JP2005210094A - Rare earth magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare earth magnet exhibiting sufficient corrosion resistance. <P>SOLUTION: The rare earth magnet 100 comprises a magnet element 10 containing a rare earth element, and a protective layer 20 formed on the surface of the magnet element 10 to have sulfuration resistance and containing an oxide of one kind or more of elements selected from a group of Al, Ta, Zr, Hf, Nb, Si, Ti, Mg, Cr, Ni, Ba, Mo, V, W, Zn, Sr, Fe, Bi, B, Ca, Ga, Ge, La, Pb and In. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

  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 formed on the magnet surface as described in, for example, Patent Documents 3 to 9 so far. Proposals have been made.

More specifically, for example, in Patent Document 5, R (R is at least one of rare earth elements including Y) 8 atomic% to 30 in order to improve the oxidation resistance of the R—Fe—B based magnet. An oxidation-resistant chemical conversion coating and a resin layer are sequentially laminated on the surface of a permanent magnet body mainly composed of atomic%, B2 atomic% to 28 atomic%, and Fe 42 atomic% to 90 atomic% and the main phase is a tetragonal phase. A permanent magnet has been proposed.
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

  However, the present inventors have made a detailed study of conventional rare earth magnets containing rare earth elements including those described in Patent Documents 1 to 9, and such conventional rare earth magnets are not sufficient. It was found that it does not have good corrosion resistance. That is, the rare earth magnet provided with a conventional SiO2 film or Ni plating as a protective layer is for the purpose of improving resistance to oxygen or water in the atmosphere, that is, oxidation resistance, and resistance to other substances. It became clear that it was not considered. A conventional rare earth magnet obtained only for the purpose of improving the oxidation resistance is not necessarily excellent in corrosion resistance 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 rare earth magnet having sufficiently excellent corrosion resistance.

  The rare earth magnet of the present invention that solves the above problems includes a magnet element containing a rare earth element, and Al, Ta, Zr, Hf, Nb formed on the surface of the magnet element so as to have sulfidation resistance. One or more selected from the group consisting of Si, Ti, Mg, Cr, Ni, Ba, Mo, V, W, Zn, Sr, Fe, Bi, B, Ca, Ga, Ge, La, Pb and In And a protective layer containing an oxide of the element. Here, whether or not the rare earth magnet has “sulfuration resistance” is determined by, for example, an “oil resistance test” performed as follows. That is, in the “oil resistance test”, first, a rare earth magnet is immersed in a test oil at 150 ° C. (API SL / EC ILSAC GF-3 SAE5W-30, manufactured by Nippon Oil Corporation) for 500 hours. Thereafter, the rare earth magnet is taken out from the test oil, and it is confirmed whether or not sulfur is present in the magnet body. As a result, if there is no sulfur in the magnet body that is more than the amount originally contained in the magnet body, it has “sulfuration resistance”.

  Such a rare earth magnet of the present invention can sufficiently suppress corrosion caused by sulfides even in the presence of sulfides in the environment of use. Also, Al, Ta, Zr, Hf, Nb, Si, Ti, Mg, Cr, Ni, Ba, Mo, V, W, Zn, Sr, Fe, Bi, B, Ca, Ga, Ge, La, Pb or Any oxide of In is considered to be more easily corroded by sulfide than corroded by oxygen or water (water vapor). Therefore, by sufficiently suppressing the corrosion by sulfide, it is caused by oxygen or water. Corrosion can be sufficiently suppressed. Furthermore, among rare earth magnet applications, rare earth magnets are exposed to relatively harsh atmospheres such as automobile motors, special motors, servo motors, linear actuators, voice coil motors, equipment motors, and industrial motors. In view of this, a rare earth magnet that can sufficiently suppress corrosion due to sulfide, oxygen, and water has sufficiently excellent corrosion resistance.

  In addition, since the above-described oxides are considered to have relatively high chemical stability, the protective layer using these oxides may cause defects such as pinholes during the formation process and / or use. It can be sufficiently suppressed. For this reason, it is presumed that the rare earth magnet of the present invention has sufficient corrosion resistance. However, the factor that the rare earth magnet of the present invention has sufficiently excellent corrosion resistance is not limited thereto.

  In the rare earth magnet of the present invention, the protective layer may be a single oxide layer containing an oxide, and is composed of a plurality of layers formed along the stacking direction of the magnet body and the protective layer. One or more of the layers are Al, Ta, Zr, Hf, Nb, Si, Ti, Mg, Cr, Ni, Ba, Mo, V, W, Zn, Sr, Fe, Bi, B, Ca, Ga, It may be an oxide layer containing an oxide of one or more elements selected from the group consisting of Ge, La, Pb and In. Since the protective layer is composed of a plurality of layers, the adhesion between the magnet body and the protective layer can be improved, the reaction between the magnet body and the protective layer can be suppressed, and / or the surface roughness of the magnet body can be controlled. Therefore, the rare earth magnet of the present invention can be further imparted with effects such as improvement of magnetic properties and further suppression of deterioration.

  Moreover, when the rare earth magnet of the present invention includes a plurality of protective layers, it is preferable that at least a layer formed at a position farthest from the magnet body among the protective layers is the above-described oxide layer. With such a configuration of the protective layer, the oxide layer can sufficiently prevent corrosion of other layers included in the protective layer. As a result, the rare-earth magnet of the present invention is unlikely to impair the functions possessed by those layers, so that the lifetime tends to be further increased.

  Furthermore, it is preferable that at least a layer formed adjacent to the magnet element body is made of metal among these protective layers. By making the protective layer in this configuration, the adhesion between the magnet body and the protective layer is further increased, so that corrosion that may occur when the protective layer is peeled off from the magnet body, deterioration of magnetic properties due to it, etc. Can be further suppressed.

  In the rare earth magnet of the present invention, it is preferable that the protective layer covers the entire surface of the magnet body. By providing such a configuration, the rare earth magnet of the present invention can be used for a wider range of applications.

  In the rare earth magnet of the present invention, the oxygen content of the oxide layer in the protective layer is preferably smaller than the stoichiometric amount of oxygen in the oxide. That is, for example, when the oxide used in the oxide layer is a single oxide and the metal element constituting the oxide is an n-valent oxide, the stoichiometric ratio of the metal element and oxygen in the oxide Becomes 2: n. In such a case, the oxygen content of the oxide layer in the protective layer is preferably less than n / 2 times the metal element content. When the oxide layer has such a composition, the rare earth magnet of the present invention is further excellent in corrosion resistance.

