KR102647274B1 - Manufacturing method of sintered magnet - Google Patents

Abstract

A method of manufacturing a sintered magnet according to an embodiment of the present invention includes preparing a mixture by mixing rare earth oxide, iron, boron, a reducing agent, and heavy rare earth oxide; Heating the mixture at a temperature of 800 to 1100 degrees Celsius to synthesize magnet powder using a reduction-diffusion method; and manufacturing a sintered magnet by sintering the magnet powder, wherein the heavy rare earth oxide includes Dy ₂ O ₃ .

Description

Manufacturing method of sintered magnet {MANUFACTURING METHOD OF SINTERED MAGNET}

The present invention relates to a method of manufacturing a sintered magnet, and more specifically to a method of manufacturing an R-Fe-B based sintered magnet.

NdFeB-based magnets are permanent magnets with a composition of Nd ₂ Fe ₁₄ B, a compound of rare earth elements neodymium (Nd) and iron and boron (B), and have been used as general-purpose permanent magnets for 30 years since their development in 1983. These NdFeB-based magnets are used in various fields such as electronic information, automobile industry, medical devices, energy, and transportation. In particular, in line with the recent trend of light weight and miniaturization, it is being used in products such as machine tools, electronic information equipment, home appliance electronics, mobile phones, motors for robots, wind power generators, and small motors and drive motors for automobiles.

Strip/mold casting or melt spinning methods based on metal powder metallurgy methods are known for general manufacturing of NdFeB-based magnets. First, in the case of the strip/mold casting method, an ingot is manufactured by melting metals such as neodymium (Nd), iron (Fe), and boron (B) through heating, and the crystal grains are coarsely ground. This is a process of manufacturing micro particles through a micronization process. By repeating this, magnet powder is obtained, and an anisotropic sintered magnet is manufactured through pressing and sintering processes under a magnetic field.

In addition, the melt spinning method melts metal elements, pours them into a wheel rotating at high speed, cools them rapidly, jet mills them, blends them with polymers to form a bonded magnet, or presses them into a magnet. manufacture.

However, these methods all have problems in that a grinding process is essential, the grinding process takes a long time, and a process of coating the surface of the powder is required after grinding.

Recently, a method of producing magnetic powder using a reduction-diffusion method has been attracting attention. For example, uniform NdFeB fine particles can be manufactured through a reduction-diffusion process in which Nd ₂ O ₃ , Fe, and B are mixed and reduced to Ca, etc.

However, in the case of the process of obtaining a sintered magnet by sintering the magnet powder manufactured by the reduction-diffusion method, grain growth is accompanied when sintering is performed in a temperature range of 1000 to 1250 degrees Celsius, and this grain growth reduces the coercive force. It acts as a factor. To elaborate, during sintering, grain growth (more than 1.5 times the size of the initial powder) and abnormal grain growth (more than 2 times the size of the normal grain size) occur, greatly reducing the theoretical coercivity that the initial powder can have.

Accordingly, methods to suppress the growth of grains during sintering include the HDDR (Hydrogenation, disproportionation, desorption and recombination) process, a method of reducing the size of the initial powder through jet mill pulverization, and a triple point method by adding elements that can form a secondary phase. There are methods to suppress the movement of grain boundaries by forming a .

However, although the coercivity of the sintered magnet can be secured to some extent through the various methods described above, the process itself is very complicated and the effect on suppressing grain growth during sintering is still insufficient. In addition, other problems occur, such as a decrease in the properties of the sintered magnet due to a significant change in the microstructure due to grain movement, and a decrease in magnetic properties due to added elements.

In addition, magnet powder manufactured by the reduction-diffusion method essentially requires a cleaning process to remove by-products such as calcium oxide (CaO) remaining in the particles.

However, during this cleaning process, the particles of the magnet powder may be oxidized and an oxide film may be formed on the surface. The oxide film not only hinders the sintering of the magnet powder, but also promotes the decomposition of the column phase, causing a decrease in the physical properties of the sintered magnet, such as coercive force.

Korean Patent Publication No. 10-2019-0062187 (publication date 2019.06.05.) Korean Patent Publication No. 10-2012-0116116 (publication date 2012.10.22.) Korean Patent Publication No. 10-2015-0033528 (publication date 2015.04.01.) Korean Patent Publication No. 10-1534717 (Published on July 24, 2015)

Embodiments of the present invention have been proposed to solve the above problems, and are intended to provide a method of manufacturing a sintered magnet that can significantly improve the coercive force of an R-Fe-B based sintered magnet.

