WO2004103909A1 - Magnetoplumbite type ferrite particle, anisotropic sintered magnet, and producing method of the same - Google Patents

Magnetoplumbite type ferrite particle, anisotropic sintered magnet, and producing method of the same Download PDF

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Publication number
WO2004103909A1
WO2004103909A1 PCT/KR2003/001091 KR0301091W WO2004103909A1 WO 2004103909 A1 WO2004103909 A1 WO 2004103909A1 KR 0301091 W KR0301091 W KR 0301091W WO 2004103909 A1 WO2004103909 A1 WO 2004103909A1
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powders
sintered magnet
ferrite
added
composition
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PCT/KR2003/001091
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French (fr)
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Sung Woo Shon
Jae Won Bae
Myung Kwon Kim
Young Cheul Park
Sung Il Hong
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Pacific Metals Co., Ltd.
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Priority to AU2003241195A priority Critical patent/AU2003241195A1/en
Publication of WO2004103909A1 publication Critical patent/WO2004103909A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G49/00—Compounds of iron
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/10—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials non-metallic substances, e.g. ferrites, e.g. [(Ba,Sr)O(Fe2O3)6] ferrites with hexagonal structure
    • H01F1/11—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials non-metallic substances, e.g. ferrites, e.g. [(Ba,Sr)O(Fe2O3)6] ferrites with hexagonal structure in the form of particles
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G49/00—Compounds of iron
    • C01G49/0018—Mixed oxides or hydroxides
    • C01G49/0036—Mixed oxides or hydroxides containing one alkaline earth metal, magnesium or lead
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G49/00—Compounds of iron
    • C01G49/009—Compounds containing, besides iron, two or more other elements, with the exception of oxygen or hydrogen
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G51/00—Compounds of cobalt
    • C01G51/006—Compounds containing, besides cobalt, two or more other elements, with the exception of oxygen or hydrogen
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G51/00—Compounds of cobalt
    • C01G51/40—Cobaltates
    • C01G51/42—Cobaltates containing alkali metals, e.g. LiCoO2
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/26—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on ferrites
    • C04B35/2683—Other ferrites containing alkaline earth metals or lead
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
    • H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
    • H01F41/0266—Moulding; Pressing
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/42—Magnetic properties

Definitions

  • the present invention relates to highly-efficient hexagonal ferrite magnetic powders and an anisotropic sintered magnet, in particular to hexagonal ferrite magnetic powders and a ferrite anisotropic sintered magnet using the same, wherein residual magnetic flux density is improved without reducing coercive force by adding Li element or Li and Co elements, and thus maximum energy product is correspondingly improved.
  • the present invention relates a method of manufacturing a ferrite anisotropic sintered magnet by mixing, calcinating and coarse-crashing raw powders, adding Li element or Li and Co elements to the powders and fine-crushing them whereby preparing hexagonal ferrite magnetic powders, and molding and sintering the magnetic powders in a magnetic field.
  • ferrite anisotropic sintered magnets have very excellent magnetic properties, can be prepared using inexpensive raw materials, and thus are widely used in electronic devices, etc.
  • mi iiatirrization and high effectiveness of the electronic devices are recently issued, it is strongly required for highly-efficient magnets having high residual magnetic flux density (Br) and coercive force (iHc), i.e., high maximum energy product ((BH)max).
  • iHc coercive force
  • BH maximum energy product
  • CaO and SiO 2 of additives which are added to the ferrite anisotropic sintered magnet induce a liquid-phase sintering within the ferrite anisotropic sintered magnet and thus controls a sintered density and a size of a grain according to the added amounts and addition proportions thereof.
  • Al O 3 and Cr 2 O 3 significantly constraints grains of the ferrite sintered magnet from growing, thereby improving the coercive force.
  • Al 2 O 3 and Cr 2 O 3 lowers the density of the sintered body and forms a nonmagnetic solid solution within the grains of the ferrite sintered magnet, thereby reducing the residual magnetic flux density, the kinds and amounts of additives have been properly selected correspondingly to the performance of the magnet required.
  • the object of the present invention is to provide hexagonal ferrite magnetic powders having improved residual magnetic flux density and a maximum energy product without reducing coercive force by adding Li element or Li and Co elements and a hexagonal anisotropic sintered magnet using the powders.
  • another object of the invention is to provide a method of a ferrite anisotropic sintered magnet, wherein a sintered magnet having excellent magnetic properties can be prepared witliout making the prior manufacturing processes be complex regardless of using very large diameter of particles by mixing, calcinating and coarse-crashing raw powders, adding Li element or Li and Co elements to the powders and fme-crashing, thus preparing hexagonal ferrite magnetic powders, molding and sintering the magnetic powders in a magnetic field, and thus preparing a sintered magnet, and a time of molding cycle can be resultingly shorten and a molding productivity can be improved.
