CN115206665B - Neodymium-iron-boron permanent magnet and preparation method thereof - Google Patents
Neodymium-iron-boron permanent magnet and preparation method thereof Download PDFInfo
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- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
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- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
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- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
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- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
- H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
- H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
- H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
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- H01F41/026—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets protecting methods against environmental influences, e.g. oxygen, by surface treatment
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- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
- H01F41/0293—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets
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Abstract
The invention provides a neodymium iron boron permanent magnet and a preparation method thereof. The preparation method of the neodymium iron boron permanent magnet comprises the following steps: preparing powder from copper powder, aluminum powder, lanthanum powder, boron powder, neodymium powder and iron powder; sequentially carrying out vacuum melting, melt-spinning and flaking, hydrogen crushing and air flow grinding on the powder to obtain matrix magnetic powder; preparing composite magnetic powder by adopting ammonium bicarbonate, silicon nitride, zirconium powder, silicon powder and matrix magnetic powder; filling the matrix magnetic powder into a mold, and performing compression molding to obtain a blank; mixing the composite magnetic powder with ethanol to prepare slurry, coating the slurry on the surface of the blank body, and drying to obtain a raw magnet; sintering the green magnet to obtain a sintered body; applying a heavy rare earth dopant to the surface layer of the sintered body to obtain a blank body; and tempering the blank body to obtain the neodymium iron boron permanent magnet. The neodymium iron boron permanent magnet obtained by the method has better intrinsic coercive force and mechanical strength.
Description
Technical Field
The invention relates to the technical field of permanent magnet manufacturing, in particular to a neodymium iron boron permanent magnet and a preparation method thereof.
Background
The Nd-Fe-B permanent magnet is made of Nd, fe and B 2 Fe 1 4B) The tetragonal magnetic material is formed. This magnetic material is today a permanent magnet, second only to absolute zero holmium magnets, and is also the most commonly used rare earth magnet.
At present, the neodymium iron boron permanent magnet is widely applied to a plurality of fields such as electronics, electric machinery, medical appliances, toys, packaging, hardware machinery, aerospace, and the like. The neodymium-iron-boron permanent magnet is an essential element in the production and manufacturing processes of various electronic devices such as a permanent magnet motor, a loudspeaker, a magnetic separator, a computer disk drive, magnetic resonance imaging equipment, instruments, a hard disk, a mobile phone, an earphone and the like.
According to different manufacturing processes and properties of finished products, the neodymium iron boron permanent magnet is mainly divided into sintered neodymium iron boron and bonded neodymium iron boron. The main preparation process of the sintered neodymium iron boron sequentially comprises the following steps: proportioning, smelting and melt spinning, hydrogen breaking, milling by airflow milling, molding, sintering and tempering. The main preparation process of the bonded neodymium iron boron sequentially comprises the following steps: preparing materials, preparing powder, adding an additive and resin, mixing powder, molding and curing.
Although the bonded neodymium iron boron has better corrosion resistance, and can be made into various magnets with complex shapes. However, the preparation process of the bonded neodymium iron boron is relatively complex, and the bonded neodymium iron boron is inferior to the anisotropic sintered neodymium iron boron in both magnetism and density due to the characteristic of isotropy. Therefore, sintered neodymium iron boron is still the mainstream process in the market at present.
With respect to sintered nd-fe-b, the current process makes its maximum magnetic energy product close to the theoretical limit, but the intrinsic coercivity of sintered nd-fe-b is still far lower than the theoretical limit. The traditional method for improving the intrinsic coercivity of the sintered neodymium iron boron is to add heavy rare earth dysprosium (Dy) and terbium (Tb) through a grain boundary diffusion process.
The principle of grain boundary diffusion is to first apply a compound containing a heavy rare earth element to the outside of the permanent magnet by a method such as coating or immersion, and then diffuse the heavy rare earth element into the inside of the magnet along a liquid Nd-rich grain boundary phase by heat treatment. The coercive force of the sintered Nd-Fe-B is determined by the anisotropy field of the main phase particles, and the density is highDiffusion of heavy rare earth to form (Nd, dy) 2 Fe 14 Phase B OR (Nd, tb) 2 Fe 14 Phase B having a magnetocrystalline anisotropy field ratio Nd 2 Fe 14 B is large, so the grain boundary diffusion process can improve the intrinsic coercive force of the sintered neodymium iron boron permanent magnet.
One of the deficiencies in the prior art is: the traditional grain boundary diffusion technology is used for coating or brushing the surface of a permanent magnet, because the diffusion uniformity degree of heavy rare earth elements is poor, the heavy rare earth elements are unevenly distributed on the surface of the permanent magnet, the addition amount of the heavy rare earth elements is large, but the increase degree of coercive force is limited.
Disclosure of Invention
The present invention is directed to solving at least one of the above problems.
Therefore, the first purpose of the invention is to provide a preparation method of the neodymium iron boron permanent magnet.
The second purpose of the invention is to provide a neodymium iron boron permanent magnet.
In order to achieve the first object of the present invention, an embodiment of the present invention provides a method for preparing a neodymium-iron-boron permanent magnet, including the following steps:
s100, according to the copper powder: aluminum powder: lanthanum powder: boron powder: neodymium powder: iron powder = (0.1-0.2): (0.2-0.4): (1-2): (1-1.2): (30-32): (64-68), weighing and mixing the materials to prepare powder;
s200, sequentially carrying out vacuum melting, melt-spinning and flaking, hydrogen crushing and air flow grinding on the powder to obtain matrix magnetic powder;
s300, according to the weight ratio of ammonium bicarbonate: silicon nitride: zirconium powder: silicon powder: matrix magnetic powder = (2-4): (4-6): (6-8): (6-8): (74-82) weighing and mixing the materials according to the mass ratio to prepare the composite magnetic powder;
s400, filling the matrix magnetic powder into a mold, and carrying out compression molding to obtain a blank;
s500, mixing the composite magnetic powder with ethanol to prepare slurry, wherein the weight ratio of the composite magnetic powder: matrix magnetic powder = (3-4): coating the slurry on the surface of the blank body according to the mass ratio of 100, and drying to obtain a green magnet;
s600, sintering the green magnet to obtain a sintered body;
s700, applying a heavy rare earth dopant to the surface layer of the sintered body in a supercritical extraction mode to obtain a blank body;
and S800, tempering the blank body to obtain the neodymium iron boron permanent magnet.
