JP2014207341A - Iron carbide material, manufacturing method thereof, and magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an iron carbide material superior in magnetic property, and a method for manufacturing such an iron carbide material.SOLUTION: An iron carbide material consists of powder which comprises: FeCparticles, and a carbon coating layer on at least a part of the surface of each particle. A method for manufacturing the iron carbide material comprises: a preparation step which includes preparing iron powder; a mixing step which includes adding carbon powder to the iron powder, and mixing up the iron powder and the carbon powder, thereby producing iron powder with carbon attached thereto; a carbonization step which includes performing a reduction heat treatment on the iron powder with carbon attached thereto in a reducing gas atmosphere to cause a reaction of a part of the iron and carbon to produce FeC and to synthesize precursor particles including the remaining iron and FeC, and forming a carbon coating layer on the surface of each precursor particle, thereby producing precursor powder; and a diffusion step which includes performing a diffusion heat treatment on the precursor powder with a magnetic field applied thereto to synthesize FeCparticles from the remaining iron and FeC, to produce iron carbide powder having a coating layer on the surface of each FeCparticle.

Description

  The present invention relates to an iron carbide material, a method for manufacturing an iron carbide material, and a magnet.

  As permanent magnets used for motors, generators, etc., ferrite magnets using iron oxide, metal magnets using Fe-Al-Ni-Co alloys and Fe-Cr-Co alloys, Nd-Fe-B Rare earth magnets using an alloy based on Sm-Fe-N are used.

Recently, research has been conducted on magnet materials that do not use rare metals such as Ni, Co, and rare earth metals. As an alternative material candidate, iron nitride (Fe ₁₆ N ₂ ) has attracted attention (see Patent Documents 1 and 2). Fe ₁₆ N ₂ is expected as a magnet material because of its high saturation magnetization and theoretically high maximum energy product (BH) max.

On the other hand, iron carbide (Fe ₁₆ C ₂ ), which is an interstitial iron compound similar to Fe ₁₆ N ₂ , is known (see Patent Document 3). Patent Document 3 describes that an Fe ₁₆ C ₂ film is used as a recording medium film. In Patent Document 3, an Fe ₁₆ C ₂ film having a structure in which C is intruded into an Fe lattice is manufactured by accelerating and injecting C ions into an Fe single crystal film and then performing heat treatment.

JP 2012-246174 A JP 2012-253248 A JP-A-8-203735

In Patent Document 3, a film of Fe ₁₆ C ₂ is produced and used as a recording medium film. However, since it is a film, it is difficult to use it for a magnet that requires an arbitrary size and shape. . In the case of using the Fe ₁₆ C ₂ magnetic material such as a magnet, it is desired to be excellent in magnetic properties.

This invention is made | formed in view of the said situation, and one of the objectives of this invention is to provide the iron carbide material of the powder form or molded object form which is excellent in a magnetic characteristic.
Another object of the present invention is to provide a method for producing an iron carbide material capable of producing a powdered or molded iron carbide material having excellent magnetic properties with high productivity.
Another object of the present invention is to provide a magnet having excellent magnetic properties.

The iron carbide material of the present invention is a powder comprising Fe ₁₆ C ₂ particles and a carbon coating layer on at least a part of the surface of the particles.

The iron carbide material of the present invention is a molded body including Fe ₁₆ C ₂ particles and a grain boundary phase of carbon between the particles.

The manufacturing method of the iron carbide material of this invention is equipped with the following processes.
(A) A preparation step of preparing iron powder containing iron oxide particles.
(B) A mixing step of adding carbon powder containing carbon particles to the iron powder, mixing the iron powder and the carbon powder, and attaching the carbon particles to the surface of the iron oxide particles to produce the carbon-attached iron powder.
(C) A reduction heat treatment is performed on the carbon-adhered iron powder in a reducing gas atmosphere, and a part of Fe generated by reducing iron oxide reacts with carbon to generate Fe ₃ C, and the remaining Fe and Fe A carbonization step of synthesizing precursor particles containing ₃ C and forming a precursor powder by forming a coating layer of carbon on the surface of the precursor particles.
(D) subjected to a diffusion heat treatment while applying a magnetic field to the precursor powder, to synthesize particles of _Fe 16 _{C 2} from the rest and the Fe ₃ C of _Fe, comprises a coating layer on the surface of the _Fe 16 _{C 2} particles A diffusion process for producing iron carbide powder.

