Rare earth diffusant, high-performance neodymium iron boron permanent magnet and preparation method and application of high-performance neodymium iron boron permanent magnet

Abstract

The invention discloses a rare earth dispersing agent, a high-performance neodymium-iron-boron permanent magnet and a preparation method and application of the high-performance neodymium-iron-boron permanent magnet. The dispersing agent comprises the following components: a rare earth R composition, a metal composition, an organic solvent and organic powder, wherein in terms of the total mass of the dispersing agent, the weight ratio of the rare earth R composition is 40-60 wt%, the weight ratio of the metal composition is 5-15 wt%, and the weight ratio of the organic solvent is 25-45 wt%; the weight ratio of the organic powder to the organic solvent is (10-20): 100. The neodymium-iron-boron permanent magnet is obtained by carrying out a diffusion process on a sintered magnet matrix by adopting the diffusant disclosed by the invention. By adopting the novel diffusant developed by the invention and optimizing diffusion process conditions, the high-performance neodymium-iron-boron permanent magnet is prepared, and the magnetic performance of the high-performance neodymium-iron-boron permanent magnet is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet materials, specifically relating to a rare earth diffusing agent, a neodymium iron boron permanent magnet, its preparation method and application. Background Technology

[0002] Rare earth magnets, especially neodymium iron boron (NdFeB) magnets, are finding increasingly widespread applications in new energy and intelligent manufacturing. Electric vehicle drive motors and motors for intelligent electronic products, in particular, place higher demands on the performance of NdFeB magnets. Early methods involved directly adding heavy rare earth elements (Tb) and / or Dy during the smelting process to improve the anisotropy of NdFeB magnets. This method not only increased costs but also resulted in a significant decrease in remanence, failing to meet performance requirements. The development of grain boundary diffusion technology represents a major breakthrough in high-performance NdFeB manufacturing. This technology involves infiltrating heavy rare earth elements into the magnet's interior via grain boundary diffusion, effectively improving the magnet's coercivity while minimizing the decrease in remanence and significantly reducing the heavy rare earth content, resulting in a high cost-performance ratio. Furthermore, due to the complex microstructure of NdFeB magnets, a series of heat treatments, including diffusion treatment and aging treatment, are required during their preparation to improve the internal composition distribution and enhance the overall performance of the magnet.

[0003] Considering the relatively high operating temperatures of electric motors and generators, magnets are generally thicker. However, with increasing magnet thickness, the concentration of rare earth elements or other beneficial elements from the surface to the interior of the magnet varies significantly, resulting in limited diffusion depth and insufficient increase in coercivity for thick magnets. Secondly, existing diffusion and aging treatment techniques often fail to effectively control the internal crystal structure of the magnet, preventing it from achieving optimal magnetic properties. Furthermore, existing diffusion and aging treatments often achieve deep diffusion by extending the diffusion time, which consumes a lot of energy and indirectly increases the cost of magnet fabrication. Therefore, optimizing the diffusion agent formulation and increasing the diffusion rate to enhance diffusion depth are currently the main research directions for grain boundary diffusion in thick magnets. Summary of the Invention

[0004] To address the above-mentioned shortcomings of the existing technology, the technical solution of the present invention is as follows:

[0005] A dispersant comprising the following components: a rare earth R composition, a metal composition, an organic solvent, and an organic powder; wherein,

[0006] Based on the total mass of the dispersant, the rare earth R composition accounts for 40-60 wt% by weight, the metal composition accounts for 5-15 wt% by weight, and the organic solvent accounts for 25-45 wt% by weight.

[0007] The weight ratio of the organic powder to the organic solvent is (10-20):100.

[0008] According to an embodiment of the present invention, the rare earth R composition is selected from at least one or a combination of two or more rare earth metals, rare earth alloys, rare earth oxides or rare earth hydrides, wherein the rare earth comprises RH and / or RL; RH represents a heavy rare earth element selected from at least one of Dy, Tb and Ho; RL represents a light rare earth element selected from at least one of Pr, Nd, La and Ce.

[0009] According to an embodiment of the present invention, the metal composition comprises substance M1 and substance M2.

[0010] According to an embodiment of the present invention, the mass ratio of substance M1 to substance M2 is 1:(0.6 to 1.4), for example, 1:0.7 or 1:1.

