JP3115506B2 - Hexagonal Ba ferrite sintered magnet, method for producing the same, and polar anisotropic ring magnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hexagonal barium ferrite magnet, a method for producing the same, and a polar anisotropic ring magnet.

[0002]

2. Description of the Related Art Currently, magnetoplumbite (M type) hexagonal Sr ferrite or Ba ferrite is mainly used as an oxide permanent magnet material. Being manufactured. In order to manufacture Sr or Ba ferrite sintered magnet, the raw material Fe ₂
O ₃ and SrCO ₃ or BaCO ₃ are mixed and mixed,
This is calcined, pulverized, molded in a magnetic field and fired.
At this time, for example, JP-A-3-291901 and 4-
As shown in Examples such as Japanese Patent No. 5802, CaCO
It is common to add ₃ and SiO ₂ in combination.

[0003] Hexagonal Ba ferrite is advantageous in reducing the production cost because BaCO ₃ used as a raw material is less expensive than SrCO _{3 in} the case of Sr ferrite. Since the anisotropy is about 10% smaller than that of Sr ferrite,
It is difficult to obtain Hc (coercive force). Therefore, for example, 3 kO
e Hexagonal Sr ferrite sintered magnets are used for products requiring iHc above.

On the other hand, when producing Sr ferrite or Ba ferrite sintered magnets, CaCO ₃ and S
When iO ₂ is added in combination, the shrinkage during sintering is
The ratio is largely different in the axial direction, and the ratio is usually about 1.5 to 2.1 in the c-axis direction / a-axis direction. For this reason, large deformation occurs due to shrinkage during sintering. For example, it is necessary to design a mold in which the amount of deformation is calculated in advance, or to sufficiently perform post-processing such as polishing and grinding, thereby increasing manufacturing costs. It may be done.

A polar anisotropic ring magnet is known as an example in which the deformation due to the difference in shrinkage is large. This magnet has a ring shape and its inner or outer peripheral surface is oriented so as to be strongly multipolar magnetized, and is used for a stepping motor or the like. In order to manufacture this ring magnet, when obtaining a ring-shaped formed body, different magnetic poles are alternately arranged on the peripheral surface to orient the magnetic field, and the c-axis is oriented in the direction of the arrow in FIG. Is sintered. However, since the shrinkage ratio has a large anisotropy as described above, the peripheral surface is deformed as shown by a broken line in FIG. 7B, so that the convex portions appearing on the peripheral surface must be polished. In addition, the polishing cost must be increased.

[0006]

SUMMARY OF THE INVENTION The main object of the present invention is to improve the sintering density and coercive force, and to further reduce the deformation during sintering due to the difference between the c-axis shrinkage and the a-axis shrinkage. It is an object of the present invention to provide a hexagonal Ba ferrite sintered magnet and a method for manufacturing the same, and a polar anisotropic ring magnet using the same, which can reduce or eliminate post-processing such as polishing.

[0007]

This and other objects are achieved by any one of the following constitutions (1) to (12). (1) Ba ferrite as main phase and Sr as grain boundary component
And the main phase has an average grain size of 1.0 μm or less, iHc of 2.5 kOe or more, Br
Is a hexagonal Ba ferrite sintered magnet having a value of 4.1 kG or more. (2) The sintered hexagonal Ba ferrite magnet according to (1), wherein the Si content of the grain boundary is 2 to 50 at%. (3) The hexagonal Ba ferrite sintered magnet according to the above (1) or (2), wherein the Sr content of the grain boundary is 0.5 to 10 at%. (4) The sintered hexagonal Ba ferrite magnet according to any one of the above (1) to (3), wherein the Si content at the grain boundaries is 2 to 100 times the Si content inside the main phase grains. (5) The sintered hexagonal Ba ferrite magnet according to any one of the above (1) to (4), wherein the Sr content at the grain boundaries is 1.1 to 20 times the Sr content inside the main phase grains. (6) The hexagonal Ba according to any one of the above (1) to (5), wherein Ba is contained as a grain boundary component, and the content of Ba in the grain boundary is 1.1 to 20 times the content of Ba in the main phase grains. Ferrite sintered magnet. (7) The calcined body powder of hexagonal Ba ferrite is pulverized, Ba ferrite raw material particles obtained by pulverization are molded in a magnetic field, and the obtained compact is sintered to obtain a hexagonal Ba ferrite sintered magnet. A method for producing a compound, wherein the Ba ferrite particles have an average particle size of 1 μm or less, and a silicon compound or a silicon component of a compound that becomes silicon oxide by firing, and a strontium oxide or a compound that becomes strontium oxide by firing. (1)
A method for producing a hexagonal Ba ferrite sintered magnet, which obtains the hexagonal Ba ferrite sintered magnet according to any one of (6) to (6). (8) The Si component is 0.1 to 2.0 wt% with respect to the Ba ferrite raw material particles in terms of SiO ₂ , and the Sr component is 0.5 to 5 wt% with respect to the Ba ferrite raw particles in terms of SrCO _3. The method for producing a hexagonal Ba ferrite sintered magnet according to (7), wherein the Si and Sr components are contained such that the molar ratio of SrCO ₃ / SiO ₂ is 0.5 to 3. (9) The method for producing a hexagonal Ba ferrite sintered magnet according to the above (7) or (8), wherein the Si component and the Sr component are added in combination during the pulverization. (10) A method for producing a sintered hexagonal Ba ferrite magnet in which the molded body according to any of the above (7) to (9) is crushed, magnetically molded, and sintered. (11) The above (7) to which Ba is precipitated at the grain boundary during sintering
(10) The method for producing a hexagonal Ba ferrite sintered magnet according to any of (10). (12) The hexagonal Ba ferrite sintered magnet according to any one of the above (1) to (6), which is a ring-shaped, polar-anisotropic ring having an inner peripheral surface or an outer peripheral surface oriented in multiple poles. magnet.

