KR20150046921A - Magnet powders, production methods thereof, and magnets including the same - Google Patents

Abstract

Provided is a magnetic powder producing method comprising: a step of obtaining a raw material composite; a step of calcining the raw material composite at a temperature of 600-1350°C to obtain a calcined material containing hexaferrite and particles with protruded defects on the surface indicated by the following [Formula 1]: A1-xR_xFe_12-yM_yO_19 wherein A is Sr, Ba, Ca, or a combination thereof; R is at least one or more types selected from a rare-earth element; and Bi. The M is at least one or more types selected from Co, Mn, Zn, Zr, Ni, Ti, Cu, Al, Ge, and As; and the formula satisfies 0 <= x < 0.5, 0 <= y < 0.5. The present invention includes a step of dipping the calcined material into an acid aqueous solution to obtain the magnetic powder containing the particles wherein the protruded defects are removed.

Description

TECHNICAL FIELD [0001] The present invention relates to a magnetic powder, a method of manufacturing the same, and a magnet including the same. BACKGROUND ART [0002]

Magnetic powder, a production method thereof, and a magnet including the same.

Ferrite sintered magnets produced from hexaferrite magnetic powders are used in various applications such as generators, various motors, and speakers. The hexaferrite magnetic powder may be produced by substituting Sr or Ba with a different metal such as Sr hexaferrite, Ba hexaferrite, or Sr or Ba hexaferrite, and / or partially replacing Fe with a metal such as Zn, Mg, &Lt; RTI ID = 0.0 &gt; hexaferrite. &Lt; / RTI &gt;

In recent years, researches on high performance of ferrite sintered magnets have been actively carried out in order to miniaturize and lighten the parts for automobile electronic parts and electronic devices. Most of these studies are concerned with changes in the content / type of the substituted elements, Focusing on the control of equi-magnetic powder components. Since hexaferrite magnets used in parts for home appliances, automobile parts, and the like have a significant effect on the energy efficiency of the parts, it is desirable to develop a technique capable of improving the performance of the ferrite sintered magnet.

In one embodiment, the present invention is directed to a method of making a hexaferrite-based magnetic powder having improved magnetic properties.

In another embodiment, the present invention is directed to a hexaferrite magnetic powder produced by the above process.

In another embodiment, the present invention is directed to a magnet comprising the magnetic powder.

One embodiment provides a method of making a magnetic powder comprising the steps of:

Obtaining a raw material mixture; And

Calcining the raw material mixture at a temperature of 600 ° C. to 1350 ° C. to obtain a calcined product containing hexaferrite represented by the following general formula 1 and having protruded defects on its surface; And

[Formula 1]

A _{1- x} R _x Fe _{12 - y} M _y O ₁₉

M is at least one element selected from the group consisting of Co, Mn, Zn, Zr, Ni, Ti, Cu, Al, Ge, and As, wherein A is at least one element selected from the group consisting of Sr, Ba, Ca, 0 < x < 0.5, 0 &lt; y &lt;0.5; And

And immersing the calcined product in an aqueous acid solution to obtain a magnetic powder containing the particles from which the protruding defects have been removed.

The raw material mixture contains a metal compound powder containing Sr, Ba, or Ca and an Fe oxide or hydroxide powder, and optionally an oxide or hydroxide powder of an rare earth metal or Bi and / or a powder of Co, Mn, Zn, Zr, Ni, Ti, Cu, Al, Ge, or As.

The raw material mixture contains metal hydroxides and Fe hydroxides including Sr, Ba, or Ca, and optionally a hydroxide of a rare earth metal or Bi and / or a hydroxide of Co, Mn, Zn, Zr, Ni, Ti, , Ge, or As. &Lt; / RTI &gt; The calcined product can be obtained by calcining the raw material mixture containing the above-mentioned hydroxides at a temperature of 600 to 1350 degrees Celsius.