[0011] According to an embodiment of the present invention, the M1 substance is selected from pure metals, metal alloys, or metal oxides with melting points between 500 and 660°C, such as nickel trioxide, magnesium, aluminum, copper-aluminum alloys, magnesium-aluminum alloys, etc. The present invention does not specifically limit the aluminum content in the copper-aluminum alloy, as long as it reaches the melting point of the aforementioned M1 substance; for example, the mass ratio of Al to Cu is 97:3.

[0012] According to an embodiment of the present invention, the M2 substance is selected from pure metals, metal alloys or metal oxides with melting points between 700 and 850°C, for example, at least one of barium, calcium, etc.

[0013] According to an embodiment of the present invention, the rare earth R composition is a powder, and the average particle size of the rare earth R composition powder is less than or equal to 10 μm, preferably less than or equal to 5 μm, for example: 1.8 μm, 2.2 μm, 2.6 μm, 3.4 μm, 6.0 μm.

[0014] According to an embodiment of the present invention, both substance M1 and substance M2 are powders. Preferably, the average particle size of the powder of substance M1 and the powder of substance M2 is the same or different, and the average particle size of the powder of substance M1 and the powder of substance M2 is less than or equal to 10 μm, preferably less than or equal to 3 μm, for example: 1.8 μm, 2.2 μm, 2.6 μm, 3.4 μm, 6.0 μm.

[0015] The inventors discovered that by adding substance M1, whose melting point is lower than that of the neodymium-rich phase (i.e., the grain boundary phase), to the diffuser, substance M1 can act as a preliminary liquid phase carrier during diffusion treatment. When the melting point of substance M1 is reached, substance M1 preferentially melts and flows. This is equivalent to initially and uniformly dispersing the rare earth R composition (e.g., heavy rare earth element RH) in the diffuser before diffusion and rapidly conducting heat to the magnet matrix, thereby promoting the initial melting of the rare earth R composition in the diffuser. When the temperature is higher than 660°C, based on the molten state of substance M1, the neodymium-rich phase of the magnet matrix melts rapidly, and substance M1 enters the grain boundary to provide more liquid phase, further providing diffusion channels for the rare earth R composition in the diffuser, especially the heavy rare earth element RH, increasing the diffusion rate of the diffuser, thereby forming a thin, continuous grain boundary phase in the magnet. When the temperature reaches above 700℃, the M2 substance in the diffuser begins to melt, which increases the amount of liquid phase in the grain boundary and increases the creep force of the second diffusion. This effectively reduces the self-diffusion activation energy of the magnet, promotes the flow of heavy rare earth element RH to a deeper part of the magnet core, and increases the diffusion depth of the diffuser in the magnet.

[0016] According to an embodiment of the present invention, the organic solvent is a low-boiling-point, volatile organic solvent that will not remain on the NdFeB magnet during high-temperature diffusion, thus not affecting the diffusion effect and not impacting the performance of the magnet. Preferably, the organic solvent is selected from at least one or a combination of two or more polar organic solvents such as methanol, ethanol, butanol, xylene, toluene, and isopropanol.

[0017] According to an embodiment of the present invention, the organic powder is selected from thickening solid powder, and the thickening solid powder has the following properties:

[0018] a) Soluble in the above-mentioned organic solvents (such as methanol, ethanol, isopropanol and other polar organic solvents) at room temperature;

[0019] b) It has a certain viscosity (e.g., 30-1000 mPa) after dissolving in organic solvents;

[0020] c) The carbonization temperature is 250-350℃.

[0021] In this invention, adding a thickening solid powder with the aforementioned properties to an organic solvent not only prevents the rare earth R composition and the metal composition from precipitating too quickly in the organic solvent, but also reduces the impact of the organic powder on the magnetic properties of the magnet matrix by preventing the organic powder from carbonizing and volatilizing during the diffusion heating process. Exemplarily, the thickening solid powder is selected from at least one or two or more organic compounds selected from hydroxypropyl cellulose and ethyl cellulose.

[0022] According to an embodiment of the present invention, the thickening solid powder is commercially available. The present invention does not specifically limit the particle size of the thickening solid powder, and particle sizes known in the art can be selected, such as 60 mesh, 80 mesh, and 100 mesh.

