High-crystallinity ultrafine nickel powder and method for preparing the same

Abstract

The application discloses high-crystallinity superfine nickel powder and a preparation method thereof, and utilizes ultrasonic waves to adjust the size of nickel powder in liquid phase, and combines with molten salt heat treatment to obtain high-crystallinity superfine nickel powder, and specifically comprises the following steps: mixing an aqueous solution in which a nickel precursor is dissolved with a reducing agent, and adding an alkaline solution under the action of ultrasonic waves to carry out reaction, so as to prepare nickel powder particles with adjustable particle size; then, the nickel powder is uniformly mixed with combined salts with different proportions, and is heat-treated at different temperatures; the product after cooling is washed, separated, and finally high-crystallinity superfine nickel powder with a size of 100-200 nm is obtained. The nickel powder has good size uniformity, oxidation resistance and thermal shrinkage resistance, and can be applied to many fields such as conductive paste, metal electrode, magnetic shielding material and the like.

Description

Technical Field

[0001] This invention belongs to the field of electronic materials and metal powder materials, specifically relating to a highly crystalline ultrafine nickel powder and its preparation method, and more specifically to a method for obtaining highly crystalline ultrafine nickel powder by using ultrasonic waves to adjust the size of nickel powder generated in the liquid phase and combining it with molten salt heat treatment. Background Technology

[0002] Ultrafine nickel powder, due to its excellent electrical conductivity, catalytic properties, and magnetic properties, is widely used in conductive pastes, catalysis, and magnetic materials. The preparation methods for ultrafine nickel powder mainly include physical and chemical methods. Physical methods involve mechanical grinding, evaporation-condensation, and other physical processes. This method is relatively simple and environmentally friendly, but it requires sophisticated equipment, consumes a lot of energy, and often produces nickel powder with uneven particle size. Chemical methods generally prepare nickel powder through reduction, mainly including chemical vapor deposition (CVD), sol-gel methods, microemulsion methods, liquid-phase reduction methods, and hydrothermal methods.

[0003] For example, Chinese invention patent CN116525320A discloses a method for preparing nickel particles. This method involves grinding nickel chloride powder, methanol, and zirconium oxide balls in a planetary ball mill jar, followed by the introduction of argon gas and then high-temperature hydrogen gas to reduce the nickel chloride into nickel powder with an average particle size of 200–700 nm. This method requires hydrogen reduction and produces relatively large nickel particles. Chinese invention patent CN118086951A discloses a method for preparing uniform and stable nickel nanoparticles on a silicon substrate. This method uses nickel sulfate hexahydrate, L-histidine, and boric acid to prepare an electroplating solution. Through constant potential deposition, L-histidine-complexed nickel ions are precipitated and reduced to nickel nanoparticles with an average particle size of 15–18 nm, which are then loaded onto a silicon substrate. Chinese invention patent CN102133644A discloses a method for preparing nickel nanoparticles. This method dissolves nickel nitrate, ethanolamine, and polyvinylpyrrolidone in ethanol, then heats the solution in an oil bath to 66°C to obtain nickel nanoparticle powder with an average particle size of 10 nm. This method requires the use of organic solvents, and due to the low reaction temperature, the crystallinity of the nickel particles is not high enough.

[0004] Based on reported literature, the preparation of ultrafine nickel powder mainly faces the following problems. First, nickel powder prepared by CVD method is generally larger than 200 nanometers, and preparing smaller nickel powder is technically challenging, costly, and results in non-uniform powder size. Physical vapor deposition (PVD) method also has drawbacks in preparing ultrafine nickel powder, especially nanoscale nickel powder, such as the tendency for the powder to agglomerate into chains and poor particle size uniformity. Among chemical liquid-phase methods for nickel powder preparation, organic liquid-phase methods are costly due to the use of oil-soluble organic solvents. Although aqueous reduction methods can relatively easily obtain nickel powder with uniform size and near-spherical shape, ranging from tens to hundreds of nanometers, the low reaction temperature (room temperature to 100℃) results in poor crystallinity of the powder. Individual nickel particles are often secondary structures formed by the agglomeration of multiple smaller nickel primary particles, and the surface smoothness of the particles is also poor, which is detrimental to applications. Summary of the Invention

[0005] This invention addresses the above-mentioned problems by providing a method for producing highly crystalline ultrafine nickel powder. This method utilizes ultrasound to regulate the nucleation process of nickel in an aqueous phase, thereby obtaining small-sized raw nickel powder. Further combined with molten salt heat treatment, it ultimately yields highly crystalline ultrafine nickel powder with uniform size and a near-spherical shape, ranging from 100 to 200 nanometers. Compared to ultrafine nickel powder prepared by conventional aqueous phase reduction methods, the nickel powder prepared by this invention exhibits better oxidation resistance and heat shrinkage resistance, and can be applied in numerous fields such as conductive pastes, metal electrode materials, and magnetic shielding materials.

[0006] The present invention adopts the following technical solution:

[0007] A method for preparing highly crystalline ultrafine nickel powder includes the following steps:

[0008] (1) Weigh a certain amount of nickel precursor and dissolve it in deionized water, then add hydrazine hydrate and stir until homogeneous. This solution is denoted as solution A. An alkaline aqueous solution is obtained and denoted as solution B.

[0009] (2) Mix the solution B and the solution A, and then perform ultrasonic treatment;

[0010] (3) After ultrasonic treatment, the reaction solution is stirred and reacted for a period of time. The reaction products are then separated by magnetic separation, followed by washing and drying to obtain nickel powder.

[0011] (4) The nickel powder is mixed with the combined salt and then heated. A protective gas is introduced and the reaction is kept at a constant temperature for a period of time, and then cooled. The combined salt contains at least two different chloride salts in a binary mixed salt.

[0012] (5) The product obtained in step (4) is washed, magnetically separated and dried to obtain highly crystalline ultrafine nickel powder.

