Composite flame-retardant heavy rare earth grain boundary diffusion source as well as preparation method and application thereof

Abstract

The invention provides a composite flame-retardant heavy rare earth grain boundary diffusion source and a preparation method and application thereof, the composite flame-retardant heavy rare earth grain boundary diffusion source comprises a heavy rare earth metal alloy, an organic diffusant and a composite flame retardant, and the heavy rare earth metal alloy is (LaaCe1-a) x (PrbNd1-b) y (DycTbdHoeGd1-c-d-e) zM1-x-y-z, the composite flame retardant comprises organophosphate and / or borate; the organic diffusant comprises one or more of alcohols, ketones and esters. According to the composite flame-retardant heavy rare earth grain boundary diffusion source, by optimizing a formula and a process, agglomeration of rare earth powder is effectively inhibited, safety is improved, meanwhile, uniformity and stability of magnet performance are guaranteed, and the technical problems that in an existing grain boundary diffusion process, heavy rare earth slurry is prone to agglomeration and flammable and explosive are solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of rare earth permanent magnet materials, and particularly relates to a composite flame-retardant heavy rare earth grain boundary diffusion source and a preparation method and application thereof. BACKGROUND

[0002] High-performance sintered neodymium-iron-boron (Nd-Fe-B) magnets are widely used in new energy vehicles, wind power generation, consumer electronics and industrial motors due to their excellent magnetic properties. With the increasing demand for magnet performance in modern industry, improving the coercivity (Hcj) of the magnet has become one of the key research directions. However, the coercivity of neodymium-iron-boron magnets is limited by its microstructure, especially in high-temperature environments, which is prone to demagnetization, limiting its application in high-end fields. In order to overcome this problem, the grain boundary diffusion (GBD) process is widely used, which significantly improves the coercivity by diffusing heavy rare earth elements (such as terbium Tb or dysprosium Dy) to the grain boundaries of the magnet, while reducing the amount of heavy rare earth elements and reducing production costs.

[0003] In the grain boundary diffusion process, heavy rare earth elements are usually prepared in the form of compounds (such as TbH3, DyH3) or oxides (such as Tb4O7, Dy2O3) into a slurry, coated on the surface of the magnet, and then through heat treatment to diffuse the rare earth elements along the grain boundaries. However, due to the high chemical activity of rare earth powders (especially hydrides), agglomeration easily occurs during slurry preparation and storage, forming local high concentration areas. This agglomeration not only affects the uniformity of diffusion and reduces the consistency of magnet performance, but more seriously, the agglomerated rare earth powders may cause severe oxidation reaction due to local overheating or friction during drying or sintering, leading to combustion or even explosion accidents. In recent years, there have been several safety accidents caused by improper handling of rare earth slurry at home and abroad, which has seriously threatened production safety and personnel health.

[0004] To solve this problem, researchers have tried to add flame retardants to the slurry to inhibit the agglomeration of rare earth powders and reduce the risk of combustion. The addition of flame retardants can improve the rheological properties of the slurry, reduce direct contact between particles, and thus reduce the probability of deflagration caused by friction or local heat accumulation. In addition, some flame retardants can also form a protective layer at high temperatures, delaying the oxidation reaction of rare earths, further improving the process safety. Currently, common flame retardants include organic phosphates, borates, aluminum hydroxide, etc., but their effects on slurry stability, diffusion efficiency and final magnet performance still need systematic research.

[0005] Therefore, developing an efficient and stable flame retardant system and optimizing its application in the grain boundary diffusion slurry is not only of great significance to improving the performance consistency of sintered Nd-Fe-B magnets, but also a key technical breakthrough to ensure the safety of industrial production. In the future, with the advancement of flame retardant technology, the grain boundary diffusion process is expected to achieve safe and efficient application in a wider range of fields, promoting the sustainable development of high-performance Nd-Fe-B magnets. SUMMARY

[0006] The technical problem to be solved by the present application is to overcome the deficiencies in the prior art and provide a composite flame-retardant heavy rare earth grain boundary diffusion source and a preparation method thereof. In order to solve the technical problems of easy agglomeration and easy explosion of heavy rare earth slurry in the existing grain boundary diffusion process, the present application optimizes the formula and process, effectively inhibits the agglomeration of rare earth powder, improves safety, and at the same time ensures the uniformity and stability of the magnet performance.