The manufacturing method of the iron carbide material of this invention is equipped with the following processes.
(A) A preparation step of preparing iron powder containing iron oxide particles.
(B) A mixing step of adding carbon powder containing carbon particles to the iron powder, mixing the iron powder and the carbon powder, and attaching the carbon particles to the surface of the iron oxide particles to produce the carbon-attached iron powder.
(C) A pre-molding step in which carbon-adhered iron powder is pressure-molded to produce an intermediate molded body
(D) The intermediate formed body is subjected to a reduction heat treatment in a reducing gas atmosphere, and a part of Fe produced by reducing iron oxide is reacted with carbon to produce Fe ₃ C, and the remaining Fe and the Fe A carbonization step of synthesizing precursor particles containing ₃ C and producing a precursor compact by forming a grain boundary phase of carbon between the precursor particles.
(E) is subjected to diffusion heat treatment while applying a magnetic field to the precursor molded bodies were synthesized particles _Fe 16 _{C 2} from the rest and the Fe ₃ C of _Fe, the grain boundary phase between _Fe 16 _{C 2} particles A diffusion process for producing an iron carbide formed body.

The iron carbide material of the present invention is excellent in magnetic properties and can be suitably used for magnetic materials such as magnets.
Moreover, the manufacturing method of the iron carbide material of this invention can manufacture the iron carbide material of a powder form or a molded object excellent in a magnetic characteristic with sufficient productivity.

[Description of Embodiment of the Present Invention]
Even if iron, iron alloy, or iron compound is simply carbonized to synthesize iron carbide, the carbon is taken in excessively and Fe ₃ C, which is inferior in magnetic properties to Fe ₁₆ C _2, is generated. This is because iron carbide is more stable in the Fe ₃ C state than in the Fe ₁₆ C ₂ state. As a result of intensive studies by the present inventors, it has been found that Fe ₁₆ C ₂ can be efficiently synthesized from Fe and Fe ₃ C by subjecting a compound containing Fe and Fe ₃ C to a specific heat treatment. The contents of the embodiments of the present invention will be listed and described below.

(1) The iron carbide material of the embodiment is a powder comprising Fe ₁₆ C ₂ particles and a carbon coating layer on at least a part of the surface of the particles.

According to the iron carbide material (powder) of the above-described embodiment, the magnetic properties are excellent by providing ferromagnetic Fe ₁₆ C ₂ particles (hereinafter, sometimes simply referred to as “Fe ₁₆ C ₂ particles”). The term “Fe ₁₆ C ₂ particles” as used herein refers to particles containing Fe ₁₆ C ₂ as a main component, and the content of the Fe ₁₆ C ₂ component in the particles is 80% by volume or more. .

The iron carbide material (powder) of the embodiment can be suitably used for a magnetic material such as a magnet. When the iron carbide powder of the embodiment is used as a magnetic material, it can be formed into an arbitrary size and shape. For example, a molded body obtained by solidifying a powder with a binder resin or a molded body obtained by compression molding a powder can be used. When such a molded body is used as a magnet material, it is easy to demagnetize if Fe ₁₆ C ₂ particles are adhered to each other (magnetically coupled). However, the iron carbide material (powder) of the embodiment is provided with a nonmagnetic carbon coating layer (hereinafter sometimes simply referred to as “carbon coating layer”) on the surface of Fe ₁₆ C ₂ particles, so that the coating layer is It works to break the magnetic coupling between the Fe ₁₆ C ₂ particles, thereby improving the magnetic properties.

  (2) As one form of the iron carbide material (powder) of embodiment, the average particle diameter of the said particle | grain is 50 nm or more and 100 nm or less.