[0013] In a specific embodiment, the following steps may be adopted:

[0014] (1) Weigh a certain amount of nickel precursor and dissolve it in deionized water, then add a certain proportion of hydrazine hydrate, stir well, and record it as solution A; weigh a certain amount of sodium hydroxide and dissolve it in deionized water, and record it as solution B.

[0015] Preferably, the nickel precursor is selected from at least one of nickel acetate, nickel sulfate, and nickel chloride. The concentration of the nickel precursor is 0.04–1.60 mol / L; the molar ratio of hydrazine hydrate to the nickel precursor is 3:1–15:1. The concentration of solution B is 20–75 mol / L.

[0016] (2) Add solution B to solution A in a certain proportion (relative to A), and turn on the ultrasonic oscillator before adding solution B, and sonicate for a period of time with a certain ultrasonic power.

[0017] Preferably, the volume ratio of solution B to solution A is 1:1 to 10:1, and more preferably 1:4 to 10:1.

[0018] Preferably, the ultrasonic power is 20-200W, more preferably 40-150W, and even more preferably 50-100W.

[0019] Preferably, the ultrasound duration is 0 to 60 minutes. More preferably, it is 1 to 15 minutes.

[0020] (3) Turn off the ultrasonic machine, stir the reaction solution at a certain stirring rate for a period of time, separate the reaction products with a magnet, wash the reaction products with deionized water and ethanol, dry them, and obtain ultrafine nickel powder.

[0021] Preferably, the stirring rate is 50-600 rpm, more preferably 100-300 rpm; the reaction time is 5 minutes to 2 hours, more preferably 30 minutes to 2 hours.

[0022] (4) The prepared ultrafine nickel powder and a specific combination salt are mixed in a certain proportion by a mixer and then placed in a crucible. The crucible is placed in a tube furnace, a protective gas is introduced, and the mixture is heated to a certain temperature. The mixture is kept warm for a period of time and then naturally cooled to room temperature.

[0023] Preferably, the combined salt is selected from at least one of the binary mixed salt systems of AlCl3-NaCl, AlCl3-MgCl2, AlCl3-KCl, AlCl3-CaCl2, AlCl3-LiCl, FeCl3-NaCl, and ZnCl2-KCl.

[0024] Preferably, the molar ratios of the combined salts are as follows: AlCl3 to NaCl is 1:0.1 to 1:0.7; AlCl3 to MgCl2 is 1:0.1 to 1:0.5; AlCl3 to KCl is 1:0.1 to 1:0.7; AlCl3 to CaCl2 is 1:0.1 to 1:0.5; AlCl3 to LiCl is 1:0.1 to 1:0.8; FeCl3 to NaCl is 1:0.1 to 1:0.4; and ZnCl2-KCl is 1:0.1 to 1:0.6.

[0025] Preferably, the ratio of the ultrafine nickel powder to the combined salt is 1:1 to 1:10, and more preferably 1:3 to 1:7.

[0026] Preferably, the heating temperature is 300–650°C, more preferably 350–550°C;

[0027] Preferably, the protective atmosphere is selected from argon, nitrogen, an argon-hydrogen mixture, or a nitrogen-hydrogen mixture, and more preferably argon or nitrogen.

[0028] Preferably, the heat preservation time is 0.1 to 5 hours.

[0029] (5) The product obtained in step (4) is first washed once with a certain concentration of dilute acid, then washed several times with deionized water and ethanol water, separated by magnet, and dried to finally obtain highly crystalline ultrafine nickel powder with a particle size in the range of 100 to 200 nanometers.

[0030] Preferably, the dilute acid is any one of hydrochloric acid, sulfuric acid, nitric acid, and acetic acid, with a concentration of 0.1 to 1 mol / L.

[0031] This invention also protects the high crystallinity ultrafine nickel powder prepared by the method described above, which has at least one of the following (1) to (4):

[0032] (1) The particle size of the highly crystalline ultrafine nickel powder is 100-200 nanometers and the size is uniform;

[0033] (2) The temperature at which the highly crystalline ultrafine nickel powder begins to oxidize when heated in air is greater than or equal to 300°C;

[0034] (3) Compared with the nickel powder obtained in step (3), the highly crystalline ultrafine nickel powder has sharper diffraction peaks and higher crystallinity due to the molten salt treatment in step (4);

[0035] (4) The highly crystalline ultrafine nickel powder is made into a slurry and coated on a ceramic substrate to form a thin film, which has the property of resisting heat shrinkage.

[0036] This invention also protects the application of the highly crystalline ultrafine nickel powder in conductive materials, catalytic materials, or magnetic shielding materials.

[0037] Furthermore, the conductive material is a conductive paste, a metal electrode, or a ceramic capacitor.

[0038] Beneficial effects:

[0039] This invention utilizes nickel salt as a precursor, hydrazine hydrate as a reducing agent, and water as a solvent in an ultrasonic field. By adjusting the power of the ultrasonic machine, ultrafine nickel powder with an adjustable particle size of 100–200 nm is prepared. Compared to other methods for controlling metal particle size, ultrasonic technology can effectively control the particle growth stage, preventing the reduced nickel crystal nuclei from agglomerating into larger particles, thus facilitating the production of smaller nickel powder products and reducing the formation of byproducts. Different ultrasonic powers also allow for adjustable particle sizes to meet the diverse application requirements of nickel powder. Furthermore, using water as a reaction solvent offers advantages such as environmental friendliness, low toxicity, and low cost compared to using organic solvents.

