A method for preparing flaky molybdenum powder

Abstract

The present invention discloses a method for preparing flaky molybdenum powder. The method comprises adding silicone oil as a primary grinding aid along with an auxiliary grinding aid to spherical molybdenum powder, mixing to form a suspension, and then subjecting the mixture to intermittent ball milling and post-processing to obtain flaky molybdenum powder having an aspect ratio greater than 100. This preparation method utilizes silicone oil as a primary grinding aid to coat and modify the molybdenum powder surface, and achieves efficient preparation of flaky molybdenum powder by controlling ball milling parameters. The method has the advantages of strong operability and a high flake yield. The prepared flaky molybdenum powder exhibits a smooth surface, uniform particle size distribution, high specific surface area, and a large aspect ratio.

Description

Technical Field

[0001] The invention belongs to the technical field of metal powder preparation, and particularly relates to a method for preparing flaky molybdenum powder. Background Art

[0002] The refractory metal molybdenum has high melting point and boiling point, extremely high strength and hardness, good wear resistance, corrosion resistance, high temperature resistance, electrical and thermal conductivity and low thermal expansion coefficient. Therefore, it is widely used in aerospace, electronics, machinery manufacturing, national defense, metallurgy and other fields.

[0003] The application performance of metal powder is closely related to its shape. Powders of different shapes can have significantly different performance under the same operating conditions. Compared to spherical and granular metal powders, flake metal powders have a larger specific surface area, which not only maintains good dispersion of micron-sized powders but also ensures high surface activity. In terms of conductivity, compared to flake metal powder, spherical and granular metal powders have point contact between particles, resulting in poor conductivity, high metal powder usage, and high costs. However, flake metal powder particles not only have a larger specific surface area, but also have line and surface contact between particles, significantly increasing the contact area between flake metal powder particles. Therefore, compared with spherical and granular metal powders, the amount of flake metal powder required to form a conductive path with the same conductivity is significantly reduced. Furthermore, viscous products formulated with flake metal powder exhibit thixotropic properties, significantly improving the product's sedimentation stability. Therefore, using flake metal powder to formulate conductive electronic materials can significantly improve the product's conductivity, adhesion, and storage stability, while significantly reducing metal powder usage, saving resources, reducing production costs, and improving economic benefits. In terms of surface treatment, due to its good dispersibility and large specific surface area, coatings or chemical reagents can more easily penetrate the gaps between flake particles, significantly improving the effectiveness and efficiency of surface treatment. In terms of chemical catalysis, electromagnetic shielding, and radar wave reflection, flake metal powders have shown excellent catalytic performance, electromagnetic shielding performance, and radar wave reflection performance due to their significantly larger specific surface area than spherical metal powders and granular metal powders. Therefore, the preparation technology of flake metal powders has attracted much attention.

[0004] Currently, molybdenum powder production primarily focuses on amorphous, blocky, and spherical molybdenum powders. There are currently no publicly available preparation technologies suitable for producing flake molybdenum powder. This is primarily due to the following difficulties in producing flake molybdenum powder: 1. Molybdenum is relatively brittle. Unlike aluminum, copper, and zinc powders, which exhibit excellent plasticity and ductility, molybdenum powder is prone to cracking and fragmentation. 2. Molybdenum powder has a narrow processing window for morphological transformation. The preparation of flake molybdenum powder requires precise control of plastic deformation without fragmentation or excessive refinement, a process that requires meticulous adjustment of ball milling parameters. 3. Powder agglomeration. Molybdenum powder is prone to cold welding and agglomeration during ball milling, which not only affects the uniformity of the final product but can also damage the flake structure. 4. Uniformity control is difficult. The thickness and diameter of the flake powder must maintain a certain ratio to meet specific application requirements. 5. High energy consumption. Prolonged ball milling increases energy consumption and production costs. Therefore, a suitable ball milling process is needed to shorten milling time while ensuring the quality of the flake molybdenum powder. Summary of the Invention

[0005] To address the challenges of the prior art, the present invention aims to provide a method for preparing flaky molybdenum powder. This method uses silicone oil as the primary grinding aid and adds a certain amount of auxiliary grinding aid to coat and modify the molybdenum powder. This method can be achieved by controlling the parameters of the ball milling process, resulting in advantages such as strong operability and a high flaking rate. The molybdenum powder obtained by this method has a smooth surface, two micron-scale dimensions in its three-dimensional structure, and a submicron-scale third dimension. It exhibits advantages such as uniform particle size distribution, high specific surface area, and a large aspect ratio, greatly expanding the application scenarios and overall performance of molybdenum powder.

