JP2014075373A - Method for manufacturing rare earth alloy powder, anisotropic bonded magnet and sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of manufacturing rare earth alloy powder excellent in magnetic properties by improving an HDDR method.SOLUTION: The method for manufacturing rare earth alloy powder by a hydrogenation decomposition and dehydrogenation recombination method comprises the steps of: (a) hydrocracking a raw material alloy containing a rare earth element to obtain the decomposition product; (b) discharging hydrogen from the decomposition product to reduce hydrogen concentration of the decomposition product; and (c) further discharging hydrogen from the decomposition product at a hydrogen discharge speed lower than that in the step (b) to obtain the rare earth alloy powder. The method is transferred from the step (b) to the step (c) when in the cross section of the decomposition product, an area ratio of a RFeB phase (R represents a rare earth element) covering a rare earth hydride phase becomes 25 to 55% on the basis of the total area of the cross section.

Description

  The present invention relates to a method for producing a rare earth alloy powder, and an anisotropic bonded magnet and a sintered magnet.

  The HDDR method (hydrocracking / dehydrogenation recombination method) is known as a method for producing an alloy powder for a magnet. The HDDR method is a process of sequentially executing hydrogenation, disproportionation, dehydrogenation, and recombination.

  Since the HDDR method involves a solid-phase-gas phase reaction, the reaction mechanism is complicated, and the magnetic properties such as the coercive force of the obtained magnetic powder vary depending on the manufacturing conditions. For this reason, in the production of magnet powder using the HDDR method, attempts have been made to improve the magnetic properties of the magnet powder by adjusting the production conditions. For example, Patent Document 1 proposes to improve the magnetic properties of the magnet powder by changing the reaction rate by controlling the atmosphere during the dehydrogenation recombination process.

JP 2001-115220 A

  However, even if the atmosphere is controlled as in Patent Document 1, it is difficult to obtain a sufficiently high coercive force. For this reason, it is required to establish a method for producing rare earth alloy powders having excellent magnetic properties using the HDDR method.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method improved from the HDDR method and capable of producing a rare earth alloy powder having excellent magnetic properties. Moreover, it aims at providing the anisotropic bonded magnet and sintered magnet containing the rare earth alloy powder manufactured by the said method.

A method for producing a rare earth alloy powder according to the present invention is a method for producing a rare earth alloy powder by a hydrocracking / dehydrogenation recombination method,
(A) hydrocracking a raw material alloy containing a rare earth element to obtain a decomposition product;
(B) releasing hydrogen from the decomposition product to reduce the hydrogen concentration of the decomposition product;
(C) a step of further releasing hydrogen from the decomposition product at a release rate lower than the release rate of hydrogen in step (b) to obtain a rare earth alloy powder;
In the cross section of the decomposition product, the R ₂ Fe ₁₄ B phase (R represents a rare earth element) covers the rare earth hydride phase, and the area ratio of the R ₂ Fe ₁₄ B phase is the entire area of the cross section. As a reference, the process shifts from the step (b) to the step (c) at a time of 25 to 55%.

The above method is an improved method of hydrocracking / dehydrogenation recombination method, and can produce rare earth alloy powder having excellent magnetic properties. The main factors for obtaining such a rare earth alloy powder are that the hydrogen release rate in step (c) is smaller than the hydrogen release rate in step (b), and steps (b) to (b). It is conceivable that the timing of shifting to (c) is defined by the degree of grain growth of the R ₂ Fe ₁₄ B phase. That is, the dehydrogenation recombination treatment for the decomposition product obtained in the step (a) is performed in the step (b) and the step (c), whereby the nucleus of the R ₂ Fe ₁₄ B phase generated in the decomposition product. It is considered that a rare earth alloy powder having a refined R ₂ Fe ₁₄ B phase can be obtained.

The manufacturing method of the present invention may further include a step of determining the timing of transition from step (b) to step (c) by observing the morphology of the cross section. By carrying out this process, for example, even when a rare earth alloy powder having a new composition is produced or the production conditions are changed, the rare earth alloy powder having a refined R ₂ Fe ₁₄ B phase can be stabilized. Can be made.

  Moreover, this invention provides the anisotropic bonded magnet containing the rare earth alloy powder which has the anisotropy manufactured by said manufacturing method, and resin. Since the anisotropic bonded magnet of the present invention contains an anisotropic rare earth alloy powder having excellent magnetic properties, it has excellent magnetic properties.

