Ferrite sintered magnet and method for producing ferrite sintered magnet

Abstract

The ferrite magnet has a hexagonal ferrite main phase and a second phase. The second phase is an oxide phase containing: element A which is at least one selected from Ca, Sr, Ba, Bi, and a rare earth element; a transition metal element T which contains at least Fe; and element G which is at least one selected from Si, Al, B, F, K, Na, Li, P, and S. When the total atomic number of element A, the transition metal element T, and element G of the second phase is set to 100 at%, element A accounts for 30 to 80 at%, element G accounts for 15 to 40 at%, and the transition metal element T accounts for less than 4 at%.

Description

Technical Field

[0001] This application relates to ferrite sintered magnets and methods for manufacturing the same. Background Technology

[0002] As magnetic materials used in ferrite sintered magnets, various hexagonal ferrites, such as magnetoplumule type (M type) ferrites, are known (see, for example, Patent Documents 1-3).

[0003] [Existing Technical Documents]

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent No. 4591684

[0006] Patent Document 2: Japanese Patent Application Publication No. 2005-45167

[0007] Patent Document 3: Japanese Patent No. 6769482 Summary of the Invention

[0008] In existing hexagonal ferrite sintered magnets, techniques have been explored to improve both the residual magnetic flux density Br and the coercivity HcJ by adding Si oxides.

[0009] However, for example, in ferrite sintered magnets containing La, it is difficult to sufficiently improve the properties.

[0010] The present invention was developed in view of the above-mentioned technical problems, and its purpose is to provide a new ferrite sintered magnet and a method for manufacturing the same, which can improve both residual magnetic flux density and coercivity.

[0011] One aspect of the present invention provides a sintered magnet having a hexagonal ferrite main phase and a second phase, wherein...

[0012] The second phase is an oxide phase, which contains:

[0013] Element A is selected from at least one of Ca, Sr, Ba, Bi and rare earth elements;

[0014] Transition metal element T, which contains at least Fe; and

[0015] Element G is selected from at least one of Si, Al, B, F, K, Na, Li, P, and S.

[0016] When the total number of atoms of element A, transition metal element T, and element G in the second phase is set to 100 at%,

[0017] Element A accounts for 30-80 at%.

[0018] Element G accounts for 15-40 at%.

[0019] Transition metal element T accounts for less than 4 at%.

[0020] Here, the sintered magnet may contain 0.05 to 10% by mass of the second phase.

[0021] In addition, the second phase may contain La 4.67 Apatite compounds based on the [SiO4]3O phase.

[0022] The hexagonal ferrite can be a magnetoplumbium-type ferrite.

[0023] One aspect of the present invention provides a method for manufacturing a sintered magnet, comprising:

[0024] The process of calcining raw material powder to obtain calcined body;

[0025] The process of pulverizing the calcined body to obtain hexagonal ferrite powder;

[0026] The process of adding additional powder to the ferrite powder to obtain a mixed powder;

[0027] The process of shaping the mixed powder to obtain a shaped article; and

[0028] The process of firing the shaped body.

[0029] in,

[0030] The added powder contains at least element A and element G, wherein element A is selected from at least one of Ca, Sr, Ba, Bi and rare earth elements, and element G is selected from at least one of Si, Al, B, F, K, Na, Li, P and S.

[0031] The added powder may also contain the transition metal element T.

[0032] When the total number of atoms of element A, transition metal element T, and element G in the added powder is set to 100 at%,

[0033] Element A accounts for 30-80 at%.

[0034] Element G accounts for 15-40 at%.

[0035] Transition metal element T accounts for less than 4 at%.

[0036] In the method, the amount of the added powder can exceed 0.05% by mass and be less than 8.0% by mass.

[0037] In the method, the additional powder may contain La 4.67 Apatite compounds based on the [SiO4]3O phase.

[0038] In the method, the hexagonal ferrite can be a magnetoplumbleite ferrite.

[0039] The present invention provides a ferrite sintered magnet capable of improving both residual magnetic flux density and coercivity, and a method for manufacturing the same. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of a cross-section of a ferrite sintered magnet. Detailed Implementation

[0041] The following describes several embodiments of the present invention in detail.

[0042] (Sintered magnet)

[0043] Figure 1 This is a cross-sectional schematic diagram of a ferrite sintered magnet 100 according to an embodiment of the present invention. The ferrite sintered magnet 100 according to an embodiment of the present invention has a hexagonal ferrite main phase (grains) 4 and a second phase 6 existing between the hexagonal ferrite main phases (grains) 4. Grain boundary phases 7 may also exist between the hexagonal ferrite main phases 4.

[0044] (Hexagonal ferrite main phase)

[0045] Hexagonal ferrites are ferrites with a hexagonal crystal structure. Examples of such ferrites include magnetoplumule-type (M-type) ferrites, W-type ferrites, X-type ferrites, Y-type ferrites, and Z-type ferrites. Among these, M-type ferrites are preferred.

[0046] Hexagonal ferrite is an oxide containing elements A1, A2 and transition metal element T, wherein element A1 is selected from at least one of Ca, Sr and Ba, element A2 is selected from at least one of rare earth elements and Bi, and transition metal element T contains at least Fe.

[0047] Examples of rare earth elements include 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).

[0048] Examples of transition metal elements T other than Fe include Co, Zn, Ti, V, Cr, Mn, Ni, and Cu.

[0049] Element A1 preferably contains at least Ca, and if Ca is present, element A1 may further contain Sr and / or Ba.

[0050] Element A2 preferably contains at least La.

[0051] Element T preferably contains both Fe and Co.

[0052] In the hexagonal ferrite main phase, when the total number of atoms of elements A1 and A2 is set to 1, the number of atoms of element T can be set to 8 to 13, preferably 10 to 13.

[0053] When the total number of atoms of element T is set to 100 at%, the atomic proportion of Fe can be set to 90-100 at%, preferably 96-100 at%. Furthermore, the atomic proportion of Co is preferably set to 0-5 at%.

[0054] In the hexagonal ferrite main phase, when the total number of atoms of elements A1 and A2 is set to 1, the proportion of atoms of element A2 can be 0.1 to 1.0, preferably 0.4 to 1.0.

[0055] In the hexagonal ferrite main phase, when the total number of atoms of elements A1 and A2 is set to 1, the proportion of La atoms is preferably 0.4 or more.

[0056] In the hexagonal ferrite main phase, when the total number of Al atoms is set to 1, the proportion of Ca atoms is preferably set to 0.1 or higher.

[0057] M-type ferrite can be represented by the following formula (III).

[0058] MX 12 O 19 (III)

[0059] A portion of elements A1 and A2 can enter the M site. A portion of elements T and A2 can enter the X site.

[0060] Furthermore, the ratio of M (site A) and X (site B) and the ratio of oxygen (O) in equation (III) above actually deviate slightly from the above range. Therefore, the values ​​can also deviate by about 10%.

[0061] In this specification, "main phase" refers to the crystalline phase with the highest mass proportion in a ferrite sintered magnet.

[0062] Relative to the overall sintered magnet, the hexagonal ferrite main phase can be 70% or more by mass, 80% or more by mass, 90% or more by mass, or 95% or more by mass. The mass ratio of the hexagonal ferrite main phase can be determined by X-ray diffraction and other methods.

[0063] The average grain size of the hexagonal ferrite main phase (grains) in ferrite sintered magnets can be, for example, less than 5 μm, less than 4.0 μm, or 0.5–3.0 μm. This average grain size further enhances coercivity. The average grain size of the ferrite main phase (grains) can be determined using cross-sectional observation images from TEM or SEM. Specifically, the cross-sectional area of ​​each hexagonal ferrite main phase in an SEM or TEM cross-section containing hundreds of ferrite main phases (grains) is determined through image analysis. Then, the diameter of the circle containing this cross-sectional area (circle equivalent diameter) is defined as the grain size of the main phase particle in that cross-section, and the grain size distribution is measured. Based on the measured grain size distribution, the average value of the number of hexagonal ferrite main phase (grains) grain sizes is calculated. This measured average value is set as the average grain size of the hexagonal ferrite main phase.

