JP2005197280A - Rare earth magnet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a rare earth magnet which obtains the rare earth element magnet having sufficiently excellent corrosion resistance, and also to provide the rare earth magnet. <P>SOLUTION: The method of manufacturing the rare earth magnet includes a step of forming a protective layer containing an oxygen and/or a nitrogen near the front surface of the metal layer, by bringing a mixed chemical seed containing plasma-excited oxygen and/or the nitrogen and a rare gas into contact with the metal layer provided on the front surface of a magnet element containing the rare earth element. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a rare earth magnet and a rare earth magnet, and more particularly to a method for producing a rare earth magnet having a protective layer on the surface and the rare earth magnet.

  In recent years, so-called R—Fe—B magnets (R represents a rare earth element such as Nd) have been developed as permanent magnets having a high energy product of 25 MGOe or more. R-Fe-B magnets that are formed by high-speed rapid cooling are disclosed in Patent Document 2. However, since R-Fe-B magnets contain rare earth elements and iron that are relatively easily oxidized as main components, their corrosion resistance is relatively low, and as a result, magnets are manufactured and used. As a result, there are problems such as deterioration in performance and / or reliability of manufactured magnets being relatively low. For the purpose of improving the corrosion resistance of such R-Fe-B magnets, various protective films have been applied to the surface of the magnet body as described in, for example, Patent Documents 3 to 9 so far. Proposals to make are made.

  More specifically, for example, in Patent Document 3, R (where R is at least one of rare earth elements including Y) is intended to improve the oxidation resistance of a permanent magnet mainly composed of rare earth, boron, and iron. Species) Oxidation-resistant plating layer is coated on the surface of permanent magnet body consisting mainly of tetragonal phase with 8 to 30 atom%, B2 to 28 atom%, and B42 to 90 atom% as the main component. Permanent magnets have been proposed. Patent Document 3 discloses plating of metal or alloy having oxidation resistance such as Ni, Cu, Zn, or composite plating thereof.

  Patent Document 10 discloses that a wet oxidation method is used on the surface of a metal layer formed on the surface of a magnet body in order to improve the corrosion resistance of a permanent magnet mainly composed of rare earth, boron, and iron. The fact that a film is formed is described.

Further, in Patent Document 11, with the aim of improving the oxidation resistance of a permanent magnet mainly composed of rare earth, boron, and iron, Al ₂ O ₃ , that a protective layer made of a metal oxide such as cr ₂ O ₃ is disclosed.
JP 59-46008 A JP-A-60-9852 JP-A-60-54406 JP-A-60-63901 JP 60-63902 A Japanese Patent Laid-Open No. 61-130453 JP-A-61-166115 JP 61-166116 A JP 61-270308 A JP-A-7-302705 JP-A-61-150201

  However, the present inventors have studied in detail the conventional rare earth magnets containing the rare earth elements including those described in Patent Documents 1 to 11 described above. It was found that it does not have good corrosion resistance. That is, for example, a rare earth magnet provided with the above-described oxidation-resistant plating layer described in Patent Document 3, a rare earth magnet provided with a chromate film described in Patent Document 10, or a metal oxide described in Patent Document 11 The present inventors have found that when a salt spray test specified in JIS-C-0023 is performed on a rare earth magnet provided with a layer made of the above, corrosion is observed in the magnet body of the rare earth magnet. .

  Here, the “salt spray test” means, for example, a 5 ± 1 mass% NaCl aqueous solution (pH = 6.5 to 7.2) under a temperature condition of about 35 ° C. for 24 hours in a fine damp and dense fog state. This is done by contacting the sample and checking the corrosion state of the sample. As a factor in which corrosion is recognized in the magnet body by the salt spray test, it is considered that pinholes are generated in the protective layer (oxidation-resistant plating layer). When a pinhole is generated in the protective layer of the rare earth magnet, a corrosive substance in the atmosphere enters from the pinhole and becomes a factor that corrodes the magnet body. In particular, rare earth magnets corrode very easily due to the presence of a slight amount of corrosive substances. Therefore, conventional rare earth magnets in which corrosion is observed in the magnet body by the salt spray test are also used in actual usage environments. It cannot be said that it is necessarily excellent in corrosion resistance.

  Further, in Patent Document 10, although there is a description that a predetermined resistance is exhibited with respect to the salt spray test, it has been clarified that the corrosion resistance is not necessarily excellent in an actual use environment.

  Accordingly, the present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing a rare earth magnet for obtaining a rare earth magnet having sufficiently excellent corrosion resistance and the rare earth magnet.

  The method for producing a rare earth magnet of the present invention that solves the above-described problem is a method of mixing plasma-excited oxygen and / or nitrogen and a rare gas in a metal layer provided on the surface of a magnet body containing a rare earth element. It is characterized by having a step of forming a protective layer containing oxygen and / or nitrogen in the vicinity of the surface of the metal layer by contacting a chemical species. Here, “mixed chemical species” refers to a mixture of chemical species and molecules excited in a plasma state such as ions, electrons, excited atoms and free atoms (radicals). In addition, “metal” includes Si and B.

  Further, the method for producing a rare earth magnet of the present invention contains oxygen and / or nitrogen and a rare gas in a decompression vessel in which a base comprising a metal layer is provided on the surface of a magnet element body containing a rare earth element. The method includes a step of forming a protective layer containing oxygen and / or nitrogen in the vicinity of the surface of the metal layer by introducing the mixed gas and exciting the mixed gas with plasma.

  Furthermore, in the method for producing a rare earth magnet of the present invention, oxygen and / or nitrogen and a rare gas are contained in a decompression vessel in which a base formed by providing a metal layer on the surface of a magnet body containing a rare earth element is disposed. After introducing the mixed gas, the mixed gas is plasma-excited to form a protective layer containing oxygen and / or nitrogen in the vicinity of the surface of the metal layer.

  A rare earth magnet obtained by such a manufacturing method includes a magnet body, a metal layer formed on the surface of the magnet body, and a metal oxide and / or metal nitridation formed on the surface of the metal layer. And a protective layer containing the product. The present inventors currently consider the following factors that cause this rare earth magnet to have sufficiently excellent corrosion resistance. However, the factor is not limited to this.