  Furthermore, this invention provides the sintered magnet obtained by sintering the molded object of the rare earth alloy powder which has the anisotropy manufactured by said manufacturing method. Since the sintered magnet of the present invention contains an anisotropic rare earth alloy powder having excellent magnetic properties, the sintered magnet has excellent magnetic properties.

  ADVANTAGE OF THE INVENTION According to this invention, the rare earth alloy powder which has the outstanding magnetic characteristic can be manufactured, and the anisotropic bonded magnet and sintered magnet which have the outstanding magnetic characteristic can be provided.

It is a time chart of the manufacturing method of the rare earth alloy powder concerning this embodiment. It is a schematic cross section which expands and shows the fine structure of the decomposition product in the manufacturing process of the rare earth alloy powder concerning this embodiment at the time of the 1st dehydrogenation recombination process end. It is a perspective view which shows the anisotropic bonded magnet which concerns on this embodiment. It is a perspective view which shows the sintered magnet which concerns on this embodiment. It is a cross-sectional SEM photograph of the decomposition product at the time of completion | finish of the 1st dehydrogenation recombination process in the manufacturing process of the rare earth alloy powder which concerns on a present Example. It is a cross-sectional SEM photograph of the decomposition product at the time of a 1st dehydrogenation recombination process end.

<Method for producing rare earth alloy powder>
The method for producing a rare earth alloy powder of the present embodiment is a method for producing a rare earth alloy powder by a so-called hydrocracking / dehydrogenation recombination method (HDDR method). This production method, the content of rare earth element to prepare a raw material alloy is [rho (mass%), the alloy in a hydrogen atmosphere, the hydrogen storage step of holding a predetermined time at a temperature T _0, than the temperature T ₀ A hydrocracking step (step (a)) for hydrocracking at a high temperature T ₁ to obtain a cracked product having a hydrogen concentration η ₁ (mass%), and from a temperature T ₁ to a temperature T ₂ higher than the temperature T ₁ Hydrogen is released from the decomposition product at a predetermined rate at a temperature raising step for raising the temperature and at a temperature T ₂ , and the hydrogen concentration of the decomposition product is reduced from η ₁ (mass%) to η ₂ (mass%). The hydrogen concentration η of the cracked product is further reduced by lowering the hydrogen release rate from the cracked product than in the first dehydrogenated recombining step (step (b)) and the first dehydrogenated recombining step. And a second dehydrogenation recombination step (step (c) for obtaining a rare earth alloy powder substantially free of hydrogen. ) And has a cooling step of cooling the rare earth alloy powder to room temperature.

  FIG. 1 is a time chart of a method for producing a rare earth alloy powder according to the present embodiment. FIG. 1A is a time chart of temperature, and FIG. 1B is a time chart of hydrogen concentrations of raw material alloy, decomposition product, and rare earth alloy powder. Hereinafter, the manufacturing method of this embodiment will be described with reference to FIG. 1 as appropriate.

In the hydrogen storage step (I in FIG. 1), the raw material alloy having a rare earth element content of ρ (mass%) is held in a hydrogen atmosphere at a temperature T ₀ for a predetermined time to cause the raw material alloy to store hydrogen. It is a process. As the raw material alloy, an R—Fe—B alloy represented by R ₂ Fe ₁₄ B can be used. From the viewpoint of obtaining a rare earth alloy powder having more excellent magnetic properties, the composition of the R—Fe—B alloy is R: 25 to 35 mass%, B: 1 to 1.6 mass%, Fe: 63.4 to It is preferably 74% by mass. R may be one or more selected from Y, La, Ce, Pr, Nd, Sm, Gd, Td, Dy, Ho, Er, Tm, and Lu. Among these, from the viewpoint of manufacturing cost and magnetic properties, R preferably contains Nd.

  The mass-based R content ρ (mass%) in the rare earth metal is preferably 25 to 35 mass%, more preferably 27 to 33 mass%, although it depends on the type of rare earth metal used.

  The above-mentioned raw material alloy can be prepared by a normal casting method such as a strip casting method, a book mold method, or a centrifugal casting method. The raw material alloy may be subjected to a homogenization heat treatment. The raw material alloy may contain impurities.

  The homogenization heat treatment is performed by holding the raw material alloy in a vacuum or an inert gas atmosphere such as argon or nitrogen at a temperature of 1000 to 1200 ° C. for 5 to 48 hours. By performing such a homogenization heat treatment, the raw material alloy can be melted and the raw material alloy can be homogenized.

  The homogenized material alloy is preferably pulverized using a pulverizing means such as a stamp mill or a jaw crusher and then sieved. Thereby, a powdery raw material alloy having a particle size of 10 mm or less can be prepared.

