JP2024131943A - Ferrite calcined body and its manufacturing method - Google Patents

Abstract

To make it possible to provide a ferrite temporary sintered body containing Na, which is a new component that differs from conventional SrLaCo magnets and CaLaCo magnets and a manufacturing method for the same.SOLUTION: Concerning the ferrite temporary sintered body, in a general formula: NaxRySr1-x-yFe2n-zCoz, indicating the atomic ratio of metal elements of Na, R, Sr, Fe, and Co (where R is at least one of the rare earth elements and is an element containing La essentially), the x, y and z and n (where 2n is a molar ratio and is represented by 2n=(Fe+Co)/(Na+R+Sr)), satisfy 0.25≤x≤0.5, 0.3≤y≤0.45, 7≤2n-z≤10, 0<z≤0.25.SELECTED DRAWING: None

Description

This disclosure relates to a ferrite calcined body and a method for producing the same.

Although the maximum energy product of ferrite sintered magnets is only about one-tenth that of rare earth sintered magnets (e.g., NdFeB sintered magnets), they offer excellent cost performance because their main raw material is inexpensive iron oxide, and they are characterized by being extremely chemically stable. For this reason, they are used for a variety of applications, including various motors and speakers, and are still the most widely produced magnet material worldwide.

A typical sintered ferrite magnet is Sr ferrite having a magnetoplumbite structure, and its basic composition is represented by SrFe ₁₂ O _19. In the late 1990s, Sr-La- ^Co sintered ferrite magnets (hereinafter sometimes abbreviated as "SrLaCo magnets") were put into practical use, in which part of the Sr ²⁺ in SrFe ₁₂ O ₁₉ was replaced with La ³⁺ and part of the Fe ³⁺ was replaced with Co 2+, and the magnetic properties of ferrite magnets were greatly improved. In 2007, Ca-La-Co sintered ferrite magnets (hereinafter sometimes abbreviated as "CaLaCo magnets") with further improved magnetic properties were put into practical use. The SrLaCo magnets are disclosed in Patent Documents 1 and 2. The CaLaCo magnets are disclosed in Patent Document 3.

Japanese Patent Application Publication No. 10-149910 Japanese Patent Application Publication No. 11-154604 JP 2006-104050 A

Embodiments of the present disclosure make it possible to provide a ferrite calcined body containing Na, a new component that differs from conventional SrLaCo magnets and CaLaCo magnets, and a method for producing the same.

Non-limiting exemplary ferrite calcined bodies of the present disclosure include:
In the general formula Na _x R _y Sr _{1-x-y Fe 2n-z Co z} , which shows the atomic ratio of metal elements Na, R, Sr, _Fe and _Co (wherein R is at least one rare earth element and essentially contains La), the x, y, z and n (wherein 2n is a molar ratio expressed as 2n=(Fe+Co)/(Na+R+Sr)) are:
0.25≦x≦0.5,
0.3≦y≦0.45,
7≦2n−z≦10,
0<z≦0.25,
Satisfy.

In one embodiment,
The x is in the range of 0.3≦x≦0.45.
The y satisfies 0.35≦x≦0.4.
The aforementioned 1-xy satisfies 0.15≦(1-xy)≦0.35.
The aforementioned 1-xy satisfies 0.2≦(1-xy)≦0.3.
The 2n-z satisfies 8.5≦(2n-z)≦9.5, and the z satisfies 0.1≦z≦0.2.

In one embodiment,
The saturation magnetization σ _s is 72 A·m ² /kg or more, and the anisotropic magnetic field H _A is 1690 kA/m or more.
The ratio of a compound phase having a hexagonal magnetoplumbite (M-type) structure is 95 mass % or more.

A non-limiting exemplary method for producing a ferrite calcined body according to the present disclosure includes the steps of:
In the general formula Na _x R _y Sr _{1-x-y Fe 2n-z Co z} , which shows the atomic ratio of metal elements Na, R, Sr, _Fe and _Co (wherein R is at least one rare earth element and essentially contains La), the x, y, z and n (wherein 2n is a molar ratio expressed as 2n=(Fe+Co)/(Na+R+Sr)) are:
0.25≦x≦0.5,
0.3≦y≦0.45,
7≦2n−z≦10,
0<z≦0.25,
A raw material powder preparation process for preparing raw material powder blended to satisfy the above.
a raw material powder mixing step of mixing the raw material powders to obtain a mixed raw material powder;
a calcination step of calcining the mixed raw material powder to obtain a calcined body;
Includes.

