JPS60204803A - Production of magnetic particle powder of acicular crystal metal consisting essentially of metallic iron - Google Patents

Abstract

PURPOSE:To produce titled particle powder consisting essentially of metallic iron having excellent oxidation stability by reducing acicular crystal ferric oxide particles under heating and treating the particles to an immersion treatment in an org. solvent then treating the particles in an aq. soln. contg. ferrous hydroxide under adequate conditions. CONSTITUTION:Acicular crystal ferric oxide particles consisting essentially of Fe2O3 are used as a starting material and are reduced in a reducing gas under heating. The particles consisting essentially of the resulting metallic iron are subjected to an immersion treatment in an org. solvent and are dried at 20-50 deg.C after filtration. The dried particles are dispersed into an aq. soln. contg. ferrous hydroxide. The dispersion thereof is treated in a non-oxidative atmosphere in the range of 0.05-3.0mol/l concn. of an OH group and 50-100 deg.C. A magnetite film is formed on the particle surfaces by such treatment, by which the particles can be safely taken out into air and the decrease in the saturation magnetization sigmas owing to oxidation in the air is prevented. The magnetic particle powder of the acicular crystal metal consisting essentially of the metallic iron having excellent oxidation stability is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention creates a thin magnetite film that is dense and has good adhesion on the particle surface of acicular metal magnetic particles whose main component is metallic iron, so that they are stable in the air. A method for producing acicular metal magnetic particles whose main component is metallic iron, which can be taken out and has excellent oxidation stability, such as preventing a decrease in saturation magnetization σS due to oxidation after being taken out into the air. It is related to.

In recent years, as magnetic recording and reproducing equipment has become smaller and lighter, there has been an increasing need for higher performance recording media. That is, high-density recording, high output characteristics, and especially improvement in frequency characteristics are required.

The characteristics of a magnetic material suitable for satisfying the above requirements for a magnetic recording medium are that it has a large saturation magnetization and a high coercive force.

By the way, the magnetic materials conventionally used in magnetic recording media are magnetic powders such as magnetite, magnetite, and chromium dioxide, and these magnetic powders have a saturation magnetization σs7
0-85elIu/g, coercive force Hc 250-5000
e.

In particular, the σS of the oxide magnetic particles is at most 85 emu.
/g, and generally (Is To~80em
The u/g ratio is the main reason for limiting the reproduction output and recording density. Furthermore, Co-magnetite and Co-maghemite magnetic powders containing Co are also used, but these magnetic particles have a coercive force Hc.
It is characterized by a high magnetization of 400 to 8000e, but on the other hand, the saturation magnetization σS is low at 60 to 80 emu/g.

Recently, there has been active development of magnetic particles with characteristics suitable for high-output and high-density recording, that is, magnetic particles with large saturation magnetization and high coercive force. There is an acicular metal magnetic particle powder whose main component is metallic iron, which is obtained by heating and reducing acicular ferric oxide particles whose main component is , Fears, in a reducing gas.

As mentioned above, the acicular metal magnetic particles whose main component is metallic iron currently have the most required properties as magnetic recording materials, that is, the saturation magnetization σS is extremely large (for example, 90 to 200 ea+u/g). ), coercive force H
It is characterized by a high c (for example, 600 to 20,000e), and when coated as a magnetic recording medium, it has a large residual magnetic flux density Br and a high coercive force Hc, so it can achieve high density recording and high output characteristics. It is attracting attention because it can be
It has been put into practical use in recent years.

As mentioned above, acicular metal magnetic particles mainly composed of metallic iron have large saturation magnetization and high coercive force. Because crystalline metal magnetic particles are extremely fine particles of 1 μm or less, the surface activity of the particles is extremely high, and when taken out into the air after reduction, it rapidly reacts with oxygen in the air, causing heat generation and ignition. It is extremely unstable. At the same time, because it becomes an oxide due to the above oxidation reaction,
This results in a significant decrease in magnetic properties, especially saturation magnetization, making it impossible to obtain magnetic particles with the desired high coercive force and high saturation magnetization.

In the past, various attempts have been made to stably extract acicular metal magnetic particles containing metallic iron as a main component into the air without impairing their properties, and representative methods include (1) A method in which acicular metal magnetic particles containing metallic iron as a main component are immersed in a solvent.

(2) A method in which acicular metal magnetic particles containing metallic iron as a main component are treated in an atmosphere in which the partial pressure of oxygen is adjusted.

There is.

In either case, an oxide film is formed on the surface of the acicular metal magnetic particles containing metallic iron as a main component.

