Flexible neodymium-iron-nitrogen magnet and preparation method thereof

Abstract

The invention discloses a flexible neodymium-iron-nitrogen magnet and a preparation method thereof, and belongs to the technical field of magnetic materials, the preparation method comprises the following steps: performing ball milling on neodymium oxide, iron oxide powder and / or iron powder, calcium powder and / or calcium hydride in a vacuum ball milling tank for mixing; the mixed raw material is subjected to a reduction diffusion reaction in argon to obtain a neodymium-iron alloy block containing reaction by-products; the neodymium-iron alloy blocks are crushed and subjected to nitriding treatment, and neodymium-iron-nitrogen coarse powder containing reaction by-products is obtained; the nitrided neodymium-iron-nitrogen coarse powder is rapidly washed with ultrapure water, reaction by-products are removed, and pure neodymium-iron-nitrogen coarse powder slurry is obtained; and the obtained neodymium-iron-nitrogen slurry is subjected to ball-milling refining with absolute ethyl alcohol as a medium and vacuum drying, and the neodymium-iron-nitrogen magnetic powder is obtained. And finally, collecting and drying to obtain target neodymium-iron-nitrogen magnetic powder, and banburying and calendering the target neodymium-iron-nitrogen magnetic powder and a binder. The prepared Nd-Fe-N magnetic material is excellent in magnetic performance, relatively excellent in flexibility and stability and capable of meeting the requirement for preparing a flexible magnet.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetic materials, and in particular relates to a flexible NdFeN magnet and a preparation method thereof. Background Art

[0002] Flexible NdFeN magnets are a type of bonded permanent magnets, which are widely used in the fields of home appliances, computers, automobiles, processing and factory automation. With the rapid development of global information, electronics, transportation and other industries and the rapid rise of my country's IT industry, the computer, automobile industry and consumer electronics market will also show a rapid growth trend in demand for high-performance magnetic materials. The demand for manufacturing various micro-motors and magnetic devices is also increasing, and bonded permanent magnets are growing at a rate of about 30% per year. Flexible NdFeN magnets have high magnetic properties, good flexibility and antioxidant ability, and are suitable for a variety of complex shapes and miniaturized applications, such as consumer electronics, micromotors and wearable devices. In addition, this magnet also has excellent corrosion resistance and anti-demagnetization ability, which can meet the needs of high-end applications.

[0003] The patent application with the publication number CN1594209A discloses a flexible rare earth bonded magnet and a manufacturing method thereof, wherein anisotropic neodymium-iron-nitrogen magnetic powder, a binder and a processing aid are uniformly mixed, and then made by calendering, flat pressing or a combination of calendering and flat pressing. The components and weight content of the magnet are: 80-98% anisotropic neodymium-iron-nitrogen magnetic powder, 1.5-15% binder, 0-5% vulcanizer, and 0.1-5% processing aid. It has the characteristics of excellent magnetic properties, good flexibility, and low cost. However, the final molding method adopted in this method is molding in a vulcanization mold. Due to the limitations of the size of the vulcanizer and the vulcanization process, this molding method will limit the size and production efficiency of the magnet. Therefore, it is impossible to produce a magnet with basically unlimited length, and the production process is complicated and inefficient. Summary of the invention

[0004] The purpose of the present invention is to provide a flexible NdFeN magnet and a preparation method thereof, so as to solve the problem that the production process of the NdFeN magnet is too complicated.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for preparing a flexible NdFeN magnet comprises preparing a NdFe alloy by a reduction diffusion method, and then preparing NdFeN magnetic powder by crushing, nitriding, washing, ball milling and drying processes; then coating the NdFeN magnetic powder and mixing it with a binder for internal kneading and rolling, and obtaining the flexible NdFeN magnet after magnetization.

[0007] As a further preferred embodiment of the present invention, the reaction temperature in the reduction diffusion method is 950-1200° C. and the reaction time is 2-8 h.

[0008] As a further preferred embodiment of the present invention, the reduction diffusion method comprises the following steps:

[0009] Under vacuum conditions, neodymium oxide, iron oxide powder and / or iron powder, and a calcium reducing agent are fully ball-milled to mix, and then reacted in an argon atmosphere to obtain a neodymium-iron alloy; the calcium reducing agent is calcium powder and / or calcium hydride; the neodymium element is in excess of 10% to 30% based on a neodymium-iron molar ratio of 2:17, and the calcium reducing agent is in excess of 20% to 60% in the ball-milled mixture.