In one embodiment,
The x is in the range of 0.3≦x≦0.45.
The y satisfies 0.35≦x≦0.4.
The aforementioned 1-xy satisfies 0.15≦(1-xy)≦0.35.
The aforementioned 1-xy satisfies 0.2≦(1-xy)≦0.3.
The 2n-z satisfies 8.5≦(2n-z)≦9.5, and the z satisfies 0.1≦z≦0.2.

In one embodiment,
In the calcination step, the calcination temperature is 1150°C to 1250°C.
In the calcination step, the calcination temperature is 1150°C to 1200°C.

According to an embodiment of the present disclosure, it is possible to provide a ferrite calcined body containing Na, a new component different from conventional SrLaCo magnets and CaLaCo magnets, and a method for producing the same.

1. Ferrite Calcined Body The ferrite calcined body according to an embodiment of the present disclosure has a general formula Na x R y Sr _1-x-y Fe _2n-z Co _z , which indicates the atomic ratio of metal elements Na _{, R} , Sr, Fe, and Co (wherein R is at least one rare earth element and essentially contains La), in which x, y, z, and n (wherein 2n is a molar ratio expressed as 2n=(Fe+Co)/(Na+R+Sr)) are:
0.25≦x≦0.5,
0.3≦y≦0.45,
7≦2n−z≦10,
0<z≦0.25,
Satisfy.

In the ferrite calcined body of the embodiment of the present disclosure, the atomic ratio x (Na content) is 0.25≦x≦0.5. When x is less than 0.25 or exceeds 0.5, the ratio of nonmagnetic phase (heterogeneous phase) increases, and the magnetic properties ( _σs and H _A ) decrease. In the SrLaCo magnet and CaLaCo magnet, the nonmagnetic phase (heterogeneous phase) tends to be generated more easily when the Co content increases, but in the ferrite calcined body of the embodiment of the present disclosure, when the Na content is within the above range, the generation of the nonmagnetic phase (heterogeneous phase) can be suppressed even if the Co content increases. A more preferable range is 0.25≦x≦0.5.

The atomic ratio y (content of R) is 0.3≦x≦0.45. If y is less than 0.3 or exceeds 0.45, the ratio of non-magnetic phases (heterogeneous phases) increases, and the magnetic properties ( _σs and H _A ) decrease. A more preferred range is 0.35≦x≦0.4. R is at least one rare earth element, and is an element that essentially contains 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).

The atomic ratio 1-xy (Sr content) is preferably 0.15≦(1-xy)≦0.35. If 1-xy is less than 0.15 or exceeds 0.35, the ratio of the nonmagnetic phase (heterogeneous phase) increases, which may result in a decrease in the magnetic properties ( _σs and H _A ), and is therefore undesirable. A more preferable range is 0.2≦(1-xy)≦0.3.

The atomic ratio 2n-z (Fe content) is 7≦2n-z≦10. If 2n-y is less than 7 or equal to or greater than 10, the ratio of nonmagnetic phases (heterogeneous phases) increases, resulting in a decrease in magnetic properties ( _σs and H _A ). A more preferable range is 8.5≦2n-z≦9.5.

The atomic ratio z (Co content) is 0<y≦0.25. When y is 0, the magnetic properties ( _σs and H _A ) are degraded, and when y exceeds 0.25, the amount of Co used increases, leading to an increase in the raw material cost. A more preferable range is 0.1≦z≦0.2.

The general formula is shown in terms of the atomic ratio of metal elements, but the composition containing oxygen (O) is expressed by the general formula: Ca _x R _1-x Fe _2n-y Co _y O _α . The number of moles of oxygen α is basically α=19, but it varies depending on the valences of Fe and Co, and the values of x, y, and n. In addition, the ratio of oxygen to metal elements changes due to oxygen vacancies (vacancies) when fired in a reducing atmosphere, changes in the valence of Fe in the ferrite phase, changes in the valence of Co, and the like. Therefore, the actual number of moles of oxygen α may deviate from 19. Therefore, in the embodiment of the present disclosure, the composition is expressed in terms of the atomic ratio of metal elements whose composition is easiest to identify.

