Sintered ferrite magnets, ferrite particles, bonded magnets, and rotating electrical machines

Abstract

To provide a ferrite sintered magnet and the like, excellent in Br and squareness.SOLUTION: There is provided a magnet that is a ferrite sintered magnet containing a ferrite phase having a magnetoplumbite-type crystal structure. The ferrite sintered magnet contains at least Ca, a metal element A, a metal element R, Bi, Fe, and a metal element M. The metal element A is at least one kind of element selected from the group consisting of Sr, Ba, and Pb, the metal element R is at least one kind of element selected from the group consisting of rare earth elements including Y and essentially includes La, the metal element M is at least one kind of element selected from the group consisting of Co, Ni, Zn, Al, Cu, and Cr, and essentially includes Co, and when an atonic ratio of the metal elements is expressed by formula (1), c, a, r, b, f, and m in formula (1) satisfy the following expressions (2) to (8).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to sintered ferrite magnets, ferrite particles, bonded magnets, and rotating electric machines. [Background technology]

[0002] Ba ferrite, Sr ferrite, and Ca ferrite, which have a hexagonal crystal structure, are known as magnetic materials used in sintered ferrite magnets. The magnetoplumbite type (M type) is known as the crystal structure of such ferrites. M type ferrites are usually made of AFe 12 O 19 It is expressed by the general formula:

[0003] As such an M-type ferrite, Patent Document 1 discloses a magnet powder having a main phase of M-type ferrite in which Fe is substituted with an element M such as Zn and an element A such as Sr or Ba is substituted with an element R such as La. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-115715 Summary of the Invention [Problem to be solved by the invention]

[0005] Magnetoplumbite (M-type) ferrite is used as a magnetic material for motors, etc., and motors are required to be small and have high torque, so sintered ferrite magnets are required to have even higher magnetic properties.

[0006] Residual magnetic flux density (Br) and squareness (Hk / HcJ) are used as indicators of the magnetic properties of sintered ferrite magnets. The magnet powder disclosed in Patent Document 1 leaves room for improvement in terms of Br and squareness.

[0007] An object of one aspect of the present invention is to provide a sintered ferrite magnet or the like that is excellent in Br and squareness. [Means for solving the problem]

[0008] One aspect of the present invention is a sintered ferrite magnet containing a ferrite phase having a magnetoplumbite crystal structure, which contains at least Ca, metal element A, metal element R, Bi, Fe, and metal element M, where metal element A is at least one element selected from the group consisting of Sr, Ba, and Pb, metal element R is at least one element selected from the group consisting of rare earth elements including Y and must contain La, and metal element M is at least one element selected from the group consisting of Co, Ni, Zn, Al, Cu, and Cr and must contain Co, and when the atomic ratios of the metal elements are expressed by formula (1), c, a, r, b, f, and m in formula (1) satisfy the following formulas (2) to (8). Ca c A a R r Bi b Fe f M m (1) 0.15≦c<0.5 (2) 0.01≦a≦0.1 (3) 0.45 <r≦0.80 (4) 0.01≦b<0.1 (5) 9.35 <f<11.90 (6) 0.1≦m≦0.50 (7) c+a+r+b=1 (8)

[0009] In one embodiment, the sintered ferrite magnet may further satisfy the following formulas (3-1), (5-1), (6-1), and (7-1). 0.03≦a≦0.05 (3-1) 0.01≦b≦0.05 (5-1) 9.35 <f≦11.25 (6-1) 0.25≦m≦0.45 (7-1)

[0010] Another aspect of the present invention is a rotating electrical machine including the ferrite sintered magnet.

[0011] Still another aspect of the present invention is ferrite particles containing a ferrite phase having a magnetoplumbite-type crystal structure, which contain at least Ca, metal element A, metal element R, Bi, Fe, and metal element M, wherein metal element A is at least one element selected from the group consisting of Sr, Ba, and Pb, metal element R is at least one element selected from the group consisting of rare earth elements including Y and necessarily contains La, metal element M is at least one element selected from the group consisting of Co, Ni, Zn, Al, Cu, and Cr and necessarily contains Co, and when the atomic ratios of the metal elements are represented by formula (1), in formula (1), c, a, r, b, f, and m satisfy the following formulas (2) to (8): Ca c A a R r Bi b Fe f M m (1) 0.15 ≦ c < 0.5 (2) 0.01 ≦ a ≦ 0.1 (3) 0.45 < r ≦ 0.80 (4) 0.01 ≦ b < 0.1 (5) 9.35 < f < 11.90 (6) 0.1 ≦ m ≦ 0.50 (7) c + a + r + b = 1 (8)

[0012] Still another aspect of the present invention is a bonded magnet including the ferrite particles and a resin.

[0013] Still another aspect of the present invention is a rotating electrical machine including the bonded magnet.

Advantages of the Invention

[0014] According to one aspect of the present invention, there is provided a ferrite sintered magnet excellent in Br and rectangularity.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments.

