Ferrite calcined body

Abstract

To provide a Co-free ferrite calcined body having a high saturation magnetization σs. [Solution] General formula showing the atomic ratio of metallic elements Ca, R, Fe, and Zn (where R is at least one rare earth element and must contain La): Ca 1-x R x Fe 2n-y Zn y A ferrite calcined body in which x, y, and n (where 2n is a molar ratio and is expressed as 2n = (Fe + Zn) / (Ca + R)) satisfy the following conditions: 0.35 ≤ x ≤ 0.7, 0 ≤ y < 0.5, and 4.5 ≤ n ≤ 6.0.

Description

Technical Field

[0001] This disclosure relates to a ferrite calcined body.

Background Art

[0002] Although the maximum energy product of ferrite sintered magnets is only about 1 / 10 of that of rare-earth sintered magnets (e.g., NdFeB sintered magnets), they have excellent cost performance because their main raw material is inexpensive iron oxide and have the feature of being extremely chemically stable. Therefore, they are used in various applications such as various motors and speakers, and the global production volume is still the largest among magnet materials even now.

[0003] A typical ferrite sintered magnet is Sr ferrite having a magnetoplumbite structure, and its basic composition is represented by SrFe 3+ O 19 Since the practical application of Sr-La-Co system ferrite sintered magnet (hereinafter simply referred to as "SrLaCo magnet") in which part of Sr of SrFe 12 O 19 is replaced by La 2+ and part of Fe 3+ is replaced by Co 3+ 2+ , the magnetic properties of ferrite magnets have been greatly improved. In addition, in 2007, Ca-La-Co system ferrite sintered magnet (hereinafter simply referred to as "CaLaCo magnet") with further improved magnetic properties was put into practical use.

[0004] Since CaLaCo magnets exhibit the highest-class magnetic properties among currently mass-produced ferrite sintered magnets, they are used in motors for automotive electric equipment and motors for home appliances, etc., where there is a strong demand for high performance. However, in specific applications (e.g., motors for home appliances), for the purpose of improving motor output, the residual magnetic flux density B r (hereinafter simply referred to as "B r ​Improvements in the following areas are desired: "[...]. Furthermore, in recent years, against the backdrop of soaring prices of rare earth raw materials and the emergence of procurement risks, applications to industrial motors and drive motors / generators for EVs (Electric Vehicles) / HEVs, where only rare earth magnets have been used until now, are being considered, and further improvements in magnetic properties are desired.

[0005] However, CaLaCo magnets contain approximately 0.3% Co (Co / Fe = 0.03, or about 3% of the Fe content) on an atomic ratio. Since the price of Co (Co oxide) is 10 to 100 times higher than that of iron oxide, the main raw material for ferrite sintered magnets, increased raw material costs are unavoidable compared to Sr ferrite (which basically contains no Co) and SrLaCo magnets (which contain approximately 0.2% Co (Co / Fe = 0.017, or about 1.7% of the Fe content) on an atomic ratio). Furthermore, as is well known, Co is concentrated in certain producing countries, its price fluctuates wildly, and it is one of the metals whose supply is most at risk. Therefore, the urgent challenge is how to reduce the amount of Co used while maintaining magnetic properties. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2018-30751 [Patent Document 2] Patent No. 6414372 [Patent Document 3] Japanese Patent Publication No. 2000-223307 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Patent Document 1 describes a high saturation magnetization σs and a high anisotropic magnetic field H A We propose a CaLaCo-based ferrite compound having the following properties. According to the ferrite compound described in Patent Document 1, the high B required for improving motor output is rAlthough it is expected, it contains Co with an atomic ratio of 0.1 to 0.24, and the risk of using Co is not avoided.

[0008] Patent Document 2 proposes a magnet in which a part of Co in a CaLaCo-based magnet is replaced with Zn, suppressing a decrease in coercive force H cJ (hereinafter, sometimes simply referred to as "coercive force" or "H cJ ") while improving B r According to the magnet described in Cited Document 2, in a preferred embodiment, an extremely high B of 0.480 T r is obtained, and the amount of Co used is also reduced, but Co with an atomic ratio of 0.15 or more and less than 0.4 is required, and the risk of using Co is not avoided.

[0009] Patent Document 3 discloses a CaLaM-based magnet (M = Co, Ni, Zn), and in FIG. 11 of Patent Document 3, Ca 0.5 La 0.5 Fe 10 M 0.5 the saturation magnetization σs of the calcined body in the composition is described, and when Zn is used as M, the saturation magnetization σs is about 70 emu / g (about 70 A·m 2 / kg) is described to appear at a calcination temperature of 1200°C.

[0010] Embodiments of the present disclosure enable the provision of a Co-free ferrite calcined body having a high saturation magnetization σs.