[0010] In the present invention, the ball milling mixing method is to ball mill and mix the raw materials, which are neodymium oxide, iron oxide powder / iron oxide powder and / or iron powder, calcium powder and / or calcium hydride particles, in a vacuum ball mill, with a ball milling speed of 150-550rpm and a ball milling time of 0.5h-3h; the raw materials are fully ground in the vacuum ball mill, with the purpose of thoroughly dispersing and refining the agglomerated raw material particles without oxidizing the Fe and Ca raw materials, so that the raw materials are fully mixed and evenly mixed, which is conducive to the generation of the neodymium-iron alloy phase.

[0011] The NdFe alloy block obtained by the reduction diffusion reaction is crushed with a vibration crusher, and the crushed coarse NdFe alloy powder is nitrided. The powder is a mixture of NdFe alloy after reduction diffusion and a large amount of CaO and Ca. The coarse NdFe alloy particles are initially nitrided to generate Nd2Fe 17 The N3 phase, on the one hand, further improves the magnetic properties of the powder, and on the other hand, improves the oxidation resistance of the NdFe alloy and reduces the oxidation of the powder in the subsequent washing steps.

[0012] As a further preferred embodiment of the present invention, the nitridation step is carried out in a heat treatment furnace at a temperature of 450 to 500° C. in a N 2 atmosphere for 3 to 6 hours.

[0013] As a further preferred scheme of the present invention, the washing method is ultrasonic stirring washing, and the powder is quickly cleaned and decalcified using an ultrasonic stirring device. The cleaning medium is ultrapure water, and the mass ratio of material to water is 1 to 10:250; the washing time is 5 to 10 minutes, and the washing cycle is 3-6 times; wherein the stirring speed is 500 to 2000 rpm, and the ultrasonic frequency is 30 to 60 kHz.

[0014] As a further preferred embodiment of the present invention, the crude NdFeN slurry obtained after washing is ball-milled, and further ball-milled in a ball mill with anhydrous ethanol as the ball-milling medium. During ball-milling, the ball-to-material ratio is 5-10:1, the ball-milling speed is 200-600 rpm, and the ball-milling time is 5-16 hours.

[0015] As a further preferred solution of the present invention, the drying step is: collecting the slurry after ball milling and drying it in a vacuum dryer to obtain pure NdFeN magnetic powder, wherein the particle size of the fine powder is ≤10 μm;

[0016] As a further preferred embodiment of the present invention, the binder includes at least one of silicone rubber, nitrile rubber, ethylene propylene rubber, CPE (chlorinated polyethylene) and PVC (polyvinyl chloride);

[0017] As a further preferred embodiment of the present invention, the banburying temperature is 70-200° C. and the banburying pressure is 0.5-10 MPa.

[0018] As a further preferred embodiment of the present invention, the calendering temperature is 40-100°C; the calendering thickness is 1mm; the calendered magnetic sheet is cut and magnetized, the cutting size is 80×40mm, the magnetizing voltage is 2500V, and the magnetizing spacing is 4mm.

[0019] As a further preferred embodiment of the present invention, a method for preparing a flexible NdFeN magnet comprises the following steps:

[0020] (1) Neodymium oxide, iron oxide powder and / or iron powder, calcium powder and / or calcium hydride are fully ball-milled and mixed in a vacuum ball mill.

[0021] (2) subjecting the mixed raw materials to a reduction diffusion reaction in argon to obtain a neodymium iron alloy block containing reaction by-products;

[0022] (3) crushing the NdFe alloy block and performing nitriding treatment to obtain NdFeN coarse powder containing reaction by-products;

[0023] (4) washing the nitrided NdFeN coarse powder with ultrapure water to remove reaction byproducts and obtain pure NdFeN coarse powder slurry;

[0024] (5) The obtained NdFeN slurry is ball-milled with anhydrous ethanol as a medium and vacuum-dried to obtain NdFeN magnetic powder.