[0017] (Ferrite Sintered Magnet and Ferrite Particles) The ferrite sintered magnet and ferrite particles according to this embodiment will be described.

[0018] The ferrite sintered magnet and ferrite particles according to this embodiment contain a ferrite phase having a magnetoplumbite-type crystal structure.

[0019] The ferrite sintered magnet and ferrite particles according to this embodiment contain at least Ca, metal element A, metal element R, Bi, Fe, and metal element M.

[0020] The metal element A is at least one element selected from the group consisting of Sr, Ba, and Pb.

[0021] The atomic ratio of Ba in the metal element A can be 50 atomic% or more, 70 atomic% or more, 90 atomic% or more, 95 atomic% or more, 97 atomic% or more, 99 atomic% or more, or 100 atomic% in order to further improve Br and rectangularity. There is no particular limitation on the ratio of atoms other than Ba in the metal element A.

[0022] The atomic ratio of Sr in the metal element A can be 50 atomic % or more, 70 atomic % or more, 90 atomic % or more, 95 atomic % or more, 97 atomic % or more, 99 atomic % or more, or even 100 atomic %, since it further improves Br and squareness. There is no particular limitation on the ratio of atoms other than Sr in the metal element A.

[0023] The metal element R is at least one element selected from the group consisting of rare earth elements containing Y, and necessarily contains La.

[0024] The rare earth elements are yttrium (Y), scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0025] In the metal element R, La can be contained in an amount of 50 atomic % or more, 95 atomic % or more, 99 atomic % or more, or even 100 atomic %.

[0026] The metal element M is at least one element selected from the group consisting of Co, Ni, Zn, Al, Cu, and Cr, and necessarily contains Co.

[0027] In the metal element M, Co can be contained in an amount of 50 atomic % or more, 95 atomic % or more, 99 atomic % or more, or even 100 atomic %.

[0028] When the metal element M contains Al, in the metal element M, Al can be contained in an amount of 1 atomic % or more, 5 atomic % or more, 13 atomic % or less, or 10 atomic % or less.

[0029] When the metal element M contains Ni, Ni can be contained in the metal element M at 1 atomic % or more, can be contained at 5 atomic % or more, and can be contained at 13 atomic % or less.

[0030] When the metal element M contains Zn, Zn can be contained in the metal element M at 1 atomic % or more, can be contained at 5 atomic % or more, and can be contained at 13 atomic % or less.

[0031] When the metal element M contains Cu, Cu can be contained in the metal element M at 1 atomic % or more, can be contained at 5 atomic % or more, and can be contained at 13 atomic % or less.

[0032] When the metal element M contains Cr, Cr can be contained in the metal element M at 1 atomic % or more, can be contained at 5 atomic % or more, and can be contained at 15 atomic % or less.

[0033] For the ferrite sintered magnet and ferrite particles according to this embodiment, when the atomic ratio of the metal elements is represented by the formula (1), in the formula (1), c, a, r, b, f, and m satisfy the following formulas (2) to (8). Ca c A a R r Bi b Fe f M m (1) 0.15 ≦ c < 0.5 (2) 0.01 ≦ a ≦ 0.1 (3) 0.45 < r ≦ 0.80 (4) 0.01 ≦ b < 0.1 (5) 9.35 < f < 11.90 (6) 0.1 ≦ m ≦ 0.50 (7) c + a + r + b = 1 (8)

[0034] For the ferrite sintered magnet and ferrite particles according to another embodiment, when the atomic ratio of the metal elements is represented by the formula (1), in the formula (1), c, a, r, b, f, and m satisfy the following formulas (2) to (8). Ca c A a R rBi b Fe f M m (1) 0.2 ≤ c < 0.5 (2) 0.01 ≤ a ≤ 0.1 (3) 0.45 < r ≤ 0.75 (4) 0.01 ≤ b < 0.1 (5) 9.35 < f < 11.90 (6) 0.1 ≤ m ≤ 0.45 (7) c + a + r + b = 1 (8)

[0035] In formula (1), c may be 0.20 or more, may be 0.25 or more, or may be 0.30 or more. c may also be 0.45 or less, or may be 0.40 or less.

[0036] In formula (1), since the ratio of the heterogeneous phase is reduced and Br, HcJ, and squareness are further improved, a may be 0.01 or more, or may be 0.03 or more. From the same perspective, a may also be 0.08 or less, or may be 0.05 or less.

[0037] In formula (1), since Br is further improved and the low-temperature demagnetization of the coercive force tends to be suppressed, r may be 0.50 or more, or may be 0.55 or more. Since the decrease in the coercive force tends to be suppressed and firing is possible even at a temperature lower than high temperature, r may be less than 0.80, may be 0.75 or less, may be 0.70 or less, or may be 0.65 or less.

[0038] In formula (1), from the perspective of lowering the calcination temperature and further improving the squareness of the coercive force, b may be 0.015 or more, or may be 0.020 or more. Since the ratio of the heterogeneous phase is further reduced, b may also be 0.08 or less, may be 0.06 or less, or may be 0.05 or less.

[0039] In formula (1), f may be 9.50 or more, may be 9.70 or more, from the viewpoint of enhancing magnetization and further reducing the heterogeneous phase, and may be 11.50 or less, may be 11.25 or less, since Br, HcJ and squareness are further improved.

[0040] In formula (1), m may be 0.15 or more, may be 0.20 or more, may be 0.25 or more, from the viewpoint of enhancing magnetization and coercive force and further reducing the heterogeneous phase. In formula (1), m may be 0.45 or less, may be 0.40 or less, from the same viewpoint.

[0041] The ferrite sintered magnet and ferrite particles according to this embodiment preferably further satisfy the following formulas (3-1), (5-1), (6-1) and (7-1) because HcJ is further improved and the ratio of the heterogeneous phase is further reduced.

[0042] 0.03 ≦ a ≦ 0.05 (3-1) 0.01 ≦ b ≦ 0.05 (5-1) 9.35 < f ≦ 11.25 (6-1) 0.25 ≦ m ≦ 0.45 (7-1)

[0043] The ferrite sintered magnet and ferrite particles according to this embodiment may contain Si in order to further improve HcJ. The content of Si in the ferrite sintered magnet and ferrite particles may be 0.01% by mass or more, may be 0.05% by mass or more, may be 0.10% by mass or more, when converted to SiO2, from the viewpoint of further improving HcJ. The content of Si in the ferrite sintered magnet and ferrite particles may be 0.70% by mass or less, may be 0.60% by mass or less, may be 0.40% by mass or less, when converted to SiO2, from the same viewpoint.

[0044] The ferrite sintered magnet and ferrite particles according to this embodiment may contain Al in order to further improve HcJ. The content of Al in the ferrite sintered magnet and ferrite particles may be 0.01% by mass or more, 0.05% by mass or more, or 0.10% by mass or more in terms of Al2O3 in order to further improve HcJ. The content of Al in the ferrite sintered magnet and ferrite particles may be 0.70% by mass or less, 0.60% by mass or less, or 0.40% by mass or less in terms of Al2O3 from the same viewpoint.

[0045] In addition to the above-described components, the ferrite sintered magnet and ferrite particles may contain impurities contained in the raw materials or inevitable components derived from the manufacturing equipment. Examples of such components include Ti (titanium), Mn (manganese), Mo (molybdenum), and V (vanadium). These components may be contained in the ferrite sintered magnet and ferrite particles as their respective oxides or composite oxides. The sub-components may segregate at the grain boundaries of the ferrite crystal grains in the ferrite sintered magnet to form a heterogeneous phase.

[0046] The content ratio of the metal elements in the ferrite sintered magnet and ferrite particles can be measured by fluorescent X-ray analysis.

[0047] The content of semi-metal elements such as Si (silicon) in the ferrite sintered magnet and ferrite particles can be measured by inductively coupled plasma optical emission spectrometry (ICP optical emission spectrometry).

[0048] FIG. 1 is a schematic cross-sectional view of a ferrite sintered magnet (ferrite particles) 100 according to this embodiment. As shown in FIG. 1, the ferrite sintered magnet (ferrite particles) 100 according to this embodiment has a ferrite phase (crystal grains) 4 having a magnetoplumbite type (M-type) crystal structure and a grain boundary phase 6 existing between the ferrite phases (crystal grains) 4.

[0049] The M-type ferrite has a hexagonal crystal structure. An example of the M-type ferrite is the ferrite represented by the following formula (III). AX 12 O 19 (III) A necessarily contains Ca and La, and may contain Sr and / or Ba. M may contain R. X contains Fe and may contain Co. Note that the ratios of A (A site) and X (B site) and the ratio of oxygen (O) in the above formula (III) actually show values slightly deviated from the above ranges, so they may deviate slightly from the above numerical values.

[0050] From the viewpoint of sufficiently enhancing the magnetic properties, the ferrite sintered magnet and the ferrite particles according to the present embodiment preferably have the above ferrite phase 4 as the main phase. In the present specification, "as the main phase" means the crystal phase having the largest mass ratio in the ferrite sintered magnet and the ferrite particles according to the present embodiment. The ferrite sintered magnet and the ferrite particles according to the present embodiment may have a crystal phase (heterophase) different from the main phase. The ratio of the heterophase may be 30% or less, 20% or less, 15% or less, 10% or less, or 5% or less based on the ferrite phase (M phase).

[0051] Examples of the heterophase include the Fe2O3 phase and the LaFeO3 phase. The ratio of the Fe2O3 phase is obtained as a value obtained by measuring the XRD pattern of the ferrite sintered magnet or the ferrite particles and dividing the peak intensity (2θ: 33.21°) derived from the (104) plane of the Fe2O3 phase by the peak intensity (2θ: 32.35°) derived from the (107) plane of the M-type phase. The ratio of the LaFeO3 phase is obtained as a value obtained by measuring the XRD pattern of the ferrite sintered magnet or the ferrite particles and dividing the peak intensity (2θ: 22.67°) derived from the (101) plane of the LaFeO3 phase by the peak intensity derived from the (107) plane of the M-type phase.

[0052] In the ferrite sintered magnet according to this embodiment, the average grain size of the ferrite phase (crystalline grains) may be, for example, 5 μm or less, 4.0 μm or less, or 0.5 to 3.0 μm. By having such an average grain size, the coercive force (HcJ) can be further increased. The average grain size of the ferrite phase (crystalline grains) can be determined using an observation image of a cross-section by TEM or SEM. Specifically, after obtaining the cross-sectional area of each main phase particle in the cross-section of SEM or TEM including hundreds of ferrite phases (crystalline grains) by image analysis, the diameter of the circle (equivalent circle diameter) having the cross-sectional area is defined as the grain size of the main phase particle in the cross-section, and the grain size distribution is measured. From the measured number-based grain size distribution, the number-based average value of the grain size of the ferrite phase (crystalline grains) is calculated. The average value measured in this way is taken as the average grain size of the ferrite phase.

[0053] The grain boundary phase 6 is mainly composed of an oxide. Specifically, examples of the oxide include oxides having at least one selected from the group consisting of Si, Ca, Sr, Ba, Fe, Mn, Co, Cr, Zn, and Al, and composite oxides of two or more of these. Examples of such oxides include SiO2, CaO, BaO, SrO, Fe2O3, Co3O4, ZnO, Al2O3, MnO, and Cr2O3. It may also contain silicate glass. The mass ratio of the oxide can be 90% by mass or more, 95% by mass or more, or 97% by mass or more.

[0054] In the cross-section of the ferrite sintered magnet according to this embodiment, the area ratio of the grain boundary phase 6 in the total of the ferrite phase 4 and the grain boundary phase 6 can be 0.1 to 5%.

[0055] The shape of the ferrite sintered magnet according to this embodiment is not particularly limited, and it can take various shapes, for example, an arc segment (C-type) shape in which the end face is curved to be arc-shaped, a flat plate shape, etc.

[0056] The ferrite particles can be obtained, for example, by the pulverization process described later. The average particle diameter of the ferrite particles is, for example, 0.1 to 7 μm. The average particle diameter of the ferrite particles can also be determined using an observation image of the ferrite particles by TEM or SEM in the same manner as the average grain diameter of the crystal grains of the ferrite sintered magnet. Specifically, after obtaining the area of each main phase particle of SEM or TEM containing several hundred ferrite particles by image analysis, the diameter of the circle (equivalent circle diameter) having the area is defined as the particle diameter of the ferrite particle, and the particle size distribution is measured. From the measured particle size distribution based on the number, the average value based on the number of the particle diameters of the ferrite particles is calculated. The average value measured in this way is taken as the average particle diameter of the ferrite particles.

[0057] The Br at 23°C of the ferrite sintered magnet and the ferrite particles according to the present embodiment may be, for example, 4500 G or more, may be 4600 G or more, or may be 4700 G or more.

[0058] The HcJ at 23°C of the ferrite sintered magnet and the ferrite particles according to the present embodiment may be, for example, 1800 Oe or more, may be 2000 Oe or more, or may be 2200 Oe or more.

[0059] The rectangularity at 23°C of the ferrite sintered magnet and the ferrite particles according to the present embodiment may be 80% or more, may be 82% or more, or may be 85% or more.

[0060] The Br, HcJ, and rectangularity of the ferrite sintered magnet and the ferrite particles according to the present embodiment can be measured using a DC recording fluxmeter.

[0061] (Function and effect) The ferrite sintered magnet and the ferrite particles according to the present embodiment contain a combination of Ca, metal element A, metal element R, Bi, Fe, and metal element M, necessarily contain La, necessarily contain Co, and by setting the contents thereof within a range satisfying the formulas (2) to (8), Br and rectangularity become excellent.

[0062] In addition, the ferrite sintered magnet and ferrite particles according to the present embodiment contain a combination of Ca, metal element A, metal element R, Bi, Fe, and metal element M, necessarily contain La, necessarily contain Co, and by setting the contents thereof within the range satisfying formulas (2) to (8), they can be fired at a low temperature, have excellent HcJ, and tend to have a reduced ratio of heterogeneous phases.

[0063] (Bonded magnet) Next, the bonded magnet according to the present embodiment will be described.

[0064] The bonded magnet according to the present embodiment contains the ferrite particles according to the above embodiment and a resin. Examples of the resin include thermosetting resins such as epoxy resin, phenolic resin, resin having a polyaromatic ring, and resin having a triazine ring (triazine resin); polyamide-based elastomers such as styrene-based, olefin-based, urethane-based, polyester-based, and nylon, ionomers, ethylene-propylene copolymer (EPM), and thermoplastic resins such as ethylene-ethyl acrylate copolymer.

