A method for preparing ultrafine spherical cobalt powder

Abstract

The present application belongs to the technical field of metal powder preparation, and particularly relates to a preparation method of superfine spherical cobalt powder. The method uses anhydrous cobalt chloride as raw material, and after calcination under inert atmosphere, ammonia gas is introduced for ammoniation treatment to obtain a cobalt chloride ammonia complex. Then, aging treatment is carried out under the conditions of heat preservation and moisture retention, so that the cobalt element is converted from divalent state to trivalent state to obtain a precursor powder containing trivalent cobalt. Finally, reduction is carried out under hydrogen atmosphere to obtain superfine spherical cobalt powder with a particle size of 0.5-0.8 microns. The present application firstly proposes a cobalt powder preparation method through a cobalt chloride ammonia complex path. The aging treatment realizes the conversion of cobalt valence and the regulation of precursor structure, so that the reduction temperature is lower, the cobalt powder particles are finer and more uniform, and the problems such as high cost, complex process and environmental pollution of the existing cobalt powder preparation method are solved.

Description

Technical Field

[0001] This invention belongs to the field of metal powder preparation technology, specifically relating to a method for preparing ultrafine spherical cobalt powder. Background Technology

[0002] Cobalt powder is widely used in the manufacture of cemented carbide, high-temperature alloys, special tools, magnetic materials, batteries, catalysts, and other fields due to its excellent physical, chemical, and mechanical properties, such as high specific surface area, high chemical reactivity, and a large number of specific surface area atoms. Its application is particularly extensive in the powder metallurgy field, including the manufacture of cemented carbide and special tools.

[0003] Cobalt, as a binder metal, is the best binder for cemented carbide. Therefore, the development of the cemented carbide industry and the cobalt industry are mutually reinforcing. The production of cemented carbide involves mixing, pressurizing, and sintering processes, which generate mechanical flow, plastic flow, and thermal diffusion phenomena. Therefore, cobalt powder used in cemented carbide production must possess the following three characteristics: high purity, fine particle size, and high sphericity. High purity of the prepared cobalt powder is required because, on the one hand, pure cobalt can completely wet tungsten carbide and has a high holding force on it, thereby improving the strength of the cemented carbide. On the other hand, the presence of other impurities in the cobalt powder, such as lead, silicon, calcium, and sulfur, will affect the microstructure and properties of the alloy during sintering. The effect of cobalt powder refinement is mainly reflected in its ability to not only inhibit the early growth of ultrafine WC-Co cemented carbide grains but also improve the wear resistance and crack resistance of the cemented carbide. Furthermore, cobalt powder with higher sphericity will effectively shorten the ball milling time, resulting in a more uniform and denser microstructure of the cemented carbide.

[0004] Cobalt powder is one of the main raw materials for cemented carbide, and its demand both domestically and internationally is increasing year by year. With the development of the cemented carbide industry, some existing preparation processes can no longer meet the production needs of high-performance cobalt powder. Currently, the main methods for preparing cobalt powder include water mist method, reduction method, polyol method, and hydrazine liquid-phase reduction method. However, these methods all have certain shortcomings when applied to industrial production. The water mist method for producing cobalt powder is easy to control in terms of preparation conditions and has low labor intensity, but it requires large equipment investment and has high costs, making it difficult to achieve industrial production. The reduction method mainly uses cobalt oxalate as a raw material, and the cobalt powder reduced by this method is easily oxidized. The polyol method has the disadvantages of high cost, long reaction time, and low production efficiency. Furthermore, like the hydrazine liquid-phase reduction method, the raw materials and organic byproducts generated during production cause a certain degree of environmental pollution. Therefore, it is necessary to invent a low-cost, high-efficiency, and environmentally friendly method for preparing cobalt powder. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing preparation methods and provide a method for preparing ultrafine spherical cobalt powder using anhydrous cobalt chloride as raw material through an ammonia complex pathway.

