Nanometer nickel powder with high particle size concentration and preparation method and application thereof

Abstract

This application relates to the field of nanomaterials technology, specifically to a high-particle-size-concentration nickel nanopowder, its preparation method, and its application. The preparation method includes: providing a nickel precursor solution comprising a nickel source and an optional complexing agent, wherein the nickel source comprises nickel ions; providing a reducing solution comprising a reducing agent and an alkaline solution; the molar ratio of the reducing agent to the nickel ions is (0.6-1.8):1; mixing the nickel precursor solution and the reducing solution using a micro-mixer to form initial crystal nuclei; the mixing time is ≤50 milliseconds; ensuring the concentration of the reactants is below the secondary nucleation threshold, and enabling all particles to achieve diffusion-limited synchronous growth in a uniform flow field to obtain nickel nanopowder. This application can improve the particle size concentration and sphericity of nickel nanopowder, and adjust the median particle size of nickel nanopowder within a suitable range, thereby achieving precise control of the particle size of nickel nanopowder.

Description

Technical Field

[0001] This application relates to the field of nanomaterials technology, specifically to a high particle size concentration nano-nickel powder, its preparation method, and its application. Background Technology

[0002] As a key functional material, nickel nanoparticles have broad application prospects in multilayer ceramic capacitors (MLCCs), conductive pastes, high-efficiency catalysts, and magnetic devices due to their unique volume effect, surface effect, high conductivity, ferromagnetism, ductility, and corrosion resistance. With the miniaturization and high-capacitance development of MLCCs, the thickness of the internal electrode layer has evolved from the micrometer level to the submicrometer level and even the nanometer level, which places more stringent requirements on the particle size uniformity of nickel nanoparticles. Summary of the Invention

[0003] This application provides a high particle size concentration nano-nickel powder, its preparation method and application, which can improve the particle size concentration and sphericity of nano-nickel powder, and adjust the median particle size of nano-nickel powder within a suitable range, thereby achieving precise control of nano-nickel powder particle size.

[0004] In a first aspect, this application provides a method for preparing nano-nickel powder, comprising: providing a nickel precursor solution, the nickel precursor solution comprising a nickel source and an optional complexing agent, the nickel source comprising nickel ions; providing a reducing solution, the reducing solution comprising a reducing agent and an alkaline solution; the molar ratio of the reducing agent to nickel ions being (0.6-1.8):1; mixing the nickel precursor solution and the reducing solution using a micro mixer to form initial crystal nuclei; the mixing time being ≤50 milliseconds; ensuring the concentration of the reactants is below the secondary nucleation threshold, and enabling all particles to achieve diffusion-limited synchronous growth in a uniform flow field to obtain nano-nickel powder.

[0005] In some embodiments, the micromixer includes one or more of a microchannel reactor, an impingement flow mixer, a static mixer, and a rotary disc mixer.

[0006] In some embodiments, the step of mixing the nickel precursor solution and the reducing solution using a micro mixer to form an initial crystal nucleus includes: feeding the nickel precursor solution and the reducing solution by pulse injection with an injection time ≤100 milliseconds; and mixing the nickel precursor solution and the reducing solution by ultrasonic cavitation.

[0007] In some embodiments, the step of reducing the concentration of reactants below the secondary nucleation threshold and enabling all particles to achieve diffusion-limited synchronous growth in a uniform flow field to obtain nano-nickel powder includes: controlling the reactant concentration to free Ni²⁺. + The concentration was maintained at 30%-70% of the secondary nucleation threshold.

[0008] In some embodiments, the uniform flow field is achieved by controlling the stirring Reynolds number Re ≥ 10000, or by employing an oscillating flow mixer.

[0009] In some embodiments, the nickel source comprises a nickel salt, which includes one or more of nickel chloride, nickel sulfate, nickel nitrate, and nickel acetate; the concentration of the nickel salt is 0.05 mol / L to 1 mol / L.

[0010] In some embodiments, the reducing agent includes one or more of hydrazine hydrate, sodium borohydride, and potassium borohydride.