Means for Solving the Problems

[0011] A non-limiting exemplary ferrite calcined body of the present disclosure has a general formula showing the atomic ratio of metal elements of Ca, R, Fe, and Zn (where R is at least one rare earth element and an element essentially containing La): Ca 1-x R x Fe 2n-y Zn y in which x and y, and n (where 2n is a molar ratio and 2n = (Fe + Zn) / (Ca + R)) satisfy 0.35 ≤ x ≤ 0.7, 0 ≤ y < 0.5, 4.5 ≤ n ≤ 6.0.

[0012] In one embodiment, the ferrite calcined body has a saturation magnetization σs of 71.1 A·m 2 It is over / kg.

[0013] In one embodiment, the ferrite calcined body has a saturation magnetization σs of 75.0 A·m 2 It is 1 kg or more.

[0014] In one embodiment, x is 0.4 ≤ x ≤ 0.55.

[0015] In one embodiment, y is 0.17 ≤ y ≤ 0.35.

[0016] In one embodiment, n is 5.0 ≤ n ≤ 5.5. [Effects of the Invention]

[0017] According to embodiments of this disclosure, it is possible to provide a Co-free ferrite calcined body having a high saturation magnetization σs. [Modes for carrying out the invention]

[0018] The ferrite calcined body of this disclosure is given by the general formula: Ca, R, Fe, and Zn, which express the atomic ratio of the metallic elements (where R is at least one rare earth element and must contain La). 1-x R x Fe 2n-y Zn y In this configuration, x and y, as well as n (where 2n is a molar ratio and is expressed as 2n = (Fe + Zn) / (Ca + R)), satisfy the following conditions: 0.35 ≤ x ≤ 0.7, 0 ≤ y < 0.5, and 4.5 ≤ n ≤ 6.0.

[0019] The ferrite calcined material of this disclosure is 71.1 A·m 2 / kg (σs>71.1A·m) 2 It exhibits a high saturation magnetization σs ( / kg). In a preferred embodiment, it is 75.0 A·m. 2It exhibits a saturation magnetization σs of 1 kg or more.

[0020] The ferrite calcined body of this disclosure has a high saturation magnetization σs, and therefore can exhibit high performance when used in sintered magnets, bonded magnets, magnetic recording media, etc. In particular, when the ferrite calcined body of this disclosure is used in the manufacture of ferrite sintered magnets, the high B required to improve motor output can be achieved. r A ferrite sintered magnet possessing the following properties can be obtained without using Co (coal). Because it is Co-free, it can be offered at a lower cost than conventional CaLaCo-based magnets, and there is no risk associated with using Co.

[0021] The atomic ratio x (content of R) is 0.35 ≤ x ≤ 0.7. R is at least one rare earth element that must contain La. The content of rare earth elements other than La is preferably 50% or less of the total amount of R in molar ratio, and more preferably 0% (R=La, excluding impurities). If x is less than 0.35 or greater than 0.7, a high saturation magnetization σs cannot be obtained. It is more preferable that x is 0.4 ≤ x ≤ 0.55.

[0022] The atomic ratio y (Zn content) is 0 ≤ y < 0.5. If y is greater than or equal to 0.5, a high saturation magnetization σs cannot be obtained. It is more preferable that y is 0.20 ≤ x ≤ 0.30.

[0023] The molar ratio n is 4.5 ≤ n ≤ 6.0. If n is less than 4.5 or greater than 6.0, a high saturation magnetization σs cannot be obtained. It is more preferable that n is 5.0 ≤ n ≤ 5.5. 2n is the molar ratio and is expressed as 2n = (Fe + Zn) / (Ca + R). 2n-y is the Fe content, and since 4.5 ≤ n ≤ 6.0 and 0 ≤ y < 0.5, it becomes 8.5 < 2n-z ≤ 12.0. It is more preferable that 2n-y is 9.5 < 2n-z ≤ 11.0.

[0024] The above general formula is shown in terms of the atomic ratio of metal elements, but the composition containing oxygen (O) is shown in the general formula: Ca 1-x R x Fe 2n-y Zny O α It is expressed as follows. The number of moles of oxygen α is basically α=19, but it varies depending on the valence of Fe, the values ​​of x, y and n, etc. Also, the ratio of oxygen to metal elements changes due to oxygen vacancies (vacancies) when calcined in a reducing atmosphere, changes in the valence of Fe in the ferrite phase, etc. Therefore, the actual number of moles of oxygen α may deviate from 19. For this reason, in this embodiment, the composition is expressed in terms of the atomic ratio of metal elements, which is the easiest to identify.