[0040] Secondly, heat treatment of ultrafine nickel powder in molten salt (i.e., combined salt) is a novel method to improve its particle crystallinity. During the reaction, molten ionic liquid appears in the molten salt, effectively isolating particles from fusion. The spatial confinement effect of the molten salt ensures high particle dispersion. Simultaneously, the strong polarizing forces provided by anions and cations in the molten salt restrict the diffusion of nickel atoms at high temperatures, making it difficult for particles to connect and fuse. Therefore, after heat treatment with molten salt at an appropriate temperature, the size and morphology of the initially synthesized nickel particles are largely maintained, while also achieving high crystallinity. The binary mixed salt system described in this invention provides a suitable molten liquid phase at an appropriate temperature for improving the crystallinity of nickel particles. Furthermore, after heat treatment with molten salt, the oxidation resistance and thermal shrinkage resistance of the nickel particles are significantly improved. In the application of multilayer ceramic capacitors (MLCCs), the significant difference in the coefficients of thermal expansion between ultrafine nickel powder and dielectric ceramics can lead to severe delamination and cracking during subsequent sintering, causing discontinuity in the nickel electrode layer. The highly crystalline ultrafine nickel powder prepared by this invention, due to its improved crystallinity and resistance to thermal shrinkage, is beneficial for obtaining a continuous nickel electrode layer with fewer defects, which is of great significance for manufacturing high-capacity ultrathin capacitors. In the field of magnetic shielding materials, high crystallinity also improves the saturation magnetization of nickel, especially for nanoscale nickel powder, which is beneficial for its magnetic shielding effect.

[0041] Finally, common CVD methods for preparing nickel powder with a particle size of around 100 nanometers suffer from drawbacks such as high technical difficulty, high cost, and non-uniform powder size. PVD methods also have limitations, including the tendency for nickel powder particles to agglomerate and resulting in non-uniform size. This invention utilizes the regulating effect of ultrasound to obtain ultrafine nickel powder with a particle size as low as 100 nanometers and relatively uniform size. It also achieves high crystallinity, oxidation resistance, and heat shrinkage resistance, overcoming the drawback of conventional aqueous reduction-prepared nickel powder, which, while exhibiting good size uniformity, lacks high crystallinity. Attached Figure Description

[0042] Figure 1 The image shown is a scanning electron microscope (SEM) image of the ultrafine nickel powder prepared in Example 1, with a scale bar of 200 nm.

[0043] Figure 2 The image shows the XRD pattern of the ultrafine nickel powder prepared in Example 1.

[0044] Figure 3 The image shown is a scanning electron microscope (SEM) image of the ultrafine nickel powder prepared in Example 2, with a scale bar of 200 nm.

[0045] Figure 4 The image shows the XRD pattern of the ultrafine nickel powder prepared in Example 2.

[0046] Figure 5 The TG curve of the ultrafine nickel powder prepared in Example 2 is shown.

[0047] Figure 6 The image shown is a scanning electron microscope (SEM) image of the ultrafine nickel powder prepared in Example 3, with a scale bar of 200 nm.

[0048] Figure 7 The image shows the XRD pattern of the ultrafine nickel powder prepared in Example 3.

[0049] Figure 8 The image shown is a scanning electron microscope (SEM) image of the ultrafine nickel powder prepared in Example 4, with a scale bar of 200 nm.

[0050] Figure 9 The image shown is a scanning electron microscope (SEM) image of the ultrafine nickel powder prepared in Example 5, with a scale bar of 200 nm.

[0051] Figure 10 The image shows the XRD pattern of the ultrafine nickel powder prepared in Example 5.

[0052] Figure 11 The image shown is a scanning electron microscope (SEM) image of the ultrafine nickel powder prepared in Example 6, with a scale bar of 200 nm.

[0053] Figure 12 The image shows the XRD pattern of the ultrafine nickel powder prepared in Example 6.

[0054] Figure 13The image shown is a scanning electron microscope (SEM) image of the ultrafine nickel powder prepared in Example 7, with a scale bar of 200 nm.

[0055] Figure 14 The image shown is a scanning electron microscope (SEM) image of the ultrafine nickel powder prepared in Example 8, with a scale bar of 200 nm.

[0056] Figure 15 The image shown is a scanning electron microscope image of the ultrafine nickel powder prepared in Example 9, with a scale bar of 200 nm.

[0057] Figure 16 The image shows the XRD pattern of the ultrafine nickel powder prepared in Example 9.

[0058] Figure 17 The image shows a scanning electron microscope (SEM) image of the ultrafine nickel powder prepared in Example 10, with a scale bar of 200 nm.

[0059] Figure 18 The image shows the XRD pattern of the ultrafine nickel powder prepared in Example 10.

[0060] Figure 19 The image shows a scanning electron microscope (SEM) image of the ultrafine nickel powder prepared in Example 11, with a scale bar of 200 nm.

[0061] Figure 20 The image shows the XRD pattern of the ultrafine nickel powder prepared in Example 11.

[0062] Figure 21 The image shown is a scanning electron microscope (SEM) image of the ultrafine nickel powder prepared in Comparative Example 1, with a scale bar of 200 nm.

[0063] Figure 22 The image shows the XRD pattern of the ultrafine nickel powder prepared in Comparative Example 1.

[0064] Figure 23 The TG curve of the ultrafine nickel powder prepared in Comparative Example 1 is shown.

[0065] Figure 24 The image shown is a scanning electron microscope (SEM) image of the ultrafine nickel powder prepared in Comparative Example 2. The scale bar is 1 μm.

[0066] Figure 25 The image shown is a scanning electron microscope (SEM) image of the ultrafine nickel powder prepared in Comparative Example 3. The scale bar is 10 μm.

[0067] Figure 26 The image shown is a scanning electron microscope (SEM) image of the ultrafine nickel powder prepared in Comparative Example 4. The scale bar is 10 μm. Detailed Implementation

[0068] The embodiments of the present invention are described in detail below. These embodiments are intended to explain the present invention and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products. Unless otherwise stated, all percentages are by weight.

