Antioxidant neodymium-iron-boron permanent magnet powder and method for producing the same

Abstract

The application discloses an anti-oxidation neodymium-iron-boron permanent magnetic powder and a preparation method thereof. The preparation method comprises the following steps: mixing the neodymium-iron-boron permanent magnetic powder, a polyvinylpyrrolidone solution, a sodium borohydride solution and a ferrous salt solution under an oxygen-free condition, and performing a hydrothermal reaction to obtain the anti-oxidation neodymium-iron-boron permanent magnetic powder. The anti-oxidation neodymium-iron-boron permanent magnetic powder prepared by the application forms a dense anti-oxidation shell protective layer on the surface of the neodymium-iron-boron permanent magnetic powder, effectively blocks oxygen and moisture, avoids oxidation of the magnetic powder, prolongs the service life of the magnetic powder, ensures that the magnetism of the permanent magnetic powder is not affected, realizes the best balance between the anti-oxidation protection of the neodymium-iron-boron permanent magnetic powder and the maintenance of the magnetism, and simultaneously, the permanent magnetic powder does not need to be isolated from air, and the subsequent manufacturing of the neodymium-iron-boron magnet can be performed in air, which not only reduces the storage cost, but also ensures safe use, and is suitable for large-scale batch and continuous production.

Description

Technical Field

[0001] This invention belongs to the field of magnetic material preparation, specifically relating to an antioxidant neodymium iron boron permanent magnet powder and its preparation method. Background Technology

[0002] Neodymium iron boron (NdFeB) magnetic materials, as high-performance permanent magnets, have shown potential in the medical field due to their strong magnetism and high energy density. However, their susceptibility to oxidation limits their biological applications. In the in vivo environment, NdFeB magnetic materials are prone to oxidation and corrosion when exposed to body fluids, leading to a decline in magnetic properties and the release of toxic neodymium and iron ions, which can cause inflammation or tissue damage. Therefore, improving the stability and biosafety of NdFeB magnetic materials can promote their clinical application.

[0003] Neodymium iron boron (NdFeB) permanent magnet powder, used as a raw material in the manufacture of NdFeB magnetic materials, reacts rapidly with oxygen and moisture in the air when freshly exposed. This reaction forms an oxide layer and continuously releases heat. If the accumulated heat cannot dissipate in time, the temperature can reach the ignition point of neodymium, causing the NdFeB permanent magnet powder to burn. Specifically, NdFeB permanent magnet powder contains the metallic elements neodymium and iron, both of which are chemically reactive. Neodymium, in particular, is highly susceptible to oxidation in its powdered state. The oxidation reaction of neodymium releases a large amount of heat, and the large surface area of ​​the powder accelerates the reaction rate, leading to spontaneous combustion. Therefore, obtaining a NdFeB permanent magnet powder with good oxidation resistance is of great significance for expanding the application range of NdFeB permanent magnet powder. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide an antioxidant neodymium iron boron permanent magnet powder and its preparation method.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0006] A method for preparing antioxidant neodymium iron boron permanent magnet powder includes the following steps: (1) Under hypoxic conditions, NdFeB permanent magnet powder and polyvinylpyrrolidone solution were mixed, sodium borohydride solution was added, and the mixture was sonicated. Then, ferrous salt solution was added and sonicated again to obtain a mixed solution. (2) The mixed solution obtained in step (1) is subjected to hydrothermal reaction to obtain antioxidant neodymium iron boron permanent magnet powder.

[0007] In a further improvement to the above preparation method, in step (1), the volume ratio of the polyvinylpyrrolidone solution, sodium borohydride solution, and ferrous salt solution is 2-10:0.1-1:5-40; the concentration of the polyvinylpyrrolidone solution is ≤5 mmol / L, the pH value of the polyvinylpyrrolidone solution is 8-11, the concentration of the sodium borohydride solution is ≤10 mmol / L, the concentration of the ferrous salt solution is ≤10 mmol / L, and the ferrous salt solution is a ferrous chloride solution.

[0008] In a further improvement to the above preparation method, in step (1), the concentration of the sodium borohydride solution is 1 mmol / L to 10 mmol / L, and the concentration of the ferrous salt solution is 0.5 mmol / L to 5 mmol / L.

