JPS63310729A - Production of hexagonal magnetoplumbite type ferrite magnetic powder - Google Patents

Abstract

PURPOSE:To obtain the title fine ferrite magnetic powder having a sharp particle diameter distribution and appropriate for a magnetic recording medium for high-density recording by using hematite having a specified specific surface as the raw iron material for producing ferrite magnetic powder. CONSTITUTION:(A) Hematite having 50-250m<2>/g specific surface, (B) >=1 kind among the compds. of Ba, Sr, and Pb (e.g., barium hydroxide), (C) >=1 kind among the compds. of Ni, Co, Zn, and Cu, and (D) an Sn compd. are prepared as the starting materials. An alkali hydroxide is added to an aq. soln. contg. the starting materials so that the alkali hydroxide concn. in the soln. after mixing is controlled to >=1mol./l, and a precipitate is formed. The slurry contg. the precipitate is hydrothermally treated at 130-300 deg.C, then a flux is mixed into the formed precipitate, the precipitate is calcined at 700-950 deg.C, the calcined material is washed, and hexagonal magneto-plumbite type ferrite magnetic powder is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing hexagonal magneto-1-lambite ferrite magnetic powder.

More specifically, the present invention is suitable for use in magnetic recording media for high-density recording, and has a specific surface area of 20 to 70 d/CJ,
The present invention relates to a method for producing magnetoplumbite-type ferrite magnetic powder having a coercive force of 200 to 15,000 e, fine particles, and a sharp particle size distribution.

In recent years, with the demand for higher density magnetic recording, development of perpendicular magnetic recording systems using ferrite magnetic powder as a magnetic recording medium has been progressing.

As the ferrite magnetic powder used in the perpendicular magnetic recording system, it is desired that the coercive force is an appropriate value (200 to 15,000 e), the particles are fine, and the particle size distribution is sharp.

(Prior art and its problems) Conventionally, various methods have been known for producing ferrite magnetic powder, such as coprecipitation, glass crystallization, and hydrothermal synthesis. Special Public Service 1986-15
Regarding the hydrothermal synthesis method, see Japanese Patent Application Laid-open No. 574, for example.
9-175707, JP 60-12973, JP 60-15576, JP 60-1
This is proposed in Publication No. 37002 and the like.

In the above synthesis method, 'i' is used as a substituent element, but Ti is not necessarily effective in making particles finer and sharpening the particle size distribution.

On the other hand, in JP-A-60-122726, JP-A-61-219720, etc., Ti is used as a substitution element.
Instead, attempts are being made to miniaturize the metal by adding Sn. However, since Fe3O4, iron oxyhydroxide, iron hydroxide, etc. are used as iron raw materials, valence change of Fe and dehydration reaction occur during ferrite formation by hydrothermal treatment or heat treatment, so the particle size distribution is It wasn't always possible to make it sharp.

(Object of the Invention) The object of the present invention is to solve the above-mentioned problem and create a hexagonal magnetoplumbite-type ferrite magnetic material with fine particles and a sharp particle size distribution suitable for use in a magnetic recording medium for high-density recording. The purpose is to provide a method for producing powder.

(Means for Solving the Problems) As a result of intensive studies, the present inventors have found that as an iron raw material for producing ferrite magnetic powder,
It has been found that by using hematite of d/g, a hexagonal magnetoplumbite-type ferrite magnetic material with fine particles and a sharp particle size distribution can be obtained.

That is, the present invention uses starting materials with a specific surface performance of 50 to 2.
50rrr/g of hematite, at least one of Ba, Sr, and Pb compounds, and Ni and Co.

At least one of the compounds of zn, cuu"
- and an sn compound to an aqueous solution containing the starting material,
Alkali hydroxide is added to form a precipitate so that the alkali hydroxide concentration in the mixed solution is 1 mol/ρ or more, and the slurry containing the precipitate is hydrothermally treated at 130 to 300°C, and then the precipitate is formed. A flux was mixed with the precipitate, and the mixture was heated to 70%
The present invention relates to a method for producing hexagonal magnet 1 to brambite type ferrite magnetic powder, which is characterized by firing at 0 to 950°C and washing the fired product.

