JPH0831627A - Hexagonal ba ferrite sintered magnet, manufacture thereof, and polar anisotropic ring magnet - Google Patents

Abstract

PURPOSE:To provide a method of manufacturing a hexagonal Ba ferrite sintered magnet which is small in anisotropy of shrinkage factor, less deformed at sintering, enhanced in sintering density and coercive force, and capable of simplifying or dispensing with an after polishing process and a polar anisotropic ring magnet. CONSTITUTION:A magnet is manufactured through such a method that hexagonal Ba ferrite calcinated pellets are ground down into material powder used for a ferrite magnet, material powder is molded in a magnetic field, and a molded body is sintered into a magnet, wherein an Si component such as SiO2 or the like and an Sr component such as SrCO3 or the like are contained in the above molded body. In result, a magnet of organizational structure which contains Ba ferrite as a main phase and Sr and Si as a grain boundary component can be obtained.

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 At present, magnetoplumbite type (M type) hexagonal Sr ferrite or Ba ferrite is mainly used as an oxide permanent magnet material, and its sintered magnet or bond magnet is used. Being manufactured. To produce a 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, crushed, molded in a magnetic field and fired.
At this time, for example, JP-A-3-291901 or 4-
As shown in Examples such as Japanese Patent No. 5802, CaCO
It is general to add ₃ and SiO ₂ in combination.

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

On the other hand, when producing a Sr ferrite or Ba ferrite sintered magnet, CaCO ₃ and S are conventionally used.
When iO ₂ is added in combination, the shrinkage rate during sintering is in the c-axis direction and a
The ratio differs greatly 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, a large amount of deformation occurs due to shrinkage during sintering, and for example, it is necessary to design a mold that takes into account the amount of deformation in advance and to sufficiently perform post-processing such as polishing and grinding, which increases manufacturing costs. There is a case to let you.

A polar anisotropic ring magnet is known as an example in which the deformation due to the difference in the shrinkage ratio is large. This magnet has a ring shape, and its inner peripheral surface or outer peripheral surface is oriented so as to be strongly magnetized in multiple poles, and is used for a stepping motor or the like. In order to manufacture this ring magnet, when obtaining a ring-shaped molded body, different poles are alternately arranged on the peripheral surface to perform magnetic field orientation, and the c-axis is oriented in the arrow direction of FIG. 7 (a). To sinter. However, as described above, since the contraction rate has a large anisotropy, the peripheral surface is deformed as shown by the broken line in FIG. 7B, so that the convex portion appearing on the peripheral surface must be polished. However, a large polishing allowance must be taken.

[0006]

The main object of the present invention is to improve the sintering density and coercive force, and further, to improve the deformation during sintering due to the difference between the shrinkage ratio in the c-axis direction and the shrinkage ratio in the a-axis direction. The present invention is to provide a hexagonal Ba ferrite sintered magnet which can reduce or eliminate post-processes such as polishing, a manufacturing method thereof, and a polar anisotropic ring magnet using these.

[0007]