[0009] In a further improvement to the above preparation method, in step (1), the concentration of the ferrous salt solution is 2.5 mmol / L to 3.5 mmol / L.

[0010] In a further improvement to the above preparation method, in step (2), the temperature of the hydrothermal reaction is 100℃~220℃ and the time of the hydrothermal reaction is 1h~12h.

[0011] In a further improvement of the above preparation method, in step (1), the oxygen-deficient condition is that the oxygen content is <1ppm; In step (2), the hydrothermal reaction is followed by the following treatment: the reaction product is filtered under reduced pressure, washed, and dried; the washing is performed with ethanol, and the washing is performed 3 to 5 times.

[0012] The above preparation method is further improved in that, in step (1), the preparation method of the neodymium iron boron permanent magnet powder includes the following steps: (1.1) The raw materials are prepared according to the mass percentage of each component in the permanent magnet powder, added to the quick-setting furnace, and smelted to obtain quick-setting sheets; (1.2) The quick-setting sheets obtained in step (1.1) are subjected to heat treatment and hydrogen crushing treatment in sequence to obtain hydrogen-crushed powder; (1.3) Under a nitrogen atmosphere, the hydrogen-broken powder obtained in step (1.2) is placed in an air jet mill for refining until the particle size is 2.5μm to 3μm, thus obtaining neodymium iron boron permanent magnet powder. In a further improvement to the above preparation method, in step (1.1), the permanent magnet powder comprises the following components by mass percentage: 28.5%–33% R element, 61.5%–66.5% Fe element, 0.85%–0.95% B element, and 0.1%–3.0% M element; wherein the R element is one or more of La, Ce, Nd, and Pr elements, and the M element is one or more of Cu, Al, Co, Zr, and Ga elements; the melting temperature is 700℃–1400℃, and the thickness of the quick-setting sheet is 40μm–300μm.

[0013] In a further improvement to the above preparation method, in step (1.2), the heat treatment temperature is 610℃ and the heat treatment time is 8h; the hydrogen decomposition treatment is as follows: under a hydrogen atmosphere, hydrogen absorption is performed at a temperature of 200℃~300℃ and a pressure of 0.1MPa~0.5MPa for 1h~3h, followed by dehydrogenation under vacuum conditions or an inert atmosphere at a temperature of 500℃~700℃ for 1h~3h; the purity of the hydrogen is ≥99.99%, and the vacuum condition is a vacuum degree <10. -3 Pa; In step (1.3), the average diameter of the neodymium iron boron permanent magnet powder is 1μm to 3μm, the grinding pressure of the air jet mill is 520kPa to 620kPa, and the rotation speed of the sorting wheel is 4000rpm to 6000rpm.

[0014] As a general technical concept, the present invention also provides an antioxidant NdFeB permanent magnet powder prepared by the above-mentioned method for preparing antioxidant NdFeB permanent magnet powder.

[0015] Compared with the prior art, the advantages of the present invention are as follows: This invention discloses a method for preparing antioxidant NdFeB permanent magnet powder. Using sodium borohydride and ferrous salt as raw materials, an antioxidant material is uniformly coated onto the surface of NdFeB permanent magnet powder particles via a hydrothermal reaction, forming a "magnetic core-antioxidant shell" composite structure, thereby obtaining antioxidant NdFeB permanent magnet powder. The antioxidant NdFeB permanent magnet powder prepared by this invention, by forming a dense antioxidant shell protective layer on the surface of the NdFeB permanent magnet powder, not only effectively blocks oxygen and moisture, preventing powder oxidation and extending the powder's lifespan, but also ensures that the magnetic properties of the permanent magnet powder are not affected, achieving an optimal balance between antioxidant protection and maintenance of magnetic properties. The preparation method of the present invention has the advantages of high production efficiency, low cost and simple operation; the antioxidant NdFeB permanent magnet powder obtained therefrom can be used to manufacture subsequent NdFeB magnets in the air without the need to isolate the air, which reduces storage costs and ensures safe use, making it suitable for large-scale batch and continuous production. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the preparation process of the antioxidant NdFeB permanent magnet powder in Example 1 of the present invention.