[0006] In order to achieve the above technical objectives, the present invention provides a method for preparing flaky molybdenum powder, which comprises adding silicone oil as a main grinding aid together with an auxiliary grinding aid to spherical molybdenum powder, mixing to form a suspension, and then subjecting the suspension to intermittent ball milling and post-treatment to obtain flaky molybdenum powder with a diameter-to-thickness ratio greater than 100; the auxiliary grinding aid is at least one of polyethylene glycol and citric acid; and the mass ratio of the spherical molybdenum powder, silicone oil, and auxiliary grinding aid is (100-200):(100-200):(0.2-2.5).

[0007] The key to the technical solution of the present invention lies in the selection of grinding aids and the combination of wet ball milling process. First, silicone oil is used as the main grinding aid because there is no direct reaction between silicone oil and molybdenum powder. After stirring, it can form a suspension with a certain viscosity with the molybdenum powder, reducing the friction of particles during the ball milling process and preventing molybdenum powder from agglomerating, thereby improving the dispersion effect. In this way, under the mechanical force of the ball milling process, the molybdenum powder particles are not easily broken or fractured, thereby improving the effect and efficiency of ball milling and the operability of the process. To optimize the ball milling effect, the present invention also adds other grinding aids. These substances can work together with silicone oil to form a protective layer on the surface of the powder particles, improving the fluidity and oxidation resistance of the powder, thereby improving the uniformity of the particle size distribution of the flaky molybdenum powder. In this way, the morphology of the molybdenum powder can be changed by controlling the parameters of the ball milling process. During the ball milling process, strong collisions and friction will occur between the grinding balls in the ball mill and the molybdenum powder. These mechanical forces will apply shear force to the spherical molybdenum powder, causing it to gradually undergo plastic deformation, that is, gradually transforming from its original spherical shape into a flat flaky structure. This is because the lattice structure of molybdenum powder will slip under repeated impact and shear, resulting in a change in particle shape. By adjusting factors such as ball milling time, ball milling speed, ball-to-material ratio, and ball milling cooling time, this deformation process can be controlled to transform spherical molybdenum powder into flake molybdenum powder.

[0008] The inventors discovered that the mass ratio of the spherical molybdenum powder, silicone oil, and auxiliary grinding aid in the present invention has a direct impact on the effectiveness of ball milling. When the amount of silicone oil used is too small, it cannot effectively form a protective film and cushioning force, and the ball millability of the molybdenum powder cannot be effectively improved during the ball milling process, and the spherical molybdenum powder is prone to shattering. When the amount of silicone oil used is too high, it is not conducive to the subsequent removal of the solvent and will also indirectly affect the quality of the flaky molybdenum powder. When the amount of auxiliary grinding aid used is too low, the improvement in the flowability of the flaky molybdenum powder is weak, and the prepared flaky molybdenum powder has an uneven particle size distribution and poor surface quality. When the amount of auxiliary grinding aid used is too high, the protective and cushioning effects provided are weakened, which can cause the molybdenum powder to shatter and crack.

[0009] As a preferred embodiment, the viscosity of the silicone oil is 100-1200 Pa.s. Appropriate viscosity maintains uniform particle dispersion during ball milling, mitigates mechanical collisions between the grinding balls and the molybdenum powder, and promotes the formation of a uniform, complete, flaky morphology. Too low a viscosity is detrimental to particle dispersion and the buffering of mechanical collisions during ball milling. Too high a viscosity impairs silicone oil fluidity, making it difficult to evenly disperse the powder, which in turn affects the powder's uniformity and morphology.

[0010] As a preferred embodiment, the particle size of the spherical molybdenum powder ranges from 20 to 150 μm. The particle size of the spherical molybdenum powder in the present invention has a certain impact on the quality of the prepared flaky molybdenum powder. A larger particle size of the spherical molybdenum powder results in a larger diameter-to-thickness ratio of the prepared flaky molybdenum powder, a narrower particle size distribution, and a more uniform particle size distribution of the prepared flaky molybdenum powder. However, if the particle size is too large, the spherical molybdenum powder is prone to fragmentation during the ball milling process, which is detrimental to the particle size uniformity of the prepared flaky molybdenum powder. If the particle size is too small, the prepared flaky powder will also be smaller in size, failing to fully realize the application advantages of flaky powder.