[0007] In order to solve the above technical problems, the present application provides a composite flame-retardant heavy rare earth grain boundary diffusion source, which comprises a heavy rare earth metal alloy, an organic diffusion agent and a composite flame retardant. The heavy rare earth metal alloy is (LaaCe1-a)x(PrbNd1-b)y(DycTbdHoeGd1-c-d-e)zM1-x-y-z, wherein 0≤a≤1, 0≤b≤1, 0≤c≤1, 0≤d≤1, 0≤e≤1; 0≤x≤1, 0≤y≤1, 0≤z≤1, and 0.2≤x+y+z≤1; M is any one or more of Al, Cu, Ga, In, Sn, Fe, Co and Zr. The composite flame retardant comprises an organic phosphate and / or a borate. The organic phosphate comprises one or more of ammonium polyphosphate, aluminum phosphate or triphenyl phosphate. The borate comprises one or more of hexagonal boron nitride, boric acid or zinc borate. The organic diffusion agent comprises one or more of alcohols, ketones and esters.

[0008] The composite flame-retardant heavy rare earth grain boundary diffusion source described above, further, the heavy rare earth metal alloy is pretreated with a silane coupling agent, and the silane coupling agent comprises one or more of KH550, KH900 and KH602.

[0009] The composite flame-retardant heavy rare earth grain boundary diffusion source described above, further, the mass ratio of the heavy rare earth metal alloy and the silane coupling agent is 1:0.02 to 1:0.06.

[0010] The composite flame-retardant heavy rare earth grain boundary diffusion source described above, further, the mass ratio of the heavy rare earth metal alloy, the organic dispersant and the composite flame retardant is 1:1:0.05 to 1:1.5:0.08; and / or, the mass ratio of the organic phosphate and the borate is 2.5:1 to 5:1.

[0011] Based on the same technical concept, the application also provides a preparation method of the composite flame-retardant heavy rare earth grain boundary diffusion source, which comprises the following steps: S1, mixing a composite flame retardant, a heavy rare earth metal alloy powder and an organic dispersant; S2, ball milling under the protection of argon to obtain a homogenized composite flame-retardant heavy rare earth grain boundary diffusion source.

[0012] The preparation method further comprises that the rotating speed of the ball milling is 100-500 r / min, and the ball milling time is 0.5-5 h.

[0013] The preparation method further comprises that the heavy rare earth metal alloy is pretreated, and the pretreatment method comprises the following steps: S1-1, dispersing and hydrolyzing a silane coupling agent in a solution containing water and ethanol to obtain a hydrolyzed silane coupling agent; and pulverizing a heavy rare earth metal alloy by airflow milling to obtain a heavy rare earth metal alloy powder; S1-2, spraying the hydrolyzed silane coupling agent onto the heavy rare earth metal alloy powder to form a hydrophobic protective film.

[0014] In S1-1, the molar ratio of the silane coupling agent, water and ethanol is 1:1:5-1:6:12, and the dispersing and hydrolyzing is specifically magnetic stirring at room temperature for 0.5-5 h. The average particle size of the heavy rare earth metal alloy powder is 1-10 μm.

[0015] Based on one general technical concept, the application provides an application of the composite flame-retardant heavy rare earth grain boundary diffusion source in preparing a neodymium-iron-boron magnet, wherein the composite flame-retardant heavy rare earth grain boundary diffusion source is coated on the surface of a sintered substrate of the neodymium-iron-boron to perform a grain boundary diffusion process treatment of a heavy rare earth alloy, so as to obtain the neodymium-iron-boron magnet.

[0016] The application further comprises the following steps in the grain boundary diffusion process treatment of the heavy rare earth alloy: S1, coating the composite flame-retardant heavy rare earth grain boundary diffusion source on the surface of a sintered substrate of the neodymium-iron-boron, drying at 80-120℃ for 3-15 min, and then performing heat treatment in a vacuum sintering furnace at a vacuum degree lower than 1.0×10 -3 Pa, a heat treatment temperature of 800-1020℃ and a heat treatment time of 10 h; S2, annealing at 450-600℃ for 2 h; S3, air cooling to room temperature to obtain a sintered sintered neodymium-iron-boron magnet.

