阅读说明：本技术 铁氧体烧结磁体 (Ferrite sintered magnet ) 是由 石仓友和 池田真规 村川喜堂 森田启之 室屋尚吾 于 2020-09-21 设计创作，主要内容包括：本发明提供一种铁氧体烧结磁体,包含具有六方晶结构的铁氧体结晶颗粒,其中,铁氧体烧结磁体以由下述式(1)表示的原子比含有金属元素。式(1)中,R为选自由稀土元素及Bi中的至少一种元素且至少含有La。式(1)中,w、x、z及m满足下述式(2)～(5)。上述铁氧体烧结磁体中,与c轴平行的截面中的晶粒的直径的变动系数进一步为低于45％。Ca-(1－w－x)R-wSr-xFe-zCo-m···(1)0.360≦w≦0.420···(2)0.110≦x≦0.173···(3)8.51≦z≦9.71···(4)0.208≦m≦0.269···(5)。(The present invention provides a ferrite sintered magnet comprising ferrite crystal particles having a hexagonal crystal structure, wherein the ferrite sintered magnet contains a metal element in an atomic ratio represented by the following formula (1). In the formula (1), R is at least one element selected from rare earth elements and Bi, and at least La is contained. In the formula (1), w, x, z and m satisfy the following formulas (2) to (5). In the above ferrite sintered magnet, the coefficient of variation in the diameter of crystal grains in a cross section parallel to the c-axis is further less than 45%. Ca 1－w－x R w Sr x Fe z Co m ···(1)0.360≦w≦0.420···(2)0.110≦x≦0.173···(3)8.51≦z≦9.71···(4)0.208≦m≦0.269···(5)。)

1. A ferrite sintered magnet comprising ferrite crystal particles having a hexagonal crystal structure,

the ferrite sintered magnet contains a metal element in an atomic ratio represented by the following formula (1),

Ca_1－w－xR_wSr_xFe_zCo_m···(1)

in the formula (1), R is at least one element selected from rare earth elements and Bi and contains at least La,

in the formula (1), w, x, z and m satisfy the following formulas (2) to (5),

0.360≦w≦0.420···(2)

0.110≦x≦0.173···(3)

8.51≦z≦9.71···(4)

0.208≦m≦0.269···(5)

the coefficient of variation of the diameter of crystal grains in a cross section parallel to the c-axis is less than 45%.

2. The ferrite sintered magnet as claimed in claim 1,

the ferrite sintered magnet has a magnetic permeability of H₃BO₃And 0.037 to 0.181 mass% of B in terms of the total amount of the composition.

3. The ferrite sintered magnet as claimed in claim 1 or 2,

the ferrite sintered magnet is made of Al₂O₃And 0.03 to 0.3 mass% of Al in terms of Al content.

4. The ferrite sintered magnet as claimed in any one of claims 1 to 3,

the ferrite sintered magnet further contains 0.001 to 0.068 mass% of Ba in terms of BaO.

Technical Field

The present invention relates to a ferrite sintered magnet.

Background

As a material of the permanent magnet composed of an oxide, hexagonal M-type (magnetoplumbite-type) Sr ferrite or Ba ferrite is known. Ferrite magnets made of these ferrites are supplied as permanent magnets in the form of ferrite sintered magnets or bonded magnets. In recent years, with the miniaturization and high performance of electronic components, ferrite magnets are also required to have high magnetic properties while being miniaturized.

As indices of magnetic properties of the permanent magnet, residual magnetic flux density (Br) and coercive force (HcJ) are generally used, and it is evaluated that the higher these indices are, the higher the magnetic properties are. In order to increase Br and HcJ of permanent magnets, studies have been made to change the composition of ferrite magnets to include predetermined elements and the like.

For example, patent document 1 discloses an oxide magnetic material and a sintered magnet in which Br and HcJ can be increased by adding M-type Ca ferrite to at least La and Co.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2006-104050

Disclosure of Invention

Problems to be solved by the invention

As described above, in order to obtain both Br and HcJ well, various attempts have been made to change the combination of elements added to the main composition, but it has not been known which combination of added elements imparts higher characteristics.

In addition, even with the same composition, the sintering temperature may greatly affect the magnetic properties of the magnet. Therefore, in order to obtain stable magnetic properties, it is necessary to narrow the allowable range of the sintering temperature in the production process of the magnet, and the production control is difficult.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a ferrite sintered magnet which has less dependence on a sintering temperature and can stably obtain excellent magnetic properties.