  That is, in the method for producing a rare earth magnet according to the present invention, the protective layer uses oxygen and / or nitrogen (hereinafter referred to as “excited active oxygen”) activated by plasma excitation in a mixed chemical species as a raw material. I think it is formed. This excited active oxygen has a very high energy compared to oxygen atoms used in the wet oxidation method, so when forming the protective layer, the metal in the metal layer or another adjacent It is presumed to interact strongly with excited active oxygen and the like. Excited active oxygen, etc., returns to normal oxygen molecules (oxygen ions), etc. by forming a protective layer, but the metal-oxygen etc. in the protective layer or between the excited active oxygens is in a very close state. The protective layer is considered to be excellent in denseness. Therefore, it is presumed that the rare earth magnet provided with such a protective layer satisfies a sufficiently excellent corrosion resistance requirement due to the denseness of the protective layer.

  Further, among the conventional rare earth magnets, those having a protective layer made of a metal oxide cause stress in the protective layer due to the close contact with the magnet body, resulting in that It is thought that cracks are likely to occur. Furthermore, when a protective layer made of a metal oxide is formed by using a vapor deposition method such as sputtering, the protective layer has oxygen vacancies, and it is considered that pinholes are likely to occur near the oxygen vacancies. As a result, it is presumed that the rare earth magnet corrodes the magnet body relatively easily due to the entry of corrosion factors such as salt water and sulfide from cracks or pinholes generated in the protective layer.

  Moreover, since the conventional rare earth magnet provided with the chromate film as a protective layer as disclosed in Patent Document 10 forms a protective layer by a wet method, the treatment liquid penetrates into the inside through the surface irregularities. Cheap. As a result, corrosion and internal stress caused by the treatment liquid are relatively easily generated in an actual use environment in which temperature and humidity change. Therefore, such a rare earth magnet exhibits relatively excellent corrosion resistance under a mild environment, but eventually does not exhibit excellent corrosion resistance under a severe environment during actual use.

  On the other hand, the rare earth magnet obtained by the method for producing a rare earth magnet of the present invention is provided with a metal layer having excellent extensibility between the magnet element body and the protective layer, so that stress is generated inside the protective layer. hard. Furthermore, as described above, since the protective layer formed using excited active oxygen or the like hardly generates oxygen vacancies, the generation of pinholes is sufficiently suppressed. Moreover, since this manufacturing method is a dry process, the intrusion of unnecessary components such as a processing solution in the process of manufacturing a rare earth magnet is sufficiently suppressed. As a result, it is considered that the rare earth magnet is sufficiently excellent in corrosion resistance as compared with a rare earth magnet provided with a protective layer made of a metal oxide.

  Further, when a protective layer is formed by directly contacting excited activated oxygen or the like with the surface of the magnet body, the magnetic properties (coercive force, residual magnetic flux density, etc.) of the obtained rare earth magnet are There is a tendency to greatly decrease compared to this. However, the rare earth magnet obtained by the method for producing a rare earth magnet of the present invention is provided with a metal layer on the surface of the magnet body before the formation of the protective layer using excitation activated oxygen or the like. Therefore, since the protective layer can be formed without directly bringing excited activated oxygen or the like into contact with the surface of the magnet body, the above-described significant deterioration in magnetic properties tends to be sufficiently suppressed.

  As the rare gas for generating this excited active oxygen or the like, it is preferable to use Kr (krypton) because a denser protective layer can be formed. Excited active oxygen or the like is usually generated by colliding electrons with oxygen molecules or nitrogen molecules, but by colliding rare gas excited by electrons with oxygen molecules or the like, The generation efficiency can be improved. This is due to the fact that the collision cross section of rare gas with oxygen molecules and the like is much larger than that of electrons. In particular, since Kr has the same molecular size as oxygen molecules and nitrogen molecules, the collision cross section is larger than that of other rare gases, and as a result, the generation efficiency of excited active oxygen and the like is further improved. To do. Thus, it is considered that a denser protective film can be obtained when Kr is used as a rare gas.

  Further, when Kr is used, the electron temperature in the decompression vessel can be lowered as compared with the case where other rare gases are used, so that the damage to the magnet body tends to be further reduced. Also from this point of view, the corrosion resistance of the obtained rare earth magnet is further improved.

  In the method for producing a rare earth magnet of the present invention, a metal layer provided on the surface of a magnet body containing a rare earth element is brought into contact with a mixed chemical species containing oxygen and nitrogen excited by plasma. Forming a protective layer containing oxygen in the vicinity of the surface of the substrate.

  In the method for producing a rare earth magnet of the present invention, a mixed gas containing oxygen and nitrogen is introduced into a decompression vessel in which a base having a metal layer provided on the surface of a magnet body containing a rare earth element is disposed. And a step of forming a protective layer containing oxygen in the vicinity of the surface of the metal layer by plasma-exciting the mixed gas.

  Furthermore, in the method for producing a rare earth magnet of the present invention, a mixed gas containing oxygen and nitrogen is introduced into a decompression vessel in which a base comprising a metal layer is provided on the surface of a magnet element body containing a rare earth element. After that, the method has a step of forming a protective layer containing oxygen in the vicinity of the surface of the metal layer by plasma-exciting the mixed gas.

  A rare earth magnet obtained by such a manufacturing method includes a magnet body, a metal layer formed on the surface of the magnet body, and a metal oxide and / or metal nitridation formed on the surface of the metal layer. A protective layer containing the product, and the content ratio of oxygen atoms in the protective layer is larger than the content ratio of nitrogen atoms. This is because oxygen molecules are more easily plasma-excited than nitrogen molecules. This rare earth magnet is also considered to have sufficiently excellent corrosion resistance due to the same factors as the rare earth magnet described above. However, the factors are not limited to the above.