[0017] Compared with the prior art, the application has the following advantages: (1) The present application provides a composite flame-retardant heavy rare earth grain boundary diffusion source. By introducing a composite flame-retardant system (organic phosphate-borate), a stable flame-retardant barrier is formed in the heavy rare earth grain boundary diffusion source. The organic phosphate (such as TPP) generates PO· free radicals at high temperature, which block the combustion chain reaction. The borate (such as zinc borate) melts into a glassy coating layer at high temperature, which insulates oxygen and inhibits the exothermic oxidation of rare earth, effectively reducing the risk of flammable and explosive slurry and improving production safety.

[0018] (2) The present application provides a composite flame-retardant heavy rare earth grain boundary diffusion source. The flame-retardant system is a composite flame retardant of organic phosphate (such as APP) and borate (such as boric acid). The decomposition products of the flame retardant (such as B2O3, P2O5) can form stable compounds with rare earth, without introducing harmful impurities. The remanence (Br) and maximum magnetic energy product ((BH)max) of the magnet have no significant difference compared with samples without adding flame retardant.

[0019] (3) The present application provides a composite flame-retardant heavy rare earth grain boundary diffusion source. Silane coupling agent (such as KH-550) is used to coat the heavy rare earth metal alloy powder, reducing the van der Waals force between particles and inhibiting agglomeration. The particle size distribution of the slurry can be controlled below 5 μm, improving the uniformity of diffusion and ensuring that the coercive force fluctuation range of the magnet after the diffusion process is reduced from ±10% to ±3%.

[0020] In addition to the purposes, features and advantages described above, the present application has other purposes, features and advantages. The present application will be further described below with reference to the accompanying drawings and tables. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings of the embodiments of the present application.

[0022] Figure 1 Preparation flow chart of the composite flame-retardant heavy rare earth grain boundary diffusion source. DETAILED DESCRIPTION

[0023] The present application will be further described below with reference to specific preferred embodiments, but the protection scope of the present application is not limited thereby. The materials, reagents and instruments used in the following examples can be obtained from commercial channels. The experimental methods in the following examples are conventional methods in the art, unless otherwise specified.

[0024] This invention provides a composite flame-retardant heavy rare earth grain boundary diffusion source, comprising a heavy rare earth metal alloy, an organic dispersant, and a composite flame retardant. The heavy rare earth metal alloy is (LaaCe1-a)x(PrbNd1-b)y(DycTbdHoeGd1-cde)zM1-xyz, where 0≤a≤1, 0≤b≤1, 0≤c≤1, 0≤d≤1, 0≤e≤1; 0≤x≤1, 0≤y≤1, 0≤z≤1, and 0.2≤x+y+z≤1; M is any one or more of Al, Cu, Ga, In, Sn, Fe, Co, and Zr. This invention combines the heavy rare earth metal alloy, organic dispersant, and composite flame retardant to achieve multiple performance optimizations. 1. Improved production safety: The introduced composite flame retardant forms a stable flame-retardant barrier in the heavy rare earth grain boundary diffusion source, effectively reducing the flammability and explosion risk of the slurry. 2. Optimized diffusion effect: Organic diffusing agents can improve the dispersion and uniformity of the diffusion source, promote the uniform distribution of rare earth elements, and enhance the flame-retardant synergy of the diffusion source. 3. Enhanced flame-retardant performance: Through the thermal barrier effect of the composite flame retardant, the thermal stability range of the material is broadened, which can effectively inhibit heat transfer and isolate oxygen contact, significantly improving the flame-retardant performance of the heavy rare earth grain boundary diffusion source and suppressing its tendency for high-temperature spontaneous combustion. 4. Synergistic mechanism of composite flame retardants: The classic synergistic system of organic phosphate esters and borates is adopted. Organic phosphate esters decompose at high temperatures to generate phosphoric acid substances, which can promote char formation and isolate oxygen; borates form a glassy coating layer at high temperatures, which can inhibit the exothermic oxidation of rare earth elements. This significantly improves the flame-retardant performance of the heavy rare earth grain boundary diffusion source and suppresses its tendency for high-temperature spontaneous combustion.

