CN109887696B - Organic slurry coated on neodymium iron boron magnet and preparation of high-coercivity neodymium iron boron magnet - Google Patents
Organic slurry coated on neodymium iron boron magnet and preparation of high-coercivity neodymium iron boron magnet Download PDFInfo
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Abstract
The invention belongs to the technical field of rare earth permanent magnets, and particularly relates to organic slurry coated on a neodymium iron boron magnet and a preparation method of the neodymium iron boron magnet with high coercivity. The organic slurry comprises the following components in percentage by weight: 30-70% of simple substance metal powder, 5-10% of thermoplastic resin powder, 3-5% of accelerator and the balance of organic solvent. The preparation method comprises the following steps: and after surface treatment, coating the organic slurry, drying and then carrying out aging treatment to obtain the required magnet.
Description
Technical Field
The invention belongs to the technical field of rare earth permanent magnets, and particularly relates to organic slurry coated on a neodymium iron boron magnet and a preparation method of the neodymium iron boron magnet with high coercivity.
Background
The rare earth permanent magnet neodymium iron boron magnet is used as a third generation magnet, and is widely applied to the fields of new energy automobiles, air-conditioning compressors, various motors, acoustics and the like due to high performance. Meanwhile, the development of supporting new energy automobiles is greatly advocated in the country in recent years, and the sintered neodymium-iron-boron magnet is used as a main component of the permanent magnet motor, so that great market demand exists. Since the local temperature of Nd-Fe-B sintered magnets is about 300 ℃, the application temperature of some products using the magnets exceeds the local temperature, and when the temperature rises above the predetermined temperature, the magnets are demagnetized by heat. The environment of use therefore imposes higher temperature stability requirements on the magnet. The traditional manufacturing process can improve the temperature stability of the magnet, namely improve the coercive force (the higher the coercive force of the magnet is in use of the magnet, the better the temperature stability) only by adding expensive heavy rare earth Dy/Tb in the alloy smelting process, the addition of the heavy rare earth Dy/Tb in the magnet can greatly improve the coercive force of the magnet, improve the Curie temperature of the magnet, improve the temperature stability of the magnet, greatly improve the maximum usable temperature of materials, and simultaneously, the wet-heat corrosion resistance and the electrochemical corrosion resistance of the magnet are obviously improved, but the addition of the traditional method can deteriorate the remanence of the magnet and greatly increase the material cost.
The grain boundary diffusion technology widely applied in the field of powder metallurgy can be effectively applied to sintered neodymium iron boron, so that the coercive force of the magnet can be effectively improved on the basis of not reducing the residual magnetism of the magnet, and the coercive force of the magnet can be greatly improved by using a small amount of heavy rare earth. The grain boundary diffusion method published in the field of neodymium iron boron at present mainly comprises a sputtering method, an evaporation method, an electrophoresis method, a surface coating method and an immersion method, but the method for mass production in the industrial field mainly comprises the sputtering method and the coating method, and the sputtering method has the defects of high equipment cost, severe operating environment, low yield in unit time and the like, and the coating method has the advantages of simple operation, loose environmental requirements and suitability for mass production. Slurry prepared by preparing a fluoride containing Dy/Tb or a heavy rare earth simple substance published by Japan shin-Etsu chemistry is coated on the surface of a magnet, and slurry coating methods published by tobacco terrace Zhenghai and Dadi bear companies have the defects that a surface coating layer is easy to drop, the contents of oxygen and carbon in the magnet are increased after diffusion is finished, the magnet is easy to adhere after the diffusion is finished, the surface of the magnet is uneven, and the surface of the magnet needs to be cleaned by machining.
Disclosure of Invention
Aiming at the defects in the prior art, the invention adopts the organic slurry formed by mixing the simple substance metal powder, the thermoplastic resin powder and the accelerant to coat the surface of the magnet, greatly improves the coercive force of the magnet on the basis of not reducing the residual magnetism of the magnet, and is beneficial to industrialized mass production.
