JPS5953601A - Manufacture of stable ferromagnetic metallic powder - Google Patents

Abstract

PURPOSE:To manufacture stably ferromagnetic metallic powder with especially high coercive force and high saturation magnetizability in a fine-grained state by reducing a starting material contg. acicular iron oxyhydroxide or ferric oxide as the principal component with a reducing gas, and immersing the resulting magnetic metallic powder in an aqueous soln. of a corrosion controller. CONSTITUTION:Said magnetic metallic powder, that is, fine acicular powder of iron or Fe-Co-Ni is immersed in an aqueous soln. contg. a corrosion controller by 5-1,000wt% of the amount of the powder. The temp. of the soln. is <=50 deg.C, practically 10-50 deg.C. Nitrite, boric acid, borate, silicate, phosphate or the like is used as the corrosion controller. For example, when an aqueous soln. of NaNO2 is used, the concn. is preferably adjusted to 25-100%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing ferromagnetic metal powder including magnetic iron powder. The purpose of this invention is to stably produce ferromagnetic metal powder in the form of fine particles, which has particularly high coercive force and large saturation magnetization. Its main use is as magnetic material powder for magnetic recording tapes.

In recent years, with the miniaturization of magnetic recording devices, there has been a need for magnetic materials that have high recording density performance, high output characteristics, and excellent frequency characteristics. Magnetic metal powder has high coercive force and large saturation magnetization, and is a magnetic material with performance that exactly meets the demands of the times. On the other hand, there are problems such as the risk of fire occurring during the manufacturing process, deterioration of magnetic properties during storage, and gelation of the paint due to the development of catalytic activity during the magnetic paint manufacturing process. The reason for this is that when the particle size is set to 1 μm or less, which is suitable for magnetic recording media, the magnetic metal powder has a large specific surface area of 10 to 50 m 2 /g and becomes very chemically active.

The following three methods are used to stabilize magnetic metal powder.

(1) Gently oxidize magnetic metal powder with a small amount of oxygen to form a thin oxide film on the surface.

(2) The magnetic metal powder is oxidized with dissolved oxygen by immersing it in an organic solvent to form an oxide film on the surface, followed by rinsing and drying.

(3) An oxidation-resistant film is formed on the surface of the magnetic metal powder by immersing it in an aqueous solution of an oxidizing agent, followed by rinsing, washing with water, washing with an aqueous organic solvent, and then drying.

Method (1) is described, for example, in JP-A-48-79153. This method is the easiest to extract the metal magnetic powder out of the three methods mentioned above, but it is difficult to accurately control the degree of oxidation. Method (2) is disclosed in Japanese Patent Application Laid-open Nos. 49-97738 and 1977-1358.
It is the most well-known method and is disclosed in specifications such as No. 35 and Japanese Patent Application Laid-Open No. 47-12958. However, this method has a fundamental problem in that immediately after production, fine particulate magnetic metal powder, which is highly ignitable, is brought into contact with a flammable organic solvent. The method (3) is described in, for example, the specifications of JP-A-53-41798 and JP-A-51-112465.

This method has not yielded magnetic metal powder with satisfactory magnetic properties. A method characterized in that an alkali compound is used instead of an oxidizing agent and no organic solvent is used at all is also disclosed in Japanese Patent Publications No. 56-12282 and No. 56-12283; The magnetic property values cannot be said to be fully satisfactory.

In view of the current situation, the inventors of the present invention continued their intensive research and attempted to use a corrosion inhibitor that can be used as an aqueous solution for stabilizing magnetic metal powder, obtained good results, and developed the present invention. I ended up completing it.

Conventionally, a simple method is known in which corrosion inhibitors are added to a corrosive environment in order to protect metals exposed to the corrosive environment. According to the Metal Corrosion Prevention Technology Handbook (edited by the Japan Society for the Promotion of Science, published by Nikkan Kogyo Shimbun, 1975, p. 546), corrosion inhibitors are broadly classified into inorganic compounds and organic compounds. The former is said to cause a chemical change on the metal surface in conjunction with the action of dissolved oxygen in water and passivate the metal surface, while the latter adsorbs to the metal surface without causing any change and forms a dense metal. It is said to form a protective film that protects metal surfaces from contact with corrosive substances.

In the present invention, the above-mentioned inorganic compounds are used, namely nitrites, boric acid, borates, silicates, phosphates, molybdates, tungstates, carbonates, bicarbonates and nitrates. . In the case of phosphates, it is more preferable to use them in combination with magnesium, calcium or zinc salts. Zinc sulfate and perboric acid were also used, but the magnetic properties of the magnetic metal powder obtained when these were used were not so excellent. Although chromate and dichromate are well-known corrosion inhibitors, they were not used due to the toxicity of hexavalent chromium.