[0006] To achieve the above objectives, the present invention provides a method for preparing ultrafine spherical cobalt powder, comprising the following steps: (1) Place the raw material, anhydrous cobalt chloride, in a heating device and calcine it by introducing an inert gas. The calcination temperature is 300℃~500℃, and the holding time is 1h~3h. After calcination, ammoniation treatment is performed to obtain cobalt chloride ammonium complex; (2) The obtained cobalt chloride ammonium complex was kept warm and moist for 6h to 120h at a temperature of 30℃ to 80℃ and a humidity of 40%RH to 95%RH to obtain precursor powder. (3) The obtained precursor powder is placed in a heating device, a reducing atmosphere is introduced, and the temperature is raised and reduced at a suitable heating rate. The reduction temperature is 300℃~500℃, and the reduction time is 1h~3h, thereby obtaining sponge-like cobalt powder.

[0007] Preferably, the calcination and ammoniation processes described in step (1) can be achieved using heating equipment such as a rotary kiln or a tube furnace, wherein the inert gas used is argon and the ammoniation gas is ammonia. The rotation speed of the rotary kiln is 8–12 r / min.

[0008] Preferably, the calcination temperature in step (1) is 300℃~500℃, and the holding time is 1h~3h. The ammoniation treatment starts at 100℃~200℃.

[0009] The aging process described in step (2) can be achieved by using equipment such as a heat preservation and humidification machine or a biological incubator. During the aging process, the powder should be turned over once every 4 to 8 hours.

[0010] Preferably, the aging temperature in step (2) is 30℃~80℃, the humidity is 40%RH~95%RH, and the aging time is 6h~120h.

[0011] Preferably, the reduction process in step (3) can be achieved by heating equipment such as a rotary kiln or a tube furnace, wherein the selected reduction atmosphere is hydrogen.

[0012] Preferably, the reduction temperature in step (3) is 300℃~500℃, and the reduction time is 1h~3h. The reduction heating rate is ≤6℃ / min.

[0013] Preferably, the ultrafine spherical cobalt powder prepared by the aforementioned method has a particle size of 0.5 μm to 0.8 μm and a purity of ≥99.7%.

[0014] This invention is the first to use the technical route of "anhydrous cobalt chloride → cobalt chloride ammonium complex → aging (divalent cobalt → trivalent cobalt) → hydrogen reduction" to prepare ultrafine spherical cobalt powder.

[0015] First, this invention uses cobalt chloride to generate a cobalt chloride-ammonia complex under ammonia conditions. Compared to traditional methods that commonly use cobalt oxalate or cobalt carbonate as raw materials, this method has a stronger complexing ability, and the ammonia reacts with Co... 2+ Preferred coordination forms [Co(NH3)6] 2+ It is easily oxidized to [Co(NH3)6] 3+ (Trivalent cobalt ammonia complex) is helpful for subsequent aging and reduction treatments to prepare ultrafine, spherical cobalt powder.

[0016] Secondly, in this invention, the cobalt chloride ammonium complex is aged before hydrogen reduction. In the cobalt chloride ammonium complex ([Co(NH3)6]Cl2) obtained after ammoniation treatment, cobalt exists in a divalent state (Co... 2+ It exists in the form of ). When the complex is aged in a temperature- and humidity-controlled environment, it undergoes decomposition and oxidation reactions under the combined effects of humidity and temperature, and the cobalt element changes from a divalent state to a trivalent state (Co). 3+ The process ultimately forms a precursor powder containing trivalent cobalt (mainly trivalent cobalt compounds such as CoOOH or Co(OH)3).

[0017] The scientific significance of this aging process lies in the following: First, trivalent cobalt oxides are more readily reduced by hydrogen. Thermodynamic analysis shows that the standard Gibbs free energy of formation for trivalent cobalt oxides is lower than that for divalent cobalt oxides, resulting in a lower activation energy for the reduction reaction during hydrogen reduction. Therefore, efficient reduction can be achieved at lower temperatures. The hydrogen reduction temperature of the aged precursor can be 50–100°C lower than that of the unaged divalent cobalt precursor, and the reduction reaction is more complete.

