WO2012128371A1

WO2012128371A1 - Rare-earth magnetic powder, method for manufacturing same, compound of same, and bond magnet of same

Info

Publication number: WO2012128371A1
Application number: PCT/JP2012/057645
Authority: WO
Inventors: 本蔵　義信; 御手洗　浩成; 松岡　浩; 千里三嶋; 健児野口; 洋幸土井
Original assignee: 愛知製鋼株式会社
Priority date: 2011-03-23
Filing date: 2012-03-23
Publication date: 2012-09-27
Also published as: JP2014132599A

Abstract

A rare-earth magnetic powder for obtaining a bond magnet having exceptional environmental resistance is provided. This rare-earth magnetic powder is characterized in comprising: pulverulent particles obtained by aggregation of R₂TM₁₄B₁ crystals that are tetragonal compounds of a rare-earth element (R), boron (B), and a transition metal (TM); the outer surface of the pulverulent particles being covered by a passive state film. The magnetic properties of a bond magnet manufactured using the pulverulent particles are not readily degraded by oxidation or moisture even in severe environments because the bond magnet comprises pulverulent particles covered by the passive state film. Specifically, a bond magnet having highly exceptional environmental resistance is obtained using this rare-earth magnetic powder.

Description

Rare earth magnet powder, manufacturing method thereof, compound thereof and bond magnet thereof

The present invention relates to a rare earth magnet powder excellent in oxidation resistance, a manufacturing method thereof, a compound using the rare earth magnet powder, and a bonded magnet.

Since rare earth magnets exhibit extremely high magnetic properties, they are being used in various appliances such as electric appliances and automobiles that are desired to be energy-saving and lightweight. Rare earth magnets include a dense magnet made of a sintered body of a rare earth magnet powder (referred to as “magnet powder” as appropriate) or a dense molded body, and a bonded magnet in which the magnet powder is solidified with a binder resin. Recently, bond magnets having a high degree of freedom in molding and suitable for manufacturing light and thin parts tend to be used frequently.

By the way, since the magnet powder constituting the bonded magnet is mainly composed of iron and rare earth elements, it is easily oxidized by oxygen and moisture during the manufacturing process and during transportation as well as during the use of the bonded magnet. Such oxidation degrades the magnet powder and reduces the magnetic properties of the bonded magnet.

In order to suppress such oxidation, it is conceivable to coat the surface of the magnet powder or bonded magnet with resin or plating. However, all of them are expensive and a sufficient antioxidant effect cannot be obtained, so that they have not been put into practical use.

JP-A-4-87305

In the above-mentioned Patent Document 1, it is proposed to form a passive film that suppresses oxidation on a magnet powder, unlike the coating described above. However, Patent Document 1 only describes that the oxidation treatment is performed at an oxygen concentration of 1 to 20% and an atmospheric temperature of 60 to 200 ° C. It is not described at all whether the oxidation treatment should be performed.

Moreover, FIG. 1 in Patent Document 1 shows that no demagnetization occurs over a long period of time by forming a passive film. FIG. 2 of the same publication shows that the coercive force of the magnet powder subjected to the oxidation treatment is reduced to about 2/3 or less of the coercivity of the magnet powder not subjected to the oxidation treatment. However, based on the common general technical knowledge in the field, such a situation cannot be considered at all in the processing under the described conditions. In other words, the contents described in the above-mentioned Patent Document 1 are clearly doubtful, merely describe desired contents, and are substantially equivalent to not making any effective technical proposal.

The present invention has been made under such circumstances. That is, an object is to provide a realistic rare earth magnet powder having excellent oxidation resistance. Moreover, it aims at providing the manufacturing method of the magnet powder, the compound and bond magnet using the rare earth magnet powder together.

As a result of intensive research and trial and error to solve this problem, the inventor has obtained a passive state that can greatly improve the oxidation resistance of the magnet powder on the surface of the powder particle of the magnet powder oxidized in a specific atmosphere. It was newly found that a film is formed. By further developing this result, the present invention described below has been completed.

<Rare earth magnet powder>
(1) The rare earth magnet powder of the present invention is composed of powder particles in which R ₂ TM ₁₄ B ₁ type crystals, which are tetragonal compounds of rare earth elements (R), boron (B), and transition elements (TM), are aggregated. The rare earth magnet powder is characterized in that the powder particles have a passive film covering the outer surface.

(2) The rare earth magnet powder of the present invention (referred to as “magnet powder” as appropriate) is composed of powder particles whose outer surface is coated with a chemically stable passive film. By this passive film, the magnet powder of the present invention is prevented from being oxidized and exhibits excellent oxidation resistance. For this reason, not only the storage and handling properties of the magnet powder itself of the present invention are improved, but also bond magnets using this magnet powder exhibit excellent environmental resistance and high magnetic properties over a long period of time. It can be used stably and its range of use can be further expanded.

