KR20150055901A - A high-crystallinity ferrite magnetic powder and a sintered magnet prepared by using bimodal ferrite powders comprising the same - Google Patents

Abstract

According to one embodiment of the present invention, plate-shaped high crystalline ferrite magnetic powder is R-Fe-O ferrite magnetic powder wherein the R is selected one or more among groups formed of Sr, Co, and Ba and has 0.1-10 μm of a grain size. Also, a method to manufacture high crystalline ferrite magnetic powder comprises: a step of mixing ferrite precursors and salts; a step of forming droplets by spraying the mixture; and a step of growing ferrite grains by passing the droplets through a reaction chamber with carrier gas. The magnetic power facilitates magnetization, has excellent arrangement in an axial direction, and prevents agglomeration between the grains. According to the other embodiment of the present invention, bimodal ferrite powder comprises magnetic powder (First powder) according to one among claim 1-5 and ferrite nanopowder (second powder) with 0.01-0.5 μm of a grain size. Also, the present invention relates to a bimodal ferrite sintered magnet manufactured using the same. Furthermore, a method to manufacture a sintered magnet comprises: a step of manufacturing slurry by mixing the bimodal ferrite powder with a water-based solvent; a step of applying a magnetic field to the slurry; and a step of sintering the slurry to which the magnetic field is applied. The sintered magnet has high sintered density and excellent coercive force and remained magnetic flux density to be applied to electronic devices requiring miniaturization and weight lightening.

Description

TECHNICAL FIELD [0001] The present invention relates to a high-crystallinity ferrite magnetic powder and a bimodal ferrite powder containing the same, and more particularly to a sintered magnet produced by using a high crystallinity ferrite magnetic powder and a bimodal ferrite powder containing the same.

The present invention relates to a highly crystalline ferrite magnetic powder, a method for producing the same, a bimodal ferrite powder containing the magnetic powder, a magnet manufactured using the same, and a manufacturing method of the magnet. In addition, by increasing the sintered density of the magnet using a bimodal ferrite powder mixed with a plate-like highly crystallized ferrite magnetic powder containing a salt and preventing agglomeration between the particles and a nano powder of a different size, a lightweight and compact bimodal To a ferrite sintered magnet.

Soft ferrite is a material that has a high magnetic susceptibility even when it is magnetized only a little, and it is sufficient to weaken or invert the residual magnetism and sufficient magnetic field to sufficiently magnetize the material. device and is used for deflection yoke (DY) and flyback transformer (FBT), which are cathode ray tube parts, to improve the function of electron deflection and power supply. Recently, in addition to the consumer electronics industry such as a flat TV (TV) and a digital TV (TV), a communication core for IMT and electromagnetic interference (EMI) for electromagnetic wave absorption and noise removal ) Core (core) are the main players.

Hard ferrite is a permanent magnet made of ferrite. It requires a strong reverse magnetic field even when removing or reversing residual magnetism. It does not need to apply voltage and can generate a certain magnetic field without generating heat itself. It is used for many purposes and is mainly applied to the conversion of electromechanical energy such as a speaker, a permanent magnet motor, a movable coil type device, a magnet generator, a microphone, etc., and is also used for a storage medium.

The application of ferrite is made by molding and sintering, and it can be used in a wide range of fields because of its various shapes and low cost. In order to apply the ferrite magnetic material to various fields as described above, it is important to obtain a fine terminal powder having excellent dispersibility since the physical properties of the magnetic material required for the ferrite magnetic material are deeply related to the finer terminal powder which has a coercive force and a residual magnetic flux density.

However, when the size of the crystal grains is made finer, the phenomenon of agglomeration between the grains occurs due to the increase of the surface area, and the heat treatment of the sintering process required for manufacturing the sintered magnet is 1000 Lt; RTI ID = 0.0 > ° C, < / RTI > so that a phenomenon occurs in which fine grain growth occurs in this process and thus coercive force and alignment degree are reduced together.

In order to control the degree of alignment for maximizing cohesion and magnetism, there is an example using ferrite particles having a homogeneous size of high crystallinity. However, it is expected that these particles can be aligned in the direction of the easy magnetization axis, There is still a problem that a magnetic repulsive force is generated due to the same polarity in a direction perpendicular to the C axis, which is an easy axis of magnetization in the C axis direction, and the degree of alignment is reduced.

