WO2023210842A1 - Method for manufacturing rare earth permanent magnet - Google Patents

Abstract

A method for manufacturing a rare earth permanent magnet according to the present invention comprises: a step of preparing a rare earth sintered magnet (hereinafter referred to as a "base material") of Re-Fe-TM-B (Re=rare earth element, Fe=iron, TM=3d transition metal, and B=boron); a step of preparing a rare earth compound slurry and an additive; a step of preparing a coating agent by mixing and stirring the rare earth compound slurry and the additive; a coating step of coating the surface of the base material with the coating agent; a grain boundary diffusion step of heating the sintered magnet coated with the rare earth compound to diffuse the grain boundary; and heat-treating the grain boundary-diffused sintered magnet.

Description

Manufacturing method of rare earth permanent magnets

The present invention relates to a method of manufacturing rare earth permanent magnets. Specifically, a rare earth compound coating agent is applied to the surface of a rare earth sintered magnet of Re-Fe-TM-B (Re = rare earth element, Fe = iron, TM = 3d transition metal, B = boron) and heated to a predetermined temperature to form a rare earth compound. This relates to a method of manufacturing a rare earth permanent magnet that improves the residual magnetic flux density and coercive force by diffusing the separated rare earth metal into the grain boundaries of the rare earth sintered magnet.

Demand for Re-Fe-TM-B sintered magnets is gradually increasing for use in motors such as hybrid cars, and it is required to further increase its coercive force (Hcj). In order to increase the coercive force (Hcj) of the Re-Fe-TM-B sintered magnet, a method of substituting part of Nd with Dy or Tb is known, but resources of Dy or Tb are scarce and are ubiquitous in some areas. In addition, the problem is that the residual magnetic flux density (Br) or maximum energy product ((BH)max) of the Re-Fe-TM-B sintered magnet decreases due to the substitution of these elements.

Recently, when Dy or Tb is attached to the surface of a Re-Fe-TM-B sintered magnet by sputtering and heated to 700-1000℃, the residual magnetic flux density (Br) of the magnet is hardly reduced and the coercive force (Br) is increased. It has been discovered that Hcj) can be increased.

Dy or Tb attached to the magnet surface is sent into the sintered body through the grain boundaries of the sintered body, and diffuses from the grain boundaries into the interior of each particle of the main phase (grain boundary diffusion). At this time, since the Re-rich phase at the grain boundary is liquefied by heating, the diffusion rate of Dy or Tb in the grain boundary is much faster than the diffusion rate from the grain boundary into the interior of the columnar grain.

By using this difference in diffusion rate to adjust the heat treatment temperature and time, it is possible to achieve a state in which the concentration of Dy or Tb is high only in the area (surface area) extremely close to the grain boundaries of the columnar particles in the sintered body throughout the entire sintered body. there is. Since the coercive force (Hcj) of the Re-Fe-TM-B sintered magnet is determined by the state of the surface area of the columnar particles, the Re-Fe-TM-B sintered magnet with crystal grains with a high concentration of Dy or Tb in the surface area is It has high coercivity. Additionally, as the concentration of Dy or Tb increases, the residual magnetic flux density (Br) of the magnet decreases, but since such an area is only the surface area of each columnar particle, the residual magnetic flux density (Br) of the columnar particles as a whole hardly decreases. No. In this way, it is possible to manufacture Re-Fe-TM-B sintered magnets with high coercive force (Hcj) and residual magnetic flux density (Br) that do not substitute Dy or Tb, and high-performance magnets that do not change much. This method is performed using the grain boundary diffusion method. It is said.

In Patent Document 1 (Korean Patent Publication No. 10-2015-0131092, November 24, 2015), the coercive force of the NdFeB-based sintered magnet is increased by adding silicone grease to the coating agent when producing a grain boundary diffusion coating agent for manufacturing grain boundary diffusion NdFeB sintered magnets, but the coating agent When manufacturing silicone grease, silicone oil, and dispersant, a large amount of carbon remains in the magnet after grain boundary diffusion treatment, which limits the ability to improve residual magnetic flux density and coercive force after grain boundary diffusion.