However, the problems to be solved by the embodiments of the present invention are not limited to the above-described problems and can be expanded in various ways within the scope of the technical idea included in the present invention.

A method of manufacturing a sintered magnet according to an embodiment of the present invention includes preparing a mixture by mixing rare earth oxide, iron, boron, a reducing agent, and heavy rare earth oxide; Heating the mixture at a temperature of 800 to 1100 degrees Celsius to synthesize magnet powder using a reduction-diffusion method; and manufacturing a sintered magnet by sintering the magnet powder, wherein the heavy rare earth oxide includes Dy ₂ O ₃ .

The heavy rare earth oxide may be mixed in an amount of 3% to 10% by mass compared to the mixture.

The rare earth oxide may include at least one of Nd ₂ O ₃ , La ₂ O ₃ , Ce ₂ O ₃ , Pr ₂ O ₃ , Pm ₂ O ₃ , Sm ₂ O ₃ and Eu ₂ O ₃ .

The sintered magnet is an R-Fe-B based sintered magnet, and R may be Nd, La, Ce, Pr, Pm, Sm, or Eu.

The reducing agent may include at least one of Ca, CaH ₂ and Mg.

The step of manufacturing a sintered magnet may include mixing the magnet powder and rare earth hydride powder to produce a mixed powder and sintering the mixed powder at 1000 to 1100 degrees Celsius.

The method of manufacturing the sintered magnet may further include a heat treatment step after heating the sintered magnet to 500 to 800 degrees Celsius.

The method of manufacturing the sintered magnet may further include coating the surface of the sintered magnet with heavy rare earth powder and heat treating the coated sintered magnet to diffuse the heavy rare earth elements into the grain boundary.

According to embodiments of the present invention, a sintered magnet with high coercive force can be manufactured by manufacturing magnet powder by adding heavy rare earth oxide during the reduction-diffusion method and sintering the magnet powder.

1 is a BH curve graph for the sintered magnets of Examples 1-1 and 1-2.
Figure 2 is a BH curve graph for the sintered magnets of Example 2-1 and Example 2-2.
Figure 3 is a BH curve graph for the sintered magnet of Comparative Example 1.

Hereinafter, with reference to the attached drawings, various embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. The invention may be implemented in many different forms and is not limited to the embodiments described herein.

In addition, throughout the specification, when a part is said to "include" a certain component, this means that it may further include other components rather than excluding other components, unless specifically stated to the contrary.

A method for manufacturing a sintered magnet according to an embodiment of the present invention includes the steps of mixing rare earth oxide, iron, boron, a reducing agent, and heavy rare earth oxide to prepare a mixture, heating the mixture at a temperature of 800 to 1100 degrees Celsius to reduce - It includes synthesizing magnet powder using a diffusion method and sintering the magnet powder to produce a sintered magnet. At this time, the heavy rare earth oxide includes Dy ₂ O ₃ .

The magnet powder synthesized by this reduction-diffusion method may be an R-Fe-B-based magnet powder, and the sintered magnet manufactured by sintering the R-Fe-B-based magnet powder may be an R-Fe-B-based sintered magnet. .

Here, R refers to a rare earth element and may be Nd, La, Ce, Pr, Pm, Sm, or Eu. That is, R described below means one of Nd, La, Ce, Pr, Pm, Sm, or Eu.

In this example, the R-Fe-B based magnet powder is manufactured through a reduction-diffusion method. The reduction-diffusion method is a method of preparing a mixture by mixing rare earth oxide, iron, boron, and a reducing agent, and then heating the mixture to reduce the rare earth oxide and simultaneously synthesize the powder of R ₂ Fe ₁₄ B.

The rare earth oxide corresponds to the rare earth element R and includes at least one of Nd ₂ O ₃ , La ₂ O ₃ , Ce ₂ O ₃ , Pr ₂ O ₃ , Pm ₂ O ₃ , Sm ₂ O ₃ and Eu ₂ O ₃ can do.

The reduction-diffusion method is inexpensive because it uses rare earth oxides as a raw material, and has the advantage of not requiring a separate grinding process such as coarse grinding, hydrogen crushing, or jet mill, or a surface treatment process.

