Hydrogen-resistant iron-based sintered rare earth permanent magnet material and preparation method thereof

Abstract

The application relates to the technical field of permanent magnet material preparation, in particular to a hydrogen-resistant iron-based sintered rare earth permanent magnet material and a preparation method thereof. The method comprises the following steps: pretreating a sintered rare earth iron-based permanent magnet, then immersing and coating the sintered rare earth iron-based permanent magnet in a boric acid ester / catechol modified polyorganosilazane coating solution to form a film, then spraying an acid micro-water liquid and a weak alkaline micro-water liquid in sequence, finally spraying an outer layer catalytic liquid containing a platinum catalyst and performing segmented heating and curing, so that a protective layer with gradually changed cross-linking density from inside to outside is formed on the surface of the magnet; the obtained material has high adhesion, low hygrothermal weight loss, low hydrogen environment weight gain rate and high neutral salt spray resistance, and is suitable for new energy automobile motor, wind power and servo motor fields.

Description

Technical Field

[0001] This invention relates to the field of permanent magnet material preparation technology, specifically to a hydrogen-resistant iron-based sintered rare earth permanent magnet material and its preparation method. Background Technology

[0002] Sintered neodymium iron boron (NdFeB) permanent magnets are widely used in new energy vehicles, wind power generation, rail transportation, and precision servo motors due to their excellent magnetic energy product. However, these magnets are highly chemically reactive and prone to corrosion failure in humid, hot, salt spray, and especially hydrogen-containing environments. Hydrogen atoms or molecules can rapidly penetrate into the magnet's interior along grain boundaries, reacting with the neodymium-rich phase to form hydrides. This leads to lattice expansion, increased internal stress, and consequently, surface pulverization, spalling, and irreversible magnetic performance degradation—a phenomenon known as "hydrogen embrittlement." Therefore, developing a surface protective layer with both high interfacial bonding strength and high hydrogen barrier capability is crucial for extending the service life of sintered NdFeB magnets in harsh hydrogen environments.

[0003] In existing technologies, surface protection for NdFeB magnets mainly employs methods such as electroplating (e.g., zinc plating, nickel plating), electroless plating (e.g., nickel-phosphorus plating), physical vapor deposition (e.g., aluminum plating), and organic or inorganic coatings (e.g., epoxy resin, silanization treatment). While electroplating and electroless plating offer good density, the plating process is prone to hydrogen embrittlement, and the significant difference in thermal expansion coefficients between the coating and the magnet substrate makes them susceptible to interfacial delamination under temperature cycling or mechanical impact. Organic coatings, such as epoxy resin, can provide a certain physical barrier, but their chemical bonding with the metal substrate is weak, and organic polymers themselves have a certain degree of hydrogen permeability, making it difficult to block hydrogen permeation in the long term. Ordinary silanization treatment can form a thin organic-inorganic hybrid film on the magnet surface, but due to the limited thickness of the silane layer (usually less than 1 μm) and the tendency to generate microcracks during curing shrinkage, these microcracks become rapid hydrogen diffusion channels, leading to premature coating failure.

[0004] In recent years, polysilazane precursors have attracted attention due to their ability to be converted into dense silica or silicon oxynitride ceramic layers. However, existing polysilazane coatings still have significant shortcomings in practical applications with NdFeB magnets: First, polysilazanes have limited chemical affinity for metal surfaces, and unmodified polysilazane coatings often exhibit low adhesion to the NdFeB substrate, easily leading to interfacial debonding under humid heat or hydrogen pressure. Second, polysilazanes release ammonia gas and undergo volume shrinkage during curing. If the coating is thick or the curing rate is too fast, shrinkage stress will cause microcracks or pinholes within the coating. These defects not only reduce the barrier properties of the coating itself but also become preferential pathways for hydrogen to penetrate into the substrate.

[0005] Furthermore, to improve adhesion, some studies have attempted to introduce silane coupling agents into polysilazane or pre-coat the magnet surface with a primer layer. However, this multi-layer stacking method not only increases process complexity and cost, but also creates weak points at the interfaces between different coatings, making it difficult to form a continuous transition structure from the substrate to the coating surface. In addition, simply increasing the coating thickness to improve hydrogen barrier performance can exacerbate curing shrinkage defects and reduce the magnet's heat dissipation efficiency, affecting the overall performance of the device. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose a hydrogen-resistant iron-based sintered rare earth permanent magnet material and its preparation method, so as to solve the problem that the surface protective layer of existing sintered NdFeB magnets is difficult to achieve both high interfacial bonding strength and high hydrogen barrier performance in hydrogen medium, and is prone to rapid decay of magnetic properties due to hydrogen permeation channels caused by micro-defects.

[0007] To achieve the above objectives, this invention provides a method for preparing hydrogen-resistant iron-based sintered rare-earth permanent magnet materials, comprising the following steps: (1) The iron-based sintered rare earth permanent magnet is pretreated to obtain a pretreated magnet; (2) The pretreated magnet was immersed in the borate ester / catechol modified polyorganosilazane coating solution, pulled into a film, and then leveled and dried to obtain a continuous wet film sample; (3) Acidic micro-aqueous solution and weakly alkaline micro-aqueous solution were sprayed onto the surface of the continuous wet film sample in sequence. After standing and drying, the intermediate treatment sample was obtained. (4) The outer catalytic liquid containing platinum catalyst is sprayed onto the surface of the membrane layer of the intermediate treatment sample, and after standing, heating and curing, and standing again, hydrogen-resistant iron-based sintered rare earth permanent magnet material is obtained.

