Preparation method of magnesium powder with narrow particle size

Abstract

According to the preparation method of the narrow-particle-size magnesium powder, the first-time grinding products are screened and classified, the grinding products larger than the first size and smaller than the second size are first-class products, and the grinding products larger than the second size and smaller than the third size are second-class products. According to the method, the oxide layer is formed on the surface of the first-class product, the first-class product with the oxide layer formed and the second-class product are mixed and then ground for the second time, the non-reworkable defective product rate can be effectively reduced, the yield can be effectively increased, the particle size distribution of magnesium powder in a good product is closer to the target particle size, and the particle size distribution of the magnesium powder is more ideal.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium powder manufacturing, and particularly to a method for preparing narrow particle size magnesium powder. Background Art

[0002] Magnesium metal, with its excellent physical properties such as high specific strength and specific stiffness, excellent processing and forming ability, excellent damping and shock absorption effect, and strong electromagnetic shielding ability, has occupied a pivotal position in many fields such as automobile manufacturing, aerospace, rail transit, electronic communication, and national defense industry, and is known as the "green engineering material of the 21st century". Its application in the biomedical field is even more remarkable. With excellent biocompatibility and biodegradability, it is known as the "revolutionary medical metal material". In addition to the above applications, the active chemical properties of magnesium also bring more possibilities. Magnesium plays a key role in steel desulfurization and strategic metal reduction. Especially spherical magnesium and magnesium powder, due to their large specific surface area and strong surface activity, are not only widely used in the production of chemical products, the manufacture of explosives, and the fireworks industry, but also become efficient reducing agents, desulfurizing agents, and high-quality raw materials for 3D printing. In addition, magnesium powder has also found its application in high-tech fields such as advanced magnesium powder pigments and conductive paste for the backplane of solar photovoltaic cells. Especially in the automotive and building materials industries, magnesium powder pigments have demonstrated their unique value.

[0003] China's magnesium resource reserves are extremely rich, and it has maintained the world's leading position in primary magnesium production for many years. With decades of unremitting efforts and continuous research, significant progress and achievements have been made in the applied research of magnesium metal in many fields such as alloy production, hydrogen storage materials, and medical materials. However, in the field of magnesium powder preparation, China's research started relatively late and the development speed is relatively slow. At present, the processing of magnesium powder mainly includes high-temperature atomization method and mechanical powder making method. The former is suitable for making ultra-fine magnesium powder, with high precision and good particle uniformity, but the production efficiency is low. The latter has relatively low precision, but low production cost and high efficiency. Currently, the mechanical powder making method is generally used in general scenarios. However, when the existing mechanical powder making method is used to produce magnesium powder with a smaller particle size, the final yield of good products is low.

[0004] The information disclosed in the background art part of this application is only intended to deepen the understanding of the general background art of this application, and should not be regarded as an admission or any form of suggestion that this information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0005] The applicant has found that when using the mechanical powder-making method to produce magnesium powder with a narrow particle size, since the particle size of the ground magnesium powder approximately follows a normal distribution, taking the production of magnesium powder with a particle size of 0.15 mm as an example, a certain error is generally allowed, that is, magnesium powder with a particle size of 0.12 mm - 0.18 mm is considered a qualified product. Among the products finally ground by the existing mechanical powder-making method, the proportion of products with a particle size less than 0.12 mm is about 5%, and the proportion of magnesium powder with a particle size greater than 0.18 mm is about 3%. Moreover, within the range of 0.12 mm - 0.18 mm, the proportion of particles close to 0.12 mm or 0.18 mm is also relatively high. The magnesium powder with a larger particle size can be processed into a qualified product through a second grinding, but the magnesium powder with a smaller particle size can only be remelted into magnesium ingots as unqualified products or sold as by-products, which affects the final yield rate.

[0006] Based on this, it is necessary to provide a method for preparing narrow-particle-size magnesium powder to address the problem of poor particle size uniformity existing in the current production of narrow-particle-size magnesium powder.

