JP2018014157A - Atomizing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of an amorphous body for hexagonal ferrite powder, by which an amorphous body as a precursor of the hexagonal ferrite powder can be obtained by increasing cooling rate of a melt having a relatively large diameter in order to produce the hexagonal ferrite powder suitable for high-density magnetic recording with a high yield, and to provide a production method of the hexagonal ferrite powder.SOLUTION: A production method of an amorphous body for hexagonal ferrite powder, includes an atomizing step of supplying a melt comprising at least raw material of a hexagonal ferrite component and raw material of a glass component from molten metal supply unit, and injecting atomizing gas from an atomizing gas injection unit onto the supplied melt so as to finely pulverize the melt. In the atomizing step, at least a part of the fine powder obtained by finely pulverizing the melt is made to collide with a cooling member disposed to surround the fine powder, below the atomizing gas injection unit, thereby inducing plastic deformation of the powder.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for producing an amorphous body for hexagonal ferrite powder, a method for producing hexagonal ferrite powder, and an atomizing device, and more specifically, hexagonal ferrite suitable for high-density magnetic recording using the atomizing device. The present invention relates to a method for producing an amorphous body for powder.

In recent years, a technique for transferring a larger amount of data at a higher speed has been developed, and a technique for storing the data has also become necessary. Examples of techniques for storing data include:
Magnetic recording using the magnetization of a magnetic material is used.

Examples of the magnetic material used for magnetic recording include metal magnetic powder such as Fe-based magnetic powder. In order to achieve high-density magnetic recording using such metal magnetic powder, the metal magnetic powder is finely divided.

However, there is a problem that deterioration of magnetic characteristics due to oxidation of the magnetic powder when the metal magnetic powder is made into fine particles, and there is a limit to the formation of fine particles.

Therefore, it has been studied to use hexagonal ferrite powder as a magnetic powder with little deterioration in magnetic properties due to oxidation and high coercive force. Since hexagonal ferrite is an oxide, the above problem does not occur even if it is made fine particles, and is suitable for high-density magnetic recording.

In order to obtain such hexagonal ferrite powder, for example, the following glass crystallization method is used (see Patent Documents 1 and 2). In the glass crystallization method, first, a glass component and a ferrite component, which is a magnetic material, are melted at a high temperature to obtain a melt. Next, an amorphous body (glass body) is obtained by rapidly cooling the melt from a molten state. By heat-treating the obtained amorphous body, a precursor of hexagonal ferrite powder in which hexagonal ferrite is precipitated in the amorphous body is obtained. By separating the glass component from the precursor of the hexagonal ferrite powder, a particulate hexagonal ferrite powder can be obtained.

JP 2011-213544 A JP 2011-181130 A

In order to improve the magnetic properties of the hexagonal ferrite powder obtained by the above method, for example, the cooling rate of the melt during rapid cooling is increased. As a method of rapidly cooling the melt, Patent Document 1 discloses a method of cooling by supplying the melt between a pair of rotating rolling rolls. Further, Patent Document 2 discloses a method in which atomized gas is injected into a melt to rapidly cool the melt as a fine powder.

On the other hand, in the market of high-density magnetic recording media such as data storage for computers, magnetic powder capable of achieving both high characteristics and stable supply is required. Therefore, there is a demand for improving the yield of hexagonal ferrite powder suitable for high-density magnetic recording.

However, the cooling method using a rolling roll as shown in Patent Document 1 has a problem that a large-scale apparatus is required, and that maintenance requires cost and time, and it is difficult to realize a stable supply. It was. Moreover, in the cooling method by gas atomization as shown to patent document 2, since what has a comparatively small diameter among the fine powder-like melts is easy to be cooled, a cooling rate can be made sufficiently fast. However, the cooling rate of the fine powdered melt that occupies most of the fine powdered melt and has a relatively large diameter cannot be sufficiently increased. As a result, the hexagonal ferrite powder having low characteristics increases, and there is a problem that the production efficiency of the hexagonal ferrite powder suitable for high-density magnetic recording is deteriorated.