In Patent Document 2 (Korean Patent Publication No. 10-2018-0068272, June 21, 2018), a coating agent application method using a dipping method is repeatedly performed 1 to 50 times to produce grain boundary diffusion NdFeB sintered magnets, and this method is used to It is difficult to precisely control the amount of coating agent used, and there is a problem that peeling of the coating agent may occur during the grain boundary diffusion process.

[Prior art literature]

[Patent Document]

(Patent Document 1) Korean Patent Publication No. 10-2015-0131092 (2015.11.24)

(Patent Document 2) Korean Patent Publication No. 10-2018-0068272, 2018.06.21)

The present invention relates to a method for manufacturing rare earth permanent magnets, which involves applying a coating agent to the surface of a rare earth sintered magnet of Re-Fe-TM-B (Re = rare earth element, Fe = iron, TM = 3d transition metal, B = boron). Application step; This is a method of manufacturing rare earth permanent magnets that heats a sintered magnet coated with a rare earth compound to spread grain boundaries. Ethyl cellulose is added as an additive in the step of preparing the double coating agent to increase the adhesion between the sintered magnet and the coating agent, resulting in grain boundary diffusion process. We provide a method for manufacturing rare earth permanent magnets that improves the residual magnetic flux density and coercive force by improving the bonding force during sintering, reducing the peeling phenomenon between the sintered magnet and the coating agent, and preventing the coercive force from lowering by lowering the carbon residue after grain boundary diffusion .

In order to achieve the above-described object, the method for manufacturing a rare earth permanent magnet according to the present invention includes the steps of preparing a rare earth sintered magnet of Re-Fe-TM-B (hereinafter referred to as 'base material'); Preparing rare earth compound slurry and additives; Preparing a coating agent by mixing and stirring a rare earth compound slurry and additives; An application step of applying a coating agent to the surface of the base material; A grain boundary diffusion step of heating the base material coated with the rare earth compound to spread the grain boundaries; A method of manufacturing a rare earth permanent magnet, characterized in that it consists of the step of heat treating the grain boundary-diffused base material.

In the method for manufacturing a rare earth permanent magnet according to the present invention, the rare earth compound is rare earth hydride or rare earth fluoride.

In the method of manufacturing a rare earth permanent magnet according to the present invention, the rare earth compound is one or more of DyH, TbH, HoH, NdH, PrH, and CeH, and the rare earth fluoride is one or more of PrF, NdF, GdF, TbF, DyF, and HoF. There is more than one.

The rare earth compound slurry is made by mixing rare earth hydride or rare earth fluoride and ethanol at a ratio of 1:1 by weight.

The additive is mixed with ethanol and ethyl cellulose in an amount of 10 parts by weight: 0.5 to 2 parts by weight or 10 parts by weight: 0.7 to 1.5 parts by weight.

Preferably, the additive is a mixture of ethanol and ethyl cellulose at 10 parts by weight: 1 part by weight.

The coating agent is prepared by mixing and stirring 10 parts by weight: 0.1 to 1 part by weight or 10 parts by weight: 0.3 to 0.7 parts by weight of the rare earth compound slurry and additives.

Preferably, the coating agent is prepared by mixing and stirring 10 parts by weight: 0.5 parts by weight of rare earth compound slurry and additives.

In the step of preparing the base material, the surface of the sintered base material in the thickness direction is polished to a roughness of 10㎛ or less, then immersed in a 2-5% nitric acid solution or a 3% nitric acid solution for 80 seconds, and then immersed in an ethanol solution for 20-20 seconds. After washing for 40 seconds or 25 to 35 seconds, wash in distilled water for 20 to 40 seconds or 25 to 35 seconds.

The coating agent is applied to the surface of the base material by dipping or spraying.

The grain boundary diffusion step is performed in a vacuum atmosphere at 850 to 900° C. for 7 to 15 hours, preferably 8 to 12 hours.

Preferably, the grain boundary diffusion step is performed at 900° C. for 10 hours in a vacuum atmosphere.

After the grain boundary diffusion process, heat treatment is performed at 400 to 700° C. for 1 to 3 hours.

Preferably, heat treatment is performed at 450 to 550°C for 1.5 to 2.5 hours.

According to the method of manufacturing a rare earth permanent magnet according to the present invention, the coating agent applied to the surface of the base material reduces the phenomenon of peeling from the base material after application, so that the rare earth metal contained in the coating agent diffuses well to the grain boundaries and remains during grain boundary diffusion. Magnets with high magnetic flux density can be manufactured.