[0007] The above object is achieved by the following technical solutions: A method for preparing narrow-particle-size magnesium powder, which includes: Prepare magnesium ingot raw materials; Pickle the magnesium ingot to remove the oxide layer on the surface of the magnesium ingot; Transfer the pickled magnesium ingot into a milling machine or a cutting machine and process it into long chips; Transfer the processed long chips into a chip breaker and process them into short chips; Put the short chips into a grinding machine and perform the first grinding to obtain the first grinding product; Screen and classify the first grinding product according to the particle size. The grinding products larger than the first size and smaller than the second size are the first type of products; the grinding products larger than the second size and smaller than the third size are the second type of products; Form an oxide layer on the surface of the first type of products, and mix the first type of products with the oxide layer formed thereon with the second type of products and then perform the second grinding; Collect the ground magnesium powder and pack and store it.

[0008] In one embodiment, the thickness of the oxide layer on the surface of the first type of products is 1% - 8% of the target particle size.

[0009] In one embodiment, the first size is 50% - 90% of the target particle size, and the second size is 110% - 150% of the target particle size.

[0010] In one embodiment, forming an oxide layer on the surface of the first type of products, and mixing the first type of products with the oxide layer formed thereon with the second type of products and then performing the second grinding further includes: The grinding products larger than the fourth size are products to be reworked. Mix the products to be reworked with the first type of products and grind for a preset time, then mix in the second type of products and continue grinding.

[0011] In one embodiment, an oxide layer is formed on the surface of the first type of products. After mixing the first type of products with the oxide layer formed thereon with the second type of products, a second grinding is performed. It further includes: Heat the first type of products to form an oxide layer on the surface of the first type of products.

[0012] In one embodiment, after sieving and classifying the first grinding products according to particle size, the grinding products larger than the first size and smaller than the second size are the first type of products; the grinding products larger than the second size and smaller than the third size are the second type of products. It further includes: The grinding products larger than the fourth size are products to be reworked. Perform one more grinding on the products to be reworked.

[0013] In one embodiment, when short chips are put into a grinding machine for the first grinding to obtain the first grinding products, an inert protective gas is introduced into the grinding machine.

[0014] In one embodiment, when the first type of products with the oxide layer formed thereon are mixed with the second type of products for the second grinding, an inert protective gas is introduced into the grinding machine.

[0015] In one embodiment, the inert protective gas is a gas that does not react with magnesium, and at least includes one or any combination of helium, neon, argon, krypton, xenon, and radon.

[0016] In one embodiment, after sieving and classifying the first grinding products according to particle size, the grinding products larger than the first size and smaller than the second size are the first type of products; the grinding products larger than the second size and smaller than the third size are the second type of products. It further includes: The grinding products smaller than the first size are by-products. Collect the by-products and store them in packages.

[0017] The beneficial effects of the present invention are: The method for preparing narrow particle size magnesium powder provided by the embodiments of the present invention screens and classifies the first grinding products. The grinding products larger than the first size and smaller than the second size are the first type of products, and the grinding products larger than the second size and smaller than the third size are the second type of products. An oxide layer is formed on the surface of the first type of products. After mixing the first type of products with the oxide layer formed thereon with the second type of products, a second grinding is performed, which can effectively reduce the defective product rate of non-reworkable products, improve the yield rate, and the particle size distribution of magnesium powder in the qualified products is closer to the target particle size, and the particle size distribution of magnesium powder is more ideal. Description of the Drawings

[0018] Figure 1 Schematic structural diagram of the method for preparing narrow particle size magnesium powder provided by an embodiment of the present invention; Figure 2 Particle size distribution table of magnesium powder produced by one-time grinding in the mechanical powder making method in the prior art; Figure 3 Particle size distribution table of magnesium powder after the first grinding in the method for preparing narrow particle size magnesium powder provided by an embodiment of the present invention; Figure 4 Particle size distribution table of magnesium powder after the second grinding in the method for preparing narrow particle size magnesium powder provided by an embodiment of the present invention. Detailed implementation manners

[0019] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] The block diagrams shown in the accompanying drawings are only functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities can be implemented in the form of software, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontroller devices.

[0021] In several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only illustrative. For example, the division of the units is only a logical function division, and there can be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed mutual coupling or direct coupling or communication connection can be an indirect coupling or communication connection through some interfaces, devices or units, and can also be an electrical, mechanical or other form of connection.