[0069] Example 1

[0070] (1) Mix 65 mL of nickel acetate tetrahydrate (0.73 mol / L) with 36 mL of hydrazine hydrate, and label this solution A. Prepare 24 mL of sodium hydroxide aqueous solution (25 mol / L), and label this solution B. Add solution B to solution A, and react for 1 hour with the ultrasonic machine off (i.e., ultrasonic power zero) at a stirring rate of 250 rpm. Wash three times with deionized water and once with ethanol. Separate the product using a magnet and dry it in a vacuum drying oven at 80 °C for 4 hours to obtain ultrafine nickel powder for further processing.

[0071] (2) After mechanically mixing 2g of the ultrafine nickel powder prepared in step (1) with a combination salt of 10.31g aluminum chloride hexahydrate and 1.47g sodium chloride, the mixture is placed in a crucible and placed in a tube furnace. The crucible is sealed, the heating device is turned on, argon gas is introduced, the temperature is raised to 400℃, and the temperature is maintained for 2 hours. After naturally cooling to room temperature, the mixture is washed with dilute hydrochloric acid, deionized water and ethanol respectively. The product is separated by magnetic separation and placed in a vacuum drying oven at 80℃ for 4 hours to obtain highly crystalline ultrafine nickel powder.

[0072] Figure 1 The image shows a scanning electron microscope (SEM) image of the product. The particles are spherical with an average particle size of approximately 180 nm.

[0073] Figure 2 The XRD pattern of the product is shown below, along with the XRD pattern of the product of Comparative Example 1 (without step (2)). Figure 22 Compared to the previous method, the diffraction peaks are significantly sharper, indicating that the product has a higher degree of crystallinity.

[0074] Example 2

[0075] (1) Mix 65 mL of nickel acetate tetrahydrate (0.73 mol / L) with 36 mL of hydrazine hydrate, and label this solution A. Prepare 24 mL of sodium hydroxide aqueous solution (25 mol / L), and label this solution B. Add solution B to solution A, and react for 1 hour with the ultrasonic machine off (i.e., ultrasonic power zero) at a stirring rate of 250 rpm. Wash three times with deionized water and once with ethanol. Separate the product using a magnet and dry it in a vacuum drying oven at 80 °C for 4 hours to obtain ultrafine nickel powder for further processing.

[0076] (2) After mechanically mixing 2g of the ultrafine nickel powder prepared in step (1) with a combination salt of 10.31g aluminum chloride hexahydrate and 1.47g sodium chloride, the mixture is placed in a crucible and sealed. The heating device is turned on and argon gas is introduced. The temperature is raised to 500℃ and held for 2 hours. After naturally cooling to room temperature, the mixture is washed once with dilute hydrochloric acid, twice with deionized water, and once with ethanol. The product is separated by magnetic separation and dried in a vacuum drying oven at 80℃ for 4 hours to obtain highly crystalline ultrafine nickel powder.

[0077] Figure 3 The image shows a scanning electron microscope (SEM) image of the product. The particles are spherical and have a smoother surface compared to Example 1.

[0078] Figure 4 The XRD pattern of the product is shown below, along with the XRD pattern of the product of Comparative Example 1 (without step (2)). Figure 22 Compared to the previous method, the diffraction peaks are significantly sharper, indicating that the product has a higher degree of crystallinity.

[0079] Figure 5 The thermogravimetric analysis (TG) curve of the product shows that the temperature at which the highly crystalline ultrafine nickel powder begins to oxidize in air is approximately 300°C. This is compared to the TG results of the product from Comparative Example 1 (untreated in step (2)). Figure 23 Compared to [previous product], its antioxidant properties have been significantly improved.

[0080] Example 3

[0081] (1) Mix 65 mL of nickel acetate tetrahydrate (0.73 mol / L) with 36 mL of hydrazine hydrate, and label this solution A. Prepare 24 mL of sodium hydroxide aqueous solution (25 mol / L), and label this solution B. Add solution B to solution A, and react for 1 hour with the ultrasonic cleaner off (i.e., ultrasonic power zero) at a stirring speed of 250 rpm. Wash three times with deionized water and once with ethanol. Separate the product using a magnet and dry it in a vacuum drying oven at 80 °C for 4 hours to obtain ultrafine nickel powder for further processing.

[0082] (2) After mechanically mixing 2g of the ultrafine nickel powder prepared in step (1) with a combination salt of 10.31g aluminum chloride hexahydrate and 1.47g sodium chloride, the mixture was placed in a crucible and placed in a tube furnace. The crucible was sealed, the heating device was turned on, and argon gas was introduced. The temperature was raised to 550℃ and held for 2 hours. After naturally cooling to room temperature, the mixture was washed once with dilute hydrochloric acid, twice with deionized water, and once with ethanol. The product was separated by magnetic separation and dried in a vacuum drying oven at 80℃ for 4 hours to obtain highly crystalline ultrafine nickel powder.

[0083] Figure 6 The image shows a scanning electron microscope image of the product. The particles are still spherical, and their dispersibility is similar to that of the product in Example 2.

[0084] Figure 7 The XRD pattern of the product is shown below, along with the XRD pattern of the product in Comparative Example 1. Figure 22 Compared to the previous method, the diffraction peaks are sharper, indicating that the product has a higher degree of crystallinity.

[0085] Example 4

[0086] (1) Mix 65 mL of nickel acetate tetrahydrate (0.73 mol / L) with 36 mL of hydrazine hydrate, and label this solution A. Prepare 24 mL of sodium hydroxide aqueous solution (25 mol / L), and label this solution B. Add solution B to solution A, and react for 1 hour with the ultrasonic machine off (i.e., ultrasonic power zero) at a stirring rate of 250 rpm. Wash three times with deionized water and once with ethanol. Separate the product using a magnet and dry it in a vacuum drying oven at 80 °C for 4 hours to obtain ultrafine nickel powder for further processing.