[0025] Furthermore, the composite flame retardant includes organophosphates and / or borates; the organophosphates include one or more of ammonium polyphosphate (APP), aluminum phosphate, or triphenyl phosphate (TPP); the borates include one or more of hexagonal boron nitride (h-BN), boric acid (H3BO3), or zinc borate. The organophosphates (such as TPP) decompose at high temperatures to generate PO· free radicals, blocking the combustion chain reaction. The borates (such as zinc borate) melt at high temperatures to form a glassy coating layer, isolating oxygen and inhibiting the exothermic oxidation of rare earth elements, effectively reducing the risk of flammability and explosion of the slurry and improving production safety. The decomposition products of the flame retardant (such as B2O3, P2O5) can form stable compounds with rare earth elements without introducing harmful impurities. The remanence (Br) and maximum energy product ((BH)max) of the magnet are not significantly different from those of the sample without added flame retardant.

[0026] Furthermore, organic diffusing agents include one or more of alcohols, ketones, and esters. The polar groups (hydroxyl, carbonyl, ester groups) in the molecules of alcohols (such as ethanol and glycerol), ketones (such as acetone and cyclohexanone), and esters (such as ethyl acetate and phthalates) can interact with the surface of heavy rare earth metal alloy particles (e.g., hydrogen bonding, dipole attraction), reducing van der Waals forces between particles, effectively dispersing agglomerated rare earth particles, and ensuring their uniform distribution in the diffusion source system. The nonpolar carbon chains of these organic compounds are well compatible with the organic phase (such as resins and adhesives) or matrix material (such as the organic coating on the surface of NdFeB magnets) in the diffusion source, reducing interfacial repulsion and allowing the diffusion source to uniformly adhere to the matrix surface or penetrate to the grain boundaries, providing a uniform "supply channel" for the subsequent diffusion of rare earth elements.

[0027] The aforementioned composite flame-retardant heavy rare earth grain boundary diffusion source further includes a pretreatment of the heavy rare earth metal alloy with a silane coupling agent, comprising one or more of KH550, KH900, and KH602. The silane coupling agent enhances the interfacial bonding force between the composite flame retardant and the heavy rare earth metal alloy powder, and generates a SiO2 protective film through high-temperature pyrolysis. This invention uses silane coupling agents such as KH550, KH900, and KH602 to coat the heavy rare earth metal alloy powder, reducing interparticle van der Waals forces, inhibiting agglomeration, controlling the slurry particle size distribution to below 5 μm, improving diffusion uniformity, and ensuring that the coercivity fluctuation range of the magnet after the diffusion process is reduced from ±10% to ±3%.

[0028] In the aforementioned composite flame-retardant heavy rare earth grain boundary diffusion source, the mass ratio of the heavy rare earth metal alloy to the silane coupling agent is further specified as 1:0.02 to 1:0.06. If this ratio is lower than 1:0.02, i.e., insufficient silane coupling agent, the interfacial bonding force between the heavy rare earth alloy and the matrix will decrease, diffusion efficiency will be reduced, alloy particles will easily agglomerate, and uniformity will deteriorate, thus affecting the grain boundary modification effect. If this ratio is higher than 1:0.06, i.e., excessive silane coupling agent, it will cause residue problems. Excessive unreacted coupling agent can form free substances, reducing the thermal stability of the material or introducing impurities.

[0029] The mass ratio of the heavy rare earth metal alloy, organic dispersant, and composite flame retardant is 1:1:0.05 to 1:1.5:0.08; and / or, if this ratio is lower than 1:1:0.05, i.e., insufficient organic dispersant, it will cause uneven dispersion, easy aggregation of alloy particles, uneven distribution of flame retardant, and lead to decreased flame retardant efficiency or local performance defects. If this ratio is higher than 1:1.5:0.08, i.e., excessive organic dispersant, it may affect processability (such as coating or diffusion processes) and even hinder the synergistic effect between flame retardant and alloy. Too little flame retardant (e.g., below 0.05) makes it difficult to achieve the expected flame retardant rating, increasing the flammability risk of the material. Too much flame retardant (e.g., above 0.08) may damage the material structure, leading to a decrease in mechanical properties, such as reduced strength or toughness. The mass ratio of the organic phosphate ester to borate is 2.5:1 to 5:1. If this ratio is lower than 2.5:1, i.e., the proportion of borate is too high, it can inhibit the gas-phase flame retardant effect of the organic phosphate ester and reduce the overall flame retardant efficiency. A ratio higher than 5:1, i.e., an excessively high proportion of organic phosphate esters, will lead to a decrease in the quality of the char layer (such as looseness) and weaken the flame-retardant effect of the condensed phase.