  • hexagonal ferrite magnetic powders having a composition of the following fonnula 1;
  • the hexagonal ferrite magnetic powders according to the invention further comprise Al or Cr element and thus have a composition of the following formula 2;
  • M is at least one of Al and Cr
  • x indicates a composition ratio of Li
  • y indicates a composition ratio of Co
  • z indicates a composition ratio of Al or Cr x
  • y, z and n satisfy the following ranges: 0.01 ⁇ x ⁇ 0.3
  • mole ratio of oxygen (O) is shown as 3n+ ⁇ , wherein ⁇ is 1 according to a stoichiometric composition ratio, but is actually varied according to kinds of L and M or values of x, y and z and has a value of 1 or more.
  • a ferrite amsotropic sintered magnet according to the invention is formed with the above magnetic powders.
  • a method of manufacturing hexagonal ferrite magnetic powders comprising steps of (a) mixing and calcinating SrCO 3 andFe 2 O 3 ; (b) crashing the calcinated bodies of step (a); and (c) adding Li 2 CO 3 or Li 2 O to input Li or adding LiCoO 2 alone or Li 2 CO 3 or Li 2 O together with Co 3 O to input Li and Co to the crushed powders of step (b) and fine- crashing them, thereby preparing magnetic powders satisfying the composition of the formula 1 or 2.
  • the step (c) of the method of manufacturing hexagonal ferrite magnetic powders according to the invention Cr 2 O 3 or Al O 3 is added to input Al or Cr as M.
  • a method of manufacturing a ferrite anisotropic sintered magnet comprising steps of (a) mixing and calcinating SrCO 3 and Fe 2 O 3 ; (b) crushing the calcinated bodies of step (a); (c) adding Li CO or Li O to input Li or adding LiCoO 2 alone or Li CO 3 or Li 2 O together with Co 3 O to input Li and Co to the crushed powders of step (b) and fine- crashing them, thereby preparing magnetic powders satisfying the composition of the formula 1 or 2; and (d) molding and sintering the mixed powders of step (c), thereby preparing a sintered magnet.
  • step (c) of the method of manufacturing ferrite anisotropic sintered magnet according to the invention Cr 2 O 3 or Al O 3 is added to input Al or Cr as M.
  • the crashing is carried out for an average diameter of particles to be about 1.0 ⁇ m when fme-crashing in the step (c), in order to shorten a time of molding cycle to below 60 seconds.
  • a dispersion agent of polycarbonate or phosphate is added in an amount of 0.1-2.5 wt%, just before the fme-crashing step of (c) or the molding step of (d).
  • prior coarse powders having a general composition by adding predetennined amounts of CaO and SiO to ferrite magnetic coarse-powders having a certain range of mole ratio are added with (1) Li 2 CO 3 or Li 2 O to add Li element to the whole composition, or (2) LiCoO 2 alone or Li 2 CO 3 or Li 2 O together with Co 3 O to add Li and Co elements to the whole composition, thereby making it possible to make a highly-efficient ferrite anisotropic sintered magnet having improved residual magnetic flux density.
  • at least one of Cr 2 O 3 and Al 2 O 3 is added to obtain high coercive force necessary for industrial use.
  • Magnetic powders and a method of manufacturing a sintered magnet according to the invention are described below.
  • SrCO 3 and Fe 2 O 3 which are raw materials, are mixed to be a certain mole ratio, calcinated to synthesize them to a ferrite clinker state, and then coarse- crashed, thereby providing ferrite magnetic powders.
  • SrO, CaO and SiO 2 which are T KR2003/001091
  • agents of aiding a sintering are added to the coarse powders hi a proper amount within a range of 0.2 wt.%-1.0 wt.%, respectively.
  • Li 2 CO 3 or Li 2 O is added to add Li element to the whole composition
  • LiCoO 2 alone or Li 2 CO or Li 2 O together with Co 3 O 4 is added to add Li and Co elements to the whole composition.
  • at least one of Cr O 3 and Al 2 O 3 may be added in a predetermined amount.
  • the mixed powders are fine-crushed to have a proper average diameter.
  • sintering is carried out at an appropriate temperature, thereby preparing a high-density of an anisotropic sintered magnet.
  • the magnetic powders of the invention may be made as a bond magnet by mixing rubber or a light weight of plastics, etc. At this time, the magnet powders of the mvention are mixed with binder and additives, and then subject to molding process after kneading.
  • FIG. 1 is a graph showing residual magnetic flux densities (Br) and coercive forces (iHc) of ferrite amsotropic sintered magnets prepared by Examples 1 and 2 according to embodiments of the invention and Comparative example 1;
  • FIG. 2 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 3 and 4 according to embodiments of the invention and Comparative example 1;
  • FIG. 3 is a graph showing maximum energy products ((BH)max) of ferrite anisotropic sintered magnets prepared by Examples 3 and 4 according to embodiments of the invention and Comparative example 1 ;
  • FIG. 4 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 5 and 6 according to embodiments of the invention and Comparative examples 2 and 3;
  • FIG. 5 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 5 and 7 according to embodiments of the invention in order to compare the magnetic properties of the sintered magnets according to the average size of particles;
  • FIG. 6 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 8 according to an embodiment of the invention and Comparative example 4;
  • FIG. 7 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared while changing the mole ratio of Fe by Example 9 according to an embodiment of the invention.