In the hydrogen storage step, the powdery raw material alloy is held at a temperature T ₀ until time t ₁ in a hydrogen atmosphere having a hydrogen partial pressure of 100 to 300 kPa. Thereby, hydrogen is occluded in the crystal lattice of the raw material alloy, and a hydrogen occlusion alloy having a hydrogen concentration η ₀ (mass%) can be obtained. Hydrogen concentration (eta) ₀ shall be the range of 0.3-0.5 mass%, for example. At this stage, the raw material alloy is not decomposed.

Temperature _{T 0} in the hydrogen absorbing step is preferably 100 to 200 ° C.. Further, the time required _{t 1} of the hydrogen-absorbing step is preferably 0.5 to 2 hours.

In the hydrocracking step (II in FIG. 1), the hydrogen storage alloy is hydrocracked by holding the hydrogen storage alloy at a temperature T ₁ higher than the temperature T ₀ in a hydrogen atmosphere, and the hydrogen concentration η ₁ (mass%) ) Decomposition product is obtained.

The hydrogen partial pressure of the atmosphere in the hydrocracking step is preferably ₁₀ to 100 kPa, and the temperature T ₁ is preferably 700 to 850 ° C. By performing hydrogenolysis of the hydrogen storage alloy under these conditions, a rare earth alloy powder having magnetic anisotropy can be obtained. If the hydrogen partial pressure is less than 10 kPa, hydrocracking tends not to proceed sufficiently, and if it exceeds 100 kPa, anisotropic rare earth alloy powder tends to be difficult to obtain.

When the temperature T ₁ is less than 700 ° C., it tends to hydrogenolysis of the material alloy does not sufficiently proceed. On the other hand, when the temperature T ₁ is greater than 850 ° C., the desired degradation products (hydrides) tends to be difficult to obtain.

The time required for the hydrocracking step (t ₂ -t _{1 in} FIG. ₁ ) is preferably 0.5 to 60 hours. If this time is less than 0.5 hours, the hydrocracking of the raw material alloy tends not to proceed sufficiently, and if it exceeds 60 hours, rare earth alloy powder having magnetic anisotropy tends to be difficult to obtain. is there.

The decomposition product obtained in the hydrocracking step contains a hydride such as RH _X and an iron compound such as α-Fe and Fe ₂ B. The decomposition products at this stage form a fine matrix of the order of 100 nm.

The upper limit of the hydrogen concentration η ₁ (mass%) of the above-described decomposition product is usually a concentration at which all of the contained rare earth elements become hydrides (RH _X , x = 2 to 3). Although hydrogen concentration (eta) ₁ (mass%) is based also on the kind of rare earth element, it becomes the range of 0.35-0.6 mass%, for example.

In the temperature raising step (III in Fig. 1), it is heated to a higher temperature _{T 2} than temperature _{T 1} of the temperature of the decomposition products from the temperatures _{T 1.} Temperature _{T 2} is higher than the temperature _{T 1,} preferably from 720-950 ° C., and more preferably 750 to 950 ° C.. In addition, there is no restriction | limiting in particular in the temperature increase rate. The time required for the temperature raising step (t ₃ -t ₂ in FIG. 1) is, for example, 1 to 10 minutes.

In the first dehydrogenation recombination step (IV in FIG. 1), hydrogen is released from the decomposition product at a predetermined release rate at a temperature T ₂ higher than the temperature T ₁ , and the hydrogen concentration of the decomposition product is reduced. , Η ₁ (mass%) to η ₂ (mass%). This process is thought to produce nuclei of rare earth alloys in the matrix of cracked products obtained in the hydrocracking process.

The release rate of hydrogen from the decomposition product having a hydrogen concentration η ₁ (mass%) may be 0.75 to 30% by mass / hour based on the mass of the entire decomposition product before releasing hydrogen. preferable. Thereby, the nuclei of the rare earth alloy can be generated more uniformly. Further, hydrogen is released until the hydrogen concentration η of the decomposition product is in the range of 0.1 to 0.35% by mass, preferably in the range of 0.2 to 0.3% by mass. Thereby, the nuclei of the rare earth alloy can be generated more uniformly. Note that the hydrogen concentration η ₂ (mass%) of the decomposition product can be known by measuring the mass of the decomposition product.

