JP4665694B2 - Rare earth magnet manufacturing method - Google Patents

Description

The present invention relates to a method for producing a rare earth magnet.

  Rare earth magnets are known as high performance permanent magnets. Rare earth magnets are being studied not only for household appliances such as conventional air conditioners and refrigerators, but also for drive motors for industrial machines, robots, fuel cell vehicles, hybrid cars, etc. Is expected to be realized. Among such rare earth magnets, an R-T-B (R is a rare earth element, T is a transition element) type magnet is a high performance magnet that exhibits a higher energy product than other magnets. Collecting.

  However, since such rare earth magnets contain rare earth elements that are very easily oxidized as the main component of the magnet, they have low corrosion resistance, and it has been difficult to avoid deterioration of magnetic characteristics over time due to long-term use. It was.

Therefore, for the purpose of improving the corrosion resistance of the rare earth magnet, a resin layer (patented as a protective layer for protecting the element body on the surface of the magnet element body having the RT (Fe) -B system composition) Documents 1) and oxidation-resistant plating layers (Patent Document 2) are known.
JP-A-60-63901 JP-A-60-54406

  However, although the rare earth magnet provided with the resin layer and the oxidation-resistant plating layer as the protective layer as described above can exhibit excellent corrosion resistance when used under the conditions assumed heretofore, As a result, the magnet body deteriorates, and the protective layer bulges or peels off, so that sufficient corrosion resistance tends to be hardly obtained.

  In recent years, rare earth magnets have been desired to be used in motors for automobiles, such as drive motors and generators for hybrid cars. Therefore, high-temperature and high-humidity can be used in such applications. Under these circumstances, it is required to exhibit excellent corrosion resistance.

  Therefore, the present invention has been made to meet such demands, and an object thereof is to provide a rare earth magnet that can exhibit excellent corrosion resistance even under high temperature and high humidity.

In order to achieve the above object, a method for producing a rare earth magnet according to the present invention is a method for producing a rare earth magnet comprising a magnet body containing a rare earth element, a transition element, and boron, and includes a rare earth element, a transition element and boron. respect sintered body after performing the process of removing a surface portion of the sintered body, the carbon dioxide concentration 0.1 ppm or less of nitrogen - oxygen mixed atmosphere (21% oxygen), at a processing temperature of 250 to 500 ° C. Heat treatment is performed to obtain a magnet body having a carbonate content of 0.4 μg or less in terms of carbon dioxide with respect to a surface area of 1 cm ² .

  Thus, since the rare earth magnet of the present invention has a carbonate content equal to or less than the predetermined amount, the rare earth magnet can exhibit excellent corrosion resistance as compared with the prior art. Such factors are not necessarily clear, but are estimated as follows.

  That is, in rare earth magnets, carbonates inevitably contained in the magnet body produce carbon dioxide under high temperature and high humidity conditions, which penetrate into the magnet and form acidic conditions that promote oxidation of rare earth elements. In addition, when this carbon dioxide is released to the outside, it is thought that the protective layer on the surface may cause blistering or peeling. And it is estimated that the deterioration of the conventional rare earth magnet under high temperature and high humidity is caused by the influence of the carbonate contained in the rare earth magnet.

  On the other hand, the rare earth magnet of the present invention is adjusted so that the carbonate content of the magnet body is not more than the predetermined amount described above, so that even when exposed to high temperature and high humidity conditions, It is difficult to generate carbon dioxide to the extent that it causes the above problems. Therefore, there is little deterioration of the magnet body due to carbon dioxide, and the protective layer formed on the surface is less prone to blistering or peeling, and can exhibit sufficiently excellent corrosion resistance even under high temperature and high humidity conditions. It becomes. However, the action is not limited to these.

Further, the method of producing the rare-earth magnet of the present invention, a rare earth element, a manufacturing method of a rare earth magnet Ru comprising a magnet body containing a transition element and boron, with respect to a sintered body containing a rare earth element, a transition element and boron After the treatment for removing the surface portion of the sintered body, the heat treatment is performed at a treatment temperature of 250 to 500 ° C. in an oxidizing atmosphere having a carbon dioxide concentration of 300 ppm or less, and carbon dioxide that can be desorbed by heating. A magnet body having a total amount of 0.4 μg or less with respect to a surface area of 1 cm ² may be obtained .

  Even if the rare earth magnet of the present invention is exposed to high-temperature and high-humidity conditions because the amount of carbon dioxide desorbed from the magnet body when heated is below the above specified amount. Deterioration of the magnet body due to the carbon dioxide, peeling of the protective layer, and the like hardly occur. Therefore, the rare earth magnet of the present invention can exhibit excellent corrosion resistance even under high temperature and high humidity conditions.