[0023] The present invention also provides a neodymium iron boron permanent magnet, which is obtained by diffusion process of the above-mentioned diffusing agent on a sintered magnet matrix.

[0024] According to an embodiment of the present invention, the sintered magnet matrix may be selected from neodymium iron boron sintered magnets known in the art. Preferably, the sintered magnet matrix comprises at least the following components:

[0025] R, which includes at least Nd, and may also be selected from any one or more of the rare earth elements Pr, Ce, Tb, Dy, Gd and Ho, with the content of R being 27-34 wt%.

[0026] B, the content of which is 0.8-1.3 wt%;

[0027] T, T is selected from at least one of Co, Ti, Ga, Cu, Al, Cr, Mn, Zr, Nb, Si, W and Mo, and the content of T is 0-5 wt%.

[0028] The remaining content consists of Fe and unavoidable impurities.

[0029] According to an embodiment of the present invention, at 20°C, the Hcj of the neodymium iron boron permanent magnet is greater than 1900 kA / m, preferably greater than 1950 kA / m, for example 1984 kA / m.

[0030] The present invention provides a method for preparing the neodymium iron boron permanent magnet, the method comprising: performing a diffusion process on a sintered magnet matrix using the above-mentioned diffusing agent to obtain the neodymium iron boron permanent magnet.

[0031] According to an embodiment of the present invention, the diffusion process includes diffusion treatment and aging treatment, wherein the diffusion treatment includes: heating during the diffusion stage, diffusion holding during the diffusion stage, and cooling during the diffusion stage; the aging treatment includes: heating during the aging stage, aging holding during the aging stage, and cooling during the aging stage.

[0032] According to an embodiment of the present invention, the diffusion stage heating is a stepped heating, specifically including: a first stage heating and a second stage heating.

[0033] Preferably, the initial heating stage includes: first heating to 300-400℃ and then holding at that temperature for 1-3 hours. In this invention, the purpose of setting the holding temperature and time for the initial heating stage is to ensure that the organic solvent and organic powder in the dispersant can be fully carbonized and / or volatilized, thereby not affecting the subsequent diffusion effect of the dispersant.

[0034] Preferably, the two-stage heating includes heating to 750-850℃ and holding for 2-6 hours. In this invention, the purpose of setting the holding temperature and time for the two-stage heating is twofold: firstly, to ensure effective dehydrogenation, and secondly, to homogenize the temperature at various points within the diffusion furnace. This lays the groundwork for uniform temperature at all points within the diffusion furnace during the diffusion holding stage, thereby increasing the effective holding time for subsequent diffusion.

[0035] According to an embodiment of the present invention, the diffusion insulation is a stepped heating method, specifically including: a first-stage insulation and a second-stage insulation.

[0036] Preferably, the first stage of heat preservation specifically includes: heating to 850-1000℃ and then maintaining the temperature for 10-20 hours. Preferably, the second stage of heat preservation specifically includes: cooling to 800-950℃ and then maintaining the temperature for 3-10 hours.

[0037] The inventors discovered that during the first stage of heat preservation, the viscosity of the neodymium-rich phase decreases and its fluidity increases, which can promote the full entry of heavy rare earth elements in the dispersant into the interior of the magnet's grain boundary phase. However, as the heat preservation time increases, the diffusion concentration difference in the grain boundary phase weakens relatively, and the diffusion driving force deteriorates. Therefore, by cooling to enter the second stage of heat preservation, the force of cooling contraction indirectly increases the compression, causing the neodymium-rich phase to continue to creep deeper into the magnet's grain boundary phase. This not only reduces the number of large neodymium-rich phases in the grain boundary phase, narrowing the diffusion channel, but also effectively increases the diffusion depth from a kinetic perspective, thereby reducing the negative impact of the neodymium-rich phase eroding the main phase grains when diffusion is not driven by force.

[0038] According to an embodiment of the present invention, the diffusion stage cooling includes gas-filled cooling and air cooling. Preferably, the gas-filled cooling specifically involves filling with 30-90 kPa inert gas for cooling for 0.5-1 h. Preferably, the air cooling specifically involves blowing air (e.g., using a fan) after the gas-filled cooling until the temperature is below 250°C.

