JPH04149031A - Needle-like barium ferrite magnetic powder and its production - Google Patents

Abstract

PURPOSE:To save sintering and to improve saturation magnetization by coating a needle-like iron oxyhydroxide or iron oxide with BaCO3 by specified method, and further coating the needle-like powder with (hydr)oxide of Si and/or Al, and then filtering and calcining. CONSTITUTION:(A) 5-7g/l of needle-like iron oxyhydroxide or iron oxide having the average major axial length of 0.1-1.0mum and the average minor axial length, of 0.01-0.1mum and (B) water-soluble barium compd. are dispersed in (C) water, to which (D) alkali hydroxide is added to obtain a water-dispersion slurry of >=pH8. Then, to this slurry, (E) carbonic acid gas and/or carbonate are added to control the pH to 8-12 and to coat the surface of the (A) component with BaCO3. Then the surface is further coated with (F) (hydr)oxide of Si and/or Al, and the slurry is filtered, washed with water, dried and calcined at 700-1000 deg.C to obtain the magnetic powder of this purpose.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for producing acicular barium ferrite magnetic powder for use in coated media of perpendicular magnetic recording for high-density magnetic recording, and more particularly, to a method for producing acicular barium ferrite magnetic powder. , relates to a method for producing barium ferrite magnetic powder with extremely little sintering and high saturation magnetization.

[Prior Art] Conventionally, fried powder is known to be plate-shaped and needle-shaped. The manufacturing method for plate-shaped items is as follows:
For example, various methods are known, such as a coprecipitation method, a glass crystallization method, and a hydrothermal synthesis method. In addition, as a method for producing needle-shaped objects, for example, a method of coating needle-shaped iron oxyhydroxide with barium carbonate or the like and then firing it (Japanese Patent Application Laid-Open No. 61-1046
(see Publication No. 02) is known.

[Problem to be solved by the invention]

However, it is difficult to maintain the needle-like shape of the raw material iron compound during firing, and if the firing temperature is low, the needle-like shape can be maintained, but the saturation magnetization will be low, and if the firing temperature is high, Although the saturation magnetization can be increased, there is a problem in that the needle shape cannot be maintained due to sintering. There is also a method of lowering the firing temperature and increasing the firing time, but sintering still progresses over time, and this is not a preferable method in terms of production efficiency.

Furthermore, in the manufacturing method described in JP-A-61-104602, iron oxyhydroxide is coated with barium carbonate by reacting barium chloride with sodium bicarbonate or soda carbonate. However, it was not possible to coat iron oxohydroxide with barium carbonate as sufficiently fine colloidal particles, and the resulting barium ferrite magnetic powder had insufficient magnetic properties. This is because the barium carbonate produced is not sufficiently fine and a portion of the barium is eluted.

Therefore, an object of the present invention is to solve the above-mentioned problems and to produce halium ferrite l-[fried powder] which is acicular, unsintered, and has dramatically improved saturation magnetization compared to conventional ones. Our goal is to provide the following.

[Failure to solve the problem]

To achieve the above object (as a result of intensive studies, the present inventors have found that when producing acicular barium ferrite magnetic powder by firing acicular iron oxyhydroxide or iron oxide coated with a barium compound, - By coating the surface of the iron oxyhydroxide or iron oxide particles with the oxide and/or hydroxide of at least one element of Si and AI, sintering can be reduced and saturation magnetization can be reduced. It has been found that acicular barium ferrite magnetic powder with improved properties can be obtained.

In addition, when coating acicular iron oxyhydroxide or iron oxide with a barium compound, the present inventors applied a slurry of acicular iron oxyhydroxide or iron oxide containing a water-soluble barium compound such as barium chloride. , add alkali hydroxide to adjust the pH to 8.
By adding carbon dioxide gas or a carbonate source to this slurry and precipitating barium carbonate in the pH range of 8 to 12, fine barium carbonate colloidal particles can be generated, and the oxyhydroxide It has been found that iron or iron oxide can be uniformly coated with barium carbonate, and acicular barium ferrite magnetic powder with excellent magnetic properties can be obtained.

The present invention was made based on the above-mentioned findings, and is based on the above-mentioned findings. Add gas and/or carbonate to pH 8~
As step 12, the surface of the iron oxyhydroxide or iron oxide is coated with barium carbonate, and then the iron oxyhydroxide or iron oxide coated with barium carbonate is treated with an oxide of at least one element of Si and Al and/or After further coating with hydroxide, then filtration, water washing and drying, 700-1000
The present invention provides a method for producing acicular barium ferrite magnetic powder, which is characterized by firing at ℃.

Hereinafter, the method for producing the barium ferrite magnetic powder of the present invention will be described in detail.

The acicular iron oxyhydroxide and iron oxide used in the present invention include α-Fe00)1, β-Fe00H, 7-Fe
Any of OOI (, α-FezO・1, and r-FezO) may be used, but in order to obtain good acicular barium ferrite, it is preferable that there is no branching and that the particle size distribution is uniform. It is preferable to use a material having a long axis length of 0.1 to 1.0 μm and an average short axis length of 0.01 to 0.1 μm.