This and other objects are achieved by any one of the following constitutions (1) to (15). (1) Ba ferrite as a main phase and Sr as a grain boundary component
And a hexagonal Ba ferrite sintered magnet containing Si. (2) The hexagonal Ba ferrite sintered magnet according to the above (1), wherein the grain boundary has a Si content of 2 to 50 at%. (3) The hexagonal Ba ferrite sintered magnet according to (1) or (2) above, wherein the Sr content in the grain boundary is 0.5 to 10 at%. (4) The hexagonal Ba ferrite sintered magnet according to any of (1) to (3) above, wherein the Si content in the grain boundary is 2 to 100 times the Si content in the main phase grains. (5) The hexagonal Ba ferrite sintered magnet according to any one of (1) to (4), wherein the Sr content in the grain boundary is 1.1 to 20 times the Sr content in the main phase grains. (6) Hexagonal Ba containing any one of the above (1) to (5), containing Ba as a grain boundary component, and having a Ba content in the grain boundary of 1.1 to 20 times the Ba content in the main phase grains. Ferrite sintered magnet. (7) The hexagonal Ba ferrite sintered magnet according to any of (1) to (6), wherein the average grain diameter of the main phase is 1.0 μm or less. (8) The calcined powder of hexagonal Ba ferrite is pulverized, the Ba ferrite raw material particles obtained by pulverization are compacted in a magnetic field, and the compact thus obtained is sintered to obtain a hexagonal Ba ferrite sintered magnet. A method for manufacturing, wherein the molded body has a silicon component or a Si component of a compound that becomes silicon oxide by firing,
A method for producing a hexagonal Ba ferrite sintered magnet containing strontium oxide or an Sr component of a compound which becomes strontium oxide by firing. (9) The Si component is 0.1 to 2.0 wt% in terms of SiO ₂ with respect to the Ba ferrite raw material particles, and the Sr component is 0.5 to 5 wt% in terms of SrCO ₃ with respect to the Ba ferrite raw material particles. The method for producing a hexagonal Ba ferrite sintered magnet according to the above (8), wherein the Si and Sr components are contained so that SrCO ₃ / SiO ₂ has a molar ratio of 0.5 to 3. (10) The method for producing a hexagonal Ba ferrite sintered magnet according to the above (8) or (9), wherein the Si component and the Sr component are added together during the pulverization. (11) The average particle size of the Ba ferrite raw material particles is 1 μm.
Hexagonal crystal B according to any one of the above (8) to (10), which is m or less
a Method for manufacturing a sintered ferrite magnet. (12) A method for producing a hexagonal Ba ferrite sintered magnet, which comprises crushing the molded body according to any one of (8) to (11) above, magnetic field molding and sintering the same. (13) The above (8) to deposit Ba at the grain boundary during sintering.
The method for producing a hexagonal Ba ferrite sintered magnet according to any one of (12). (14) The method for producing a hexagonal Ba ferrite sintered magnet according to any one of (8) to (13), wherein the hexagonal Ba ferrite sintered magnet according to any one of (1) to (7) above is obtained. (15) The hexagonal Ba ferrite sintered magnet according to any one of the above (1) to (7), which has a ring shape and in which an inner peripheral surface or an outer peripheral surface is multipolarly oriented. magnet.

[0008]

FUNCTION AND EFFECT The hexagonal Ba ferrite sintered magnet of the present invention has improved sintering density and coercive force.
Coercive force comparable to that of ferrite can be obtained. Thereby, the raw material cost can be reduced. Furthermore, the reduction ratio in the c-axis direction and a
The ratio (Shc / Sha) to the axial reduction ratio is close to 1. Therefore, the deformation during sintering is small, and therefore the polishing process and the like can be simplified or omitted. Therefore, a particularly excellent effect can be obtained when manufacturing a magnet requiring a special orientation such as a polar anisotropic ring magnet.

[0009]

Specific Structure The specific structure of the present invention will be described in detail below.

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

The hexagonal Ba ferrite sintered magnet of the present invention contains SrO and SiO ₂ as grain boundary components. Although there are various methods for confirming the presence of Sr and Si in the grain boundary component, it is preferable to use the following first method or second method, in particular, because the quantification thereof is easy. Especially, because the measurement can be performed accurately and stably,
It is preferable to use the first method.

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

Since the two-crystal grain boundary and the polycrystal grain boundary are continuous, it is considered that the constituent components of both are basically the same. Further, in the case of an anisotropic sintered body in which particles are oriented, there are two types of grain boundaries, an a-plane grain boundary and a c-plane grain boundary, which 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. Quenching is from 800 to 1000 ° C to 50
It may be cooled in water, for example, at about 0 to 2000 ° C./sec. This causes the magnet to break along the grain boundaries. A flat fracture surface as flat as possible is analyzed by ESCA or Auger electron spectroscopy, but in terms of separation of spectra of analytical elements, E
SCA analysis is preferred. At this time, the profile of each element in the depth direction is measured while performing ion milling.
The fracture surface does not necessarily occur at the center of the grain boundary phase, but the ESCA measurement range is about 10 ³ to 10 ⁵ μm square, and since this is averaged and counted, it was determined from the initial value of the count. The atomic percentage of each element is the content of the grain boundary. Also, ion milling progresses to 100 to 2
The average value when the concentration becomes a constant value at a depth of 00A or more is the content in the main phase grains.