[0030] This invention also provides a method for preparing the above-mentioned composite flame-retardant heavy rare earth grain boundary diffusion source, the preparation method comprising the following steps: S1. Mix the composite flame retardant, heavy rare earth metal alloy powder, and organic dispersant; S2. Ball milling under argon protection to obtain a homogenized composite flame-retardant heavy rare earth grain boundary diffusion source.

[0031] This invention involves physically mixing a composite flame retardant, heavy rare earth metal alloy powder, and an organic solvent under a nitrogen protective atmosphere (mixing methods include, but are not limited to, a three-dimensional mixer) to form a homogenized composite flame retardant heavy rare earth grain boundary diffusion source. This process uses an inert gas environment to inhibit material oxidation and ensure uniform component dispersion.

[0032] In the above preparation method, the ball milling speed is 100-500 r / min and the ball milling time is 0.5-5 h.

[0033] Ball milling at excessively low speeds (<100 r / min) results in uneven mixing, making it difficult to break up particle agglomerates and leading to uneven component distribution. Furthermore, excessively low speeds result in low mixing efficiency, requiring significantly longer milling times to achieve homogenization. Ball milling at excessively high speeds (>500 r / min) over-fines the heavy rare earth alloy or flame retardant particles, causing a surge in specific surface area and making subsequent processes (such as diffusion) difficult to control. Ball milling for excessively short times (<0.5 h) leads to insufficient dispersion and incomplete homogenization of components, potentially resulting in flame retardant "island" agglomerations or uneven distribution of rare earth alloys. Ball milling for excessively long times (>5 h) can damage the material structure, causing lattice distortion or amorphization of heavy rare earth alloys, affecting subsequent diffusion kinetics. Organic flame retardants (such as phosphate esters) may degrade due to mechanical forces, reducing flame retardant efficiency.

[0034] The above-described preparation method further includes pretreatment of the heavy rare earth metal alloy, wherein the pretreatment method includes the following steps: S1-1. The silane coupling agent is dispersed and hydrolyzed in a solution containing water and ethanol to obtain the hydrolyzed silane coupling agent; the heavy rare earth metal alloy is pulverized by an air jet mill to obtain heavy rare earth metal alloy powder. S1-2, The hydrolyzed silane coupling agent is sprayed onto the heavy rare earth metal alloy powder to form a hydrophobic protective film.

[0035] There are many ways to coat the surface of a magnet substrate with a composite flame-retardant heavy rare earth grain boundary diffusion source, including spraying, dip coating, and screen printing. This invention preferably uses spraying, i.e., spraying the composite grain boundary diffusion source onto the magnet substrate surface using a spray gun. This invention does not impose a particular limitation on the weight of the sprayed diffusion source, which can be adjusted according to the shape and thickness of the magnet substrate. Preferably, the weight of the composite flame-retardant heavy rare earth grain boundary diffusion source in this invention is 1–5 wt% of the weight of the NdFeB sintered magnet substrate.

[0036] In the above preparation method, further, in step S1-1, the molar ratio of silane coupling agent, water, and ethanol is 1:1:5 to 1:6:12, and the dispersion and hydrolysis specifically involves magnetic stirring at room temperature for 0.5 to 5 hours. When this ratio is lower than 1:1:5, insufficient water may lead to incomplete hydrolysis, insufficient ethanol may reduce solubility, and the silane coupling agent may precipitate or disperse unevenly. When this ratio is higher than 1:6:12, excessive water may cause excessive condensation to form silanol gel, and excessive ethanol will dilute the reaction concentration. Magnetic stirring for less than 0.5 hours will result in insufficient coupling agent activity and incomplete hydrolysis. Magnetic stirring for more than 5 hours may cause excessive condensation of silanol to form -Si-O-Si- intermediates, increasing solution viscosity and even causing gelation.

[0037] The average particle size of the heavy rare earth metal alloy powder is 1–10 μm. The finer particle size facilitates uniform distribution of the powder within the organic dispersant and composite flame retardant in the composite flame-retardant heavy rare earth grain boundary diffusion source, reducing sedimentation. It also facilitates liquefaction of the powder during diffusion heat treatment, resulting in more uniform element diffusion and a better diffusion effect.

[0038] Based on a general technical concept, this invention provides an application of the composite flame-retardant heavy rare earth grain boundary diffusion source in the preparation of NdFeB magnets. The composite flame-retardant heavy rare earth grain boundary diffusion source is coated on the surface of a sintered NdFeB substrate and subjected to a grain boundary diffusion process of heavy rare earth alloys to obtain NdFeB magnets.