The particles have a plate-like laminated form, and the average crystal grain size identified by XRD may be 250 nm or more.

The protruding defect may have a longest length of 100 nm or less.

The acid aqueous solution may comprise an organic acid, an inorganic acid, or a combination thereof.

The inorganic acid may be selected from HCl, HF, HBr, HI, HClO ₄ , H ₂ SO ₄ , HNO ₃ , H ₃ PO ₄ and combinations thereof.

The acid aqueous solution may have a pH of 2 or less.

The acid aqueous solution may have a concentration of 3 M (mole / L) or more.

The magnetic powder including the particles from which the protruding defects are removed may contain an average of not more than 5 protruding defects per 1 μm ² of the area of the SEM image when measured by a scanning electron microscope.

After removal of the protruding defect, the magnetic powder may exhibit a coercive force higher by 10% or more based on the coercive force before removal of the protruding defect.

Another embodiment comprises particles comprising hexaferrite represented by the following general formula 1, wherein the total number of protruding defects existing on the surface of the particles when measured by a scanning electron microscope is in the range of 1 탆 ² A magnetic powder having an average of not more than 5 per molecule is provided:

[Formula 1]

A _{1- x} R _x Fe _{12 - y} M _y O ₁₉

M is at least one element selected from the group consisting of Co, Mn, Zn, Zr, Ni, Ti, Cu, Al, Ge, and combinations thereof; and A is at least one element selected from the group consisting of Sr, Ba, Ca, As, and 0? X <0.5 and 0? Y <0.5.

The particles have a plate-like laminated form, and the average crystal grain size identified by XRD may be 250 nm or more.

The protruding defect may have a longest length of 100 nm or less.

When measured by a scanning electron microscope, the total number of protruding defects present on the surface of the particles can be an average of 3 or less per 1 탆 ² area of the SEM image.

In other embodiments, to include, but the particle containing the hexa ferrite represented by formula 1, the average total number of defects per ^second projecting area 1㎛ the SEM image from the surface of the particles as measured by a scanning electron microscope There are provided no more than five magnets made from magnetic powder:

[Formula 1]

A _{1- x} R _x Fe _{12 - y} M _y O ₁₉

M is at least one element selected from the group consisting of Co, Mn, Zn, Zr, Ni, Ti, Cu, Al, Ge, and combinations thereof; and A is at least one element selected from the group consisting of Sr, Ba, Ca, As, and 0? X <0.5 and 0? Y <0.5.

It is possible to provide a hexaferrite magnetic powder exhibiting an enhanced coercive force without a substantial reduction in the saturation magnetization value.

1 is an SEM image of the calcined powder (A) before the acid treatment and the magnetic powder (B) after the acid treatment, prepared in Example 1. Fig.
Fig. 2 shows the magnetic characteristic curves of the calcined powder (A) before the acid treatment and the magnetic powder (B) after the acid treatment, which were prepared in Example 1. Fig.
Fig. 3 shows the magnetic characteristic curves of the calcined powder before the acid treatment and the magnetic powder after the acid treatment, prepared in Example 2. Fig.
Fig. 4 shows SEM images of the calcined powder before the acid treatment and the magnetic powder after the acid treatment, which were prepared in Example 4. Fig.
Fig. 5 shows an SEM image of the magnet (A) produced from the calcination powder before the acid treatment and the magnet (B) produced from the calcination powder after the acid treatment, prepared in Example 4.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Thus, in some implementations, well-known techniques are not specifically described to avoid an undesirable interpretation of the present invention. Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. Also, commonly used predefined terms are not ideally or excessively interpreted unless explicitly defined otherwise. Whenever a component is referred to as "including" an element throughout the specification, it is to be understood that the element may include other elements, not the exclusion of any other element, unless the context clearly dictates otherwise.

Also, singular forms include plural forms unless the context clearly dictates otherwise.