  Although the reason why the rare earth magnet of the present invention having such an oxide layer is further improved in corrosion resistance has not been clarified, the present inventors currently consider as follows. However, the factors are not limited to these. In other words, if the oxygen content in the oxide layer exceeds the stoichiometric amount of oxygen in the oxide, for example, the oxide itself becomes unstable and becomes more stable in an atmosphere where sulfide exists. Is estimated to release oxygen. As a result, oxygen defects that were not generated when the oxide layer was formed are generated, and as a result, pinholes and / or cracks are generated in the oxide layer, resulting in a decrease in corrosion resistance. Presumed to be. On the other hand, if the oxygen content in the oxide layer is less than the stoichiometric amount of oxygen in the oxide, since there is no release of oxygen as described above, pinholes and cracks are unlikely to occur. A rare earth magnet having a physical layer is considered to have sufficiently excellent corrosion resistance.

  Further, in the conventional rare earth magnet, even if an oxide layer made of an oxide is provided on the surface of the magnet body, the adhesion between the oxide layer and the magnet body is not relatively good. The oxide layer easily peeled off, and as a result, the corrosion resistance tended to decrease. On the other hand, in the rare earth magnet of the present invention provided with the oxide layer described above, the amount of oxygen contained in the oxide layer is made smaller than the stoichiometric amount, so that the oxide layer and the magnet element are closely adhered. It is considered that the corrosion resistance tends to be improved as a result.

  From the same viewpoint, it is more preferable that the oxygen content is an amount corresponding to more than 94% and less than 100% with respect to the stoichiometric amount of oxygen in the oxide. When the oxygen content is an amount corresponding to 94% or less of the stoichiometric amount of oxygen in the oxide, for example, when the rare earth magnet is placed in an atmosphere containing sulfide, the oxide layer It is presumed that the sulfur component in the atmosphere tends to be further taken into the inside. As a result, although the oxide incorporating the sulfur component is more stabilized, the corrosion resistance tends to be lowered. Corrosion resistance may be reduced by the movement of the sulfur component incorporated into the oxide layer into the magnet body or the internal stress associated with the change in the state of the oxide layer from the time of film formation due to the incorporation of the sulfur component. Occurrence, etc. can be considered, but the factors are not limited to these.

  In the rare earth magnet of the present invention, the oxide contained in the protective layer is aluminum oxide, tantalum oxide, titanium oxide, zirconium oxide, hafnium oxide, niobium oxide, silicon oxide (silica), magnesium oxide (magnesia), chromium oxide, oxidation From nickel, barium oxide, molybdenum oxide, vanadium oxide, tungsten oxide, zinc oxide, strontium oxide, iron oxide, bismuth oxide, boron oxide, calcium oxide (calcia), gallium oxide, germanium oxide, lanthanum oxide, lead oxide and indium oxide From the viewpoint of film formation and ease of composition control, it is preferable that the oxide is one kind selected from the group consisting of aluminum oxide, tantalum oxide, titanium oxide, molybdenum oxide, tungsten oxide, zirconium oxide. , Hafnium oxide and acid More If it is one oxide selected from the group consisting of niobium preferred.

  In the rare earth magnet of the present invention, when the oxide layer of the protective layer is formed adjacent to the magnet body, the first partial layer including the surface adjacent to the magnet body is opposite to the above surface. A second partial layer including a side surface, and the oxygen content ratio in the first partial layer is preferably smaller than the oxygen content ratio in the second partial layer.

  Since such an oxide layer tends to contain a large amount of metal components in the first partial layer adjacent to the magnet element body, the adhesion between the magnet element body and the protective layer tends to increase. Further, since the second partial layer has a composition (structure) as a metal oxide, it tends to have more excellent corrosion resistance.

  The oxide layer in the protective layer provided in the rare earth magnet of the present invention is preferably formed by a vapor deposition method (dry process). For example, the magnet body of the R-Fe-B rare earth magnet described above mainly includes a main phase 50, a rare earth rich phase 60 containing a relatively large amount of rare earth elements, and boron as schematically shown in FIG. And a boron-rich phase 70 containing a relatively large amount. Of these, most of the rare earth-rich phase 60 is considered to exist between the particles of the main phase 50. When the protective layer is formed on the surface of the magnet body having such a configuration using an acidic aqueous solution, the rare earth-rich phase 60 containing a relatively large amount of rare earth elements having a very low redox potential (standard electrode potential) It is considered that a local battery is formed with the main phase 50 or the boron rich phase 70 by contacting the acidic aqueous solution from the portion existing on the surface of the element body. As a result, the rare earth-rich phase 60 elutes in order from the surface existing on the surface of the magnet body, causing a phenomenon such as intergranular corrosion of the main phase 50, and the magnet body sufficiently functions as a magnet. It is estimated that it tends to disappear. Therefore, it is preferable to employ a vapor phase growth method that does not require the use of an aqueous solution when forming the protective layer.

  The rare earth magnet of the present invention preferably has a protective layer thickness of 0.01 to 20 μm and an oxide layer thickness of 0.01 from the viewpoint of further enhancing corrosion resistance and ensuring sufficient magnetic properties. It is preferable that it is ˜20 μm. From the same viewpoint, it is more preferable that the protective layer has a thickness of 0.1 to 20 μm, and it is more preferable that the oxide layer has a thickness of 0.01 to 10 μm.

  According to the present invention, it is possible to provide a rare earth magnet having sufficiently excellent corrosion resistance.

  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.

  FIG. 1 is a schematic perspective view showing a first embodiment of a rare earth magnet according to the present invention, and FIG. 2 is a diagram schematically showing a cross section that appears when the rare earth magnet of FIG. 1 is cut along line II. It is. As is apparent from FIGS. 1 and 2, the rare earth magnet 100 of the first embodiment is composed of a magnet element body 10 and a protective layer 20 formed so as to cover the entire surface of the magnet element body 10. It is.

(Magnet body)
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, lanthanoids are 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. Moreover, when the content ratio of R exceeds 40 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. 5, 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 magnet body 10 is manufactured, for example, 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.

(Protective layer)
The protective layer 20 is formed on the surface of the magnet body 10 so as to be sulfide-resistant, and is an oxide of one or more elements selected from the group consisting of Al, Ta, Zr, Hf, and Nb. Or one selected from the group consisting of Si, Ti, Mg, Cr, Ni, Ba, Mo, V, W, Zn, Sr, Fe, Bi, B, Ca, Ga, Ge, La, Pb and In Oxides of the above elements, that is, Al, Ta, Zr, Hf, Nb, Si, Ti, Mg, Cr, Ni, Ba, Mo, V, W, Zn, Sr, Fe, Bi, B, Ca, Ga And an oxide of one or more elements selected from the group consisting of Ge, La, Pb and In.

  In the present embodiment, the protective layer 20 is a single oxide layer. Therefore, the oxide layer in the present embodiment is in an exposed state, exposed to the atmosphere around the rare earth magnet 100 and adjacent to the magnet body 10.

  As described above, the protective layer 20 is formed so as to have sulfidation resistance, and more specifically, if it has been confirmed by the above-mentioned “oil resistance test” that it has sulfidation resistance. It is not necessary to perform an oil resistance test each time a rare earth magnet is formed. That is, after forming the protective layer 20 on the surface of the magnet body 10 using a specific method for forming the protective layer, the rare earth magnet 100 including the protective layer 20 is “sulphid resistant” by an oil resistance test. If it is confirmed that the rare earth magnet obtained by using the same method for forming a protective layer does not have an oil resistance test, it is recognized as having “sulfur resistance”.

