it, atomize it into fine droplets and solidify it into powder.

[0038] Step 4: The powder obtained in Step 3 is dropped into the nickel plating solution in the powder collection bucket in Step 2. After reacting for a certain period of time, it is filtered, vacuum dried, and crushed to obtain nickel-plated copper powder.

[0039] Step 5: Place the nickel-plated copper powder obtained in Step 4 into a vacuum atmosphere furnace, evacuate the vacuum, heat to 300~900℃, and heat treat for 1~10 hours.

[0040] Step 6: Sieve the heat-treated powder to obtain copper powder with high sphericity and low oxygen content and the required particle size.

[0041] Preferably, the ratio of electrolytic copper ingots, copper-boron alloy ingots, and nickel plating solution is 3~6kg:20~60g:40~60L.

[0042] Preferably, in step one, the boron content in the copper-boron alloy is 1-10%, and the amount of copper-boron alloy added is determined according to the amount of boron added to the copper powder being 0.005-0.1%.

[0043] Preferably, in step one, a copper-boron alloy is used to introduce boron into the copper powder. Boron acts as an oxygen absorber, achieving low-oxygen modification of the powder through trace doping, precisely controlling the oxygen content of the copper powder, and avoiding negative impacts on the electrical and thermal conductivity of the copper powder. First, boron can act as a highly efficient oxygen absorber to deoxidize the copper powder. Boron possesses excellent oxygen-loving properties and diffusion capabilities, allowing it to diffuse into the copper powder lattice at high temperatures, effectively capturing adsorbed oxygen and free oxygen components present on the surface and within the matrix of the copper powder, undergoing an oxidation reaction to generate stable boron oxide. Boron oxide exhibits excellent high-temperature thermal stability, not undergoing thermal decomposition or releasing oxygen atoms at high temperatures. Furthermore, boron oxide does not undergo secondary reactions with the copper powder, effectively locking in oxygen elements within the system for a long period, fundamentally inhibiting secondary oxidation of the copper powder and stably maintaining its low-oxygen state. Second, trace amounts of boron and boron oxide doping have no significant negative impact on the electrical and thermal conductivity of the copper powder. Boron atoms have very small atomic radii. When the boron or boron oxide content is controlled at 0.005%~0.1%, it will not significantly damage the lattice integrity, electron transport channels, or phonon conduction paths of the copper matrix. Therefore, copper powder modified with trace amounts of boron can not only achieve low oxygen content but also maintain excellent electrical and thermal conductivity.

[0044] Preferably, in step one, the vacuum degree is ≤50Pa and the melting temperature is 1200~1500℃.

[0045] Preferably, in step two, a nickel plating solution is pre-placed in the powder collection bin at the bottom of the atomization chamber. This enables in-situ surface nickel plating modification of the copper powder after atomization, fundamentally solving the technical problem of easy oxidation of ultrafine copper powder and simplifying the powder surface pretreatment process. Firstly, in-situ coating modification effectively prevents copper powder oxidation. After the molten copper is atomized, broken, and cooled to form copper powder, it can be directly immersed in the nickel plating solution in the powder collection bin. A uniform and dense metallic nickel coating layer is rapidly generated on the surface of the copper powder particles through a liquid-phase deposition mechanism. This nickel layer acts as a physical barrier, isolating the copper powder from contact with oxidizing media such as air and water vapor, effectively inhibiting oxidation and corrosion reactions on the surface of the copper particles, and maximizing the preservation of the copper powder's high electrical and thermal conductivity. Secondly, the high activity of the powder surface eliminates the need for pretreatment activation and sensitization processes. During the atomization process, the copper powder undergoes a dynamic process of melting, breaking, and rapid solidification. The newly formed powder surface contains numerous lattice defects, dangling bonds, and highly active sites, exhibiting extremely strong reactivity. Compared to conventional copper powder, atomized new copper powder can react directly with nickel plating solution without the need for traditional surface pretreatment processes such as acid washing, activation, and sensitization. It directly and uniformly deposits a nickel layer on the surface of the copper powder, which simplifies the surface pretreatment process, reduces losses, avoids corrosion and contamination of the copper powder during the surface pretreatment process, and ensures the purity of the coated powder.