Means for solving the problems

The present invention provides a ferrite sintered magnet comprising ferrite crystal particles having a hexagonal crystal structure, wherein the ferrite sintered magnet contains a metal element in an atomic ratio represented by the following formula (1),

Ca_1－w－xR_wSr_xFe_zCo_m···(1)

in the formula (1), R is at least one element selected from rare earth elements and Bi and contains at least La,

in the formula (1), w, x, z and m satisfy the following formulas (2) to (5),

0.360≦w≦0.420···(2)

0.110≦x≦0.173···(3)

8.51≦z≦9.71···(4)

0.208≦m≦0.269···(5)

the coefficient of variation of the diameter of crystal grains in a cross section parallel to the c-axis is less than 45%. The ferrite sintered magnet has less dependence on the sintering temperature and can be easily produced into a product having stable magnetic characteristics.

The ferrite sintered magnet may be H₃BO₃And 0.037 to 0.181 mass% of B in terms of the total amount of the composition. This makes it easy to manufacture a product having stable magnetic characteristics with little dependence on the burn-in temperature.

The ferrite sintered magnet is preferably made of Al₂O₃And 0.03 to 0.3 mass% of Al in terms of Al content. The ferrite sintered magnet contains Al in the above range, and thereby HcJ can be further improved.

The ferrite sintered magnet may further contain 0.001 to 0.068 mass% of Ba in terms of BaO. Even if the ferrite sintered magnet contains Ba in the above range, HcJ of the ferrite sintered magnet can be maintained at a high value. However, when 0.068 mass% or more of Ba is contained in terms of BaO, the dependency on the sintering temperature tends to be poor and the coercive force tends to be lowered.

Effects of the invention

According to the present invention, a ferrite sintered magnet and a method for manufacturing the same can be provided, in which the dependence on the sintering temperature is small and stable magnetic characteristics can be obtained.

Drawings

Fig. 1 is an enlarged schematic view of a cross section of a plane parallel to the c-axis of a ferrite sintered magnet according to an embodiment of the present invention.

Description of the symbols

100 … ferrite sintered magnet, CG … grains, g … center of gravity.

Detailed Description

Preferred embodiments of the present invention will be described below. However, the present invention is not limited to the following embodiments.

(ferrite sintered magnet)

The ferrite sintered magnet of the present embodiment includes ferrite particles (crystal grains) having a hexagonal crystal structure. As the ferrite, a magnetoplumbite-type ferrite (M-type ferrite) is preferable.

The ferrite sintered magnet according to the present embodiment is an oxide containing a metal element at an atomic ratio represented by the following formula (1).

Ca_1－w－xR_wSr_xFe_zCo_m···(1)

In the formula (1), R is at least one element selected from rare earth elements (containing Y) and Bi and contains at least La.

In the formula (1), w, x, z and m satisfy the following formulas (2) to (5). When w, x, z and m satisfy the following expressions (2) to (5), the ferrite sintered magnet can have a stable and excellent residual magnetic flux density Br and coercive force HcJ.

0.360≦w≦0.420···(2)

0.110≦x≦0.173···(3)

8.51≦z≦9.71···(4)

0.208≦m≦0.269···(5)

In the sintered ferrite magnet according to the present embodiment, the coefficient of variation in the diameter of crystal grains in a cross section parallel to the c-axis is less than 45%.

The composition and the like of the sintered ferrite magnet according to the present embodiment will be described in more detail below.

The coefficient (1-w-x) of Ca in the atomic ratio of the metal element in the ferrite sintered magnet of the present embodiment is preferably more than 0.435 and less than 0.500. When the Ca coefficient (1-w-x) exceeds 0.435, the ferrite is likely to be an M-type ferrite. In addition, in addition to reducing alpha-Fe₂O₃And the like, and also suppresses the generation of a nonmagnetic hetero-phase such as orthoferrite due to the excessive amount of R,there is a tendency that the decrease of the magnetic properties (particularly Br or HcJ) can be suppressed. From the same viewpoint, the coefficient of Ca (1-w-x) is more preferably 0.436 or more, and still more preferably more than 0.445. On the other hand, when the Ca coefficient (1-w-x) is less than 0.500, the ferrite is easily changed to an M-type ferrite, and CaFeO is reduced_3－xAnd the like, and excellent magnetic characteristics are easily obtained. From the same viewpoint, the coefficient of Ca (1-w-x) is more preferably 0.491 or less.

