A method for modifying the surface of rapidly quenched neodymium-iron-boron magnetic powder by environmentally friendly surface composite treatment

Abstract

This invention relates to the field of rare earth permanent magnet materials technology, and discloses an environmentally friendly surface composite modification method for rapidly quenched NdFeB magnetic powder. The method includes preparing low-oxygen, highly active magnetic powder using a dynamic vacuum rapid quenching process, inducing spontaneous film formation of rare earth cerium salts at room temperature, and using rare earth cerium salts and silane coupling agents as core processing raw materials, completely eliminating the use of hexavalent chromium, trivalent chromium, and phosphating solutions. This invention constructs a nanoscale passivation film by controlling the film formation rate, exhibiting excellent magnetic property retention. The passivation film layer possesses a redox cycle mechanism of trivalent and tetravalent cerium, enabling self-repair of film damage. An integrated double-layer composite protective structure is formed through cerium-oxygen-silicon chemical bonding, resulting in excellent corrosion resistance. The strong cerium-oxygen-neodymium chemical bond formed by cerium and neodymium, both rare earth elements, provides excellent interfacial bonding. The addition of cobalt and zirconium to the master alloy, synergistically with the surface modification process, comprehensively optimizes the high-temperature stability, corrosion resistance, and magnetic properties of the magnetic powder.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet materials technology, specifically to an environmentally friendly surface composite modification treatment method for rapidly quenched NdFeB magnetic powder. Background Technology

[0002] Neodymium iron boron (Nd-Fe-B) permanent magnets are widely used in new energy, energy-saving home appliances, and precision medical fields due to their excellent magnetic properties. However, rapidly quenched Nd-Fe-B magnetic powder contains a highly chemically active Nd-rich phase with a large specific surface area, making it extremely prone to oxidation in humid air, leading to a significant decay in magnetic properties.

[0003] Currently, traditional surface modification technologies still have certain limitations in practical applications, mainly in terms of environmental friendliness, energy consumption, magnetic performance loss, and protection mechanisms. Specifically, while hexavalent chromium passivation offers good protection, it is highly carcinogenic and strictly restricted by the RoHS directive; phosphating or conventional passivation processes typically require a heating environment of 40-90℃ and have a slow film formation rate of 20-60 minutes, resulting in high energy consumption and low efficiency; furthermore, the films formed by these methods are usually quite thick, 200-500 nm, which easily dilutes the magnetic energy product, leading to a magnetic performance loss that typically reaches 10-15%; simultaneously, existing films are mostly physical barriers, and once damaged, the exposed highly reactive substrate will rapidly undergo electrochemical corrosion, lacking self-healing capabilities.

[0004] To improve the performance of magnetic powder, patent document CN103578735B discloses a method for preparing flexible rubber NdFeB magnets, which improves the adhesion between magnetic powder and rubber through surface modification treatment; patent document CN117542641B discloses a method for preparing heat-resistant NdFeB magnets, which uses KH550 to modify the surface of magnetic powder. However, the above methods mainly focus on improving the interfacial bonding force or macroscopic dimensional stability between magnetic powder and the substrate, but there is still room for further improvement in terms of the environmental friendliness and energy efficiency of the surface modification process, the control of the protective layer thickness, and the durability of the protective effect. Conventional room temperature modification processes often fail to form a dense film due to insufficient reaction kinetics, making it difficult to achieve both low energy consumption and high protection.

[0005] Therefore, how to construct an ultra-thin, highly protective, and self-healing surface coating on the magnetic powder surface in situ while reducing process energy consumption is a technical challenge that the industry urgently needs to solve. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an environmentally friendly surface composite modification treatment method for rapidly quenched NdFeB magnetic powder.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides an environmentally friendly surface composite modification treatment method for rapidly quenched NdFeB magnetic powder, comprising the following steps:

[0009] S1: The rapidly quenched NdFeB magnetic powder is pretreated by degreasing and surface activation with dilute nitric acid. The rapidly quenched NdFeB magnetic powder is prepared by a dynamic vacuum rapid quenching process and has an oxygen content of less than 400 ppm.

[0010] S2: Immerse the pretreated magnetic powder in a passivation solution and react at 15℃~30℃ for 5min~20min to form a self-healing surface on the magnetic powder. Nanocomposite passivation film;

[0011] The passivation solution comprises: 10 g / L to 30 g / L cerium salt, 5 mL / L to 15 mL / L hydrogen peroxide, 5 g / L to 10 g / L complexing agent, 0.5 g / L to 2 g / L accelerator NaF, and a pH value of 3.0 to 5.0.