[0064] (Second phase)

[0065] The second phase 6 is an oxide phase containing element A, transition metal element T and element G, wherein element A is selected from at least one of Ca, Sr, Ba, Bi and rare earth elements (including Y), transition metal element T contains at least Fe, and element G is selected from at least one of Si, Al, B, F, K, Na, Li, P and S.

[0066] When the total atomic number of element A, transition metal element T, and element G is set to 100 at%, in the second phase, element A accounts for 30–80 at%, element G accounts for 15–40 at%, and transition metal element T accounts for less than 4 at%. When the total atomic number of element A, transition metal element T, and element G is set to 100 at%, the total atomic number of elements A and G in the second phase can be above 80 at%, above 90 at%, or above 95 at%.

[0067] In other examples, the second phase 6 is an oxide phase containing element A, transition metal element T, and Si, wherein element A is selected from at least one of Ca, Sr, Ba, Bi, and rare earth elements (including Y), and transition metal element T contains at least Fe.

[0068] In this case, when the total number of atoms of all metallic elements and all half-metallic elements is set to 100 at%, in the second phase, element A can account for 30–80 at%, Si can account for 10–40 at% (or more than 15 at%), and transition metal element T can account for less than 4 at%. When the total number of atoms of all metallic elements and all half-metallic elements is set to 100 at%, in the second phase, the total number of atoms of elements A and Si can be more than 80 at%, more than 90 at%, or more than 95 at%.

[0069] Element A may contain: at least one element selected from Ca, Sr, and Ba; and at least one element selected from Bi and rare earth elements. Element A may contain: at least one element selected from Ca, Sr, and Ba, and La. Element A may contain both Ca and La.

[0070] When the total number of atoms of all metallic and half-metallic elements is set to 100 at%, or when the total number of atoms of element A, transition metal element T, and element G is set to 100 at%, the total proportion of at least one element selected from Ca, Sr, and Ba in the second phase can be 0 to 80 at%, and in particular, the proportion of Ca can be set to 5 to 50 at%.

[0071] When the total number of atoms of all metallic and semi-metallic elements is set to 100 at%, or when the total number of atoms of element A, transition metal element T, and element G is set to 100 at%, the total proportion of at least one element selected from Bi and rare earth elements in the second phase can be 30 to 80 at%, and in particular, the proportion of La can be set to 10 to 65 at%.

[0072] When the total atomic number of element A, transition metal element T, and element G is set to 100 at%, the atomic proportion of element G in the second phase is 15–40 at%, preferably 18–40 at%, and even more preferably 20–40 at%. In this case, when the total atomic number of element A, transition metal element T, and element G is set to 100 at%, the atomic proportion of Si in the second phase can be 5 at% or more, or 10 at% or more, or 15 at% or more, or 18 at% or more, or 20 at% or more, or 25 at% or more, or 30 at% or more.

[0073] When the total number of atoms of all metallic and semi-metallic elements is set to 100 at%, the atomic proportion of Si in the second phase can be 10-40 at%, 15-40 at%, more preferably 18-40 at%, and even more preferably 20-40 at%.

[0074] When the total number of atoms of all metallic and semi-metallic elements is set to 100 at%, or when the total number of atoms of element A, transition metal element T, and element G is set to 100 at%, the atomic proportion of Fe in the second phase can be less than 4 at% or less than 3 at%.

[0075] When the total number of atoms of all metallic and semi-metallic elements is set to 100 at%, or when the total number of atoms of element A, transition metal element T, and element G is set to 100 at%, the atomic proportion of Co in the second phase can be less than 4 at%, and the atomic proportion of Zn can be less than 4 at%.

[0076] The second phase can be 0.05 to 10% by mass relative to the sintered magnet as a whole.

[0077] The second phase may contain La 4.67 Apatite compounds based on the [SiO4]3O phase. This structure is referred to as the oxyapatite structure. For example, the above structure is described as Q. 4.67 In the case of [EO4]3O, Q can be element A, and E can be element G containing Si and transition metal element T. This compound can also have a P63 / m structure.

[0078] In addition to compounds containing the oxyapatite structure, the second phase can also contain compounds with the Pnma structure. This Pnma structure is called the orthoferrite structure.

[0079] The second phase can also be a mixture of compounds with an oxyapatite structure and compounds with a ferrite structure.

[0080] The mass ratio of the oxyapatite-structured compound to the ferrite-structured compound in the second phase can be 3 or more, 4 or more, or 5 or more. The upper limit of this mass ratio can be below 40, 30, 25, or 20. This mass ratio can be determined from the maximum peak ratio of each structure using CuKα radiation XRD.

[0081] XRD and electron beam diffraction in TEM confirmed that at least a portion of the second phase possesses an oxyapatite structure. The crystal structure and composition of the second phase were confirmed by XRD and STEM-EDX, respectively.

[0082] There are no particular limitations on the shape of ferrite sintered magnets. For example, they can be various shapes such as arc-shaped segments (C-type) with the end faces curved into arcs, flat plates, etc.

[0083] The coercivity of the ferrite sintered magnet at 20°C can be, for example, 300 kA / m or more. The residual magnetic flux density Br of the ferrite sintered magnet at 20°C can be 400 mT or more. The ferrite sintered magnet of this embodiment exhibits excellent performance in both coercivity (HcJ) and residual magnetic flux density (Br).

[0084] The mass ratio of metallic and semi-metallic elements in the hexagonal ferrite main phase and the second phase of ferrite sintered magnets can be determined by STEM-EDX fluorescence X-ray analysis.

[0085] (Manufacturing method of ferrite sintered magnets)

[0086] Next, an example of a method for manufacturing a ferrite sintered magnet according to the embodiment will be described. The manufacturing method described below includes a mixing process, a calcination process, a pulverizing process, a powder addition and mixing process, a forming process, and a firing process. The details of each process will be described below.

[0087] (Preparation process)

[0088] The blending process is the process of preparing the raw material powder for calcination. The raw material powder for calcination contains the constituent elements of the hexagonal ferrite main phase, namely, elements Al, A2, and T. In the blending process, it is preferable to use a mill or ball mill to mix the mixture of powders containing each element for 1 to 20 hours and then pulverize it to obtain the raw material powder.

[0089] Examples of powders containing various elements include the elemental form, oxides, hydroxides, carbonates, nitrates, silicates, and organometallic compounds. A powder may contain two or more metal elements, or it may actually contain only one metal element.

[0090] Examples of powders containing Ca include CaCO3. Examples of powders containing Sr include SrCO3. Examples of powders containing Ba include BaCO3. Examples of powders containing La include La2O3 and La(OH)3. Examples of powders containing Fe include Fe2O3. Examples of powders containing Co include Co3O4.

[0091] The ratio of each metal element in the raw material powder can be appropriately set according to the composition of the hexagonal ferrite main phase mentioned above.

[0092] There is no particular limitation on the average particle size of the raw material powder, for example, it is 0.1 to 5.0 μm.

[0093] Preferably, after the mixing process, the raw material powder is dried as needed, and coarse particles are removed by sieving.

[0094] (Calcination process)

[0095] In the calcination process, the raw material powder obtained in the blending process is calcined to obtain a calcined body. Calcination is preferably carried out in an oxidizing atmosphere, such as air. The calcination temperature can be, for example, 1100–1400°C or 1100–1350°C. The calcination time can be, for example, 1 minute–10 hours or 1 minute–3 hours. The proportion of the hexagonal ferrite main phase in the calcined body obtained by calcination can be, for example, 70% by mass or more or 75% by mass or more. This proportion of the hexagonal ferrite main phase can be obtained in the same manner as the proportion of the hexagonal ferrite main phase in sintered ferrite magnets.