The present invention was made in view of the above situation, in order to produce a hexagonal ferrite powder suitable for high-density magnetic recording with a high yield, the cooling rate of a melt having a relatively large diameter is increased, It is an object to provide a method for producing an amorphous body for hexagonal ferrite powder and a method for producing the hexagonal ferrite powder capable of obtaining an amorphous body as a precursor of hexagonal ferrite powder. . Another object of the present invention is to provide an atomizing device capable of increasing the cooling rate of atomized powder such as an amorphous material.

The present inventors pay attention to the manufacturing process of an amorphous body as a precursor of hexagonal ferrite powder,
In order to increase the cooling rate of the melt having a relatively large diameter, the surface area of the melt is increased when the melt is cooled, and the above-mentioned problem is solved by rapidly cooling to the inside of the melt. We have found what we can do and have completed the present invention.

That is, the aspect of the present invention is
An atomizing process in which a melt containing at least a raw material of a hexagonal ferrite component and a raw material of a glass component is supplied from a molten metal supply unit, and atomized gas is injected into the supplied melt from an atomizing gas injection unit to pulverize the melt. Have
In the atomization process, at least a part of the fine powder obtained by atomizing the melt is made to collide with a cooling member arranged so as to surround the fine powder below the atomizing gas injection part, and is amorphous for hexagonal ferrite powder to be plastically deformed. It is a manufacturing method of a mass.

In the present specification, “the fine powder is plastically deformed” means that the fine powder has different shapes before and after the fine powder collides with the cooling member, and the fine powder maintains the shape after the collision. To do.

Preferably, at least a part of the fine powder is made to collide with the cooling member in a molten state to plastically deform at least a part of the fine powder into a flat shape, and the fine powder is cooled while maintaining the flat shape to obtain an amorphous body.

In the present specification, “flat” means a shape obtained by crushing a solid shape such as a spherical shape or a lump shape in one direction. Note that the flat shape is partially uneven and includes a flat plate or a thin rectangular parallelepiped, and includes a flaky shape and a flaky shape when viewed as a whole even if deformation is observed. For example, what is generally called flake shape is also included in this. In addition, “spherical” means a three-dimensional shape closer to a cube than a rectangular parallelepiped when viewed as a whole even when there is unevenness and deformation is seen, and includes a granular shape.

Preferably, the cooling member is a cylindrical member. More preferably, the cooling member is a cylindrical member. Alternatively, preferably, the cooling member is composed of a plurality of members.

  Preferably, the cooling member has a vibration mechanism for vibrating the cooling member.

Preferably, the cooling member has a mechanism for cooling by circulating a fluid in the cooling member.

  Preferably, the raw material of the hexagonal ferrite component contains barium carbonate.

Preferably, the pressure of the atomizing gas is 0.2 to 1.0 MPa. Moreover, Preferably, the flow volume of atomizing gas is 1.5-10 Nm < ³ > / min.

Another aspect of the present invention is a method for producing a hexagonal ferrite powder having the method for producing an amorphous body for a hexagonal ferrite powder as described above.

Another aspect of the present invention provides:
A chamber;
A melt supply unit for supplying the melt into the chamber;
An atomizing gas injection unit for injecting atomizing gas into the melt;
A cooling member,
The cooling member is an atomizing device arranged so as to surround the fine powder below the atomizing gas injection section so that at least a part of the fine powder obtained by atomizing the melt with the atomizing gas collides with the cooling member.

Preferably, the cooling member is a cylindrical member. Alternatively, preferably, the cooling member is composed of a plurality of members.

According to the present invention, in order to produce a hexagonal ferrite powder suitable for high-density magnetic recording with a high yield, the cooling rate of the amorphous body as a precursor of the hexagonal ferrite powder can be increased. A method for producing an amorphous body for hexagonal ferrite powder can be provided. Moreover, according to this invention, the atomizing apparatus which can make the cooling rate of atomized powder, such as an amorphous body, faster can be provided.

FIG. 1 is a flowchart showing a method for producing an amorphous body for hexagonal ferrite powder and a method for producing hexagonal ferrite powder according to the present embodiment. FIG. 2 is a schematic cross-sectional view of the atomizing apparatus according to this embodiment. FIG. 3 is a schematic view showing a cross-sectional shape of a cooling member included in the atomizing apparatus shown in FIG. FIG. 4 is a schematic view showing a cross-sectional shape of a cooling member in a modified example. FIG. 5 is a scanning electron microscope (SEM) photograph of amorphous bodies according to examples and comparative examples of the present invention. FIG. 6 is a graph showing the relationship between coercivity and particle volume of hexagonal ferrite powders according to examples and comparative examples of the present invention.