[0087] (2) After mechanically mixing 2g of the ultrafine nickel powder prepared in step (1) with a combination salt of 13.58g aluminum chloride hexahydrate and 1.10g magnesium chloride, the mixture was placed in a crucible and placed in a tube furnace. The crucible was sealed, the heating device was turned on, and argon gas was introduced. The temperature was raised to 500℃ and held for 2 hours. After naturally cooling to room temperature, the mixture was washed once with dilute hydrochloric acid, twice with deionized water, and once with ethanol. The product was separated by magnetic separation and dried in a vacuum drying oven at 80℃ for 4 hours to obtain highly crystalline ultrafine nickel powder.

[0088] Figure 8 The scanning electron microscope image of the product shows that the particle surface is smoother compared to Comparative Example 1.

[0089] Example 5

[0090] (1) Mix 65 mL of nickel acetate tetrahydrate aqueous solution (0.73 mol / L) with 36 mL of hydrazine hydrate, and label this solution A. Prepare 24 mL of sodium hydroxide aqueous solution (25 mol / L), and label this solution B. Add solution B to solution A, and turn on the ultrasonic machine 10 seconds before adding solution B. Set the power to 100% of the rated power (100 W), sonicate for 3 minutes, and react for 1 hour at a stirring rate of 250 rpm. Wash three times with deionized water and once with ethanol. Separate the product using a magnet and dry it in a vacuum drying oven at 80 °C for 4 hours to obtain ultrafine nickel powder for further processing.

[0091] (2) After mechanically mixing 2g of the ultrafine nickel powder prepared in step (1) with a combination salt of 10.31g aluminum chloride hexahydrate and 1.47g sodium chloride, the mixture is placed in a crucible and sealed. The heating device is turned on and argon gas is introduced. The temperature is raised to 500℃ and held for 2 hours. After naturally cooling to room temperature, the mixture is washed once with dilute hydrochloric acid, twice with deionized water, and once with ethanol. The product is separated by magnetic separation and dried in a vacuum drying oven at 80℃ for 4 hours to obtain highly crystalline ultrafine nickel powder.

[0092] Figure 9 The image shown is a scanning electron microscope (SEM) image of the product, with a particle size of approximately 100–110 nm. Compared to Examples 1, 2, 3 and Comparative Example 1, it exhibits a smaller particle size, demonstrating the regulating effect of ultrasonic treatment on the particle size of nickel powder.

[0093] Figure 10 The XRD pattern of the product is shown below, along with the XRD pattern of the product of Comparative Example 1 (without step (2)). Figure 22 Compared to the previous method, the diffraction peaks are significantly sharper, indicating that the product has a higher degree of crystallinity.

[0094] Example 6

[0095] (1) Mix 65 mL of nickel acetate tetrahydrate aqueous solution (0.73 mol / L) with 36 mL of hydrazine hydrate, and label this solution A. Prepare 24 mL of sodium hydroxide aqueous solution (25 mol / L), and label this solution B. Add solution B to solution A, and turn on the ultrasonic machine 10 seconds before adding solution B. Set the power to 100% of the rated power (100 W), sonicate for 3 minutes, and react for 1 hour at a stirring rate of 250 rpm. Wash three times with deionized water and once with ethanol. Separate the product using a magnet and dry it in a vacuum drying oven at 80 °C for 4 hours to obtain ultrafine nickel powder for further processing.

[0096] (2) After mechanically mixing 2g of the ultrafine nickel powder prepared in step (1) with a combination salt of 10.31g aluminum chloride hexahydrate and 1.47g sodium chloride, the mixture was placed in a crucible and placed in a tube furnace. The crucible was sealed, the heating device was turned on, and argon gas was introduced. The temperature was raised to 400℃ and held for 2 hours. After naturally cooling to room temperature, the mixture was washed once with dilute hydrochloric acid, twice with deionized water, and once with ethanol. The product was separated by magnetic separation and dried in a vacuum drying oven at 80℃ for 4 hours to obtain highly crystalline ultrafine nickel powder.

[0097] Figure 11 The image shown is a scanning electron microscope (SEM) image of the product, with a particle size of approximately 100 nm. Compared to Examples 1, 2, 3 and Comparative Example 1, it has a smaller particle size, demonstrating the regulating effect of ultrasonic treatment on the particle size of nickel powder.

[0098] Figure 12The XRD pattern of the product is shown below, along with the XRD pattern of the product of Comparative Example 1 (without step (2)). Figure 22 Compared to the previous method, the diffraction peaks are significantly sharper, indicating that the product has a higher degree of crystallinity.

[0099] Example 7

[0100] (1) Mix 65 mL of nickel acetate tetrahydrate aqueous solution (0.73 mol / L) with 36 mL of hydrazine hydrate, and label this solution A. Prepare 24 mL of sodium hydroxide aqueous solution (25 mol / L), and label this solution B. Add solution B to solution A, and turn on the ultrasonic machine 10 seconds before adding solution B. Set the power to 70% of the rated power (100 W), sonicate for 3 minutes, and react for 1 hour at a stirring rate of 250 rpm. Wash three times with deionized water and once with ethanol. Separate the product using a magnet and dry it in a vacuum drying oven at 80 °C for 4 hours to obtain ultrafine nickel powder for further processing.

[0101] (2) After mechanically mixing 2g of the ultrafine nickel powder prepared in step (1) with a combination salt of 10.31g aluminum chloride hexahydrate and 1.47g sodium chloride, the mixture is placed in a crucible and sealed. The heating device is turned on and argon gas is introduced. The temperature is raised to 500℃ and held for 2 hours. After naturally cooling to room temperature, the mixture is washed once with dilute hydrochloric acid, twice with deionized water, and once with ethanol. The product is separated by magnetic separation and dried in a vacuum drying oven at 80℃ for 4 hours to obtain highly crystalline ultrafine nickel powder.

[0102] Figure 13 The image shown is a scanning electron microscope (SEM) image of the product, with a particle size of approximately 130 nm. Compared to Examples 1, 2, 3 and Comparative Example 1, it has a smaller particle size, demonstrating the regulating effect of ultrasonic treatment on the particle size of nickel powder.

