A method for preparing narrow particle size distribution nano-nickel powder for MLCC electrode

Abstract

The application relates to the technical field of metal powder preparation, and discloses a preparation method of narrow-particle-size-distribution nano nickel powder for MLCC electrodes. In the method, a nickel source solution is divided into a first nickel source solution and a second nickel source solution; the first nickel source solution is allowed to react with a first hydrazine hydrate solution to form first-stage nickel powder particles; an alkalinity adjusting solution without nickel salt and hydrazine hydrate is added to adjust the state of the reaction solution; then, the second nickel source solution and a second hydrazine hydrate solution are added, so that nickel ions continue to deposit on the surfaces of the formed particles. The application can reduce the continuous generation of second-stage fine particles, inhibit the increase of coarse powder, and obtain the narrow-particle-size-distribution nano nickel powder suitable for the MLCC electrodes.

Description

Technical Field

[0001] This invention relates to the field of metal powder preparation technology, and in particular to a method for preparing narrow-particle-size nickel nanoparticles for MLCC electrodes. Background Technology

[0002] The internal electrodes of multilayer ceramic capacitors are typically formed by printing, laminating, and co-firing nickel powder conductive paste. As MLCCs (multilayer ceramic capacitors) develop towards miniaturization and high capacitance, the thickness of the internal electrode layer is continuously decreasing. Nickel powder not only needs to have a smaller average particle size but also a narrower particle size distribution. If the proportion of fine powder ends in the nickel powder is too high, it can easily cause fluctuations in paste viscosity and shrinkage behavior in the early stage of sintering. If there are too many coarse powder ends, local protrusions may form in the printed electrode layer, affecting the continuity of the electrodes in the thin layer and the reliability between layers. Therefore, for nano-nickel powder used in MLCC electrodes, simply controlling D50 is not enough; it is also necessary to control the particles at both ends of D10 and D90. Here, D10, D50, and D90 represent the particle sizes corresponding to a cumulative volume distribution of 10%, 50%, and 90%, respectively.

[0003] Regarding nickel powder for MLCC electrodes, existing technologies have proposed various wet preparation methods. For example, patent document CN113976905A discloses a nickel powder, a method for manufacturing nickel powder, and an internal electrode paste, which involves wet reduction using water-soluble nickel salts, hydrazine, and alkali metal hydroxides, with hydrazine added after the reduction reaction begins. Patent document CN1597198A discloses a method for manufacturing nickel powder, which involves reacting a nickel salt solution containing copper ions with a hydrazine compound solution and adding a hydroxyl-containing organic compound to obtain nanoscale nickel powder suitable for conductive paste of internal electrodes in multilayer ceramic capacitors. Patent document CN116441528B discloses an ultrafine spherical nickel powder and its preparation method, which improves the particle size and morphology of nickel powder by combining nickel salts, complexing agents, nucleating agents, reducing agents, and pH stabilizers.

[0004] Existing technologies can improve the preparation effect of nickel powder by adjusting the amount of reducing agent, nucleating agent, complexing agent, or pH stability. However, there is still a prominent problem in actual wet production: after the initial nickel powder particles have been formed, if the reaction solution continues to maintain a high alkalinity and strong hydrazine hydrate effect, new fine particles are easily generated in the system when nickel source is added or the reaction continues. If these fine particles are encouraged to continue to grow by extending the heat preservation and increasing the amount of reducing agent added in the later stage, the main particles that have already been formed will also grow synchronously, thereby increasing the coarse powder end. The resulting powder may have a D50 in the target nanoscale range, but the D10 is low and the D90 is high, and the overall particle size distribution is still not concentrated enough. Summary of the Invention

[0005] The technical problem to be solved by this invention is that the existing technology cannot reduce the reaction intensity of the subsequent stage and reduce the continued generation of fine particles after the initial nickel powder particles are formed, while avoiding the excessive growth of the main particles. To this end, we propose a method for preparing narrow particle size distribution nano-nickel powder for MLCC electrodes.

[0006] To achieve the above objectives, this application adopts the following technical solution: A method for preparing narrow-particle-size nickel nanoparticles for MLCC electrodes, comprising the following steps: S1: Preparing a nickel source solution by mixing nickel salt, a complexing agent, and water, and dividing the nickel source solution into a first nickel source solution and a second nickel source solution, wherein the first nickel source solution accounts for 6-15% of the total nickel source solution, and the second nickel source solution is the remainder of the nickel source solution excluding the first nickel source solution; adding water and a dispersing agent to the reaction vessel, and adjusting the pH to 11.0-11.6 to obtain the reaction base solution; S2: Adding the first nickel source solution and a first hydrazine hydrate solution to the reaction base solution, such that the molar ratio of hydrazine hydrate in the first hydrazine hydrate solution to nickel ions in the first nickel source solution is 0.80-1. S3: After the first stage of nickel powder particles are formed, stop adding nickel source solution and hydrazine hydrate solution, and add alkalinity adjustment solution to adjust the pH of the reaction solution to 10.0-10.5; S4: After the alkalinity adjustment is completed, add the second nickel source solution and the second hydrazine hydrate solution to the reaction vessel, so that the nickel ions in the second nickel source solution continue to be deposited on the surface of the first stage of nickel powder particles after reduction. The molar ratio of hydrazine hydrate in the second hydrazine hydrate solution to nickel ions in the second nickel source solution is 0.50-0.75:1; S5: After the second nickel source solution and the second hydrazine hydrate solution are added, the mixture is kept warm, separated from solids, washed and dried to obtain nano-nickel powder.