In the present invention, first, the specific surface area of the starting material is 50 to 2.
50d/g of hematite, at least one of Ba, Sr, and Pb compounds, Ni, and Co.

At least one of Zn and Cu compounds and a Sn compound are dissolved or suspended in water, and alkali hydroxide is added to form a precipitate.

If the specific surface roughness of hematite, which is a starting material, is smaller than 50 i/g, the particle size of the magnetic powder obtained becomes large;
If it is larger than 50rrr/g, the particle size distribution will be wide. Therefore, a recording medium using such magnetic powder is undesirable because the noise level becomes high and the recording density becomes low. The amount of hematite used is preferably 1 to 10% by weight.

If the concentration is less than 1% by weight, the amount of magnetoplumbite ferrite produced will be small and the crystallinity will be poor. Moreover, if it exceeds 10% by weight, the ferrite particles become large and the magnetic properties deteriorate, which is not preferable.

Compounds of Ba, Sr, and Pb include their nitrates,
At least one of the chlorides, hydroxides, etc. is used. The amount of these compounds used is at a concentration of 0.03
In order to obtain hexagonal particles with good crystallinity, it is desirable that the content be in the range of 0.50 mol/p.

As the compounds of Ni, Co, Zn, and Cu, at least one of their chlorides, nitrates, etc. is used.

As the Sn compound, tin chloride, tin nitrate, sodium stannate, etc. are used.

The addition amount of these substitution elements is preferably in the range of 0.1 to 25 gram atoms per molecule of hexagonal ferrite.If the addition amount is out of the above range, the coercive force may be too high or the axis of easy magnetization may change. This is not preferable because it may deviate from the C-axis.

As the alkali hydroxide, sodium hydroxide, potassium hydroxide, etc. are used. The amount of alkali hydroxide used is the alkali hydroxide in the solution after mixing the alkali hydroxide;
The amount is required so that the degree is 1 mol/l or more, and the range of 2 to 8 mol/l is preferable.

If the amount of alkali hydroxide is too small, the particles will become large or the particle size distribution will become wide. Further, it is not economical to increase the amount of alkali hydroxide excessively.

There is no particular restriction on the method of mixing the alkali hydroxide into the aqueous solution of the starting material, but for example, there are methods of directly adding the alkali hydroxide or adding an aqueous solution of the alkali hydroxide to the aqueous solution of the starting material. .

Furthermore, a small amount of water-soluble compounds such as Si and Ca, such as silicic acid, sodium silicate, calcium nitrate, and calcium chloride, can be added in advance to the aqueous solution of the starting material or the aqueous solution of alkali hydroxide. These additives are preferred for controlling particle shape.

Next, by hydrothermally treating the slurry containing the precipitate,
Fine crystals of hexagonal ferrite are formed and precipitated. The temperature of hydrothermal treatment is 130-300℃, preferably 140-2
The temperature is 80°C. If the temperature is too low, crystal formation will not be sufficient, and if the temperature is too high, the particle size of the final hexagonal ferrite powder will become large, which is undesirable.The hydrothermal treatment time is usually 0.5 to 20 hours. An autoclave is usually used for hydrothermal treatment.

Next, the fine crystal precipitate produced by the hydrothermal treatment is washed with water to remove stray alkaline components, and then a flux is mixed with the obtained precipitate. As the flux, at least one of sodium chloride, potassium chloride, barium chloride, strontium chloride, and sodium fluoride is used. The amount of flux used is 1 for the precipitate (dry basis).
0 to 180% by weight, preferably 30 to 120% by weight is suitable. If the amount of flux is too small, sintering of the particles will occur,
Also, even if the amount is too large, there is no advantage and it is not economical. There are no particular restrictions on the method of mixing the precipitate and the flux. For example, after adding the flux to the slurry of the precipitate and wet mixing, the slurry is dried. or after drying the precipitate,
A flux may be added and dry mixed.