[0039] The grain boundary diffusion process for heavy rare earth alloys includes the following steps: (1) The composite flame-retardant heavy rare earth grain boundary diffusion source is coated on the surface of the sintered NdFeB substrate, dried at 80-120℃ for 3-15 min, and then sintered in a vacuum furnace at a vacuum degree lower than 1.0×10 -3 The heat treatment was carried out at a temperature of 800–1020℃ for 10 hours. (2) Anneal at 450-600℃ for 2 hours; (3) Cool to room temperature to obtain sintered NdFeB magnets.

[0040] Example 1 A composite flame-retardant heavy rare earth grain boundary diffusion source 1 of the present invention comprises 0.15g of silane coupling agent KH550 and 7.5g of heavy rare earth metal alloy powder TbH 3、 7.5g of organic dispersant, 0.32g of ammonium polyphosphate (APP) and 0.13g of boric acid.

[0041] The preparation method of the composite flame-retardant heavy rare earth grain boundary diffusion source includes the following steps: (1) Take 0.15g of silane coupling agent KH550 and disperse and hydrolyze it in water-ethanol solution. The molar ratio of silane coupling agent, water and ethanol is 1:3:8. Stir the reaction magnetically at room temperature for 2h until the hydrolysis is basically completed to obtain silane coupling agent solution.

[0042] (2) Spray 0.15g of silane coupling agent solution onto the surface of 7.5g of heavy rare earth metal alloy powder TbH3 (the mass ratio of heavy rare earth metal alloy powder to silane coupling agent is 1:0.02) to form a hydrophobic protective film and obtain pretreated heavy rare earth metal alloy powder TbH3.

[0043] (3) Mix 7.5g of pretreated heavy rare earth metal alloy powder TbH3 with 7.5g of organic dispersant and 0.45g of composite flame retardant (the mass ratio of TbH3, organic dispersant and composite flame retardant is 1:1:0.06), place in a ball mill jar, and ball mill for 2 hours (200 r / min) under inert gas (such as Ar) protection to ensure uniform coating. The composite flame retardant includes 0.32g of ammonium polyphosphate (APP) and 0.13g of boric acid (the ratio of ammonium polyphosphate and boric acid is 2.5:1).

[0044] Comparative Example 1 A composite flame-retardant heavy rare earth grain boundary diffusion source 2 of the present comparative example comprises 7.5g TbH3 heavy rare earth metal alloy powder and 7.5g organic diffusing agent.

[0045] Example 2 A composite flame-retardant heavy rare earth grain boundary diffusion source 3 of the present invention comprises 7.5g of heavy rare earth metal alloy powder Dy80Al20, 7.5g of organic diffusing agent, 0.32g of ammonium polyphosphate (APP) and 0.13g of boric acid.

[0046] The preparation process is described in [link to preparation process]. Figure 1 Specifically, it includes the following steps: (1) Take 0.15g of silane coupling agent KH602 and disperse and hydrolyze it in water-ethanol solution. The molar ratio of silane coupling agent, water and ethanol is 1:3:8. Stir the reaction magnetically at room temperature for 2h until the hydrolysis is basically completed to obtain silane coupling agent solution.

[0047] (2) Spray 0.15g of silane coupling agent solution onto the surface of 7.5g of heavy rare earth metal alloy powder Dy80Al20 (the mass ratio of heavy rare earth metal alloy powder to silane coupling agent is 1:0.02) to form a hydrophobic protective film and obtain pretreated heavy rare earth metal alloy powder Dy80Al20.

[0048] (3) Mix 7.5g of pretreated heavy rare earth metal alloy powder Dy80Al20 with 7.5g of organic dispersant and 0.45g of composite flame retardant (the mass ratio of TbH3, organic dispersant and composite flame retardant is 1:1:0.06), place in a ball mill jar, and ball mill for 2 hours (200 r / min) under inert gas (such as Ar) protection to ensure uniform coating. The composite flame retardant includes 0.32g of ammonium polyphosphate (APP) and 0.13g of zinc borate (the ratio of ammonium polyphosphate to zinc borate is 2.5:1).