Korean Patent Publication No. 10-2006-0057651

Disclosed is a sintered magnet produced by using bimodal ferrite powder having improved coercive force and residual magnetic flux density while improving sintering density to be applied to fields requiring a miniaturized and lightweight magnet. In addition, as a self-component material contained in the bimodal ferrite powder for producing the sintered magnet, it is possible to prevent aggregation between particles by containing a salt thereon, to facilitate production into a plate shape, To provide a plate-like highly crystalline ferrite magnetic powder, and to provide a method for producing the same.

The sheet-like highly crystalline ferrite magnetic powder according to one embodiment of the present invention is a ferrite magnetic powder having a grain size of 0.1 to 10 탆 (at least one selected from the group consisting of Sr, Co and Ba) of R-Fe-O Lt; / RTI >

The magnetic powder may have an aspect ratio of 3: 1 to 5: 1, and the magnetic powder may have an aspect ratio of 3.3: 1 to 4: 1.

The magnetic powder may be grown in the presence of a salt, and may contain a salt.

According to another embodiment of the present invention, there is provided a method of manufacturing a magnetic powder, comprising: mixing a ferrite precursor with a salt; Spraying the mixture to form droplets; And passing the droplet along with the carrier gas to a reaction chamber to grow the ferrite particles.

The ferrite precursor _{Ba (NO 3) 2, BaCO} 3, BaCl 2, BaSO 4, BaO 2, Sr (NO 3) 2, SrCO 3, SrCl 2, SrSO 4, Sr (OH) 2, La (NO 3) ₃ , LaCl ₃ , La ₂ (SO ₄ ) ₃ and La (OH) ₃ ; And _{Fe (NO 3) 3, FeCO} 3, FeCl 3, Fe 2 O 3, FeCl 2, Fe (OH) 3, Co (NO 3) 2, CoCO 3, CoCl 2 and 1 are selected from the group consisting of CoSO ₄ Or more than one species.

The reaction chamber may be heated to a temperature higher than the melting point of the salt before the droplet is introduced.

Wherein the salt is at least one nitrate metal salt selected from NaNO ₃ , KNO ₃ , LiNO ₃ , Ca (NO ₃ ) ₂ and Mg (NO ₃ ) ₂ , Na ₂ SO ₄ , K ₂ SO ₄ , Li ₂ SO ₄ , CaSO ₄ and MgSO ₄ , or at least one metal chloride salt selected from the group consisting of NaCl, KCl, LiCl, CaCl ₂ and MgCl ₂ .

A bimodal ferrite powder according to another embodiment of the present invention comprises (1) a magnetic powder (first type powder) according to any one of claims 1 to 5, and (2) And a ferrite nano powder (second type powder) having a thickness of 0.01 to 0.5 탆.

The first type powder and the second type powder may have a particle size of 0.7 to 2.0 탆 and 0.1 to 0.2 탆, respectively, and the second type powder may have a crystal structure of M type or W type, Lt; / RTI >

The content of the first type powder may be 20 to 99% by weight, the content of the second type powder may be 1 to 80% by weight, and preferably the mixing ratio of the first type powder to the second type powder is And may be in a weight ratio of 3: 7 to 7: 3.

The sintered magnet according to another embodiment of the present invention is obtained by sintering the bimodal ferrite powder.

The sintered magnet may further comprise lanthanum (La), and the sintered magnet may include 95 to 99.9 wt% of bimodal ferrite powder and 0.1 to 5 wt% of lanthanum.

According to still another embodiment of the present invention, there is provided a method of manufacturing a sintered magnet. Mixing the bimodal ferrite powder with an aqueous solvent to prepare a slurry; Applying a magnetic field to the slurry; And sintering the slurry to which the magnetic field is imparted.

The sintering may be performed by any one method selected from the group consisting of pressure sintering, hot pressing, hot isostatic pressing, gas pressure sintering and spark plasma sintering. .

Hereinafter, the present invention will be described in more detail.

The sheet-like highly crystalline ferrite magnetic powder according to an embodiment of the present invention is a ferrite magnetic component of R-Fe-O (R is at least one selected from the group consisting of Sr, Co, and Ba). The R-Fe-O ferrite magnetic powder may have a crystal structure of M type and W type in a hard magnetic phase.

The plate-like highly crystalline ferrite magnetic powder may have a particle diameter of 0.1 to 10 탆, preferably 0.7 to 2.0 탆, and more preferably 0.9 to 1.0 탆.