In the sintered ferrite magnet according to the present embodiment, R in the atomic ratio of the metal element is at least one element selected from the group consisting of rare earth elements and Bi, and contains at least La. Examples of the rare earth elements include: la, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y. R is preferably La. When R is La, the anisotropic magnetic field can be increased.

The coefficient (w) of R in the atomic ratio of the metal element in the ferrite sintered magnet according to the present embodiment is 0.360 to 0.420. When the coefficient (w) of R is in the above range, good Br, HcJ and squareness ratio Hk/HcJ can be obtained. When the coefficient (w) of R is 0.360 or more, the amount of Co dissolved in the ferrite sintered magnet becomes sufficient, and the decrease in Br and HcJ can be suppressed. From the same viewpoint, the coefficient (w) of R is preferably more than 0.370, and more preferably 0.380 or more. On the other hand, when the coefficient (w) of R is 0.420 or less, the ferrite sintered magnet can be a practical magnet with high HcJ while suppressing the generation of nonmagnetic hetero-phases such as orthoferrite. From the same viewpoint, the coefficient (w) of R is preferably less than 0.410.

The Sr coefficient (x) in the atomic ratio of the metal elements in the ferrite sintered magnet according to the present embodiment is 0.110 to 0.173. When the Sr coefficient (x) is within the above range, good Br, HcJ and Hk/HcJ can be obtained. When the Sr coefficient (x) is 0.110 or more, the ratio of Ca and/or La becomes small, and the decrease of HcJ can be suppressed. On the other hand, when the Sr coefficient (x) is 0.173 or less, sufficient Br and HcJ are easily obtained. From the same viewpoint, the coefficient (x) of Sr is preferably less than 0.170, more preferably less than 0.165.

The coefficient (z) of Fe in the atomic ratio of the metal elements in the sintered ferrite magnet according to the present embodiment is 8.51 to 9.71. When the Fe coefficient (z) is in the above range, good Br, HcJ and Hk/HcJ can be obtained. From the viewpoint of obtaining a more favorable HcJ, the coefficient (z) of Fe is preferably more than 8.70 and less than 9.40. In addition, from the viewpoint of obtaining a more favorable Hk/HcJ, the coefficient (z) of Fe is preferably more than 8.90 and less than 9.20.

The coefficient (m) of Co in the atomic ratio of the metal elements in the ferrite sintered magnet according to the present embodiment is 0.208 or more and 0.269 or less. When the Co coefficient (m) is 0.208 or more, a more excellent HcJ can be obtained. From the same viewpoint, the Co coefficient (m) is preferably more than 0.210, more preferably more than 0.220, and still more preferably 0.250 or more. On the other hand, when the Co coefficient (m) is 0.269 or less, more excellent Br can be obtained. From the same viewpoint, the Co coefficient (m) is preferably 0.250 or less. Further, by containing Co in the ferrite sintered magnet, the anisotropic magnetic field can be improved.

The coefficient of variation (CV value) of the grain size in the cross section parallel to the c-axis of the sintered ferrite magnet of the present embodiment is less than 45%.

The c-axis is the easy axis. Fig. 1 is a schematic diagram showing a cross section of a ferrite sintered magnet 100 parallel to the c-axis. The ferrite sintered magnet 100 has a plurality of crystal grains CG of a ferrite structure.

In the present specification, the diameter of each crystal grain is the maximum value Lmax of the length of a straight line passing through the center of gravity g of each crystal grain CG and overlapping the crystal grain CG. The number n of samples of crystal grains may be 500.

The coefficient of variation (CV value) is the standard deviation σ of the grain diameter divided by the arithmetic mean AV of the grain diameter (σ/AV). A smaller variation coefficient indicates less difference in the grain diameter.

The coefficient of variation of the diameter of the crystal grains in the cross section parallel to the c-axis may be 40% or less, 35% or less, or 30% or less.

When the variation coefficient is less than 45%, the dependency of HcJ on the sintering temperature can be reduced, and variations in HcJ in the chair product can be reduced. The coefficient of variation may be 44% or less, may be 43% or less, may be 42% or less, may be 41% or less, and may be 40% or less.