  In addition, as a method of forming the rare earth magnet 100 of this embodiment so as to have sulfidation resistance, for example, the content of oxygen that is a constituent material of the protective layer 20 is adjusted, and the film thickness of the protective layer 20 is adjusted. The method of adjusting the formation method of the protective layer 20 can be mentioned, but it is not limited to these.

The constituent material of the protective layer 20 is an oxide of one or more elements selected from the group consisting of Al, Ta, Zr, Hf and Nb, or Si, Ti, Mg, Cr, Ni, Ba, Mo, V, An oxide of one or more elements selected from the group consisting of W, Zn, Sr, Fe, Bi, B, Ca, Ga, Ge, La, Pb and In, that is, Al, Ta, Zr, Hf, Nb, One or more elements selected from the group consisting of Si, Ti, Mg, Cr, Ni, Ba, Mo, V, W, Zn, Sr, Fe, Bi, B, Ca, Ga, Ge, La, Pb and In And an oxide of one or more elements selected from the group consisting of oxides. All oxides of these elements have a relatively strong resistance to corrosion by oxygen-containing compounds such as oxygen or water (water vapor). On the other hand, any of the oxides of the above elements is considered to be weaker in resistance to corrosion by sulfides such as H ₂ S compared to resistance to corrosion by oxygen or water. Therefore, the rare earth magnet 100 that has been confirmed to have sulfidation resistance through the above-described “oil resistance test” sufficiently suppresses not only corrosion by sulfides but also corrosion by oxygen or water. Can do.

  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 sufficient resistance to corrosion since it has resistance to sulfidation.

  Furthermore, Al, Ta, Zr, Hf, Nb, Si, Ti, Mg, Cr, Ni, Ba, Mo, V, W, Zn, Sr, Fe, Bi, B, Ca, Ga, Ge, La, Pb or The oxide of In is considered to have a relatively high chemical stability. Therefore, defects such as pinholes are unlikely to occur in the protective layer 20 using these metal oxides. For this reason, it is presumed that the rare earth magnet 100 of this embodiment has sufficient corrosion resistance.

  The constituent material of the protective layer (hereinafter also referred to as “oxide layer” in some cases in this embodiment) 20 of the present embodiment is made of aluminum oxide, tantalum oxide, titanium oxide, zirconium oxide, hafnium oxide, and niobium oxide. One oxide selected from the group is preferable, and silicon oxide (silica), magnesium oxide (magnesia), chromium oxide, nickel oxide, barium oxide, molybdenum oxide, vanadium oxide, tungsten oxide, zinc oxide, strontium oxide, One kind of oxide selected from the group consisting of iron oxide, bismuth oxide, boron oxide, calcium oxide (calcia), gallium oxide, germanium oxide, lanthanum oxide, lead oxide and indium oxide is also preferable. That is, the constituent material of the protective layer 20 is aluminum oxide, tantalum oxide, titanium oxide, zirconium oxide, hafnium oxide, niobium oxide, silicon oxide (silica), magnesium oxide (magnesia), chromium oxide, nickel oxide, barium oxide, molybdenum oxide. , Vanadium oxide, tungsten oxide, zinc oxide, strontium oxide, iron oxide, bismuth oxide, boron oxide, calcium oxide (calcia), gallium oxide, germanium oxide, lanthanum oxide, lead oxide and indium oxide It is preferable that the oxide is. More preferably, the oxide is one oxide selected from the group consisting of aluminum oxide, tantalum oxide, titanium oxide, molybdenum oxide, tungsten oxide, zirconium oxide, hafnium oxide, and niobium oxide. 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 protective layer 20 may be crystalline, amorphous, or a mixture of these states.

In this embodiment, it is preferable that the oxygen content in the oxide layer 20 is less than the stoichiometric amount of oxygen in the oxide. Hereinafter, the case where the constituent material of the oxide layer 20 is a single oxide of aluminum oxide will be described as an example. The “stoichiometric amount of oxygen” in aluminum oxide is the oxygen content of aluminum oxide having a stoichiometric composition, that is, Al ₂ O ₃ . 1.5 times. In the present embodiment, this oxygen content is preferably less than 1.5 times on an atomic basis with respect to the aluminum content.

When the constituent material of the oxide layer 20 is a composite oxide of titanium and zirconium, the “stoichiometric amount of oxygen” in the composite oxide is 1: 1 (atomic basis) of titanium and zirconium. ) Is the oxygen content in the composite oxide of stoichiometric composition, that is, TiZrO ₄ . Therefore, the “stoichiometric amount of oxygen” in the composite oxide is preferably doubled on an atomic basis with respect to the total content of titanium and zirconium, and the oxygen content is preferably smaller.

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 above “stoichiometric amount of oxygen” is (2n + 5m / 2) / (n + m) times on an atomic basis with respect to the total content of titanium and tantalum, and oxygen content Preferably, the amount is less than this.

  In general, not only oxides but also many compounds, particularly solid compounds, are considered to have high chemical stability (for example, corrosion hardly occurs) when they have a stoichiometric composition. However, this is considered to be applicable to bulk compound materials having a crystal structure, such as single crystals and polycrystals. In other words, if the compound is amorphous, or if the compound has a crystalline phase but is a thin film, it is not necessarily chemically high just because the compound has a stoichiometric composition. It does not always show stability. In particular, when the solid (layer) composed of the compound forms an interface with another solid (layer), and when the solid (layer) composed of the compound is sandwiched between other solids (layer), etc. It is considered that when the composition of the compound is slightly deviated rather than the stoichiometric composition, the chemical stability is relatively high.

  The same can be said for the present embodiment. At present, the present inventors consider the factors as follows. However, the factor is not limited to this.

  When the oxygen content in the oxide layer is greater than or equal to the stoichiometric amount, for example, when a rare earth magnet having the oxide layer is placed in an atmosphere in which sulfide exists, the oxide itself constituting the oxide layer is Estimated to release oxygen to become chemically unstable and more stable. As a result, oxygen defects that did not occur when the oxide layer was formed on the surface of the magnet body were generated in the oxide layer, and as a result, pinning in the oxide layer occurred. It is considered that holes and / or cracks are generated. As a result, it is estimated that the corrosion resistance of the rare earth magnet is lowered.

  On the other hand, in the rare earth magnet 100 of the present embodiment, since the oxygen content in the oxide layer 20 is less than the stoichiometric amount of oxygen in the oxide, it is considered that there is no release of oxygen as described above. . Therefore, pinholes and cracks are hardly generated in the oxide layer 20, and as a result, the rare earth magnet 100 including the oxide layer 20 is presumed to have sufficiently excellent corrosion resistance.

  The oxygen content in the oxide layer 20 in this embodiment 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.