In addition, since the coating agent applied to the surface of the base material has a low carbon content, the carbon residue after grain boundary diffusion can be reduced to suppress the lowering of the coercive force.

In addition, when using a coating agent containing ethylcellulose, the coercivity of the rare earth permanent magnet can be increased by grain boundary diffusion while minimizing the use of expensive heavy rare earth elements.

1 is a flow chart of the manufacturing method according to the present invention.

Figure 2 is a flowchart of steps for preparing a base material in the manufacturing method according to the present invention.

Figure 3 is a flowchart of steps for manufacturing a coating agent in the manufacturing method according to the present invention.

Figure 4 is a photograph after applying the coating agent of Comparative Example 1-2 of the present invention by dipping.

Figure 5 is a photograph after applying the coating agent of Comparative Example 3-2 of the present invention by dipping.

Figure 6 is a photograph after application of the coating agent of Example 2-2 of the present invention by the dipping method.

Figure 7 is a photograph after applying the coating agent of Example 2-5 of the present invention by spraying.

Figure 8 is a photograph after grain boundary diffusion of Comparative Example 1-2 of Figure 4.

Figure 9 is a photograph after grain boundary diffusion of Comparative Example 3-2 of Figure 5.

Figure 10 is a photograph after grain boundary diffusion of Example 2-2 of Figure 6.

Figure 11 is a photograph after grain boundary diffusion of Example 2-5 of Figure 7.

Hereinafter, the present invention will be described in more detail. Hereinafter, “upward,” “downward,” “front,” and “rear” and other directional terms are defined based on the states shown in the drawings.

The manufacturing method of the present invention is as shown in Figure 1, and the step of preparing the rare earth sintered magnet (base material) is prepared in the order shown in Figure 2. Additionally, the manufacturing method of the coating agent applied to the base material is prepared in the same order as Figure 3. .

Hereinafter, the description will be based on the manufacturing method shown in FIGS. 1 to 3.

[Manufacturing method]

(1) Step of manufacturing rare earth sintered magnet of Re-Fe-TM-B

The raw material Re-Fe-TM-B powder (Re = rare earth element, Fe = iron, TM = 3d transition metal, B = boron) is melted, and the melt is injected into a cooling roll rotating at high speed to form a ribbon-shaped alloy. was manufactured. The ribbon-shaped ingot produced through the rolling process is milled with a stamp mill and pulverized to a size of about 100 to 300 ㎛ to produce Re-Fe-TM-B magnetic powder, then molded and applied with a magnetic field, and then sintered. Manufactures rare earth sintered magnets of Re-Fe-TM-B

(2) Polishing and cleaning the Re-Fe-TM-B rare earth sintered magnet

The preparation steps for the rare earth sintered magnet (base material) shown in Figure 2 are:

After polishing the surface of the base material in the thickness direction to 10㎛ or less, immersion in a 2-5% nitric acid solution or a 3% nitric acid solution for 80 seconds, washing in ethanol solution for 20-40 seconds or 25-35 seconds, and then washing with distilled water. Wash in distilled water for 20 to 40 seconds or in distilled water for 20 to 40 seconds or 25 to 35 seconds.

(3) Production of rare earth compound slurry in coating agent

Figure 3 is a flowchart of steps for manufacturing a coating agent in the manufacturing method according to the present invention. The rare earth compound to be applied to the surface of the cleaned sintered magnet is at least one of rare earth hydride and rare earth fluoride.

The rare earth hydride is one or more of DyH, TbH, HoH, NdH, PrH, and CeH, and the rare earth fluoride is one or more of PrF, NdF, GdF, TbF, DyF, and HoF, and the rare earth hydride or rare earth fluoride is each alone. It can be used by mixing rare earth hydrides and rare earth fluorides.

A rare earth compound slurry is prepared by mixing the rare earth hydride or rare earth fluoride, rare earth hydride, rare earth fluoride, and ethanol in a ratio of 1 part by weight:1 part by weight.