[0018] Secondly, the aging process is conducive to the formation of loosely structured nanoscale precursors. Under warm and humid conditions, the cobalt chloride ammonium complex slowly decomposes and oxidizes in situ, releasing NH3 and HCl gases. During the gas escape process, a large number of microporous structures are formed inside and on the surface of the precursor particles, giving the precursor a loose, sponge-like morphology. This structural feature is conducive to the rapid diffusion of hydrogen and the uniform nucleation of reduction products during the subsequent hydrogen reduction process, thereby obtaining spherical cobalt powder with finer particle size and more uniform distribution. At the same time, aging time and humidity are key parameters for controlling the morphology of the precursor and the degree of cobalt valence state conversion. Too short an aging time or insufficient humidity will lead to insufficient cobalt valence state conversion, leaving a large amount of divalent cobalt in the precursor, which is prone to forming large particles with irregular morphology during the subsequent reduction process. An appropriate aging time (6-120h) can achieve complete cobalt conversion, ensuring the ultrafineness and sphericity of the reduction products.

[0019] Third, direct reduction without aging has significant drawbacks. If the cobalt chloride ammonium complex obtained in step (1) is directly reduced with hydrogen without aging, the reduction reaction needs to be carried out at a higher temperature (usually >500℃) because the cobalt in the precursor is divalent and has a dense structure. The resulting cobalt powder particles are coarse (average particle size ≥2μm), irregular in morphology, and poorly dispersible. Furthermore, the reduction reaction is incomplete, and unreduced cobalt compounds remain in the product, seriously affecting the quality of the cobalt powder. Therefore, the aging step is an indispensable key step in the technical solution of this invention.

[0020] The present invention has the following beneficial effects: This invention is the first to use anhydrous cobalt chloride as raw material to prepare ultrafine spherical cobalt powder via an ammonia complex intermediate, providing a brand-new technical approach for the preparation of cobalt powder and breaking through the limitations of traditional processes such as cobalt oxalate reduction and water misting.

[0021] This invention utilizes the heat preservation and moisture retention treatment during the aging process to simultaneously achieve the conversion of cobalt from a divalent to a trivalent state and the formation of a loose and porous precursor structure. The trivalent cobalt precursor is more easily reduced by hydrogen, and the reduction temperature is 50-100°C lower than that of traditional methods; the loose, sponge-like structure is conducive to hydrogen diffusion and uniform nucleation, ultimately yielding ultrafine spherical cobalt powder with a particle size of 0.5-0.8 μm.

[0022] This invention requires only anhydrous cobalt chloride as a raw material, eliminating the need for expensive or harmful reagents such as oxalic acid, polyols, and hydrazine hydrate, thus significantly reducing raw material costs. The equipment used consists of conventional industrial equipment such as rotary kilns, tube furnaces, and heat preservation and humidification machines, requiring no specially customized equipment and facilitating industrial-scale production. The entire preparation process does not produce any toxic or harmful byproducts, and gases such as ammonia and hydrogen can be recovered and recycled, meeting the requirements of green chemical development. Attached Figure Description

[0023] Figure 1 The image shows the X-ray diffraction pattern of the ultrafine cobalt powder obtained in Example 1.

[0024] Figure 2 The image shows a scanning electron microscope (SEM) image of the morphology of the ultrafine cobalt powder obtained in Example 2.

[0025] Figure 3 The image shows a scanning electron microscope (SEM) image of the morphology of the ultrafine cobalt powder obtained in Example 3.

[0026] Figure 4 The X-ray diffraction pattern of the cobalt powder obtained in Comparative Example 1 is shown.

[0027] Figure 5 The X-ray diffraction pattern of the cobalt powder obtained in Comparative Example 2 is shown. Detailed Implementation

[0028] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention. Example 1

[0029] Step 1: Place the raw material, anhydrous cobalt chloride, in a rotary kiln and calcine it at a constant rotation speed of 10 r / min under an argon atmosphere. The calcination temperature is set to 360℃, and the calcination time is 1 hour. After calcination, wait for the furnace temperature to drop to 180℃, then begin ammonia gas to ammonification, and gently tap the tube wall to prevent the powder from sticking and clumping, until it is removed at room temperature.