[0008] Preferably, the iron-based sintered rare earth permanent magnet in step (1) comprises the following raw materials in parts by weight: 610-630 parts praseodymium-neodymium alloy, 19-21 parts metallic boron, 16-18 parts metallic cobalt, 2-3 parts electrolytic copper, 4-5 parts metallic aluminum, 3-4 parts metallic gallium and 1325-1345 parts electrolytic iron; Preferably, the iron-based sintered rare earth permanent magnet in step (1) is obtained by mixing and melting raw materials, casting them into ingots, crushing them to form magnetic powder, and finally pressing, sintering, and aging the magnetic powder.

[0009] Preferably, the melting temperature is 1500-1600℃.

[0010] Preferably, the magnetic powder has an average particle size of 3.8-4.2 μm.

[0011] Preferably, the magnetic field strength of the pressing molding is 1.5-2.0T.

[0012] Preferably, the pressure of the magnetic field orientation pressing during the pressing and molding process is 4-10 MPa.

[0013] Preferably, the sintering temperature is 1078-1082℃ and the sintering time is 1.8-2.2h.

[0014] Preferably, the aging treatment is a first-stage aging treatment performed by holding at 875-885℃ for 1.8-2.2 hours, followed by a second-stage aging treatment performed by holding at 515-525℃ for 1.8-2.2 hours.

[0015] Preferably, the pretreatment procedure in step (1) is as follows: cleaning, drying, sanding, and settling.

[0016] Preferably, the sanding is performed using 2000-mesh silicon carbide sandpaper.

[0017] Preferably, the static environment is maintained at 25°C and 45-55% relative humidity for 12-18 minutes.

[0018] Preferably, the surface roughness Ra of the pretreated magnet in step (1) is 0.15-0.25 μm.

[0019] Preferably, the preparation steps of the borate ester / catechol modified polyorganosilazane coating liquid in step (2) are as follows: 4-allyl catechol is dissolved in anhydrous toluene to form a first catechol precursor liquid; 4-allyl catechol, phenylboronic acid, anhydrous toluene and activated 4Å molecular sieve are stirred under dry nitrogen protection and then filtered to form a second catechol precursor liquid; then polyorganosilazane resin is dissolved in anhydrous xylene, and the first catechol precursor liquid and the second catechol precursor liquid are added sequentially under dry nitrogen protection. After cooling, platinum catalyst is added dropwise, and after keeping the reaction at a constant temperature, 1-ethynyl-1-cyclohexanol is added to terminate the reaction. The mixture is then diluted and filtered to obtain the final product. Preferably, based on 100 parts by weight of the pretreated magnet, the amounts of the polyorganosilazane resin, 4-allyl catechol in the first catechol precursor solution, 4-allyl catechol in the second catechol precursor solution, phenylboronic acid, platinum catalyst, and 1-ethynyl-1-cyclohexanol in step (2) are 38-42 parts, 0.65-0.75 parts, 0.25-0.35 parts, 0.22-0.26 parts, 0.05 parts, and 0.07-0.09 parts, respectively.

[0020] Preferably, the polyorganosilazane resin in step (2) is Durazane 1800.

[0021] Preferably, the acidic microaqueous solution in step (3) is obtained by dissolving glacial acetic acid in a mixed solution of anhydrous ethanol and deionized water; the weight ratio of glacial acetic acid to the mixed solution is 0.18-0.22:100.

[0022] Preferably, the weakly alkaline micro-aqueous solution in step (3) is obtained by dissolving ammonia in a mixed solution of anhydrous ethanol and deionized water; the weight ratio of ammonia to the mixed solution is 0.25-0.35:100.

[0023] Preferably, based on 100 parts by weight of the continuous wet film sample, the amounts of the acidic micro-aqueous solution and the weakly alkaline micro-aqueous solution used in step (3) are 0.09-0.11 parts and 0.05-0.07 parts, respectively.

[0024] Preferably, based on 100 parts by weight of the intermediate treatment sample, the amount of the outer catalytic liquid containing the platinum catalyst in step (4) is 0.09-0.11 parts.

[0025] Preferably, the outer catalytic liquid in step (4) is a platinum catalyst stock solution and anhydrous xylene in a weight ratio of 0.04-0.06:9.94-9.96. Preferably, the heating and curing in step (4) involves first maintaining the temperature at 118-122℃ for 18-22 minutes, and then maintaining the temperature at 148-152℃ for 28-32 minutes.

[0026] Preferably, in step (4), the object is kept in an environment at 25°C and relative humidity not exceeding 30% for 20-28 hours. Furthermore, the present invention also provides a hydrogen-resistant iron-based sintered rare earth permanent magnet material.