[0096] (Grinding process)

[0097] In the pulverization process, the calcined body, which is pulverized into granules or blocks through the calcination process, is obtained as ferrite powder. The pulverization process can also be divided into two stages: coarse pulverization and fine pulverization. The coarse pulverization process is the process of pulverizing the calcined powder into coarse powder, while the fine pulverization process is the process of further pulverizing after the coarse pulverization process.

[0098] Coarse grinding can be carried out, for example, using a vibratory mill, until the average particle size of the calcined body is 0.1 to 10.0 μm.

[0099] In micronization, the coarse powder obtained from coarse grinding is further pulverized using a wet mill, ball mill, spray mill, etc. Micronization can be carried out to achieve an average particle size of, for example, 0.08–5.0 μm. The specific surface area of ​​the micronized powder (obtained, for example, by the BET method) is, for example, 7–12 m². 2 / g degree. The appropriate grinding time varies depending on the grinding method; for example, the grinding time is 30 minutes to 10 hours when using a wet mill, and 10 to 50 hours when using a ball mill for wet grinding. The specific surface area of ​​the obtained powder can be measured using a commercially available BET specific surface area measuring device (Mountech, trade name: HM Model-1210).

[0100] In the micronization process, to improve the magnetic orientation of the sintered body obtained after firing, for example, a compound of general formula C can be added. n (OH) n H n+2 The term refers to a polyol. In the general formula, n can be, for example, 4 to 100, or 4 to 30. Examples of polyols include sorbitol. Furthermore, two or more polyols can be used in combination. In addition to polyols, other known dispersants can also be used in combination.

[0101] When polyols are added, the amount added relative to the target material (e.g., coarse powder) can be, for example, 0.05 to 5.0% by mass or 0.1 to 3.0% by mass. Furthermore, the polyols added in the micronization process will be removed by thermal decomposition in the firing process described later.

[0102] (Additional powder addition process)

[0103] Next, the ferrite powder and additional powder are mixed to obtain a mixed powder.

[0104] The additional powder can be mixed into the pulverized ferrite powder obtained in the pulverization process. Preferably, the additional powder is added to the powder in the pulverization process, and the ferrite powder and the additional powder are mixed at the same time as the calcined body and the additional powder are pulverized.

[0105] The added powder contains at least: element A, which is selected from at least one of Ca, Sr, Ba, Bi, and rare earth elements (including Y); and element G, which is selected from at least one of Si, Al, B, F, K, Na, Li, P, and S. The added powder may also contain transition metal element T. When the total atomic number of element A, transition metal element T, and element G in the added powder is set to 100 at%, element A accounts for 30–80 at%, element G accounts for 15–40 at%, and transition metal element T accounts for less than 4 at%. When the total atomic number of element A, transition metal element T, and element G is set to 100 at%, the total atomic number of element A and element G in the added powder can be 80 at% or more, 90 at% or more, or 95 at% or more.

[0106] In other examples, the added powder contains at least: element A selected from at least one of Ca, Sr, Ba, Bi, and rare earth elements (including Y); and Si. The added powder may also contain transition metal element T. When the total number of atoms of metal elements and half-metal elements in the added powder is set to 100 at%, element A accounts for 30–80 at%, Si accounts for 10–40 at% (or more than 15 at%), and transition metal element T accounts for less than 4 at%. When the total number of atoms of all metal elements and all half-metal elements is set to 100 at%, the total number of atoms of elements A and Si in the added powder can be more than 80 at%, more than 90 at%, or more than 95 at%.

[0107] Element A may contain: at least one element selected from Ca, Sr, and Ba; and at least one element selected from Bi and rare earth elements. Element A may contain at least one element selected from Ca, Sr, and Ba, and La. Element A may contain both Ca and La.

[0108] When the total number of atoms of all metallic and semi-metallic elements is set to 100 at%, or when the total number of atoms of element A, transition metal element T, and element G is set to 100 at%, the total proportion of at least one element selected from Ca, Sr, and Ba in the above-mentioned additional powder can be 0 to 80 at%, and in particular, the proportion of Ca can be set to 5 to 50 at%.

