JP6623995B2 - Method for producing RTB based sintered magnet - Google Patents

Description

  The present disclosure relates to a method for producing an RTB based sintered magnet (R is a rare earth element, T is Fe or Fe and Co).

R-T-B sintered magnets having an R ₂ T ₁₄ B-type compound as a main phase are known as the most high-performance magnets among permanent magnets, such as a voice coil motor (VCM) of a hard disk drive, It is used for various motors such as motors for hybrid vehicles and home electric appliances.

In the _RTB -based sintered magnet, the irreversible thermal demagnetization occurs because the intrinsic coercive force H _cJ (hereinafter simply referred to as “H _cJ ”) decreases at a high temperature. In order to avoid irreversible thermal demagnetization, it is required to maintain high _HcJ even at high temperatures when used for motors and the like.

It is known that the R-T-B based sintered magnet has an improved H _cJ when a part of R in the R ₂ T ₁₄ B-type compound phase is replaced with a heavy rare earth element RH (Dy, Tb). . In order to obtain a high H _cJ at a high temperature, it is effective to add a large amount of heavy rare earth element RH to the RTB based sintered magnet. However, in the RTB-based sintered magnet, when the light rare earth element RL (Nd, Pr) is replaced with a heavy rare earth element RH as R, the _HcJ is improved, while the residual magnetic flux density _Br (hereinafter simply referred to as " _R "). B _r ) is reduced. In addition, since the heavy rare earth element RH is a scarce resource, it is required to reduce its usage.

In recent years, so as not to reduce the B _r, to improve the H _cJ of the R-T-B based sintered magnets have been studied with less heavy rare-earth element RH. For example, a fluoride or oxide of the heavy rare earth element RH, or various metals M or M alloys may be used alone or mixed on the surface of the sintered magnet and heat-treated in that state to improve the coercive force. It has been proposed to diffuse the contributing heavy rare earth element RH into the magnet.

  Patent Document 1 discloses using powder of R oxide, R fluoride, and R oxyfluoride.

  Patent Document 2 discloses that powder of an RM (M is at least one selected from Al, Cu, Zn, Ga, etc.) alloy is used.

  Patent Documents 3 and 4 disclose RM alloys (M is one or more selected from Al, Cu, Zn, Ga, and the like), M1M2 alloy (M1M2 is one or more selected from Al, Cu, Zn, Ga, and the like), and It is disclosed that by using a mixed powder of RH oxide, it is possible to partially reduce the RH oxide by an RM alloy or the like at the time of heat treatment and introduce the heavy rare earth element RH into the magnet.

WO 2006/043348 JP 2008-263179 A JP 2012-248827 A JP 2012-248828 A WO 2015/163397

  Patent Documents 1 to 4 described above disclose a method of performing heat treatment by causing a mixed powder containing a powder of an RH compound to be present on the entire magnet surface (entire magnet surface). According to specific examples of these methods, a magnet is immersed in a slurry in which the mixed powder is dispersed in water or an organic solvent and pulled up (immersion pulling method). In the case of the immersion pulling method, hot air drying or natural drying is performed on the magnet pulled up from the slurry. Instead of immersing the magnet in the slurry, it is also disclosed that the slurry is spray-coated on the magnet (spray coating method).

In these methods, the slurry can be applied to the entire surface of the magnet. Therefore, the heavy rare earth element RH can be introduced into the magnet from the entire surface of the magnet, and _HcJ after the heat treatment can be further improved. However, in the immersion pulling method, the slurry is necessarily biased toward the lower part of the magnet due to gravity. Further, in the spray coating method, the coating thickness at the end of the magnet is increased by the surface tension. In either method, it is difficult to make the RH compound uniformly exist on the magnet surface.

When the coating layer is thinned using a slurry having a low viscosity, the unevenness of the thickness of the coating layer can be improved to some extent. However, since the amount of slurry applied is small, _HcJ after the heat treatment cannot be significantly improved. If coating is performed a plurality of times in order to increase the amount of slurry applied, the production efficiency will be extremely reduced. In particular, when the spray coating method is adopted, the slurry is also applied to the inner wall surface of the spray coating device, and the use yield of the slurry is reduced. As a result, there is a problem that the heavy rare earth element RH which is a scarce resource is wasted.