Hereinafter, the present invention will be described in detail in the following order based on embodiments shown in the drawings.
1. 1. Hexagonal ferrite powder 2. Method for producing hexagonal ferrite powder Effect of the present embodiment 4. Modified example

(1. Hexagonal ferrite powder)
The hexagonal ferrite powder produced by the method according to this embodiment is an aggregate of hexagonal ferrite particles. Hexagonal ferrite particles have a hexagonal crystal structure and the composition formula is AFe
It is mainly composed of hexagonal ferrite represented by ₁₂ O ₁₉ . Hexagonal ferrite is a hard ferrite that exhibits magnetic anisotropy due to the c-axis anisotropy of the crystal and has a high coercivity.

“A” in the composition formula is preferably an alkaline earth metal. In this embodiment, “A”
Is preferably Ba. Further, the hexagonal ferrite particles may contain an additive component depending on desired characteristics. As an additive component, a divalent or tetravalent element may be contained in order to adjust the coercive force, bismuth (Bi) may be contained in order to control the shape of the particle, or the heat of the particle. Niobium (Nb) may be contained to increase the stability.

The hexagonal ferrite powder produced by the method according to the present embodiment has a high coercive force per particle volume and is a magnetic powder suitable for high-density magnetic recording.

(2. Manufacturing method of hexagonal ferrite powder)
In the present embodiment, a method for producing the above hexagonal ferrite powder will be described with reference to the flowchart shown in FIG. The hexagonal ferrite powder is produced from an amorphous material produced using a glass crystallization method. Therefore, the method for producing the hexagonal ferrite powder includes a method for producing the amorphous body for the hexagonal ferrite powder. First, as a starting material, a glass component material and a hexagonal ferrite component material are prepared, and an additional component material is further prepared as necessary.

The raw material for the glass component is not particularly limited as long as it is various compounds that become amorphous by rapid cooling, but boric acid is used as a raw material in this embodiment. In addition, as a raw material for the hexagonal ferrite component, various compounds that form hexagonal ferrite by a heat treatment process described later can be used. Examples thereof include oxides, carbonates, oxalates, nitrates, hydroxides, halides, and the like. In this embodiment, iron oxide and barium carbonate are used as raw materials. Further, as the raw material of the additive component, various compounds contained in the hexagonal ferrite by the heat treatment step described later can be used in the same manner as the raw material of the hexagonal ferrite component. In this embodiment, niobium oxide is used as a raw material.

The prepared starting materials (a glass component raw material, a hexagonal ferrite component raw material, and an additive component raw material) are weighed and mixed to obtain a predetermined composition ratio to obtain a mixture. As long as the starting materials are uniformly mixed, the mixing method is not particularly limited, but in the present embodiment, dry mixing performed using a dry mixer is exemplified.

(Melting step S10)
In the melting step S10, the obtained mixture is melted to obtain a molten metal (melt). Melting temperature is 1
It is preferable that it is 250-1500 degreeC, It is more preferable that it is 1300-1500 degreeC, It is further more preferable that it is 1350-1450 degreeC. At the time of melting, stirring may be performed while mixing the molten metal. The melting time is preferably shorter as long as the glass component, the hexagonal ferrite component, and the additive component are uniformly melted.

(Atomization process S20)
In the atomizing step S20, the molten metal obtained in the melting step S10 is rapidly cooled using a gas atomizing method to form a fine powdery amorphous body. This amorphous body is composed of a glass component, a hexagonal ferrite component and an additive component. In the present embodiment, the atomizing step S20 is performed using the atomizing apparatus shown in FIG.

