KR20210045243A - Manufacturing method of sintered magnet - Google Patents

Abstract

According to an embodiment of the present invention, a method of manufacturing a sintered magnet includes the steps of: preparing a mixture by mixing a rare earth oxide, iron, boron, a reducing agent and a metal fluoride; heating the mixture at a temperature of 800 degrees Celsius to 1100 degrees Celsius to synthesize magnetic powder using a reduction-diffusion method; and sintering the magnet powder to prepare the sintered magnet, wherein the metal fluoride includes at least one of MoF^4, MoF^5, MoF^6, WF^4, WF^6, ZrF^4, TaF^5 and NbF^5. The present invention provides the sintered magnet in which fine grains are uniformly distributed by effectively suppressing grain growth.

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

For the general manufacture of NdFeB-based magnets, a strip/mold casting or melt spinning method based on a metal powder metallurgy method is known. First, in the case of the strip/mold casting method, metals such as neodymium (Nd), iron (Fe), and boron (B) are melted through heating to produce an ingot, and the grain particles are coarsely pulverized. And, it is a process of manufacturing microparticles through a micronization process. By repeating this, magnetic powder is obtained, and an anisotropic sintered magnet is manufactured through a pressing and sintering process under a magnetic field.

In addition, in the melt spinning method, metal elements are melted, poured into a wheel rotating at a high speed, and then quenched, jet milled, pulverized, blended with a polymer to form a bonded magnet, or pressed to form a magnet. To manufacture.

Recently, attention has been paid to a method of manufacturing a magnetic powder by a reduction-diffusion method. For example, it is possible to prepare uniform NdFeB fine particles through a reduction-diffusion process of mixing _{Nd 2} O _{3, Fe, and B and reducing it to Ca.}

However, in the case of the process of obtaining a sintered magnet by sintering the magnet powder produced by the reduction-diffusion method, grain growth accompanies the sintering in a temperature range of 1000 to 1250 degrees Celsius, and the growth of such grains decreases the coercive force. It acts as a factor to make. The relationship between the grain size and the coercive force has been found experimentally as shown in Equation 1.

[Equation 1]

HC = a + b/D (HC: magnetic moment, a and b: constant, D: grain size)

According to Equation 1, the coercive force of the sintered magnet tends to decrease as the grain size increases. In addition, during sintering, grain growth (more than 1.5 times the size of the initial powder) occurs, and abnormal grain growth (more than twice the size of the normal grain size) occurs, greatly reducing the theoretical coercivity that the initial powder can have.

Therefore, as a method to suppress the growth of crystal grains during sintering, the HDDR (Hydrogenation, disproportionation, desorption and recombination) process, a method of reducing the size of the initial powder through jet mill grinding, and a triple point by adding an element capable of forming a secondary phase. There is a method of suppressing the movement of grain boundaries by forming.

However, although the coercive force 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, the microstructure is greatly changed due to grain migration, and thus another problem occurs, such as a decrease in properties of a sintered magnet and a decrease in magnetic properties due to an additional element.

The embodiments of the present invention have been proposed to solve the above problems of the previously proposed methods, and in a method of manufacturing a sintered magnet for sintering magnetic powder manufactured by a reduction-diffusion method, crystal grain growth is effectively suppressed. An object thereof is to provide a sintered magnet in which fine grains are uniformly distributed.

However, the problems to be solved by the embodiments of the present invention are not limited to the above-described problems and may be variously expanded 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 a rare earth oxide, iron, boron, a reducing agent, and a metal fluoride; Heating the mixture at a temperature of 800°C to 1100°C to synthesize magnetic powder using a reduction-diffusion method; And by sintering the magnet powder, and a step for producing a sintered magnet, the metal fluoride comprises MoF _4, MoF _5, MoF _6, WF _4, WF _6, ZrF _4, TaF ₅ and NbF at least one of the _five .

Preparing the mixture may include adding Ga to the mixture.

Preparing the mixture may include adding at least one of Na and K to the mixture.