The Si content C _1o of the grain boundary determined by each of the above methods is preferably 2 to 50 at%. Also, C _1o
Is divided by the Si content C _1i inside the grain to obtain a value of 2 to 10
It is preferably 0. On the other hand, the grain boundary Sr content C _2o
Is preferably 0.5 to 10 at%, and the value obtained by dividing this by the Sr content C _2i in the grain is 1.1 to 20.
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
It is preferably 25 at%, and the value obtained by dividing C _1o by C _1i is 2 to 100, particularly 10 to 80.
On the other hand, the Sr content C _2o is 0.5 to 8 at%, especially 1 to 4
It is preferably at%, and the value obtained by dividing C _2o by C _2i is preferably _1.1 to 20, particularly preferably 3 to 15.

When 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 _{1 o} by C 1 _i is 2 to 50, particularly preferably 4 to 20. On the other hand, 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, particularly 1.2 to
It is preferably 3.

The magnet of the present invention usually contains S as a grain boundary component.
It contains Ba 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 that inside the grain. Although Ba is the main component of the grain, in the magnet of the present invention, Ba is precipitated at the grain boundary due to sintering, and the Ba concentration at the grain boundary becomes higher than the Ba concentration inside the grain. Specifically, the value obtained by dividing the Ba content C _3o at the grain boundary by the Ba content C _3i inside the grain is 1.1 to 20, particularly 1.5 to 5. Incidentally, C _3o and C _3i are measured by the above-mentioned first method. In a conventional Ba ferrite sintered magnet that does not contain Si and Sr as grain boundary components, the Ba concentration at the grain boundary is equal to the Ba concentration inside the grain, and a Ba ferrite magnet having the above Ba distribution is conventionally used. unknown.

When analyzed by ESCA, iHc is particularly improved and the reduction ratio approaches 1 by having the above profile. In the measurement by ESCA, the average thickness of the grain boundary phase may be set to be twice the distance at which the concentration in the depth direction analysis has a constant value, and this thickness is generally 20 to 300 A, particularly 40 ~ 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 Ba ferrite sintered magnet generally exhibits an iHc of 2.5 kOe or more, and in a preferred embodiment, an iHc of 3 kOe or more, particularly 3.4 to 4.0 kOe is obtained. And, compared with iHc in the case of the conventional composite addition of Ca and Si, an improvement of 10 to 25% can be seen with the same amount. In addition, Br is about 4.1 to 4.4 kG. Also c
The reduction ratio (Shc / Sha) between the axial direction and the a-axis direction is 0.8-
A value of 1.5, especially 0.9 to 1.2, is obtained.

In order to manufacture such a hexagonal Ba ferrite sintered magnet, first, a calcined powder of hexagonal Ba ferrite is pulverized, and Ba ferrite powder particles obtained by pulverization are used as raw material particles to generate a magnetic field. Medium molding is performed, and the obtained molded body is sintered. At this time, the molded body is made to contain the Si component of silicon oxide or a compound which becomes silicon oxide by firing, and the Sr component of strontium oxide or a compound which becomes strontium oxide by firing. The content of Si component is
0.1 in terms of Ba ₂ ferrite raw material particles in terms of SiO ₂
.About.2.0 wt%, especially 0.2 to 1.5 wt%, and even 0.1.
3 to 1.0 wt% is preferable. The content of the Sr component, calculated as SrCO ₃ , is preferably 0.5 to 5 wt%, particularly 1.0 to 2.5 wt%, and more preferably 1.2 to 2.2 wt% based on the Ba ferrite raw material particles. And this SrCO
The molar ratio of ₃ / SiO ₂ is 0.5 to 3, especially 0.7 to
It is preferably 2.5, and more preferably 0.9 to 2.0. By adding these components in such a range, the iHc value is improved, and the shrinkage ratio in the c-axis direction and the shrinkage ratio in the a-axis direction become substantially equal.

