JPS5832027A - Preparation of ferromagnetic powder of cobalt-containing iron oxide - Google Patents

Abstract

PURPOSE:To obtain the title ferromagnetic powder useful as a material for magnetic recording medium, by treating ferromagnetic iron oxide powder with an aqueous solution containing a Co salt and a ferrous salt and an alkali so that the surface of the particle is coated with the Co-containing metal compound, followed by steam treatment. CONSTITUTION:Powder of ferromagnetic iron oxide such as gamma-Fe2O3, etc. is treated with an aqueous solution of a Co salt (e.g., cobalt chloride) and a ferrous salt (e.g., ferrous chloride) and/or another metal salt (e.g., a salt of transition metal such as Mn, etc.) and an alkali such as NaOH, etc. By this treatment, the Co-containing metal compound is attached to the surface of ferromagnetic iron oxide particle. In the coating, for example, the magnetic iron oxide powder is dispersed into the aqueous solution of the metal salt, and the alkali solution is added to it. The coating with the dispersion is carried out at <=50 deg.C. The iron oxide powder after the coating is filtered, and treated with steam at 100- 300 deg.C, preferably at 100-250 deg.C, to give the desired Co-containing ferromagnetic iron oxide powder.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing cobalt-containing iron oxide ferromagnetic powder useful as a material for magnetic recording media.

Cobalt-containing iron oxide ferromagnetic powder has a high coercive force, and recording media using it are capable of high-density recording and have excellent sensitivity in the high frequency range, and have been widely used in fields such as videotapes in recent years. . Many methods have been proposed for incorporating cobalt into magnetic iron oxide, for example,
(1) A method of treating r -Fθ205 powder in a solution containing ferrous salt and cobalt salt at a specific OH group concentration, at high temperature, and in a non-oxidizing atmosphere (Japanese Patent Publication No. 52-36751), (
2) After coating ferromagnetic iron oxide with a compound of cobalt ions and iron ions, 120 to 23
A method of heat treatment at a temperature of 0°C (Japanese Unexamined Patent Publication No. 54-1
24297), (3) A method in which magnetic iron oxide powder is subjected to a hydrothermal reaction in an alkaline solution containing a transition metal salt (
Special Publication No. 48-44040). However, with these conventional methods, it has been difficult to obtain a sufficiently high coercive force, and even if one with a high coercive force is obtained, the thermal properties and stability over time are often poor, so improvements are desired.

On the other hand, it is known that ferrite can be produced by steam-treating a coprecipitate, a precipitated wet mixture, or a precipitated dry mixture of components to form ferrite, "Powder and Powder Metallurgy", Vol. 13, No. 3, pp. 20-25. Although reported in □, there is no example of coating iron oxide magnetic powder with a metal compound containing copalt and treating it with steam.

The method of the present invention differs from any conventional method in that the cobalt-coated iron oxide powder is treated with steam. Furthermore, both the cobalt deposition treatment and the steam treatment are carried out at a temperature lower than conventionally thought, and it has the advantage that a magnetic powder with high coercive force and excellent thermal properties and stability over time can be obtained.

The present invention involves treating iron oxide ferromagnetic powder with an aqueous solution of cobalt salt, ferrous salt and/or other metal salts, and an alkali to coat the particle surface with a metal compound containing cobalt, and then characterized by steam treatment of
This is a method for producing ferromagnetic iron oxide powder containing Koba44.

As the ferromagnetic iron oxide used in the present invention, γ-Fe20
3, Fe3O4, or bertolide compounds obtained by partially reducing r-Fe2Q3. As the cobalt salt, cobalt chloride, cobalt sulfate, cobalt acetate, etc. are used, and as the ferrous salt, ferrous chloride, ferrous sulfate, etc. are used. Other metal salts that may be used as necessary are:
Salts of transition metals such as manganese, zinc, chromium, and nickel are appropriately selected.

Cobalt-containing metal compounds can be deposited by dispersing iron oxide magnetic powder in an aqueous metal salt solution and adding an alkaline solution to it, or by dispersing iron oxide magnetic powder in a mixture of a metal salt aqueous solution and an alkaline solution. A method in which iron oxide magnetic powder is dispersed in water and an aqueous metal salt solution and an alkaline solution are added thereto, or a method in which iron oxide magnetic powder is dispersed in an aqueous alkaline solution and an aqueous metal salt solution is added thereto. In addition, cobalt, ferrous iron, and other metals may be partially or completely treated at the same time or sequentially, or an appropriate method may be employed. In any case, an alkali such as sodium hydroxide is added in an amount equal to or more than a white layer relative to the metal salt in the dispersion.

Surprisingly, it has been found that performing this treatment without any heating of the liquid brings about better results. The reason for this is not clear, but at low temperatures, a cobalt ferrite layer containing ferrous iron is formed in the surface coating layer of the magnetic powder, and the H
It is presumed that this is because the crystallization of cobalt ferrite is promoted by the reaction progressing through the diffusion of ions through 2O as a medium.

The dispersion is heated to a temperature below 50°C, preferably 30°C.
The metal compound containing cobalt is deposited on the surface of the iron oxide powder particles by stirring at a very low temperature until the reaction is completed.

The amount of cobalt deposited is 0.0 on a weight basis relative to iron oxide.
5 to 30 inches, preferably 1 to 10 inches, ferrous iron is 1 to 30 inches
%, preferably 2 to 20 inches, and for other metals about θ to 10 inches.