[0017] Figure 2 These are powder diffraction patterns of the antioxidant NdFeB permanent magnet powder in Examples 1 to 4 of the present invention, the NdFeB permanent magnet powder in Comparative Example 1, and the modified NdFeB permanent magnet powder in Comparative Example 2.

[0018] Figure 3 The images show SEM images of the antioxidant NdFeB permanent magnet powder in Examples 1 to 4 of this invention, the NdFeB permanent magnet powder in Comparative Example 1, and the modified NdFeB permanent magnet powder in Comparative Example 2.

[0019] Figure 4 This is a comparison chart of the magnetic properties of the antioxidant NdFeB permanent magnet powder in Examples 1 to 4 of the present invention, the NdFeB permanent magnet powder in Comparative Example 1, and the modified NdFeB permanent magnet powder in Comparative Example 2. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. All materials and instruments used in the following embodiments are commercially available.

[0021] Example 1 A method for preparing antioxidant neodymium iron boron permanent magnet powder according to the present invention, such as... Figure 1 As shown, it includes the following steps: (1) Preparation of neodymium iron boron permanent magnet powder (1.1) According to (PrNd) 32.85 Cu 0.2 Al 0.6 Co 1.5 Ga 0.5 Zr 0.2 B 0.88 Fe 63.27 The mass percentages of each component in the permanent magnet powder are determined, and the powder is added to a rapid solidification furnace and smelted at 1380℃ to obtain a rapid solidification sheet; the thickness of the rapid solidification sheet is controlled between 40 and 300 μm.

[0022] (1.2) The above-mentioned quick-setting sheets were placed in a rotary heat treatment furnace for heat treatment at a temperature of 610 °C for 8 h. Subsequently, the heat-treated product was subjected to hydrogen annealing, specifically: under a hydrogen atmosphere (purity ≥ 99.99%), hydrogen was absorbed at a temperature of 250 °C and a pressure of 0.4 MPa for 1.5 h, followed by evacuation to a vacuum degree < 10. -3 Pa was dehydrogenated at 530 °C for 3 h to obtain hydrogen-broken powder.

[0023] (1.3) Under nitrogen protection, the hydrogen-broken powder obtained in step (1.2) is placed in an air jet mill. The grinding pressure of the air jet mill is set to 600 kPa and the sorting wheel speed is set to 6000 rpm to refine the powder until the average diameter of the powder particles is 2.5 to 3.0 μm, thus obtaining neodymium iron boron permanent magnet powder.

[0024] (2) Prepare a 1 mmol / L polyvinylpyrrolidone (PVP) solution and adjust the pH of the PVP solution to 10 with ammonia; prepare a 5 mmol / L sodium borohydride (NaBH4) solution; prepare a 1 mmol / L ferrous chloride solution using FeCl2H2O as raw material; in a glove box, control the oxygen content in the glove box to <1 ppm, and add the NdFeB permanent magnet powder obtained in step (1.3) to the PVP solution according to the volume ratio of PVP solution, sodium borohydride solution and ferrous chloride solution as 6:0.5:20, and after ultrasonic vibration with a stirrer, add sodium borohydride solution, ultrasonic vibration, and then add ferrous chloride solution, ultrasonic vibration to mix the solution evenly, and then obtain a mixed solution.

[0025] (3) Pour the mixed solution obtained in step (2) into a high-pressure reactor and carry out hydrothermal reaction, that is, heat up to 220℃ and keep warm for 5 h. Extract the product powder by vacuum filtration, then ultrasonically clean it with anhydrous ethanol 3 to 5 times, and dry it to obtain antioxidant neodymium iron boron permanent magnet powder.

[0026] Example 2 An antioxidant neodymium iron boron permanent magnet powder is prepared in a manner that is basically the same as the preparation method of the antioxidant neodymium iron boron permanent magnet powder in Example 1, except that in step (2), the concentration of the ferrous chloride solution is 2 mmol / L.