(3) The passive film of the present invention is a dense oxide film having a high oxygen shielding property (in other words, a low oxygen permeability), although details of its composition and form are not necessarily clear at present. it is conceivable that. More specifically, the passive film according to the present invention is considered to be a passive oxide film made of an oxide of R and / or TM inferred from the composition of the magnet powder. Of course, when the powder particles have a metal element other than R or TM (for example, Al, Ga, Zn, etc., which are typical metal elements), the passive oxide film has an oxide of such a metal element (for example, Al _2). It is possible to consist of O ₃ ). Incidentally, such a metal element may exist from the beginning of the master alloy, or may be supplied later by diffusion treatment or the like, and any of them may be used. Further, the passive oxide film is not limited to a single oxide, but may be a composite oxide film composed of a plurality of oxides.

Note that the passive film made of an oxide film is formed at a relatively low cost and is thin, so that it hardly affects the magnetic properties of the magnet powder.

(4) The passive film of the present invention is not limited in its composition, structure, form, etc., but it is preferable that the film has a certain film thickness in order to exhibit chemically stable and excellent oxygen shielding properties over a long period of time. is there. Specifically, the thickness of the passive film is preferably 30 nm or more, 40 nm or more, and more preferably 50 nm or more.

Incidentally, since the passive film is a dense film excellent in oxygen shielding property unlike a simple oxide film, its film thickness is unlikely to be excessive in the first place. If it dares to say, it is preferable that the film thickness of a passive film is about 300 nm or less further about 200 nm or less.

In addition, the film thickness of the passive film was specified from the graph regarding the depth (Depth) -intensity obtained by observing the surface of the powder particle by Auger Electron Spectroscopy (AES). Specifically, first, the maximum intensity (Imax) on the graph is specified, and the 15% intensity (Is = 0.15 × Imax) is obtained. The intersection point Ps between the line Ls which becomes the intensity Is and the graph is obtained. The depth (Ds) of Ps is defined as the “film thickness” of the coating film formed on the surface of the powder particles in this specification. This is illustrated in FIGS. 1A and 1B. In the case of FIG. 1A, Imax = 69300, Is = 10400, Ds = 104 nm, and the film thickness referred to in the present invention is specified as 104 nm. Incidentally, in the case of FIG. 1B, Imax = 67100, Is = 10100, Ds = 22.5 nm, and the film thickness is specified as 22.5 nm.

《Rare earth magnet powder manufacturing method》
The present invention can also be grasped as a method for producing the rare earth magnet powder described above. That is, the present invention includes an oxidation process in which powder particles in which R ₂ TM ₁₄ B ₁ type crystals, which are tetragonal compounds of R, B, and TM, are aggregated are heated in an oxidizing atmosphere, and the oxidizing process includes the oxidizing atmosphere. And a first oxidation step for bringing the oxidizing atmosphere to a second treatment temperature higher than the first treatment temperature, and a method for producing a rare earth magnet powder comprising: But you can.

Note that the oxidizing atmosphere is specified by, for example, the oxygen concentration. When the oxidizing atmosphere is composed of a mixed gas, the oxygen concentration is expressed, for example, as a volume% of oxygen contained in the mixed gas when the entire mixed gas is in a standard state (1 atm, 20 ° C.). And this oxygen concentration is calculated | required, for example with the oxygen concentration meter (OXYMAN galvanic cell type oxygen concentration meter made from a Taiho Electric Co., Ltd.) attached to the processing furnace.

<Compound and bonded magnet>
(1) The present invention can also be grasped as a compound using the above-mentioned rare earth magnet powder. That is, the present invention may be a compound for a rare earth bonded magnet characterized by comprising the above rare earth magnet powder and a binder resin capable of binding powder particles of the rare earth magnet powder.

(2) Moreover, this invention can be grasped | ascertained also as a bonded magnet which consists of the above-mentioned rare earth magnet powder and a compound. That is, the present invention may be a rare earth anisotropic bonded magnet comprising the above rare earth magnet powder and a binder resin that binds the powder particles of the rare earth magnet powder.

<Others>
(1) The rare earth element referred to in this specification is one or more of yttrium (Y), lanthanoid and actinoid. Among them, lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium ( Typical examples are Er), thulium (TM element), and lutetium (Lu). These rare earth elements (R) may be one kind or two or more kinds.

Here, as R, Nd is typical, but Pr may also be included. This is because even if a part of Nd in the magnet raw material or the diffusion raw material is replaced with Pr, there is little influence on the magnetic properties, and a mixed rare earth raw material (zidymium) mixed with Nd and Pr is available at a relatively low cost. In addition, since coercive force improving elements such as Dy, Tb, or Ho are rare elements and are expensive, it is preferable to suppress their use. Therefore, it is preferable that the magnet raw material (mother alloy) or the diffusion raw material used for the production of the magnet powder does not contain Dy, Tb and Ho.