(4) Preparation of additives in coating agents

The additive to be added to the rare earth compound slurry to be applied to the surface of the cleaned sintered magnet shown in FIG. 3 is a mixture of ethanol and ethyl cellulose, of which ethyl cellulose has a bonding force with rare earth hydride or rare earth fluoride. It functions to increase the thickness of the coating layer and prevent it from peeling off from the base material, and the polymer chain of ethylcellulose facilitates the diffusion of rare earth metals separated from the rare earth compounds in the coating agent from the surface of the base material to the internal grain boundaries. I do it.

In addition, when using a coating agent containing the additive ethylcellulose, the coercivity of the rare earth magnet sintered body can be increased while minimizing the use of expensive rare earth materials.

The additives, ethanol and ethyl cellulose, are mixed in an amount of 10 parts by weight: 0.5 to 2 parts by weight or 10 parts by weight: 0.7 to 1.5 parts by weight. Preferably, the additive is 10 parts by weight of ethanol and ethyl cellulose. Part: Mix 1 part by weight.

Ethyl cellulose, an additive ingredient, is a substance that dissolves in organic solvents such as ethanol, and its solubility is low, so when ethyl cellulose exceeds 2 parts by weight in 10 parts by weight of ethanol, the viscosity increases and when applied to the base material, It has the disadvantage of being difficult to apply thinly and increasing the amount of application, which increases residual carbon. Carbon may be generated in the temperature range of 300 to 500 ℃ where ethylcellulose decomposes during the grain boundary diffusion process, and the residual carbon causes a decrease in magnetic properties. can do.

Additionally, if the amount of ethyl cellulose per 10 parts by weight of ethanol is less than 0.5 parts by weight, the viscosity required to coat and maintain the surface of the rare earth compound is lowered.

(5) Preparation of coating agent

The coating agent is prepared by mixing and stirring the rare earth compound slurry and additives in an amount of 10 parts by weight: 0.1 to 1 part by weight or 10 parts by weight: 0.3 to 0.7 parts by weight. Preferably, the coating agent contains a rare earth compound slurry and additives in an amount of 10 parts by weight: 0.5 parts by weight. Mix and stir.

(6) Application of coating agent to base material

The prepared coating agent is applied to the base material. The application method is applied by dipping or spraying.

The amount of coating agent applied is 0.6 to 1.0 parts by weight based on 100 parts by weight of the base material on the surface of the prepared base material.

The weight of the coating agent refers to the difference between the mass of the base material measured before application and the mass measured after application.

(7) Grain boundary diffusion process of the applied base material

The base material coated with the coating agent is subjected to grain boundary diffusion in a vacuum atmosphere at 850 to 900° C. for 7 to 15 hours, preferably for 8 to 12 hours.

(8) Heat treatment process of grain boundary diffused base material

After the grain boundary diffusion process, heat treatment is performed at 400 to 700° C. for 1 to 3 hours. Preferably, heat treatment is performed at 450 to 550°C for 1.5 to 2.5 hours.

Hereinafter, more specific embodiments of the present invention will be described using experimental examples.

[Example 1]

In this example, the experiment was conducted using a commercially available Re-Fe-TM-B sintered magnet (hereinafter referred to as base material) with a thickness of 6.0 mm as a base material.

Before the grain boundary diffusion (GBD) process, the thickness direction surface of the base material was polished to a roughness of 10㎛ or less using SiC paper.

Afterwards, the polished base material was immersed in a 3% nitric acid (HNO ₃ ) solution for 80 seconds to etch the surface, washed with ethanol for 30 seconds, and then washed with distilled water for 30 seconds to prepare the base material.

A coating agent for grain boundary diffusion was prepared for application to the prepared base material surface.

The coating agent was prepared by mixing ethanol and TbH ₃ powder in a ratio of 1 part by weight:1 part by weight to prepare a TbH ₃ powder slurry. The additive to be added to the coating agent was prepared by reacting ethanol and ethylene glycol in a ratio of 10 parts by weight: 1 part by weight, and ethanol and ethylcellulose in a ratio of 10 parts by weight: 1 part by weight.

Afterwards, the pre-prepared TbF powder slurry and additives containing ethylene glycol and additives containing ethylcellulose were stirred in an amount of 10 parts by weight and 0.5 parts by weight, respectively, to prepare coating agents as follows.