[0008]

The operation and effect of the sintered hexagonal Ba ferrite magnet of the present invention are improved in the sintered density and the coercive force.
A coercive force comparable to ferrite can be obtained. Thereby, the raw material cost can be reduced. Further, the contraction ratio in the c-axis direction and a
The ratio (Shc / Sha) to the axial shrinkage ratio is close to 1. For this reason, deformation during sintering is small, and therefore, a polishing step or the like can be simplified or omitted. For this reason, particularly excellent effects can be obtained when manufacturing a magnet requiring a special orientation such as a polar anisotropic ring magnet.

[0009]

[Specific Configuration] Hereinafter, a specific configuration of the present invention will be described in detail.

The hexagonal Ba ferrite sintered magnet of the present invention has a main phase of hexagonal Ba ferrite and a final composition of B
aO · nFe ₂ O ₃ (n is 4.5 to 6.5) is preferably. Further, Ca, Pb, Al, Ga, S
n, Zn, In, Co, Ni, Ti, Cr, Mn, C
u, Ge, Nb, Zr, Cr, La, Nd, Sm, P
r, Ce, Li, etc. may be contained in 5% or less of the whole. Ba is less than 50 at%, for example, 0 to 40 at%.
, In particular, about 0 to 5 at% of Sr.

The hexagonal Ba ferrite sintered magnet of the present invention contains SrO and SiO ₂ as grain boundary components. There are various methods for confirming the presence of Sr and Si in the grain boundary component, but it is preferable to use the first method or the second method below, particularly in that the determination is easy. In particular, since the measurement can be performed accurately and stably,
Preferably, the first method is used.

In the first method, TEM (transmission electron microscope) observation and EDS (Energy Dispersive X-ray Sp
ectroscopy: Analytical electron microscope (Analytical Elect) that can simultaneously perform local analysis with energy dispersive X-ray spectroscopy
ron Microscopy). In this method using TEM-EDS, a magnet slice prepared by polishing is used as a measurement sample. The grain boundary phase and the ferrite phase in the grain can be easily distinguished from the crystal structure image. The grain boundary phase does not exist with a uniform thickness around the grains, but exists particularly concentrated at the polycrystalline grain boundary portion. The polycrystalline grain boundary portion means a boundary of three or more grains, such as a tricrystalline grain boundary (triple point) as shown in FIG. When analyzing the composition of the grain boundaries, it is preferable to measure at such polycrystalline grain boundaries. 2
Since the thickness of the grain boundary phase is small at the two crystal grain boundary portions existing at the boundaries between the individual grains, it is difficult to accurately analyze the grain boundary components during EDS local analysis.

Since the two crystal grain boundaries and the polycrystalline grain boundaries are continuous, it is considered that the components of both are basically the same. In the case of an anisotropic sintered body in which grains are oriented, there are two types of grain boundaries, an a-plane grain boundary and a c-plane grain boundary, and either type may be measured.

In the second method, ESCA (Electron Sp.
(Ectroscopy for Chemical Analysis) or Auger electron spectroscopy (AES). First, the magnet is heated and rapidly cooled. Rapid cooling is from 800 to 1000 ° C to 50
It may be cooled at about 0 to 2000 ° C./sec, for example, in water. This causes the magnet to break along the grain boundaries. The flattened cross section is analyzed by ESCA or Auger electron spectroscopy.
SCA analysis is preferred. At this time, the profile of each element in the depth direction is measured while performing ion milling.
Although the fracture surface does not necessarily occur at the center of the grain boundary phase, the measurement range of ESCA is about 10 ³ to 10 ⁵ μm square, and this is averaged and counted. The atomic percentage of each element is defined as the content of the grain boundary. In addition, ion milling progresses to 100-2
The average value when the concentration becomes constant at a depth of 00A or more is defined as the content inside the main phase grains.

It is preferable that the Si content C _1o of the grain boundary obtained by each of the above methods is 2 to 50 at%. Also, C _1o
Divided by the Si content C _1i inside the grains is 2 to 10
It is preferably 0. On the other hand, the Sr content C _2o
Is preferably 0.5 to 10 at%, and the value obtained by dividing this by the Sr content C _2i inside the grain is 1.1 to 20 at%.
It is preferred that

More specifically, when the first method is used, the Si content C _1o is 2 to 30 at%, particularly 5 to 30 at%.
It is preferably 25 at%, and the value obtained by dividing C _1o by C _1i is preferably 2 to 100, particularly preferably 10 to 80.
On the other hand, the Sr content C _2o is 0.5 to 8 at%, particularly 1 to 4 at%.
It is preferably at%, and the value obtained by dividing C _2o by C _2i is preferably from _1.1 to 20, particularly preferably from 3 to 15.

In the case where the second method is used, Si
The content C _1o is preferably 2 to 30 at%, particularly 5 to 20 at%, and the value obtained by dividing C _1o by C _1i is preferably 2 to 50, particularly preferably 4 to 20. On the other hand, the Sr content C _2o
Is preferably 1 to 5 at%, particularly 2 to 4 at%, and the value obtained by dividing C _2o by C _2i is 1.1 to 5, especially 1.2 to 5 at%.
It is preferably 3.