[0011] As a preferred solution, the mixing condition is: stirring at room temperature for 5 to 30 minutes. By fully stirring and mixing, the molybdenum powder and the grinding aid can be more fully reacted to control the viscosity of the suspension.

[0012] As a preferred solution, the conditions for the ball milling process are: a rotation speed of 50 to 500 rpm, a ball-to-material ratio of (15 to 20):1, a time of 10 to 16 hours, and after every 5 to 20 minutes of ball milling, the process is paused for 10 to 30 minutes for cooling. The ball milling process of the present invention is mainly to change the morphology of spherical molybdenum powder. The parameter setting of the ball milling process can effectively improve the product yield and particle size uniformity of flaky molybdenum powder. In the present invention, the higher the ball-to-material ratio, the higher the probability of collision between the grinding balls and the powder during the grinding process, which can improve the grinding efficiency and the uniformity of the powder grinding; the lower the rotation speed, the smaller the force of the grinding balls on the powder, so that the powder will not break during the grinding process. Therefore, using a lower rotation speed and a higher ball-to-material ratio can effectively improve the grinding efficiency and the particle size uniformity of the flaky molybdenum powder. More preferably, the rotation speed is 200 to 400 rpm; further, the rotation speed is 250 to 350 rpm and the time is 12 to 16 hours. The ball milling process is an exothermic process, and the molybdenum powder targeted by the present invention is more brittle than copper powder and aluminum powder, which have better ductility. If the temperature is too high during continuous ball milling, it will not only easily cause the molybdenum to shatter and crack, but will also have an adverse effect on the grinding aid and form partial agglomeration. Therefore, intermittent ball milling is required. At the same time, the cooling time also needs to be controlled. If the cooling time is too long, the ball milling efficiency will be reduced. Therefore, it is further preferred to adopt a ball milling method of 10 minutes per ball milling and 20 minutes of cooling pause.

[0013] As a preferred solution, the ball milling process includes pouring the mixed liquid into a tank body of a ball mill, the material of the ball mill tank is one of polyurethane, nylon, polytetrafluoroethylene, corundum, stainless steel, agate, zirconium oxide, silicon carbide and cemented carbide, and the material of the grinding balls is one of polyurethane, corundum, stainless steel, agate, zirconium oxide, silicon carbide and cemented carbide.

[0014] As a preferred solution, the post-processing includes filtering, washing, and drying the sample after ball milling. The filtering, washing, and drying processes can effectively remove the residual grinding aid in the flaky molybdenum powder, thereby ensuring the quality of the prepared flaky molybdenum powder.

[0015] As a preferred solution, the cleaning treatment includes sequentially performing alkali washing, distilled water washing and ethanol washing on the filtered sediment.

[0016] As a preferred solution, the concentration of the alkaline washing solution is 10-20% w / w.

[0017] As a preferred solution, ultrasonic treatment and mechanical stirring treatment are used in the cleaning process.

[0018] As a preferred solution, the drying treatment includes placing the cleaned sample in a vacuum drying oven and drying it at 40-80° C. for 4-16 hours under vacuum.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1) The present invention combines silicone oil with molybdenum powder to form a molybdenum powder suspension, which reduces particle friction during ball milling, prevents molybdenum powder agglomeration, and improves dispersion. This reduces the mechanical forces of the ball milling process, making the molybdenum powder particles less susceptible to breakage and fracture, thereby improving the effectiveness and efficiency of the ball milling and the operability of the process. To optimize the ball milling effect, the present invention also adds auxiliary grinding aids, which can form a protective layer on the surface of the powder particles together with the silicone oil, improving the wettability, flowability, and oxidation resistance of the powder, thereby increasing the uniformity of the particle size distribution of the flaky molybdenum powder.

[0021] 2) The preparation method of the present invention has strong operability, short production cycle, is convenient for industrial scale-up production, and has high film forming rate and good film forming effect.

[0022] 3) The flaky molybdenum powder prepared by the present invention has a three-dimensional structure with two dimensions at the micron level and a third at the submicron level. It also has a smooth surface, uniform particle size distribution, and a high specific surface area. Furthermore, the flaky molybdenum powder of the present invention has a significant advantage in aspect ratio, which not only provides good dispersibility but also ensures high surface quality during application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Microscopic images of the raw material spherical molybdenum powder used in the examples and comparative examples of the present invention.

[0024] Figure 2 This is a microscopic image of the molybdenum powder prepared in Example 1 of the present invention.