From the viewpoint of improving the magnetic properties, the Fe ₁₆ C ₂ particles are preferably fine, and the average particle size of the particles is preferably, for example, nano-order (1000 nm or less). In particular, when the iron carbide material (powder) of the embodiment is used as a magnet material, the average particle size of the Fe ₁₆ C ₂ particles is more preferably 50 nm or more and 100 nm or less.

  (3) As one form of the iron carbide material (powder) of embodiment, it is mentioned that the average thickness of the said coating layer is 2.5 nm or more.

When utilizing compact molded carbonized iron (powder) embodiment the magnet material, as described above, the carbon coating layer is worked off magnetic coupling between the particles of Fe ₁₆ C _2. Here, from the viewpoint of breaking the magnetic coupling, it is preferable that the Fe ₁₆ C ₂ particles are separated by 5 nm or more with a non-magnetic material. When the powder of the iron carbide material of the embodiment is molded, since the coating layer of each particle is interposed between adjacent particles, the average thickness of the carbon coating layer on the particle surface in the powder is 2.5 nm or more preferable. On the other hand, the upper limit of the average thickness of the carbon coating layer is preferably 10% or less of the average particle diameter of the Fe ₁₆ C ₂ particles from the viewpoint of securing the Fe ₁₆ C ₂ component in the powder.

  (4) The iron carbide material of the embodiment is obtained by molding the iron carbide material powder of the above-described embodiment.

  An iron carbide material compact (iron carbide powder compact) obtained by molding the iron carbide powder of the embodiment is an aggregate of powder particles having an arbitrary size and shape. Examples of the molded body include a form in which powder is solidified with a binder resin and a form in which powder is compression-molded.

(5) The iron carbide material according to another embodiment is a molded body including Fe ₁₆ C ₂ particles and a carbon grain boundary phase between the particles.

According to the iron carbide material (molded body) of the above-described embodiment, the magnetic properties are excellent by providing the particles of the ferromagnetic phase Fe ₁₆ C ₂ . The shaped body of the iron carbide material of the embodiment has a structure in which Fe ₁₆ C ₂ particles are bonded together by a grain boundary phase interposed between the particles, and can have an arbitrary size and shape.

The iron carbide material (molded body) of the embodiment can be suitably used for a magnetic material such as a magnet. When the molded body of the iron carbide material of the embodiment is used as a magnet material, it is easy to demagnetize if the Fe ₁₆ C ₂ particles are bonded (magnetically coupled). However, the iron carbide material (molded body) of the embodiment includes a non-magnetic carbon grain boundary phase (hereinafter sometimes simply referred to as “carbon grain boundary phase”) between Fe ₁₆ C ₂ grains. The magnetic phase is improved by acting to cut the magnetic coupling between the grains having the field phase of Fe ₁₆ C ₂ .

  (6) As one form of the iron carbide material (molded body) of the embodiment, the average particle diameter of the particles is 50 nm or more and 100 nm or less.

From the viewpoint of improving the magnetic properties, the Fe ₁₆ C ₂ particles are preferably fine, and the average particle size of the particles is preferably, for example, nano-order (1000 nm or less). In particular, when the iron carbide material (molded body) of the embodiment is used as a magnet material, the average particle size of the Fe ₁₆ C ₂ particles is more preferably 50 nm or more and 100 nm or less.

  (7) As one form of the iron carbide material (molded body) of the embodiment, the average thickness of the grain boundary phase is 5 nm or more.

When the iron carbide material (molded body) of the embodiment is used as a magnet material, as described above, the carbon grain boundary phase has a function of cutting the magnetic coupling between Fe ₁₆ C ₂ particles. Here, from the viewpoint of breaking the magnetic coupling, the average thickness of the carbon grain boundary phase which is a nonmagnetic phase is preferably 5 nm or more. On the other hand, the upper limit of the average thickness of the carbon grain boundary phase is preferably 20% or less of the average particle diameter of the Fe ₁₆ C ₂ particles from the viewpoint of securing the Fe ₁₆ C ₂ component in the molded body.