  • SrCO 3 and Fe 2 O were wet-mixed so that in SrFe 2n O 3n+1 , which is a general formula of a hexagonal ferrite sintered magnet, n was 5.9, and calcinated at 1280°C for 2 hours in the atmosphere.
  • Calcination clinker was dry coarse-crashed in a disk mill, and then Li CO 3 or Li 2 O was added ' so that in SrFe 2n Li x+ yM z O 3n+ ⁇ , that is SrFe 2n Li ⁇ C ⁇ yM z O 3n+ ⁇ , x was 0.15 and y and z were 0.
  • CaO and SiO 2 which are sintering accelerants, were added in an amount of 0.5 wt.% and 0.35 wt.%, respectively.
  • Added coarse powders were wet fine- crushed so that the average diameter thereof was 0.8 ⁇ m.
  • the fine-crushed slurry was wet-molded in a vertical magnetic field of 10 kOe, and then the molded body was sintered at 1200-1240 °C for 2 hours in the atmosphere, so that hexagonal ferrite anisotropic sintered magnet havmg a composition was prepared.
  • a hexagonal ferrite anisotropic sintered magnet having a composition of SrFe ⁇ .8Lio. ⁇ C ⁇ o.osOi 8 . 8 ⁇ was prepared by the same method as the Example I, except that Li O or Li CO 3 was added together with Co 3 O so that in SrFe 2n Li x C ⁇ yM z O 3n+ ⁇ , x was 0.1 , y was 0.05 and z was 0. ⁇ Example 3>
  • a hexagonal ferrite anisotropic sintered magnet having a composition of SrFen.8Lio.05Coo.05Oi8.792 was prepared by the same method as the Example 1, except that LiCoO 2 only was added or Li 2 O or Li 2 CO 3 was added together with Co 3 O 4 so that x and y were 0.05 and z was 0.
  • a hexagonal ferrite anisotropic sintered magnet having a composition of
  • SrFen.8 io.05Coo.05Oi8.792 was prepared by the same method as the Example 3, except that dispersion agent consisting of polycarbonate or phosphate was added in an amount of 0.2 wt.% to solid powders of slurry for reducing viscosity of fine-crashed slurry and improving fluidity of ferrite magnetic particles.
  • Fig. 1 is a graph showing residual magnetic flux densities (Br) and coercive forces (iHc) of ferrite anisotropic sintered magnets prepared by Examples 1 and 2 according to embodiments of the invention and Comparative example 1.
  • Fig. 2 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 3 and 4 according to embodiments of the invention and Comparative example 1.
  • Fig. 3 is a graph showing maximum energy products ((BH)max) of ferrite anisotropic sintered magnets prepared by Examples 3 and 4 according to embodiments of the invention and Comparative example 1. As shown in Fig. 3, the maximum energy product was also significantly improved in the ferrite sintered magnets having Li and Co added thereto according to the invention.
  • a hexagonal ferrite anisotropic sintered magnet having a composition of SrFe .8Lio.05Coo.05Cro.nOi8.957 was prepared by the same method as the Example 3, except that M was Cr and Cr 2 O 3 was added for z to be 0.11.
  • a hexagonal ferrite anisotropic sintered magnet having a composition of SrFen.8Lio.05Coo.05Alo.nOi 8 . 957 was prepared by the same method as the Example 3, except that M was Al and Al 2 O 3 was added for z to be 0.11. ⁇ Comparative example 2>
  • Fig. 4 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 5 and 6 according to embodiments of the invention and Comparative examples 2 and 3. As shown in Fig. 4, the sintered magnets of Examples 5 and 6, wherein
  • FIG. 5 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 5 and 7 according to embodiments of the invention to in order to compare the magnetic properties of the sintered magnets according to the average size of particles.
  • Example 7 showed more excellent magnetic properties than the magnet (Comparative example 2) having a general composition to which Li and Co components were never added and an average diameter of 0.8 ⁇ m.
  • the average diameter of powders is below 0.8 ⁇ m, a dehydrating property becomes poor in molding and thus molding time is lengthened and abnormal growth of particles occurs in sintering. Accordingly, the average diameter of powders is preferred to be 0.8 ⁇ m or more in order to improve the productivity and to stabilize the magnetic properties. Considering cutting down on expenses, it is most efficient that the average diameter is about 1.0 ⁇ m.
  • a hexagonal ferrite anisotropic sintered magnet having a composition of
  • Fig. 6 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 8 according to an embodiment of the invention and Comparative example 4. As shown in Fig. 6, the coercive force generally increases as the z value increases.
  • Example 8 to which Li and Co components were added has an outstandingly excellent residual magnetic flux density, compared to Comparative example 4 having a general composition to which Li and Co components were not added, in a same level of coercive force.
  • Hexagonal ferrite anisotropic sintered magnets having various compositions were prepared by the same method as the Example 3, except that x and y were fixed to be 0.05 and n was changed to 5.0, 5.3, 5.5, 5.7, 5.9, 6.1, 6.3, .5 and 6.7.