The metal fluoride may be mixed in an amount of 0.2% to 3.0% by mass based on 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.

At least one of an R-F phase and an R-O-F phase may be formed on the inside and the surface of the sintered magnet particles.

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

The manufacturing of the sintered magnet may include preparing a mixed powder by mixing the magnetic powder and the rare earth hydride powder, and sintering the mixed powder at 1000°C to 1100°C.

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.

According to embodiments of the present invention, high melting point metal fluoride is added in the process of reduction-diffusion to prepare magnetic powder, and by sintering the magnetic powder, crystal grain growth is effectively suppressed and fine grains are uniformly distributed. You can make a magnet. Accordingly, the square ratio and coercivity of the sintered magnet can be improved.

In addition, a rare earth element and a fluorine compound are distributed inside and on the surface of the sintered magnet, so that corrosion resistance can be improved by stabilizing the surface of the sintered magnet.

1 is a BH curve graph for each of the sintered magnets of Example 1, Example 2, and Comparative Example 1.
2 is a BH curve graph for each of the sintered magnets of Example 3, Example 4, and Comparative Example 2.
3 is a SEM photograph of the sintered magnet of Example 1.
4 is a SEM photograph of the sintered magnet of Example 2.
5 is a SEM photograph of the sintered magnet of Comparative Example 1.
6 is an XRD pattern for each of the sintered magnets of Example 1, Example 2, and Comparative Example 1.
7 is an XRD pattern for each of the sintered magnets of Example 3, Example 4, and Comparative Example 2.

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

In addition, throughout the specification, when a certain part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

The method of manufacturing a sintered magnet according to an embodiment of the present invention includes preparing a mixture by mixing rare earth oxides, iron, boron, reducing agent, and metal fluoride, and heating the mixture at a temperature of 800 to 1100 degrees Celsius to reduce-diffusion. And synthesizing the magnetic powder using a method, and sintering the magnetic powder to produce a sintered magnet.

The metal fluorides include _{MoF 4, MoF 5, MoF 6} , WF 4, WF 6, ZrF 4, TaF 5 , and at least one of NbF _5. However, it is more preferable to include at least one of _{TaF 5} and NbF _5.

The magnet powder synthesized by the 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 embodiment, the R-Fe-B-based magnet powder is produced through a reduction-diffusion method. In the reduction-diffusion method, a mixture is prepared by mixing rare earth oxides, iron, boron, and a reducing agent, and then the mixture is heated to reduce the rare earth oxides, and at the same time, _{the powder on R 2} Fe ₁₄ B is synthesized.

The rare earth oxide 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 in correspondence with the rare earth element R. can do.

Since the reduction-diffusion method uses rare earth oxides as a raw material, the price is inexpensive, and a separate grinding process such as coarse grinding, hydrogen grinding, or jet mill or surface treatment process is not required.

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. In this case, the reduction-diffusion method has an advantage in that it is easier to manufacture magnetic powder having fine particles compared to other methods.

However, in the case of sintering the 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 twice the size of normal grain size) may occur during the sintering process. There is a problem that the grain size distribution of the magnet is not uniform, and magnetic performance such as coercivity is deteriorated.

Accordingly, in this embodiment, a metal fluoride containing at least one _{of MoF 4} , MoF ₅ , MoF ₆ , WF ₄ , WF ₆ , ZrF ₄ , _{TaF 5} and _{NbF 5} is further added to the rare earth oxides, iron, boron, and reducing agent. And synthesized R-Fe-B-based magnetic powder using the mixture.

The metal fluoride is a fluoride of a high melting point metal, and when it is added to the mixture, it induces precipitation of the high melting point metal in the reduction-diffusion step, thereby minimizing the particle size of the synthesized magnetic powder. The distribution of can also be formed evenly. As described above, it is possible to manufacture a sintered magnet having fine grains through the magnet powder having fine grains.

Furthermore, when sintering of the magnet _{powder, MoF 4, MoF 5, MoF} 6, WF 4, WF 6, ZrF 4, due to the TaF ₅ or NbF ₅ may be a crystal grain growth in the sintering process effectively limits. Accordingly, a sintered magnet with improved squareness ratio and coercivity can be manufactured by making the crystal grains finer and uniform.