In one embodiment, a method of making a magnetic powder comprises the steps of:

Obtaining a raw material mixture; And

Calcining the raw material mixture at a temperature of 600 ° C. to 1350 ° C. to obtain a calcined product containing hexaferrite represented by the following general formula 1 and having protruding defects on its surface:

[Formula 1]

A _{1- x} R _x Fe _{12 - y} M _y O ₁₉

M is at least one element selected from the group consisting of Co, Mn, Zn, Zr, and Zr; A is at least one element selected from the group consisting of Sr, Ba, Ca, 0 < x < 0.4 and 0 < y < 0.5, for example, 0 &lt; y &lt;0.4; and at least one selected from the group consisting of Ni, Ti, Cu, Al, Ge and As. And

And immersing the calcined product in an aqueous acid solution to obtain a magnetic powder containing the particles with the protruding defects removed.

The raw material mixture may comprise any metal compound / oxide used for the production of hexaferrite. For example, the raw material mixture may contain a metal compound powder containing Sr, Ba or Ca, and Fe oxide or hydroxide. Optionally, the raw material mixture comprises an oxide or hydroxide powder of a rare earth metal (e.g., La, Ce, Nd, etc.) or Bi; And / or an oxide or hydroxide powder of MCO ₃ or metal M wherein M is Co, Mn, Zn, Zr, Ni, Ti, Cu, Al, Ge, or As. The metal compound powder containing Sr, Ba or Ca may be SrCO ₃ , BaCO ₃ , CaCO _{3 ,} SrO, SrO ₂ , BaO, BaO ₂ , CaO, CaO ₂ , Ca metal hydroxide powder, but is not limited thereto. Fe oxide, Fe ₂ O _3, FeO, Fe ₃ O _4, or may be a combination thereof, but is not limited thereto. The Fe hydroxide may be Fe (OH) ₂ .

The rare earth metal or the oxide or hydroxide powder of Bi is at least one selected from the group consisting of La ₂ O ₃ , La (OH) ₃ , Bi ₂ O ₃ , bismuth hydroxide (Bi (OH) ₃ and the like), Nd ₂ O ₃ and cerium hydroxide (OH) _{4, etc.), Ce 2 O 3, CeO} 2, or may be a combination thereof, but is not limited thereto. Compound of a metal M (wherein, M is Co, Mn, Zn, Zr, Ni, Ti, Cu, Al, Ge or As) is, MCO ₃ (In other words, A carbonate containing metal M), a hydroxide of M, or an oxide powder of metal M. For example, the compound of the metal M may be an oxide such as CoO, Co ₃ O ₄ , Co ₂ O ₃ , or ZnO, a hydroxide of a metal M such as CoOOH or Co (OH) ₂ , or a carbonate such as CoCO ₃ It is not limited.

In the raw material mixture, the proportions of the respective compounds can be adjusted to obtain the desired composition of hexaferrite. The particle size of the powder for the raw material mixture is not particularly limited and can be appropriately selected. In a non-limiting example, the particle size of the powder for the raw material mixture may be in the range of 10 탆 or less, such as 1 탆 to 5 탆, but is not limited thereto.

In another embodiment, the raw material mixture may be a mixture of metal hydroxides prepared by the so-called coprecipitation method. For example, in consideration of the intermetallic molar ratio in hexaferrite, a precursor metal salt of the raw material mixture is dissolved in water to prepare an aqueous solution, and a strong base (for example, sodium hydroxide, potassium hydroxide, or a combination thereof) To obtain a mixture of metal hydroxides having a desired composition as a raw material mixture. The kind of the precursor metal salt is not particularly limited as long as it is a water-soluble salt which can be dissolved in water. For example, the salt may be, but is not limited to, a nitrate (e.g., strontium nitrate, barium nitrate, iron nitrate, etc.), a sulfate, carbonate, bicarbonate, oxalate, sulfide,

The raw material mixture is calcined to obtain a calcined product comprising particles (hereinafter referred to as hexaferrite particles) containing hexaferrite represented by the following general formula 1 as a major phase:

[Formula 1]

A _{1- x} R _x Fe _{12 - y} M _y O ₁₉

Where A, R, M, x and y are as defined above.