  • Fig. 7 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared while changing the mole ratio of Fe by Example 9 according to an embodiment of the invention.
  • the residual magnetic flux density is improved without lowering the coercive force by adding Li element or Li and Co elements and thus the maximum energy product is also improved.
  • the method of manufacturing a ferrite anisotropic sintered magnet a sintered magnet having excellent magnetic properties can be prepared without making the prior manufacturing processes be complex regardless of using very large diameter of particles, by mixing, calcinating and coarse-crashing raw powders, adding Li element or Li and Co elements to the crushed powders and fme-crashing them, thus preparing hexagonal ferrite magnetic powders, molding and sintering the magnetic powders in a magnetic field, and thus preparing a sintered magnet, and a time of molding cycle can be also resultingly shorten and a molding productivity can be improved.
  • the hexagonal ferrite magnetic powders and the ferrite anisotropic sintered magnet using the powders have a high residual magnetic flux density and coercive force. As a result, the maximum energy product thereof is also very excellent. Accordingly, various kinds of DC power motors used for home apphance and devices for a vehicle can be miniaturized and hght-weighted and a high efficient motor can be manufactured.

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Abstract

Ferrite particles with a hexagonal structure according to the present invention have a composition of the following formula I [Formula I] SrFe2nLx+yO3n+Θ (wherein, L is lithium or lithium and cobalt, x represents composition ratio of lithium, y represents composition ratio of cobalt, and x, y, and n satisfy the following ranges: 0.01≤ x≤ 0.3, 0.0≤ y≤ 0.3, and 5.5≤ n≤ 6.3) The sintered magnet according to the present invention is prepared by the above-described ferrite particles.

Description

MAGNETOP UMBITE TYPE FERRITE PARTICLE,
ANISOTROPIC SINTERED MAGNET, AND PRODUCING
METHOD OF THE SAME
TECHNICAL FIELD
The present invention relates to highly-efficient hexagonal ferrite magnetic powders and an anisotropic sintered magnet, in particular to hexagonal ferrite magnetic powders and a ferrite anisotropic sintered magnet using the same, wherein residual magnetic flux density is improved without reducing coercive force by adding Li element or Li and Co elements, and thus maximum energy product is correspondingly improved. hi addition, the present invention relates a method of manufacturing a ferrite anisotropic sintered magnet by mixing, calcinating and coarse-crashing raw powders, adding Li element or Li and Co elements to the powders and fine-crushing them whereby preparing hexagonal ferrite magnetic powders, and molding and sintering the magnetic powders in a magnetic field.
BACKGROUND ART
Generally, ferrite anisotropic sintered magnets have very excellent magnetic properties, can be prepared using inexpensive raw materials, and thus are widely used in electronic devices, etc. However, as mi iiatirrization and high effectiveness of the electronic devices are recently issued, it is strongly required for highly-efficient magnets having high residual magnetic flux density (Br) and coercive force (iHc), i.e., high maximum energy product ((BH)max). There have been methods of increasing saturated magnetization (Is) of main magnetic phase, increasing sintered density of sintered bodies or improving a degree of orientation of particles of magnetic phase as a method of improving residual magnetic flux density of ferrite anisotropic sintered magnets.
Meanwhile, there is known a method of increasing an anisotropic magnetic field (HA) of main magnetic phase or increasing a proportion of a magnitude of single domain particle in sintered magnets as a method of improving coercive force. .
Like this, in order to improve the performance of a ferrite anisotropic sintered magnet, there have been various investigations regarding manufacturing conditions such as a composition of a ferrite sintered magnet or additives, resulting in developments of ferrite sintered magnets having various compositions. However, since the final shape of the magnets having various compositions is also a sintered body, when a density of the sintered body is increased to improve the residual magnetic flux density, unnecessary growth of grains occurs and thus the coercive force is reduced. That is, it is very difficult to improve both the residual magnetic flux density and the coercive force at the same time.
Meanwhile, CaO and SiO2 of additives which are added to the ferrite anisotropic sintered magnet induce a liquid-phase sintering within the ferrite anisotropic sintered magnet and thus controls a sintered density and a size of a grain according to the added amounts and addition proportions thereof. In addition, Al O3 and Cr2O3 significantly constraints grains of the ferrite sintered magnet from growing, thereby improving the coercive force. However, since Al2O3 and Cr2O3 lowers the density of the sintered body and forms a nonmagnetic solid solution within the grains of the ferrite sintered magnet, thereby reducing the residual magnetic flux density, the kinds and amounts of additives have been properly selected correspondingly to the performance of the magnet required. In other words, since the prior additives improve the residual magnetic flux density but reduce the coercive force in the ferrite sintered magnet, there have been attempts of improving the residual magnetic flux density and the coercive force at the same time by regulating the manufacturing conditions such as an addition timing and a sintering temperature or making the average diameter of particles be more small. However, the attempts were not efficient.
Like this, since the manufacturing processes and conditions are varied according to the performance of magnet required, the processes become complicated and costs of manufacturing are increased. Accordingly, there is a need of a novel economic sintered magnet having improved magnetic properties and being easily manufactured and a manufacturing method thereof.