The Si component is a core of the grain boundary glass component, and if it exceeds the above range, the nonmagnetic glass phase increases and Br deteriorates. On the other hand, if the amount is too small, grain growth during firing cannot be controlled and iHc deteriorates.

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

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

In order to obtain particularly fine ferrite particles after calcination, for example, during mixing, iron oxide is first wet-milled, and an aqueous solution of a water-soluble salt of Ba is added thereto in the presence of Na ₂ CO _3. You may add. As a result, Ba carbonate is precipitated and mixed with the fine iron oxide particles with high accuracy.
Alternatively, a fine Ba carbonate may be used and sufficiently mixed with iron oxide. After this, it is washed, dried and calcined. The calcination may be performed in the atmosphere at 1000 to 1350 ° C. for 1 second to 10 hours, particularly 1 second to 3 hours. Further, the raw materials may be sufficiently pulverized and mixed by a dry pulverizer.

As for the calcined powder, iron oxide powder as a raw material and the powder containing Ba are mixed and pulverized, and before the mixture is calcined, Ba-
Rich oxides [eg BaFe ₂ O ₄ or BaFeO
_3-x (0 ≦ x <1), etc.] may be obtained by heat treatment under the condition that an intermediate phase is formed, and then pulverizing a mixture containing this intermediate phase and then calcining.

The calcined powder thus obtained has a substantially magnetoplumbite type ferrite structure, and the average primary particle size is 0.1 to 1 .mu.m, particularly 0.1 to 0. It is preferably 5 μm. The average particle size may be measured with a scanning electron microscope (SEM). The saturation magnetization σs is preferably 65 to 69 emu / g and the coercive force iHc is preferably 4000 to 6000 Oe.

Next, the calcined powder is crushed. In the present invention, the Si component and the Sr component are added within the above range, but these components may be added at the time of magnetic field molding,
The time of addition may be any time from pulverization of the calcined body to before molding, but it is particularly preferable to add at the time of pulverizing the powder of the calcinated body, usually at the beginning of the pulverizing step.
SiO ₂ is generally used as the Si component. Further, SrCO ₃ is generally used as the Sr component. Besides this, Si
You may use the compound etc. of these. The particle size when added as a powder is about 0.01 to 5 μm.

In the calcination step of pulverizing the calcined body, it is preferable to introduce crystal strain into the calcined powder to reduce bHc. The calcinated body particles become finer (single domain particles), resulting in iHc and b.
When Hc increases, a magnetic force acts between particles, which facilitates aggregation of ferrite particles. 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. The larger bHc in the hysteresis loop of one ferrite particle, the larger the surface magnetic flux density, and as a result, the larger the cohesive force. Therefore, in order to weaken the cohesive force of the ferrite particles, it is more advantageous to reduce the bHc and the squareness of the second quadrant by introducing crystal strain. As a result, a high degree of orientation can be obtained during magnetic field orientation. Then, the strain introduced into these particles is removed in the firing step after the magnetic field molding, and a permanent magnet having high magnetic characteristics can be obtained.

When the iHc of Ba ferrite particles is reduced by the crystal strain, there is a new effect that the amount of change of iHc with respect to the temperature is reduced. The temperature coefficient of iHc decreases to about 1 to 6 Oe / ° C at -100 to + 150 ° C. For this reason, the strained particles can be used as they are as magnetic powder for a magnetic recording medium.

Mechanical crushing is effective for introducing such crystal strain. In order to perform such pulverization, it is preferable to first perform dry pulverization to introduce sufficient crystal strain. As a pulverizer used for dry pulverization, a dry vibration mill, a dry attritor (medium agitation type mill), a dry ball mill or the like can be used, but a dry vibration mill is particularly preferably used.