In general, one crystal grain has the same easy axis of magnetization. When the magnetic powder is larger than 100 mu m, there are many crystal grains in one grain, and thus the directions of the easy axis of magnetization are different from each other, There may occur a phenomenon in which the degree of alignment of the axis is not increased, coarsening of crystal grains in the magnetic powder may occur during sintering and the coercive force may be lowered. When the magnetic powder is smaller than 0.1 mu m, the powder particles are smaller in size than the terminal sphere, so that the easy magnetization axis can not be present in the crystal grains, and the magnetism itself may not occur. That is, in the case of a size of 0.7 to 2.0 탆, the size of the powder particle is similar to the size of the terminal sphere, so that only a small number of crystal grains are present in the particle and the alignment degree of the easy axis of magnetization is maximized. Can be suppressed.

The magnetic powder is in the form of a plate, and the aspect ratio of the powder may be 3: 1 to 5: 1, preferably 3.3: 1 to 4: 1. When the magnetic powder is in the form of a plate, it can be densely laminated at the time of manufacturing a subsequent magnet, so that the sintering density can be improved and the degree of alignment in the direction of easy magnetization axis (C axis) have. When the squareness ratio is smaller than 3: 1 (a / c; see FIG. 2), the increase in the degree of alignment is insignificant. When the squareness ratio is larger than 5: 1, the powder may be broken during sintering, So that the coercive force and the residual magnetic flux density can be reduced. That is, when the squareness ratio is 3.3: 1 to 4: 1, cracking or breakage of the magnetic powder can be prevented, and the degree of alignment can be greatly increased.

The magnetic powder may be grown in the presence of a salt. In contrast to a top-down technique such as milling a magnetic powder by a conventional milling process or the like, When the particles are produced by bottom-up techniques such as through growth, the particles are produced without impact and damage. Therefore, there are fewer surface defects, more uniform particle size, and superior crystallinity can do.

The magnetic powder may contain a salt. When the magnetic powder is prepared by growing the magnetic powder by the bottom-up technique, the salt may be used as a substrate so that the magnetic powder can grow well. The magnetic powder is easily produced in the form of a plate, and the coagulation phenomenon between the magnetic powders can be prevented.

According to another embodiment of the present invention, there is provided a method of preparing a sheet-like highly crystalline ferrite magnetic powder, comprising: mixing a ferrite precursor with a salt; Spraying the mixture to form droplets; And passing the droplet along with the carrier gas to a reaction chamber to grow the ferrite particles.

Wherein the ferrite precursor is selected from the group consisting of Ba (NO ₃ ) ₂ , BaCO ₃ , BaCl ₂ , BaSO ₄ , BaO ₂ , Sr (NO ₃ ) ₂ , SrCO ₃ , SrCl ₂ , SrSO _{4 , Sr (OH) 2, La} (NO 3) 3, LaCl 3, La 2 (SO 4) 3 and La (OH) or more selected from the group consisting of ₃₁ kinds _{of material, Fe (NO 3) 3,} FeCO ₃ , FeCl ₃ , Fe ₂ O ₃ , FeCl ₂ , Fe (OH) ₃ , Co (NO ₃ ) ₂ , CoCO ₃ , CoCl ₂ and CoSO ₄ , But is not limited thereto.

The salt may be a metal nitrate such as NaNO ₃ , KNO ₃ , LiNO ₃ , Ca (NO ₃ ) ₂ and Mg (NO ₃ ) ₂ , Na ₂ SO ₄ , K ₂ SO ₄ , Li ₂ SO ₄ , CaSO ₄ and MgSO ₄ , or a metal chloride salt such as NaCl, KCl, LiCl, CaCl _2, and MgCl ₂ . These salts preferably use a salt having a melting point lower than the temperature at which the ferrite magnetic powder is synthesized in the present invention.

The ferrite precursor and the salt may be mixed with, for example, 40 to 99.9% by weight of the ferrite precursor and 0.1 to 60% by weight of the salt.

The step of forming the droplet may be a step of injecting a mixture of the ferrite precursor and the salt into an atomizer and making the mixture into a droplet form using the ultrasonic vibrator in the atomizer into which the mixture is injected. This droplet maximizes the reaction surface area and uniformly disperses it in a large area when the particles grow into the magnetic powder in the reaction chamber of the next step, so that the particles grow uniformly and the reaction efficiently occurs.