This can be considered as a phenomenon in which the characteristics of the magnetic powder, in which normal or abnormal grain growth occurs largely, is effectively suppressed by the added Mo, W, Zr, Ta, or Nb elements and F elements.

Meanwhile, in the synthesized magnetic powder or the manufactured sintered magnet, at least one of an R-F phase and an R-O-F phase may be formed on the inside and the surface of the particles. Since the fluoride-containing phase is more stable than the oxide, the existing oxides present near the particles of the magnetic powder are reduced and easily change to the fluoride-containing phase, making it difficult to generate oxides other than the R-O-F phase. In addition, since the R-O-F phase can stably capture oxygen, the corrosion resistance of the sintered magnet can be improved because new reactions such as oxidation or hydroxylation of the magnet powder are difficult to proceed.

In addition, since the metal fluoride is added to the mixture prepared to synthesize the magnetic powder by the reduction-diffusion method, the metal fluoride can be evenly distributed inside the particles of the magnetic powder. , Zr, Ta, and Nb are not locally present in the particle and on the surface, but can be uniformly distributed, and the RF phase and the ROF phase can be uniformly distributed on the inside and the surface of the sintered magnet likewise. That is, by adding metal fluoride in the reduction-diffusion step, the effects such as improvement of the square ratio or coercivity through the above-mentioned grain growth limitation, improvement of corrosion resistance through surface stabilization, etc. can be further increased, and to be evenly expressed in the entire sintered magnet. can do.

In addition, since the high melting point metal is added in the form of a fluoride having a lower melting point rather than in a pure metal state, it is more advantageous in distributing it evenly throughout the sintered magnet.

Preparing the mixture may include adding Ga to the mixture. In other words, Ga may be further included in the mixture. When Ga is included in the mixture, the nonmagnetic phase can be more easily induced at the grain boundary of the sintered magnet. Accordingly, generation and transition of inverse magnetic domains at the grain boundary are suppressed, and an increase in coercivity can be expected.

Preparing the mixture may include adding at least one of Na and K to the mixture. Specifically, in order to control the particle size, size, and shape of the magnetic powder, at least one of Na and K may be further included in the mixture.

The metal fluoride may be mixed in an amount of 0.2% to 3.0% by mass based on the mixture. When the metal fluoride is mixed in an amount of less than 0.2% by mass relative to the mixture, there may be a problem that the effect of controlling grain growth is hardly observed. When the metal fluoride is mixed in an amount greater than 3.0% by mass relative to the mixture, the sinterability may be affected, resulting in a decrease in the sintering density, and accordingly, there may be a problem in that the magnetic performance is deteriorated such as a decrease in the residual magnetic flux density.

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

First, a step of preparing an R-Fe-B-based magnet powder by a reduction-diffusion method will be described. Preparation of the R-Fe-B-based magnetic powder according to the reduction-diffusion method includes mixing raw materials to prepare a mixture, heating the mixture to synthesize magnetic powder, and washing steps.

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

As mentioned earlier, the metal fluoride is MoF _4, MoF _5, MoF _6, WF _4, WF _6, ZrF _4, TaF ₅ and NbF includes at least one of ₅ and rare earth oxides are _{Nd 2 O 3, La 2 O} 3, It may include at least one of Ce ₂ O ₃ , Pr ₂ O ₃ , Pm ₂ O ₃ , Sm ₂ O ₃ and Eu ₂ O _3. The reducing agent may include at least one _{of Ca, CaH 2 and Mg.}

It is preferable to mix the metal fluoride in a powder form, and the size of the powder may be 0.05 to 100 micrometers.