[0027] The beneficial effects of this invention are: This invention introduces two catechol sources onto the same polyorganosilazane resin backbone and combines time-sequential wet curing and delayed crosslinking processes to create a gradient structure in the protective layer with gradually changing chemical composition and crosslinking density from the inside out. This design allows the same coating liquid to have both immediate adhesion and post-reinforcement capabilities without introducing a second resin, significantly improving the interfacial contact quality in the early stages of film formation.

[0028] This invention first sprays an acidic micro-aqueous liquid after the wet film is formed, and then sprays a weakly alkaline micro-aqueous liquid, achieving an interface strengthening effect of first occupying sites and then reinforcing them. This dual-time sequence micro-aqueous path of "acid first, then alkali" is coupled with the release sequence of catechol sites, so that the coating exhibits a continuous transition from high bonding strength to high density from the inside to the outside, avoiding the through-cracks caused by the asynchronous shrinkage of the surface and inner layers under traditional single curing conditions.

[0029] In this invention, the platinum catalyst is introduced in a dilute solution form only after the entire wet curing process is completed. This delayed introduction causes the addition crosslinking reaction to mainly occur in the middle and outer layers of the coating, rather than the entire coating being crosslinked simultaneously, further reducing the hydrogen permeability.

[0030] This invention achieves simultaneous improvements in high interfacial bonding, low damp heat weight loss, excellent hydrogen environment stability, and extended neutral salt spray life using only a single modified polysilazane system without employing multiple independent coatings. This provides a reliable protection solution for the long-term service of sintered NdFeB magnets in hydrogen media. Attached Figure Description

[0031] Figure 1 This is a process flow diagram of a method for preparing hydrogen-resistant iron-based sintered rare earth permanent magnet materials provided by the present invention; Figure 2 This is a process flow diagram of the preparation steps of the borate ester / catechin modified polyorganosilazane coating liquid in this invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the following is combined with... Figure 1 and Figure 2 The present invention will be further described in detail below with reference to specific embodiments.

[0033] Raw material source: Durazane 1800, a polyorganosilazane resin, part number 214049.

[0034] Example 1: A method for preparing a hydrogen-resistant iron-based sintered rare-earth permanent magnet material, the specific steps of which are as follows: S1: Take 620g of praseodymium-neodymium alloy, 20g of metallic boron, 17g of metallic cobalt, 2g of electrolytic copper, 4g of metallic aluminum, 3g of metallic gallium, and 1334g of electrolytic iron. Melt them three times in a vacuum induction furnace under vacuum conditions not exceeding 5Pa and 1500℃, and then cast them into a master alloy ingot. The obtained master alloy is made into a fast-quenched thin strip using a conventional strip spinning process under a protective argon atmosphere. Then, it is coarsely crushed and air-jet ground to obtain magnetic powder with an average particle size of 4μm. The magnetic powder is pressed into shape in an orientation magnetic field and then cold isostatically shaped (1.5T, 4MPa). It is then sintered at 1080℃ for 2h, and then... The magnets underwent a two-stage aging process, first holding them at 880℃ for 2 hours and then at 520℃ for 2 hours. The resulting magnets were then cut into 20mm × 10mm × 3mm samples. The samples were first ultrasonically cleaned with 200g acetone for 5 minutes, then ultrasonically cleaned with 200g anhydrous ethanol for 5 minutes. After removal, they were dried with dry nitrogen gas. Subsequently, they were lightly ground in the same direction using 2000-mesh silicon carbide sandpaper to control the surface roughness within the range of Ra0.15-Ra0.25μm. Finally, the samples were placed in an environment of 25℃ and 50% relative humidity for 15 minutes to form pretreated samples for later use. S2: First, prepare a platinum catalyst stock solution by taking 0.1g of platinum(0)-1,3-divinyltetramethyldisiloxane complex and 0.9g of anhydrous xylene; then take 0.70g of 4-allyl catechol and 8g of anhydrous toluene, stir at 35℃ until completely dissolved to form the first catechol precursor solution, then take 0.30g of 4-allyl catechol, 0.24g of phenylboronic acid, 10g of anhydrous toluene and 2.00g of activated 4Å molecular sieve and add them to a 100mL round-bottom flask that has been dried at 120℃ for 2h and cooled to room temperature, stir at 45℃ for 30min under dry nitrogen protection, and filter while hot through a 0.45μm polytetrafluoroethylene filter membrane to form the second catechol precursor solution; then take 40g of polyorganosilazane resin Durazane 1800 g of anhydrous xylene and 80 g of acetal were added to a three-necked flask that had been dried at 120 °C for 2 h and cooled to room temperature. The mixture was stirred for 10 min under dry nitrogen protection with a dew point not exceeding -40 °C. First and second catechol precursor solutions were added sequentially, and the mixture was stirred for another 10 min and then cooled to 15 °C. Subsequently, 0.5 g of platinum catalyst stock solution was added dropwise over 5 min, and the mixture was kept at 15 °C for 30 min, then raised to 25 °C and kept at 20 min. Immediately afterwards, 0.08 g of 1-ethynyl-1-cyclohexanol was added and the mixture was stirred for another 10 min to terminate the low-grafting-degree grafting reaction. Then, 200 g of anhydrous xylene was added for dilution, and the mixture was stirred for another 10 min. The mixture was then filtered through a 0.45 μm polytetrafluoroethylene filter membrane to obtain a borate ester / catechin modified polyorganosilazane coating solution, which was used within 4 h under dry nitrogen protection. S3: Take 150g of the obtained borate ester / catechol modified polyorganosilazane coating liquid and place it in a dry dip coating tank. Take the pretreated magnet sample and immerse it completely for 30s. Then, pull it up at a uniform speed of 2mm / s. After pulling up, level it in a dry nitrogen environment at 25℃ and relative humidity not higher than 15% for 5min, and then keep it at 50℃ for 5min to obtain a continuous wet film sample. S4: Mix 95g of anhydrous ethanol, 5g of deionized water, and 200mg of glacial acetic acid to obtain an acidic micro-aqueous solution; mix 97g of anhydrous ethanol, 3g of deionized water, and 0.3g of ammonia (25wt%) to obtain a weakly alkaline micro-aqueous solution; after the surface temperature of the continuous wet film sample obtained in step S3 drops to 30℃~35℃, spray 0.1g of acidic micro-aqueous solution evenly onto the surface of the wet film sample using conventional atomization spraying method. After spraying, let it stand for 3min, and then maintain it at 80℃ for 10min under a dry nitrogen atmosphere; then cool the obtained sample to about 35℃, and spray 60mg of weakly alkaline micro-aqueous solution only onto the outer surface of the film layer of the same batch of samples using conventional atomization spraying method. After spraying, let it stand for 2min, and then maintain it at 80℃ for 5min under a dry nitrogen atmosphere to obtain an intermediate-treated sample; S5: Mix 0.05g of platinum catalyst stock solution and 9.95g of anhydrous xylene to obtain an outer catalyst solution; after cooling the sample obtained in S4 to below 40℃, spray 0.1g of the outer catalyst solution evenly onto the film surface using conventional atomization spraying method. After spraying, let it stand for 2min, then keep it at 120℃ for 20min and then at 150℃ for 30min under a dry nitrogen atmosphere. Finally, place the obtained sample in an environment of 25℃ and relative humidity not exceeding 30% for 24h to obtain hydrogen-resistant iron-based sintered rare earth permanent magnet material.