DISCLOSURE OF THE INVENTION Accordingly, the present invention has been made to solve the above- mentioned problems occurring in the prior art. The object of the present invention is to provide hexagonal ferrite magnetic powders having improved residual magnetic flux density and a maximum energy product without reducing coercive force by adding Li element or Li and Co elements and a hexagonal anisotropic sintered magnet using the powders.
In addition, another object of the invention is to provide a method of a ferrite anisotropic sintered magnet, wherein a sintered magnet having excellent magnetic properties can be prepared witliout making the prior manufacturing processes be complex regardless of using very large diameter of particles by mixing, calcinating and coarse-crashing raw powders, adding Li element or Li and Co elements to the powders and fme-crashing, thus preparing hexagonal ferrite magnetic powders, molding and sintering the magnetic powders in a magnetic field, and thus preparing a sintered magnet, and a time of molding cycle can be resultingly shorten and a molding productivity can be improved. In order to accomplish the objects, there is provided hexagonal ferrite magnetic powders having a composition of the following fonnula 1;
[formula 1]
Figure imgf000006_0001
wherein, L is Li element or Li and Co elements, x indicates a composition ratio of Li, y indicates a composition ratio of Co, x, y and n satisfy the following ranges:
0.01 ≤ x ≤ 0.3,
0.01 <y< 0.3, and 5.5 <n < 6.3.
The hexagonal ferrite magnetic powders according to the invention further comprise Al or Cr element and thus have a composition of the following formula 2;
[formula 2]
Figure imgf000006_0002
wherein, L is Li element or Li and Co elements,
M is at least one of Al and Cr, x indicates a composition ratio of Li, y indicates a composition ratio of Co, z indicates a composition ratio of Al or Cr x, y, z and n satisfy the following ranges: 0.01 <x < 0.3,
0.01 <y< 0.3,
0.01 <z < 0.8, and
5.5 <n < 6.3. In the above formulas 1 and 2, mole ratio of oxygen (O) is shown as 3n+Θ, wherein Θ is 1 according to a stoichiometric composition ratio, but is actually varied according to kinds of L and M or values of x, y and z and has a value of 1 or more.
A ferrite amsotropic sintered magnet according to the invention is formed with the above magnetic powders. According to another embodiment of the invention, there is provided a method of manufacturing hexagonal ferrite magnetic powders comprising steps of (a) mixing and calcinating SrCO3 andFe2O3; (b) crashing the calcinated bodies of step (a); and (c) adding Li2CO3 or Li2O to input Li or adding LiCoO2 alone or Li2CO3 or Li2O together with Co3O to input Li and Co to the crushed powders of step (b) and fine- crashing them, thereby preparing magnetic powders satisfying the composition of the formula 1 or 2. h the step (c) of the method of manufacturing hexagonal ferrite magnetic powders according to the invention, Cr2O3 or Al O3 is added to input Al or Cr as M.
According to another embodiment of the invention, there is provided a method of manufacturing a ferrite anisotropic sintered magnet comprising steps of (a) mixing and calcinating SrCO3 and Fe2O3; (b) crushing the calcinated bodies of step (a); (c) adding Li CO or Li O to input Li or adding LiCoO2 alone or Li CO3 or Li2O together with Co3O to input Li and Co to the crushed powders of step (b) and fine- crashing them, thereby preparing magnetic powders satisfying the composition of the formula 1 or 2; and (d) molding and sintering the mixed powders of step (c), thereby preparing a sintered magnet.
In the step (c) of the method of manufacturing ferrite anisotropic sintered magnet according to the invention, Cr2O3 or Al O3 is added to input Al or Cr as M. hi the method of manufacturing ferrite anisotropic sintered magnet according to the invention, the crashing is carried out for an average diameter of particles to be about 1.0 μm when fme-crashing in the step (c), in order to shorten a time of molding cycle to below 60 seconds. hi the method of manufacturing ferrite anisotropic sintered powders according to the invention, a dispersion agent of polycarbonate or phosphate is added in an amount of 0.1-2.5 wt%, just before the fme-crashing step of (c) or the molding step of (d).
According to the invention, prior coarse powders having a general composition by adding predetennined amounts of CaO and SiO to ferrite magnetic coarse-powders having a certain range of mole ratio are added with (1) Li2CO3 or Li2O to add Li element to the whole composition, or (2) LiCoO2 alone or Li2CO3 or Li2O together with Co3O to add Li and Co elements to the whole composition, thereby making it possible to make a highly-efficient ferrite anisotropic sintered magnet having improved residual magnetic flux density. h addition, according to the invention, at least one of Cr2O3 and Al2O3 is added to obtain high coercive force necessary for industrial use.
Magnetic powders and a method of manufacturing a sintered magnet according to the invention are described below.
Firstly, SrCO3 and Fe2O3, which are raw materials, are mixed to be a certain mole ratio, calcinated to synthesize them to a ferrite clinker state, and then coarse- crashed, thereby providing ferrite magnetic powders. SrO, CaO and SiO2, which are T KR2003/001091
agents of aiding a sintering, are added to the coarse powders hi a proper amount within a range of 0.2 wt.%-1.0 wt.%, respectively.