The organic slurry coated on the neodymium iron boron magnet comprises the following components in parts by weight:
30 to 70 percent of simple substance metal powder,
5 to 10 percent of thermoplastic resin powder,
3 to 5 percent of accelerant,
the balance of organic solvent.
Preferably, the oxygen content of the organic slurry is controlled to be less than 100ppm in the preparation process.
Preferably, the elementary metal is one or more of Tb, Dy, Pr and Ho.
Preferably, the thermoplastic resin is one or more of polyvinyl butyral, polyvinyl acetal, and polyvinyl alcohol.
Preferably, the accelerator is one or more of cobalt isooctanoate, magnesium isooctanoate, zinc isooctanoate and zirconium isooctanoate and/or one or more of N, N-dimethylaniline, N-diethylaniline and N, N-dimethyl-p-toluidine.
Preferably, the organic solvent is one or more of esters, ketones or alcohols.
The other purpose of the invention can be realized by the following technical scheme: a preparation method of a high-coercivity neodymium iron boron magnet comprises the steps of carrying out surface treatment on a sintered neodymium iron boron magnet, coating the organic slurry, drying, and carrying out aging treatment to obtain the required magnet.
Preferably, the organic slurry coating has a thickness of 5 to 50 μm.
Preferably, the drying temperature is between 80 and 120 ℃, and the drying time is between 3 and 10 minutes.
Preferably, the aging treatment comprises primary aging treatment and secondary aging treatment; the temperature of the first-stage aging is 750-950 ℃, the time is 3-25h, the temperature of the second-stage aging is 450-650 ℃, and the time is 0.5-12 h.
Compared with the prior art, the invention has the beneficial effects that:
1) the thermoplastic resin powder used in the invention has good adhesion effect, can effectively prevent the organic coating from falling off, and has low decomposition temperature and short curing time, thereby reducing the content of oxygen and carbon entering the magnet;
2) the accelerant used in the invention can improve the caking property of the thermoplastic resin, promote the rapid solidification of the slurry, increase the activity and the fluidity of the elemental metal, accelerate the diffusion of the elemental metal to the grain boundary, effectively reduce the infiltration of C, O element in the grain boundary, and improve the uniform diffusion of the elemental metal in the magnet by compounding the accelerant and the thermoplastic resin powder;
3) the organic slurry used in the invention can effectively prevent the mutual adhesion problem between the magnets after the aging is finished, the uniform distribution of the organic slurry is beneficial to more uniformly distributing the elemental metal elements on the surface of the magnets, the condition that the magnet surface is uneven after the aging and the product cannot be processed and scrapped can not be caused, and the elemental metal is uniformly distributed on the surface of the magnets, so that the elemental metal can more uniformly enter the crystal boundary to improve the coercive force of the magnets;
4) the invention can greatly improve the coercive force of the magnet on the basis of using a small amount of heavy rare earth, reduces the material cost, has simple and easy operation method and is easy for industrialized batch production.
Detailed Description
The technical solutions of the present invention are further described and illustrated by the following specific examples, but the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. The raw materials used in the examples of the present invention are those commonly used in the art, and the methods used in the examples are those conventional in the art, unless otherwise specified.
In one embodiment of the present invention, the organic paste coated on the ndfeb magnet is composed of the following components in percentage by weight:
30 to 70 percent of simple substance metal powder,
5 to 10 percent of thermoplastic resin powder,
3 to 5 percent of accelerant,
the balance of organic solvent.
The organic slurry is coated on the surface of the neodymium iron boron magnet, the elementary metal in the organic slurry is used as a diffusion source by utilizing the principle of grain boundary diffusion, the elementary metal is diffused into the main phase of the sintered magnet from the surface along the grain boundary of the magnet through heat treatment, the organization structure and the components of the joint part of the grain boundary and the main phase are improved, the utilization rate of the elementary metal can be greatly improved, the use amount of the elementary metal is reduced, and the coercive force of the magnet can be greatly improved. The thermoplastic resin powder exists as a binder and is mixed with the simple substance metal powder in the organic solvent, so that the formed slurry has strong binding power with the magnet matrix, and the interaction between the metal powder is strong.
