JPS60161341A - Preparation of hexagonal ferrite - Google Patents

Abstract

PURPOSE:To prepare hexagonal ferrite having small particle size and sharp crystal size distribution by dissolving fundamental components of hexagonal ferrite and cooling quickly the soln. on a single roll and treating obtd. amorphous product with heat and weak acid. CONSTITUTION:Components for hexagonal ferrite such as Fe, Ba, Sr, etc., substitutable components for reducing coercive force such as Co, Ti, etc., and glass forming substances such as H3BO3, BaO, etc., are mixed in the form of, if necessary, oxides, or carbonates, etc. The mixture is charged in a Pt vessel 3 provided with a nozzle 1 and melted by heating at ca. 1,350 deg.C with a high frequency heater 2 in the atmosphere of O2-contg. gas. Then, the vessel 3 is pressurized with O2-contg. gas through a solenoid valve 4, and the melt is quenched by blowing from a nozzle 1 onto a single roll 5 revolving at high speed to form completely uniform amorphous body 6 having ca. 5-20mu thickness. Then, the amorphous body 6 is heat-treated at ca. 450-850 deg.C for 1-10hr in the O2-contg. gas atmosphere, further, treated with a weak acid such as acetic acid to remove glass forming substances and impurities by dissolving in the acid. Thus fine particulate hexagonal ferrite having superior quality is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for producing particulate hexagonal ferrite.

More specifically, the present invention relates to a method for producing fine-grain hexagonal ferrite suitable as a magnetic powder for coating-type high-density perpendicular magnetic recording media.

In recent years, with the demand for higher density magnetic recording, perpendicular magnetic recording systems using hexagonal ferrites, such as magnetobrambite barium ferrites, as magnetic recording media have been developed and put into practical use.

Hexagonal ferrite has a flat plate shape and the axis of easy magnetization is perpendicular to the plane, so it can be easily aligned perpendicularly, making it suitable for use as a perpendicular magnetic recording medium, but the coercive force is usually 5000 Oe or more. Too expensive, as the head saturates during recording under current conditions.

As a hexagonal crystal thread ferrite used as a perpendicular magnetic recording medium, a part of its basic component iron is replaced with an appropriate substitute component to obtain an appropriate value (500 to 150 CIO θ) corresponding to the head.
A method of reducing the coercive force to a degree of

Substituting components for reducing coercive force include 2, for example, Ti, c
o, Mn, Zn+ Ge, Nb, V, Ta.

sb etc. are known.

・For hexagonal ferrite used as a perpendicular magnetic recording medium, it is preferable to have small grains, but if the grains are too small, they will not exhibit ferromagnetism, and if they are too thick, the magnetic properties will be dispersive. etc. becomes worse, so 0.01μ
A material with a large plate-like ratio in the range of about 0.3 μm, a sharp particle size distribution, a well-defined shape, and a high saturation magnetization without agglomeration or sintering is desired.

Conventionally, various methods are known for producing hexagonal ferrite, such as a coprecipitation method, a hydrothermal synthesis method, and a glass crystallization method. Among these, the basic components of hexagonal ferrite, substitute components for reducing coercive force, and glass-forming substances are mixed and melted, the melt is rapidly cooled, and the resulting amorphous body is heat-treated to precipitate fine ferrite particles. 1. Glass crystallization method involves removing glass components, impurities, etc. by treatment with a weak acid.

Compared to other methods, this method has the advantage that it is easier to obtain particles that are smaller in particle size and suitable as perpendicular magnetic recording media.

Methods for producing hexagonal crystal ferrite by glass crystallization include 7, for example, JP-A-56-67904, JP-A-5
'67125' 2 L9 Publication, JP-A-56-16
4'522, JP-A-56-155022,
JP-A-51-16912'8, JP-A-J7-56
This method has been proposed in JP-A No. 629, JP-A-5'7-56328, and JP-A-57-567-26.

However, when the raw material melt is poured onto twin rolls and rapidly cooled using the proposed method 2, for example, JP-A-56-125
As is clear from the description in the lower right column on page 2 of Publication No. 219, it is not possible to obtain a completely uniform amorphous body, and -
! The resulting flakes (amorphous ribbons) are mutually agglomerated, and even if they are heat-treated, large ferrite crystals with a grain size of 1μ or more are mixed in, resulting in grains with a thick plate-like ratio. Dispersion with a well-shaped diameter distribution.

It is difficult to obtain macrogonal ferrite with good orientation.

The present inventors have conducted intensive research on a method for producing hexagonal ferrite using the crow crystallization method, with the aim of solving the above-mentioned difficulties in the previously proposed method of rapid cooling using twin rolls. Single roll of raw material melt,
When used for rapid cooling.

The hexagonal ferrite obtained by heat treatment can easily be made into a completely uniform amorphous material, and the grain size of the hexagonal ferrite obtained by the conventionally proposed method is smaller than that of the plate-shaped ferrite. It was discovered that the grain size distribution of the cylindrical grain is sharp and the dispersibility, orientation, etc. are excellent, leading to the invention of the present invention.

The present invention involves mixing and melting a basic component of hexagonal ferrite, a substitute component for reducing coercive force, and a glass-forming substance,
The melt is rapidly cooled, and the resulting amorphous material is heat-treated to precipitate ferrite particles.

The present invention relates to a method for producing hexagonal ferrite in the form of fine particles by treatment with a weak acid, which is characterized in that the melt is rapidly cooled on a single roll.

When rapidly cooled in a single roll according to the present invention.

Compared to the case using twin rolls, the thickness of the amorphous material is thinner at about 5 to 20μ compared to about 50μ for twin rolls, so it is effective for rapid cooling and uniform amorphization of melts with a small heat transfer coefficient. Since it does not require crimping of the rolls together as with two-inch rolls, the roll surface has excellent smoothness and durability.

The amorphous material obtained by rapid cooling on a trench single roll has a particle size distribution of 0.05 to 0.10μ by subsequent heat treatment.
The result is a hexagonal ferrite with a sharper grain size distribution, smaller grain size, and larger plate-like ratio than the hexagonal ferrite obtained by rapid cooling on twin rolls and heat treatment. .

Excellent dispersibility, orientation, etc.

In the present invention, known basic components of hexagonal ferrite, substitute components for reducing coercive force, and glass-forming substances are used, and are mixed and heated to melt by a method known per se. The basic component of hexagonal ferrite is F.
e and Ba, Sr+ Pb, etc., and these are generally FeC1゜Fe2O3, Ba, O,
Ba, C03, P'bO, PbCO3, SrO.

It is used as an oxide or carbonate such as S r CO3.

Substitution components for reducing coercive force include CO and Ti.

Zn, Mn, ()e, V, 'Nb, Ta, Sb, etc. can be mentioned, and these are also generally used as oxides.

The glass-forming substance is generally H3BO3.

Boron compounds such as B2O3 and BaO, BaCO3+ S
rO.

SrC! Alkaline earth metal compounds such as 03 are used. These original $1. (7) The mixing ratio is 12 to 80 mol of the basic component of hexagonal crystal structure, 0.5 to 0.8 mol of the substitute component for reducing coercive force, and 20 to 88 mol of the glass forming substance. It is appropriate to set it within the molar range. It is appropriate that the heating melting be carried out in an oxygen-containing gas atmosphere at a temperature higher than the melting point of the raw material mixture, generally at a temperature of about 1350°C, to completely melt and dissolve the material into a uniform melt.

In the present invention, it is particularly important that the melt is rapidly cooled on a single roll into an amorphous form.

When rapidly cooling a common product on a single roll, it is preferable to use a method in which a projectile material is sprayed onto a single roll rotating at high speed. As a single roll (d) Rolls that can be cooled with refrigerant or the like may be used, or rolls that are not capable of being cooled may be used. It is also possible to form a fully uniform amorphous material at room temperature by using a melt.Also, when spraying a melt onto a single roll, generally oxygen-containing gas pressure is applied to the melt and the melt is sprayed from a nozzle onto the roll. The thickness of the amorphous material obtained by rapid cooling on a single roll is:

The viscosity of the melt, the speed at which the melt is blown onto a single roll,
Although it varies depending on the number of rotations of the rolls, it is about 5 to 20 μm, and it is possible to obtain a product that is relatively thinner and has a higher degree of amorphism than when using twin rolls.

The amorphous body is heated under an oxygen-containing gas atmosphere to 450-8
When heat treated at 50"C for 1 to 10 hours.