[0109] When the total number of atoms of all metallic and semi-metallic elements is set to 100 at%, or when the total number of atoms of element A, transition metal element T, and element G is set to 100 at%, the total proportion of at least one element selected from Bi and rare earth elements in the above-mentioned additional powder can be 30 to 80 at%, and in particular, the proportion of La can be set to 10 to 65 at%.

[0110] When the total atomic number of element A, transition metal element T, and element G is set to 100 at%, the atomic proportion of element G in the above-mentioned additional powder is 15 to 40 at%, preferably 18 to 40 at%, and even more preferably 20 to 40 at%. In this case, when the total atomic number of element A, transition metal element T, and element G is set to 100 at%, the atomic proportion of Si in the above-mentioned additional powder can be 5 at% or more, or 10 at% or more, or 15 at% or more, or 18 at% or more, or 20 at% or more, or 25 at% or more, or 30 at% or more.

[0111] When the total number of atoms of all metal elements and half-metal elements is set to 100 at%, the atomic proportion of Si in the above-mentioned additional powder can be 10-40 at%, or 15-40 at%, more preferably 18-40 at%, and even more preferably 20-40 at%.

[0112] When the total number of atoms of all metal elements and half-metal elements is set to 100 at%, or when the total number of atoms of element A, transition metal element T and element G is set to 100 at%, the atomic concentration of Fe in the above-mentioned additional powder is preferably 4 at% or less, and more preferably 3 at% or less.

[0113] Regarding the aforementioned additional powder, when the total number of atoms of all metal elements and half-metal elements is set to 100 at%, or when the total number of atoms of element A, transition metal element T, and element G is set to 100 at%, the atomic concentration of Co can be set to 0-4 at%, and the atomic concentration of Zn can be set to 0-4 at%.

[0114] The added powder can be an oxide or a salt such as a carbonate. The added powder can also be a mixture of various compounds, such as a mixture of various oxides, a mixture of various salts, or a mixture of salts and oxides.

[0115] Examples of oxides are La 4.67 Oxyapatite compounds are based on the [SiO4]3O phase. An example of such oxyapatite is La8Ca2[SiO2]6O2. Additionally, the added powder can be a compound with a ferrite structure or a mixture thereof.

[0116] An example of salt is CaCO3.

[0117] The added powder may contain more than 50% by mass of a compound with an oxygen apatite structure, more than 70% by mass, or more than 90% by mass.

[0118] The amount of additional powder is preferably 0.05% by mass or more and less than 8.0% by mass relative to 100 parts by mass of ferrite powder.

[0119] When the calcined body is pulverized in two stages, additional powder can be added at any time before or after the coarse pulverization process, or the additional powder can be divided into two parts and added separately before and after coarse pulverization.

[0120] (Forming process)

[0121] In the forming process, the mixed powder obtained in the additional powder mixing process (e.g., the pulverizing process) is formed in a magnetic field to obtain a shaped body. Forming can also be performed by either dry forming or wet forming. From the viewpoint of improving the magnetic orientation degree, wet forming is preferred.

[0122] In the case of forming by wet forming, for example, a slurry is obtained by performing the above-mentioned micronization process in a wet manner, and then the slurry is concentrated to a specified concentration to obtain a wet forming slurry. This wet forming slurry can be used for forming. The concentration of the slurry can be carried out by centrifugation or a filter press. The content of ferrite particles in the wet forming slurry is, for example, 30-80% by mass. Water can be used as a dispersion medium for dispersing the ferrite particles in the slurry. Surfactants such as gluconic acid, gluconate, and sorbitol can also be added to the slurry. Non-aqueous solvents can also be used as dispersion media. Organic solvents such as toluene and xylene can be used as non-aqueous solvents. In this case, surfactants such as oleic acid can also be added. Furthermore, the wet forming slurry can also be prepared by adding a dispersion medium to the micronized and dried ferrite particles.

