JPS63143802A - Manufacture of magnetic iron powder - Google Patents

Abstract

PURPOSE:To form a fine oxide film which has high oxidation resisting stability by suspending metal magnetic powder in an organic solvent which dissolves a specific metal salt for denaturation and by stirring a suspension heated in a state that the upper surface of the suspension is brought into contact with a gas which contains oxygen. CONSTITUTION:Metal magnetic powder is suspended in an organic solvent which dissolves a metal salt for metamorphosis selected from a group consisting of a nickel salt, a zinc salt and a copper salt to form a suspension. For the organic solvent, alcohol is especially used. In order to prevent cohesion or sedimentation, stirring appropriately with such as a propeller stirrer and heating are necessary. The temperature of the suspension is desirable to be 100 deg.C or higher and 300 deg.C or lower. The concentration of the oxygen contained in a gas brought into contact with is desirable to be 0.1 vol % or more and 25 vol % or less. Since oxidation proceeds comparatively slowly even under a high temperature, the metal atom of the metal salt for denaturation dissolved in the suspension is caught in an oxide film through the formation process of the oxide film and as a result the fine oxide film which has excellent oxidation resisting stability is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing magnetic iron powder for magnetic recording, which has excellent oxidation resistance and stability.

In order to achieve high output and low noise in a wide recording wavelength range, magnetic materials for magnetic recording are made of highly uniform fine-shaped particles, have high coercive force (Hc), and have low saturation magnetization (Hc). σ,)
, both residual magnetization (σr) are large, and the squareness ratio (Rs-σ
r/σ, ) is basically required to have as large a magnetic property as possible. Among these, regarding magnetic powder as a magnetic material,
Magnetic iron powder (hereinafter referred to as metal magnetic powder or magnetic iron powder), which is made of ferromagnetic metal powder, has excellent magnetic properties.
It was first put into practical use as a material for audio magnetic tape,
It has also been put into practical use as a material for 8M video. Magnetic iron powder is produced by a method of heating and reducing acicular iron oxyhydroxide to -M. As needle-shaped iron oxyhydroxide,
The α, β, and T transformations are known, and the manufacturing method is different for each variant, but α-FeOOH has twin or resinous crystals as a starting material for magnetic iron powder for magnetic recording. less,
It is excellent because it has a high acicular ratio of around 10. More specifically, α-FeOOH synthesis on the alkaline side consists of passing an oxygen-containing gas through a suspension containing FeC0N)t, obtained by reacting an aqueous ferrous salt solution with an aqueous alkaline solution and having a pH of 11 or more. This method is particularly excellent, and 1 liter of α-FeOO synthesized exclusively on the alkali side is used as a starting material for magnetic iron powder.

In the synthesis of α-FeOOH, Ni, Mn, Co, Cr + A are added to the ferrous salt aqueous solution or alkaline aqueous solution.
I, Si.

By adding salts such as Zn, Mg, Ca, Cu, Zr, etc., α-FeO is co-precipitated with these salts.
OH can be obtained, and these co-precipitated α-Fe00H are often used as a starting material for magnetic iron powder.

To obtain magnetic iron powder mainly composed of metallic iron by thermally reducing acicular iron oxyhydroxide, first, iron oxyhydroxide is heated and dehydrated in a non-reducing atmosphere such as air to form iron oxide. After that, α-FeOOH can be obtained by reducing the iron oxide by heating in a reducing atmosphere such as hydrogen or by omitting the process of converting it into iron oxide.
A known method is to directly heat-reduce in a reducing atmosphere such as hydrogen.

However, depending on the size and composition of the iron oxyhydroxide starting material, the acicular particles may sinter or disintegrate during the above-mentioned thermal dehydration or thermal reduction, resulting in the final metal being obtained. The magnetic properties of magnetic iron powder mainly composed of iron may deteriorate significantly. For this reason, before reducing the iron oxyhydroxide, Si, P, B, ^1, Cr, Ni are added to the surface of the iron oxyhydroxide or particles mainly composed of α-Fe203 obtained by heating and dehydrating the iron oxyhydroxide.
, Mn, Co, Zn, Mg, Ca, C
By depositing compounds such as u+Ti alone or in combination, it is possible to prevent the collapse of the acicular particles and the sintering of the acicular particles during the subsequent reduction or thermal reduction, thereby producing magnetic iron with excellent magnetic properties. Methods for obtaining flour are also known.