[0065] The content rate of the resin in the bonded magnet according to the present embodiment may be, for example, 0.5 to 10% by mass or 1 to 5% by mass from the viewpoint of achieving both excellent magnetic properties and excellent shape retention. The content rate of the resin in the bonded magnet can be adjusted by changing the resin concentration in the solution containing the resin used during production or the molding pressure during production of the molded body. From the same viewpoint, the content rate of the ferrite particles in the bonded magnet may be, for example, 90 to 99.5% by mass or 95 to 99% by mass.

[0066] The shape of the bonded magnet is not particularly limited and can be the same as that of the ferrite sintered magnet.

[0067] The ferrite sintered magnet and the bonded magnet according to this embodiment can be used as magnetic field generating members such as rotary electric machines such as motors and generators, magnets for speakers and headphones, magnetron tubes, magnetic field generating devices for MRI, clamps for CD-ROMs, sensors for distributors, sensors for ABS, fuel / oil level sensors, magnetic clutches, or isolators. Further, it can also be used as a target (pellet) when forming the magnetic layer of a magnetic recording medium by a vapor deposition method, a sputtering method, or the like.

[0068] (Rotary electric machine) Subsequently, the motor 200 according to this embodiment is shown in FIG. 2. The motor 200 includes a stator 31 and a rotor 32. The rotor 32 has a shaft 36 and a rotor core 37. In the motor 200 of this embodiment, a C-shaped ferrite sintered magnet or a bonded magnet 100, which is a permanent magnet, is provided in the stator 31, and an electromagnet (coil) is provided in the rotor core 37 of the rotor 32.

[0069] Note that a motor in which a ferrite sintered magnet is provided in the rotor and an electromagnet (coil) is provided in the stator may also be used. There is no particular limitation on the form of the motor. Another example of a rotary electric machine is a generator having a rotor and a stator. The ferrite sintered magnet can be provided in the rotor or the stator.

[0070] (Manufacturing method of ferrite sintered magnet, etc.) Next, an example of a method for manufacturing ferrite particles, ferrite sintered magnets, and bonded magnets will be described. The manufacturing method described below includes a blending step, a pre-firing step, a pulverizing step, a molding step, and a main firing step. Details of each step will be described below.

[0071] The blending step is a step of preparing a mixed powder for pre-firing. The mixed powder for pre-firing can contain constituent elements of ferrite, for example, Ca, metal element A, metal element R, Bi, Fe, and metal element M. In the blending step, it is preferable to mix a mixture of powders containing each element for about 1 to 20 hours using an attritor or a ball mill or the like and perform a pulverization treatment to obtain a mixed powder.

[0072] Additive elements such as Si may be contained in the above powder in advance, or another powder containing the additive element may be further added in the blending step to obtain a mixed powder for calcination. Examples of the other powder are powders containing Si.

[0073] Examples of the powder containing each element are simple substances, oxides, hydroxides, carbonates, nitrates, silicates, and organometallic compounds of each element. One powder may contain two or more metal elements, or one powder may contain substantially only one metal element.

[0074] Examples of the powder containing Ca are CaCO3 and CaO. Examples of the powder containing Sr are SrCO3 and SrO. Examples of the powder containing R are La2O3 and La(OH)3. Examples of the powder containing Bi are Bi2O3. Examples of the powder containing Fe are Fe2O3. Examples of the powder containing Co are Co3O4. Examples of the powder containing Zn are ZnO. Examples of the powder containing Al are Al2O3. Examples of the powder containing Si are SiO2.

[0075] The average particle size of the raw material powder is not particularly limited, and is, for example, 0.1 to 2.0 μm.

[0076] After the blending step, if necessary, it is preferable to dry the raw material composition and remove coarse particles by sieving.

[0077] In the calcination step, the raw material composition obtained in the blending step is calcined. The calcination is preferably carried out, for example, in an oxidizing atmosphere such as air. The calcination temperature may be, for example, 1050 to 1350 °C, may be 1200 to 1310 °C, or may be 1220 to 1310 °C. The calcination time may be, for example, 1 minute to 10 hours, may be 1 minute to 5 hours, or may be 1 minute to 2 hours.

[0078] In the grinding process, the calcined powder that has become granular or lumpy through the calcination process is ground. In this way, ferrite particles are obtained. The grinding process may be divided into two steps, for example, first grinding the calcined powder into a coarse powder (coarse grinding step), and then further grinding it finely (fine grinding step).

[0079] Coarse grinding can be carried out, for example, using a vibration mill or the like until the average particle size of the calcined powder becomes 0.1 to 5.0 μm.