[0012] S3: The passivated magnetic powder is coated with a silane coupling agent to form an organic-inorganic composite protective layer.

[0013] S4: Curing and drying at 80℃~120℃ for 2h~4h.

[0014] Furthermore, the cerium salt is cerium nitrate or cerium chloride, and the complexing agent is citric acid or tartaric acid.

[0015] Further, in step S3, the silane coupling agent is one or both of KH560 and KH550, and a 1wt% to 5wt% silane coupling agent solution is used for coating treatment. The solution solvent is a mixture of ethanol and water in a volume ratio of 8:2 to 9:1, the solution pH value is 4.0 to 5.0, and the coating treatment time is 20 min to 40 min.

[0016] Furthermore, the dynamic vacuum rapid quenching process is as follows: rapid quenching is performed using a molybdenum roller with a linear velocity of 30m / s to 40m / s under an argon dynamic laminar flow protective atmosphere of 200Pa to 1330Pa; the alloy composition of the rapidly quenched NdFeB magnetic powder is: Co1 is wt% to 3wt%, Zr is 0.2wt% to 0.5wt%, and the balance is Nd, B and Fe.

[0017] Furthermore, in step S1, the degreasing pretreatment uses an alkaline degreasing agent, and the degreasing solution formula is: NaOH at 5g / L to 10g / L. The concentration of HNO3 solution is 10 g / L to 20 g / L, the concentration of surfactant OP-10 is 1 g / L to 2 g / L, the treatment temperature is 50℃ to 60℃, and the treatment time is 5 min to 10 min; for surface activation treatment with dilute nitric acid, a 5 wt% to 10 wt% HNO3 solution is used, the treatment temperature is room temperature, and the treatment time is 1 min to 3 min.

[0018] Furthermore, the passivation process in step S2 is performed with ultrasonic assistance at a frequency of 40 kHz.

[0019] Secondly, the present invention also provides an environmentally friendly fast-quenching NdFeB magnetic powder, prepared using the method described above. The magnetic powder surface has a double-layer composite coating structure, which, from the inside out, consists of: Nanocomposite passivation film, silane organic hybrid layer; wherein, the The thickness of the nanocomposite passivation film is 50nm to 200nm, and the porosity is less than 3% as determined by the BET surface area method; the thickness of the silane organic hybrid layer is 50nm to 100nm; the content of hexavalent chromium in the magnetic powder is less than 0.001wt%, and the content of phosphorus is less than 0.01wt%.

[0020] Furthermore, the passivation film of the magnetic powder has a self-healing function. After the film is scratched according to standard conditions, the repair rate is greater than 80% after 48 hours in an environment of 85℃ / 85%RH.

[0021] Thirdly, the present invention also provides an isotropic bonded NdFeB magnet, which is prepared by mixing the magnetic powder and the organic binder, wherein the volume fraction of the magnetic powder loading is 50-65% and the content of the organic binder is 8wt% to 15wt%.

[0022] Furthermore, the organic binder is one of epoxy resin, nylon 12, polyphenylene sulfide, or ethylene-vinyl acetate copolymer.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] This invention prepares low-oxygen, high-activity magnetic powder through a dynamic vacuum rapid quenching process, which induces rare earth cerium salts to spontaneously form films at room temperature without the need for heating activation, significantly reducing process energy consumption and improving production efficiency. Rare earth cerium salts and silane coupling agents are used as core processing raw materials, and hexavalent chromium, trivalent chromium, and phosphating solutions are completely avoided. The content of hexavalent chromium and phosphorus in the product is lower than the detection limit, which fully complies with international environmental regulations.

[0025] By precisely controlling the film formation rate through the concentration of citric acid complexing agent and pH, a nanoscale passivation film is constructed on the surface of magnetic powder, exhibiting excellent magnetic property retention. The constructed passivation film has a redox cycle mechanism of trivalent and tetravalent cerium, which can redeposit cerium dioxide at the damaged site to repair the film, effectively avoiding substrate corrosion after film damage and significantly extending the service life of magnetic powder.