Preferably, if a second heat treatment is performed at 450 to 650°C for 1 to 10 hours, and then a second heat treatment is performed at 750 to 850°C for 1 to 10 hours, fine grains of hexagonal ferrite will precipitate. 2 For example, by treating with a weak acid such as acetic acid, diluted nitric acid, hydrochloric acid, or phosphoric acid, and removing glass-forming substances and impurities by dissolving and washing, the material is made into an amorphous state using twin rolls, and then heated and treated with a weak acid. It is possible to obtain fine-grained hexagonal ferrite which is even better than that of the conventional method.

Next, Examples and Comparative Examples will be shown.

Example 1 B20326.7 mol%, 13a03 Ro, Romol section.

Fe2O3 filter 0゜4 mo/l/%, 0o04.8 mole ratio and Ti024.8 mole ratio + H3BO
3. BaO03.

Fe2O3, CoCO3, and TiO2 powders were mixed, and the mixture 1007 was placed in a platinum container B having a nozzle 1 at the tip as shown in Fig. 1 and a high-frequency heater 2 on the outside, and heated and melted at 1350°C. After that, the solenoid valve 4 for gas pressure injection provided above the platinum container B was activated to apply 02 gas pressure of 1.5 kg/crlr to the melted material in the platinum container 6. Nozzle 1 (discharge port diameter 0-8
Spray the melted material from mm) and quench it.

Amorphous ribbon 6 (thickness approximately 15 shades) was obtained.

The amorphous ribbon was analyzed using X-ray diffraction analysis.
No diffraction peaks were observed, indicating that it was a completely uniform amorphous material. The saturation magnetization (Bm) and remagnetization force (Hc) of the amorphous ribbon were both 0.

The amorphous ribbon was then heated at 650°C in an air atmosphere for 10
After a secondary heat treatment at 780°C for 2 hours, it is treated with acetic acid to dissolve and remove BaO phase, BaO・B2O3 phase, etc., washed with water, and dried to produce magnetobrambite barium ferrite. (Bal Fe10.
4 Coo,s Ti0.80+9) fine particle powder was obtained.

The obtained barium ferrite fine particles had a uniform hexagonal plate shape. Specific surface area of barium ferrite fine particle powder9 Particle size distribution, saturation magnetization (Bm), coercive force (H
c) and platelet ratio (as determined by transmission electron microscope) as shown in Table 1.

Example 2 Example 1 except that the 02 gas pressure was changed to 2.5 Kg/(74) and the rotation speed of the single roll was changed to 4.000 r, p, m.

An amorphous ribbon was obtained in the same manner as in Example 1, followed by heat treatment and acetic acid treatment to obtain a fine particle powder of magnetobrambite barium ferrite. The amorphous ribbon has a thickness of approximately 5μ,
Although it was analyzed using X-ray diffraction analysis, no diffraction peak was observed.
It was a completely uniform amorphous body.

The obtained barium ferrite fine particles had a uniform hexagonal plate shape. The specific surface area, particle size distribution, saturation magnetization (Bm), coercive force (Ha), and plate-like ratio of the barium ferrite fine particles were as shown in Table 1.

Comparative Example 1 Instead of a single roll in Example 1, a roll diameter of 20 C was used.
Jn, 1 The amorphous ribbon was heated in the same manner as in Example 1, except that twin rolls rotating at 1500 rotations, r, p, and m were used, followed by heat treatment and acetic acid treatment to obtain magnetopranobite. The amorphous ribbon is about 50μ thick)! ¥<, Results of measuring saturation magnetization (Bm) and coercive force (Hc).

Bm=4.9 emu/V. Hc = 2 7 0
Barium ferrite crystals were observed.

Also, some barium ferrite fine particles have a particle size of 0.
．． Large crystals larger than 6μ were mixed together. Specification table I7Il product of barium ferrite fine particle powder.

The particle size distribution, saturation magnetization (Bm), coercive force (Hc), and plate ratio were as shown in Table 1.

Table 1

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the apparatus used to carry out the present invention. 1. Nozzle, 2. High-frequency heater. Ro... Platinum container, 4.・Solenoid valve for gas pressure injection.

Claims (1)

[Claims] A basic component of macrogonal ferrite, a substitute component for reducing coercive force, and a glass-forming substance are mixed and melted, the melt is rapidly cooled, and the resulting amorphous body is heat-treated to form ferrite fine particles. 1. A method for producing hexagonal ferrite in the form of fine particles by precipitation and treatment with a weak acid, characterized in that the melt is rapidly cooled on a single roll.