  According to the above-described method for producing a rare earth magnet of the present invention, a protective layer having sufficiently excellent denseness can be obtained, so that the thickness of the protective layer tends to be reduced. Therefore, it has sufficiently excellent corrosion resistance without affecting the magnetic properties (coercivity, residual magnetic flux density, etc.) of the rare earth magnet, and sufficiently reduces the magnetic properties of the magnet body due to the provision of the protective layer. It can also be suppressed. Furthermore, by providing sufficiently excellent corrosion resistance, it is possible to sufficiently prevent the magnetic properties of the obtained rare earth magnet from aging.

  In the method for producing a rare earth magnet of the present invention, it is preferable that plasma excitation is performed using electromagnetic waves. When a protective layer is formed using excited active oxygen or the like excited into a plasma state using electromagnetic waves as a raw material, the resulting rare earth magnet has even better corrosion resistance. This is considered to be because the denseness of the protective layer is further improved by using electromagnetic waves.

  Furthermore, when the electromagnetic wave having a frequency of 2.45 GHz is used, a rare earth magnet having much higher corrosion resistance can be obtained. This electromagnetic wave is one of so-called microwaves. In the method of manufacturing a rare earth magnet of the present invention, by using this microwave, the electron temperature is lower and the ion energy is lower than when other electromagnetic waves are used. The damage of the metal layer contained in the layer or due to ion irradiation is further suppressed. On the other hand, the generation efficiency of excited active oxygen and the like by microwaves is comparable to other electromagnetic waves. As a result, it is considered that the obtained rare earth magnet is further excellent in corrosion resistance.

  In the method for producing a rare earth magnet of the present invention, the metal layer preferably contains one or more metals selected from the group consisting of Si, Al, Ta, Ti, Zr, Hf and Nb. By providing the metal layer containing these metals, the obtained rare earth magnet has a further excellent corrosion resistance. From the same viewpoint, the metal layer preferably contains Si and / or Al, and more preferably contains Al.

  The rare earth magnet of the present invention is obtained by using the above-described method for producing a rare earth magnet of the present invention, and is sufficiently excellent in corrosion resistance. This rare earth magnet may contain a rare gas such as Kr in the protective layer. When a rare gas atom such as Kr is appropriately taken in the protective layer, the film tends to be mechanically strengthened by the rare gas atom entering the inside of the film structure. Alternatively, when a strong tensile stress is generated in the protective layer, the stress of the film tends to be relieved by the penetration of the rare gas atoms.

  In the rare earth magnet of the present invention, the thickness of the protective layer is preferably 0.5 to 100 nm, and more preferably 1.0 to 30 nm, from the viewpoint of further enhancing the corrosion resistance and ensuring sufficient magnetic properties. From the same viewpoint, the total thickness of the protective layer and the metal layer is preferably 0.1 to 20 μm, more preferably 0.3 to 10 μm. Since the protective layer or the like has a film thickness within this range, an oxide film (passive film) stronger than the natural oxide film is formed, and it is considered that the protective layer has better corrosion resistance.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the rare earth magnet for obtaining the rare earth magnet which has the sufficiently excellent corrosion resistance, and the rare earth magnet can be provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as necessary. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

  First, a rare earth magnet obtained by the method for producing a rare earth magnet according to a preferred embodiment of the present invention will be described.

  FIG. 1 is a schematic perspective view showing a rare earth magnet according to this embodiment, and FIG. 2 is a diagram schematically showing a cross section that appears when the rare earth magnet of FIG. 1 is cut along the line II. As is apparent from FIGS. 1 and 2, the rare earth magnet 100 of this embodiment includes a base body 18 composed of a magnet body 10 and a metal layer 15 formed so as to cover the entire surface of the magnet body 10, and The protective layer 20 is formed by covering the entire surface of the substrate 18.

  The magnet body 10 contains R, iron (Fe), and boron (B). R represents one or more rare earth elements, specifically, one or more selected from the group consisting of scandium (Sc), yttrium (Y) and lanthanoids belonging to Group 3 of the long-period periodic table. Indicates an element. Here, the lanthanoid is lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy). , Holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).

  The composition of the above-described elements in the magnet body 10 is preferably as described below when the magnet body 10 is manufactured by a sintering method.

  R preferably includes one or more elements of Nd, Pr, Ho, and Tb among those described above, and further includes 1 of La, Sm, Ce, Gd, Er, Eu, Tm, Yb, and Y. It is also preferable to include more than one element.

  The content ratio of R in the magnet body 10 is preferably 8 to 40 atomic% with respect to the total amount of atoms constituting the magnet body 10. When the content ratio of R is less than 8 atomic%, the crystal structure has a cubic structure having the same structure as that of α-iron. Therefore, the rare earth magnet 100 having a high coercive force (iHc) tends not to be obtained. Further, when the content ratio of R exceeds 30 atomic%, the R-rich nonmagnetic phase increases, and the residual magnetic flux density (Br) of the rare earth magnet 100 tends to decrease.

  The content ratio of Fe in the magnet body 10 is preferably 42 to 90 atomic% with respect to the total amount of atoms constituting the magnet body 10. If the Fe content is less than 42 atomic%, the Br of the rare earth magnet 100 tends to decrease, and if it exceeds 90 atomic%, the iHc of the rare earth magnet 100 tends to decrease.

  The content ratio of B in the magnet body 10 is preferably 2 to 28 atomic% with respect to the total amount of atoms constituting the magnet body 10. If the B content is less than 2 atomic%, the crystal structure has a rhombohedral structure, so the iHc of the rare earth magnet 100 tends to be insufficient. If it exceeds 28 atomic%, there are many B-rich nonmagnetic phases. Therefore, the Br of the rare earth magnet 100 tends to decrease.

  Further, the magnet body 10 may be configured by replacing part of Fe with cobalt (Co). By adopting such a configuration, the temperature characteristics tend to be improved without impairing the magnetic characteristics of the rare earth magnet 100. In this case, the content ratio of Fe and Co after substitution is preferably such that Co / (Fe + Co) is 0.5 or less on an atomic basis. If the amount of substitution of Co is larger than this, the magnetic properties of the rare earth magnet 100 tend to deteriorate.