[0011] In some embodiments, the alkaline solution includes one or more of ammonia, sodium hydroxide, and potassium hydroxide.

[0012] In some embodiments, the pH of the reducing solution is 11-14.

[0013] In some embodiments, the complexing agent includes one or more of triethanolamine, sodium citrate, and ethylenediaminetetraacetic acid.

[0014] In some embodiments, the molar ratio of the complexing agent to the nickel ions is (0.1-2):1.

[0015] Secondly, this application provides a nano-nickel powder, which is prepared by the preparation method described in the first aspect of this application.

[0016] In some embodiments, the particle size distribution width (D) of the nano-nickel powder max -D min ) / D 50 ≤0.8.

[0017] In some embodiments, the polydispersity index (PDI) of the nano-nickel powder is ≤ 0.1.

[0018] In some embodiments, the sphericity of the nano-nickel powder is ≥0.95.

[0019] In some embodiments, the median diameter D50 of the nickel nanopowder is 50nm-300nm.

[0020] Thirdly, this application provides the application of nano-nickel powder prepared by the preparation method described in the first aspect or the nano-nickel powder described in the second aspect in multilayer ceramic capacitors, conductive pastes, catalysts, and magnetic devices.

[0021] This application provides a narrow-distribution control method for preparation using "transient-limited supersaturation driving and diffusion field homogenization". Initial crystal nuclei are formed by mixing a nickel precursor solution and a reducing solution using a micro-mixer. The mixing time is ≤50 milliseconds, i.e., a millisecond-level micro-mixing system is used. The ultra-high-speed micro-mixer enables instantaneous and uniform mixing of the nickel precursor and reducing agent at the molecular scale, triggering explosive uniform nucleation, allowing all crystal nuclei to be formed simultaneously. The reactant concentration is kept below the secondary nucleation threshold, enabling all particles to achieve diffusion-limited synchronous growth in a uniform flow field. Specifically, a constant reactant concentration control system during the growth stage ensures strictly diffusion-limited synchronous growth of all particles, allowing them to grow at the same rate. Through the synergistic effect of these two steps, all crystal nuclei are formed simultaneously and grow synchronously under completely uniform conditions, resulting in nano-nickel powder with monodispersity reaching the theoretical limit, improving the particle size concentration and sphericity of the nano-nickel powder. By setting the molar ratio of reducing agent to nickel ions to (0.6-1.8):1 and keeping the concentration of reactants below the secondary nucleation threshold, the median particle size of nickel nanopowder can be adjusted within a suitable range, thereby achieving particle size control of nickel nanopowder. Attached Figure Description

[0022] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0023] Figure 1 Flowcharts of preparation methods provided for some embodiments of this application; Figure 2 A schematic diagram illustrating the principle of the preparation method provided in some embodiments of this application; Figure 3 Scanning electron microscope (SEM) images of nickel nanoparticles of different particle sizes prepared in some embodiments of this application; Figure 4 This is a scanning electron microscope image of the nickel nanoparticles prepared in Example 1; Figure 5 The image shows a scanning electron microscope image of the nickel nanoparticles prepared in Example 2. Figure 6 The image shows a scanning electron microscope image of the nickel nanoparticles prepared in Example 3. Figure 7 The image shows a scanning electron microscope image of the nickel nanoparticles prepared in Comparative Example 1. Figure 8 The image shows a scanning electron microscope image of the nickel nanoparticles prepared in Comparative Example 2. Figure 9The image shows a scanning electron microscope image of the nickel nanoparticles prepared in Comparative Example 3. Detailed Implementation

[0024] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of this application.

[0025] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms "comprising" and "having" and any variations thereof in the specification, claims and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0026] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0027] In the description of the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0028] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two).

[0029] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0030] In the process of preparing nano-nickel powder by liquid-phase chemical reduction, achieving ultra-high monodispersity is difficult. The intertwining of uneven mixing of reactants and the nucleation growth process is the fundamental reason for the broadening of the particle size distribution. Specifically, in traditional reactors (such as stirred tanks), the mixing time of the precursor and reducing agent is usually on the order of seconds or even minutes, which is much slower than the intrinsic kinetic rate of the nucleation reaction. This leads to: uneven mixing causing multiple local supersaturated regions in the reaction system; nucleation occurring dispersedly in time and space, resulting in a long nucleation period (usually lasting tens of seconds to several minutes); significant differences in the growth initiation time between the first and later formed nuclei; and huge differences in particle growth rate at different locations due to the inhomogeneity of the diffusion field. The combination of these three factors results in a persistently high polydispersity index (PDI) of the final product, typically with a CV value (coefficient of variation) >20%.

[0031] In related technologies, metal salts (Cu, Pd) that are less reactive than nickel are added as nucleating agents, and a reducing agent is added in batches to try to improve the particle size distribution. However, this method is essentially still a macroscopic reaction control. Although the stepwise addition can partially extend the nucleation window, it cannot fundamentally solve the problems of uneven mixing and asynchronous growth. The particle size distribution control capability is limited, and the process is complex and introduces precious metal impurities.

[0032] Therefore, this application provides a method for preparing nano-nickel powder, such as... Figure 1 As shown, the preparation method includes the following steps: S10: Provide a nickel precursor solution, the nickel precursor solution comprising a nickel source and an optional complexing agent, the nickel source comprising nickel ions; S20: Provide a reducing solution comprising a reducing agent and an alkaline solution; the molar ratio of the reducing agent to nickel ions is (0.6-1.8):1; S30: The nickel precursor solution and the reducing solution are mixed using a micro mixer to form initial crystal nuclei; the mixing time is ≤50 milliseconds; S40: The concentration of reactants is lower than the secondary nucleation threshold, and all particles achieve diffusion-limited synchronous growth in a uniform flow field to obtain nano-nickel powder.

[0033] This application provides a narrow-distribution control method for preparation using "transient-limited supersaturation driving and diffusion field homogenization". Initial crystal nuclei are formed by mixing a nickel precursor solution and a reducing solution using a micro-mixer. The mixing time is ≤50 milliseconds, i.e., a millisecond-level micro-mixing system is used. The ultra-high-speed micro-mixer enables instantaneous and uniform mixing of the nickel precursor and reducing agent at the molecular scale, triggering explosive uniform nucleation, allowing all crystal nuclei to be formed simultaneously. The reactant concentration is kept below the secondary nucleation threshold, enabling all particles to achieve diffusion-limited synchronous growth in a uniform flow field. Specifically, a constant reactant concentration control system during the growth stage ensures strictly diffusion-limited synchronous growth of all particles, allowing them to grow at the same rate. Through the synergistic effect of these two steps, all crystal nuclei are formed simultaneously and grow synchronously under completely uniform conditions, resulting in nano-nickel powder with monodispersity reaching the theoretical limit, improving the particle size concentration and sphericity of the nano-nickel powder. By setting the molar ratio of reducing agent to nickel ions to (0.6-1.8):1 and keeping the concentration of reactants below the secondary nucleation threshold, the median particle size of nickel nanopowder can be adjusted within a suitable range, thereby achieving particle size control of nickel nanopowder.

[0034] Furthermore, the preparation method of this application embodiment uses an all-aqueous reaction system, requiring no organic solvents, no precious metal nucleating agents, and no batch addition of reducing agents, making the process simple and environmentally friendly.

[0035] It should be noted that the above-mentioned "diffusion-restricted synchronous growth" means that all particles grow at the exact same rate. The tiny size differences at the "birth" stage are not amplified during the growth process, but instead remain relatively uniform due to the same growth rate.

[0036] In some embodiments, the nickel precursor solution includes a nickel source and a complexing agent.

[0037] The addition of a complexing agent can further optimize the release kinetics of nickel ions. However, it should be noted that the embodiments of this application do not rely on the complexing agent to achieve particle size control; its role is only to assist in the adjustment.

[0038] In some embodiments, the micromixer includes one or more of a microchannel reactor, an impinging flow mixer, a static mixer, and a rotating disc mixer. The aforementioned micromixers have mature industrial designs, wide process windows, and are easily scaled up.

