JP3488882B2 - Method for producing single-phase γ'-Fe4N ultrafine particles - Google Patents

Description

Detailed Description of the Invention

[0001]

This invention relates to a single phase γ'-Fe ₄ N.
The present invention relates to a method for producing ultrafine particles. More specifically, the present invention relates to a single-phase production method of γ'-Fe ₄ N ultrafine particles having a large saturation magnetization and a very high stability and useful for magnetic recording media and the like.

[0002]

2. Description of the Related Art Iron nitride is used in magnetic recording materials such as magnetic tapes and floppy disks, electrophotographic methods, electrostatic recording methods, etc. because it has a large magnetic moment and high hardness. It has applications such as magnetic materials. In particular, γ'-Fe ₄ N has a large saturation magnetization and a very good stability, and is therefore advantageous as a magnetic recording medium or the like. Since these material characteristics are greatly influenced by the purity and particle size of the magnetic powder, a high-purity, fine powder having a sharp particle size distribution is required as a raw material powder for a homogeneous magnetic material.

Conventionally, various methods have been proposed for producing such ultrafine iron nitride particles, but unfortunately, a suitable production method for obtaining a single phase of γ'-Fe ₄ N ultrafine particles. Has not been found. For example, an attempt was made to produce acicular iron nitride powder by the ammonia nitriding method,
It has not been put to practical use. Further, an evaporation method in an ammonia gas in which iron is evaporated in an ammonia atmosphere to obtain a nitride, a microwave plasma nitriding method, and an iron chloride-ammonia-based gas phase reaction method are known, but either method is also known. ,
In addition to γ′-Fe ₄ N, ε-Fe _x N (2 <x ≦ 3),
The fact is that ζ-Fe ₂ N, α-Fe, γ-Fe, and the like are mixed, and single-phase γ′-Fe ₄ N ultrafine particles have not been obtained.

Therefore, the inventors of the present invention have already
It proposes a method for producing ultrafine metal nitride particles by generating an arc in nitrogen or a mixed gas of nitrogen and an inert gas or hydrogen to evaporate, cool and condense the metal. However, even with this manufacturing method, a nitride of a metal such as iron having a low affinity for nitrogen cannot be obtained.

Further, a method of introducing metal vapor generated by arc melting of a metal to a nitriding apparatus and performing a nitriding treatment to obtain a metal nitride has been developed, but an example of iron has been reported. No, in fact, the manufacturing conditions therefor are completely unknown. The present invention has been made in view of the circumstances as described above, eliminates the drawbacks of the conventional method, and allows the γ '
It is an object of the present invention to provide a new production method capable of obtaining a single phase of —Fe ₄ N ultrafine particles.

[0006]

In order to solve the above-mentioned problems, the present invention is to dilute ammonia with an inert gas into a mixed gas, and to keep the ambient ammonia concentration in the mixed gas at 40% or less. Provided is a method for producing single-phase γ′-Fe ₄ N ultrafine particles by melting, evaporating and condensing pure iron by a DC arc generated in this atmosphere. Further, in the method of the present invention, using a DC arc plasma generator consisting of a vertical cylindrical closed container, ammonia and an inert gas in a tangential direction from a gas inlet provided on the upper side of the closed container. While introducing a mixed gas to generate a swirling airflow downward, arc discharge is performed while ejecting an atmosphere gas from the gas inlet provided in the upper part of the arc discharge electrode to the periphery of the arc discharge electrode, melting pure iron and Single-phase γ'- produced by evaporation
Another aspect is that the Fe ₄ N ultrafine particles are quickly passed through a cooling section below the arc discharge electrode to be cooled and then collected in a collector.

[0007]

As described above, the present invention enables the production of single-phase γ'-Fe ₄ N ultrafine particles by arc discharge under a characteristic ammonia concentration condition of 40% or less. In this case, the ammonia concentration is in a limited range of 40% or less, and for example, about 1 to 40% is exemplified.

Thus, the ambient ammonia concentration is 40%
In the following, the generation mechanism by which single-phase γ'-Fe ₄ N ultrafine particles are obtained is considered as follows. That is, when the heat of the arc dissociates ammonia and the resulting hydrogen dissolves in the molten iron and is released as a molecular gas, metal vapor is generated (forced evaporation). The metal vapor is cooled and condensed to form ultrafine particles.At this time, the metal vapor and ammonia whose reactivity is increased by the radiant heat of the arc efficiently react with each other to form an iron nitride. It is considered that single-phase γ'-Fe ₄ N ultrafine particles can be obtained by condensing and cooling the iron nitride.

When the atmospheric ammonia concentration exceeds 40%, γ'-Fe ₄ N single-phase ultrafine particles cannot be obtained, and a mixture of α-Fe and γ-Fe is obtained. This is because the hydrogen produced by the dissociation of ammonia becomes excessively large, which increases the generation rate of metal vapor and condenses and cools with insufficient nitriding, so in addition to γ'-Fe ₄ N, α-F.
It is considered that this is because ultrafine particles in which e and γ-Fe are mixed are generated. For this reason, the nitriding ratio is determined by the relationship between the generation rate of metal vapor and the ammonia concentration around the arc. Therefore, in order to produce iron nitride ultrafine particles having a relatively low affinity for nitrogen, the above-mentioned 40% is used. Mixing of by-products is unavoidable unless it is manufactured under the limited condition of ammonia concentration of less than or equal to%.

In this case, ammonia is diluted with an inert gas such as argon (Ar) or helium (He) before use. The current condition for arc discharge is usually preferably about 100 to 300 A, and the voltage condition is determined by the device. Atmospheric gas pressure is
It may be at or near atmospheric pressure. Further, the purity of the pure iron as a raw material is about the same as that of ordinary electrolytic iron, and a commercially available product may be used.