The organic slurry needs to be operated in a glove box filled with nitrogen in the preparation process, and the oxygen content in the glove box is strictly controlled to be below 100ppm, because the elemental metal is easily oxidized and even burnt at high temperature in the environment with high oxygen content, the diffusivity of the elemental metal is influenced, and the oxidized metal brings oxygen in the grain boundary diffusion, so that the overall magnetic performance of the magnet is reduced.
In one embodiment of the present invention, the elemental metal is one or more of Tb, Dy, Pr, Ho. The Tb, Dy, Pr and Ho rare earth heavy metal elements are infiltrated into the crystal boundary surface of the magnet by a crystal boundary diffusion method, and compared with the traditional method in which the elements are added in the smelting process, the coercive force, the high-temperature stability, the magnetic energy product and other magnet performances of the magnet can be greatly improved on the basis of not influencing the remanence of the magnet. The Tb, Dy, Pr and Ho elements are added in a simple substance form, and are easier to diffuse to a grain boundary phase compared with diffusion treatment in an oxide, fluoride or other alloy forms, and an oxide layer and a fluoride layer are not easy to form on the surface of the magnet, so that subsequent machining and cleaning operations are not needed.
The thermoplastic resin is one or more of polyvinyl butyral, polyvinyl acetal and polyvinyl alcohol. Besides good cohesiveness, the polyvinyl butyral, polyvinyl acetal and polyvinyl alcohol resin have low thermal decomposition temperature, are easy to decompose and volatilize in a high-temperature environment, and reduce the infiltration of C, O elements.
The accelerant is one or more of cobalt isooctanoate, magnesium isooctanoate, zinc isooctanoate and zirconium isooctanoate and/or one or more of N, N-dimethylaniline, N-diethylaniline and N, N-dimethyl-p-methylaniline. The accelerant used in the invention improves the bonding efficiency of the thermoplastic resin binder and the elemental metal powder in the organic solvent, enhances the bonding property of the thermoplastic resin, can be coated on the surface of the magnet after being stirred for a short time, promotes the slurry to be rapidly cured, forms a uniform coating on the surface of the magnet, keeps the surface of the magnet smooth and clean, removes unevenness, can also increase the activity and the fluidity of the elemental metal, accelerates the diffusion of the elemental metal to a crystal boundary, and can effectively reduce the infiltration of C, O element in the crystal boundary.
Further preferably, the accelerator is a mixture of cobalt iso-octoate and N, N-dimethylaniline, and the mixing mass ratio is 1: (1-2). The two promoters are compounded for use, so that the synergistic effect of the two promoters can be exerted to a greater extent, the cobalt element in the cobalt iso-octoate can also be diffused into a crystal boundary, and the trace cobalt element is beneficial to improving the magnetic property.
The organic solvent is one or more of esters, ketones or alcohols. Ester solvents such as methyl acetate, ethyl valerate, ethyl lactate, etc., ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, etc., and alcohol solvents such as methanol, ethanol, propanol, ethylene glycol, etc. Ester, ketone or alcohol organic solvents which have high solubility to the accelerator and the thermoplastic resin powder and are volatile at high temperature can be applied to the invention.
In an embodiment of the present invention, the method for preparing the high coercivity neodymium iron boron magnet comprises the following steps: after the surface treatment is carried out on the sintered neodymium-iron-boron magnet, organic slurry is coated, and the organic slurry consists of the following components in percentage by weight: 30-70% of simple substance metal powder, 5-10% of thermoplastic resin powder, 3-5% of accelerator and the balance of organic solvent. And (5) carrying out aging treatment after drying to obtain the required magnet.
The sintered Nd-Fe-B magnet is prepared from Nd, Fe, B and other trace elements or other rare earth elements except Nd through smelting, hydrogen crushing, pulverizing, shaping and sintering. The surface treatment of the sintered neodymium iron boron magnet comprises the steps of oil removal, acid cleaning, drying and the like, so that oil stains and impurities on the surface of the magnet are removed, and the adhesive force of slurry is improved. The means for coating the organic slurry on the surface of the magnet can be wetting, manual coating, mechanical coating, and the like, and is not particularly limited.