To carry out the method for producing barium ferrite magnetic powder of the present invention, first, the iron oxyhydroxide or iron oxide (hereinafter referred to as raw material iron compound) is coated with barium carbonate as follows.

A raw material iron compound and a water-soluble barium compound such as barium chloride are added to water to prepare a water-dispersed slurry of the raw material iron compound. At this time, the slurry concentration is 5 to 7 g of raw material iron compound.
It is preferable to set it to about /l.

Next, alkali hydroxide is added to the slurry to make the P of the slurry 8 or higher, and then carbon dioxide gas and/or carbonate is added to precipitate barium carbonate in a pH range of 8 to 12. Obtain a raw material iron compound coated with barium.That is, for example, when barium chloride is used as a water-soluble barium compound, barium chloride in the slurry becomes barium hydroxide by adding alkali hydroxide, but p
Above H8, the solubility of barium hydroxide in water is Ba
Since it is 3.84 g/100 g (20° C.) in terms of O, barium hydroxide will be dissolved if the concentration is kept below the solubility. When a carbonate source is added in this state, fine barium carbonate quickly precipitates and adheres to the raw material iron compound. At this time, the pH of the slurry should be maintained in the range of 8 to 12 because if the pH is below 7, barium carbonate will begin to dissolve, and if the pH is above 12, fine barium carbonate will not be obtained in the slurry. It is from.

The alkali hydroxide is preferably sodium hydroxide, and the carbonate is preferably sodium carbonate, sodium hydrogen carbonate, etc. Next, the raw iron compound coated with barium carbonate as described above is , further coated with an oxide and/or hydroxide of at least one element of Si and AI as follows.

Raw material iron compound coated with barium carbonate, water glass,
By adding Si compounds such as sodium silicate and/or Al compounds such as sodium aluminate and aluminum chloride, Si,
Deposit Al oxide and/or hydroxide.

At this time, when using an alkaline material such as water glass or sodium silicate as Si and sodium aluminate as Al, add hydrochloric acid or carbon dioxide, etc., or use an acidic material such as aluminum chloride. When using, by adding alkali, the pH of each
is preferably adjusted to 8-12.

The amount of Si, AI oxide and/or hydroxide deposited is
Si is preferably 0.1 to 2.0 mol% with respect to Fe.
, more preferably 0.5 to 1.0 mol%, Al preferably 0.1 to 4.0 mol%, more preferably 0.5 to 2
．． It is 0 mol%.

Next, the slurry of the raw iron compound coated with the oxide and/or hydroxide of Si and AI as described above is filtered, washed with water, and dried to obtain a powder.

Thereafter, the powder described in "2" is fired at 700 to 1000 DEG C. to obtain acicular barium ferrite magnetic powder according to the present invention.

When the firing temperature is as low as 700°C, sufficient saturation magnetization can be obtained by firing for a long time such as 100 hours. Further, when firing is performed at a high temperature such as 1000° C., sufficient saturation magnetization can be obtained in several minutes to several tens of minutes. More preferably, 5 hours at so o'c or 900'
The firing conditions were as follows: C for 1 hour. That is, firing temperature 8
00 to 900" C1 firing time of 1 to 5 hours can be recommended as a realistic range, but in the present invention, Si or A
By addition of 1 oxide and/or hydroxide, 900~
Barium ferrite magnetic powder with little sintering can be obtained even at 1000°C.

The barium ferrite magnetic powder according to the present invention obtained in this way has a length of 0.1 to 1.0 μm and a width of 0°01 to 0.
．． It is an acicular powder of 1 am, with very little sintering and high saturation magnetization.

In addition, in the present invention, boron oxide (B2o
A flux such as Bz) or bismuth oxide (BizOs) may be added.Bz(h has the effect of improving saturation magnetization at temperatures above 750°C, but also promotes sintering. In other words, it has the effect of improving the saturation magnetization near the melting point of Bi and O3.When these fluxes are added at about 1% by weight to barium ferrite, sintering hardly progresses.Therefore, when adding fluxes, , the preferable addition amount is 1 to 5% by weight.

Further, in the present invention, Co and T1 can be added as a coercive force control law, and these additions may be performed at the same time as the barium compound deposition or before or after the deposition.

[Example] The present invention will be explained in more detail by referring to Examples and Comparative Examples below.

Examples 1 to 4 Acicular goethite (α-FeOOf+) 66.6 g
and ° Barium chloride (BaC1z4HzO) 16.8
g to deionized water to make a 10f dispersion slurry,
While stirring this, add sodium hydroxide (NaOH)
Add 11 g dissolved in deionized water to reduce the slurry's p.
Set H to 12.

Carbon dioxide gas is passed through this at a rate of 3j2/min for 8 minutes to adjust the pH of the slurry to 10.5. Water glass was added as Si in the proportions shown in Table 1 below, and the mixture was stirred well. The obtained slurry is filtered, washed with water, and dried to obtain a solid product. The obtained solid material was fired in an air atmosphere at 9 o'clock for 5 hours to obtain acicular halium ferrite! - [Fried flour was obtained respectively.