The calcination treatment may be performed in an oxygen-containing atmosphere or a non-oxidizing atmosphere. The non-oxidizing atmosphere may be an atmosphere having an oxygen partial pressure of 10 ^-3 atm or less. The non-oxidizing atmosphere may be a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, a combination thereof, or a vacuum atmosphere. The calcination temperature may range from 600 degrees Celsius to 1400 degrees Celsius, such as 900 degrees Celsius to 1400 degrees Celsius, 1000 degrees Celsius to 1350 degrees Celsius, or 1050 degrees Celsius to 1300 degrees Celsius. If the raw material mixture is a mixture of hydroxides obtained by coprecipitation, the calcination temperature may be in the range of 600 to 1300 degrees Celsius, for example, 700 to 900 degrees Celsius (e.g., 800 degrees Celsius).

The hexaferrite particles obtained by calcination may have protruding defects on the surface. The hexaferrite particles have a plate-like laminated form, and the size of the average crystal grain identified by XRD may be 250 nm or more, for example, 300 nm or more. The protruding defect may be a nucleus or the like for forming a new layer during the firing process, and the longest length may be 100 nm or less, for example, 90 nm or less or 80 nm or less.

The obtained hexaferrite powder is immersed in an aqueous acid solution to obtain a magnetic powder containing the particles from which the protruding defects have been removed. The acid aqueous solution may comprise an organic acid, an inorganic acid, or a combination thereof. The organic acid may be acetic acid, formic acid, or a combination thereof. The inorganic acid may be an acid selected from HCl, HF, HBr, HI, HClO ₄ , H ₂ SO ₄ , HNO ₃ , H ₃ PO ₄ and combinations thereof. The acid aqueous solution may have a pH of 2 or less. The acid aqueous solution may have a concentration of 3M (mol / L) or more. The immersion time is not particularly limited and can be appropriately selected. For example, the immersion time may be 1 second or more, for example, 1 minute or more. After immersion, the magnetic powder is filtered and dried.

By such an acid treatment, a magnetic powder containing hexaferrite particles from which protruding defects have been removed can be obtained. The hexaferrite particles from which the protruding defects have been removed can have a smooth surface. After the acid treatment, the magnetic powder contains an average of not more than 5, for example, not more than 4, not more than 3, not more than 2, or one protruding defect per 1 μm ² area of the SEM image, as measured by a scanning electron microscope can do. In the present specification, the average number of protruding defects means an average value of the number of protruding defects having a maximum length of 100 nm or less in an area of 1 탆 ² when 10 or more 100,000-fold magnification SEM images are analyzed for a given sample.

In a non-limiting example, when observed with a scanning electron microscope after acid treatment, the hexaferrite magnetic powder may have no protruding defects per 1 탆 ² area of the SEM image.

The magnetic powder containing the hexaferrite particles having no protruding defect can exhibit remarkably improved coercive force as compared with the powder before the defect removal. The magnetic powder comprising hexaferrite particles without protruding defects may have a similar level of saturation magnetization value (e.g., substantially the same) when compared to the calcination powder before the acid treatment. Namely, by removing the protruding defects present on the surface of the hexaferrite particles by the acid treatment, it is possible to remarkably improve the coercive force without changing the saturation magnetization value. The magnetic powder containing acid-treated hexaferrite particles may exhibit a coercive force of 10% or more, for example, 20% or more, 25% or more, or 30% or more higher than the calcination powder before the acid treatment.

Most of the prior art attempts to improve the coercive force of hexaferrite by optimizing powder components (for example, raw material mixture, grain growth inhibitor, lubricant, etc.). In this case, it is difficult to avoid a decrease in saturation magnetization value. However, the method according to one embodiment can remarkably improve the coercive force without changing the saturation magnetization value, and can provide the magnetic powder with higher performance.