In one embodiment of the invention, the organic slurry coating thickness is 5-50 μm. The drying temperature is between 80 and 120 ℃, and the drying time is 3 to 10 minutes. The aging treatment comprises primary aging treatment and secondary aging treatment; the temperature of the first-stage aging is 750-950 ℃, the time is 3-25h, the temperature of the second-stage aging is 450-650 ℃, and the time is 0.5-12 h. The aging treatment is further preferably carried out at the temperature of 800-900 ℃ for 8-14h for the first-stage aging treatment, at the temperature of 500-600 ℃ for the second-stage aging treatment, and for 3-10 h. In the process of high-temperature sintering recrystallization of the neodymium-iron-boron magnet, a plurality of cavities are reserved in the grain boundary phase due to rapid diffusion of rare earth elements such as Nd, Pr, Tb and Dy, and the boundary cavities can be effectively eliminated by primary aging, so that the grain boundary phase is more uniformly distributed at the boundary. The secondary aging is used for further repairing the defects between the main phase and the rare earth-rich phase at the crystal boundary, and is beneficial to the neodymium iron boron permanent magnet material to obtain a good microstructure, so that the squareness of the magnet is improved and the coercivity is improved.
Example 1
Cutting a sintered NdFeB magnet with the mark of 38H into blocks (marked as 38H matrix samples) with the sizes of 50mm x 6mm, uniformly coating the prepared organic slurry on the matrix samples after oil removal, acid cleaning and drying treatment, keeping the coating thickness at 20 mu m, preserving the heat at 100 ℃ for 10min, then carrying out primary aging treatment at 880 ℃ for 12H, cooling and carrying out secondary aging treatment at 520 ℃ for 4H to obtain the required magnet.
The organic slurry comprises 60 percent of terbium simple substance (Tb) powder, 8 percent of polyvinyl butyral powder, 2 percent of cobalt isooctanoate, 2 percent of N, N-dimethylaniline and the balance of analytically pure acetone. The oxygen content of the organic slurry is controlled to be below 100ppm in the preparation process.
Example 2
Cutting a sintered NdFeB magnet with the mark of 38H into blocks (marked as 38H matrix samples) with the sizes of 50mm x 6mm, uniformly coating the prepared organic slurry on the matrix samples after oil removal, acid cleaning and drying treatment, keeping the coating thickness at 20 mu m, preserving the heat at 100 ℃ for 10min, then carrying out primary aging treatment at 880 ℃ for 12H, cooling and carrying out secondary aging treatment at 520 ℃ for 4H to obtain the required magnet.
The organic slurry comprises 60 percent of terbium simple substance (Tb) powder, 8 percent of polyvinyl butyral powder, 4 percent of cobalt isooctanoate and the balance of analytically pure acetone. The oxygen content of the organic slurry is controlled to be below 100ppm in the preparation process.
Example 3
Cutting a sintered NdFeB magnet with the mark of 38H into blocks (marked as 38H matrix samples) with the sizes of 50mm x 6mm, uniformly coating the prepared organic slurry on the matrix samples after oil removal, acid cleaning and drying treatment, keeping the coating thickness at 20 mu m, preserving the heat at 100 ℃ for 10min, then carrying out primary aging treatment at 880 ℃ for 12H, cooling and carrying out secondary aging treatment at 520 ℃ for 4H to obtain the required magnet.
The organic slurry comprises 60 percent of terbium simple substance (Tb) powder, 8 percent of polyvinyl butyral powder, 4 percent of N, N-dimethylaniline and the balance of analytically pure acetone. The oxygen content of the organic slurry is controlled to be below 100ppm in the preparation process.
