Method for producing a neodymium-iron-boron magnet and a neodymium-iron-boron magnet produced thereby

Abstract

The present invention provides a method for preparing a neodymium-iron-boron magnet and a neodymium-iron-boron magnet prepared thereby. Specifically, the method for preparing the neodymium-iron-boron magnet comprises the following steps: (1) mixing and melting a neodymium-iron-boron magnet raw material to obtain an alloy sheet; (2) subjecting the alloy sheet to hydrogen decrepitation treatment to obtain a coarse powder; (3) subjecting the coarse powder to micro-pulverization treatment in an air jet mill to obtain a fine powder; (4) pressing the fine powder into a green body; and (5) subjecting the green body to sintering treatment to obtain the neodymium-iron-boron magnet, wherein: an impurity removal agent is introduced in the air jet mill of step (3) above, the impurity removal agent comprising one or more of ammonia, chlorine, difluoromethane, and chloroform. The neodymium-iron-boron magnet prepared according to the method of the present invention has a greatly reduced content of non-metallic impurities (e.g., C, O, and N, etc.), and in turn has improved magnetic properties (especially, intrinsic coercivity).

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of preparation of neodymium-iron-boron magnetic material, in particular, to a preparation method of neodymium-iron-boron magnet and a neodymium-iron-boron magnet prepared therefrom. BACKGROUND

[0002] Neodymium-iron-boron permanent magnet material is an important kind of rare earth functional material, which has excellent comprehensive magnetic properties and is widely used in electronic industry, electric vehicles and many other fields.

[0003] The magnetic properties of neodymium-iron-boron magnet mainly depend on its microstructure, including grain size, grain boundary phase and distribution of rare earth-rich phase. One of the current research focuses is to improve the magnetic properties of neodymium-iron-boron magnet material by further optimizing its structure in the existing technology. Specifically, according to the grain boundary diffusion technology, the coercivity of the magnet can be improved by introducing heavy rare earth elements such as dysprosium (Dy) at the grain boundary. In the grain refinement process, the number of grain boundaries can be increased by reducing the size of the grains, thereby improving the coercivity of the magnet. In addition, the magnetic properties of the magnet can also be improved by adding elements such as cobalt (Co), gallium (Ga), etc. In addition, the microstructure of the magnet can also be optimized and the magnetic properties can be improved by optimizing the sintering and heat treatment process, such as by precisely controlling the sintering and heat treatment process. At present, further improving the magnetic properties of neodymium-iron-boron permanent magnet is still a popular research direction for technical personnel.

[0004] However, it is still of great significance to develop a simple process for preparing neodymium-iron-boron magnet that can further improve the magnetic properties (especially the intrinsic coercivity). SUMMARY

[0005] In view of the above technical problems, one of the purposes of the present application is to provide a preparation method of neodymium-iron-boron magnet and a neodymium-iron-boron magnet prepared therefrom, according to which the process is simple and the prepared neodymium-iron-boron magnet has improved magnetic properties (especially the intrinsic coercivity).

[0006] Specifically, in one aspect, the present application provides a preparation method of neodymium-iron-boron magnet, comprising the following steps:

[0007] (1) mixing and smelting neodymium-iron-boron magnet raw materials to obtain alloy sheets;

[0008] (2) hydrogen breaking the alloy sheets to obtain coarse powder;

[0009] (3) micro-pulverizing the coarse powder in an air flow mill to obtain micro powder;

[0010] (4) pressing the micro powder into a green body; and

[0011] (5) subjecting the green compact to a sintering treatment to obtain the neodymium-iron-boron magnet, wherein:

[0012] The impurity removal agent introduced in the jet mill in the above step (3) comprises one or more of ammonia gas, chlorine gas, difluoromethane and chloroform.

[0013] According to certain preferred embodiments of the present application, the temperature in the jet mill is in the range of 10-25°C and the pressure is in the range of 0.55-0.65 MPa.