In another embodiment, the magnetic powder comprises hexaferrite-containing particles represented by the following general formula 1, and when measured by a scanning electron microscope, the total number of protruding defects existing on the surface of the particles is not less than 1 占 퐉 ^The average is less than 5 per ² :

[Formula 1]

A _{1 - x} R _x Fe _{12 - y} M _y O _{19 - d}

Where A, R, M, x and y are as defined above.

The content of the magnetic powder is as described above. For example, the particles have a plate-like laminated form, and the average crystal grain size identified by XRD is 250 nm or more. The protruding defect has a longest length of 100 nm or less. The powder, SEM pictures for 1㎛ ² Average of 5 or less, per unit area for example, may include a convex defect of not more than 1 not more than 4, 3 or less, 2 or less, more.

Another embodiment is to include, but the particle containing the hexa ferrite represented by the general formula [1], the total number of defects protruding from the surface of the as determined by scanning electron microscopic particle having an average of 5 per ² SEM image area 1㎛ Lt; RTI ID = 0.0 &gt;%&lt; / RTI &gt; magnetic powder:

[Formula 1]

A _{1- x} R _x Fe _{12 - y} M _y O ₁₉

Where A, R, M, x and y are as defined above.

The magnet may be produced from the magnetic powder by any known method. For example, the magnetic powder can be manufactured by magnetic pressing and annealing. The improved coercive force of the magnetic powder can be maintained even when it is made of a magnet. The conditions and methods of magnetic field shaping are known. For example, the magnetic field shaping can be performed by applying a magnetic field of 10000 Oe or more to the magnetic powder at a pressure of 80 MPa or more, or in a direction perpendicular to or in the compression direction, but is not limited thereto. In a non-limiting example, compression may be performed by cold isostatic pressure, uniaxial pressure, or the like. Annealing conditions after magnetic field shaping are also known. For example, the annealing may be performed for at least 60 minutes in an oxygen-containing atmosphere at a temperature of 1100 degrees Celsius or more, but is not limited thereto.

The magnet produced from the magnetic powder having the existing protruding defect has an angular shape of the corner portion on the hexagonal plate. However, the magnet made of the magnetic powder from which the protruding defect has been removed has a problem that the edge portion It is blunt.

Hereinafter, specific embodiments of the present invention will be described. It is to be understood, however, that the embodiments described below are only for illustrative purposes or to illustrate the present invention, and the present invention should not be limited thereby.

[ Example ]

How to measure magnetic properties

Samples are mounted on a vibrating sample magnetometer (VSM) and the magnetic hysteresis curves are obtained as follows:

The magnetic field was applied to the specimen at a speed of 200 Oe / s up to 50000 Oe, the magnetic field was reduced at a speed of 100 Oe / s to -50000 Oe, and then the magnetic field was increased to 500 Oe at a rate of 100 Oe / Measure the magnetization value.

The saturation magnetization value was measured as the magnetization value of the sample when the applied magnetic field reached 50000 Oe and the coercive force was obtained by measuring the magnetic field strength when the magnetization intensity (magnetization value) reached zero.

Example 1 :

(1) SrCO ₃ powder (average particle diameter: 10 탆 or less, manufactured by Kojundo Chemical Research Institute) and Fe ₂ O ₃ powder (average particle diameter: 10 탆 or less, manufacturer: Weighed and mixed, and the mixture of the weighed powders was mixed with ethanol And ball milled for 20 hours to obtain a slurry.

The slurry is placed in a container and dried in an oven to obtain a dried raw material mixture. The dried mixture is calcined in air at a temperature of 1140 DEG C for 4 hours to obtain a calcined powder containing particles of a plate-like laminate (single-phase SrFe ₁₂ O ₁₉ ) having an average crystal grain size of about 300 nm as measured by XRD .