Example 4
Cutting a sintered NdFeB magnet with the mark of 38H into blocks (marked as 38H matrix samples) with the sizes of 50mm x 6mm, uniformly coating the prepared organic slurry on the matrix samples after oil removal, acid cleaning and drying treatment, keeping the coating thickness at 20 mu m, preserving the heat at 100 ℃ for 10min, then carrying out primary aging treatment at 880 ℃ for 12H, cooling and carrying out secondary aging treatment at 520 ℃ for 4H to obtain the required magnet.
The organic slurry comprises 60 percent of terbium simple substance (Tb) powder, 8 percent of polyvinyl butyral powder, 2 percent of magnesium isooctanoate, 2 percent of N, N-diethylaniline and the balance of analytically pure acetone. The oxygen content of the organic slurry is controlled to be below 100ppm in the preparation process.
Example 5
Cutting the sintered NdFeB magnet with the mark of N50 into blocks (marked as N50 matrix samples) with the sizes of 50mm, 50mm and 6mm, carrying out oil removal, acid cleaning and drying treatment, uniformly coating the prepared organic coating on the matrix samples, wherein the thickness of the coating is 30 mu m, carrying out heat preservation at 120 ℃ for 5min, carrying out primary aging treatment at 820 ℃ for 14h, cooling, and carrying out secondary aging treatment at 600 ℃ for 5h to obtain the required magnet.
The organic slurry comprises 62 percent of Tb simple substance powder, 7 percent of polyvinyl alcohol powder, 1.5 percent of cobalt isooctanoate, 1.8 percent of N, N-dimethylaniline and the balance of analytically pure isopropanol. The oxygen content of the organic slurry is controlled to be below 100ppm in the preparation process.
Example 6
Cutting the sintered NdFeB magnet with the mark of N35 into blocks (marked as N35 matrix samples) with the thickness of 50mm 6mm, degreasing, pickling and drying, uniformly coating the prepared organic coating on the matrix samples with the thickness of 10 mu m, preserving heat at 110 ℃ for 7min, then carrying out primary aging treatment at 900 ℃ for 11h, cooling and carrying out secondary aging treatment at 500 ℃ for 5h to obtain the required magnet.
The organic slurry comprises 60 percent of Dy elemental powder, 7 percent of polyvinyl acetal powder, 1.5 percent of cobalt iso-octoate, 3 percent of N, N-dimethylaniline and the balance of analytically pure ethanol. The oxygen content of the organic slurry is controlled to be below 100ppm in the preparation process.
Comparative example 1
Comparative example 1 is different from example 1 in that the metal powder in the organic slurry of comparative example 1 is terbium fluoride instead of the elemental powder of terbium in example 1, and the rest is the same as example 1.
Comparative example 2
Comparative example 2 is different from example 1 in that the metal powder in the organic slurry of comparative example 2 is terbium oxide instead of the elemental powder of terbium in example 1, and the rest is the same as example 1.
Comparative example 3
Comparative example 3 is different from example 1 in that the metal powder in the organic slurry of comparative example 3 is terbium hydride instead of the elemental powder of terbium in example 1, and the other is the same as example 1.
Comparative example 4
Comparative example 4 is different from example 5 in that the content of polyvinyl alcohol powder in the organic slurry of comparative example 4 is 1%, and the rest is the same as example 5.
Comparative example 5
Comparative example 5 is different from example 5 in that the content of polyvinyl alcohol powder in the organic slurry of comparative example 5 is 12%, and the rest is the same as example 5.
Comparative example 6
Comparative example 6 is different from example 5 in that the organic slurry of comparative example 6 does not contain polyvinyl alcohol powder, and the rest is the same as example 1.
Comparative example 7
Comparative example 7 is different from example 6 in that the organic slurry of comparative example 7 has a cobalt isooctanoate content of 0.4% and an N, N-dimethylaniline content of 0.6%, and is otherwise the same as example 6.
Comparative example 8
Comparative example 8 is different from example 6 in that comparative example 8 has an organic slurry containing 2.5% of cobalt isooctanoate and 5% of N, N-dimethylaniline, and is otherwise the same as example 6.