[0026] Chemical anchoring of the inorganic passivation film and the organosilanes is achieved through cerium-oxygen-silicon chemical bonding, forming an integrated double-layer composite protective structure. This significantly improves the oxidation initiation temperature of the magnetic powder and enhances its corrosion resistance. Utilizing the fact that cerium and neodymium are both rare earth elements, a strong cerium-oxygen-neodymium chemical bond is formed at the magnetic powder interface, resulting in excellent interfacial adhesion and effectively preventing film detachment during subsequent magnetic powder processing. The addition of cobalt and zirconium to the master alloy further enhances the Curie temperature of the magnetic powder. Cobalt refines the grains and forms a zirconium oxide grain boundary barrier, working synergistically with the subsequent surface composite modification process. This comprehensive and synergistic optimization of the high-temperature stability, corrosion resistance, and magnetic properties of the magnetic powder is achieved. Attached Figure Description

[0027] Figure 1 This is a flowchart of a composite modification method for low-oxygen rapid quenching synergistic cerium salt room temperature passivation proposed in this invention;

[0028] Figure 2 This is a comparison diagram of the oxidation initiation temperature of the embodiments and comparative examples of the present invention;

[0029] Figure 3 This is a comparison diagram of the salt spray test lifespan of embodiments and comparative examples of the present invention;

[0030] Figure 4 This is a comparison chart of the magnetic property retention rates of embodiments and comparative examples of the present invention. Detailed Implementation

[0031] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0032] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0033] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0034] like Figures 1-4As shown, this invention provides a composite modification method for low-oxygen rapid quenching synergistic cerium salt room temperature passivation. The method is characterized by utilizing a low-oxygen, highly active magnetic powder interface prepared by a dynamic vacuum rapid quenching process to induce rare-earth cerium salt to spontaneously form a chemically bonded film with self-healing function at room temperature. The specific steps are as follows:

[0035] S1: The ingredients are formulated according to the following composition: Nd 12at%, B 6at%, Co 2wt%, Zr 0.3wt%, and Fe balance. The content is less than or equal to... Refined at 1480℃ in a vacuum induction melting furnace at 1330Pa, and rapidly quenched using a molybdenum roller (linear speed 35m / s) under dynamic laminar flow protection of argon at 1330Pa. By directionally replacing residual oxygen in the furnace, the average oxygen content of the rapidly quenched strip is controlled below 400ppm. It is then rapidly crystallized at 620℃ (heating rate 700℃ / min) and broken down to 150-250μm under nitrogen protection to maintain high active sites on the surface of the magnetic powder.

[0036] S2: NaOH concentration is 8g / L. The surface was treated with a 15 g / L solution and an OP-10 solution with a 1 g / L concentration at 60°C for 8 min to remove oil stains. Then, it was treated with 8 wt% dilute nitric acid at 25°C for 2 min to micro-etch and roughen the surface (Ra reaches 0.8-1.2 μm), exposing the highly active Nd-rich phase.

[0037] The magnetic powder is immersed in a passivation solution and reacted at 15-30℃ (preferably 25℃) for 5-20 minutes. The passivation solution contains: a main film-forming agent; (10-30 g / L); Oxidizing agent: (5-15 mL / L); Complexing agent: citric acid (5-10 g / L); Accelerator: NaF (0.5-2 g / L); pH value: 3.0-5.0. This step is performed through... Oxidation-reduction process to grow 50-200nm particles in situ on the surface of magnetic powder. Nanocomposite passivation film.

[0038] S3: Using a 2wt% KH560 silane coupling agent solution (ethanol / water = 9:1, pH = 4.5), the mixture is treated at room temperature for 30 min. The silane hydrolysis products are anchored to the hydroxyl groups on the passivation film surface through Ce-O-Si chemical bonds, forming a total coating layer of 150-300 nm.

[0039] S4: Curing with hot air circulation at 100℃ for 2 hours to promote complete silane polycondensation.

[0040] Example 1:

[0041] Weigh 100g of rapidly quenched NdFeB magnetic powder: commercial grade, particle size 150-250μm, oxygen content 450ppm. Place the magnetic powder in an alkaline degreasing solution with the following formula: NaOH 8g / L. The concentrations were 15 g / L for OP-10 and 1 g / L for OP-10. The mixture was mechanically stirred at 200 rpm for 8 min at 60 °C, washed with deionized water until neutral, and then vacuum dried at 60 °C for 30 min.