The γ'-Fe ₄ N single-phase ultrafine powder obtained by the present invention is ultrafine particles having a high purity and a sharp particle size distribution. The size is 1 μm or less in particle size, and more preferably 0.001 to 0.3 μm. As an apparatus for carrying out the present invention, various apparatuses such as an ordinary arc melting furnace can be used.

FIG. 1 is a vertical side view of a DC arc plasma generator using a vertical cylindrical closed container as an example. This apparatus has a DC power source (1) and a closed container (2), and a gas inlet (7) opened in the cutting line direction is provided on the vessel wall of this closed container (2) to form a closed container (2). A cooler (8) is provided in the lower part of the. Also,
An arc (3) is generated by the direct current from the direct current power supply (1) between the arc discharge electrode (6) and the pure iron (4) placed on the metal melting table (5) which is a water-cooled copper hearth. Pure iron (4) is melted and evaporated by this arc (3),
Reacts with ammonia to produce ultrafine iron nitride.
The generated ultrafine particles of iron nitride are carried into the cooler (8) by the downward swirling airflow of the ammonia-argon mixed gas ejected from the gas introduction port (7), and are rapidly cooled and collected in the collector ( It is guided to 9) and collected. It is preferable that the generated ultrafine particles of iron nitride are rapidly cooled and collected. In addition, by spraying an atmospheric gas around the electrode from a gas inlet (7 ') provided on the arc discharge electrode (6), the electrode is protected and the generated iron nitride ultrafine particles are transferred to the swirling airflow. Will be more effective.

Hereinafter, the present invention will be described in more detail with reference to examples. Of course, the present invention is not limited to the following examples.

[0014]

EXAMPLES In the following examples, the apparatus of FIG. 1 was used, the atmospheric gas pressure was 0.1 MPa, and the atmospheric gas flow rate was 3
0 l / min, arc current 150 A, voltage 26-56
A DC arc discharge was generated at V. Example 1 Ultrafine particles were produced in an atmosphere of 20% ammonia-80% argon. The powder X-ray diffraction pattern of the obtained ultrafine particles was a single phase of γ'-Fe ₄ N as shown in FIG. Example 2 Ultrafine particles were produced in an atmosphere of 30% ammonia-70% argon. The powder X-ray diffraction pattern of the obtained ultrafine particles was γ'-Fe ₄ N single phase as shown in FIG. Example 3 Ultrafine particles were produced in an atmosphere of 40% ammonia-60% argon. The powder X-ray diffraction pattern of the obtained ultrafine particles was a single phase of γ'-Fe ₄ N as shown in FIG. Comparative Example 1 Ultrafine particles were produced in an atmosphere of 50% ammonia-50% argon. The powder X-ray diffraction pattern of the obtained ultrafine particles is α-Fe, γ-Fe, γ'-F as shown in FIG.
The particles were ultrafine particles mixed with e ₄ N.

[0015]

According to the method of the present invention, when a pure iron is melted, evaporated and condensed by a direct current arc generated in a mixed gas atmosphere of ammonia and an inert gas to produce ultrafine iron nitride particles, the ammonia concentration in the atmosphere is increased. By setting 1 to 40%, single-phase γ'-Fe ₄ N ultrafine particles can be obtained without any special post-treatment in the nitriding furnace, and there is no problem of mixing by-products in the conventional method. Absent.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a DC arc melting device.

FIG. 2 is a powder X-ray diffraction pattern as an example of iron nitride ultrafine particles obtained by the method of the present invention.

FIG. 3 is a powder X-ray diffraction pattern as another example of the iron nitride ultrafine particles obtained by the method of the present invention.

FIG. 4 is a powder X-ray diffraction pattern as yet another example of the iron nitride ultrafine particles obtained by the method of the present invention.

FIG. 5 is a powder X-ray diffraction pattern as a comparative example of iron nitride ultrafine particles.

[Explanation of symbols]

1 DC power supply 2 closed container 3 arc 4 pure iron 5 Metal melting table 6 Arc discharge electrode 7 gas inlet 7'gas inlet 8 cooler 9 collector

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazunori Takagi, 217, Jyuji, Kashiwa City, Chiba Prefecture, Powder Tech Co., Ltd. (72) Inventor, Toshio Honjo, 217, Jyuji, Kyoji City, Chiba Prefecture, Powder Tech Co., Ltd. (72) Inventor Masaya Ozawa, 217 Jujiji, Kashiwa-shi, Chiba Powder Tech Co., Ltd. (56) References JP-A-61-141606 (JP, A) JP-A-57-26101 (JP, A) JP-A-62- 283805 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C01B 21/00-21/50

Claims (2)

(57) [Claims] 1. A method for producing ultrafine iron nitride particles by melting and evaporating pure iron by arc discharge generated in a mixed gas atmosphere of ammonia and an inert gas,
A method for producing single-phase γ'-Fe ₄ N ultrafine particles, characterized in that the atmospheric ammonia concentration is 40% or less. 2. A direct current arc plasma generator comprising a vertical cylindrical hermetic container, wherein a mixed gas of ammonia and an inert gas is introduced tangentially from a gas inlet provided on the upper side of the hermetic container to a lower side. The generated single phase melts and evaporates pure iron by generating a swirling air flow to the arc discharge electrode and discharging the atmospheric gas from the gas inlet provided on the upper part of the arc discharge electrode to the periphery of the arc discharge electrode. of γ'-Fe ₄ N producing single phase γ'-Fe ₄ N ultrafine particles according to claim 1, characterized in that collecting the collector after cooling through the cooling unit of the ultrafine particles arcing electrode downward Method.