However, in the case of the above method, the formation of an oxide film is not sufficient, and therefore, after being taken out into the air,
Acicular metal magnetic particles containing metallic iron as a main component have the disadvantage that they are gradually oxidized by air, resulting in a significant decrease in saturation magnetization σS.

In view of the above, the present inventor has developed a metal iron with excellent oxidation stability that can be stably taken out into the air and prevents a decrease in saturation magnetization σS due to oxidation after being taken out into the air. The present invention was achieved as a result of various studies in order to obtain acicular metal magnetic particles containing as a main component.

That is, the present invention uses acicular ferric oxide particles containing FezO3 as a main component as a starting material, and heat-reduces the starting material in a reducing gas to obtain acicular ferric oxide particles containing metallic iron as a main component. After immersing the crystalline metal magnetic particles in an organic solvent and separating them in a furnace, 2
Drying at a temperature range of 0°C to 50°C, the particles are then dispersed in an aqueous solution containing ferrous hydroxide, and the O
H group concentration 0.05-3.0 mol/1.50-100
Acicular crystals mainly composed of metallic iron are produced by forming a magnetite film on the surface of the above-mentioned acicular metallic magnetic particles mainly composed of metallic iron by processing in a non-oxidizing atmosphere in the temperature range of ℃. This is a method for producing crystalline metal magnetic particles.

The structure and effects of the present invention will be explained as follows.

First, various findings on which the present invention is based will be described.

The present inventor has found that, in comparison to the prior art described above, it can be stably taken out into the air, and has excellent oxidation stability that prevents the saturation magnetization σS from decreasing due to oxidation after being taken out into the air. In order to obtain acicular metal magnetic particles whose main component is metallic iron, the metal oxide film formed on the particle surface must be sufficient to completely prevent oxidation by air, etc. In addition, we thought that it must not impair the characteristics of the acicular metal magnetic particles whose main component is metallic iron. Considering the characteristics of such a metal oxide film, it is preferable that it be as dense as possible, have good adhesion, and be as thin as possible, and various studies have been conducted on the types and manufacturing methods of the metal oxide film.

Coloring Materials Association Journal Vol. 49 No. 11 (1976) 659-66
On page 8, the ``Mechanism of Rust Generation'' is explained in detail, ``During the process of rust layer formation, Fe5Oa, which has good electronic conductivity, adheres to the base metal, and if it is uniformly distributed over the entire surface, it becomes stable.'' It becomes a protective film.'' Also, ``The adhesive rust layer has a blackish-purple color, and when measured with an S rometer, it has a value of 1.
It can be seen that it is FezOa that has an electronic conductivity of 0Ω to several 100Ω and is in close contact with the base metal.”

The present inventor paid attention to this description and considered that a magnetite film is the most suitable type of thin metal oxide film that is dense and has good adhesion.

Therefore, as a result of various studies on techniques for forming a thin magnetite film that is dense and has good adhesion, the inventors of the present invention used needle-shaped ferric oxide particles containing FezOa as a main component as a starting material, and found that the starting material The acicular metal magnetic particles mainly composed of metallic iron obtained by heating reduction in a reducing gas are immersed in an organic solvent, separated in a furnace, and then dried at a temperature range of 20°C to 50°C. Then, the particles are dispersed in an aqueous solution containing ferrous hydroxide, and the OH group concentration of the dispersion is 0.05.
~3.0IIIol/l, when treated in a non-oxidizing atmosphere in the temperature range of 50 to 100°C, a thin magnetite film that is dense and has good adhesion can be formed on the particle surface. To obtain acicular crystalline metal magnetic particles whose main component is metallic iron, which can be stably taken out and which has excellent oxidation stability and is prevented from decreasing in saturation magnetization σS due to oxidation after being taken out into the air. We obtained new knowledge that it is possible.

Next, the generation mechanism of the magnetite film in the present invention will be described.

The present inventor has been engaged in the production and development of iron oxide for many years, and in the process, Fe (
It has already been found that when OH)z is applied, magnetite is produced according to the reaction formula +11.

FezO3+Fe(OH)x −' Fe3Oa ・・
” fl) The generation mechanism of this magnetite is FexOa
It is believed that this is because a polycondensation reaction occurs between Fe (0) 1) x and OH groups, and ferrous ions diffuse into FexOa.

The formation mechanism of the metal oxide film formed on the particle surface of the acicular metal magnetic particle powder mainly composed of metallic iron according to the present invention can be explained by the above-mentioned equation (1).

