Preparation method of flaky molybdenum powder

Abstract

The invention discloses a preparation method of flaky molybdenum powder, which comprises the following steps of: adding silicone oil serving as a main grinding aid and an auxiliary grinding aid into spherical molybdenum powder together, mixing to form a suspension, and performing intermittent ball milling and post-treatment to obtain the flaky molybdenum powder of which the radius-thickness ratio is greater than 100. According to the preparation method, the silicon oil is adopted as the main grinding aid to conduct surface coating and modification on the molybdenum powder, efficient preparation of the flaky molybdenum powder is achieved by controlling parameters of ball milling treatment, the preparation method has the advantages of being high in operability, high in flaky rate and the like, and the prepared flaky molybdenum powder is smooth in surface and has the advantages of being uniform in particle size distribution, high in specific surface area, large in radius-thickness ratio and the like.

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, boiling point, extremely high strength, 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 have very different performances under the same use conditions. Compared with spherical metal powder and granular metal powder, flake metal powder has a larger specific surface area, which can not only maintain the good dispersibility of micron-level powder, but also ensure its high surface activity. In terms of conductivity, compared with flake metal powder, the contact between spherical metal powder and granular metal powder particles is point contact, poor conductivity, large amount of metal powder, and high cost of use; while flake metal powder particles not only have a large specific surface area, but also have line contact and surface contact between particles, which greatly increases the contact area between flake metal powder particles. Therefore, compared with spherical metal powder and granular metal powder, the amount of flake metal powder required for flake metal powder particles to form a conductive channel with the same conductivity is significantly reduced, and the viscous product prepared with flake metal powder also has thixotropic properties, and the sedimentation stability of the product is significantly improved; therefore, the use of flake metal powder to prepare conductive electronic materials can not only significantly improve the conductivity, adhesion and storage stability of the product, but also significantly reduce the amount of metal powder, save resources, reduce production costs, and improve economic benefits. In terms of surface treatment, due to good dispersibility and large specific surface area, coatings or chemical reagents are more likely to penetrate into the gaps between flake particles, so the effect and efficiency of surface treatment can be significantly improved. In terms of chemical catalysis, electromagnetic shielding and radar wave reflection, flaky metal powders have a significantly larger specific surface area than spherical metal powders and granular metal powders, and thus show excellent catalytic performance, electromagnetic shielding performance and radar wave reflection performance. Therefore, the preparation technology of flaky metal powders has attracted much attention.

[0004] At present, the production of molybdenum powder is mainly based on amorphous block molybdenum powder, nearly spherical molybdenum powder and spherical molybdenum powder. There is no public preparation technology suitable for the production of flaky molybdenum powder. This is mainly because there are several difficulties in preparing flaky molybdenum powder: 1. Molybdenum is brittle. Unlike aluminum powder, copper powder and zinc powder in the prior art, which have good plasticity and ductility, molybdenum powder is prone to cracking and breaking. 2. The morphology transformation processing window of molybdenum powder is narrow. In the preparation process of flaky molybdenum powder, it is necessary to accurately control the plastic deformation of the powder without breaking or over-refining. This process requires careful adjustment of the ball milling parameters. 3. The powder is easy to agglomerate. Molybdenum powder is prone to cold welding and agglomeration during ball milling, which not only affects the uniformity of the final product, but also may cause the destruction of the flake structure. 4. Uniformity control is difficult. The thickness and diameter of the flaky powder need to maintain a certain ratio to meet specific application requirements. 5. High energy consumption. Long-term ball milling will increase energy consumption and increase production costs. Therefore, a suitable ball milling process is required to shorten the ball milling time while ensuring the quality of the flaky molybdenum powder. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for preparing flaky molybdenum powder, which uses silicone oil as a main grinding aid and adds a certain amount of auxiliary grinding aid to coat and modify the molybdenum powder, and can be achieved by controlling the parameters of the ball milling process, and has the advantages of strong operability and high flake rate. The molybdenum powder obtained by this method has a smooth surface, two dimensions of the three-dimensional structure are micron-level, and the third dimension is submicron-level, and has the advantages of uniform particle size distribution, high specific surface area and large diameter-to-thickness ratio, which greatly expands the application scenarios and comprehensive 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 having 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 molybdenum powder, reduce the friction of particles in the ball milling process, prevent molybdenum powder from agglomerating, and improve the dispersion effect. In this way, under the mechanical force of the ball milling process, molybdenum powder particles are not easy to break and fracture, thereby improving the effect and efficiency of ball milling, and also improving the operability of the process. In order to optimize the ball milling effect, the present invention also adds other grinding aids, which can work together with silicone oil on the surface of powder particles to form a protective layer, improve the fluidity and oxidation resistance of the powder, thereby improving the uniformity of the particle size distribution of flaky molybdenum powder. In this way, the morphology of molybdenum powder can be changed by controlling the parameters of ball milling. In the ball milling process, strong collision and friction will occur between the grinding balls in the ball mill and the molybdenum powder. These mechanical forces will exert shear force on the spherical molybdenum powder, causing it to gradually undergo plastic deformation, that is, gradually transform from the original spherical shape into a flat flaky structure. This is because under repeated impact and shearing, the lattice structure of molybdenum powder will slip, resulting in changes in particle shape. By adjusting factors such as ball milling time, ball milling speed, ball-to-material ratio, ball milling cooling time, etc., the deformation process can be controlled to transform spherical molybdenum powder into flake molybdenum powder.

