A method for preparing highly dispersed and highly crystalline nano nickel powder

Abstract

A method for preparing a highly crystalline and highly dispersed nano nickel powder is provided, comprising: 1) dissolving a nickel salt and citric acid in an organic solvent to prepare an organosol; 2) mixing the organosol with a water-soluble salt, standing or centrifuging to allow the water-soluble salt to settle, removing excess organosol from the upper portion, and obtaining a mixture of an organosol containing metallic nickel and a water-soluble salt; 3) heat preservation to convert the organosol into a gel to obtain a dry gel film coated on the surface of water-soluble salt particles; 4) calcining at above 400°C and below the melting point of the salt to form a calcined product; 5) calcining the calcined product in a reducing atmosphere at 400-600°C to convert nickel oxide into nickel nanoparticles; 6) washing with water and drying to obtain nano nickel powder. The method can be rapidly mass-produced, and the obtained product has good dispersibility and crystallinity, and the particle size is less than 50nm, which is suitable for preparing materials such as conductive pastes.

Description

Technical Field

[0001] The invention relates to a technology for preparing highly dispersed and highly crystalline nano nickel powder, belonging to the technical field of metal nano particle preparation. Background Art

[0002] Nano-metal nickel powder has excellent electrical and magnetic properties, and has broad application prospects in the fields of magnetic properties, electrode materials, catalysts, magnetic fluids, etc. In particular. In recent years, with the rapid development of multilayer ceramic capacitors (MLCC), the demand for nano-nickel powder has continued to grow, and research on its preparation technology has become more extensive. MLCC is developing towards ultra-thin layers. At present, the thinnest thickness of the internal electrode has reached 0.6-0.7μm, and the corresponding particle size of nano-nickel powder is about 100nm. With the continuous increase in the number of MLCC layers and the continuous thinning of the internal electrode thickness, the particle size of nano-nickel powder will need to be further reduced in the future.

[0003] For the nano nickel powder used in MLCC internal electrodes, not only a small particle size is required, but also high requirements are placed on the dispersion and crystallinity of the nano particles. The production of MLCC internal electrodes requires the process of debinding and sintering, which requires the nano nickel powder to have good crystallinity in order to have sufficient antioxidant properties. In addition, highly crystalline nickel particles have high density and less shrinkage after sintering. At the same time, the nano nickel powder also needs to have good dispersion, otherwise the agglomeration of particles will lead to problems such as discontinuity and leakage of the internal electrode.

[0004] Nano nickel powders prepared by existing methods generally have problems such as large particle size, poor dispersibility or low anti-oxidation temperature. The anti-oxidation performance of nano nickel powder depends on its crystallinity, which in turn depends heavily on the preparation temperature. Highly crystalline nano nickel metal needs to be prepared at a higher temperature, and it is difficult for nano particles to avoid agglomeration and sintering at high temperatures, so it is difficult to achieve the unity of high crystallinity, high dispersion and small particle size. Although methods such as liquid phase reduction and electrolytic precipitation can prepare nano nickel powder with a particle size less than 100nm, due to the low preparation temperature (<100℃), poor crystallinity, oxidation will occur at room temperature. At present, the commercial MLCC nano nickel powder adopts chemical vapor condensation or physical vapor condensation method, which can prepare nano nickel powder of about 100-300nm, with good oxidation resistance and high dispersibility, but it is difficult to prepare nano nickel powder with smaller particle size, and the preparation process is complicated, the equipment is expensive, and the production cost is extremely high.

[0005] Using high melting point water-soluble salt as the isolation phase can prevent the agglomeration and sintering of nanoparticles at high temperature, and the water-soluble salt is easy to wash and remove, which is conducive to the preparation of highly crystalline and highly dispersed nanoparticles. In the early stage of this project team, a variety of methods were used to develop nano-nickel powder, such as water-soluble sulfate co-precipitation method (Chinese patent CN201810037875.7), water-soluble salt nanoparticle isolation method (Chinese patent CN201810037620.0) and metal acetylacetonate solution impregnation method (2019101041603), but these methods still have the disadvantages of complex process and uneven particle size, making it difficult to prepare highly crystalline and highly dispersed nano-nickel powder on a large scale. Summary of the invention

[0006] Technical problem: The present invention provides a method for rapidly synthesizing highly crystalline and highly dispersed nano-nickel powder, which can be used to mass-produce nano-nickel powder with a particle size of less than 50 nm, uniform particle size, and good dispersion. This preparation technology has good application prospects in the fields of conductive slurries, magnetic fluids, and microwave absorbing materials.