In any of the above technical solutions, S200 specifically includes:
s210, feeding the powder into a smelting furnace at 10 -2 Pa to 10 -3 Carrying out vacuum melting for 3 to 4 hours under the vacuum degree condition of Pa and the temperature condition of 1300 to 1400 ℃ to obtain molten liquid;
s220, pouring the molten liquid into a water-cooling roller, and performing melt spinning sheet forming to obtain melt spinning sheets;
s230, putting the melt-spun sheet into a hydrogen breaking furnace, vacuumizing until the vacuum degree is less than or equal to 3Pa, introducing hydrogen, and keeping the pressure at 1.5 multiplied by 10 5 Pa to 1.8X 10 5 Pa, performing hydrogen breaking treatment for 4 to 5 hours, pumping out residual hydrogen, heating the hydrogen breaking furnace to 450 to 480 ℃, and preserving heat for 4 hours;
s240, collecting the crushed powder, sending the powder into an airflow grinder for airflow grinding to obtain matrix magnetic powder with the particle size of 3-4 microns.
In any of the above technical solutions, S400 specifically includes:
s410, filling the matrix magnetic powder into a mold in a protective atmosphere and under a 3.5T-4.5T pulse magnetic field, and carrying out compression molding to obtain the material with the density of 3.2g/cm 3 To 3.4g/cm 3 The embryo body of (1).
In any of the above technical solutions, in S500, the addition amount of the composite magnetic powder in the slurry is 15wt% to 25 wt%.
In any of the above technical solutions, S600 specifically includes:
s610, heating the green magnet to 700-750 ℃ along with a furnace in a protective atmosphere, and sintering for 1-2 h;
and S620, continuously heating the green magnet to 1050-1150 ℃ in a protective atmosphere, sintering for 2-3 h, and cooling along with the furnace to obtain a sintered body.
In any of the above technical solutions, S700 specifically includes:
s710, preparing heavy rare earth powder by adopting raw materials including dysprosium chloride and terbium chloride;
s720, carrying out ultrasonic dispersion on the heavy rare earth powder in ethanol to obtain a heavy rare earth dopant;
s730, placing the sintered body in a closed container, vacuumizing, placing the heavy rare earth dopant in a reaction kettle matched with the closed container, sealing the reaction kettle, raising the temperature and the pressure, opening a valve between the reaction kettle and the closed container under the conditions that the temperature of the reaction kettle reaches 275-300 ℃ and the pressure reaches 7-8 MPa, so that the ethanol in a supercritical state drives the heavy rare earth to continuously flow into the closed container under the action of pressure difference, keeping the temperature and the pressure for 0.5-1 h, stopping heating, closing the valve, and standing the closed container for 0.5-1 h to obtain a blank body.
In any of the above technical solutions, S800 specifically includes:
and S810, heating the blank body to 320-360 ℃ along with the furnace in the protective atmosphere, and tempering for 2-3 h to obtain the neodymium iron boron permanent magnet.
In any of the above technical solutions, in S100, the powder further includes:
butyl octadecenoate: the addition amount is 0.2 to 0.3 weight percent of the weight of the iron powder;
antioxidant: the addition amount is 1.4wt% to 1.6wt% of the mass of the iron powder.
In any of the above technical solutions, after S800, the method further includes:
and S900, applying an electroplated metal anticorrosive coating on the surface of the neodymium iron boron permanent magnet.
In order to achieve the second object of the invention, the invention also provides a neodymium iron boron permanent magnet, which is obtained by adopting the preparation method of any one of the above technical schemes.
Advantageous effects
Firstly, when preparing the powder required by the neodymium iron boron permanent magnet, the powder is added with lanthanum powder, boron powder, neodymium powder and iron powder, and also added with copper powder and aluminum powder. Copper and aluminum can improve the intrinsic coercive force of the neodymium iron boron permanent magnet and promote the Curie temperature of the neodymium iron boron permanent magnet to be reduced. Furthermore, the invention carries out vacuum melting, strip forming, hydrogen breaking treatment and air flow grinding on the powder to obtain the matrix magnetic powder. Then, the matrix magnetic powder is pressed into a blank body, sintered and tempered. Before the blank is sintered, the surface of the blank is coated with the composite magnetic powder. The composite magnetic powder is obtained by adding ammonium bicarbonate, silicon nitride, zirconium powder and silicon powder on the basis of the original matrix magnetic powder component. By adding silicon nitride, zirconium powder and silicon powder, the mechanical strength of the composite magnetic powder is superior to that of the matrix magnetic powder. Therefore, the mechanical strength of the neodymium iron boron permanent magnet can be improved by brushing and applying the slurry containing the composite magnetic powder on the surface of the blank body and then sintering the blank body. In addition, in the sintering process, a small amount of ammonium bicarbonate added into the composite magnetic powder enables the surface of the sintered body to form tiny cavities, so that heavy rare earth elements can be more uniformly and effectively diffused along a grain boundary phase on the surface layer of the sintered body, and the intrinsic coercive force of the neodymium iron boron permanent magnet is improved.
Detailed Description
In order that the above objects, features and advantages of the present invention can be more clearly understood, the present invention will be described in further detail with reference to specific embodiments. It should be noted that the embodiments and features of the embodiments of the present application may be combined with each other without conflict.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced in other ways than those specifically described herein, and therefore the scope of the present invention is not limited by the specific embodiments disclosed below.
