JP2005260098A - Rare earth magnet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare earth magnet which is superior in corrosion resistance and can obtain a superior magnetic characteristic and to provide a manufacturing method of the magnet. <P>SOLUTION: The magnet has a magnet element assembly 11 including a rare earth element and a protection film 12 formed in the magnet element assembly 11. The protection film 12 is composed of a semiconductor and has a Schottky barrier with the magnet element assembly 11. Thus, discharge of electrons from the magnet element assembly 11 is suppressed and corrosion is suppressed. An oxide semiconductor is desirable as the semiconductor constituting the protection film 12, and thickness is desirable to be less than 5 μm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rare earth magnet having a magnet body containing a rare earth element and a protective film provided on the magnet body, and a method for manufacturing the same.

As rare earth magnets, for example, Sm—Co ₅ series, Sm ₂ —Co ₁₇ series, Sm—Fe—N series, or R—Fe—B series (R represents a rare earth element) are known and have high performance. It is used as a permanent magnet. Among these, the R—Fe—B system mainly uses neodymium (Nd), which is more abundant than samarium (Sm) as a rare earth element and is relatively inexpensive, and iron (Fe) is also inexpensive. In particular, it has attracted attention because it has a magnetic performance equivalent to or better than that of the Sm—Co system.

  However, since this R—Fe—B rare earth magnet contains rare earth elements that are easily oxidized and iron as main components, the corrosion resistance is relatively low, and degradation and variations in performance are problems.

In order to improve the low corrosion resistance of such rare earth magnets, it has been proposed to form a protective film made of an oxidation-resistant metal or the like on the surface (for example, see Patent Documents 1 to 7). .)
JP-A-60-54406 JP-A-60-63901 JP 60-63902 A JP 61-13453 A JP-A-61-166115 JP 61-166116 A JP 61-270308 A

  However, although these protective films certainly improve the corrosion resistance of rare earth magnets, further improvements have been demanded. For example, the metal or alloy protective film disclosed in Patent Document 1 does not pass the salt spray test, and it is difficult to obtain sufficient corrosion resistance.

  In addition, since the R—Fe—B rare earth magnet mainly includes a main phase, a rare earth-rich phase, and a boron-rich phase, when a protective film is formed using, for example, an acidic aqueous solution, redox reduction is performed. The rare earth-rich phase with a remarkably low potential forms a local battery with the main phase or boron-rich phase and elutes. Since the rare earth-rich phase exists at the grain boundary of the main phase, the elution of the rare earth-rich phase causes the R—Fe—B rare earth magnet to become grain boundary corrosion. It is difficult to completely cover this corroded portion. For example, even with nickel electroplating, a film thickness of 10 μm or more is required. Therefore, it is desirable that the thickness of the protective film is as thin as possible so as not to deteriorate the magnetic characteristics. However, if the film thickness is insufficient, pinholes are formed in the protective film, and sufficient corrosion resistance cannot be obtained. There was also a problem that it was difficult to reduce the thickness.

  Furthermore, for practical use, it is also desired that mass production is possible at low cost.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a rare earth magnet having excellent corrosion resistance and excellent magnetic properties and a method for producing the same.

  The rare earth magnet according to the present invention includes a magnet body containing a rare earth element and a protective film provided on the magnet body and having a Schottky barrier between the magnet body.

  The protective film is silicon (Si), boron (B), germanium (Ge), aluminum (Al), gallium (Ga), indium (In), tin (Sn), lead (Pb), bismuth (Bi). , Titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron, cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), zirconium ( Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), lanthanum ( La), phosphorus (P), sulfur (S), arsenic (As), selenium (Se), oxygen (O) and nitrogen (N), one or more of the group consisting of It is preferably made of a semiconductor including element, for example, an oxide semiconductor. The protective film is preferably made of an amorphous semiconductor, and the thickness of the protective film is preferably less than 5 μm.

  In the rare earth magnet according to the present invention, since a protective film having a Schottky barrier is provided between the magnet body and the energy exceeding the Schottky barrier is not applied, electrons are not emitted from the magnet body. Corrosion of the magnet body is caused by electrons being emitted to the outside and being oxidized, so that emission of electrons is suppressed by the Schottky barrier, and corrosion is suppressed.

  In the method for producing a rare earth magnet according to the present invention, a protective film having a Schottky barrier is formed on a magnet body containing a rare earth element by a chemical vapor deposition (CVD) method. It includes a process.

  For example, alkoxide is preferably used as a raw material for forming the protective film.

