JPH0251204A - Production of plate-like barium ferrite minute powder - Google Patents

Abstract

PURPOSE:To have fine and uniform grain diameter and obtain a useful hexagonal plate-like barium ferrite fine powder superior in diffusion as a magnetic powder for a vertical magnetic recording medium by holding magnetite substituted by at least Ba for a portion of Fe at specific temperature in a high boiling point organic solvent. CONSTITUTION:Magnetite in which a portion of Fe is substituted by at least Ba can be produced by an arbitrary method, but for example, iron (II) compound and barium compound, namely, alkali is added to solution in which Co, Mn, Ti and other base metal compounds are dissolved in an organic solvent together with these at room temperature and pressure to produce a suspension of alkaline iron hydroxide (II) and an oxygen containing gas is introduced at a specific temperature in a reaction liquid to preferably oxidize. Thereby, a plate-like barium ferrite fine powder can be produced by holding the reaction liquid at a temperature of 180-280 deg.C as it is. Further, when the magnetite is produced, pH of the reaction liquid is preferably set at 10-13.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing fine barium ferrite powder in the form of a plate, and in particular to a method for producing fine barium ferrite powder in the form of a hexagonal plate, which is used as a magnetic powder for perpendicular magnetic recording media capable of high-density recording. The present invention relates to a method for producing fine ferrite powder.

(Prior Art) Recently, perpendicular magnetic recording media capable of high-density recording have attracted attention, and methods for producing magnetic powder for the magnetic recording media include (a) an alkaline aqueous solution containing Ba ions and ferrous ions; A method of adding a predetermined amount of a predetermined titanium compound and fatty acid to and then hydrothermally treating it at 200 to 300°C (
(Japanese Unexamined Patent Publication No. 62-128102), (b) After heating and melting a mixture consisting of a glass-forming substance, iron oxide, and a barium compound at a high temperature, the mixture is rapidly cooled to produce an amorphous body, which is then heat-treated at a high temperature. A method of precipitating barium ferrite fine particles in an amorphous body and then removing the glass-forming substance by pickling (Japanese Patent Application Laid-open No. 155504/1983), (
c) A polyhydric alcohol solution in which iron, barium, etc. are dissolved and a polyhydric alcohol solution in which alkali hydroxide is dissolved are reacted to form a precipitate, and an alkali hydroxide is added to the precipitate, and water is added in an autoclave. A method has been proposed in which the resulting product is surface-grained with an aqueous solution of a silicon salt or aluminum salt and then heat-geographiced (Japanese Patent Laid-Open Publication No. 247505/1982).

(Problem to be Solved by the Invention) However, with the method (a), it is difficult to obtain fine barium ferrite with uniform grain size, and there are many grains that cannot be called hexagonal plate crystals, which are suitable for perpendicular magnetic recording media. There is a problem in that it is difficult to use as magnetic powder. In addition, in method (b), the conditions for making the melt amorphous are complicated, making it difficult to obtain fine and uniform barium ferrite powder, and the process of pickling the glass-forming material is also troublesome. However, if it is not sufficiently pickled, the remaining glass components will cause particles to aggregate, reducing dispersibility.
The problem is that the magnetic properties of the final product are significantly reduced. Furthermore, in method (c), FeCl, .6H20 is used as an iron compound as a starting material, and Fe20H
Hydrolysis proceeds until 3 is produced, but iron oxides are difficult to generate and do not decompose under normal pressure, so the next step requires hydrothermal synthesis under high pressure using an autoclave. Therefore, grain growth progresses too much during the hydrothermal synthesis stage, making it difficult to obtain the fine particles necessary for a high-density recording medium, and furthermore, the cost increases, making it unsuitable for mass production.

Therefore, the present invention was made with the object of obtaining a hexagonal plate-shaped barium ferrite fine powder having a fine and uniform particle size, excellent dispersibility, and useful as a magnetic powder for perpendicular magnetic recording media.

(Means for Solving the Problems) The present invention provides Fe
The present invention provides a method for producing fine plate-shaped barium ferrite powder, which comprises maintaining magnetite in which at least a portion of the magnetite is substituted with Ba in a high-boiling organic solvent at a temperature of 180 to 280°C.

The magnetite in which a part of the Fe is replaced with at least Ba can be produced by any method, for example, by using iron (II).
) compounds and barium compounds, optionally together with C
An alkali is added to a solution of O, Mn, Ti, and other base metal compounds dissolved in an organic solvent at room temperature and pressure to form a suspension of alkaline iron (II) hydroxide. It is preferable to adopt a method of introducing an oxygen-containing gas at a temperature of 0.degree. C. for oxidation. This is because plate-shaped barium ferrite fine powder can be produced simply by maintaining this reaction solution at a temperature of 180 to 280°C.

By allowing Co, Mn, Ti, or other base metal compounds to coexist as a modification agent in the reaction system, plate-shaped barium ferrite fine particles having desired magnetic properties can be produced.

Note that even if Ba ions exist in the reaction solution, Ba(O
H) Since the solubility of 2 is high, no problems arise.

Further, when producing magnetite in which a part of Fe is replaced with Ba, it is preferable to set the pH of the reaction solution to 10 to 13.

The iron(II) compounds include FeSO4 and Fe
Cl□, etc., and barium salts such as BaC12,
Ba (No,) 2 and the like are suitable.