Magnetic iron powder is usually a fine particle with a length of 1 μm or less in the long axis direction and a processing time of about 10 minutes in the short axis direction, so its oxidation activity against air is extremely strong and it cannot be used as a magnetic recording medium if it remains reduced. Not available.

Therefore, after reduction, the surface of magnetic powder mainly composed of reduced metallic iron is oxidized to form an oxide film on the surface of the magnetic powder, and the oxidation activity against air is suppressed. used.

As described above, methods for oxidizing the surface of magnetic powder mainly composed of reduced metallic iron to form an oxide film on the surface of the magnetic powder include a method in which the oxidation is carried out by a gas phase catalytic reaction, and a method in which the oxidation is carried out by a gas phase catalytic reaction, and a method in which the oxidation is carried out by a gas phase catalytic reaction, and a method in which the oxidation is carried out by a gas phase catalytic reaction, and a liquid phase reaction. There are known methods to do this, for example, the
6-28961, JP-A-55-164001, JP-A-57-219305, and JP-A-58-135102.

In this case, the thicker the oxide film formed on the surface of the magnetic iron powder, the higher the corrosion resistance (oxidation resistance stability) of the magnetic iron powder. As the thickness increases, the saturation magnetization f(σ,), which is one of the important characteristics of magnetic iron powder, decreases, so it is not possible to form a thick oxidized liquid without thinking. do not have.

This can be understood from the fact that one of the characteristics of magnetic iron powder is that σ3 is higher than that of oxide-based magnetic iron oxide powder.

The value of σ of magnetic iron powder varies depending on the size, composition, and purpose of use of the magnetic iron powder, so it cannot be stated definitively, but for example, if the specific surface area used for audio applications is 30r,
For magnetic iron powder of about rf/g, σ3 is about 150 emu/g, and the specific surface area used for 8 mm video is 5 Onf/g.
For magnetic iron powder of about 100 to 100 mm, σ needs to be about 120 emu/g, and values less than this are not preferred because the properties of the final product magnetic tape will deteriorate.

Therefore, in order to obtain magnetic iron powder with high oxidation resistance stability that can be produced within a limited range of oxide film thickness, the film quality of the oxide film provided on the surface of the iron powder must be as dense as possible. It needs to be coated.

The corrosion resistance of magnetic iron powder can be quantitatively evaluated from the change in σ before and after exposing the magnetic iron powder to an oxidizing atmosphere at high temperature and high humidity for a certain period of time.

For example, when magnetic iron powder is exposed continuously for weeks at 60°C under high humidity air with a relative humidity of 90%, the magnetic iron powder is The oxidation stability of powder can be quantitatively evaluated.

In magnetic iron powder for audio, the initial σ is 150e+n
Under the above conditions, the oxidation resistance stability of a material of about U/g is 0.10 or less, and for magnetic iron powder for 8 mm video, the initial a is about 120ea + u/g under the above conditions. For the oxidation resistance stability, this ratio is preferably 0.15 or less,
Conventional oxidation removal methods have not been able to form a dense oxide film with such high oxidation resistance stability.

- In order to achieve this goal, the present inventors have worked diligently to develop a method for obtaining magnetic iron powder with excellent oxidation resistance stability by forming a dense oxide film on the surface of metal magnetic powder mainly composed of iron. As a result of our investigation, we found that metal magnetic powder was suspended in an organic solvent in which a specific metamorphic metal salt was dissolved, and the suspension was heated while the upper surface of the suspension was in contact with an oxygen-containing gas. The present invention was achieved by discovering that an extremely dense oxide film can be formed on the surface of metal magnetic powder by stirring!

That is, the present invention involves suspending metal magnetic powder in an organic solvent in which at least one metamorphic metal salt selected from the group consisting of nickel salts, zinc salts, and copper salts is dissolved. The suspension is stirred under heat while the upper surface of the liquid is in contact with an oxygen-containing gas! A method for stabilizing oxidation of metal magnetic powder, which is characterized by oxidation stabilization, is a component of the present invention.

The present invention will be explained in detail below.

In the present invention, metal magnetic powder is suspended in an organic solvent in which at least one metamorphic metal salt selected from the group consisting of nickel salts, zinc salts, and copper salts is dissolved to form a suspension.