The magnet of the present invention usually has S as a grain boundary component.
Ba is included in addition to i and Sr. The grain boundary component in this case means an element whose concentration at the grain boundary is higher than the concentration inside the grain. Ba is a main component of grains, but in the magnet of the present invention, Ba precipitates at the grain boundaries by sintering, and the Ba concentration at the grain boundaries becomes higher than the Ba concentration inside the grains. Specifically, the value obtained by dividing the Ba content C _3o at the grain boundary by the Ba content C _3i inside the grains is 1.1 to 20, particularly 1.5 to 5. Note that C _3o and C _3i are measured by the first method described above. In a conventional Ba ferrite sintered magnet that does not contain Si and Sr as grain boundary components, the Ba concentration at the grain boundaries is equivalent to the Ba concentration inside the grains, and the Ba ferrite magnet having the above-described Ba distribution is conventionally used. unknown.

When the analysis is performed by ESCA, iHc is particularly improved by having the above profile, and the ratio of the shrinkage ratio approaches 1. In the measurement by ESCA, the average thickness of the grain boundary phase may be twice as long as the distance at which the concentration in the depth direction analysis becomes a constant value, and this thickness is generally 20 to 300 A, particularly 40 A. ~ 200A. The average grain diameter of the main phase is 1 μm or less, especially 0.5 to
It is about 1.0 μm. The grain diameter is measured by a scanning electron microscope (SEM).

Such a Ba ferrite sintered magnet is
Exhibits an iHc of 2.5 koe or more, and in a preferred embodiment, 3
An iHc of at least koe, especially 3.4 to 4.0 koe is obtained. Then, an improvement of 10 to 25% can be seen with the same amount as compared with the conventional iHc in the case of the composite addition of Ca and Si. In addition, Br is 4.1 kG or more and 4.1-4.4 kG.
It is about. Also, the shrinkage ratio between the c-axis direction and the a-axis direction (Sh
c / Sha) is 0.8 to 1.5, particularly 0.9 to 1.2.

In order to manufacture such a hexagonal Ba ferrite sintered magnet, a calcined body powder of hexagonal Ba ferrite is first pulverized, and powder particles of the Ba ferrite obtained by the pulverization are used as raw material particles in a magnetic field. It is medium-formed and the obtained formed body is sintered. At this time, the molded body contains an Si component of silicon oxide or a compound that becomes silicon oxide when fired, and an Sr component of strontium oxide or a compound that becomes strontium oxide when fired. The content of the Si component is
0.1% with respect to Ba ferrite raw material particles in terms of SiO ₂
-2.0 wt%, especially 0.2-1.5 wt%, and more preferably 0.2-1.5 wt%.
3 to 1.0 wt% is preferred. Further, the content of the Sr component is preferably 0.5 to 5% by weight, particularly 1.0 to 2.5% by weight, more preferably 1.2 to 2.2% by weight based on the Ba ferrite raw material particles in terms of SrCO ₃ . And this SrCO
The molar ratio of ₃ / SiO ₂ is 0.5-3, especially 0.7-
It is preferably 2.5, more preferably 0.9 to 2.0. By adding these components in such a range, the iHc value is improved, and the contraction ratio in the c-axis direction and the contraction ratio in the a-axis direction become substantially equal.

The Si component is a component serving as a nucleus of the grain boundary glass component. If the content is more than the above range, the nonmagnetic glass phase increases and Br deteriorates. On the other hand, if the amount is too small, the grain growth during firing cannot be controlled, and iHc deteriorates.

If the amount of Sr component or the ratio of SrCO ₃ / SiO ₂ is larger or smaller than the above range, iHc is particularly lowered and the shrinkage ratio (Shh / Shφ, etc.) is also increased.

In order to obtain the calcined powder of hexagonal Ba ferrite used in the present invention, a predetermined amount of iron oxide powder and powder containing Ba are mixed as raw material powders and calcined. B
The powder containing a is not particularly limited as long as it is an oxide or a powder that becomes an oxide upon subsequent firing, such as a carbonate, a hydroxide, or a nitrate. Usually, a carbonate may be used.
The average particle size is not particularly limited, but the iron oxide is preferably a fine powder, and is preferably a primary particle of 1 μm or less, particularly 0.5 μm or less. In the present invention, Ca, Sr, Pb, La,
Nd, Sm, Pr, Ce, Al, Ga, Cr, Sn, Z
n, In, Co, Ni, Ti, Cr, Mn, Cu, G
e, Nb, Zr, Li, Si, etc. may be added.

In order to obtain particularly fine ferrite particles after calcination, for example, at the time of mixing, first, iron oxide is wet-pulverized, and an aqueous solution of a water-soluble salt of Ba is added thereto in the presence of Na ₂ CO ₃ or the like. It may be added. Thereby, the carbonate of Ba precipitates out and is mixed with the fine iron oxide particles with high precision.
Further, fine Ba carbonate may be used to sufficiently mix with iron oxide. Thereafter, it is washed, dried and calcined. The calcination may be performed in the air at, for example, 1000 to 1350 ° C. for 1 second to 10 hours, particularly about 1 second to 3 hours. Further, the raw materials may be sufficiently pulverized and mixed by a dry pulverizer.

The calcined body powder is obtained by mixing and pulverizing the iron oxide powder and the powder containing Ba as raw materials, and calcining the mixture before calcining the mixture.
Rich oxides such as BaFe ₂ O ₄ and BaFeO
_3-x (0 ≦ x <1) etc.], and a mixture containing the intermediate phase may be pulverized and then calcined.

The calcined body powder thus obtained has a substantially magnetoplumbite-type ferrite structure, and its primary particles have an average particle size of 0.1 to 1 μm, especially 0.1 to 0. It is preferably 5 μm. The average particle size may be measured by a scanning electron microscope (SEM). Further, the saturation magnetization s is preferably 65 to 69 emu / g, and the coercive force iHc is preferably 4000 to 6000 Oe.