  The oxide layer 20 has a first partial layer including a surface 32 adjacent to the magnet body 10 and a second partial layer including a surface 34 opposite to the surface 32, and the first partial layer. It is preferable that the content ratio of oxygen in the inside is smaller than the content ratio of oxygen in the second partial layer. Here, the “first partial layer” and the “second partial layer” may be layers in which the oxygen content of each partial layer is substantially constant in the thickness direction.

  By adjusting the oxygen composition distribution in the oxide layer 20 in this way, sufficient adhesion between the magnet body 10 and the protective layer 20 can be ensured even if the protective layer 20 is a single layer. . In addition, it is possible to ensure sufficiently excellent corrosion resistance of the rare earth magnet 100. That is, in the first partial layer including the surface 32 adjacent to the magnet body 10 in the oxide layer 20, the content ratio of the metal atoms constituting the metal oxide is relatively high. It tends to be possible to sufficiently increase the adhesion with the magnet body 10. On the other hand, in the second partial layer including the surface 34 of the oxide layer 20 that is in contact with the atmosphere in which a corrosion factor substance such as sulfide exists, the composition (structure) as a metal oxide by containing a relatively large amount of oxygen. Therefore, it tends to have sufficiently excellent corrosion resistance.

  In this case, another partial layer may be provided between the first partial layer and the second partial layer, and the oxygen content in the other partial layer is not particularly limited. Therefore, the oxygen content ratio in the other partial layer may be greater than that of the second partial layer, or less than that of the first partial layer, and between the oxygen content ratios of the first and second partial layers. A numerical value such as Moreover, since the suitable thickness of a 1st partial layer and a 2nd partial layer changes with the constituent materials of the magnet element | base_body 10, the oxide layer 20, etc., it is not uniquely determined.

  Furthermore, the content ratio of oxygen in the oxide layer 20 is away from the magnet body 10 from the side close to the magnet body 10 (surface 32 side adjacent to the magnet body 10) (exposed surface 34 side). It may change continuously toward the outer side of the thickness direction of the oxide layer 20, that is, toward the thickness direction. For example, the content ratio of oxygen may decrease continuously toward the outer side in the thickness direction of the oxide layer 20.

  In this case, from the viewpoint of further improving the corrosion resistance of the rare earth magnet 100, the oxygen content at and near the surface 34 in the oxide layer 20 is 94% with respect to the stoichiometric amount of oxygen constituting the oxide layer 20. It is more preferable that the amount corresponds to less than 100%. Further, on the surface of the oxide layer 20 on the side of the interface 32 with the magnet body 10 and in the vicinity thereof, the lower the oxygen content, the more the adhesiveness with the magnet body 10 can be improved.

  The content of each constituent material such as oxygen in the oxide layer 20 is EPMA (X-ray microanalyzer method), XPS (X-ray photoelectron spectroscopy), AES (Auger electron spectroscopy) or EDS (energy dispersive fluorescent X-ray). It can be confirmed using a known composition analysis method such as spectroscopy. 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 0.01 to 20 μm, and preferably 0.1 to 20 μm from the viewpoint of improving corrosion resistance and securing sufficient magnetic properties. More preferably, it is more preferably 0.3 to 10 μm from the viewpoint of production cost and the like.

  As a method for forming the protective layer (oxide layer) 20, a vapor deposition method such as a vacuum deposition method, a sputtering method, an ion plating method, a CVD method or a thermal spraying method, a liquid phase growth method such as a coating method or a solution deposition method. Alternatively, a known film forming technique such as a sol-gel method can be used. Among these, from the viewpoint of preventing the functional degradation of the rare earth magnet 100 due to elution of the constituent material of the magnet body 10 and from the viewpoint of more easily controlling the oxygen content in the oxide layer 20, the vapor phase growth method. (Dry process) is preferably used, and a reactive vacuum deposition method, a reactive sputtering method, a reactive ion plating method, a plasma CVD method, a thermal CVD method, or a Cat-CVD method is more preferable.

  Further, from the viewpoint of forming the protective layer 20 at a lower cost, it is preferable to use a method capable of uniformly forming a large area at a time. Examples of a method for forming such a protective layer 20 include a sputtering method and a CVD method. These methods can be applied by applying film forming techniques for uniformly forming a large area layer in the field of flat panel displays.

  On the other hand, in the vacuum deposition method, since the deposition source is generally a point source, there is a disadvantage in using it for forming a display that needs to form a large-area layer uniformly at a time. Since the rare earth magnet 100 is relatively small, the protective layer 20 can be easily formed as compared with the formation of a display. However, the vacuum deposition method tends to increase the cost of forming the protective layer 20 because the area that can be formed at one time is small in the first place. In the case of using the vacuum deposition method, it is necessary to increase the deposition rate in order to reduce the formation cost of the protective layer 20. However, when the film formation rate increases, coarse particles such as splash are generated, and as a result, there is a tendency that the protective layer 20 having a uniform surface cannot be obtained.

  In the ion plating method, a coating material (a constituent material of the protective film 20 in the present embodiment) is disposed as an anode and a substrate to be coated (a magnet body 10 in the present embodiment) is disposed as a cathode in a vacuum container. In the presence or absence of reactive gas, the anode is heated to make the coating material atomic, molecular, or particulate, and the ionized material is attached to the cathode-coated substrate. It is a technique.

  In the ion plating method, as a method for heating the substance to be ionized, a crucible or direct resistance heating resistance heating method, a high frequency induction heating method, an electron beam heating method, or the like can be used. Of these, the resistance heating method tends to be unsuitable for forming an inorganic compound having a low vapor pressure. In addition, although the electron beam heating method can evaporate various materials, when the film formation rate increases, coarse particles such as splash are generated, and as a result, the protective layer 20 having a uniform surface is obtained. There is no tendency.

  Furthermore, in the ion plating method, since the vapor deposition source is a point source, it is difficult to form the protective layer 20 at a relatively low cost as in the case of the vacuum vapor deposition method. Therefore, in order to form the protective layer 20 at a relatively low cost by using the ion plating method, the pressure gradient type hollow cathode plasma proposed in the September issue of 1999, page 28 of “Monthly Display”. A film forming apparatus using high-density plasma by a gun may be used. This method is a kind of ion plating method and uses a sheet-like plasma as described in JP-A-2-209475, so that a large-area layer can be uniformly formed at a relatively low cost. it can. In addition, this method has an extremely high ionization rate of the plasma gun as compared with the conventional one, so the ionization rate of the evaporated particles is high, and the film density can be kept high even when the substrate temperature is relatively low. There is a tendency that effects of improving film quality such as crystallinity and reactivity including the surface shape can be obtained.

  The film formation temperature when forming the protective layer 20 is not particularly limited, but it is preferable that the thermal history during film formation is such that the magnetic properties of the magnet body 10 are not deteriorated. From such a viewpoint, the film forming temperature is preferably 500 ° C. or lower, and more preferably 300 ° C. or lower.