[0007] Preferably, in S1, the nickel ion concentration in the nickel source solution is 0.25-0.70 mol / L, and the pH of the nickel source solution is 7.5-9.0.

[0008] Preferably, in S1, the complexing agent is selected from one or more of ammonium citrate, ammonium lactate, and glycine, and the molar ratio of the complexing agent to nickel ions is 0.06-0.25:1.

[0009] Preferably, in S1, the dispersing agent is selected from one or more of polyethylene glycol, polyvinylpyrrolidone, and ammonium polyacrylate.

[0010] Preferably, in step S2, the mass concentration of the first hydrazine hydrate solution is 5-15 wt%, and the reaction continues for 3-8 minutes after the first hydrazine hydrate solution is added.

[0011] Preferably, in S3, the alkalinity adjustment solution does not contain nickel salt and hydrazine hydrate, but contains a buffer salt selected from one or more of ammonium acetate, ammonium bicarbonate, and ammonium sulfate.

[0012] Preferably, the alkalinity-correcting solution further contains an auxiliary complexing agent, which is selected from one or more of ammonium citrate, ammonium lactate, and glycine.

[0013] Preferably, in S3, the amount of alkalinity adjustment solution added accounts for 3-12% of the volume of the reaction liquid before the addition of alkalinity adjustment solution, and the alkalinity adjustment solution is maintained for 3-10 minutes after addition.

[0014] Preferably, in step S4, the mass concentration of the second hydrazine hydrate solution is 3-10 wt%, and the reaction temperature is 76-86°C during the addition of the second nickel source solution and the second hydrazine hydrate solution.

[0015] Preferably, the obtained nano-nickel powder has a D50 of 120-260 nm, a D10 / D50 of 0.55-0.80, a D90 / D50 of 1.30-1.75, and a Span value of 0.55-1.20.

[0016] The technical effects and advantages of this invention are as follows:

[0017] In this invention, the nickel source solution is divided into a first nickel source solution and a second nickel source solution. The first nickel source solution reacts with a first hydrazine hydrate solution to form first-stage nickel powder particles. Before adding the second nickel source solution, an alkalinity adjustment solution is introduced to adjust the state of the reaction solution that has already formed powder. Then, the second nickel source solution is combined with the second hydrazine hydrate solution for subsequent reaction. Compared with the prior art, which maintains a strong reducing state after particle formation, this invention can prevent the second-stage reaction from continuing the rapid powder formation state of the first stage, reducing the situation of continuing to generate fine new powder in the second stage. At the same time, it avoids the excessive growth of the formed particles due to prolonged reaction or enhanced reduction. Thus, both the fine and coarse powder ends of the obtained nano-nickel powder are controlled, resulting in nano-nickel powder with a narrow particle size distribution that is more suitable for use in the inner electrode of MLCC thin films. Attached Figure Description

[0018] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0019] Figure 1 This is a schematic flowchart of the preparation method of the present invention;

[0020] Figure 2 This is a scatter plot of the particle size test results of the present invention;

[0021] Figure 3 This is a matrix diagram showing the particle size test results of the present invention. Detailed Implementation

[0022] The present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are used to illustrate the preparation process and parameter selection of the present invention, and are not intended to limit the scope of protection of the present invention. Without departing from the core processing relationship of the present invention, those skilled in the art can make adaptive adjustments to the conventional process conditions according to the purity of raw materials, reaction scale and equipment conditions.

[0023] Reference Figure 1 As shown, this embodiment provides a method for preparing narrow-particle-size nickel nanoparticles for MLCC electrodes. A nickel source solution is prepared using nickel salts, and a reduction reaction is carried out in an aqueous system using hydrazine hydrate as a reducing agent.

[0024] The nickel source solution is prepared from nickel salt, complexing agent and water, and is used in two separate solutions: a first nickel source solution and a second nickel source solution.

[0025] The nickel salt is selected from one or more of nickel sulfate, nickel nitrate, and nickel chloride, preferably nickel sulfate or nickel nitrate. When nickel chloride is used, residual chloride ions should be controlled during subsequent washing.

[0026] The complexing agent is selected from one or more of ammonium citrate, ammonium lactate, and glycine, with ammonium citrate being preferred as the complexing agent. Ammonia is used to adjust the pH of the nickel source solution so that the nickel source solution does not release nickel ions too quickly after being added to the reaction solution.

[0027] The hydrazine hydrate is added in two parts: a first hydrazine hydrate solution and a second hydrazine hydrate solution. The first nickel source solution is combined with the first hydrazine hydrate solution to form first-stage nickel powder particles in the reaction solution. Then, an alkalinity adjustment solution is added to adjust the reaction solution that has already formed powder. The second nickel source solution and the second hydrazine hydrate solution are then added to the reaction solution so that the nickel ions in the second nickel source continue to be deposited on the surface of the formed nickel powder particles after reduction.