[0080] In fine grinding, the coarse powder obtained by coarse grinding is further ground by a wet attritor, ball mill, jet mill, or the like. In fine grinding, the grinding is carried out so that the average particle size of the obtained fine powder (ferrite particles) becomes, for example, about 0.08 to 2.0 μm. The specific surface area of the fine powder (obtained by, for example, the BET method) is, for example, about 7 to 12 m 2 / g. The suitable grinding time varies depending on the grinding method. For example, in the case of a wet attritor, it is 30 minutes to 10 hours, and in the case of wet grinding by a ball mill, it is 10 to 50 hours. The specific surface area of the ferrite particles can be measured using a commercially available BET specific surface area measuring device (manufactured by Mountech, product name: HM Model-1210).

[0081] In the fine grinding step, in order to increase the magnetic orientation degree of the sintered body obtained after final sintering, for example, a polyhydric alcohol represented by the general formula C n (OH) n H n+2 may be added. n in the general formula may be, for example, 4 to 100, or may be 4 to 30. Examples of the polyhydric alcohol include sorbitol. Also, two or more kinds of polyhydric alcohols may be used in combination. Further, in addition to the polyhydric alcohol, other known dispersants may be used in combination.

[0082] When adding a polyhydric alcohol, the addition amount may be, for example, 0.05 to 5.0% by mass, or 0.1 to 3.0% by mass, based on the object to which it is added (e.g., coarse powder). The polyhydric alcohol added in the fine pulverization step is thermally decomposed and removed in the main firing step described later.

[0083] Note that, instead of mixing all of the raw material powders in the blending step, it is preferable to add some of the raw material powders, for example, some of the CaCO3 powder, some or all of the SiO2 powder, some or all of the Al2O3 powder, and some or all of the BaCO3 powder, in the coarse pulverization step and / or the fine pulverization step. By adding a powder containing such components after the pre-firing, the sinterability in the main firing step and the magnetic properties can be improved. Note that since these sub-components may flow out together with the solvent of the slurry when performing wet molding, they can be blended in an amount more than the target content in 100% by mass of the ferrite sintered magnet.

[0084] For example, when adding some of the powder containing Ca after pre-firing, the addition amount of Ca may be 0.01% by mass or more, or 1.60% by mass or less, in terms of Ca converted to CaCO3, based on the entire ferrite magnet.

[0085] In the molding step, the ferrite particles obtained in the pulverization step are molded in a magnetic field to obtain a molded body. The molding can be performed by any method of dry molding and wet molding. From the viewpoint of increasing the magnetic orientation degree, it is preferably performed by wet molding.

[0086] When forming by wet forming, for example, after obtaining a slurry by performing the above-described fine pulverization step wet, the slurry is concentrated to a predetermined concentration to obtain a slurry for wet forming. Forming can be performed using this slurry for wet forming. Concentration of the slurry can be performed by centrifugation, filter press, or the like. The content of ferrite particles in the slurry for wet forming is, for example, 30 to 80% by mass. In the slurry, examples of the dispersion medium for dispersing ferrite particles include water. A surfactant such as gluconic acid, gluconate, or sorbitol may be added to the slurry. A non-aqueous solvent may be used as the dispersion medium. As the non-aqueous solvent, organic solvents such as toluene and xylene can be used. In this case, a surfactant such as oleic acid may be added. Note that the slurry for wet forming may be prepared by adding a dispersion medium or the like to the dried ferrite particles after fine pulverization.

[0087] In wet forming, next, magnetic field forming is performed on this slurry for wet forming. In that case, the forming pressure is, for example, 9.8 to 196 MPa (0.1 to 2.0 ton / cm 2 ). The applied magnetic field is, for example, 398 to 1194 kA / m (5 to 15 kOe).

[0088] In this firing step, the formed body obtained in the forming step is fired to obtain a ferrite sintered magnet. Firing of the formed body can be performed in an oxidizing atmosphere such as air. The firing temperature may be, for example, 1050 to 1350°C, may be 1200 to 1310°C, or may be 1200 to 1280°C. Also, the firing time (the time held at the firing temperature) may be, for example, 0.5 to 3 hours, or may be 0.5 to 1 hour.

[0089] In this firing process, before reaching the sintering temperature, for example, from room temperature to about 100 °C, heating may be performed at a heating rate of about 0.5 °C / min. By doing so, the green body can be sufficiently dried before sintering progresses. Also, the surfactant added in the forming process can be sufficiently removed. Note that these treatments may be performed at the beginning of this firing process, or may be separately performed before this firing process.

[0090] In this way, a ferrite sintered magnet can be manufactured. When manufacturing a bonded magnet instead of a ferrite sintered magnet, a bonded magnet can be obtained by impregnating the green body obtained in the above-described forming process with a resin and heating to cure the resin. Specifically, the green body is immersed in a previously prepared resin-containing solution, and degassed by reducing the pressure in a sealed container to allow the resin-containing solution to penetrate into the voids of the green body. Then, the green body is taken out from the resin-containing solution, and the excess resin-containing solution adhering to the surface of the green body is removed. A centrifuge or the like may be used to remove the excess resin-containing solution.