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

Then, the dry pulverized powder is usually wet pulverized. By wet pulverization, the BET specific surface area is increased to about 1 to 4 times, particularly about 1 to 3 times, and the average particle diameter is adjusted to 0.
The BET specific surface area is 6 to 12 m ² / g. Even with this wet pulverization, 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 the strain amount and Hc can be set to such a value by omitting the dry pulverization and only by the wet pulverization, the pulverization may be only the wet pulverization. Alternatively, only dry grinding may be used. The σs after crushing is about 50 to 67 emu / g. A ball mill, an attritor, a vibration mill or the like is preferably used for such wet pulverization.

The solvent used in this 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 the solvent of the slurry during this wet pulverization. As the non-aqueous solvent to be used, organic compounds such as various organic solvents which are liquid at room temperature may be used, but hydrocarbons such as heptane, industrial gasoline, kerosene, cyclohexane, toluene, xylene, ethylbenzene, turpentine oil, etc .; halogenated Hydrocarbons such as 1,2-dibromoethane, tetrachloroethylene, perchloroethylene, dichloropentane, monochlorobenzene and the like; monohydric alcohols, phenols, ethers such as methanol, ethanol, n-propyl alcohol, n- Butyl alcohol, cyclohexanol, phenol, n
-Butyl ether, etc .; Acids, esters, such as butyl acetate, etc .; Polyhydric alcohols and their ethers, esters, such as ethylene glycol, etc .; Aldehydes, acetals, ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone Etc .; 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, and particularly 0.4 to 1.5 cps.
s is preferred. Thereby, the moldability and the degree of orientation of the molded product are significantly 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 the boiling point thereof is 50 to 300 ° C, more preferably 50 to 200 ° C. Further, it is preferable that the non-aqueous solvent constitutes about 10 to 90% by weight in the slurry during the wet pulverization, and the ferrite particles in the slurry are 10 to 90% by weight.

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

The surfactant used is a cationic type,
It may be any of anionic type, nonionic type and amphoteric type, but especially carboxylic acid or a salt thereof, for example, stearic acid, oleic acid, Zn stearate, stearic acid C.
a, 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 at least one saturated or unsaturated fatty acid of about 4 to 30 or a salt thereof are preferably used.
Of these, use of a fatty acid, more preferably Ca salt of stearic acid, is advantageous because the solvent removal property at the time of molding is improved and cracking of the molded body is prevented without impairing the orientation. It is considered that this is because the density of the molded body decreases from 3.0 g / cm ³ to 2.8 g / cm ³ and the solvent is easily removed. Also, especially Ca, Ba,
Sr, Al, Cr, Ga, Cu, Zn, Mn, Co, T
By adding an organic substance (metal salt of organic surfactant such as metal salt of fatty acid described above) containing an effective additive element that may be added to the ferrite such as i, the element is added around ferrite particles. High dispersion is also possible. In addition, known sulfonic acids or salts thereof; sulfuric acid esters or salts thereof; phosphoric acid esters or salts thereof; aliphatic amine salts or quaternary ammonium salts thereof; aromatic quaternary ammonium salts; pyridinium salts; imidazolinium salts; betaine At least one of aminocarboxylic acid salt; imidazoline derivative; natural surfactant is also preferably used.

If such a surfactant is added to the non-aqueous solvent slurry containing the calcined powder and wet pulverized, the slurry can be directly used for wet molding.
Alternatively, a part or all of this surfactant may be added at the time of dry pulverization of the calcined powder, which is performed prior to the wet molding or is performed alone. Further, a part or all of the surfactant may be added after the wet pulverization of the non-aqueous 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 body is realized. The amount of the surfactant added in each stage may be set so as to be the above-mentioned amount in the slurry during the wet molding.

In the wet pulverization, when an aqueous solvent, particularly water or a mixed solvent of water is preferably used from the viewpoint of handling property, the raw material powder in the slurry during the wet pulverization is 10 to 7
It is about 0% by weight. However, even if a surfactant is added to the water slurry and the wet molding is not expected to improve the degree of orientation of the molded body, it is preferable to replace the solvent with a non-aqueous solvent. For solvent replacement, for example, decantation may be performed while the raw material powder is magnetically held. In addition, also in this wet molding, dry pulverization can be performed in advance.