[0103] Example 8

[0104] (1) Mix 65 mL of nickel acetate tetrahydrate aqueous solution (0.73 mol / L) with 36 mL of hydrazine hydrate uniformly, and label this solution A. Prepare 24 mL of sodium hydroxide aqueous solution (25 mol / L), and label this solution B. Add solution B to solution A, and turn on the ultrasonic machine 10 seconds before adding solution B. Set the power to 40% of the rated power (100 W), sonicate for 3 minutes, and react for 1 hour at a stirring rate of 250 rpm. Wash three times with deionized water and once with ethanol. Separate the product using a magnet and dry it in a vacuum drying oven at 80 °C for 4 hours to obtain ultrafine nickel powder for further processing.

[0105] (2) After mechanically mixing 2g of the ultrafine nickel powder prepared in step (1) with a combination salt of 10.31g aluminum chloride hexahydrate and 1.47g sodium chloride, the mixture is placed in a crucible and sealed. The heating device is turned on and argon gas is introduced. The temperature is raised to 500℃ and held for 2 hours. After naturally cooling to room temperature, the mixture is washed once with dilute hydrochloric acid, twice with deionized water, and once with ethanol. The product is separated by magnetic separation and dried in a vacuum drying oven at 80℃ for 4 hours to obtain highly crystalline ultrafine nickel powder.

[0106] Figure 14 The image shown is a scanning electron microscope (SEM) image of the product, with a particle size of approximately 150 nm. Compared to Examples 1, 2, 3 and Comparative Example 1, it exhibits a smaller particle size, demonstrating the regulating effect of ultrasonic treatment on the particle size of nickel powder.

[0107] Example 9

[0108] (1) Mix 65 mL of nickel sulfate aqueous solution (0.73 mol / L) with 40 mL of hydrazine hydrate, and label this solution A. Prepare 30 mL of sodium hydroxide aqueous solution (25 mol / L), and label this solution B. Add solution B to solution A, and turn on the ultrasonic machine 10 seconds before adding solution B. Set the power to 75% of the rated power (200 W), sonicate for 3 minutes, and react for 1 hour at a stirring rate of 300 rpm. Wash three times with deionized water and once with ethanol. Separate the product using a magnet and dry it in a vacuum drying oven at 80 °C for 4 hours to obtain ultrafine nickel powder for further processing.

[0109] (2) The ultrafine nickel powder prepared in step (1) is mechanically mixed evenly with a combination salt of aluminum chloride hexahydrate and calcium chloride, and then placed in a crucible. The molar ratio of AlCl3 to CaCl2 is 1:0.1, and the mass ratio of nickel powder to the combination salt is 1:5. The crucible is placed in a tube furnace, sealed, and the heating device is turned on to introduce argon gas. The temperature is raised to 400℃ and held for 2 hours. After naturally cooling to room temperature, the product is washed once with dilute hydrochloric acid, twice with deionized water, and once with ethanol. The product is separated by magnetic separation and dried in a vacuum drying oven at 80℃ for 4 hours to obtain highly crystalline ultrafine nickel powder.

[0110] Figure 15 The image shown is a scanning electron microscope (SEM) image of the product, with a particle size of approximately 150 nm. Compared to Examples 1, 2, 3 and Comparative Example 1, it exhibits a smaller particle size, demonstrating the regulating effect of ultrasonic treatment on the particle size of nickel powder.

[0111] Figure 16 The XRD pattern of the product is shown below, along with the XRD pattern of the product of Comparative Example 1 (without step (2)). Figure 22 Compared to the previous method, the diffraction peaks are significantly sharper, indicating that the product has a higher degree of crystallinity.

[0112] Example 10

[0113] (1) Mix 65 mL of nickel chloride aqueous solution (0.73 mol / L) with 50 mL of hydrazine hydrate, and label this solution A. Prepare 35 mL of sodium hydroxide aqueous solution (25 mol / L), and label this solution B. Add solution B to solution A, and turn on the ultrasonic machine 10 seconds before adding solution B. Set the power to 60% of the rated power (200 W), sonicate for 3 minutes, and react for 1 hour at a stirring rate of 400 rpm. Wash three times with deionized water and once with ethanol. Separate the product using a magnet and dry it in a vacuum drying oven at 80 °C for 4 hours to obtain ultrafine nickel powder for further processing.

[0114] (2) The ultrafine nickel powder prepared in step (1) is mechanically mixed evenly with a combination salt of zinc chloride and potassium chloride and then placed in a crucible. The molar ratio of zinc chloride to potassium chloride is 1:0.3, and the mass ratio of nickel powder to the combination salt is 1:3. The crucible is placed in a tube furnace, sealed, and the heating device is turned on to introduce argon gas. The temperature is raised to 400℃ and held for 2 hours. After naturally cooling to room temperature, the product is washed once with dilute sulfuric acid (concentration of 0.5mol / L), twice with deionized water, and once with ethanol. The product is separated by magnetic separation and dried in a vacuum drying oven at 80℃ for 4 hours to obtain highly crystalline ultrafine nickel powder.

[0115] Figure 17 The image shown is a scanning electron microscope (SEM) image of the product, with a particle size of approximately 140 nm. Compared to Examples 1, 2, 3 and Comparative Example 1, it has a smaller particle size, demonstrating the regulating effect of ultrasonic treatment on the particle size of nickel powder.

[0116] Figure 18 The XRD pattern of the product is shown below, along with the XRD pattern of the product of Comparative Example 1 (without step (2)). Figure 22 Compared to the previous method, the diffraction peaks are significantly sharper, indicating that the product has a higher degree of crystallinity.