TM is particularly preferably at least one of 3d transition element or 4d transition element. The 3d transition element is atomic number 21 (Sc) to atomic number 29 (Cu), and the 4d transition element is atomic number 39 (Y) to atomic number 47 (Ag). Among them, TM is preferably any of group 8 iron (Fe), cobalt (Co), or nickel (Ni), and more preferably Fe. Further, a part of boron can be substituted with carbon (C).

(2) The powder particles according to the present invention may contain “modified element” which is an element effective for improving the characteristics in addition to R, B and TM described above. There are various kinds of modifying elements, the combination of each element is arbitrary, and the content thereof is usually very small. Of course, the rare earth magnet powder of the present invention may also contain “unavoidable impurities” that are difficult to remove due to cost or technical reasons.

(3) “Rare earth magnet powder” as used herein includes both anisotropic rare earth magnet powder and isotropic rare earth magnet powder. In addition, when simply referred to as “powder particles”, the hydrogen-treated particles obtained by subjecting the magnet alloy to hydrogenation treatment, the diffusion-treated particles obtained by subjecting the hydrogenation treatment to diffusion treatment, and the hydrogen-treated particles. Alternatively, it means any one of the oxidation-treated particles obtained by subjecting the diffusion-treated particles to the oxidation treatment, the coating-treated particles obtained by subjecting these particles to resin coating, or a plurality or all of them. The same applies to the constituent particles when simply called “magnet powder”.

(4) The “average particle diameter” as used herein is specified by the volume sphere equivalent diameter (VMD) obtained by measuring the sample powder with a HELOS & RODOS laser diffraction particle size distribution measuring device.

(5) “x to y” in the present specification includes the lower limit value x and the upper limit value y unless otherwise specified. Further, a new numerical range such as “ab” can be configured by arbitrarily combining various lower limit values or upper limit values described in this specification. Furthermore, any numerical value included in the numerical value range described in the present specification can be used as an upper limit value or a lower limit value for setting a new numerical value range.

3 is a graph obtained by measuring the surface of oxidized powder particles (Sample No. 1-3) by Auger electron spectroscopy. It is the graph which measured the surface of the powder particle which has not been oxidized by the Auger electron spectroscopy. Sample No. 7 is a graph showing the relationship between the amount of demagnetization (flux loss) and the elapsed time of bond magnets according to 1-1 to 1-6. Sample No. 2-1, sample no. It is a graph which shows the relationship between the demagnetization amount of the bonded magnet concerning 2-2, and elapsed time. Sample No. 3 is a graph showing the relationship between the amount of demagnetization and the elapsed time of bond magnets according to 3-1 to 3-4. 6 is a graph showing the relationship between the Auger spectrum peak ratio (Nd-MNN / O) and the depth on the surface of powder particles (Sample No. 8-1 and Sample No. 8-2). This is an SAED related to the particle surface of an oxidation-treated powder (Sample No. 8-1). It is a figure which shows the intensity distribution of the radial direction based on the SAED. 3 is a TEM image obtained by observing the particle surface of powder particles (Sample No. 8-1).

The present invention will be described in more detail with reference to embodiments of the invention. The contents described in this specification including the following embodiments can be applied not only to the rare earth magnet powder according to the present invention, but also to a manufacturing method thereof, a compound using the magnet powder, and a bonded magnet. One or more configurations arbitrarily selected from the present specification may be added to the configuration of the present invention described above. At this time, the structure related to the manufacturing method can be a structure related to an object if understood as a product-by-process. Note that which embodiment is the best depends on the target, required performance, and the like.

<Oxidation process>
(1) The passive film according to the present invention has, for example, a magnetic powder having an oxygen concentration of 0.1 to 20% by volume when the mixed gas total pressure is in a standard state (1 atm, 20 ° C.) as described above. It can be obtained by heating in an oxidizing atmosphere. Even if the oxygen concentration is too low or too high, it is difficult to stably form a dense passive oxide film having excellent oxygen shielding properties. The oxygen concentration is more preferably 0.1 to 7%, 1 to 6%, and more preferably 2 to 5%.

In order to uniformly form such a passive oxide film on the surface of each powder particle, it is preferable to use, for example, a rotary furnace (rotary kiln furnace or the like) or a rotary mixer (Henschel mixer or the like) that can control the oxidizing atmosphere. The control of the oxidizing atmosphere can be performed, for example, by introducing oxygen into the furnace in a vacuum atmosphere or an inert gas atmosphere while controlling the flow rate.

(2) The treatment pattern (or heat pattern) of the oxidation step is, for example, a treatment temperature of about 80 to 200 ° C., more preferably about 90 to 170 ° C., and a treatment time of about 0.5 to 5 hours, further about 1 to 4 hours. preferable. Specific processing conditions may be appropriately adjusted according to the composition near the surface of the powder particles, the environmental resistance required for the bonded magnet, and the like.