The ferrite sintered magnet of the present embodiment may contain B (boron) as a component other than the above-described metal elements. B content in ferrite sintered magnet is represented by H₃BO₃Converted to 0.037 mass% or more and 0.181 mass% or less. Sintering of magnets with ferrite to H₃BO₃When B is contained in an amount of 0.037 mass% or more, the dependence of HcJ on the burn-in temperature can be reduced. From the same viewpoint, the content of B is represented by H₃BO₃The conversion is preferably 0.050% by mass or more, and more preferably 0.070% by mass or more. On the other hand, the content of B in the ferrite sintered magnet is set to H₃BO₃The HcJ can be maintained at a high level when converted to 0.181 mass% or less. From the same viewpoint, the content of B is represented by H₃BO₃The content is preferably 0.165% by mass or less, and more preferably 0.150% by mass or less in terms of conversion.

The ferrite sintered magnet of the present embodiment may further contain Al (aluminum). Al content in ferrite sintered magnet₂O₃The conversion is preferably 0.03 mass% or more and 0.3 mass% or less. Sintering of magnets with Al by means of ferrites₂O₃When Al is contained in an amount of 0.03 mass% or more, grain growth during the pre-firing and the sintering is suppressed, and the coercive force of the obtained ferrite sintered magnet is further improved. From the same viewpoint, the content of Al is expressed as Al₂O₃The content is preferably 0.10% by mass or more in terms of conversion. On the other hand, by making Al content in the ferrite sintered magnet to be Al₂O₃When converted to 0.3% by mass or less, excellent Br and HcJ can be obtained.

The ferrite sintered magnet of the present embodiment may further contain Si (silicon). The Si content in the ferrite sintered magnet can be SiO₂Converted to 0.1 to 3% by mass. When the ferrite sintered magnet contains Si within the above range, high HcJ can be easily obtained. From the same viewpoint, the Si content may be SiO₂Converted to 0.5to 1.0 mass%.

The ferrite sintered magnet of the present embodiment may further contain Ba (barium). When the ferrite sintered magnet contains Ba, the content of Ba in the ferrite sintered magnet can be 0.001 to 0.068 mass% in terms of BaO. Even if the ferrite sintered magnet contains Ba in the above range, HcJ of the ferrite sintered magnet can be maintained at a high value. However, when Ba is contained in an amount exceeding 0.068 mass% in terms of BaO, the dependency on the sintering temperature tends to be poor and the coercive force tends to be lowered.

The ferrite sintered magnet according to the present embodiment may further include: cr, Ga, Mg, Cu, Mn, Ni, Zn, In, Li, Ti, Zr, Ge, Sn, V, Nb, Ta, Sb, As, W, Mo and the like. The content of each element is preferably 3% by mass or less, and more preferably 1% by mass or less in terms of oxide. From the viewpoint of avoiding a decrease in magnetic properties, the total content of these elements may be 2 mass% or less.

The ferrite sintered magnet of the present embodiment preferably does not contain an alkali metal element (Na, K, Rb, etc.). The alkali metal element tends to easily reduce the saturation magnetization of the ferrite sintered magnet. However, the alkali metal element may be contained in a raw material for obtaining a ferrite sintered magnet, for example, and may be contained in the ferrite sintered magnet if it is contained to such an extent that it is unavoidable. The content of alkali metal elements which do not greatly affect magnetic characteristics is 3% by mass or less.

The composition of the ferrite sintered magnet can be determined by fluorescent X-ray quantitative analysis. In addition, the presence of the main phase can be confirmed by X-ray diffraction or electron beam diffraction.

The average diameter of the crystal grains in the sintered ferrite magnet of the present embodiment is preferably 2.0 μm or less, more preferably 1.7 μm or less, and still more preferably 1.5 μm or less. By having such average grain diameter, a higher HcJ is easily obtained. The average diameter of the crystal grains of the ferrite sintered magnet is an arithmetic mean of 500 of the diameters of the crystal grains measured by the above definition.

(method for producing ferrite sintered magnet)

An example of the method for producing a sintered ferrite magnet according to the present embodiment will be described below. The manufacturing method comprises a raw material powder preparation step, a pre-sintering step, a crushing step, a forming step and a firing step. In the above-described manufacturing method, a drying step and a kneading step of finely pulverizing the slurry may be provided between the pulverizing step and the molding step, or a degreasing step may be provided between the molding step and the firing step. The respective steps will be explained below.