[0117] Example 11

[0118] (1) Mix 65 mL of nickel acetate tetrahydrate (0.73 mol / L) with 45 mL of hydrazine hydrate, and label this solution A. Prepare 24 mL of potassium hydroxide aqueous solution (30 mol / L), and label this solution B. Add solution B to solution A. Turn on the ultrasonic machine 10 seconds before adding solution B, set the power to 100% of the rated power (200 W), sonicate for 3 minutes, and react for 1 hour at a stirring rate of 500 rpm. Wash three times with deionized water and once with ethanol. Separate the product using a magnet and dry it in a vacuum drying oven at 80 °C for 4 hours to obtain ultrafine nickel powder for further processing.

[0119] (2) After mechanically mixing 2g of the ultrafine nickel powder prepared in step (1) with the combined salt of ferric chloride and sodium chloride, the mixture is placed in a crucible. The molar ratio of ferric chloride to sodium chloride is 1:0.3, and the mass ratio of nickel powder to the combined salt is 1:8. The crucible is placed in a tube furnace, sealed, and the heating device is turned on to introduce argon gas. The temperature is raised to 400℃ and held for 2 hours. After naturally cooling to room temperature, the mixture is washed once with dilute hydrochloric acid (concentration of 0.5mol / L), twice with deionized water, and once with ethanol. The product is separated by magnetic separation and dried in a vacuum drying oven at 80℃ for 4 hours to obtain highly crystalline ultrafine nickel powder.

[0120] Figure 19 The image shown is a scanning electron microscope (SEM) image of the product, with a particle size of approximately 120 nm. Compared to Examples 1, 2, 3 and Comparative Example 1, it has a smaller particle size, demonstrating the regulating effect of ultrasonic treatment on the particle size of nickel powder.

[0121] Figure 20 The XRD pattern of the product is shown below, along with the XRD pattern of the product of Comparative Example 1 (without step (2)). Figure 22 Compared to the previous method, the diffraction peaks are significantly sharper, indicating that the product has a higher degree of crystallinity.

[0122] Comparative Example 1

[0123] (1) Mix 65 mL of nickel acetate tetrahydrate (0.73 mol / L) with 36 mL of hydrazine hydrate and label this solution A. Prepare 24 mL of sodium hydroxide aqueous solution (25 mol / L) and label this solution B. Add solution B to solution A and react for 1 hour at a stirring rate of 250 rpm without turning on the ultrasonic cleaner. Wash three times with deionized water and once with ethanol. Separate the product using a magnet and dry it in a vacuum drying oven at 80 °C for 4 hours to obtain ultrafine nickel powder.

[0124] Figure 21 An electron microscope image shows that the particle size is approximately 180 nm, and the particle surface is relatively rough.

[0125] Figure 22 The XRD pattern shows that the diffraction peaks are significantly wider than those in Examples 1-11, indicating that the crystallinity of the nickel powder is relatively low without the heat treatment of the combined salt.

[0126] Figure 23 The TG curve of the product shows that the initial oxidation temperature of the nickel powder in air is about 250°C, which is lower than that of the nickel powder prepared in Examples 1 to 11, indicating poor oxidation resistance.

[0127] Comparative Example 2

[0128] (1) Mix 65 mL of nickel acetate tetrahydrate aqueous solution (0.73 mol / L) with 36 mL of hydrazine hydrate uniformly, and label this solution A. Prepare 24 mL of sodium hydroxide aqueous solution (25 mol / L), and label this solution B. Add solution B to solution A, and turn on the ultrasonic machine 10 seconds before adding solution B. Set the power to 40% of the rated power (100 W), sonicate for 3 minutes, and react for 1 hour at a stirring rate of 250 rpm. Wash three times with deionized water and once with ethanol. Separate the product using a magnet and dry it in a vacuum drying oven at 80 °C for 4 hours to obtain ultrafine nickel powder for further processing.

[0129] Weigh 2g of the above-mentioned ultrafine nickel powder and place it in a crucible. Place the crucible in a tube furnace, seal it, turn on the heating device, and introduce argon gas. The heat treatment temperature is 550℃, and the holding time is 2 hours. After natural cooling to room temperature, the product is obtained.

[0130] Figure 24 The scanning electron microscope image of the product shows that the spherical morphology is destroyed, and some particles have fused and sintered. This indicates that if the treatment method in step (2) of the examples is not adopted (refer to Examples 1-11), the nickel powder particles will not be able to maintain the initial state of synthesis, which is not conducive to subsequent applications.

[0131] Comparative Example 3

[0132] The ultrafine nickel powder prepared in Comparative Example 1 was added to a mixture containing 50 vol% ethylene glycol and 50 vol% ethylene glycol methyl ether. The mixture was ultrasonicated and stirred to prepare a slurry with a solid content of 60 wt%. The slurry was coated onto a ceramic substrate to form a thin film. The film was then calcined at 1200 °C for 1 hour in a 5% (volume ratio) hydrogen-argon mixed atmosphere to form a conductive film.

[0133] Figure 25 The scanning electron microscope image of the sintered film of nickel powder prepared for Comparative Example 1 shows that the film surface is severely shrunken, with large areas of unconnected regions.

[0134] Comparative Example 4

[0135] The ultrafine nickel powder prepared in Example 3 was added to a mixture containing 50 vol% ethylene glycol and 50 vol% ethylene glycol methyl ether. The mixture was ultrasonicated and stirred to prepare a slurry with a solid content of 60 wt%. The slurry was coated onto a ceramic substrate to form a thin film. The film was then calcined at 1200 °C for 1 hour in a 5% (volume ratio) hydrogen-argon mixed atmosphere to form a conductive film.

[0136] Figure 26 The image shows a scanning electron microscope (SEM) image of the prepared nickel sintered film. Compared with Comparative Example 3, the film surface shrinkage is smaller and the connected area is larger, showing better resistance to thermal shrinkage.