The step of growing the ferrite particles is a step in which the mixture droplets generated in the atomizer are transferred to the reaction chamber using the carrier gas and the growth is performed in the reaction chamber preheated before the mixture droplet is introduced. O ₂ , Ar / O ₂ and the like may be used as the carrier gas, and the preheating of the reaction chamber may be preheated to a temperature higher than the melting point of the salt before the droplet is introduced.

In the reaction chamber, particles are grown while pyrolysis and oxidation reactions occur. At this time, the salt is melted to form a matrix between the ferrite particles. The matrix serves as a substrate for growing ferrite particles, May form a condition for better growth, and may also serve to prevent aggregation between particles that may occur in the droplets of the sprayed mixture.

The pyrolysis and oxidation reaction occurring in the reaction chamber occurs in a method called spray pyrolysis. The spray pyrolysis method has an advantage that particles can be synthesized at one time without a complicated post heat treatment process in a short time. However, There is a disadvantage in that strong aggregation occurs between particles within the particles. However, in the present invention, the spray pyrolysis method may be applied since the particles are contained in a salt to prevent such aggregation.

A bimodal ferrite powder according to another embodiment of the present invention is a ferrite magnetic powder of a tabular shape having the above-mentioned characteristics (first type powder) and a ferrite nano powder having a particle diameter of 0.01 to 0.5 탆 2 type powder).

The description of the highly crystalline ferrite magnetic powder is the same as described above and thus the description thereof will be omitted.

In this case, it is preferable that the magnetic powder (type 1) is larger in particle size than the nano powder (type 2). That is, the first type powder may preferably have a particle diameter of 0.7 to 2.0 탆, and the second type powder may preferably have a particle diameter of 0.1 to 0.2 탆. In addition, the nano powder may have a crystal structure of M or W type or may be spherical, and the crystal structure may have the same characteristics as the magnetic powder of the first type powder.

Each of the powders contained in the bimodal ferrite powder may contain 20 to 99% by weight of the first type powder and 1 to 80% by weight of the second type powder. It is also preferable that the mixing ratio of the first type powder to the second type powder is 3: 7 to 7: 3 by weight.

A sintered magnet according to another embodiment of the present invention is obtained by sintering a bimodal ferrite powder having the above-described characteristics.

Since the description of the bimodal ferrite powder is the same as described above, the description thereof will be omitted.

(Type 1) which is made into a plate-like form including a salt and has an improved degree of alignment in the direction of easy axis of magnetization and has excellent magnetic properties, and a nano powder (type 2) By manufacturing a sintered magnet using modal ferrite powder, nano powder can be inserted into the space between the magnetic powder and the sintered magnet manufactured using only the magnetic powder, so that the sintered density of the magnet can be further improved. In addition, since the sintered density can be improved, the volume can be greatly reduced and the performance of the magnet can be improved. As a result, the weight of the magnet can be reduced compared with a magnet having the same coercive force and residual magnetic flux density, It can be applied as a core part of various electronic products which are required to be lightweight.

Furthermore, the sintered magnet may further comprise lanthanum (La), and may be a sintered magnet including 95 to 99.9% by weight of bimodal ferrite powder and 0.1 to 5% by weight of lanthanum.

In order to improve the performance of the magnet by adding the lanthanum, it is necessary to add about 8 to 10 wt.% Of lanthanum to the weight of the whole magnet. In order to improve the performance of the sintered magnet, lanthanum is added to improve the coercivity and residual magnetic flux density. % Should be added. However, even when only 0.1 to 5% by weight, preferably 0.2 to 1% by weight, of lanthanum is added to the sintered magnet of the present invention, the performance of the magnet can be improved. And a powder having a large degree of alignment in the direction of easy magnetization axis is used for the reasons such as the above.

That is, even though only a very small amount of lanthanum is added as compared with the conventional lanthanum addition amount, the effect can be further improved. The lanthanum added for improving the performance of the magnet has a problem that the cost of the raw material is high because the amount of the lanthanum is small and the supply and demand is unstable and the price thereof is high. However, the sintered magnet of the present invention has a sufficient effect even in a very small amount Therefore, there is an advantage that it can be less affected by the above problems.

According to another aspect of the present invention, there is provided a method of manufacturing a sintered magnet, comprising: mixing a bimodal ferrite powder with an aqueous solvent to prepare a slurry; Applying a magnetic field to the slurry; And sintering the slurry to which the magnetic field is imparted.