  The release rate of hydrogen from the decomposition product can be adjusted by controlling the rate of decrease in hydrogen partial pressure in the atmosphere. That is, if the decrease rate of the hydrogen partial pressure is increased, the release rate of hydrogen from the decomposition product can be increased. The rate of decrease in the hydrogen partial pressure can be adjusted, for example, by introducing argon gas or reducing the pressure. The rate of decrease in the hydrogen partial pressure in the first dehydrogenation recombination step is preferably 10 to 40 kPa / min, and more preferably 12 to 20 kPa / min.

The temperature T ₂ of the decomposition product in the first dehydrogenation recombination step is preferably higher than the temperature T ₁ and is 750 to 950 ° C. By making the temperature T ₂ of the decomposition product higher than the temperature T ₁ , hydrogen is easily released from the decomposition product, and the nuclei of the rare earth alloy can be generated more uniformly. The temperature difference between the temperature T ₂ and the temperature T ₁ may be 20 ° C. or more, or 100 ° C. or more. By setting the temperature difference to 100 ° C. or more, it is possible to further reduce the number of segregated materials while maintaining the uniformity of particle size.

When temperature T ₂ is less than 750 ° C., can not be sufficiently increased the release rate of the hydrogen from the cracked products, tend to nucleation of rare earth alloy becomes uneven. On the other hand, when the temperature T ₂ exceeds 950 ° C., in order to release rate of the hydrogen from the cracked products is too large, there is a tendency that it becomes difficult to control the hydrogen concentration η of degradation products.

The time for the first dehydrogenation recombination step (t ₄ -t _{3 in} FIG. 1) is, for example, 0.1 to 0.5 hours. This time depends on the release rate of hydrogen from the decomposition product.

  In the second dehydrogenation recombination step (V in FIG. 1), the hydrogen release rate from the decomposition products is made smaller than in the first dehydrogenation recombination step, thereby further reducing the hydrogen concentration of the decomposition products. Then, the hydrogen partial pressure in the atmosphere is lowered to less than 1 Pa to obtain a rare earth alloy powder.

It is preferable that the temperature of the _second dehydrogenation recombination step is the same as the temperature T2 in the first dehydrogenation recombination step. Thereby, the release of hydrogen from the decomposition product can proceed smoothly.

The release rate of hydrogen from the decomposition product having a hydrogen concentration η ₂ (mass%), that is, the rate of decrease in the hydrogen concentration η of the decomposition product is determined before hydrogen is released (before the start of the first dehydrogenation recombination step). ) Is preferably 0.01 to 0.4% by mass / hour based on the mass of the entire decomposition product. As a result, the growth of the nuclei of the rare earth alloy precipitated in the decomposition product proceeds gradually, and segregation can be prevented from remaining in the grains of the rare earth alloy. When the rate of decrease in the hydrogen concentration η exceeds 0.4 mass%, α-Fe and iron-rich phases contained in the decomposition products tend not to be recombined and tend to be left in the grains of the rare earth alloy. On the other hand, if the rate of decrease in the hydrogen concentration η is less than 0.01% by mass, the time required for the process becomes too long and abnormal grain growth of the recombined rare earth alloy tends to occur.

  Examples of segregated materials include α-Fe, iron-rich compounds, and compounds derived from impurities such as Nb contained in the raw material alloy. If such a segregated substance is present in the primary particles of the rare earth alloy powder, a reverse magnetic domain is generated and it is difficult to obtain a high coercive force.

The time of the second dehydrogenation recombination step (t ₅ -t _{4 in} FIG. 1) can be, for example, 0.3 to 5 hours. This time depends on the hydrogen release rate from the decomposition products. In addition, it is preferable that the fall rate of the hydrogen partial pressure in a 2nd dehydrogenation recombination process shall be 0.01-0.2 kPa / min.

  Finally, in the cooling step, the rare earth alloy powder obtained in the second dehydrogenation recombination step is cooled to room temperature (VI in FIG. 1). Through the above steps, an anisotropic rare earth alloy powder in which the segregated matter in the primary particles is sufficiently reduced can be obtained. This rare earth alloy powder usually has the same composition as the raw material alloy.

The manufacturing method of the rare earth alloy powder of the present embodiment is such that the first dehydrogenation recombination step and the second dehydrogenation recombination step are performed by observing an enlarged cross section of the decomposition product that has been subjected to the dehydrogenation recombination treatment. You may further have the process of determining the timing which transfers to a coupling | bonding process. According to this step, the hydrogen release rate in the first and second dehydrogenation recombination steps may be determined. By carrying out this process, for example, even when a rare earth alloy powder having a new composition is produced or the production conditions are changed, the rare earth alloy powder having a refined R ₂ Fe ₁₄ B phase can be stabilized. Can be made. In this step, the morphology of the cross section of the decomposition product in the first dehydrogenation recombination step is observed by, for example, SEM and the morphology is observed.