[0039] According to an embodiment of the present invention, the diffusion process can be carried out under an inert gas and / or vacuum condition, as long as the above diffusion process can be achieved to obtain the neodymium iron boron permanent magnet of the present invention. Further, the inert gas is selected from gases known in the art, such as Ar.

[0040] According to an embodiment of the present invention, the aging process includes, in sequence, aging stage heating, aging hold-up, and aging stage cooling.

[0041] According to an embodiment of the present invention, the aging stage heating includes: heating to 250-350℃ and holding for 1-2 hours. In this invention, the purpose of the aging stage heating is to ensure the temperature of the entire furnace is uniform beforehand, laying the groundwork for more effective subsequent heating to reach the aging holding temperature, and ensuring temperature consistency at various points within the furnace, thereby better guaranteeing the aging effect at all points in the furnace and increasing the effective aging holding time.

[0042] According to an embodiment of the present invention, the aging and heat preservation specifically involves heating to 400-680℃ and maintaining the temperature for 3-10 hours.

[0043] According to an embodiment of the present invention, the aging stage cooling includes a first-stage cooling and a second-stage cooling. Preferably, the first-stage cooling specifically involves introducing an inert gas at 30-90 kPa for cooling for 0.5-1 hours. Preferably, the second-stage cooling specifically involves blowing air to cool the air after the first-stage cooling until the temperature is below 120°C.

[0044] According to an embodiment of the present invention, in the diffusion process, the heating rate during heating is, for example, 3-10 °C / min, and the cooling rate during cooling is, for example, 5-15 °C / min.

[0045] The present invention also provides applications of the above-mentioned neodymium iron boron permanent magnets in new energy and intelligent manufacturing fields, such as electric vehicle drive motors and motors for intelligent electronic products.

[0046] Beneficial effects

[0047] This invention provides a highly efficient dispersant. When combined with the diffusion process of this invention, the heating during the diffusion stage and the diffusion heat preservation stage are both stepped heating. On the one hand, this can ensure effective dehydrogenation, and on the other hand, it can make the temperature of each point in the diffusion furnace uniform. That is, it lays the foundation for the uniformity of temperature of each point in the diffusion furnace during the diffusion heat preservation stage, thereby increasing the effective time of subsequent diffusion heat preservation.

[0048] By using the novel diffusing agent developed in this invention and by optimizing the diffusion process conditions, a high-performance neodymium iron boron permanent magnet was prepared, and its magnetic properties were effectively improved. Detailed Implementation

[0049] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0050] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0051] Example 1

[0052] (1) Preparation of RFeBM flakes by melting: The raw materials were melted in an argon atmosphere. The raw material formula is as follows (mass fraction): 31.1wt% PrNd, 0.96wt% B, 0.12wt% Zr, 0.30wt% Cu, 0.1wt% Al%, 0.1wt% Ga, with the balance being Fe and unavoidable impurities. The raw materials were prepared according to the above formula and added to the melting furnace. After the alloy melted, the temperature was raised to 1440℃ and held for 10 minutes. Then it was cooled to 1380℃ and cast. The fast-solidified flakes with an average thickness of 0.25mm were obtained by the strip casting process.

[0053] (2) Powdering: Powder with an average particle size of 2.8 μm was finally obtained by hydrogen explosion + air jet milling;

[0054] (3) Pressing: The blank is pressed into a compact under a magnetic field and then isostatically pressed to form a compact with a density of approximately 4.6 g / cm³. 3 The pressed blank;

[0055] (4) Sintering and forming: First, the temperature is held at 350℃ for 3 hours, then the temperature is raised to 850℃ and held for 1 hour for degassing, then the temperature is held at 1060℃ for 120 minutes for sintering, and finally the temperature is held at 520℃ for 300 minutes to form a sintered NdFeB magnet matrix.

[0056] The magnets obtained in step (4) are processed to obtain products with dimensions of 45-20-4mm (4mm is the orientation direction). Then, surface chemical pretreatment is carried out by degreasing, cleaning and pickling to make the substrate surface free of oxide skin and prevent the diffusion of diffusion source.

[0057] (5) The dispersant is composed of Dy powder (average particle size 2.6 μm), nickel trioxide powder (average particle size 1.8 μm), Ca powder (average particle size 2.2 μm), ethanol, and hydroxypropyl cellulose (100 mesh) in a weight ratio of 50:6:4:34.7:5.3; (6) The dispersant is coated on the surface of the substrate, and after the surface is dried, the weight of the heavy rare earth coating is 0.8% of the substrate.