That is, in the present invention, acicular metal magnetic particles containing metallic iron as a main component are treated in an organic solvent, separated in a furnace, and then dried.
On the particle surface of the acicular metal magnetic particles whose main component is metallic iron, the acicular metal magnetic particles whose main component is metallic iron are brought into gentle contact with air by gradually evaporating the solvent. It is considered that an oxide film (Fego3) is formed by this process.

Next, the acicular metal magnetic particles containing metallic iron as a main component and having an oxide film (FezOi) formed thereon are dispersed in an aqueous solution containing ferrous hydroxide, and the OH group concentration of the dispersion is reduced to 0.0.
Since it is treated in a non-oxidizing atmosphere at a temperature range of 5 to 3.0 mol/1.50 to 100°C, the oxide film (pezox) generated on the particle surface and Fe (OH
) It is thought that a condensation polymerization reaction occurred between z and OH groups, resulting in the formation of a magnetite film.

As mentioned above, the generation mechanism of the magnetite film in the present invention is based on the oxide film (peios) produced on the particle surface.
) and Fe(OH)z undergo a polycondensation reaction via the Of( group, so the Fe" of Fe(OH)z diffuses into the oxide film (Feast) generated on the particle surface. Therefore, it is thought that a thin magnetite film that is dense and has good adhesion is formed.

Conventionally, methods for forming a magnetite film on the particle surface of acicular metal magnetic particles containing metallic iron as a main component in an aqueous solution include, for example, Japanese Patent Publication No. 56-12282 and Japanese Patent Application Laid-Open No. 58-161704. There is a method described in the official gazette.

The method described in Japanese Patent Publication No. 56-12282 discloses that acicular metal magnetic particles containing metallic iron as a main component are heated at a temperature of 5°C to 70°C.
After suspending in an aqueous solution of sulfur-IJ hydroxide having a temperature of A magnetite film is produced by aerating oxygen-containing gas, and its production mechanism is such that acicular metal magnetic particles, whose main component is metallic iron, are suspended in an aqueous sodium hydroxide solution. , a small amount of oxygen dissolved in the sodium hydroxide aqueous solution causes an oxygen-consuming corrosion reaction Fe+2H""'AO*"Fe" +H,0, and the Fe1 generated on the particle surface becomes 01( −
When combined with Fe (010), the Fe (OH) * is oxidized to form a magnetite film by passing an oxygen-containing gas through the atmosphere.

The method described in JP-A-58-161704 involves oxidizing acicular metal magnetic particles containing metallic iron as a main component while controlling the amount of oxygen gas in a liquid phase or gas phase to remove the metallic iron. An oxide film is formed on the surface of the acicular metal magnetic particles that are the main component, and then the treated particles are dispersed in an aqueous solution containing ferrous salt and an alkali, and an oxidizing gas is blown into the solution to cause a reaction. This produces a magnetite film.

Considering the film formation mechanism in the invention described in JP-A-58-161704, it is found that acicular metal magnetic particles containing metallic iron as a main component are grown in a liquid phase or a gas phase while controlling the amount of oxygen gas. A magnetite coating is formed on the particle surface by oxidation treatment, and then the particles with the magnetite coating formed thereon are dispersed in an aqueous solution containing a ferrous salt and an alkali, and an oxidizing gas is blown into the solution to cause a reaction. It is thought that this causes the magnetite coating formed on the particle surface to grow epitaxially toward the outside of the particle.

The above-mentioned conventional techniques for producing a magnetite film on the particle surface of acicular metal magnetic particles containing metallic iron as a main component are all oxidation reactions as described above, and therefore require steps such as aeration of oxygen-containing gas. However, in the case of the present invention, since the polycondensation reaction is mediated by OH groups, steps such as aerating oxygen-containing gas are not required.

Furthermore, according to the invention described in the above-mentioned Japanese Patent Application Laid-Open No. 58-161704, after forming a magnetite film on the surface of the acicular metal magnetic particles containing metal iron as a main component, cleaning with acetone must be carried out. This is thought to be because the magnetite film was not sufficiently formed.

The following is a description of some of the many experimental examples conducted by the present inventor.

Figure 1 shows the change in saturation magnetization over time at a temperature of 50°C and a relative humidity of 80% when acicular metal magnetic particles containing metallic iron as the main component are taken out into the air. The value obtained by dividing the difference (ΔσS) before and after the change by the saturation magnetization before the change is expressed as a percentage.

In FIG. 1, curve a represents the case where a magnetite film is formed on the particle surface of acicular metal magnetic particles mainly composed of metallic iron, and curve bib represents the acicular crystalline metal magnetic particles mainly composed of metallic iron. This is a case where crystalline metal magnetic particles are taken out in an organic solvent.