The molar ratio of rare earth oxides, boron and iron may be between 1:14:1 and 1.5:14:1. Rare earth oxides, boron, and iron are _{raw materials for producing R 2} Fe ₁₄ B magnet powder, and when the above molar ratio is satisfied, R ₂ Fe ₁₄ B magnet powder can be produced with a 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 column phase is distorted and the R-rich grain boundary phase is not formed.If the molar ratio is greater than 1.5:14:1, the amount of rare earth elements is excessive. Thus, there may be a problem in that the reduced rare earth element remains, and the remaining rare earth element is _{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 degrees Celsius to 1100 degrees Celsius in an inert gas atmosphere. If the heating time is less than 10 minutes, the powder cannot be sufficiently synthesized, and if the heating time is more than 6 hours, the size of the powder becomes coarse and there may be a problem in which primary particles are aggregated.

The magnetic powder thus prepared may be _{R 2} Fe _{14 B.} In addition, the size of the manufactured magnetic powder may be in the range of 0.3 micrometers to 10 micrometers. In addition, the size of the magnetic powder manufactured according to an embodiment may be 0.3 micrometers to 5 micrometers.

_{That is, the R 2} Fe ₁₄ B magnet powder may be formed by heating the raw material at a temperature of 800 to 1100 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 magnet powder such as _{Nd 2} Fe ₁₄ B, the raw material is melted at a high temperature of 1500 to 2000 degrees Celsius and then rapidly cooled to form a mass of raw material, and the mass is coarsely pulverized and hydrogenated. Crushing or the like is performed to obtain R ₂ Fe ₁₄ B magnet powder. However, in the case of such a method, a high temperature temperature for melting the raw material is required, and a process of cooling and pulverizing the raw material is required, so that the process time is long and complicated. In addition, a _{separate surface treatment process is required for the coarsely pulverized R 2} Fe ₁₄ B magnet powder in order to enhance corrosion resistance and improve electrical resistance.

However, in the case of 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. . In this step, since the size of the magnetic powder is formed in units of several micrometers, a separate grinding process is not required.

In addition, in the case of the process of obtaining a sintered magnet by sintering the magnetic powder afterwards, when sintering is performed in a temperature range of 1000 to 1100 degrees Celsius, crystal grain growth is necessarily accompanied, and the growth of such grains acts as a factor reducing the coercivity. 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 be 0.5 micrometers to 10 micrometers, like the magnet powder according to an embodiment of the present invention, the coercive force is then Improved sintered magnets can be manufactured.

In addition, it is possible to control the size of the alloy powder produced by adjusting the size of the iron powder used as a raw material.

However, in the case of manufacturing the magnetic powder by the reduction-diffusion method, by-products such as calcium oxide or magnesium oxide may be generated during the manufacturing process, and a cleaning step of removing the magnetic powder may be required.

In order to remove such by-products, a washing step in which the produced magnetic powder is immersed in an aqueous solvent or a non-aqueous solvent and washed is followed. This cleaning can 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, an ammonium salt or acid may be dissolved in an aqueous solvent or a non-aqueous solvent, and specifically, _{at least one of NH 4} NO ₃ , NH ₄ Cl and ethylenediaminetetraacetic acid (EDTA) may be dissolved.

Thereafter, the step of sintering the R-Fe-B-based magnet powder that has undergone the synthesis step and the washing step as described above is followed.

A mixed powder can be prepared by mixing R-Fe-B magnetic powder and rare earth hydride powder.

The rare earth hydride powder is preferably mixed in an amount of 3 to 15% by mass relative to the mixed powder.

If the content of the rare earth hydride powder is less than 3% by mass, there is a problem in that sufficient wetting between the particles is not provided and sintering is not performed well, and the role of suppressing the columnar decomposition of R-Fe-B is not sufficiently performed. I can. In addition, when the content of the rare earth hydride powder is more than 15% by mass, the volume ratio of the R-Fe-B column in the sintered magnet decreases, resulting in a decrease in the residual magnetization value, and there may be a problem in that particles grow excessively due to liquid phase sintering. have. When the size of the crystal grains increases due to the overgrowth of the particles, the coercivity decreases because it is vulnerable to magnetization reversal.

