JPH02271503A - Magnetic alloy powder and its manufacture - Google Patents

Abstract

PURPOSE:To obtain an alloy magnetic powder whose grain-size distribution is uniform, which is branched little and whose oxidation-resistant property is excellent by a method wherein, in a magnetic alloy powder composed mainly of iron and cobalt, a BET specific surface area and an axial ratio are specified. CONSTITUTION:In an iron-cobalt alloy magnetic powder, a hydroxide is coprecipitated by using a ferric salt and a cobalt salt; this coprecipitate is treated by using an autoclave. Regarding an alloy magnetic powder which has been obtained by heating and reducing an obtained cobalt-contained alpha-iron oxyhydroxide, its saturation magnetization amount is large, it has a structure which is not branched, its grain size distribution is uniform, its axial ratio is 4.5 to 6.0 and its BET-method specific surface area is 25 to 35m<2>/g. Thereby, it is possible to obtain the alloy magnetic powder whose oxidation-resistant property has been improved.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to iron-cobalt alloy magnetic powder.

More specifically, it relates to improving its corrosion resistance.

[Conventional technology]

Alloy magnetic powder, especially iron-cobalt alloy powder.

Because it has a higher saturation magnetization than metallic iron magnetic powder, it can be used as an isomagnetic material to improve the performance of magnetic recording media.

Iron-cobalt alloy magnetic powder is generally produced by heating and reducing cobalt-containing α-iron oxyhydroxide powder. Cobalt-containing α-ferrous oxyhydroxide powder is usually produced by adding an alkaline bath solution to a bath solution of ferrous salt and cobalt salt to form a precipitate of cobalt-containing ferrous hydroxide;
It is obtained by blowing air into it and oxidizing it.

With the above method, cobalt-containing Mα-iron oxyhydroxide with a large axial ratio can be obtained, but the particle size distribution of one particle is poor;
It branches out and becomes soil particles. As a result, the alloy magnetic powder obtained by thermal reduction of cobalt-containing iron oxyhydroxide was
It has a large specific surface area and lacks oxidation resistance.

[Problem that the invention seeks to solve]

This invention solves the drawback that conventional magnetic alloy powders have a narrow particle size distribution that is branched, and thus has a uniform particle size distribution with less branching and excellent oxidation resistance. The purpose is to provide alloy magnetic powder.

[Friendly means of solving problems]

As a result of various studies conducted by the present inventors in order to solve the above-mentioned drawbacks, the following results were obtained: 7. When producing balt-containing α-iron oxyhydroxide powder, an aqueous solution containing trivalent iron ions and divalent cobalt ions was found. is reacted with the metal ion in an aqueous alkali hydroxide solution of an equivalent amount or more at a temperature of 30°C or less to produce cobalt-containing ferric hydroxide. A cobalt-containing α-iron oxyhydroxide powder with a uniform particle size distribution and no branching is obtained by hydrothermally reacting diiron in an autoclave, and an iron-cobalt alloy magnetic powder obtained by heating and reducing this powder. discovered that the oxidation resistance could be improved by using an alloy powder with a small specific surface area and a uniform particle size distribution, and came up with the present invention.In the present invention, trivalent iron ions and
When adding 6C of the aqueous alkaline hydroxide solution to the water bath containing cobalt ions, the degree of OfM is set to 30°C or higher.

The crystal growth of cobalt-containing ferric hydroxide is difficult to control, making it impossible to obtain cobalt-containing ferric hydroxide powder with a uniform particle size distribution.

Also, the temperature of the hydrothermal reaction in the autoclave is 120°C.
Preferably, the temperature is in the range of ~250°C. This temperature is 12
At temperatures below 0°C, it takes a long time to transform the cobalt-containing α-iron hydroxide, and at temperatures above -250°C, cobalt-containing α-iron oxides coexist and the particle shape collapses. Undesirable.

As the raw material salt for trivalent iron ions, aqueous ferric salts such as ferric chloride, ferric sulfate, and ferric nitrate can be used.

As the raw material salt for divalent cobalt ions, water-soluble cobalt salts such as cobalt chloride, cobalt sulfate, and cobalt nitrate may be used.

Thus obtained is a cobalt-containing α-iron oxyhydroxide powder with a uniform particle size distribution and no branching.

In order to prevent sintering and deformation during washing, filtration, and heating reduction after drying, it is preferable to coat the surface with an anti-sintering agent such as a silicon compound.

The α-iron oxyhydroxide containing cobalt and coated with an anti-sintering agent is reduced by heating at a temperature of 300° C. to 600° C. in a hydrogen stream. If the a degree is less than 300°C, it will take a long time for reduction, while if it is 600°C, the 1-alloy magnetic powder will sinter and lose its shape, which is not preferable.

Mol/l 1kft sodium hydroxide water bath solution 104
and 1 mol/1 concentration of sodium orthosilicate water fIjf
While stirring, carbon dioxide gas was blown into the mixed solution of the three liquids with fL1.31 to neutralize it until the pH became 8 or less.

A silicic acid sol was deposited on the cobalt-containing α-iron oxyhydroxide surface, washed with water, and dried.