In addition, in order to improve the magnetic performance of the sintered magnet, it is essential to refine the grains of the sintered magnet, and the size of the grains of the sintered magnet is directly related to the size of the initial magnet powder. At this time, the reduction-diffusion method has the advantage of being easier to produce magnet powder with fine particles compared to other methods.

However, when sintering magnetic powder manufactured by the reduction-diffusion method, grain growth (more than 1.5 times the initial powder size) or abnormal grain growth (more than 2 times the normal grain size) may occur during the sintering process. There is a problem that the crystal grain size distribution of the magnet is not uniform, and magnetic performance such as coercive force is deteriorated.

In addition, magnet powder manufactured by the reduction-diffusion method essentially requires a cleaning process to remove by-products such as calcium oxide (CaO) remaining on the particles, but an oxide film is formed due to oxidation of the magnet powder particles during the cleaning process. It can be. This oxide film not only hinders the sintering of the magnet powder, but also promotes columnar decomposition, thereby lowering the physical properties of the sintered magnet, such as coercive force.

Accordingly, a method for increasing the coercive force of the sintered magnet is needed. In this embodiment, a mixture is prepared by further adding a heavy rare earth oxide containing Dy ₂ O ₃ to the rare earth oxide, iron, boron, and a reducing agent, and the mixture is Synthesize R-Fe-B magnetic powder using this method.

Since heavy rare earth oxide containing Dy ₂ O ₃ is added, Dy with a large anisotropy coefficient is distributed inside the sintered magnet, and the coercive force can be improved.

In addition, this embodiment has the feature of adding Dy ₂ O ₃ in the step of manufacturing magnet powder by a reduction-diffusion method.

When Dy ₂ O ₃ is added in a subsequent sintering step, Dy ₂ O ₃ is difficult to phase decompose, so it may remain as Dy ₂ O ₃ and maintain a non-magnetic state. This remaining Dy ₂ O ₃ may act as a factor in reducing the residual magnetic flux density (Br) of the sintered magnet.

On the other hand, when Dy ₂ O ₃ is added in the step of synthesizing magnet powder by the reduction-diffusion method as in this example, Dy ₂ O ₃ added in the step where the raw materials are reduced is also It may be reduced to form a Dy-Fe-B phase. This is a factor that can increase the coercive force of the sintered magnet and does not have a significant effect on the residual magnetic flux density of the sintered magnet.

In addition, in this embodiment, Dy ₂ O ₃ was added in the step of synthesizing the magnet powder by a reduction-diffusion method to homogeneously distribute Dy resulting from Dy ₂ O ₃ throughout the entire area of the sintered magnet manufactured thereafter. do. The addition of Dy ₂ O ₃ is intended to improve coercive force, but if Dy resulting from Dy ₂ O ₃ exists locally in the sintered magnet, the effect may be minimal. Adding Dy ₂ O ₃ in the sintering step has a high possibility that Dy will exist locally in the sintered magnet, but adding Dy ₂ O ₃ in the step of synthesizing magnet powder using a reduction-diffusion method as in this example does not Since it is added at the stage when R-Fe-B magnet powder particles are synthesized, even distribution of Dy is possible. In other words, the effect of improving coercivity can be further maximized.

Specifically, by adding Dy ₂ O ₃ in the step of synthesizing the magnet powder by the reduction-diffusion method, the coercive force of the sintered magnet can be increased by 5 to 15 kOe (Kiloersted), resulting in a coercive force of 20 to 30 kOe. A sintered magnet can be implemented.

In addition, since Dy is added in the step of synthesizing the magnet powder by the reduction-diffusion method, it is preferable to add Dy ₂ O ₃ in the form of an oxide that can be reduced.

Meanwhile, heavy rare earth oxides may be mixed in an amount of 3% to 10% by mass compared to the mixture. If the heavy rare earth oxide is mixed in an amount of less than 3% by mass compared to the mixture, there may be a problem of insufficient coercive force improvement due to insufficient Dy content. If the heavy rare earth oxide is mixed in an amount exceeding 10% by mass compared to the mixture, there may be a problem that the residual magnetic flux density of the sintered magnet is excessively reduced due to the addition of more than necessary.

Then, each step will be described in more detail below.