In order to improve the residual magnetic flux density without reducing the coercive force, (1) Li2CO3 or Li2O is added to add Li element to the whole composition, or (2) LiCoO2 alone or Li2CO or Li2O together with Co3O4 is added to add Li and Co elements to the whole composition. At this time, in order to improve the coercive force to a very high level, at least one of Cr O3 and Al2O3 may be added in a predetermined amount.
Then, the mixed powders are fine-crushed to have a proper average diameter. After molding the fine-crashed slurry in a magnetic filed, sintering is carried out at an appropriate temperature, thereby preparing a high-density of an anisotropic sintered magnet.
The magnetic powders of the invention may be made as a bond magnet by mixing rubber or a light weight of plastics, etc. At this time, the magnet powders of the mvention are mixed with binder and additives, and then subject to molding process after kneading.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a graph showing residual magnetic flux densities (Br) and coercive forces (iHc) of ferrite amsotropic sintered magnets prepared by Examples 1 and 2 according to embodiments of the invention and Comparative example 1; FIG. 2 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 3 and 4 according to embodiments of the invention and Comparative example 1;
FIG. 3 is a graph showing maximum energy products ((BH)max) of ferrite anisotropic sintered magnets prepared by Examples 3 and 4 according to embodiments of the invention and Comparative example 1 ;
FIG. 4 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 5 and 6 according to embodiments of the invention and Comparative examples 2 and 3;
FIG. 5 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 5 and 7 according to embodiments of the invention in order to compare the magnetic properties of the sintered magnets according to the average size of particles;
FIG. 6 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 8 according to an embodiment of the invention and Comparative example 4;
FIG. 7 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared while changing the mole ratio of Fe by Example 9 according to an embodiment of the invention; and
FIG. 8 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared while changing the values of x and y (x=y) by Example 10 according to an embodiment of the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.
<Example 1>
SrCO3 and Fe2O were wet-mixed so that in SrFe2nO3n+1, which is a general formula of a hexagonal ferrite sintered magnet, n was 5.9, and calcinated at 1280°C for 2 hours in the atmosphere.
Calcination clinker was dry coarse-crashed in a disk mill, and then Li CO3 or Li2O was added' so that in SrFe2nLix+yMzO3n+©, that is SrFe2nLiχCθyMzO3n+Θ, x was 0.15 and y and z were 0.
In addition, CaO and SiO2, which are sintering accelerants, were added in an amount of 0.5 wt.% and 0.35 wt.%, respectively. Added coarse powders were wet fine- crushed so that the average diameter thereof was 0.8 μm. The fine-crushed slurry was wet-molded in a vertical magnetic field of 10 kOe, and then the molded body was sintered at 1200-1240 °C for 2 hours in the atmosphere, so that hexagonal ferrite anisotropic sintered magnet havmg a composition
Figure imgf000011_0001
was prepared.
<Examρle 2>
A hexagonal ferrite anisotropic sintered magnet having a composition of SrFeιι.8Lio.ιCθo.osOi8.8π was prepared by the same method as the Example I, except that Li O or Li CO3 was added together with Co3O so that in SrFe2nLixCθyMzO3n+β, x was 0.1 , y was 0.05 and z was 0. <Example 3>
A hexagonal ferrite anisotropic sintered magnet having a composition of SrFen.8Lio.05Coo.05Oi8.792 was prepared by the same method as the Example 1, except that LiCoO2 only was added or Li2O or Li2CO3 was added together with Co3O4 so that x and y were 0.05 and z was 0.
<Example 4>
A hexagonal ferrite anisotropic sintered magnet having a composition of
SrFen.8 io.05Coo.05Oi8.792 was prepared by the same method as the Example 3, except that dispersion agent consisting of polycarbonate or phosphate was added in an amount of 0.2 wt.% to solid powders of slurry for reducing viscosity of fine-crashed slurry and improving fluidity of ferrite magnetic particles.
<Comparative example 1> A hexagonal ferrite anisotropic smtered magnet having a general composition of SrFe .8θi8.7 was prepared by the same method as the Example 1, wherein Li and Co components were also not added (i.e., x=y=z=0) as well as Al and Cr components.
Fig. 1 is a graph showing residual magnetic flux densities (Br) and coercive forces (iHc) of ferrite anisotropic sintered magnets prepared by Examples 1 and 2 according to embodiments of the invention and Comparative example 1.
As shown in Fig. 1, coercive force was little reduced and residual magnetic flux density (Br) was significantly improved in the ferrite sintered magnets (Examples 1 and 2) having Li or Li and Co components added thereto, compared to the ferrite sintered magnet (Comparative example 1) having a general composition to which Li and Co components were never added. W
Fig. 2 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 3 and 4 according to embodiments of the invention and Comparative example 1.