[0014] According to certain preferred embodiments of the present application, in the above step (3), the impurity removal agent is introduced into the inert gas leading to the jet mill.

[0015] According to certain preferred embodiments of the present application, when the impurity removal agent is ammonia gas, chlorine gas or a mixture thereof, the content of the impurity removal agent in the inert gas is in the range of 1 ppm to 10000 ppm.

[0016] According to certain preferred embodiments of the present application, when the impurity removal agent is ammonia gas, chlorine gas or a mixture thereof, the content of the impurity removal agent in the inert gas is in the range of 10 ppm to 100 ppm.

[0017] According to certain preferred embodiments of the present application, when the impurity removal agent is difluoromethane, chloroform or a mixture thereof, the weight ratio of the impurity removal agent to the inert gas is in the range of 1 μg / g to 1000 μg / g.

[0018] According to certain preferred embodiments of the present application, when the impurity removal agent is difluoromethane, chloroform or a mixture thereof, the weight ratio of the impurity removal agent to the inert gas is in the range of 10 μg / g to 100 μg / g.

[0019] According to certain preferred embodiments of the present application, the inert gas is nitrogen or argon.

[0020] According to certain preferred embodiments of the present application, the flow rate of the inert gas containing the impurity removal agent in the jet mill is in the range of 35-45 m 3 / min.

[0021] According to certain preferred embodiments of the present application, step (3) results in the D 50 particle size of the fine powder being in the range of 3.8-4.2 μm.

[0022] According to certain preferred embodiments of the present application, the neodymium-iron-boron magnet raw material comprises the following components:

[0023] R: 28-33 wt%, the R being a rare earth element, the R comprising Nd and Pr;

[0024] Al: <0.5 wt%;

[0025] Cu: 0.1-0.6 wt%;

[0026] Co: >0.4 wt%;

[0027] Ga: <0.3 wt%;

[0028] Ti: <0.4 wt%;

[0029] B: 0.98-1.2 wt%;

[0030] Fe: 62-69 wt%, wherein the wt% is the percentage of the mass of each component to the total mass of the neodymium-iron-boron magnet raw material.

[0031] In another aspect, the present application provides a neodymium-iron-boron magnet prepared by the preparation method according to any one of the above.

[0032] Compared with the preparation method of the prior art neodymium-iron-boron magnet, the preparation method of the neodymium-iron-boron magnet according to the present application has the advantage that by supplementing the impurity removal agent (for example, one or more of ammonia, chlorine, difluoromethane and chloroform) in the airflow milling process, the content of non-metallic impurities such as carbon (C), oxygen (O) and nitrogen (N) in the neodymium-iron-boron magnet can be effectively reduced, which helps to reduce the negative impact of these impurities on the magnetic properties, thereby improving the magnetic properties (especially the intrinsic coercivity) of the prepared neodymium-iron-boron magnet. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Process flow chart for the preparation method of the neodymium-iron-boron magnet according to the present application. DETAILED DESCRIPTION

[0034] The present application will be further described in detail below in conjunction with the drawings and specific embodiments. It will be understood that other embodiments are contemplated and can be practiced without departing from the scope or spirit of the present application. Therefore, the following detailed description is non-limiting.

[0035] Unless otherwise indicated, all numbers expressing features, quantities and physical characteristics in the specification and claims are to be understood as approximations based on the teaching of the present disclosure. Accordingly, unless otherwise indicated, the numerical parameters set forth in the specification and claims are approximations that can vary depending on the requirements of the desired properties sought to be obtained by those skilled in the art using teachings disclosed herein. The numerical ranges recited herein are inclusive of all the numbers within the range and any range that would be derived from the upper and lower limits of the ranges, e.g., the range 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4, 5 and so forth.