  FIG. 2 is a schematic cross-sectional view showing, in an enlarged manner, the microstructure of the decomposition product at the end of the first dehydrogenation recombination step in the method for producing a rare earth alloy powder according to the present embodiment. Such a fine structure can be confirmed by observing the cross section of the decomposition product with a scanning electron microscope.

At the end of the first dehydrogenation recombination step, the rare earth alloy powder (decomposition product) is mainly composed of an R hydride phase (rare earth hydride phase) 10, an iron compound phase 20 such as α-Fe and Fe ₂ B, and R ₂ Fe ₁₄ B phase 30 is formed, and R hydride phase 10 is covered with R ₂ Fe ₁₄ B phase 30. At this time, the area ratio of the R ₂ Fe ₁₄ B phase is 25 to 55% based on the entire cross-sectional area, preferably 28 to 43%, and more preferably 30 to 40%. That is, in the dehydrogenation recombination step, the time from the start to the end of nucleation of the R ₂ Fe ₁₄ B phase 30 is shortened as much as possible to increase the time during which the grain growth of the R ₂ Fe ₁₄ B phase 30 proceeds slowly, and By setting the area ratio of the R ₂ Fe ₁₄ B phase to the above numerical range, it is possible to suppress the R ₂ Fe ₁₄ B phase 30 from finally becoming coarse particles. Thereby, since fine particles of the R ₂ Fe ₁₄ B phase 30 are formed, a rare earth alloy powder having an excellent coercive force can be obtained.

The area ratio of the R ₂ Fe ₁₄ B phase 30 based on the entire area of the cross section in the cross section of the decomposition product can be calculated by the following method. The decomposition product is embedded in a resin, a mirror sample is prepared by sandpaper and buffing, and a reflected electron image of the sample is observed with a scanning electron microscope (SEM, magnification: 20,000). The area of about 4.5 μm × 6.0 μm is observed by two visual fields, and the areas of the R hydride phase 10, the iron compound phase 20 such as α-Fe and Fe ₂ B, and the R ₂ Fe ₁₄ B phase 30 are respectively determined. Based on the difference in contrast, the area ratio of the R ₂ Fe ₁₄ B phase can be determined by image analysis processing based on the entire cross-sectional area.

In the method for producing a rare earth alloy powder of the present embodiment, at the end of the first dehydrogenation recombination step, the R hydride phase is covered with the R ₂ Fe ₁₄ B phase in the cross section of the decomposition product, and R ₂ The area ratio of the Fe ₁₄ B phase is 25 to 55% based on the entire cross-sectional area. The decomposition in the first dehydrogenation recombination step is performed by making the rate of decrease in the hydrogen partial pressure in the first dehydrogenation recombination step larger than the rate of decrease in the hydrogen partial pressure in the second dehydrogenation recombination step. The hydrogen release rate from the product is larger than that in the second dehydrogenation recombination step. In addition, since the temperature (T ₂ ) of the first dehydrogenation recombination step is higher than the temperature (T ₁ ) of the hydrocracking step, the decomposition product from the decomposition product in the first dehydrogenation recombination step. Hydrogen release rate can be increased. As a result, the nucleation in the rare earth alloy becomes finer and more uniform than in the past, and it is considered that segregation can be prevented from being precipitated in the grains during the nucleation.

Since the rare earth alloy powder obtained by the method for producing a rare earth alloy powder of the present embodiment has a refined R ₂ Fe ₁₄ B phase, it can be suitably used as an alloy powder for a rare earth magnet. That is, if a magnet is produced using the rare earth alloy powder obtained by the above production method, a magnet having excellent magnetic properties (particularly coercive force) can be obtained.

  From the viewpoint of producing a rare earth alloy powder having even more excellent magnetic properties, the composition of the R—Fe—B alloy, which is the main component of the rare earth alloy powder, is R: 25 to 35 mass%, B: 1 to 1.6 mass. %, Fe: 63.4 to 74% by mass is preferable. R may be one or more selected from Y, La, Ce, Pr, Nd, Sm, Gd, Td, Dy, Ho, Er, Tm, and Lu. Among these, from the viewpoint of manufacturing cost and magnetic properties, R preferably contains Nd.

  The rare earth alloy powder is preferably a magnet powder having magnetic anisotropy. Thus, it can be suitably used as a raw material for anisotropic bonded magnets and sintered magnets having excellent magnetic properties.

