Method for preparing high-performance neodymium-iron-boron magnet by adopting grain boundary diffusion technology

Abstract

The invention discloses a method for preparing a high-performance neodymium-iron-boron magnet by adopting a grain boundary diffusion technology, and relates to the technical field of rare earth magnetic materials, and the method comprises the following steps: S1, dissolving a diffusion source in a solvent to obtain a solution; s2, spraying the solution prepared in the step S1 on the surface of the neodymium-iron-boron magnet through an ultrasonic spraying process, and forming a coating on the surface of the neodymium-iron-boron magnet after drying; and S3, performing diffusion treatment and annealing treatment on the neodymium-iron-boron magnet with the coating prepared in the step S2 under a vacuum condition. According to the method, the grain boundary diffusion technology and the ultrasonic spraying technology are combined, the uniformity and thickness control precision of a coating formed on the surface of the neodymium-iron-boron magnet can be improved, the utilization rate of heavy rare earth elements can be increased, the use amount of the heavy rare earth elements is reduced, and the high-performance neodymium-iron-boron magnet is obtained while the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth magnetic materials, and particularly relates to a method for preparing high-performance NdFeB magnets by using the grain boundary diffusion technology. Background Art

[0002] A magnet refers to a material that can generate a magnetic field, which can attract some substances and repel some substances. Magnets are generally divided into permanent magnets and soft magnets. A permanent magnet can maintain its magnetism for a long time, belonging to a hard magnet, not easy to lose magnetism, and not easy to be magnetized. Common hard magnets include NdFeB magnets, SmCo magnets, AlNiCo magnets, etc. Among them, NdFeB magnets have a high magnetic volume and coercivity, and are one of the currently strongest permanent magnetic materials, and its maximum magnetic volume far exceeds other types of permanent magnetic materials. The high magnetic performance of NdFeB magnets enables them to generate a strong magnetic field and is suitable for application prospects requiring high-performance magnets.

[0003] NdFeB magnets are divided into two types: sintered NdFeB magnets and bonded NdFeB magnets. Sintered NdFeB magnets are made by powder metallurgy technology. It is necessary to first pulverize the melted alloy and press it into shape in a magnetic field, and then sinter it in an inert gas or vacuum to achieve densification. Bonded NdFeB magnets are magnets made of rapidly quenched NdFeB magnetic powder and a binder through die pressing or injection molding. Compared with sintered NdFeB magnets, bonded NdFeB magnets are formed in one step without secondary processing and can be made into complex magnets of various shapes. However, sintered NdFeB magnets have excellent magnetic properties, so they are widely used in fields such as motors, generators, sensors, and magnetic machinery.

[0004] The grain boundary diffusion technology is a technical means that can effectively improve the magnetic properties of sintered NdFeB magnets. By forming a heavy rare earth film on the surface of the magnet and subjecting it to vacuum heat treatment, the heavy rare earth enters the magnet interior along the grain boundaries. At the same time, the heavy rare earth atoms replace the Nd atoms around the main phase grains to form a high coercivity shell layer. This unique microstructure can greatly improve the coercivity of the magnet on the basis of a very low residual magnetic drop value. Currently, the grain boundary diffusion technology mainly includes magnetron sputtering method, evaporation diffusion method, electrodeposition method, surface coating method, etc. However, the magnetron sputtering method, evaporation diffusion method, and electrodeposition method all have the disadvantage of high equipment cost, while the surface coating method has the disadvantage of uneven coating. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing high-performance NdFeB magnets by using the grain boundary diffusion technology. Through the ultrasonic spraying process, not only can the uniformity and thickness control accuracy of the coating formed on the surface of the NdFeB magnet be improved, enabling the NdFeB magnet to have better magnetic properties, but also the utilization rate of heavy rare earth elements can be increased and the cost can be reduced.

[0006] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0007] One of the objectives of the present invention is to provide a method for preparing a high-performance neodymium-iron-boron magnet by using the grain boundary diffusion technology, comprising the following steps:

[0008] S1. Dissolve the diffusion source in a solvent to obtain a solution;

[0009] S2. Spray the solution prepared in step S1 onto the surface of the neodymium-iron-boron magnet through an ultrasonic spraying process, and after drying, form a coating on the surface of the neodymium-iron-boron magnet;

[0010] S3. Perform diffusion treatment and annealing treatment on the neodymium-iron-boron magnet with the coating prepared in step S2 under vacuum conditions.