[0035] Example 2: A method for preparing a hydrogen-resistant iron-based sintered rare-earth permanent magnet material, the specific steps of which are as follows: S1: Take 610g of praseodymium-neodymium alloy, 19g of metallic boron, 16g of metallic cobalt, 2g of electrolytic copper, 4g of metallic aluminum, 3g of metallic gallium, and 1325g of electrolytic iron. Melt them three times in a vacuum induction furnace under vacuum conditions not exceeding 8Pa and 1550℃, and then cast them into a master alloy ingot. The obtained master alloy is processed into a rapid quenching thin strip using a conventional strip spinning process under a protective argon atmosphere. Then, it is coarsely crushed and air-jet milled to obtain magnetic powder with an average particle size of 3.8-4.2μm. The magnetic powder is pressed into shape in an orientation magnetic field and then cold isostatically shaped (2T, 6MPa), and sintered at 1078℃ for 1.8h. The samples were then subjected to a two-stage aging process, first held at 875℃ for 1.8 hours and then at 515℃ for 1.8 hours. Finally, they were cut into 20mm×10mm×3mm samples. The resulting magnet samples were first ultrasonically cleaned with 180g of acetone for 4 minutes, and then ultrasonically cleaned with 180g of anhydrous ethanol for 4 minutes. After removal, they were dried with dry nitrogen gas. Then, they were lightly ground in the same direction with 2000-mesh silicon carbide sandpaper to control the surface roughness within the range of Ra of 0.15-0.25μm. The samples were then placed in an environment of 25℃ and 45% relative humidity for 12 minutes to form pretreated samples for later use. S2: First, prepare a platinum catalyst stock solution by taking 0.10g of platinum(0)-1,3-divinyltetramethyldisiloxane complex and 0.90g of anhydrous xylene; then take 0.65g of 4-allyl catechol and 7g of anhydrous toluene, stir at 33℃ until completely dissolved to obtain the first catechol precursor solution; then take 0.25g of 4-allyl catechol, 0.22g of phenylboronic acid, 9g of anhydrous toluene and 1.8g of activated 4Å molecular sieve and add them to a round-bottom flask that has been dried at 120℃ for 2h and cooled to room temperature, stir at 43℃ for 25min under dry nitrogen protection, and filter while hot through a 0.45μm polytetrafluoroethylene filter membrane to obtain the second catechol precursor solution; then take 38g of polyorganosilazane resin Durazane 1800 g and 75 g of anhydrous xylene were added to a three-necked flask that had been dried at 120 °C for 2 h and cooled to room temperature. The mixture was stirred for 10 min under dry nitrogen protection with a dew point not higher than -40 °C. The first and second catechol precursor solutions were added sequentially, and the mixture was stirred for another 10 min and then cooled to 13 °C. 0.50 g of platinum catalyst stock solution was then added dropwise over 5 min, and the mixture was kept at 13 °C for 25-35 min, then raised to 23 °C and kept at 23 °C for 15 min. 0.07 g of 1-ethynyl-1-cyclohexanol was added immediately and the mixture was stirred for another 10 min to terminate the low-grafting-degree grafting reaction. 190 g of anhydrous xylene was then added for dilution, and the mixture was stirred for another 10 min. The mixture was then filtered through a 0.45 μm polytetrafluoroethylene membrane to obtain a borate ester / catechin modified polyorganosilazane coating solution. This solution was used within 4 h under dry nitrogen protection to obtain a continuous wet film sample. S3: Place 145g of borate ester / catechol modified polyorganosilazane coating liquid in a dry dip coating tank, immerse 100g of the obtained pretreated magnet sample in the tank for 25s, and then pull it up at a uniform speed of 1.8mm / s. After pulling up, level it in a dry nitrogen environment at 25℃ and relative humidity not higher than 15% for 4min, and then keep it at 48℃ for 4min to make the wet film continuous, thus obtaining a continuous wet film sample. S4: Mix 94g of anhydrous ethanol, 6g of deionized water, and 0.18g of glacial acetic acid to obtain an acidic micro-aqueous solution; mix 96g of anhydrous ethanol, 4g of deionized water, and 0.25g of ammonia (25wt%) to obtain a weakly alkaline micro-aqueous solution; after the surface temperature of the continuous wet film sample obtained in step S3 drops to 30℃, spray 0.09g of acidic micro-aqueous solution evenly onto the surface of the wet film sample using conventional atomization spraying method. After spraying, let it stand for 2 minutes, and then maintain it at 78℃ for 8 minutes under a dry nitrogen atmosphere; then cool the obtained sample to about 35℃, and spray 0.05g of weakly alkaline micro-aqueous solution only onto the outer surface of the film layer of the same batch of samples using conventional atomization spraying method. After spraying, let it stand for 1 minute, and then maintain it at 78℃ for 4 minutes under a dry nitrogen atmosphere to obtain an intermediate-treated sample; S5: Mix 0.04g of platinum catalyst stock solution and 9.96g of anhydrous xylene to obtain an outer catalyst solution; after cooling the sample obtained in step S4 to below 40℃, spray 0.09g of the outer catalyst solution evenly onto the film surface using conventional atomization spraying method. After spraying, let it stand for 1min, and then keep it at 118℃ for 18min and then at 148℃ for 28min under a dry nitrogen atmosphere. Finally, place the obtained sample in an environment of 25℃ and relative humidity not exceeding 30% for 20h to obtain hydrogen-resistant iron-based sintered rare earth permanent magnet material.