  The present applicant discloses in Patent Document 5 a method of performing diffusion heat treatment in a state where an RLM alloy powder and an RH fluoride powder are present on the surface of an RTB-based sintered magnet. It is hard to say that a method for uniformly dispersing these powders on the RTB-based sintered magnet surface is well established.

The present disclosure relates to forming a layer of powder particles containing a heavy rare earth element RH on a magnet surface in order to diffuse heavy rare earth element RH into an RTB-based sintered magnet to improve H _cJ , The particles can be uniformly and efficiently applied to the entire surface of the RTB-based sintered magnet without waste, and the _HcJ can be greatly improved by diffusing the heavy rare earth element RH from the magnet surface into the inside. Provide a method.

  The method of manufacturing an RTB based sintered magnet according to the present disclosure includes a step of preparing an RTB based sintered magnet (R is a rare earth element, T is Fe or Fe and Co), and a method of preparing Dy and Tb. An alloy or compound of at least one of the heavy rare earth elements RH (RH is at least one selected from Dy and Tb, and the RH compound is at least one selected from RH fluoride, RH oxyfluoride, and RH oxide) Preparing a granulated powder granulated together with a binder, heating at least a surface of the RTB based sintered magnet, and applying the granulated powder to the surface of the RTB based sintered magnet; And heating the RTB-based sintered magnet to which the granulated powder is attached at a temperature equal to or lower than the sintering temperature of the RTB-based sintered magnet. The heavy rare earth element RH contained in the powder is transferred to the surface of the RTB-based sintered magnet. Including, a diffusion step of diffusing inside Luo.

  In one embodiment, the granulated powder includes an RH compound powder.

  In one embodiment, the granulated powder is an RLM1M2 alloy (RL is at least one selected from Nd and Pr, M1 and M2 are at least one selected from Cu, Fe, Ga, Co, Ni, and Al; M1 = M2).

  In one embodiment, the granulated powder comprises a powder of the RLM1M2 alloy, and a powder of the RH compound having a particle size smaller than that of the powder of the RLM1M2 alloy, wherein the powder of the RLM1M2 alloy and the powder of the RH compound are mixed. The powder is a granulated powder granulated together with a binder.

  In one embodiment, the attaching step is a step of attaching the granulated powder to the entire surface of the RTB-based sintered magnet.

  In one embodiment, the amount of RH contained in the granulated powder attached to the entire surface of the RTB-based sintered magnet is 0.7 to 0.7% with respect to the RTB-based sintered magnet. 2.0% by mass.

  In one embodiment, the adhering step comprises immersing the heated RTB-based sintered magnet in the fluidized granulated powder, thereby forming the RTB-based sintered magnet. And attaching the granulated powder to the entire surface of the substrate.

  In one embodiment, in the attaching step, the granulated powder adhered to the RTB-based sintered magnet has a thickness of 100 μm or more and 350 μm or less. Adjust the surface temperature and immersion time.

According to the embodiment of the present disclosure, in order to diffuse the heavy rare-earth element RH into the RTB-based sintered magnet and improve H _cJ , the layer of the powder particles containing the heavy rare-earth element RH is formed by the RTB-based method. The coating can be uniformly and efficiently applied to the entire surface of the sintered sintered magnet without waste.

It is a perspective view showing an example of a processing container which can be used by a fluid immersion method. FIG. 2 is a perspective view showing a position where the layer thickness of the particle size adjusting powder on the RTB based sintered magnet 100 is measured. 5 is a graph showing the relationship between the amount of Tb deposited, the preheating temperature, and the immersion time for an experimental example. It is a graph which shows the relationship between Tb adhesion amount, preheating temperature, and immersion time about another experimental example.