[0028] The amount of hydrazine hydrate relative to nickel ions in the second hydrazine hydrate solution is lower than that in the first hydrazine hydrate solution.

[0029] The alkalinity adjustment solution is used to adjust the reaction state after the formation of nickel powder particles in the first stage. The alkalinity adjustment solution does not contain nickel salts or hydrazine hydrate, but includes a buffer salt, which is selected from one or more of ammonium acetate, ammonium bicarbonate, and ammonium sulfate.

[0030] To make the alkalinity correction process smoother, the alkalinity correction solution may also contain an auxiliary complexing agent, which is selected from one or more of ammonium citrate, ammonium lactate, and glycine.

[0031] The complexing agent in the nickel source solution is used in the nickel source solution preparation stage, and the auxiliary complexing agent in the alkalinity adjustment solution is used in the adjustment stage after the formation of nickel powder particles in the first stage. The two can be the same or different complexing components.

[0032] Specifically, the method for preparing narrow-particle-size nickel nanoparticles for MLCC electrodes provided in this embodiment includes the following steps:

[0033] S1: Add nickel salt to deionized water, stir to dissolve, and prepare a nickel salt solution with a nickel ion concentration of 0.25-0.70 mol / L. After the nickel salt is completely dissolved, add a complexing agent and adjust the pH of the solution to 7.5-9.0 to obtain the nickel source solution.

[0034] The molar ratio of the complexing agent to nickel ions is 0.06-0.25:1, preferably 0.10-0.18:1;

[0035] If the amount of complexing agent is too low, the nickel source will be released too quickly during the second stage of feeding. If the amount of complexing agent is too high, the deposition rate of nickel ions on the surface of the nickel powder particles after reduction in the second stage will be too slow, which may easily lead to insufficient particle growth in the second stage.

[0036] The pH adjuster is selected from ammonia, sodium hydroxide solution or a combination thereof, with ammonia being the primary adjuster. If sodium hydroxide is used as an auxiliary pH adjuster, soluble ion residues are controlled by subsequent water washing.

[0037] S2: Add deionized water and dispersant to the reactor, purge with nitrogen to replace the air in the reactor, raise the temperature to 72-82℃, and adjust the pH to 11.0-11.6 to obtain the reaction base liquid;

[0038] The dispersant is selected from one or more of polyethylene glycol, polyvinylpyrrolidone, and ammonium polyacrylate. The amount of the dispersant, calculated as nickel ions in the nickel source solution in terms of metallic nickel, is 0.03-0.20 wt%, preferably 0.05-0.12 wt%.

[0039] If the amount of dispersant is too low, the newly formed nickel powder particles will easily adhere to each other; if the amount of dispersant is too high, it will increase the burden of subsequent washing.

[0040] The pH of the reaction solution is controlled at 11.0-11.6 to ensure that nickel powder particles can be formed quickly after the nickel source is added. If the pH is below 11.0, the powder formation speed will be slow. If the pH is above 11.6, the reaction will be too strong and the proportion of fine powder will increase.

[0041] S3: Add 6-15% of the first nickel source solution to the reaction base solution, followed by the addition of the first hydrazine hydrate solution, so that the molar ratio of hydrazine hydrate to nickel ions in the first hydrazine hydrate solution is 0.80-1.30:1. After the first hydrazine hydrate solution is added, continue the reaction for 3-8 minutes to form the first stage nickel powder particles in the reaction solution.

[0042] The mass concentration of the first hydrazine hydrate solution is 5-15 wt%.

[0043] When the amount of the first nickel source solution added is less than 6% of the total amount, the number of nickel powder particles formed in the first stage is insufficient, and some particles are easily coarse when the second stage is fed. When the amount of the first nickel source solution added is more than 15% of the total amount, the reaction amount is too large, and too many fine particles are easily formed under the action of higher alkalinity and higher hydrazine hydrate.

[0044] When the molar ratio of hydrazine hydrate to nickel ions in the first stage is less than 0.80:1, the powdering is insufficient; when it is greater than 1.30:1, the residual hydrazine hydrate in the reaction solution has a stronger effect, which is not conducive to slowing down the reaction state in the later stage.

[0045] In actual operation, when the reaction solution gradually turns grayish-black and forms a uniform nickel powder slurry, it can be used as an auxiliary judgment to determine when the powdering is complete.

[0046] S4: After the nickel powder particles are formed in the first stage, stop adding nickel source solution and hydrazine hydrate solution, add alkalinity adjustment solution to the reaction solution to adjust the pH of the reaction solution to 10.0-10.5 and maintain it for 3-10 minutes;

[0047] In the alkalinity adjustment solution, the buffer salt concentration is 0.05-0.30 mol / L. When the alkalinity adjustment solution contains an auxiliary complexing agent, the concentration of the auxiliary complexing agent is 0.01-0.08 mol / L. The amount of alkalinity adjustment solution added accounts for 3-12% of the reaction liquid volume.

[0048] If too little alkalinity-correcting solution is added, the reaction solution will not be able to fully correct its state; if too much alkalinity-correcting solution is added, the reaction system will be diluted, affecting the feeding efficiency of the second stage.