Next, the mixed powder is heated at a temperature of 700 to 900 degrees Celsius. In this step, the rare earth hydride is separated into rare earth metal and hydrogen gas, and hydrogen gas is removed. 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 of removing hydrogen from the mixed powder. In this case, heating may be performed in a vacuum atmosphere.

Next, the heated mixed powder is sintered at a temperature of 1000 to 1100 degrees Celsius. In this case, the step of sintering the heated mixed powder at a temperature of 1000 degrees 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 at 700 to 900 degrees Celsius is put into a graphite mold, compressed, and oriented by applying a pulsed magnetic field to prepare a molded body for a sintered magnet. The sintered magnet is manufactured by heat-treating the molded body for a sintered magnet at 300 to 400 degrees Celsius in a vacuum atmosphere and then sintering at a temperature of 1000 to 1100 degrees Celsius.

In this sintering step, liquid phase sintering by rare earth elements is induced. That is, between the R-Fe-B-based magnet powder produced by the conventional reduction-diffusion method and the added rare-earth hydride powder, liquid phase sintering occurs by the rare-earth element. Through this, R-rich and ROx phases are formed in the grain boundary area inside the sintered magnet or the grain boundary area of the columnar grains of the sintered magnet. The thus formed R-Rich region or ROx phase improves the sinterability of the magnetic powder and prevents the decomposition of the columnar particles in the sintering process for manufacturing a sintered magnet. Therefore, it is possible to stably manufacture a sintered magnet.

The manufactured sintered magnet has a high density and may have a size of 1 micrometer to 10 micrometers.

Next, after heating the sintered magnet to 500 to 800 degrees Celsius in a vacuum atmosphere, a heat treatment step may be followed. Through such post-heat treatment, a nonmagnetic interface may be formed in a certain thickness in the sintered magnet, and thus coercivity may be improved.

As previously mentioned, MoF _4, MoF _5, MoF _6, WF _4, WF _6, ZrF _4, TaF ₅ and NbF and synthesizing the R-Fe-B based magnet powder by the addition of a metal fluoride comprises at least one of _5, Since it is sintered, normal or abnormal grain growth that may occur during the sintering process can be effectively suppressed. Accordingly, it is possible to refine the crystal grains of the sintered magnet and uniformize the grain size distribution, thereby improving the squareness ratio and coercivity.

At the same time, R-F and R-O-F phases are formed inside and on the surface of the sintered magnet particles, so that effects such as improvement of corrosion resistance through surface stabilization can be obtained. That is, it is possible to prevent the magnet particles from undergoing an oxidation or hydroxylation reaction.

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

Example 1: NbF ₅ adding

Nd ₂ O ₃ 4.05g, Fe 7.00g, B 0.12g, Cu 0.319g, _{NbF 5} 0.094g, Ca 2.89g and Mg 0.28g are uniformly mixed together with Na and K in a sealed plastic container to prepare a mixture .

The mixture is put in a stainless steel container of any shape and pressed, and reacted in a tube electric furnace for 10 minutes to 3 hours at 900 to 920 degrees Celsius in an inert gas (Ar) atmosphere. Then, the reactants are coarsely pulverized with an automatic grinder.

Next, a washing step is performed to remove Ca and CaO, which are reduction by-products. After uniformly mixing 30g to 35g of NH4NO3 with the synthesized powder, it is immersed in ~200ml of methanol, and for effective cleaning, a homogenizer and an ultrasonic cleaning (ultra sonic) are alternately repeated once or twice. Next, 10 g of powder, _{0.5 g of NH 4} NO ₃ and 50 g of zirconia balls were mixed with 100 ml of methanol, and pulverized for 1 to 2 hours using a turbuler mixer, and single-phase Nd-Fe having an average particle size of 0.3 to 20 micrometers -B magnet powder is obtained.

Thereafter, 10% by mass of NdH ₂ was added to the magnet powder, mixed, and compression-molded in a graphite mold, and the powder was oriented by applying a pulsed magnetic field of 5T or more to prepare a sintered magnet molded body.