The atomizing device includes a chamber 10, a crucible 11, a molten metal supply unit 12, an atomizing gas injection unit 13, and a cooling member 20. The crucible 11 holds the molten metal 50 obtained in the melting step S10. The molten metal supply unit 12 supplies the molten metal 50 into the chamber 10 through a nozzle communicating with the crucible 11. The atomizing gas injection unit 13 disposed at the lower part of the molten metal supply unit 12 ejects the atomized gas to the molten metal 50 supplied from the molten metal supply unit 12 to make the molten metal 50 into a fine powder form. The fine powder is accelerated in the direction of the arrow shown in FIG. 2 by the atomizing gas, and a part of the fine powder (for example, a fine powder having a relatively small diameter) is cooled without colliding with the cooling member to become an amorphous body. The fine powder other than the cooling member 20 in the molten state
And is deformed plastically and cooled to become an amorphous body. The fine powdery amorphous body is collected in the cyclone 15 from the lower part of the chamber 10 and is collected by being sucked by a blower.

The molten metal supply unit 12 is disposed so that the molten metal 50 flowing out from the molten metal supply unit 12 passes through a space surrounded by the wall surface of the cooling member 20 (inside the cooling member 20). Moreover, what is necessary is just to determine the amount of molten metal supplied from the molten metal supply part 12 according to a desired characteristic.

The atomizing gas injection unit 13 preferably has an injection angle adjusted so that the injected atomized gas atomizes the molten metal 50 and the atomized molten metal 50 collides with the cooling member 20. Moreover, the kind of gas used as atomizing gas will not be restrict | limited especially if it is gas normally used in the gas atomizing method, For example, inert gas, such as air and argon, etc. are illustrated. The flow rate and pressure of the atomizing gas may be determined according to the amount of molten metal, the shape of the fine powder, the particle diameter of the fine powder, etc., but in this embodiment, the flow rate is 1.5 to 10 Nm ³ / min. The pressure is preferably 0.2 to 1.0 MPa.

The cooling member is installed below the atomizing gas injection unit 13 so as to surround the fine powder generated when the atomized gas is injected from the injection unit into the molten metal 50, and at least a part of the fine powder collides with the cooling member, As long as it is configured to cause plastic deformation, its structure and dimensions are not limited. In the present embodiment, the cooling member 20 is a cylindrical member, and is arranged so that the inner wall surface surrounds the generated fine powder in order to collide the fine powder accelerated by the atomizing gas with the inner wall surface of the cylindrical member. ing. Therefore, in this embodiment, it is preferable that the cooling member 20 is installed with one of the openings at both ends of the cylindrical member facing the atomizing gas injection unit.

By using the cylindrical member as the cooling member, almost all of the fine powder accelerated by the atomizing gas collides with the cooling member 20, and therefore the amount of plastic deformation of the fine powder in the molten state can be increased. Therefore, the fine powder having a relatively large diameter becomes flat, and heat exchange with the cooling member can be efficiently advanced. As the cylindrical member, for example, as shown in FIG. 3 (a), a cylindrical member having a circular cross-sectional shape, and as shown in FIG. 3 (b), the cross-sectional shape is a polygon such as a hexagon. A polygonal cylindrical member or the like is exemplified. In addition, although a clearance gap like a slit can be provided in a cylindrical member, in order to raise the probability that a fine powder will collide with a cooling member, it is preferable not to provide a clearance gap.

In particular, in the present embodiment, as the cylindrical member, it is preferable to use a cylindrical tube having both ends opened as shown in FIG. Since the cylindrical tube as a cylindrical member does not have a corner on the side,
It can suppress that a fine powder adheres to a corner | angular part. As a result, the fine powder recovery rate can be increased. The dimensions of the cylindrical tube are, for example, a length of 300 mm and an inner diameter of about φ60.

The material of the cooling member 20 is not particularly limited as long as the material can sufficiently exchange heat with the fine powder. In the present embodiment, a material having a thermal conductivity in the range of 10 W / mK to 400 W / mK is used. Specifically, SUS304, copper, etc. are illustrated. In addition, the cooling member 2
At 0, it is preferable to smooth the portion where the fine powder collides. It is because adhesion of fine powder can be suppressed.

In FIG. 2, the cooling member 20 has a cylindrical tube shape with both ends open, and one end is open to the molten metal supply unit 12 and the atomizing gas injection unit 13 side, and the outer peripheral direction of the cylindrical tube And a flange portion projecting from the head. The other end is open to the lower side of the chamber 10. The cooling member 20 includes a molten metal supply unit 12 and an atomized gas injection unit 13.
Is located below and close to them. In addition, a gap is provided between the flange portion of the cooling member 20 and the lid portion of the chamber to form a gas flow path. By disposing the cooling member 20 so as to surround the fine powder, the flow path of the gas is limited, and the flow path including the flow path of the generated fine powder can be controlled. Air flow stability can also be achieved. As will be described later, the cooling member 20 has an upper end located above the extended line in the atomizing gas injection direction in order to increase the probability that fine powder formed by the atomization gas being injected into the molten metal will collide with the cooling member 20. It is preferable to provide it.