[0008] The inventors found 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 effect of ball milling. When the amount of silicone oil is too little, it is impossible to effectively form a protective film and buffer force, and the ball millability of the molybdenum powder cannot be effectively improved during the ball milling process, and the spherical molybdenum powder is easy to break; when the amount of silicone oil is too high, it is not conducive to the subsequent removal of the solvent, and it will also indirectly affect the quality of the flaky molybdenum powder. When the amount of auxiliary grinding aid is small, the improvement of the flowability of the flaky molybdenum powder is weak, the particle size distribution of the prepared flaky molybdenum powder is uneven, and the surface quality is poor; when the amount of auxiliary grinding aid is large, the protection and buffering effect provided are weakened, which will cause the molybdenum powder to break.

[0009] As a preferred solution, the viscosity of the silicone oil is 100-1200 Pa.S. Appropriate viscosity can maintain uniform dispersion of particles during ball milling, buffer mechanical collision between grinding balls and molybdenum powder, and promote the formation of uniform and complete flaky morphology. Too low viscosity is not conducive to particle dispersion and buffering mechanical collision of grinding balls during ball milling. Too high viscosity will lead to poor fluidity of silicone oil, and powder is not easy to disperse evenly, which will affect the uniformity and morphology of powder.

[0010] As a preferred solution, the particle size of the spherical molybdenum powder is in the range of 20 to 150 μm. The particle size of the spherical molybdenum powder in the present invention has a certain influence on the quality of the prepared flaky molybdenum powder. When the particle size of the spherical molybdenum powder is larger, the diameter-to-thickness ratio of the prepared flaky molybdenum powder is larger, the particle size distribution is narrower, and the particle size distribution of the prepared flaky molybdenum powder is more uniform. When the particle size is too large, the spherical molybdenum powder is prone to breakage during the ball milling process, which is not conducive to the uniformity of the particle size of the prepared flaky molybdenum powder. If the particle size is too small, the particle size of the prepared flaky powder is also small, and the application advantages of the flaky powder cannot be brought into play.

[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 act more fully to control the viscosity of the suspension.

[0012] As a preferred solution, the conditions of the ball milling treatment 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 during the ball milling process, the operation is suspended for 10 to 30 minutes for cooling. The ball milling treatment of the present invention is mainly to change the morphology of spherical molybdenum powder, and the parameter setting of the ball milling treatment 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 ball and the powder during the grinding process, which can improve the grinding efficiency and the uniformity of powder grinding; the lower the rotation speed, the smaller the force of the grinding ball on the powder, so that the powder will not be broken during the grinding process. Therefore, the use of 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. Further 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 break, but also have an adverse effect on the grinding aid to form partial agglomeration. Therefore, it is necessary to adopt an intermittent ball milling method. 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 ball is one of polyurethane, corundum, stainless steel, agate, zirconium oxide, silicon carbide and cemented carbide.

[0014] As a preferred solution, the post-treatment includes filtering, cleaning and drying the ball-milled sample in sequence. The residual grinding aid in the flaky molybdenum powder can be effectively removed by filtering, cleaning and drying, 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 to 80° C. for 4 to 16 hours under vacuum.