(1) Preparation of RTB Based Sintered Magnet Base Material An RTB based sintered magnet base material to be diffused by the heavy rare earth element RH is prepared. In this specification, for the sake of simplicity, the RTB-based sintered magnet to be diffused by the heavy rare earth element RH may be strictly referred to as an RTB-based sintered magnet base material. The term "RTB based sintered magnet" is intended to include such "RTB based sintered magnet base material". As the RTB-based sintered magnet base material, known ones can be used, and for example, have the following composition.
Rare earth element R: 12 to 17 atomic%
B (part of B (boron) may be substituted by C (carbon)): 5 to 8 atomic%
The additional element M (selected from the group consisting of Al, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi At least one): 0 to 2 atomic%
T (transition metal element mainly composed of Fe and may contain Co) and unavoidable impurities: balance

  Here, the rare earth element R is mainly a light rare earth element RL (at least one element selected from Nd and Pr), but may contain a heavy rare earth element. When a heavy rare earth element is contained, it is preferable to contain at least one of Dy and Tb.

  The RTB-based sintered magnet base material having the above composition is manufactured by any manufacturing method. The RTB-based sintered magnet base material may be finished after sintering, or may be subjected to cutting or polishing.

(2) Preparation of granulated powder [diffusing agent]
The granulated powder is formed by granulating an alloy or compound powder of the heavy rare earth element RH, which is at least one of Dy and Tb, with a binder. All of these alloys and compound powders function as diffusing agents.

  The alloy of the heavy rare earth element RH is, for example, an RHM1M2 alloy (M1 and M2 are at least one selected from Cu, Fe, Ga, Co, Ni, and Al, and M1 = M2).

  The method for producing the RHM1M2 alloy powder is not particularly limited. An alloy ribbon may be produced by a roll quenching method, and may be produced by a method of pulverizing the alloy ribbon, or may be produced by a known atomizing method such as a centrifugal atomizing method, a rotating electrode method, a gas atomizing method, or a plasma atomizing method. You may. The ingot produced by the casting method may be pulverized. When the quenching method or the casting method is used, it is preferable that M1 ≠ M2 in order to improve the pulverizability. Typical examples of the RHM1M2 alloy include a DyFe alloy, a DyAl alloy, a DyCu alloy, a TbFe alloy, a TbAl alloy, a TbCu alloy, a DyFeCu alloy, and a TbCuAl alloy. The particle size of the RHM1M2 alloy powder is, for example, 500 μm or less, and the small one is about 10 μm.

  The compound of the heavy rare earth element RH is at least one selected from RH fluoride, RH oxyfluoride, and RH oxide, and these are collectively referred to as RH compounds. The RH oxyfluoride may be included in the RH fluoride as an intermediate in the RH fluoride manufacturing process. Powders of these compounds may be used alone, or may be used as a mixture with RLM1M2 alloy powder described later. The particle size of many available RH compound powders is 20 μm or less, typically 10 μm or less, and small particles are about several μm of primary particles in the size of aggregated secondary particles.

[Diffusion aid]
The granulated powder may include an alloy powder that functions as a diffusion aid. One example of such an alloy is the RLM1M2 alloy. RL is one or more selected from Nd and Pr, M1 and M2 are one or more selected from Cu, Fe, Ga, Co, Ni, and Al, and M1 = M2. Typical examples of the RLM1M2 alloy include NdCu alloy, NdFe alloy, NdCuAl alloy, NdCuCo alloy, NdCoGa alloy, NdPrCu alloy, NdPrFe alloy and the like. Powders of these alloys are used by mixing with the above-mentioned RH compound powder. A plurality of types of RLM1M2 alloy powder and RH compound powder may be mixed and used. The method for producing the RLM1M2 alloy powder is not particularly limited. When produced by a quenching method or a casting method, in order to improve the pulverizability, it is preferable that M1 ≠ M2, and for example, a ternary or higher alloy such as an NdCuAl alloy, an NdCuCo alloy, or an NdCoGa alloy is used. The particle size of the RLM1M2 alloy powder is, for example, 500 μm or less, and the small one is about 10 μm.