[0039] In some embodiments, the step of mixing the nickel precursor solution and the reducing solution using a micro-mixer to form initial crystal nuclei includes: feeding the nickel precursor solution and the reducing solution by pulse injection, with an injection time ≤100 milliseconds. This can further enhance the instantaneousness and uniformity of the mixing.

[0040] In some embodiments, the preparation method includes mixing the nickel precursor solution with the reducing solution by ultrasonic cavitation.

[0041] Figure 2 This diagram illustrates the principle of the preparation method provided in some embodiments of this application, showing the nucleation and growth process of the preparation method in the embodiments of the application. Ultrasonic cavitation impingement flow enables rapid molecular-level mixing, overcoming the bottleneck of traditional reaction mass transfer, reducing parameter sensitivity, and enhancing process tolerance. This allows for precise control of the nucleation and growth process, eliminating batch-to-batch differences, and achieving uniform microsphere size within a single batch and across multiple batches.

[0042] In some embodiments, the step of reducing the concentration of reactants below the secondary nucleation threshold and enabling all particles to achieve diffusion-limited synchronous growth in a uniform flow field to obtain nano-nickel powder includes: controlling the reactant concentration to free Ni²⁺. + The concentration is maintained at 30%-70% of the secondary nucleation threshold, for example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any two of the above values.

[0043] Free Ni² in the embodiments of this application + The concentration of Ni² can be monitored in real time using an ion-selective electrode. + A sensitive membrane with a special response converts ion activity into a potential signal.

[0044] By controlling the reactant concentration within the above range, it is possible to achieve the following: no new crystal nuclei can be formed, i.e., no secondary nucleation; the driving force for particle growth is constant and uniquely controlled by Ni². + The diffusion rate from the bulk solution to the particle surface; in a homogeneous flow field created by thorough stirring, the diffusion environment of each particle is highly consistent.

[0045] At the same time, due to Ni² in the solution + The concentration was always kept at a low level, and the solubility difference between large and small particles (Kelvin effect) was insufficient to drive significant Ostwald ripening, further consolidating the narrowing of the particle size distribution.

[0046] In some embodiments, the uniform flow field is achieved by controlling the stirring Reynolds number Re ≥ 10000.

[0047] In some embodiments, the uniform flow field is achieved by employing an oscillating flow mixer.

[0048] This allows for macroscopic uniformity of the flow field within the reactor, and all crystal nuclei grow synchronously under identical and uniquely controlled diffusion rates, completely suppressing secondary nucleation and Ostwald ripening.

[0049] In some embodiments, the step of obtaining nano-nickel powder by making the concentration of reactants below the secondary nucleation threshold and enabling all particles to achieve diffusion-limited synchronous growth in a uniform flow field further includes: separating the solid product, washing and drying it to obtain nano-nickel powder. Exemplarily, the black precipitate is separated by centrifugation or magnetic separation, washed alternately with deionized water and anhydrous ethanol 3-5 times, and vacuum dried at 40℃-60℃ to obtain nano-nickel powder.

[0050] In some embodiments, the total reaction time is 20 min to 60 min, for example, it can be 20 min, 30 min, 40 min, 50 min, 60 min, or any range of two of the above values.

[0051] In some embodiments, the nickel source comprises a nickel salt, which includes one or more of nickel chloride, nickel sulfate, nickel nitrate, and nickel acetate.

[0052] In some embodiments, the concentration of the nickel salt is 0.05 mol / L to 1 mol / L, for example, it can be 0.05 mol / L, 0.07 mol / L, 0.09 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, or any range of two of the above values. By adjusting the concentration of the nickel salt within the above range, and in conjunction with the amount of reducing agent and ensuring that the concentration of the reactants is below the secondary nucleation threshold, the particle size of the nano-nickel powder can be precisely controlled.

[0053] In some embodiments, the reducing agent includes one or more of hydrazine hydrate, sodium borohydride, and potassium borohydride.

[0054] In some embodiments, the alkaline solution includes one or more of ammonia, sodium hydroxide, and potassium hydroxide.