Comparative example 9
Comparative example 9 is different from example 6 in that comparative example 9 does not include cobalt isooctanoate and N, N-dimethylaniline in the organic slurry, and the rest is the same as example 6.
Comparative example 10
Comparative example 10 differs from example 6 in that comparative example 10 organic slurry had an oxygen content of 500ppm in the glove box during the formulation, and the rest was the same as example 6.
The magnets of examples 1 to 6 and comparative examples 1 to 10 were subjected to magnetic property tests, and the results of the tests are shown in tables 1 to 4.
Table 1 examples 1-6 magnet properties
| Experimental group | Remanence (kGs) | Coercive force (kOe) | Magnetic energy product (MGOe) | Hk/Hcj(％) |
| 38H matrix sample | 12.41 | 17.5 | 37.85 | 97.5 |
| Example 1 | 12.40 | 27.9 | 38.63 | 96.7 |
| Example 2 | 12.31 | 26.0 | 37.55 | 96.2 |
| Example 3 | 12.30 | 25.7 | 37.16 | 96.1 |
| Example 4 | 12.34 | 26.5 | 37.87 | 96.5 |
| N50 matrix sample | 14.08 | 13.51 | 48.51 | 97.2 |
| Example 5 | 14.06 | 23.82 | 48.72 | 96.8 |
| N35 matrix sample | 11.72 | 12.85 | 33.55 | 97.0 |
| Example 6 | 11.71 | 23.11 | 33.22 | 96.5 |
As can be seen from table 1, when the organic slurry of the present invention was applied to the surface of the matrix magnet, the coercive force of the magnet was greatly increased relative to the matrix sample, for example, the coercive force of the magnet in examples 1 to 4 was increased by 10.4kOe, 8.5kOe, 8.2kOe, and 9kOe relative to the coercive force of the matrix sample of 38H, the coercive force of the magnet in example 5 was increased by 10.31kOe relative to the coercive force of the matrix sample of N50, the coercive force of the magnet in example 6 was increased by 10.26kOe relative to the coercive force of the matrix sample of N35, and the remanence was not significantly decreased. In contrast, the coercive force of the magnet of the examples 2 to 4 is not as good as that of the magnet of the example 1, and the remanence is slightly lower than that of the magnet of the example 1, because the example 1 adopts the optimal accelerator of the invention: the mixture of cobalt iso-octoate and N, N-dimethylaniline is mixed according to the mass ratio of 1: 1; the cobalt iso-octoate and the N, N-dimethylaniline are mixed and used according to a proper proportion, and the cobalt iso-octoate and the N, N-dimethylaniline can play a strong synergistic effect, promote the diffusion of a simple substance terbium on a grain boundary surface, reduce the infiltration of C, O elements and further improve the performance of the magnet.
TABLE 2 magnet Properties of example 1, comparative examples 1-3
| Experimental group | Remanence (kGs) | Coercive force (kOe) | Magnetic energy product (MGOe) | Hk/Hcj(％) |
| 38H matrix sample | 12.41 | 17.5 | 37.85 | 97.5 |
| Example 1 | 12.40 | 27.9 | 38.63 | 96.7 |
| Comparative example 1 | 12.27 | 26.0 | 36.53 | 94.8 |
| Comparative example 2 | 12.28 | 25.8 | 36.78 | 94.9 |
| Comparative example 3 | 12.32 | 26.5 | 36.95 | 95.9 |
As can be seen from table 2, in comparative examples 1 to 3, in which terbium fluoride, terbium oxide and terbium hydride were used in the organic slurry, respectively, the coercive force of the magnet was also increased by 8.5kOe, 8.3kOe and 9.0kOe, respectively, after the diffusion was completed, but they were all smaller than the increase amount of example 1, and the remanence was decreased by 0.14kGs, 0.13kGs and 0.09kGs, respectively. The terbium fluoride and the terbium oxide are used as terbium-containing compounds, so that the heavy rare earth Tb can enter a grain boundary in the process of grain boundary diffusion, and meanwhile, fluorine elements and oxygen elements can be brought into the grain boundary, so that the remanence of the magnet is deteriorated, and the remanence of the magnet is reduced while the coercive force is improved; terbium hydride does not diffuse as fast as terbium, and remains on the surface of the magnet, thereby affecting the magnetic properties.