[0036] As mentioned above, it is still of great significance to develop a process simple method for preparing neodymium-iron-boron magnets with further improved magnetic properties (especially, intrinsic coercivity). The inventors of the present disclosure have found in their research that the impurities present in neodymium-iron-boron magnets, such as carbon (C), oxygen (O) and nitrogen (N), can have a significant negative impact on the performance of the magnets. For example, during the production of neodymium-iron-boron magnets, carbon mainly comes from raw materials and process steps, such as smelting, powdering and forming. Carbon impurities can form carbides with rare earth elements in neodymium-iron-boron magnets, which can increase the internal stress of the magnets and thus reduce the magnetic properties of the magnets, especially the coercivity. In addition, oxygen in neodymium-iron-boron magnets is usually in the form of rare earth oxides or iron oxides. The increase of oxygen can lead to a decrease in the intrinsic coercivity of the magnets, because oxygen can form oxides with rare earth elements, and the distribution of these oxides at the grain boundaries can interfere with the magnetization process of the magnets. In addition, nitrogen in neodymium-iron-boron magnets can exist in the form of nitrides, and the formation of nitrides can consume rare earth elements in the magnets, reducing the amount of effective magnetic material and leading to a decrease in the magnetic properties of the magnets. According to the technical solution of the present disclosure, by supplementing impurity removal agents (for example, one or more of ammonia, chlorine, difluoromethane and chloroform) during the airflow milling process, the content of non-metallic impurities such as carbon (C), oxygen (O) and nitrogen (N) in neodymium-iron-boron magnets can be effectively reduced, which helps to reduce the negative impact of these impurities on the magnetic properties, thereby improving the magnetic properties (especially, intrinsic coercivity) of the prepared neodymium-iron-boron magnets.

[0037] In particular, the present disclosure provides a method for preparing a neodymium-iron-boron magnet, the method comprising the following steps:

[0038] (1) mixing and smelting neodymium-iron-boron magnet raw materials to obtain alloy pieces;

[0039] (2) hydrogen decrepitation treatment of the alloy pieces to obtain coarse powder;

[0040] (3) micro-pulverization of the coarse powder in an airflow mill to obtain fine powder;

[0041] (4) compacting the micro-powder into a green body; and

[0042] (5) sintering the green body to obtain the Nd-Fe-B magnet, wherein:

[0043] In the jet mill of step (3) above, an impurity removal agent is introduced, the impurity removal agent comprising one or more of ammonia, chlorine, difluoromethane, and chloroform.

[0044] Figure 1 A process flow chart for the method of preparing a Nd-Fe-B magnet according to the present application. Specifically, the method of preparation comprises the following steps:

[0045] S1 : mixing and melting a Nd-Fe-B magnet raw material to obtain an alloy sheet;

[0046] S2: hydrogen decrepitation of the alloy sheet to obtain a coarse powder;

[0047] S3: micro-pulverization of the coarse powder in a jet mill to obtain a micro-powder;

[0048] S4: compacting the micro-powder into a green body; and

[0049] S5: sintering the green body to obtain the Nd-Fe-B magnet.

[0050] In the present application, unless otherwise specified, the term "impurity removal agent" refers to a substance that is capable of removing or reducing impurities such as carbon (C), oxygen (O), and nitrogen (N) present in a Nd-Fe-B magnet under specific conditions (e.g., temperature and pressure). The inventors of the present application have found in their research that by supplementing an impurity removal agent (e.g., one or more of ammonia, chlorine, difluoromethane, and chloroform) during the jet milling process, the content of non-metallic impurities such as carbon (C), oxygen (O), and nitrogen (N) in the resulting Nd-Fe-B magnet can be effectively reduced. Although the mechanism by which the impurity removal agent (e.g., one or more of ammonia, chlorine, difluoromethane, and chloroform) removes or reduces impurities such as carbon (C), oxygen (O), and nitrogen (N) is not clear, without being bound by theory, it is believed that one or more of ammonia, chlorine, difluoromethane, and chloroform introduced during the jet milling process forms a less stable complex with carbon species, oxygen species, and nitrogen species in the coarse powder of the Nd-Fe-B magnet raw material under specific temperature and pressure, which is removed from the Nd-Fe-B system in subsequent process steps (e.g., high-temperature sintering treatment, etc.).