  The composition of the atmospheric gas at the time of forming the protective layer 20 is not particularly limited, but when the oxygen content in the oxide layer is less than the stoichiometric amount of oxygen in the oxide, the deposition rate, the substrate It is preferable to adjust the temperature or the oxygen concentration in the atmospheric gas. For example, when aluminum oxide is used as the constituent material of the oxide layer, the oxygen content in the obtained oxide layer is Al-containing when the film formation conditions are adjusted so that the film formation rate is 0.4 nm / second or more. The amount tends to be less than 1.5 times on an atomic basis. The film forming condition here refers to, for example, the heating condition of the substance to be ionized in the case of the ion plating method described above. In addition, in the resistance heating method and the high frequency induction heating method, the input power corresponds to the film forming condition, and in the electron beam heating method, the amount of electron beam current corresponds to the film forming condition.

  Further, when forming the protective layer 20, first, after forming a metal element constituting the oxide, the amount of oxygen may be controlled by post-treatment such as a high-temperature oxidation method, a plasma oxidation method, or an anodic oxidation method.

  Next, a second embodiment of the rare earth magnet of the present invention will be described with reference to FIG. 3 which is a schematic sectional view of the rare earth magnet.

  The rare earth magnet 200 according to the second embodiment of the present invention is composed of a magnet body 10 and a protective layer 20 formed by covering the entire surface of the magnet body 10. Further, the protective layer 20 is formed by laminating the functional layer 22 and the oxide layer 24 in this order from the interface side with the magnet body 10.

  Here, the oxide layer 24 contains the same constituent material as the oxide layer 20 in the first embodiment described above. In addition, the functional layer 24 has functions for improving the adhesion between the magnet body 10 and the protective layer 20, preventing reactivity between the layers, and controlling the surface roughness of the magnet body 10. It is provided to grant.

  In the rare earth magnet 200 of the present embodiment, the oxide layer 24 is provided so as to be exposed to the atmosphere, and the functional layer 22 and the magnet body 10 are further covered with the oxide layer 24 so that the oxide layer 24 is completely removed from the atmosphere. Since it is interrupted, the rare earth magnet 200 tends to have better corrosion resistance. In particular, when the functional layer 22 is made of a material that corrodes relatively easily, if the functional layer 22 is not formed by covering the functional layer 22 with the oxide layer 24, the rare earth magnet is caused by the corrosion of the functional layer 22. Since the magnetic characteristics and the like as 200 tend to be lowered, it is more preferable to provide the oxide layer 24.

  In addition, it is preferable that the functional layer 22 is a layer made of a metal because the adhesiveness with the magnet body 10 can be further improved, and as a result, the magnetic characteristics and corrosion resistance are further improved. Examples of such metals include Al, Cr, Si, Ti, and Ni. These can be used singly or in combination of two or more.

  Alternatively, it is preferable to select a material having a thermal expansion coefficient that is relatively close to the thermal expansion coefficient of the constituent material of the magnet body 10 as the constituent material of the functional layer 22 that enhances the adhesion between the magnet body 10 and the protective layer 20. . Such a material can maintain better adhesion even when the rare earth magnet 200 is exposed to a high temperature or is subjected to a thermal shock that is repeatedly exposed to high and low temperature atmospheres. Examples of such a material include an epoxy resin and a polyimide resin in addition to the above metal, and any material having the above-described thermal expansion coefficient may be used.

The constituent material of the functional layer 22 that prevents the reaction between the magnet body 10 and the protective layer 20 includes metals such as Al, Ni, Cr, Si, and Ti, resins such as epoxy resins and polyimide resins, and inorganic oxides Inorganic compounds such as inorganic nitrides and inorganic carbides may be used. Among these, when a metal is used as a constituent material of the functional layer 22, it is preferable to form an alloy with the constituent material of the magnet body 10 so as not to deteriorate the magnetic characteristics. In the case of using the resin, at the time of deposition of the functional layer 22, H 2 _O, preferably with those which do not contain residual impurities such as O _2, also thermosetting resin shape is stable in a high temperature atmosphere Etc. are preferable.

  Further, the inorganic compound may contain a constituent material (element) of the oxide layer 24, or may be a constituent material different from the oxide layer 24. In particular, when the inorganic compound includes the constituent material of the oxide layer 24, the composition range of oxygen, carbon, and / or nitrogen included is adjusted so that the reaction with the constituent material of the magnet body 10 does not occur. Anything is acceptable.

  The constituent material of the functional layer 22 that controls the surface roughness of the magnet body 10 may be the same as the constituent material of the functional layer that improves the adhesion described above. When the surface of the magnet body 10 is rough, the coverage with the protective layer 20 is lowered, and for example, pinholes tend to be generated. Therefore, by applying the above-described material on the surface of the magnet body 10 and making the surface flat to some extent, the function of the protective layer 20 tends to be more effectively and reliably extracted.

In order to make the surface of the magnet body 10 flat to some extent using the above-described material, the functional layer 22 may be formed using the material prepared in an amorphous state or a state close thereto. For example, SiO ₂ is more preferable as such a material. SiO ₂ is suitable because it has a high fluidity on the substrate surface during film formation, and it is easy to obtain the effect of selectively covering the recesses, and it has a property that it is difficult to crystallize even when slowly cooled from a high temperature state. Can be used.

  In the rare earth magnet 200 of the present embodiment, the thickness of the protective layer 20 is preferably 0.01 to 20 μm, more preferably 0.1 to 20 μm, from the viewpoint of ensuring sufficient magnetic properties and the like. Furthermore, it is more preferable that it is 0.3-10 micrometers from viewpoints, such as production cost. The thickness of the oxide layer 24 is preferably 0.01 to 20 μm, more preferably 0.01 to 10 μm from the viewpoint of improving corrosion resistance, and 0.01 to 0.01 μm from the viewpoint of production cost. More preferably, it is 5 μm.

  Next, a third embodiment of the rare earth magnet of the present invention will be described with reference to FIG. 4 which is a schematic sectional view of the rare earth magnet.

  The rare earth magnet 300 according to the third embodiment of the present invention includes a magnet body 10 and a protective layer 20 formed so as to cover the entire surface of the magnet body 10. Furthermore, the protective layer 20 is formed by laminating the first functional layer 22, the second functional layer 26, and the oxide layer 24 in this order from the interface side with the magnet body 10.

  Among these, the constituent material of the oxide layer 24 can be the same as that in the second embodiment, and the constituent material of the first functional layer 22 is the functional layer 22 in the second embodiment. The same can be used.