  Furthermore, even if a part of B is replaced with one or more elements selected from the group consisting of carbon (C), phosphorus (P), sulfur (S), and copper (Cu), the magnet body 10 is configured. Good. By adopting such a configuration, the productivity of the rare earth magnet 100 is improved and the production cost tends to be reduced. In this case, the content of C, P, S and / or Cu is preferably 4 atom% or less with respect to the amount of all atoms constituting the magnet body 10. When the content of C, P, S and / or Cu is more than 4 atomic%, the magnetic properties of the rare earth magnet 100 tend to deteriorate.

  Further, from the viewpoint of improving the coercive force of the rare earth magnet 100, improving productivity, and reducing the cost, aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), bismuth ( Bi), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), antimony (Sb), germanium (Ge), tin (Sn), zirconium (Zr), nickel (Ni), silicon ( The magnet body 10 may be configured by adding one or more elements of Si), gallium (Ga), copper (Cu), and / or hafnium (Hf). In this case, it is preferable that the addition amount of the element is 10 atomic% or less with respect to the total amount of atoms constituting the magnet body 10. When the addition amount of these elements exceeds 10 atomic%, the magnetic properties of the rare earth magnet 100 tend to deteriorate.

  In the magnet body 10, oxygen (O), nitrogen (N), carbon (C), and / or calcium (Ca), etc. as unavoidable impurities are included in the amount of all atoms constituting the magnet body 10. And may be contained within a range of 3 atomic% or less.

  As shown in FIG. 3, the magnet body 10 includes a main phase 50 having a substantially tetragonal crystal structure, a rare earth-rich phase 60 containing a relatively large amount of rare earth elements, and a boron rich material containing a relatively large amount of boron. And the phase 70 is formed. The particle size of the main phase 50 which is a magnetic phase is preferably about 1 to 100 μm. The rare earth-rich phase 60 and the boron-rich phase 70 are nonmagnetic phases and exist mainly at the grain boundaries of the main phase 50. These nonmagnetic phases 60 and 70 are usually contained in the magnet body 10 by about 0.5 volume% to 50 volume%.

  The metal layer 15 improves the adhesion between the protective layer 20 and the magnet body 10 and prevents cracks in the protective layer 20 that may occur when the protective layer 20 is laminated directly on the magnet body 10. It has a function. The constituent material of the metal layer 15 is not particularly limited as long as it has the functions described above. Among them, the metal oxides, nitrides, and oxynitrides are selected from the group consisting of Si, Al, Ta, Ti, Zr, Hf, and Nb from the viewpoint of imparting better corrosion resistance to rare earth magnets. One or more metals are preferably used as the constituent material of the metal layer 10, Si and / or Al are more preferable, and Al is more preferable.

  The film thickness of the metal layer 15 functions to prevent damage to the magnet body 10 described above, improve adhesion between the protective layer 20 and the magnet body 10, and prevent cracks in the protective layer 20, and further, a rare earth magnet. There is no particular limitation as long as the magnetic characteristics of 100 are maintained in a practical range. A suitable film thickness of the metal layer 10 varies depending on the constituent material of the magnet body 10 and the metal layer 10 and cannot be uniquely determined. However, when Al is used as the constituent material of the metal layer 15, it is 0.3. It is preferable that it is about 10 micrometers.

  The protective layer 20 contains a metal oxide, a metal nitride, or a metal oxynitride as a constituent material. Those constituent materials are not particularly limited except that they contain a metal oxide, nitride or oxynitride constituting the metal layer 15 as a constituent material. Among them, from the viewpoint of imparting further excellent corrosion resistance to the protective layer 20, the metal component constituting the protective layer is one or more selected from the group consisting of Si, Al, Ta, Ti, Zr, Hf and Nb. Preferably, the metal is Si and / or Al, and more preferably Al.

  When the constituent material of the protective layer 20 is a metal oxide (hereinafter, the protective layer is referred to as “oxide layer” in this case), the protective layer 20 is made of one or more metal oxides selected from the above-described metal components. And preferred. When the protective layer 20 is composed of such a single oxide, the protective layer tends to be easily formed and the composition can be controlled, and the chemical stability tends to be higher.

The oxygen content in the oxide layer 20 is preferably less than the stoichiometric amount of oxygen in the oxide. For example, when the constituent material of the oxide layer 20 is a single oxide of aluminum oxide, this oxygen content is preferably less than 1.5 times on an atomic basis with respect to the aluminum content. In addition, when the constituent material of the oxide layer 20 is a composite oxide of titanium and zirconium, it is preferable that the oxygen content is less than twice the atomic content with respect to the total content of titanium and zirconium. Further, the oxide layer 20 is composed of titanium oxide (stoichiometric composition: TiO ₂ ) and tantalum oxide (stoichiometric composition: Ta ₂ O ₅ ), and titanium and tantalum are contained in the constituent material at n: m ( When it is contained on an atomic basis, the oxygen content is preferably less than (2n + 5m / 2) / (n + m) times on an atomic basis with respect to the total content of titanium and tantalum. When the oxygen content in the oxide layer 20 falls within this range, the corrosion resistance of the rare earth magnet 100 tends to be further improved.

  The oxygen content in the oxide layer 20 is more preferably an amount corresponding to more than 94% and less than 100% with respect to the stoichiometric amount of oxygen in the oxide constituting the oxide layer 20. If the oxygen content is an amount corresponding to 94% or less of the stoichiometric amount of oxygen in the oxide, oxygen defects are excessively present and the chemical stability tends to decrease. It is considered that a component in the atmosphere, for example, a sulfur component tends to be taken into the oxide layer as an anion component in order to replenish defects. As a result, the oxide layer 20 incorporating the sulfur component is more stabilized, but the corrosion resistance tends to be lowered. As a cause of a decrease in corrosion resistance, the sulfur component taken into the oxide layer 20 moves to the magnet body 10 or changes in the state of the oxide layer 20 from the time of film formation due to the incorporation of the sulfur component. Although generation | occurrence | production of an internal stress etc. can be considered, a factor is not limited to these.