TABLE 3 magnet Properties of example 5 and comparative examples 4-6
| Experimental group | Remanence (kGs) | Coercive force (kOe) | Magnetic energy product (MGOe) | Hk/Hcj(％) |
| N50 matrix sample | 14.08 | 13.51 | 48.51 | 97.2 |
| Example 5 | 14.05 | 23.82 | 48.72 | 96.8 |
| Comparative example 4 | 13.96 | 18.55 | 47.53 | 95.9 |
| Comparative example 5 | 13.86 | 19.48 | 47.36 | 95.6 |
| Comparative example 6 | 13.90 | 14.75 | 48.22 | 95.5 |
As can be seen from Table 3, comparative example 4 using 1% polyvinyl alcohol, comparative example 5 using 12% polyvinyl alcohol, and comparative example 6 without polyvinyl alcohol had coercive force improved by 5.04kOe, 5.97kOe, and 1.24kOe, respectively, which were less than the improvement amount of example 5, and the remanence of comparative examples 4 to 6 was reduced by 0.12kGs, 0.22kGs, and 0.18kGs, respectively. The good cohesiveness of the polyvinyl alcohol under the action of the accelerator is realized, so that terbium powder can be uniformly adhered to the surface of the magnet after coating and drying, and if the polyvinyl alcohol is not added or the addition amount of the polyvinyl alcohol is too small, the terbium powder cannot be uniformly distributed on the magnet and falls off, so that enough terbium element cannot enter a crystal boundary in the subsequent aging process, and the coercive force of the magnet is remarkably improved; when the addition amount of the polyvinyl alcohol is too large, a small amount of C, O elements can be infiltrated into the magnet, so that the remanence is reduced.
TABLE 4 magnet Properties of example 6 and comparative examples 7-10
| Experimental group | Remanence (kGs) | Coercive force (kOe) | Magnetic energy product (MGOe) | Hk/Hcj(％) |
| N35 matrix sample | 11.72 | 12.85 | 33.55 | 97.0 |
| Example 6 | 11.71 | 23.11 | 33.22 | 96.5 |
| Comparative example 7 | 11.63 | 17.52 | 32.98 | 95.6 |
| Comparative example 8 | 11.56 | 19.94 | 33.04 | 96.1 |
| Comparative example 9 | 11.60 | 14.89 | 32.80 | 95.1 |
| Comparative example 10 | 11.55 | 19.85 | 33.02 | 95.8 |
As can be seen from table 4, the coercive force of the magnet of comparative example 7 using 1% accelerator, comparative example 8 using 7.5% accelerator, and comparative example 9 without addition of accelerator were improved by 4.67kOe, 7.09kOe, and 2.04kOe, respectively, which were less than the improvement amount of example 6, and the remanence of comparative examples 7 to 9 were reduced by 0.09, 0.16, and 0.12kGs, respectively. This is because the accelerator in the organic slurry has the functions of promoting the diffusion of the elemental element, reducing the infiltration of C, O element, and enhancing the adhesion of the binder, and if no accelerator is added to the organic slurry or the amount of accelerator added is too small, the adhesion and uniformity of dysprosium powder on the surface of the magnet will be poor, the diffusion at the grain boundary surface will also be adversely affected, while if too much accelerator is added, other miscellaneous elements will infiltrate into the interface of the magnet crystal, thereby affecting the performance of the magnet. The organic slurry of comparative example 10 was prepared in an environment with an oxygen content of 500ppm, and during the subsequent aging sintering process, in an environment with a higher oxygen content, the elemental dysprosium powder was easily oxidized to dysprosium oxide, thereby deteriorating the remanence of the magnet and causing the coercive force of the magnet to be increased and the remanence to be decreased.