  According to the rare earth magnet of the present invention, since the protective film having the Schottky barrier is provided between the magnet body, it is possible to suppress the emission of electrons from the magnet body and improve the corrosion resistance. be able to. In addition, the thickness of the protective film can be reduced, and high magnetic characteristics can be obtained.

  In particular, if the protective film is made of an amorphous semiconductor, since there is no grain boundary, the homogeneity can be improved and higher corrosion resistance can be obtained. Also, the film thickness can be made thinner.

  According to the method of manufacturing a rare earth magnet according to the present invention, since a chemical vapor deposition method is used, a thin and good protective film can be formed easily and inexpensively.

  Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 1 shows a configuration of a rare earth magnet according to an embodiment of the present invention. This rare earth magnet has a magnet body 11 containing a rare earth element and a protective film 12 provided on the magnet body 11.

  The magnet body 11 is composed of a permanent magnet including a transition metal element and a rare earth element. Rare earth elements are yttrium (Y) and lanthanoid lanthanum, cerium (Ce), praseodymium (Pr), neodymium, promethium (Pm), samarium, europium (Eu), gadolinium belonging to group 3 of the long-period periodic table It is a general term for 16 elements of (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

  As a permanent magnet which comprises the magnet element | base_body 11, the thing containing 1 or more types of rare earth elements, iron, and a boron is mentioned, for example. The magnet body 11 has a main phase having a substantially tetragonal crystal structure, a rare earth-rich phase, and a boron-rich phase. The particle size of the main phase is preferably 100 μm or less. The rare earth-rich phase and the boron-rich phase are nonmagnetic phases and exist mainly at the grain boundaries of the main phase. The nonmagnetic phase is usually contained in an amount of 0.5% to 50% by volume.

  As the rare earth element, for example, at least one of neodymium, dysprosium, praseodymium, and terbium is preferably included.

  The rare earth element content is preferably 8 atomic% to 40 atomic%. If it is less than 8 atomic%, since the crystal structure becomes the same cubic structure as α-iron, a high coercive force (iHc) cannot be obtained, and if it exceeds 40 atomic%, there are many rare earth-rich nonmagnetic phases. This is because the residual magnetic flux density (Br) decreases.

  The iron content is preferably 42 atom% to 90 atom%. This is because if the iron content is less than 42 atomic%, the residual magnetic flux density decreases, and if it exceeds 90 atomic%, the coercive force decreases.

  The boron content is preferably 2 to 28 atomic%. If the boron content is less than 2 atomic%, the rhombohedral structure is formed, so that the coercive force is insufficient. If the boron content exceeds 28 atomic%, the boron-rich nonmagnetic phase increases and the residual magnetic flux density decreases.

A part of iron may be replaced with cobalt. This is because the temperature characteristics can be improved without impairing the magnetic characteristics. In this case, the substitution amount of cobalt is preferably in the range where x is 0.5 or less in terms of atomic ratio in terms of Fe _1-x Co _x . This is because if the substitution amount is larger than this, the magnetic characteristics are deteriorated.

  A part of boron may be substituted with at least one of carbon (C), phosphorus, sulfur, and copper. This is because productivity can be improved and costs can be reduced. In this case, the carbon, phosphorus, sulfur and copper contents are preferably 4 atomic% or less. This is because if it exceeds the above range, the magnetic properties will deteriorate.

  Furthermore, aluminum, titanium, vanadium, chromium, manganese, bismuth, niobium, tantalum, molybdenum, tungsten, antimony (Sb), germanium, tin, zirconium are used to improve coercivity, improve productivity, and reduce costs. One or more of nickel, silicon, gallium, copper or hafnium may be added. In this case, the total addition amount is preferably 10 atomic% or less of the total. This is because if it exceeds the above range, the magnetic characteristics will be deteriorated.

  In addition, as an unavoidable impurity, oxygen, nitrogen, carbon, calcium, or the like may be contained within a range of 3 atomic% or less.

Examples of the permanent magnet constituting the magnet body 11 include those containing one or more rare earth elements and cobalt, or those containing one or more rare earth elements, iron, and nitrogen. It is done. Specifically, for example, those containing samarium and cobalt such as Sm—Co ₅ or Sm ₂ —Co ₁₇ (numbers are atomic ratios), or neodymium and iron such as Nd—Fe—B The thing containing boron is mentioned.

  The protective film 12 is made of, for example, a semiconductor, and has a Schottky barrier between the protective film 12 and the magnet body 11. Thereby, it can suppress that an electron is discharge | released from the magnet element | base_body 11, and can suppress corrosion.

  Examples of the semiconductor constituting the protective film 12 include silicon, boron, germanium, aluminum, gallium, indium, tin, lead, bismuth, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, cadmium, Containing one or more of the group consisting of zirconium, niobium, molybdenum, hafnium, tantalum, tungsten, magnesium, calcium, strontium, barium, lanthanum, phosphorus, sulfur, arsenic, selenium, oxygen and nitrogen as constituent elements Things.

  Specifically, for example, a simple semiconductor such as a simple substance of silicon (Si), a simple substance of boron, or a simple substance of germanium, gallium arsenide (GaAs), indium phosphide (InP), cadmium sulfide (CdS), zinc sulfide (ZnS). , Strontium sulfide (SrS), or a compound semiconductor such as zinc selenide (ZnSe), an oxide semiconductor, a nitride semiconductor, or an oxynitride semiconductor. Note that an oxide, a nitride, or an oxynitride generally becomes a semiconductor when a cation or an anion slightly deviates from the stoichiometric composition due to a Schottky defect or a Frenkel defect.

  Among these, an oxide semiconductor, a nitride semiconductor, or an oxynitride semiconductor is preferable because a favorable thin film can be formed easily and inexpensively, and an oxide semiconductor is particularly preferable.

Examples of the oxide semiconductor include silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), tin oxide (SnO ₂ ), lead oxide (PbO, PbO ₂ ), bismuth oxide (Bi ₂ O ₃ ), and oxidation. Titanium (TiO ₂ ), vanadium oxide (V ₂ O ₅ ), chromium oxide (Cr ₂ O ₃ ), manganese oxide (MnO ₂ , Mn ₂ O ₃ ), iron oxide (FeO, Fe ₂ O ₃ ), cobalt oxide ( Co ₃ O ₄ , CoO), nickel oxide (NiO), copper oxide (Cu ₂ O), zinc oxide (ZnO), zirconium oxide (ZrO ₂ ), niobium oxide (Nb ₂ O ₅ ), molybdenum oxide (MoO ₃ ) , hafnium oxide (HfO _2), tantalum oxide (Ta ₂ O _5), tungsten oxide (WO _3), magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), oxide Helium (BaO), or lanthanum oxide (La ₂ O ₃₎ can be mentioned. Note that the chemical formula of the oxide semiconductor in this specification has a stoichiometric composition, and actually deviates slightly from this composition.

An example of the nitride semiconductor is silicon nitride (Si ₃ N ₄ ). Examples of the oxynitride semiconductor include silicon oxynitride (SiO _x N _1-x (0 <x <1). Note that the chemical formulas of the nitride semiconductor and the oxynitride semiconductor shown in this specification are also stoichiometric. It is of a composition and is actually slightly deviating from this composition.

  These semiconductors may be added with various metal elements for adjusting characteristics, metalloid elements such as boron, or nonmetal elements such as phosphorus.

As a semiconductor constituting the protective film 12, a semiconductor having a large Schottky barrier formed between the magnet body 11 is preferable. For example, the case where the protective film 12 made of ZrO ₂ is formed on the magnet body 11 containing neodymium as a rare earth element will be described as an example. The work function of metal neodymium is about 2.7 eV, and the conduction of ZrO ₂ Since the band bottom level is about −1.5 eV on the basis of the vacuum level and the Fermi level is −3.1 eV, in this case, there is theoretically about 1 between the magnet body 11 and the protective film 12. A 2 eV Schottky barrier is formed. 1 eV is energy required for changing one electron by 1 V, and 1 eV = 1.602 × 10 ⁻¹⁹ J. Therefore, in order for neodymium electrons to be emitted from the magnet element 11, the potential of the magnet element 11 must be about 1.2V. Considering that the potential difference required for electrolysis of water is 1.23 V, it is considered that the potential difference is sufficient to suppress the emission of electrons. For example, the size of the Schottky barrier formed between the magnet body 11 and the protective film 12 is preferably 0.5 eV or more.

  The protective film 12 is preferably made of an amorphous semiconductor. This is because there is no grain boundary, so that a uniform protective film 12 can be obtained, higher corrosion resistance can be obtained, and the film thickness can be made thinner.

  The thickness of the protective film 12 is preferably less than 5 μm, for example, and more preferably less than 1 μm. This is because a thinner film can obtain higher magnetic characteristics.

  This rare earth magnet can be manufactured, for example, by forming the magnet body 11 and then forming the protective film 12 on the magnet body 11.