  When the constituent material of the protective layer 20 is a metal nitride (hereinafter, the protective layer is referred to as “nitride layer” in this case), the protective layer 20 is made of one or more kinds of metal nitrides selected from the metal components described above. And preferred. When the protective layer 20 is made of such a single nitride, the protective layer tends to be easily formed and the composition can be controlled, and the chemical stability tends to be higher.

The nitrogen content in the nitride layer 20 is preferably less than the stoichiometric amount of nitrogen in the nitride. For example, when the constituent material of the nitride layer 20 is a single nitride of silicon nitride, an amorphous compound represented by SiN _x is often formed instead of Si ₃ N ₄ which is a stoichiometric composition. . In this case, since the refractive index of the nitride layer (nitride film) 20 changes depending on the film composition (the numerical value of X), the film composition can be defined by the refractive index of the nitride layer 20. The nitride layer 20 preferably has a film composition having a refractive index of 1.7 to 2.3, and more preferably 1.9 to 2.1. By adjusting the nitrogen content of the nitride layer 20 so that the refractive index of the layer is in the above numerical range, the corrosion resistance of the rare earth magnet 100 tends to be further improved.

  When the constituent material of the protective layer 20 is a metal oxynitride (hereinafter, the protective layer is referred to as “oxynitride layer” in this case), from one or more metal oxynitrides selected from the above-described metal components. Preferably configured. When the protective layer 20 is composed of such a single oxynitride, the protective layer tends to be easily formed and the composition can be controlled, and the chemical stability tends to be higher.

  The oxygen content in the oxynitride layer 20 is preferably an amount corresponding to 50 atomic% or less with respect to the total content of oxygen and nitrogen in the oxynitride layer 20. By adjusting the oxygen content in the oxynitride layer 20 to be within this range, the rare earth magnet 100 of the present embodiment has more excellent corrosion resistance.

  If there are more oxygen atoms (oxide ions) than nitrogen atoms (nitride ions) in the oxynitride layer 20, the corrosion resistance effect of the oxynitride layer 20 tends to decrease. The cause of this is not clear, but in order to maintain the electrical neutral condition in the oxynitride layer 20, the site where the metal atom (metal ion) should exist becomes a point defect (hole). An empty site can be generated. This is presumably because pinholes or the like are generated in the vicinity of the generated empty site and the denseness of the oxynitride layer 20 is lowered.

  In addition, when the number of oxygen atoms is significantly larger than that of nitrogen atoms, the oxynitride layer 20 is considered to be stabilized as an oxide structure rather than an oxynitride structure. Thus, when the oxynitride layer 20 has an oxide structure, as described above, the denseness of the layer 20 is lowered, so that the corrosion resistance effect of the layer 20 tends to be lowered. . However, the improvement factor of corrosion resistance by adjusting the content ratio of an oxygen atom and a nitrogen atom is not limited to these.

  From the viewpoint of further improving the density of the oxynitride layer, the oxygen content in the oxynitride layer 20 is 0.1 to 30 atomic% with respect to the total content of oxygen and nitrogen in the oxynitride layer 20. The amount corresponding to is more preferable. When the oxygen content is less than 0.1 atomic%, the oxynitride layer 20 is considered to be stabilized as a nitride structure rather than as an oxynitride structure. As described above, when the oxynitride layer 20 has a nitride structure as described above, the internal stress of the layer 20 increases, and as a result, the oxynitride layer 20 peels from the metal layer 15. It is estimated that it tends to be easier.

  The protective layer 20 may be crystalline, amorphous, or a mixture of these states.

  Rare earth magnets are used for line printers, starters and motors for automobiles, special motors, servo motors, disk drives for magnetic recording devices, linear actuators, voice coil motors, motors for devices, industrial motors, speakers, and nuclear magnetic resonance. Such as a diagnostic magnet. In particular, when used in an environment where oil such as an automobile motor is splashed, it is difficult to obtain a rare earth magnet having sufficiently excellent corrosion resistance if the protective layer has only oxidation resistance. Also from this point of view, the rare earth magnet 100 of the present embodiment has a sufficiently excellent corrosion resistance because it has resistance to various corrosion factor substances such as sulfide and salt water.

  The content of each constituent material such as oxygen in the protective layer 20 is EPMA (X-ray microanalyzer method), XPS (X-ray photoelectron spectroscopy), AES (Auger electron spectroscopy) or EDS (energy dispersive X-ray fluorescence spectroscopy). It can be confirmed using a known composition analysis method such as (Method). Furthermore, each layer in the rare earth magnet 100 exposed by using a known method such as etching or a cross section that appears by cutting the rare earth magnet 100 is analyzed by using the above-described composition analysis method. The composition distribution of the constituent material of each layer can be grasped.

  In the rare earth magnet 100 of the present embodiment, the thickness of the protective layer 20 is preferably 0.5 to 100 nm from the viewpoint of improving corrosion resistance and ensuring sufficient magnetic properties, and even more sufficient magnetic properties. It is more preferable in it being 1.0-30 nm from a viewpoint of ensuring.

  Next, a preferred method for manufacturing the rare earth magnet 100 of this embodiment will be described. In the preferred method of manufacturing the rare earth magnet 100 of the present embodiment, first, a base body 18 is prepared by coating the magnet body 10 with the metal layer 15, and then a protective layer 20 is formed on the surface of the base body 18. A magnet 100 is obtained. Further, the base 18 is obtained by forming the metal layer 15 on the surface of the prepared magnet body 10.

  The magnet body 10 is prepared, for example, by being manufactured by a sintering method as described below. First, a desired composition containing the elements described above is cast to obtain an ingot. Subsequently, the obtained ingot is roughly pulverized to a particle size of about 10 to 100 μm using a stamp mill or the like, and then finely pulverized to a particle size of about 0.5 to 5 μm using a ball mill or the like to obtain a powder. .

Next, the obtained powder is preferably molded in a magnetic field to obtain a molded body. In this case, the magnetic field strength in the magnetic field is preferably 10 kOe or more, and the molding pressure is preferably about 1 to 5 ton / cm ² .