In the atomizing step S <b> 20, when the molten metal 50 flows out linearly from the molten metal supply unit 12, the molten metal 50 passes through the inside of the cooling member 20. Further, the atomized gas injected from the atomized gas injection unit 13 is also injected toward the inside of the cooling member 20 (in the direction of the arrow shown in FIG. 2). Therefore, the molten metal 50 is pulverized in the vicinity of the cooling member 20. At this time, the fine powder is almost spherical due to its surface tension. Further, since the cooling member 20 is disposed so as to surround at least a part of the fine powder, in the vicinity of the cooling member 20, many fine powders are spherical and kept in a molten state and are not solidified.

Further, since the atomized gas is injected toward the inside of the cooling member 20, the fine powder is accelerated in the atomizing gas injection direction (the direction of the arrow shown in FIG. 2) and collides with the cooling member 20 on the extension line. To do. At this time, the fine powder having a relatively small diameter is cooled before colliding with the cooling member 20 and becomes an amorphous body, but many fine powders remain in a molten state while being kept in the molten state.
Collides with 0 and easily deforms at the time of collision. As a result, the shape of the fine powder changes from spherical to flat,
By increasing the contact area with the cooling member 20, the heat of the fine powder is efficiently exchanged for the cooling member 20. That is, the cooling member 20 plastically deforms the fine powder and cools the fine powder.

Moreover, since the size of the cooling member 20 is sufficiently larger than the size of the fine powder, heat exchange is quickly performed and the fine powder is rapidly cooled. As a result, the fine powder is solidified in a flat state to become an amorphous body, passes through the other end of the cooling member 20, falls in the chamber 10, and then falls into the chamber 10.
After being sucked from the lower part of the water, it is recovered by the cyclone 15.

Therefore, by making the shape of the fine powder having a relatively large diameter flat, the molten metal 5
The fine powder of 0 can be solidified by increasing the cooling rate to obtain an amorphous body. As a result, the cooling rate of the molten metal pulverized by the atomizing gas can be increased.

In the present embodiment, as a cooling mechanism for forcibly cooling the cooling member 20, the jacket 21 is disposed so as to cover the outer periphery of the cooling member 20, and the cooled fluid circulates inside the jacket 21. ing. The fluid removes heat applied to the cooling member 20 by heat exchange with the fine powder, and keeps the cooling member 20 at a constant temperature, whereby heat exchange between the fine powder and the cooling member 20 can be performed more efficiently. it can.

Moreover, in this embodiment, the cooling member 20 has the piston vibrator 22 as a vibration mechanism which vibrates this cooling member. When the fine powder collides with the inner wall of the cooling member 20 in a molten state, the fine powder may adhere to the inner wall in some cases. When the fine powder adheres to the inner wall, the recovery rate of the fine powder tends to decrease, and heat exchange between the fine powder and the cooling member 20 may not proceed efficiently. Therefore, by vibrating the cooling member 20 by the piston vibrator 22, adhesion of fine powder can be eliminated, and the collection rate of fine powder can be increased. Although the attachment position of the piston vibrator 22 is not particularly limited, it is preferably attached to the lower portion of the cooling member 20. In addition, since the vibration by the piston vibrator 22 hardly generates an air flow around the cooling member 20, the gas flow is not hindered.

The recovered amorphous fine powder may be pulverized. The pulverization method is not particularly limited, and a known method can be adopted depending on the desired particle diameter. For example, pulverization by a ball mill is exemplified. In addition, it is preferable to screen the amorphous fine powder to remove coarse particles contained in the fine powder. By setting the particle size of the fine powder within a predetermined range, a hexagonal ferrite powder having uniform magnetic properties can be easily obtained.