  Moreover, it is preferable that the rare earth magnet of the present invention having the above configuration further includes a protective layer made of a material different from that of the magnet body on the surface of the magnet body. The rare earth magnet having such a configuration can exhibit extremely excellent corrosion resistance as compared with the prior art because the magnet body is not easily deteriorated under high temperature and high humidity conditions and is further protected by a protective layer. It will be a thing. In addition, the protective layer makes it very difficult to form a carbonate due to carbon dioxide in the atmosphere during storage or use, and excellent corrosion resistance can be maintained well.

Furthermore, it is more preferable that the rare earth magnet of the present invention has an oxide layer containing a rare earth element and oxygen in the region near the surface. Thus, the magnet body having the oxide layer on the surface has a carbonate content that is extremely reduced and has excellent corrosion resistance, and the oxide layer also has a function as a protective layer. Even alone, the corrosion resistance can be maintained well. Moreover, it is preferable to perform the process which removes the surface part of a sintered compact by giving an acid washing with respect to a sintered compact, and melt | dissolves 5 micrometers or more in average thickness from the surface of a sintered compact by this acid cleaning. Is more preferable. Furthermore, it is preferable to perform the process which removes the surface part of a sintered compact in the atmosphere whose carbon dioxide concentration is 300 ppm or less.

  According to the present invention, it is possible to provide a rare earth magnet capable of exhibiting excellent corrosion resistance even under high temperature and high humidity.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.

  FIG. 1 is a perspective view schematically showing a rare earth magnet according to the embodiment. FIG. 2 is a diagram schematically showing a cross-sectional structure along the line II-II of the rare earth magnet 1 shown in FIG.

  The rare earth magnet 1 is composed of a magnet body including a magnet portion 2 and an oxide layer 4 formed on the surface of the magnet portion 2 and has a substantially rectangular parallelepiped structure. The magnet part 2 is an RTB-based rare earth magnet containing a rare earth element, a transition element, and boron. Here, the rare earth element means an element belonging to the third period of the long-period periodic table and an element belonging to the lanthanoid. Examples of such a rare earth element include yttrium (Y), lanthanum (La), and cerium ( Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium ( Tm), ytterbium (Yb), lutetium (Lu) and the like.

  The magnet part 2 preferably contains at least one element selected from the group consisting of Nd, Dy, Pr and Tb as a rare earth element, and these elements include La, Sm, Ce, Gd, Er, What further contains at least one element selected from the group consisting of Eu, Tm, Yb and Y is more preferable.

  Examples of the transition element constituting the magnet part 2 include transition elements other than the rare earth elements, including at least iron (Fe), cobalt (Co), titanium (Ti), vanadium (V), chromium (Cr), Selected from the group consisting of manganese (Mn), nickel (Ni), copper (Cu), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W) It is preferable to further contain at least one element. Especially, as a transition element, it is more preferable that Fe and Co are included.

  More specifically, the constituent material of the magnet part 2 is preferably one having an R—Fe—B-based composition containing iron (Fe) as a transition element. Such a material has a main phase having a substantially tetragonal crystal structure, and a rare earth-rich phase having a high rare earth element content in the grain boundary portion of the main phase, and a boron atom content ratio. Has a high boron-rich phase. These rare earth-rich phase and boron-rich phase are nonmagnetic phases that do not have magnetism, and such a nonmagnetic phase is usually contained in an amount of 0.5 to 50% by volume in the magnet constituting material. Moreover, the particle size of the main phase is usually about 1 to 100 μm.

  In the magnet part 2 having an R-Fe-B-based configuration, the rare earth element content is preferably 8 to 40 atomic%. When the rare earth element content is less than 8 atomic%, the crystal structure of the main phase becomes almost the same as that of α-iron, and the coercive force (iHc) tends to decrease. On the other hand, if it exceeds 40 atomic%, a rare earth-rich phase is excessively formed, and the residual magnetic flux density (Br) tends to be small.

  The Fe content is preferably 42 to 90 atomic%. When the Fe content is less than 42 atomic%, Br decreases, and when it exceeds 90 atomic%, iHc tends to decrease. Furthermore, the B content is preferably 2 to 28 atomic%. When the content of B is less than 2 atomic%, a rhombohedral structure is likely to be formed, and this tends to reduce iHc, and when it exceeds 28 atomic%, a boron-rich phase is excessively formed. Br tends to be small.

  In the constituent materials described above, a part of Fe in R—Fe—B may be substituted with Co. Thus, if a part of Fe is replaced by Co, the temperature characteristics can be improved without deteriorating the magnetic characteristics. In this case, it is desirable that the amount of substitution of Co not be larger than the content of Fe. When the Co content exceeds the Fe content, the magnetic properties of the magnet part 2 tend to be small.