There are three types of liniments prepared in this way:

① TbH ₃ + Ethanol

② TbH ₃ + Ethanol + Ethylene Glycol

③ TbH ₃ + ethanol + ethylcellulose, and was used for grain boundary diffusion as a Tb diffusion source.

Based on the base material thickness of 6mm, the above three types of coating agents are used. 0.6 to 1.0 parts by weight of the coating agent is applied to the surface of the base material prepared prior to the grain boundary diffusion process, based on 100 parts by weight of the base material, and the weight of the coating agent is the difference between the weight of the base material measured before application and the weight measured after application.

The application method was applied by dipping or spraying and a comparative experiment was conducted.

After application to the surface of the base material, it was dried in a vacuum desiccator to ensure complete drying.

After completely drying the base material to which the coating agent had been applied, a grain boundary diffusion process was performed for 10 hours at a temperature of 850-900°C in a vacuum atmosphere for grain boundary diffusion. After the grain boundary diffusion process, the grain boundary-diffused base material was additionally heated to a temperature of 500°C. After heat treatment for 2 hours, it was cooled to room temperature.

Finally, magnetic properties analysis of grain boundary diffused rare earth permanent magnets was conducted using B-H tracer.

sample	liniment	equipment	Application amount (part by weight)	Grain boundary diffusion Temperature (℃)	residual magnetic flux Density (Br(kG))	coercivity Hcj(kOe)
raw	X	M1	X	X	13.54	22.07
Comparative Example 1-1	①	M1	0.6	900℃	13.21	31.98
Comparative Example 1-2	①	M1	0.8	900℃	13.23	30.40
Comparative Example 1-3	①	M1	1.0	900℃	13.02	32.80
Comparative Example 2-1	②	M1	0.6	850℃	13.31	28.01
Comparative Example 2-2	②	M1	0.8	850℃	13.23	29.29
Comparative Example 2-3	②	M1	1.0	850℃	13.11	29.04
Comparative Example 2-4	②	M1	0.6	900℃	13.18	32.98
Comparative Example 2-5	②	M1	0.8	900℃	13.27	29.62
Comparative Example 2-6	②	M1	1.0	900℃	13.31	28.18
Example 1-1	③	M1	0.6	850℃	13.34	26.83
Example 1-2	③	M1	1.0	850℃	13.13	28.01
Example 1-3	③	M1	0.6	900℃	13.29	32.71
Example 1-4	③	M1	0.8	900℃	13.21	33.33
Example 1-5	③	M1	1.0	900℃	12.91	33.84

* Coating agent ① TbH ₃ + ethanol, ② TbH ₃ + ethanol + ethylene glycol, ③ TbH ₃ + ethanol + ethylcellulose

* Base material M1 is 6.0mm thick

Table 1 shows the magnetic properties according to the difference between the three types of coating agents and the weight of the coating agent (0.6 to 1.0 parts by weight).

Comparative Examples 1-1, 1-2, and 1-3 are cases in which 0.6, 0.8, and 1.0 parts by weight of ① TbH ₃ + ethanol was spread across grain boundaries as a coating agent, and Figure 4 shows a sample of the coating agent of Comparative Example 1-2 of the present invention. This is a photo after application using the land method, and Figure 8 is a photo after grain boundary diffusion of Comparative Example 1-2 of Fig. 4.

Comparative Example 2-1. 2-2. 2-3, 2-4, 2-5, and 2-6 are cases in which 0.6, 0.8, and 1.0 parts by weight of ② TbH ₃ + ethanol + ethylene glycol as a coating agent were dispersed at grain boundary diffusion temperatures of 900°C and 850°C.

In Examples 1-1, 1-2, 1-3, 1-4, and 1-5, 0.6, 0.8, and 1.0 parts by weight of ③ TbH ₃ + ethanol + ethylcellulose as a coating agent were added to the grain boundary at a grain boundary diffusion temperature of 900°C and 850°C. This is a case of spread.

Comparative Examples 1-1, 1-2, and 1-3 are cases where a coating agent (① TbH ₃ + ethanol) containing no additives was applied, and Comparative Example 2-1. 2-2. 2-3, 2-4, 2-5, and 2-6 are cases where ethylene glycol-added coating agent (② TbH ₃ + ethanol + ethylene glycol) was applied, Examples 1-1, 1-2, 1- 3, 1-4, and 1-5 are cases where a coating agent containing ethylcellulose (③ TbH ₃ + ethanol + ethylcellulose) was applied.