(2) The calcined powder obtained in (1) was analyzed by a scanning electron microscope (manufacturer: FEI, model name: Nova 450), and the results are shown in Fig. As shown in Fig. 1 (A), there are a plurality of protruding defects (defect maximum length: 80 nm) on the surface of the particles after calcination. The calcined powder was subjected to magnetic field molding under a pressure of 100 MPa and a magnetic field of 13000 Oe, and the formed body was annealed at 1240 deg. C in an air atmosphere for 2 hours to prepare a magnet 1.

(3) The calcined powder obtained in (1) is immersed in a 37% HCl solution (purchased from Junsei) for 10 minutes, separated and dried. (Acid treated and dried) calcined powders were analyzed by a scanning electron microscope, and the results are shown in Fig. 1 (B). (Acid treated and dried) calcined powder has a smooth surface without a plurality of protruding defects present on the surface of the particles before the acid treatment. The acid-treated calcined powder was subjected to magnetic field molding under a pressure of 100 MPa and a magnetic field of 13000 Oe, and the molded body was annealed at 1240 deg. C in an air atmosphere for 2 hours to prepare magnet 2.

(4) The hysteresis curves of the calcined powder before the acid treatment and the calcined powder after the acid treatment were determined in accordance with the above-mentioned method, and the results are shown in Fig. The calcination powder before the acid treatment has a coercive force of 3685 Oe, while the calcined powder after the acid treatment has a coercive force of 4915 Oe and has a coercive force of about 33% higher. It is confirmed that the calcined powders after the acid treatment have a saturation magnetization (Ms) value substantially the same level. Therefore, it is confirmed that the coercive force can be greatly improved without decreasing the saturation magnetization value by removing the micro protruding type defect on the surface by the acid treatment.

(5) For the magnet 1 and the magnet 2, the saturation magnetization value and the coercive force are measured according to the above-described method. As a result, it is confirmed that the magnet 1 and the magnet 2 have substantially the same level of saturation magnetization, while the coercive force of the magnet 1 is 3360 Oe and the coercive force of the magnet 2 is 4630 Oe. It is confirmed that the magnet 2 using the powder after the acid treatment has a coercive force about 38% higher than that of the magnet 1. From the above results, it is confirmed that the effect of increasing the coercive force shown in the magnetic powder is maintained even after magnetic field forming and sintering (i.e., after the final product is manufactured).

Example 2 :

SrCO ₃ powder (average particle size: less than 10㎛, Manufacturer: purity Chemical Research), Fe ₂ O ₃ powder (average particle size: less than 10㎛, Manufacturer: purity Chemical Laboratory), La ₂ O _3, powder (average particle size: 10㎛ And a Co ₃ O ₄ powder (average particle diameter: 10 μm or less, manufacturer: High Purity Chemical Research Institute) having an Fe / Sr ratio of 11 and an x value of 0.25 in the following formula And a powder containing particles in a plate-like laminate form having an average crystal grain size of about 300 nm measured by XRD is obtained in the same manner as in Example 1 except that the calcination temperature is set to 1240 degrees Celsius :

Sr _{1 - x} La _x Fe _{12 - x} Co _x O ₁₉ (x = 0.25)

The hysteresis curves of the calcined powder before the acid treatment and the calcined powder after the acid treatment were determined in accordance with the above-mentioned method, and the results are shown in Fig. The calcination powder before the acid treatment has a coercive force of 3970 Oe, while the calcined powder after the acid treatment has a coercive force of 4750 Oe and has a coercive force of about 20% higher. It is confirmed that the calcined powders after the acid treatment have a saturation magnetization (Ms) value substantially the same level. Therefore, it is confirmed that the coercive force can be greatly improved without decreasing the saturation magnetization value by removing the micro protruding type defect on the surface by the acid treatment.