  Subsequently, the obtained molded body is sintered at 1000 to 1200 ° C. for about 0.5 to 5 hours and rapidly cooled. The sintering atmosphere is preferably an inert gas atmosphere such as Ar gas. And preferably, the magnet body 10 as described above is obtained by performing heat treatment (aging treatment) at 500 to 900 ° C. for 1 to 5 hours in an inert gas atmosphere.

  In addition to the above, the magnet body 10 can be prepared by, for example, a well-known super rapid cooling method, a warm brittle processing method, a casting method, or a mechanical alloying method. Further, a commercially available magnet body 10 may be prepared.

  Next, a metal layer 15 is formed on the entire surface of the magnet body 10 to obtain a base 18 (see FIG. 4). As a method for forming the metal layer 15, any conventionally known metal film forming method can be used without any particular limitation. However, a method in which the magnet body 10 does not corrode when the metal layer 15 is formed is preferable. Examples of the method for forming the metal layer 15 include vapor deposition methods such as vacuum deposition, EB (electron beam) deposition, RF sputtering, and ion plating. Among these, the ion plating method is preferable because the entire magnet body 10 can be easily covered.

  Subsequently, the protective layer 20 is formed on the entire surface of the obtained base 18 to obtain the rare earth magnet 100. FIG. 4 shows a schematic front view of an apparatus 200 (hereinafter referred to as “protective layer forming apparatus”) 200 for forming a protective layer of a rare earth magnet according to the present embodiment. The protective layer forming apparatus 200 shown in FIG. 4 is of an ECR (Electron Cyclotron Resonance) type in which plasma excitation is usually performed using a microwave having a frequency of 2.45 GHz. The protective layer forming apparatus 200 includes a discharge chamber 240 as a decompression vessel that generates plasma, a waveguide 210 that introduces microwaves into the discharge chamber 240, and microwaves from the waveguide 210 into the discharge chamber 240. A dielectric window 220 that passes through the electrode chamber 230, an electrode coil 230 that generates a magnetic field in the discharge chamber 240, and a sample chamber 250 that is provided below the discharge chamber 240 and communicates with the discharge chamber 240. The sample chamber 250 is provided with a sample stage 260 on which the base 18 can be placed in an electrically insulated state.

  The plasma generation mechanism (plasma excitation mechanism) in the discharge chamber 240 is generally as follows. That is, when a microwave is introduced into the discharge chamber 240 in which a magnetic field is applied in the vertical direction of FIG. 5 by the electrode coil 230, electrons are influenced by the electric field rotating around the magnetic field lines extending in the vertical direction of FIG. Thus, it is accelerated downward while rotating spirally around its axis. At this time, the energy of the microwave is efficiently absorbed by the electrons by making the rotation frequency of the electric field and the frequency of the microwave coincide with each other by the optimum magnetic flux density and resonate. The electrons that have absorbed energy collide with the gas molecules and excite the gas molecules, thereby generating plasma.

  The discharge chamber 240, the sample chamber 250, and the electrode coil 230 are generated by the electrode coil 230 in the region in order to cause plasma to stably exist between the dielectric window 220 and the sample stage 260 in the discharge chamber 240. The positional relationship is such that the applied magnetic field is applied.

  The waveguide 210 is connected to a magnetron device (not shown) for generating microwaves at the opposite end of the dielectric window 220. As the waveguide 210, a waveguide of a conventionally known ECR plasma apparatus can be used. For example, a combination of a circular discharge tube and a rectangular discharge tube can be adopted.

  The discharge chamber 240 and the sample chamber 250 are connected to a vacuum pump (not shown) so that the inside of the discharge chamber 240 and the sample chamber 250 can be set to a predetermined decompression condition. Furthermore, the discharge chamber 240 and the sample chamber 250 are connected to a gas supply container (not shown) such as a gas cylinder at the tip so that a mixed gas can be introduced into the discharge chamber 240 and the sample chamber 250. The dielectric window 220 is made of quartz or alumina so that the attenuation of the microwave from the waveguide 210 can be suppressed as much as possible. Furthermore, the sample stage 260 includes a heater (not shown) so that the temperature of the base 18 can be adjusted, and a fixing member (not shown) such as an adhesive is provided so that the base 18 can be fixed. It may be.

  Next, a method for forming the protective layer 20 on the surface of the substrate 18 will be described in more detail.

  First, the base 18 prepared as described above is placed on the sample stage 260 in the sample chamber 250. Next, a magnetic field is applied to the discharge chamber 240 and the sample chamber 250 by the electrode coil 230. The magnetic flux density of this magnetic field is normally adjusted to 875G. The inside of the discharge chamber 240 and the sample chamber 250 is reduced to a predetermined pressure using a vacuum pump, and the pressure is reduced.

  Subsequently, a mixed gas containing at least two kinds of oxygen gas, nitrogen gas, and rare gas is introduced into the discharge chamber 240 and the sample chamber 250 while maintaining a predetermined pressure reduction condition.

  Specifically, when a layer made of a metal oxide is to be formed as the protective layer 20, a mixed gas consisting of oxygen gas and rare gas, or a mixed gas consisting of oxygen and nitrogen gas is introduced into the discharge chamber 240 and the sample chamber 250. Introduce. When it is desired to form a metal nitride layer as the protective layer 20, a mixed gas consisting of nitrogen gas and rare gas is introduced into the discharge chamber 240 and the sample chamber 250. Further, when it is desired to form a layer made of a metal oxynitride layer as the protective layer 20, a mixed gas consisting of oxygen gas, nitrogen gas and rare gas is introduced into the discharge chamber 240 and the sample chamber 250.

Here, the “predetermined decompression condition” differs depending on the film thickness of the target protective layer 20 and the introduction time of the microwave, and therefore cannot be uniquely determined. It is preferable in it being 0 * 10 < ^-3 > Pa-10Pa. Note that the mixed gas described above may contain a small amount of inevitable impurities.

  In addition, the content ratio of each gas component in the mixed gas may be adjusted so that the content ratio of the metal, oxygen, and / or nitrogen in the protective layer 20 becomes a desired one.