Since the description of the bimodal ferrite powder is the same as described above, the description thereof will be omitted.

In the step of preparing the slurry, the mixing may be carried out in two stages. The mixing may be performed by using a vibrator for 1 to 24 hours so that the bimodal ferrite powder can be mixed well in a dry state by primary mixing. have. Then, a sintering auxiliary agent serving as a sintering aid to the aqueous solvent may be added by secondary mixing, and the bimodal ferrite powder may be mixed to prepare a slurry.

The aqueous solvent is not particularly limited as long as it can be mixed with the bimodal ferrite powder to form a slurry, and examples thereof include methanol, ethanol, hexane, and toluene. When the aqueous solvent is mixed with the bimodal ferrite powder, the concentration of the slurry in the slurry state is preferably 5 to 50%, more preferably 10 to 30%. The concentration range is such that the magnetic field can be effectively applied to each powder when the magnetic field is applied after the slurry is produced.

The sintering aid may be a sintering aid as long as it has a role similar to that of the catalyst when sintering occurs. For example, CaCO ₃ , SrCO ₃ , Al ₂ O ₃ , Bi ₂ O ₃ , It is preferable to use a mixture of 0.5 to 1.5% by weight of CaCO ₃ , 0.1 to 1.0% by weight of SrCO _3, 0.1 to 1.0% by weight of Al ₂ O _{3 and} 0.1 to 1.0% by weight of Bi ₂ O ₃ .

Further mixing of lanthanum at this stage may be included, but the description thereof will be omitted since it is redundant with the description of the sintered magnet described above.

The step of applying a magnetic field to the slurry is a step of applying a magnetic field having a magnetic field strength of about 0.5 to 2 T using a device capable of applying a magnetic field to the slurry. If the intensity of the magnetic field is too weak, alignment of the magnetic field in the direction of the easy axis is not completed and the magnet performance is degraded. If the magnetic field is too high, the performance is not improved in proportion to the intensity, but unnecessary energy is wasted , It is effective to give a magnetic field of the aforementioned intensity.

The sintering step is preferably performed at a temperature condition at which the salt is melted or at a temperature and a pressure at which the salt is melted. In the case where pressurization is not performed during the sintering, sintering is preferably performed at a temperature higher than the melting point of the salt (for example, 800 ° C for NaCl and 776 ° C for KCl), and when pressure is applied during the sintering, It is possible to melt the salt even at a low temperature. The pressing during the sintering is preferably performed in a range of about 20 to 200 MPa.

The sintering is not particularly limited, and various methods can be applied. Examples of the sintering include atmospheric pressure sintering, hot pressing, hot isostatic pressing, gas pressure sintering and spark plasma sintering.

The high crystallinity ferrite magnetic powder (type 1) of the present invention can be prepared in the form of a plate in which the salt forms a matrix to increase the crystallinity of the powder particles and improve the degree of alignment in the easy axis direction by containing a salt , It is possible to provide a magnetic powder capable of preventing agglomeration between powder particles. In addition, when a bimodal ferrite sintered magnet is produced as a bimodal ferrite powder in which the magnetic powder and a nano powder (second type) having a size smaller than that are mixed at a certain ratio, two particles having different sizes are mixed to form a sintered magnet It is possible to provide a sintered magnet having improved density and magnetic properties due to the magnetic powder in the form of a plate.

Further, since the sintered density is improved and the magnetic property is excellent, it is possible to reduce the volume and the weight of the magnet having the same magnetic characteristics to a great extent, so that it is required to have high energy efficiency, light weight and miniaturization such as electric automobile, hydride automobile, air conditioner and refrigerator And because the abundance of the main element of bimodal ferrite powder is abundant, it is possible to provide advantages such as stability of raw material supply, high productivity, and low cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an image obtained by scanning electron microscopy of a plate-like highly crystalline ferrite magnetic powder (type 1); FIG.
2 is an enlarged image of a transmission electron microscope of a magnetic powder showing squareness ratio of magnetic powder.
3 is an image of a nano powder (type 2) taken by a scanning electron microscope.
4 is an image of a section of a bimodal ferrite sintered magnet made of bimodal ferrite powder by a scanning electron microscope.
5 is a graph showing a magnetic hysteresis curve of the bimodal ferrite sintered magnet of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example