In this way, when the wet pulverization is carried out using a water-based solvent, which is different from the slurry solvent at the time of wet molding, and then the solvent is replaced, the surfactant is added in the above-mentioned addition amount at the time of final wet molding. Must exist
For this purpose, the surfactant may be added at any one stage of dry pulverization, wet pulverization, and final slurry preparation. In any of the above cases, the final wet-forming slurry is adjusted so that the amount of non-aqueous solvent is about 5 to 30% by weight and the amount of raw material particles is about 70 to 95% by weight.

After the final non-aqueous solvent slurry containing the surfactant is prepared in this way, molding in a magnetic field is carried out while removing the non-aqueous solvent in the slurry. Removal of the solvent may be carried out according to a conventional method, for example, forced decompression, and the molding pressure is 0.1.
Approximately 0.5 ton / cm ² and applied magnetic field is approximately 5 to 15 kG. The orientation degree, Ir / Is, of the obtained molded body is 75% or more, for example, 78 to 86%. And such a high degree of orientation is realized only when a non-aqueous solvent and a surfactant are used in combination, and high orientation cannot be obtained even if the surfactant is added to the water slurry.

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

Further, the molded body is crushed by using a crusher or the like, and the average particle size is 100 to 700 μm by a sieve or the like.
A magnetic field oriented granule was obtained by sizing to about m, and using this, a hexagonal Ba ferrite sintered magnet of the present invention having various forms was formed by dry magnetic field forming and sintering in the same manner as above. May be.

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 carried out by dry or wet pulverization as described above, and water or a mixed solvent of water is preferable as the solvent of the slurry at the time of wet pulverization performed in a preferable form, from the viewpoint of easy handling. When wet grinding,
The solvent constitutes about 10 to 90% by weight in the slurry, especially 30 to 90% by weight in the water slurry, and the ferrite particles in the slurry are 10 to 90% by weight, especially 1 in the water slurry.
It is preferably from 0 to 70% by weight.

If wet pulverization is performed using such preferably water or an aqueous slurry, the slurry can be directly used for wet molding. Further, as described above, the dry calcining of the calcined powder may be performed prior to the wet molding. Further, a solvent for wet molding may be prepared after dry grinding to prepare a slurry for wet molding. Furthermore, the above wet pulverization may be carried out in another solvent different from the molding slurry, and then the solvent used at the time of pulverization may be replaced with water, preferably prior to the wet molding. For solvent replacement, for example, decantation may be performed while the raw material powder is magnetically held. In addition, also in this wet molding, dry pulverization can be performed in advance. In any of the above cases, the final wet-forming slurry contains 5 to 30% by weight of a solvent such as water.
The amount of raw material particles is adjusted to about 70 to 95% by weight.

When wet pulverizing an aqueous slurry,
It is desirable to add a dispersant during pulverization. As this dispersant, it is desirable to use a polymer dispersant,
In particular, ammonium polycarboxylate type is preferable.
Further, it is preferable to add 0.1 to 1% by weight of the dispersant to the raw material powder.

[0046]

EXAMPLES 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 raw 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

Fe ₂ O ₃ powder and Na ₂ CO ₃ were added to 1.6 parts of water.
It was pulverized together with L by a wet attritor for 1.5 hours to obtain a slurry. Then, an aqueous solution containing BaCl ₂ .2H ₂ O was dropped into the attritor containing the above slurry and further pulverized for 0.5 hour. In this step, a 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. This slurry was washed until NaCl was 0.2% or less, dehydrated, dried and granulated, and then calcined in air at 1175 ° C. for 3 hours to obtain a calcined powder.