The main phase constituting the ferrite calcined body of the embodiment of the present disclosure is a compound phase (ferrite phase) having a hexagonal magnetoplumbite (M-type) structure. In general, magnetic materials, particularly sintered magnets, are composed of multiple compounds, and the compound that determines the characteristics (physical properties, magnetic properties, etc.) of the magnetic material is defined as the "main phase."

On the other hand, hematite phase (α-Fe ₂ O ₃ ), orthoferrite phase (LaFeO _3, etc.), and spinel ferrite phase (CoFe ₂ O _4, etc.) other than the ferrite phase (M phase) are "heterogeneous phases" and non-magnetic phases. In order to obtain high magnetic properties, it is effective to increase the constituent phase ratio (hereinafter sometimes referred to as "phase ratio") of the ferrite phase (hereinafter sometimes referred to as "M phase"), which is the main phase of the ferrite calcined body, and to decrease the ratio of the non-magnetic phase. In the ferrite calcined body of the embodiment of the present disclosure, the ratio of the compound phase (M phase) having a hexagonal magnetoplumbite (M type) structure is 95 mass% or more.

"Having a hexagonal magnetoplumbite (M-type) structure" means that in powder X-ray diffraction measurement of the calcined ferrite body under typical conditions, an X-ray diffraction pattern that is primarily indicative of a hexagonal magnetoplumbite (M-type) structure is observed.

2. Method for Producing Ferrite Calcined Body The method for producing a ferrite calcined body according to an embodiment of the present disclosure is a method for producing a ferrite calcined body according to a general formula Na _x R _y Sr _1-x-y Fe 2n- _{z Co z,} which indicates the atomic ratio of metal elements Na, R, Sr, Fe, and Co (wherein R is at least one rare earth element and essentially contains La), and wherein x, y, z, and n (wherein 2n is a molar ratio and is expressed as 2n=(Fe+Co)/(Na+R+Sr)) are:
0.25≦x≦0.5,
0.3≦y≦0.45,
7≦2n−z≦10,
0<z≦0.25,
A raw material powder preparation process for preparing raw material powder blended to satisfy the above.
a raw material powder mixing step of mixing the raw material powders to obtain a mixed raw material powder;
and a calcination step of calcining the mixed raw material powder to obtain a calcined body.

(1) Raw material powder preparation process As the raw material powder, compounds such as oxides, carbonates, hydroxides, nitrates, and chlorides of each metal can be used regardless of the valence. A solution in which the raw material powder is dissolved may also be used. Examples of Na compounds include Na carbonates, _hydroxides , oxides, and chlorides. Examples of R compounds include, for example, oxides such as _La2O3 , hydroxides such as La(OH) ₃ , and carbonates such as _La2 ( _CO3 ) _3.8H2O . Examples of Sr compounds include Sr carbonates, oxides, and _chlorides . Examples of Fe compounds include iron oxide, iron hydroxide, iron chloride, and mill scale. Examples of Co compounds include oxides _such as CoO and _Co3O4 , hydroxides such as CoOOH and _Co ( _OH ) ₂ , carbonates such as _CoCO3 , and basic carbonates such as _m2CoCO3.m3Co ( _{OH)2.m4H2O ( m2 , m3} , and _m4 are positive numbers).

_The raw material powders, for example, _Na2CO3 powder, La(OH) ₃ powder, _SrCO3 powder _{, Fe2O3 powder} , and _Co3O4 powder, are weighed and mixed so as to satisfy the range of the general formula, to prepare the raw material powder.

In order to promote the reaction during calcination, compounds containing B (boron), such as B ₂ O ₃ and H ₃ BO ₃ , may be added up to about 1 mass% as necessary. In particular, the addition of H ₃ BO ₃ is effective in improving the magnetic properties. The amount of _{H 3} BO ₃ added is preferably 0.3 mass% or less, and most preferably about 0.1 mass%. _{H 3} BO ₃ also has the effect of controlling the shape and size of crystal grains during sintering, so it may be added after calcination (before pulverization or sintering), or it may be added both before and after calcination.

(2) Raw material powder mixing process The raw material powders prepared in the raw material powder preparation process are mixed to obtain a mixed raw material powder. The raw material powders may be mixed in either a wet or dry manner. In the case of wet mixing, a water solvent is usually used as a dispersion medium, but since Na raw material powder, for example _Na2CO3 powder _, is soluble in water, it is more preferable to wet mix using ethanol. Furthermore, it is preferable to stir with a medium such as a steel ball, since it can be mixed more uniformly. In order to increase the dispersibility of the raw material powder, a known dispersant such as ammonium polycarboxylate or calcium gluconate may be used. The mixed raw material slurry may be calcined after drying, or may be calcined as it is.