Also, the oxidizing atmosphere does not need to be constant during processing, and may be changed during processing. For example, after the oxidation atmosphere is set to the first treatment temperature (first oxidation step), the oxidation atmosphere may be set to a second treatment temperature higher than the first treatment temperature (second oxidation step). Further, the oxygen concentration in the oxidizing atmosphere may substantially change in response to the change in the processing temperature. For example, when only a certain amount of oxygen is introduced into a closed processing furnace at the beginning of the treatment, the oxygen concentration can be substantially reduced as the oxidation process proceeds. In such a case, the formation of a passive oxide film can be promoted by raising the temperature of the oxidizing atmosphere in the latter half of the oxidation step.

On the contrary, if the oxygen concentration in the oxidizing atmosphere can be adjusted arbitrarily by controlling the flow rate of the introduced gas, the oxygen concentration in the first half of the oxidation process is relatively low and the oxygen concentration in the second half is relatively high. Also good. As a result, in the first half of the oxidation process, the formation of the oxide film gradually proceeds to stably form a dense and uniform passive oxide film on the surface of the powder particles. In the second half of the oxidation process, the passive oxide film is formed. It is also conceivable that the film thickness can be easily secured. In any case, in the oxidation step, the oxidizing atmosphere may be changed stepwise, or the oxidizing atmosphere may be changed continuously.

<Powder particles>
(1) The powder particles forming the passive film consist of an aggregate of fine R ₂ TM ₁₄ B ₁ type crystals, and particles obtained by subjecting a magnet alloy (mother alloy) to hydrogenation treatment can be The particle | grains after the diffusion process which made the diffusion raw material diffuse may be sufficient.

(2) The hydrogenation treatment includes a disproportionation step in which a magnet alloy (mother alloy) absorbs hydrogen to cause a disproportionation reaction, and recombination that dehydrogenates and recombines the mother alloy after the disproportionation step. Process. Examples of this hydrogenation treatment include the HDDR method (hydrogenation-decomposition) (or disposition) -deposition-recombination, the d-HDDR method (dynamic-HDDR), and the like. According to the d-HDDR method, a rare earth anisotropic magnet powder having particularly high magnetic properties can be obtained.

The d-HDDR method comprises a low-temperature hydrogenation process, a high-temperature hydrogenation process, a controlled exhaust process, and a forced exhaust process. The above disproportionation process is a high-temperature hydrogenation process, and the recombination process is a controlled exhaust process. Correspond. By the way, in the low-temperature hydrogenation process, the hydrogen pressure is reduced in the low temperature range below the temperature at which the hydrogenation / disproportionation reaction occurs so that the hydrogenation / disproportionation reaction in the next process (high-temperature hydrogenation process) proceeds slowly. This is a step for sufficiently dissolving hydrogen. The high-temperature hydrogenation step is a step of causing a hydrogenation / disproportionation reaction to the magnet alloy. The controlled exhaust process is a process in which the tissue that has undergone the three-phase decomposition in the high-temperature hydrogenation process is recombined. The forced exhaust process is a process for removing hydrogen remaining in the magnet alloy and completing the dehydrogenation process. Details of these steps are described in JP-A-2006-28602.

(3) Diffusion treatment is performed by mixing a mixed raw material (mixed powder) obtained by mixing a magnetic raw material (magnet powder) with a diffusion raw material, for example, at an anti-oxidation atmosphere (vacuum atmosphere or inert atmosphere, etc.) at 400 to 900 ° C. ).

As the diffusion raw material, an R—Cu alloy, an R—Cu—Al alloy, an R—TM alloy or the like is suitable. Thereby, the coercive force of the magnet powder can be increased while suppressing the use of rare elements such as Dy and Ga. Among them, R—Cu based alloys and R—Cu—Al based alloys are preferable from the viewpoint of cost or resources, and the diffusion raw material has a Cu content of 1 to 47 at%, further 6 to 39 at%, when the whole is 100 at%, It is preferable that the remaining rare earth element and inevitable impurities are included. When the diffusion raw material contains Al, it is preferable that Cu is 5 to 27 at%, Al: 20 to 55 at% when the entire diffusion raw material is 100 at%, and the remaining rare earth element and inevitable impurities.

The diffusion raw material may include Co, Ni, Si, Mn, Cr, Mo, Ti, V, Ga, Zr, Ge, Fe, or the like instead of Cu or Al. The total amount of these elements is preferably 5 to 64 at% with respect to 100 at% of the entire diffusion raw material. As an alternative to Cu and Al, there is an R-TM alloy, specifically, an Nd-Co alloy.