[Granulation]
These powders may be mixed or granulated alone or with a binder. By granulating with the binder, the powder particles can be easily attached to the surface of the RTB-based sintered magnet simply by bringing the granulated powder into contact with the surface of the heated RTB-based sintered magnet. it can. When a mixture of a plurality of types of powders is used, a granulated powder having a uniform mixing ratio can be produced by granulating with a binder. For this reason, it becomes easy to make these powders uniformly exist at the desired mixing ratio on the RTB-based sintered magnet surface. When a powder having a small particle size, such as an RH compound powder, is used alone, if the particle size is increased to some extent by granulation, it becomes easy to uniformly and efficiently adhere to the magnet surface.

  The binder preferably has thermoplasticity and does not stick or agglomerate when the dried or mixed solvent is removed, and the granulated powder preferably has fluidity. Examples of the binder include polyester and PVA (polyvinyl alcohol). The mixture may be appropriately made using an aqueous solvent such as water or an organic solvent such as NMP (N-methylpyrrolidone). The solvent evaporates and is removed in the process of granulation described below.

  When the powder of the RLM1M2 alloy and the powder of the RH compound are mixed and used, mixing these powders alone sometimes makes it difficult to mix them uniformly. This is because the powder of the RH compound generally has a relatively smaller particle size than the powder of the RLM1M2 alloy. For example, the particle size of the RLM1M2 alloy powder is typically 500 μm or less, and the particle size of the RH compound powder is typically 20 μm or less. For this reason, by employing granulated powder obtained by granulating the powder of the RLM1M2 alloy and the powder of the RH compound together with the binder, there is an advantage that the mixing ratio of the powder of the RLM1M2 alloy and the powder of the RH compound can be made uniform throughout the powder. is there. In addition, it becomes possible to make these powder particles uniformly exist on the magnet surface.

  The method of granulating the powder with the binder may be any method. Granulation methods include, for example, tumbling granulation, fluidized bed granulation, vibration granulation, high-speed impact in a gas stream (hybridization), mixing a powder and a binder to produce a paste or slurry, Then, a method of solidifying and crushing, and the like can be mentioned.

  The particle size of the granulated powder is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. If the particle size of the granulated powder is too large, it is difficult to control the amount of powder particles attached. The size of the smallest particle contained in the granulated powder is about 10 μm.

When the powder of the RLM1M2 alloy and the powder of the RH compound are mixed, the abundance ratio (before heat treatment) of the powdered RLM1M2 alloy and the RH compound on the surface of the RTB-based sintered magnet is represented by the mass ratio of the RLM1M2 alloy. : RH compound = 96: 4 to 50:50. That is, the powder of the RLM1M2 alloy can be 50% by mass or more and 96% by mass or less in the entire mixed powder contained in the granulated powder. The abundance ratio may be RLM1M2 alloy: RH compound = 95: 5 to 60:40. That is, the powder of the RLM1M2 alloy may be 60% by mass or more and 95% by mass or less of the whole of the mixed powder. When the RLM1M2 alloy and the RH compound are mixed and used at this mass ratio, the RLM1M2 alloy efficiently reduces the RH compound. As a result, sufficiently reduced RH diffuses into the _RTB -based sintered magnet, and _HcJ can be greatly improved with a small amount of RH. When the RH compound contains a fluoride or oxyfluoride of RH, the RLM1M2 alloy efficiently reduces the RH compound, so that fluorine contained in the RH compound does not enter the RTB-based sintered magnet, and the RLM1M2 It has been confirmed by another experiment of the inventors that the RL of the alloy is left outside the RTB-based sintered magnet in association with the RL of the alloy. Of fluorine in the interior of the R-T-B based sintered magnet to prevent entry is considered to be a factor that does not reduce significantly the B _r of the R-T-B based sintered magnet. According to the embodiment of the present disclosure, the fluorine concentration inside the RTB-based sintered magnet (for example, at a depth of 100 μm from the magnet surface) is 1% by mass or less of the entire magnet.