[0025] Figure 3 This is a microscopic image of the molybdenum powder prepared in Example 2 of the present invention.

[0026] Figure 4 This is a microscopic image of the molybdenum powder prepared in Example 3 of the present invention.

[0027] Figure 5 This is a microscopic image of the molybdenum powder prepared in Comparative Example 1 of the present invention.

[0028] Figure 6 This is a microscopic image of the molybdenum powder prepared in Comparative Example 2 of the present invention.

[0029] Figure 7 This is a microscopic image of the molybdenum powder prepared in Comparative Example 3 of the present invention.

[0030] Figure 8 This is a microscopic image of the molybdenum powder prepared in Comparative Example 4 of the present invention. DETAILED DESCRIPTION

[0031] In order to further illustrate the present invention, the contents of the present invention are described in detail below in conjunction with the examples. However, it should be understood that these examples are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating processes are provided only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention. The scope of protection of the present invention is not limited to the following examples.

[0032] The silicone oil used in the examples and comparative examples of the present invention is dimethyl silicone oil, purchased from Dow Corning, model number PMX-200.

[0033] Example 1

[0034] 100g of spherical molybdenum powder (median particle size of 35μm) was Figure 1 As shown, 0.2g of citric acid is added to 100g of silicone oil (viscosity of 400Pa.S), and mixed for 30min under the combined action of stirring and ultrasonic waves to form a molybdenum powder suspension; then poured into a ball mill, the ball mill speed is set to 300rpm, the ball-to-material ratio is 20:1, the time is set to 16h, each ball milling is 10min, and the cooling is paused for 20min; after the ball milling is completed, the precipitate after filtering the ball-milled sample is ultrasonically and stirred with a 20% w / w sodium hydroxide solution for 15min; ultrasonically and stirred with deionized water until the solution pH is neutral; then ultrasonically and stirred with ethanol for 15min, and the operation is repeated twice; then the sample is placed in a vacuum drying oven and treated at 60°C for 4h to obtain flaky molybdenum powder.

[0035] Example 2

[0036] 150g of spherical molybdenum powder (median particle size of 35μm) was Figure 1 As shown, 2g of polyethylene glycol is added to 200g of silicone oil (viscosity of 200Pa.S), and mixed for 30min under the combined action of stirring and ultrasonic waves to form a molybdenum powder suspension; then poured into a ball mill, the ball mill speed is set to 350rpm, the ball-to-material ratio is 15:1, the time is set to 14h, each ball milling is 10min, and the cooling is paused for 20min; after the ball milling is completed, the precipitate after filtering the ball-milled sample is ultrasonically and stirred with a 20% w / w sodium hydroxide solution for 15min; ultrasonically and stirred with deionized water until the solution pH is neutral; then ultrasonically and stirred with ethanol for 15min, and the operation is repeated twice; then the sample is placed in a vacuum drying oven and treated at 60°C for 4h to obtain flaky molybdenum powder.

[0037] Example 3

[0038] 200g of spherical molybdenum powder (median particle size of 35μm) was Figure 1 As shown, 2g of polyethylene glycol and 0.5g of citric acid are added to 200g of silicone oil (viscosity of 200Pa.S), and mixed for 30min under the combined action of stirring and ultrasonic waves to form a molybdenum powder suspension; then poured into a ball mill, the speed of the ball mill is set to 300rpm, the ball-to-material ratio is 20:1, the time is set to 10h, each ball milling is 10min, and the cooling is paused for 20min; after the ball milling is completed, the precipitate after filtering the ball-milled sample is ultrasonically and stirred with a 20% w / w sodium hydroxide solution for 15min; deionized water is ultrasonically and stirred to clean the solution until the pH value is neutral; then ethanol is ultrasonically and stirred for 15min, and the operation is repeated twice; then the sample is placed in a vacuum drying oven and treated at 60°C for 4h to obtain flaky molybdenum powder.

[0039] Comparative Example 1

[0040] The only difference between this comparative example and Example 1 is that no auxiliary grinding aid, polyethylene glycol, was added to obtain molybdenum powder.

[0041] Comparative Example 2

[0042] The only difference between this comparative example and Example 2 is that the ball milling time is 36 h to obtain molybdenum powder.

[0043] Comparative Example 3

[0044] The only difference between this comparative example and Example 3 is that the silicone oil is replaced by deionized water to obtain molybdenum powder.

[0045] Comparative Example 4

[0046] The only difference between this comparative example and Example 1 is that intermittent ball milling is not used in the ball milling process to obtain molybdenum powder.

