JPH06251925A - Manufacture of needlelke barium ferrite fine particle - Google Patents

Abstract

PURPOSE:To enhance the coercive force of needlelike barium ferrite fine particles by a method wherein Al-containing needlelike goethite fine particles and barium salt are mixed, fired to manufacture the needlelike barium ferrite fine particles. CONSTITUTION:Needlelike barium ferrite fine particles are manufactured by a method wherein Al-containing needlelike goethite fine particles and barium salt are mixed and fired. The Al content of the needlelike goethite fine particles to Fe, Al/Fe, is 1 to 2 to 12 atomic %. Thereby, needlelike barium ferrite fine particles of large coercive force, which are a needlelike crystal substance consisting of a magnet plumbite phase and point the direction vertical to the major axis of the needlelike crystal substance to an easy magnetization direction, can be manufactured. Moreover, as the needlelike barium ferrite fine particles are needlelike crystals having a uniform particle diameter, they are used as a paint, which is superior in dispersibility and orientation property, when being manufactured as a magnetic paint.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing acicular barium ferrite fine particles suitable for use in a perpendicular magnetic recording medium.

[0002]

2. Description of the Related Art As is well known, barium ferrite sintered bodies are now widely used as permanent magnets, and barium ferrite amorphous powders are used as magnetic recording media such as magnetic cards and highway pass tickets. Is also widely used as. In addition, recently, a method for producing thin hexagonal plate-shaped barium ferrite fine particles has been developed, and attention has been paid to its application to a perpendicular magnetic recording medium.

The coercive force of barium ferrite is acicular γ-F.
Since it is much larger than that of e ₂ O ₃ , the magnetic recording medium using barium ferrite is characterized by being extremely stable against an external magnetic field and being inexpensive.

However, in the above amorphous barium ferrite powder, it is difficult to orient the C axis (crystal axis), which is the easy axis of magnetization of each powder particle, in the same direction by the applied magnetic field. Further, the hexagonal plate-shaped barium ferrite flakes,
Since the dispersibility in the magnetic paint is poor, the surface property of the magnetic layer becomes problematic when coated on a non-magnetic support. Further, even when the magnetic coating material is oriented, it is not easy to orient the crystal so that the C axis of the barium ferrite thin piece becomes perpendicular to the non-magnetic support.

[0005]

In order to improve the above-mentioned problems of dispersibility and orientation, it is conceivable that the barium ferrite is needle-shaped as disclosed in Japanese Patent Publication No. 4-30724. It was The acicular barium ferrite has an easy axis of magnetization in the direction perpendicular to the long axis and is excellent in dispersibility and orientation, and thus is very useful as a magnetic powder for a perpendicular magnetic recording medium. Further, by handling the acicular powder, it is possible to make use of the abundant experience and technology used in manufacturing the magnetic recording medium using γ-Fe ₂ O ₃ .

However, the fine powder of acicular barium ferrite has not been able to sufficiently exhibit the coercive force originally possessed by barium ferrite.

Therefore, the present invention has been proposed in view of such conventional circumstances, and an object thereof is to provide a method for producing acicular barium ferrite fine powder which exhibits excellent magnetic characteristics.

[0008]

The present invention has been proposed to achieve the above object. That is, the method for producing fine acicular barium ferrite powder of the present invention is characterized by mixing acicular goethite fine particles containing Al and barium salt and firing the mixture.

As a method for producing acicular barium ferrite, as disclosed in Japanese Patent Publication No. 30724/1992, barium salt such as acicular goethite (α-FeOOH) in the form of colloidal barium carbonate (BaCO ₃ ) is used. And a small amount of low-melting point oxide B ₂ O ₃ or Bi ₂ O ₃ are added, and heating is performed in a temperature range of 820 to 880 ° C.

The acicular barium ferrite thus obtained is an acicular crystal body composed of a magnetoplumbite phase, and the direction perpendicular to the major axis of the acicular crystal body is the easy magnetization direction.

In the present invention, the acicular Goethite fine particles have an Al content Al / Fe of 2 to 12 with respect to Fe.
It is preferably atomic%. When the acicular goethite fine powder containing the above-mentioned amount of Al is used to produce acicular barium ferrite fine powder, the coercive force is greatly improved.

If the Al content is less than 2 atomic% with respect to Fe, the effect of improving the coercive force of the acicular barium ferrite will not be sufficiently exerted, and conversely it will be 12 atomic%.
If it is more, the saturation magnetization of the acicular barium ferrite tends to deteriorate rapidly.

[0013]

[Function] When needle acicular goethite fine particles and barium salt are mixed and fired to produce acicular barium ferrite fine particles, if needle acicular goethite fine particles as a raw material contain Al, the obtained acicular needle barium ferrite fine particles are retained. The magnetic force is greatly improved.

Further, by using barium ferrite in the form of needle-shaped fine particles, it becomes easy to disperse it in the magnetic paint, so that the coating film surface can be smoothed. In addition, acicular barium ferrite has better orientation than amorphous or hexagonal tabular ones, so it is easy to apply a magnetic field for crystal orientation. The produced magnetic recording medium reflects the high magnetic properties of barium ferrite.