[0025] (6) Finally, the target NdFeN magnetic powder is collected and dried, and then mixed with a binder and rolled to obtain a flexible NdFeN magnetic sheet.

[0026] A flexible NdFeN magnet is prepared by the preparation method.

[0027] Beneficial effects of the present invention:

[0028] The invention discloses a flexible NdFeN magnet and a preparation method thereof. The method comprises the following steps: firstly preparing a NdFe alloy by a reduction diffusion method, and then preparing NdFeN magnetic powder by crushing, nitriding, washing, ball milling, and drying processes; then coating the NdFeN magnetic powder and rolling it with a mixed binder, and obtaining the flexible NdFeN after magnetization. The NdFeN prepared by the invention has excellent magnetic properties, relatively good flexibility and stability, and meets the needs of preparing flexible magnets. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Obviously, the following descriptions are only some examples or embodiments of the present application. For ordinary technicians in this field, the present application can also be applied to other similar scenarios without creative work. In addition, it can also be understood that although the efforts made in this development process may be complicated and lengthy, for ordinary technicians in the field related to the content disclosed in this application, some changes in design, manufacturing or production based on the technical content disclosed in this application are just conventional technical means, and should not be understood as insufficient content disclosed in this application.

[0031] However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially the same structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the following description is provided for those skilled in the art to fully understand the present application and is not intended to limit the subject matter described in the claims.

[0032] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution, and all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0033] Example 1

[0034] This embodiment provides a method for preparing a flexible NdFeN magnet, comprising the following steps:

[0035] (1) Ingredients: 44.3 g of neodymium oxide (of which neodymium oxide is 25% in excess on a theoretical basis); 100.0 g of iron powder; 22.1 g of calcium particles (of which calcium is 40% in excess on a theoretical basis). The raw materials are sealed in a vacuum ball mill protected by argon gas;

[0036] (2) Mixing: The raw materials were fully ball milled and mixed in a horizontal ball mill at a ball mill speed of 250 rpm, a ball milling time of 3 h, and a ball-to-material mass ratio of 8:1;

[0037] (3) Loading: Take the ball-milled mixture out of a glove box filled with argon and load it into an iron crucible and compact it;

[0038] (4) Reduction diffusion reaction: The crucible with the reaction raw materials is placed in a heat treatment furnace for reduction diffusion reaction. The entire reaction is carried out under an argon atmosphere at a reaction temperature of 1100° C. and a reaction time of 4 h.

[0039] (5) Crushing and nitriding: The NdFe alloy block containing a large amount of reaction by-products generated after the reaction is crushed in a crusher under neutral atmosphere; the crushed NdFe alloy mixture is then nitrided in a tubular furnace at a nitriding temperature of 500° C. for 9 hours to obtain a NdFeN mixed powder containing a large amount of calcium impurities (Ca, CaO);

[0040] (6) Rapid cleaning: The NdFeN mixed coarse powder is quickly cleaned and decalcified using an ultrasonic stirring device. The cleaning medium is ultrapure water, and the mass ratio of material to water is 8:250. The washing time is 8 minutes, and the washing cycle is repeated 4 times. The stirring speed is 1000 rpm and the ultrasonic frequency is 50 kHz.

[0041] (7) Ball milling: The nitrided NdFeN was ball milled with anhydrous ethanol as the medium to further refine the powder. The ball-to-material mass ratio was 10:1, the ball milling speed was 450 rpm, and the ball milling time was 7 hours. Then, the washed NdFeN was washed with anhydrous ethanol to remove excess water stains and reduce the degree of oxidation of NdFeN during ball milling and drying. The material-to-anhydrous ethanol mass ratio was 1:20, the washing time was 8 minutes, and the washing times were 2 times.

[0042] (8) Collecting and drying: collecting the NdFeN magnetic powder slurry obtained by ball milling, and drying it in a vacuum drying oven to obtain a crude NdFeN alloy powder;

[0043] (9) Mixing: Mix the dried NdFeN magnetic powder and nitrile rubber in a mixer at 140°C and 3 MPa at a speed of 150 rpm for 1 h;

[0044] (10) Rolling and magnetization: the powder after internal mixing is rolled into a NdFeN sheet with a thickness of 1 mm at 65°C; and the obtained NdFeN sheet is cut into a size of 80×40 mm and magnetized at a magnetizing voltage of 2500 V and a magnetizing spacing of 4 mm to obtain the flexible NdFeN magnet.