Incidentally, the magnet raw material to be subjected to the diffusion treatment usually has R of 11 to 15 at%, but preferably has a theoretical composition. Specifically, R is 11.6 to 12.7 at%, 11.7 to 12.5 at%, 11.8 to 12.4 at%, further 11.9 to 12.3 at%, and B is 5. It is preferably 5 to 7 at%, more preferably 5.9 to 6.5 at%. By using a magnet raw material having a theoretical composition, a magnet powder with high magnetization (residual magnetic flux density) can be obtained. Accordingly, if a magnetic material having a theoretical composition is subjected to a diffusion treatment, a magnet powder having high magnetization and high coercive force can be obtained.

The powder particles after such diffusion treatment are Cu: 0.05-2 at%, 0.05-1 at%, 0.05-0.8 at%, 0.2-0. It is preferably 8 at%, more preferably 0.3 to 0.7 at%. Further, when the whole powder particle is 100 at%, Al is preferably 0.1 to 5 at%, more preferably 0.5 to 3.0 at%.

(4) Magnet raw materials include titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), nickel (Ni), chromium (Cr), manganese as a modifying element such as coercive force. (Mn), molybdenum (Mo), hafnium (Hf), tungsten (W), tantalum (Ta), etc., as well as aluminum (Al), gallium (Ga), silicon (Si), zinc (Zn), tin (Sn) ) Or the like. These modifying elements are preferably 3 at% or less in total when the final powder particles as a whole are 100 at%.

Among the reforming elements, Ga is an element that is particularly effective for improving the coercive force. Therefore, it is preferable that the powder particles contain 0.05 to 1 at% Ga when the whole is 100 at%. Further, since Nb is an element effective for improving the residual magnetic flux density, it is preferable that the powder particles contain 0.05 to 0.6% Nb when the whole is 100 at%. Of course, it is more preferable that the powder particles contain both at the same time. Since Co is an element effective for improving the magnet powder or the Curie point of the magnet, and hence the heat resistance thereof, it is preferable that the powder particles contain 0.1 to 10 at% Co when the total is 100 at%.

<Compound and bonded magnet>
(1) A compound as a raw material for a bonded magnet can be obtained by heat-kneading the magnetic powder of the present invention with a binder resin. If this compound is compression molded or injection molded, a bonded magnet can be obtained.

In the case of injection molding, the binder resin is preferably a thermoplastic resin such as polyphenylene sulfide (PPS) or polyamide (PA) such as nylon. In the case of compression molding, the binder resin is preferably a thermosetting resin, such as an epoxy resin, or a binder resin.

(2) The magnet powder constituting the compound or bonded magnet may be a mixed magnet powder obtained by mixing a plurality of types of magnet powder. For example, the magnet powder of the present invention may be a composite rare earth magnet powder obtained by mixing a magnet powder having a large average particle diameter (coarse powder) and a magnet powder having a small average particle diameter (fine powder). Specifically, the coarse powder is preferably an R-TM-B magnet powder and the fine powder is preferably an Sm—Fe—N magnet powder.

<Application>
Permanent magnets (bonded magnets, etc.) according to the present invention are excellent in environmental resistance, stably exhibit high magnetic properties, and are used in severe environments of high temperature and high humidity as well as equipment used in normal temperatures. It is also suitable for equipment.

The present invention will be described more specifically with reference to examples.

<Example 1>
<Production of sample>
Each sample shown in Table 1 was manufactured as follows.

(1) Magnet raw material Each magnetic raw material shown in Table 1 was prepared as follows. Master alloys prepared for each composition of the magnet raw materials shown in Table 1 were obtained by the strip cast (SC) method. This mother alloy was held in an Ar gas atmosphere at 1140 ° C. for 10 hours to homogenize the structure (homogenization heat treatment step). After cooling this to room temperature, hydrogen pulverization was performed in a hydrogen atmosphere at a hydrogen pressure of 0.13 MPa to obtain a mother alloy powder.

The mother alloy powder was subjected to hydrogenation (d-HDDR) to obtain a rare earth anisotropic magnet powder. This hydrogenation treatment was performed as follows. First, 15 g of the mother alloy powder was put in a processing furnace and exposed to a low temperature hydrogen atmosphere at room temperature × 0.1 MPa for 1 hour (low temperature hydrogenation step). Subsequently, the powder after the low-temperature hydrogenation step was exposed to a high-temperature hydrogen atmosphere of 780 ° C. × 0.03 MPa for 30 minutes (high-temperature hydrogenation step). Thereafter, the atmosphere was heated to 840 ° C. over 5 minutes, and the powder of the high-temperature hydrogenation process was exposed to a high-temperature hydrogen atmosphere of 840 ° C. × 0.03 MPa for 60 minutes (structure stabilization process). In this way, while adjusting the reaction rate, a powder in which a forward transformation that decomposes into three phases (α-Fe, RH ₂ , Fe ₂ B) was generated was obtained (disproportionation step). Thereafter, hydrogen is continuously exhausted from the inside of the processing furnace, and the inside of the processing furnace is placed in an atmosphere of 840 ° C. × 5 to 1 kPa for 90 minutes to produce R ₂ TM ₁₄ B type ₁ crystals in the alloy after forward transformation. The reverse transformation was generated (controlled exhaust process / recombination process).