[0058] (7) Diffusion process: The NdFeB substrate after being coated with a diffusing agent in step (6) is placed into a diffusion furnace, and the vacuum is evacuated to below 100 Pa before heating. The first heating stage of the diffusion heating section is 350℃*2h, and the second heating stage is 800℃*2h. Then, the temperature is raised to the diffusion heating section of 880℃*15h and then lowered to 860℃*10h. The average heating rate of each stage is 6℃ / min. The cooling rate is 10℃ / min. Then, the temperature is cooled to 200℃ and evacuated to below 100 Pa again. The aging stage is heated to 500℃ and held for 6h. Then, the temperature is cooled to below 120℃ before being removed from the furnace to obtain the diffused NdFeB magnet M1.

[0059] Comparative Example 1

[0060] The preparation method of the diffused NdFeB magnet in Comparative Example 1 is basically the same as that in Example 1, except that:

[0061] Step (5): The dispersant is composed of Dy powder (average particle size 2.6 μm), ethanol, and hydroxypropyl cellulose (100 mesh) in a weight ratio of 60:34.7:5.3;

[0062] The rest is the same as in Example 1, and a diffused NdFeB magnet D1 is prepared.

[0063] Comparative Example 2

[0064] The preparation method of the diffused NdFeB magnet in Comparative Example 2 is basically the same as that in Example 1, except that:

[0065] Step (5): The dispersant is composed of Dy powder (average particle size 2.6 μm), nickel trioxide powder (average particle size 1.8 μm), ethanol, and hydroxypropyl cellulose (100 mesh) in a weight ratio of 50:10:34.7:5.3.

[0066] The rest is the same as in Example 1, and a diffused NdFeB magnet D2 is prepared.

[0067] Comparative Example 3

[0068] The preparation method of the diffused NdFeB magnet in Comparative Example 3 is basically the same as that in Example 1, except that:

[0069] Step (5): The dispersant is composed of Dy powder (average particle size 2.6 μm), Ca powder (average particle size 2.2 μm), ethanol, and hydroxypropyl cellulose (100 mesh) in a weight ratio of 50:10:34.7:5.3.

[0070] The rest is the same as in Example 1, and a diffused NdFeB magnet D3 is prepared.

[0071] Comparative Example 4

[0072] The preparation method of the diffused NdFeB magnet in Comparative Example 4 is basically the same as that in Example 1, except that:

[0073] Step (5): The dispersant is composed of Dy powder (average particle size 2.6 μm), nickel trioxide powder (average particle size 1.8 μm), Ca powder (average particle size 2.2 μm), and ethanol in a weight ratio of 50:6:4:40.

[0074] The rest is the same as in Example 1, and a diffused NdFeB magnet D4 is prepared.

[0075] Comparative Example 5

[0076] The preparation method of the diffused NdFeB magnet in Comparative Example 5 is basically the same as that in Example 1, except that:

[0077] Step (5): In the dispersant, the weight ratio of Dy powder (average particle size 2.6 μm), nickel oxide powder (average particle size 1.8 μm), Ca powder (average particle size 2.2 μm), ethanol, and hydroxypropyl cellulose (100 mesh) is 50:6:4:30:10.

[0078] Because the dispersant was too viscous, it could not be stirred evenly and could not be uniformly coated on the magnet surface. The subsequent coating experiment (7) and diffusion process (8) were not carried out, and a diffused NdFeB magnet was not prepared.

[0079] Comparative Example 6

[0080] The preparation method of the diffused NdFeB magnet in Comparative Example 6 is basically the same as that in Example 1, except that:

[0081] Step (7) The diffusion process is as follows: the vacuum is reduced to below 100 Pa before heating begins. The first heating stage of the diffusion heating section is held at 350℃ for 2 hours, and the second heating stage is held at 800℃ for 2 hours. Then, the temperature is raised to 880℃ for 20 hours and then cooled to 200℃. The vacuum is then reduced to below 100 Pa again, and the aging stage is started. The temperature is then raised to 500℃ and held for 6 hours. Finally, the temperature is cooled to below 120℃ before the material is removed from the furnace to obtain the diffused NdFeB magnet.