In Comparative Examples 2-1 to 2-6 and Examples 1-1 to 1-5, the coercivity increased by about 4 to 14% when the grain boundary diffusion temperature was 900°C compared to when the grain boundary diffusion temperature was 850°C.

In Example 1-3, when 0.6 parts by weight of the coating agent containing ethylcellulose was applied, a residual magnetization value of 13.29 kG was confirmed. In Example 1-5, when 1.0 parts by weight of the coating agent containing ethylcellulose was applied, the highest coercive force of 33.84 kOe was shown.

The reason for this experimental result is that by using ethylcellulose as a grain boundary diffusion coating agent in the rare earth magnet sintered body, the ethylcellulose polymer chain facilitates the diffusion of the rare earth metal in the coating agent to the grain boundaries of the matrix material, and the surface of the matrix material at the grain boundary diffusion temperature This is because it plays a role in preventing peeling from occurring.

[Example 2]

In this example, the experiment was conducted using commercially available Re-Fe-TM-B sintered magnets (hereinafter referred to as base materials) with thicknesses of 4.5 and 2.5 mm as the base material.

The process for preparing the base material is the same as Example 1.

The process for manufacturing the coating agent for grain boundary diffusion for application to the prepared base material surface is the same as Example 1.

There are two types of liniments prepared in this way:

② TbH ₃ + Ethanol + Ethylene Glycol

③ TbH ₃ + ethanol + ethylcellulose, and was used for grain boundary diffusion as a Tb diffusion source.

Apply the two types of coating agents above to a base material thickness of 4.5 and 2.5 mm. Prior to the grain boundary diffusion process, 0.4, 0.6, and 0.8 parts by weight of the coating agent are applied to the surface of the prepared base material based on 100 parts by weight of the base material. The weight of the coating agent is the difference between the weight of the base material measured before application and the weight measured after application. .

The application method was applied by dipping or spraying and a comparative experiment was conducted.

After application to the surface of the base material, it was dried in a vacuum desiccator to ensure complete drying.

After completely drying the base material to which the coating agent had been applied, a grain boundary diffusion process was performed for 10 hours at 900°C in a vacuum atmosphere for grain boundary diffusion. After the grain boundary diffusion process, the grain boundary diffused base material was additionally heated at 500°C for 2 hours. After heat treatment for a while, it was cooled to room temperature.

Finally, magnetic properties analysis of grain boundary diffused rare earth permanent magnets was conducted using B-H tracer.

sample	liniment	equipment	Application amount (part by weight)	Grain boundary diffusion Temperature (℃)		Application method	residual magnetic flux Density (Br(kG))	coercivity Hcj(kOe)
Comparative Example 3-1	②	M2	0.2	900℃		immersion	13.36	34.65
Comparative Example 3-2	②	M2	0.6	900℃		immersion	13.40	34.41
Comparative Example 3-3	②	M2	0.8	900℃		immersion	13.33	33.33
Comparative Example 3-4	②	M2	0.4	900℃		immersion	13.45	34.95
Comparative Example 3-5	②	M2	0.6	900℃		immersion	13.37	33.09
Comparative Example 3-6	②	M2	0.8	900℃		immersion	13.44	33.39
Comparative Example 3-7	②	M3	0.6	900℃		immersion	13.53	33.61
Comparative Example 3-8	②	M3	0.8	900℃		immersion	13.20	33.06
Example 2-1	③	M2	0.4	900℃		immersion	13.77	32.62
Example 2-2	③	M2	0.6	900℃		immersion	13.47	33.51
Example 2-3	③	M2	0.8	900℃		immersion	13.89	34.41
Example 2-4	③	M2	0.4	900℃		spray	13.44	33.98
Example 2-5	③	M2	0.6	900℃		spray	13.43	37.49
Example 2-6	③	M2	0.8	900℃		spray	13.35	38.97
Example 2-7	③	M3	0.6	900℃		immersion	13.53	33.03
Example 2-8	③	M3	0.8	900℃		immersion	13.67	33.96

* Coating agent ② TbH ₃ + ethanol + ethylene glycol, ③ TbH ₃ + ethanol + ethylcellulose

* Base material M2 is 4.5mm thick, M3 is 2.5mm thick

Table 2 shows the magnetic properties according to the difference between the two types of coating agents and the weight of the coating agents (0.4, 0.6, and 0.8 parts by weight).