The powder thus obtained was rapidly cooled (first cooling step). This powder was crushed in an inert gas atmosphere in a mortar and then adjusted in particle size to obtain each magnet powder (magnet raw material) having an average particle size of 100 to 120 μm. Specifically, the average particle diameter is the sample No. 1-1 to 1-6 and sample no. 2-1 and 2-2 are 105 μm, sample no. 3-1 to 3-4 were 117 μm.

(2) Diffusion raw materials Diffusion raw materials having the respective compositions shown in Table 1 were prepared as follows. Raw material alloys (ingots) prepared for the respective compositions of the diffusion raw materials shown in Table 1 were obtained by the book mold method. This raw material alloy was pulverized with hydrogen and further pulverized with a dry ball mill to obtain a powdery raw material (hydride) having an average particle size of 6 μm. Thus, a powdery diffusion raw material was obtained.

(3) Diffusion treatment A diffusion raw material was added to the magnet raw material and mixed in an inert gas atmosphere to obtain a mixed raw material (mixing step). The mixing ratio shown in Table 1 is the mass ratio of the diffusion raw material when the entire mixed raw material is 100 mass%. This mixed raw material was heated in a vacuum atmosphere of 10 ⁻¹ Pa at 800 ° C. for 1 hour (diffusion process). Following this, the mixed raw material was rapidly cooled (second cooling step). In this manner, a diffusion-treated magnet powder (referred to as “diffusion magnet powder” as appropriate) was obtained.

(4) Oxidation treatment Diffusion magnet powder was put into a cylindrical reactor. While rotating the reaction furnace, the diffusion magnet powder was heated in an oxidizing atmosphere (oxidation step). Adjustment of the oxidizing atmosphere was performed by mixing an inert gas (Ar gas) and oxygen gas at a desired ratio before introduction into the reaction furnace, and introducing the obtained mixed gas into the reaction furnace. The oxygen concentration in the oxidizing atmosphere was controlled to 2 to 3% for all samples. The processing temperature and processing time at this time were performed in various patterns shown in Table 1. In addition, when performing this oxidation process by 2 steps, the 2nd oxidation process was performed after the 1st oxidation process. In this way, an oxidized magnetic powder (referred to as “oxidized magnet powder” as appropriate) was obtained.

(5) Resin coating A coupling liquid in which 0.33 g of titanate coupling agent was uniformly dispersed in 0.65 g of hexane was prepared. The coupling liquid and 130 g of the oxidized magnet powder were mixed and then evacuated and dried (coupling treatment). This obtained the magnet powder by which the surface was coat | covered with the coupling agent.

Next, a coating solution was prepared by dissolving 0.39 g of epoxy resin in 1.56 g of methyl ethyl ketone (MEK). This coating liquid and the oxidized magnet powder (130 g) subjected to the coupling treatment were mixed, and then evacuated and dried. The dried magnet powder was further heated in vacuum at 100 ° C. for 2 hours. Thus, a magnet powder (first magnet powder) uniformly coated with an epoxy resin whose surface was cured was obtained.

(6) Comparative Sample Magnet powders (Sample Nos. 1-6, 2-2, and 3-4) that were not subjected to the above-described oxidation treatment were also prepared as comparative samples. This magnet powder is also referred to as a first magnet powder for convenience.

<Production of compound>
124 g of the first magnet powder, 21.9 g of rare earth magnet powder (second magnet powder) composed of SmFeN and 4.1 g of epoxy (solid) resin were mixed with a small rocking mixer, and the resulting mixture was subjected to Laboplast Mill (Toyo And kneading (110 ° C.) for 10 minutes. After cooling to room temperature, the particle size was adjusted to obtain a compound.

<Manufacture of bonded magnets>
The compound was put into a cavity of a mold and warm-molded (150 ° C. × 1 t / cm ² (98 MPa)) in an orientation magnetic field (1.5 T) to obtain a 14 mm square cubic compact. This molded body was heated in Ar gas at 150 ° C. for 1 hour (curing treatment) to cure the epoxy resin as the binder resin. This was magnetized in a 4.5 T pulse magnetic field to obtain a bonded magnet.

<< Surface observation >>
Sample No. The results of observing the particle surface of the 1-3 oxidized magnet powder and the particle surface before the oxidation treatment by Auger electron spectroscopy (AES) are shown in FIGS. 1A and 1B, respectively. In addition, the depth direction analysis by AES was performed while performing argon ion etching on the particle surface.

