JPS624805A - Production of fine barium ferrite powder - Google Patents

Abstract

PURPOSE:To obtain fine barium ferrite powder having a uniform and small particle size and a high plate ratio by hydrothermally treating a slurry obtd. by mixing an aqueous iron (III) salt soln. with an aqueous barium hydroxide soln., separating the resulting product by filtration and washing it. CONSTITUTION:An aqueous soln. of iron (III) chloride or nitrate as one of starting materials is mixed with an aqueous soln. of barium hydroxide as the other to produce a slurry by precipitation. This slurry is hydrothermally treated in an autoclave and the resulting product is separated by filtration, washed and dried to obtain fine barium ferrite powder having a hexagonal platelike shape. The fine powder obtd. by this method has high crystallizability and superior magnetic characteristics.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing hexagonal plate-shaped barium ferrite fine powder, but is not particularly limited to the following:
The present invention relates to a method for producing ultrafine magnetic powder particles by hydrothermal treatment suitable for, for example, magnetic powder for perpendicular magnetic recording.

[Prior Art] The magnetic powder applied to perpendicular magnetic recording media is fine particles that are sized to a constant particle size of 0.5 μm or less in order to form a single magnetic domain, and that are separated one by one and have a beautiful hexagonal plate shape. It is important that

A hydrothermal treatment method is known as one of the methods for producing fine barium ferrite powder. This involves mixing a mixed aqueous solution of salts such as barium nitrate and iron (III) nitrate with a strong alkaline aqueous solution such as sodium hydroxide to obtain an amorphous precipitated slurry.
This is a method in which the slurry is hydrothermally treated at 150 to 300°C to directly form barium ferrite crystal grain precipitates having a crystal structure of 13 a Fe , , O, in the solution.

[Problems to be Solved by the Invention] However, in the conventional method as described above, - although individual fine particles can be obtained, the particle size of the barium ferrite Ha powder produced when carried out is non-uniform. Therefore, controlling the synthesis conditions is extremely complicated. Furthermore, under conditions that would satisfy the magnetic properties required for a perpendicular magnetic recording medium, the grain size would become too large and the plate ratio would deteriorate; There was a drawback that the magnetic properties deteriorated under conditions that could be satisfied.In addition, the above method required a large amount of strong alkaline aqueous solution (sodium hydroxide aqueous solution, etc.), which increased production costs. It also has the disadvantage of complicating the manufacturing process.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to produce barium ferrite fine powder that has uniform particle size, is sufficiently small, has a good plate-like ratio, and has little deterioration in magnetic properties. The goal is to provide a method that can be used.

[Means for Solving the Problems] The present invention, which can achieve the above objects, mixes an aqueous solution containing iron(III) chloride or nitrate and an aqueous solution containing barium hydroxide to form a non-containing solution. This is a manufacturing method in which a precipitated slurry of crystalline ferrite is obtained, the slurry is hydrothermally treated at 200 to 330°C, and the product is filtered and washed with water to obtain hexagonal plate-shaped barium ferrite fine powder.

First, the starting material is an aqueous solution containing iron (I[) chloride or nitrate. Here, iron is also aluminum,
It may also contain chromium, indium, titanium, cobalt, nickel, zinc, vanadium, etc. In particular, the reason why such an aqueous solution is used as a starting material is that metal salts other than those mentioned above are unsuitable because they exhibit poor solubility in water or are expensive.

In the present invention, an aqueous solution containing barium hydroxide is mixed with such an aqueous solution. This is precisely the major feature of the present invention. The present invention utilizes the strong alkalinity of barium hydroxide to synthesize ferrite without particularly using an alkaline aqueous solution such as sodium hydroxide.

By the way, barium ferrite, like strontium ferrite, has a magnetoblanbite crystal structure, has similar lattice constants and magnetism, and is said to exhibit almost the same behavior in both cases regarding the production of ferrite. Therefore, in the present invention, an aqueous solution containing barium hydroxide means that it may also contain strontium, and thereby it is also possible to change the magnetic properties.

The amount of barium hydroxide mixed here is suitably about 1.6 to 6.1 times the molar amount of iron(III) chloride or nitrate.

α-Fe, O when the molar amount is less than 1.6 times.

This is because a different phase will occur, and if the amount is more than 6.1 times, the obtained particles will be finer, which is preferable, but if it exceeds 6.1 times, the atomization effect will be small and it will be uneconomical.

As described above, by mixing an aqueous solution containing iron(III) chloride or nitrate with an aqueous solution containing barium hydroxide, a precipitated slurry of amorphous barium ferrite can be obtained. This precipitated slurry is hydrothermally treated in a subsequent step. It is sufficient to carry out the hydrothermal treatment at about 200 to 330°C for several hours. If the temperature is below 200°C, the crystallinity will be insufficient and the particle shape will not only become almost amorphous, but also the post-process filtration and washing will be very complicated and unsuitable.On the other hand, if it exceeds 330°C, the particle size will increase. This is because it is too high and also unsuitable for synthesis as it involves handling high temperatures and pressures.

This hydrothermal treatment crystallizes the amorphous barium ferrite precursor. Thereafter, the magnetic fine powder may be separated by filtering, washing with water, and drying the slurry.

[Operation] By mixing an aqueous solution containing iron (III) chloride or nitrate as a starting material and an aqueous solution containing barium hydroxide, a precipitation reaction can be carried out without using a strong alkaline solution such as sodium hydroxide. occurs, and a precipitated slurry containing amorphous barium ferrite is obtained. This is because barium hydroxide itself exhibits strong alkalinity.

For example, the reaction when using iron (III) chloride is thought to be represented by the following formula.

19Ba (OH)z +12FeCI*→18B
aCIt+BaFe+z○,.