  In addition, a part of B in the constituent material may be substituted with an element such as C, P, S, or Cu. By replacing a part of B in this way, the magnet body can be easily manufactured and the manufacturing cost can be reduced. At this time, the substitution amount of these elements is desirably an amount that does not substantially affect the magnetic properties, and is preferably 4 atomic% or less with respect to the total amount of constituent atoms.

  Further, from the viewpoint of improving iHc and reducing manufacturing costs, the magnet unit 2 is made of aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn) in addition to the above-described configuration. Bismuth (Bi), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), antimony (Sb), germanium (Ge), tin (Sn), zirconium (Zr), nickel (Ni) Further, elements such as silicon (Si), gallium (Ga), copper (Cu), hafnium (Hf) may be further contained.

  These addition amounts are also preferably in a range that does not affect the magnetic properties, and are preferably 10 atomic% or less with respect to the total amount of constituent atoms. In addition, oxygen (O), nitrogen (N), carbon (C), calcium (Ca), etc. are conceivable as components inevitably mixed, and these are about 3 atomic% with respect to the total amount of constituent atoms. It may be contained in the following amounts.

The oxide layer 4 is a layer formed in a region near the surface of the rare earth magnet 1 (magnet body) and covers substantially the entire surface of the magnet portion 2. The oxide layer 4 contains the same rare earth element and oxygen as those contained in the magnet portion 2, and more preferably contains an oxide of the rare earth element. Specifically, for example, when the magnet part 2 contains a large amount of Nd as a rare earth element, the oxide layer 4 preferably contains Nd ₂ O ₃ .

The oxide layer 4 preferably contains a transition element contained in the magnet portion 2 in addition to the rare earth element. This transition element is contained, for example, in the form of a simple metal or an oxide. For example, when the magnet part 2 contains a lot of Fe as a transition element, the oxide layer 4 can contain Fe, FeO, Fe ₂ O ₃ , Fe ₃ O _{4 and the} like. Furthermore, the oxide layer 4 may further contain elements other than the elements contained in the magnet part 2 in a large amount, and these elements may be contained in the form of oxides. Note that the oxide layer 4 is not necessarily limited to a single layer, and may have two or more layers having different compositions.

  The oxide layer 4 is preferably not a layer separately provided on the surface of the magnet part 2 but a layer formed by processing the surface of the magnet part 2. In this case, the adhesion of the oxide layer 4 to the magnet portion 2 is very good, and the rare earth magnet 1 can exhibit more excellent corrosion resistance. Specifically, the oxide layer 4 is preferably an oxide film obtained by oxidizing the surface of the magnet part 2.

  The constituent elements of the oxide layer 4 are, for example, EPMA (X-ray microanalyzer method), XPS (X-ray photoelectron spectroscopy), AES (Auger electron spectroscopy) or EDS (energy dispersive X-ray fluorescence spectroscopy). ) And other known composition analysis methods.

  The thickness of the oxide layer 4 is preferably 20 nm to 5 μm, and more preferably 50 nm to 3 μm. According to the oxide layer 4 having a suitable thickness, extremely excellent corrosion resistance can be obtained. However, if the oxide layer 4 is too thick, cracks and the like are liable to occur, and therefore the thickness is preferably set to the upper limit value or less.

The rare earth magnet 1 has a carbonate content of 0.4 μg or less in terms of carbon dioxide relative to its surface area of 1 cm ² . Here, the carbonate in the rare earth magnet 1 is included when the element constituting the rare earth magnet 1 reacts with carbon dioxide in the air during the production of the rare earth magnet 1 or the like. Examples of the carbonate include carbonates of rare earth elements contained in the magnet part 2. When the rare earth element is Nd, Nd ₂ (CO ₃ ) ₃ can be exemplified. A large amount of such carbonate is usually contained in the grain boundary portion of the magnet portion 2.

When the content of the carbonate is 0.4 μg or less in terms of carbon dioxide with respect to 1 cm ² of the surface area of the rare earth magnet 1, the carbonate is retained when the rare earth magnet 1 is held under high temperature and high humidity conditions. The generation amount of carbon dioxide derived from is suppressed to such an extent that the rare earth magnet 1 is not deteriorated. As a result, the rare earth magnet 1 has excellent corrosion resistance even under high temperature and high humidity conditions. However, since the carbonate may increase the adhesion between the rare earth magnet 1 and the protective layer depending on the material of the protective layer of the rare earth magnet 1, an amount that does not decrease the corrosion resistance, for example, about 5 ng is included. Also good.