<Anisotropic bonded magnet>
FIG. 3 is a perspective view showing the anisotropic bonded magnet according to the present embodiment. An anisotropic bonded magnet 50 shown in FIG. 3 includes a resin and an anisotropic magnet powder bonded by the resin. As the anisotropic magnet powder, the rare earth alloy powder described above can be used. Examples of resins include thermosetting resins such as epoxy resins and phenol resins, styrene-based, olefin-based, urethane-based, polyester-based, polyamide-based elastomers, ionomers, ethylene-propylene copolymers (EPM), and ethylene-ethyl acrylate. Examples thereof include thermoplastic resins such as polymers. Especially, a thermosetting resin is preferable and an epoxy resin or a phenol resin is more preferable.

  The anisotropic bonded magnet 50 of this embodiment has excellent magnetic properties because anisotropic magnet powder is oriented in a specific direction. The content ratio of the magnet powder and the resin in the anisotropic bonded magnet 50 preferably includes, for example, 0.5 to 20 parts by mass of resin with respect to 100 parts by mass of the magnet powder. If the resin content is less than 0.5 parts by mass with respect to 100 parts by mass of the magnet powder, shape retention tends to be impaired. If the resin exceeds 20 parts by mass, sufficiently excellent magnetic properties are obtained. It tends to be difficult to obtain.

  Such an anisotropic bonded magnet can be manufactured by a usual method. An example of the manufacturing method will be described below. First, the resin binder containing the above-mentioned resin and magnet powder are kneaded with a pressure kneader (pressure kneader) to prepare a compound (composition) for an anisotropic bonded magnet containing the resin binder and magnet powder. A coupling agent and other additives may be added to the anisotropic bonded magnet compound as necessary.

An anisotropic bonded magnet can be obtained by preparing a compound for the above-mentioned anisotropic bonded magnet and then performing a molding process in which the compound is compressed and molded in a magnetic field. The compression molding can be performed using a compression molding machine such as a mechanical press or a hydraulic press. In this way, an anisotropic bonded magnet including oriented anisotropic magnet powder and resin can be obtained. This anisotropic bonded magnet has excellent magnetic properties because the particles of the R ₂ Fe ₁₄ B phase 30 contain fine anisotropic magnet powder and the magnet powder is oriented in a specific direction. Have.

  In addition, the manufacturing method of an anisotropic bonded magnet is not limited to the method by the above-mentioned compression molding, For example, you may shape | mold by injection molding. In this case, the anisotropic bonded magnet compound is heated to the melting temperature of the binder (thermoplastic resin) as necessary to obtain a fluid state, and then the compound has a predetermined shape and a magnetic field is applied. Injection into a mold and molding in a magnetic field. Then, it cools and takes out the molded article (anisotropic bond magnet) which has a predetermined shape from a metal mold | die. In this way, an anisotropic bonded magnet can be manufactured.

<Sintered magnet>
FIG. 4 is a perspective view schematically showing the sintered magnet 60 according to the present embodiment. The sintered magnet 60 shown in FIG. 4 consists of a sintered body containing anisotropic magnet powder. As the anisotropic magnet powder, the rare earth alloy powder described above can be used. The sintered magnet 60 of this embodiment has excellent magnetic properties because anisotropic magnet powder is oriented in a specific direction.

Such a sintered magnet 60 can be manufactured by a normal method. An example of the manufacturing method will be described below. First, the above-mentioned anisotropic magnet powder is compressed and molded in a magnetic field to produce a molded body. The compression molding can be performed using a compression molding machine such as a mechanical press or a hydraulic press. In this case, the applied magnetic field strength is preferably 800 kA / m or more, and the molding pressure is preferably about 100 to 500 MPa. Moreover, when producing a molded body, an appropriate amount of a binder (for example, PVA) may be added to the anisotropic magnet powder. Next, the prepared molded body is sintered at 1000 to 1200 ° C. for about 0.5 to 5 hours and rapidly cooled to prepare a sintered body. The sintering atmosphere is preferably an inert gas atmosphere such as argon gas. If necessary, an aging treatment for heating the sintered body at 400 to 900 ° C., preferably 450 to 700 ° C. for 1 to 5 hours may be performed in an inert gas atmosphere. In this way, a sintered magnet can be obtained. This sintered magnet has excellent magnetic properties because the particles of the R ₂ Fe ₁₄ B phase 30 contain fine anisotropic magnet powder and the magnet powder is oriented in a specific direction. However, the manufacturing method of a sintered magnet is not limited to the above-mentioned method.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, the anisotropic bonded magnet is not limited to the above-described shape, and is an anisotropic bonded magnet having a desired shape (for example, a columnar shape, a flat plate shape, or a C-shaped shape) by changing a mold. be able to.