+19H20 The barium ferrite in the precipitated slurry thus obtained is an amorphous powder that can also be called a precursor.

Thereafter, when hydrothermal treatment is performed, the amorphous barium ferrite precursor is crystallized and transformed into barium ferrite crystal powder exhibiting a beautiful hexagonal plate shape. The obtained powder is fine and has good dispersibility, and is particularly useful as a fine powder for perpendicular magnetic recording.

Next, examples based on the method of the present invention and comparative examples based on the prior art will be described.

[Example 1] Iron chloride (F eCI3' 6 Hz, O) 32.
An aqueous solution of 44g dissolved in pure water and barium hydroxide (B
a (OH)z '8Hz 0)63. Log to 80℃
A reddish-brown precipitate slurry was obtained by mixing with an aqueous solution dissolved in pure water heated to .

Next, this precipitated slurry was put into an autoclave and heated to 300
After hydrothermal treatment at ℃ for 5 hours, the mixture was filtered, washed with water, and dried to obtain a fine powder. The barium ferrite fine powder thus obtained was a hexagonal plate-shaped powder with an average particle size of 0.5 μm and good dispersibility. Vibrating sample magnetometer (VS
In the measurement by M), the saturation magnetization σs ”45.19e
mu/g + coercive force H, -1350 Oersteds.

[Example 2] 200.70 g of iron chloride (FeC13・6Hz ○),
Chloride': Jba) Lt (CoC1g ・6Hz O)
3.02g and titanium chloride (TiC14) 2.43g
is dissolved in pure water and barium hydroxide (Ba
(OH) 2 ・8 Hz O) 403°81
A reddish-brown precipitate slurry was obtained by mixing with an aqueous solution prepared by dissolving g in pure water heated to 80°C.

Next, this precipitated slurry was put into an autoclave and heated to 300
After hydrothermal treatment at ℃ for 4 hours, it was filtered, washed with water, and dried. This made it possible to obtain fine barium ferrite powder containing titanium and cobalt as a solid solution. This barium ferrite fine powder has an average particle size of 0.25μ as shown in Figure 1.
The powder was in the shape of a hexagonal plate of m and had good dispersibility.

[Comparative example] 200.70 g of iron chloride (FeC13-6H,0), 3.02 g of cobalt chloride (CoC1□ 6Hzo), 2.43 g of titanium chloride (TiC1a), and barium chloride (
An aqueous solution of 31.27 g of BaC1z 2Ht 0) dissolved in pure water and 10% of sodium hydroxide (NaOH)
A reddish-brown precipitate slurry was obtained by mixing an aqueous solution in which 2.4 g was dissolved in pure water.

Thereafter, a barium ferrite powder was obtained by hydrothermal treatment in the same manner as in Example 2. As shown in FIG. 2, this powder had an average particle size of 1 μm or more and a large particle size distribution.

[Effects of the Invention] According to the present invention, barium hydroxide is used as a raw material for barium without using an alkaline aqueous solution such as sodium hydroxide, and an amorphous precipitation reaction is performed using the alkalinity of barium hydroxide. Since sodium hydroxide and the like are not required, it is possible not only to reduce the cost but also to simplify the manufacturing process.

In addition, in the present invention, it is easy to control the synthesis conditions, and the powder obtained after hydrothermal treatment is extremely fine and has good crystallinity, making it possible to synthesize fine barium ferrite powder with excellent magnetic properties. It has a positive effect.

The barium ferrite fine powder obtained in this way is
For example, it is extremely effective as a magnetic powder for perpendicular magnetic recording, and is also useful as a raw material powder for magnets.

[Brief explanation of the drawing]

FIG. 1 is an electron micrograph showing an example of barium ferrite fine powder obtained by the method of the present invention, and FIG. 2 is an electron micrograph showing an example of barium ferrite a powder obtained by the conventional technique. Patent Applicant Fuji Electrochemical Co., Ltd. Representative Minoru Shigeru Preface to the drawing (no changes to the content) Figure 1 0.3pm Figure 2 0.3pm October 21, 1985 Patent Application No. 1985 142309 No. 2, Name of the invention Method for manufacturing fine barium ferrite powder 3, Relationship with the case of the person making the amendment Patent applicant address 5-36-11 Shinbashi, Minato-ku, Tokyo Name Fuji Denki Kagaku Co., Ltd. 4 Agent address 3rd floor, Kikuya 1st Building, 5-12-4 Shinbashi, Minato-ku, Tokyo 105 Phone number 433-37996, "Brief explanation of drawings" column of the specification subject to amendment and contents of drawing amendment fil Specification No. 11 In lines 2 to 6 of the page, it says, ``Figure 1 is... (omitted)... a photograph.''
Correct it like a written sentence. ``Figure 1 is an explanatory diagram illustrating an electron microscope photograph showing an example of barium ferrite fine powder obtained by the method of the present invention, and Figure 2 is an electron microscope photograph showing an example of barium ferrite fine powder obtained by the conventional technique. This is an explanatory diagram based on a photograph.j (2) The drawings, Figures 1 and 2, are corrected as shown in the attached sheet.

Claims (1)

[Claims] 1. A precipitated slurry of amorphous ferrite is obtained by mixing an aqueous solution containing iron (III) chloride or nitrate with an aqueous solution containing barium hydroxide, and the slurry is
1. A method for producing barium ferrite fine powder, which comprises hydrothermally treating the product at °C and then filtering and washing the product to obtain hexagonal plate-shaped barium ferrite fine powder. 2. The manufacturing method according to claim 1, wherein the amount of barium hydroxide mixed is 1.6 to 6.1 times the molar amount of iron(III) chloride or nitrate.