[0036] Example 3: A method for preparing a hydrogen-resistant iron-based sintered rare-earth permanent magnet material, the specific steps of which are as follows: S1: Take 630g of praseodymium-neodymium alloy, 21g of metallic boron, 18g of metallic cobalt, 3g of electrolytic copper, 5g of metallic aluminum, 4g of metallic gallium, and 1345g of electrolytic iron. Melt them three times in a vacuum induction furnace under vacuum conditions not exceeding 8Pa and 1600℃, and then cast them into a master alloy ingot. The obtained master alloy is then processed into a rapid-quenching thin strip using a conventional strip spinning process under a protective argon atmosphere. After coarse crushing and air jet milling, magnetic powder with an average particle size of 3.8-4.2μm is obtained. The magnetic powder is pressed into shape in an orientation magnetic field and then cold isostatically shaped (2T, 10MPa), and sintered at 1082℃ for 2.2h. The samples were then subjected to a two-stage aging process, first at 885℃ for 2.2 hours and then at 525℃ for 2.2 hours. Finally, they were cut into 20mm×10mm×3mm samples. The resulting magnet samples were first ultrasonically cleaned with 220g acetone for 6 minutes, and then ultrasonically cleaned with 220g anhydrous ethanol for 6 minutes. After removal, they were dried with dry nitrogen gas. Then, they were lightly ground in the same direction with 2000-mesh silicon carbide sandpaper to control the surface roughness within the range of Ra 0.15-0.25μm. The samples were then placed in an environment of 25℃ and 55% relative humidity for 18 minutes to form pretreated samples for later use. S2: First, prepare a platinum catalyst stock solution by taking 0.10g of platinum(0)-1,3-divinyltetramethyldisiloxane complex and 0.90g of anhydrous xylene; then take 0.75g of 4-allyl catechol and 9g of anhydrous toluene, stir at 37℃ until completely dissolved to obtain the first catechol precursor solution. Then, take 0.35g of 4-allyl catechol, 0.26g of phenylboronic acid, 11g of anhydrous toluene and 2.2g of activated 4Å molecular sieve and add them to a round-bottom flask that has been dried at 120℃ for 2h and cooled to room temperature. Stir at 47℃ for 35min under dry nitrogen protection, and filter while hot through a 0.45μm polytetrafluoroethylene filter membrane to obtain the second catechol precursor solution; then take 42g of polyorganosilazane resin Durazane. 1800 g and 85 g of anhydrous xylene were added to a three-necked flask that had been dried at 120 °C for 2 h and cooled to room temperature. The mixture was stirred for 10 min under dry nitrogen protection with a dew point not higher than -40 °C. The first and second catechol precursor solutions were added sequentially, and the mixture was stirred for another 10 min and then cooled to 17 °C. Subsequently, 0.50 g of platinum catalyst stock solution was added dropwise over 5 min, and the mixture was kept at 17 °C for 35 min, then raised to 27 °C and kept at 25 min. Immediately afterwards, 0.09 g of 1-ethynyl-1-cyclohexanol was added and the mixture was stirred for another 10 min to terminate the low-grafting-degree grafting reaction. Then, 210 g of anhydrous xylene was added for dilution, and the mixture was stirred for another 10 min. The mixture was then filtered through a 0.45 μm polytetrafluoroethylene filter membrane to obtain a borate ester / catechin modified polyorganosilazane coating solution. This solution was used up within 4 h under dry nitrogen protection to obtain a continuous wet film sample. S3: Place 155g of borate ester / catechol modified polyorganosilazane coating liquid in a dry dip coating tank, immerse 100g of the obtained pretreated magnet sample in the tank for 35s, and then pull it up at a uniform speed of 2.2mm / s. After pulling up, level it in a dry nitrogen environment at 25℃ and relative humidity not higher than 15% for 6min, and then keep it at 52℃ for 6min to make the wet film continuous. S4: Mix 96g of anhydrous ethanol, 4g of deionized water, and 0.22g of glacial acetic acid to obtain an acidic micro-aqueous solution; mix 98g of anhydrous ethanol, 2g of deionized water, and 0.35g of ammonia (25wt%) to obtain a weakly alkaline micro-aqueous solution; after the surface temperature of the continuous wet film sample obtained in step S3 drops to 35℃, spray 0.11g of acidic micro-aqueous solution evenly onto the surface of the wet film sample using conventional atomization spraying method. After spraying, let it stand for 4min, and then maintain it at 82℃ for 12min under a dry nitrogen atmosphere; then cool the obtained sample to about 35℃, and spray 0.07g of weakly alkaline micro-aqueous solution only onto the outer surface of the film layer of the same batch of samples using conventional atomization spraying method. After spraying, let it stand for 3min, and then maintain it at 82℃ for 6min under a dry nitrogen atmosphere to obtain an intermediate-treated sample; S5: Mix 0.06g of platinum catalyst stock solution and 9.94g of anhydrous xylene to obtain an outer catalytic solution; after cooling the sample obtained in step S4 to below 40℃, spray 0.11g of the outer catalytic solution evenly onto the film surface using a conventional atomization spraying method. After spraying, let it stand for 3min, then maintain it at 122℃ for 22min and then at 152℃ for 32min under a dry nitrogen atmosphere. Finally, place the obtained sample in an environment of 25℃ and relative humidity not exceeding 30% for 28h to obtain a hydrogen-resistant iron-based sintered rare earth permanent magnet material.