Next, the calcined powder is pulverized. In the present invention, the Si component and the Sr component are added in the above range, but these components may be added at the time of magnetic field molding.
The timing of addition may be any time from pulverization of the calcined body to before molding, but it is particularly preferable to add the powder at the time of pulverizing the calcined body powder, usually at the beginning of the pulverizing step.
SiO ₂ is generally used as the Si component. As the Sr component, SrCO ₃ is generally used. In addition, Si
And the like. The particle size when added as a powder is about 0.01 to 5 μm.

In the calcined body pulverizing step, it is preferable to introduce crystal strain into the calcined powder to reduce bHc. The calcined particles become finer (single magnetic domain particles) to form iHc and b
When Hc increases, a magnetic force acts between the particles, whereby the ferrite particles tend to aggregate. As a result, anisotropy due to the magnetic field is prevented. The attractive force (cohesive force) between the ferrite particles is proportional to the square of the magnetic flux density on the surface of the particles. As bHc in the hysteresis loop of one ferrite particle increases, the surface magnetic flux density increases, and as a result, the cohesive force increases. Therefore, in order to reduce the cohesive force of the ferrite particles, it is more advantageous to reduce bHc and reduce the squareness of the second quadrant by introducing crystal strain. Thereby, a high degree of orientation can be obtained at the time of magnetic field orientation. Then, the strain introduced into the particles is removed in a firing step after the magnetic field is formed, and a permanent magnet having high magnetic properties can be obtained.

When the iHc of the Ba ferrite particles is reduced by the crystal strain, a new effect that the amount of change of the iHc with respect to the temperature is reduced is produced. The temperature coefficient of iHc is reduced to about 1 to 6 Oe / ° C at -100 to + 150 ° C. Therefore, the particles into which the strain has been introduced can be used as they are as the magnetic powder for the magnetic recording medium.

In order to introduce such crystal distortion, mechanical pulverization is effective. In order to perform such pulverization, for example, it is preferable to first perform dry pulverization to introduce a sufficient crystal strain. As a pulverizer used for dry pulverization, a dry vibrating mill, a dry attritor (medium stirring type mill), a dry ball mill, or the like can be used, but a dry vibrating mill is particularly preferable.

By this dry pulverization, the BET specific surface area is 2
It is pulverized until it becomes about 10 to 10 times, and for example, about 3 × 10 ^{−4 to} 7 × 10 ⁻⁴ of crystal strain of the (206) plane is introduced. At this time, the average particle size of the dry pulverized powder is about 0.1 to 1 μm,
The T specific surface area is about 4 to 10 m ² / g.

Next, the dry pulverized powder is usually wet pulverized. By the wet pulverization, the BET specific surface area is made to be about 1 to 4 times, particularly about 1 to 3 times, and the average particle size is set to 0.1.
1 to 0.8 μm, and the BET specific surface area is 6 to 12 m ² / g. Even in this wet grinding, the crystal strain increases, and the final ferrite particles are adjusted to the above Hc with a strain amount of 10 ^-4 or more. It should be noted that since such a distortion amount and Hc can be obtained only by wet pulverization without dry pulverization, pulverization may be performed only by wet pulverization. Alternatively, only dry pulverization may be used. Note that σs after the completion of the pulverization is about 50 to 67 emu / g. For such wet pulverization, a ball mill, an attritor, a vibration mill or the like is preferably used.

The solvent used in the wet pulverization may be an aqueous solvent such as water, but in the present invention, it is preferable to use a non-aqueous solvent as a solvent for the slurry in the wet pulverization. As the non-aqueous solvent to be used, an organic compound which is liquid at normal temperature such as various organic solvents may be used, and hydrocarbons such as heptane, industrial gasoline, kerosene, cyclohexane, toluene, xylene, ethylbenzene, turpentine oil, etc .; Hydrocarbons, for example, 1,2-dibromoethane, tetrachloroethylene, perchloroethylene, dichloropentane, monochlorobenzene, etc .; monohydric alcohols, phenols, ethers, for example, methanol, ethanol, n-propyl alcohol, n- Butyl alcohol, cyclohexanol, phenol, n
-Butyl ethers and the like; acids and esters such as butyl acetate; polyhydric alcohols and their ethers and esters such as ethylene glycol; aldehydes, acetals and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone. Silicone oils, such as low viscosity silicone oils; nitrogen-containing compounds such as ethylenediamine; sulfur compounds such as carbon disulfide; paint thinners such as
Lacquer thinner or the like or a mixed solvent thereof can be used. In this case, such a non-aqueous solvent alone or as a mixed solvent has a viscosity at 20 ° C. of 0.3 to 3 cps, more preferably 0.3 to 2.0 cps, particularly 0.4 to 1.5 cps.
It is preferably s. Thereby, the moldability and the degree of orientation of the molded body are remarkably improved. The vapor pressure of the non-aqueous solvent at 20 ° C. is 0.1 to 200 mmHg, more preferably 1 to 200 mmHg.
mmHg, and its boiling point is 50-300 ° C, more preferably 50-200 ° C. In wet grinding, the non-aqueous solvent constitutes about 10 to 90% by weight of the slurry, and the ferrite particles in the slurry preferably accounts for 10 to 90% by weight.