  In the embodiment of the present disclosure, it is not necessarily excluded that a powder (third powder) other than the powder of the RLM1M2 alloy and the RH compound is present on the surface of the RTB-based sintered magnet. Care must be taken not to prevent RH in the RH compound from diffusing into the RTB based sintered magnet. The mass ratio of the “RLM1M2 alloy and RH compound” powder to the entire powder present on the surface of the RTB based sintered magnet is desirably 70% or more.

[Adhesion]
The preheated magnet is brought into contact with the granulated powder described above. By this contact, the binder of the granulated powder can be melted by the heat of the magnet surface to adhere the granulated powder to the magnet surface. The heated magnet selectively melts the binder in the granulated powder in contact with its surface, so that the powder particles constituting the granulated powder can be uniformly and uniformly applied to the entire surface of the RTB-based sintered magnet. It can be attached efficiently. Therefore, according to the method of the present disclosure, unlike the conventional immersion method or spray method, the thickness of the coating film is not biased by gravity or surface tension. Further, since the granulated powder does not adhere to anything other than the preheated magnet, there is no waste. Further, since the pre-granulated powder is used, the required amount of powder particles can be uniformly adhered to the magnet surface by one coating operation, which is efficient.

  Hereinafter, the attaching step in the embodiment of the present disclosure will be described in more detail.

  (1) Preheat the RTB-based sintered magnet. The purpose of the preheating is to melt the binder of the granulated powder by the heat of the magnet surface and attach it to the RTB based sintered magnet surface. The lower limit of the heating temperature is equal to or higher than the melting temperature of the binder used for the granulated powder (the temperature at which melting starts and can be adhered to the magnet surface). On the other hand, if the heating temperature is too high, a large amount of the granulated powder adheres, making it difficult to control the amount of adhesion. Therefore, the upper limit of the heating temperature is 230 ° C, preferably 180 ° C, more preferably 150 ° C.

  (2) Adhere the granulated powder. The granulated powder is attached to the pre-heated RTB-based sintered magnet. Any method may be used for the attachment, for example, a method in which a preheated RTB-based sintered magnet is immersed in a processing container containing granulated powder, a method in which a preheated RTB-based magnet is used. A method of sprinkling granulated powder on a sintered magnet. At this time, vibration may be applied to the processing container containing the granulated powder, or the granulated powder may be caused to flow by air. Above all, a so-called fluidized bed coating process in which a preheated RTB-based sintered magnet is immersed in fluidized granulated powder is preferred.

  Hereinafter, an example in which the fluid immersion method is applied to the attaching step in the present disclosure will be described. The fluid immersion method is a method widely used in the field of powder coating, in which a heated object is immersed in a fluidized thermoplastic powder coating, and the coating is heated by the heat of the surface of the object. Is a method of fusing. In this example, in order to apply the fluidized immersion method to a magnet, instead of a thermoplastic powder coating, a metal or a metal compound such as an RH alloy or a compound of a diffusing agent or an RL alloy of a diffusing agent is heated as described above. Used by granulating with a plastic binder.

  The method of flowing the granulated powder may be any method. For example, as one specific example, a method using a container provided with a porous partition wall at the bottom will be described. In this example, the granulated powder is put in a container, pressure is applied to a gas such as the atmosphere or an inert gas from the lower part of the partition wall, and the granulated powder is injected into the container. Can be fluidized. In the method of the present disclosure, since the granulated powder is heavier than the powder coating, the flow rate of the gas needs to be larger than that in the case of powder coating.

  The time for immersing the RTB-based sintered magnet in the granulated powder flowing inside the container depends on the preheating temperature, but is, for example, about 0.5 to 5.0 seconds. In this method, the amount of adhesion can be controlled by adjusting the preheating temperature and the immersion time. When it is desired to achieve a certain desired adhesion amount, the immersion time can be shortened by increasing the preheating temperature, but if it is too high, it becomes difficult to control the immersion time. On the other hand, if the preheating temperature is too low, the immersion time will be too long and the efficiency will be poor. It should be noted that the attached amount tends to increase as the specific surface area per unit volume increases for the same immersion time. Depending on the shape of the magnet, the preheating temperature and the immersion time when a desired amount of adhesion is desired can be determined by experiments.