[0046] Preferably, in step two, the concentration of nickel sulfate is 0.01~0.8 mol / L and the concentration of sodium hypophosphite is 0.01~1.5 mol / L.

[0047] Preferably, in step two, the buffer is any one of acetic acid-sodium acetate, citric acid-sodium citrate, or potassium hydrogen phthalate, with a concentration of 0.1~1 mol / L, and the pH of the plating solution is adjusted to 3~6 using acetic acid or citric acid.

[0048] Preferably, in step two, the complexing agent is any one of boric acid, citric acid, malic acid, succinic acid, and salicylic acid, with a concentration of 0.1~1 mol / L.

[0049] Preferably, in step two, the surfactant is any one of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, and ammonium polyacrylate, and the amount used is 0.1~5wt%.

[0050] Preferably, in step three, the heating device is installed at the bottom of the powder collecting tank to heat the nickel plating solution. The nickel plating solution needs to be above 80°C to initiate the nickel plating reaction. The ultrasonic device is installed on both sides of the powder collecting tank, with an ultrasonic frequency of 10~50kHz. When the copper powder falls into the nickel plating solution and begins the nickel plating reaction, the ultrasonic device disperses the copper powder, inhibits agglomeration, and improves the uniformity of coating.

[0051] Preferably, in step three, the pressure of the cryogenic nitrogen gas is 3~7 MPa.

[0052] Preferably, in step four, the copper powder falls into the nickel plating solution. Under the catalytic action of the copper powder surface, a nickel plating reaction occurs, achieving in-situ nickel plating coating of the atomized copper powder. This isolates the copper powder from reactions with air and moisture, effectively reducing oxygen content and improving oxidation resistance. This solves the problem of easy secondary oxidation and performance degradation of conventional low-oxygen copper powder during storage, significantly improving the stability of product storage and use. When the copper powder does not fall into the nickel plating solution, the system lacks catalytically active sites and cannot trigger the chemical nickel plating reaction.

[0053] Preferably, in step four, during the atomization process, the surface of the newly formed powder is in a highly active state, and there is no need for traditional pretreatment processes such as acid washing, activation, and sensitization. The nickel layer can be directly and uniformly deposited, which simplifies the process flow and avoids problems such as copper powder agglomeration and exposure oxidation caused by too many processes. It is also more conducive to achieving low oxygen content in copper powder.

[0054] Preferably, in step four, the nickel plating reaction time is 5-60 minutes. If the reaction time is too short, the nickel layer thickness will be too low, making it difficult to form a complete and continuous coating layer, which cannot effectively prevent the copper powder from contacting air and moisture, resulting in insufficient anti-oxidation effect of the powder. If the reaction time is too long, the nickel layer thickness will continue to increase, which will seriously affect the electrical and thermal conductivity of the copper powder itself.

[0055] Preferably, in step four, the drying process for the copper powder is as follows: vacuum degree ≤100Pa, temperature 80~180℃, time 1~24h.

[0056] Preferably, in step four, slight agglomeration may occur during the nickel plating drying process of copper powder, which needs to be broken up to open the agglomerates.

[0057] Preferably, in step five, the heat treatment plays multiple key roles in achieving and maintaining the low-oxygen state of the nickel-plated copper powder. Firstly, heat treatment can densify the nickel plating layer through high-temperature grain recrystallization, improving the microstructure. Nickel plating layers prepared at room temperature often exhibit a loose structure with disordered, finely packed grains, numerous intergranular gaps and micropores, and poor structural integrity. After heat treatment, the grains inside the plating layer grow and fuse, transforming from a loose, fine-grained state to a uniform, continuous, dense, coarse-grained structure. This effectively improves the density and integrity of the plating layer, significantly enhancing its physical barrier and protective properties, and substantially strengthening the overall oxidation and corrosion resistance of the powder, providing a better basic protective barrier for the copper powder matrix. Secondly, during the heat treatment process, the boron element in the plating layer can react with the adsorbed oxygen and free oxygen components of the copper powder, fixing these components and generating boron oxide. This effectively consumes and reduces the internal oxygen components of the copper powder, achieving internal deoxidation and precise control of the oxygen content in the copper powder. Third, the dense nickel plating layer after heat treatment modification can form a long-lasting closed protective structure, which can effectively isolate the corrosion of air, water vapor, etc., prevent the copper substrate from undergoing secondary oxidation, prevent the addition of oxygen impurities to the system, and keep the nickel-plated copper powder in a stable low oxygen content state.