Considering the magnetic property values (coercive force Hc, maximum magnetic flux density σm, squareness ratio σr/σm) of the obtained metal magnetic powder, the usage amount of each treatment agent is expressed in weight% with respect to the metal magnetic powder.
The following is true. In the case of sodium nitrite, 5 to
Although it can be used in a wide range of 1000%, if it is less than 25%, the σm value will decrease slightly, and if it is more than 100%, it will be used too much, so a range of 25 to 100% is suitable.

In the case of boric acid, sodium borate, and ammonium borate, 50-500% and 50-1000%, respectively.
%, and a range of 50 to 1000% gives good results, but in practice 50 to 100% is sufficient.

Sodium silicate (No. 2) gives satisfactory results in a range of 5 to 1000%, but a range of 10 to 100% is preferred.

In the case of sodium metaphosphate, the amount used is relatively small. It gives satisfactory results in the range of 11.5-23%.

In the case of sodium molybdate and sodium tungstate, considering their solubility in water, the
100% is practical. Perhaps because these have weak oxidizing power, some of the obtained iron powder was burned during drying. It seems necessary to take measures such as using air blowing together.

For sodium carbonate and sodium bicarbonate, 1
Although it can be used over a range of 0 to 500%,
In practice, 50-100% is sufficient.

In the case of sodium nitrate, when the amount used is increased, the σm value of the obtained metal magnetic powder decreases. Therefore 1
A preferred range is 0-100%. In the case of a combination of sodium metaphosphate and magnesium acetate, the former is 0.
8-24%, the latter in the range 1.6-32%.

However, if one is in a small amount, the obtained magnetic metal powder may burn during drying (see the results of sample numbers 11c and 11e in Table 2 below). Therefore, it is desirable to use the former in a range of 3 to 24% and the latter in a range of 3 to 32%.

The combination of sodium metaphosphate and calcium acetate can be used in the ranges of 2.4 to 230% and 0.8 to 90%, respectively. However, if the amount of the treatment agent is too small, the obtained magnetic metal powder may burn in the air (Tables 2, 12a and 12c), and if it is too large, the σm value of the magnetic metal powder decreases. Preferred amounts used are 5 to 100% for sodium metaphosphate and 5 to 50% for calcium acetate.

On the other hand, in the combination of sodium metaphosphate and zinc acetate, 0.8-16% and 1.6-3%
It can be used in a range of 2%. Considering that the magnetic metal powder obtained when the amount used is small (Table 2, 13c), sodium metaphosphate is
It is desirable to use zinc acetate in a range of 5 to 32%.

On the other hand, the temperature of the treatment liquid has a very large effect on the magnetic properties of the obtained magnetic metal powder. When treated at a temperature of 60° C. or higher, the σm and especially the IIc value of the magnetic metal powder obtained show that the acicularity of the magnetic metal powder is completely lost. Therefore, the desirable temperature range of the treatment liquid is 50°C or less, and in practice, a range of 10 to 50°C is suitable.

Note that the ferromagnetic metal powder in the present invention refers to fine acicular powder of iron, iron-cobalt, iron-cobalt-nickel, iron-cobalt-nickel-chromium, and the like.

Hereinafter, the present invention will be explained in detail with reference to Examples. Tables 1 and 2 show the processing agent, the amount of the processing agent, the temperature of the processing solution, and the magnetic property values of the obtained magnetic iron powder. The magnetic property value is
Measurements were made using a vibrating magnetometer in a magnetic field of 10K0e. In Examples 1 to 13, differences in the concentration of processing agents were indicated by alphabetical letters of sample numbers. In addition, Examples 1 to 10 and Comparative Examples 1 to 3 are shown in Table 1, and Examples 11 to 13 are shown in Table 2.
Shown below.

Example 1 Goethite with an average particle size of 0.8 μm and an axial ratio of 20 was used as a raw material. This goethite is 0.8 atomic% based on iron atoms.
Sintering prevention treatment was performed by immersing it in an aqueous solution containing potassium silicate, filtering it, and drying it. The treated goethite was reduced in an electric furnace at 450° C. for 30 minutes under a stream of hydrogen.

After cooling the inside of the electric furnace to 25°C, the reduced iron powder was taken out under a nitrogen stream, and 5 to 100
It was immersed in an aqueous solution (50 ml) containing 0 wt % sodium nitrite and kept at 25°C. After standing for 2 hours, the mixture was filtered, washed with water, and washed with acetone to obtain stabilized ferromagnetic iron powder.

Example 2 Instead of sodium nitrite, 50 to 100
Stabilized magnetic iron powder was obtained in exactly the same manner as in Example 1, except that 0 wt % boric acid was used.

Example 3 Instead of sodium nitrite, 50 to 100
Example 1 except that 0 WT% sodium borate was used.
Stabilized magnetic iron powder was obtained in exactly the same manner as described above.