[0037] Comparative Example 1: The difference from Example 1 is that in step S2, the second catechol precursor solution is no longer prepared, but 1.00g of 4-allyl catechol is used entirely to prepare the first catechol precursor solution, and 240mg of phenylboronic acid is no longer added in step S2. The other conditions are the same as in Example 1.

[0038] Comparative Example 2: The difference from Example 1 is that in step S4, the acidic micro-aqueous solution is not sprayed and the 80°C holding time for 10 minutes is not performed. Only the weakly alkaline micro-aqueous solution is sprayed and the subsequent treatment is retained. The other conditions are the same as in Example 1.

[0039] Comparative Example 3: The difference from Example 1 is that in step S4, only the acidic micro-aqueous liquid is sprayed and kept at 80°C for 10 minutes, and the weakly alkaline micro-aqueous liquid is no longer sprayed. The other conditions are the same as in Example 1.

[0040] Comparative Example 4: The difference from Example 1 is that in step S4, a weakly alkaline micro-aqueous solution is sprayed first and kept at 80°C for 5 minutes, and then an acidic micro-aqueous solution is sprayed and kept at 80°C for 10 minutes. The other conditions are the same as in Example 1.

[0041] Comparative Example 5: The difference from Example 1 is that in step S2, 50 mg of the platinum catalyst stock solution described in step S2 is added to the borate ester / catechol modified polyorganosilazane coating solution and stirred for 10 min. In step S5, the outer layer of catalyst solution is no longer sprayed. To ensure consistent platinum usage, the total amount of platinum catalyst stock solution added in step S2 is increased from 500 mg to 550 mg. The other conditions are the same as in Example 1.