As shown in Fig. 2, coercive force was little reduced and residual magnetic flux density (Br) was significantly unproved in the ferrite sintered magnet (Example 3) to which Li and Co were added together in a same proportion and the ferrite sintered magnet (Example 4) which was molded and sintered with dispersion agent inputted before a molding step, compared to the ferrite sintered magnet (Comparative example 1) having a general composition to which Li and Co components were never added. Fig. 3 is a graph showing maximum energy products ((BH)max) of ferrite anisotropic sintered magnets prepared by Examples 3 and 4 according to embodiments of the invention and Comparative example 1. As shown in Fig. 3, the maximum energy product was also significantly improved in the ferrite sintered magnets having Li and Co added thereto according to the invention.
<Example 5>
A hexagonal ferrite anisotropic sintered magnet having a composition of SrFe .8Lio.05Coo.05Cro.nOi8.957 was prepared by the same method as the Example 3, except that M was Cr and Cr2O3 was added for z to be 0.11.
<Example 6>
A hexagonal ferrite anisotropic sintered magnet having a composition of SrFen.8Lio.05Coo.05Alo.nOi8.957 was prepared by the same method as the Example 3, except that M was Al and Al2O3 was added for z to be 0.11. <Comparative example 2>
A hexagonal ferrite anisotropic sintered magnet havmg a general composition of SrFe .8Cro.nOi8.75 was prepared by the same method as the Example 1, except that Li and Co components were not added (i.e., x=y=0), M was Cr and Cr2O3 was added for z to be 0.il.
<Comparative example 3>
A hexagonal ferrite anisotropic sintered magnet having a general composition of SrFe .sAlo.ιιOι.8.75 was prepared by the same method as the Example 1, except that Li and Co components were not added (i.e., x=y=0), M=A1 and Al2O3 was added for z to be 0.11.
Fig. 4 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 5 and 6 according to embodiments of the invention and Comparative examples 2 and 3. As shown in Fig. 4, the sintered magnets of Examples 5 and 6, wherein
LiCoO2 was added alone or Li2CO3 or LiO2 and Co3O were added to Comparative examples 2 and 3, to which M (M=Cr or Al) was added, for improving coercive force (iHc) of the ferrite magnet having a general composition, showed very excellent magnetic properties.
<Example 7>
A hexagonal ferrite anisotropic sintered magnet having a composition of SrFe .8Lio.05Coo.05Cro.nOi8.95 was prepared by the same method as the Example 5, except for making the average diameter of particles be 1.0 μm when wet fine-crushing. Fig. 5 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 5 and 7 according to embodiments of the invention to in order to compare the magnetic properties of the sintered magnets according to the average size of particles.
As shown in Fig. 5, in Examples 5 and 7 having a same composition, to which Li and Co components were added, the magnetic properties of the ferrite smtered magnet were deteriorated when the average diameter of particles was increased from 0.8 μm to 1.0 μm. However, it can be seen that Example 7 showed more excellent magnetic properties than the magnet (Comparative example 2) having a general composition to which Li and Co components were never added and an average diameter of 0.8 μm.
Therefore, according to the invention, it is possible to make a sintered magnet having excellent magnetic properties regardless of using powders having a large diameter, and thus to shorten a tune of molding cycle of processes and to improve the molding productivity. When the average diameter of powders is below 0.8 μm, a dehydrating property becomes poor in molding and thus molding time is lengthened and abnormal growth of particles occurs in sintering. Accordingly, the average diameter of powders is preferred to be 0.8 μm or more in order to improve the productivity and to stabilize the magnetic properties. Considering cutting down on expenses, it is most efficient that the average diameter is about 1.0 μm.
<Example 8>
A hexagonal ferrite anisotropic sintered magnet having a composition of
SrFen.8Lio.o5Cθo.o5CrzO n © was prepared by the same method as the Example 5, except that M was Cr and Cr2O3 was added for z to be 0.15, 0.30, 0.45, 0.60 and 0.75. •^Comparative example 4>
A hexagonal ferrite anisotropic sintered magnet having a general composition of SrFen.8CrzO3n+Θ was prepared by the same method as the Comparative example 2, except that Li and Co components were not added (i.e., x=y=0), M was Cr and Cr2O3 was added for z to be 0.15, 0.30, 0.45, 0.50 and 0.75.
Fig. 6 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared by Examples 8 according to an embodiment of the invention and Comparative example 4. As shown in Fig. 6, the coercive force generally increases as the z value increases. Example 8 to which Li and Co components were added has an outstandingly excellent residual magnetic flux density, compared to Comparative example 4 having a general composition to which Li and Co components were not added, in a same level of coercive force.
<Example 9>
Hexagonal ferrite anisotropic sintered magnets having various compositions were prepared by the same method as the Example 3, except that x and y were fixed to be 0.05 and n was changed to 5.0, 5.3, 5.5, 5.7, 5.9, 6.1, 6.3, .5 and 6.7.
<Example 10>
Hexagonal ferrite anisotropic sintered magnets having various compositions were prepared by the same method as the Example 2, except that n was fixed to be 5.90 and x and y (x=y) were all changed from 0 to 0.50. Fig. 7 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic sintered magnets prepared while changing the mole ratio of Fe by Example 9 according to an embodiment of the invention.