[0058] Preferably, in step five, the vacuum degree is ≤100 Pa. Further, more preferably, it is carried out in a hydrogen atmosphere, where the oxygen content in the copper powder is further reduced by hydrogen reduction during the heat treatment process.

[0059] Preferably, the heat treatment in step five can be omitted in certain applications. For example, in the preparation of diamond copper, the copper powder and diamond powder from step four can be directly mixed and then hot-pressed. During the hot-pressing process, the doped boron element can react with the adsorbed oxygen, free oxygen, and other oxygen components inside the diamond copper to fix them and generate boron oxide, effectively reducing the oxygen content in the diamond copper. This process can achieve a low oxygen content in the final product without step five.

[0060] Preferably, in step six, the final oxygen content of the copper powder is ≤50ppm; after being left for 10 days, the oxygen content is ≤100ppm.

[0061] Example 1

[0062] This embodiment provides a method for preparing low-oxygen-content copper powder based on in-situ reduction, the steps of which are as follows:

[0063] 1) Smelting metal ingots

[0064] Electrolytic copper ingots and copper-boron alloy ingots were placed in a 1M sulfuric acid solution for 5 hours, cleaned, and dried. 5 kg of electrolytic copper ingots were weighed and placed in the melting furnace of an atomizing powder-making device. A vacuum of 30 Pa was applied, and the temperature was raised to 1350℃ to completely melt the copper ingots. Then, 30 g of copper-boron alloy ingots (with a boron content of 5%) were added and completely melted to obtain molten copper.

[0065] 2) Prepare the nickel plating solution

[0066] Prepare a 50L nickel plating solution, containing 0.08 mol / L nickel sulfate and 0.4 mol / L sodium hypophosphite. Use citric acid-sodium citrate as the buffer, with a sodium citrate concentration of 0.2 mol / L. Adjust the pH of the solution to 5 using citric acid. Use boric acid as the complexing agent, with a boric acid concentration of 0.2 mol / L. Use ammonium polyacrylate as the surfactant, added at 1.2 wt%.

[0067] 3) Add nickel plating solution

[0068] The nickel plating solution is poured into the powder collection bin at the bottom of the atomization chamber. The temperature is then raised to 85°C using the heating device at the bottom of the bin. The ultrasonic device on the outside of the powder collection bin is then turned on, with an ultrasonic frequency of 25kHz.

[0069] 4) Atomization powder production

[0070] The molten copper is poured into the tundish and directed to the atomizing nozzle. Simultaneously, low-temperature nitrogen gas is turned on to begin atomization and powder production. The nitrogen pressure is 4.5 MPa, and the diameter of the guide tube used is 3.8 mm.

[0071] 5) Nickel plating

[0072] The copper powder obtained from gas atomization falls into the nickel plating solution in the powder collection tank, where it is dispersed under ultrasonic action. The nickel plating reaction begins at 85℃ under the catalytic action of the highly active copper powder surface, with a reaction time of 20 minutes.

[0073] 6) Drying and crushing

[0074] The obtained nickel-plated copper powder was filtered and then dried in a vacuum drying oven at a vacuum level of ≤100 Pa, a temperature of 120℃, and a drying time of 6 hours. The dried nickel-plated copper powder was then crushed using a crusher.

[0075] 7) Heat treatment

[0076] The nickel-plated copper powder was placed in a vacuum atmosphere furnace, evacuated to 50 Pa, heated to 650 °C, and held for 2 hours.

[0077] 8) Screening

[0078] The heat-treated nickel-plated copper powder was sieved to obtain nickel-plated copper powder with a thickness of 75~150μm.

[0079] 9) Detection

[0080] The energy dispersive spectroscopy (EDS) analysis showed that the nickel content of the copper powder was 0.8%. According to the national standard GB / T 5121.8-2024, the oxygen content of the copper powder was 43 ppm using the inert gas melting-infrared absorption method. After the copper powder was placed at room temperature for 10 days, the oxygen content was 68 ppm.