[0042] The dried magnetic powder was immersed in an 8wt% dilute nitric acid solution and gently stirred at 100 rpm for 2 minutes at 25°C. It was then quickly washed with deionized water, dried with nitrogen, and a passivation solution was prepared. 20g / L (30%) is 10 mL / L, citric acid is 8 g / L, NaF is 1 g / L, and the pH is adjusted to 4.0 with ammonia.

[0043] The activated magnetic powder was immersed in a passivation solution with a solid-liquid ratio of 1:8 (g / mL), treated with 40kHz ultrasound at 25℃ for 10 min, washed three times with deionized water, and vacuum dried at 60℃ for 30 min.

[0044] Preparation of silane solution: KH560 is 2wt%, solvent is ethanol / water mixture with a volume ratio of 9:1, pH is adjusted to 4.5 with acetic acid, and allowed to stand at room temperature for 30 min to mature. The passivated magnetic powder is immersed in the silane solution and gently stirred at 150 rpm at 25℃ for 30 min. It is then washed with deionized water and dried with hot air circulation at 100℃ for 2 h.

[0045] Performance test results: Cerium salt film thickness 120nm (TEM measurement), total coating thickness 180nm, oxidation onset temperature (DSC) 450℃, oxidation weight gain at 300℃ 0.32%, salt spray test (5% NaCl, 35℃) 132 hours, self-healing performance (after artificial scratch, 85℃ / 85%RH×48h) repair rate 82%, environmental protection testing... Not detected (<0.001wt%), P<0.01wt%, Magnetic properties (BH)max10.8MGOe (retention rate 98%).

[0046] Example 2:

[0047] Weigh 100g of rapidly quenched NdFeB magnetic powder: commercial grade, particle size 150-250μm, oxygen content 450ppm. Place the magnetic powder in an alkaline degreasing solution with the following formula: NaOH 8g / L. The concentrations were 15 g / L for OP-10 and 1 g / L for OP-10. The mixture was mechanically stirred at 200 rpm for 8 min at 60 °C, washed with deionized water until neutral, and then vacuum dried at 60 °C for 30 min.

[0048] The dried magnetic powder was immersed in an 8wt% dilute nitric acid solution and gently stirred at 100 rpm for 2 minutes at 25°C. It was then quickly washed with deionized water, dried with nitrogen, and a passivation solution was prepared. 15g / L 5g / L (30%) consists of 10 mL / L of citric acid, 8 g / L of NaF, and pH adjusted to 4.0 with ammonia.

[0049] The activated magnetic powder was immersed in a passivation solution with a solid-liquid ratio of 1:8 (g / mL), treated with 40kHz ultrasound at 25℃ for 10 min, washed three times with deionized water, and vacuum dried at 60℃ for 30 min.

[0050] Preparation of silane solution: KH560 is 2wt%, solvent is ethanol / water mixture with a volume ratio of 9:1, pH is adjusted to 4.5 with acetic acid, and allowed to stand at room temperature for 30 min to mature. The passivated magnetic powder is immersed in the silane solution and gently stirred at 150 rpm at 25℃ for 30 min. It is then washed with deionized water and dried with hot air circulation at 100℃ for 2 h.

[0051] Performance test results: The membrane density is improved, the porosity is <2%, the self-healing performance is maintained after 150 hours of salt spray testing (the repair rate is more than 80%), and the cost is reduced by about 15%.

[0052] Example 3:

[0053] The raw materials were weighed and proportioned according to the alloy composition: Nd 12 at%, B 6 at%, Co 2 wt%, Zr 0.3 wt%, and Fe balance, and then placed in a vacuum induction melting furnace. Refining is carried out at 1480℃ under vacuum, and electromagnetic stirring promotes uniform composition.

[0054] Molten alloy is sprayed onto the surface of a molybdenum roller through a quartz nozzle at a roller speed of 35 m / s. The argon pressure inside the furnace is 1330 Pa, with dynamic laminar flow protection. The thickness of the rapidly quenched strip is 28 μm, and the oxygen content is 350 ppm. The rapidly quenched strip is placed in a crystallization furnace and heated to 620 °C at a heating rate of 700 °C / min. It is held at that temperature for 10 min and then rapidly cooled under nitrogen protection.