As is clear from FIG. 1, the acicular metal magnetic particle powder containing metallic iron as a main component obtained by the present invention can be stably taken out into the air, and is not oxidized after being taken out into the air. This indicates that a very dense and thin film with good adhesion is formed because the decrease in saturation magnetization σS is prevented and the film has excellent oxidation stability. As is clear from the description in the Coloring Materials Association magazine, it can be understood that it is magnetite. Furthermore,
It can also be understood that the acicular metal magnetic particles obtained by the method of the present invention are magnetite from the fact that they have a large saturation magnetization.

Next, various conditions for implementing the method of the present invention will be described.

In the present invention, the acicular ferric oxide particles containing FezO1 as a main component include acicular α-1β-1T-hydrated ferric oxide particles, acicular hematite particles, acicular magnetite particles,
Acicular crystal maghemite particles and CO1Mg, AJ, Crs Zns N, which are conventionally added to these particles during the production of needle crystal metal magnetic particle powders containing metallic iron as a main component.
i5 Refers to those containing different metals other than Fe such as Ti, Mn, Sn, and Pb.

What is obtained by heating and reducing these starting materials in a reducing gas is acicular crystal metal iron magnetic particle powder and F
In the present invention, these particles are collectively referred to as acicular metal magnetic particles containing metal iron as a main component.

Further, depending on the type of starting material, the magnetite coating naturally becomes a magnetite coating in which different metals other than Fe are dissolved in solid solution, but in the present invention, all of these are collectively referred to as the magnetite coating.

As the organic solvent in the present invention, toluene, xylene, methyl ethyl ketone, butyl acetate, etc. can be used.

The drying temperature after organic solvent treatment in the present invention is from 20°C to
The temperature is 50°C.

The drying temperature is related to the thickness of the FezO3 coating formed on the particle surface of the acicular metal magnetic particles mainly composed of metallic iron, and if the drying temperature is 20°C or less, the Fe2O3
If the film is not sufficiently formed and the temperature is 50° C. or higher, the thickness of the FezO3 film becomes thicker than necessary, resulting in a decrease in saturation magnetization σS.

The aqueous solution containing ferrous hydroxide in the present invention can be produced using ferrous sulfate, ferrous chloride as the ferrous salt, and sodium hydroxide, potassium hydroxide, etc. as the alkali. In the present invention, the acicular metal magnetic particles containing metallic iron as a main component are treated with ferrous hydroxide by dispersing them in an aqueous solution containing ferrous hydroxide or in an alkali. Any method of adding iron salt may be used.

The OH group concentration in the present invention is 0.05 to 3. Omol
/1.

0.05mol/j! If it is below, the polycondensation reaction will not occur sufficiently, and the magnetite film will not be formed sufficiently.

Although it is possible to generate a magnetite film when the amount is 3.0 mol/1 or more, there is no point in adding more than necessary, and since a large amount of water is required in the subsequent washing process, it is not industrially or economically viable. do not have.

The temperature of the dispersion liquid in the present invention is 50 to 100°C. The temperature of the dispersion liquid is related to the processing time, and if the temperature is set to 50° C. or lower, it is difficult to form a magnetite film in the present invention, and even if it is formed, an extremely long processing time is required.

The reason why the method of the present invention is carried out in a non-oxidizing atmosphere is to prevent oxidation of ferrous hydroxide in the dispersion.

This is because when ferrous iron is a hydroxide, the above (1)
This is because the reaction of Eq.

According to the present invention as described above, by forming a thin magnetite film that is dense and has good adhesion on the particle surface of acicular metal magnetic particles whose main component is metallic iron, they can be stably taken out into the air. Needle-like roar y mainly composed of metallic iron has excellent oxidation stability, such as preventing a decrease in saturation magnetization σS due to oxidation after being taken out into the air.
Since AMi particle powder can be obtained, it is suitable as a magnetic material for high output and high density recording, which is currently required in quantity.

In addition, the present invention does not require a process such as blowing oxygen-containing gas such as air when forming a magnetite film on the particle surface of acicular metal magnetic particles containing metallic iron as a main component, and is industrially and economically efficient. It is very advantageous in terms of

Furthermore, according to the present invention, the magnetite coating formed on the particle surface of the acicular metal magnetic particles containing metallic iron as a main component is dense and has good adhesion. It has the effect that it can be stably taken out into the air simply by washing with water and drying.

Next, the present invention will be explained with reference to Examples and Comparative Examples.

In addition, the axial ratio (long axis: short axis) and long axis of particles in the following Examples and Comparative Examples are both shown as average values of numerical values measured from electron micrographs.