Thereafter, the compact was heated in a vacuum sintering furnace at a temperature of 1070 degrees Celsius for 1 to 2 hours to perform sintering, thereby manufacturing a sintered magnet. Finally, heat treatment was performed after heating at 500 to 800 degrees Celsius in a vacuum atmosphere.

Example 2: TaF ₅ adding

Nd ₂ O ₃ 4.05 g, Fe 7.00 g, B 0.12 g, Cu _{0.319 g, TaF 5} 0.138 g, Ca 2.89 g and Mg 0.28 g were mixed with Na and K, and then magnetic powder in the same manner as in Example 1. Synthesis, cleaning, sintering and post heat treatment were performed.

Comparative Example 1: No high melting point metal fluoride added

Nd ₂ O ₃ 4.05 g, Fe 7.00 g, B 0.12 g, Cu 0.319 g, Ca 2.89 g and Mg 0.28 g were mixed with Na and K, and then synthesized, washed, and sintered in the same manner as in Example 1. And post-heat treatment.

Example 3: NbF ₅ And Ga addition

Nd ₂ O ₃ 4.05g, Fe 7.00g, B 0.12g, Cu 0.319g, Ga 0.069g, _{NbF 5} 0.094g, Ca 2.89g and Mg 0.28g were mixed with Na and K, the same as in Example 1 As a method, magnetic powder synthesis, washing, sintering, and post-heat treatment were performed.

Example 4: TaF ₅ And Ga addition

Nd ₂ O ₃ 4.05g, Fe 7.00g, B 0.12g, Cu 0.319g, Ga 0.069g, TaF ₅ 0.138g, Ca 2.89g and Mg 0.28g were mixed with Na and K, the same as in Example 1 As a method, magnetic powder synthesis, washing, sintering, and post-heat treatment were performed.

Comparative Example 2: No addition of high melting point metal fluoride and addition of Ga

After mixing Nd ₂ O ₃ 4.05g, Fe 7.00g, B 0.12g, Cu 0.319g, Ga 0.069g, Ca 2.89g and Mg 0.28g with Na and K, magnetic powder synthesis in the same manner as in Example 1 , Washing, sintering and post-heat treatment were performed.

Evaluation Example 1: B-H curve graph

_{The residual magnetic flux density (Br), coercive force (H CB} ), advanced magnetic force (H _CJ ), and BH max for each of the sintered magnets of Example 1, Example 2 and Comparative Example 1 were measured and shown in Table 1, and the BH curve The graph is shown in FIG. 1.

powder Br(kG) H _CB (kOe) H _CJ (kOe) BH max(MGOe) Example 1 Nd _2.4 Fe _12.5 B _1.1 Cu _0.05 Nb _0.05 13.05 7.846 9.020 40.25 Example 2 Nd _2.4 Fe _12.5 B _1.1 Cu _0.05 Ta _0.05 13.12 7.406 8.53 40.62 Comparative Example 1 Nd _2.4 Fe _12.5 B _1.1 Cu _0.05 13.24 7.843 9.441 36.23

_{Referring to Table 1 and FIG. 1, when NbF 5} or TaF ₅ was added like the sintered magnets of Examples 1 and 2, the angle ratio was improved on the BH curve graph compared to the sintered magnet of Comparative Example 1 without adding them, It can be seen that the BH max value is improved.

Next, the residual magnetic flux density (Br), coercive force (H _CB ), advanced magnetic force (H _CJ ) and BH max for each of the sintered magnets of Example 3, Example 4 and Comparative Example 2 were measured and shown in Table 2, The BH curve graph is shown in FIG. 2.

powder Br(kG) H _CB (kOe) H _CJ (kOe) BH max(MGOe) Example 3 Nd _2.4 Fe _12.5 B _1.1 Cu _0.05 Ga _0.1 Nb _0.05 12.53 11.880 13.730 38.50 Example 4 Nd _2.4 Fe _12.5 B _1.1 Cu _0.05 Ga _0.1 Ta _0.05 12.42 11.020 13.310 37.24 Comparative Example 2 Nd _2.4 Fe _12.5 B _1.1 Cu _0.05 Ga _0.1 12.64 10.05 13.150 38.21

_{Referring to Table 2 and FIG. 2, when NbF 5} or TaF ₅ was added as in the sintered magnets of Examples 3 and 4, the angle ratio was improved on the BH curve graph compared to the sintered magnet of Comparative Example 2 without adding them, It can be seen that the coercivity value has increased. In addition, compared to Example 1 and the like, it can be seen that when Ga is added, the nonmagnetic phase is easily induced at the grain boundary surface of the sintered magnet, and the coercive force is improved.