Example 3 :

(1) SrCO ₃ powder (average particle size: less than 10㎛, Manufacturer: purity Chemical Research), Fe ₂ O ₃ powder (average particle size: less than 10㎛, Manufacturer: purity Chemical Laboratory), La ₂ O _3, powder (average particle diameter: And a Co ₃ O ₄ powder (average particle diameter: 10 탆 or less, manufacturer: High Purity Chemical Research Institute) having an Fe / Sr ratio of 11 and a formula Sr _{1 - x} La _x Weighed and mixed in an amount such that the x value was 0.35 in Fe _{12 - x} Co _x O ₁₉ (x = 0.35), and the mixture of the weighed powders was mixed with ethanol And ball milled for 20 hours to obtain a slurry. The slurry is placed in a container and dried in an oven to obtain a dried raw material mixture. The dried raw material mixture is calcined in the air at a temperature of 1250 degrees centigrade for 4 hours to obtain a calcined powder containing particles in the form of a platelike layer having an average crystal grain size of approximately 300 nm as measured by XRD.

(2) The calcined powder obtained in (1) was analyzed by a scanning electron microscope. The results are shown in Fig. 4 (A). As can be seen in Fig. 4 (A), there are a plurality of protruding defects on the surface of the particles after calcination. The calcined powder was subjected to magnetic field molding under a pressure of 100 MPa and a magnetic field of 13000 Oe, and the compact was annealed in 1240 degree air for 2 hours to prepare a magnet 1. The magnet 1 was analyzed by a scanning electron microscope, and the result is shown in Fig. 5 (A). From FIG. 5 (A), it is confirmed that the magnet 1 includes hexagonal plate-shaped angular particles.

(3) In (1), the calcined powder is immersed in a 37% HCl solution (purchased from Junsei) for 10 minutes and then separated and dried. (Acid treated and dried) calcined powders were analyzed by a scanning electron microscope (manufacturer: FEI, model name: Nova 450). The results are shown in Fig. 4 (B). (Acid treated and dried) calcined powder has a smooth surface, without a plurality of protruding defects present on the surface of the particles before the acid treatment.

The acid-treated calcined powder was subjected to magnetic field molding under a pressure of 100 MPa and a magnetic field of 13000 Oe, and the molded body was annealed in 1240 degree air for 2 hours to prepare a magnet 2. Magnet 2 was analyzed by a scanning electron microscope, and the result is shown in Fig. 5 (B). From FIG. 5 (B), it is confirmed that the magnet 2 contains particles that are more steeper than those of the hexagonal plate-like angular particles of FIG. 5 (A). Fig. 5 (A) shows sharp corners on the hexagonal plate, while Fig. 5 (B) shows a mixture of sharp corners and rounded corners.

For the magnet 1 and the magnet 2, the saturation magnetization value and the coercive force are measured according to the above-described method. As a result, it is confirmed that the magnet 1 and the magnet 2 have substantially the same level of saturation magnetization, while the coercive force of the magnet 1 is 4335 Oe and the coercive force of the magnet 2 is 6070 Oe. It is confirmed that the magnet 2 using the powder after the acid treatment has a coercive force about 40% higher than that of the magnet 1. From the above results, it is confirmed that the effect of increasing the coercive force shown in the magnetic powder is maintained even after magnetic field forming and sintering (i.e., after the final product is manufactured).

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, And falls within the scope of the invention.

Claims (18)