[0123] In wet forming, the wet forming slurry is then formed in a magnetic field. In this case, the forming pressure is, for example, 9.8–196 MPa (0.1–2.0 ton / cm²). 2 The applied magnetic field is, for example, 398–1194 kA / m (5–15 kOe).

[0124] (Firing process)

[0125] In the firing (main firing) process, the shaped body obtained in the forming process is fired to obtain a ferrite sintered magnet. The firing of the shaped body can be carried out in an oxidizing atmosphere such as the atmosphere. The firing temperature can be, for example, 1050–1300°C or 1080–1290°C. Furthermore, the firing time (the time to hold the firing temperature) is, for example, 0.5–3 hours.

[0126] In the firing process, heating can be performed before reaching the sintering temperature, for example, from room temperature to 100°C, at a heating rate of approximately 0.5°C / min. This allows the molded body to be thoroughly dried before sintering. Additionally, surfactants added during the forming process can be thoroughly removed. Furthermore, these treatments can be performed at the start of the firing process or additionally before the firing process.

[0127] In this way, the aforementioned ferrite sintered magnets can be manufactured.

[0128] Alternatively, the forming and firing processes can be performed in the following order. Specifically, the forming process can be performed using CIM (Ceramic Injection Molding) or PIM (Powder Injection Molding). In CIM forming, firstly, dry mixed powder and binder resin are heated and kneaded together to form granules. These granules are then injected into a mold under a magnetic field to obtain a pre-formed body. The pre-formed body is then subjected to a binder removal treatment to obtain the final formed body. Next, in the firing process, the binder-removed formed body is sintered, for example, in air, preferably at 1100–1300°C, more preferably at 1160–1290°C, for 0.2–3 hours, thereby obtaining a ferrite sintered magnet.

[0129] [Example]

[0130] The present invention will be described in more detail with reference to the embodiments and comparative examples, but the present invention is not limited to the embodiments described below.

[0131] (Comparative Examples 1-4, 6-8, Examples 1-11, 14-21)

[0132] As raw materials, prepare powders of calcium carbonate (CaCO3), barium carbonate (BaCO3), strontium carbonate (SrCO3), lanthanum hydroxide (La(OH)3), iron oxide (Fe2O3), and cobalt oxide (Co3O4).

[0133] These raw material powders were blended according to the metal atomic ratios shown in Table 1 for the main phase composition of M-type ferrite. The mixtures were then mixed and pulverized using a wet mill and a ball mill to obtain a slurry (blending process). The slurry was dried, coarse particles were removed, and then calcined at 1280°C in air to obtain calcined powder (calcination process).

[0134] Table 1

[0135]

[0136] The calcined powder was coarsely ground using a small rod vibratory mill to obtain coarse powder. (Coarse grinding process)

[0137] Prepare the additional powders listed in Table 1. Furthermore, the compositions of oxyapatite #1 to #14 are shown in Table 2.

[0138] Each oxyapatite particle was obtained by the following method: raw material powders (calcium carbonate (CaCO3), barium carbonate (BaCO3), strontium carbonate (SrCO3), lanthanum hydroxide (La(OH)3), iron oxide (Fe2O3), cobalt oxide (Co3O4), zinc oxide (ZnO), and silicon dioxide (SiO2)) were weighed in accordance with the metal composition shown in Table 2, mixed using an agate mortar, calcined in atmosphere, and then finely pulverized using a ball mill. The calcination temperature was 1200℃.

[0139] In addition to the coarse powder, the powder is added in such a way that it becomes 100% of the composition in Table 1 by mass relative to the coarse powder. The powder is then micronized and mixed using a wet ball mill to obtain a slurry containing ferrite particles (pulverization and powder mixing process).

[0140]

[0141] The moisture content of the slurry obtained after micronization is adjusted to obtain a wet molding slurry. The wet molding slurry is then molded using a wet magnetic field molding machine in an applied magnetic field of 796 kA / m (10 kOe) to obtain a cylindrical molded body with a diameter of 30 mm and a thickness of 15 mm (molding process).

