JPS62247505A - Manufacture of finely divided particle of barium ferrite for magnetic recording - Google Patents

Abstract

PURPOSE:To obtain a superior barium ferrite for magnetic recording by a method wherein a polyhydric alcohole solution, wherein salts of iron barium and the like are dissolved, and polyhydric alcohole solution, wherein alkali hydroxide is dissolved, are reacted with each other, precipitate is separated and, after alkali hydroxide is added, the precipitate is subjected to a surface treatment and is treated by heating. CONSTITUTION:A polyhydric alcohole solution, wherein iron, barium and so on are dissolved, and a polyhydric alcohole solution, wherein alkali hydroxide of an equivalent or more to the total amount of iron, barium and so on is dissolved, are reacted with each other at 120-200 deg.C and precipitate produced is separated. Alkali hydroxide is added to the precipitate obtained in such a way that 7-11 mol become excessive per 1 (l), the precipitate is charged in an autoclave and is treated by heating at 120-250 deg.C and the precipitate produced is separated, cleansed and dried. The product is dipped into a solution of silicate or aluminate, subjected to a surface treatment, and then treated by heating at 600-1000 deg.C. As the polyhydric alcohole, ethylene glycol, polyethylene glycol, propylene glycol, glycerine other than nitrate and so on are desirable.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing fine particulate barium ferrite for magnetic recording.

[Conventional technology]

Barium ferrite has been widely used as a permanent magnet material, but since the perpendicular magnetic recording method was proposed in recent years, it has suddenly become popular as a high-density magnetic recording material.

Barium ferrite magnetic powder can be used as a coated perpendicular magnetic recording medium, so it has the advantage of being able to utilize conventional coating techniques and being stable because it is an oxide. In order to use this for magnetic recording, it is necessary to suppress the coercive force to 20,000 s or less.

As a method for controlling this coercive force, a method has also been proposed in which part of the iron is replaced with cobalt, titanium, etc. (Japanese Patent Laid-Open No. 56-1
49328).

So far, known methods for producing barium ferrite magnetic powder include 1) solid phase reaction method, 2) co-precipitation heating reaction method, 3) flux method, and 4) glass point method.As a perpendicular magnetic recording material, It cannot be said that the material is satisfactory.

That is, since method 1) involves firing at a high temperature of 1000 C or more, intra-particle sintering is significant, resulting in coarse particles and irregular shapes. In method 2), when the coprecipitate is reacted and grown at high temperature, it is inevitable that some particles will partially sinter and agglomerate.

Method 3) yields only large particles. Method 4) uses a large amount of boron oxide as a matrix, making it difficult to completely remove it and resulting in poor yield and high cost. Method 5) can only yield particles with a particle size of 0.1 μm or more, which is too large for perpendicular magnetic recording.

Since perpendicular magnetic recording aims at a submicron recording wavelength, it is necessary to control the particle size to 0.1 μm or less, so none of the proposals can be said to be a preferable method. In addition to the above production method, a hydrothermal synthesis method has been known for a long time, and since barium ferrite crystals can be obtained directly in a solution, there is no mutual sintering of particles, and relatively uniform particles can be obtained. It has many advantages and is one of the most powerful processes.

However, with the processes proposed so far, it is difficult to synthesize barium ferrite with a hexagonal plate shape and uniform grain size of 0.1 μm or less, and even more so with even finer particles, such as 0.05 μm level, aimed at high-density recording. There were problems such as difficulty in making particles.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method for producing an excellent barium ferrite for magnetic recording without the above-mentioned drawbacks.

(Means for solving the problem) A polyhydric alcohol solution in which iron, barium, etc. A first step in which the alcohol solution is reacted with stirring at a temperature range of 120 to 200C, preferably 120 to 170C, and the resulting precipitate is separated by, for example, filtration or washing with ionized water, and the precipitate obtained in the first step. a second step in which alkali hydroxide is added in an excess of 7 to 11 moles per liter, the mixture is charged into an autoclave, and the resulting precipitate is hydrothermally treated at 120 to 250 C, and the resulting precipitate is separated, washed, and dried; 600-1000 t11' preferably 700-85 after surface treatment by immersing the product in an aqueous solution of silicon salt or aluminum salt
This is a method for producing hexagonal barium ferrite fine particles, which includes a third step of heat treatment at 0C.

[Effect]

Iron (FoI) and barium (Ball) used in the method of the present invention are known sulfates, nitrates, chlorides, hydroxides, etc., and the alkali hydroxides include sodium hydroxide, potassium hydroxide, etc. It is preferable to use one that is soluble in polyhydric alcohol.

Although the polyhydric alcohol is not specified, ethylene glyfur, polyethylene glycol, polypropylene glyfur, propylene glycol, glycerin other than nitrate, and the like are preferred.

In the method of the present invention, the reaction temperature in the first step is 120 mm.
Below this temperature, not only is the reaction rate slow, but the particles tend to become coarse, and even if the temperature is higher than this, not only does it not show any remarkable effect, but the vapor pressure of the polyhydric alcohol becomes high, requiring a pressure-resistant container. 0 The reason why the precipitate thus obtained is hydrothermally treated in the autoclave at a temperature range of 120 to 250 C in the second step is to form a precipitate with good dispersibility by the hydrothermal treatment. If the treatment temperature is below 120C, the reaction is too slow to be practical. Further, even if the temperature is 250C or higher, no particular effect is observed.