[0030] Step 2: Place the powder obtained in Step 1 in an open container, spread it evenly, and then place it in a heat preservation and humidification machine. Set the heat preservation temperature to 40℃ and the humidity to 65%RH for 72 hours. During the heat preservation and humidification process, turn the powder over every 6 hours. After the heat preservation and humidification is completed, the precursor powder is obtained.

[0031] Step 3: The precursor powder is loaded into a quartz boat and placed in a tube furnace for reduction under a hydrogen atmosphere. The temperature is raised to 360°C at a rate of 4°C / min and held for 90 minutes. After complete reduction, ultrafine spherical cobalt powder is obtained.

[0032] The cobalt powder prepared by the above process has high purity (≥99.7%), fine and uniform particle size (average particle size of 0.54 μm), and high sphericity. The X-ray diffraction pattern of the ultrafine cobalt powder obtained in this example is shown below. Figure 1 As shown. Example 2

[0033] Step 1: Place the raw material, anhydrous cobalt chloride, in a rotary kiln and calcine it at a constant rotation speed of 10 r / min under an argon atmosphere. Set the calcination temperature to 360℃ and the calcination time to 1 hour. After calcination, wait for the furnace temperature to drop to 150℃, then introduce ammonia gas for ammoniation, and gently tap the tube wall to prevent the powder from sticking and clumping. Remove the powder at room temperature.

[0034] Step 2: Place the powder obtained in Step 1 in an open container, spread it evenly, and then place it in a heat preservation and humidification machine. Set the heat preservation temperature to 50℃ and the humidity to 75%RH for 72 hours. During the heat preservation and humidification process, turn the powder over every 6 hours. After the heat preservation and humidification is completed, the precursor powder is obtained.

[0035] Step 3: The precursor powder is loaded into a quartz boat and placed in a tube furnace for reduction under a hydrogen atmosphere. The temperature is raised to 360°C at a rate of 5°C / min and held for 120 minutes. After complete reduction, ultrafine spherical cobalt powder is obtained.

[0036] The cobalt powder prepared by the above process has high purity (≥99.7%), fine and uniform particle size (average particle size of 0.57 μm), and high sphericity. The scanning electron microscope image of the morphology of the ultrafine cobalt powder obtained in this example is shown below. Figure 2 As shown. Example 3

[0037] Step 1: Place the raw material, anhydrous cobalt chloride, in a rotary kiln and calcine it at a constant rotation speed of 10 r / min under an argon atmosphere. The calcination temperature is set to 360℃, and the calcination time is 1 hour. After calcination, wait for the furnace temperature to drop to 180℃, then begin ammonia gas to ammonification, and gently tap the tube wall to prevent the powder from sticking and clumping, until it is removed at room temperature.

[0038] Step 2: Place the powder obtained in Step 1 in an open container, spread it evenly, and then place it in a heat preservation and humidification machine. Set the heat preservation temperature to 60℃ and the humidity to 85%RH for 48 hours. During the heat preservation and humidification process, turn the powder over every 6 hours. After the heat preservation and humidification is completed, the precursor powder is obtained.

[0039] Step 3: The precursor powder is loaded into a quartz boat and placed in a tube furnace for reduction under a hydrogen atmosphere. The temperature is raised to 380°C at a rate of 4°C / min and held for 90 minutes. After complete reduction, ultrafine spherical cobalt powder is obtained.

[0040] The cobalt powder prepared by the above process has high purity (≥99.7%), fine and uniform particle size (average particle size of 0.62 μm), and high sphericity. The scanning electron microscope image of the morphology of the ultrafine cobalt powder obtained in this example is shown below. Figure 3 As shown.

[0041] Comparative Example 1, without aging treatment Step 1: Place the raw material, anhydrous cobalt chloride, in a rotary kiln and calcine it at a constant rotation speed of 10 r / min under an argon atmosphere. The calcination temperature is set to 360℃, and the calcination time is 1 hour. After calcination, wait for the furnace temperature to drop to 180℃, then begin ammonia gas to ammonification, and gently tap the tube wall to prevent the powder from sticking and clumping, until it is removed at room temperature.