[0051] According to the technical solution of the present application, in step (1), a Nd-Fe-B magnet raw material is mixed and melted to obtain an alloy sheet.

[0052] The formulation of the Nd-Fe-B magnet raw material that can be used in the present application is not particularly limited. Preferably, the Nd-Fe-B magnet raw material comprises the following components:

[0053] R: 28-33 wt%, the R being a rare earth element, the R comprising Nd and Pr;

[0054] Al: ≤0.5 wt%;

[0055] Cu: 0.1-0.6 wt%;

[0056] Co: ≥0.4 wt%;

[0057] Ga: ≤0.3 wt%;

[0058] Ti: ≤0.4 wt%;

[0059] B: 0.98-1.2 wt%:

[0060] Fe: 62-69 wt%, wherein the wt% is the percentage of the mass of each component to the total mass of the neodymium-iron-boron magnet raw material.

[0061] Specifically, the prepared neodymium-iron-boron magnet raw material is uniformly mixed, then smelted at a temperature in the range of 1400-1550°C, and then cast into an alloy sheet by a rapid quenching method.

[0062] According to the technical scheme of the present application, in step (2), the obtained alloy sheet is subjected to hydrogen decrepitation treatment to obtain a coarse powder. Preferably, the hydrogen decrepitation treatment comprises hydrogen absorption, hydrogen desorption and cooling. The hydrogen absorption is carried out under the condition of hydrogen pressure of 0.09-0.29 MPa. The hydrogen desorption is carried out under the condition of vacuumizing and temperature rising, and the hydrogen desorption temperature is 350-550°C.

[0063] According to the technical scheme of the present application, in step (3), the coarse powder is subjected to a micro-pulverization treatment in an air flow mill to obtain a micro-powder.

[0064] The air flow mill process plays an important role in the preparation of neodymium-iron-boron magnets, and is mainly used for preparing alloy ingots or spun ribbon sheets into fine powders. The air flow mill used for neodymium-iron-boron magnets is usually a fluidized bed type air flow mill, which is composed of an air flow mill, a cyclone separator, a dust collector and an induced draft fan to form a complete pulverization system. Generally, inert gas such as nitrogen is used as the power gas, and the material is repeatedly collided, rubbed and sheared under the action of high-pressure gas to be pulverized.

[0065] According to the technical scheme of the present application, preferably, the impurity removal agent (for example, one or more of ammonia, chlorine, difluoromethane and chloroform) is introduced into the inert gas leading to the air flow mill.

[0066] According to the technical solution of the present application, preferably, when the impurity removal agent is a gas such as ammonia, chlorine or a mixture thereof, the impurity removal agent is introduced at the inlet pipe of the gas compressor of the jet mill. Preferably, when the impurity removal agent is a liquid such as difluoromethane, chloroform or a mixture thereof, the impurity removal agent is introduced at the outlet pipe of the gas compressor of the jet mill.

[0067] According to the technical solution of the present application, in order to further improve the removal effect of non-metallic impurities (such as C, O and N, etc.), the temperature in the jet mill is in the range of 10-25℃, and the pressure is in the range of 0.55-0.65 MPa. The inventors of the present application found in the research that when the above temperature and pressure range are not met, the effect of removing or reducing the content of non-metallic impurities (such as C, O and N, etc.) from the neodymium-iron-boron magnet cannot be achieved.