[0049] When the pH is below 10.0, the nickel ions in the second nickel source solution are reduced and deposited on the surface of the already formed nickel powder particles at a slower rate, which can easily lead to insufficient particle growth. When the pH is above 10.5, the reaction solution is still close to the rapid powdering state of the first stage, and fine new powder can still be easily generated when the second stage is fed.

[0050] S5: After the alkalinity adjustment is completed, under the conditions of pH 10.0-10.5 and temperature 76-86℃, the second nickel source solution, which accounts for 85-94% of the total nickel source solution, and the second hydrazine hydrate solution are simultaneously added to the reaction vessel.

[0051] The mass concentration of the second hydrazine hydrate solution is 3-10 wt%, and the molar ratio of hydrazine hydrate to nickel ions in the second hydrazine hydrate solution is 0.50-0.75:1.

[0052] When the molar ratio of hydrazine hydrate to nickel ions in the second stage is less than 0.50:1, the reduction in the second stage is insufficient, the particles that have already formed do not continue to grow to a sufficient extent, and the proportion of fine powder ends is not easy to reduce. When it is greater than 0.75:1, the reaction state in the second stage is too strong, and fine particles are easily generated again.

[0053] S6: After the second nickel source solution and the second hydrazine hydrate solution are added, the mixture is kept at 78-86℃ for 15-35 minutes and the pH is maintained at 9.8-10.3. After the heat preservation is completed, the reaction solution is cooled to below 40℃ to obtain nano nickel powder slurry.

[0054] S7: The obtained nano-nickel powder slurry is subjected to solid-liquid separation, washed with deionized water until the conductivity of the washing liquid is not higher than 80 μS / cm, preferably not higher than 50 μS / cm, and then washed once with ethanol or isopropanol. The washed wet powder is vacuum dried at 45-70℃ or dried under nitrogen protection to obtain nano-nickel powder.

[0055] After drying, the nano-nickel powder can be selectively subjected to a light deagglomeration treatment with a deagglomeration time of 10-60 seconds. This is used to break up the loose clumps formed during the drying process. High-intensity ball milling or high-energy pulverization should not be used to avoid damaging the morphology of the nickel powder particles or introducing impurities.

[0056] This embodiment also provides a nano-nickel powder prepared by the above preparation method, wherein the D50 of the nano-nickel powder is controlled at 120-260nm, preferably 150-220nm, the D10 / D50 is 0.55-0.80, the D90 / D50 is 1.30-1.75, and the Span (particle size distribution width) value is 0.55-1.20, preferably 0.65-1.00, wherein the Span value is calculated as (D90-D10) / D50.

[0057] To facilitate understanding of the technical solution of the present invention, the present invention will be further described below with reference to specific embodiments. The following embodiments are only used to illustrate the possible implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Without departing from the core processing relationship of the present invention, those skilled in the art can make adaptive adjustments to the feeding amount, stirring speed and conventional post-processing conditions according to the actual production scale, raw material purity and equipment conditions.

[0058] First embodiment: This embodiment provides a method for preparing narrow-particle-size nickel nanoparticles for MLCC electrodes, specifically including the following steps:

[0059] S1: Weigh 262.85g of nickel sulfate hexahydrate, add it to deionized water and stir to dissolve it, and make up to about 1.61L to prepare a nickel sulfate solution with a nickel ion concentration of about 0.62mol / L. After the nickel sulfate is completely dissolved, add ammonium citrate to make the molar ratio of citrate to nickel ions 0.22:1, and adjust the pH of the solution to 8.7 with ammonia water to obtain the nickel source solution.

[0060] Take 0.226 L of nickel source solution as the first nickel source solution, which contains 0.14 mol of nickel ions, and use the remainder as the second nickel source solution, which contains 0.86 mol of nickel ions.

[0061] S2: Add 1.00L of deionized water to the reactor and add 0.094g of polyethylene glycol as a dispersion protectant. Purge the reactor with nitrogen to replace the air, raise the temperature to 81℃, and adjust the pH of the reaction solution to 11.5. Control the stirring speed to 600r / min to obtain the reaction base solution.

[0062] S3: Add the first nickel source solution to the reaction base solution, followed by 13wt% of the first hydrazine hydrate solution. The molar ratio of hydrazine hydrate in the first hydrazine hydrate solution to nickel ions in the first nickel source solution is 1.22:1. After the first hydrazine hydrate solution is added, continue the reaction for 7 minutes to form the first stage nickel powder particles in the reaction solution.

[0063] S4: After the nickel powder particles are formed in the first stage, stop adding the nickel source solution and hydrazine hydrate solution, and add alkalinity adjustment solution to the reaction solution. The alkalinity adjustment solution is prepared by 0.25 mol / L ammonium acetate and 0.06 mol / L ammonium citrate. The amount of alkalinity adjustment solution added is 10% of the volume of the reaction solution before the addition of alkalinity adjustment solution. After the alkalinity adjustment solution is added, adjust the pH of the reaction solution to 10.4 and maintain it for 8 minutes.