[0011] Further, the diffusion source is a heavy rare earth element or a heavy rare earth oxide. Among them, the heavy rare earth element is selected from one or more of gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and yttrium (Y). The heavy rare earth oxide is selected from one or more of gadolinium oxide (Gd 2 O 3 ), terbium oxide (Tb 4 O 7 ), dysprosium oxide (Dy 2 O 3 ), holmium oxide (Ho 2 O 3 ), erbium oxide (Er 2 O 3 ), thulium oxide (Tm 2 O 3 ), ytterbium oxide (Yb 2 O 3 ), lutetium oxide (Lu 2 O 3 ), and yttrium oxide (Y 2 O 3 ).

[0012] Further, the solvent is an inorganic acid. The mixing method of the diffusion source and the solvent can adopt mechanical stirring, magnetic stirring or ultrasonic treatment.

[0013] Further, the neodymium-iron-boron magnet is a sintered neodymium-iron-boron magnet. In the present invention, the specific composition of the neodymium-iron-boron magnet is not limited, and as long as it is a neodymium-iron-boron magnet (including sintered neodymium-iron-boron magnets and bonded neodymium-iron-boron magnets), the method described in the present invention can be used to prepare high-performance neodymium-iron-boron magnets.

[0014] Further, the frequency of the ultrasonic spraying is 40 - 60 kHz, the power is 10 - 100 W, and the flow rate is 1 - 100 mL / min. Compared with the commonly used surface coating methods in the art, ultrasonic spraying has the advantages of high coating uniformity, high raw material utilization rate, high coating thickness control accuracy, thinner coating thickness, less spatter, non-clogging of the nozzle, and low maintenance cost.

[0015] Further, the temperature of the diffusion treatment is 800 - 1000 °C, the time is 1 - 12 h, and the vacuum degree is lower than 10 - 2 Pa. The grain boundary diffusion of the neodymium iron boron magnet refers to the migration of atoms on the grain boundary at high temperature, which leads to changes in the structure and properties of the grain boundary region. The main reason for carrying out the grain boundary diffusion of the neodymium iron boron magnet under vacuum is to reduce the influence of oxidation reaction and impurities, thereby improving the performance and stability of the neodymium iron boron magnet.

[0016] Further, the temperature of the annealing treatment is 400 - 600 °C, the time is 0.5 - 5 h, and the vacuum degree is lower than 10 - 3 Pa. The influence of the annealing treatment on the neodymium iron boron magnet is mainly reflected in the changes of the microstructure and magnetic properties. After annealing, the Nd-rich phase will be continuously and uniformly distributed at the grain boundaries of the main phase Nd 2 Fe 14 B grains. The main reason for annealing the neodymium iron boron magnet under vacuum is also to reduce the influence of oxidation reaction and impurities, thereby improving the performance and stability of the neodymium iron boron magnet.

[0017] The second object of the present invention is to provide a high-performance neodymium iron boron magnet prepared by the foregoing method.

[0018] The beneficial effects of the present invention are as follows: The present invention combines the grain boundary diffusion technology with the ultrasonic spraying process, which can not only improve the coating uniformity and thickness control accuracy of the coating formed on the surface of the neodymium iron boron magnet, but also improve the utilization rate of heavy rare earth elements, reduce the dosage of heavy rare earth elements, and obtain a high-performance neodymium iron boron magnet while reducing costs. Specific Embodiments

[0019] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0020] The neodymium iron boron magnets in the following examples and comparative examples are neodymium iron boron magnets processed and produced in the same batch, and their compositions are as follows: Nd 28%, Ce 13%, Ho 4%, Pr 2%, Co 1.5%, Al 1.2%, Cu 1%, B 1%, Ga 0.8%, and the balance is Fe and unavoidable impurities.

[0021] Example 1

[0022] S1. Dissolve Tb and Dy with a mass ratio of 1:1 in 50% nitric acid to obtain a solution.

[0023] S2. Spray the solution prepared in step S1 onto the surface of a sintered neodymium-iron-boron magnet through an ultrasonic spraying process. The frequency of ultrasonic spraying is 45 kHz, the power is 20 W, and the flow rate is 50 mL / min. After drying, a coating with a thickness of 10 μm is formed on the surface of the neodymium-iron-boron magnet.

[0024] S3. Carry out diffusion treatment and annealing treatment on the neodymium-iron-boron magnet with the coating prepared in step S2 under vacuum conditions. The temperature of the diffusion treatment is 1000 °C, the time is 5 h, and the vacuum degree is 10 -3 Pa, the temperature of the annealing treatment is 500 °C, the time is 3 h, and the vacuum degree is 5×10 -4 Pa.