First, a mixture is prepared by mixing rare earth oxide, iron, boron, reducing agent, and heavy rare earth oxide. The mixture is then heated to a temperature of 800 to 1100 degrees Celsius. R-Fe-B based magnet powder is synthesized by reduction and diffusion of raw materials at a temperature of 800 to 1100 degrees Celsius.

As previously mentioned, heavy rare earth oxides include Dy ₂ O ₃ , and rare earth oxides include Nd ₂ O ₃ , La ₂ O ₃ , Ce ₂ O ₃ , Pr ₂ O ₃ , Pm ₂ O ₃ , Sm ₂ O ₃ and Eu It may include at least one of ₂ O ₃ . The reducing agent may include at least one of Ca, CaH ₂ and Mg.

Heavy rare earth oxides are preferably mixed in powder form, and the size of the powder may be 1 to 5 micrometers.

The molar ratio of rare earth oxide, boron and iron may be between 1:14:1 and 1.5:14:1. Rare earth oxides, boron, and iron are raw materials for manufacturing R ₂ Fe ₁₄ B magnet powder, and when the above molar ratio is satisfied, R ₂ Fe ₁₄ B magnet powder can be manufactured with high yield. If the molar ratio is less than 1:14:1, there is a problem in that the composition of the R ₂ Fe ₁₄ B main phase is distorted and the R-rich grain boundary phase is not formed, and if the molar ratio is more than 1.5:14:1, the amount of rare earth elements is excessive. As a result, the reduced rare earth elements remain, and there may be a problem in that the remaining rare earth elements are changed to R(OH) ₃ or RH ₂ .

The heating is for synthesis and may be performed for 10 minutes to 6 hours at a temperature of 800 to 1,100 degrees Celsius in an inert gas atmosphere. If the heating time is less than 10 minutes, the powder may not be sufficiently synthesized, and if the heating time is more than 6 hours, the size of the powder may become coarse and primary particles may clump together.

The magnetic powder prepared in this way may be R ₂ Fe ₁₄ B. Additionally, the size of the produced magnetic powder may be 0.3 micrometers to 10 micrometers. Additionally, the size of the magnet powder manufactured according to one embodiment may be 0.3 micrometer to 5 micrometer.

That is, R ₂ Fe ₁₄ B magnet powder can be formed by heating the raw material at a temperature of 800 to 1,100 degrees Celsius, and the R ₂ Fe ₁₄ B magnet powder is a neodymium magnet and exhibits excellent magnetic properties.

Typically, in order to form R ₂ Fe ₁₄ B magnetic powder such as Nd ₂ Fe ₁₄ B, raw materials are melted at a high temperature of 1500 to 2000 degrees Celsius and then rapidly cooled to form raw material lumps, and these lumps are coarsely ground and hydrogenated. R ₂ Fe ₁₄ B magnet powder is obtained by crushing, etc. However, this method requires a high temperature to melt the raw materials, and then cools them again and then grinds them, making the process time-consuming and complicated. In addition, a separate surface treatment process is required to strengthen corrosion resistance and improve electrical resistance for the coarsely ground R ₂ Fe ₁₄ B magnet powder.

However, when manufacturing R-Fe-B magnet powder by the reduction-diffusion method as in this embodiment, R ₂ Fe ₁₄ B magnet powder is formed by reduction and diffusion of the raw materials at a temperature of 800 to 1100 degrees Celsius. . At this stage, since the size of the magnet powder is formed in the order of several micrometers, a separate grinding process is not required.

In addition, in the subsequent process of sintering the magnet powder to obtain a sintered magnet, grain growth is necessarily accompanied when sintering is performed in a temperature range of 1000 to 1100 degrees Celsius, and this grain growth acts as a factor in reducing coercive force. Since the size of the crystal grains of the sintered magnet is directly related to the size of the initial magnet powder, if the average size of the magnet powder is controlled to 0.3 micrometer to 10 micrometer, as in the magnet powder according to an embodiment of the present invention, then the coercive force is Improved sintered magnets can be manufactured.

Additionally, the size of the alloy powder produced can be adjusted by adjusting the size of the iron powder used as a raw material.

However, when magnetic powder is manufactured using this reduction-diffusion method, by-products such as calcium oxide or magnesium oxide may be generated during the manufacturing process, and a cleaning step to remove them is required.

To remove these by-products, a cleaning step is followed in which the prepared magnet powder is washed by immersing it in an aqueous solvent or a non-aqueous solvent. This cleaning may be repeated two or more times.