[0064] S5: After the alkalinity adjustment is completed, the second nickel source solution and 8wt% second hydrazine hydrate solution are simultaneously added to the reactor. The molar ratio of hydrazine hydrate in the second hydrazine hydrate solution to nickel ions in the second nickel source solution is 0.70:1. During the addition process, the temperature of the reaction solution is controlled at 84℃ and the pH is controlled at 10.3-10.5.

[0065] S6: After the second nickel source solution and the second hydrazine hydrate solution are added, the mixture is kept at 84°C for 30 minutes and the pH is maintained at 10.2. After the heat preservation is completed, the reaction solution is cooled to below 40°C to obtain nano-nickel powder slurry.

[0066] S7: The obtained nano-nickel powder slurry is subjected to solid-liquid separation, washed with deionized water until the conductivity of the washing solution is lower than 50 μS / cm, and then washed once with ethanol replacement. The washed wet powder is vacuum dried at 65℃, and after drying, it is slightly depolymerized for 50s to obtain the finished nano-nickel powder.

[0067] Second embodiment: This embodiment provides another method for preparing narrow-particle-size nickel nanoparticles for MLCC electrodes, specifically including the following steps:

[0068] S1: Weigh 262.85g of nickel sulfate hexahydrate, add it to deionized water and stir to dissolve it, and make up to about 3.13L to prepare a nickel sulfate solution with a nickel ion concentration of about 0.32mol / L. After the nickel sulfate is completely dissolved, add ammonium citrate to make the molar ratio of citrate to nickel ions 0.08:1, and adjust the pH of the solution to 7.8 with ammonia water to obtain the nickel source solution.

[0069] Take 0.219 L of nickel source solution as the first nickel source solution, which contains 0.07 mol of nickel ions, and use the remainder as the second nickel source solution, which contains 0.93 mol of nickel ions.

[0070] S2: Add 1.20L of deionized water to the reactor and add 0.029g of polyethylene glycol as a dispersion protectant. Purge the reactor with nitrogen to replace the air, raise the temperature to 74℃, and adjust the pH of the reaction solution to 11.1. Control the stirring speed to 400r / min to obtain the reaction base solution.

[0071] S3: Add the first nickel source solution to the reaction base solution, followed by 6 wt% of the first hydrazine hydrate solution. The molar ratio of hydrazine hydrate in the first hydrazine hydrate solution to nickel ions in the first nickel source solution is 0.88:1. After the first hydrazine hydrate solution is added, continue the reaction for 4 minutes to form the first stage nickel powder particles in the reaction solution.

[0072] S4: After the nickel powder particles are formed in the first stage, stop adding the nickel source solution and hydrazine hydrate solution, and add alkalinity adjustment solution to the reaction solution. The alkalinity adjustment solution is prepared by 0.08 mol / L ammonium bicarbonate and 0.015 mol / L ammonium lactate. The amount of alkalinity adjustment solution added is 4% of the reaction solution volume before the addition of alkalinity adjustment solution. After the alkalinity adjustment solution is added, adjust the pH of the reaction solution to 10.1 and maintain it for 4 minutes.

[0073] S5: After the alkalinity adjustment is completed, the second nickel source solution and 4wt% second hydrazine hydrate solution are simultaneously added to the reactor. The molar ratio of hydrazine hydrate in the second hydrazine hydrate solution to nickel ions in the second nickel source solution is 0.55:1. During the addition process, the temperature of the reaction solution is controlled at 78℃ and the pH is controlled at 10.0-10.2.

[0074] S6: After the second nickel source solution and the second hydrazine hydrate solution are added, the mixture is kept at 79°C for 18 minutes and the pH is maintained at 9.9. After the heat preservation is completed, the reaction solution is cooled to below 40°C to obtain nano-nickel powder slurry.

[0075] S7: The obtained nano-nickel powder slurry is subjected to solid-liquid separation, washed with deionized water until the conductivity of the washing solution is lower than 50 μS / cm, and then washed once with ethanol replacement. The washed wet powder is vacuum dried at 50℃, and after drying, it is slightly depolymerized for 15s to obtain the finished nano-nickel powder.

[0076] Comparative Example: This comparative example provides a method for preparing nano-nickel powder. This comparative example is based on Example 1, with the difference being that: after the nickel powder particles are formed in the first stage, a second nickel source solution and a second hydrazine hydrate solution are directly added. Specifically, it includes the following steps:

[0077] S1: Weigh 262.85g of nickel sulfate hexahydrate, add it to deionized water and stir to dissolve it, and make up to about 1.61L to prepare a nickel sulfate solution with a nickel ion concentration of about 0.62mol / L. After the nickel sulfate is completely dissolved, add ammonium citrate to make the molar ratio of citrate to nickel ions 0.22:1, and adjust the pH of the solution to 8.7 with ammonia water to obtain the nickel source solution.

[0078] Take 0.226 L of nickel source solution as the first nickel source solution, which contains 0.14 mol of nickel ions, and use the remainder as the second nickel source solution, which contains 0.86 mol of nickel ions.

[0079] S2: Add 1.00L of deionized water to the reactor and add 0.094g of polyethylene glycol as a dispersion protectant. Purge the reactor with nitrogen to replace the air, raise the temperature to 81℃, and adjust the pH of the reaction solution to 11.5. Control the stirring speed to 600r / min to obtain the reaction base solution.