  Examples of the rare gas contained in the above mixed gas include He (helium), Ne (neon), Ar (argon), Kr (krypton), and Xe (xenon). Among these, when Kr is used. The protective layer 20 is preferred because it tends to be a denser layer. The reason for this is that Kr has the same molecular size as oxygen and nitrogen molecules, so the cross-sectional area of collision with these molecules is larger than that of other rare gases, resulting in excitation activity. It is conceivable that the generation efficiency of oxygen and the like is further improved.

  Next, a microwave having a frequency of 2.45 GHz is generated using a magnetron device, and the microwave is introduced into the discharge chamber 240 via the waveguide 210 and the dielectric window 220. Thereby, the mixed gas introduced into the discharge chamber 240 is excited into a plasma state (plasma excitation), and mixed chemical species are generated. Then, when the mixed chemical species and the metal layer 15 of the base 18 come into contact with each other, the protective layer 20 is formed in the vicinity of the surface of the metal layer 15. Here, FIG. 6 shows a schematic cross-sectional view of the vicinity of the surface of the metal layer 15 on which the protective layer 20 is formed when oxygen gas and rare gas are used as the mixed gas. According to FIG. 6, the oxygen atoms 22 form a dense layer on the surface of the metal layer 15 and also enter the thickness direction magnet body 10 side from the surface of the metal layer 15, so that the metal atoms and oxygen A mixed layer with atoms is formed. Since the protective layer 20 is in the range shown in the figure, the “surface vicinity” means a layer made of oxygen on the surface of the metal layer 15 and plasma-excited oxygen or the like can enter the metal layer 15. The area up to the depth.

  The temperature of the substrate 18 when the microwave is introduced into the discharge chamber 240 and the sample chamber 250 differs depending on the target constituent material of the protective layer 20, the constituent material of the magnet body 10, and the like. However, it is usually preferable that the temperature is 50 to 500 ° C., since the protective layer 20 can be efficiently formed without damaging the substrate 18. In addition to the internal pressures of the discharge chamber 240 and the sample chamber 250 described above, the film thickness of the protective layer 20 can be adjusted by the temperature of the substrate 18 and the microwave introduction time.

  Note that the introduction of the mixed gas and the introduction of the microwave may be performed simultaneously, or the introduction of the microwave may be performed first, and then the mixed gas may be introduced into the discharge chamber 240 and the sample chamber 250. In these cases, when the mixed gas is introduced into the discharge chamber 240 and the sample chamber 250, the protective layer 20 is formed.

  The rare earth magnet 100 according to the present embodiment obtained in this way has sufficient corrosion resistance and sufficiently suppresses deterioration of magnetic properties. In the present embodiment, the ECR type protective layer forming apparatus 200 plasma-excites the mixed gas using microwaves having a frequency of 2.45 GHz among electromagnetic waves. By using microwaves, the manufacturing method of the rare earth magnet of the present embodiment has higher energy efficiency, higher film formation rate, and higher speed compared to the case where the mixed gas is plasma-excited using other plasma generation mechanisms. The protective layer 20 can be formed with accurate film forming properties. Such high energy efficiency and high film formation speed lead to further reduction of damage to the magnet body 10 due to plasma. In addition, the high-precision film forming property enables the denser protective layer 20 to be formed. Therefore, the rare earth magnet 100 obtained by utilizing plasma excitation by microwaves is much more excellent in corrosion resistance.

  The preferred embodiments of the rare earth magnet and the manufacturing method thereof of the present invention have been described above, but the present invention is not limited to the above embodiments.

  For example, in another embodiment of the method for producing a rare earth magnet of the present invention, the surface of the metal layer may be reverse sputtered by a known method before forming the protective layer. Thereby, even if the natural oxide film is already formed on the outermost surface of the metal layer, the natural oxide film is removed to form the protective layer according to the present invention. When the protective film according to the present invention is formed on a relatively sparse natural oxide film, the natural oxide film tends to be peeled off from the metal layer. Therefore, the protective film according to the present invention formed on the natural oxide film together with the natural oxide film tends to peel off from the metal layer. The layer tends to peel easily. Since the reverse sputtering tends to prevent this, it is preferable because it provides a means for further improving the corrosion resistance of the rare earth magnet.

  Further, as a plasma excitation method, a method other than the ECR type that generates microwaves, such as a thermionic discharge type, a bipolar discharge type, a magnetic field discharge type, or an electrodeless type may be adopted. Furthermore, plasma excitation may be performed using another electromagnetic wave other than the microwave, for example, RF, helicon wave, or the like. Moreover, you may use what has frequencies, such as 8.3 GHz, other than what has a frequency of 2.45 GHz as a microwave.

  In the method for producing a rare earth magnet of the present invention, when a rare gas is contained in the mixed gas, the rare gas may be contained in the protective layer of the obtained rare earth magnet.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

(Example 1)
A sintered body having a composition of 14Nd-1Dy-7B-78Fe (numbers are atomic ratio) prepared by powder metallurgy is heat-treated at 600 ° C. for 2 hours in an argon gas atmosphere, and then 56 × 40 × 8 (mm ) And then chamfered by barrel polishing to obtain a magnet body.

Next, this magnet body was washed with an alkaline degreasing solution, then the surface was activated with a nitric acid solution, and then sufficiently washed with water. Subsequently, the magnet body was fixed on a holder in a vacuum film formation chamber, and the inside of the chamber was evacuated under reduced pressure until an ultimate vacuum of 1 × 10 ⁻³ Pa or less was obtained.

  Next, an Al metal layer was formed on the surface of the magnet body by electron beam heating vapor deposition to obtain a substrate. The film formation rate was adjusted to 2 nm / second, the film thickness to 5 μm, and the substrate temperature to 150 ° C.

  Subsequently, while maintaining the reduced pressure atmosphere, the magnet body was transported and installed in the sputtering chamber, Kr gas was introduced into the chamber, and the substrate surface was subjected to reverse sputtering for 10 minutes. The conditions were an RF power of 300 W and a Kr gas pressure of 1.0 Pa.