[0068] According to the technical solution of the present application, when the impurity removal agent is ammonia, chlorine or a mixture thereof, the content of the impurity removal agent in the inert gas is in the range of 1 ppm to 10000 ppm. The inventors of the present application found in the research that the content of the impurity removal agent (such as ammonia, chlorine or a mixture thereof) in the inert gas has an important influence on the removal of impurities. When the content of the impurity removal agent (such as ammonia, chlorine or a mixture thereof) in the inert gas is less than 1 ppm, the reduction of the content of non-metallic impurities (such as C, O and N, etc.) in the obtained neodymium-iron-boron magnet cannot be detected and the magnetic performance of the obtained neodymium-iron-boron magnet is poor; when the content of the impurity removal agent (such as ammonia, chlorine or a mixture thereof) in the inert gas is greater than 10000 ppm, the presence of excessive impurity removal agent can cause the magnetic performance of the obtained neodymium-iron-boron magnet to deteriorate. Preferably, when the impurity removal agent is ammonia, chlorine or a mixture thereof, in order to further improve the removal effect of non-metallic impurities (such as C, O and N, etc.), the content of the impurity removal agent (such as ammonia, chlorine or a mixture thereof) in the inert gas is in the range of 10 ppm to 100 ppm.

[0069] According to the technical scheme of the present application, when the impurity removal agent is difluoromethane, chloroform or a mixture thereof, the weight ratio of the impurity removal agent to the inert gas is in the range of 1 μg / g to 1000 μg / g. The inventors of the present application have found in research that the content of the impurity removal agent (e.g. difluoromethane, chloroform or a mixture thereof) in the inert gas has an important influence on the removal of impurities. When the weight ratio of the impurity removal agent (e.g. difluoromethane, chloroform or a mixture thereof) to the inert gas is less than 1 μg / g, the content of non-metallic impurities (e.g. C, O and N, etc.) in the obtained neodymium-iron-boron magnet cannot be detected to be reduced and the magnetic properties of the obtained neodymium-iron-boron magnet are poor; when the weight ratio of the impurity removal agent (e.g. difluoromethane, chloroform or a mixture thereof) to the inert gas is greater than 1000 μg / g, the presence of excessive impurity removal agent (e.g. difluoromethane, chloroform or a mixture thereof) can cause the magnetic properties of the obtained neodymium-iron-boron magnet to deteriorate. Preferably, when the impurity removal agent is difluoromethane, chloroform or a mixture thereof, in order to further improve the removal effect on non-metallic impurities (e.g. C, O and N, etc.), the weight ratio of the impurity removal agent to the inert gas is in the range of 10 μg / g to 100 μg / g.

[0070] According to the technical scheme of the present application, preferably, the inert gas is nitrogen or argon.

[0071] According to the technical scheme of the present application, preferably, in order to further improve the removal effect on non-metallic impurities (e.g. C, O and N, etc.), the flow rate of the inert gas containing the impurity removal agent in the jet mill is in the range of 35-45 m 3 / min, preferably 38-40 m 3 / min.

[0072] After the airflow milling, optionally, a lubricant such as zinc stearate can be added to the obtained micropowder. The amount of the lubricant added can be 0.05-0.15% of the mass of the micropowder obtained after the milling, for example 0.12%.

[0073] According to the technical scheme of the present application, in step (4), the micropowder is pressed into a green body. The pressing can be performed by using conventional methods in the prior art. For example, a normal orientation pressing method can be used. For example, the forming can be performed by using a magnetic field forming method. In the magnetic field forming, for example, a magnetic field strength of 1.8-2.5 T is used.

[0074] Finally, according to the technical scheme of the present application, in step (5), the green body is subjected to a sintering treatment to obtain the neodymium-iron-boron magnet. The sintering process can be a conventional sintering process in the art. In the sintering, the temperature can be 1000-1100 °C. In the sintering, the time can be 4-8 h.

[0075] In another aspect of the present application, there is provided a neodymium-iron-boron magnet prepared by the preparation method described above.

[0076] The present application will be described in more detail with reference to the following examples. It is to be noted that these descriptions and examples are intended to facilitate the understanding of the present application, and are not intended to limit the present application. The scope of protection of the present application is defined by the appended claims.