[0080] S3: Add the first nickel source solution to the reaction base solution, followed by 13wt% of the first hydrazine hydrate solution. The molar ratio of hydrazine hydrate in the first hydrazine hydrate solution to nickel ions in the first nickel source solution is 1.22:1. After the first hydrazine hydrate solution is added, continue the reaction for 7 minutes to form the first stage nickel powder particles in the reaction solution.

[0081] S4: After the nickel powder particles are formed in the first stage, the second nickel source solution and 8wt% second hydrazine hydrate solution are directly added to the reactor simultaneously. The molar ratio of hydrazine hydrate in the second hydrazine hydrate solution to nickel ions in the second nickel source solution is 0.70:1. During the addition process, the temperature of the reaction solution is controlled at 84℃.

[0082] S5: After the second nickel source solution and the second hydrazine hydrate solution were added, the pH of the reaction solution was measured to be approximately 10.2. Then, the solution was kept at 84°C for 30 minutes. After the holding time was completed, the reaction solution was cooled to below 40°C to obtain nano-nickel powder slurry.

[0083] S6: The obtained nano-nickel powder slurry is subjected to solid-liquid separation, washed with deionized water until the conductivity of the washing solution is lower than 50 μS / cm, and then washed once with ethanol replacement. The washed wet powder is vacuum dried at 65℃, and after drying, it is slightly depolymerized for 50s to obtain the finished nano-nickel powder.

[0084] To verify the effect of the preparation method of the present invention on the control of the particle size distribution of nano-nickel powder, the particle size distribution of the nano-nickel powder obtained in Example 1, Example 2 and Comparative Example 1 was tested.

[0085] Before testing, each sample was thoroughly mixed and the powder to be tested was obtained by multi-point sampling. Five dispersions were prepared in parallel for each sample. 0.50g of nano nickel powder was weighed for each dispersion and added to 100mL of anhydrous ethanol to obtain a pre-dispersion.

[0086] The pre-dispersed liquid was placed in an ultrasonic disperser for short-term dispersion. The ultrasonic power was set to 120W and the ultrasonic time was 2min. During the ultrasonic dispersion process, the temperature of the dispersion was controlled at 25℃. After dispersion, it was added to the wet circulation tank of a laser particle size analyzer for testing. The amount added was adjusted to control the light shading rate of the test at 8%-12%.

[0087] The test results are expressed as volumetric distribution particle size. D10, D50, D90, D10 / D50, D90 / D50, and Span values ​​were recorded. D10 represents the particle size corresponding to a cumulative volume distribution of 10%, D50 represents the particle size corresponding to a cumulative volume distribution of 50%, and D90 represents the particle size corresponding to a cumulative volume distribution of 90%. Five dispersions were prepared independently for each sample and tested separately. The test results are shown in Table 1 below. Figure 2 As shown: Table 1. Particle size test results

[0088] From Table 1 and Figure 2 The test results show that in the five tests of Example 1, D50 was 226-232nm, D10 was 145-151nm, and D90 was 369-382nm; in the five tests of Example 2, D50 was 157-163nm, D10 was 93-98nm, and D90 was 249-263nm. Examples 1 and 2 used different combinations of process parameters, and the main particle size positions of the resulting powders were different, but the particle size distribution of the two groups of samples did not show the phenomenon of fine powder extending downwards or coarse powder extending outwards.

[0089] The D50 of Comparative Example 1 is 232-244 nm, which is close to that of Example 1, indicating that nanoscale nickel powder can still be obtained without alkalinity adjustment. However, the D10 of Comparative Example 1 is only 76-85 nm, which is lower than that of Example 1; the D90 increases to 535-574 nm, which is also higher than that of Example 1. Correspondingly, the D10 / D50 of Comparative Example 1 is only 0.33-0.35, the D90 / D50 increases to 2.31-2.36, and the Span value reaches 1.98-2.02, indicating that although Comparative Example 1 can make the median particle size fall within the nanoscale range, the particle size distribution at both ends has been significantly widened.

[0090] Examining D50 alone can easily mask the changes at the fine and coarse powder ends. In Comparative Example 1, the second nickel source solution and the second hydrazine hydrate solution were added directly after the nickel powder particles were formed in the first stage. The reaction solution did not undergo alkalinity adjustment, and fine particles were still easily generated in the second stage. At the same time, in order for the second nickel source solution to continue to participate in the reaction, some of the particles that had already been formed would continue to grow, resulting in a decrease in D10 and an increase in D90.

[0091] Based on the repeatability of the five parallel tests, the D50, D90, and Span values ​​of Examples 1 and 2 fluctuated less, indicating that the particle size distribution of the obtained powder has good stability. Although the data of Comparative Example 1 also showed repeatability, the results of lower D10, higher D90, and larger Span value were repeated, indicating that the widening of the particle size distribution was not an accidental test error, but was related to the preparation process without alkalinity adjustment.