< Process for producing raw Material powder >

In the raw material powder preparation step, raw materials of the ferrite sintered magnet are mixed and, if necessary, pulverized to obtain a raw material powder. First, as a raw material of the ferrite sintered magnet, a compound (raw material compound) containing 1 or 2 or more of elements constituting the raw material is exemplified. The starting compound is preferably in the form of, for example, a powder. Examples of the raw material compound include oxides of the respective elements and compounds (carbonate, hydroxide, nitrate, etc.) which become oxides by firing. For example, can be exemplified: SrCO₃、La₂O₃、Fe₂O₃、BaCO₃、CaCO₃、Co₃O₄、H₃BO₃、Al₂O₃And SiO₂And the like.

The raw materials are weighed so as to obtain a desired composition of the ferrite sintered magnet, for example, and mixed and then pulverized using a wet mill, a ball mill, or the like for about 0.1 to 20 hours. For example, the average particle diameter of the powder of the raw material compound is preferably about 0.1 to 5.0 μm from the viewpoint of enabling uniform blending. From the viewpoint of reducing the coefficient of variation in the diameter of the crystal grains of the ferrite sintered magnet and reducing the dependence of the magnetic properties on the firing temperature, it is preferable to mix the raw materials for a long time to obtain a uniform composition distribution and to achieve uniform grain growth during the calcination or sintering.

The raw material powder contains at least Ca, R, Sr, Fe, and Co. When the ferrite sintered magnet contains B, the raw material powder contains B. When the raw material powder contains B, the influence of the fluctuation of the calcination temperature that affects the magnetic properties is easily reduced. In addition, when the ferrite sintered magnet contains Al, the raw material powder also contains Al. This suppresses grain growth during the pre-firing and sintering, improves the magnetic properties, and reduces the dependence of the magnetic properties on the pre-firing and sintering temperatures.

Part of the raw material may be added in the pulverizing step described later. However, in the present embodiment, it is preferable that a part of the raw material is not added in the pulverization step. That is, all of Ca, R, Sr, Fe, Co and B (except for the inevitably mixed elements) constituting the obtained ferrite sintered magnet are preferably supplied from the raw material powder in the raw material powder preparation step. In particular, it is preferable that all of B constituting the ferrite sintered magnet is supplied from the raw material powder in the raw material powder preparation step. Further, it is preferable that all Al constituting the ferrite sintered magnet is supplied from the raw material powder in the raw material powder preparation step. This makes it easier to obtain the above-described effects caused by the raw material powder containing B or Al.

< Pre-burning Process >

In the pre-firing step, the raw material powder obtained in the raw material powder preparation step is pre-fired. The calcination is preferably performed in an oxidizing atmosphere such as air (atmospheric air). The temperature of the pre-firing is preferably in the range of 1100 to 1400 ℃, more preferably 1100 to 1300 ℃, and even more preferably 1150 to 1240 ℃ from the viewpoint of reducing the coefficient of variation in the grain size of the ferrite sintered magnet and reducing the dependence of the magnetic properties on the firing temperature. In the method for producing a ferrite sintered magnet containing B, stable magnetic characteristics can be easily obtained at any temperature of the above-described pre-firing temperature. The time of the calcination (the time of holding at the temperature of the calcination) may be 1 second to 10 hours, preferably 1 second to 5 hours. The calcined body obtained by the calcination contains 70% or more of the main phase (M phase) as described above. The primary particle diameter of the calcined body is preferably 5 μm or less, more preferably 2 μm or less, and still more preferably 1 μm or less. By suppressing the grain growth of the calcined body and reducing the primary particle size of the calcined body (for example, to 1 μm or less), the HcJ of the obtained ferrite sintered magnet can be further improved.

< crushing Process >

In the pulverizing step, the calcined body in the pulverizing and calcining step is made into a powdery or granular state again. This facilitates the molding in the molding step described later. In the pulverization step, raw materials not mixed in the raw material powder preparation step may be further added. However, from the viewpoint of obtaining the effect of the pre-firing temperature dependency or the effect of suppressing the grain growth during the pre-firing, it is preferable that the raw materials are all mixed in the raw material powder preparation step. The grinding step may be a step including two stages, for example, a step of grinding the calcined body to coarse powder (coarse grinding) and then further grinding the ground body finely (fine grinding).