The content of carbonate contained in the rare earth magnet 1 is a value converted to carbon dioxide as described above. Such a value can be measured as the amount of carbon dioxide desorbed when the rare earth magnet 1 is subjected to temperature programmed desorption analysis. Specifically, first, the ionic strength of the component (carbon dioxide) of the mass number (m / z) 44 in the gas desorbed from the rare earth magnet 1 by heating the rare earth magnet 1 with a mass spectrometer (MS). taking measurement. Then, the ionic strength of carbon dioxide is continuously recorded as a function of temperature from the start of heating to a temperature at which the amount of desorbed gas becomes extremely small, and an integrated value for the temperature of ionic strength is calculated. Then, using the obtained integrated value, the total generation amount of carbon dioxide desorbed from the rare earth magnet 1 is calculated from the proportional relationship with the value obtained with the standard sample (Si substrate treated with hydrofluoric acid). Then, the value of this total generation amount is divided by the total surface area (cm ² ) of the rare earth magnet 1 to calculate the carbon dioxide desorption amount per 1 cm ² of the surface area, and this value is calculated as the rare earth magnet 1 as described above. The content of the carbonate with respect to 1 cm ² of the surface area.

  In such a temperature programmed desorption analysis, the rare earth magnet 1 can be suitably heated using infrared rays. At this time, in order to accurately measure the generation of gas from the rare earth magnet 1, the analysis is preferably performed under vacuum. A suitable temperature raising condition for causing desorption of carbon dioxide is 1 to 200 ° C./min, and the temperature range for raising the temperature is preferably a temperature range of 50 to 600 ° C.

  Note that the carbonate contained in the rare earth magnet 1 is not necessarily completely desorbed as carbon dioxide by the temperature-programmed desorption analysis as described above. For example, when desorbing as carbon monoxide, the rare earth magnet 1 In some cases, it is taken into the structure and does not desorb. Therefore, in the present embodiment, the amount of carbonate contained in the rare earth magnet 1 is a value that can be quantified as carbon dioxide desorbed by heating.

  Next, a method for manufacturing the rare earth magnet 1 having the above-described configuration will be described. The rare earth magnet 1 is manufactured by, for example, obtaining a sintered body by a powder metallurgy method and then subjecting the sintered body to a heat treatment in an oxidizing atmosphere to form an oxide layer in a region near the surface. .

That is, first, the sintered body is manufactured by the following powder metallurgy method. In this method, first, an alloy having a desired composition is manufactured by a known alloy manufacturing process such as a casting method or a strip casting method. Next, this alloy was pulverized to a particle size of 10 to 100 μm using a coarse pulverizer such as a jaw crusher, brown mill, or stamp mill, and then further pulverized by a fine pulverizer such as a jet mill or an attritor. Grind to a particle size of 5-5 μm. The powder thus obtained is preferably molded at a pressure of 0.5 to ⁵ t / cm ² in a magnetic field having a magnetic field strength of 600 kA / m or more.

  Thereafter, the obtained compact is preferably sintered in an inert gas atmosphere or vacuum at 1000 to 1200 ° C. for 0.5 to 10 hours and then rapidly cooled. Furthermore, this sintered body is subjected to heat treatment at 500 to 900 ° C. for 1 to 5 hours in an inert gas atmosphere or vacuum, and the sintered body is processed into a desired shape as necessary.

Next, various treatments for reducing the carbonate content of the rare earth magnet 1 (magnet body) to 0.4 μg / cm ² or less are performed on the obtained sintered body. Examples of the treatment for reducing the carbonate content include a method for removing the surface portion of the sintered body containing a large amount of carbonate, and a method for thermally decomposing the carbonate contained in the sintered body. By adjusting the conditions in these methods, the carbonate content of the rare earth magnet 1 (magnet body) can be set within a desired range.

  Examples of the method for removing the surface portion of the sintered body include buffing, shot blasting, and cleaning with an acid solution (acid cleaning). Among these, acid cleaning that can effectively remove the surface portion is preferable. These surface removal steps are preferably performed in an atmosphere having a carbon dioxide concentration of 300 ppm or less in order to prevent the formation of carbonate by carbon dioxide in the air.

  Of the two methods described above, the latter method of pyrolysis is preferred as a method for reducing the carbonate content, and the former method of removing the surface and the latter method of pyrolysis may be combined. More preferred. Hereinafter, a method of combining surface removal (particularly acid cleaning) and thermal decomposition will be specifically described as an example.

  That is, first, cleaning with an acid solution (acid cleaning) is performed on the sintered body obtained by the powder metallurgy method described above. Thereby, in addition to removing the surface portion of the sintered body containing a large amount of carbonate, the surface of the sintered body can be cleaned, so that the oxide layer 4 formed by heat treatment to be described later and the magnet portion 2 inside thereof are formed. The effect that the adhesiveness of this improves is acquired.