[0025] Example 2

[0026] S1. Dissolve Tb, Dy, and Ho with a mass ratio of 1:1:1 in 50% nitric acid to obtain a solution.

[0027] S2. Spray the solution prepared in step S1 onto the surface of a sintered neodymium-iron-boron magnet through an ultrasonic spraying process. The frequency of ultrasonic spraying is 55 kHz, the power is 30 W, and the flow rate is 10 mL / min. After drying, a coating with a thickness of 10 μm is formed on the surface of the neodymium-iron-boron magnet.

[0028] S3. Carry out diffusion treatment and annealing treatment on the neodymium-iron-boron magnet with the coating prepared in step S2 under vacuum conditions. The temperature of the diffusion treatment is 950 °C, the time is 6 h, and the vacuum degree is 10 -3 Pa, the temperature of the annealing treatment is 400 °C, the time is 5 h, and the vacuum degree is 10 -4 Pa.

[0029] Example 3

[0030] S1. Dissolve Gd, Tb, Dy, and Ho with a mass ratio of 1:1:1:1 in 50% nitric acid to obtain a solution.

[0031] S2. Spray the solution prepared in step S1 onto the surface of a sintered neodymium-iron-boron magnet through an ultrasonic spraying process. The frequency of ultrasonic spraying is 40 kHz, the power is 50 W, and the flow rate is 20 mL / min. After drying, a coating with a thickness of 12 μm is formed on the surface of the neodymium-iron-boron magnet.

[0032] S3. Diffuse and anneal the NdFeB magnet with the coating prepared in step S2 under vacuum conditions. The temperature for the diffusion treatment is 900 °C, the time is 8 h, and the vacuum degree is 5×10 -3 Pa. The temperature for the annealing treatment is 600 °C, the time is 3 h, and the vacuum degree is 2×10 -4 Pa.

[0033] Example 4

[0034] S1. Dissolve Gd 2 O 3 and Tb 4 O 7 with a mass ratio of 1:1 in 50% nitric acid to obtain a solution.

[0035] S2. Spray the solution prepared in step S1 onto the surface of the sintered NdFeB magnet through an ultrasonic spraying process. The frequency of ultrasonic spraying is 60 kHz, the power is 100 W, and the flow rate is 40 mL / min. After drying, a coating with a thickness of 15 μm is formed on the surface of the NdFeB magnet.

[0036] S3. Diffuse and anneal the NdFeB magnet with the coating prepared in step S2 under vacuum conditions. The temperature for the diffusion treatment is 800 °C, the time is 10 h, and the vacuum degree is 2×10 -3 Pa. The temperature for the annealing treatment is 550 °C, the time is 4 h, and the vacuum degree is 10 -4 Pa.

[0037] Example 5

[0038] S1. Dissolve Tb 4 O 7 , Dy 2 O 3 and Ho 2 O 3 with a mass ratio of 1:1:1 in 50% nitric acid to obtain a solution.

[0039] S2. Spray the solution prepared in step S1 onto the surface of the sintered NdFeB magnet through an ultrasonic spraying process. The frequency of ultrasonic spraying is 50 kHz, the power is 80 W, and the flow rate is 80 mL / min. After drying, a coating with a thickness of 15 μm is formed on the surface of the NdFeB magnet.

[0040] S3. Diffuse and anneal the NdFeB magnet with the coating prepared in step S2 under vacuum conditions. The temperature for the diffusion treatment is 1000 °C, the time is 12 h, and the vacuum degree is 10 -3 Pa. The temperature for the annealing treatment is 500 °C, the time is 3 h, and the vacuum degree is 10 -4 Pa.

[0041] Comparative Example 1

[0042] Sintered NdFeB magnet without grain boundary diffusion.

[0043] The magnetic properties of the NdFeB magnets prepared in Examples 1 to 5 and Comparative Example 1 above were tested in accordance with GB / T 3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnet) Materials", and the test results are shown in Table 1.

[0044] Table 1

[0045] Br(T) Hcj (kOe) (BH)max (MGOe) Example 1 1.26 14.7 48.1 Example 2 1.30 14.2 49.3 Example 3 1.28 14.5 50.2 Example 4 1.26 15.1 50.9 Example 5 1.32 15.3 48.7 Comparative Example 1 1.39 12.4 41.5

[0046] As can be seen from Table 1, the NdFeB magnets prepared by the grain boundary diffusion technology of the present invention have excellent magnetic properties.