(3) Calcination process The mixed raw material powder obtained by wet mixing or dry mixing is heated using an electric furnace, a gas furnace, or the like to form a ferrite compound having a hexagonal magnetoplumbite (M-type) structure by a solid-phase reaction. This process is called "calcination," and the resulting compound is called a "calcined body." Therefore, the ferrite calcined body of the embodiment of the present disclosure can be rephrased as a ferrite compound.

In the calcination process, a solid-phase reaction in which a ferrite phase is formed progresses as the temperature rises. If the calcination temperature is too low, unreacted hematite (iron oxide) remains, resulting in poor magnetic properties. On the other hand, if the calcination temperature is too high, the crystal grains grow too much, and the pulverization process may take a long time. Conventional SrLaCo magnets and CaLaCo magnets are often calcined at temperatures exceeding 1200°C (approximately 1250°C to 1300°C). However, in the embodiment of the present disclosure, calcination can be performed at a relatively low temperature of 1150°C to 1250°C, and more preferably 1150°C to 1200°C. This allows the process cost to be reduced. The calcination time is preferably 0.5 to 5 hours. The calcined body after calcination is preferably coarsely pulverized using a hammer mill or the like.

By going through the above steps, the ferrite calcined body according to the embodiment of the present disclosure can be obtained.

The embodiments of the present disclosure will be described in more detail with reference to examples, but the embodiments of the present disclosure are not limited thereto.

Experimental Example 1
As an experimental example based on an embodiment of the present disclosure, Na _{2 CO 3 powder} , La(OH _{) 3 powder} , SrCO ₃ powder, Fe 2 _{O 3 powder} , and Co 3 O ₄ powder were weighed out so that the atomic ratios of x, y, 1-x-y, 2n-z, and z were as shown in Sample Nos. 1 to ₁₉ in Table 1 in the general formula Na _{x La} y Sr _1-x - _y Fe _{2n- Co} z, and 0.1 mass% of H ₃ BO ₃ powder was added to the total of 100 mass% of the weighed powders to prepare each raw material powder.

Each of the prepared raw material powders was mixed in a wet ball mill for 4 hours using ethanol as a dispersion medium, and then dried and sized to obtain 19 types of mixed raw material powders.

The resulting mixed raw material powders were calcined in air at 1200°C for 3 hours to obtain 19 types of calcined bodies. Each of the resulting calcined bodies was then coarsely crushed in a small mill to obtain 19 types of coarsely crushed powders (calcined powders).

The ratio (mass%) of the constituent phases contained in the 19 types of coarsely pulverized powders was determined. The results are shown in Table 1. X-ray diffraction measurements were performed using an X-ray diffractometer (D8 ADVANCE TXS manufactured by Bruker AXS), and the constituent phase ratios were determined from the obtained diffraction patterns by Rietveld analysis. The measurement results of σ _s and H _A of the obtained 19 types of ferrite calcined bodies are shown in Table 1.

The atomic ratios of samples No. 1 to 19 in Table 1 indicate the atomic ratios (compositions) when the raw material powders are blended. Although a small amount of H ₃ BO ₃ is added, the composition is basically the same as the atomic ratios in the calcined body after calcination (calcined body composition). When the calcined body composition is to be determined strictly, it can be calculated based on the atomic ratios at the time of blending, taking into account the amount of additives (H ₃ BO ₃ , etc.) added before the calcination process. The calculated values are basically the same as the results of analyzing the ferrite calcined body with an ICP emission spectrometer (for example, Shimadzu ICPV-1017, etc.).

As comparative examples _, a known _SrLaCo magnet (general formula: _{Sr0.8La0.2Fe11.8Co0.2} ) and a known CaLaCo magnet (general formula: _{Ca0.5La0.5Fe10.1Co0.3} ) were produced based on the descriptions in the above Patent Documents 1 to 3, and the saturation magnetization _σs and _anisotropic magnetic field _{H A} were measured. As a result, the saturation magnetization _σs of the SrLaCo magnet was _74.2 A· ^m2 /kg, and the anisotropic magnetic field H _A was 1.78 MA/m, while the saturation magnetization _σs of the _CaLaCo magnet was 75.3 A· ^m2 /kg, and the anisotropic magnetic field H _A was 2.17 MA/m.