  Nitric acid is preferably used as the acid used in the acid cleaning. Usually, when a general steel material is plated, a non-oxidizing acid such as hydrochloric acid or sulfuric acid is often used. However, when a rare earth element is included as in the sintered body of the present embodiment, when the treatment is performed using these acids, hydrogen generated by the acid is occluded on the surface of the sintered body, and the occlusion site is brittle. May generate a large amount of powdery undissolved material. Since this powdery undissolved material may cause surface roughness, defects, or poor adhesion after the surface treatment, it is preferable not to include the non-oxidizing acid described above in the acid cleaning solution. Therefore, it is preferable to use nitric acid, which is an oxidizing acid that generates little hydrogen, for the acid cleaning.

  The amount of dissolution of the surface of the sintered body by such acid cleaning is preferably 5 μm or more, preferably 10 to 15 μm in average thickness from the surface. By doing so, the carbonate existing in the vicinity of the surface of the sintered body can be effectively removed, and the rare earth magnet 1 having a reduced carbonate content can be obtained. In addition, the deteriorated layer and the oxide layer can be removed by processing the surface of the sintered body, and the oxide layer can be formed with high accuracy by a heat treatment described later.

  The concentration of nitric acid in the treatment solution used for the acid cleaning is preferably 1 N or less, particularly preferably 0.5 N or less. If the nitric acid concentration is too high, the dissolution rate of the sintered body is extremely high, and the amount of dissolution tends to be difficult to control. In particular, in large-scale processing such as barrel processing, the variation becomes large, and it may be difficult to maintain the dimensional accuracy of the product. If the nitric acid concentration is too low, the amount of dissolution tends to be insufficient. For this reason, the nitric acid concentration is preferably 1 N or less, and more preferably 0.5 to 0.05 N. The amount of Fe dissolved at the end of the treatment is preferably about 1 to 10 g / l.

  In order to completely remove a small amount of undissolved substances and residual acid components from the surface of the sintered body that has been subjected to acid cleaning, it is more preferable to perform cleaning using ultrasonic waves. This ultrasonic cleaning is preferably performed in pure water with very few chlorine ions that generate rust on the surface of the sintered body. Moreover, you may perform the same water washing before and behind the said ultrasonic cleaning, and in each process of acid cleaning as needed.

Next, the sintered body after the acid cleaning is subjected to heat treatment, and the carbonate in the sintered body is further thermally decomposed. In this pyrolysis, the carbonate contained in the sintered body becomes carbon dioxide and desorbs. As described above, the rare earth magnet 1 has a carbonate content of 0.4 μg or less in terms of carbon dioxide with respect to a surface area of 1 cm ² . Such a carbonate content can be obtained by appropriately changing the conditions for the heat treatment together with the conditions for the acid cleaning described above. That is, by controlling the amount of carbon dioxide desorbed in the heat treatment, the carbonate content in the rare earth magnet 1 can be adjusted.

  The heat treatment can be performed, for example, by heating the sintered body in an oxidizing atmosphere containing an oxidizing gas. By heating the sintered body in the oxidizing atmosphere in this way, the carbonate in the sintered body is removed and the constituent materials in the vicinity of the surface are partially oxidized. Thereby, the rare earth magnet 1 having the oxide layer 4 on the surface of the magnet portion 2 is obtained. The oxide layer 4 thus formed is mainly composed of an oxide of an element contained in the magnet part 2. That is, for example, the rare earth element in the oxide layer 4 is derived from the rare earth element in the magnet part 2, and the transition element in the oxide layer 4 is derived from the transition element in the magnet part 2. .

  Here, the oxidizing atmosphere is not particularly limited as long as it contains an oxidizing gas. For example, the atmosphere, oxygen atmosphere (preferably oxygen partial pressure adjustment atmosphere), water vapor atmosphere (preferably water vapor partial pressure adjustment atmosphere) ) And the like in which the oxidation is promoted. Thus, oxygen, water vapor, etc. are mentioned as oxidizing gas.

  For example, the oxygen atmosphere is an atmosphere having an oxygen concentration of 0.1% or more, and an inert gas coexists with oxygen in the atmosphere. Such inert gas includes nitrogen. That is, as an aspect of the oxygen atmosphere, there is an atmosphere composed of oxygen and an inert gas. For example, the water vapor atmosphere is an atmosphere having a water vapor partial pressure of 10 hPa or more, and an inert gas coexists with the water vapor in the atmosphere. Such inert gas includes nitrogen. That is, as an aspect of the water vapor atmosphere, there is an atmosphere composed of water vapor and an inert gas. Furthermore, the oxidizing atmosphere may be an atmosphere containing oxygen, water vapor, and an inert gas.