The invention provides a preparation method of a neodymium iron boron permanent magnet, which comprises the following steps:
s100, according to the copper powder: aluminum powder: lanthanum powder: b, boron powder: neodymium powder: iron powder = (0.1-0.2): (0.2-0.4): (1-2): (1-1.2): (30-32): (64-68), weighing and mixing the materials to prepare powder;
s200, sequentially carrying out vacuum melting, melt-spinning and flaking, hydrogen crushing and air flow grinding on the powder to obtain matrix magnetic powder;
s300, according to the weight ratio of ammonium bicarbonate: silicon nitride: zirconium powder: silicon powder: matrix magnetic powder = (2-4): (4-6): (6-8): (6-8): (74-82) weighing and mixing the materials to prepare the composite magnetic powder;
s400, filling the matrix magnetic powder into a mold, and carrying out compression molding to obtain a blank;
s500, mixing the composite magnetic powder with ethanol to prepare slurry, wherein the weight ratio of the composite magnetic powder: matrix magnetic powder = (3-4): coating the slurry on the surface of the blank body according to the mass ratio of 100, and drying to obtain a green magnet;
s600, sintering the green magnet to obtain a sintered body;
s700, applying a heavy rare earth dopant to the surface layer of the sintered body in a supercritical extraction manner to obtain a blank body;
and S800, tempering the blank body to obtain the neodymium iron boron permanent magnet.
The raw materials and corresponding equipment adopted by the invention can be obtained by commercial purchase. The invention adopts the whole process that: proportioning, smelting and melt spinning, hydrogen breaking and jet milling, press forming, sintering, heavy rare earth application and tempering.
In S100, before weighing and mixing, the raw material powders may be subjected to processes such as impurity removal, crushing, grinding, and the like, so as to ensure the purity of the raw material powders, ensure that the particle size difference between the raw material powders is small, and further ensure that the uniformity of the mixed material is good.
Preferably, the particle size of each raw material powder may be controlled to be between 2 μm and 15 μm.
It is understood that as the neodymium powder of the present invention, pure neodymium powder having a purity of 99.5% or more may be used, and praseodymium neodymium powder may also be used.
Boron powder, neodymium powder and iron powder are used as main materials, and copper powder, aluminum powder and lanthanum powder are used as auxiliary materials. Under the condition that the adding proportion of the main materials is fixed, the addition amount and the adding proportion of the auxiliary materials can be freely selected and adjusted by a person skilled in the art according to actual needs.
The technical personnel in the field can also add auxiliary materials of other metal elements such as bismuth, vanadium, titanium, zirconium, tantalum and the like according to the actual needs.
In addition, in S100, the powder material can also comprise butyl octadecenoate serving as a lubricant and an antioxidant. The addition amount of the butyl octadecenoate is 0.2wt% to 0.3wt% of the mass of the iron powder. The addition amount of the antioxidant is 1.4wt% to 1.6wt% of the mass of the iron powder.
The skilled person can freely select the kind of antioxidant, such as a polymeric antioxidant, e.g. antioxidant 1010, or a natural antioxidant, e.g. vitamin polyphenol.
In some embodiments of the present invention, S200 specifically includes:
s210, feeding the powder into a smelting furnace at 10 -2 Pa to 10 -3 Carrying out vacuum melting for 3 to 4 hours under the vacuum degree condition of Pa and the temperature condition of 1300 to 1400 ℃ to obtain molten liquid;
s220, pouring the molten liquid into a water-cooling roller, and performing melt spinning to obtain melt spinning pieces;
s230, putting the melt-spun sheet into a hydrogen breaking furnace, vacuumizing until the vacuum degree is less than or equal to 3Pa, introducing hydrogen, and keeping the pressure at 1.5 multiplied by 10 5 Pa to 1.8X 10 5 Pa, performing hydrogen breaking treatment for 4-5 h, pumping out residual hydrogen, heating the hydrogen breaking furnace to 450-480 ℃, and preserving heat for 4h;
s240, collecting the crushed powder, sending the powder into an airflow grinder for airflow grinding to obtain matrix magnetic powder with the particle size of 3-4 microns.
It should be noted that most of the matrix magnetic powder obtained in S200 is used for preparing the green body by a die pressing method, but a small part of the matrix magnetic powder obtained in S200 needs to be reserved for preparing the composite magnetic powder applied on the surface layer of the matrix magnetic powder green body.
The composite magnetic powder is prepared by S300. In S300, silicon nitride, zirconium powder, and silicon powder are used to improve the mechanical strength of the green body.
Preferably, the particle size range of ammonium bicarbonate, silicon nitride, zirconium powder and silicon powder is between 10nm and 100 nm.
The matrix magnetic powder used to formulate the composite magnetic powder is preferably further ground to bring the particle size of the matrix magnetic powder closer to that of other powders such as ammonium bicarbonate, silicon nitride, zirconium powder, and silicon powder.
Preferably, the particle size of the ammonium bicarbonate ranges from 10nm to 20nm. The function of ammonium bicarbonate is understood to be a pore former, and therefore, the smaller the particle size of ammonium bicarbonate, the more advantageous the reduction of the size of the voids or pores and the improvement of the uniformity of the distribution of the voids or pores.
The ammonium bicarbonate can be replaced by chitosan, glucose or other substances with low thermal decomposition temperature according to actual needs by the technicians in the field. However, the applicant found in actual practice that the mechanical strength and intrinsic coercive force of the neodymium iron boron permanent magnet obtained with ammonium bicarbonate as a pore former are higher than those of other pore formers.
Without being bound by any theory, the applicant believes that the ammonium bicarbonate is used as the pore-forming agent and does not influence the product performance of the neodymium iron boron permanent magnet because the ammonium bicarbonate is more thoroughly thermally decomposed in the sintering process and hardly has carbon residue in the neodymium iron boron permanent magnet.
In some embodiments of the present invention, S400 specifically includes:
s410, filling the matrix magnetic powder into a mold in a protective atmosphere and under a pulse magnetic field of 3.5T to 4.5T, and carrying out compression molding to obtain the magnetic powder with the density of 3.2g/cm 3 To 3.4g/cm 3 The embryo body of (2).