  The content of the present invention will be described in detail below using examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
An Nd ₂ Fe ₁₄ B raw material alloy having the following composition was prepared by a strip casting method.

Nd: 28.00 mass%
Fe: 70.01 mass%
B: 1.08 mass%
Ga: 0.36% by mass
Nb: 0.30 mass%

This raw material alloy contained a small amount of inevitable impurities (0.2 to 0.3% by mass of the whole raw material alloy) in addition to the elements described above. This raw material alloy was held in a vacuum at a temperature range of 1000 to 1200 ° C. for 24 hours (homogenization heat treatment step). The homogenized heat-treated Nd ₂ Fe ₁₄ B raw material alloy was pulverized using a stamp mill and sieved to obtain a powdery raw material alloy (particle diameter of 1 to 2 mm).

  This raw material alloy was filled in a molybdenum-made container and charged in a tubular heat treatment furnace having an infrared heating method, and subjected to a treatment by hydrocracking / dehydrogenation recombination (HDDR treatment) under the following conditions. In addition, the time chart of the said process was as showing in FIG.

First, hydrogen gas is introduced into a tubular heat treatment furnace, and a hydrogen occlusion process (I in FIG. 1) holds the raw material alloy powder for 2 hours under the hydrogen gas atmosphere under the conditions of a hydrogen partial pressure of 100 kPa and a temperature (T ₀ ) of 100 ° C. ) Thus, hydrogen was occluded in the raw material alloy to obtain a hydrogen occlusion alloy.

Subsequently, the hydrogen partial pressure in the furnace is lowered and the furnace temperature is raised at 10 ° C./second, and the hydrogen storage alloy is heated for 1.5 hours under conditions of a hydrogen partial pressure of 40 kPa and a temperature T ₁ (= 800 ° C.). A retained hydrocracking step was performed (II in FIG. 1). Thus, the hydrogen storage alloy was hydrocracked to obtain a cracked product.

Thereafter, the temperature in the furnace was raised to a temperature T ₂ (= 850 ° C.) at 10 ° C./second (temperature raising step, III in FIG. 1). After raising the furnace temperature to T ₂ , hydrogen gas is exhausted using a vacuum pump, and the pressure (hydrogen partial pressure) in the furnace is reduced at a rate of 16 kPa / min, whereby hydrogen contained in the decomposition product Was started (first dehydrogenation recombination step, IV in FIG. 1).

In the first dehydrogenation recombination step, hydrogen is released from the decomposition product at a hydrogen release rate a of 3.5% by mass / hour, based on the mass of the entire decomposition product before releasing hydrogen. The hydrogen concentration in the decomposition product was reduced to a hydrogen concentration η ₂ (0.230% by mass). The exhaust speed switching pressure at this time was a hydrogen partial pressure of 6 kPa.

When the hydrogen concentration in the decomposition product is reduced to the hydrogen concentration η ₂ , the hydrogen gas exhaust rate from the inside of the furnace is changed so that the dropping rate of the furnace pressure (hydrogen partial pressure) is 0.1 kPa / min. . Thereby, the hydrogen release rate b from the decomposition product was adjusted to 0.35% by mass / hour based on the mass of the entire decomposition product before releasing hydrogen. Thereafter, hydrogen is continuously released until the pressure in the furnace (= hydrogen partial pressure) becomes less than 1 Pa, whereby hydrogen is almost completely removed from the decomposition product (second dehydrogenation recombination step). , V in FIG. In addition, the time required for the 1st dehydrogenation recombination process was about 2 minutes, and the time required for the 2nd dehydrogenation recombination process was 40 to 50 minutes.

When the pressure in the furnace (hydrogen partial pressure) became less than 1 Pa, the release of hydrogen was stopped. Thereafter, the inside of the furnace was cooled to room temperature (about 20 ° C.) to obtain HDDR-treated anisotropic Nd ₂ Fe ₁₄ B powder.

[Evaluation of magnetic properties]
The obtained Nd ₂ Fe ₁₄ B powder was pulverized using a mortar in an inert atmosphere and sieved to obtain Nd ₂ Fe ₁₄ B powder having a particle size of 53 to 212 μm. The powder and paraffin were packed in a case, and a magnetic powder of 1 Tesla was applied in a state where the paraffin was melted to orient the magnet powder. A magnetic field of 6 Tesla was applied in a direction parallel to the orientation direction of the magnet powder, and the magnetization-magnetic field curve was measured using a vibrating sample magnetometer (VSM) to obtain the magnetic characteristics. Table 1 shows the measurement results of residual magnetic flux density (Br) and coercive force (Hcj).