Silicon compound-coated cobalt-containing α-hydroxide water 30-
60 moles of sodium hydroxide dissolved in water and 60 moles of sodium hydroxide
04 and mixed with salt water #[@salinity 10°C to obtain a brown precipitate. The mixture was then allowed to stand at room temperature for 24 hours, and then a portion of the supernatant was removed.

Place the remainder in an autoclave and heat at 180°C for 2 hours.
T! a. A hydrothermal reaction was performed. After the reaction, the yellow precipitate produced was washed with water, filtered, and dried to obtain cobalt-containing α-iron oxyhydroxide powder.

Next, a solution obtained by dispersing the iron hydroxide powder SOOG in 40 g of water and 45 g of air was added to the obtained cobalt-containing α-O medium.
Heat to 0°C and reduce to obtain iron-cobalt alloy powder with 88% strength.

The obtained magnetic powder has no branching and has a uniform particle size distribution.
The major axis diameter is 190 nm, the minor axis diameter is 35 nm, and the axial ratio is 5.
．． 4 has a specific surface area of 2Brl/11 by the BET method.

Example 2 In Example 1, 10 ferric nitrate was used instead of ferric chloride.
An iron-cobalt alloy magnetic powder was obtained in the same manner as in Example 1 except that 0.5 mole of cobalt nitrate was used instead of cobalt chloride.

The magnetic powder is unbranched, has a uniform particle size distribution, and has a long axis diameter of 17
5 nm, minor axis diameter is 35 nm, axial ratio is 5.0 and BE
The specific surface area determined by the T method was 27 ze/y.

implementation? IJ3 In Example 2, when the aqueous solution obtained by dissolving ferric nitrate and cobalt nitrate and the sodium hydroxide aqueous solution are mixed, J
! Iron-cobalt alloy magnetic powder was obtained in the same manner as in Example 2 except that the O liquid temperature was 25°C.

The magnetic powder is unbranched, has a uniform particle size distribution, and has a long axis i182.
nm, short axis diameter 35 runs, axial ratio 5.2, specific surface area 30
I had a hard time with fftl/I.

Comparative Example 1 - Itcio moles of sulfur and 0.5 moles of cobalt sulfate were dissolved in 404 VCflJ of water to form a submerged bath liquid and 70 moles of sodium hydroxide.
Mol was dissolved in water at 40jlC, and then mixed with aqueous solution at a temperature of 25°C to obtain a pale green precipitate. This suspension was heated at 50°C in a constant temperature bath.
Air was blown at a rate of 10 4 per minute while heating the mixture for 6 hours to obtain a yellow precipitate, which was washed with water and dried to obtain a cobalt-containing α-iron oxyhydroxide powder.

Next, in the same manner as in Example 1, after treatment with a silicon compound, heat reduction was performed to obtain an iron-cobalt alloy magnetic powder.

The magnetic powder has a major axis diameter of 300 nm and a minor axis diameter of 30 nm.
rl.

The axial ratio is 10 and the specific surface area is 47rd/9.

Comparative Example 2 10 mol of ferrous sulfate was dissolved in 40 $ Icl of water, and 70 mol of sodium hydroxide was dissolved in 401 kg of water. 10 per minute while heating the suspension to 50°C in a constant temperature bath.
Air was blown in step 4 and the oxidation reaction was carried out for 6 hours to obtain a yellow precipitate.

The yellow precipitated #O silicon compound was thermally reduced in a hydrogen stream in the same manner as in Example 1 to obtain metallic iron magnetic powder.

The long axis diameter of the magnetic powder is 200 nm, the short axis diameter is 50 nm,
At a ratio of 4.0, the specific surface area was 28 rl/l.

60°C, 90%R as an index of coercive force, saturation magnetization, and oxidation resistance of the 9 alloy magnetic powder obtained in each of the above Examples and Comparative Examples
Leave it under H conditions and measure the amount of saturation magnetization at predetermined time intervals.
The rate of decrease from the saturation magnetization before being left was measured.

〔Effect of the invention〕

As explained above, in the IC iron-cobalt alloy magnetic powder, hydroxide is coprecipitated with ferric salt and cobalt salt, and this coprecipitate is also autoclaved into 4 liters of cobalt-containing α-iron oxyhydroxide. The magnetic alloy obtained by MJ thermal reduction of the powder has a large amount of a-sulfide, an unbranched structure, and a uniform particle size distribution.

The axial ratio is 4.5 to 6.0! It is clear that the powder has a specific surface area of less than 3 s-/I according to the 1lflET method, and has significantly improved oxidation resistance, making it a specific alloy powder.

Claims (2)

[Claims] (1) Magnetic alloy powder mainly composed of iron and cobalt has a BET specific surface area of 25 m^2/g to 35 m^2/g
A magnetic alloy powder having an axial ratio of 4.5 to 6.0. (2) Cobalt-containing ferric hydroxide is produced by reacting an aqueous solution containing trivalent iron ions and divalent cobalt ions with an aqueous solution containing alkali hydroxide in an amount equal to or more than the equivalent of the metal ions, and After filtration and drying of the reaction product obtained by hydrothermally reacting the ferric hydroxide containing ferric hydroxide in an autoclave,
A method for producing a magnetic alloy powder, which comprises heating and reducing the iron-cobalt alloy powder in a reducing gas to obtain an iron-cobalt alloy magnetic powder.