[0137] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for preparing highly crystalline ultrafine nickel powder, characterized in that, Includes the following steps: (1) Weigh a certain amount of nickel precursor and dissolve it in deionized water, then add hydrazine hydrate and stir until homogeneous, and record this as solution A; obtain an alkaline aqueous solution, and record this as solution B; the nickel precursor is selected from at least one of nickel acetate, nickel sulfate and nickel chloride; the concentration of the solution obtained by dissolving the nickel precursor in deionized water is 0.04~1.60 mol / L; the molar ratio of hydrazine hydrate to nickel precursor is 3:1~15:1; the concentration of hydroxide ions in solution B is 20~75 mol / L; the volume ratio of solution B to solution A is 1:1~5:1; (2) Mix the solution B and the solution A, and then perform ultrasonic treatment; (3) After ultrasonic treatment, the reaction solution is stirred and reacted for a period of time. The reaction products are then separated by magnetic separation, followed by washing and drying to obtain nickel powder. (4) The nickel powder is mixed with the combined salt and then heated. A protective gas is introduced and the reaction is kept at a certain temperature for a period of time, and then cooled. The combined salt contains at least two different chloride salts in a binary mixed salt system. The combined salt is selected from at least one of the binary mixed salt systems of AlCl3-NaCl, AlCl3-MgCl2, AlCl3-KCl, AlCl3-CaCl2, AlCl3-LiCl, FeCl3-NaCl, and ZnCl2-KCl. (5) The product obtained in step (4) is washed, magnetically separated and dried to obtain highly crystalline ultrafine nickel powder.

2. The method for preparing highly crystalline ultrafine nickel powder according to claim 1, characterized in that, In step (2), the power of the ultrasonic treatment is 20~200W; the duration of the ultrasonic treatment is 0~60 minutes.

3. The method for preparing highly crystalline ultrafine nickel powder according to claim 2, characterized in that, In step (2), the power of the ultrasonic treatment is 40~150W.

4. The method for preparing highly crystalline ultrafine nickel powder according to claim 3, characterized in that, In step (2), the power of the ultrasonic treatment is 50~100W.

5. The method for preparing highly crystalline ultrafine nickel powder according to claim 2, characterized in that, The duration of the ultrasonic treatment is 1 to 30 minutes.

6. The method for preparing highly crystalline ultrafine nickel powder according to claim 5, characterized in that, The duration of the ultrasonic treatment is 1 to 15 minutes.

7. The method for preparing highly crystalline ultrafine nickel powder according to claim 2, characterized in that, In step (3), the stirring rate is 50 to 600 rpm; the reaction time is 5 minutes to 2 hours.

8. The method for preparing highly crystalline ultrafine nickel powder according to claim 7, characterized in that, In step (3), the stirring rate is 100~300 rpm.

9. The method for preparing highly crystalline ultrafine nickel powder according to claim 7, characterized in that, In step (3), the reaction time is 30 minutes to 2 hours.

10. The method for preparing highly crystalline ultrafine nickel powder according to claim 1, characterized in that, In step (4), the proportions of the combined salts are: the molar ratio of AlCl3 to NaCl is 1:0.1 to 1:0.7; or the molar ratio of AlCl3 to MgCl2 is 1:0.1 to 1:0.5; or the molar ratio of AlCl3 to KCl is 1:0.1 to 1:0.7; or the molar ratio of AlCl3 to CaCl2 is 1:0.1 to 1:0.5; or the molar ratio of AlCl3 to LiCl is 1:0.1 to 1:0.8; or the molar ratio of FeCl3 to NaCl is 1:0.1 to 1:0.4; or the molar ratio of ZnCl2-KCl is 1:0.1 to 1:0.

6.

11. The method for preparing highly crystalline ultrafine nickel powder according to claim 1, characterized in that, In step (4), the mass ratio of the nickel powder to the combined salt is 1:1 to 1:

10.

12. The method for preparing highly crystalline ultrafine nickel powder according to claim 11, characterized in that, In step (4), the mass ratio of the nickel powder to the combined salt is 1:1 to 1:

8.

13. The method for preparing highly crystalline ultrafine nickel powder according to claim 12, characterized in that, In step (4), the mass ratio of the nickel powder to the combined salt is 1:1 to 1:

5.

14. The method for preparing highly crystalline ultrafine nickel powder according to claim 11, characterized in that, In step (4), the temperature of the heating treatment is 300~650℃; the protective gas is selected from argon, nitrogen, argon-hydrogen mixture, and nitrogen-hydrogen mixture; and the heat preservation reaction time is 0.1~5 hours.

15. The method for preparing highly crystalline ultrafine nickel powder according to claim 14, characterized in that, In step (4), the temperature of the heat treatment is 400~600℃.

16. The method for preparing highly crystalline ultrafine nickel powder according to claim 15, characterized in that, In step (4), the temperature of the heat treatment is 500~550℃.

17. The method for preparing highly crystalline ultrafine nickel powder according to claim 14, characterized in that, In step (5), the washing includes: washing once with dilute acid, and washing several times with deionized water and ethanol water. The dilute acid is any one of hydrochloric acid, sulfuric acid, nitric acid and acetic acid, with a concentration of 0.1~1 mol / L.

18. The highly crystalline ultrafine nickel powder prepared by the method according to any one of claims 1-17 is characterized in that, It has at least one of the following (1) to (4): (1) The particle size of the highly crystalline ultrafine nickel powder is 100~200 nanometers and the size is uniform; (2) The temperature at which the highly crystalline ultrafine nickel powder begins to oxidize when heated in air is greater than or equal to 300°C; (3) Compared with the nickel powder obtained in step (3), the highly crystalline ultrafine nickel powder has sharper diffraction peaks and a higher degree of crystallinity; (4) The highly crystalline ultrafine nickel powder is made into a slurry and coated on a ceramic substrate to form a thin film, which has the property of resisting heat shrinkage.

19. The application of the highly crystalline ultrafine nickel powder of claim 18 in conductive materials, catalytic materials or magnetic shielding materials.

20. The application according to claim 19, characterized in that, The conductive material is a conductive paste, a metal electrode, or a ceramic capacitor.

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