[0047] The present invention also provides a method for preparing a high-performance NdFeB magnet by using a grain boundary diffusion technology, comprising the following steps:

[0048] S1. Dissolve a diffusion source in a solvent to obtain a solution;

[0049] S2. Spray the solution prepared in step S1 onto the surface of the NdFeB magnet by an ultrasonic spraying process, and form a coating on the surface of the NdFeB magnet after drying;

[0050] S3. Perform diffusion treatment and annealing treatment on the NdFeB magnet with the coating prepared in step S2 under vacuum conditions;

[0051] S4. Uniformly coat an anticorrosive coating on the NdFeB magnet treated in step S3, and cure it into a film to form an anticorrosive coating on the surface of the NdFeB magnet.

[0052] Furthermore, the diffusion source is a heavy rare earth element or a heavy rare earth oxide. Among them, the heavy rare earth element is selected from one or more of gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and yttrium (Y). The heavy rare earth oxide is selected from gadolinium oxide (Gd 2 O 3 ), terbium oxide (Tb 4 O 7 ), dysprosium oxide (Dy 2 O 3 ), holmium oxide (Ho 2 O 3 ), erbium oxide (Er 2 O 3 ), thulium oxide (Tm 2 O 3 ), ytterbium oxide (Yb 2 O 3 ), lutetium oxide (Lu 2O 3 )), yttrium oxide (Y 2 O 3 )) or one or more of them.

[0053] Furthermore, the solvent is an inorganic acid. The mixing method of the diffusion source and the solvent can be mechanical stirring, magnetic stirring or ultrasonic treatment.

[0054] Furthermore, the NdFeB magnet is a sintered NdFeB magnet. In the present invention, the specific composition of the NdFeB magnet is not limited, as long as it is a NdFeB magnet (including sintered NdFeB magnets and bonded NdFeB magnets), the method described in the present invention can be used to prepare high-performance NdFeB magnets.

[0055] Furthermore, the frequency of the ultrasonic spraying is 40 - 60 kHz, the power is 10 - 100 W, and the flow rate is 1 - 100 mL / min. Compared with the commonly used surface coating methods in the art, ultrasonic spraying has the advantages of high coating uniformity, high raw material utilization rate, high coating thickness control accuracy, thinner coating thickness, less spatter, non-clogging of the nozzle, and low maintenance cost.

[0056] Furthermore, the temperature of the diffusion treatment is 800 - 1000 °C, the time is 1 - 12 h, and the vacuum degree is lower than 10 - 2 Pa. The grain boundary diffusion of NdFeB magnets refers to the migration of atoms on the grain boundaries at high temperatures, which leads to changes in the structure and properties of the grain boundary regions. The main reason for the grain boundary diffusion of NdFeB magnets to be carried out under vacuum is to reduce the influence of oxidation reactions and impurities, thereby improving the performance and stability of NdFeB magnets.

[0057] Furthermore, the temperature of the annealing treatment is 400 - 600 °C, the time is 0.5 - 5 h, and the vacuum degree is lower than 10 - 3 Pa. The influence of the annealing treatment on NdFeB magnets is mainly reflected in the changes in the microstructure and magnetic properties. After annealing, the Nd-rich phase will be continuously and uniformly distributed at the grain boundaries of the main phase Nd 2 Fe 14 B grains. The main reason for the NdFeB magnets to be annealed under vacuum is also to reduce the influence of oxidation reactions and impurities, thereby improving the performance and stability of NdFeB magnets.

[0058] Furthermore, the anticorrosive coating contains polyurethane-modified epoxy resin, curing agent and diluent. Among them, the mass ratio of the polyurethane-modified epoxy resin to the curing agent is 50:(10 - 30); the solid content of the anticorrosive coating is 30 - 50%.

[0059] Preferably, the diluent is an organic solvent commonly used in the art, including alcohol solvents, alcohol ether solvents, ketone solvents, ester solvents, etc.

[0060] Preferably, the synthesis method of the polyurethane-modified epoxy resin includes: heating and reacting bisphenol A epoxy resin, toluene diisocyanate dimer and an organotin catalyst, and adding polydimethylsiloxane capped with ε-caprolactone to continue the reaction after the reaction between bisphenol A epoxy resin and toluene diisocyanate is complete. Among them, the mass ratio of the bisphenol A epoxy resin, toluene diisocyanate dimer, and polydimethylsiloxane capped with ε-caprolactone is 50:(15 - 30):(5 - 20).