[0055] The crystallized ribbons were crushed and sieved under nitrogen protection to obtain magnetic powder with a particle size of 180-220 μm. 100 g of the prepared magnetic powder was weighed and placed in an alkaline degreasing solution with the following formula: NaOH 8 g / L. The concentration of the powder was 15 g / L for OP-10 and 1 g / L for OP-10. The powder was mechanically stirred at 200 rpm for 8 min at 60 °C, washed with deionized water until neutral, and vacuum dried at 60 °C for 30 min. The dried magnetic powder was then immersed in an 8 wt% dilute nitric acid solution and gently stirred at 100 rpm for 2 min at 25 °C. The powder was then quickly washed with deionized water and dried with nitrogen.

[0056] Preparation of passivation solution: 20g / L (30%) is 10 mL / L, citric acid is 8 g / L, and NaF is 1 g / L. The pH is adjusted to 4.0 with ammonia. The activated magnetic powder is immersed in the passivation solution with a solid-liquid ratio of 1:8 (g / mL). It is treated with 40 kHz ultrasound at 25 °C for 10 min, washed with deionized water 3 times, and vacuum dried at 60 °C for 30 min.

[0057] Preparation of silane solution: KH560 is 2wt%, solvent is ethanol / water mixture with a volume ratio of 9:1, pH is adjusted to 4.5 with acetic acid, and allowed to stand at room temperature for 30 min to mature. The passivated magnetic powder is immersed in the silane solution and gently stirred at 150 rpm at 25℃ for 30 min. It is then washed with deionized water and dried with hot air circulation at 100℃ for 2 h.

[0058] Performance test results: Oxidation initiation temperature 480℃, oxidation weight gain rate at 300℃ 0.28%, oxidation weight gain rate at 500℃ 0.085%, salt spray test 168 hours, damp heat life (85℃ / 85%RH) 1800 hours, self-healing rate 85%, bonded magnet (BH) max 11.2 MGOe, demagnetization rate <0.1%.

[0059] Example 4:

[0060] Weigh 100g of rapidly quenched NdFeB magnetic powder (commercial grade, particle size 150-250μm, oxygen content 450ppm), and place the magnetic powder in an alkaline degreasing solution. The degreasing solution formula is: NaOH 8g / L. The concentrations were 15 g / L for OP-10 and 1 g / L for OP-10. The mixture was mechanically stirred at 200 rpm for 8 min at 60 °C, washed with deionized water until neutral, and then vacuum dried at 60 °C for 30 min.

[0061] The dried magnetic powder was immersed in an 8wt% dilute nitric acid solution and gently stirred at 100 rpm for 2 minutes at 25°C. It was then quickly washed with deionized water, dried with nitrogen, and a passivation solution was prepared. 0g / L (30%) consisted of 5 mL / L of citric acid, 5 g / L of NaF, and pH adjusted to 3.5 with ammonia. The activated magnetic powder was immersed in a passivation solution with a solid-liquid ratio of 1:8 (g / mL), treated with 40 kHz ultrasound at 25 °C for 5 min, washed three times with deionized water, and vacuum dried at 60 °C for 30 min.

[0062] Preparation of silane solution: KH560 is 2wt%, solvent is ethanol / water mixture with a volume ratio of 9:1, pH is adjusted to 4.5 with acetic acid, and allowed to stand at room temperature for 30 min to mature. The passivated magnetic powder is immersed in the silane solution and gently stirred at 150 rpm at 25℃ for 30 min. It is then washed with deionized water and dried with hot air circulation at 100℃ for 2 h.

[0063] Performance test results: Oxidation initiation temperature 420℃, salt spray test 108 hours.

[0064] Example 5:

[0065] Weigh 100g of rapidly quenched NdFeB magnetic powder: commercial grade, particle size 150-250μm, oxygen content 450ppm. Place the magnetic powder in an alkaline degreasing solution with the following formula: NaOH 8g / L. The concentrations were 15 g / L for OP-10 and 1 g / L for OP-10. The mixture was mechanically stirred at 200 rpm for 8 min at 60 °C, washed with deionized water until neutral, and then vacuum dried at 60 °C for 30 min.

[0066] The dried magnetic powder was immersed in an 8wt% dilute nitric acid solution and gently stirred at 100 rpm for 2 minutes at 25°C. It was then quickly washed with deionized water, dried with nitrogen, and a passivation solution was prepared. 20g / L (30%) consisted of 10 mL / L of citric acid, 8 g / L of NaF, and pH adjusted to 4.0 with ammonia. The activated magnetic powder was immersed in a passivation solution with a solid-liquid ratio of 1:8 (g / mL), treated with 40 kHz ultrasound at 25 °C for 10 min, washed three times with deionized water, and vacuum dried at 60 °C for 30 min.