[0027] Example 3 An antioxidant neodymium iron boron permanent magnet powder is prepared in a manner that is basically the same as the preparation method of the antioxidant neodymium iron boron permanent magnet powder in Example 1, except that in step (2), the concentration of the ferrous chloride solution is 3 mmol / L.

[0028] Example 4 An antioxidant neodymium iron boron permanent magnet powder is prepared in a manner that is basically the same as the preparation method of the antioxidant neodymium iron boron permanent magnet powder in Example 1, except that in step (2), the concentration of the ferrous chloride solution is 5 mmol / L.

[0029] Comparative Example 1 A neodymium iron boron permanent magnet powder is prepared by the same method as the neodymium iron boron permanent magnet powder prepared in Example 1.

[0030] Comparative Example 2 A modified neodymium iron boron permanent magnet powder is prepared in a manner that is basically the same as the preparation method of the antioxidant neodymium iron boron permanent magnet powder in Example 1, except that: in step (2), ferrous chloride solution is not added.

[0031] The antioxidant NdFeB permanent magnet powders prepared in Examples 1 to 4, the NdFeB permanent magnet powders prepared in Comparative Example 1, and the powders prepared in Comparative Example 2 were subjected to surface scanning treatment and magnetic performance tests.

[0032] Figure 2 These are powder diffraction patterns of the antioxidant NdFeB permanent magnet powder used in Examples 1-4 of this invention, the NdFeB permanent magnet powder in Comparative Example 1, and the modified NdFeB permanent magnet powder in Comparative Example 2. From... Figure 2 It can be seen that, compared with the NdFeB permanent magnet powder in Comparative Example 1 and the modified NdFeB permanent magnet powder (uncoated NdFeB permanent magnet powder) in Comparative Example 2, the powder diffraction patterns of the antioxidant NdFeB permanent magnet powders prepared in Examples 1 to 4 are consistent in phase, indicating that the main components of the NdFeB permanent magnet powder before and after coating are consistent.

[0033] Figure 3 These are SEM images of the antioxidant NdFeB permanent magnet powder from Examples 1 to 4 of this invention, the NdFeB permanent magnet powder from Comparative Example 1, and the modified NdFeB permanent magnet powder from Comparative Example 2. From... Figure 3 It can be seen that, compared with the NdFeB permanent magnet powder in Comparative Example 1 and the modified NdFeB permanent magnet powder in Comparative Example 2, the outer surface of the antioxidant NdFeB permanent magnet powder prepared in Examples 1 to 4 is completely coated, indicating that the coating effect is very good.

[0034] Figure 4 This is a comparison chart of the magnetic properties of the antioxidant NdFeB permanent magnet powder in Examples 1 to 4 of this invention, the NdFeB permanent magnet powder in Comparative Example 1, and the modified NdFeB permanent magnet powder in Comparative Example 2. From... Figure 4 It can be seen that, compared with NdFeB permanent magnet powder and the modified NdFeB permanent magnet powder in Comparative Example 2, the magnetic properties of the oxidation-resistant NdFeB permanent magnet powders prepared in Examples 1 to 4 are slightly reduced, but the reduction is very small. In particular, the oxidation-resistant NdFeB permanent magnet powder prepared in Example 4 has the least impact on its magnetic properties.