In such wet pulverization, it is preferable to add one or more surfactants to the slurry.
The amount of the surfactant added is based on the dry-ground material powder.
It is preferably 0.1 to 5.0% by weight, particularly preferably 0.3 to 3.0% by weight. This surfactant is generally amphiphilic, can be adsorbed on the surface of the raw material powder ferrite particles in the slurry, and is soluble in the non-aqueous solvent used in the adsorbed state. That is, it has a hydrophilic group that can be adsorbed on the surface of ferrite particles, and a lipophilic group (hydrophobic group) that is soluble in the non-aqueous solvent used. It is preferable that the solubility parameter (SP value) of the surfactant used is similar to the solubility parameter (SP value) of the non-aqueous solvent used. Further, it is preferable that substantially all of the raw material powder is adsorbed to the raw material powder in the slurry. By causing such adsorption and solubilization to form micelles, the primary particles are very well dispersed in the slurry after the wet pulverization, and the degree of orientation is significantly improved by forming the primary particles in a wet magnetic field. .

The surfactant used is a cationic type,
Any of anionic, nonionic, and amphoteric types may be used. In particular, carboxylic acids or salts thereof such as stearic acid, oleic acid, Zn stearate, and stearic acid C
a, the number of carbon atoms of Sr stearate, Ba stearate, Mg stearate, Al stearate, Zn oleate, Ca oleate, Sr oleate, Ba oleate, Mg oleate, Al oleate, ammonium oleate, etc. Those containing one or more of about 4 to 30 saturated or unsaturated fatty acids or salts thereof are preferably used.
Among these, the use of a Ca salt of a fatty acid, more preferably stearic acid, is advantageous because the solvent removal during molding is improved without impairing the orientation and cracks in the molded article are prevented. This is considered to be because the density of the molded body was reduced from, for example, 3.0 g / cm ³ to 2.8 g / cm ³ , and the solvent was easily removed. In particular, Ca, Ba,
Sr, Al, Cr, Ga, Cu, Zn, Mn, Co, T
By adding an organic substance (a metal salt of an organic surfactant such as the above-mentioned metal salt of a fatty acid) containing an effective additive element that may be added to the ferrite such as i, such an element can be added around the ferrite particles. High dispersion is also possible. In addition, known sulfonic acids or salts thereof; sulfate esters or salts thereof; phosphate esters or salts thereof; aliphatic amine salts or quaternary ammonium salts; aromatic quaternary ammonium salts; pyridinium salts; imidazolinium salts; Aminocarboxylates; imidazoline derivatives; and at least one of natural surfactants are also preferably used.

If such a surfactant is added to a slurry of a non-aqueous solvent containing a calcined body powder and wet-pulverized, the slurry can be used as it is for wet molding.
Alternatively, a part or all of the surfactant may be added at the time of dry pulverization of the calcined powder, which is performed prior to the wet molding or performed alone. In addition, part or all of the surfactant may be added after wet pulverization of the nonaqueous solvent slurry. Further, a slurry for wet molding may be prepared by adding a surfactant and a non-aqueous solvent after dry grinding. In any case, since the surfactant is present in the slurry during the wet magnetic field molding, the effect of improving the degree of orientation of the molded article is realized. The amount of the surfactant added at each stage may be set so that the amount finally becomes the above-mentioned amount in the slurry at the time of wet molding.

When a water-based solvent, particularly water or a mixed solvent of water is preferably used for wet pulverization, the raw material powder in the slurry at the time of wet pulverization is 10 to 7%.
It is about 0% by weight. However, even when a surfactant is added to the water slurry and wet molding is performed, the degree of orientation of the molded body cannot be improved, and thus it is preferable to replace the solvent with a non-aqueous solvent. In order to perform the solvent replacement, for example, decantation may be performed while the raw material powder is magnetically held. In this wet molding, dry pulverization can be performed in advance.

As described above, when the wet pulverization using a preferably aqueous solvent different from the slurry solvent at the time of wet molding is performed, and then the solvent is replaced, the surfactant is added in the above-described amount during the final wet molding. Must exist.
For this purpose, a surfactant may be added to any one of the steps of dry pulverization, wet pulverization, and preparation of the final slurry. In any of the above cases, the final wet molding slurry is adjusted so that the amount of the non-aqueous solvent is about 5 to 30% by weight and the amount of the raw material particles is about 70 to 95% by weight.

After preparing the final non-aqueous solvent slurry containing the surfactant in this way, molding in a magnetic field is performed while removing the non-aqueous solvent in the slurry. The solvent may be removed according to a conventional method, for example, by forcible removal under reduced pressure.
~0.5ton / cm ² or so, the applied magnetic field is about 5～15KG. The degree of orientation, Ir / Is, of the obtained molded body is 75% or more, for example, 78 to 86%. Such a high degree of orientation is realized for the first time by the combined use of a non-aqueous solvent and a surfactant, and high orientation cannot be obtained even when the surfactant is added to the water slurry.

Thereafter, the molded body was placed in air or nitrogen for 1 hour.
Heat treatment is performed at a temperature of 00 to 500 ° C. to degrease and remove the added surfactant. Then, the molded body is, for example, 1150 to 1250 ° C. in the atmosphere, particularly 1160 to 122 ° C.
By sintering at 0 ° C. for about 0.5 to 3 hours, sintered hexagonal Ba ferrite magnets of the present invention in various shapes are obtained.

Further, the molded body is crushed using a crusher or the like, and the average particle size is 100 to 700 μm by sieving or the like.
m to obtain magnetic-field-oriented granules, using this, dry-magnetic-field-molding and sintering in the same manner as above to obtain hexagonal Ba ferrite sintered magnets of the present invention in various forms. You may.

In the production method of the present invention, it is also possible to introduce only mechanical strain by pulverization without using a surfactant. The pulverization is performed by dry or wet pulverization as described above. As a solvent of the slurry at the time of wet pulverization performed in a preferable form, water or a mixed solvent of water is preferable in terms of easy handling. For wet grinding,
The solvent constitutes about 10 to 90% by weight of the slurry, especially 30 to 90% by weight in the water slurry, and the ferrite particles in the slurry contain 10 to 90% by weight, particularly 1 to 90% by weight in the water slurry.
It is preferably from 0 to 70% by weight.