[0067] Preparation of silane solution: KH560 is 2wt%, solvent is ethanol / water mixture with a volume ratio of 9:1, pH is adjusted to 4.5 with acetic acid, and allowed to stand at room temperature for 30 min to mature. The passivated magnetic powder is immersed in the silane solution and gently stirred at 150 rpm at 25℃ for 30 min. It is then washed with deionized water and dried with hot air circulation at 100℃ for 2 h.

[0068] Performance test results: Oxidation initiation temperature 450℃, salt spray test 132 hours.

[0069] Example 6:

[0070] Weigh 100g of rapidly quenched NdFeB magnetic powder: commercial grade, particle size 150-250μm, oxygen content 450ppm. Place the magnetic powder in an alkaline degreasing solution with the following formula: NaOH 8g / L. The concentrations were 15 g / L for OP-10 and 1 g / L for OP-10. The mixture was mechanically stirred at 200 rpm for 8 min at 60 °C, washed with deionized water until neutral, and then vacuum dried at 60 °C for 30 min.

[0071] The dried magnetic powder was immersed in an 8wt% dilute nitric acid solution and gently stirred at 100 rpm for 2 minutes at 25°C. It was then quickly washed with deionized water, dried with nitrogen, and a passivation solution was prepared. 30g / L (30%) was 15 mL / L, citric acid 10 g / L, and NaF 1 g / L, with the pH adjusted to 4.5 using ammonia. The activated magnetic powder was immersed in a passivation solution with a solid-liquid ratio of 1:8 (g / mL), and treated with 40 kHz ultrasound at 25 °C for 20 min. It was then washed three times with deionized water and vacuum dried at 60 °C for 30 min.

[0072] Preparation of silane solution: KH560 is 2wt%, solvent is ethanol / water mixture with a volume ratio of 9:1, pH is adjusted to 4.5 with acetic acid, and allowed to stand at room temperature for 30 min to mature. The passivated magnetic powder is immersed in the silane solution and gently stirred at 150 rpm at 25℃ for 30 min. It is then washed with deionized water and dried with hot air circulation at 100℃ for 2 h.

[0073] Performance test results: Oxidation initiation temperature 455℃.

[0074] Comparative Example 1:

[0075] Weigh 100g of rapidly quenched NdFeB magnetic powder: commercial grade, particle size 150-250μm, oxygen content 450ppm. Place the magnetic powder in an alkaline degreasing solution with the following formula: NaOH 8g / L. The concentrations were 15 g / L for OP-10 and 1 g / L for OP-10. The mixture was mechanically stirred at 200 rpm for 8 min at 60 °C, washed with deionized water until neutral, and then vacuum dried at 60 °C for 30 min.

[0076] The dried magnetic powder was immersed in an 8 wt% dilute nitric acid solution and gently stirred at 100 rpm for 2 minutes at 25°C. It was then quickly rinsed with deionized water, dried with nitrogen, and a chromate passivation solution was prepared. 5g / L The concentration is 10 g / L, and the pH is adjusted to 2.0 with dilute nitric acid.

[0077] The pretreated magnetic powder was immersed in a passivation solution with a solid-liquid ratio of 1:8 (g / mL), treated at 45℃ for 20 min, washed with deionized water, and dried without silane coating.

[0078] Performance test results: Oxidation initiation temperature 320℃, salt spray test 96h, magnetic property retention rate 94%, environmental protection test results. The content is 0.12wt%, which does not comply with the RoHS standard.

[0079] Comparative Example 2:

[0080] Weigh 100g of rapidly quenched NdFeB magnetic powder: commercial grade, particle size 150-250μm, oxygen content 450ppm. Place the magnetic powder in an alkaline degreasing solution with the following formula: NaOH 8g / L. The concentration of the sample was 15 g / L, and the concentration of OP−10 was 1 g / L. The sample was mechanically stirred at 200 rpm for 8 min at 60 °C, washed with deionized water until neutral, and then vacuum dried at 60 °C for 30 min.

[0081] The dried magnetic powder was immersed in an 8wt% dilute nitric acid solution and gently stirred at 100 rpm for 2 minutes at 25°C. It was then quickly washed with deionized water, dried under nitrogen, and a phosphating solution was prepared with ZnO concentrations of 1.2 g / L. 15g / L The concentration was 0.8 g / L. The pretreated magnetic powder was immersed in phosphating solution with a solid-liquid ratio of 1:8 (g / mL), treated at 60℃ for 20 min, washed with deionized water, and dried.