(Heat treatment step S30)
In the heat treatment step S30, the amorphous fine powder obtained in the atomization step S20 is heat treated. By this heat treatment, hexagonal ferrite particles are precipitated in the amorphous fine powder to obtain a precursor of hexagonal ferrite powder. At this time, the amorphous fine powder may be left standing for heat treatment, or the heat treatment may be performed while rolling.

The temperature of the heat treatment is not particularly limited as long as the hexagonal ferrite particles are precipitated in the amorphous fine powder. In the present embodiment, the heat treatment temperature is preferably in the range of 450 ° C. or higher and 750 ° C. or lower, and more preferably in the range of 500 ° C. or higher and 750 ° C. or lower. The heat treatment may be a so-called one-stage process performed at a single processing temperature, or a so-called multi-stage process performed in several stages at different processing temperatures. The heat treatment time is preferably 30 minutes or more, and more preferably 1 hour or more.

(Separation step S40)
In the separation step S40, the amorphous component is separated and removed from the precursor containing the hexagonal ferrite particles precipitated in the heat treatment step S30 to obtain a hexagonal ferrite powder. A chemical method is preferable as a method for separating the amorphous component. In this embodiment, it is preferable to dissolve and remove the amorphous component using an acid. For example, dilute acetic acid diluted to about 10% by mass can be used. The treatment temperature is preferably 50 ° C. or higher. In order to remove the amorphous component, acetic acid may be boiled, or it may be stirred to remove the amorphous component uniformly. At this time, the pH of the treatment liquid is preferably 4.0 or less acidic. In this way, the hexagonal ferrite powder can be obtained by separating the amorphous component.

Thereafter, the obtained hexagonal ferrite powder is washed and dried as necessary. Washing and drying may be performed by a known method.

From the above, the hexagonal ferrite powder obtained by the method according to the present embodiment has a high coercive force in addition to a small number of coarse particles and a narrow particle size distribution. Therefore, it is suitable as a magnetic powder for high-density magnetic recording.

(3. Effects of the present embodiment)
According to the method according to the present embodiment, immediately after the molten metal becomes fine powder shape by atomizing gas injection, fine powder having a relatively large diameter collides with the cooling member in a molten state. For this reason, in addition to the plastic powder being deformed plastically from a spherical shape to a flat shape due to the impact of a collision, the heat of the fine powder is rapidly exchanged with the cooling member due to the temperature difference between the molten fine powder and the cooling member. The As a result, a fine powder of an amorphous body solidified in the flat shape is obtained. In particular, when the shape of the fine powder is flat, even the fine powder having a relatively large diameter is rapidly cooled to the inside of the fine powder. Therefore, not only the fine powder having a relatively small diameter but also the fine powder having a relatively large diameter can increase the cooling rate.

Therefore, a hexagonal ferrite powder having a high coercive force per particle volume can be obtained with a high yield by separating the glass component from the precursor obtained by heat-treating the amorphous material obtained after cooling the fine powder. In particular, when the hexagonal ferrite powder is a barium ferrite powder, the magnetic properties are easily affected by the cooling rate, and it is difficult to obtain good magnetic properties when the cooling rate is slow. Is preferred.

When the cooling member is cylindrical, most of the fine powder of the melt that has been atomized by the atomizing gas collides with the cooling member and is plastically deformed and cooled. Furthermore, since the melt is pulverized in the space surrounded by the wall surface of the cooling member, it is not affected by the turbulence of the airflow generated in the chamber. As a result, a fine powder with few coarse particles and a good particle size distribution can be obtained, and a hexagonal ferrite powder with uniform magnetic properties can be obtained.

Moreover, since the cooling member is provided with a jacket for circulating the cooling water, heat exchange with the fine powder can be performed more efficiently, so that the cooling speed of the fine powder becomes faster and the above effect is further enhanced. Can do.

Moreover, since the cooling member is provided with the piston vibrator, the fine powder can be prevented from adhering to the inner wall of the cooling member, so that the fine powder recovery rate can be increased. As a result, the production efficiency of the hexagonal ferrite powder can be improved.

Since the atomizing apparatus according to this embodiment includes the cooling member described above, the cooling rate of the atomized powder can be increased.