The aqueous solvent may include deionized water (DI water), and the non-aqueous solvent may include at least one of methanol, ethanol, acetone, acetonitrile, and tetrahydrofuran.

Meanwhile, to remove by-products, an ammonium salt or acid may be dissolved in an aqueous or non-aqueous solvent. Specifically, at least one of NH ₄ NO ₃ , NH ₄ Cl and ethylenediaminetetraacetic acid (EDTA) may be dissolved. You can.

However, during this cleaning process, the produced magnet powder particles are exposed to oxygen in the aqueous solution, and the oxygen remaining in the aqueous solution oxidizes the surface of the produced magnet powder particles, and an oxide film may be formed on the surface. The oxide film not only hinders the sintering of the magnet powder, but also promotes the decomposition of the column phase, causing a decrease in the physical properties of the sintered magnet, such as coercive force.

Accordingly, in this example, a heavy rare earth oxide containing Dy ₂ O ₃ was added and the coercive force was improved through this to compensate for the above-mentioned decrease in coercive force.

Thereafter, the step of sintering the R-Fe-B-based magnet powder that has undergone the synthesis and cleaning steps as described above follows.

A mixed powder can be produced by mixing R-Fe-B-based magnet powder and rare earth hydride powder.

Rare earth hydride powder is preferably mixed in an amount of 3 to 15% by mass based on the mixed powder.

If the content of the rare earth hydride powder is less than 3% by mass, sufficient wetting between particles may not be provided, resulting in poor sintering, and there may be problems in that the role of suppressing the columnar decomposition of R-Fe-B is not sufficiently performed. You can. In addition, if the content of rare earth hydride powder exceeds 15% by mass, the volume ratio of the R-Fe-B main phase in the sintered magnet decreases, thereby reducing the residual magnetization value, and there may be a problem of excessive growth of particles due to liquid phase sintering. there is. When the size of the crystal grains increases due to overgrowth of particles, the coercive force decreases because it is vulnerable to magnetization reversal.

Next, the mixed powder can be heated at a temperature of 700 to 900 degrees Celsius. In this step, the rare earth hydride is separated into the rare earth metal and hydrogen gas, and the hydrogen gas is removed. That is, for example, when the rare earth hydride powder is NdH ₂ , NdH ₂ is separated into Nd and H ₂ gas, and H ₂ gas is removed. That is, heating at 700 to 900 degrees Celsius is a process for removing hydrogen from the mixed powder. At this time, heating may be performed in a vacuum atmosphere.

Next, the heated mixed powder is sintered at a temperature of 1000 to 1100 degrees Celsius. At this time, the step of sintering the heated mixed powder at a temperature of 1000 to 1100 degrees Celsius may be performed for 30 minutes to 4 hours. This sintering process can also be performed in a vacuum atmosphere.

More specifically, the mixed powder heated to 700 to 900 degrees Celsius can be compressed in a graphite mold and oriented by applying a pulse magnetic field to produce a molded body for a sintered magnet. The sintered magnet molded body is heat-treated at 300 to 400 degrees Celsius in a vacuum atmosphere and then sintered at a temperature of 1000 to 1100 degrees Celsius to produce a sintered magnet.

In this sintering step, liquid phase sintering is induced by rare earth elements. In other words, liquid phase sintering by rare earth elements occurs between the R-Fe-B magnet powder manufactured by the existing reduction-diffusion method and the added rare earth hydride powder. Through this, R-rich and ROx phases are formed at the grain boundaries inside the sintered magnet or in the grain boundary region of the columnar grains of the sintered magnet. The R-Rich region or ROx phase formed in this way improves the sinterability of the magnet powder and prevents decomposition of the columnar particles in the sintering process for manufacturing sintered magnets. Therefore, sintered magnets can be stably manufactured.

The manufactured sintered magnet has a high density and the grain size may be 1 micrometer to 10 micrometers.

Next, to further improve the coercivity, the sintered magnet may be heated to 500 to 800 degrees Celsius in a vacuum atmosphere, followed by a heat treatment step.

Meanwhile, a grain boundary diffusion process (GBDP) may be performed on the sintered magnet.