[0081] Example 2

[0082] This embodiment provides a method for preparing low-oxygen-content copper powder based on in-situ reduction, the steps of which are as follows:

[0083] 1) Smelting metal ingots

[0084] Electrolytic copper ingots and copper-boron alloy ingots were placed in a 1M sulfuric acid solution for 5 hours, cleaned, and dried. 5 kg of electrolytic copper ingots were weighed and placed in the melting furnace of an atomizing powder-making device. A vacuum of 30 Pa was applied, and the temperature was raised to 1350℃ to completely melt the copper ingots. Then, 50 g of copper-boron alloy ingots (8% boron content) were added and completely melted to obtain molten copper.

[0085] 2) Prepare the nickel plating solution

[0086] Prepare a 50L nickel plating solution with nickel sulfate at a concentration of 0.16 mol / L and sodium hypophosphite at a concentration of 0.4 mol / L. Use acetate-sodium acetate as the buffer, with sodium acetate at a concentration of 0.2 mol / L. Adjust the pH of the solution to 4.5 using glacial acetic acid. Use boric acid as the complexing agent, with a concentration of 0.2 mol / L. Use polyvinylpyrrolidone as the surfactant, added at a concentration of 2 wt%.

[0087] 3) Add nickel plating solution

[0088] The nickel plating solution is poured into the powder collection bin at the bottom of the atomization chamber. The temperature is then raised to 85°C using the heating device at the bottom of the bin. The ultrasonic device on the outside of the powder collection bin is then turned on, with an ultrasonic frequency of 32kHz.

[0089] 4) Atomization powder production

[0090] The molten copper is poured into the tundish and directed to the atomizing nozzle. Simultaneously, low-temperature nitrogen gas is turned on to begin atomization and powder production. The nitrogen pressure is 3.5 MPa, and the diameter of the guide tube used is 5 mm.

[0091] 5) Nickel plating

[0092] The copper powder obtained from gas atomization falls into the nickel plating solution in the powder collection tank, where it is dispersed under ultrasonic action. At 85℃, under the catalytic action of the highly active copper powder surface, the nickel plating reaction begins, with a reaction time of 15 minutes.

[0093] 6) Drying and crushing

[0094] The obtained nickel-plated copper powder was filtered and then dried in a vacuum drying oven at a vacuum level of ≤100 Pa, a temperature of 120℃, and a drying time of 6 hours. The dried nickel-plated copper powder was then crushed using a crusher.

[0095] 7) Heat treatment

[0096] The nickel-plated copper powder was placed in a vacuum atmosphere furnace, evacuated to 50 Pa, heated to 800 °C, and held for 2.5 hours.

[0097] 8) Screening

[0098] The heat-treated nickel-plated copper powder was sieved to obtain nickel-plated copper powder with a thickness of 15~53μm.

[0099] 9) Detection

[0100] The energy dispersive spectroscopy (EDS) analysis showed that the nickel content of the copper powder was 2.4%. According to the national standard GB / T 5121.8-2024, the oxygen content of the copper powder was 37 ppm using the inert gas melting-infrared absorption method. After the copper powder was placed at room temperature for 10 days, the oxygen content was 66 ppm.

[0101] Example 3

[0102] This embodiment provides a method for preparing low-oxygen-content copper powder based on in-situ reduction, the steps of which are as follows:

[0103] 1) Smelting metal ingots

[0104] Electrolytic copper ingots and copper-boron alloy ingots were placed in a 1M sulfuric acid solution for 5 hours, cleaned, and dried. 5 kg of electrolytic copper ingots were weighed and placed in the melting furnace of an atomizing powder-making device. A vacuum of 30 Pa was applied, and the temperature was raised to 1350℃ to completely melt the copper ingots. Then, 30 g of copper-boron alloy ingots (with a boron content of 5%) were added and completely melted to obtain molten copper.

[0105] 2) Prepare the nickel plating solution

[0106] Prepare a 50L nickel plating solution, containing 0.10 mol / L nickel sulfate and 0.5 mol / L sodium hypophosphite. Use citric acid-sodium citrate as the buffer, with a sodium citrate concentration of 0.2 mol / L. Adjust the pH of the solution to 5 using citric acid. Use boric acid as the complexing agent, with a boric acid concentration of 0.2 mol / L. Use polyethylene glycol as the surfactant, added at 0.8 wt%.