If wet pulverization is carried out using such preferably water or an aqueous slurry, wet molding can be carried out using this slurry as it is. Further, as described above, the dry pulverization of the calcined powder may be performed prior to the wet molding. Further, a slurry for wet molding may be prepared by adding a solvent after dry grinding. Further, the above-mentioned wet pulverization may be performed in another solvent different from the slurry for molding, and thereafter, the solvent used at the time of pulverization may be preferably replaced with water prior to wet molding. In order to perform the solvent replacement, for example, decantation may be performed while the raw material powder is magnetically held. Note that dry pulverization can also be performed in advance during the wet molding. In any of the above cases, the final slurry for wet molding contains 5 to 30% by weight of a solvent such as water.
And the raw material particle amount is adjusted to be about 70 to 95% by weight.

When the aqueous slurry is wet-pulverized,
At the time of pulverization, it is desirable to add a dispersant. As the dispersant, it is desirable to use a polymer dispersant,
Particularly, an ammonium polycarboxylate type is desirable.
The dispersant is preferably added in an amount of 0.1 to 1% by weight based on the raw material powder.

[0046]

The present invention will be specifically described below with reference to examples and comparative examples.

Examples 1 and 2 and Comparative Examples 1 to 4 The following materials were used. Fe ₂ O ₃ powder (primary particle diameter 0.3 μm) 1000 g BaCl ₂ .2H ₂ O (first grade reagent) 321.4 g Na ₂ CO ₃ (special grade reagent) 111.6 g

The Fe ₂ O ₃ powder and Na ₂ CO ₃ were mixed with water 1.6
Together with L 2, the mixture was pulverized with a wet attritor for 1.5 hours to obtain a slurry. Next, an aqueous solution containing BaCl ₂ .2H ₂ O was dropped into the attritor containing the slurry, and pulverized for 0.5 hour. In this step, very fine barium carbonate is precipitated and precipitated by the reaction of BaCl ₂ + Na ₂ CO ₃ → BaCO ₃ ↓ + 2NaCl, and is mixed with the iron oxide particles with high precision. The slurry was washed until NaCl was 0.2% or less, dehydrated, dried and granulated, and calcined at 1175 ° C. for 3 hours in the air to obtain a calcined body powder.

The magnetic properties of the obtained powder were measured with a sample vibration magnetometer (VSM). As a result, σs = 68 emu / g, iH
c = 4.5 kOe. In addition, a scanning electron microscope (S
When observed by EM), the primary particle size was 0.3 μm and the BET specific surface area was 2 m ² / g.

To the calcined body powder, 0.6 wt% of SiO ₂ (average particle diameter 0.01 μm) and SrCO ₃ or CaCO ₃ (both having an average particle diameter of 1 μm) were added in amounts shown in Table 1. The ferrite powder was pulverized by a dry vibration mill until the specific surface area of the ferrite powder became 7 m ² / g. By this treatment, pulverization strain is introduced into the ferrite powder and iH
c decreased from 4.5 kOe to 2.2 kOe.

Next, wet grinding was performed in a ball mill using xylene as a non-aqueous solvent and oleic acid as a surfactant. Oleic acid was added at 1.5 wt% to the powder obtained by dry grinding. The ferrite concentration of the xylene slurry was 33% by weight. Crushing
The process was performed until the specific surface area became 8 m ² / g. As a result of measuring the magnetic properties of the powder of the obtained pulverized slurry in the same manner as described above, σ
s = 63 emu / g and iHc = 2.0 kOe. Also,
The average particle size was 0.3 μm.

The pulverized slurry was adjusted by suction filtration so that the ferrite concentration in the slurry was 80 to 85% by weight. While removing the solvent from the slurry, about 13
It was formed into a cylinder having a diameter of 30 mm and a height of 15 mm in a height direction magnetic field of kG. Table 1 shows the degree of orientation (Ir / Is) of the compact at this time.

Next, each compact was fired in air at a temperature shown in Table 1 for 1 hour. When the molded body is fired, it is necessary to remove oleic acid in air in advance.
Degreasing was sufficiently performed at 00 to 300 ° C. Magnetic properties, degree of orientation, sintered density and shrinkage ratio in the height direction Shh (c) of the obtained sintered body
The shrinkage ratio (Shh / Shφ) between the shrinkage ratio Shφ in the axial direction) and the shrinkage ratio in the radial direction (Sh-axis direction) was evaluated. Table 1 shows the obtained results. In addition, SrCO ₃ = 2.3%, CaCO ₃ = 1.
It becomes the same mol% as 56%.

[0054]

[Table 1]

As shown in Table 1, in the sample to which SrCO ₃ was added instead of CaCO ₃ , iHc was improved, and the shrinkage ratio (Shh / Shφ) was almost 1. Example 1 in which the amount of addition in mole percentage is the same and the firing temperature is the same
And Comparative Example 3 and Example 2 and Comparative Example 4 show that adding SrCO ₃ instead of CaCO ₃ improves the sintering density.

Examples 3 to 5 The following materials were used. Fe ₂ O ₃ powder (primary particle diameter 0.3 μm) 1000 g BaCO ₃ powder (primary particle diameter 2 μm) 215.5 g SiO ₂ (primary particle diameter 0.01 μm) 2.30 g CaCO ₃ (primary particle diameter 1 μm) 1.72 g

The mixture having the above composition was pulverized with 2 L of water for 2 hours in a wet attritor, dried and sized, and then dried.
Calcination was performed in air at 75 ° C. for 3 hours to obtain a calcined body powder.