[0042] Performance testing For each of the hydrogen-resistant iron-based sintered rare-earth permanent magnet material samples prepared according to the examples and comparative examples, at least 30 finished magnet samples with dimensions of 20mm × 10mm × 3mm were prepared in each group. Ten samples in each group were used for magnetic performance, hydrogen environment exposure, and magnetic performance retention rate after hydrogen exposure testing; 10 samples were used for weight loss testing; and 10 samples were used for adhesion, film thickness, and neutral salt spray testing. Simultaneously, using 30mm × 30mm polished single-crystal silicon wafers and 50mm × 50mm polytetrafluoroethylene release sheets, which had been ultrasonically cleaned with acetone and anhydrous ethanol for 5 minutes each and then dried, as parallel substrates, parallel coating samples were prepared concurrently according to steps S3 to S5 of each example or comparative example. Dry film thickness test: The dry film thickness is tested in accordance with GB / T 4956-2003. A magnetic thickness gauge is used to measure 5 points on both sides of each finished magnet sample. At least 3 samples are measured in each group, for a total of 30 data points. The average value is taken. Pull-off adhesion test: The test was conducted in accordance with GB / T 5210-2006. Finished magnet samples were selected, and a 10mm aluminum pull-out head that had been polished and degreased was used as the loading head. Two-component epoxy structural adhesive was used to bond the sample to the coating surface. After curing at 25℃ for 24 hours, the pull-off adhesion tester was used to load the sample at a speed of 1mm / min. The stress value at failure was recorded. Five parallel points were tested for each sample, and the average value was taken. Initial magnetic performance test: In accordance with GB / T 3217-2013, the finished magnet samples were saturated with a pulse magnetization device and the magnetization field strength was 4.0T; then, the remanence and intrinsic coercivity were measured with a permanent magnet measuring instrument at 23℃. Five samples were tested in each group and the average value was taken. Weight loss test and constant humidity and heat test: The weight loss test was conducted according to GB / T 40792-2021, using a saturated water vapor mode. The finished magnet sample was placed at 120℃, 100% relative humidity, and 2.0 atm for 96 hours. Before the test, the sample was vacuum dried at 25℃ for 2 hours and the initial mass was weighed. After the test, the sample was removed, and loose adhering materials were gently removed with a soft brush. After vacuum drying at 25℃ for 2 hours, the final mass was weighed. The weight loss value was calculated based on the exposed area, with the unit being mg / cm². 2 The constant humidity and heat test was conducted in accordance with GB / T 43489-2023. The finished magnet sample was exposed to 85℃ and 85% relative humidity for 240h. After the test, it was placed at 23℃ for 2h and the intrinsic coercivity was measured again. The retention rate was calculated by the ratio of the intrinsic coercivity before and after the test. Hydrogen environmental exposure and magnetic property retention test after hydrogen exposure: The test was conducted according to GB / T 34542.2-2018. A pressure-resistant stainless steel high-pressure reactor was used as the hydrogen environment chamber. Nitrogen gas was first introduced to purge the sample three times, followed by hydrogen gas with a purity of not less than 99.999% to 0.50 MPa. The temperature was then increased to 120℃ at a rate of 3℃ / min and maintained for 24 hours. After the test, the sample was cooled to room temperature, the hydrogen gas was purged, and the sample was purged with nitrogen for 15 minutes. After removal, the sample was allowed to stand at 23℃ for 30 minutes. The mass was first weighed, and the weight gain was calculated based on the initial mass. The intrinsic coercivity was then measured again, and the retention rate was calculated using the ratio of intrinsic coercivity before and after hydrogen exposure. Neutral salt spray test: The neutral salt spray test was conducted in accordance with GB / T 10125-2021. A 5.0% sodium chloride solution was prepared with a pH of 6.5-7.2. The test chamber temperature was 35℃, and the angle between the sample and the vertical direction was 20°. Continuous spraying was performed, and the sample surface was observed every 24 hours. The time when the first visible red rust spots, blistering under the film, or localized corrosion spread to the exposed substrate was recorded as the neutral salt spray failure time. The results of the above performance tests are shown in Table 1.

[0043] Table 1 Performance Test Results Data analysis: As can be seen from the data of the embodiments in Table 1, the hydrogen-resistant iron-based sintered rare earth permanent magnet material prepared by the present invention exhibits good overall balance in terms of dry film thickness, interfacial bonding, damp heat stability, hydrogen environment stability and neutral salt spray tolerance.

[0044] As can be seen from the data of Example 1 and Comparative Example 1 in Table 1, when the second catechol precursor liquid is no longer prepared in step S2 and phenylboronic acid is no longer added, the initial magnetic properties of the sample do not change much, but the adhesion, intrinsic coercivity retention rate after wet heat, intrinsic coercivity retention rate after hydrogen exposure, and neutral salt spray failure time all deteriorate significantly. It can be seen that the biscatechin grafting unit is not simply adding components, but achieving a synergistic effect of first occupying and then reinforcing in the same step.

[0045] As can be seen from the data in Table 1 for Example 1 and Comparative Example 2, after the acidic micro-aqueous solution in step S4 was removed, several key indicators deteriorated simultaneously, and the degree of deterioration was the greatest. The main reason for this is that the acidic micro-aqueous solution in this invention is not a simple wet treatment, but simultaneously performs two functions: the release of the second catechol precursor liquid and the local hydrolysis and condensation of the inner layer.

[0046] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 3 and 4, retaining only the acidic microaqueous solution while omitting the weakly alkaline microaqueous solution, or reversing the order of the weakly alkaline and acidic microaqueous solutions, will degrade the sample performance. The main reason is that with only the acidic microaqueous solution, a certain binding region can be formed in the inner layer, but the residual silanol sites in the middle and outer layers are difficult to repair in time, and the surface layer is more likely to have defect channels. If the weakly alkaline microaqueous solution is treated first and then the acidic microaqueous solution is treated, the original spatial order of "building the interface in the inner layer first and repairing the surface layer in the outer layer" will be disrupted, causing the effective ranges of the two microaqueous solutions to partially overlap and weaken each other.