[0107] 3) Add nickel plating solution

[0108] The nickel plating solution is poured into the powder collection bin at the bottom of the atomization chamber. The temperature is then raised to 85°C using the heating device at the bottom of the bin. The ultrasonic device on the outside of the powder collection bin is then turned on, with an ultrasonic frequency of 35kHz.

[0109] 4) Atomization powder production

[0110] The molten copper is poured into the tundish and directed to the atomizing nozzle. Simultaneously, low-temperature nitrogen gas is turned on to begin atomization and powder production. The nitrogen pressure is 5 MPa, and the diameter of the guide tube used is 5.5 mm.

[0111] 5) Nickel plating

[0112] The copper powder obtained from gas atomization falls into the nickel plating solution in the powder collection tank, where it is dispersed under ultrasonic action. The nickel plating reaction begins at 85℃ under the catalytic action of the highly active copper powder surface, with a reaction time of 10 minutes.

[0113] 6) Drying and crushing

[0114] The obtained nickel-plated copper powder was filtered and then dried in a vacuum drying oven at a vacuum level of ≤100 Pa, a temperature of 150℃, and a drying time of 4 hours. The dried nickel-plated copper powder was then crushed using a crusher.

[0115] 7) Heat treatment

[0116] The nickel-plated copper powder is placed in a vacuum atmosphere furnace, evacuated to 50 Pa, hydrogen is introduced, heated to 500℃, and held for 3 hours.

[0117] 8) Screening

[0118] The heat-treated nickel-plated copper powder was sieved to obtain nickel-plated copper powder with a thickness of 50~100μm.

[0119] 9) Detection

[0120] The energy dispersive spectroscopy (EDS) analysis showed that the nickel content of the copper powder was 1.3%. According to the national standard GB / T 5121.8-2024, the oxygen content of the copper powder was 28 ppm using the inert gas melting-infrared absorption method. After the copper powder was placed at room temperature for 10 days, the oxygen content was 42 ppm.

[0121] Comparative Example 1

[0122] This comparative example provides a method for preparing low-oxygen-content copper powder based on in-situ reduction, the steps of which are as follows:

[0123] 1) Smelting metal ingots

[0124] Electrolytic copper ingots were placed in a 1M sulfuric acid solution for 5 hours, then washed and dried. 5 kg of electrolytic copper ingots were weighed and placed in the melting furnace of an atomizing powder-making device. A vacuum of 30 Pa was applied, and the temperature was raised to 1350℃ to completely melt the copper ingots, yielding molten copper.

[0125] 2) Prepare the nickel plating solution

[0126] Prepare a 50L nickel plating solution, containing 0.08 mol / L nickel sulfate and 0.4 mol / L sodium hypophosphite. Use citric acid-sodium citrate as the buffer, with a sodium citrate concentration of 0.2 mol / L. Adjust the pH of the solution to 5 using citric acid. Use boric acid as the complexing agent, with a boric acid concentration of 0.2 mol / L. Use ammonium polyacrylate as the surfactant, added at 1.2 wt%.

[0127] 3) Add nickel plating solution

[0128] The nickel plating solution is poured into the powder collection bin at the bottom of the atomization chamber. The temperature is then raised to 85°C using the heating device at the bottom of the bin. The ultrasonic device on the outside of the powder collection bin is then turned on, with an ultrasonic frequency of 25kHz.

[0129] 4) Atomization powder production

[0130] The molten copper is poured into the tundish and directed to the atomizing nozzle. Simultaneously, low-temperature nitrogen gas is turned on to begin atomization and powder production. The nitrogen pressure is 4.5 MPa, and the diameter of the guide tube used is 3.8 mm.

[0131] 5) Nickel plating

[0132] The copper powder obtained from gas atomization falls into the nickel plating solution in the powder collection tank, where it is dispersed under ultrasonic action. The nickel plating reaction begins at 85℃ under the catalytic action of the highly active copper powder surface, with a reaction time of 20 minutes.

[0133] 6) Drying and crushing

[0134] The obtained nickel-plated copper powder was filtered and then dried in a vacuum drying oven at a vacuum level of ≤100 Pa, a temperature of 120℃, and a drying time of 6 hours. The dried nickel-plated copper powder was then crushed using a crusher.