The coarse pulverization is carried out by, for example, a vibration mill until the average particle diameter becomes 0.5to 5.0. mu.m. In the micro-pulverization, the coarsely pulverized material obtained in the coarse pulverization is further pulverized by a wet mill, a ball mill, a jet mill, or the like. In the fine grinding, the average particle size of the obtained fine ground material is preferably 0.08 to 2.0. mu.m, more preferably 0.1 to 1.0. mu.m, and still more preferably 0.1 to 0.5. mu.m. The specific surface area of the finely divided material (for example, as determined by the BET method) is preferably 4 to 12m²Degree of/g. The preferable pulverization time varies depending on the pulverization method, and for example, about 30 minutes to 20 hours is preferable in the case of a wet mill, and about 10 to 50 hours is preferable in the case of wet pulverization by a ball mill.

In the case where a wet method is used in the fine pulverization step, a nonaqueous dispersion medium such as toluene or xylene may be used as the dispersion medium in addition to water. When a nonaqueous dispersion medium is used, high orientation tends to be obtained in wet molding described later. On the other hand, in the case of using an aqueous dispersion medium, it is advantageous from the viewpoint of production efficiency.

In the fine grinding step, for example, a dispersant of the general formula C may be added to improve the degree of orientation of the sintered body obtained after firing_n(OH)_nH_n+2The polyol of (1). Here, as the polyhydric alcohol, in the general formula, n is preferably 4 to 100, more preferably 4 to 30, and further preferablyThe concentration is selected from 4 to 20, and particularly preferably from 4 to 12. Examples of the polyhydric alcohol include sorbitol. In addition, 2 or more kinds of polyhydric alcohols may be used in combination. In addition, other known dispersants may be used in combination with the polyol.

When the polyol is added, the amount of the polyol added is preferably 0.05 to 5.0% by mass, more preferably 0.1 to 3.0% by mass, and still more preferably 0.2 to 2.0% by mass, based on the object to be added (for example, the coarsely ground material). The polyol added in the fine pulverization step is thermally decomposed and removed in a firing step described later.

< Molding Process >

In the molding step, the pulverized material (preferably, a finely pulverized material) obtained after the pulverizing step is molded in a magnetic field to obtain a molded body. The molding can be performed by either dry molding or wet molding. From the viewpoint of improving the degree of orientation of magnetic properties, wet forming is preferably performed.

In the case of forming by wet forming, for example, it is preferable to obtain a slurry by performing the above-mentioned fine pulverization step in a wet manner, then obtain a wet forming slurry by concentrating the slurry to a predetermined concentration, and form the slurry by using the wet forming slurry. The concentration of the slurry can be performed by centrifugal separation, a filter press, or the like. The amount of the finely ground material is preferably about 30 to 80 mass% of the total amount of the wet molding slurry. In this case, a surfactant such as gluconic acid, gluconate, sorbitol, or the like may be added to the slurry. In addition, a nonaqueous dispersion medium may be used as the dispersion medium. As the nonaqueous dispersion medium, an organic dispersion medium such as toluene or xylene can be used. In this case, a surfactant such as oleic acid is preferably added. The wet molding slurry may be prepared by adding a dispersion medium or the like to the finely pulverized material in a dry state after the fine pulverization.

In the wet molding, the slurry for wet molding is then molded in a magnetic field. In this case, the molding pressure is preferably 9.8 to 49MPa (0.1 to 0.5 ton/cm)²) The applied magnetic field is preferably set to be about 398 to 1194kA/m (5 to 15 kOe).

< firing Process >

In the firing step, the compact obtained in the molding step is fired to produce a sintered body. Thus, a ferrite sintered magnet, which is a sintered body of the ferrite magnet as described above, is obtained. Firing can be performed in an oxidizing atmosphere such as the atmosphere. The firing temperature is preferably 1050 to 1270 ℃, and more preferably 1080 to 1240 ℃. The firing time is preferably about 0.5to 3 hours.

In the case where a molded body is obtained by wet molding as described above, when the molded body is rapidly heated in a firing step in a state where the molded body is not sufficiently dried, the dispersion medium or the like is rapidly volatilized, and there is a possibility that cracks are generated in the molded body. Therefore, from the viewpoint of avoiding such a problem, it is preferable to sufficiently dry the molded body by heating the molded body at a low temperature rise rate of about 1 ℃/min, for example, from room temperature to about 100 ℃ before the molded body reaches the above-mentioned sintering temperature, thereby suppressing the occurrence of cracks. When a surfactant (dispersant) or the like is added, it is preferable to sufficiently remove the surfactant (dispersant) by heating at a temperature rise rate of about 3 ℃/min in a temperature range of about 100 to 500 ℃. These treatments may be performed at the beginning of the firing step, or may be performed separately before the firing step.