[0082] Performance test results: Oxidation initiation temperature 400℃, salt spray test 84h, magnetic property retention rate 90%, film thickness approximately 300nm.

[0083] Comparative Example 3:

[0084] Weigh 100g of rapidly quenched NdFeB magnetic powder: commercial grade, particle size 150-250μm, oxygen content 450ppm. Place the magnetic powder in an alkaline degreasing solution with the following formula: NaOH 8g / L. The concentrations were 15 g / L for OP-10 and 1 g / L for OP-10. The mixture was mechanically stirred at 200 rpm for 8 min at 60 °C, washed with deionized water until neutral, and then vacuum dried at 60 °C for 30 min.

[0085] The dried magnetic powder was immersed in an 8 wt% dilute nitric acid solution and gently stirred at 100 rpm for 2 min at 25°C. It was then quickly washed with deionized water, dried under nitrogen, and a silane solution was prepared: 2 wt% KH560 and a 9:1 volume ratio ethanol / water mixture as solvent. The pH was adjusted to 4.5 with acetic acid, and the mixture was allowed to stand at room temperature for 30 min to mature. The pretreated magnetic powder was then immersed in the silane solution and gently stirred at 150 rpm for 30 min at 25°C. It was then washed with deionized water and dried with hot air circulation at 100°C for 2 h.

[0086] Performance test results: Oxidation initiation temperature 300℃, salt spray test 48h, magnetic property retention rate 97%, no self-healing function.

[0087] Table 1 Comparison of process parameters and performance between the examples and comparative examples.

[0088] serial number Oxygen content of magnetic powder (ppm) Co / Zr microalloying passivation process Passivation temperature (°C) Passivation time (min) Silane coating Oxidation initiation temperature (°C) Salt spray test (h) Magnetic property retention rate (%) Self-repair rate (%) Environmental compliance Example 1 450 none Cerium salt passivation (Ce 20 g / L) 25 10 have 450 132 98 82 conform to Example 2 450 none Ce-La composite salt passivation 25 10 have — 150 — Keep conform to Example 3 350 Co 2wt%, Zr 0.3wt% Cerium salt passivation (Ce 20 g / L) 25 10 have 480 168 98 and above 85 conform to Example 4 450 none Cerium salt passivation (Ce 10 g / L) 25 5 have 420 108 — — conform to Example 5 450 none Cerium salt passivation (Ce 20 g / L) 25 10 have 450 132 — — conform to Example 6 450 none Cerium salt passivation (Ce 30 g / L) 25 20 have 455 — — — conform to Comparative Example 1 450 none Chromate passivation 45 20 none 320 96 94 none Does not meet Comparative Example 2 450 none Phosphating 60 20 none 400 84 90 none Phosphorus Comparative Example 3 450 none none — — have 300 48 97 none conform to

[0089] It should be noted that this invention prepares low-oxygen, highly active magnetic powder through a dynamic vacuum rapid quenching process, and combines rare-earth cerium salt room-temperature passivation with silane coupling agent coating treatment to construct an integrated double-layer composite protective structure with self-healing function. Compared with traditional surface modification techniques, this invention completely avoids the use of hexavalent chromium, trivalent chromium, and phosphating solutions, complying with international environmental regulations. Through the synergistic effect of front-end low-oxygen rapid quenching and back-end room-temperature film formation, process energy consumption is significantly reduced and production efficiency is improved. Utilizing the characteristic that cerium and neodymium are both rare-earth elements, a strong chemical bond is formed at the interface, and the self-repair of film damage is achieved by combining the redox cycle mechanism of trivalent and tetravalent cerium, significantly extending the service life of the magnetic powder. By adding cobalt and zirconium elements to the master alloy, in synergy with the surface modification process, the high-temperature stability, corrosion resistance, and magnetic properties of the magnetic powder are comprehensively optimized. Its application in the preparation of isotropic bonded magnets can meet the demand for high-performance neodymium iron boron magnets in high-end application fields.