The magnet body 11 is preferably formed by a sintering method, for example, as follows. First, an alloy having a desired composition is cast to produce an ingot. Next, the obtained ingot is coarsely pulverized to a particle size of about 10 μm to 800 μm by a stamp mill or the like, and further pulverized to a powder having a particle size of about 0.5 μm to 5 μm by a ball mill or the like. Subsequently, the obtained powder is preferably shaped in a magnetic field. In this case, the magnetic field strength is preferably 10 kOe or more, and the molding pressure is preferably about ¹ Mg / cm ² to ⁵ Mg / cm ² .

  After that, the obtained molded body is sintered at 1000 ° C. to 1200 ° C. for 0.5 to 24 hours and cooled. The sintering atmosphere is preferably an inert gas atmosphere such as argon (Ar) gas or a vacuum. Furthermore, after that, it is preferable to perform an aging treatment at 500 ° C. to 900 ° C. for 1 hour to 5 hours in an inert gas atmosphere. This aging treatment may be performed a plurality of times.

  In addition, when using 2 or more types of rare earth elements, you may make it use mixtures, such as a misch metal, as a raw material. The magnet body 11 may be manufactured by a method other than the sintering method, for example, by a so-called rapid cooling method when manufacturing a bulk magnet.

  The protective film 12 is preferably formed by, for example, chemical vapor deposition. This is because a high-quality film can be easily obtained at low cost. As the chemical vapor deposition method, any one of a thermal CVD method, a plasma CVD method, a Cat-CVD method, and other methods may be used. For example, when the protective film 12 is formed of an oxide semiconductor, an alkoxide is used as a raw material. It is preferable to form by the atmospheric pressure CVD method used. This is because a good quality film can be obtained at low cost.

The alkoxide used as the raw material, _{e.g., Si (OC 2 H 5)} 4, Al (CH 3 COCHCOCH 3) 2, Al (O-i-C 3 H 7) 3, Ga (O-i-C 3 H 7 ) ₃ , In (Oi-C ₃ H ₇ ) ₃ , Sn (Oi-C ₃ H ₇ ) ₄ , Pb (Oi-C ₃ H ₇ ) ₂ , Bi (Ot-C _{5 H 11) 3, Ti (O} -i-C 3 H 7) 4, TiO (CH 3 COCHCOCH 3) 2, V (OC 2 H 5) 3, VO (CH 3 COCHCOCH 3) 2, Cr (CH 3 COCHCOCH _{3) 3, Mn (CH 3} COCHCOCH 3) 2, Fe (O-i-C 3 H 7) 3, Fe (CH 3 COCHCOCH 3) 2, Co (CH 3 COCHCOCH 3) 3, Co (CH 3 COCHCOCH 3 ) ₂ , Ni (CH ₃ COCHCOCH ₃ ) ₂ , Cu (CH ₃ COCHCOCH ₃ ) ₂ , Zn (OC ₂ H ₅ ) ₂ , Zn (CH ₃ COCHCOCH ₃ ) ₂ , Zr (Oi-C ₃ H ₇ ) ₄ , Zr (Ot-C ₄ H ₉ ) ₄ , Zr (O— _{n-C 4 H 9) 4} , Nb (OC 2 H 5) 5, Mo (OC 2 H 5) 5, Hf (O-i-C 3 H 7) 4, Ta (OC 2 H 5) 5, W (OC ₂ H ₅ ) ₅ , Mg (OC ₂ H ₅ ) ₂ , Ca (OC ₂ H ₅ ) ₂ , Sr (Oi-C ₃ H ₇ ) ₂ , Ba (OC ₂ H ₅ ) ₂ , or La And metal alkoxides such as (Oi-C ₃ H ₇ ) ₃ . The raw material is selected according to the type of semiconductor forming the protective film 12.

  Further, the protective film 12 may be formed by a method other than the chemical vapor deposition method, for example, a sol-gel method or a diffusion permeation method. In the diffusion permeation method, for example, when the protective film 12 is formed of an oxide semiconductor, a silicon or metal film is formed by sputtering or the like and then heated to 200 ° C. to 500 ° C. for air oxidation.

  Note that a pretreatment may be performed before the protective film 12 is formed. Examples of the pretreatment include activation by alkali degreasing, degreasing with an organic solvent, or subsequent acid treatment.