Comparative Examples 3-1 to 3-8 are cases in which 0.4, 0.6, and 0.8 parts by weight of ② TbH ₃ + ethanol + ethylene glycol as a coating agent were spread across grain boundaries at a grain boundary diffusion temperature of 900°C, and Figure 5 is a comparative example of the present invention. This is a photograph after application of the coating agent of 3-2 by dipping, and Figure 9 is a photograph of Comparative Example 3-2 of Figure 5 after grain boundary diffusion.

Examples 2-1 to 2-8 are cases in which 0.4, 0.6, and 0.8 weight additions of ③ TbH ₃ + ethanol + ethyl cellulose as a coating agent were spread across grain boundaries at a grain boundary diffusion temperature of 900°C.

The residual magnetization value of Examples 2-1 to 2-8 was measured to be 1.24% higher than that of Comparative Examples 3-1 to 3-8, and the coercivity was confirmed to be more than 34.0 kOe.

In Comparative Examples 3-1 to 3-8 with a base material thickness of 2.5 mm (M3), the coating agent containing ethylene glycol exhibited magnetic properties when applied in an amount of 0.8 parts by weight or more, and Examples 2-1 to 2- In Fig. 8, it was confirmed that the coating agent containing ethylcellulose exhibited magnetic properties when applied in an amount of 0.6 parts by weight or more. This confirmed that the coating agent with ethylcellulose added to the 2.5mm base material can increase the coercive force with a smaller application amount due to its higher sintering bond with the base material than the coating agent with ethylene glycol added.

Examples 2-1 to 2-3 were coated with a coating agent containing ethylcellulose by a dipping method on the surface of a base material with a thickness of 4.5 mm (M2). Figure 6 shows the coating agent of Example 2-2 of the present invention. This is a photograph after application by the dipping method, and Figure 10 is a photograph after grain boundary diffusion of Example 2-2 of Figure 6.

Examples 2-4 to 2-6 were coated with a coating agent containing ethylcellulose by spraying on the surface of a base material with a thickness of 4.5 mm (M2), and Figure 7 shows the coating agent of Example 2-5 of the present invention. This is a photograph after application by spraying, and Figure 11 is a photograph after grain boundary diffusion of Example 2-5 of Figure 7.

It was confirmed that when the coating agent containing ethylcellulose was applied in both the dipping and spraying methods of Examples 2-1 to 2-6, it was possible to manufacture rare earth permanent magnets with a residual magnetization value > 13.4 kG and a coercive force value > 32 kOe. , it was confirmed that when the coating agent containing ethylcellulose was applied by spraying, it was possible to manufacture a rare earth permanent magnet with a residual magnetization value > 13.4 kG and a coercive force value > 37 kOe.

It was confirmed in Figure 6 that local application of the coating agent occurred when the coating agent was applied to the surface of the base material by the dipping method as in Examples 2-1 to 2-3, and Examples 2-4 to 2-6 As shown in Figure 7, a photograph of the evenly applied surface was confirmed due to uniform spraying of the coating agent when applied by spraying.

In Table 2, when applied with a coating agent containing ethylcellulose as in Examples 2-1 to 2-6, it is possible to manufacture rare earth permanent magnets with a residual magnetization value > 13.4 kG and a coercive force value > 32 kOe.

In particular, when a coating agent containing ethylcellulose is applied by spraying, it is possible to manufacture a sintered magnet with a residual magnetization value > 13.4 kG and a coercive force value > 37 kOe.

Figure 8 is a photograph after grain boundary diffusion of Comparative Example 1-2 of Figure 4, Figure 9 is a photograph after grain boundary diffusion of Comparative Example 3-2 of Figure 5, and Figure 10 is a photograph of grain boundary diffusion of Example 2-2 of Figure 6. This is an after photo, and FIG. 11 is a photo after grain boundary diffusion of Example 2-5 of FIG. 7.

Depending on the type of coating agent, there is a difference in the shape of the aggregated portion of the coating agent applied after grain boundary diffusion.