(4. Modifications)
In said embodiment, although the cylindrical member by which both ends were open | released was used as a cooling member, for example, using a some member so that it may have the cross-sectional shape shown to Fig.4 (a)-(c), The cooling member may be configured so as to surround a space in the chamber through which the melt flows out linearly. In the cooling member configured as described above, a gap is formed between the members.
Therefore, compared with the case where a cylindrical cooling member is used, there exists a tendency for the fine powder which does not collide with a member to increase.

  Moreover, the structure where a cross-sectional shape becomes large toward the downward direction of a cylindrical tube may be sufficient.

As mentioned above, although embodiment of this invention has been described, this invention is not limited to the embodiment mentioned above at all, and can be variously modified within the range which does not deviate from the summary of this invention.

Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.

Example 1
As the raw material for the hexagonal ferrite component, 5551 g of iron oxide (HRT made by Tetgen) and 8186 g of barium carbonate (made by SOLVAY / industrial) are prepared, and as the raw material for the glass component, 3713 g of boric acid (made by Borax / industrial) are prepared. Niobium oxide (as a raw material for additive components)
99.9 g of a high purity chemical laboratory / reagent) was prepared. Each of the prepared starting materials was weighed and mixed with a Henschel mixer so as to be uniform. The obtained mixture was put into a platinum crucible and held at 1400 ° C. for 60 minutes, whereby the mixture was completely dissolved to obtain a molten metal (melt).

Next, in the atomizing apparatus, a cylindrical tubular cooling member was installed at a position 28 mm below the lower part of the atomizing gas injection part located below the nozzle of the molten metal supply part. The cooling member has a length of 300 mm and an inner diameter of 59.5 mm. The material is SUS304 (
Thermal conductivity: 16.7 W / mK). Also, 150m in the length direction from the upper end of the cooling member
The jacket which covers the outer peripheral part of a cooling member was provided to the position of m, and the piston vibrator (EXV Corporation EPV18) was installed in the position of 19 mm in the length direction from the lower end of the cooling member.

The obtained molten metal is put into a crucible of an atomizing device and supplied from a nozzle of a molten metal supply unit, and room temperature air as an atomizing gas is supplied at a flow rate of 3.7 Nm ³ / min and a pressure of 0.4 MPa.
Atomized by spraying into the molten metal under the conditions of

During atomization, 60% water and 40% ethanol were mixed in the jacket of the cooling member, and the antifreeze liquid cooled to −20 ° C. was circulated. The cooling member was vibrated by a piston vibrator.

At least part of the molten metal atomized by atomization collides with the cooling member and plastically deforms into a flat shape, and is rapidly cooled by heat exchange with the cooling member to become amorphous fine powder. Collected by suction with a blower. An SEM photograph of the obtained amorphous body is shown in FIG.

The recovered amorphous fine powder was sieved. The obtained particle size distribution is shown in Table 1. Moreover, when sieving using a mesh having an opening of 250 μm, particles remaining on the mesh were removed as coarse particles, and fine powder that passed through the mesh was used in the subsequent steps.

The obtained amorphous fine powder was heated to 670 ° C. at a temperature increase rate of 5 ° C./min, and 5% at 670 ° C.
Heat treatment was carried out by holding for a time to obtain a precursor in which hexagonal ferrite was generated in amorphous fine powder.

A glass component is removed by immersing the precursor in which hexagonal ferrite is formed in 10% by mass acetic acid heated to 60 ° C. for 60 minutes, and acetic acid adhering to the surface of the powder is removed using pure water. Ferrite powder was obtained. Furthermore, this hexagonal ferrite powder was washed with 1.0 mol / L caustic soda, and washing was repeated until the electrical conductivity of the filtrate was 0.8 mS / m or less. Thereafter, the hexagonal ferrite powder was washed with pure water and dried in air at 110 ° C. for 4 hours. For the hexagonal ferrite powder after drying, the following measurement of coercive force Hc and calculation of particle volume were performed.

(Coercivity Hc)
Hexagonal ferrite powder is packed in a plastic container of φ6 mm, and an external magnetic field is 795.8 kA / m (1) using a vibrating sample magnetometer (VSM-P7-15 manufactured by Toei Kogyo Co., Ltd.).
The coercive force Hc (kA / m) was measured under the condition of 0 kOe). The results are shown in Table 2.