The protective atmosphere in S410 may be nitrogen or argon, and the compression molding process may be replaced with isostatic pressing. On the premise of ensuring that the density of the blank body reaches the standard, the technical personnel in the field can select and adjust parameters such as the shape, the size, the compression molding pressure, the compression molding time and the like of the mold by using conventional technical means.
S500 is to apply the composite magnetic powder to the surface of the blank in a covering manner. In order to improve the uniformity of the covering application, the composite magnetic powder with the mass of 3-4% of the mass of the matrix magnetic powder used for preparing the blank is weighed firstly and mixed with ethanol to prepare slurry with the mass concentration of 15-25 wt%. Furthermore, the invention can apply the slurry to the surface of the blank by manual painting or mechanical spraying. Wherein the concentration of the slurry within the above range can be selected and adjusted by a person skilled in the art according to the size and shape of the embryo body.
In some embodiments of the present invention, S600 specifically includes:
s610, heating the green magnet to 700-750 ℃ along with a furnace in a protective atmosphere, and sintering for 1-2 h;
s620, continuously heating the green magnet to 1050-1150 ℃ in a protective atmosphere, sintering for 2-3 h, and cooling along with the furnace to obtain a sintered body.
The protective atmosphere in S600 may be nitrogen or argon. The rate of temperature increase in S600 can be selected and adjusted by one skilled in the art. In the sintering process, a small amount of ammonium bicarbonate added to the composite magnetic powder is thermally decomposed into gas and water in the sintering process, and the decomposition is complete, so that tiny cavities are formed on the surface of the sintered body, and thus heavy rare earth elements are more uniformly and effectively diffused along a grain boundary phase on the surface layer of the sintered body, and the intrinsic coercive force of the neodymium iron boron permanent magnet is improved.
The density of the surface layer part of the neodymium iron boron permanent magnet is slightly reduced due to a small amount of residual carbon after the pyrolysis of the ammonium bicarbonate, but the overall quality of the iron boron permanent magnet is not influenced, and the addition of the silicon nitride, the zirconium powder and the silicon powder and the crystal phase transformation of the silicon nitride, the zirconium powder and the silicon powder at high temperature can enable the iron boron permanent magnet to still keep higher mechanical strength under the condition that a pore cavity exists on the surface.
In some embodiments of the present invention, S700 specifically includes:
s710, preparing heavy rare earth powder by adopting raw materials comprising dysprosium chloride and terbium chloride;
s720, ultrasonically dispersing the heavy rare earth powder in ethanol to obtain a heavy rare earth dopant;
s730, placing the sintered body in a closed container, vacuumizing, placing the heavy rare earth dopant in a reaction kettle matched with the closed container, sealing the reaction kettle, raising the temperature and the pressure, opening a valve between the reaction kettle and the closed container under the conditions that the temperature of the reaction kettle reaches 275-300 ℃ and the pressure reaches 7-8 MPa, so that the ethanol in a supercritical state drives the heavy rare earth to continuously flow into the closed container under the action of pressure difference, keeping the temperature and the pressure for 0.5-1 h, stopping heating, closing the valve, and standing the closed container for 0.5-1 h to obtain a blank body.
In some embodiments of the present invention, S700 specifically includes:
s710, adding sodium chloride: dysprosium chloride: terbium chloride: potassium lignosulfonate: polyvinyl alcohol: water = (4-6): (6-8): (6-8): (12-14): (16-20): weighing 100 parts by mass, mixing, feeding into a reaction kettle, reacting for 1-1.5 h under the conditions of the temperature of 140-160 ℃ and the pressure of 0.8-1.2 MPa, and cooling to obtain heavy rare earth colloid;
s720, performing first-order freeze-drying treatment on the heavy rare earth colloid for 1 to 1.5 hours at a temperature of between 50 ℃ below zero and 60 ℃ below zero, performing second-order freeze-drying treatment on the heavy rare earth colloid for 6 to 8 hours at a temperature of between 30 ℃ below zero and 20 ℃ below zero, and crushing and grinding the heavy rare earth colloid after the freeze-drying treatment is finished to obtain heavy rare earth powder;
s730, mixing heavy rare earth powder: ethanol = (6-8): 100, ultrasonically dispersing the heavy rare earth powder in ethanol for 15min to 20min to obtain a heavy rare earth dopant;
s740, placing the sintered body in a closed container, vacuumizing, placing the heavy rare earth dopant in a reaction kettle matched with the closed container, sealing the reaction kettle, raising the temperature and the pressure, opening a valve between the reaction kettle and the closed container under the conditions that the temperature of the reaction kettle reaches 275-300 ℃ and the pressure reaches 7-8 MPa, so that the ethanol in a supercritical state drives the heavy rare earth to continuously flow into the closed container under the action of pressure difference, keeping the temperature and the pressure for 0.5-1 h, stopping heating, closing the valve, and standing the closed container for 0.5-1 h to obtain a blank body.
It is understood that the amount of ethanol used in S740 can be selected and adjusted by one skilled in the art according to actual needs, so as to achieve the extraction of heavy rare earth. Experiments show that the extraction and application of the heavy rare earth can be basically completed by adding ethanol with the weight 12 to 16 times of that of the heavy rare earth powder and maintaining the temperature and the pressure for 1 h. It can be understood that the equipment specification has a certain influence on the ethanol addition, and ethanol can be injected into the reaction kettle at any time for supplement when the original ethanol dosage in S740 is not enough to maintain the temperature and pressure balance.
It can be understood that when the pressure is lower than 7MPa, the valve can be temporarily closed, and the valve is opened after the temperature and the pressure are raised to meet the ethanol supercritical condition.
In some embodiments of the present invention, S800 specifically includes:
and S810, heating the blank body to 320-360 ℃ along with the furnace in the protective atmosphere, and tempering for 2-3 h to obtain the neodymium iron boron permanent magnet.
The protective atmosphere in S810 may be nitrogen or argon,
in some embodiments of the present invention, after S800, the method further includes:
s900, applying an electroplated metal anticorrosive coating on the surface of the neodymium iron boron permanent magnet.