[0007] Technical solution: The method for preparing highly crystalline and highly dispersed nano nickel powder of the present invention comprises the following steps:

[0008] 1) dissolving a nickel salt and citric acid in an organic solvent to prepare an organosol containing nickel, wherein the organic solvent is one of ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol butyl ether, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol and propylene glycol;

[0009] 2) mixing the organosol containing nickel with a water-soluble salt, allowing the water-soluble salt to settle by standing or centrifugation, and removing excess organosol from the upper portion to obtain a mixture of the organosol containing the metal element and the water-soluble salt;

[0010] 3) The mixture is kept at 60° C. to 120° C. to cause a sol-gel transition, and after the gel dries, a layer of dry gel film is coated on the surface of the water-soluble salt particles;

[0011] 4) calcining the water-soluble salt coated with the dry gel film at a temperature above 400° C. and below the melting point of the salt, so that the dry gel film is converted into nickel oxide nanoparticles, which are dispersed and attached to the surface of the water-soluble salt particles to form a calcined product;

[0012] 5) reducing the calcined product at 400° C. to 600° C. in a reducing atmosphere to convert the nickel oxide nanoparticles dispersed and attached to the surface of the water-soluble salt particles into nickel nanoparticles;

[0013] 6) washing the reduced product with water and drying it to obtain highly crystalline and highly dispersed nano nickel powder.

[0014] Furthermore, in the method of the present invention, the water-soluble salt in step 2) is potassium sulfate, sodium sulfate, potassium chloride or sodium chloride.

[0015] Furthermore, in the method of the present invention, in the nickel-containing organosol in step 1), the molar concentration of nickel is between 0.01M and 1M, and the molar ratio of nickel nitrate to citric acid is 1:0.1-1.

[0016] Furthermore, in the method of the present invention, in the organosol containing nickel in step 1), the nickel salt is nickel nitrate, nickel acetate or nickel chloride.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0018] Existing methods for preparing nano nickel powders make it difficult to simultaneously achieve high crystallinity, high dispersibility and small particle size. The nano nickel powders prepared by liquid phase reduction and electrolytic precipitation methods have poor crystallinity and are easily oxidized. The nano nickel powders prepared by chemical vapor condensation or physical vapor condensation methods have the disadvantages of large particle size, complex process, expensive equipment and high production cost. The project team has previously tried to use a variety of methods such as water-soluble sulfate co-precipitation, water-soluble salt nanoparticle isolation and metal acetylacetonate solution impregnation to prepare nano nickel powders, but these methods still have the disadvantages of complex process and uneven particle size, making it difficult to prepare highly crystalline and highly dispersed nano nickel powders on a large scale.

[0019] The present invention uses an organic sol containing nickel to impregnate water-soluble salts. The organic sol undergoes a sol-gel transition in a subsequent heat preservation process. When the organic solvent in the gel evaporates, the gel shrinks. After being completely dried, a layer of dry gel film can be coated on the surface of water-soluble salt particles. In a subsequent high-temperature calcination process, organic matter in the dry gel film is calcined and decomposed to generate nickel oxide nanoparticles. The generated nickel oxide nanoparticles are dispersed and attached to the surface of the water-soluble salt particles. The particles are then reduced in a reducing atmosphere at 400 to 600° C. to convert the nickel oxide nanoparticles dispersed and attached to the surface of the water-soluble salt particles into nickel nanoparticles. After cooling, the particles are washed with water to remove the salt, thereby obtaining metal nickel nanoparticles with good dispersibility and crystallinity.