Preparation of Ferrite Magnetic Powder (Type 1)

Sr (NO ₃ ) ₂ and Fe (NO ₃ ) ₃ .9H ₂ O were used as precursors of strontium ferrite. The precursor of the strontium ferrite was such that Sr (NO ₃ ) ₂ and Fe (NO ₃ ) ₃ .9H ₂ O were mixed in a molar ratio of 5:60. A mixture was prepared by adding sodium chloride as a metal chloride salt to the strontium ferrite precursor, and the mixture was injected into a spraying apparatus. At this time, the mixing ratio of the strontium ferrite precursor to the sodium chloride was about 5: 1 by weight.

Ultrasonic waves were generated in the spraying apparatus to generate the droplets as droplets by vibrating the droplets, and the droplets were introduced into the reaction chamber heated at a temperature of 400 ° C at the inlet and 850 ° C at the outlet using the carrier gas. The strontium ferrite precursor and sodium chloride introduced into the reaction chamber undergo thermal decomposition and oxidation reaction to prepare a salt-containing strontium ferrite magnetic powder (type 1).

The prepared magnetic powder was observed with a scanning electron microscope (SEM) and is shown in FIG. As a result, it can be seen that the magnetic powder is uniform in size, the shape is plate-like, and the length of the major axis is about 1 탆 with reference to the scale bar. The magnetic powder was photographed by a transmission electron microscope (TEM) and is shown in FIG. The squareness ratios of the measured magnetic powders are shown in Table 1 below (see Fig. 2 for the a and c axes).

Square Ratio Sample 1 Sample 2 Sample 3 a / c 3.38 3.50 3.82

Bimodal  Preparation of ferrite powder

The ferrite nano powder (type 2) was prepared in the same manner as in the preparation of the ferrite magnetic powder (type 1) except that the salt was not mixed and the pyrolysis and oxidation reaction times were performed for a short time.

The nanopowder thus prepared was observed with a scanning electron microscope (SEM) and is shown in FIG. As a result, it was found that the nanopowder was uniform in size, spherical in shape, and had a diameter of about 0.2 탆 with reference to the scale bar.

The magnetic powder (Type 1) and the nano powder (Type 2) prepared above were mixed at a ratio (weight ratio) of 7: 3, 5: 5 and 3: 7 as shown in Table 2 below, Bismuth ferrite powders were prepared.

Bimodal  Manufacture of ferrite sintered magnets

Mixed powders obtained by mixing the bimodal ferrite powders prepared above were added to an aqueous solvent to prepare mixed powder slurries. Thereafter, a magnetic field of about 1.2 T was applied to each of the above slurries to give a magnetic field, and the slurry was dried. Each of the dried mixed powders was sintered at a temperature of 1200 ° C and an atmospheric pressure.

The produced bimodal ferrite sintered magnet was observed with a scanning electron microscope and is shown in FIG. As a result, it was confirmed that the nano powder (the second type) having a smaller size was inserted into the empty space where the magnetic powder (the first type) was collected and the sintered magnet having a very dense structure was inserted. It was confirmed that defects (cracks, dents, etc.) were hardly seen on the cross section.

The performance of the bimodal ferrite sintered magnet thus produced was evaluated. The sintered density was measured by the Archimedes method. The coercive force and residual magnetic flux density were measured using VSM (vibrating sample magnetometer, Lake Shore # 7300 USA, maximum 20 kOe).

Measurement of sintered density, coercive force and residual magnetic flux density of each bimodal ferrite sintered magnet prepared by mixing magnetic powder and nano powder at the weight ratio of 7: 3, 5: 5 and 3: 7 using the above evaluation criteria and apparatus Values are shown in Table 2 below, and the magnetic hysteresis curves for the sintered magnets prepared by mixing the magnetic powder at a weight ratio of 7: 3 are shown in FIG.

Mixing ratio (first: second) Residual magnetic flux density (G) Coercivity (G) Sintered density (g / cm ³ ) 7: 3 4462 3552 4.93 5: 5 4334 3358 4.89 3: 7 4021 3381 4.83

Referring to Table 2, it was confirmed that the sintered density of the bimodal ferrite sintered magnet was significantly improved to 97% of the theoretical density by filling the void space of the magnetic powder with the nano powder, and the coercive force And the residual magnetic flux density were also excellent.