[0049] Comparative Example 2 A composite flame-retardant heavy rare earth grain boundary diffusion source 4 of the present comparative example includes 7.5g of heavy rare earth metal alloy powder Dy80Al20 and 7.5g of organic diffusing agent.

[0050] Example 3 A composite flame-retardant heavy rare earth grain boundary diffusion source 5 of the present invention comprises 7.5g of heavy rare earth metal alloy powder Dy80Al20, 7.5g of organic diffusing agent, 0.32g of ammonium polyphosphate (APP) and 0.13g of boric acid.

[0051] The preparation process is described in [link to preparation process]. Figure 1 Specifically, it includes the following steps: (1) Take 0.3g of silane coupling agent KH900 and disperse and hydrolyze it in water-ethanol solution. The molar ratio of silane coupling agent, water and ethanol is 1:3:8. Stir the reaction magnetically at room temperature for 2h until the hydrolysis is basically completed to obtain silane coupling agent solution.

[0052] (2) Spray the silane coupling agent solution onto the surface of 10g of heavy rare earth metal alloy powder Dy78Al22 (the mass ratio of heavy rare earth metal alloy powder to silane coupling agent is 1:0.03) to form a hydrophobic protective film and obtain the pretreated heavy rare earth metal alloy powder Dy78Al22.

[0053] (3) Mix 10g of pretreated heavy rare earth metal alloy powder Dy78Al22 with 15g of organic dispersant and 0.5g of composite flame retardant (the ratio of heavy rare earth metal alloy powder Dy78Al22, organic dispersant and composite flame retardant is 1:1.5:0.05), put it into a ball mill jar, protect it with an inert gas (such as Ar), and ball mill for 2 hours (200 r / min) to ensure uniform coating. The composite flame retardant includes 0.40g of hexagonal boron nitride (h-BN) and 0.10g of zinc borate (the ratio of hexagonal boron nitride to zinc borate is 4:1).

[0054] Experiment 1: Investigating the stability of composite flame-retardant heavy rare earth grain boundary diffusion sources.

[0055] Examples 1 to 3, and the composite flame-retardant heavy rare earth grain boundary diffusion sources of Comparative Examples 1 and 2 were subjected to TG analysis. The stability results are listed in Table 1.

[0056] Table 1: Stability results of composite flame-retardant heavy rare earth grain boundary diffusion sources

[0057] The results in Table 1 show that, based on the stability comparison data of diffusion source 1 and diffusion source 2, the grain boundary diffusion source slurry without the addition of composite flame retardant exhibits spontaneous combustion, and TG analysis indicates that the magnet undergoes oxidation within the temperature range of room to 100℃. However, after adding the composite flame retardant, the spontaneous combustion of the slurry is effectively suppressed, and TG analysis shows that the magnet's weight gain is less than 1%. This demonstrates that the composite flame retardant can effectively prevent the spontaneous combustion of heavy metal grain boundary diffusion source slurry.

[0058] Example 4 The application of a composite flame-retardant heavy rare earth grain boundary diffusion source 1 to 5 in the preparation of ferromagnetic magnets, the application method includes the following steps: (1) 3wt% composite flame-retardant heavy rare earth grain boundary diffusion sources 1 to 5 were uniformly coated onto the surface of the sintered NdFeB substrate (pre-sintered magnet size Φ10*3mm) by spraying. The coating surface was perpendicular to the c-axis. The substrate was placed in an oven and dried at 100℃ for 3 to 15 minutes under a nitrogen atmosphere.

[0059] (2) Grain boundary diffusion of heavy rare earth alloys: heat treatment diffusion is carried out in a horizontal vacuum sintering furnace, and the required vacuum level needs to be lower than 1.0 × 10⁻⁶. -3 The heat treatment was carried out at 900℃ for 10 hours. After the heat treatment, annealing was performed at 520℃ for 2 hours. After the heating was completed, the magnets were air-cooled to room temperature to obtain high-performance sintered NdFeB magnets 1 to 5.

[0060] Experiment 2: Investigating the magnetic properties of iron-rich magnets.

[0061] The high-performance sintered NdFeB magnets 1 to 5 were subjected to this magnetic performance test, and the test results are listed in Table 2.

[0062]

[0063] The results in Table 2 show that by comparing the magnetic properties of magnets 1 and 2, and magnets 3 and 4 and 5, the increase in coercivity remained consistent before and after the addition of the composite flame retardant. This indicates that the composite flame retardant has good compatibility with the grain boundary diffusion source and will not affect the diffusion efficiency.