[0055] In some embodiments, the pH value of the reducing solution is 11-14, for example, it can be 11, 11.5, 12, 12.5, 13, 13.5, 14, or a range consisting of any two of the above values.

[0056] In some embodiments, the complexing agent includes one or more of triethanolamine, sodium citrate, and ethylenediaminetetraacetic acid.

[0057] In some embodiments, the molar ratio of the complexing agent to the nickel ions is (0.1-2):1, for example, it can be 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1, or any range of two of the above values.

[0058] This application provides a nano-nickel powder, which is prepared by the above-described preparation method. Figure 3 Scanning electron microscope (SEM) images of nickel nanoparticles of different particle sizes prepared in some embodiments of this application.

[0059] In some embodiments, the particle size distribution width (D) of the nano-nickel powder max -D min ) / D 50 ≤0.8.

[0060] In some embodiments, the polydispersity index (PDI) of the nano-nickel powder is ≤ 0.1.

[0061] In some embodiments, the sphericity of the nickel nanoparticles is ≥0.95. By keeping the concentration of the reactants below the secondary nucleation threshold, i.e., by limiting the growth mode through diffusion, it is beneficial to form a thermodynamically stable spherical morphology, thereby improving the sphericity of the nickel nanoparticles. Spherical nickel nanoparticles (sphericity ≥0.95) have good flowability in slurry, which is conducive to the formation of a dense and uniformly conductive electrode layer, and is crucial to the performance of components such as MLCCs.

[0062] In some embodiments, the median diameter D50 of the nano-nickel powder is 50nm-300nm, for example, it can be 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 150nm, 200nm, 250nm, 300nm, or any range of two of the above values.

[0063] This application presents a novel technology that breaks through the limitations of traditional liquid-phase reduction methods in particle size control, achieving "ultra-high monodispersity" of nano-nickel powder. This meets the stringent uniformity requirements of high-end electronic devices for nano-nickel powder. Nano-nickel powder can be applied in multilayer ceramic capacitors, conductive pastes, catalysts, and magnetic devices, providing a material basis for core internal electrode materials in ultra-high capacitance thin-film MLCCs.

[0064] This application elevates the classic LaMer model (separation of nucleation and growth) from a macroscopic "separation of time sequence" to a microscopic "instantaneous global synchronization." By precisely designing the reactor's fluid dynamics and mass transfer processes, a "instantaneously global homogeneous" extreme reaction microenvironment is created. Through a novel narrow-distribution control process of "transient extreme supersaturation driving" and "diffusion field homogenization," the scientific and engineering challenge of ensuring "absolutely consistent growth history for all particles" at the nanoscale is solved.

[0065] A micro-mixer is employed to achieve molecular-scale, globally homogeneous mixing of the nickel precursor and reducing agent within milliseconds. Compared to the mixing time of several seconds to tens of seconds in traditional stirred tank reactors, the mixing time of this application is shortened by 2-3 orders of magnitude, far exceeding the intrinsic nucleation timescale of the nickel ion reduction reaction. This ensures that when mixing is complete, the supersaturation at all locations in the entire reaction system simultaneously crosses the critical nucleation threshold, triggering an instantaneous (sub-millisecond) "burst" of homogeneous nucleation, with all crystal nuclei being born at the same moment. This design eliminates the "birth time difference" of crystal nuclei from the outset, laying a decisive foundation for subsequent synchronous growth. After millisecond-level mixing, the supersaturation in the entire reaction system simultaneously crosses the critical threshold within a sub-millisecond time, triggering an "burst" of homogeneous nucleation, with all crystal nuclei being born at the same instant.

[0066] After nucleation is complete (usually within 1-5 seconds after mixing), if free reactants remain in the reaction system, secondary nucleation and Ostwald ripening will disrupt the formed monodisperse system. In this embodiment, a uniform and precise feeding technique is used to strictly maintain the reactant concentration at a "subcritical" level slightly below the secondary nucleation threshold after nucleation. Under these conditions: no new nuclei can form (no secondary nucleation); the driving force for particle growth is constant and solely controlled by Ni². + The diffusion rate from the bulk solution to the particle surface; in a homogeneous flow field created by thorough stirring, the diffusion environment of each particle is highly consistent.