[0022] The embodiment of the present invention provides a method for preparing narrow particle size magnesium powder, which is mainly used to improve the yield of final good products when preparing narrow particle size magnesium powder. It can be understood that it can also be applied to the preparation of magnesium powder with a wider particle size, or the preparation of metal powders with the same or similar properties as magnesium.

[0023] Specifically, as Figure 1 shown, the method for preparing narrow particle size magnesium powder provided by the embodiment of the present invention includes: S100, prepare magnesium ingot raw materials; S200, pickling the magnesium ingot to remove the oxide layer on the surface of the magnesium ingot; S300, the pickled magnesium ingot is moved into a milling machine or a cutting machine to be processed into chips; S400, moves the processed long chips into the chip breaker and processes them into short chips; S500, putting the short chips into the grinder, performing the first grinding, and obtaining the first grinding product; S600, screening and classifying the first grinding products according to the particle size, wherein the grinding products larger than the first size and smaller than the second size are first-class products; and the grinding products larger than the second size and smaller than the third size are second-class products; S700, forming an oxide layer on the surface of the first type of product, mixing the first type of product with the oxide layer formed with the second type of product and then performing a second grinding; S800 collects the ground magnesium powder and packs it for storage.

[0024] Among them, in step S100, the raw material for making magnesium powder is magnesium ingot, and the industry currently stores magnesium raw materials in the form of magnesium ingots. It is understandable that any other form of magnesium that can be cut or ground can be applied to the present invention, such as magnesium balls with larger particle sizes.

[0025] In step S200, since the surface of the magnesium ingot is prone to produce an oxide layer during storage and transportation, the oxide layer is easily mixed into the magnesium chips when the magnesium ingot is cut into magnesium chips. Due to the large differences in the various physical and chemical properties of the oxide layer and the magnesium element, it is not only easy to reduce the purity of the final magnesium powder, but also cause processing defects during the processing of the magnesium powder, especially in the cutting and grinding process, the impurity particles of the oxide layer will cause large processing defects in cutting and grinding, so it is necessary to pickle the magnesium ingot before cutting to remove the oxide layer. In addition, when the magnesium ingot is stored and transported, dust and other pollutants will be attached to the surface. In order to avoid contamination of the pickling tank, the magnesium ingot is cleaned and dried before entering the pickling tank to remove the pollutants attached to the surface of the magnesium ingot. The cleaning can be done by washing with water, cleaning liquid, or cleaning with the same liquid as the liquid in the pickling tank. After cleaning, in order to avoid the cleaning liquid from entering the pickling tank, the cleaned magnesium ingot can be dried until the surface of the magnesium ingot is no longer attached with liquid.

[0026] In step S300 to step S500, the magnesium ingot is cut, chip broken, and ground in sequence to produce magnesium powder of a preset size according to 1.5 times the target particle size. For ease of description, this embodiment and the following embodiments are described by taking the production of magnesium powder with a target particle size of 0.2 mm as an example.

[0027] In the prior art, a cutting, chip breaking, and grinding process similar to steps S300 - S500 of the present application is directly carried out according to the target particle size of 0.2 mm, and the particle size distribution of the finally produced magnesium powder is as Figure 2 shown in the table. It can be seen from the table that among every ten thousand magnesium powder particles, the number of magnesium powder particles with a particle size less than 0.15 mm is 350, and the quantity proportion is 3.5%; the number of magnesium powder particles with a particle size greater than 0.15 mm and less than 0.17 mm is 1200, and the quantity proportion is 12%; the number of magnesium powder particles with a particle size greater than 0.17 mm and less than 0.19 mm is 1600, and the quantity proportion is 16%; the number of magnesium powder particles with a particle size greater than 0.19 mm and less than 0.21 mm is 2700, and the quantity proportion is 27%; the number of magnesium powder particles with a particle size greater than 0.21 mm and less than 0.23 mm is 1800, and the quantity proportion is 18%; the number of magnesium powder particles with a particle size greater than 0.23 mm and less than 0.25 mm is 1400, and the quantity proportion is 14%; the number of magnesium powder particles with a particle size greater than 0.25 mm is 950, and the quantity proportion is 9.5%. Among them, the magnesium powder particles with a particle size less than 0.15 mm cannot be processed into qualified products with a particle size in the range of 0.15 mm - 0.25 mm through rework or other means, while the magnesium powder particles with a particle size greater than 0.25 mm can be processed into qualified products with a particle size in the range of 0.15 mm - 0.25 mm through rework or other means.