[0047] The particle morphology, particle size range, and product yield of the products of Examples 1 to 3 and Comparative Examples 1 to 4 were tested. The test results are shown in Table 1. The particle morphology of the products was observed under a microscope, the particle size distribution range was measured by a laser particle size analyzer, and the product yield of the flaky powder was measured by the following formula: Product yield = (total weight of powder - mass of powder passing through a 400-mesh test sieve) ÷ total weight of powder × 100%.

[0048] Table 1

[0049] Particle morphology Particle size distribution range / μm Product yield Example 1 Flake 25～255 93％ Example 2 Flake 30～222 96％ Example 3 Flake 35～200 98％ Comparative Example 1 Flake + irregular shape 10～213 88％ Comparative Example 2 Irregular shape 1～20 1％ Comparative Example 3 Irregular shape 1～22 2％ Comparative Example 4 Irregular shape 1～18 1％

[0050] Depend on Figures 2-4 It can be seen that the flaky molybdenum powders of Examples 1 to 3 of the present invention all have flaky particle morphology and relatively uniform particle size distribution. Therefore, the molybdenum powders prepared by the preparation method of the present invention have good flake effect and a controllable particle size distribution range. The diameter-to-thickness ratios of the flaky molybdenum powders of Examples 1 to 3 are 175.3, 192.9 and 225.8, respectively, and have good use value.

[0051] like Figure 5 As shown, compared with Example 1, the auxiliary grinding aid polyethylene glycol was not added in Comparative Example 1. Therefore, not only was the particle size distribution of the product more dispersed, the flaking effect was poor, and the product yield was low.

[0052] like Figure 6 As shown, compared with Example 2, the ball milling time in Comparative Example 2 is 36 hours. Since the ball milling time is too long, the powder is ground too finely, and the flaky structure is almost completely lost, resulting in powder production failure.

[0053] like Figure 7 As shown, compared with Example 3, Comparative Example 3 did not use silicone oil as the main grinding aid solvent. The ball milling force was too strong, resulting in excessive grinding of the powder, poor flake formation, and powder production failure.

[0054] like Figure 8 As shown, compared with Example 1, intermittent ball milling was not used in Comparative Example 4. Since there was no cooling process during ball milling, the temperature rose too quickly during the ball milling process, resulting in changes in the properties of silicone oil and auxiliary grinding aids, poor dispersibility of molybdenum powder, and over-fine powder grinding, poor flake formation, and powder production failure.

[0055] The above embodiments are only for illustrating the technical concept and features of the present invention. Its purpose is to enable people familiar with this technology to understand the content of the present invention and implement it. It cannot be used to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing flaky molybdenum powder, characterized in that: Silicone oil as the main grinding aid is added to the spherical molybdenum powder together with the auxiliary grinding aid, and the mixture is mixed to form a suspension, which is then subjected to intermittent ball milling and post-processing to obtain flaky molybdenum powder with an aspect ratio greater than 100; The auxiliary grinding aid is at least one of polyethylene glycol and citric acid; The mass ratio of the spherical molybdenum powder, silicone oil and auxiliary grinding aid is (100-200): (100-200): (0.2-2.5); The viscosity of the silicone oil is 100~1200 Pa.S; The particle size of the spherical molybdenum powder is 20-150 μm; The mixing conditions are: stirring at room temperature for 5 to 30 minutes; The ball milling conditions are as follows: a rotation speed of 50-500 rpm, a ball-to-material ratio of (15-20):1, a time of 10-16 hours, and a pause of 10-30 minutes for cooling after every 5-20 minutes of ball milling.

2. The method for preparing flaky molybdenum powder according to claim 1, wherein: The post-processing includes filtering, cleaning and drying the sample after ball milling.

3. The method for preparing flaky molybdenum powder according to claim 2, wherein: The cleaning process includes alkali cleaning, distilled water cleaning and ethanol cleaning.

4. The method for preparing flaky molybdenum powder according to claim 3, wherein: The solution used for the alkali washing is sodium hydroxide and / or potassium hydroxide solution.

5. The method for preparing a flaky molybdenum powder according to any one of claims 2 to 4, wherein: Ultrasonic cleaning and mechanical stirring are used in the cleaning process.

6. The method for preparing flaky molybdenum powder according to claim 5, wherein: The drying process includes placing the cleaned sample into a vacuum drying oven, and drying it at 40-80° C. for 4-16 hours under vacuum.

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