(Particle volume)
X-ray diffraction measurement was performed on the hexagonal ferrite powder, and the crystallite diameter calculated from the half-value width of the peak on the (220) diffraction plane of the hexagonal ferrite was defined as the crystallite diameter in the plate direction. The crystallite diameter calculated from the half width of the peak on the (006) diffraction plane was taken as the crystallite diameter in the plate thickness direction. Using these crystallite size values, the crystallite size volume was calculated based on the following formula.
Crystallite diameter volume = (crystallite diameter in the plate thickness direction) × π × (crystallite diameter in the plate surface direction / 2) ²
In this example, the crystallite diameter volume was defined as “particle volume”. The results are shown in Table 2. Further, the coercive force Hc per particle volume is shown in FIG.

(Comparative Example 1)
A hexagonal ferrite powder was obtained in the same manner as in Example 1, except that the cooling member was not provided in the atomizer and the molten metal was atomized with an atomizing gas and cooled. Table 2 shows the coercive force and particle volume of the obtained hexagonal ferrite. FIG. 6 shows the relationship between the particle volume and the coercive force Hc. Moreover, the SEM photograph of the obtained amorphous body is shown in FIG.5 (b).

(Comparative Example 2)
As a cooling member, a hexagonal ferrite powder was obtained in the same manner as in Example 1 except that a rotating roller was installed at the lower part of the chamber of the atomizer and the molten metal was atomized with an atomizing gas and cooled. The particle size distribution of the obtained amorphous fine powder is shown in Table 1, and the coercive force and particle volume of the obtained hexagonal ferrite powder are shown in Table 2. Further, the coercive force Hc per particle volume is shown in FIG.

From Table 1, it was confirmed that the particle size distribution of the amorphous body of the sample of Comparative Example 2 was wide and there were many coarse particles. This is considered to be because the particle size distribution is widened as a result of the airflow in the chamber of the atomizing device being disturbed due to the cooling member being provided at a location that blocks the flow of the airflow.

From FIG. 5A, it was confirmed that most of the amorphous body obtained in Example 1 was flat. Therefore, in Example 1, it is thought that the cooling rate of the fine powder having a relatively large diameter was sufficiently high. As a result, as is clear from Table 2 and FIG. 6, the sample of Example 1 has a high yield of powder having a high coercive force per particle volume,
It was confirmed that it was suitable as a magnetic powder for high-density magnetic recording and its production efficiency was high.

On the other hand, from FIG. 5B, it was confirmed that most of the amorphous body obtained in Comparative Example 1 was spherical. Therefore, in Comparative Example 1, it is considered that the cooling rate of the fine powder having a relatively large diameter was slow. As a result, as is clear from Table 2 and FIG. 6, it was confirmed that the sample of Example 1 had a poor powder yield with a high coercive force per particle volume.

DESCRIPTION OF SYMBOLS 1 ... Atomizing apparatus 10 ... Chamber 11 ... Crucible 12 ... Molten metal supply part 13 ... Atomizing gas injection part 15 ... Cyclone 20 ... Cooling member 21 ... Cooling jacket 22 ... Piston vibrator 50 ... Molten metal

Claims (6)

A chamber;
A melt supply section for supplying a melt into the chamber;
An atomizing gas injection unit for injecting atomizing gas into the melt;
A cooling member,
The cooling member surrounds the fine powder below the atomizing gas injection section so that at least a part of the fine powder obtained by pulverizing the melt with the atomizing gas collides with the cooling member and plastically deforms. An atomizing device characterized by being arranged in   The atomizing device according to claim 1, wherein the cooling member is a cylindrical member.   The atomizing device according to claim 2, wherein the cooling member includes a plurality of members.   The atomizer according to any one of claims 1 to 3 for producing an amorphous body for hexagonal ferrite powder.   The atomizing apparatus according to claim 4, wherein the amorphous body for the hexagonal ferrite powder is collected by suction. A chamber;
A melt supply section for supplying a melt into the chamber;
An atomizing gas injection unit for injecting atomizing gas into the melt;
A cooling member,
The cooling member is disposed so as to surround the fine powder below the atomizing gas injection unit so that at least a part of the fine powder in a molten state in which the melt is pulverized by the atomizing gas collides,
An atomizing apparatus characterized in that fine powder cooled by colliding with the cooling member is collected.