[0142] The resulting molded body is dried at room temperature in the atmosphere, and then fired at 1200°C in the atmosphere (firing process).

[0143] In this way, a cylindrical ferrite sintered magnet is obtained.

[0144] (Examples 12 and 13)

[0145] Except for changing the composition of the M-type ferrite main phase as shown in Table 1, it was manufactured in the same manner as in Example 1.

[0146] <Evaluation of Magnetic Properties>

[0147] After processing the upper and lower surfaces of the ferrite sintered magnet, Br and HcJ were measured at 20℃ using a B-H tracer with a maximum applied magnetic field of 29 kOe.

[0148] <Composition Analysis>

[0149] A 100 nm thick sheet was fabricated using focused ion beam (FIB) spectroscopy with ferrite sintered magnets and observed using scanning transmission electron microscopy (STEM). Using EDX attached to the STEM, particles with a Fe-containing transition metal composition of less than 20 at% in the overall metal and half-metal atom composition were identified as second-phase particles. EDX point analysis was performed on these second-phase particles to determine their composition.

[0150] In addition, XRD confirmed that the ferrite main phase is hexagonal, and the crystal structure and weight ratio of the second phase were also analyzed by XRD.

[0151] The results of each embodiment and comparative example are shown in Tables 3 to 5.

[0152] Table 3

[0153]

[0154]

[0155] Table 5

[0156]

[0157] It was confirmed that, compared with Comparative Example 1 which did not contain a second phase with the specified composition, Br and Hcj were both increased in the sintered magnet containing a second phase with the specified composition.

[0158] [Explanation of reference numerals in the attached figures]

[0159] 4. Hexagonal ferrite main phase;

[0160] 6. Second phase.

Claims

1. A sintered ferrite magnet, characterized by comprising a main phase of a hexagonal ferrite and a second phase, wherein the second phase is an oxide phase containing: an element A which is at least one selected from the group consisting of Ca, Sr, Ba, Bi and rare earth elements; a transition metal element T which contains at least Fe; and an element G which is at least one selected from the group consisting of Si, Al, B, F, K, Na, Li, P and S.

2. The sintered ferrite magnet according to claim 1, characterized by containing the second phase at 0.05 to 10 mass%.

3. The sintered ferrite magnet according to claim 1 or 2, characterized in that the hexagonal ferrite is a magnetoplumbite-type ferrite.

4. The sintered ferrite magnet according to claim 1 or 2, characterized in that the hexagonal ferrite is a magnetoplumbite-type ferrite.

5. The sintered ferrite magnet according to claim 1, characterized in that the hexagonal ferrite is a magnetoplumbite-type ferrite.

6. The sintered ferrite magnet according to claim 1, characterized in that the atomic proportion of Fe in the second phase is 3 at% or less.

7. A method for producing a sintered ferrite magnet, characterized by comprising: a step of calcining a raw material powder to obtain a calcined body; a step of pulverizing the calcined body to obtain a hexagonal ferrite powder; a step of adding an additional powder to the ferrite powder to obtain a mixed powder; a step of molding the mixed powder to obtain a molded body; and a step of firing the molded body, wherein the additional powder contains at least an element A which is at least one selected from the group consisting of Ca, Sr, Ba, Bi and rare earth elements, and an element G which is at least one selected from the group consisting of Si, Al, B, F, K, Na, Li, P and S.

8. The method according to claim 7, characterized in that the additional powder is added at 0.05 mass% or more and less than 8.0 mass%.

9. The method according to claim 7 or 8, characterized in that the hexagonal ferrite is a magnetoplumbite-type ferrite.

10. The method according to claim 7 or 8, characterized in that the hexagonal ferrite is a magnetoplumbite-type ferrite.

11. The method according to claim 9, characterized in that the hexagonal ferrite is a magnetoplumbite-type ferrite. ​ ​ ​ ​ The second phase contains a compound of the type La 4.67 apatite compounds of the type [SiO4]3O. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The additional powder contains La 4.67 apatite compounds based on the [SiO4]3O phase. ​ ​ ​ ​

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