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

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

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

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

Next, each molded body was fired in air at the temperature shown in Table 1 for 1 hour. In addition, when firing the molded body, in order to remove oleic acid
It was thoroughly degreased at 00 to 300 ° C. Magnetic properties, orientation degree, sintering density and shrinkage in the height direction Shh (c
The shrinkage ratio (Shh / Shφ) between the axial shrinkage and the radial shrinkage Shφ (a-axis direction) was evaluated. The results obtained are shown in Table 1. In addition, SrCO ₃ = 2.3%, CaCO ₃ = 1.
It is the same mol% as 56%.

[0054]

[Table 1]

As shown in Table 1, in the sample in which SrCO ₃ was added instead of CaCO ₃ , iHc was improved, and the reduction ratio (Shh / Shφ) was almost 1. In addition, Example 1 in which the addition amount is the same in terms of mole percentage and the firing temperature is the same
From the comparison between Comparative Example 3 and Comparative Example 3 and the comparison between Example 2 and Comparative Example 4, it is understood that the sintering density is improved by adding SrCO ₃ instead of CaCO ₃ .

Examples 3 to 5 The following materials were used as raw materials. 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 in a wet attritor with 2 L of water for 2 hours, dried and sized, and then 11
Calcination was performed in air at 75 ° C. for 3 hours to obtain a calcined powder.

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

0.6% by weight of Si was added to the calcined powder.
O ₂ and a predetermined amount of SrCO ₃ or 1.5 wt% CaC
O ₃ was added, and the 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, crushing strain is introduced into the ferrite powder, and i
Hc decreased from 4.3 kOe to 1.9 kOe. In addition, S
The SrCO ₃ / SiO ₂ molar ratios of the samples to which rCO ₃ is added are all within the range of 0.5 to 3.

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

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

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

In the sample to which SrCO ₃ was added, Shh was Ca
It is lower than that of the sample to which CO ₃ is added, while Shφ is high, and both shrinkage ratios are around 16%. As a result, as shown in FIGS. 1 and 2, Shh / Shφ is close to 1. Become. Further, as shown in FIG. 3, although the sample added with SrCO ₃ does not change Br to CaCO ₃ , iHc is improved and excellent magnetic characteristics are obtained. The sintered density is C
It is equal to or higher than that of the sample to which aCO ₃ is added, and the reduction ratio (Shh / Shφ) has almost no dependency on the sintering temperature.

FIG. 4 shows SiO ₂ obtained by SEM.
Of 0.6% by weight of CaCO ₃ and 1.5% by weight of CaCO ₃ (a) and 0.6% by weight of SiO ₂ and 1.7% by weight of SrCO ₃ (b) The organizational structure is shown. It can be seen that the grain is controlled to be small in (b) of the present invention.

FIG. 5 shows that SiO ₂ 0.6 wt% 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 added with ₃ 1.7 wt%. For depth milling, a Kauffman type ion gun (0.5 kV-30 mA) was used, and the sputter rate was Si.
It was performed at 144 A / min in terms of O ₂ . Table 2 shows the results of the ESCA analysis thus measured. C _1o is 5 to 2
It was 0 at%.

[0066]

[Table 2]

Analysis by TEM-EDS Comparative Example 5 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 in air at 1210 ° C. for 1 hour to obtain a sintered body sample. Details of the molded body and the sintered body sample are shown in Table 3.

[0068]

[Table 3]

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

[0070]

[Table 4]

As shown in Table 4, in the samples 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 in which Sr was not added, Sr was not found in the grain boundaries.
And Ba are present, but their concentration at the grain boundaries is comparable to that inside the grains.

Example 6 A magnetic field molded body was obtained in the same manner as in Example 3 except that SrCO ₃ added to the calcined powder was 2.0 wt%. This molded body was subjected to degreasing treatment at 240 ° C. for 3 hours, pulverized and sized with a 60 mesh (sieving diameter of 250 μm) to prepare magnetic field oriented granules. Magnetic field molding was performed using these granules. Then, it was sintered at 1220 ° C. for 1 hour to prepare 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 polar anisotropic ring magnet after firing was evaluated by a round tester. The result is shown in Fig. 6.
(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 (a) and (b) of FIG. 6, it can be seen that the polar anisotropic ring magnet of the present invention has a small deformation and a small polishing allowance. The magnetic characteristics (surface magnetic flux density) of the ring magnets of Example 6 and Comparative Example 6 were the same. Further, in each of the first, second and sixth embodiments, the third, fourth,
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. For this calcined powder, SiO ₂ , CaCO ₃ , and BaCO ₃
Alternatively, SrCO ₃ and SrCO ₃ were added as shown in Table 5, and other conditions were the same as in Examples 3 to 5 to produce sintered bodies. The shrinkage ratio of these sintered bodies was measured. The results are shown in Table 5.