The coated iron oxide powder is filtered and then treated with steam. Industrially, after filtration, it is preferable to wash with water and subject to steam treatment, or it may be dried once. Steam treatment here refers to heating in the presence of steam, such as heating in a closed container under saturated steam pressure, heating in a tubular furnace with steam flowing through it, etc. There are methods such as contacting with heated steam in a fluidized bed. In these cases, a small amount of other gas, such as air, nitrogen gas, hydrogen chloride gas, ethylene chlorohydrin, etc., may be allowed to coexist, or steam treatment may be performed that also serves as pulverization using a micronizer. can.

It is also possible to heat the wet cake as it is without drying it after filtration and washing with water, and continue heating by supplying steam as the water in the cake evaporates. The heating temperature is usually 100-300°C, preferably 15
0-250°C. Particularly desirable results are obtained if this temperature does not exceed 250°C.

After steam treatment, the desired magnetic powder can be obtained by simple drying. This material has high coercive force and excellent thermal properties and stability over time. In addition, it is the value (chi) shown by 6- coercive force)X100.

Also, stability over time is (initial coercive force) - (temperature 60°
C1 is the value shown by the coercive force after being left for 10 days at a relative humidity of 80 degrees.

Example 1゜Acicular r-Fe20s (coercive force (Hc): 4170e) 1
00g is dispersed in water 11 to make a slurry, and N2 is added to the liquid.
While blowing gas, add 1 mol of cobalt sulfate/1 solution 60
A mixture of 1n' and 125mA of ferrous sulfate 1mol/1 solution was added and stirred.
1 solution was added at 388 mA, and stirring was continued in room m (28°C) for 5 hours. The slurry after the reaction was filtered and washed with water, and the resulting wet cake was placed in a container, sealed in an autoclave with water in another container, and steamed at 2000 C for ~2 hours. After the treatment, it was dried at 600C to obtain the desired cobalt-containing iron oxide ferromagnetic powder (A).

Separately, instead of water vapor treatment, at 230°C in a N2 atmosphere.
, magnetic powder (1 hour) was prepared in the same manner except that heating was performed for 1 hour.
3), put the slurry in an autoclave and heat it to 120°C.
, Ferromagnetic powder C) was obtained in the same manner except that the aqueous treatment was carried out for 3 hours.

The obtained cobalt-containing iron oxide ferromagnetic powder was evaluated for coercive force (Hc), thermal properties (Tp), and stability over time (ΔH
a) was measured and the results shown in the following table were obtained.

Example 2゜Acicular r-Fe 203 (Ha 4170e) 10
0g was dispersed in water IL to make a slurry, and while blowing N2 gas into the liquid, 60ml of cobal sulfate) l monov1 solution was added.
1, plus 57 liters of sodium hydroxide/1 solution 388
mA was added and stirred.

Then, 125 ml of 1 mol/1 solution of ferrous sulfate was added, and stirring was continued at room temperature (28°C) for 5 hours.

The slurry after the reaction was filtered and washed with water, and the resulting cake was placed in a container, sealed in an autoclave together with water in another container, and steamed at 200'C for 2 hours.

After the treatment, it was dried at 60°C to obtain the desired ferromagnetic powder. When we measured the magnetic properties of this material, Ho=6570e.
Tp=83%, J'HQ-30e.

Example 3゜The temperature of the cobalt and ferrous adhesion treatment in the previous example was changed to 45°.
A ferromagnetic powder was obtained in the same manner as in the previous example except that C was used. When we measured the magnetic properties of this material, Ho=641
0eXTII-112, ΔHe=40e.

Example 4゜Example 1. The temperature during addition of cobalt salt and ferrous salt was set at 60°C, and the stirring after addition of alkali was set at 90°C.
A ferromagnetic powder was obtained in the same manner as in Example 16 except that the time was changed to C for 3 hours. When we measured the magnetic properties of this material, we found that Hc=636QeS'rp
= go %, ΔHc = 60e.

Example 5 Cobalt and ferrous iron were deposited as in Example 2, and the resulting cake was placed in a tube furnace and heated at 2000 C for 1 hour in a stream of steam at 1 atmosphere.

The magnetic properties of the obtained ferromagnetic powder are Ho=6490e,
Tp=82%, ΔHQ=40e.

Patent Applicant Ishihara Sangyo Co., Ltd. 10- Procedural Amendment September 25, 1980 1, Case Description 1981 Patent Application No. 117945
@'26 Title of the invention Method for producing cobalt-containing iron oxide ferromagnetic powder 3, Relationship with the case of the person making the amendment Patent applicant (550) Address 3-22-56, Shimame 3-22, Edobori, Nishi-ku, Osaka Subject of amendment Details Detailed description of the invention in the book 250°C
” is corrected to 1-preferably 100-250°C1.

(2) "In the precedent" on page 9, line 12 of the specification is corrected to -1 in Example 1.

(3) On page 9, line 13 of the specification, "precedent and -1 are replaced with "Example 1"
"I corrected myself."

(4) The following Examples 6 and 7 are inserted after the description of Example 5 in Specification 10.

Example 6 A ferromagnetic powder was obtained in the same manner as in Example 2 except that the steam treatment was carried out at 150° C. for 6 hours. , I measured the magnetic properties of the second one and found that 1Ic = 653
0e, T p = 83%, Δ■-IC = 308.

Example 7 In Example 2, the steam treatment was carried out at 100°C for 12
A ferromagnetic powder was obtained in the same manner except that the process was carried out for a longer time. This horn magnetic property is also filled constant L Tatokoro I (c=
6100a, Tp=85%, ΔHc=20e.

Below 1- 12 complete-

Claims (1)

[Claims] Iron oxide ferromagnetic powder is treated with an aqueous solution of cobalt salt and ferrous salt and/or other metal salts and an alkali to deposit a cobalt-containing metal compound on the particle surface, and then treated with steam. A method for producing cobalt-containing iron oxide ferromagnetic powder, characterized by: