Method for producing neodymium-iron-boron magnetic powder

Abstract

The application relates to the technical field of neodymium-iron-boron magnet materials, in particular to a preparation method of neodymium-iron-boron magnetic powder, which comprises the following steps: preparing hydrogen explosion powder from neodymium-iron-boron raw materials; adding an antioxidant into the hydrogen explosion powder and uniformly mixing to obtain mixed coarse powder; wherein the components of the antioxidant include 5%-15% of hexachloroethane and the rest of at least one of aviation gasoline or monochlorobenzene; performing airflow mill treatment on the mixed coarse powder under oxygen-free condition to obtain intermediate powder; then adding a lubricant and uniformly stirring under a protective atmosphere to obtain neodymium-iron-boron magnetic powder; wherein the lubricant includes at least one of tributyl borate or methyl laurate. According to the preparation method, the antioxidant can wrap the fresh fracture of the mixed coarse powder in the instant of the breaking of the mixed coarse powder, so that the oxidation of the mixed coarse powder is limited to the maximum extent; meanwhile, the above-mentioned lubricant is added, the flowability of the prepared magnetic powder is effectively improved, and then the filling uniformity of the magnetic powder in the subsequent processing process and the rotation or movement in the orientation process are accelerated.

Description

Technical field

[0001] The present application relates to the technical field of neodymium iron boron magnet materials, and in particular to a method for preparing neodymium iron boron magnetic powder. [Background Technology]

[0002] Neodymium iron boron magnets are man-made permanent magnets and currently possess the strongest magnetic force. Their maximum magnetic energy product (BHmax) is over 10 times higher than that of ferrites, and in their bare state, their magnetic force can reach approximately 3500 gauss. They offer high cost-effectiveness, compact size, light weight, excellent mechanical properties, and strong magnetic properties. Therefore, they are widely used in electric vehicles, hybrid vehicles, wind power generation, variable-frequency air conditioners, medical equipment, elevators, audio equipment, and mineral sorting.

[0003] In order to obtain NdFeB magnets with excellent magnetic properties, it is necessary to reduce oxidation corrosion and facilitate the magnetization process during the NdFeB magnetic powder molding process. Improving the oxidation resistance and lubricity of NdFeB magnetic powder has become an urgent problem to be solved. [Summary of the invention]

[0004] In view of this, the present application provides a method for preparing NdFeB magnetic powder, which can limit the oxidation process of NdFeB magnetic powder to the greatest extent; and improve the powder fluidity of NdFeB magnetic powder, improve its filling uniformity in subsequent processing and rotation or movement in the orientation process.

[0005] The present application provides a method for preparing NdFeB magnetic powder, comprising the following steps:

[0006] The NdFeB raw material is subjected to a casting process to obtain a NdFeB alloy casting sheet, and the NdFeB alloy casting sheet is subjected to a hydrogen explosion process to obtain NdFeB hydrogen explosion powder;

[0007] Adding an antioxidant to the NdFeB hydrogen explosion powder and mixing them uniformly to obtain a coarse mixed powder; wherein the antioxidant comprises 5% to 15% by weight of hexachloroethane and the remainder comprises at least one of aviation gasoline or monochlorobenzene;

[0008] Under oxygen-free conditions, the mixed coarse powder is subjected to air flow milling to obtain an intermediate powder;

[0009] A lubricant is added to the intermediate powder and stirred uniformly under a protective atmosphere to obtain NdFeB magnetic powder; wherein the lubricant includes at least one of tributyl borate or methyl laurate.

[0010] In some embodiments, the casting process specifically includes a melting and strip-spinning process and a cooling process.

[0011] In some embodiments, the hydrogen explosion process is specifically as follows: the NdFeB alloy casting sheet absorbs hydrogen to form a hydride, and the hydride expands and explodes to obtain the NdFeB hydrogen explosion powder.

[0012] In some embodiments, the antioxidant accounts for 0.5‰ to 2.5‰ by mass in the mixed coarse powder.

[0013] In some embodiments, the mixing time of the NdFeB hydrogen explosion powder and the antioxidant is ≥2 h.

[0014] In some embodiments, the jet milling process is at least one of a fluidized bed jet milling process and a target jet milling process.

[0015] In some embodiments, the average particle size D50 of the intermediate powder is 2 μm to 4 μm.

[0016] In some embodiments, the mass ratio of the lubricant in the NdFeB magnetic powder is 0.5‰ to 1.5‰.

[0017] In some embodiments, the stirring time after adding the lubricant is 5s to 15s, the number of stirring times is 2 to 4 times, and the interval between adjacent stirring times is 9min to 11min.

[0018] The above technical solution has the following beneficial effects:

[0019] The preparation method of NdFeB magnetic powder provided by the present application adds the above-mentioned antioxidant containing solid and liquid components during the preparation process. The antioxidant can wrap the fresh fracture of the mixed coarse powder at the moment of crushing, thereby limiting the oxidation of the mixed coarse powder to the greatest extent, and thus obtaining NdFeB magnetic powder with a low oxygen content; at the same time, the present application also adds the above-mentioned lubricant into the intermediate powder before forming and orientation. The lubricant can effectively improve the fluidity of the prepared NdFeB magnetic powder, thereby improving the filling uniformity of the NdFeB magnetic powder in the subsequent processing process and accelerating the rotation or movement during the orientation process.

Brief Description of the Drawings

[0020] Figure 1 This is a comparison chart of the test results of Examples 1 to 4 of the present application and Comparative Examples 1 to 2. [Specific implementation method]

[0021] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0022] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0023] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0024] Neodymium iron boron magnets are man-made permanent magnets and currently possess the strongest magnetic force. Their maximum magnetic energy product (BHmax) is over 10 times higher than that of ferrites, and in their bare state, their magnetic force can reach approximately 3500 gauss. They offer high cost-effectiveness, compact size, light weight, excellent mechanical properties, and strong magnetic properties. Therefore, they are widely used in electric vehicles, hybrid vehicles, wind power generation, variable-frequency air conditioners, medical equipment, elevators, audio equipment, and mineral sorting.

[0025] In order to obtain NdFeB magnets with excellent magnetic properties, it is necessary to reduce oxidation corrosion and facilitate the magnetization process during the NdFeB magnetic powder molding process. Improving the oxidation resistance and lubricity of NdFeB magnetic powder has become an urgent problem to be solved.

[0026] In view of this, the present application provides a method for preparing NdFeB magnetic powder, comprising the following steps:

[0027] Step S10, subjecting the NdFeB raw material to a casting process to obtain NdFeB alloy sheets, and subjecting the NdFeB alloy sheets to a hydrogen explosion process to obtain NdFeB hydrogen explosion powder;

[0028] Step S20, adding an antioxidant to the NdFeB hydrogen explosion powder and mixing them uniformly to obtain a coarse mixed powder; wherein the antioxidant comprises 5% to 15% by weight of hexachloroethane and the remainder comprises at least one of aviation gasoline or monochlorobenzene;

[0029] Step S30, in an oxygen-free condition, jet milling the coarse mixed powder to obtain an intermediate powder;

[0030] Step S40: adding a lubricant to the intermediate powder and stirring the mixture uniformly under a protective atmosphere to obtain NdFeB magnetic powder; wherein the lubricant comprises at least one of tributyl borate and methyl laurate.

[0031] In the above scheme, the preparation method of NdFeB magnetic powder provided by the present application adds the above-mentioned antioxidant containing solid and liquid components during the preparation process. The antioxidant can wrap the fresh fracture of the mixed coarse powder at the moment of crushing, thereby limiting the oxidation of the mixed coarse powder to the greatest extent, and thus obtaining NdFeB magnetic powder with low oxygen content; at the same time, the present application also adds the above-mentioned lubricant to the intermediate powder before forming and orientation. The lubricant can effectively improve the fluidity of the prepared NdFeB magnetic powder, thereby improving the filling uniformity of the NdFeB magnetic powder in the subsequent processing process and accelerating the rotation or movement during the orientation process.

[0032] The preparation method of the present application is explained below with reference to specific examples:

[0033] Step S10: subjecting the NdFeB raw material to a casting process to obtain NdFeB alloy sheets, and subjecting the NdFeB alloy sheets to a hydrogen explosion process to obtain NdFeB hydrogen explosion powder.

[0034] In step S10, the NdFeB raw material mainly includes metallic neodymium, pure iron and boron-iron alloy. At the same time, in order to enhance the magnetic properties of the NdFeB magnet, a small amount of rare earth metal elements or other precious metal elements, such as La element, Ce element, Tb element, Gd element, etc., can also be added. Among them, the acquisition cost of La element and Ce element is low, which can reduce the production cost of NdFeB magnet, but will reduce the remanence and coercive force of NdFeB magnet; the addition of Tb element can greatly improve the coercive force of the magnet, but will increase the production cost of NdFeB magnet; the addition of Gd element can prepare high-temperature resistant NdFeB magnet, but will reduce the remanence of NdFeB magnet. Other elements can also be added to prepare NdFeB magnet, which is not limited here.

[0035] After the NdFeB raw materials undergo pretreatment processes such as weighing, breaking, cutting, and rust removal, the casting process can be carried out. The casting process used for the NdFeB raw materials in this application includes a melting and strip-spinning process and a cooling process. The pretreated NdFeB raw materials and the added elements are mixed in proportion, added to a vacuum melting furnace, and melted at high temperature under argon protection, followed by a strip-spinning process, thereby obtaining NdFeB alloy castings with uniform composition, high crystal orientation, good structural consistency, and low α-Fe generation.

[0036] At this point, the NdFeB alloy casting is subjected to a hydrogen explosion process to obtain NdFeB hydrogen explosion powder. The hydrogen explosion process specifically involves placing the NdFeB alloy casting in a vacuum hydrogen treatment furnace. Utilizing the hydrogen absorption properties of the metal compounds in the NdFeB alloy casting, hydrogen enters the NdFeB alloy casting along the NdFeB phase thin layer in a hydrogen environment, causing it to expand, burst, and break. This loosens the structure of the NdFeB alloy casting, facilitating the efficiency of powder refinement in subsequent processing and reducing production costs. Furthermore, during this process, the NdFeB alloy casting cracks along the NdFeB phase thin layer, without affecting the integrity of the main phase grains and the boundary phase between the NdFeB grains. It also has the following effects: First, the hydrogen explosion process is pollution-free, noiseless, less oxidized and highly efficient; second, single crystal particles account for a large proportion of the NdFeB hydrogen explosion powder crushed by the hydrogen explosion process, which is beneficial to improving the magnetic properties; third, the hydrogen explosion powder crushed by the hydrogen explosion process has brittle particles, and subsequent air flow milling treatment can easily further grind it, and can greatly save the grinding time of air flow milling (the efficiency of air flow milling is increased by 3-4 times); fourth, NdFeB hydrogen explosion powder is prepared in vacuum and hydrogen atmosphere, so it contains less oxygen, which is beneficial to improving the magnetic properties; fifth, the NdFeB magnetic powder prepared by the hydrogen explosion process will release hydrogen during subsequent sintering. Hydrogen has reducing properties, which can further prevent the NdFeB magnetic powder from oxidizing during the sintering process.

[0037] In step S20, the above-mentioned NdFeB hydrogen explosion powder can be mixed with an antioxidant to obtain a mixed coarse powder. The amount of NdFeB hydrogen explosion powder added in the mixed coarse powder of the present application is 1kg to 3kg. Optionally, the amount of NdFeB hydrogen explosion powder added can be specifically 1kg, 1.3kg, 1.6kg, 1.9kg, 2.2kg, 2.5kg, 2.8kg and 3kg, etc., or other values ​​within the range. It can be selected according to actual needs and is not limited here. If the amount of NdFeB hydrogen explosion powder added is too low, the preparation efficiency is low; if the amount of NdFeB hydrogen explosion powder added is too high, it is not conducive to the subsequent refinement process. Preferably, the amount of NdFeB hydrogen explosion powder added is 2kg.

[0038] The antioxidant used in the present application includes 5% to 15% by mass of hexachloroethane, and the balance includes at least one of aviation gasoline or monochlorobenzene. For example, the antioxidant component can be a combination of hexachloroethane and aviation gasoline, or a combination of hexachloroethane and monochlorobenzene, or a combination of hexachloroethane, aviation gasoline and monochlorobenzene. The composition of the antioxidant can be selected according to actual needs and is not limited here.

[0039] The specific weight content of hexachloroethane can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or other values ​​within this range. This value can be selected based on actual needs and is not limited herein. It will be appreciated that when the weight content of hexachloroethane in the antioxidant is within the above range, the antioxidant exhibits excellent antioxidant properties.

[0040] The mass proportion of the antioxidant in the coarse powder is 0.5‰ to 2.5‰. Optionally, the mass proportion of the antioxidant in the coarse powder can be 0.5‰, 0.8‰, 1.1‰, 1.4‰, 1.7‰, 2.0‰, 2.3‰ and 2.5‰, etc., or other values ​​within the range. It can be selected according to actual needs and is not limited here. If the amount of antioxidant added is too low, it will not have a good antioxidant effect, which will cause the oxygen content of the prepared NdFeB magnetic powder to be too high, affecting the magnetic properties; if the amount of antioxidant added is too high, the amount of NdFeB hydrogen explosion powder added will be reduced, and NdFeB magnetic powder with the required performance will not be obtained.

[0041] The mixing time of NdFeB hydrogen explosion powder and antioxidant is ≥2h. Optionally, the mixing time of NdFeB hydrogen explosion powder and antioxidant can be 2h, 2.2h, 2.4h, 2.6h, 2.8h, 3h, etc., or other values ​​within the range. It can be selected according to actual needs and is not limited here. If the mixing time is too short, the NdFeB hydrogen explosion powder and antioxidant in the prepared coarse powder will be unevenly distributed, and the antioxidant will not play a good antioxidant role, which will lead to excessively high oxygen content in the prepared NdFeB magnet, reducing the magnetic properties.

[0042] In step S30, the air flow milling treatment is at least one of fluidized bed air flow milling treatment or target air flow milling treatment. The air flow milling treatment for powder making is to crush the mixed coarse powder by high-speed collision of the mixed coarse powder itself. This treatment method has no wear and pollution to the inner wall of the mill chamber and can efficiently prepare intermediate powder. The air flow milling treatment method can be selected according to actual needs and is not limited here.

[0043] After the air flow milling process, an intermediate powder with an average particle size D50 of 2μm to 4μm can be obtained. Optionally, the average particle size of the intermediate powder can be 2μm, 2.3μm, 2.6μm, 2.9μm, 3.2μm, 3.5μm, 3.8μm and 4μm, etc., or other values ​​within the range. It can be selected according to actual needs and is not limited here. If the average particle size of the intermediate powder is too small, the air flow milling process takes a long time, which will reduce the preparation efficiency of the NdFeB magnetic powder; if the average particle size of the intermediate powder is too large, it will be detrimental to the subsequent filling and orientation process of the NdFeB hydrogen explosion powder.

[0044] In step S40 again, a lubricant can be added to the intermediate powder, and the lubricant includes at least one of tributyl borate or methyl laurate. Exemplarily, the lubricant can be tributyl borate, methyl laurate, or a composition of tributyl borate and methyl laurate. The type of lubricant can be selected according to actual needs and is not limited here. It is understandable that the main influencing factor affecting the fluidity of the NdFeB magnetic powder when it is in a loose state is the magnetic agglomeration of the powder, and the main factor affecting the fluidity when it is in a dense state is the friction between the powders. Adding an appropriate amount of lubricant can reduce the agglomeration between the powder particles, significantly reduce the powder friction, improve the powder fluidity, and then improve the orientation degree, remanence and magnetic energy product of the NdFeB magnet prepared.

[0045] In this application, the mass ratio of lubricant in NdFeB magnetic powder is 0.5‰ to 1.5‰. Optionally, the mass ratio of lubricant in NdFeB magnetic powder can be 0.5‰, 0.7‰, 0.9‰, 1‰, 1.2‰ and 1.5‰, etc., or other values ​​within the range. It can be selected according to actual needs and is not limited here. If the amount of lubricant added is too low, it will not have a good lubricating effect and will reduce the fluidity of NdFeB magnetic powder; if the amount of lubricant added is too high, the preparation cost will increase.

[0046] After the lubricant of the above type and mass ratio is added to the intermediate powder, the stirring time is 5s to 15s, the stirring frequency is 2 to 4 times, and the interval between adjacent stirring times is 9min to 11min, thereby obtaining the NdFeB magnetic powder with excellent magnetic properties of the present application. Preferably, the stirring time is 10s, the stirring frequency is 3 times, and the interval between adjacent stirring times is 10min.

[0047] The following further describes the embodiments of the present invention in multiple embodiments. The embodiments of the present invention are not limited to the following specific embodiments. Within the scope of the unchanged main rights, appropriate changes can be made to the implementation.

[0048] Example 1:

[0049] (1) Take 2 kg of 48M brand NdFeB hydrogen explosion powder, mix it with 1.5‰ of monochlorobenzene and hexachloroethane with a mass ratio of 90:5, put it into a V-type mixer and mix it for 2 hours, then take it out to obtain a coarse mixed powder.

[0050] (2) Under oxygen-free conditions, the coarse mixed powder is ground into an intermediate powder with an average particle size D50 of 3 μm using a target jet mill MJT.

[0051] (3) Take out the intermediate powder and put it into a traditional Chinese medicine grinder. At the same time, add 1‰ of an equal proportion of tributyl borate and methyl laurate as a lubricant. Run the traditional Chinese medicine grinder for 10s × 3 times with an interval of 10min. Stir evenly under a protective atmosphere to obtain neodymium iron boron magnetic powder.

[0052] Example 2:

[0053] (1) Take 2 kg of 48M brand NdFeB hydrogen explosion powder, mix it with 1.5‰ of monochlorobenzene and hexachloroethane with a mass ratio of 95:5, put it into a V-type mixer and mix it for 2 hours, then take it out to obtain a coarse mixed powder.

[0054] (2) Under oxygen-free conditions, the coarse mixed powder is ground into an intermediate powder with an average particle size D50 of 3 μm using a target jet mill MJT.

[0055] (3) Take out the intermediate powder and put it into a Chinese medicine grinder, add 1‰ methyl laurate as a lubricant, run the Chinese medicine grinder for 10s×3 times, and the interval time is 10min. Stir evenly under a protective atmosphere to obtain NdFeB magnetic powder.

[0056] Example 3:

[0057] (1) Take 2 kg of 48M brand NdFeB hydrogen explosion powder, mix it with 1.5‰ of monochlorobenzene and hexachloroethane with a mass ratio of 95:5, put it into a V-type mixer and mix it for 2 hours, then take it out to obtain a coarse mixed powder.

[0058] (2) Under oxygen-free conditions, the coarse mixed powder is ground into an intermediate powder with an average particle size D50 of 3 μm using a target jet mill MJT.

[0059] (3) Take out the intermediate powder and put it into a traditional Chinese medicine grinder, add 1‰ tributyl borate as a lubricant, run the traditional Chinese medicine grinder for 10s × 3 times, and the interval time is 10min, stir evenly under a protective atmosphere to obtain neodymium iron boron magnetic powder.

[0060] Example 4:

[0061] (1) Take 2 kg of 48M brand NdFeB hydrogen explosion powder, mix it with 1.5‰ of monochlorobenzene and hexachloroethane with a mass ratio of 85:15, put it into a V-type mixer and mix it for 2 hours, then take it out to obtain a coarse mixed powder.

[0062] (2) Under oxygen-free conditions, the coarse mixed powder is ground into an intermediate powder with an average particle size D50 of 3 μm using a target jet mill MJT.

[0063] (3) Take out the intermediate powder and put it into a traditional Chinese medicine grinder. At the same time, add 1‰ of an equal proportion of tributyl borate and methyl laurate as a lubricant. Run the traditional Chinese medicine grinder for 10s × 3 times with an interval of 10min. Stir evenly under a protective atmosphere to obtain neodymium iron boron magnetic powder.

[0064] Comparative Example 1:

[0065] The difference from Example 1 is that conventional lubricant is added in Comparative Example 1.

[0066] Comparative Example 2:

[0067] Different from Example 1, no lubricant was added in Comparative Example 2.

[0068] Test: Use a tap density meter to load a fixed amount of NdFeB magnetic powder, vibrate it for different times, and calculate the density of the powder after each vibration.

[0069] Test results:

[0070] Figure 1 The test results of Examples 1 to 4 of the present application and Comparative Examples 1 to 2 are compared as shown in FIG. Figure 1 As shown, the present application adds a lubricant to the intermediate powder before molding and orientation. The lubricant includes at least one of tributyl borate or methyl laurate. The lubricant can effectively improve the fluidity of the prepared NdFeB magnetic powder, thereby improving the filling uniformity of the NdFeB magnetic powder in the subsequent processing process and accelerating the rotation or movement during the orientation process, thereby increasing the tap density.

[0071] The above embodiments describe in detail the structure, features and effects of the present invention. The above are only preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which do not exceed the scope covered by the specification, should be within the scope of protection of the present invention.

Claims

1. A method for preparing NdFeB magnetic powder, characterized in that: The steps include: The NdFeB raw material is subjected to a casting process to obtain a NdFeB alloy casting sheet, and the NdFeB alloy casting sheet is subjected to a hydrogen explosion process to obtain NdFeB hydrogen explosion powder; Adding an antioxidant to the NdFeB hydrogen explosion powder and mixing them uniformly to obtain a coarse mixed powder; wherein the antioxidant comprises 5% to 15% by weight of hexachloroethane and the remainder comprises at least one of aviation gasoline or monochlorobenzene; Under oxygen-free conditions, the mixed coarse powder is subjected to air flow milling to obtain an intermediate powder; A lubricant is added to the intermediate powder and stirred uniformly under a protective atmosphere to obtain NdFeB magnetic powder; wherein the lubricant includes at least one of tributyl borate or methyl laurate.

2. The method for preparing NdFeB magnetic powder according to claim 1, wherein: The casting process specifically includes a melting and strip-spinning process and a cooling process.

3. The method for preparing NdFeB magnetic powder according to claim 1, wherein: The hydrogen explosion process is specifically as follows: the NdFeB alloy casting sheet absorbs hydrogen to form a hydride, and the hydride expands and explodes to obtain the NdFeB hydrogen explosion powder.

4. The method for preparing NdFeB magnetic powder according to claim 1, wherein: The antioxidant accounts for 0.5‰ to 2.5‰ by mass in the mixed coarse powder.

5. The method for preparing NdFeB magnetic powder according to claim 1, wherein: The mixing time of the NdFeB hydrogen explosion powder and the antioxidant is ≥2h.

6. The method for preparing NdFeB magnetic powder according to claim 1, wherein: The air flow milling process is at least one of a fluidized bed air flow milling process and a target air flow milling process.

7. The method for preparing NdFeB magnetic powder according to claim 1, wherein: The average particle size D50 of the intermediate powder is 2 μm to 4 μm.

8. The method for preparing NdFeB magnetic powder according to claim 1, wherein: The mass proportion of the lubricant in the NdFeB magnetic powder is 0.5‰ to 1.5‰.

9. The method for preparing NdFeB magnetic powder according to claim 1, wherein: The stirring time after adding the lubricant is 5s to 15s, the stirring times are 2 to 4 times, and the interval between adjacent stirrings is 9min to 11min.

Images