[0061] Example 6

[0062] The difference between Example 6 and Example 5 is only that the preparation of the anti-corrosion coating is added.

[0063] S1. Dissolve Tb 4 O 7 , Dy 2 O 3 and Ho 2 O 3 in 50% nitric acid to obtain a solution.

[0064] S2. Spray the solution prepared in step S1 onto the surface of the sintered neodymium iron boron magnet by an ultrasonic spraying process. The frequency of ultrasonic spraying is 50 kHz, the power is 80 W, and the flow rate is 80 mL / min. After drying, a coating with a thickness of 15 μm is formed on the surface of the neodymium iron boron magnet.

[0065] S3. Perform diffusion treatment and annealing treatment on the neodymium iron boron magnet with the coating prepared in step S2 under vacuum conditions. The temperature of the diffusion treatment is 1000 °C, the time is 12 h, and the vacuum degree is 10 -3 Pa. The temperature of the annealing treatment is 500 °C, the time is 3 h, and the vacuum degree is 10 -4 Pa.

[0066] S4. Uniformly coat the anti-corrosion coating on the neodymium iron boron magnet treated in step S3, and cure it into a film to form an anti-corrosion coating with a thickness of 30 μm on the surface of the neodymium iron boron magnet. Among them, the anti-corrosion coating contains polyurethane-modified epoxy resin, a curing agent, and ethanol.

[0067] The mass ratio of the polyurethane-modified epoxy resin to the curing agent is 50:20; the solid content of the anticorrosive coating is 30%; the synthesis method of the polyurethane-modified epoxy resin includes: heating 50 g of bisphenol A epoxy resin E51, 20 g of tolylene diisocyanate dimer and 0.05 g of dibutyltin dilaurate to 90 °C and reacting for 4 h. After the reaction of bisphenol A epoxy resin and tolylene diisocyanate is complete, 10 g of polydimethylsiloxane capped with caprolactone is added and the reaction continues at 90 °C for 2 h, and then cooled to room temperature to obtain the polyurethane-modified epoxy resin.

[0068] Example 7

[0069] The difference between Example 7 and Example 5 is only that the preparation of the anticorrosive coating is added.

[0070] S1. Dissolve Tb 4 O 7 , Dy 2 O 3 and Ho 2 O 3 with a mass ratio of 1:1:1 in 50% nitric acid to obtain a solution.

[0071] S2. Spray the solution prepared in step S1 onto the surface of the sintered neodymium iron boron magnet by an ultrasonic spraying process. The frequency of ultrasonic spraying is 50 kHz, the power is 80 W, and the flow rate is 80 mL / min. After drying, a coating with a thickness of 15 μm is formed on the surface of the neodymium iron boron magnet.

[0072] S3. Carry out diffusion treatment and annealing treatment on the neodymium iron boron magnet with the coating prepared in step S2 under vacuum conditions. The temperature of the diffusion treatment is 1000 °C, the time is 12 h, and the vacuum degree is 10 -3 Pa, and the temperature of the annealing treatment is 500 °C, the time is 3 h, and the vacuum degree is 10 -4 Pa.

[0073] S4. Uniformly coat the anticorrosive coating on the neodymium iron boron magnet treated in step S3 and cure it into a film to form an anticorrosive coating with a thickness of 35 μm on the surface of the neodymium iron boron magnet. Among them, the anticorrosive coating contains polyurethane-modified epoxy resin, curing agent and ethanol.

[0074] The mass ratio of the polyurethane-modified epoxy resin to the curing agent is 50:15; the solid content of the anticorrosive coating is 40%; the synthesis of the polyurethane-modified epoxy resin: heat 50 g of bisphenol A epoxy resin E51, 20 g of tolylene diisocyanate dimer and 0.05 g of dibutyltin dilaurate to 95 °C and react for 4 h. After the reaction of bisphenol A epoxy resin and tolylene diisocyanate is complete, 10 g of polydimethylsiloxane capped with caprolactone is added and the reaction continues at 95 °C for 1.5 h, and then cooled to room temperature to obtain the polyurethane-modified epoxy resin.

[0075] Comparative Example 2

[0076] The difference between Comparative Example 2 and Example 7 is only that polyethylene glycol 400 is used to replace the polydimethylsiloxane capped with caprolactone during the synthesis of the polyurethane-modified epoxy resin.