[0020] The present invention utilizes the shrinkage characteristics of the gel during drying to generate a uniform dry gel film on the surface of the water-soluble salt particles. During high-temperature calcination, the organic matter decomposes, and the dry gel film becomes nickel oxide nanoparticles dispersed on the surface of the water-soluble salt particles. Our research shows that these nanoparticles are tightly attached to the surface of the salt particles and have a strong binding force with the water-soluble salt particles. When they are reduced to nickel nanoparticles again, they will not fall off the surface of the salt particles. At the same time, since these nickel nanoparticles do not contact each other, diffusion and mass transfer will not occur, and agglomeration and sintering will not occur. Moreover, the reduction temperature of the present invention can be as high as 800°C, the nickel nanoparticles are perfectly crystallized, and there are almost no crystal defects inside the particles. Therefore, the present invention can obtain highly crystalline and highly dispersed nano nickel powder.

[0021] After optimization, the present invention uses four water-soluble salts, namely potassium sulfate (melting point 1067° C.), sodium sulfate (melting point 884° C.), sodium chloride (melting point 801° C.), and potassium chloride (melting point 770° C.), to prepare nano nickel powder.

[0022] If a surfactant is added to the organic sol, the uniformity of the particle size of the nano nickel powder can be further improved. The surfactant includes polyethylene glycol, polyvinyl pyrrolidone, carboxylic acid surfactant, etc.

[0023] The preparation method of the invention has simple process and is easy for large-scale production, and can quickly prepare highly crystalline and highly dispersed nano nickel powder in batches, with a particle size of less than 50 nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The nano nickel powder is prepared by reduction at 600° C. using the method of the invention, has a particle size of about 30-50 nm and good dispersibility. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the embodiments and the accompanying drawings.

[0026] Embodiment 1: Nickel nitrate and citric acid are dissolved in ethylene glycol methyl ether to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel nitrate to citric acid is 1:0.5. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of the organosol and potassium sulfate. The mixture is kept warm at 60°C to 120°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0027] Embodiment 2: Nickel nitrate and citric acid are dissolved in ethylene glycol methyl ether to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel nitrate to citric acid is 1:0.5. The organosol is mixed with sodium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of organosol and potassium sulfate. The mixture is kept warm at 60°C to 120°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of sodium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0028] Embodiment 3: Nickel nitrate and citric acid are dissolved in ethylene glycol methyl ether to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel nitrate to citric acid is 1:0.5. The organosol is mixed with potassium chloride, and the excess organosol is poured off after sedimentation to obtain a mixture of organosol and potassium sulfate. The mixture is kept warm at 60°C to 120°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium chloride, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0029] Embodiment 4: Nickel nitrate and citric acid are dissolved in ethylene glycol methyl ether to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel nitrate to citric acid is 1:0.5. The organosol is mixed with sodium chloride, and the excess organosol is poured off after sedimentation to obtain a mixture of organosol and potassium sulfate. The mixture is kept warm at 60°C to 120°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of sodium chloride, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0030] Example 5: Nickel nitrate and citric acid are dissolved in ethylene glycol methyl ether to prepare an organosol, wherein the molar concentration of nickel is 0.01M, and the molar ratio of nickel nitrate to citric acid is 1:0.5. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of the organosol and potassium sulfate. The mixture is kept warm at 60°C to 120°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0031] Example 6: Nickel nitrate and citric acid are dissolved in ethylene glycol methyl ether to prepare an organosol, wherein the molar concentration of nickel is 1M, and the molar ratio of nickel nitrate to citric acid is 1:0.5. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of organosol and potassium sulfate. The mixture is kept warm at 60°C to 120°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0032] Example 7: Nickel nitrate and citric acid are dissolved in ethylene glycol methyl ether to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel nitrate to citric acid is 1:0.1. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of organosol and potassium sulfate. The mixture is kept warm at 60°C to 120°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0033] Example 8: Nickel nitrate and citric acid are dissolved in ethylene glycol methyl ether to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel nitrate to citric acid is 1:1. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of organosol and potassium sulfate. The mixture is kept warm at 60°C to 120°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0034] Example 9: Nickel nitrate and citric acid are dissolved in ethylene glycol ether to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel nitrate to citric acid is 1:0.5. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of organosol and potassium sulfate. The mixture is kept warm at 60°C to 120°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0035] Example 10: Nickel nitrate and citric acid are dissolved in ethylene glycol butyl ether to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel nitrate to citric acid is 1:0.5. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of the organosol and potassium sulfate. The mixture is kept warm at 60°C to 120°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0036] Example 11: Nickel nitrate and citric acid are dissolved in ethanol to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel nitrate to citric acid is 1:0.5. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of the organosol and potassium sulfate. The mixture is kept warm at 60°C to 75°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0037] Example 12: Nickel nitrate and citric acid are dissolved in n-propanol to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel nitrate to citric acid is 1:0.5. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of the organosol and potassium sulfate. The mixture is kept warm at 60°C to 90°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0038] Example 13: Nickel nitrate and citric acid are dissolved in isopropanol to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel nitrate to citric acid is 1:0.5. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of the organosol and potassium sulfate. The mixture is kept warm at 60°C to 75°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0039] Example 14: Nickel nitrate and citric acid are dissolved in n-butanol to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel nitrate to citric acid is 1:0.5. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of the organosol and potassium sulfate. The mixture is kept warm at 60°C to 110°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0040] Example 15: Nickel nitrate and citric acid are dissolved in ethylene glycol to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel nitrate to citric acid is 1:0.5. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of organosol and potassium sulfate. The mixture is kept warm at 60°C to 120°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0041] Example 16: Nickel nitrate and citric acid are dissolved in propylene glycol to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel nitrate to citric acid is 1:0.5. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of organosol and potassium sulfate. The mixture is kept warm at 60°C to 120°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0042] Example 17: Nickel acetate and citric acid are dissolved in ethylene glycol methyl ether to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel acetate to citric acid is 1:0.5. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of organosol and potassium sulfate. The mixture is kept warm at 60°C to 120°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