[0077] Example

[0078] In the present application, unless otherwise specified, the reagents used are commercially available products, which are used directly without further purification treatment. In addition, the "%" and "wt%" mentioned are "weight percent", and the "parts" mentioned are "weight parts".

[0079] Example 1

[0080] First, the neodymium-iron-boron magnet raw materials are uniformly mixed according to the specified formulation ratio and are smelted into alloy pieces. The formulation includes 30wt% PrNd (praseodymium-neodymium alloy), 0.05wt% Al (aluminum), 0.2wt% Cu (copper), 0.5wt% Co (cobalt), 0.3wt% Ga (gallium), 0.2wt% Ti (titanium), 0.98wt% B (boron), and the rest is Fe (iron). The smelting temperature is 1520±5℃.

[0081] Then, the neodymium-iron-boron alloy pieces are subjected to hydrogen decrepitation treatment to obtain coarse powder. Hydrogen decrepitation treatment is a common powdering process, which makes the structure of the alloy loose by treating it in a hydrogen atmosphere, facilitating subsequent jet mill powdering. Hydrogen decrepitation treatment includes hydrogen absorption, hydrogen desorption and cooling. Hydrogen absorption is carried out under the condition of hydrogen pressure 0.098MPa. Hydrogen desorption is carried out under the condition of vacuumizing and heating, and the hydrogen desorption temperature is 550℃.

[0082] Next, the coarse powder is refined using a jet mill. In this step, the gas of the jet mill is selected to be nitrogen, and ammonia gas is introduced as an impurity removal agent at the inlet pipe of the gas compressor of the jet mill. Among them, the content of the impurity removal agent, i.e. ammonia gas, in the nitrogen gas is 10ppm; the temperature in the jet mill is 15-20℃, and the pressure is 0.6-0.63MPa; the flow rate of nitrogen gas containing ammonia in the jet mill is 38-40m 3 / min; the jet mill produces alloy micro powder with a particle size D 50 of 4.0-4.2μm.

[0083] Subsequently, the alloy micro powder is pressed into a green body by using a conventional orientation pressing method.

[0084] The green body was then sintered. The sintering process was designed with multiple degassing temperatures, including 150°C - 300°C - 550°C - 800°C, and the degassing time was set to 1-3 hours, to obtain the NdFeB magnet.

[0085] The sintered NdFeB green body product obtained in Example 1 was sampled at multiple points to test the total amount of non-metallic impurities, namely carbon (C), oxygen (O), and nitrogen (N), wherein each sample was tested twice and the average value was calculated. The results are shown in Table 1 below.

[0086] The magnetic properties (including residual magnetism (Br), intrinsic coercive force (Hcj), magnetic energy product / coercive force (Hk / Hcj), apparent coercive force (Hcb), and maximum magnetic energy product (BH) max ) of the sintered NdFeB green body product obtained in Example 1 were measured. The results are shown in Table 2 below.

[0087] Example 2

[0088] The NdFeB magnet was prepared in a similar manner to Example 1, except that the content of the impurity removal agent, ammonia gas in nitrogen gas, was changed from 10 ppm to 25 ppm.

[0089] The sintered NdFeB green body product obtained in Example 2 was sampled at multiple points to test the total amount of non-metallic impurities, namely carbon (C), oxygen (O), and nitrogen (N), wherein each sample was tested twice and the average value was calculated. The results are shown in Table 1 below.

[0090] The magnetic properties (including residual magnetism (Br), intrinsic coercive force (Hcj), magnetic energy product / coercive force (Hk / Hcj), apparent coercive force (Hcb), and maximum magnetic energy product (BH) max ) of the sintered NdFeB green body product obtained in Example 2 were measured. The results are shown in Table 2 below.

[0091] Example 3

[0092] The NdFeB magnet was prepared in a similar manner to Example 1, except that the impurity removal agent was changed from ammonia gas to chlorine gas.

[0093] The sintered NdFeB green body product obtained in Example 3 was sampled at multiple points to test the total amount of non-metallic impurities, namely carbon (C), oxygen (O), and nitrogen (N), wherein each sample was tested twice and the average value was calculated. The results are shown in Table 1 below.