[0077]

[Table 5]

From Table 5, the composite addition of Si + Sr is
It is understood that the ferrite sintered magnet has no effect.

[Brief description of drawings]

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

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

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

FIG. 4 is a drawing-substituting photograph obtained by a scanning electron microscope showing the crystal structures of the hexagonal Ba ferrite sintered magnets of the present invention (b) and Comparative (a).

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

FIG. 6 is a diagram showing the degree of deformation of the polar anisotropic ring magnets of the present invention (a) and comparison (b) after firing.

FIG. 7A and FIG. 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.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Teruo Mori 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDC Corporation

Claims (15)

[Claims] 1. A hexagonal Ba ferrite sintered magnet containing Ba ferrite as a main phase and containing Sr and Si as grain boundary components. 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 hexagonal Ba ferrite sintered magnet according to claim 1, wherein the Sr content in 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 boundary is 2 to 100 times the Si content in the main phase grains. 5. The hexagonal Ba ferrite sintered magnet according to claim 1, wherein the Sr content in the grain boundary is 1.1 to 20 times the Sr content in the main phase grains. 6. Ba as a grain boundary component containing Ba as a grain boundary component
The content is 1.1 to 20 of the Ba content inside the main phase grains.
The hexagonal Ba ferrite sintered magnet according to any one of claims 1 to 5, which is double. 7. The average diameter of the grains of the main phase is 1.0 μm.
The hexagonal Ba ferrite sintered magnet according to any one of claims 1 to 6, which is m or less. 8. A hexagonal Ba ferrite sintered magnet obtained by pulverizing a calcined powder of hexagonal Ba ferrite, pulverizing and pulverizing Ba ferrite raw material particles in a magnetic field, and sintering the obtained compact. A hexagonal Ba ferrite firing method, wherein the molded body contains Si component of silicon oxide or a compound that becomes silicon oxide by firing, and Sr component of strontium oxide or a compound that becomes strontium oxide by firing. A method for manufacturing a magnet. 9. The Si component is the Ba in terms of SiO _2.
0.1 to 2.0 wt% with respect to the ferrite raw material particles, 0.5 to 5 wt% of the Sr component in terms of SrCO ₃ with respect to the Ba ferrite raw material particles, and SrCO ₃ / SiO ₂ in a molar ratio of 0.5. 9. The method for producing a hexagonal Ba ferrite sintered magnet according to claim 8, wherein the Si and Sr components are contained so as to be 3 to 3. 10. The hexagonal Ba of claim 8 or 9, wherein the Si component and the Sr component are added together during the pulverization.
Manufacturing method of sintered ferrite magnet. 11. The method for manufacturing a hexagonal Ba ferrite sintered magnet according to claim 8, wherein the average particle diameter of the Ba ferrite raw material particles is 1 μm or less. 12. A method for producing a hexagonal Ba ferrite sintered magnet, which comprises crushing the molded body according to any one of claims 8 to 11, magnetic field molding this, and sintering. 13. The method for producing a hexagonal Ba ferrite sintered magnet according to claim 8, wherein Ba is precipitated at a grain boundary during sintering. 14. The hexagonal Ba according to claim 1.
The method for producing a hexagonal Ba ferrite sintered magnet according to claim 8, wherein a ferrite sintered magnet is obtained. 15. The hexagonal Ba of any one of claims 1 to 7.
A polar anisotropic ring magnet which is a ferrite sintered magnet and has a ring shape and whose inner peripheral surface or outer peripheral surface is oriented in multiple poles.