[0067] Example The following embodiments describe the contents of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0068] Example 1 Precursor solution preparation: Weigh 23.8 g of NiCl2·6H2O (0.1 mol) and dissolve it in 1000 mL of deionized water to prepare a 0.1 mol / L nickel precursor solution. Add 15 mL of triethanolamine (approximately 1:1 molar ratio with Ni) as an auxiliary complexing agent. Reducing agent solution preparation: Dissolve 5 mL of 80% hydrazine hydrate (approximately 0.08 mol, 0.8:1 molar ratio with Ni) in 500 mL of deionized water and adjust the pH to 12.5 with NaOH.

[0069] Mixing and nucleation: The two solutions are delivered to the microchannel reactor (channel hydraulic diameter 200μm, total length 2m) at the same flow rate (100mL / min each) by metering pumps, and mixing is completed within 20 milliseconds. After mixing, burst nucleation is triggered instantaneously.

[0070] Growth control: After nucleation, the free Ni²⁺ in the reactor is controlled using an online concentration monitoring and feedback control system. + The concentration was maintained at 0.03-0.05 mol / L (approximately 30%-50% of the critical nucleation concentration of 0.1 mol / L). The reactor was equipped with a high-speed stirrer (1200 rpm, Re≈2×10⁻⁶). 4 The reaction temperature was 65℃, and the total reaction time was 30 min. Post-treatment: centrifugation, washing four times alternately with deionized water and anhydrous ethanol, and vacuum drying at 50℃. Product characterization: SEM showed that the particles were perfectly spherical.

[0071] Figure 4 Scanning electron microscope image of the nickel nanoparticles prepared in Example 1. Particle size analysis: D min =70.07nm, D 50 =120.82nm, D max =146.10nm, (D max -D min ) / D 50 =0.62, PDI=0.03.

[0072] Example 2 Precursor solution preparation: Weigh 29.1 g of Ni(NO3)2·6H2O (0.1 mol) and dissolve it in 1000 mL of deionized water to prepare a 0.1 mol / L nickel precursor solution without adding a complexing agent. Reducing agent solution preparation: Dissolve 3.75 mL of 80% hydrazine hydrate (approximately 0.06 mol, molar ratio to Ni 0.6:1) in 500 mL of deionized water and add KOH to adjust the pH to 13.0. Mixing and nucleation: Using an impinging flow mixer, the two solutions collide under high pressure (0.5 MPa), with a pulse injection time of 50 ms and a mixing time ≤10 ms, resulting in instantaneous nucleation. Growth control: Free Ni²⁺... +The concentration was maintained at 50%-70% of the critical nucleation concentration (approximately 0.05-0.07 mol / L), the reaction temperature was 70°C, mass transfer was enhanced using an oscillating flow mixer, and the reaction time was 40 min. Post-treatment: Same as in Example 1.

[0073] Figure 5 Scanning electron microscope image of the nickel nanoparticles prepared in Example 2. Particle size analysis: D min =91.40nm, D 50 =146.13nm, D max =175.45nm, (D max -D min ) / D 50 =0.58, PDI=0.06.

[0074] Example 3 Precursor solution preparation: Weigh 26.3 g of NiSO4·6H2O (0.1 mol) and dissolve it in 2000 mL of deionized water to prepare a 0.05 mol / L nickel precursor solution. Add 8.8 g of sodium citrate (molar ratio to Ni 0.3:1). Reducing agent solution preparation: Dissolve 11.25 mL of 80% hydrazine hydrate (approximately 0.18 mol, molar ratio to Ni 1.8:1) in 1000 mL of deionized water and add NaOH to adjust the pH to 13.5. Mixing and nucleation: Use a rotary disc mixer (3000 rpm) to rapidly spread and mix the two solutions on the disc surface for approximately 5 milliseconds, initiating a supersaturated nucleation explosion. Growth control: Add free Ni²⁺... + The concentration was maintained at 0.01-0.02 mol / L (25%-50% of the critical nucleation concentration of approximately 0.04 mol / L), the reaction temperature was 80℃, and the reaction time was 20 min.