[0028] In the present application, first, after the cutting and chip breaking processes, the first grinding is carried out according to 1.5 times the target particle size (i.e., 0.3 mm), and the particle size distribution of the magnesium powder produced by the first grinding is as Figure 3 shown in the table. It can be seen from the table that among every ten thousand magnesium powder particles, the number of magnesium powder particles with a particle size less than 0.15 mm is 50, and the quantity proportion is 0.5%; the number of magnesium powder particles with a particle size greater than 0.15 mm and less than 0.17 mm is 250, and the quantity proportion is 2.5%; the number of magnesium powder particles with a particle size greater than 0.17 mm and less than 0.19 mm is 400, and the quantity proportion is 4%; the number of magnesium powder particles with a particle size greater than 0.19 mm and less than 0.21 mm is 600, and the quantity proportion is 6%; the number of magnesium powder particles with a particle size greater than 0.21 mm and less than 0.23 mm is 750, and the quantity proportion is 7.5%; the number of magnesium powder particles with a particle size greater than 0.23 mm and less than 0.25 mm is 1200, and the quantity proportion is 12%; the number of magnesium powder particles with a particle size greater than 0.25 mm is 6750, and the quantity proportion is 67.5%. It can be seen from this that after the first grinding, most of the magnesium powder particles have a particle size greater than the acceptable range of the target particle size, so subsequent second grinding is required.

[0029] In step S600, the grinding products of the first grinding are screened and classified according to the particle size. The grinding products larger than the first size and smaller than the second size are the first type of products; the grinding products larger than the second size and smaller than the third size are the second type of products. Among them, the first size is the acceptable lower limit of the target particle size, that is, 0.15mm, the second size is the upper limit of the target particle size, that is, 0.25mm, and the third size is the upper limit of the target particle size during the first grinding, that is, 0.4mm.

[0030] In step S700, an oxide layer is formed on the surface of the first type of product, and the first type of product after the oxide layer is formed is mixed with the second type of product and then ground for the second time. Since magnesium is relatively active in nature, it can react with oxygen to form a dense oxide layer on its surface. After the oxide is formed, it can isolate the magnesium inside the oxide from continuing to react with oxygen. The oxide is generally magnesium oxide, and its Mohs hardness is about 6, while the Mohs hardness of magnesium alone is about 2.5. Therefore, after an oxide layer is formed on the surface of the first type of product with a smaller particle size but meeting the requirements of the target particle size, it is mixed with the second type of product and ground for the second time. During grinding, since the hardness of the oxide layer on the surface of the first type of product is higher, the size reduction caused by grinding is smaller, while the hardness of the oxide layer on the surface of the second type of product is lower, the size reduction caused by grinding is larger. The particle size distribution of the magnesium powder finally produced by grinding is as follows: Figure 4 As shown in the table. It can be seen from the table that among every 10,000 magnesium powders, the number of magnesium powders with a particle size less than 0.15mm is 100, accounting for 1%; the number of magnesium powders with a particle size greater than 0.15mm and less than 0.17mm is 450, accounting for 4.5%; the number of magnesium powders with a particle size greater than 0.17mm and less than 0.19mm is 1600, accounting for 16%; the number of magnesium powders with a particle size greater than 0.19mm and less than 0.21mm is 4000, accounting for 40%; the number of magnesium powders with a particle size greater than 0.21mm and less than 0.23mm is 2100, accounting for 21%; the number of magnesium powders with a particle size greater than 0.23mm and less than 0.25mm is 1050, accounting for 10.5%; the number of magnesium powders with a particle size greater than 0.25mm is 700, accounting for 7%. Compared with the grinding in the prior art, the product of the two grinding processes has only 1% of the magnesium powder that cannot be reworked, which is much lower than the 3.5% after only one grinding; and within the acceptable range of good products, 40% of the magnesium powder particles are between 0.19mm-0.21mm, which is much higher than the 27% after only one grinding. Therefore, the narrow particle size magnesium powder preparation method provided by the embodiment of the invention can effectively reduce the defective rate of non-reworkable products and improve the good rate. In the good products, the particle size distribution of the magnesium powder is closer to the target particle size, and the particle size distribution of the magnesium powder is more ideal.

[0031] In step S800, the ground product that meets the requirements of the target particle size is packaged and stored.

[0032] In one embodiment, the thickness of the surface oxide layer of the first type of product is 1% - 8% of the target particle size. The thickness of the oxide layer is adjusted according to actual production requirements. For example, the larger the target particle size, the thicker the oxide layer should be; or the larger the acceptable range of the target particle size, the thicker the oxide layer should be.

[0033] In one embodiment, the first size is 50% - 90% of the target particle size, and the second size is 110% - 150% of the target particle size. As can be seen from the above, the first size is the lower limit value of the acceptable range of the target particle size, and the second size is the upper limit value of the target particle size. Generally, the acceptable range of the target particle size is between 50% - 150% of the target particle size. It can be understood that when the acceptable range of the target particle size changes according to actual production requirements, the first size and the second size should also change accordingly.

[0034] In one embodiment, an oxide layer is formed on the surface of the first type of product. After mixing the first type of product with the formed oxide layer and the second type of product, secondary grinding is performed, and it further includes: the grinding product larger than the fourth size is a product to be reworked. The product to be reworked is mixed with the first type of product and ground for a preset time, and then the second type of product is mixed in and grinding continues. Among them, the fourth size is twice the target size, that is, 0.4 mm. Since this size has a large difference from the target particle size, it is first mixed and ground with the first type of product. After grinding for a period of time, the size of the product to be reworked has been reduced to an appropriate range, and then the second type of product is added and ground together. It should be noted that since the first type of product is first mixed and ground with the product to be reworked, and then mixed and ground with the product to be reworked and the second type of product, compared with the process of only mixing and grinding the first type of product with the second type of product, the oxide layer on the surface of the first type of product should be thicker.

[0035] In other embodiments, for the product to be reworked, it can also be ground again and then screened and classified, and after classification, continue according to step S600 and step S700.

[0036] In one embodiment, an oxide layer is formed on the surface of the first type of product. After mixing the first type of product with the formed oxide layer and the second type of product, secondary grinding is performed, and it further includes: heating the first type of product to form an oxide layer on the surface of the first type of product. Of course, other methods that can form an oxide layer on the magnesium powder surface can also be applied to the present invention.

[0037] In one embodiment, when short chips are put into a grinding machine for the first grinding to obtain the first grinding product, an inert protective gas is introduced into the grinding machine. Since the presence of magnesium oxide will affect the normal grinding and the purity of the final product, except in step S700, the formation of magnesium oxide needs to be avoided as much as possible.

[0038] Similarly, in one embodiment, when the first type of product after the formation of the oxide layer is mixed with the second type of product for the second grinding, an inert protective gas is introduced into the grinding machine.

[0039] In the above embodiments, the inert protective gas is a gas that does not react with magnesium, and includes at least one or any combination of helium, neon, argon, krypton, xenon, and radon.

[0040] It should be noted that although magnesium oxide will affect the purity of the final product, on the one hand, the amount of magnesium oxide powder deliberately generated on the first type of product is small, and a considerable part of the magnesium oxide is ground off and sieved during the grinding process; on the other hand, magnesium powder often inevitably reacts with air in the subsequent process to form a certain amount of magnesium oxide. Therefore, although the oxide layer generated in step S700 affects the purity of the final product to a certain extent, the amount of its influence is relatively small.

[0041] In one embodiment, after screening and classifying the first grinding product according to the particle size, the grinding product larger than the first size and smaller than the second size is the first type of product; the grinding product larger than the second size and smaller than the third size is the second type of product, and it further includes: the grinding product smaller than the first size is a by-product, and the by-product is collected and stored in packages.

[0042] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use, and processing of relevant data need to comply with the relevant laws, regulations, and standards of relevant countries and regions.

[0043] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above methods. Among them, any reference to a memory, database, or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memories. Non-volatile memories can include read-only memory (ROM), magnetic tapes, floppy disks, flash memories, optical memories, high-density embedded non-volatile memories, resistive random access memories (ReRAM), magnetoresistive random access memories (MRAM), ferroelectric random access memories (FRAM), phase change memories (PCM), graphene memories, etc. Volatile memories can include random access memory (RAM) or external cache memories, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc. The databases involved in the embodiments provided in the present application can include at least one of relational databases and non-relational databases. Non-relational databases can include distributed databases based on blockchain, etc., without limitation. The processors involved in the embodiments provided in the present application can be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, data processing logics based on quantum computing, etc., without limitation.

[0044] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0045] The above-described embodiments merely represent several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A method for preparing narrow particle size magnesium powder, characterized in that: include: Prepare magnesium ingot raw materials; Pickling the magnesium ingot to remove the oxide layer on the surface of the magnesium ingot; The pickled magnesium ingot is moved into a milling machine or cutting machine to be processed into long chips; The processed long chips are moved into the chip breaker to be processed into short chips; Put the short chips into the grinder, perform the first grinding, and obtain the first grinding product; The first grinding products are screened and classified according to the particle size, and the grinding products larger than the first size and smaller than the second size are the first type of products; the grinding products larger than the second size and smaller than the third size are the second type of products; An oxide layer is formed on the surface of the first type of product, and the first type of product with the oxide layer formed is mixed with the second type of product and then subjected to a second grinding; Collect the ground magnesium powder and pack it for storage.

2. The method for preparing narrow particle size magnesium powder according to claim 1, characterized in that: The thickness of the surface oxide layer of the first type of product is 1%-8% of the target particle size.

3. The method for preparing narrow particle size magnesium powder according to claim 1, characterized in that: The first size is 50%-90% of the target particle size, and the second size is 110%-150% of the target particle size.

4. The method for preparing narrow particle size magnesium powder according to any one of claims 1 to 3, characterized in that: An oxide layer is formed on the surface of the first type of product, and the first type of product after the oxide layer is formed is mixed with the second type of product and then subjected to a second grinding, and further comprising: The grinding products larger than the fourth size are the products to be reworked. The products to be reworked are mixed with the first type of products and then ground for a preset time, and then the second type of products are mixed in and continue to be ground.

5. The method for preparing narrow particle size magnesium powder according to any one of claims 1 to 3, characterized in that: An oxide layer is formed on the surface of the first type of product, and the first type of product after the oxide layer is formed is mixed with the second type of product and then subjected to a second grinding, and further comprising: The first type of product is heated to form an oxide layer on the surface of the first type of product.

6. The method for preparing narrow particle size magnesium powder according to claim 1, characterized in that: The first grinding products are screened and classified according to the particle size, and the grinding products larger than the first size and smaller than the second size are first-class products; Grinding products larger than the second size and smaller than the third size are classified as second-class products, and also include: The grinding products larger than the fourth size are to be reworked, and the reworked products are ground again.

7. The method for preparing narrow particle size magnesium powder according to claim 1, characterized in that: The short chips are placed in the grinder for the first grinding. When the first grinding product is obtained, an inert protective gas is introduced into the grinder.

8. The method for preparing narrow particle size magnesium powder according to claim 1, characterized in that: When the first type of product after forming the oxide layer is mixed with the second type of product and then subjected to a second grinding, an inert protective gas is introduced into the grinding machine.

9. The method for preparing narrow particle size magnesium powder according to claim 7 or 8, characterized in that: The inert protective gas is a gas that does not react with magnesium, and includes at least one of helium, neon, argon, krypton, xenon, and radon, or any combination of several of them.

10. The method for preparing narrow particle size magnesium powder according to any one of claims 1-3, 7-8, characterized in that: The first grinding products are screened and classified according to the particle size, and the grinding products larger than the first size and smaller than the second size are first-class products; Grinding products larger than the second size and smaller than the third size are classified as second-class products, and also include: The grinding products smaller than the first size are by-products, which are collected and packaged for storage.

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