  (8) As one form of the iron carbide material (molded body) of the embodiment, the squareness ratio is 0.8 or more.

  When the squareness ratio is 0.8 or more, a strong magnet having high magnetic anisotropy can be obtained. More preferably, the squareness ratio is 0.85 or more.

(9) The manufacturing method of the iron carbide material of embodiment comprises the following processes.
(A) Preparatory step of preparing iron powder containing iron oxide particles (B) Adding carbon powder containing carbon particles to iron powder, mixing the iron powder and carbon powder, on the surface of the iron oxide particles A mixing step in which carbon particles are adhered to produce carbon-adhered iron powder.
(C) Reducing heat treatment of the carbon-attached iron powder in a reducing gas atmosphere to react part of Fe produced by reducing iron oxide with carbon to produce Fe ₃ C, and the rest of Fe and Fe ₃ A carbonization step of synthesizing precursor particles containing C and forming a precursor powder by forming a coating layer of carbon on the surface of the precursor particles.
(D) subjected to a diffusion heat treatment while applying a magnetic field to the precursor powder, to synthesize particles of _Fe 16 _{C 2} from the rest and the Fe ₃ C of _Fe, comprises a coating layer on the surface of the _Fe 16 _{C 2} particles A diffusion process for producing iron carbide powder.

According to the method for producing an iron carbide material (powder) of the embodiment described above, precursor particles containing Fe and Fe ₃ C can be synthesized by subjecting the carbon-adhered iron powder to a reduction heat treatment in the carbonization step. . At the same time, a carbon coating layer can be formed on the surface of the precursor particles. In the diffusion step, a diffusion heat treatment is performed with a magnetic field applied to the precursor powder to synthesize Fe ₁₆ C ₂ from Fe and Fe ₃ C, and a coating layer is formed on the surface of the Fe ₁₆ C ₂ particles. The iron carbide powder provided is obtained. Here, by applying a magnetic field in the diffusion step, the Fe basic lattice (body-centered cubic lattice; BCC) is stretched in the magnetic field application direction, and Fe atoms-Fe atoms are aligned in one direction along the stretched lattice axis. It is possible to make it easy for C to enter in between and make it difficult for C to enter in the other two directions. That is, the intrusion direction of C can be regulated. Therefore, by performing diffusion heat treatment in a state where a magnetic field is applied, in the precursor particles containing Fe and Fe ₃ C, C atoms existing in the lattice where Fe ₃ C is not stretched are diffused, and due to the magnetostriction of Fe Fe ₁₆ C ₂ can be efficiently synthesized from Fe and Fe ₃ C by selectively intruding and rearranging between Fe atoms-Fe atoms arranged in one direction along the stretched lattice axis. Further, since a carbon coating layer is simultaneously formed on the surface of the precursor particles in the carbonization step, it is not necessary to separately coat a nonmagnetic material on the surface of the finally obtained iron carbide powder. Therefore, according to the manufacturing method of the iron carbide material (powder) of the above-described embodiment, a powdered iron carbide material having excellent magnetic properties can be manufactured with high productivity. The term “iron powder containing iron oxide particles” as used herein refers to a powder mainly composed of iron oxide particles, and contains 80 vol% or more of iron oxide particles. The “carbon powder containing carbon particles” is a powder mainly composed of carbon particles, and contains 80% by volume or more of carbon particles.

(10) The manufacturing method of the iron carbide material of another embodiment is provided with the following processes.
(A) A preparation step of preparing iron powder containing iron oxide particles.
(B) A mixing step of adding carbon powder containing carbon particles to the iron powder, mixing the iron powder and the carbon powder, and attaching the carbon particles to the surface of the iron oxide particles to produce the carbon-attached iron powder.
(C) A pre-molding step in which carbon-adhered iron powder is pressure-molded to produce an intermediate molded body.
(D) The intermediate formed body is subjected to a reduction heat treatment in a reducing gas atmosphere, and a part of Fe produced by reducing iron oxide is reacted with carbon to produce Fe ₃ C, and the remainder of Fe and Fe ₃ A carbonization step of synthesizing precursor particles containing C and forming a precursor grain by forming a grain boundary phase of carbon between the precursor particles.
(E) is subjected to diffusion heat treatment while applying a magnetic field to the precursor molded bodies were synthesized particles _Fe 16 _{C 2} from the rest and the Fe ₃ C of _Fe, the grain boundary phase between _Fe 16 _{C 2} particles A diffusion process for producing an iron carbide formed body.