Example 4 Instead of sodium nitrite, 50 to 100
Stabilized magnetic iron powder was obtained in exactly the same manner as in Example 1, except that 0 wt % ammonium borate was used.

Example 5 Instead of sodium nitrite, add 5 to 1000 to iron powder
Stabilized magnetic iron powder was obtained in exactly the same manner as in Example 1, except that WT% sodium silicate No. 2 was used.

Example 6 Instead of sodium nitrite, 2.3 to 23
Stabilized magnetic iron powder was obtained in exactly the same manner as in Example 1 except that 0 wt % sodium metaphosphate was used.

Example 7 Instead of sodium nitrite, 10 to 100
Stabilization was attempted in exactly the same manner as in Example 1, except that WT% ammonium molybdate was used. Treatment agent is 5
Only in the case of 0 WT%, stabilized iron powder was obtained. In other cases, the iron powder burned during drying.

Example 8 Instead of sodium nitrite, 10 to 100
Stabilized magnetic iron powder was obtained in exactly the same manner as in Example 1 except that WT% ammonium tungstate was used.

Example 9 Instead of sodium nitrite, 10 to 500
Stabilized magnetic iron powder was obtained in exactly the same manner as in Example 1, except that WT% sodium hydrochloride was used.

Example 10 Instead of sodium nitrite, 10 to 500
A stabilized magnetic iron powder was obtained in exactly the same manner as in Example 1, except that WT% sodium bicarbonate was used.

Comparative Example 1 In the same manner as in Example 1, iron powder (0.31 g) obtained by reducing goethite was added to distilled water (50 g) kept at 25°C.
0 ml). After standing for 2 hours, it was filtered, washed with water, and dried under reduced pressure to obtain magnetic iron powder.

Comparative Example 2 Magnetic iron powder was obtained in exactly the same manner as in Example 1, except that the temperature of the aqueous solution containing 50 wt% sodium sulfite relative to the iron powder was changed from 25°C to 60°C.

Comparative Example 3 Magnetic iron powder was obtained in exactly the same manner as in Example 1, except that the temperature of the aqueous solution containing 50 wt% sodium nitrite relative to the iron powder was changed from 25°C to 80°C.

Example 11 Goethite with an average particle diameter of 0.8 μm and an axial ratio of 20 was used as a raw material. This goethite is 0.8 atomic% based on iron atoms.
Sintering prevention treatment was performed by immersing the sample in an aqueous solution containing potassium silicate, rinsing, and drying. The treated goethite was reduced in an electric furnace at 450° C. for 30 minutes under a stream of hydrogen.

After cooling the inside of the electric furnace to 25°C, the reduced iron powder was taken out under a nitrogen stream, and the reduced iron powder was 0.79 to 2
3.8% sodium metaphosphate and 1.59-32.4
% magnesium acetate and maintained at 25°C (50 ml). After leaving it for 2 hours, pass the mouth.
The mixture was washed with water and acetone, and dried under reduced pressure to obtain stabilized magnetic iron powder.

Example 12 Example 11 except that an aqueous solution (50 ml) containing 2.38 to 230% sodium metaphosphate and 0.81 to 89.8% calcium acetate was used with respect to iron powder (0.31 g). Stabilized magnetic iron powder was obtained in exactly the same manner as described above.

Example 13 The same procedure was carried out except that an aqueous solution (50 ml) containing 0.79 to 31.8% sodium metaphosphate and 1.59 to 31.8% zinc acetate was used with respect to iron powder (0.31 g). Example 11
Stabilized magnetic iron powder was obtained using exactly the same method as ■

Claims (6)

[Claims] 1. Stable ferromagnetism characterized by immersing magnetic metal powder obtained by reducing a raw material mainly composed of acicular iron hydroxide oxide or ferric oxide with a reducing gas in an aqueous solution of a corrosion inhibitor. Method for producing metal powder. 2. Corrosion inhibitors include nitrites, boric acid, borates, silicates, phosphates, molybdates, tungstates,
2. The method of claim 1, wherein the salt is a carbonate, bicarbonate, or nitrate. 3. The amount of corrosion inhibitor used is 5 to 50% relative to the magnetic metal powder.
3. A method according to claim 1 or 2, wherein the amount is in the range of 1000% by weight. 4. Claim 1, wherein the corrosion inhibitor is a combination of phosphate and a salt of magnesium, calcium or zinc.
The method described in section. 5. The amount of corrosion inhibitor used is 0.00% relative to the magnetic metal powder.
5. The method of claim 4, wherein the amount ranges from 8 to 230% by weight. 6. The method according to claim 1, 2, 3, 4 or 5, characterized in that the temperature of the aqueous solution of the corrosion inhibitor is maintained at 10 to 50°C.