[0082] Comparative Example 7

[0083] The preparation method of the diffused NdFeB magnet in Comparative Example 7 is basically the same as that in Example 1, except that:

[0084] Step (5): In the dispersant, the weight ratio of Dy powder (average particle size 2.6 μm), nickel oxide powder (average particle size 1.8 μm), Ca powder (average particle size 2.2 μm), ethanol, and hydroxypropyl cellulose (100 mesh) is 50:9:1:34.7:5.3.

[0085] The rest is the same as in Example 1, and a diffused NdFeB magnet D7 is prepared.

[0086] Comparative Example 8

[0087] The preparation method of the diffused NdFeB magnet in Comparative Example 8 is basically the same as that in Example 1, except that:

[0088] Step (5): In the dispersant, the weight ratio of Dy powder (average particle size 2.6 μm), nickel oxide powder (average particle size 1.8 μm), Ca powder (average particle size 2.2 μm), ethanol, and hydroxypropyl cellulose (100 mesh) is 50:3:7:34.7:5.3.

[0089] The rest is the same as in Example 1, and a diffused NdFeB magnet D8 is prepared.

[0090] Comparative Example 9

[0091] The preparation method of the diffused NdFeB magnet in Comparative Example 9 is basically the same as that in Example 1, except that:

[0092] Step (5): In the dispersant, the weight ratio of Dy powder (average particle size 2.6 μm), nickel oxide powder (average particle size 1.8 μm), Ca powder (average particle size 2.2 μm), ethanol, and hydroxypropyl cellulose (100 mesh) is 40:12:8:30:10.

[0093] The rest is the same as in Example 1, and a diffused NdFeB magnet D9 is prepared.

[0094] Example 2

[0095] The preparation method of the diffused NdFeB magnet in Example 2 is basically the same as that in Example 1, except that:

[0096] Step (5): In the dispersant, the weight ratio of Tb powder (average particle size 2.6 μm), Al powder (average particle size 1.8 μm), Ca powder (average particle size 2.2 μm), methanol, and ethyl cellulose (100 mesh) is 50:6:4:36.4:4.6.

[0097] Step (6): Apply the dispersant to the surface of the substrate, and after the surface is dried, the weight of the heavy rare earth coating is 0.8% of the substrate.

[0098] Step (7): Diffusion process: The NdFeB substrate coated with the diffusing agent in step (6) is placed into the diffusion furnace, and the pressure is reduced to below 100 Pa before heating begins. The first holding time in the diffusion heating section is 350℃*2h, and the second holding time is 850℃*2h. Then the temperature is raised to 900℃ in the diffusion holding section.

[0099] After holding at 880℃ for 15 hours, the temperature was lowered to 880℃ and held for 10 hours. The heating rate at each stage was 6℃ / min, and the cooling rate was 10℃ / min. After cooling to 200℃, the temperature was evacuated to below 100Pa, and the aging stage was heated to 500℃ and held for 6 hours. The temperature was then cooled to below 120℃ before being removed from the furnace to obtain the diffused NdFeB magnet.

[0100] Twenty-five samples of each of the diffused NdFeB magnets prepared in the above examples and comparative examples were taken as a group. Br and Hcj were tested at 20℃ using a magnetic meter, and the average value of the test results for each group was calculated. The results are recorded in Table 1.

[0101] Table 1. Magnetic Properties Test of Diffused NdFeB Magnets

[0102]

[0103] As can be seen from Comparative Example 1 and Comparative Example 1, when the composition of metals M1 and M2 is added to the diffuser, its Hcj increases by about 90 kA / m. The addition of the metal M composition results in three melting actions in the diffusion process, which in turn increases the creep force three times, effectively reducing the self-diffusion activation energy, promoting the flow of heavy rare earth atoms to deeper depths, increasing the effective utilization rate of heavy rare earths, and thus resulting in a higher Hcj increase.

[0104] Comparing Example 1 with Comparative Examples 2 and 3, it can be seen that Comparative Example 3, which lacks M1 in the dispersant, performs slightly worse than Comparative Example 2, which lacks M2, but both show a slightly lower increase than when both metals are added. The main reason is that the initial melting of M1 and the melting of the neodymium-rich phase are more conducive to the early diffusion of heavy rare earth concentrations; however, if either of these is missing, the diffusion effect is not as good as in Example 1, and consequently, the increase in Hcj is relatively smaller.