According to the method for manufacturing the iron carbide material (molded body) of the above-described embodiment, in the carbonization step, the intermediate molded body obtained by pressure-molding the carbon-adhered iron powder is subjected to a reduction heat treatment, thereby including Fe and Fe ₃ C. Precursor particles can be synthesized. At the same time, a grain boundary phase of carbon can be formed between the precursor particles. Then, in the diffusion step, a diffusion heat treatment is performed in a state where a magnetic field is applied to the precursor compact, whereby Fe ₁₆ C ₂ is synthesized from Fe and Fe ₃ C, and a coating layer is formed on the surface of the Fe ₁₆ C ₂ particles. Is obtained. As described above, by diffusion heat treatment while applying a magnetic field, C atoms in the precursor particles containing Fe and Fe ₃ C is repositioned, the _Fe 16 _{C 2} from Fe and Fe ₃ C efficiently Can be synthesized. Therefore, according to the manufacturing method of the iron carbide material (molded body) of the above-described embodiment, a molded iron carbide material having excellent magnetic properties can be manufactured with high productivity.

Moreover, in the manufacturing method of the iron carbide material (molded body) of the above-described embodiment, since the diffusion step is performed in the state of the molded body, the synthesized Fe ₁₆ C ₂ crystals can be oriented in the magnetic field application direction, Magnetic anisotropy can be imparted to the finally obtained iron carbide molded body.

(11) as a form of the manufacturing method of the embodiment of the carbide steel material (powder or molded body), and that the iron oxide is γ-Fe ₂ O _3.

Since iron oxide is γ-Fe ₂ O ₃ (maghemite), it can be easily reduced in the carbonization step and oxygen can be easily removed, so that the productivity of the iron carbide material can be improved. Moreover, since it is easy to reduce, the temperature of the reduction heat treatment can be lowered.

  (12) As one form of the manufacturing method of the iron carbide material (powder or molded object) of embodiment, the addition amount of carbon is 2.6 mass% or more and 4.0 mass% or less with respect to content of Fe in iron powder. And so on.

Carbon powder (carbon particles) serves as a carbon source for generating Fe ₃ C in the carbonization step. The amount of Fe ₃ C produced changes by adjusting the amount of carbon added. By making the addition amount of carbon 2.6 mass% or more with respect to the Fe content in the iron powder, Fe ₃ C is sufficiently generated in the carbonization step, and Fe ₁₆ C ₂ can be sufficiently synthesized in the diffusion step. , Magnetic properties can be improved. On the other hand, by making the addition amount of carbon 4.0% by mass or less with respect to the Fe content in the iron powder, it is possible to suppress excessive generation of Fe ₃ C in the carbonization step, and Fe ₁₆ in the diffusion step. Since C ₂ can be sufficiently synthesized and Fe ₃ C hardly remains, the magnetic characteristics can be improved. The carbon powder also acts as a carbon source for the carbon coating layer or carbon grain boundary phase.

  (13) As one form of the manufacturing method of the iron carbide material (powder or molded object) of embodiment, reducing gas in a carbonization process is made into CO gas.

By using the reducing gas as CO gas, it is possible to suppress the escape of C from the surface of the synthesized precursor particles, and to easily make the C concentration of Fe ₃ C contained in the particles uniform from the surface to the inside. As a result, it becomes easy to synthesize Fe ₁₆ C ₂ in the diffusion step.

  (14) As one form of the manufacturing method of the iron carbide material (powder or molded object) of embodiment, it is mentioned that the temperature of the diffusion heat processing in a diffusion process shall be 200 degreeC or more and 210 degrees C or less.