In FIGS. 8 to 11, 'A' and 'B' represent the shape in which carbon remains after grain boundary diffusion by applying the coating agent, and the 'A' shape represents the shape in which carbon is discharged without penetrating into the base material during grain boundary diffusion. , The 'B' shape shows the shape when carbon penetrates into the base material during grain boundary diffusion.

Figure 8 is a photograph of the case where ① TbH ₃ + ethanol was used as a coating agent, where ethanol and TbH ₃ powder were mixed at a ratio of 1 part by weight: 1 part by weight, TbH ₃ powder slurry was applied, and grain boundary diffusion was achieved. In Figure 8, it can be seen that there are many agglomerated areas. Since delamination occurs in the agglomerated areas and creates conditions for carbon to penetrate into the base material, it is desirable to reduce the agglomerated areas.

Figure 9 shows a case where ② TbH ₃ + ethanol + ethylene glycol was used as a coating agent. A TbH ₃ powder slurry was prepared by mixing 1 part by weight of TbH ₃ and ethanol and 10 parts by weight of ethanol and ethylene glycol. This is a photo showing grain boundary diffusion after preparing the additive prepared by reacting with a mole and then applying a coating agent in which 10 parts by weight of the TbH ₃ powder slurry and the additive were mixed and stirred at 0.5 parts by weight. In Figure 9, it can be seen that the agglomerated portion is smaller than in Figure 8, which means that the phenomenon of TbH ₃ as a diffusion agent being peeled off from the surface of the base material has been reduced.

Figures 10 and 11 show the case of using ② TbH ₃ + ethanol + ethylcellulose as a coating agent. A TbH ₃ powder slurry was prepared by mixing 1 part by weight of TbH ₃ and ethanol, and 10 parts by weight of ethanol and ethylcellulose: This is a photo of grain boundary diffusion after preparing an additive prepared by reacting 1 part by weight, and applying a coating agent obtained by mixing and stirring 10 parts by weight of TbH ₃ powder slurry and 0.5 parts by weight of the additive. In Figures 10 and 11, it can be seen that the agglomerated portion is smaller than in Figures 8 and 9, which means that the phenomenon of TbH ₃ as a diffusion agent being peeled off from the surface of the base material has been reduced.

In addition, when comparing the case of application by the dipping method of Figure 10 and the case of application by the spray method of Figure 11, the 'B' shaped agglomerated portion was relatively less when the spray method was used than the dipping method, and the carbon penetrated into the base material. It can be confirmed that the peeling phenomenon of the 'A' shaped cohesive part discharged without spraying occurs less often when using the spray method.

When applying the coating agent to the surface of the base material using a dipping method, localized application of the coating agent occurred, but when applying the coating agent using a spraying method, the evenly applied surface could be confirmed through photographs due to uniform spraying of the coating agent.

Claims (5)

1. Preparing a rare earth sintered magnet of Re-Fe-TM-B (Re = rare earth element, Fe = iron, TM = 3d transition metal, B = boron);

   Preparing rare earth compound slurry and additives;

   Preparing a coating agent by mixing and stirring a rare earth compound slurry and additives;

   An application step of applying a coating agent to the surface of the base material;

   A grain boundary diffusion step of heating a sintered magnet coated with a rare earth compound to spread grain boundaries;

   A method of manufacturing a rare earth permanent magnet comprising the step of heat treating the grain boundary diffused sintered magnet.
2. According to claim 1,

   A method of manufacturing a rare earth permanent magnet, wherein the rare earth compound is a rare earth hydride or a rare earth fluoride.
3. According to claim 2,

   The rare earth hydride is one or more of DyH, TbH, HoH, NdH, PrH, and CeH, and the rare earth fluoride is one or more of PrF, NdF, GdF, TbF, DyF, and HoF. A method of manufacturing a rare earth permanent magnet.
4. According to claim 1,

   A method of producing a rare earth permanent magnet, characterized in that the rare earth compound slurry is mixed with rare earth hydride or rare earth fluoride and ethanol in a ratio of 1:1 by weight.
5. According to claim 1,

   A method of producing a rare earth permanent magnet, characterized in that the additive is mixed with 10 parts by weight of ethanol and ethyl cellulose: 0.5 to 2 parts by weight.

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