Although a preferred method for producing a ferrite sintered magnet has been described above, the method for producing a ferrite sintered magnet of the present invention is not limited to the above-described production method, and conditions and the like can be appropriately changed.

The shape of the ferrite sintered magnet is not particularly limited. The ferrite sintered magnet may be in the form of a plate such as a disk, a column such as a cylinder or a quadrangular prism, a C-shape, a bow shape, an arch shape, or a ring shape.

The ferrite sintered magnet according to the present embodiment can be used for, for example, a rotating electrical machine such as a motor or a generator, various sensors, and the like.

Examples

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

(production of ferrite sintered magnet)

[ example 1]

< Process for producing raw Material powder >

As raw materials of metal elements constituting the ferrite sintered magnet, prepared were: calcium carbonate (CaCO)₃) Lanthanum oxide (La)₂O₃) Strontium carbonate (SrCO)₃) Iron oxide (Fe)₂O₃: the impurities include Mn, Cr, Al, Si and Cl, and cobalt oxide (Co)₃O₄). These raw materials were weighed and mixed so that w is 0.390, x is 0.173, z is 9.11, and m is 0.240 in a ferrite sintered magnet containing a metal element at an atomic ratio represented by the following formula (1 a). The obtained raw material mixture was mixed and pulverized with a wet mill for 5 hours, and then dried to obtain a raw material powder.

Ca_1－w－xLa_wSr_xFe_zCo_m···(1a)

< Pre-sintering/pulverizing Process >

The raw material powder was calcined at 1200 ℃ for 2 hours in the air to obtain a calcined body. The obtained calcined body has a specific surface area of 0.5to 2.5m as determined by the BET method²In the form of a/g, coarse comminution is carried out using a small bar vibration mill. The obtained coarse pulverized material is finely pulverized for 32 hours by using a wet ball mill to obtain a powder having a specific surface area of 7.0 to 10m as determined by the BET method²(iv) a slurry for wet molding of the fine ground particles. The slurry after the micro-pulverization is dehydrated by a centrifugal separator, and the solid content concentration is adjusted to 70-80 mass%, thereby obtaining a slurry for wet forming.

< Molding and firing Process >

The slurry for wet molding was molded in an applied magnetic field of 10kOe using a wet magnetic field molding machine to obtain a cylindrical molded body having a diameter of 30mm × a thickness of 15 mm. The obtained molded body was sufficiently dried at room temperature in the air. Next, firing was performed at 1200 ℃ for 1 hour in the air to obtain a sintered ferrite magnet of example 1.

Examples 2 to 28 and comparative examples 1 to 8

Ferrite sintered magnets of examples 2 to 28 and comparative examples 1 to 8 were obtained in the same manner as in example 1, except that the mixing ratio of the raw materials was changed as shown in tables 1 and 2.

Comparative examples 9 and 10

As shown in table 3, the procedure was carried out in the same manner as in example 4 except that the mixing and pulverizing times of the wet grinder in the raw material powder preparation step were changed from 5 hours to 1 hour and 0.5 hour, respectively.

Example 29, comparative example 11 and comparative example 12

The same procedure as in example 4 was repeated, except that the calcination temperatures were changed from 1200 ℃ to 1170 ℃, 1250 ℃ and 1300 ℃, respectively, as shown in Table 3.

Examples 30 to 34 and comparative example 13

As shown in Table 4, boric acid (H) was further prepared as a raw material of the metal elements constituting the ferrite sintered magnet₃BO₃). In the raw material powder preparation step, the boron content of the entire ferrite sintered magnet is set to H₃BO₃Boric acid was weighed in terms of 0.037 mass%, 0.072 mass%, 0.109 mass%, 0.144 mass%, 0.181 mass%, and 0.215 mass%, respectively, and was added to the mixture, and the procedure was carried out in the same manner as in example 4, thereby obtaining sintered ferrite magnets of examples 30 to 34 and comparative example 13.

Examples 35 to 38 and comparative example 14

As shown in Table 4, alumina (Al) was further prepared as a raw material of the metal element constituting the ferrite sintered magnet₂O₃). In the raw material powder preparation step, Al is added to the entire ferrite sintered magnet obtained in the amount of Al₂O₃Example 35E to 0.03 mass%, 0.10 mass%, 0.20 mass%, 0.30 mass%, 0.40 mass% of alumina conversion method weighing, and their addition to the mixture, in the same manner as example 4, obtain38. The ferrite sintered magnet of comparative example 14.