[0035] In summary, the preparation method of the oxidized NdFeB permanent magnet powder of the present invention uses sodium borohydride and ferrous salt as raw materials. Through a hydrothermal reaction, an antioxidant material is uniformly coated onto the surface of the NdFeB permanent magnet powder particles, forming a "magnetic core-antioxidant shell" composite structure, thereby producing antioxidant NdFeB permanent magnet powder. The antioxidant NdFeB permanent magnet powder obtained by the present invention, by forming a dense antioxidant shell protective layer on the surface of the NdFeB permanent magnet powder, not only effectively blocks oxygen and moisture, preventing powder oxidation and extending the powder's lifespan, but also ensures that the magnetic properties of the permanent magnet powder are not affected, achieving the optimal balance between antioxidant protection and maintenance of magnetic properties in the NdFeB permanent magnet powder.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for preparing antioxidant neodymium iron boron permanent magnet powder, characterized in that, Includes the following steps: (1) Under hypoxic conditions, neodymium iron boron permanent magnet powder and polyvinylpyrrolidone solution are mixed, sodium borohydride solution is added, and the mixture is sonicated. Then, ferrous salt solution is added and sonicated again to obtain a mixed solution. The volume ratio of polyvinylpyrrolidone solution, sodium borohydride solution and ferrous salt solution is 2-10:0.1-1:5-40. The concentration of polyvinylpyrrolidone solution is ≤5 mmol / L, the concentration of sodium borohydride solution is 1 mmol / L-10 mmol / L, and the concentration of ferrous salt solution is 0.5 mmol / L-5 mmol / L. The hypoxic condition is that the oxygen content is <1 ppm. The pH value of the polyvinylpyrrolidone solution is 8-11; The method for preparing the neodymium iron boron permanent magnet powder includes the following steps: (1.1) The permanent magnet powder is batched according to the mass percentage of each component, added to a rapid solidification furnace, and smelted to obtain rapid solidification sheets; the permanent magnet powder contains the following components by mass percentage: 28.5% to 33% of R element, 61.5% to 66.5% of Fe element, 0.85% to 0.95% of B element, and 0.1% to 3.0% of M element; the R element is one or more of La element, Ce element, Nd element and Pr element, and the M element is one or more of Cu element, Al element, Co element, Zr element and Ga element; (1.2) The quick-setting sheets obtained in step (1.1) are subjected to heat treatment and hydrogen crushing treatment in sequence to obtain hydrogen-crushed powder; (1.3) Under a nitrogen atmosphere, the hydrogen-crushed powder obtained in step (1.2) is placed in an air jet mill for refining until the particle size is 2.5μm to 3μm, to obtain neodymium iron boron permanent magnet powder; (2) The mixed solution obtained in step (1) is subjected to a hydrothermal reaction to obtain antioxidant neodymium iron boron permanent magnet powder; the temperature of the hydrothermal reaction is 100℃~220℃.

2. The method for preparing antioxidant NdFeB permanent magnet powder according to claim 1, characterized in that, In step (1), the ferrous salt solution is a ferrous chloride solution.

3. The method for preparing antioxidant NdFeB permanent magnet powder according to claim 2, characterized in that, In step (1), the concentration of the ferrous salt solution is 2.5 mmol / L to 3.5 mmol / L.

4. The method for preparing antioxidant NdFeB permanent magnet powder according to any one of claims 1 to 3, characterized in that, In step (2), the hydrothermal reaction takes 1 to 12 hours.

5. The method for preparing antioxidant NdFeB permanent magnet powder according to any one of claims 1 to 3, characterized in that, In step (2), the hydrothermal reaction is followed by the following treatment: the reaction product is filtered under reduced pressure, washed, and dried; the washing is performed with ethanol, and the washing is performed 3 to 5 times.

6. The method for preparing antioxidant NdFeB permanent magnet powder according to any one of claims 1 to 3, characterized in that, In step (1.1), the melting temperature is 700℃~1400℃, and the thickness of the quick-setting sheet is 40μm~300μm.

7. A method for preparing antioxidant NdFeB permanent magnet powder according to any one of claims 1 to 3, characterized in that, In step (1.2), the heat treatment temperature is 610℃, and the heat treatment time is 8 hours; the hydrogen decomposition treatment is as follows: under a hydrogen atmosphere, hydrogen is absorbed at a temperature of 200℃~300℃ and a pressure of 0.1MPa~0.5MPa for 1 hour to 3 hours, followed by dehydrogenation under vacuum conditions or an inert atmosphere at a temperature of 500℃~700℃ for 1 hour to 3 hours; the purity of the hydrogen is ≥99.99%, and the vacuum condition is a vacuum degree <10. -3 Pa; In step (1.3), the average diameter of the neodymium iron boron permanent magnet powder is 1μm to 3μm, the grinding pressure of the air jet mill is 520kPa to 620kPa, and the rotation speed of the sorting wheel is 4000rpm to 6000rpm.

8. An antioxidant NdFeB permanent magnet powder prepared by any one of claims 1 to 7.

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