[0094] The magnetic properties (including residual magnetism (Br), intrinsic coercive force (Hcj), magnetic energy product / coercive force (Hk / Hcj), apparent coercive force (Hcb), and maximum magnetic energy product (BH)max ) were measured. The results are shown in Table 2 below.

[0095] Example 4

[0096] A neodymium-iron-boron magnet was prepared in a similar manner to Example 1, except that the impurity removing agent was changed from ammonia gas to chlorine gas, and the content of the impurity removing agent, i.e. chlorine gas, in the nitrogen gas was changed from 10 ppm to 25 ppm.

[0097] The sintered neodymium-iron-boron blank product obtained in Example 4 was sampled at multiple points to test the total amount of non-metallic impurities, i.e. carbon (C), oxygen (O), and nitrogen (N), wherein each sample was tested twice and the average value was calculated. The results are shown in Table 1 below.

[0098] The magnetic properties (including residual magnetism (Br), intrinsic coercive force (Hcj), magnetic energy product / coercive force (Hk / Hcj), apparent coercive force (Hcb), and maximum magnetic energy product (BH) max ) of the sintered neodymium-iron-boron blank product obtained in Example 4 were measured. The results are shown in Table 2 below.

[0099] Example 5

[0100] A neodymium-iron-boron magnet was prepared in a similar manner to Example 1, except that the impurity removing agent was changed from ammonia gas to dichloromethane, and the weight ratio of the impurity removing agent, i.e. dichloromethane, to the inert gas was 10 μg / g.

[0101] The sintered neodymium-iron-boron blank product obtained in Example 5 was sampled at multiple points to test the total amount of non-metallic impurities, i.e. carbon (C), oxygen (O), and nitrogen (N), wherein each sample was tested twice and the average value was calculated. The results are shown in Table 1 below.

[0102] The magnetic properties (including residual magnetism (Br), intrinsic coercive force (Hcj), magnetic energy product / coercive force (Hk / Hcj), apparent coercive force (Hcb), and maximum magnetic energy product (BH) max ) of the sintered neodymium-iron-boron blank product obtained in Example 5 were measured. The results are shown in Table 2 below.

[0103] Example 6

[0104] A neodymium-iron-boron magnet was prepared in a similar manner to Example 1, except that the impurity removing agent was changed from ammonia gas to dichloromethane, and the weight ratio of the impurity removing agent, i.e. dichloromethane, to the inert gas was 25 μg / g.

[0105] The sintered neodymium-iron-boron blank product obtained in Example 6 was sampled at multiple points to test the total amount of non-metallic impurities, i.e., carbon (C), oxygen (O), and nitrogen (N), wherein each sample was tested twice and the average value was calculated. The results are shown in Table 1 below.

[0106] The magnetic properties (including residual magnetism (Br), intrinsic coercive force (Hcj), magnetic energy product / coercive force (Hk / Hcj), apparent coercive force (Hcb), and maximum magnetic energy product (BH) max ) of the sintered neodymium-iron-boron blank product obtained in Example 6 were measured. The results are shown in Table 2 below.

[0107] Comparative Example 1

[0108] A neodymium-iron-boron magnet was prepared in a similar manner to Example 1, except that no impurity removing agent was introduced in the jet mill process.

[0109] The sintered neodymium-iron-boron blank product obtained in Comparative Example 1 was sampled at multiple points to test the total amount of non-metallic impurities, i.e., carbon (C), oxygen (O), and nitrogen (N), wherein each sample was tested twice and the average value was calculated. The results are shown in Table 1 below.

[0110] The magnetic properties (including residual magnetism (Br), intrinsic coercive force (Hcj), magnetic energy product / coercive force (Hk / Hcj), apparent coercive force (Hcb), and maximum magnetic energy product (BH) max ) of the sintered neodymium-iron-boron blank product obtained in Comparative Example 1 were measured. The results are shown in Table 2 below.