For the sintered Nd-Fe-B permanent magnet, the corrosion resistance is poor, so that the corrosion resistance can be improved by applying an anticorrosive coating on the surface of the sintered Nd-Fe-B permanent magnet. The anti-corrosion coating can be applied by various methods such as metal plating, chemical plating, organic coating, physical vapor deposition and the like. One skilled in the art can select a well-established composition and process of the electroplated metal corrosion protection coating for use in step S900 of the present application.
Illustratively, the specific operation manner of step S900 may be: before electroplating treatment, chamfering, deoiling, rinsing, acid washing and rinsing are carried out on the neodymium iron boron permanent magnet; and (3) placing the neodymium iron boron permanent magnet into a nickel plating solution, and carrying out electroplating treatment under the conditions that the temperature is 55-65 ℃ and the pH value is 4-6. Wherein the current density of the electroplating treatment is 2A/dm 2 To 4A/dm 2 The electroplating time is 30min to 40min.
In the prior art, a person skilled in the art will choose to add silicon, zirconium, aluminum, silicon carbide, and silicon nitride as auxiliary materials in the raw materials for preparing the neodymium-iron-boron permanent magnet. For example, a plurality of auxiliary materials are directly added during the material preparation, or some auxiliary materials including silicon carbide are prepared into a coating and sprayed on the surface of the sintered neodymium iron boron permanent magnet.
Compared with the prior art, the invention has one difference that before sintering, the auxiliary materials capable of enhancing the mechanical strength of the neodymium iron boron permanent magnet are coated on the surface of the blank body, and then sintering is carried out. The sintering process can synchronously sinter the matrix magnetic powder and the composite magnetic powder on the surface of the matrix magnetic powder, so that the composite magnetic powder and the matrix magnetic powder are tightly combined, the mechanical strength of the neodymium-iron-boron permanent magnet is improved, the use amount of substances such as silicon, zirconium, silicon carbide and the like can be directly reduced, and the production cost is reduced.
In addition, in the prior art, a person skilled in the art also chooses to artificially make defects or holes on the surface of the neodymium iron boron permanent magnet to improve the diffusion efficiency or diffusion dimension of the heavy rare earth. For example, the surface of the neodymium iron boron permanent magnet is formed with honeycomb or briquette-shaped hole defects by means of laser pulse perforation.
In the research of the applicant, the method has the defects of complex process and high cost and also has the defect of uncontrollable rare earth diffusion degree. Heavy rare earth can quickly diffuse into the interior of the Nd-Fe-B permanent magnet from the grain boundary along the hole defects, resulting in Nd 2 Fe 1 The 4B major phase volume fraction decreases and results in a decrease in remanence.
Therefore, the invention adopts a processing mode of forming the hole defects by taking ammonium bicarbonate as a pore forming agent and utilizing pyrolysis of the ammonium bicarbonate, and the mode has simple process and low cost and ensures that the size of the hole defects is more controllable. In addition, the applicant has found in the research that the mechanical strength and intrinsic coercive force of the neodymium iron boron permanent magnet obtained by the present invention are ideal, and not limited to any theory, the applicant believes that the difference in the microstructure and structure between the inside and the surface of the green magnet after being sintered to form a sintered body is caused by the crystal phase transformation of the composite magnetic powder due to the addition of auxiliary materials such as zirconium, silicon and the like at high temperature. Therefore, after the heavy rare earth is diffused on the surface layer of the sintered body, the existence of a micro-morphology interface limits or hinders the heavy rare earth dopant from continuously and deeply diffusing from the surface to the interior of the sintered body so as to avoid or limit Nd 2 Fe 14 The volume ratio of the B main phase is reduced.
The purpose of S700 is to apply heavy rare earth to the surface of the sintered body after sintering and before tempering, and to improve the uniformity of heavy rare earth application. The addition of the heavy rare earth elements such as terbium, dysprosium and the like can obviously improve the coercive force of the sintered neodymium-iron-boron magnet through grain boundary diffusion, so that the heavy rare earth elements such as terbium, dysprosium and the like are indispensable important components in the production and manufacture of the high-performance neodymium-iron-boron magnet. However, terbium, dysprosium and other heavy rare earths are expensive, and it is very important to reduce the consumption of terbium and dysprosium as much as possible on the premise of ensuring higher coercivity. One of the effective ways to reduce the dosage of terbium and dysprosium is to improve the uniformity of application. Compared with the applying modes of brushing, soaking and the like in the prior art, the heavy rare earth is prepared into the chloride colloid material which can be dissolved in ethanol, and the ethanol is used as a solvent for supercritical extraction, so that the heavy rare earth can be promoted to be more uniformly distributed on the surface layer of the sintered body. Specifically, dysprosium chloride and terbium chloride are mixed with sodium chloride, potassium lignosulfonate, polyvinyl alcohol and water, and are heated and pressurized to react to prepare heavy rare earth colloid, the heavy rare earth prepared by a hydrothermal method in a colloid state has small particle size and uniform particle size distribution, and the colloid is subjected to two-stage low-temperature freeze-drying treatment to store the microscopic morphology of the heavy rare earth, so that the heavy rare earth chloride powder with a small particle size structure is obtained. Finally, the heavy rare earth chloride powder soluble in ethanol is ultrasonically dispersed in an ethanol solvent, and the ethanol is heated and pressurized to a supercritical state, so that the heavy rare earth can be extracted by utilizing the property that the gas-liquid two-phase property of a substance in the supercritical state is very close to that of the substance so as not to be distinguished. Namely: the heavy rare earth chloride which is easily dissolved in ethanol is uniformly applied to the surface of the sintered body by using ethanol in a supercritical state. Under the action of capillary, the ethanol in a supercritical state drives the heavy rare earth chloride to enter pores on the surface of the sintered body and deposit in the pores to form a uniform and compact rare earth deposited film.
Example 1
This example prepares a neodymium iron boron permanent magnet, which is prepared by the following steps.