<Degradation of magnetic flux over time>
The time-dependent change of magnetic flux was measured for the bonded magnet in an air atmosphere at 120 ° C. Specifically, the measurement was performed as follows. First, the magnetized bonded magnet was exposed to an air atmosphere at 120 ° C. for 1 hr (initial demagnetization). The bonded magnet was cooled to room temperature, and the amount of magnetic flux φ1 was measured using a flux meter. Each time a predetermined time passed, it was cooled to room temperature, and the magnetic flux amount φt of the bond magnet at that time was similarly measured. The ratio ((φt−φ1) / φ1) of the demagnetization component (φt−φ1) to φ1 is expressed as a percentage, and is defined as the demagnetization rate (Flux-loss:%) after a predetermined time. The history of demagnetization rates of various bonded magnets is shown in Figs. Table 1 also shows the demagnetization rates after 1000 hours of various bonded magnets.

<Evaluation>
(1) Thickness of Passive Oxide Film First, as can be seen from FIG. 1B, oxygen (O) is also present on the surface of the powder particles before the oxidation treatment. However, the depth (thickness) is only about 23 nm at most. In addition, the change in the amount of O in the vicinity of the surface is abrupt and there is no stable region. From this, it is considered that a stable oxide film has not yet been formed in the vicinity of the surface of the powder particles before the oxidation treatment.

Next, it can be seen from FIG. 1A that O is sufficiently present over a depth (thickness) of 0 to 104 nm on the surface of the oxidized powder particles. Further, in the middle (38 to 75 nm), there is a stable region of O in which the rate of change in intensity is moderate. From the distribution of the amount of O in the vicinity of the surface, it is considered that a stable oxide film is formed on the surface of the powder particles.

(2) Environmental resistance (demagnetization factor) of bonded magnet
From the results of Table 1 and FIGS. 2 to 4, it was found that all the oxidized samples (bond magnets) had a reduced demagnetization factor (flux loss) after a long period of time and were excellent in environmental resistance. It was also found that the demagnetization rate of the bonded magnet is improved when the oxidation treatment is performed in two steps (the first oxidation step and the second oxidation step), although there is a slight difference from the composition of the magnet raw material or the diffusion raw material.

From the above, it was confirmed that a passive oxide film having excellent oxidation resistance according to the present invention was formed on the surface of the powder particles of the magnet powder subjected to the oxidation treatment as in this example.

<Example 2>
<Production and measurement of sample>
As shown in Table 2, magnet powders were produced in which the magnet raw material, diffusion treatment, oxidation treatment, or resin coating was variously changed with respect to Example 1. The oxidation treatment in this example was performed by controlling the oxygen concentration in the mixed gas composed of Ar gas and oxygen gas to 5%. Other processing conditions were the same as in Example 1. Using the magnet powder according to each sample shown in Table 2, the same bonded magnet as in Example 1 was manufactured. The demagnetization rate after 1000 hours of each bonded magnet was measured. At this time, the test environment for exposing the bonded magnet was not 120 ° C. but in an air atmosphere of 150 ° C. Except this, the measurement was performed in the same manner as in Example 1. Table 2 shows the demagnetization factor thus obtained.

<Evaluation>
Table 2 shows the following. First, for any sample, the demagnetization rate of the bonded magnet was improved and its environmental resistance was improved by using the magnet powder subjected to the oxidation treatment according to the present invention. In particular, sample no. From 4-1 to 4-3, it can be seen that the demagnetization rate becomes smaller and improved as the number of oxidation processes is increased. However, it has been clarified that the demagnetization factor can be sufficiently improved by performing only one-step oxidation treatment (only one of the first oxidation process and the second oxidation process). At this time, sample no. Considering the results of 1-1, 1-2 and 1-6 together, it can also be seen that the oxidation treatment temperature can be freely adjusted within the range of 80 to 200 ° C., more preferably 90 to 190 ° C.

Sample No. 4-4 and sample no. From 4-5, it is clear that even when the resin coating is not applied, the effect of reducing the demagnetization rate can be obtained similarly by the oxidation treatment.

Furthermore, sample No. From 4-1 to 6-2, even when the mixing ratio and type of the diffusion raw material were changed, the demagnetization rate was similarly improved by the oxidation treatment. Sample No. From 7-1 to 7-4, even when the diffusion treatment was not performed, the demagnetization rate was similarly improved by the oxidation treatment regardless of the presence or absence of the resin coating.

<Example 3>
<Production of sample>
Sample No. The oxidation-treated powder (sample No. 8-1) produced in the same manner as in 4-4, An oxidation-untreated powder (sample No. 8-2) produced in the same manner as in 4-5 was prepared.

<Measurement and evaluation>
(1) The particle surfaces of both magnet powders were analyzed by AES. FIG. 5 shows the result of analyzing the peak ratio (Nd-MNN / O) of the Nd and O Auger spectrum obtained in this way from the outermost surface of the powder particle to the depth direction. Note that Nd-MNN on the high energy side was adopted as the peak value of the Auger spectrum related to Nd.