The grain boundary diffusion process is a process of distributing heavy rare earth elements such as Dy along the grain boundaries of the R-Fe-B sintered magnet, and can increase coercive force without reducing residual magnetization. During the heat treatment process for grain boundary diffusion, heavy rare earth elements are replaced by Nd in the Nd-rich phase and diffuse along the grain boundaries. This diffusion results in the formation of a shell structure with a high content of heavy rare earth elements around the crystal grains.

However, in the case of the grain boundary diffusion process using Dy, there was a difference in concentration of Dy depending on the depth of the sintered magnet, so there was a limit to increasing the coercive force. However, as in this embodiment, when Dy ₂ O ₃ is added in the step of synthesizing the magnet powder by the reduction-diffusion method, the difference in concentration of Dy depending on the depth can be minimized.

In other words, if Dy is additionally diffused on the grain boundaries of the crystal grains through a grain boundary diffusion process for a sintered magnet in which Dy is evenly distributed, the coercive force can be further improved, and the disadvantages that the grain boundary diffusion process using Dy may have are It can complement.

Specifically, the grain boundary diffusion process may include coating the surface of the sintered magnet with heavy rare earth powder and heat treating the coated sintered magnet to diffuse the heavy rare earth elements at the grain boundary.

The step of coating the heavy rare earth powder on the surface of the sintered magnet may include mixing the heavy rare earth powder in a solvent and then applying it to the surface of the sintered magnet. The solvent may be anhydrous alcohol, but is not limited thereto.

Afterwards, heat treatment is performed on the sintered magnet coated with heavy rare earth powder, so that the heavy rare earth elements can be diffused into the grain boundaries of the sintered magnet.

The heat treatment may include a first heat treatment of heating to 790 degrees Celsius to 910 degrees Celsius and then a secondary heat treatment of heating to 450 degrees Celsius to 550 degrees Celsius. This is because in this temperature range, the diffusion action of diffusing the heavy rare earth elements contained in the heavy rare earth powder to the surface of the sintered magnet proceeds smoothly.

The heavy rare earth powder may contain at least one of Dy and Tb, but it is more preferable to contain Dy.

Then, below, a method for manufacturing a sintered magnet according to an embodiment of the present invention will be described through specific examples.

Example 1-1: Dy ₂ O ₃ 3% by mass

A mixture was prepared by mixing 15.46 g of Nd ₂ O ₃ , 31.71 g of Fe, 0.52 g of B, 0.51 g of Co, 0.14 g of Cu, and 0.18 g of Al using a ball mill, and the Dy ₂ O ₃ powder was compared to the mixture. It was added at 3% by mass, and 6.1g of Ca was additionally mixed.

The mixture is pressed into a stainless steel container of arbitrary shape and reacted in a tube electric furnace at 900 to 920 degrees Celsius for 30 minutes to 3 hours in an inert gas (Ar) atmosphere. Afterwards, the reactant is roughly pulverized using an automatic grinder.

Next, a cleaning step is performed to remove reduction by-products such as Ca and CaO. After mixing 30g to 35g of NH ₄ NO ₃ uniformly with the synthesized powder, it is soaked in ~200 ml of methanol and the homogenizer and ultrasonic cleaning are repeated alternately once or twice for effective cleaning. Next, it is washed with acetone, acid washed with a solution of acetic acid in methanol, and final washed with methanol. Afterwards, it is vacuum dried to obtain single-phase Nd-Fe-B magnet powder.

Thereafter, 6% by mass of NdH ₂ was added to the magnet powder and mixed, placed in a graphite mold, compression molded, and a pulsed magnetic field of 5T or more was applied to orient the powder, thereby producing a molded body for a sintered magnet.

Afterwards, the molded body was sintered by heating it in a vacuum sintering furnace at a temperature of 1065 degrees Celsius for 2 hours to produce a sintered magnet. The composition of the manufactured Nd-Fe-B based sintered magnet is Nd _2.12 Dy _0.22 Fe _13.1 B _1.1 Co _0.2 Cu _0.05 Al _0.15 .

Example 1-2: Dy ₂ O ₃ 3% by mass

Magnet powder synthesis and cleaning were performed using the same raw materials as in Example 1-1 in the same manner as in Example 1-1. Thereafter, the same sintering process as Example 1-1 was performed, except that it was heated to a temperature of 1040 degrees Celsius for 4 hours.