S1, weighing and mixing copper powder, aluminum powder, lanthanum powder, boron powder, neodymium powder and iron powder according to the mass ratio shown in Table 1 to prepare powder;
s2, feeding the powder into a smelting furnace at 10 -2 Pa to 10 -3 Vacuum melting is carried out for 4 hours under the condition of Pa vacuum degree and the temperature of 1350 +/-20 ℃ to obtain molten liquid;
s3, pouring the molten liquid into a water-cooling roller, and performing melt spinning to obtain melt spinning pieces;
s4, putting the melt-spun sheet into a hydrogen breaking furnace, vacuumizing until the vacuum degree is less than or equal to 3Pa, introducing hydrogen, and keeping the pressure at (1.6 +/-0.1) multiplied by 10 5 Pa, performing hydrogen breaking treatment for 4 hours, pumping out residual hydrogen, heating the hydrogen breaking furnace to 460 ℃, and preserving heat for 4 hours;
s5, collecting the crushed powder, sending the powder into an airflow grinder for airflow grinding to obtain matrix magnetic powder with the particle size of 3-4 microns;
s6, weighing and mixing ammonium bicarbonate, silicon nitride, zirconium powder, silicon powder and matrix magnetic powder according to the mass ratio shown in the table 1 to prepare composite magnetic powder;
s7, filling the matrix magnetic powder into a mold in a nitrogen protective atmosphere and under a 4.0T pulse magnetic field, and carrying out compression molding at a pressure of 4MPa to 6MPa to obtain the matrix magnetic powder with a density of (3.3 +/-0.05) g/cm 3 The embryo body of (a);
s8, mixing the composite magnetic powder with ethanol to prepare 15wt% of slurry, wherein the weight ratio of the composite magnetic powder: matrix magnetic powder =4: coating the slurry on the surface of the blank body according to the mass ratio of 100, and drying to obtain a green magnet;
s9, heating the raw magnet to 720 ℃ along with the furnace in the nitrogen protective atmosphere, and sintering for 1.5h;
s10, continuously heating the green magnet to 1100 ℃ in a nitrogen protective atmosphere, sintering for 2.5 hours, and cooling along with the furnace to obtain a sintered body;
s11, mixing sodium chloride, dysprosium chloride, terbium chloride, potassium lignosulfonate, polyvinyl alcohol and water according to the mass ratio shown in the table 1, feeding the mixture into a reaction kettle, reacting for 1.5 hours under the temperature condition of 150 ℃ and the pressure condition of 1.0MPa, and cooling to obtain heavy rare earth colloid;
s12, performing first-order freeze-drying treatment on the heavy rare earth colloid for 1h at the temperature of minus 60 ℃, performing second-order freeze-drying treatment on the heavy rare earth colloid for 8h at the temperature of minus 30 ℃, and crushing and grinding after the freeze-drying treatment is finished to obtain heavy rare earth powder;
s13, according to the weight ratio of the heavy rare earth powder: ethanol =6:100, ultrasonically dispersing the heavy rare earth powder in ethanol for 20min to obtain a heavy rare earth dopant;
s14, placing the sintered body in a closed container, vacuumizing, placing a heavy rare earth dopant in a reaction kettle matched with the closed container, sealing the reaction kettle, raising the temperature and the pressure, opening a valve between the reaction kettle and the closed container under the conditions that the temperature of the reaction kettle reaches 275-300 ℃ and the pressure reaches 7-8 MPa, so that the heavy rare earth is driven to continuously flow into the closed container by ethanol in a supercritical state under the action of pressure difference, keeping the temperature and the pressure for 1h in the range of 275-300 ℃ and the pressure of 7-8 MPa, stopping heating, closing the valve, and standing the closed container for 0.5h to obtain a blank body;
s15, heating the blank body to 340 ℃ along with the furnace in the protective atmosphere, and tempering for 2.5 hours to obtain the neodymium iron boron permanent magnet.
Examples 2 to 3
The overall manufacturing process of examples 2-3 is the same as that of example 1, except that the component ratios of steps S1, S6 and S11 are different, and the detailed ratios of examples 2-3 can be seen in table 1.
Comparative example 1
This comparative example prepared a neodymium iron boron permanent magnet prepared by the following steps.
S1, weighing and mixing copper powder, aluminum powder, lanthanum powder, boron powder, neodymium powder and iron powder according to the mass ratio shown in Table 1 to prepare powder;
s2, feeding the powder into a smelting furnace at 10 -2 Pa to 10 -3 Vacuum melting is carried out for 4 hours under the condition of Pa vacuum degree and the temperature of 1350 +/-20 ℃ to obtain molten liquid;
s3, pouring the molten liquid into a water-cooling roller, and performing melt spinning sheet forming to obtain melt spinning sheets;
s4, throwing the melt-spun piecePutting into hydrogen breaking furnace, vacuumizing to vacuum degree less than or equal to 3Pa, introducing hydrogen, and maintaining pressure at (1.6 + -0.1) × 10 5 Pa, performing hydrogen breaking treatment for 4 hours, pumping out residual hydrogen, heating the hydrogen breaking furnace to 460 ℃, and preserving heat for 4 hours;
s5, collecting the crushed powder, sending the powder into an airflow grinder for airflow grinding to obtain matrix magnetic powder with the particle size of 3-4 microns;
s6, filling the matrix magnetic powder into a mold in a nitrogen protective atmosphere and under a 4.0T pulse magnetic field, and carrying out compression molding under the pressure of 4MPa to 6MPa to obtain the matrix magnetic powder with the density of (3.3 +/-0.05) g/cm 3 Drying the blank body to obtain a green magnet;
s7, heating the raw magnet to 720 ℃ along with the furnace in the nitrogen protective atmosphere, and sintering for 1.5h;
s8, continuously heating the green magnet to 1100 ℃ in a nitrogen protective atmosphere, sintering for 2.5h, and cooling along with the furnace to obtain a sintered body;
s9, mixing sodium chloride, dysprosium chloride, terbium chloride, potassium lignosulfonate, polyvinyl alcohol and water according to the mass ratio shown in the table 1, feeding the mixture into a reaction kettle, reacting for 1.5h under the temperature condition of 150 ℃ and the pressure condition of 1.0MPa, and cooling to obtain heavy rare earth colloid;
s10, performing first-order freeze-drying treatment on the heavy rare earth colloid for 1h at the temperature of minus 60 ℃, performing second-order freeze-drying treatment on the heavy rare earth colloid for 8h at the temperature of minus 30 ℃, and crushing and grinding after the freeze-drying treatment is finished to obtain heavy rare earth powder;
s11, according to the weight rare earth powder: ethanol =6:100, ultrasonically dispersing the heavy rare earth powder in ethanol for 20min to obtain a heavy rare earth dopant;
s12, placing the sintered body in a closed container, vacuumizing, placing a heavy rare earth dopant in a reaction kettle matched with the closed container, sealing the reaction kettle, raising the temperature and the pressure, opening a valve between the reaction kettle and the closed container under the condition that the temperature of the reaction kettle reaches 275-300 ℃ and the pressure reaches 7-8 MPa, so that the heavy rare earth is driven to continuously flow into the closed container under the action of pressure difference by ethanol in a supercritical state, keeping the temperature and the pressure for 1h in the range of 275-300 ℃ and the pressure of 7-8 MPa, stopping heating, closing the valve, and standing the closed container for 0.5h to obtain a blank body;
s13, heating the blank body to 340 ℃ along with the furnace in the protective atmosphere, and tempering for 2.5 hours to obtain the neodymium iron boron permanent magnet.