Excessive amount of alkali hydroxide during autoclaving
The reason why the treatment is carried out in the presence of mol or more, preferably 11 mol or less, is because if the excess alkali concentration is 7 mol or less, the particle size of the formed precipitate becomes coarse, and if it exceeds 11 mol, the viscosity of the alkaline aqueous solution increases. This is because it is difficult to obtain fine particles in the third step.2.
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The silicon salts and aluminum salts used in the third step are not specified, but include known sodium orthosilicate, sodium metasilicate, potassium metasilicate, silicon alkoxides, nitric acid, sulfuric acid, aluminum salts such as chlorides, aluminum alkoxides, etc. preferable. Heat treatment is 600~
It is carried out in air at 100 m, preferably 700 to 850 m. Below 600C, unreacted iron oxide (Cubi
c) may be generated or the product may become amorphous, resulting in
If it exceeds C, the particles become coarse.

According to the method of the present invention, a well-dispersed hexagonal barium ferrite having an average particle size of 0.1 μm or less, or barium ferrite in which a part of the ferrite is replaced with fuvardium, titanium, etc., can be stably obtained.

〔Example〕

Examples will be described below.

Example 1 219 g of ferric chloride (FeC13.6H20,0,81
mol) and 14 g barium chloride (BaOl 2.0
．． 067 mol) in ethylene glycol 11,
To this was added a solution of 42 g (1.05 mol) of sodium hydroxide dissolved in 2.51 g of coethylene glycol,
After stirring at 450 rpm and maintaining the temperature at 170C for 30 minutes, the mixture was allowed to cool to room temperature, and the precipitate formed was separated by filtration and washing.

Next, the precipitate obtained in the first step was charged into an autoclave with 11 liters of aqueous sodium hydroxide solution in an amount such that the alkali concentration was 10 moles per 17, and heated at 240C for 3 hours while stirring with the stirrer attached to the autoclave. Hydrothermal treatment was performed for a period of time, and the resulting precipitate was separated using a suction filter, washed with hot water, treated with alcohol, and then dried in vacuum.

The thus obtained ferrite powder was immersed in a 0.3% by weight aqueous water glass solution for 30 minutes, and the precipitate was separated by suction filtration.Then, the powder was placed in a Matsufuru furnace maintained at soot temperature and heat-treated for 1 hour.

The chemical composition of the obtained fine particles was determined by fluorescent X-ray analysis, the particle state by transmission electron microscopy (hereinafter referred to as TEM), the identification by X-ray diffraction, and the specific surface area of the particles by BET method. The molar ratio of Ba is 12.1, and as observed by TKM, barium hexaferrite has satisfactory properties such as well-dispersed hexagonal particles with an average particle size of 0.08 #m and a specific surface area of 48.7 m and 7 g. Obtained.

Example 2 Same as Example 1 except that the reaction temperature in the first step was 140C, the autoclave treatment in the second step was 280C', the heat treatment temperature for precipitation in a Matsufuru furnace was 850C, and nitrate was used as the raw material for Ba and F''e. When ferrite was manufactured in the same manner and its physical properties were measured, the Fe/Ba molar ratio was 11.
8. It was a well-dispersed hexagonal barium hexaferrite with an average particle size of 0.09 μm as determined by TEM observation, and the product had sufficient physical properties with a specific surface area of 43 m 7 g.

Comparative Example When the same process as in Example 1 was carried out except that the first step was carried out at 115C for 2 hours, barium ferrite of 0.1 μm or less was not obtained.

〔Effect of the invention〕

Hexagonal barium ferrite having an average particle size in the range of 0.05 to 0.8 μm can be efficiently obtained.

Applicant: Sumitomo Metal Mining Co., Ltd. Procedural Amendment dated September 1, 1986 1, Indication below Patent Application No. 091006 No. 091006 of 1988 3, Person filing the amendment: Filing Address: Minato-ku, Tokyo 5-11-3, Shinbashi Name: Sumitomo Metal Mining Co., Ltd. 4, Agent address: 1-12-15 (2) Shinjuku, Shinjuku-ku, Tokyo
``0.8μm'' in the first line of page 10 is ``o, osμm''.
I am corrected.

Claims (1)

[Claims] (1) A polyhydric alcohol solution in which iron, barium, etc. are dissolved, and a polyhydric alcohol solution in which alkali hydroxide is dissolved in an amount equal to or more than the total amount of iron, barium, etc. mentioned above.
The first step is to separate the precipitate produced by the reaction at 0 to 200°C, and to the precipitate obtained in the first step, alkali hydroxide is added in an excess of 7 to 11 moles per liter, and the mixture is charged into an autoclave. The second step is to separate the precipitate produced by hydrothermal treatment at 120 to 250°C, wash and dry it, and the product of the second step is surface treated by immersing it in an aqueous solution of silicon salt or aluminum salt. A method for producing barium ferrite fine particles for magnetic recording, comprising a third step of heat treatment at 1000°C.