Example 2-1: Dy ₂ O ₃ 6% by mass

A mixture was prepared by mixing 11.67 g of Nd ₂ O ₃ , 31.71 g of Fe, 0.52 g of B, 0.51 g of Co, 0.14 g of Cu, and 0.18 g of Al using a ball mill, and the Dy ₂ O ₃ powder was compared to the mixture. It was added at 6% by mass, and 5.32g of Ca was additionally mixed.

Afterwards, the magnet powder was synthesized, cleaned, and sintered in the same manner as Example 1-1. The composition of the manufactured Nd-Fe-B based sintered magnet is Nd _1.9 Dy _0.44 Fe _13.1 B _1.1 Co _0.2 Cu _0.05 Al _0.15 .

Example 2-2: Dy ₂ O ₃ 6% by mass

Magnet powder synthesis and cleaning were performed using the same raw materials as in Example 2-1 in the same manner as in Example 2-1. Thereafter, the same sintering process as Example 2-1 was performed, except that it was heated to a temperature of 1040 degrees Celsius for 4 hours.

Comparative Example 1: Dy ₂ O ₃ Not added

A mixture was prepared by mixing 17.06 g of Nd ₂ O ₃ , 31.7 g of Fe, 0.52 g of B, 0.51 g of Co, 0.14 g of Cu, and 0.18 g of Al using a ball mill, and 6.1 g of Ca was additionally mixed. . Dy ₂ O ₃ powder was not added.

Afterwards, the magnet powder was synthesized, cleaned, and sintered in the same manner as Example 1-1. The composition of the manufactured Nd-Fe-B based sintered magnet is Nd _2.34 Fe _13.1 B _1.1 Co _0.2 Cu _0.05 Al _0.15 .

Evaluation Example 1: B-H curve graph

The B-H curve graph for the sintered magnets of Example 1-1 and Example 1-2 is shown in Figure 1, and the B-H curve graph for the sintered magnets of Example 2-1 and Example 2-2 is shown in Figure 2. , and the B-H curve graph for the sintered magnet of Comparative Example 1 is shown in Figure 3.

Referring to Figures 1 to 3, when Dy ₂ O ₃ was added as in Example 1-1, Example 1-2, Example 2-1, and Example 2-2, the Compared to the case, it was confirmed that the coercivity value increased by about 5 to 15 kOe.

In particular, the sintered magnets of Examples 2-1 and 2-2, which had a relatively large amount of Dy ₂ O ₃ added, showed increased coercive force compared to the sintered magnets of Examples 1-1 and 1-2. Confirmed.

Additionally, when the sintering temperature for the same raw material was increased to 1065 degrees Celsius, it was confirmed that the residual magnetic flux density slightly increased.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims are also possible. falls within the scope of rights.

Claims (8)

Preparing a mixture by mixing rare earth oxides, iron, boron, a reducing agent, and heavy rare earth oxides;
Heating the mixture at a temperature of 800 to 1100 degrees Celsius to synthesize magnet powder using a reduction-diffusion method; and
Comprising the step of manufacturing a sintered magnet by sintering the magnet powder,
The heavy rare earth oxide includes Dy ₂ O ₃ ,
The heavy rare earth oxide is mixed in an amount of 3% to 10% by mass compared to the mixture,
Manufacturing method of sintered magnet. delete In paragraph 1:
The rare earth oxide is Nd ₂ O ₃ , La ₂ O ₃ , Ce ₂ O ₃ , Pr ₂ O ₃ , Pm ₂ O ₃ , Sm ₂ O ₃ and Eu ₂ O ₃ Method for producing a sintered magnet. In paragraph 1:
The sintered magnet is an R-Fe-B sintered magnet,
Wherein R is Nd, La, Ce, Pr, Pm, Sm or Eu. In paragraph 1:
A method of manufacturing a sintered magnet wherein the reducing agent includes at least one of Ca, CaH ₂ and Mg. In paragraph 1:
The manufacturing of the sintered magnet includes the steps of mixing the magnet powder and the rare earth hydride powder to produce a mixed powder and sintering the mixed powder at 1000 to 1100 degrees Celsius. In paragraph 1:
A method of manufacturing a sintered magnet further comprising a heat treatment step after heating the sintered magnet to 500 to 800 degrees Celsius. In paragraph 1:
A method of manufacturing a sintered magnet further comprising coating the surface of the sintered magnet with heavy rare earth powder and heat treating the coated sintered magnet to diffuse the heavy rare earth elements into grain boundaries.

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