The magnetic properties of the obtained powder were measured with a sample vibration magnetometer (VSM). As a result, σs = 68 emu / g, iH
c = 4.3 kOe. The primary particle size is 0.5μ
m and the BET specific surface area was 2 m ² / g.

With respect to the calcined powder, 0.6 wt% of Si
O ₂ and a predetermined amount of SrCO ₃ or 1.5 wt% CaC
O ₃ was added and pulverized by a dry vibration mill until the ferrite powder had a specific surface area of 7 m ² / g. By this treatment, pulverization strain is introduced into the ferrite powder, and i
Hc decreased from 4.3 kOe to 1.9 kOe. Note that S
The SrCO ₃ / SiO ₂ molar ratio of each of the samples to which rCO ₃ was added was in the range of 0.5 to 3.

Next, wet grinding was performed in a ball mill using xylene as a non-aqueous solvent and oleic acid as a surfactant. Oleic acid was added at 1.3 wt% to the powder obtained by dry grinding. The ferrite concentration of the xylene slurry was 33% by weight. Crushing
The process was performed until the specific surface area became 8 m ² / g. As a result of measuring the magnetic properties of the powder of the obtained pulverized slurry in the same manner as described above, σ
s = 63 emu / g and iHc = 1.6 kOe. Also,
The average particle size was 0.3 μm.

The pulverized slurry was adjusted by suction filtration so that the ferrite concentration in the slurry became 80 to 85 wt%. While removing the solvent from the slurry, about 13
It was formed into a cylinder having a diameter of 30 mm and a height of 15 mm in a height direction magnetic field of kG.

Next, in air at 1190-1220 ° C., 1
The sintering was performed for a time and a temperature rising / falling rate of 5 ° C./min.
In order to remove oleic acid when firing the molded body, the molded body was sufficiently degreased at 100 to 300 ° C. in air and then fired.
Shrinkage ratio (Shh and Shφ), shrinkage ratio (Sh
h / Shφ), magnetic properties and shrinkage ratio (Shh / Shφ) were evaluated for sintering temperature dependence. The obtained results are shown in FIGS. 1, 2 and 3.

In the sample to which SrCO ₃ was added, Shh was Ca
As compared with the sample to which CO ₃ was added, Shφ was high, while Shφ was high, and the shrinkage ratio was around 16%. As a result, as shown in FIGS. 1 and 2, Shh / Shφ was close to 1. Become. Further, as shown in FIG. 3, in the sample to which SrCO ₃ is added, Br is not different from CaCO ₃ , but iHc is improved and excellent magnetic characteristics are obtained. The sintered density is C
Compared with the sample to which aCO ₃ was added, it was equal or higher, and the shrinkage ratio (Shh / Shφ) hardly depended on the sintering temperature.

FIG. 4 shows the SiO ₂ obtained by SEM.
Of a sintered body (a) to which 0.6 wt% of Ca ₂ and 1.5 wt% of CaCO ₃ were added, and a sintered body sample (b) of which 0.6 wt% of SiO ₂ and 1.7 wt% of SrCO ₃ were added. 1 shows an organizational structure. It can be seen that the grain is controlled to be small in (b) of the present invention.

FIG. 5 shows that 0.6 wt% of SiO ₂ and SrCO
₃ is a graph showing a result of a depth analysis of a ferrite fracture surface by ESCA of a sintered body sample to which 31.7 wt% is added. Milling in the depth direction was performed using a Kauffman-type ion gun (0.5 kV-30 mA), and the sputtering rate was Si.
The test was performed at 144 A / min in terms of O ₂ . Table 2 shows the ESCA analysis results thus measured. C _1o is 5 to 2
It was 0 at%.

[0066]

[Table 2]

Comparative Example 5 by TEM-EDS A molded body produced in the same manner as in Examples 3 to 5 except that 0.6 wt% of SiO ₂ and 1.5 wt% of CaCO ₃ were added,
It was fired at 1210 ° C. for 1 hour in the air to obtain a sintered body sample. Table 3 shows details of the compact and the sintered compact sample.

[0068]

[Table 3]

The sintered body sample of Comparative Example 5 and the sintered body sample of Example 3 were polished from both sides in parallel to the c-axis to a thickness of about 100 μm, and then reduced to a thickness of about 30 μm with a Dimple-Grinder. PIPS (Precision Ar Ion Pollishing System)
Into a thin film to obtain a sample for measurement. The composition distribution was examined by TEM-EDS at four or more locations (N ≧ 4) inside the polycrystalline grain boundary portion and inside the grains of each measurement sample. TEM used JEM2000FXII manufactured by JEOL Ltd., and EDS used TN5450 manufactured by Tracer-Northern. Table 4 shows the results.

[0070]

[Table 4]

As shown in Table 4, in the sample of the present invention, S
i, Sr and Ba exist as grain boundary components. on the other hand,
In the sample of Comparative Example 5 to which Sr was not added, Sr
And Ba are present, but their concentration at the grain boundaries is equivalent to the concentration inside the grains.

Example 6 A magnetic field compact was obtained in the same manner as in Example 3 except that the amount of SrCO ₃ added to the calcined powder was 2.0 wt%. This compact was subjected to a degreasing treatment at 240 ° C. for 3 hours, pulverized, and sized with a 60 mesh (sieve diameter 250 μm) to prepare magnetically oriented granules. Magnetic field molding was performed using the granules. Thereafter, sintering was performed at 1220 ° C. for 1 hour to produce a 24-pole polar anisotropic ring magnet having an outer diameter of 31 mm, an inner diameter of 23 mm, and a height of 19 mm.

The degree of deformation of the fired polar anisotropic ring magnet was evaluated by a round tester. Fig. 6 shows the results.
(A).