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

[0020] 1) The present invention selects silicone oil and molybdenum powder to form a molybdenum powder suspension, reduces the friction of particles during ball milling, prevents molybdenum powder from agglomerating, and improves the dispersion effect. In this way, under the mechanical force of the ball milling process, the molybdenum powder particles are not easy to break and fracture, thereby improving the effect and efficiency of ball milling and the operability of the process. In order to optimize the ball milling effect, the present invention also adds auxiliary grinding aids, which can form a protective layer with silicone oil on the surface of the powder particles, improve the wettability, fluidity and oxidation resistance of the powder, thereby improving 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 three-dimensional structure of the flaky molybdenum powder prepared by the present invention has two dimensions of micron level, the third dimension of submicron level, and a smooth surface, and has advantages such as uniform particle size distribution and high specific surface area. The diameter-thickness ratio of the flaky molybdenum powder of the present invention has obvious advantages, which can not only give the flaky molybdenum powder better dispersibility during application, but also ensure its high surface quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The 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 given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention. The protection scope 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] 100 g of spherical molybdenum powder (median particle size of 35 μm) was added as Figure 1 As shown, 0.2g of citric acid is added to 100g of silicone oil (viscosity of 400Pa.S), and a molybdenum powder suspension is formed after mixing for 30min under the combined action of stirring and ultrasonic waves; 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 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] 150 g of spherical molybdenum powder (median particle size of 35 μm) was added. Figure 1 As shown, 2g of polyethylene glycol is added to 200g of silicone oil (viscosity is 200Pa.S), and a molybdenum powder suspension is formed after mixing for 30min under the combined action of stirring and ultrasonic waves; then poured into a ball mill, the speed of the ball mill 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] 200 g of spherical molybdenum powder (median particle size of 35 μm) was added. Figure 1 As shown, 2g of polyethylene glycol and 0.5g of citric acid are added to 200g of silicone oil (viscosity is 200Pa.S), and mixed for 30min under the combined action of stirring and ultrasound 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; 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.

[0039] Comparative Example 1

[0040] The difference between this comparative example and Example 1 is that no auxiliary grinding aid polyethylene glycol is 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 hours 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 difference between this comparative example and Example 1 is that the intermittent ball milling treatment 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, and the test results are shown in Table 1, wherein the particle morphology of the product 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 to 4 It can be seen that the flaky molybdenum powders of Examples 1 to 3 of the present invention have flaky particle morphology and relatively uniform particle size distribution. Therefore, the molybdenum powder prepared by the preparation method of the present invention has 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 the particle size distribution of the product was more dispersed, the flake-forming effect was poor, but also 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. Due to the long ball milling time, the powder is ground too finely and almost completely loses its flaky structure, resulting in powder production failure.

[0053] like Figure 7 As shown, compared with Example 3, the solvent with silicone oil as the main grinding aid was not used in Comparative Example 3. 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 is no cooling process in ball milling, the temperature rises too fast during ball milling, resulting in changes in the properties of silicone oil and auxiliary grinding aids, poor dispersibility of molybdenum powder, and excessive grinding of powders, poor flake formation, and powder production failure.

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

Claims

1. A method for preparing flaky molybdenum powder, characterized in that: Silicone oil as a main grinding aid is added to the spherical molybdenum powder together with an auxiliary grinding aid, and the mixture is mixed to form a suspension, and then subjected 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; The mass ratio of the spherical molybdenum powder, silicone oil and auxiliary grinding aid is (100-200):(100-200):(0.2-2.5).

2. The method for preparing flaky molybdenum powder according to claim 1, wherein: The viscosity of the silicone oil is 100-1200 Pa.S.

3. A method for preparing flaky molybdenum powder according to claim 1 or 2, characterized in that: The particle size of the spherical molybdenum powder is 20 to 150 μm.

4. The method for preparing flaky molybdenum powder according to claim 3, wherein: The mixing conditions are: stirring at room temperature for 5 to 30 minutes.

5. The method for preparing flaky molybdenum powder according to claim 1, wherein: The ball milling treatment conditions 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 a pause of 10 to 30 minutes for cooling after every 5 to 20 minutes of ball milling.

6. The method for preparing flaky molybdenum powder according to claim 1, wherein: The post-processing includes filtering, cleaning and drying the ball-milled samples in sequence.

7. The method for preparing flaky molybdenum powder according to claim 6, wherein: The cleaning treatment includes alkali cleaning, distilled water cleaning and ethanol cleaning.

8. The method for preparing flaky molybdenum powder according to claim 7, wherein: The solution used for the alkali washing is sodium hydroxide and / or potassium hydroxide solution.

9. The method for preparing flaky molybdenum powder according to any one of claims 6 to 8, characterized in that: Ultrasonic cleaning and mechanical stirring are used in the cleaning process.

10. The method for preparing flaky molybdenum powder according to claim 6, characterized in that: The drying process comprises placing the cleaned sample into a vacuum drying oven, and drying it at 40 to 80° C. for 4 to 16 hours under a vacuum state.

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