Obtaining a raw material mixture;
Calcining the raw material mixture at a temperature of 600 ° C. to 1350 ° C. to obtain a calcined product containing hexaferrite represented by the following general formula 1 and having protruded defects on its surface;
[Formula 1]
A _{1- x} R _x Fe _{12 - y} M _y O ₁₉
M is at least one element selected from the group consisting of Co, Mn, Zn, Zr, Ni, Ti, Cu, Al, Ge, and combinations thereof; and A is at least one element selected from the group consisting of Sr, Ba, Ca, As, 0? X <0.5, 0? Y <0.5; And
Immersing the calcined product in an acid aqueous solution to obtain a magnetic powder containing the particles with the protruding defects removed
&Lt; / RTI &gt; The method according to claim 1,
The raw material mixture may be a metal compound powder or metal hydroxide powder containing Sr, Ba, or Ca; And a Fe oxide or hydroxide powder. 3. The method of claim 2,
The raw material mixture may be an oxide or hydroxide powder of a rare earth metal or Bi; A metal compound powder containing a metal M (where M is Co, Mn, Zn, Zr, Ni, Ti, Cu, Al, Ge or As); Or a mixture thereof. The method according to claim 1,
The raw material mixture may include metal hydroxide including Sr, Ba or Ca; Fe hydroxide; Optionally a rare earth metal or a hydroxide of Bi; And optionally a hydroxide of a metal M wherein M is at least one selected from the group consisting of Co, Mn, Zn, Zr, Ni, Ti, Cu, Al, Ge or As, &Lt; / RTI &gt; The method according to claim 1,
Wherein the particles have a plate-like laminated form, and the average crystal grain size identified by XRD is 250 nm or more. The method according to claim 1,
Wherein the particles having protruding defects on the surface include protruding defects having a maximum length of 100 nm or less on the surface. The method according to claim 1,
Wherein the acid aqueous solution comprises an organic acid, an inorganic acid, or a combination thereof. 8. The method of claim 7,
Wherein the organic acid is acetic acid, formic acid or a combination thereof and the inorganic acid is at least one selected from the group consisting of HCl, HF, HBr, HI, HClO ₄ , H ₂ SO ₄ , HNO ₃ , H ₃ PO ₄ , Way. The method according to claim 1,
Wherein the acid aqueous solution has a pH of 2 or less. The method according to claim 1,
Wherein the magnetic powder including the particles from which the protruding defects are removed contains an average of not more than 5 protruding defects per 1 mu m ² of the area of the SEM image as measured by a scanning electron microscope. The method according to claim 1,
After removal of the protruding defect, the magnetic powder exhibits a coercive force higher by 10% or more based on the coercive force before removal of the protruding defect. To the measurement by the following formula 1 Hex comprise particles comprising a ferrite, and scanning electron microscopy indicated by, the total number of defects protruding from the surface of the particle size 1㎛ average 5 or less per ^second in the SEM image of the magnetic powder:
[Formula 1]
A _{1- x} R _x Fe _{12 - y} M _y O ₁₉
M is at least one element selected from the group consisting of Co, Mn, Zn, Zr, Ni, Ti, Cu, Al, Ge, and combinations thereof; and A is at least one element selected from the group consisting of Sr, Ba, Ca, As, and 0? X <0.5 and 0? Y <0.5. 13. The method of claim 12,
Wherein the particles have a plate-like laminated form, and the average crystal grain size identified by XRD is 250 nm or more. 13. The method of claim 12,
Wherein the protruding defect has a longest length of 100 nm or less. To include, but the particle containing the hexa ferrite represented by the general formula [1], as measured with a scanning electron microscope, the total number of defects protruding from the surface of the particles SEM image area 1㎛ average 5 or less per magnetic powder ² Magnets manufactured from:
[Formula 1]
A _{1- x} R _x Fe _{12 - y} M _y O ₁₉
M is at least one element selected from the group consisting of Co, Mn, Zn, Zr, Ni, Ti, Cu, Al, Ge, and combinations thereof; and A is at least one element selected from the group consisting of Sr, Ba, Ca, As, and 0? X <0.5 and 0? Y <0.5. 16. The method of claim 15,
Wherein said particles have a plate-like laminate morphology and have an average crystal grain size of 250 nm or more as confirmed by XRD. 16. The method of claim 15,
Wherein the protruding defect has a longest length of 100 nm or less. 16. The method of claim 15,
Wherein the magnet comprises a hexagonal plate-like particle having rounded edges.

Images