By setting the temperature of the diffusion heat treatment to 200 ° C. or more, diffusion of C can be promoted, and Fe ₁₆ C ₂ can be synthesized more efficiently. On the other hand, the stabilization of Fe ₃ C can be suppressed by setting the temperature of the diffusion heat treatment to 210 ° C. or less.

  (15) As one form of the manufacturing method of the iron carbide material (powder or molded object) of embodiment, it is mentioned that the magnetic field in a diffusion process shall be 3T or more.

By setting the magnetic field to 3T or more, the magnetostriction of the Fe basic lattice becomes larger, and Fe ₁₆ C ₂ can be synthesized more efficiently.

  (16) The magnet of the embodiment is obtained by magnetizing the iron carbide material (powder or molded body) of the above-described embodiment.

  According to the magnet of the embodiment, since the iron carbide material of the above-described embodiment is used, the magnetic characteristics are excellent.

[Details of the embodiment of the present invention]
Details of the embodiment of the present invention will be described below. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to the claim are included.

[Iron carbide]
The iron carbide material according to the embodiment includes a powdery material (iron carbide powder) and a compacted body (iron carbide molded body).

{Iron carbide powder}
The iron carbide powder includes Fe ₁₆ C ₂ particles and a carbon coating layer on at least a part of the surface of the particles. By molding the iron carbide powder into an arbitrary size and shape, a molded body of the iron carbide powder can be obtained. Examples of the molding method include solidification with a binder resin and compression molding. The iron carbide powder compact can be used as a magnet material.

(Fe ₁₆ C ₂ particles)
In the iron carbide powder, the average particle diameter of the Fe ₁₆ C ₂ particles is preferably 10 nm or more and 1000 nm or less from the viewpoint of magnetic properties, and particularly when the iron carbide powder is used as a magnet material, it is 50 nm or more and 100 nm or less. It is preferable.

(Carbon coating layer)
When using iron carbide powder compact to the magnet material, the carbon coating layer, prevents the particles of the Fe ₁₆ C ₂ to stick, there is work to cut magnetic coupling between the particles of Fe ₁₆ C ₂ . In the iron carbide powder molded body, since the coating layer of each particle is interposed between adjacent particles, the interval between the particles is twice or more the thickness of the coating layer. In the iron carbide powder, the average thickness of the carbon coating layer is preferably 2.5 nm or more from the viewpoint of breaking the magnetic coupling, and from the viewpoint of securing the Fe ₁₆ C ₂ component in the powder, the average of the Fe ₁₆ C ₂ particles The particle size is preferably 10% or less (eg, 10 nm or less).

{Iron carbide molded body}
The iron carbide formed body includes Fe ₁₆ C ₂ particles and a grain boundary phase of carbon between the particles. The iron carbide molded body has a structure in which Fe ₁₆ C ₂ particles are bonded to each other by a carbon grain boundary phase, and can have an arbitrary size and shape.

(Fe ₁₆ C ₂ particles)
In the iron carbide molded body, the average particle diameter of the Fe ₁₆ C ₂ particles is preferably 10 nm or more and 1000 nm or less from the viewpoint of magnetic properties, and particularly when the iron carbide molded body is used as a magnet material, 50 nm or more and 100 nm or less. It is preferable that

(Carbon grain boundary phase)
When the iron carbide molded body is used as a magnet material, the carbon grain boundary phase has a function of cutting the magnetic coupling between Fe ₁₆ C ₂ particles. In iron carbide formed body, the average thickness of the carbon grain boundary phase is preferably at least 5nm from the standpoint of cutting the magnetic coupling, in order to ensure a Fe ₁₆ C ₂ components in the molded body, the Fe ₁₆ C ₂ particles The average particle size is preferably 20% or less (eg, 20 nm or less).

[Method of manufacturing iron carbide]
In the manufacturing method of the iron carbide material which concerns on embodiment, there exist the manufacturing method which produces iron carbide powder, and the manufacturing method which produces an iron carbide molded object.

{Production method of iron carbide powder}
The method for producing iron carbide powder includes a preparation process, a mixing process, a carbonization process, and a diffusion process. Each step will be described in detail.