Preferred examples of such nickel salts include nickel chloride, nickel bromide, nickel iodide, nickel nitrate, nickel acetate, etc., and as zinc salts,
Preferred examples include zinc chloride, zinc sulfate, zinc nitrate, zinc carbonate, and zinc acetate.
Metal salts such as copper chloride, copper bromide, copper nitrate, and copper acetate are preferred, but those used in the present invention are those that can be dissolved in the following organic solvents under heating. , any one can be used. In addition, these salts may be used alone or in combination of two or more types, and the proportion of the metal as the metal is about 0.01 to 20% by weight relative to the magnetic iron powder to be introduced. The mixture was prepared in a solvent with a concentration of 11%.

The organic solvent used in the present invention is one that dissolves the metamorphic metals mentioned above under heating, does not itself undergo substantial deterioration when brought into contact with oxygen-containing gas at high temperatures, and is one that dissolves under normal pressure. Polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin; decyl alcohol,
Particularly preferred are m-alcohols such as 1-nonanol.

Metal magnetic powder suspended in a solvent containing metamorphic metals needs to be appropriately agitated with a propeller stirrer or the like in order to prevent agglomeration and sedimentation. However, if this suspension of metal magnetic powder in an organic solvent is heated and moderately stirred in an atmosphere of an oxygen-containing gas such as air, that is, in a state in which it is in contact with the oxygen-containing gas,
In the present invention, in order to form a dense oxide film, the temperature of the suspension is 100°C. The temperature is preferably 300°C or less; if the temperature is less than 100°C, a dense oxide film cannot be formed, while if it exceeds 300°C, non-magnetic α-FegO will be mixed in the oxide film, which is not preferred. The heating time depends on the type of iron powder, temperature,
Although it varies depending on the salt etc. used,
Usually, 1 to 10 hours is sufficient.

In the present invention, the oxygen concentration of the oxygen-containing gas is
0.1 vo 1% or more and 25 νo 1% or less are preferable.
If the oxygen concentration is less than this, the time required to form the oxide film becomes long and uneconomical. On the other hand, if the oxygen concentration exceeds 25 vol. 1%, the density of the formed oxide film will be impaired. . Air can be used as is as the oxygen-containing gas, but of course non-oxidizing inert gas,
For example, a gas mixture of nitrogen, helium, neon, argon, etc. and oxygen may be used.

Of course, the oxygen-containing gas can be forcibly blown into the suspension, but it is also possible to blow it into the suspension but into the upper part of the suspension, that is, through the free surface of the suspension. It is more preferable to adopt the method of absorption into a cloudy liquid because it is possible to form a denser oxide film.By such an operation, a dense film in which metamorphic metal atoms are incorporated into the oxide film is formed. It is possible to obtain magnetic iron powder having excellent oxidation resistance and stability.

Further, if necessary, it is also possible to heat-treat the oxide film by switching the gas phase to a non-oxidizing gas such as nitrogen to make the oxide film even more dense.

■According to the findings of the inventors, in order to form a dense oxide film, it is necessary to oxidize at an appropriate oxidation rate and to rearrange the crystals in the oxide film layer so that they become more dense. A moderate temperature is required.

Therefore, in the method of the present invention, only the part of the suspension near the gas-liquid interface in contact with the upper part of the suspension is used for oxidizing the metal magnetic powder, and the metal magnetic powder itself is covered with an organic solvent. Therefore, it is presumed that a dense oxide film is formed at an appropriate speed even at high temperatures of 100°C or higher.

Further, in the present invention, since the suspension is appropriately stirred, the metal magnetic powder oxidized at the gas-liquid interface continues to undergo surface renewal and move into the main body of the suspension. While in this body, oxidation is virtually negligible. In other words, it is thought that a dense oxidized liquid can be formed because only the crystal rearrangement of the oxide film formed on the liquid surface occurs until it moves into the suspension body and reaches the gas-liquid interface again. It will be done.

Furthermore, as mentioned above, oxidation progresses relatively slowly even at high temperatures, so the metal atoms of the metamorphic metal salt dissolved in the suspension are incorporated into the oxide film through the process of forming the oxide film. As a result, a dense oxide film with excellent oxidation resistance and stability is formed.

The method and effects of the present invention will be explained in more detail below using Examples and Comparative Examples.