[0091] Before immersing in the resin-containing solution, by immersing the green body in a solvent such as toluene while placing it in a sealed solution and maintaining a reduced-pressure atmosphere, defoaming is promoted, the impregnation amount of the resin can be increased, and the voids in the green body can be reduced.

[0092] The manufacturing methods of ferrite particles, ferrite sintered magnets, and bonded magnets are not limited to the above examples. For example, when manufacturing a bonded magnet, after performing up to the above-described pulverization process, the obtained ferrite particles and resin may be mixed and formed in a magnetic field to obtain a bonded magnet containing ferrite particles and resin.

[0093] For example, the molding process and the main firing process may be performed according to the following procedure. That is, the molding process may be performed by CIM (Ceramic Injection Molding) molding method or PIM (Powder Injection Molding, a kind of powder injection molding). In the CIM molding method, first, dried ferrite particles are heated and kneaded together with a binder resin to form pellets. These pellets are injection-molded in a mold with a magnetic field applied to obtain a preform. The preform is subjected to a debinding process to obtain a molded body. Next, in the main firing process, the debound molded body is sintered, for example, in the air at a temperature of preferably 1100 to 1280 °C, more preferably 1200 to 1280 °C for about 0.2 to 3 hours to obtain a ferrite sintered magnet.

Example

[0094] The content of the present disclosure will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0095] [Manufacture of Ferrite Sintered Magnet] (Examples 1 to 21 and Comparative Examples 1 to 21) As raw materials, powders of calcium carbonate (CaCO3), lanthanum hydroxide (La(OH)3), cobalt oxide (Co3O4), iron oxide (Fe2O3), barium carbonate (BaCO3), strontium carbonate (SrCO3), aluminum oxide (Al2O3) and bismuth oxide (Bi2O3) were prepared. These raw material powders were blended so that the atomic ratios were as shown in Tables 1 and 2. However, when aluminum oxide, calcium carbonate and barium carbonate are added during the grinding process as described later, the corresponding amounts were excluded in advance. Then, these raw material powders were mixed and ground using a steel ball mill to obtain a slurry (blending process).

[0096] This slurry was dried to obtain a dried product. Next, coarse particles were removed from the dried product. Subsequently, the dried product was calcined in air at the calcination temperatures shown in Tables 1 and 2 to obtain a calcined powder (calcination step). The calcination was carried out using an electric furnace (super burner). The obtained calcined powder was coarsely pulverized using a small rod vibration mill to obtain coarse powder. Thereafter, it was finely pulverized using a wet ball mill to obtain a slurry (pulverization step).

[0097] The moisture content of the slurry obtained after fine pulverization was adjusted using a centrifuge to obtain a slurry for wet forming. This slurry for wet forming was formed in an applied magnetic field of 796 kA / m (10 kOe) using a wet magnetic field forming machine to obtain a formed body (forming step). The formed body was cylindrical with a diameter of 30 mm and a thickness of 15 mm and had an orientation in the thickness direction. The obtained formed body was dried in air at room temperature. Subsequently, the formed body was sintered in air at the temperatures shown in Tables 1 and 2 (sintering step). The sintering was carried out using an electric furnace (super burner). In this way, a cylindrical ferrite sintered magnet was obtained.

[0098] (Examples 22 - 30) Silicon dioxide (SiO2) powder, calcium carbonate (CaCO3) powder, aluminum oxide (Al2O3) powder, barium carbonate (BaCO3) powder, and sorbitol were added to the coarse powder in amounts shown in Table 3 with respect to the mass of the ferrite sintered magnet, and then fine pulverization was carried out using a wet ball mill to obtain a slurry. Ferrite sintered magnets were obtained in the same manner as in Examples 1 - 21 and Comparative Examples 1 - 21, except for the above.

[0099] (Examples 31 - 52) Ferrite sintered magnets were obtained in the same manner as in Example 1, except that the raw material powders were blended so that the atomic ratios were as shown in Table 4.

[0100]

Table 1

[0101]

Table 2

[0102]

Table 3

[0103]

Table 4

[0104] [Evaluation of Ferrite Particles] As ferrite particles, the XRD pattern of the coarse powder was measured. For the measurement, a powder X-ray diffractometer manufactured by Rigaku Corporation was used. The measurement conditions were as follows: characteristic X-ray: Cu-Kα ray, sampling width: 2θ = 10 to 70°, scanning speed: 4.0° / min, X-ray tube voltage = 50 kV, X-ray tube current: 300 mA, divergence slit: 1°, vertical width limit of divergence slit: 10 mm, receiving slit: 0.3 mm. From the obtained XRD pattern, the ratio of the Fe2O3 phase and the ratio of the LaFeO3 phase were calculated when the M-type phase was 100%. The ratio of the Fe2O3 phase was defined as the value obtained by dividing the peak intensity (2θ: 33.21°) derived from the (104) plane of the Fe2O3 phase by the peak intensity (2θ: 32.35°) derived from the (107) plane of the M-type phase. The ratio of the LaFeO3 phase was defined as the value obtained by dividing the peak intensity (2θ: 22.67°) derived from the (101) plane of the LaFeO3 phase by the peak intensity derived from the (107) plane of the M-type phase. The results are shown in Tables 5 to 7.