(Preparation process)
In the preparation step, iron powder containing iron oxide particles is prepared. As iron oxide, for example, γ-Fe ₂ O ₃ (maghemite), α-Fe ₂ O ₃ (hematite), Fe ₃ O ₄ (magnetite) and the like can be used. Among them, _γ-Fe 2 _{O 3} is preferable in view of easy reduction in carbonization process in a later step. Basically, the size of the iron oxide particles as the raw material and the size of the finally obtained Fe ₁₆ C ₂ particles are substantially equal, so the average particle size of the iron oxide particles is also nano-order (1000 nm Or less). The average particle diameter of the particles is a particle diameter at which the integrated mass measured using, for example, a laser diffraction particle size distribution device is 50%. Further, by setting the average particle size of the iron oxide particles to nano-order, it is easy to diffuse C from the surface of the particles in the subsequent carbonization step, and to make the C concentration uniform from the surface to the inside. Such fine iron oxide particles can be produced by pulverizing an iron oxide powder or a sintered body. For example, after coarsely pulverizing until the particle size becomes several microns (eg, about 1 to 5 μm), finely pulverizing until the particle size becomes nano-order (eg, 50 to 100 nm). For coarse pulverization, mechanical pulverization such as a jaw crusher, roll crusher, stamp mill, brown mill, or ball mill can be used, and for fine pulverization, for example, a bead mill or a jet mill can be used. Nano-order fine iron oxide powder (nano iron oxide powder) can be synthesized by chemical methods such as hydrothermal synthesis, coprecipitation, reverse micelle method, sol-gel method and the like.

(Mixing process)
In the mixing step, carbon powder containing carbon particles is added to the iron powder, the iron powder and the carbon powder are mixed, and the carbon particles are attached to the surface of the iron oxide particles to produce the carbon-attached iron powder. As carbon, for example, graphene, graphite (graphite), activated carbon, carbon nanotube, fullerene, carbon black, and the like can be used. Among them, the single-layer graphene is flat and easily attached to the surface of the iron oxide particles. The average particle size of the carbon particles is preferably smaller than the average particle size of the iron oxide particles from the viewpoint of adhering to the surface of the iron oxide particles. If the surfaces of the iron oxide particles are completely covered with carbon particles, the reducing gas and the iron oxide particles do not come into contact with each other in the subsequent carbonization step, making it difficult to reduce the iron oxide particles. By mixing the iron powder and the carbon powder while adhering the carbon particles to the surface of the iron oxide particles, it is easy to make a state where the carbon particles are mottled on the surface of the iron oxide particles.

The amount of carbon added is preferably 2.6% by mass or more and 4.0% by mass or less with respect to the Fe content (mass) on the assumption that the iron powder is completely reduced. By setting the amount of carbon added to 2.6% by mass or more, Fe ₃ C is sufficiently generated in the carbonization step in the subsequent step, and Fe ₁₆ C ₂ can be sufficiently synthesized in the diffusion step. On the other hand, by making the addition amount of carbon 4.0% by mass or less, it is possible to suppress excessive generation of Fe ₃ C in the subsequent carbonization step, and to sufficiently synthesize Fe ₁₆ C ₂ in the diffusion step. . That is, when C is insufficient, Fe generated in the carbonization process increases (Fe ₃ C decreases), and soft magnetic Fe remains in the diffusion process. On the other hand, if C is excessive, Fe ₃ C produced in the carbonization process increases (Fe decreases), so Fe ₃ C remains in the diffusion process. As a result, the production amount of Fe ₁₆ C ₂ having excellent magnetic properties is reduced, and the effect of improving magnetic properties is small.

  In the mixing step, the iron oxide particles may be finely pulverized at the same time. As a result, the carbon particles are also pulverized, and the carbon particles are more easily pulverized than the iron oxide particles. Therefore, the average particle size of the carbon particles is easily made smaller than the average particle size of the iron oxide particles. For example, the carbon powder is pulverized to a particle size of several nanometers (eg, about 10 nm). Further, by performing the pulverization at the same time, it is easier to make a state where the carbon particles are mottled on the surface of the iron oxide particles. When pulverizing simultaneously with mixing of iron powder and carbon powder, it is preferable to use a bead mill.