[0111]

[0112] As can be seen from the comparison between Examples 1-6 and Comparative Example 1 shown in Table 1 above, the neodymium-iron-boron magnet prepared according to the method of the present application has a significantly reduced content of non-metallic impurities (e.g., C, O, and N, etc.) without using an impurity removing agent (e.g., one or more of ammonia, chlorine, difluoromethane, and chloroform), and thus has improved magnetic properties (especially, intrinsic coercive force).

[0113] The embodiments described in the present application are merely preferred embodiments of the present application, and are not intended to limit the concept and scope of the present application. Various modifications and improvements to the technical solutions of the present application made by those skilled in the art without departing from the design idea of the present application shall fall within the protection scope of the present application. The technical content claimed by the present application has been fully recorded in the claims.

Claims

1. A method for preparing a neodymium iron boron magnet, the method comprising the following steps: (1) The neodymium iron boron magnet raw materials are mixed and smelted to obtain an alloy sheet; (2) The alloy sheet is subjected to hydrogen pyrolysis to obtain coarse powder; (3) The coarse powder is subjected to micronization in an air jet mill to obtain micronized powder, wherein the temperature in the air jet mill is in the range of 10-25℃ and the pressure is in the range of 0.55-0.65MPa; (4) Press the micro powder into a green body; and (5) The green blank is sintered to obtain the NdFeB magnet, wherein: An impurity removal agent is introduced into the air jet mill in step (3) above. The impurity removal agent comprises one or more of ammonia, chlorine, difluoromethane, and chloroform. The neodymium iron boron magnet raw material comprises the following components: R: 28-33% by weight, where R is a rare earth element, and R includes Nd and Pr; Al: ≤0.5% by weight; Cu: 0.1-0.6% by weight; Co: ≥0.4% by weight; Ga: ≤0.3% by weight; Ti: ≤0.4% by weight; B: 0.98-1.2% by weight; Fe: 62-69% by weight, where % by weight is the percentage of the mass of each component relative to the total mass of the NdFeB magnet raw material.

2. The method for preparing a neodymium iron boron magnet according to claim 1, wherein in step (3) above, the impurity removal agent is introduced into the inert gas leading to the air jet mill.

3. The method for preparing neodymium iron boron magnets according to claim 2, wherein when the impurity removal agent is ammonia, chlorine or a mixture thereof, the content of the impurity removal agent in the inert gas is in the range of 1 ppm to 10000 ppm.

4. The method for preparing a neodymium iron boron magnet according to claim 2, wherein when the impurity removal agent is ammonia, chlorine or a mixture thereof, the content of the impurity removal agent in the inert gas is in the range of 10 ppm to 100 ppm.

5. The method for preparing a neodymium iron boron magnet according to claim 2, wherein when the impurity removal agent is difluoromethane, chloroform, or a mixture thereof, the weight ratio of the impurity removal agent to the inert gas is in the range of 1 μg / g to 1000 μg / g.

6. The method for preparing a neodymium iron boron magnet according to claim 2, wherein when the impurity removal agent is difluoromethane, chloroform or a mixture thereof, the weight ratio of the impurity removal agent to the inert gas is in the range of 10 μg / g to 100 μg / g.

7. The method for preparing a neodymium iron boron magnet according to claim 2, wherein the inert gas is nitrogen or argon.

8. The method for preparing a neodymium iron boron magnet according to claim 2, wherein the flow rate of the inert gas containing the impurity removal agent in the flow mill is 35-45 m³ / h. 3 Within the range of / min.

9. The method for preparing a neodymium iron boron magnet according to claim 1, wherein step (3) obtains the D of the micropowder 50 The particle size is in the range of 3.8-4.2 μm.

10. A neodymium iron boron magnet, said neodymium iron boron magnet being prepared by the preparation method according to any one of claims 1-9.

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