[0075] Figure 6 Scanning electron microscope image of the nickel nanoparticles prepared in Example 3. Product characterization: D min =66nm, D 50 =90nm, D max =112nm, (D max -D min ) / D 50 =0.51, PDI=0.07, sphericity 0.97.

[0076] Comparative Example 1 Except for the following differences, the preparation method of the remaining nano-nickel powder is the same as that in Example 1.

[0077] Mixing and reaction: Place the precursor solution in a 2L stirred tank (400rpm), add the reducing agent solution all at once, mix for about 5-10 seconds, and react at 65℃ for 30min.

[0078] Figure 7 The image shows a scanning electron microscope image of the nickel nanoparticles prepared in Comparative Example 1. Product characterization: D min =108nm, D 50 =450nm, D max =1088nm, (D max -D min ) / D 50 =2.17, PDI=0.34, sphericity 0.85, burst nucleation rate varies, particle size distribution is wide, and there are a large number of small and large particles.

[0079] Comparative Example 2: Mixing method: Same as in Example 1 (microchannel reactor, 20ms mixing). Growth control: No concentration control during the growth stage; allow the reaction to proceed naturally.

[0080] Figure 8 The image shows a scanning electron microscope image of the nickel nanoparticles prepared in Comparative Example 2. Product characterization: D min =109nm, D 50 =203nm, D max =324nm, (D max -D min ) / D 50 =1.06, PDI=0.28. Analysis shows that although the nucleation stage was synchronized, the particle size distribution was still relatively wide due to secondary nucleation and Ostwald ripening during the growth stage.

[0081] Comparative Example 3 Weigh 23.8 g of NiCl2·6H2O (0.1 mol) and dissolve it in 200 ml of deionized water. Add 1.97 mg of copper sulfate pentahydrate (Cu:Ni ≈ 5.0 ppm by mass) and 0.134 mg of palladium(II) ammonium chloride (Pd:Ni ≈ 0.5 ppm by mass), as well as 22.8 g of trisodium citrate as a complexing agent. Separately prepare a mixed reducing agent solution containing 4.2 g of 60% hydrazine hydrate (initial hydrazine:Ni molar ratio of 0.49) and 184 g of NaOH. Heat both solutions to 85 °C and mix them. After 10 min of reaction, add 18.7 g of hydrazine hydrate at a rate of 4.6 g / min (additional hydrazine:Ni molar ratio of 2.19).

[0082] Figure 9 The image shows a scanning electron microscope image of the nickel nanoparticles prepared in Comparative Example 3. Product characterization: D min =239nm, D 50 =322nm, D max =473nm, (D max -D min ) / D50 =0.73, but the sphericity of the particles is poor, and a lot of non-spherical particles are generated, indicating that nucleation and growth are not uniform. At the same time, the core problem of this method is that the nucleation and growth are not clearly separated due to the complex process and the segmented addition of reducing agent, resulting in secondary nucleation. Moreover, the surface state of the nucleation is highly different, resulting in the simultaneous generation of spherical and non-spherical particles.

[0083] Test section (1) PDI determination The measurements were performed using dynamic light scattering (DLS).

[0084] PDI < 0.05: Highly monodisperse, indicating that the nanoparticles are almost perfectly uniform in size, representing the highest quality standard. PDI < 0.08: Monodisperse. Generally considered the ideal monodisperse system. PDI < 0.1: Near monodisperse, with a narrow particle size distribution, meeting the requirements of most high-end applications. PDI < 0.3: Moderately dispersed, with a relatively wide distribution, but still within an acceptable range. PDI > 0.5: Wide distribution. The system has a wide particle size range and exhibits varying degrees of aggregation.

[0085] (2) Sphericity determination Characterization was performed using scanning electron microscopy (SEM) and image analysis software (such as ImageJ). Sample preparation: The powder was thoroughly dispersed on a conductive adhesive. High-magnification SEM images (typically 10,000x or higher) were taken, and at least 300 particles were randomly selected (following statistical requirements). Particle outlines were annotated using software such as ImageJ, and parameters such as roundness and aspect ratio were automatically calculated. Sphericity: Measures how closely a particle approximates a sphere; an ideal sphere is rated at 1.