[0092] Scaled-up Example: This example provides a scaled-up method for producing narrow-particle-size nickel nanoparticles for MLCC electrodes, comprising the following steps:

[0093] S1: Weigh approximately 52.6 kg of nickel sulfate hexahydrate, add it to deionized water and stir to dissolve, then bring the volume to 400 L to prepare a nickel sulfate solution with a nickel ion concentration of approximately 0.50 mol / L. After the nickel sulfate is completely dissolved, add ammonium citrate to make the molar ratio of citrate to nickel ions 0.14:1, and adjust the pH of the solution to 8.4 with ammonia water to obtain the nickel source solution.

[0094] Take 40L of nickel source solution as the first nickel source solution, which contains approximately 20mol of nickel ions, and use the remainder as the second nickel source solution, which contains approximately 180mol of nickel ions.

[0095] S2: Add 100L of deionized water to the reactor and add 5wt% polyethylene glycol aqueous solution, which is equivalent to about 11.7g of polyethylene glycol. Purge nitrogen into the reactor to replace the air, raise the temperature to 78℃, adjust the pH of the reaction solution to 11.3, and control the stirring speed to 240r / min to obtain the reaction base solution.

[0096] S3: Add the first nickel source solution to the reaction base solution, and then add 10wt% of the first hydrazine hydrate solution within 5 min. The molar ratio of hydrazine hydrate in the first hydrazine hydrate solution to nickel ions in the first nickel source solution is 1.05:1. After the first hydrazine hydrate solution is added, continue the reaction for 6 min to form the first stage nickel powder particles in the reaction solution.

[0097] S4: After the nickel powder particles are formed in the first stage, stop adding the nickel source solution and hydrazine hydrate solution, and add alkalinity adjustment solution to the reaction solution. The alkalinity adjustment solution is prepared by 0.12 mol / L ammonium acetate and 0.03 mol / L ammonium citrate. The amount of alkalinity adjustment solution added is 6% of the volume of the reaction solution before the addition of alkalinity adjustment solution. After the alkalinity adjustment solution is added, adjust the pH of the reaction solution to 10.3 and maintain it for 6 minutes.

[0098] S5: After the alkalinity adjustment is completed, the second nickel source solution and 6wt% second hydrazine hydrate solution are simultaneously added to the reactor. The molar ratio of hydrazine hydrate in the second hydrazine hydrate solution to nickel ions in the second nickel source solution is 0.65:1. During the addition process, the temperature of the reaction solution is controlled at 82℃ and the pH is controlled at 10.2-10.4.

[0099] S6: After the second nickel source solution and the second hydrazine hydrate solution are added, the mixture is kept at 82°C for 25 minutes and the pH is maintained at 10.1. After the heat preservation is completed, the reaction solution is cooled to below 40°C to obtain nano-nickel powder slurry.

[0100] S7: The obtained nano-nickel powder slurry is subjected to solid-liquid separation, washed with deionized water until the conductivity of the washing solution is less than 50 μS / cm, and then washed once with ethanol replacement. The washed wet powder is vacuum dried at 60℃, and after drying, it is slightly depolymerized for 30s to obtain the finished nano-nickel powder.

[0101] To investigate the stability of the particle size distribution of the nano-nickel powder obtained under scale-up production conditions, five batches of nano-nickel powder continuously prepared in Example 3 were sampled and tested. The five batches of samples were designated as 1-1, 1-2, 1-3, 1-4 and 1-5, respectively.

[0102] After drying and slight deagglomeration, each batch of powder was thoroughly mixed. Then, samples were taken from different locations in each batch to prepare five parallel test samples. For each sample, 0.50 g of nano-nickel powder was weighed and added to 100 mL of anhydrous ethanol to obtain a pre-dispersion. The pre-dispersion was then ultrasonically dispersed and subjected to wet laser particle size analysis. The ultrasonic power was 120 W, and the ultrasonic time was 2 min. During ultrasonication, the temperature of the dispersion was controlled at 25℃. For testing, an appropriate amount of the pre-dispersion was added to the wet circulation chamber of the laser particle size analyzer, and the amount added was adjusted to control the light-blocking rate at 8%-12%. The test results are shown in Table 2 below. Figure 3 As shown: Table 2 Production Scale-up Test Results

[0103] The test results above show that the D50 of the five batches of samples is distributed between 194-228nm. There are certain differences in particle size position between different batches. The overall particle size of batches 1-4 is slightly lower, and the overall particle size of batches 1-3 is slightly higher. This may be caused by slight differences in feeding, heat transfer, stirring and local pH adjustment during the production process. Although there are slight changes in the main particle size position, no batches showed significant deviation in D50.

[0104] Looking at the results of parallel samples within the same batch, the D10, D50, and D90 of each of the five parallel samples in the batch all showed slight fluctuations, but no individual parallel samples deviated significantly from the overall level of the batch. The D50 of 1-1 was 205-218 nm, the D50 of 1-3 was 214-228 nm, and the D50 of 1-4 was 194-207 nm. This indicates that after scale-up preparation, mixing, sampling, and dispersion testing, the particle size distribution of the powder had good repeatability within the batch.