[0135] 7) Heat treatment

[0136] The nickel-plated copper powder was placed in a vacuum atmosphere furnace, evacuated to 50 Pa, heated to 650 °C, and held for 2 hours.

[0137] 8) Screening

[0138] The heat-treated nickel-plated copper powder was sieved to obtain nickel-plated copper powder with a thickness of 15~53μm.

[0139] 9) Detection

[0140] The test results showed that the nickel content of the copper powder was 2.6%. According to the national standard GB / T 5121.8-2024, the oxygen content of the copper powder was 522 ppm using the inert gas melting-infrared absorption method. After the copper powder was placed at room temperature for 10 days, the oxygen content was 575 ppm.

[0141] Comparative Example 2

[0142] This comparative example provides a method for preparing low-oxygen-content copper powder based on in-situ reduction, the steps of which are as follows:

[0143] 1) Smelting metal ingots

[0144] Electrolytic copper ingots were placed in a 1M sulfuric acid solution for 5 hours, then washed and dried. 5 kg of electrolytic copper ingots were weighed and placed in the melting furnace of an atomizing powder-making device. A vacuum of 30 Pa was applied, and the temperature was raised to 1350℃ to completely melt the copper ingots, yielding molten copper.

[0145] 2) Atomization powder production

[0146] The molten copper is poured into the tundish and directed to the atomizing nozzle. Simultaneously, low-temperature nitrogen gas is turned on to begin atomization and powder production. The nitrogen pressure is 4.5 MPa, and the diameter of the guide tube used is 3.8 mm.

[0147] 3) Heat treatment

[0148] Copper powder was placed in a vacuum atmosphere furnace, evacuated to 50 Pa, heated to 650℃, and held at that temperature for 2 hours.

[0149] 4) Screening

[0150] The copper powder obtained by atomization was sieved to obtain copper powder with a size of 75~150μm.

[0151] 5) Testing

[0152] According to the national standard GB / T 5121.8-2024, the oxygen content of copper powder was detected to be 373 ppm using the inert gas melting-infrared absorption method. After the copper powder was placed at room temperature for 10 days, the oxygen content was 935 ppm.

[0153] Comparative Example 3

[0154] This comparative example provides a method for preparing low-oxygen-content copper powder based on in-situ reduction, the steps of which are as follows:

[0155] 1) Smelting metal ingots

[0156] Electrolytic copper ingots and copper-boron alloy ingots were placed in a 1M sulfuric acid solution for 5 hours, cleaned, and dried. 5 kg of electrolytic copper ingots were weighed and placed in the melting furnace of an atomizing powder-making device. A vacuum of 30 Pa was applied, and the temperature was raised to 1350℃ to completely melt the copper ingots. Then, 30 g of copper-boron alloy ingots (with a boron content of 5%) were added and completely melted to obtain molten copper.

[0157] 2) Atomization powder production

[0158] The molten copper is poured into the tundish and directed to the atomizing nozzle. Simultaneously, low-temperature nitrogen gas is turned on to begin atomization and powder production. The nitrogen pressure is 4.5 MPa, and the diameter of the guide tube used is 3.8 mm.

[0159] 3) Heat treatment

[0160] Copper powder is placed in a vacuum atmosphere furnace, evacuated to 50 Pa, heated to 650 °C, and held for 2 hours.

[0161] 4) Screening

[0162] The heat-treated copper powder was sieved to obtain copper powder with a particle size of 15~53μm.

[0163] 5) Testing

[0164] According to the national standard GB / T 5121.8-2024, the oxygen content of copper powder was detected to be 86 ppm using the inert gas melting-infrared absorption method. After the copper powder was placed at room temperature for 10 days, the oxygen content was 645 ppm.