  According to the above method, the thickness of the coating film is not deviated by gravity or deviated by surface tension unlike the conventional immersion method or spray method. Further, by adjusting the preheating temperature and the immersion time, it is possible to control the amount of the granulated powder adhered, and thus the amount of the adhered RH. The temperature and immersion time of the surface of the RTB-based sintered magnet may be adjusted so that the thickness of the granulated powder attached to the RTB-based sintered magnet is 100 μm or more and 350 μm or less. preferable.

  When the granulated powder is adhered to the entire surface of the RTB-based sintered magnet, the amount of the attached RH may be 0.7 to 2.0% by mass of the RTB-based sintered magnet. preferable. As the mass ratio of the heavy rare earth element RH diffused into the RTB-based sintered magnet to the RTB-based sintered magnet increases from zero, the increasing range of the coercive force increases. However, according to experiments performed separately, when the conditions other than the RH amount, such as the heat treatment conditions, are the same, the coercive force is saturated when the RH amount is around 1.0% by mass, and the RH amount is increased from 2.0% by mass. It was also found that the increase in coercive force did not increase. That is, when the amount of RH of 0.7 to 2.0% by mass of the RTB-based sintered magnet is applied to the entire surface of the RTB-based sintered magnet, it is most efficiently maintained. The magnetic force can be improved.

  (3) A post-heating step may be performed. The heating temperature is preferably from 150 to 200C. At this time, the granulated powder is more firmly fixed by the binder being melted and fixed, so that the attached granulated powder is prevented from falling off and the handling property is improved.

  (4) Diffusion heat treatment is performed. The heat treatment temperature is equal to or lower than the sintering temperature of the RTB-based sintered magnet (specifically, for example, equal to or lower than 1000 ° C.), and is higher than the melting point when the granulated powder includes RLM1M2 alloy powder. However, specifically, 500 ° C. or higher is preferable. The heat treatment time is, for example, 10 minutes to 72 hours. After the heat treatment, if necessary, heat treatment may be further performed at 400 to 700 ° C. for 10 minutes to 72 hours. The atmosphere for the heat treatment is preferably a vacuum or an inert gas atmosphere.

(Experimental example 1)
First, by a known method, the composition ratio Nd = 13.4, B = 5.8, Al = 0.5, Cu = 0.1, Co = 1.1, and the balance of Fe (atomic%) RTB A sintered magnet was produced. This was machined to obtain an RTB-based sintered magnet base material having a size of 4.9 mm × 7.5 mm × 40 mm. Magnetic properties of the obtained R-T-B based sintered magnet base material where a measured by B-H tracer, H _cJ is 1023kA / m, B _r was 1.45 T.

Next, TbF ₃ powder and NdCu powder were granulated together with a binder to prepare a granulated powder. The TbF ₃ powder was a commercially available non-spherical powder having a particle size of 10 μm or less. The NdCu powder was a spherical Nd ₇₀ Cu ₃₀ alloy powder produced by centrifugal atomization. Polyester was used as a binder, and NMP (N-methylpyrrolidone) was used as a solvent. A paste was prepared by mixing TbF ₃ powder: NdCu powder: polyester: NMP = 36: 54: 5: 5 (mass ratio). Next, the paste was dried with hot air to evaporate the solvent, pulverized in an Ar atmosphere, and classified with a sieve to obtain a granulated powder having a particle size of 106 μm or less.

  Next, a processing container 20 having a configuration schematically shown in FIG. 1A was prepared for use in the fluidized immersion method. This processing container has a roughly cylindrical shape with the upper part opened, and has a porous partition wall 30 at the bottom. The inner diameter of the processing container 20 used in the experiment was 78 mm, the height was 200 mm, the average pore diameter of the partition wall 30 was 15 μm, and the porosity was 40%. The granulated powder was put into the processing container 20 to a depth of about 50 mm. The granulated powder was caused to flow by injecting air into the processing vessel 20 from below the porous partition 30 at a flow rate of 2 liter / min. The height of the flowing powder was about 70 mm. The RTB based sintered magnet base material 100 preheated to 120 ° C. in a drying furnace is fixed with a clamp jig (not shown), immersed in flowing granulated powder for 1 second, and pulled up. -Granulated powder was adhered to the B-based sintered magnet base material 100. The jig was fixed by two-point contact on both sides of a 4.9 mm × 40 mm surface of the magnet, and the magnet was immersed with the smallest surface of 4.9 mm × 7.5 mm as the upper and lower surfaces. The magnet to which the granulated powder was attached was heated at 150 ° C. for 15 minutes to fix the granulated powder.