[0105] [Evaluation of Ferrite Sintered Magnets] <Evaluation of Magnetic Properties> After processing the upper and lower surfaces of the ferrite sintered magnet with a vertical grinding machine, Br, HcJ, Hk, and squareness (Hk / HcJ) at 23 °C were measured using a DC recording fluxmeter with a maximum applied magnetic field of 2389 kA / m. The results are shown in Tables 5 to 7.

[0106] <Composition Analysis> The content of Si (silicon) in the ferrite sintered magnet was measured by the following procedure. 0.1 g of a sample of the ferrite sintered magnet was mixed with 1 g of sodium peroxide and 1 g of sodium carbonate, heated and melted. The melt was dissolved in a solution of 40 ml of pure water and 10 ml of hydrochloric acid, and then pure water was added to make a 100 ml solution. Using this solution, the content of silicon in terms of SiO2 was determined by ICP emission spectrometry (ICP-AES). For the ICP emission spectrometry, an analytical device manufactured by Shimadzu Corporation (device name: ICPS 8100CL) was used, and matrix matching was performed during the measurement. a, b, c, r, f, and m in the ferrite sintered magnet were measured by X-ray fluorescence analysis. The results are shown in Tables 1, 2, and 4.

[0107]

Table 5

[0108]

Table 6

[0109]

Table 7

Explanation of Symbols

[0110] 4… Ferrite phase (main phase), 6… Grain boundary phase, 31… Stator (stator cover), 32… Rotor, 36… Shaft, 37… Rotor core, 100… Ferrite sintered magnet or bonded magnet, 200… Motor.

Claims

1. A ferrite sintered magnet containing a ferrite phase having a magnetoplumbite-type crystal structure, comprising at least Ca, metal element A, metal element R, Bi, Fe, and metal element M, wherein metal element A is at least one element selected from the group consisting of Sr, Ba, and Pb, metal element R is at least one element selected from the group consisting of rare earth elements including Y, and necessarily contains La, metal element M is at least one element selected from the group consisting of Co, Ni, Zn, Al, Cu, and Cr, and necessarily contains Co, and when the atomic ratios of the metal elements are represented by formula (1), in formula (1), c, a, r, b, f, and m satisfy the following formulas (2) to (8): a ferrite sintered magnet. Ca ｃ A ａ R ｒ Bi ｂ Fe ｆ M ｍ (1) 0.15 ≦ c < 0.5 (2) 0.01 ≦ a ≦ 0.1 (3) 0.45 < r ≦ 0.80 (4) 0.01 ≦ b < 0.1 (5) 9.35 < f < 11.90 (6) 0.1 ≦ m ≦ 0.50 (7) c + a + r + b = 1 (8)

2. The ferrite sintered magnet according to claim 1, further satisfying the following formulas (3-1), (5-1), (6-1), and (7-1): 0.03 ≦ a ≦ 0.05 (3-1) 0.01 ≦ b ≦ 0.05 (5-1) 9.35 < f ≦ 11.25 (6-1) 0.25 ≦ m ≦ 0.45 (7-1)

3. A rotating electrical machine comprising the ferrite sintered magnet according to claim 1 or 2.

4. Ferrite particles containing a ferrite phase having a magnetoplumbite-type crystal structure, comprising at least Ca, metal element A, metal element R, Bi, Fe, and metal element M, wherein metal element A is at least one element selected from the group consisting of Sr, Ba, and Pb, metal element R is at least one element selected from the group consisting of rare earth elements including Y, and necessarily contains La, metal element M is at least one element selected from the group consisting of Co, Ni, Zn, Al, Cu, and Cr, and necessarily contains Co, and when the atomic ratios of the metal elements are represented by formula (1), in formula (1), c, a, r, b, f, and m satisfy the following formulas (2) to (8): ferrite particles. Ca ｃ A ａ R ｒ Bi ｂ Fe ｆ M ｍ (1) 0.15 ≦ c < 0.5 (2) 0.01 ≦ a ≦ 0.1 (3) 0.45 < r ≦ 0.80 (4) 0.01 ≦ b < 0.1 (5) 9.35 < f < 11.90 (6) 0.1 ≦ m ≦ 0.50 (7) c + a + r + b = 1 (8)

5. A bonded magnet comprising the ferrite particles according to claim 4 and a resin.

6. A rotating electrical machine comprising the bonded magnet according to claim 5.

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