As the alkali, an aqueous solution such as NaOH1KOH is suitable.

As the high boiling point organic solvent, for example, glycols such as ethylene glycol, triethylene glycol, and propylene glycol, or any solvent having a boiling point of 180° C. or higher can be used.

Air is a typical example of the oxygen-containing gas, but oxygen may also be used.

(Function) An iron (II) compound and a barium compound are dissolved in a high boiling point organic solvent, and an alkali is added to the solution to adjust the pH to 10-10.
13, iron(II) hydroxide, (F e (OH)
z), resulting in the precipitation of At this time, barium hydroxide is also produced, but because of its high solubility, barium hydroxide does not precipitate and coexists in the form of ions. 70% of the resulting suspension
When the temperature is raised to ~120°C and an oxygen-containing gas such as air is blown into the magnetite, iron(II) hydroxide and barium hydroxide are oxidized, and a portion of Fe is replaced with Ba.
(B a ``F e '' (Fe 3 (F e ``O'')
-4) is generated. Add this reaction solution as it is to 180-28
When the temperature is raised to 0° C. and maintained, hexagonal plate-shaped microcrystalline barium ferrite Ba0.6 Fe 203 is precipitated.

The pH of the reaction system is set to 10 to 13 when the pH is 10.
If it is less than 13, barium hydroxide will precipitate, making it difficult to obtain homogeneous barium-substituted magnetite, and if it exceeds 13, iron hydroxide will dissolve, making it impossible to control the composition ratio and producing no magnetite.

In addition, when crystallizing hexagonal plate-shaped barium ferrite particles, the temperature is 180 to 280°C.
At less than
This is because, if the temperature exceeds 280° C., problems such as increased crystal growth and the need for various measures to be taken in terms of the safety of the device arise.

The barium ferrite produced by the above method has a hexagonal plate-like crystal structure, has fine particles with an average particle size of 0.08 μm or less, and has excellent dispersibility because the particles are individually independent. show.

(Example 1) FeCI□・nH2O 1 mol and BaClz as raw materials
・Weigh out 10 mol of 2HzOO, dissolve it in 000 ml of ethylene glycol I, put it into a three-way separable flask as a reaction tank, and adjust the pH with an aqueous Na○H solution.
12 to generate Fe(OH)2, the temperature of the reaction solution was raised to 70°C using a mantle heater, and air was blown into the reaction solution for 2 hours while stirring to oxidize the product. ;. The temperature was then raised to 190°C and held for approximately 6 hours.

The resulting precipitate was washed with water, filtered, and dried to obtain a brown ferromagnetic powder.

This product was found to be Ba0.5Fe203 by X-ray diffraction.
It was confirmed that the particles consisted only of phases, and as a result of TEM observation, it was confirmed that they were plate-shaped particles with good dispersibility and an average diameter of 0.05 μm. In addition, its magnetic properties are saturation magnetization 59
, Oe mu/g, coercive force (Hc) about 45
It was 00 Oersted.

(Example 2) FeC12・nH2O1 mol, BaCl2・2H20
0, 10mo1%Co (No3) 2・6H200,
085 mol, MnCl24H200,085 mol were weighed out and dissolved in 00 ml of ethylene glycol IO.
Using this solution, a part of Fe was replaced with C in the same manner as in Example 1.
A dark brown ferromagnetic barium ferrite powder substituted with o and Mn was obtained.

This GOl, Mn metamorphosed barium ferrite is Example 1
Similar to the above, fine particles have a hexagonal plate-like crystal structure with an average diameter of 0.05 μm, and a saturation magnetization of 54.5 emu/
g, and the coercive force (Hc) was about 990 oersted.

(Effects of the Invention) As is clear from the above description, according to the present invention, hexagonal plate-shaped barium ferrite fine particles having an average particle diameter of 0.08 μm or less and a hexagonal plate-shaped crystal structure and excellent dispersibility. A powder can be obtained.

Furthermore, the method of the present invention is very advantageous both industrially and economically since the reaction can be carried out at normal pressure without using an autoclave and at the same time, the reaction can be carried out at a high concentration.

Claims (4)

[Claims] (1) A method for producing plate-shaped barium ferrite fine powder, which comprises maintaining magnetite in which at least a portion of Fe is replaced with Ba in a high-boiling point organic solvent at a temperature of 180 to 280°C. (2) By adding an alkali to a solution prepared by dissolving an iron (II) compound and a barium compound in a high-boiling organic solvent to generate a hydroxide, and then introducing an oxygen-containing gas into the reaction solution. 2. The method for producing plate-shaped barium ferrite fine powder according to claim 1, wherein magnetite in which part of Fe is replaced with Ba is produced, and the reaction solution is maintained at a temperature range of 180 to 280°C. (3) After adding an alkali to a solution prepared by dissolving an iron (II) compound, a barium compound, a cobalt compound, and a manganese compound in a high-boiling organic solvent to generate a hydroxide,
By introducing an oxygen-containing gas into the reaction solution, some of the Fe becomes Ba.
, Co and Mn-substituted magnetite is produced, and the reaction solution is maintained in the temperature range. (4) When generating the hydroxide, the pH of the reaction solution
4. The method for producing a plate-shaped barium ferrite fine powder according to claim 2 or 3, wherein the barium ferrite powder has a value of 10 to 13.