Further, in the production of the sintered magnet, lanthanum was added to the slurry in an amount of 0.3 wt% based on the total weight of the magnet, thereby producing a sintered magnet using bimodal ferrite powder. The sintered magnet to which the lanthanum was added was subjected to performance evaluation in the same manner as described above. As a result, it was confirmed that the sintered density was the same, and that the coercive force was improved by 100 to 300 G compared to the case where the coercive force was not added.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, Of the right.

Claims (20)

R-Fe-O (R is at least one element selected from the group consisting of Sr, Co and Ba)
A high crystallinity ferrite magnetic powder of a plate type having a grain size of 0.1 to 10 탆. The magnetic powder of claim 1, wherein the magnetic powder has an aspect ratio of 3: 1 to 5: 1. The magnetic powder according to claim 2, wherein the magnetic powder has an aspect ratio of 3.3: 1 to 4: 1. The magnetic powder according to claim 1, wherein the magnetic powder is grown in the presence of a salt. The magnetic powder according to claim 1, wherein the magnetic powder contains a salt. Mixing the ferrite precursor and the salt;
Spraying the mixture to form droplets; And
Passing the droplets together with a carrier gas into a reaction chamber to grow ferrite particles
The method of producing the magnetic powder of claim 1, The method of claim 6, wherein the ferrite precursor is _{Ba (NO 3) 2, BaCO} 3, BaCl 2, BaSO 4, BaO 2, Sr (NO 3) 2, SrCO 3, SrCl 2, SrSO 4, Sr (OH) 2 _{, La (NO 3) 3,} LaCl 3, La 2 (SO 4) at least one member selected from the group consisting of _3, and La (OH) ₃ material; And
_{Fe (NO 3) 3, FeCO} 3, FeCl 3, Fe 2 O 3, FeCl 2, Fe (OH) 3, Co (NO 3) 1 type of compound selected from _2, CoCO _3, CoCl ₂ and CoSO the group consisting of ₄ RTI ID = 0.0 > 1, < / RTI > 7. The method of claim 6, wherein the reaction chamber is heated to a temperature above the melting point of the salt before the droplet is introduced. The method of claim 6, wherein the salt is at least one nitrate metal salt selected from the group consisting of NaNO ₃ , KNO ₃ , LiNO ₃ , Ca (NO ₃ ) ₂ and Mg (NO ₃ ) ₂ ,
One or more metal sulfate salts selected from the group consisting of Na ₂ SO ₄ , K ₂ SO ₄ , Li ₂ SO ₄ , CaSO ₄ and MgSO ₄ , or
NaCl, KCl, LiCl, CaCl ₂ and MgCl characterized in that the at least one metal chloride selected from the group consisting of: _2. (1) a magnetic powder (first type powder) according to any one of claims 1 to 5 and
(2) A ferrite nano powder (second type powder) having a grain size of 0.01 to 0.5 탆,
And a bimodal ferrite powder. The bimodal ferrite powder according to claim 10, wherein the first type powder and the second type powder have a particle size of 0.7 to 2.0 탆 and 0.1 to 0.2 탆, respectively. 11. The bimodal ferrite powder according to claim 10, wherein the second type powder has a M or W crystal structure or a spherical shape. The bimodal ferrite powder according to claim 10, wherein the content of the first type powder is 20 to 99% by weight and the content of the second type powder is 1 to 80% by weight. The bimodal ferrite powder according to claim 10, wherein the mixing ratio of the first type powder to the second type powder is 3: 7 to 7: 3 by weight. A sintered magnet obtained by sintering bimodal ferrite powder according to claim 10. The sintered magnet according to claim 15, wherein the sintered magnet further comprises lanthanum (La). The sintered magnet according to claim 16, wherein the sintered magnet comprises 95 to 99.9% by weight of bimodal ferrite powder and 0.1 to 5% by weight of lanthanum. Mixing the bimodal ferrite powder according to claim 10 into an aqueous solvent to prepare a slurry;
Applying a magnetic field to the slurry; And
Sintering the slurry to which the magnetic field is applied
Wherein the bismuth ferrite sintered magnet is a ferrite sintered magnet. 19. The method according to claim 18, wherein lanthanum is further mixed in the step of producing the slurry. 19. The method of claim 18, wherein the sintering is performed by any one method selected from the group consisting of pressure sintering, hot pressing, hot isostatic pressing, gas pressure sintering and spark plasma sintering.

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