Evaluation Example 2: SEM photo

SEM (Scanning Electron Microscope) pictures of each of the sintered magnets of Example 1, Example 2, and Comparative Example 1 are shown in FIGS. 3 to 5.

_{3 to 5, when NbF 5} or TaF ₅ was added like the sintered magnets of Examples 1 and 2, the growth of crystal grains was limited compared to the sintered magnet of Comparative Example 1 without the addition of them, and thus uniform particles. It can be seen that the distribution is shown.

Evaluation Example 3: XRD pattern

6 shows an XRD (X-Ray Diffraction) pattern for each of the sintered magnets of Example 1, Example 2, and Comparative Example 1.

Referring to FIG. 6, it can be seen that the NdO phase clearly identified in the sintered magnet of Comparative Example 1 was not found in the sintered magnets of Examples 1 and 2. This is because the generation of oxides of Nd was suppressed due to the Nd-F phase or the Nd-O-F phase formed by the addition of metal fluoride.

Next, XRD (X-Ray Diffraction) patterns for each of the sintered magnets of Example 3, Example 4, and Comparative Example 2 are shown in FIG. 7.

Referring to FIG. 7, it can be seen that the NdO phase clearly identified in the sintered magnet of Comparative Example 2 was not found in the sintered magnets of Examples 3 and 4. This is similarly because the Nd-F phase or the Nd-O-F phase formed by the addition of metal fluoride suppressed the formation of oxides of Nd.

That is, through the results of FIGS. 6 and 7, it can be seen that the generated fluoride phase can contribute to the improvement of corrosion resistance of the sintered magnet.

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 of those skilled in the art using the basic concept of the present invention defined in the following claims are also present. It belongs to the scope of rights of

Claims (10)

Preparing a mixture by mixing a rare earth oxide, iron, boron, a reducing agent, and a metal fluoride;
Heating the mixture at a temperature of 800°C to 1100°C to synthesize magnetic powder using a reduction-diffusion method; And
Including the step of sintering the magnet powder to produce a sintered magnet,
The metal fluoride is _{MoF 4, MoF 5, MoF 6} , WF 4, WF 6, ZrF 4, TaF 5 and NbF method for producing a sintered magnet that includes at least one of the _five. In claim 1,
The step of preparing the mixture includes adding Ga to the mixture. In claim 1,
The step of preparing the mixture comprises adding at least one of Na and K to the mixture. In claim 1,
The method of manufacturing a sintered magnet in which the metal fluoride is mixed at 0.2% to 3.0% by mass based on the mixture. In claim 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 A} method of manufacturing a sintered magnet comprising at least one of. In claim 1,
The sintered magnet is an R-Fe-B-based sintered magnet,
The R is Nd, La, Ce, Pr, Pm, Sm or Eu in the manufacturing method of the sintered magnet. In paragraph 6,
A method of manufacturing a sintered magnet in which at least one of an RF phase and an ROF phase is formed on the inside and on the surface of the sintered magnet particles. In claim 1,
The reducing agent is a method of manufacturing a sintered magnet containing at least one _{of Ca, CaH 2 and Mg.} In claim 1,
The step of manufacturing a sintered magnet comprises preparing a mixed powder by mixing the magnet powder and the rare earth hydride powder, and sintering the mixed powder at 1000 degrees to 1100 degrees Celsius. In claim 1,
The method of manufacturing a sintered magnet further comprising a heat treatment step after heating the sintered magnet to 500 to 800 degrees Celsius.

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