  The conditions to be adjusted in the heat treatment include carbon dioxide concentration, treatment temperature, treatment time, oxidizing gas partial pressure and the like. In particular, by adjusting the carbon dioxide concentration, the carbonate content in the above range can be easily obtained. More specifically, the carbon dioxide concentration in the heat treatment is preferably 300 ppm or less, and more preferably 1 ppm or less. When the carbon dioxide concentration is 300 pm or more, the above-described desorption of carbon dioxide is difficult to occur, and the carbonate in the sintered body may not be sufficiently reduced.

  The treatment temperature is preferably adjusted from a range of 200 to 550 ° C, and more preferably adjusted from a range of 250 to 500 ° C. When the processing temperature exceeds the upper limit, the magnetic properties of the rare earth magnet 1 tend to deteriorate. On the other hand, if it is less than the above lower limit value, it tends to be difficult to sufficiently reduce the carbonate content in the magnet portion 2 and it is difficult to form the desired oxide layer 4. There is also.

  The treatment time is preferably adjusted from the range of 1 minute to 24 hours, and more preferably adjusted from the range of 5 minutes to 10 hours. When the processing time exceeds the above upper limit, the magnetic properties of the rare earth magnet 1 tend to deteriorate. On the other hand, if it is less than the above lower limit value, it tends to be difficult to sufficiently reduce the carbonate content in the magnet portion 2 and it is difficult to form the desired oxide layer 4. There is also.

Through the steps as described above, the rare earth magnet 1 having the structure shown in FIG. 1 is obtained. Since the rare earth magnet 1 thus obtained has a carbonate content of 0.4 μg or less with respect to a surface area of 1 cm ² , even when it is exposed to high temperature and high humidity conditions. The amount of carbon dioxide generated from the carbonate is small, and the deterioration due to the carbon dioxide is extremely difficult to occur.

  The rare earth magnet and the manufacturing method thereof according to the preferred embodiment have been described above. However, the rare earth magnet 1 of the present invention is not limited to the above embodiment, and can be changed as appropriate without departing from the spirit of the magnet.

  For example, the rare earth magnet of the present invention may further include a predetermined protective layer on the surface of the rare earth magnet 1 described above. FIG. 3 is a diagram schematically showing a cross-sectional configuration of a rare earth magnet further provided with a protective layer. As shown in FIG. 3, the rare earth magnet 10 includes a magnet body 15 including a magnet portion 12 and an oxide layer 14 formed on the surface thereof, and a protective layer formed on the surface of the magnet body 15. 16.

  Examples of the magnet body 15 including the magnet portion 12 and the oxide layer 14 include those having the same configuration as the rare earth magnet 1 in the above-described embodiment. The protective layer 16 is not particularly limited as long as it is made of a material different from that of the magnet body 15. For example, a metal layer formed by plating or a vapor phase method, application of an alkali silicate-containing liquid, sol-gel An inorganic layer formed by a method or a vapor phase method, a resin layer formed by painting, vapor deposition polymerization method, or the like can be applied.

Examples of the metal layer include Ni, Ni-P, Cu, Zn, Cr, Sn, Al, or a combination of a plurality of layers made of these. The inorganic layer, alkali _silicates, oxides such as SiO 2, _Al 2 _{O 3,} include those made of Ti ₃ N 4, AlN nitrides such like.

  Among the above, from the viewpoint of salt water resistance and insulation, the protective layer 16 is preferably a resin layer. Examples of the resin layer include a layer made of a synthetic resin or a natural resin, a layer made of a synthetic resin is preferable, and a layer made of a thermosetting resin is more preferable.

  Thermosetting resins include phenolic resin, epoxy resin, urethane resin, silicone resin, melamine resin, epoxy melamine resin, thermosetting acrylic resin, polyimide resin, polyamideimide resin, polyparaxylylene resin, polyurea resin, epoxy A silicone resin, an acrylic silicone resin, etc. are mentioned. Moreover, as a thermoplastic resin, the vinyl resin which uses vinyl compounds, such as acrylic acid, ethylene, styrene, vinyl chloride, vinyl acetate, as a raw material is mentioned. The resin layer made of these resins may further contain metal particles, oxide particles, carbon particles and the like.

  These resin layers can be formed by, for example, dissolving a resin in an organic solvent or the like to form a coating solution, applying the solution by a dip coating method, a spin coating method, a spray coating method, or the like and then drying it. it can. The resin layer may be formed by a chemical vapor deposition method using a resin material.

  In the rare earth magnet 10 having such a protective layer 16, for example, the rare earth magnet 1 is formed in the same manner as in the above embodiment to obtain the magnet body 15, and then the protective layer is further formed on the surface of the oxide layer 14. 16 can be obtained.