[0105] The D10 of the five batches of samples ranged from 115 to 149 nm, and the D90 ranged from 312 to 386 nm; the D10 / D50 ratio ranged from 0.59 to 0.66, the D90 / D50 ratio ranged from 1.57 to 1.74, and the Span value ranged from 0.94 to 1.13. This indicates that under scale-up production conditions, the particle size distribution did not show a simple concentration of D50, but rather both the fine and coarse powder ends remained within a relatively stable range. In particular, although the D90 varied to some extent with different batches and sampling points, there was no sudden expansion of the coarse powder end. The D10 also did not show a downward trend, indicating that the generation of a large amount of fine new powder during the second-stage feeding process was suppressed.

[0106] As can be seen from the preparation process in Example 3, the method adopted in this invention, which involves first adjusting the alkalinity after the formation of nickel powder particles in the first stage, and then adding the second nickel source solution and the second hydrazine hydrate solution, can still maintain a relatively stable particle size distribution during scale-up preparation.

[0107] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A method for preparing narrow-particle-size nickel nanoparticles for MLCC electrodes, characterized in that, Includes the following steps: S1: Prepare a nickel source solution by mixing nickel salt, complexing agent and water, and divide the nickel source solution into a first nickel source solution and a second nickel source solution. The first nickel source solution accounts for 6-15% of the total nickel source solution, and the second nickel source solution is the balance of the nickel source solution excluding the first nickel source solution. Add water and dispersing agent to the reaction vessel, adjust the pH to 11.0-11.6, and obtain the reaction base solution. S2: Add a first nickel source solution and a first hydrazine hydrate solution to the reaction base solution, so that the molar ratio of hydrazine hydrate in the first hydrazine hydrate solution to nickel ions in the first nickel source solution is 0.80-1.30:1, and form first-stage nickel powder particles in the reaction solution; S3: After the nickel powder particles are formed in the first stage, stop adding nickel source solution and hydrazine hydrate solution, add alkalinity adjustment solution to the reaction solution and adjust the pH of the reaction solution to 10.0-10.5; S4: After the alkalinity adjustment is completed, the second nickel source solution and the second hydrazine hydrate solution are added to the reaction vessel, so that the nickel ions in the second nickel source solution continue to be deposited on the surface of the nickel powder particles in the first stage after reduction. The molar ratio of hydrazine hydrate in the second hydrazine hydrate solution to nickel ions in the second nickel source solution is 0.50-0.75:

1. S5: After the second nickel source solution and the second hydrazine hydrate solution are added, the mixture is kept warm, separated from solids, washed and dried to obtain nano-nickel powder.

2. The method for preparing narrow-particle-size nickel nanoparticles for MLCC electrodes according to claim 1, characterized in that: In S1, the nickel ion concentration in the nickel source solution is 0.25-0.70 mol / L, and the pH of the nickel source solution is 7.5-9.

0.

3. The method for preparing narrow-particle-size nickel nanoparticles for MLCC electrodes according to claim 1, characterized in that: In S1, the complexing agent is selected from one or more of ammonium citrate, ammonium lactate, and glycine, and the molar ratio of the complexing agent to nickel ions is 0.06-0.25:

1.

4. The method for preparing narrow-particle-size nickel nanoparticles for MLCC electrodes according to claim 1, characterized in that: In S1, the dispersing agent is selected from one or more of polyethylene glycol, polyvinylpyrrolidone, and ammonium polyacrylate.

5. The method for preparing narrow-particle-size nickel nanopowder for MLCC electrodes according to claim 1, characterized in that: In S2, the mass concentration of the first hydrazine hydrate solution is 5-15 wt%, and the reaction continues for 3-8 minutes after the first hydrazine hydrate solution is added.

6. The method for preparing narrow-particle-size nickel nanoparticles for MLCC electrodes according to claim 1, characterized in that: In S3, the alkalinity adjustment solution does not contain nickel salts or hydrazine hydrate, but contains a buffer salt selected from one or more of ammonium acetate, ammonium bicarbonate, and ammonium sulfate.

7. The method for preparing narrow-particle-size nickel nanoparticles for MLCC electrodes according to claim 6, characterized in that: The alkalinity-correcting solution also contains an auxiliary complexing agent, which is selected from one or more of ammonium citrate, ammonium lactate, and glycine.

8. The method for preparing narrow-particle-size nickel nanoparticles for MLCC electrodes according to claim 1, characterized in that: In S3, the amount of alkalinity adjustment solution added accounts for 3-12% of the volume of the reaction liquid before the alkalinity adjustment solution is added, and the alkalinity adjustment solution is maintained for 3-10 minutes after the alkalinity adjustment solution is added.

9. The method for preparing narrow-particle-size nickel nanoparticles for MLCC electrodes according to claim 1, characterized in that: In S4, the mass concentration of the second hydrazine hydrate solution is 3-10 wt%, and the reaction temperature is 76-86℃ during the addition of the second nickel source solution and the second hydrazine hydrate solution.

10. The method for preparing narrow-particle-size nickel nanopowder for MLCC electrodes according to claim 1, characterized in that: The obtained nano-nickel powder has a D50 of 120-260 nm, a D10 / D50 ratio of 0.55-0.80, a D90 / D50 ratio of 1.30-1.75, and a Span value of 0.55-1.20.

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