[0043] Example 18: Nickel chloride and citric acid are dissolved in ethylene glycol methyl ether to prepare an organosol, wherein the molar concentration of nickel is 0.1M, and the molar ratio of nickel chloride to citric acid is 1:0.5. The organosol is mixed with potassium sulfate, and the excess organosol is poured off after sedimentation to obtain a mixture of the organosol and potassium sulfate. The mixture is kept warm at 60°C to 120°C, and a loose powder is obtained after drying. The powder is calcined at 400°C to below the melting point of potassium sulfate, and then reduced in a reducing atmosphere at 400°C to 600°C. The reduced product is washed with water and dried to obtain a highly crystalline and highly dispersed nano nickel powder.

Claims

1. A method for preparing highly crystalline and highly dispersed nano nickel powder, characterized in that: The method comprises the following steps: 1) dissolving a nickel salt and citric acid in an organic solvent to prepare an organosol containing nickel, wherein the organic solvent is one of ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol butyl ether, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol and propylene glycol; 2) mixing the organosol containing nickel with a water-soluble salt, allowing the water-soluble salt to settle, and removing excess organosol from the upper portion to obtain a mixture of the organosol containing the metal element and the water-soluble salt, wherein the water-soluble salt is potassium sulfate, sodium sulfate, potassium chloride or sodium chloride; 3) The mixture is kept at 60° C. to 120° C. to cause a sol-gel transition, and after the gel dries, a layer of dry gel film is coated on the surface of the water-soluble salt particles; 4) calcining the water-soluble salt coated with the dry gel film at a temperature above 400° C. and below the melting point of the water-soluble salt, so that the dry gel film is converted into nickel oxide nanoparticles, which are dispersed and attached to the surface of the water-soluble salt particles to form a calcined product; 5) calcining the calcined product at 400° C. to 600° C. in a reducing atmosphere to convert the nickel oxide nanoparticles dispersed and attached to the surface of the water-soluble salt particles into nickel nanoparticles; 6) washing the reduced product with water and drying it to obtain highly crystalline nano nickel powder.

2. The method for preparing highly crystalline and highly dispersed nano nickel powder according to claim 1, characterized in that: In the nickel-containing organic sol, the molar concentration of nickel is between 0.01M and 1M, and the molar ratio of nickel salt to citric acid is 1:0.1-1.

3. The method for preparing highly crystalline and highly dispersed nano nickel powder according to claim 1 or 2, characterized in that: In the nickel-containing organic sol, the nickel salt is nickel nitrate, nickel acetate or nickel chloride.

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