[0105] Comparing Example 1 and Comparative Example 4, it can be seen that when no organic powder is added to the dispersant, the coating amount fluctuates greatly. The main reason is that the addition of the organic powder hydroxypropyl cellulose can form a liquid with a certain viscosity with ethanol, which helps the heavy rare earth and metal powders to be suspended in the organic solvent, resulting in a more uniform distribution of heavy rare earth and metal and a better coating effect. Without this organic powder, the low viscosity leads to uneven coating thickness, that is, the Hcj increase fluctuates greatly.

[0106] Comparing Example 1 and Comparative Example 5, it can be seen that when the addition ratio of organic powder hydroxypropyl cellulose, i.e., its weight ratio of ethanol, exceeds 20%, the dispersant will not be able to be stirred or the viscosity will be too high, which is not conducive to coating.

[0107] Comparing Example 1 and Comparative Example 6, it can be seen that when diffusion only involves one step of heat preservation, the increase in Hcj performance is slightly lower. The inventors believe that because the second cooling and heat preservation stage is missing, that is, the driving force through cooling and contraction is missing, the diffusion process of Comparative Example 6 is a non-powered diffusion. Therefore, due to the lack of driving force, some of the diffusion agent coated on the surface remains attached to the magnet surface and does not enter the magnet interior. As a result, the concentration and depth of heavy rare earth diffusion are not as good as in Example 1, and thus complete heavy rare earth diffusion does not occur inside the magnet.

[0108] As can be seen from Comparative Example 7, when the weight ratio of nickel trioxide to Ca is 9:1, that is, the amount of substance M1 is too large and the amount of substance M2 is too small, the weight ratio of substance M1 to substance M2 in Comparative Example 7 is greater than 1:0.6. Therefore, the lower proportion of substance M2 compared to Example 1 results in a less obvious secondary melting driving effect of the diffuser, a relatively lower diffusion depth, and a relatively insufficient increase in Hcj.

[0109] As shown in Comparative Example 8, when the weight ratio of nickel oxide to Ca is 1:0.43, that is, when the weight ratio of M1 to M2 is less than 1:1.4, the initial heat source is missing due to the low content of M1 in the diffuser. Furthermore, when the diffusion temperature exceeds the melting point of the neodymium-rich phase, the liquid content of the neodymium-rich phase is relatively low, and the melting driving effect of M1 is slightly weaker than that of Example 1. Therefore, the neodymium-rich phase thin layer of the magnet has relatively poor uniformity, resulting in a slightly lower Hcj increase and slightly larger fluctuations.

[0110] In Comparative Example 9, the ratio of Dy powder to the total (M1+M2) in the dispersant was 40:20. The weight percentage of the metal compositions M1 and M2 reached 20%, exceeding the 15% upper limit for the total M1+M2.

[0111] Compared to Example 1, the weight ratio of heavy rare earth element Dy in Comparative Example 9 is reduced. Therefore, when the amount of heavy rare earth element in the diffuser is the same, the amount of diffuser on the magnet substrate surface is increased compared to Example 1. Thus, under the same diffusion process, the diffusion effect of Comparative Example 9 is relatively poor, and the increase in Hcj is small.

[0112] In Example 2, when heavy rare earth element RH was used as the dispersant for Tb, the performance improvement of Hcj was more significant than that in Example 1.

[0113] The exemplary embodiments of the present invention have been described above. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A dispersant, characterized in that, The dispersant comprises the following components: a rare earth R composition, a metal composition, an organic solvent, and an organic powder; wherein, Based on the total mass of the dispersant, the rare earth R composition accounts for 40-60 wt% by weight, the metal composition accounts for 5-15 wt% by weight, and the organic solvent accounts for 25-45 wt% by weight. The weight ratio of the organic powder to the organic solvent is (10-20):

100.