Comparative example 2
This comparative example prepared a neodymium iron boron permanent magnet prepared by the following steps.
S1, weighing and mixing copper powder, aluminum powder, lanthanum powder, boron powder, neodymium powder and iron powder according to the mass ratio shown in Table 1 to prepare powder;
s2, feeding the powder into a smelting furnace at 10 -2 Pa to 10 -3 Vacuum melting is carried out for 4 hours under the condition of Pa vacuum degree and the temperature of 1350 +/-20 ℃ to obtain molten liquid;
s3, pouring the molten liquid into a water-cooling roller, and performing melt spinning to obtain melt spinning pieces;
s4, putting the melt-spun sheet into a hydrogen breaking furnace, vacuumizing until the vacuum degree is less than or equal to 3Pa, introducing hydrogen, and keeping the pressure at (1.6 +/-0.1) multiplied by 10 5 Pa, performing hydrogen breaking treatment for 4 hours, pumping out residual hydrogen, heating the hydrogen breaking furnace to 460 ℃, and preserving heat for 4 hours;
s5, collecting the crushed powder, and feeding the powder into an airflow grinder for airflow grinding to obtain matrix magnetic powder with the particle size of 3-4 microns;
s6, filling the matrix magnetic powder into a mold in a nitrogen protective atmosphere and under a 4.0T pulse magnetic field, and carrying out compression molding under the pressure of 4MPa to 6MPa to obtain the matrix magnetic powder with the density of (3.3 +/-0.05) g/cm 3 Drying the blank body to obtain a green magnet;
s7, heating the raw magnet to 720 ℃ along with the furnace in the nitrogen protective atmosphere, and sintering for 1.5h;
s8, continuously heating the green magnet to 1100 ℃ in a nitrogen protective atmosphere, sintering for 2.5h, and cooling along with the furnace to obtain a sintered body;
s9, uniformly mixing dysprosium chloride and terbium chloride obtained by a commercial purchasing way with the mass ratio of 1;
s10, according to the weight rare earth powder: ethanol =6:100, ultrasonically dispersing the heavy rare earth powder in ethanol for 20min to obtain a heavy rare earth dopant;
s11, placing the sintered body in a closed container, vacuumizing, placing a heavy rare earth dopant in a reaction kettle matched with the closed container, sealing the reaction kettle, raising the temperature and the pressure, opening a valve between the reaction kettle and the closed container under the condition that the temperature of the reaction kettle reaches 275-300 ℃ and the pressure reaches 7-8 MPa, so that the heavy rare earth is driven to continuously flow into the closed container under the action of pressure difference by ethanol in a supercritical state, keeping the temperature and the pressure for 1h in the range of 275-300 ℃ and the pressure of 7-8 MPa, stopping heating, closing the valve, and standing the closed container for 0.5h to obtain a blank body;
s12, heating the blank body to 340 ℃ along with the furnace in the protective atmosphere, and tempering for 2.5 hours to obtain the neodymium iron boron permanent magnet.
Performance testing
According to the magnetic test method of the GB/T3217 permanent magnet (hard magnet) material, the magnetic performance of the neodymium iron boron permanent magnet obtained in the examples 1 to 3 and the comparative examples 1-2 is tested, and the test results are shown in Table 2.