[0045] Example 2

[0046] This embodiment provides a method for preparing flexible NdFeN, which is the same as that of Embodiment 1, except that the nitrile rubber is replaced with silicone rubber; the remaining raw materials and preparation process remain the same as those of Embodiment 1.

[0047] Example 3

[0048] This embodiment provides a method for preparing flexible NdFeN, which is the same as that of Embodiment 1, except that the nitrile rubber is replaced with EPDM rubber; the other raw materials and preparation process remain the same as those of Embodiment 1.

[0049] Example 4

[0050] This embodiment provides a method for preparing flexible NdFeN, which is the same as that of Embodiment 1, except that the reduction diffusion reaction temperature is changed to 1000° C.; the remaining raw materials and preparation process remain the same as those of Embodiment 1.

[0051] Example 5

[0052] This embodiment provides a method for preparing flexible NdFeN, which is the same as that of Embodiment 1, except that the reduction diffusion reaction temperature is changed to 1200° C.; the remaining raw materials and preparation process remain the same as those of Embodiment 1.

[0053] Example 6

[0054] This embodiment provides a method for preparing flexible NdFeN, which is the same as that in Embodiment 1, except that the reduction diffusion reaction time is changed to 2 hours; the other raw materials and preparation process remain the same as those in Embodiment 1.

[0055] Example 7

[0056] This embodiment provides a method for preparing flexible NdFeN, which is the same as that in Embodiment 1, except that the reduction diffusion reaction time is changed to 6 hours; the other raw materials and preparation process remain the same as those in Embodiment 1.

[0057] Example 8

[0058] This embodiment provides a method for preparing flexible NdFeN, which is the same as that in Embodiment 1, except that the reduction diffusion reaction time is changed to 8 hours; the other raw materials and preparation process remain the same as those in Embodiment 1.

[0059] Comparative Example 1

[0060] This comparative example provides a method for preparing flexible NdFeN, which is the same as Example 1. The difference from Example 1 is that the Nd element in the raw material has an excess of 0%, that is, the theoretical amount is used; the other raw materials and the preparation process remain the same as Example 1.

[0061] Comparative Example 2

[0062] This comparative example provides a method for preparing flexible NdFeN, which is the same as Example 1. The difference from Example 1 is that the raw material Nd element is 40% excessive on a theoretical basis; the other raw materials and preparation process remain the same as Example 1.

[0063] Comparative Example 3

[0064] This comparative example provides a method for preparing flexible NdFeN, which is the same as Example 1, except that the reduction diffusion reaction temperature is changed to 800°C; the remaining raw materials and preparation process remain the same as Example 1.

[0065] Comparative Example 4

[0066] This comparative example provides a method for preparing flexible NdFeN, which is the same as Example 1, except that the reduction diffusion reaction temperature is changed to 1300° C.; the remaining raw materials and preparation process remain the same as Example 1.

[0067] Measurement and analysis: X-ray diffractometer (XRD) analysis of Nd2Fe 17 Nd2Fe obtained after reduction diffusion reaction 17 N3 powder, and the vibrating sample magnetometer (VSM) was used to measure the ball-milled Nd2Fe 17 N3 magnetic powder was used for hysteresis loop test.

[0068] Test tensile strength and elongation: Install the prepared flexible NdFeN magnet tensile specimen on the fixture of the tensile testing machine, and apply axial tension to the specimen at a tensile speed of 5 mm / min until the specimen breaks. During the stretching process, the testing machine automatically records the tension and displacement data, and calculates the tensile strength and elongation based on these data. Among them, the tensile strength is the ratio of the maximum tensile force the specimen withstands before breaking to the original cross-sectional area of ​​the specimen; the elongation is the ratio of the elongation when the specimen breaks to the original gauge length, and the calculation formula is as follows:

[0069] Tensile Strength: Where σ is the tensile strength and F max Maximum tensile force, original cross-sectional area of ​​A;

[0070] Elongation: Where δ is the elongation, L is the length at break, and L0 is the original length.