The values of magnetic properties are measured using a sample vibrating magnetometer in an external magnetic field of 1.
These are the results measured under 0 KOe.

Further, the oxidation stability was expressed as the saturation magnetization reduction rate (%) after being left for 7 days in an atmosphere at a temperature of 50° C. and a relative temperature of 80%.

Example 1 As a starting material, the average value of major axis is 0.8 μ, major axis: short axis = 1
Using needle-like α-Fe008 particles with 0=1, cough needle-like α
- 1500 g of FeOOH particle powder was put into a rotary retort container, and 112 gas was supplied per minute by rotating it.
Aeration was carried out at a rate of 0E and reduction was carried out at a reduction temperature of 400° C. to produce acicular crystal metal magnetic particle powder containing metallic iron as a main component.

Next, after replacing the H gas with N gas and cooling it, the acicular metal magnetic particle powder containing metal iron as a main component was taken out into a take-out container that had been sufficiently replaced with an inert gas.
After cutting off contact with air and adding it to 10 J of toluene solution with stirring, it was separated into a furnace and dried at 35°C for 60 minutes to form acicular crystals mainly composed of metallic iron with an oxide film formed on the particle surface. Metal magnetic particle powder was obtained.

1,000 g of acicular metal magnetic particles containing metallic iron as a main component on which the oxide film was formed was added to a 2.3-H sodium hydroxide aqueous solution 91 with stirring, and then
．． Add 358 mol of ferrous sulfate and water and bring the total amount to 1 liter.
1 (After setting the O1l group concentration to 2.01110180, the resulting dispersion was heated and maintained at 100°C, and the slurry was taken out after 5 hours while stirring well while preventing air from entering as much as possible. The powder was washed with water, separated by plating, and dried at 60° C. to obtain acicular crystal metal magnetic particles containing metallic iron as a main component.

FIG. 2 is an X-ray diffraction diagram of the obtained acicular metal magnetic particles whose main component is metallic iron.

In FIG. 2, peak A indicates the peak of magnetite, and peak B indicates the peak of metallic iron.

The resultant acicular metal magnetic particles having a magnetite coating and having metallic iron as a main component were observed by electron microscopy to have a long axis of 0.7 μm and a ratio of long axis to short axis of 8:l.

In addition, the magnetic properties are saturation magnetization σs 128 emu/g,
Coercive force 1 (c 12500e, saturation magnetization reduction rate 4.0
%Met.

Examples 2 to 15 Metals were prepared in the same manner as in Example 1, except that the type of starting material, reduction temperature, type of organic solvent, drying temperature, type and amount of ferrous salt, OH group concentration, and temperature were varied. Acicular metal magnetic particles containing iron as a main component were obtained.

Table 1 shows the main manufacturing conditions and properties.

As a result of X-ray diffraction, the acicular metal magnetic particles obtained in Examples 2 to 15 mainly containing metallic iron showed peaks of magnetite and metallic iron.

Comparative Example 1 The acicular metal magnetic particle powder mainly composed of metallic iron with an oxide film formed on the particle surface obtained in Example 1 was as follows:
As a result of electron microscope observation, the long axis is 0.8 μ steel, long axis: short axis =
8=1.

In addition, the magnetic properties are saturation magnetization σ3135 emu/g,
The coercive force Hc was 13200e, and the reduction rate of saturation magnetization was 22%.

[Brief explanation of drawings]

FIG. 1 shows the change over time in the saturation magnetization σS when acicular metal magnetic particles containing metallic iron as a main component are taken out into the air. FIG. 2 is an X-ray diffraction diagram of the acicular metal magnetic particles obtained in Example 1 and containing metallic iron as a main component. Patent applicant Toda Kogyo Co., Ltd. Figure 1 Chronological diary

Claims (1)

[Claims] Tl) Acicular crystal metal magnetic particles containing metallic iron as a main component obtained by heating and reducing the starting material in a reducing gas using acicular ferric oxide particles containing F8xOs as a main component. After immersion treatment in an organic solvent and furnace separation, 20℃ ~ 5℃
The particles are dried in a temperature range of 0°C, and then the particles are dispersed in an aqueous solution containing ferrous hydroxide, so that the OH group concentration of the dispersion is 0.
．． 05-3. On+ol/j! , by processing in a non-oxidizing atmosphere at a temperature range of 50 to 100 °C,
A method for producing acicular metal magnetic particles containing metallic iron as a main component, the method comprising forming a magnetite coating on the surface of the acicular metal magnetic particles containing metallic iron as a main component.