In the rare earth magnet 10 having the above-described configuration, since the carbonate content of the magnet body 15 is not more than the predetermined amount (0.4 μg / cm ² ), carbon dioxide is generated under high temperature and high humidity conditions. The amount is small and it is difficult to cause deterioration due to carbon dioxide. Further, the protective layer 16 is hardly blown out or peeled off due to desorption of carbon dioxide generated from the carbonate. Therefore, the protective effect by the protective layer 16 can be sufficiently obtained even under high temperature and high humidity, and extremely excellent corrosion resistance can be exhibited.

The rare earth magnet of the present invention may have a structure that does not necessarily have an oxide layer. For example, the rare earth magnet may be composed only of the magnet portion 2 in the rare earth magnet 1 as long as the carbonate content is a predetermined amount (0.4 μg / cm ² ) or less. Even in this case, the rare earth magnet since the content of the carbonate is less that obtained exhibits excellent corrosion resistance at high temperature and high humidity.

  The rare earth magnet may have a structure in which a protective layer is directly provided on the surface of a rare earth magnet (magnet body) composed only of the magnet portion described above. In this case, in addition to the excellent corrosion resistance of the magnet body itself, the protective layer can further improve the corrosion resistance. Further, since the swelling and peeling of the protective layer are suppressed, extremely excellent corrosion resistance can be obtained as compared with the conventional case.

  Among the rare earth magnets having the above-described configuration, from the viewpoint of obtaining good corrosion resistance, the rare earth magnet preferably has either an oxide layer or a resin layer on the surface of the magnet body, and has an oxide layer. More preferred are those having both an oxide layer and a resin layer.

EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.
[Manufacture of rare earth magnets]

Example 1
An ingot having a composition of 10.8Nd-2.5Dy-79.6Fe-1.0Co-6.1B (the number represents an atomic percentage) was produced by powder metallurgy, and this was coarsely pulverized. Thereafter, jet milling with an inert gas was performed to obtain a fine powder having an average particle size of about 3.5 μm. The obtained fine powder was filled in a mold and molded in a magnetic field. Next, after sintering in vacuum, heat treatment was performed to obtain a sintered body. The obtained sintered body was cut into a size of 10 mm × 10 mm × 2 mm and processed to obtain a magnet body.

Next, the obtained magnet body was immersed in a 2% HNO ₃ aqueous solution for 2 minutes, and then acid cleaning was performed by ultrasonic cleaning. Then, the magnet body subjected to the acid cleaning (acid treatment) is subjected to a heat treatment at 400 ° C. for 10 minutes in a nitrogen-oxygen mixed atmosphere (oxygen concentration: 21%) with a carbon dioxide concentration of 0.1 ppm or less. A rare earth magnet having an oxide layer on the surface of the element body was obtained.

(Example 2)
A rare earth magnet having an oxide layer on the surface of the magnet body was obtained in the same manner as in Example 1 except that the temperature and time conditions for the heat treatment were set at 300 ° C. for 10 minutes.

(Example 3)
A rare earth magnet having an oxide layer on the surface of the magnet body was obtained in the same manner as in Example 1 except that the heat treatment temperature and time were changed to 270 ° C. for 10 minutes.

(Comparative Example 1)
A rare earth magnet was manufactured in the same manner as in Example 1 except that acid washing and heat treatment were not performed, and a rare earth magnet consisting only of a magnet body was obtained.

(Comparative Example 2)
Except that no heat treatment was performed, a rare earth magnet was produced in the same manner as in Example 1 to obtain a rare earth magnet composed of a magnet body after acid cleaning.

(Comparative Example 3)
A rare earth magnet having an oxide layer on the surface of the magnet body was obtained in the same manner as in Example 1 except that the temperature and time conditions for the heat treatment were set at 200 ° C. for 10 minutes.

(Comparative Example 4)
A rare earth magnet having an oxide layer on the surface of the magnet body was obtained in the same manner as in Example 1 except that the temperature and time conditions for the heat treatment were set to 230 ° C. for 10 minutes.

(Examples 4-6 and Comparative Examples 5-8)
On the surfaces of the rare earth magnets obtained in Examples 1 to 3 and Comparative Examples 1 to 4, an epoxy resin was applied to a thickness of 10 μm by a spray method, followed by a curing treatment at 150 ° C. for 20 minutes. Each of the rare earth magnets having a resin layer on the surface was manufactured. In addition, the case where the rare earth magnets of Examples 1 to 3 are used corresponds to Examples 4 to 6, and the case where the rare earth magnets of Comparative Examples 1 to 4 are used corresponds to Comparative Examples 5 to 8, respectively.
[Quantification of carbonate content]

  By using the rare earth magnets of Examples 1 to 3 and Comparative Examples 1 to 4 and performing TDS (thermal desorption spectroscopy) measurement as shown below, the content of the carbonate contained in each rare earth magnet is converted to carbon dioxide. Was measured. That is, first, the rare earth magnet was heated under a temperature rising condition of 60 ° C./min with infrared rays under vacuum using a temperature programmed desorption analyzer (WA 1000 S / W, manufactured by Electronic Science Co., Ltd.). Under the present circumstances, the ion intensity | strength of the component (carbon dioxide) of the mass number (m / z) 44 was measured with the mass spectrometer (MS) among the gas isolate | separated from a rare earth magnet.