In the description herein, the description of the terms "one embodiment," "some embodiments," "specific embodiments," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. A preparation method of a neodymium iron boron permanent magnet is characterized by comprising the following steps:
s100, according to the copper powder: aluminum powder: lanthanum powder: boron powder: neodymium powder: iron powder = (0.1-0.2): (0.2-0.4): (1-2): (1-1.2): (30-32): (64-68), weighing and mixing the materials to prepare powder;
s200, sequentially carrying out vacuum melting, melt-spinning and flaking, hydrogen crushing treatment and air flow grinding on the powder to obtain matrix magnetic powder;
s300, according to the weight ratio of ammonium bicarbonate: silicon nitride: zirconium powder: silicon powder: matrix magnetic powder = (2-4): (4-6): (6-8): (6-8): (74-82) weighing and mixing the materials according to the mass ratio to prepare the composite magnetic powder;
s400, filling the matrix magnetic powder into a mold, and carrying out compression molding to obtain a blank;
s500, mixing the composite magnetic powder with ethanol to prepare slurry, wherein the weight ratio of the composite magnetic powder: matrix magnetic powder = (3-4): coating the slurry on the surface of the blank body according to the mass ratio of 100, and drying to obtain a green magnet;
s600, sintering the green magnet to obtain a sintered body;
s700, applying a heavy rare earth dopant to the surface layer of the sintered body in a supercritical extraction mode to obtain a blank body;
wherein, S700 specifically includes:
s710, according to the weight ratio of sodium chloride: dysprosium chloride: terbium chloride: potassium lignosulfonate: polyvinyl alcohol: water = (4-6): (6-8): (6-8): (12-14): (16-20): weighing 100 parts by mass, mixing, feeding into a reaction kettle, reacting for 1-1.5 h under the conditions of the temperature of 140-160 ℃ and the pressure of 0.8-1.2 MPa, and cooling to obtain heavy rare earth colloid;
s720, performing first-order freeze-drying treatment on the heavy rare earth colloid for 1h to 1.5h at the temperature of-50 ℃ to-60 ℃, performing second-order freeze-drying treatment on the heavy rare earth colloid for 6h to 8h at the temperature of-30 ℃ to-20 ℃, and crushing and grinding after the freeze-drying treatment is finished to obtain heavy rare earth powder;
s730, according to the weight ratio of the heavy rare earth powder: ethanol = (6-8): 100, ultrasonically dispersing the heavy rare earth powder in ethanol for 15min to 20min to obtain a heavy rare earth dopant;
s740, placing the sintered body in a closed container, vacuumizing, placing the heavy rare earth dopant in a reaction kettle matched with the closed container, sealing the reaction kettle, raising the temperature and the pressure, opening a valve between the reaction kettle and the closed container under the conditions that the temperature of the reaction kettle reaches 275-300 ℃ and the pressure reaches 7-8 MPa, so that the heavy rare earth is driven to continuously flow into the closed container under the action of pressure difference by ethanol in a supercritical state, keeping the temperature and the pressure for 0.5-1 h, stopping heating, closing the valve, and standing the closed container for 0.5-1 h to obtain a blank body;
and S800, tempering the blank body to obtain the neodymium iron boron permanent magnet.
2. The method according to claim 1, wherein S200 specifically comprises:
s210, feeding the powder into a smelting furnace at 10 -2 Pa to 10 -3 Carrying out vacuum melting for 3-4 h under the vacuum degree condition of Pa and the temperature condition of 1300-1400 ℃ to obtain molten liquid;
s220, pouring the molten liquid into a water-cooling roller, and performing melt spinning sheet forming to obtain a melt spinning sheet;
s230, putting the melt-spun sheet into a hydrogen breaking furnace, vacuumizing until the vacuum degree is less than or equal to 3Pa, introducing hydrogen, and keeping the pressure at 1.5 multiplied by 10 5 Pa to 1.8X 10 5 Pa, performing hydrogen breaking treatment for 4 to 5 hours, pumping out residual hydrogen, heating the hydrogen breaking furnace to 450 to 480 ℃, and preserving heat for 4 hours;
s240, collecting the crushed powder, sending the powder into an airflow grinder for airflow grinding to obtain the matrix magnetic powder with the particle size of 3-4 microns.
3. The method according to claim 1, wherein S400 specifically comprises:
s410, filling the matrix magnetic powder into the die in a protective atmosphere and under a 3.5T-4.5T pulse magnetic field, and carrying out compression molding to obtain the matrix magnetic powder with the density of 3.2g/cm 3 To 3.4g/cm 3 The embryo body of (1).
4. A producing method according to claim 1, wherein an addition amount of said composite magnetic powder in said slurry is 15wt% to 25 wt% in S500.
5. The method according to claim 1, wherein S600 specifically comprises:
s610, heating the green magnet to 700-750 ℃ along with a furnace in a protective atmosphere, and sintering for 1-2 h;
s620, continuously heating the green magnet to 1050-1150 ℃ in a protective atmosphere, sintering for 2-3 h, and cooling along with the furnace to obtain the sintered body.
6. The method according to claim 1, wherein S800 specifically comprises:
and S810, heating the blank body to 320-360 ℃ along with the furnace in a protective atmosphere, and tempering for 2-3 h to obtain the neodymium iron boron permanent magnet.
7. The method according to any one of claims 1 to 6, wherein in S100, the powder lot further comprises:
butyl octadecenoate: the addition amount is 0.2wt% to 0.3wt% of the weight of the iron powder;
antioxidant: the addition amount is 1.4wt% to 1.6wt% of the mass of the iron powder.
8. The method according to any one of claims 1 to 6, further comprising, after S800:
s900, applying an electroplated metal anticorrosive coating on the surface of the neodymium iron boron permanent magnet.
9. A neodymium iron boron permanent magnet, characterized in that the neodymium iron boron permanent magnet is obtained by the preparation method according to any one of claims 1 to 8.
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| CN1026534C (en) * | 1991-08-10 | 1994-11-09 | 北京科技大学 | Rare earth permanentlymagetic material and its preparation method |
| JP4747562B2 (en) * | 2004-06-25 | 2011-08-17 | 株式会社日立製作所 | Rare earth magnet, manufacturing method thereof, and magnet motor |
| CN1725394B (en) * | 2005-06-08 | 2010-04-07 | 浙江大学 | Method for increasing working temp and corrosion resisting property of Nd-Fe-B by adding nona silicon nitride in crystal boundary phase |
| CN101817547B (en) * | 2010-05-07 | 2011-10-05 | 沈阳工业大学 | Method for recovering mixed rare earth chlorides from neodymium iron boron permanent magnet material scraps |
| WO2012043692A1 (en) * | 2010-09-30 | 2012-04-05 | 日立金属株式会社 | R-t-b sintered magnet manufacturing method |
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| CN105895355B (en) * | 2016-04-22 | 2017-10-13 | 横店集团东磁股份有限公司 | A kind of high-performance small dimension ratio of height to thickness electroplates the preparation technology of bonded permanent magnet |
| CN105957706B (en) * | 2016-04-28 | 2018-01-02 | 北京科技大学 | A kind of Pressure Infiltration Dy3+/Tb3+The method for preparing high-performance neodymium-iron-boron magnet |
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