[0064] 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 composite flame-retardant heavy rare earth grain boundary diffusion source, characterized in that, The composite flame-retardant heavy rare earth grain boundary diffusion source comprises a heavy rare earth metal alloy, an organic diffusing agent, and a composite flame retardant. The heavy rare earth metal alloy is (La... a Ce 1-a ) x (Pr b Nd 1-b ) y (Dy c Tb d Ho e Gd 1-c-d-e ) z M 1-x-y-z , where 0≤a≤1, 0≤b≤1, 0≤c≤1, 0≤d≤1, 0≤e≤1; 0≤x≤1, 0≤y≤1, 0≤z≤1, and 0.2≤x+y+z≤1; M is any one or more of Al, Cu, Ga, In, Sn, Fe, Co, and Zr; The composite flame retardant includes organophosphates and / or borates; the organophosphates include one or more of ammonium polyphosphate, aluminum phosphate, or triphenyl phosphate; the borates include one or more of hexagonal boron nitride, boric acid, or zinc borate. The organic dispersant includes one or more of alcohols, ketones, and esters.

2. The composite flame-retardant heavy rare earth grain boundary diffusion source according to claim 1, characterized in that, The heavy rare earth metal alloy is pretreated with a silane coupling agent, which includes one or more of KH550, KH900, and KH602.

3. The composite flame-retardant heavy rare earth grain boundary diffusion source according to claim 2, characterized in that, The mass ratio of the heavy rare earth metal alloy to the silane coupling agent is 1:0.02 to 1:0.

06.

4. The composite flame-retardant heavy rare earth grain boundary diffusion source according to any one of claims 1 to 3, characterized in that, The mass ratio of the heavy rare earth metal alloy, organic dispersant and composite flame retardant is 1:1:0.05 to 1:1.5:0.08; and / or the mass ratio of the organic phosphate ester to borate is 2.5:1 to 5:

1.

5. A method for preparing a composite flame-retardant heavy rare earth grain boundary diffusion source according to any one of claims 1 to 4, characterized in that, The preparation method includes the following steps: S1. Mix the composite flame retardant, heavy rare earth metal alloy powder, and organic dispersant; S2. Ball milling under argon protection to obtain a homogenized composite flame-retardant heavy rare earth grain boundary diffusion source.

6. The preparation method according to claim 5, characterized in that, The ball milling speed is 100-500 r / min, and the milling time is 0.5-5 h.

7. The preparation method according to claim 5, characterized in that, The preparation method further includes pretreatment of the heavy rare earth metal alloy, the pretreatment method comprising the following steps: S1-1. The silane coupling agent is dispersed and hydrolyzed in a solution containing water and ethanol to obtain the hydrolyzed silane coupling agent; the heavy rare earth metal alloy is pulverized by an air jet mill to obtain heavy rare earth metal alloy powder. S1-2, The hydrolyzed silane coupling agent is sprayed onto the heavy rare earth metal alloy powder to form a hydrophobic protective film.

8. The preparation method according to claim 7, characterized in that, In S1-1, the molar ratio of silane coupling agent, water, and ethanol is 1:1:5 to 1:6:12, and the dispersion and hydrolysis are specifically carried out by magnetic stirring at room temperature for 0.5 to 5 hours. The average particle size of the heavy rare earth metal alloy powder is 1–10 μm.

9. The application of the composite flame-retardant heavy rare earth grain boundary diffusion source according to any one of claims 1 to 4 in the preparation of NdFeB magnets, characterized in that, A composite flame-retardant heavy rare earth grain boundary diffusion source was coated onto the surface of a sintered NdFeB matrix, and then subjected to a grain boundary diffusion process for heavy rare earth alloys to obtain NdFeB magnets.

10. The application according to claim 9, characterized in that, The grain boundary diffusion process of the heavy rare earth alloy includes the following steps: (1) The composite flame-retardant heavy rare earth grain boundary diffusion source is coated on the surface of the sintered NdFeB substrate, dried at 80-120℃ for 3-15 min, and then sintered in a vacuum furnace at a vacuum degree lower than 1.0×10 -3 The heat treatment was carried out at a temperature of 800–1020℃ for 10 hours. (2) Anneal at 450-600℃ for 2 hours; (3) Cool to room temperature to obtain sintered NdFeB magnets.

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