[0165] In summary, the core of the copper powder preparation method of this invention lies in the precise control of the oxygen content of copper powder through a synergistic oxygen control technology involving nickel coating, oxygen absorber introduction, in-situ reduction, and heat treatment. First, electrolytic copper ingots and copper-boron alloys are smelted in a specific ratio to introduce boron into the copper matrix. Then, boron-doped copper powder is prepared using gas atomization. During the gas atomization process, the fresh, active copper powder formed by high-temperature atomization is directly immersed in a nickel plating solution, and in-situ nickel plating is completed based on the high activity of the powder surface. After surface coating, the powder undergoes filtration, vacuum drying, and crushing to obtain boron-doped copper powder with a uniform nickel coating. To further optimize the powder performance, it is heat-treated in a vacuum or hydrogen reducing atmosphere. This heat treatment employs a dual oxygen control mechanism: on the powder surface, it effectively densifies the nickel plating layer, sealing surface pores and defects, significantly enhancing the copper powder's oxidation resistance and structural stability; inside the powder, the doped boron reacts with various oxygen components, including adsorbed and free oxygen, achieving oxygen fixation and completely eliminating active oxygen sources within the powder, thus achieving a low-oxygen state. Finally, after grading and sieving, low-oxygen copper powder with the target particle size is obtained. The modified copper powder prepared by this invention has an initial oxygen content controllable below 50 ppm; after 10 days of storage under normal conditions, the oxygen content remains stably below 100 ppm, demonstrating excellent oxidation resistance and storage stability. The powder of this invention can be used for powder metallurgy and additive manufacturing of highly conductive oxygen-free copper and highly thermally conductive diamond copper.

[0166] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing low-oxygen-content copper powder based on in-situ reduction, characterized in that, Includes the following steps: Step 1: Heat and melt the electrolytic copper ingot in a smelting furnace, then add copper-boron alloy ingot and melt to obtain molten copper; Step 2: Fill the powder collection bucket at the bottom of the atomization chamber with nickel plating solution. The nickel plating solution includes nickel sulfate, sodium hypophosphite, buffer, complexing agent, and surfactant. The pH of the nickel plating solution is 3~6. Step 3: Atomize the molten copper from Step 1 into powder; Step 4: Drop the powder from Step 3 into the nickel plating solution in the powder collection bucket from Step 2. After reacting for a certain period of time, filter, vacuum dry, and crush to obtain nickel-plated copper powder. Step 5: Place the nickel-plated copper powder from Step 4 into a vacuum atmosphere furnace, evacuate the vacuum, and perform heat treatment. Step 6: Sieve the powder after heat treatment in step 5 to obtain copper powder with high sphericity and low oxygen content.

2. The preparation method according to claim 1, characterized in that, In step one, the boron content in the copper-boron alloy is 1-10%.

3. The preparation method according to claim 1, characterized in that, In step one, the melting vacuum degree is ≤50Pa and the melting temperature is 1200~1500℃.

4. The preparation method according to claim 1, characterized in that, In step one, before smelting the electrolytic copper ingots and copper-boron alloy ingots, the electrolytic copper ingots and copper-boron alloy ingots need to be pickled, cleaned and dried.

5. The preparation method according to claim 1, characterized in that, In step two, the buffer is one or more of the following: acetic acid-sodium acetate, citric acid-sodium citrate, and potassium hydrogen phthalate.

6. The preparation method according to claim 1, characterized in that, In step two, the complexing agent is one or more of boric acid, citric acid, malic acid, succinic acid, and salicylic acid.

7. The preparation method according to claim 1, characterized in that, In step two, the surfactant is one or more of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, and ammonium polyacrylate.

8. The preparation method according to claim 1, characterized in that, In step two, the concentration of nickel sulfate is 0.01~0.8 mol / L, the concentration of sodium hypophosphite is 0.01~1.5 mol / L, the concentration of buffer is 0.1~1 mol / L, the concentration of complexing agent is 0.1~1 mol / L, and the amount of surfactant is 0.1~5 wt%.

9. The preparation method according to claim 1, characterized in that, In step three, the specific steps are as follows: a heating and ultrasonic device is installed at the bottom of the powder collection tank to heat the nickel plating solution to 80~100℃, the ultrasonic device is turned on, and at the same time, the copper liquid in step one is guided to the atomizing nozzle, and low-temperature nitrogen gas is used to impact and break it, atomizing it into fine droplets and solidifying it into powder.

10. The preparation method according to claim 1, characterized in that, In step five, the vacuum degree is ≤100Pa, the heat treatment temperature is 300~900℃, and the heat treatment time is 1~10h.

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