  In this rare earth magnet, a Schottky barrier is formed between the magnet element body 11 and the protective film 12. Therefore, electrons are not emitted from the magnet element body 11 unless energy exceeding the Schottky barrier is applied. Corrosion of the magnet body 11 occurs when electrons are released to the outside and are oxidized, so that emission of electrons is suppressed by the Schottky barrier, and corrosion is suppressed.

  As described above, according to the present embodiment, since the protective film 12 having a Schottky barrier is provided between the magnet element body 11, emission of electrons from the magnet element body 11 can be suppressed. Corrosion resistance can be improved. In addition, the thickness of the protective film 12 can be reduced, and high magnetic characteristics can be obtained.

  In particular, if the protective film 12 is made of an oxide semiconductor, a good thin film can be formed easily and inexpensively, and the characteristics can be easily improved.

  Further, if the protective film 12 is made of an amorphous semiconductor, a homogeneous film without grain boundaries can be formed, higher corrosion resistance can be obtained, and the film thickness can be made thinner. it can.

  Furthermore, if the protective film 12 is formed by a chemical vapor deposition method, the rare earth magnet according to the present embodiment can be manufactured easily and at low cost.

  Furthermore, specific examples of the present invention will be described.

  A sintered body having a composition of 14Nd-1Dy-7B-78Fe (numbers are atomic ratio) prepared by powder metallurgy is subjected to heat treatment at 600 ° C. for 2 hours in an argon atmosphere, and then 56 × 40 × 8 The magnet body 11 was obtained by processing into a size of (mm) and chamfering by barrel polishing. Next, this magnet element body 11 was washed with an alkaline degreasing solution, and then the surface was activated with a nitric acid solution and thoroughly washed with water.

Subsequently, a protective film 12 made of ZrO _{2 having} a thickness of 100 nm was formed on the surface of the magnet body 11 by atmospheric pressure CVD. At this time, the raw material used _{Zr (O-t-C 4} H 9) 4 is an alkoxide of zirconium, and Zr heated to 30 ℃ (O-t-C 4 H 9) 4, and heated to 80 ° C. Water was supplied to the magnet body 11 heated to 300 ° C. using nitrogen gas of 200 cm ³ / min as a carrier gas. Thereby, a rare earth magnet was obtained.

About the produced rare earth magnet, the humidification high temperature test for 100 hours in water vapor | steam atmosphere, 120 degreeC and 0.2 * 10 < ⁶ > Pa was done, and corrosion resistance was evaluated. When the appearance was examined with the naked eye, no rusting was observed, and sufficient corrosion resistance was obtained. That is, it was found that if the protective film 12 having a Schottky barrier is provided, excellent corrosion resistance can be obtained with a thin film thickness of about 100 nm.

  The present invention has been described with reference to the embodiments and examples. However, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the semiconductor constituting the protective film 12 has been described with specific examples, but other semiconductors may be used.

  Moreover, although the said embodiment and Example demonstrated the case where it had the magnet element | base_body 11 and the protective film 12, you may further have other components other than these. For example, another film may be provided on the protective film 12.

  The rare earth magnet according to the present invention can be suitably used for an electric vehicle motor, a hybrid vehicle motor, a robot motor, a hard disk voice coil motor, an optical pickup motor, or a spindle motor.

It is sectional drawing showing the structure of the rare earth magnet which concerns on one embodiment of this invention.

Explanation of symbols

  11 ... Magnetic body, 12 ... Protective film.

Claims (7)

A magnet body containing a rare earth element;
A rare earth magnet comprising: a protective film provided on the magnet body and having a Schottky barrier between the magnet body.   The protective film includes silicon (Si), boron (B), germanium (Ge), aluminum (Al), gallium (Ga), indium (In), tin (Sn), lead (Pb), bismuth (Bi), Titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), Zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), One or more of the group consisting of lanthanum (La), phosphorus (P), sulfur (S), arsenic (As), selenium (Se), oxygen (O) and nitrogen (N) The rare earth magnet according to claim 1, wherein the rare earth magnet is made of a semiconductor contained as a constituent element.   The rare earth magnet according to claim 1, wherein the protective film is made of an oxide semiconductor.   The rare earth magnet according to any one of claims 1 to 3, wherein the protective film is made of an amorphous semiconductor.   The rare earth magnet according to any one of claims 1 to 4, wherein the protective film has a thickness of less than 5 µm.   A method for producing a rare earth magnet, comprising a step of forming a protective film having a Schottky barrier between a rare earth element and a magnet element body by chemical vapor deposition. The method for producing a rare earth magnet according to claim 6, wherein an alkoxide is used as a raw material for forming the protective film.

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