FIG. 5 shows that in the case of the unoxidized powder, the peak ratio increases as it becomes deeper from the outermost surface, and O relatively decreases with respect to Nd. On the contrary, in the case of the oxidation-treated powder, the peak ratio was almost constant even at a position deep from the outermost surface, and O and Nd were present in a stable ratio. From this, it was found that at least Nd and O exist at a stable ratio by the oxidation treatment, and a new Nd—O film that was not present before the oxidation treatment was formed on the particle surface.

(2) FIG. 6A shows a limited-field electron diffraction pattern (SAED) obtained by observing the particle surface of the oxidized powder with a transmission electron microscope (TEM). In addition, the radial intensity distribution based thereon is shown in FIG. 6B. First, the SAED in FIG. 6A has a halo region, and the intensity distribution in FIG. 6B also has a broad peak. From each of these, the film newly formed on the particle surface by the oxidation treatment is considered to be amorphous.

This can also be seen from FIG. 7 showing a TEM image relating to the coating. That is, in this TEM image, a portion in which atoms are regularly arranged (long-range order portion / crystalline portion) and a portion without such regularity (short-range order portion / amorphous portion) are observed. It can be seen that there is at least an amorphous portion. However, the crystalline part is also very fine with a size of about 0.5 to 20 nm, and is made of a so-called nanocrystal. Since sharp diffraction indicating α-Fe is observed in FIG. 6B, at least a part of the crystalline portion in the TEM image is considered to be α-Fe. Further, when the TEM image of FIG. 7 is observed in detail, the crystalline portion of 0.5 to 20 nm (especially 2 to 7 nm) made of α-Fe is almost uniformly fine in the amorphous portion made of Nd and O. It can be seen that they are dispersed.

Considering comprehensively, the film (passive film) obtained by the oxidation treatment according to this example is a composite oxide film mainly composed of Nd, Fe, and O, and is substantially amorphous. Alternatively, it is considered to be composed of a crystalline material composed of ultrafine crystals at the nano level, or further composed of a composite material in which they are mixed. In any case, it is certain that the coating is composed of a very fine and dense structure.

It is considered that the effect of reducing the demagnetization factor as described above was obtained by forming such a dense coating on the particle surface of the magnet powder. In the present invention, such a film is called a passive film or a passive oxide film. The “oxide film” in the present specification is sufficient if oxygen is contained in the film, and it does not matter that a specific oxide is formed in the film.

<Consideration of the present invention>
Considering the above, it is considered that the passive film according to the present invention is substantially amorphous or has an amorphous-like structure and is a very dense composite film. Therefore, it can be said that the passive film according to the present invention is preferably a composite film composed of at least R (particularly Nd), TM (particularly Fe) and O. Further, it can be said that the passive film according to the present invention is preferably an amorphous film.

Claims

Consists of powder particles in which R 2 TM 14 B type 1 crystals, which are tetragonal compounds of rare earth elements (hereinafter referred to as “R”), boron (B), and transition elements (hereinafter referred to as “TM”) are assembled. Rare earth magnet powder,
The rare earth magnet powder, wherein the powder particles have a passive film covering an outer surface.
The rare earth magnet powder according to claim 1, wherein the passive film is a passive oxide film made of the oxide of R and / or TM.
The rare earth magnet powder according to claim 1 or 2, wherein the passive film has a thickness of 30 nm or more.
Comprising an oxidation step of heating powder particles in which R 2 TM 14 B type 1 crystals, which are tetragonal compounds of R, B, and TM, are gathered in an oxidizing atmosphere;
The oxidation step includes a first oxidation step in which the oxidizing atmosphere is set to a first treatment temperature;
A second oxidation step for bringing the oxidizing atmosphere to a second treatment temperature higher than the first treatment temperature;
A method for producing a rare earth magnet powder characterized by comprising:
Rare earth magnet powder according to any one of claims 1 to 3,
A binder resin capable of binding powder particles of the rare earth magnet powder;
A rare earth bonded magnet compound characterized by comprising:
The rare earth magnet powder according to claim 5, wherein the rare earth magnet powder is a composite rare earth magnet powder composed of two or more kinds having different average particle diameters.
Rare earth magnet powder according to any one of claims 1 to 3,
A binder resin that binds the powder particles of the rare earth magnet powder;
A rare earth bonded magnet characterized by comprising:
The rare earth bonded magnet according to claim 7, wherein the rare earth magnet powder is a composite rare earth magnet powder composed of two or more kinds having different average particle diameters.
4. The rare earth magnet powder according to claim 1, wherein the passive film contains an amorphous part.
10. The rare earth magnet powder according to claim 9, wherein the passive film has a crystalline part dispersed in the amorphous part.
The amorphous part is composed of R and oxygen (O),
The rare earth magnet powder according to claim 10, wherein the crystalline portion is made of the TM.