[0025] The main phase constituting the ferrite calcined body in the embodiments of this disclosure is a compound phase (ferrite phase) having a hexagonal magnetoprumbite (M-type) structure. Generally, magnetic materials are composed of multiple compounds, and the compound that determines the properties of the magnetic material (physical properties, magnetic properties, etc.) is defined as the "main phase."

[0026] "Having a hexagonal magnetoplanvite (M-type) structure" means that when the X-ray diffraction of a ferrite calcined material is measured under general conditions, the X-ray diffraction pattern mainly observed is that of a hexagonal magnetoplanvite (M-type) structure.

[0027] An example of a method for producing the ferrite calcined body according to this disclosure is described below.

[0028] As raw material powders, compounds such as oxides, carbonates, hydroxides, nitrates, and chlorides of each metal can be used, regardless of their valency. A solution of the raw material powder may also be used. Examples of Ca compounds include Ca carbonates, oxides, and chlorides. Typically, it is CaCO3. Examples of R compounds, taking La as an example, include oxides such as La2O3, hydroxides such as La(OH)3, and carbonates such as La2(CO3)3·8H2O. Typically, it is La(OH)3. Examples of Fe compounds include iron oxide, iron hydroxide, iron chloride, and mill scale. Typically, it is Fe2O3. An example of Zn compound is ZnO.

[0029] To accelerate the reaction during calcination, compounds containing boron (B), such as B2O3 and H3BO3, may be added up to approximately 1 mass% as needed. Adding H3BO3 is particularly effective in improving magnetic properties. The amount of H3BO3 added is preferably 0.3 mass% or less, with approximately 0.1 mass% being the most preferable.

[0030] Mixing raw material powders that satisfy the components and composition of the ferrite calcined body of this disclosure is performed to obtain a mixed raw material powder. The blending and mixing of the raw material powders may be carried out by either a wet or dry method. Mixing with a medium such as steel balls allows for more uniform mixing of the raw material powders. In the case of a wet method, it is preferable to use water as the dispersion medium. Known dispersants such as ammonium polycarboxylate and calcium gluconate may be used to improve the dispersibility of the raw material powders. The mixed raw material slurry may be calcined as is, or the raw material slurry may be dehydrated before calcination.

[0031] In the calcination process, the mixed raw material powder obtained by dry or wet mixing is heated using an electric furnace, gas furnace, or the like. This causes a solid-phase reaction to form a ferrite compound with a hexagonal magnetoplumbite (M-type) structure. This process is called "calcination," and the resulting compound is called a "calcined body." Therefore, the ferrite calcined body in the embodiments of this disclosure can be rephrased as a ferrite compound.

[0032] In the calcination process, a solid-state reaction proceeds in which the ferrite phase is formed as the temperature rises. If the calcination temperature is below 1100°C, unreacted hematite (iron oxide) remains, resulting in low magnetic properties. On the other hand, if the calcination temperature exceeds 1450°C, the crystal grains grow too large, which is undesirable. Therefore, the calcination temperature is preferably between 1100°C and 1450°C. The calcination time is preferably between 0.5 hours and 5 hours. After calcination, the calcined material is preferably coarsely ground using a hammer mill or the like.

[0033] The following describes an example of applying the ferrite calcined body of this disclosure to a sintered magnet.

[0034] The calcined body or coarsely ground powder of the calcined body obtained as described above is ground (finely ground) using a vibratory mill, jet mill, ball mill, attritor, etc. to obtain calcined body powder (finely ground powder). The average particle size of the calcined body powder is preferably about 0.4 μm to 1.2 μm. If improvement of magnetic properties is important, it is preferably about 0.4 μm to 0.7 μm, and more preferably about 0.5 μm to 0.65 μm. If manufacturing costs (reduction of grinding time, reduction of press cycle, etc.) are important, it is preferably about 0.7 μm to 1.2 μm. In the embodiments of this disclosure, the value measured by the air permeability method using a powder specific surface area measuring device (e.g., Shimadzu SS-100) is referred to as the average particle size (average particle size). The grinding process may be either dry grinding or wet grinding, or a combination of both. In the case of wet grinding, water and / or a non-aqueous solvent (organic solvent such as acetone, ethanol, or xylene) is used as the dispersion medium. Typically, a slurry is produced containing water (dispersant) and calcined material. Known dispersants and / or surfactants may be added to the slurry in an amount of 0.2 mass% to 2 mass% by solid content. After wet grinding, the slurry may be concentrated.

[0035] The molding process involves press-molding the slurry after the grinding process in a magnetic field or a non-magnetic field while removing the dispersion medium. Press-molding in a magnetic field allows for alignment (orientation) of the crystal orientation of the powder particles, dramatically improving the magnetic properties. Furthermore, to improve orientation, 0.1 mass% to 1 mass% each of a dispersant and a lubricant may be added to the slurry before molding. The slurry may also be concentrated before molding as needed. Concentration is preferably performed by centrifugation, filter pressing, etc.