[0071] Performance tests were performed on Examples 1 to 8 and Comparative Examples 1 to 4, and the results are shown in Table 1:

[0072] Table 1

[0073]

[0074]

[0075] According to the comparison of the test results, it can be seen that the flexible NdFeN material prepared by the present invention has excellent magnetic properties and relatively good flexibility and stability, which meets the needs of preparing flexible magnets.

[0076] During the high-temperature reaction, due to the low vapor pressure of neodymium, a part of the neodymium element will be lost at high temperature, resulting in a small amount of neodymium actually participating in the reaction. Therefore, excessive neodymium is required to ensure the magnetism of the material, but the amount of neodymium should not be too much or too little. Too high a neodymium content will increase the cost. In Comparative Examples 1 and 2, the excess of neodymium content is adjusted. Too low a neodymium content affects the improvement of magnetism, while too high a neodymium content will increase the brittleness of the material, affecting the processing and application of the magnet.

[0077] The temperature during the reduction diffusion reaction will affect the performance of the material. The reaction temperature should not be too high or too low. In Example 3, the temperature was controlled below 900°C, resulting in an incomplete reaction; while in Example 4, the temperature was controlled above 1200°C, which would cause too much neodymium metal to burn out and form a large amount of α-Fe phase (impurity phase), affecting the magnetic properties and also reducing the mechanical properties of the material.

[0078] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0079] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a flexible NdFeN magnet, characterized in that: A neodymium iron alloy is prepared by a reduction diffusion method, and then neodymium iron nitrogen magnetic powder is prepared by crushing, nitriding, washing, ball milling and drying processes; the neodymium iron nitrogen magnetic powder is then coated and mixed with a binder for internal kneading and rolling, and the flexible neodymium iron nitrogen magnet is obtained after magnetization.

2. The method for preparing a flexible NdFeN magnet according to claim 1, characterized in that: The reaction temperature in the reduction diffusion method is 950-1200° C. and the reaction time is 2-8 hours.

3. The method for preparing a flexible NdFeN magnet according to claim 1, characterized in that: The reduction diffusion method comprises the following steps: Under vacuum conditions, neodymium oxide, iron oxide powder and / or iron powder, and a calcium reducing agent are fully ball-milled for mixing, and then reacted in an argon atmosphere to obtain a neodymium-iron alloy; the calcium reducing agent is calcium powder and / or calcium hydride; the neodymium element is in excess of 10% to 30% based on a neodymium-iron molar ratio of 2:

17.

4. The method for preparing a flexible NdFeN magnet according to claim 1, characterized in that: The nitridation is carried out in a heat treatment furnace at a temperature of 450 to 500° C. in a N 2 atmosphere for 3 to 6 hours.

5. The method for preparing a flexible NdFeN magnet according to claim 1, characterized in that: The washing method is ultrasonic stirring washing, the cleaning medium is ultrapure water, the mass ratio of material to water is 1-10:250; the washing time is 5-10 minutes, and the washing cycle is 3-6 times; the stirring speed is 500-2000rpm, and the ultrasonic frequency is 30-60kHz.

6. The method for preparing a flexible NdFeN magnet according to claim 5, characterized in that: The crude NdFeN slurry obtained after washing is ball milled, with a ball-to-material ratio of 5 to 10:1, a ball milling speed of 200 to 600 rpm, and a ball milling time of 5 to 16 hours.

7. The method for preparing a flexible NdFeN magnet according to claim 1, characterized in that: The drying step is: collecting the slurry after ball milling and performing vacuum drying to obtain NdFeN magnetic powder, wherein the particle size of the fine powder is ≤10 μm.

8. The method for preparing a flexible NdFeN magnet according to claim 1, characterized in that: The adhesive includes at least one of silicone rubber, nitrile rubber, ethylene propylene rubber, CPE and PVC.

9. The method for preparing a flexible NdFeN magnet according to claim 1, characterized in that: The banburying temperature is 70-200°C; the banburying pressure is 0.5-10MPa; The calendering temperature is 40-100° C. and the calendering thickness is 1 mm. The calendered magnetic sheet is cut and magnetized, the cutting size is 80×40 mm, the magnetizing voltage is 2500 V, and the magnetizing spacing is 4 mm.

10. A flexible NdFeN magnet, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.

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