100 parts by weight of Fe, 5 parts by weight of Sing,
N1C
h 5g was dissolved in an ethylene glycol solution of 22, the suspension was heated to 180°C in the air while stirring using a propeller stirrer, the oxidation reaction was carried out for 5 hours, and then cooled to room temperature. Magnetic iron h) was recovered.

When the composition of the obtained magnetic iron powder (abbreviated as m-type powder A) was analyzed using a fluorescent X-ray analyzer, it was found that N per part by weight of FelOO.
It contained 2.6 parts by weight of i. 6. Part into magnetic powder
It was left continuously for one week under high humidity air with a relative humidity of 909 at 0°C. The powder characteristics of the obtained magnetic iron powder (abbreviated as magnetic powder B) were measured and the values shown in the table below were obtained. The magnetic properties were measured using a vibrating sample magnetometer (VSM) with a magnetic field of 10 K.
Measured at Oe. The results are shown in Table-1.

Table 1 From the table, the ratio Δσ, /σ, value (hereinafter referred to as oxidation resistance stability ratio) indicating the oxidation resistance stability of magnetic powder A for 8 mm video was calculated to be 0.092, which is excellent. I can see that it is something.

Example 2 100g of metal magnetic powder obtained by reduction in Example 1 was converted into ZnC
The suspension was suspended in an ethylene glycol solution of 21 in which 25 g of 1 was dissolved, and the suspension was heated to 180 °C in air while stirring using a propeller stirrer, and the reaction was maintained for 5 hours.
It was cooled to room temperature and the magnetic iron powder was collected.

When the composition of the obtained magnetic iron powder (abbreviated as magnetic powder C) was analyzed using a fluorescent X-ray analyzer, it was found that Z
It contained 2.6 parts by weight of n. Part of magnetic powder C is 6
The powder characteristics of 0MI powders C and D, which were obtained by leaving them continuously for one week at 0°C under high humidity air with a relative humidity of 90% (abbreviated as "magnetic powder"), were measured and the following table shows the results. A value of 2 was obtained.

Table-2 From the table, the powder characteristics of magnetic powder C are oxidation resistance stability ratio 0.089
It was recognized as being excellent.

Example 3 100g of metal magnetic powder obtained by reduction in Example 1 was converted into CuC
1t 5 g dissolved in ethylene glycol solution of 21, the suspension was heated to 180°C in air while stirring using a propeller stirrer, the reaction was maintained for 5 hours, and then cooled to room temperature. , magnetic iron powder was recovered.

When the composition of the obtained magnetic iron powder (abbreviated as magnetic powder E) was analyzed using a fluorescent X-ray analyzer, it was found that per 100 parts by weight of Fe, C
It contained 2.7 parts by weight of u. Part of the magnetic powder E is 6
Magnetic iron powder (abbreviated as magnetic powder F) was obtained by allowing it to stand continuously for one week under high humidity air with a relative humidity of 90% at 0°C. Magnetic powder E
, F were measured and the values shown in Table 2 were obtained.

Table 2 From the table, the powder characteristics of magnetic powder E are oxidation resistance stability ratio 0.091
It was recognized as being excellent.

Comparative Example 1 100 g of the metal magnetic powder obtained in Example 1 was suspended in 11 toluene, and while stirring using a propeller stirrer, a 1:1 mixed gas of air and N2 was blown into the suspension at 40°.
After performing an oxidation reaction with C for 4 hours, toluene was removed to obtain a magnetic powder (abbreviated as magnetic powder G). Magnetic powder G at 60℃,
Table 3 was obtained by measuring the powder properties of magnetic powders G and H, which were obtained by standing continuously for one week in high-humidity air with a relative humidity of 90% (abbreviated as magnetic powder H).

Table 3 The oxidation resistance stability ratio of magnetic powder G is 0.161 and Example 1~
It can be seen that it is far inferior to 3.

Claims (2)

[Claims] (1) Metal magnetic powder is suspended in an organic solvent in which at least one metamorphic metal salt selected from the group consisting of nickel salts, zinc salts, and copper salts is dissolved to form a suspension, and the upper part of the suspension is When the surface is in contact with a gas containing oxygen,
A method for oxidation stabilization of metal magnetic powder, which comprises stirring the suspension under heating. (2) Claim 1 in which the organic solvent is alcohol
The method described in section.