All of the obtained barium ferrite magnetic powders were confirmed to be magnetobrambite type by X-ray diffraction spectra. Furthermore, for each of these barium ferrite magnetic powders, the magnetic properties were measured using a vibrating sample magnetometer, and the sintering state was measured using a transmission electron microscope. The results are shown in Table 1 below.

Examples 5-B In Examples 1-4, instead of adding water glass,
Acicular barium ferrite magnetic powders were obtained in the same manner as in Examples 1 to 4 by adding aluminum chloride (AICI+.68.0) dissolved in water as AI in the proportions shown in Table 1 below.

All of the barium ferrite magnetic powders obtained were confirmed to be magnetoblanbite type by X-ray diffraction spectra. Further, the magnetic properties and sintered state of each of these halium ferrite I fried powders were measured in the same manner as in Examples 1 to 4. The results are shown in Table 1 below.

Example 9 In Example 2, except that after adding water glass, aluminum chloride (AlCl2.6H20) dissolved in water was further added as Al in the proportions shown in Table 1 below.
Acicular barium ferrite magnetic powder was obtained in the same manner as in Example 2.

The magnetic properties and sintered state of the obtained barium ferrite magnetic powder were measured in the same manner as in Examples 1 to 4. The results are shown in Table 1 below.

Example 10 Acicular goethite (α-Fe00H) 55.5 g,
Barium chloride (BaC1z・2)1zO) 16.8
g, cobalt chloride (CoC12・2820) 10.4
g and 11.9 g of titanium chloride (TiCl-) were added to deionized water to make a 10ffi dispersion slurry, and while stirring, 26 g of sodium hydroxide (NaOH) dissolved in deionized water was added to adjust the pH of the slurry. Set to 12. Add sodium carbonate (Na2C(h) 14.5
7 g dissolved in deionized water is added to bring the pH of the slurry to 10.5. Water glass was added as Si in the proportions shown in Table 1 below, and the mixture was stirred well. The obtained slurry is filtered, washed with water, and dried to obtain a solid product. The obtained solid material was fired at 1000'C in an air atmosphere for 1 hour to obtain acicular barium ferrite magnetic powder.

The magnetic properties and sintered state of the obtained barium ferrite magnetic powder were measured in the same manner as in Examples 1 to 4. The results are shown in Table 1 below.

Comparative Example 1 In Examples 1 to 4, except that water glass was not added,
Acicular barium ferrite magnetic powder was obtained in the same manner as in Examples 1 to 4.

The magnetic properties and sintered state of the obtained barium ferrite magnetic powder were measured in the same manner as in Examples 1 to 4. The results are shown in Table 1 below.

Comparative Example 2 Acicular goethite (α-Fe00H) 66.6 g and barium chloride (BaC1z・2LO) 16.8 g
was added to deionized water to make a 1ON dispersion slurry. Add to this sodium carbonate (NazCO:+) 14.57
Dissolve g in deionized water and add. Add a water glass to this
Drain, add in the proportions shown in Table 1 below, and stir well.

The obtained slurry is filtered, washed with water, and dried to obtain a solid product.

The obtained solid product was fired at 900° C. for 5 hours in an air atmosphere to obtain acicular barium ferrite magnetic powder.

The magnetic properties and sintered state of the obtained barium ferrite magnetic powder were measured in the same manner as in Examples 1 to 4. The results are shown in Table 1 below.

Comparative Example 3 In Comparative Example 2, instead of adding sodium carbonate (Na, C03), sodium hydrogen carbonate (NaHCO3) was added.
Acicular barium ferrite magnetic powder was obtained in the same manner as in Comparative Example 2 except that 11.55 g of barium ferrite powder was added.

The magnetic properties and sintered state of the obtained barium ferrite magnetic powder were measured in the same manner as in Examples 1 to 4. The results are shown in Table 1 below.

[Effects of the Invention] According to the method for producing halium ferrite fried powder of the present invention, barium ferrite magnetic powder is acicular, has extremely little sintering, and has dramatically improved saturation magnetization compared to conventional powders. Obtainable.

Patent applicant: Kanto Denka Kogyo Co., Ltd.

Claims (1)

[Claims] Carbon dioxide gas and/or carbonate is added to an aqueous dispersion slurry containing acicular iron oxyhydroxide or iron oxide, a water-soluble barium compound, and an alkali hydroxide and has a pH of 8 or higher to adjust the pH.
As steps 8 to 12, the surface of the iron oxyhydroxide or iron oxide is coated with barium carbonate, and then the iron oxyhydroxide or iron oxide coated with barium carbonate is coated with an oxide of at least one element of Si and Al. / or further coated with hydroxide, then filtered, washed with water, dried, then 700-10
A method for producing acicular barium ferrite magnetic powder characterized by firing at 00°C.