As shown in Fig. 7, when n ranges from 5.7 to 6.1, the magnetic properties are excellent, and when n ranges from 5.5 to 6.3, the magnetic properties are exhibited in a similar level. However, when n is below 5.5 or above 6.3, the magnetic properties are significantly deteriorated. The reason is that when n is away from a range of stoichiometric compositions, secondary phase having a nonmagnetic property appears and the amount thereof increases, thereby deteriorating the magnetic properties.
Fig. 8 is a graph showing residual magnetic flux densities and coercive forces of ferrite anisotropic smtered magnets prepared while changing the values of x and y (x=y) by Example 10 according to an embodiment of the invention.
As shown in Fig. 8, when x and y (x=y) range from 0.01 to 0.10, the magnetic properties are significantly increased, and when x and y range from 0.1 to 0.3, the magnetic properties are maintained in a similar level. However, when they are above 0.3, the magnetic properties are significantly deteriorated.
INDUSTRIAL APPLICABILITY
As explained above, in hexagonal ferrite magnetic powders and a ferrite amsotropic sintered magnet using the magnetic powders according to the invention, the residual magnetic flux density is improved without lowering the coercive force by adding Li element or Li and Co elements and thus the maximum energy product is also improved.
In addition, the method of manufacturing a ferrite anisotropic sintered magnet, a sintered magnet having excellent magnetic properties can be prepared without making the prior manufacturing processes be complex regardless of using very large diameter of particles, by mixing, calcinating and coarse-crashing raw powders, adding Li element or Li and Co elements to the crushed powders and fme-crashing them, thus preparing hexagonal ferrite magnetic powders, molding and sintering the magnetic powders in a magnetic field, and thus preparing a sintered magnet, and a time of molding cycle can be also resultingly shorten and a molding productivity can be improved.
The hexagonal ferrite magnetic powders and the ferrite anisotropic sintered magnet using the powders have a high residual magnetic flux density and coercive force. As a result, the maximum energy product thereof is also very excellent. Accordingly, various kinds of DC power motors used for home apphance and devices for a vehicle can be miniaturized and hght-weighted and a high efficient motor can be manufactured.
While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in fonn and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

WHAT IS CLAIMED IS
1. Hexagonal ferrite magnetic powders having a composition of the following formula 1;
[fonnula 1]
Figure imgf000019_0001
wherein, L is Li element or Li and Co elements, x indicates a composition ratio of Li, y indicates a composition ratio of Co, x, y and n satisfy the following ranges: 0.01 < x < 0.3,
0.01 <y< 0.3, and 5.5 <n < 6.3.
2. The magnetic powders according to claim 1, further comprising Al or Cr element and thus having a composition of the following formula 2;
[formula 2] SrFe2n yMz03n+© wherein, L is Li element or Li and Co elements, M is at least one of Al and Cr, x indicates a composition ratio of Li, y indicates a composition ratio of Co, z indicates a composition ratio of Al or Cr x, y, z and n satisfy the following ranges: 0.01 < x < 0.3, 0.01 < y< 0.3,
0.01 <z < 0.8, and 5.5 < n < 6.3.
3. A ferrite anisotropic sintered magnet formed with the magnetic powders according to claim 1 or 2.
4. A method of manufacturing hexagonal ferrite magnetic powders comprising steps of:
(a) mixing and calcinating SrCO3 and Fe O3; (b) crashing the calcinated bodies of step (a); and
(c) adding Li2CO3 or Li2O to input Li or adding LiCoO2 alone or Li2CO3 or Li2O together with Co3O to input Li and Co to the crashed powders of step (b) and fine-crashing them, thereby preparing the magnetic powders satisfying the composition according to claim 1 or 2.
5. The method according to claim 4, wherein in the step (c), Cr O or Al O3 is added to input Al or Cr as M.
6. A method of manufacturing a ferrite anisotropic sintered magnet comprising steps of:
(a) mixing and calcinating SrCO3 and Fe2O3;
(b) crashing the calculated bodies of step (a);
(c) adding Li2CO3 or Li2O to input Li or adding LiCoO2 alone or Li2CO3 or Li2O together with Co3O4 to input Li and Co to the crashed powders of step (b) and fine-crashing them, thereby preparing the magnetic powders satisfying the composition according to claim 1 or 2; and
(d) molding and sintering the mixed powders of step (c), thereby preparing a sintered magnet.
7. The method according to claim 6, wherein in the step (c), Cr2O3 or Al O3 is added to input Al or Cr as M.
8. The method according to claim 6, wherein the crashing is carried out for an average diameter of particles to be about 1.0 μm when fme-crashing in the step (c), in order to shorten a time of molding cycle to below 60 seconds.
9. The method according to claim 6, wherein a dispersion agent of polycarbonate or phosphate is added in an amount of 0.1-2.5 wt%, just before the fine- crashing step of (c) or the molding step of (d).
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CN103408296A (en) * 2013-08-15 2013-11-27 上海应用技术学院 Characterization analysis method for migration of lanthanum and cobalt ions in lanthanum-cobalt substituted strontium ferrite permanent magnet material

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