[ examples 39 to 42]

As shown in table 4, barium oxide (BaO) was further prepared as a raw material of the metal element constituting the ferrite sintered magnet. In the raw material powder preparation step, the ferrite sintered magnets of examples 39 to 42 were obtained in the same manner as in example 4 except that barium oxide was weighed so that the barium content was 0.013 mass%, 0.026 mass%, 0.051 mass%, and 0.068 mass%, respectively, in terms of BaO, with respect to the entire ferrite sintered magnet obtained, and these were added to the mixture.

[ example 43]

As shown in Table 4, in the raw material powder preparation step, the boron content was H in the entire ferrite sintered magnet obtained₃BO₃The procedure of example 4 was repeated except that boric acid and alumina were added to the above mixture in such an amount that the content of aluminum was 0.05% by mass in terms of 0.144% by mass, to obtain a ferrite sintered magnet of example 43.

[ example 44]

As shown in Table 4, in the raw material powder preparation step, the boron content was adjusted to H with respect to the entire ferrite sintered magnet obtained₃BO₃Converted into 0.144 mass%, and the aluminum content is calculated as Al₂O₃Boric acid, alumina, and barium oxide were weighed in terms of 0.05 mass% and barium content was 0.051 mass% in terms of BaO, and the mixture was added thereto, and the same procedure as in example 4 was carried out, thereby obtaining a ferrite sintered magnet of example 44.

Example 45, comparative examples 15 and 16

As shown in Table 5, the same procedures as in example 32 were carried out except that the calcination temperature was changed from 1200 ℃ to 1170 ℃, 1250 ℃ and 1300 ℃.

(evaluation method)

[ magnetic characteristics ]

After the upper and lower surfaces of each of the columnar sintered ferrite magnets obtained in examples and comparative examples were processed, the residual magnetic flux density Br (mt) and coercive force HcJ (kA/m) thereof were determined using a B — H tracer with a maximum applied magnetic field of 25kOe, and the external magnetic field strength (Hk) at a magnetic flux density of 90% Br was measured. The squareness ratio Hk/HcJ was determined from the measurement results of Hk and HcJ. The values of Br, HcJ and Hk/HcJ are shown in tables 1 to 5.

[ dependence of sintering temperature ]

In each of examples and comparative examples, a ferrite sintered magnet was produced in the same manner as in each of examples and comparative examples except that the sintering temperature was increased by 10 ℃ from 1200 ℃, and the coercive force HcJ was determined. Δ HcJ/Δ T is obtained by dividing the difference Δ HcJ between HcJ at the changed sintering temperature by the difference Δ T between the sintering temperatures. When Δ HcJ/Δ T ≦ 2.0, the sintering temperature dependency was judged to be good.

[ average diameter and coefficient of variation (CV value) of crystal grains of ferrite sintered magnet ]

The obtained ferrite sintered magnet was cut out in a cross section parallel to the c-axis (easy magnetization axis) direction, mirror-polished, and etched with hydrofluoric acid (concentration: 36%). Next, the etched surface was observed by a Scanning Electron Microscope (SEM) to obtain a cross-sectional image of the crystal grains. The image analysis processing was performed on the cross-sectional images of the crystal grains obtained by SEM observation, and the maximum value Lmax of the length of the overlap between the straight line passing through the center of gravity g of the crystal grains and the crystal grains was measured for each crystal grain as the diameter of the crystal grain. By this method, the standard deviation σ of the arithmetic mean AV of the diameters of the 500 crystal grains and the diameters is obtained, and the coefficient of variation (CV value) is calculated from σ/AV.

[ TABLE 1]

[ TABLE 2]

[ TABLE 3]

[ TABLE 4]

[ TABLE 5 ]

As is clear from the evaluation results in tables 1 to 5, a ferrite sintered magnet containing Ca, La, Sr, Fe, and Co in extremely limited ranges and having a coefficient of variation (CV value) of the crystal grain diameter of less than 45% exhibits a coercive force HcJ of 400kA/m or more and has low firing temperature dependency. This tendency does not change even in the B-containing system, Al-containing system, and Ba-containing system. Further, from the evaluation results of examples 36 to 40, it is understood that the addition of alumina to the production of a ferrite sintered magnet can suppress grain growth during the calcination, reduce the grain size, and improve the coercive force HcJ of the ferrite sintered magnet.