  The second functional layer 26 may be made of the same material as the constituent material of the oxide layer 24 and having a different composition ratio in order to further improve the corrosion resistance effect of the protective layer 20, and the oxide is used as the constituent material. However, a metal element different from the metal element used for the oxide layer 24 may be used. The second functional layer 26 may be made of the same material as the constituent material of the first functional layer 22 and having a different composition ratio in order to further improve the function of the first functional layer 22. Further, the second functional layer 26 may have a function different from that of the oxide layer 24 and the first functional layer 22. More specifically, when a metal such as Al, Ni, Si, Ti, or Cr is used as a constituent material of the first functional layer, an oxide containing the metal element is used as a constituent material of the second functional layer 26. preferable. By doing so, the second functional layer 26 has a function of improving the adhesion (bonding) between the first functional layer 22 and the oxide layer 24.

  As mentioned above, although preferred embodiment of the rare earth magnet of this invention was described, this invention is not limited to the said embodiment. For example, the shape of the rare earth magnet according to another embodiment of the present invention is not limited to the rectangular parallelepiped as illustrated, and may have a shape corresponding to the application. Specifically, when used in a drive portion of a hard disk device or a motor for an automobile, a column shape having an arc-shaped section may be used. Moreover, when used for an industrial processing machine, a ring shape or a disk shape may be sufficient.

Moreover, as a constituent material of the magnet body 10 of another embodiment, a material containing one or more rare earth elements and Co, or a material containing one or more rare earth elements, Fe, and nitrogen (N) Etc. Specifically, for example, a material containing Sm and Co such as Sm—Co ₅ system or Sm ₂ —Co ₁₇ system (the number represents an atomic ratio), or Nd such as Nd—Fe—B system. And those containing Fe and B.

  Furthermore, the rare earth magnet of the present invention may be provided with a plurality of oxide layers, and these oxide layers may be laminated continuously, or may be laminated with another layer provided therebetween. For example, the protective layer 20 described in the first embodiment described above, in which the oxygen content decreases toward the outer side in the thickness direction of the oxide layer 20, is the content ratio of the metal element and oxygen in the oxide. A plurality of continuously stacked oxide layers, the oxygen content of one of the plurality of layers being less than the oxygen content of a layer outside the layer It may be viewed as consisting of multiple layers.

  In addition, after forming the magnet body 10 included in the rare earth magnet 200 according to the second embodiment of the present invention, a chemical conversion treatment using nitric acid or the like is performed before the functional layer 22 that reduces the surface roughness of the magnet body 10 is provided. The protrusions on the surface of the magnet body 10 may be chemically etched. Furthermore, atoms or ions accelerated using reverse sputtering or the like may collide with the surface of the magnet body 10, and the protrusions on the surface may be physically etched. In that case, the functional layer 22 may be formed by introducing a reactive gas that causes a surface reaction in plasma. Furthermore, these methods may be combined. By using these methods, it becomes possible to further reduce the surface roughness of the magnet body 10, and in combination with the formation of the functional layer 22 described above, the function of the protective layer 20 tends to be exhibited synergistically. .

  Furthermore, in the method for forming the protective layer 20, it is preferable to form the protective layer 20 using so-called barrel deposition in order to provide the protective layer 20 so as to cover the entire surface of the magnet body 10.

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

(Example 1)
First, a sintered body having a composition of 14Nd-1Dy-7B-78Fe (the number represents an atomic ratio) manufactured by powder metallurgy was subjected to heat treatment at 600 ° C. for 2 hours in an Ar gas atmosphere. Next, the sintered body after the heat treatment was cut into a size of 56 × 40 × 8 (mm), and further chamfered by barrel polishing to obtain a magnet body.

Next, the obtained magnet body was washed with an alkaline degreasing solution, and then the surface of the magnet body was activated with a 3% nitric acid aqueous solution and further thoroughly washed with water. Subsequently, the magnet body after washing with water was fixed in a vacuum film forming chamber and evacuated until a vacuum degree of 1 × 10 ⁻³ Pa or less was obtained.

Next, a protective layer containing aluminum oxide (alumina) as a constituent material was formed on the surface of the magnet body using a vacuum vapor deposition method, which is a vapor phase growth method, so as to have a film thickness of 5 μm. The protective layer was formed by irradiating aluminum oxide particles (particle diameter of about 2 to 3 mm) with an electron beam and evaporating simultaneously with dissolution. The applied voltage when generating the electron beam was 5 kV, and the current value was 200 mA. Further, during the formation of the protective layer, oxygen gas was passed through the vacuum film formation chamber at a flow rate of 1.0 sccm, and the pressure in the chamber was maintained at 1 × 10 ⁻² Pa. The surface temperature of the magnet body at this time was adjusted to 200 ° C., and the film formation rate of 0.4 nm / second was maintained. In this way, a rare earth magnet of Example 1 having an aluminum oxide protective layer with a thickness of 5 μm was obtained.

When the X-ray fluorescence analysis of the protective layer provided in the obtained rare earth magnet was performed, the oxygen content in the protective layer was an amount corresponding to 98.5% with respect to the stoichiometric amount of oxygen in Al ₂ O ₃ . Met. When the above oil resistance test was performed on the rare earth magnet of Example 1, the presence of sulfur in the magnet body was not recognized. Further, when the rare earth magnet of Example 1 was kept in a steam atmosphere, 120 ° C., and a humidified high temperature environment of 0.2 × 10 ⁶ Pa for 24 hours, the magnetic flux deterioration of the rare earth magnet was 2% of the initial value. Was less than.

(Example 2)
The aluminum oxide protective layer having a thickness of 5 μm was formed in the same manner as in Example 1 except that the protective layer was formed under the same conditions as in Example 1 except that the current value at the time of generation of the electron beam was 300 mA and the film formation rate was 0.8 nm / second. A rare earth magnet of Example 2 comprising: As a result of fluorescent X-ray analysis of the protective layer provided in the obtained rare earth magnet, the oxygen content in the protective layer was an amount corresponding to 95.5% with respect to the stoichiometric amount of oxygen in Al ₂ O ₃ . Met. When the above oil resistance test was performed on the rare earth magnet of Example 2, the presence of sulfur in the magnet body was not recognized. Further, when the rare earth magnet of Example 2 was held in a humidified high temperature environment for 24 hours under the same conditions as in Example 1, the magnetic flux deterioration of the rare earth magnet was less than 2% of the initial value. .

(Example 3)
First, a magnet body was obtained in the same manner as in Example 1. The obtained magnet body was washed with an alkaline degreasing solution, and then the surface of the magnet body was activated with a 3% nitric acid aqueous solution and further thoroughly washed with water. Subsequently, the magnet body after washing with water was disposed at a predetermined position of the atmospheric pressure thermal CVD apparatus. As an atmospheric pressure thermal CVD device, a metal alkoxide and water vapor as a vapor deposition source are introduced into a reaction furnace by a carrier gas such as nitrogen gas, and a metal oxide protective layer derived from the vapor deposition source is formed on the arranged magnet body. What was comprised so that it could do was used.

As a deposition source, Zr (Ot-C ₄ H ₉ ) ₄ and water heated to 80 ° C. were used. Example 3 comprising nitrogen gas at a flow rate of 200 cm ³ / min as a carrier gas and supplying these vapor deposition sources to a magnet body heated to 300 ° C. for 30 minutes, thereby providing a zirconium oxide protective layer having a thickness of 0.5 μm. A rare earth magnet was obtained.