[Evaluation of microstructure]
In the above step, the hydrogen concentration in the decomposition product is reduced to a hydrogen concentration η ₂ (hydrogen partial pressure 6 kPa) (IV in FIG. 1), and then the reaction is stopped by flowing argon gas and quenching, An observation sample was prepared. FIG. 5 shows the result of observing the cross section of the primary particles of the Nd ₂ Fe ₁₄ B powder at the end of the first dehydrogenation recombination step using the backscattered electron image of the SEM using this observation sample. FIG. 5 is a cross-sectional SEM photograph of the decomposition product at the end of the first dehydrogenation recombination step in the rare earth alloy powder manufacturing step according to Example 1. Although the observation was performed in two fields of view, the Nd hydride phase (white part in the figure) was covered with the Nd ₂ Fe ₁₄ B phase (light gray part in the figure) as shown in FIG. It was. The area ratio of the Nd ₂ Fe ₁₄ B phase based on the entire cross-sectional area was 33.7% (see Table 1).

On the other hand, as a comparison with Example 1, a sectional view of the decomposition product in the case where the grain growth of the Nd ₂ Fe ₁₄ B phase has progressed is shown. FIG. 6 shows the observation sample prepared under the conditions of Example 1 except that the pressure in the furnace (partial hydrogen pressure) was reduced at a rate of 4 kPa / min in the first dehydrogenation recombination step. It is sectional drawing of the decomposition product at the time of completion | finish of a 1st dehydrogenation recombination process. As shown in FIG. 6, but Nd hydride phase is observed to have been covered by _Nd 2 _{Fe 14} B phase, when relative to the whole area of the cross _section, the area ratio of the Nd 2 _{Fe 14} B phase is 78 It was 6%. In this case, since the Nd ₂ Fe ₁₄ B phase grows into coarse grains after the second dehydrogenation recombination step, it is difficult to obtain a rare earth alloy powder having a refined Nd ₂ Fe ₁₄ B phase.

(Examples 2 to 5)
Values shown in Table 1 for exhaust speed switching pressure (hydrogen partial pressure) when switching from the first dehydrogenation recombination process to the second dehydrogenation recombination process (changing from hydrogen release speed a to hydrogen release speed b) An anisotropic Nd ₂ Fe ₁₄ B powder was obtained in the same manner as in Example 1, except that it was changed to. Then, in the same manner as in Example 1, the magnetic characteristics and the microstructure were evaluated. In any of the examples, the Nd hydride phase was covered with the Nd ₂ Fe ₁₄ B phase. Table 1 summarizes the HDDR processing conditions and evaluation results of Examples 2 to 5.

From the results shown in Table 1, fine particles of the R ₂ Fe ₁₄ B phase are formed in the Nd ₂ Fe ₁₄ B powders of Examples 1 to 5 and have excellent magnetic properties (particularly coercive force). confirmed.

10 ... R hydride phase (rare earth hydride phase), 20 ... iron compound phase, 30 _... R 2 _{Fe 14} B phase, 50 ... anisotropic bonded magnet, 60 ... sintered magnet.

Claims (4)

A method for producing a rare earth alloy powder by hydrocracking and dehydrogenation recombination,
(A) hydrocracking a raw material alloy containing a rare earth element to obtain a decomposition product;
(B) releasing hydrogen from the decomposition product to reduce the hydrogen concentration of the decomposition product;
(C) a step of further releasing hydrogen from the decomposition product at a release rate lower than the release rate of hydrogen in step (b) to obtain a rare earth alloy powder;
With
In the cross section of the decomposition product, the rare earth hydride phase is covered with an R ₂ Fe ₁₄ B phase (R represents a rare earth element), and the area ratio of the R ₂ Fe ₁₄ B phase is the total area of the cross section. The method of manufacturing a rare earth alloy powder that shifts from the step (b) to the step (c) at a time of 25 to 55% based on the above.   The method according to claim 1, further comprising the step of determining the timing of transition from step (b) to step (c) by observing the morphology of the cross section.   An anisotropic bonded magnet comprising a rare earth alloy powder having anisotropy produced by the method according to claim 1 and a resin.   A sintered magnet obtained by sintering a molded body obtained by molding an anisotropic rare earth alloy powder produced by the method according to claim 1 or 2 in a magnetic field.