[0074] In addition to the CaCO ₃ instead of Comparative Example 6 SrCO ₃ was 1.5 wt% in the same manner as in Example 6, to prepare a polar anisotropy ring magnet. The result is shown in FIG.

From the comparison between FIGS. 6A and 6B, it can be seen that the polar anisotropic ring magnet of the present invention has a small deformation and a small polishing allowance. Note that the magnetic properties (surface magnetic flux densities) of the ring magnets in Example 6 and Comparative Example 6 were equivalent. In Examples 1, 2, and 6, Examples 3, 4,
C _1o , C _1o / C _1i and C _2o / C _2i equivalent to 5 were obtained.

Comparative Examples 7 to 9 (Sr ferrite magnet) Instead of BaCO ₃ (215.5 g), SrCO ₃ (1
A calcined powder of Sr ferrite was produced in the same manner as in Examples 3 to 5, except that 61.2 g) was used. SiO ₂ , CaCO ₃ , BaCO ₃
Alternatively, SrCO ₃ was added as shown in Table 5, and the others were the same as in Examples 3 to 5 to produce sintered bodies. The shrinkage ratio of these sintered bodies was measured. Table 5 shows the results.

[0077]

[Table 5]

From Table 5, it can be seen that the composite addition of Si + Sr
It can be seen that no effect is exhibited in the sintered ferrite magnet.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the shrinkage ratio and the sintering temperature of the present invention and a comparative hexagonal Ba ferrite sintered magnet.

FIG. 2 is a graph showing the relationship between the amount of SrCO ₃ added and the shrinkage ratio (a) and the shrinkage ratio (b) of the present invention and a comparative hexagonal Ba ferrite sintered magnet.

FIG. 3 is a graph showing the relationship between the amount of SrCO ₃ added and iHc and Br in hexagonal Ba ferrite sintered magnets of the present invention and a comparative example.

FIG. 4 is a drawing substitute photograph obtained by a scanning electron microscope showing the crystal structure of the hexagonal Ba ferrite sintered magnet of the present invention (b) and comparative (a).

FIG. 5 is a graph showing a result of a depth analysis of a ferrite fracture surface by ESCA of a hexagonal Ba ferrite sintered magnet to which 1.7 wt% of SrCO ₃ is added according to the present invention.

FIG. 6 is a diagram showing the degree of deformation of the sintered polar anisotropic ring magnet of the present invention (a) and comparative (b).

FIGS. 7A and 7B are plan views for explaining a conventional polar anisotropic ring magnet.

FIG. 8 is a schematic diagram for explaining a polycrystalline grain boundary portion.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Taku Takeishi 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Inventor Teruo Mori 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK (56) References JP-A-49-114094 (JP, A) JP-A-49-109898 (JP, A)

Claims (12)

(57) [Claims] 1. A main phase comprising Ba ferrite, containing Sr and Si as grain boundary components, wherein the average grain size of the grains of this main phase is 1.0 μm or less, iHc is 2.5 kOe or more, and Br is 4. Hexagonal Ba ferrite sintered magnet having 1 kG or more. 2. The hexagonal Ba ferrite sintered magnet according to claim 1, wherein the Si content of the grain boundary is 2 to 50 at%. 3. The sintered hexagonal Ba ferrite magnet according to claim 1, wherein the Sr content of the grain boundary is 0.5 to 10 at%. 4. The hexagonal Ba ferrite sintered magnet according to claim 1, wherein the Si content in the grain boundaries is 2 to 100 times the Si content in the main phase grains. 5. The sintered hexagonal Ba ferrite magnet according to claim 1, wherein the Sr content at the grain boundaries is 1.1 to 20 times the Sr content inside the main phase grains. 6. A composition containing Ba as a grain boundary component, and Ba at the grain boundary.
The content is 1.1 to 20 of the Ba content inside the main phase grain.
The hexagonal Ba ferrite sintered magnet according to any one of claims 1 to 5, which is twice as large. 7. A sintered hexagonal Ba ferrite magnet obtained by crushing a calcined body powder of hexagonal Ba ferrite, shaping the crushed Ba ferrite raw material particles in a magnetic field, and sintering the obtained formed body. Wherein the Ba ferrite particles have an average particle size of 1 μm or less, and the formed body contains silicon oxide or a Si component of a compound that becomes silicon oxide by firing, and strontium oxide or strontium oxide by firing. A method for producing a sintered hexagonal Ba ferrite magnet, comprising obtaining the sintered hexagonal Ba ferrite magnet according to any one of claims 1 to 6 by incorporating a Sr component of the compound. Wherein said said Si component in terms of SiO ₂ Ba
0.1 to 2.0% by weight with respect to the ferrite raw material particles, the Sr component is 0.5 to 5% by weight in terms of SrCO ₃ with respect to the Ba ferrite raw material particles, and the molar ratio of SrCO ₃ / SiO ₂ is 0.5. The method for producing a hexagonal Ba ferrite sintered magnet according to claim 7, wherein the Si and Sr components are contained so as to be 3 to 3. 9. The method for producing a sintered hexagonal Ba ferrite magnet according to claim 7, wherein the Si component and the Sr component are added in a complex manner during the pulverization. 10. A method for producing a sintered hexagonal Ba ferrite magnet, comprising: crushing the compact according to claim 7; 11. The method for producing a sintered hexagonal Ba ferrite magnet according to claim 7, wherein Ba is precipitated at grain boundaries during sintering. 12. The hexagonal Ba according to claim 1,
A ferrite sintered magnet, which is a ring-shaped, polar anisotropic ring magnet whose inner or outer peripheral surface is oriented in multiple poles.