[0042] Step 2: The powder obtained in Step 1 is loaded into a quartz boat and placed in a tube furnace for reduction under a hydrogen atmosphere. The temperature is raised to 360°C at a rate of 4°C / min, and held for 90 minutes. After complete reduction, cobalt powder is obtained.

[0043] The cobalt powder prepared through the above process is not completely reduced, containing a large amount of unreduced material, making it difficult to obtain pure cobalt powder. The X-ray diffraction pattern of the cobalt powder obtained in this example is shown below. Figure 4 As shown.

[0044] Comparative Example 2: Incomplete aging reaction Step 1: Place the raw material, anhydrous cobalt chloride, in a rotary kiln and calcine it at a constant rotation speed of 10 r / min under an argon atmosphere. The calcination temperature is set to 360℃, and the calcination time is 1 hour. After calcination, wait for the furnace temperature to drop to 180℃, then begin ammonia gas to ammonification, and gently tap the tube wall to prevent the powder from sticking and clumping, until it is removed at room temperature.

[0045] Step 2: Place the powder obtained in Step 1 in an open container, spread it evenly, and then place it in a heat preservation and humidification machine. Set the heat preservation temperature to 40℃, the humidity to 65%RH, and the heat preservation and humidification time to 2 hours. After the end of the process, the precursor powder is obtained.

[0046] Step 3: The precursor powder is loaded into a quartz boat and placed in a tube furnace for reduction under a hydrogen atmosphere. The temperature is raised to 360°C at a rate of 4°C / min and held for 90 minutes. After complete reduction, cobalt powder is obtained.

[0047] The cobalt powder prepared through the above process is not completely reduced, containing some unreduced phases, resulting in cobalt powder that is not pure enough. The X-ray diffraction pattern of the cobalt powder obtained in this example is shown below. Figure 5 As shown.

[0048] The above description merely illustrates preferred embodiments of the present invention, and while the description is relatively specific and detailed, it should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications, improvements, and substitutions without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for preparing ultrafine spherical cobalt powder, characterized in that: Includes the following steps: Anhydrous cobalt chloride was placed in a heating device and calcined under an inert atmosphere. Ammonia was introduced during the cooling process to carry out ammoniation treatment, thereby obtaining a cobalt chloride ammonium complex. The cobalt chloride ammonium complex obtained in step (1) was kept warm and moist for a period of time to carry out an aging reaction, and the precursor powder was obtained. The precursor powder obtained in step (2) was reduced in a reducing atmosphere to obtain sponge-like ultrafine spherical cobalt powder.

2. The method for preparing ultrafine spherical cobalt powder according to claim 1, characterized in that: The inert atmosphere mentioned in step (1) is argon atmosphere, and the calcination temperature is 300℃~500℃ and held for 1h~3h. After calcination, the temperature is lowered to 100℃~200℃ and ammonia gas is introduced.

3. The method for preparing ultrafine spherical cobalt powder according to claim 1, characterized in that: The aging reaction in step (2) is carried out at a temperature of 30℃~80℃, a humidity of 40%RH~95%RH, and an aging time of 6h~120h.

4. The method for preparing ultrafine spherical cobalt powder according to claim 1, characterized in that: The reducing atmosphere is hydrogen, and the reduction temperature is 300℃~500℃, maintained at that temperature for 1h~3h. The heating rate of the equipment during the reduction process is controlled within 6℃ / min.

5. The method for preparing ultrafine spherical cobalt powder according to claim 1, characterized in that: The calcination and ammoniation processes described in step (1) are carried out in a rotary kiln or a tubular furnace, with the rotary kiln rotating at a speed of 8 to 12 r / min.

6. The method for preparing ultrafine spherical cobalt powder according to claim 1, characterized in that: The aging reaction described in step (2) is carried out in a heat preservation and humidification machine or a biological incubator. During the aging process, the powder is turned over once every 4 to 8 hours.

7. The method for preparing ultrafine spherical cobalt powder according to claim 1, characterized in that: The ultrafine spherical cobalt powder has a particle size of 0.5μm to 0.8μm and a purity of ≥99.7%.

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