When the X-ray fluorescence analysis of the protective layer provided in the obtained rare earth magnet was performed, the oxygen content in the protective layer was an amount corresponding to 99.2% with respect to the stoichiometric amount of oxygen in ZrO ₂ . It was. When the above oil resistance test was performed on the rare earth magnet of Example 3, no sulfur was found in the magnet body. Also. When the rare earth magnet of Example 3 was held in a steam atmosphere, 120 ° C., and a humidified high temperature environment of 0.2 × 10 ⁶ Pa for 24 hours, the magnetic flux deterioration of the rare earth magnet was less than 2% of the initial value. It was.

Example 4
First, the same procedure as in Example 3 was performed until the magnet body was arranged in the atmospheric pressure CVD apparatus. As the vapor deposition source, Mo (O—C ₂ H ₅ ) ₅ , Ti (Oi—C ₃ H ₇ ) ₄ and water heated to 60 ° C. were used. Nitrogen gas at a flow rate of 200 cm ³ / min is used as a carrier gas, and these vapor deposition sources are supplied to a magnet body heated to 200 ° C. for 10 minutes, whereby a mixed protective layer of molybdenum oxide and titanium oxide having a thickness of 0.01 μm. A rare earth magnet of Example 4 comprising:

When the X-ray fluorescence analysis of the protective layer with which the obtained rare earth magnet was provided, the metal atom composition in the protective layer was 0.9% for Mo and 99.1% for Ti. The oxygen content in the protective layer was an amount corresponding to 99.5% with respect to the stoichiometric amount of oxygen in MoO ₃ and TiO ₂ present in the above-described metal atom composition. When the above oil resistance test was performed on the rare earth magnet of Example 4, no sulfur was found in the magnet body. Also. When the rare earth magnet of Example 4 was held in a steam atmosphere, 120 ° C., and a humidified high temperature environment of 0.2 × 10 ⁶ Pa for 24 hours, the magnetic flux deterioration of the rare earth magnet was less than 2% of the initial value. It was.

(Example 5)
First, the same procedure as in Example 3 was performed until the magnet body was arranged in the atmospheric pressure CVD apparatus. As the evaporation source, W (O—C ₂ H ₅ ) ₅ and water heated to 80 ° C. were used. Nitrogen gas at a flow rate of 200 cm ³ / min was used as a carrier gas, and these vapor deposition sources were supplied to a magnet body heated to 300 ° C. for 30 minutes. Next, Ta (O—C ₂ H ₅ ) ₅ and water heated to 80 ° C. are used as a vapor deposition source, nitrogen gas at a flow rate of 200 cm ³ / min is used as a carrier gas, and these vapor deposition sources are heated to 200 ° C. The element body was supplied for 15 minutes. As a result, a rare earth magnet of Example 5 having a 0.03 μm thick tungsten oxide protective layer and a 0.02 μm thick tantalum protective protective layer laminated from the magnet body side was obtained.

In order to investigate the composition of the protective layer provided in the obtained rare earth magnet, a rare earth magnet obtained by laminating only the tungsten oxide protective layer on the same magnet magnet body as in Example 1 under the same conditions as above, and Rare earth magnets obtained by directly laminating only a tantalum oxide protective layer under the same conditions as described above without laminating a tungsten oxide protective layer on the magnet body obtained in the same manner as in Example 1 were prepared. When the X-ray fluorescence analysis of these rare earth magnets was performed, the oxygen content in the tungsten oxide protective layer was an amount corresponding to 98.3% with respect to the stoichiometric amount of oxygen in WO ₃ , and tantalum oxide. The oxygen content in the protective layer was an amount corresponding to 99.7% with respect to the stoichiometric amount of oxygen in Ta ₂ O ₅ . When the above oil resistance test was performed on the rare earth magnet of Example 5, no sulfur was found in the magnet body. Also. When the rare earth magnet of Example 5 was kept in a steam atmosphere, 120 ° C., and a humidified high temperature environment of 0.2 × 10 ⁶ Pa for 24 hours, the magnetic flux deterioration of the rare earth magnet was less than 2% of the initial value. It was.

(Example 6)
First, a magnet body was obtained in the same manner as in Example 1. The obtained magnet body was washed with an alkaline degreasing solution, and then the surface of the magnet body was activated with a 3% nitric acid aqueous solution and further thoroughly washed with water. Subsequently, the magnet body after washing with water was fixed in a vacuum film forming chamber and evacuated until a vacuum degree of 1 × 10 ⁻³ Pa or less was obtained. Next, a metal aluminum layer was formed on the surface of the magnet body using a vacuum vapor deposition method, which is a vapor phase growth method, so as to have a film thickness of 5 μm. The metal aluminum layer was formed by irradiating a metal aluminum vapor deposition source with an electron beam.

Subsequently, the magnet body on which the metal aluminum layer was laminated was disposed at a predetermined position in the same atmospheric pressure CVD apparatus as described above. As the evaporation source, Hf (Ot-C ₄ H ₉ ) ₄ and water heated to 60 ° C. were used. Nitrogen gas at a flow rate of 200 cm ³ / min is used as a carrier gas, and these deposition sources are supplied to a magnet body heated to 250 ° C. for 20 minutes, whereby a hafnium oxide protective layer having a thickness of 0.05 μm is formed on the metal aluminum layer. A rare earth magnet of Example 6 comprising:

When the X-ray fluorescence analysis of the protective layer provided in the obtained rare earth magnet was performed, the oxygen content in the protective layer was an amount corresponding to 98.5% with respect to the stoichiometric amount of oxygen in HfO ₂ . It was. When the above oil resistance test was performed on the rare earth magnet of Example 6, the presence of sulfur in the magnet body was not recognized. Also. When the rare earth magnet of Example 6 was kept in a steam atmosphere, 120 ° C., and a humidified high temperature environment of 0.2 × 10 ⁶ Pa for 24 hours, the magnetic flux deterioration of the rare earth magnet was less than 2% of the initial value. It was.

(Comparative Example 1)
Comparative Example was made in the same manner as in Example 1 except that the protective layer was formed under the condition that the film formation rate was 1.0 nm / second by setting 400 mA as the current value when generating the electron beam without circulating oxygen. 1 rare earth magnet was obtained. When the fluorescent X-ray analysis of the protective layer with which the obtained rare earth magnet was provided, the oxygen content in the protective layer was 93.0% with respect to the stoichiometric amount of oxygen in Al ₂ O ₃ . In addition, when the above oil resistance test was performed on the rare earth magnet of Comparative Example 1, the presence of sulfur in the magnet body was recognized. Further, when the rare earth magnet of Comparative Example 1 was held in a humidified high temperature environment for 24 hours under the same conditions as in Example 1, the magnetic flux deterioration of the rare earth magnet exceeded 5% of the initial value. there were.