This temperature programmed desorption was performed in the temperature range of 50-600 ° C., and the ionic strength of carbon dioxide was continuously recorded as a function of the temperature from 50 ° C. to 600 ° C. Then, an integral value with respect to the temperature of the value of the ion intensity was calculated. Then, using this integral value, the total amount of carbon dioxide desorbed from each rare earth magnet was calculated from the proportional relationship with the value obtained with the standard sample (Si substrate treated with hydrofluoric acid). Then, the value of the total generation amount was divided by the total surface area (cm ² ) of the rare earth magnet 1 to calculate the carbon dioxide desorption amount per 1 cm ² of the surface area. The obtained value was defined as the content of carbonate contained in each rare earth magnet. The obtained results are shown in Table 1.

[Evaluation of corrosion resistance under high temperature and high humidity]
First, a pressure cooker test (PCT test) was performed using the rare earth magnets of Examples 1 to 6 and Comparative Examples 1 to 8, respectively. The test conditions were that the sample was left in an environment of 120 ° C., 0.2 MPa, 100% RH for 100 hours.

In this PCT test, first, the appearance change before and after the PCT test was visually observed and evaluated. That is, it was confirmed whether or not powdering was observed on the surface of the rare earth magnet, or whether or not the resin layer was peeled off in the rare earth magnet having the resin layer on the surface. Moreover, the magnetic flux of each rare earth magnet is measured before and after the PCT test, and the magnetic flux measured before the PCT test is re-magnetized after the PCT test and the measured magnetic flux decreases thereafter (magnetic flux deterioration rate (%)). Was measured. The obtained results are shown in Table 1.

From Table 1, the rare earth magnets of Examples 1 to 6 in which the carbonate content was 0.40 μg or less with respect to the surface area of 1 cm ² in terms of carbon dioxide had no change in appearance after the PCT test. It was confirmed that the magnetic flux deterioration was extremely small as compared with the rare earth magnets of Comparative Examples 1 to 8 in which the salt content was 0.4 μm / cm ² or more. From this, it was found that the rare earth magnets of Examples 1 to 6 can exhibit excellent corrosion resistance even under high temperature and high humidity conditions. In particular, it was confirmed that the rare earth magnets of Examples 4 to 6 having a resin layer on the surface had a low magnetic flux deterioration rate and extremely excellent corrosion resistance.

It is a perspective view which shows typically the rare earth magnet which concerns on embodiment. It is a figure which shows typically the cross-sectional structure along the II-II line of the rare earth magnet 1 shown in FIG. It is a figure which shows typically the cross-sectional structure of the rare earth magnet further provided with the resin layer.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Rare earth magnet, 2 ... Magnet part, 4 ... Oxide layer, 10 ... Rare earth magnet, 12 ... Magnet part, 14 ... Oxide layer, 15 ... Magnet element | base_body, 16 ... Protective layer

Claims (5)

A method for producing a rare earth magnet comprising a magnet body containing a rare earth element, a transition element and boron,
After performing the process which removes the surface part of this sintered compact with respect to the sintered compact containing rare earth elements, a transition element, and boron, the nitrogen-oxygen mixed atmosphere (21% of oxygen concentration) of carbon dioxide concentration of 0.1 ppm or less ) , A heat treatment is performed at a processing temperature of 250 to 500 ° C. to obtain a magnet body whose carbonate content is 0.4 μg or less in terms of carbon dioxide with respect to a surface area of 1 cm ² .
A method for producing a rare earth magnet. Wherein on the surface of the magnet body, the method of producing the rare-earth magnet according to claim 1, further comprising a protective layer made of a material different from that of the magnet body. The magnet body is a method of producing a rare-earth magnet according to claim 1 or 2, characterized in that an oxide layer containing the rare earth element and oxygen near the surface area. The method for producing a rare earth magnet according to any one of claims 1 to 3 , wherein the process of removing the surface portion of the sintered body is performed by acid cleaning the sintered body. . 5. The method for producing a rare earth magnet according to claim 4 , wherein the acid cleaning dissolves 5 μm or more in average thickness from the surface of the sintered body.

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