[0090] The foregoing 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 to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for environmentally friendly surface composite modification treatment of rapidly quenched NdFeB magnetic powder, characterized in that, Includes the following steps: S1: The rapidly quenched NdFeB magnetic powder is pretreated by degreasing and surface activation with dilute nitric acid. The rapidly quenched NdFeB magnetic powder is prepared by dynamic vacuum rapid quenching process and has an oxygen content of less than 400 ppm. S2: Immerse the pretreated magnetic powder in a passivation solution and react at 15℃~30℃ for 5min~20min to form a self-healing surface on the magnetic powder. Nanocomposite passivation film; The passivation solution comprises: 10 g / L to 30 g / L cerium salt, 5 mL / L to 15 mL / L hydrogen peroxide, 5 g / L to 10 g / L complexing agent, 0.5 g / L to 2 g / L accelerator NaF, and a pH value of 3.0 to 5.

0. S3: The passivated magnetic powder is coated with a silane coupling agent to form an organic-inorganic composite protective layer. S4: Curing and drying at 80℃~120℃ for 2h~4h.

2. The environmentally friendly surface composite modification treatment method for rapidly quenched NdFeB magnetic powder according to claim 1, characterized in that, The cerium salt is cerium nitrate or cerium chloride, and the complexing agent is citric acid or tartaric acid.

3. The environmentally friendly surface composite modification treatment method for rapidly quenched NdFeB magnetic powder according to claim 1, characterized in that, In step S3, the silane coupling agent is one or both of KH560 and KH550. A 1wt% to 5wt% silane coupling agent solution is used for coating treatment. The solution solvent is a mixture of ethanol and water in a volume ratio of 8:2 to 9:

1. The solution pH value is 4.0 to 5.

0. The coating treatment time is 20 min to 40 min.

4. The environmentally friendly surface composite modification treatment method for rapidly quenched NdFeB magnetic powder according to claim 1, characterized in that, The dynamic vacuum rapid quenching process is as follows: rapid quenching is performed using a molybdenum roller with a linear velocity of 30m / s to 40m / s under an argon dynamic laminar flow protective atmosphere of 200Pa to 1330Pa; the alloy composition of the rapidly quenched NdFeB magnetic powder is: Co1 is wt% to 3wt%, Zr is 0.2wt% to 0.5wt%, and the balance is Nd, B and Fe.

5. The environmentally friendly surface composite modification treatment method for rapidly quenched NdFeB magnetic powder according to claim 1, characterized in that, In step S1, the degreasing pretreatment uses an alkaline degreasing agent, and the degreasing solution formula is: NaOH at 5g / L to 10g / L. The concentration of HNO3 solution is 10 g / L to 20 g / L, the concentration of surfactant OP-10 is 1 g / L to 2 g / L, the treatment temperature is 50℃ to 60℃, and the treatment time is 5 min to 10 min; for surface activation treatment with dilute nitric acid, a 5 wt% to 10 wt% HNO3 solution is used, the treatment temperature is room temperature, and the treatment time is 1 min to 3 min.

6. The environmentally friendly surface composite modification treatment method for rapidly quenched NdFeB magnetic powder according to claim 1, characterized in that, The passivation process in step S2 is performed with ultrasonic assistance at a frequency of 40 kHz.

7. An environmentally friendly, rapidly quenched NdFeB magnetic powder, characterized in that, Prepared using the method described in any one of claims 1-6, the magnetic powder surface has a double-layer composite coating structure, which, from the inside out, consists of: Nanocomposite passivation film, silane organic hybrid layer; wherein, the The thickness of the nanocomposite passivation film is 50nm to 200nm, and the porosity is less than 3% as determined by the BET surface area method; the thickness of the silane organic hybrid layer is 50nm to 100nm; the content of hexavalent chromium in the magnetic powder is less than 0.001wt%, and the content of phosphorus is less than 0.01wt%.

8. The magnetic powder according to claim 7, characterized in that, The passivation film of the magnetic powder has a self-healing function. After the film is scratched according to standard, the repair rate is greater than 80% after 48 hours in an environment of 85℃ / 85%RH.

9. An isotropic bonded NdFeB magnet, characterized in that, It is prepared by mixing the magnetic powder as described in claim 7 or 8 with an organic binder, wherein the volume fraction of the magnetic powder loading is 50-65% and the content of the organic binder is 8wt% to 15wt%.

10. The isotropic bonded NdFeB magnet according to claim 9, characterized in that, The organic binder is one of epoxy resin, nylon 12, polyphenylene sulfide, or ethylene-vinyl acetate copolymer.

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