JPS62252907A - Manufacture of barium ferrite fine particle for magnetic recording - Google Patents

Abstract

PURPOSE:To obtain cubic barium hexaferrite having 0.07-0.08mum of mean particle diameter by agitating polyvalency alcohol in which salt is dissolved and polyvalency alcohol in which small oxide alkali is dissolved, water-heat- treating the mixture, cleaning and drying its precipitate, surface treating it, and heat treating it. CONSTITUTION:Polyvalency alcohol solution in which iron and barium are dissolved and polyvalency alcohol solution in which hydroxide alkali having an equivalent or more with respect to the total amount of the iron and the barium are dissolved are mixed and agitated. Produced slurry is filled in an autoclave, and treated at 120-250 deg.C. Obtained precipitate is separated, cleaned and dried. The product is dipped in aqueous solution of silicon salt or aluminum salt, surface-treated, and then heattreated at 600-1000 deg.C. Thus, cubic barium hexaferrite having 0.07-0.08mum of mean particle diameter is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] 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 attracted attention as a high-density magnetic recording material.

Since barium ferrite magnetic powder can be used as a coated perpendicular magnetic recording medium, it has the advantage of being able to utilize conventional coating techniques and being stable since it is an oxide. In order to use this for magnetic recording, it is necessary to suppress the coercive force to 20,000e 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 fupartite, titanium, etc.
149328).

So far known methods for producing barium ferrite magnetic powder include 1) solid phase reaction method, 2) co-precipitation thermoresponsiveness, 3) flux method, 4] glass crystallization method, 5) molten salt method, However, all of them have drawbacks and cannot be said to be a material that is satisfactory as a perpendicular magnetic recording material.

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

Method 3) yields only large particles. In method 4), the amount of boron oxide used as IJ lux is large, 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 has become one of the most popular processes.

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

[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 problems]

A polyhydric alcohol solution in which salts such as iron and barium 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 and barium, etc. are mixed and stirred, and the mixture is placed in an autoclave. 120-25
0? A first step of hydrothermal treatment with Z', separating the generated precipitate, washing and drying, and a surface treatment of the precipitate obtained in the first step by immersing it in an aqueous solution of silicon salt or aluminum salt. This is a method for producing hexagonal barium ferrite fine particles, which comprises a second step of heat treatment with C.

[Effect]

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

Although not specified as the polyhydric alcohol, ethylene glyfur, glyethylene glycol, polypropylene glycol, tetrapyrene glycol, glycerin other than nitrates, and the like are preferred.

In the method of the present invention, the hydrothermal treatment temperature in the first step is 12
The reason why the temperature is set to 0 to 250C and preferably 200 to 260C is that if the temperature is lower than this, the reaction rate is slow and the grains tend to become coarse, and if the temperature is higher than this, the target fine-grained barium ferrite cannot be obtained due to particle growth. The reason why the surface of the precipitate is treated before the heat treatment in the second step is to prevent particles from fusing together and becoming coarse due to the heat treatment.

The silicon salts and aluminum salts used in the second step are not specified, but may include known sodium orthosilicate, sodium metasilicate, kawaium metasilicate, silicon alfuxite, aluminum salts such as nitric acid, sulfuric acid, chloride, aluminum alfuxite, etc. preferable.

Heat treatment at 600-1000 C, preferably 700-8
Performed in air at 50C. At 600 tll'IX, unreacted iron oxide (Cubic) is generated or the product becomes amorphous, and at 1000 C or higher, 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 Ferric chloride 219 g CFe01 ・6M Olo,
81 mol) and 14 g of barium chloride (BaC4, 0,0
67 mol) was dissolved in ethylene glycol 11, and a solution of 40 g (1.0 mol) of sodium hydroxide dissolved in propylene glycol 11 was added thereto.
Stir with rpri+ for 40 minutes, charge the generated slurry into an autoclave, and treat at 230C for 3 hours while stirring with the stirrer attached to the autoclave.The generated precipitate is filtered with a suction filter, washed with hot water, and treated with alcohol. After that, it was vacuum dried.

The obtained precipitate was immersed in an aqueous solution containing 0.3% by weight of water glass for 40 minutes, separated into solid and liquid, precipitated and dried, and then heated in a Matsufuru furnace maintained at soot:' for 1 hour.

The chemical composition of the thus obtained product was determined by fluorescent Xa analysis, the particle state by transmission electron microscopy (hereinafter referred to as TEM), the specific surface area by BET method, and the identification by X-ray diffraction. The ratio is 12.1, the particle size is 0.06 to 0.09 μm by TEM observation, and the specific surface area is 47.3.
It was a single phase of sharp hexagonal barium hexaferrite with a weight of 7 g, and was suitable for magnetic recording.

Example 2 A ferrite product was manufactured in the same manner as in Example 1, except that the hydrothermal treatment in the autoclave was performed at 170 C for 5 hours and the heat treatment in the Matsufuru furnace was changed to C + O'C for 1 hour. Molar ratio is 12.05, particle size is 0.07-0.08 μm, specific surface area: 49.1 m, 7 g
It was hexagonal barium hexaferrite.

Comparative Example The same process as in Example 1 was carried out except that the hydrothermal treatment in an autoclave was changed to 2600°C, and the particle size was 0.1.
It was coarse and had a specific surface area of 31.2 m/g.

〔Effect of the invention〕

Hexagonal barium hexaferrite having an average particle size of about 0.07 to 0.08 μm can be efficiently produced.

Procedural amendment September 10, 1986

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. are mixed and stirred to generate. A first step of charging the slurry into an autoclave and treating it at 120 to 250°C, separating, washing and drying the obtained precipitate, and immersing the product of the first step in an aqueous solution of silicon salt or aluminum salt. A method for producing barium ferrite fine particles for magnetic recording, comprising a second step of surface treatment and then heat treatment at 600 to 1000°C.