Next, the substrate was transferred into the chamber (sample chamber) of the protective layer forming apparatus (microwave excitation high density plasma apparatus) as described above while maintaining the reduced pressure atmosphere, and the substrate was placed on the sample stage. Then, a mixed gas of oxygen gas and Kr gas (O ₂ : Kr = 5: 95, mixed gas pressure = 100 Pa) is introduced into the chamber, microwave plasma excitation is performed, and aluminum oxide is formed on the Al metal layer. A protective layer was formed to obtain the rare earth magnet of Example 1. The plasma excitation conditions were a microwave frequency of 8.3 GHz, a discharge time of 20 minutes, and a magnet body temperature of 200 ° C.

(Comparative Example 1)
A rare earth magnet of Comparative Example 1 was obtained in the same manner as in Example 1 except that the protective layer was not formed.

<Corrosion resistance evaluation>
The obtained rare earth magnets of Example 1 and Comparative Example 1 were subjected to a 24-hour humidification high-temperature test at 120 ° C. and 0.2 × 10 ⁶ Pa in a steam atmosphere, and a 24-hour salt spray test according to JIS-C-0023. The corrosion resistance was evaluated. The appearance was inspected with the naked eye, and pass / fail was judged by the presence or absence of rusting.

  As a result, in the humidification high temperature test, no rusting was observed in the rare earth magnets of Example 1 and Comparative Example 1. In the salt spray test, rusting was not observed for the rare earth magnet of Example 1, but rusting was observed for the rare earth magnet of Comparative Example 1.

  Furthermore, after performing the said corrosion-resistance evaluation test, the state of the protective layer was confirmed by cross-sectional observation of the protective layer using the scanning electron microscope (SEM). As a result, for both rare earth magnets of Example 1 and Comparative Example 1, it was confirmed that an oxide film was formed on the surface of the Al metal layer.

It is a schematic perspective view which shows the rare earth magnet obtained by the manufacturing method of the rare earth magnet which concerns on embodiment of this invention. It is a schematic sectional drawing which shows the rare earth magnet obtained by the manufacturing method of the rare earth magnet which concerns on embodiment of this invention. It is a model enlarged view which shows the phase structure of a R-Fe-B type magnet. It is a schematic sectional drawing which shows the base | substrate obtained by the middle process of the manufacturing method of the rare earth magnet which concerns on embodiment of this invention. It is a front schematic diagram of the protective layer forming apparatus used for the manufacturing method of the rare earth magnet which concerns on embodiment of this invention. It is a partial expanded section schematic diagram of the rare earth magnet obtained by the manufacturing method of the rare earth magnet concerning the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Magnet body, 15 ... Metal layer, 18 ... Base | substrate, 20 ... Protective layer, 100 ... Rare earth magnet, 200 ... Protective layer formation apparatus.

Claims (19)

  By bringing mixed chemical species containing plasma-excited oxygen and / or nitrogen and a rare gas into contact with the metal layer provided on the surface of the magnet body containing the rare earth element, the vicinity of the surface of the metal layer And a step of forming a protective layer containing oxygen and / or nitrogen.   A mixed gas containing oxygen and / or nitrogen and a rare gas is introduced into a decompression vessel in which a base formed by providing a metal layer on the surface of a magnet body containing a rare earth element is introduced, and the mixed gas is converted into plasma. And a step of forming a protective layer containing oxygen and / or nitrogen in the vicinity of the surface of the metal layer by excitation.   After introducing a mixed gas containing oxygen and / or nitrogen and a rare gas into a vacuum vessel in which a base body provided with a metal layer is provided on the surface of a magnet body containing a rare earth element, the mixed gas is introduced. And a step of forming a protective layer containing oxygen and / or nitrogen in the vicinity of the surface of the metal layer by plasma excitation.   The method for producing a rare earth magnet according to any one of claims 1 to 3, wherein Kr is used as the rare gas.   Oxygen is contained in the vicinity of the surface of the metal layer by bringing a mixed chemical species containing oxygen and nitrogen excited by plasma into contact with the metal layer provided on the surface of the magnet body containing the rare earth element. And a step of forming a protective layer.   By introducing a mixed gas containing oxygen and nitrogen into a decompression vessel in which a base body provided with a metal layer on the surface of a magnet body containing a rare earth element is disposed, and plasma-exciting the mixed gas, And a step of forming a protective layer containing oxygen in the vicinity of the surface of the metal layer.   By introducing a mixed gas containing oxygen and nitrogen into a vacuum container in which a base body provided with a metal layer on the surface of a magnet body containing a rare earth element is disposed, and then plasma-exciting the mixed gas And a step of forming a protective layer containing oxygen in the vicinity of the surface of the metal layer.   The method for producing a rare earth magnet according to any one of claims 1 to 7, wherein the plasma excitation is performed using electromagnetic waves.   The method for producing a rare earth magnet according to claim 8, wherein the electromagnetic wave having a frequency of 2.45 GHz is used.   10. The metal layer according to claim 1, wherein the metal layer contains one or more metals selected from the group consisting of Si, Al, Ta, Ti, Zr, Hf, and Nb. A method for producing a rare earth magnet.   The method for producing a rare earth magnet according to any one of claims 1 to 9, wherein the metal layer contains Si and / or Al.   The method for producing a rare earth magnet according to claim 1, wherein the metal layer contains Al. A metal layer provided on the surface of a magnet body containing a rare earth element;
A protective layer containing oxygen and / or nitrogen in the vicinity of the surface of the metal layer,
A rare earth magnet, wherein at least the protective layer contains a rare gas atom.   The rare earth magnet according to claim 13, wherein the protective layer contains Kr atoms.   The rare earth magnet according to claim 13 or 14, wherein the protective layer has a thickness of 0.5 to 100 nm.   The rare earth magnet according to any one of claims 13 to 15, wherein a total thickness of the protective layer and the metal layer is 0.1 to 20 µm.   The said metal layer contains 1 or more types of metals chosen from the group which consists of Si, Al, Ta, Ti, Zr, Hf, and Nb, As described in any one of Claims 13-16 characterized by the above-mentioned. Rare earth magnet.   The rare earth magnet according to any one of claims 13 to 17, wherein the metal layer contains Si and / or Al. The rare earth magnet according to claim 13, wherein the metal layer contains Al.

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