[0036] In the firing process, the molded body obtained by press molding is degreased as necessary and then fired (sintered). Firing is carried out using an electric furnace, gas furnace, etc. A firing temperature of approximately 1150°C to 1250°C is preferred. A firing time of approximately 0 hours (no holding at firing temperature) to 2 hours is preferred.

[0037] After the firing process, known manufacturing processes such as processing, cleaning, and inspection may be carried out as needed. [Examples]

[0038] Embodiments of the present disclosure will be described in further detail by reference to examples, but the embodiments of the present disclosure are not limited thereto.

[0039] Experimental Example 1 As an example of an experiment based on the embodiments of this disclosure, the general formula Ca 1-x R x Fe 2n-y Zn y At (R=La), CaCO3 powder, La(OH)3 powder, Fe2O3 powder, and ZnO powder were weighed in predetermined proportions such that the atomic ratios were 1-x, x, 2n-y, and y as shown in samples No. 1 to 73 in Tables 1 and 2. After weighing, 0.1 mass% of H3BO3 powder was added to 100 mass% of the total powder, and each mixture was mixed in a wet ball mill for 4 hours. The mixture was then dried and granulated to obtain mixed raw material powders. Each of the obtained mixed raw material powders was calcined in air at 1300°C for 3 hours to obtain calcined bodies.

[0040] Each obtained calcined material was pulverized to a particle size of 75 μm or less using an atomizer and mortar. 20 mg of each calcined material powder was packed into a sample pan with resin, oriented in a magnetic field at 1 T, and each sample was prepared. The saturation magnetization σs of each sample at room temperature was measured at an applied magnetic field of 9 T using a high-field sample vibration magnetometer (Quantum Design PPMS DynaCool). The measurement results are shown in Tables 1 and 2. In addition, X-ray diffraction measurements were performed on each calcined material powder using a powder X-ray diffractometer (Rigaku SmartLab 9kW). The measurement conditions were a Co-Kα X-ray source, output of 40 kV, and 135 mA. As a result, diffraction patterns mainly of a hexagonal M-type magnetoplanvite structure were observed for each calcined material powder.

[0041] [Table 1]

[0042] [Table 2]

[0043] In Tables 1 and 2, samples without an asterisk (*) next to the sample number (samples No. 1 to 72) are experimental examples based on embodiments of this disclosure, while samples with an asterisk (*) are experimental examples that do not satisfy embodiments of this disclosure (reproduction experiment of Patent Document 3). As is clear from Tables 1 and 2, the saturation magnetization σs of the ferrite calcined body of sample No. 73* based on Patent Document 3 is 71.1 A·m 2 While the values ​​are / kg, all ferrite calcined bodies based on the embodiments of this disclosure are 71.1 A·m 2 It exhibits a saturation magnetization σs exceeding / kg. In a preferred embodiment, it is 75.0 A·m 2 It exhibits a saturation magnetization σs of 1 kg or more. [Industrial applicability]

[0044] Since the ferrite calcined body of this disclosure has a high saturation magnetization σs, when the ferrite calcined body of this disclosure is used in the manufacture of a ferrite sintered magnet, the high B required for improving motor output can be achieved. r A ferrite sintered magnet having the properties of [the specified material] can be obtained without the use of Co. The obtained ferrite sintered magnet can be suitably used in various motors and the like.

Claims

1. General formula showing the atomic ratios of metallic elements Ca, R, Fe, and Zn (where R is at least one rare earth element and must contain La): Ca １－ｘ R ｘ Fe ２ｎ－ｙ Zn ｙ In this, x and y, and n (where 2n is a molar ratio and is expressed as 2n = (Fe + Zn) / (Ca + R)) 0.35 ≤ x ≤ 0.7, 0 ≤ y < 0.5, 4.5 ≤ n ≤ 6.0, A ferrite calcined body characterized by satisfying the following conditions.

2. Saturation magnetization σs is 71.1A・m ２ A ferrite calcined body according to claim 1, which is greater than / kg.

3. Saturation magnetization σs is 75.0 A·m ２ A ferrite calcined body according to claim 1, wherein the calcined body is 1 kg or more.

4. The ferrite calcined body according to claim 1, wherein x is 0.4 ≤ x ≤ 0.

55.

5. The ferrite calcined body according to claim 1, wherein y is 0.17 ≤ y ≤ 0.

35.

6. The ferrite calcined body according to claim 1, wherein n is 5.0 ≤ n ≤ 5.5.

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