  The thickness in the 4.9 mm direction of the RTB based sintered magnet base material 100 to which the granulated powder was fixed was measured. The measurement was performed at three locations for one RTB-based sintered magnet base material at measurement positions 1, 2, and 3 in FIG. 1B (N = 5 each). At the time of immersion, the measurement position 1 was on the upper side, and the measurement position 3 was on the lower side. Table 1 shows a value (a value of an increase on one side) of 値 of a value increased from the RTB based sintered magnet base material 100 before the granulated powder is attached. The values at the three locations were almost the same, and there was almost no variation in the thickness at the measurement locations.

(Experimental example 2)
Except that the size was 4.5 mm × 15.0 mm × 26.0 mm, the same RTB based sintered magnet base material as in Experimental Example 1 and granulated powder were prepared. Granulated powder was added to the RTB-based sintered magnet base material in the same manner as in Experimental Example 1 except that the preheating temperature and the immersion time were set to the values shown in Table 2 using the same processing container as in Experimental Example 1. Attached. No post-heating step was performed. Table 2 shows the adhesion amount of the granulated powder obtained from the increase in the weight of the magnet and the adhesion amount of Tb calculated therefrom. FIG. 2 is a graph showing the relationship between the amount of deposited Tb, the preheating temperature, and the immersion time, obtained by this experiment. The vertical axis of the graph is the Tb adhesion amount (unit: mass%), and the horizontal axis is the immersion time (unit: second). The Tb adhesion amount in the graph of FIG. 2 is the mass ratio of Tb present on the magnet surface to the total mass of the RTB based sintered magnet base material. The Tb adhesion amount was determined from the mass of the granulated powder adhered to the entire surface of the RTB based sintered magnet base material and the Tb concentration in the granulated powder. From FIG. 2, it can be seen that the higher the preheating temperature of the RTB based sintered magnet base material and the longer the immersion time, the larger the amount of heavy rare earth element RH attached (the amount of RH attached), It was found that the RH adhesion amount could be controlled by adjusting the preheating temperature and the immersion time. In order to set the RH amount to 0.7 to 2.0% by mass of the RTB-based sintered magnet base material, it is preferable to adjust the preheating temperature within the range of 100 to 120 ° C. all right.

(Experimental example 3)
An experiment was conducted in which the preheating temperature was set to 90 to 120 ° C. and the immersion time was set to be longer (1 to 10 seconds). An experiment was performed in the same manner as in Experimental Example 2, using a magnet preform having the same composition, shape, and size as the RTB-based sintered magnet preform used in Experimental Example 1. Similarly, the relationship among the amount of deposited Tb, the preheating temperature, and the immersion time was determined. FIG. 3 is a graph showing the relationship between the amount of deposited Tb, the preheating temperature, and the immersion time, obtained by this experiment. The vertical axis of the graph is the Tb adhesion amount (unit: mass%), and the horizontal axis is the immersion time (unit: second). When the preheating temperature was 90 ° C., the granulated powder did not adhere to the magnet base material. For this reason, the result when the preheating temperature is 90 ° C. is not shown in the graph of FIG. From FIG. 3, the RH adhesion amount is controlled to 0.7 to 2.0% by mass of the RTB based sintered magnet base material when the preheating temperature is 100 to 120 ° C. and the immersion time is 1 to 10 seconds. I knew I could do it.