The foregoing is a detailed description of the invention with reference to specific embodiments, which are not to be construed as limiting the invention to the specific embodiments described. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.
Claims (6)
1. The organic slurry coated on the neodymium iron boron magnet is characterized by comprising the following components in parts by weight:
30 to 70 percent of simple substance metal powder,
5 to 10 percent of thermoplastic resin powder,
3 to 5 percent of accelerant,
the balance of organic solvent;
controlling the oxygen content of the organic slurry to be below 100ppm in the blending process;
the elementary metal is one or more of Tb, Dy, Pr and Ho;
the thermoplastic resin is one or more of polyvinyl butyral, polyvinyl acetal and polyvinyl alcohol;
the accelerator is a mixture of cobalt isooctanoate and N, N-dimethylaniline, wherein the mass ratio of the cobalt isooctanoate to the N, N-dimethylaniline is 1: (1-2).
2. The organic paste applied to the ndfeb magnet according to claim 1, wherein the organic solvent is one or more of esters, ketones or alcohols.
3. A preparation method of a high-coercivity NdFeB magnet is characterized in that the sintered NdFeB magnet is subjected to surface treatment, coated with the organic slurry as claimed in claim 1, dried and subjected to aging treatment to obtain the required magnet.
4. The method of manufacturing a high coercive force neodymium iron boron magnet according to claim 3, wherein the organic slurry coating thickness is 5-50 μm.
5. The method of manufacturing a high coercivity neodymium iron boron magnet according to claim 3, wherein the drying temperature is between 80-120 ℃ and the drying time is 3-10 minutes.
6. The method of manufacturing a high coercivity neodymium iron boron magnet according to claim 3, wherein the aging treatment includes a primary aging treatment and a secondary aging treatment; the temperature of the first-stage aging is 750-950 ℃, the time is 3-25h, the temperature of the second-stage aging is 450-650 ℃, and the time is 0.5-12 h.
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| CN110556244B (en) * | 2019-08-27 | 2021-07-06 | 安徽省瀚海新材料股份有限公司 | Process for preparing high-coercivity neodymium-iron-boron magnet by diffusion method |
| CN112820527A (en) * | 2019-12-17 | 2021-05-18 | 北京京磁电工科技有限公司 | Method for improving magnetic property of rare earth permanent magnet |
| CN112133512B (en) * | 2020-08-24 | 2024-04-19 | 宁波晨洋磁材科技有限公司 | Rare earth iron-based permanent magnet material, preparation method and vacuum hot press |
| CN113744947A (en) * | 2021-08-02 | 2021-12-03 | 安徽省瀚海新材料股份有限公司 | Sintered neodymium iron boron grain boundary diffusion anti-sticking coating and application thereof |
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| CN106158347A (en) * | 2016-08-31 | 2016-11-23 | 烟台正海磁性材料股份有限公司 | A kind of method preparing R Fe B class sintered magnet |
| CN108630368A (en) * | 2018-06-11 | 2018-10-09 | 安徽大地熊新材料股份有限公司 | A kind of the surface coating slurry and neodymium-iron-boron preparation of high-coercive force neodymium iron boron magnetic body |
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| JP2740901B2 (en) * | 1991-02-22 | 1998-04-15 | 同和鉱業株式会社 | R-Fe-Co-BC permanent magnet alloy with small irreversible demagnetization and excellent thermal stability |
| CN107578912A (en) * | 2017-09-25 | 2018-01-12 | 烟台正海磁性材料股份有限公司 | A kind of preparation method of the neodymium iron boron magnetic body with high-coercive force |
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| CN106158347A (en) * | 2016-08-31 | 2016-11-23 | 烟台正海磁性材料股份有限公司 | A kind of method preparing R Fe B class sintered magnet |
| CN108630368A (en) * | 2018-06-11 | 2018-10-09 | 安徽大地熊新材料股份有限公司 | A kind of the surface coating slurry and neodymium-iron-boron preparation of high-coercive force neodymium iron boron magnetic body |
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