[0047] As can be seen from the data in Table 1 for Example 1 and Comparative Example 5, incorporating the outer catalyst solution in step S5 into the coating solution in step S2 prematurely leads to a simultaneous decrease in adhesion, wet heat stability, hydrogen resistance, and salt spray lifetime. The main reason is that once the platinum catalyst stock solution enters the borate / catechol modified polyorganosilazane coating solution prematurely, the remaining Si-H sites and vinyl sites are more likely to undergo bulk addition crosslinking before or in the early stages of film formation. This weakens the ability of the catechol graft units to migrate to and oriented onto the magnet surface, making it difficult for the middle and outer layers to achieve a post-densification effect.

[0048] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing a hydrogen-resistant iron-based sintered rare-earth permanent magnet material, characterized in that, Includes the following steps: (1) The iron-based sintered rare earth permanent magnet is pretreated to obtain a pretreated magnet; (2) The pretreated magnet was immersed in the borate ester / catechol modified polyorganosilazane coating solution, pulled into a film, and then leveled and dried to obtain a continuous wet film sample; (3) Acidic micro-aqueous solution and weakly alkaline micro-aqueous solution were sprayed onto the surface of the continuous wet film sample in sequence. After standing and drying, the intermediate treatment sample was obtained. (4) The outer catalytic liquid is sprayed onto the membrane surface of the intermediate treatment sample, and then heated and cured and left to stand to obtain hydrogen-resistant iron-based sintered rare earth permanent magnet material. The preparation steps of the borate ester / catechol modified polyorganosilazane coating liquid in step (2) are as follows: 4-allyl catechol is dissolved in anhydrous toluene to form the first catechol precursor liquid; 4-allyl catechol, phenylboronic acid, anhydrous toluene and activated 4Å molecular sieve are stirred under dry nitrogen protection and then filtered to form the second catechol precursor liquid; then polyorganosilazane resin is dissolved in anhydrous xylene, and the first catechol precursor liquid and the second catechol precursor liquid are added sequentially under dry nitrogen protection. After cooling, platinum catalyst is added dropwise. After keeping the reaction at a certain temperature, 1-ethynyl-1-cyclohexanol is added to terminate the reaction. The solution is then diluted and filtered to obtain the final product.

2. The preparation method according to claim 1, characterized in that, The iron-based sintered rare earth permanent magnet in step (1) contains the following raw materials in parts by weight: 610-630 parts praseodymium-neodymium alloy, 19-21 parts metallic boron, 16-18 parts metallic cobalt, 2-3 parts electrolytic copper, 4-5 parts metallic aluminum, 3-4 parts metallic gallium and 1325-1345 parts electrolytic iron.

3. The preparation method according to claim 1, characterized in that, The iron-based sintered rare earth permanent magnet in step (1) is obtained by mixing and melting raw materials, casting them into ingots, crushing them to form magnetic powder, and finally pressing, sintering, and aging the magnetic powder.

4. The preparation method according to claim 1, characterized in that, The surface roughness Ra of the pretreated magnet in step (1) is 0.15-0.25 μm.

5. The preparation method according to claim 1, characterized in that, Based on 100 parts by weight of the pretreated magnet, the amounts of the polyorganosilazane resin, 4-allyl catechol in the first catechol precursor solution, 4-allyl catechol in the second catechol precursor solution, phenylboronic acid, platinum catalyst, and 1-ethynyl-1-cyclohexanol in step (2) are 38-42 parts, 0.65-0.75 parts, 0.25-0.35 parts, 0.22-0.26 parts, 0.05 parts, and 0.07-0.09 parts, respectively.

6. The preparation method according to claim 1, characterized in that, The polyorganosilazane resin mentioned in step (2) is Durazane 1800.

7. The preparation method according to claim 1, characterized in that, Based on 100 parts by weight of the continuous wet film sample, the amounts of the acidic microaqueous solution and the weakly alkaline microaqueous solution used in step (3) are 0.09-0.11 parts and 0.05-0.07 parts, respectively. The acidic microaqueous solution is obtained by dissolving glacial acetic acid in a mixed solution of anhydrous ethanol and deionized water. The weakly alkaline microaqueous solution is obtained by dissolving ammonia in a mixed solution of anhydrous ethanol and deionized water.

8. The preparation method according to claim 1, characterized in that, Based on 100 parts by weight of intermediate-processed sample, the amount of outer catalytic liquid containing platinum catalyst in step (4) is 0.09-0.11 parts; the outer catalytic liquid is a mixture of platinum catalyst stock solution and anhydrous xylene.

9. The preparation method according to claim 1, characterized in that, The heating and curing in step (4) involves first holding the temperature at 118-122℃ for 18-22 minutes, and then holding it at 148-152℃ for 28-32 minutes.

10. A hydrogen-resistant iron-based sintered rare-earth permanent magnet material, characterized in that, It is prepared according to any one of claims 1-9.

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