[0077] S1. Dissolve Tb 4 O 7 , Dy 2 O 3 and Ho 2 O 3 with a mass ratio of 1:1:1 in 50% nitric acid to obtain a solution.

[0078] S2. Spray the solution prepared in step S1 onto the surface of the sintered neodymium iron boron magnet through an ultrasonic spraying process. The frequency of ultrasonic spraying is 50 kHz, the power is 80 W, and the flow rate is 80 mL / min. After drying, a coating with a thickness of 15 μm is formed on the surface of the neodymium iron boron magnet.

[0079] S3. Carry out diffusion treatment and annealing treatment on the neodymium iron boron magnet with the coating prepared in step S2 under vacuum conditions. The temperature of the diffusion treatment is 1000 °C, the time is 12 h, and the vacuum degree is 10 -3 Pa, and the temperature of the annealing treatment is 500 °C, the time is 3 h, and the vacuum degree is 10 -4 Pa.

[0080] S4. Uniformly coat the anti-corrosion coating on the neodymium iron boron magnet treated in step S3 and cure it into a film to form an anti-corrosion coating with a thickness of 35 μm on the surface of the neodymium iron boron magnet. Among them, the anti-corrosion coating contains polyurethane-modified epoxy resin, curing agent and ethanol.

[0081] The mass ratio of the polyurethane-modified epoxy resin to the curing agent is 50:15; the solid content of the anti-corrosion coating is 40%; Synthesis of the polyurethane-modified epoxy resin: Heat 50 g of bisphenol A epoxy resin E51, 20 g of toluene diisocyanate dimer and 0.05 g of dibutyltin dilaurate to 95 °C and react for 4 h. After the reaction between bisphenol A epoxy resin and toluene diisocyanate is complete, add 10 g of polyethylene glycol 400 and continue to react at 95 °C for 1.5 h, and then cool to room temperature to obtain the polyurethane-modified epoxy resin.

[0082] Perform anti-corrosion performance tests on the anti-corrosion coatings prepared in the above Examples 5-7 and Comparative Example 2. The test results are the tolerance time when the coatings do not show blistering, cracking, peeling, or rusting phenomena, as shown in Table 2.

[0083] Test the acid resistance (50 g / L sulfuric acid solution) and alkali resistance (50 g / L sodium hydroxide solution) of the coating according to the immersion method of GB / T 9274-1988;

[0084] The salt spray resistance of the coating was tested in accordance with GB / T 1771-2007.

[0085] Table 2

[0086] Acid resistance (h) Alkali resistance (h) Salt spray resistance (h) Example 5 ＜12 ＜100 ＜500 Example 6 42 180 1300 Example 7 42 180 1300 Comparative Example 2 36 168 1200

[0087] As can be seen from Table 2, the polyurethane-modified epoxy resin synthesized in the present invention can endow the coating with excellent corrosion resistance, thereby improving the corrosion resistance of the coating prepared from the coating on the surface of the neodymium iron boron magnet.

[0088] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-performance NdFeB magnets using grain boundary diffusion technology, characterized in that: The following steps are involved: S1, dissolving the diffusion source in a solvent to obtain a solution; S2, spraying the solution prepared in step S1 on the surface of the NdFeB magnet by an ultrasonic spraying process, and forming a coating on the surface of the NdFeB magnet after drying; S3, subjecting the NdFeB magnet with coating prepared in step S2 to diffusion treatment and annealing treatment under vacuum conditions.

2. The method according to claim 1, characterized in that: The diffusion source is a heavy rare earth element or a heavy rare earth oxide.

3. The method according to claim 2, characterized in that: The heavy rare earth element is one or more of Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y.

4. The method according to claim 2, characterized in that: The heavy rare earth oxide is one or more of Gd2O3, Tb4O7, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3, and Y2O3.

5. The method according to claim 1, characterized in that: The solvent is an inorganic acid.

6. The method according to claim 1, characterized in that: The NdFeB magnet is a sintered NdFeB magnet.

7. The method according to claim 1, characterized in that: The frequency of the ultrasonic spraying is 40-60kHz, the power is 10-100W, and the flow rate is 1-100mL / min.

8. The method according to claim 1, characterized in that: The diffusion treatment temperature is 800-1000°C, the time is 1-12 hours, and the vacuum degree is less than 10 -2 Pa.

9. The method according to claim 1, characterized in that: The annealing treatment temperature is 400-600°C, the time is 0.5-5h, and the vacuum degree is less than 10 -3 Pa.

10. A high performance NdFeB magnet prepared by the method according to any one of claims 1 to 9.