(Experimental example 4)
A granulated powder was produced using the diffusion source shown in Table 3 and the same binder and solvent as in Experimental Example 1. The produced granulated powder was adhered to the same RTB-based sintered magnet base material as in Experimental Example 1 in the same manner as in Experimental Example 1. The preheating temperature and the immersion time were adjusted so that the increase in the amount of adhesion (adhesion thickness) on one side was in the range of 100 μm or more and 350 μm or less, and the RH adhesion amount of each sample showed the value shown in Table 3 below. Thereafter, the RTB-based sintered magnet base material to which RH was adhered was heat-treated in an Ar atmosphere of 100 Pa at a heat treatment temperature shown in Table 3 for a time shown in Table 3 to form a structure adhered to the magnet surface. The element in the diffusion source in the granular powder was diffused into the RTB based sintered magnet base material. A 4.7 mm × 7.25 mm × 6.3 mm rectangular parallelepiped was cut out from the center of the heat-treated RTB-based sintered magnet, and the coercive force was measured. Table 3 shows the value of _{ΔH cJ obtained} by subtracting the coercive force of the _RTB based sintered magnet base material from the measured coercive force. It was confirmed that the coercive force of all of these RTB-based sintered magnets was greatly improved.

The embodiment of the present invention can improve the H _cJ of the _RTB -based sintered magnet with less heavy rare earth element RH, and therefore can be used for manufacturing a rare earth sintered magnet requiring a high coercive force. .

Reference Signs List 20 processing container 30 porous partition wall 100 RTB based sintered magnet base material

Claims (8)

A step of preparing an RTB based sintered magnet (R is a rare earth element, T is Fe or Fe and Co);
Alloy or compound of heavy rare earth element RH that is at least one of Dy and Tb (RH is at least one selected from Dy and Tb, and RH compound is at least one selected from RH fluoride, RH oxyfluoride, and RH oxide B) preparing a granulated powder obtained by granulating the powder together with a binder;
Heating at least the surface of the RTB-based sintered magnet, and attaching the granulated powder to the surface of the RTB-based sintered magnet;
The RTB-based sintered magnet to which the granulated powder is attached is heat-treated at a temperature equal to or lower than the sintering temperature of the RTB-based sintered magnet, and the heavy rare earth element contained in the granulated powder is A diffusion step of diffusing RH from the surface of the RTB-based sintered magnet to the inside;
A method for producing an RTB-based sintered magnet, comprising:   The method for producing an RTB-based sintered magnet according to claim 1, wherein the granulated powder includes an RH compound powder.   The granulated powder is made of an RLM1M2 alloy (RL is one or more selected from Nd and Pr, M1 and M2 are one or more selected from Cu, Fe, Ga, Co, Ni and Al, and M1 = M2). The method for producing an RTB-based sintered magnet according to claim 2, comprising a powder. The granulated powder includes a powder of the RLM1M2 alloy and a powder of the RH compound having a particle size smaller than a particle size of the powder of the RLM1M2 alloy,
The method for producing an RTB-based sintered magnet according to claim 3, wherein the powder of the RLM1M2 alloy and the powder of the RH compound are granulated powder granulated together with a binder.   The RTB-based firing according to any one of claims 1 to 4, wherein the attaching step is a step of attaching the granulated powder to the entire surface of the RTB-based sintered magnet. Method for manufacturing magnets.   The amount of RH contained in the granulated powder adhered to the entire surface of the RTB-based sintered magnet is 0.7 to 2.0% by mass based on the RTB-based sintered magnet. The method for producing an RTB-based sintered magnet according to claim 5, wherein:   In the attaching step, the heated RTB-based sintered magnet is immersed in the fluidized granulated powder, so that the entire surface of the RTB-based sintered magnet is The method for producing an RTB-based sintered magnet according to claim 5, wherein the method is a step of attaching the granulated powder.   In the attaching step, the temperature of the surface of the RTB-based sintered magnet and the temperature of the RTB-based sintered magnet such that the thickness of the granulated powder attached to the RTB-based sintered magnet is 100 μm or more and 350 μm or less. The method for producing an RTB-based sintered magnet according to claim 7, wherein the immersion time is adjusted.

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