(Comparative Example 2)
The conditions for forming the protective layer were the same as in Example 1 except that oxygen was circulated at a flow rate of 5.0 sccm and the current value at the time of generating the electron beam was 150 mA so that the film formation rate was 0.1 nm / second. Thus, a rare earth magnet of Comparative Example 2 was obtained. When the fluorescent X-ray analysis of the protective layer with which the obtained rare earth magnet was provided, the oxygen content in the protective layer was 115.0% with respect to the stoichiometric amount of oxygen in Al ₂ O ₃ . When the above oil resistance test was performed on the rare earth magnet of Comparative Example 2, the presence of sulfur was observed in the magnet body. Further, when the rare earth magnet of Comparative Example 1 was held in a humidified high temperature environment for 24 hours under the same conditions as in Example 1, the magnetic flux deterioration of the rare earth magnet exceeded 5% of the initial value. there were.

(Comparative Example 3)
First, the magnet body obtained in the same manner as in Example 1 was washed with an alkaline degreasing solution, and then the surface of the magnet body was activated with a 3% nitric acid aqueous solution, and further sufficiently washed with water. Subsequently, a nickel film having a thickness of 10 μm was formed on the surface of the magnet body by electroplating to form a protective layer. The electroplating method includes nickel sulfate 1.0 mol / L as the nickel source, 0.25 mol / L nickel chloride as the conductive salt, 0.6 mol / L boric acid as the pH stabilizer, and a conductivity of 58 mS. A / cm plating bath was used. The average current density during plating was 1 A / dm ² or less. When the above oil resistance test was performed on the rare earth magnet of Comparative Example 3, the presence of sulfur was observed in the magnet body. Further, when the rare earth magnet of Comparative Example 3 was held in a humidified high temperature environment for 24 hours under the same conditions as in Example 1, the magnetic flux deterioration of the rare earth magnet exceeded 5% of the initial value. there were.

(Evaluation of oil resistance test of protective layer)
In order to investigate the correlation between the oxygen content in the oxide layer as the protective layer and the sulfidation resistance (chemical stability) of the protective layer itself, the following evaluation experiment was conducted.

First, an oxide layer made of aluminum oxide whose oxygen content was variously adjusted by controlling the film formation conditions was independently formed on the substrate. In these oxide layers, O / Al was set within a range of about 1.4 to 1.7 on an atomic basis. When the oxide layer is made of stoichiometric aluminum oxide (Al ₂ O ₃ ), O / Al is 1.5 on an atomic basis. Therefore, O / Al in the oxide layer described above is set within a range of 93.333 to 113.33% on an atomic basis with respect to O / Al in Al ₂ O ₃ which is a stoichiometric composition. .

Next, an oil resistance test was performed on the oxide layer formed on the substrate. After thoroughly cleaning the substrate after the oil resistance test with acetone, the composition of the oxide layer before and after the oil resistance test was measured by fluorescent X-ray analysis. As a result, when the O / Al before the oil resistance test was 94% or less on the atomic basis with respect to O / Al in Al ₂ O _3, the sulfur component was detected in the oxide layer after the oil resistance test. In addition, when O / Al before the oil resistance test was 100% or more on an atomic basis with respect to O / Al in Al ₂ O _3, no sulfur component was detected in the oxide layer after the oil resistance test. A decrease in oxygen content was confirmed. On the other hand, when O / Al before the oil resistance test was more than 94% and less than 100% on an atomic basis with respect to O / Al in Al ₂ O ₃ , no sulfur component was detected after the oil resistance test, and O Almost no change in / Al was observed.

It is a schematic perspective view which shows the rare earth magnet of the 1st Embodiment of this invention. It is a schematic sectional drawing which shows the rare earth magnet of the 1st Embodiment of this invention. It is a schematic sectional drawing which shows the rare earth magnet of the 2nd Embodiment of this invention. It is a schematic sectional drawing which shows the rare earth magnet of the 3rd Embodiment of this invention. It is a model enlarged view which shows the phase structure of a R-Fe-B type magnet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Magnet body, 20 ... Protective layer, 100 ... Rare earth magnet.

Claims (13)

  Magnet element containing rare earth element, and Al, Ta, Zr, Hf, Nb, Si, Ti, Mg, Cr, Ni, Ba formed on the surface of the magnet element so as to have sulfidation resistance A protective layer containing an oxide of one or more elements selected from the group consisting of Mo, V, W, Zn, Sr, Fe, Bi, B, Ca, Ga, Ge, La, Pb and In. A rare earth magnet comprising:   The rare earth magnet according to claim 1, wherein the protective layer is a single oxide layer containing the oxide.   The protective layer is composed of a plurality of layers formed in the stacking direction of the magnet body and the protective layer, and one or more of the protective layers are Al, Ta, Ti, Zr, Hf, Nb. Of one or more elements selected from the group consisting of Si, Mg, Cr, Ni, Ba, Mo, V, W, Zn, Sr, Fe, Bi, B, Ca, Ga, Ge, La, Pb and In The rare earth magnet according to claim 1, wherein the rare earth magnet is an oxide layer containing an oxide.   4. The rare earth magnet according to claim 3, wherein at least a layer of the protective layer formed at a position farthest from the magnet body is the oxide layer. 5.   5. The rare earth magnet according to claim 3, wherein at least a layer formed adjacent to the magnet element body of the protective layer is made of a metal.   The rare earth magnet according to claim 1, wherein the protective layer covers the entire surface of the magnet body.   The rare earth magnet according to any one of claims 2 to 6, wherein an oxygen content in the oxide layer is less than a stoichiometric amount of oxygen in the oxide.   The rare earth magnet according to claim 7, wherein the oxygen content is an amount equivalent to more than 94% and less than 100% with respect to the stoichiometric amount of oxygen in the oxide.   The oxide is aluminum oxide, tantalum oxide, titanium oxide, zirconium oxide, hafnium oxide, niobium oxide, silicon oxide, magnesium oxide, chromium oxide, nickel oxide, barium oxide, molybdenum oxide, vanadium oxide, tungsten oxide, zinc oxide, 2. An oxide selected from the group consisting of strontium oxide, iron oxide, bismuth oxide, boron oxide, calcium oxide, gallium oxide, germanium oxide, lanthanum oxide, lead oxide and indium oxide. The rare earth magnet as described in any one of -8. The oxide layer is formed adjacent to the magnet body; and
A first partial layer including a surface adjacent to the magnet body, and a second partial layer including a surface opposite to the surface;
10. The rare earth magnet according to claim 2, wherein the content ratio of oxygen in the first partial layer is less than the content ratio of oxygen in the second partial layer.   The rare earth magnet according to claim 1, wherein the oxide layer is formed by a vapor deposition method.   The rare earth magnet according to claim 1, wherein the protective layer has a thickness of 0.01 to 20 μm. The rare earth magnet according to claim 2, wherein the oxide layer has a thickness of 0.01 to 20 μm.

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