[0086] (3) D 50 D max D min Measurement Measurements and statistical analyses were performed using a high-magnification microscope and image analysis software (such as ImageJ).

[0087] D50 (median diameter): The particle size at which the cumulative particle size distribution percentage of a sample reaches 50%. That is, particles larger than D50 and particles smaller than D50 each account for 50%.

[0088] The test results of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0089] Table 1

[0090] The test results above show that the preparation method of this application can improve the particle size concentration and sphericity of nano-nickel powder, and adjust the median particle size of nano-nickel powder within a suitable range, thereby achieving precise control of the particle size of nano-nickel powder.

[0091] The above embodiments are merely illustrative of the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing high particle size concentration nano-nickel powder, characterized in that, include: A nickel precursor solution is provided, the nickel precursor solution comprising a nickel source and an optional complexing agent, the nickel source comprising nickel ions; A reducing solution is provided, the reducing solution comprising a reducing agent and an alkaline solution; the molar ratio of the reducing agent to the nickel ions is (0.6-1.8):1; The nickel precursor solution and the reducing solution are mixed using a micro mixer to form initial crystal nuclei; the mixing time is ≤50 milliseconds. By lowering the concentration of reactants below the secondary nucleation threshold and enabling all particles to grow synchronously in a homogeneous flow field under diffusion-limited conditions, nano-nickel powder is obtained.

2. The preparation method according to claim 1, characterized in that, The micro mixer includes one or more of the following: microchannel reactor, impingement flow mixer, static mixer, and rotary disc mixer.

3. The preparation method according to claim 1, characterized in that, The step of mixing the nickel precursor solution and the reducing solution using a micro mixer to form initial crystal nuclei includes: The nickel precursor solution and the reducing solution are fed via pulse injection, with an injection time ≤100 milliseconds; and / or, The nickel precursor solution and the reducing solution are mixed by ultrasonic cavitation.

4. The preparation method according to claim 1, characterized in that, The step of making the concentration of the reactants lower than the secondary nucleation threshold, making all particles achieve diffusion-limited simultaneous growth in a uniform flow field to obtain the nanometer nickel powder includes: the concentration of the reactants is controlled to be free Ni + 30%-70% of the secondary nucleation threshold; and / or, The uniform flow field is achieved by controlling the stirring Reynolds number Re ≥ 10000; and / or, The uniform flow field is achieved by using an oscillating flow mixer.

5. The preparation method according to claim 1, characterized in that, The nickel source includes nickel salts, which include one or more of nickel chloride, nickel sulfate, nickel nitrate, and nickel acetate. The concentration of the nickel salt is 0.05 mol / L to 1 mol / L.

6. The preparation method according to claim 1, characterized in that, The reducing agent includes one or more of hydrazine hydrate, sodium borohydride, and potassium borohydride; and / or, The alkaline solution includes one or more of ammonia, sodium hydroxide, and potassium hydroxide; and / or, The pH value of the reducing solution is 11-14.

7. The preparation method according to claim 1, characterized in that, The complexing agent includes one or more of triethanolamine, sodium citrate, and ethylenediaminetetraacetic acid; and / or, The molar ratio of the complexing agent to the nickel ions is (0.1-2):

1.

8. A nano-nickel powder with high particle size concentration, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

9. The nano-nickel powder according to claim 8, characterized in that, The particle size distribution width (D) of the nano-nickel powder max -D min ) / D 50 ≤0.8; and / or, The polydispersity index (PDI) of the nano-nickel powder is ≤ 0.1; and / or, The sphericity of the nano-nickel powder is ≥0.95; and / or, The median diameter (D50) of the nano-nickel powder is 50 nm to 300 nm.

10. The application of nano-nickel powder prepared by the preparation method according to any one of claims 1-7 or the nano-nickel powder according to claim 8 or 9 in multilayer ceramic capacitors, conductive pastes, catalysts and magnetic devices.

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