2. The dispersant according to claim 1, characterized in that, The rare earth R composition is selected from at least one or a combination of two or more rare earth metals, rare earth alloys, rare earth oxides or rare earth hydrides, wherein the rare earth comprises RH and / or RL; RH represents a heavy rare earth element selected from at least one of Dy, Tb and Ho; RL represents a light rare earth element selected from at least one of Pr, Nd, La and Ce. Preferably, the metal composition comprises substance M1 and substance M2. Preferably, the mass ratio of substance M1 to substance M2 is 1:(0.6 to 1.4). Preferably, the M1 material is selected from pure metals, metal alloys or metal oxides with melting points between 500 and 660°C, for example, at least one of nickel trioxide, magnesium, aluminum, copper-aluminum alloys, and magnesium-aluminum alloys. Preferably, the M2 substance is selected from pure metals, metal alloys or metal oxides with melting points between 700 and 850°C, for example, at least one of barium and calcium.

3. The dispersant according to claim 1 or 2, characterized in that, The organic solvent is selected from at least one or a combination of two or more of methanol, ethanol, butanol, xylene, toluene, and isopropanol. Preferably, the organic powder is selected from thickening solid powder.

4. A neodymium iron boron permanent magnet, characterized in that, The neodymium iron boron permanent magnet is obtained by diffusion process of the sintered magnet matrix using the diffusing agent described in any one of claims 1-3.

5. The neodymium iron boron permanent magnet according to claim 4, characterized in that, The sintered magnet matrix comprises at least the following components: R, which includes at least Nd, and may also be selected from any one or more of the rare earth elements Pr, Ce, Tb, Dy, Gd and Ho, with the content of R being 27-34 wt%. B, the content of which is 0.8-1.3 wt%; T, T is selected from at least one of Co, Ti, Ga, Cu, Al, Cr, Mn, Zr, Nb, Si, W and Mo, and the content of T is 0-5 wt%. The remaining content consists of Fe and unavoidable impurities.

6. The method for preparing the neodymium iron boron permanent magnet according to claim 4 or 5, characterized in that, The preparation method includes: performing a diffusion process on a sintered magnet matrix using the diffusing agent described in any one of claims 1-3 to obtain the neodymium iron boron permanent magnet.

7. The preparation method according to claim 6, characterized in that, The diffusion process includes diffusion treatment and aging treatment, wherein the diffusion treatment includes: heating during the diffusion stage, diffusion holding during the diffusion stage, and cooling during the diffusion stage; the aging treatment includes: heating during the aging stage, aging holding during the aging stage, and cooling during the aging stage.

8. The preparation method according to claim 6 or 7, characterized in that, The diffusion stage heating is a stepped heating, specifically including: a first stage heating and a second stage heating. Preferably, the heating process includes: first heating to 300-400℃ and then holding at that temperature for 1-3 hours. Preferably, the two-stage heating process specifically includes: heating to 750-850℃ and holding at that temperature for 2-6 hours. Preferably, the diffusion insulation is a stepped heating method, specifically including: a first-stage insulation and a second-stage insulation. Preferably, the first stage of heat preservation specifically includes: heating to 850-1000℃ and then maintaining the temperature for 10-20 hours. Preferably, the second stage of heat preservation specifically includes: cooling to 800-950℃ and then maintaining the temperature for 3-10 hours. Preferably, the diffusion stage cooling includes gas-filled cooling and air cooling. Preferably, the gas-filled cooling specifically involves filling with 30-90 kPa inert gas for 0.5-1 h to lower the temperature. Preferably, the air cooling specifically involves blowing air after the gas-filled cooling until the temperature is below 250°C. Preferably, the diffusion process is carried out under inert gas and / or vacuum conditions.

9. The preparation method according to any one of claims 6-8, characterized in that, The aging process includes, in sequence: aging stage heating, aging stage heat preservation, and aging stage cooling. Preferably, the aging stage heating includes: heating to 250-350℃ and holding for 1-2 hours. Preferably, the aging and heat preservation specifically involves heating to 400-680℃ and maintaining the temperature for 3-10 hours. Preferably, the aging stage cooling includes a first-stage cooling and a second-stage cooling. Preferably, the first-stage cooling specifically involves introducing an inert gas at 30-90 kPa for 0.5-1 hour to lower the temperature. Preferably, the second-stage cooling specifically involves blowing air to cool the area after the first-stage cooling until the temperature drops below 120°C. Preferably, in the diffusion process, the heating rate during heating is 3-10℃ / min, and the cooling rate during cooling is 5-15℃ / min.

10. The application of the neodymium iron boron permanent magnet as described in claim 4 or 5 in the fields of new energy and intelligent manufacturing.

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