In addition, known SrLaCo magnets contain Co at an atomic ratio of about 0.2 (Co/Fe = 0.017, or about 1.7% of the Fe content), while known CaLaCo magnets contain Co at an atomic ratio of about 0.3 (Co/Fe = 0.03, or about 3% of the Fe content).

As shown in Table 1, the ferrite calcined body according to the embodiment of the present disclosure exhibits magnetic properties such as a saturation magnetization _σs of 72 A· ^m2 /kg or more and an anisotropic magnetic field H _A of 1.69 MA/m or more, which are close to those of known SrLaCo magnets and CaLaCo magnets, despite the Co content being 0.2 or less in atomic ratio. Therefore, it is expected that a high-performance sintered ferrite magnet can be provided at a low cost.

The calcined body and the manufacturing method thereof according to the embodiment of the present disclosure have excellent saturation magnetization _σs and anisotropic magnetic field _HA approaching those of conventional SrLaCo magnets and CaLaCo magnets. Therefore, when used as a compound constituting a sintered ferrite magnet, a sintered ferrite magnet having high magnetic properties can be obtained, and can be suitably used in various motors, etc.

Claims (18)

In the general formula Na _x R _y Sr _{1-x-y Fe 2n-z Co z} , which shows the atomic ratio of metal elements Na, R, Sr, _Fe and _Co (wherein R is at least one rare earth element and essentially contains La), the x, y, z and n (wherein 2n is a molar ratio expressed as 2n=(Fe+Co)/(Na+R+Sr)) are:
0.25≦x≦0.5,
0.3≦y≦0.45,
7≦2n−z≦10,
0<z≦0.25,
A ferrite calcined body that satisfies the above requirements. The ferrite calcined body according to claim 1, wherein x is in the range of 0.3≦x≦0.45. The ferrite calcined body according to claim 1, wherein y is 0.35≦x≦0.4. The ferrite calcined body according to claim 1, wherein 1-x-y is 0.15≦(1-x-y)≦0.35. The ferrite calcined body according to claim 1, wherein 1-x-y is 0.2≦(1-x-y)≦0.3. The ferrite calcined body according to claim 1, wherein 2n-z satisfies 8.5≦(2n-z)≦9.5. The ferrite calcined body according to claim 1, wherein z is in the range of 0.1≦z≦0.2. 2. The calcined ferrite body according to claim 1, having a saturation magnetization _σs of 72 A·m ² /kg or more and an anisotropic magnetic field H _A of 1690 kA/m or more. The ferrite calcined body according to claim 1, in which the ratio of a compound phase having a hexagonal magnetoplumbite (M-type) structure is 95% by mass or more. In the general formula Na _x R _y Sr _{1-x-y Fe 2n-z Co z} , which shows the atomic ratio of metal elements Na, R, Sr, _Fe and _Co (wherein R is at least one rare earth element and essentially contains La), the x, y, z and n (wherein 2n is a molar ratio expressed as 2n=(Fe+Co)/(Na+R+Sr)) are:
0.25≦x≦0.5,
0.3≦y≦0.45,
7≦2n−z≦10,
0<z≦0.25,
A raw material powder preparation process for preparing raw material powder blended to satisfy the above.
a raw material powder mixing step of mixing the raw material powders to obtain a mixed raw material powder;
a calcination step of calcining the mixed raw material powder to obtain a calcined body;
A method for producing a ferrite calcined body comprising the steps of: The method for producing a ferrite calcined body according to claim 10, wherein x is 0.3≦x≦0.45. The method for producing a ferrite calcined body according to claim 10, wherein y is 0.35≦x≦0.4. The method for producing a ferrite calcined body according to claim 10, wherein 1-x-y satisfies 0.15≦(1-x-y)≦0.35. The method for producing a ferrite calcined body according to claim 10, wherein 1-x-y satisfies 0.2≦(1-x-y)≦0.3. The method for producing a ferrite calcined body according to claim 10, wherein 2n-z satisfies 8.5≦(2n-z)≦9.5. The method for producing a ferrite calcined body according to claim 10, wherein z is 0.1≦z≦0.2. The method for producing a ferrite calcined body according to claim 10, wherein the calcination temperature in the calcination step is 1150°C to 1250°C. The method for producing a ferrite calcined body according to claim 10, wherein the calcination temperature in the calcination step is 1150°C to 1200°C.