By controlling the particle size of the goethite used, the acicular barium ferrite produced can have a uniform particle size distribution.

Further, since γ-Fe ₂ O ₃ has been conventionally used as a needle-shaped magnetic powder in the manufacture of magnetic recording media, this abundant experience and technology must be applied when using needle-shaped barium ferrite as a magnetic powder. You can take advantage of it.

[0017]

EXAMPLES Preferred examples of the present invention will be described based on experimental results.

Example 1 First, acicular barium ferrite fine particles were prepared as follows. The acicular goethite fine particles used had the following elemental composition and had an acicular ratio of 25 and a particle size of 0.5 μm.
m.

Elemental composition of acicular goethite fine particles Al ・ ・ ・ Traces Si ・ ・ ・ 0.4 atom% Mn ・ ・ ・ 0.2 atom% Ni ・ ・ ・ 4.1 atom% Cu ・ ・ ・ 0.1 atom % Ca ・ ・ ・ 0.1 atom% Cl ・ ・ ・ 0.1 atom% S ・ ・ ・ 0.1 atom% P ・ ・ ・ Traces

The numbers shown in the above elemental composition are F
It is expressed as a ratio to e.

10 g of the needle-shaped goethite fine particles were placed in an aluminum sulfate solution having a predetermined concentration adjusted to pH = 9 with aqueous ammonia, stirred at room temperature for 2 hours, filtered, and dried.
l-containing goethite particles were prepared. In this example, the content ratio of Al to Fe, Al / Fe, was set to be 2.0 atom%.

5 g of the above Al-containing goethite was added to 10 parts of warm water.
Disperse in 0 cm ³ , add 1.71 g BaCl ₂ · 2H ₂ O, stir well, and add 1.18 g NaHCO 3.
₃ was added and ultrasonically dispersed for 5 minutes. Then, NaCl was washed out with about 1 liter of warm water, filtered, dried, and then the dried cake was crushed by a fine crushing mill and calcined using an alumina crucible.

When firing at 1000 ° C. or higher, needle-like properties cannot be maintained and sintering occurs, so the firing temperature is 850-90.
0 ° C is preferred. The firing time was 1 hour.

Then, after slowly cooling to room temperature, fine pulverization was carried out again to obtain barium ferrite fine particles in the form of needles. This is a sample of Example 1.

FIG. 1 is a transmission electron microscope (TEM) photograph of barium ferrite fine particles of Example 1. From this photograph, it can be seen that the obtained barium ferrite fine particles are acicular crystals having a uniform particle size.

Examples 2 and 3 Barium ferrite fine particle samples were prepared in the same manner as in Example 1 except that the amount of Al contained in goethite fine particles was set to the value shown in Table 1. As a result of observing each sample, it was found that needle-like crystals similar to the sample of Example 1 were formed.

[0027]

[Table 1]

Comparative Examples 1 and 2 Example 1 except that the amount of Al contained in goethite was larger than those in Examples 1 to 3 (the content is shown in Table 1).
A sample of Comparative Example 1 was prepared in the same manner as in, and a sample of Comparative Example 1 was prepared in the same manner as in Example 1 except that Al was not contained in goethite.

Observation of each sample revealed that needle-like crystals similar to the sample of Example 1 were formed.

Here, the magnetic characteristics of each of the samples obtained as described above were measured. Specifically, a vibration test type magnetometer (trade name VSM manufactured by Toei Industry Co., Ltd.)
Was used to investigate coercive force and saturation magnetization. The results are shown in Table 1 together with the content of Al, and also shown in FIG. 2 as a characteristic diagram. In addition, the above-mentioned measurement is based on the external magnetic field
It was performed at MA / m.

From FIG. 2, the content of Al is 2 to 12 atomic%.
It can be seen that the barium ferrite fine particles produced by using the goethite fine particles as described above have remarkably excellent coercive force as compared with those not containing Al. Further, it is understood that the saturation magnetization can be maintained as long as the Al content does not exceed 12 atomic%.

[0032]

As is apparent from the above description, Al
The acicular barium ferrite fine particles prepared from the acicular goethite fine particles containing Pt have significantly improved coercive force. Further, since the barium ferrite fine particles of the present invention are needle-shaped crystals having a uniform particle size, they are excellent in dispersibility and orientation when used as a magnetic paint.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the particle shape of barium ferrite particles prepared.

FIG. 2 is a characteristic diagram showing the relationship between the Al content and the coercive force and saturation magnetization of barium ferrite prepared.

Claims (2)

[Claims] 1. A method for producing acicular barium ferrite microparticles, which comprises mixing acicular goethite microparticles containing Al and barium salt and firing the mixture. 2. A to Fe of needle-shaped goethite fine particles
The method for producing acicular barium ferrite fine particles according to claim 1, wherein the 1 content Al / Fe is 2 to 12 atom%.