Next, by firing the obtained mixture, the hexagonal ferrite is completely crystallized. Firing temperature is 70
The temperature is 0 to 950°C, preferably 800 to 930°C. If the temperature is too low, crystallization will not proceed and the saturation magnetization will become low.

Further, if the temperature is too high, the particles will become large or sintering will occur, which is not preferable.The firing time is preferably about 10 minutes to 30 hours. The firing atmosphere is not particularly limited, but -
・Air atmosphere is generally convenient.

By washing, filtering and drying the obtained baked product,
Hexagonal ferrite magnetic powder is obtained. The cleaning may be carried out by any method as long as impurities such as flux and excess barium in the fired product can be sufficiently removed. As the cleaning liquid, water, inorganic acids such as nitric acid and hydrochloric acid, and organic acids such as acetic acid and propionic acid can be used.

(Example) Example 1 In 1300 rrJ of deionized water, 1 hcobalt [Co
CN2.6H2010, 24 mol, stannic chloride [Sn
C'J)4] 0.24 mol and the specific surface G'tlO'zr? 1.56 mol/g of hematite was added and stirred vigorously. Separately, add barium hydroxide [Ba(O) 2.8) (20] 0.0 to 1300 mN of deionized water.
45 mol and 27 mol of caustic soda (NaOH) were dissolved, and both solutions were mixed to form a precipitate.

The resulting slurry containing the precipitate was placed in an autoclave;
Hydrothermal treatment was carried out at 145°C for 8 hours.The resulting precipitate was then thoroughly washed with water, filtered and dried, and added with Na as a flux at a weight ratio of 1:1 and BaCJ2.2H20. 1 was added in an amount of 100% by weight based on the precipitate and mixed. This mixture was fired at 860°C for 2 hours in an air atmosphere. The resulting fired product was thoroughly washed with water, filtered, and dried. Barium ferrite magnetic powder was obtained.

The obtained barium ferrite magnetic powder 2 was of the hexagonal magnetoplumbite type as a result of the X-ray powder diffraction spectrum.

Furthermore, Table 1 shows the results of measuring the magnetic properties of this barium ferrite magnetic powder using a vibrating sample magnetometer and the results of observing the particle shape using a transmission electron microscope.

Example 2 Nickel chloride [N i
A barium ferrite magnetic material (CJ2.6H20) was obtained in the same manner as in Example 1 except that 0.24 mol of CJ2.6H20 was used.

Table 1 shows the results of measuring the magnetic properties of this barium ferrite magnetic powder in the same manner as in Example 1 and observing the particle shape.

Comparative Example 1 Barium ferrite magnetic powder was obtained in the same manner as in Example 1 except that hematite with a specific surface area of 15 rrr/g was used instead of hematite with a specific surface area of 105 rrr/g in Example 1.

Table 1 shows the results of measuring the magnetic properties and observing the particle shape of this barium ferrite magnetic powder in the same manner as in Example 1.

Comparative Example 2 Instead of hematite having a specific surface Wt of 105 rrr/g in Example 1, a specific surface Wt of 92 rr? Barium ferrite magnetic powder was prepared in the same manner as in Example 1 except that goethite of 1:) was used.

Table 1 shows the results of measuring the magnetic properties of this barium ferrite magnetic powder in the same manner as in Example 1 and observing the particle shape.

Table 1

Claims (1)

[Claims] As starting materials, hematite with a specific surface area of 50 to 250 m^2/g, at least one of Ba, Sr, and Pb compounds, at least one of Ni, Co, Zn, and Cu compounds, and a Sn compound. Alkali hydroxide is added to the aqueous solution containing the starting materials so that the alkali hydroxide concentration in the solution after mixing is 1 mol/l or more to form a precipitate, and the slurry containing the precipitate is ~3
Hexagonal magnetoplumbite type ferrite magnetism characterized in that after hydrothermal treatment at 00°C, a flux is mixed with the generated precipitate, the mixture is fired at 700 to 950°C, and the obtained fired product is washed. How to make powder.