(Carbonization process)
In the carbonization step, the carbon adhering iron powder is subjected to a reduction heat treatment in a reducing gas atmosphere, and a portion of Fe generated by reducing iron oxide is reacted with carbon to generate Fe ₃ C, and the remaining Fe A precursor particle containing Fe ₃ C is synthesized, and a carbon coating layer is formed on the surface of the precursor particle to produce a precursor powder. The reduction is preferably a reduction treatment using CO gas as the reducing gas. By using the reducing gas as CO gas, it is possible to suppress the escape of C from the surface of the synthesized precursor particles, and to easily make the C concentration of Fe ₃ C contained in the particles uniform from the surface to the inside. When iron oxide is γ-Fe ₂ O ₃ , γ-Fe ₂ O ₃ can be easily reduced, and can be sufficiently reduced using CO gas. In this case, the temperature of the reduction heat treatment is, for example, 700 ° C. or more and 800 ° C. or less, and the reduction heat treatment time is, for example, 30 minutes or more and 5 hours or less.

When α-Fe ₂ O ₃ or Fe ₃ O ₄ is used as the iron oxide, it is difficult to reduce compared to γ-Fe ₂ O _3, and therefore reduction treatment using hydrogen gas having a high reducing power may be employed. . In this case, in the carbonization step, it is conceivable that after O is easily released from α-Fe ₂ O ₃ or Fe ₃ O ₄ by reduction treatment using hydrogen gas, reduction is performed using CO gas. This is because Fe is not easily carbonized, Fe ₃ C is difficult to be generated, and only Fe is easily generated only by the reduction treatment using hydrogen gas.

  The carbon particles adhering to the surface of the iron oxide particles react and bond with each other in excess of carbon with Fe in the carbonization step to form a carbon coating layer.

(Diffusion process)
Diffusion process is subjected to a diffusion heat treatment while applying a magnetic field to the precursor powder, to synthesize particles of _Fe 16 _{C 2} from the rest and the Fe ₃ C of _Fe, a coating layer on the surface of the _Fe 16 _{C 2} particles An iron carbide powder is prepared. By performing diffusion heat treatment to the precursor particles by applying a magnetic field comprising Fe and Fe ₃ C, and realign the C in the particles can be efficiently synthesized _Fe 16 _{C 2} from Fe and Fe ₃ C . The diffusion heat treatment is preferably performed in an inert gas atmosphere such as argon gas or nitrogen gas or in a vacuum atmosphere. When the atmosphere of the diffusion heat treatment is a nitrogen gas atmosphere, N may intrude into a part between Fe atoms and Fe atoms, and an intrusive iron carbonitride compound or iron nitride compound may be produced in part. This is allowed.

The temperature of the diffusion heat treatment is preferably 200 ° C. or higher and 210 ° C. or lower. By setting the temperature of the diffusion heat treatment to 200 ° C. or more, diffusion of C can be promoted, and Fe ₁₆ C ₂ can be synthesized more efficiently. On the other hand, the stabilization of Fe ₃ C can be suppressed by setting the temperature of the diffusion heat treatment to 210 ° C. or less. The time for the diffusion heat treatment is, for example, 1 hour or more and 100 hours or less.

The intensity of the magnetic field is preferably 3T or more. By applying a magnetic field, the basic lattice of Fe is stretched in the direction in which the magnetic field is applied, and C diffused from Fe ₃ C is selected between Fe atoms and Fe atoms aligned in one direction along the lattice axis stretched by magnetostriction. And rearranged, and Fe ₁₆ C ₂ can be synthesized from Fe and Fe ₃ C. By setting the magnetic field to 3T or more, the magnetostriction of the Fe basic lattice becomes larger, and Fe ₁₆ C ₂ can be synthesized more efficiently. For the application of the magnetic field, a normal conducting coil such as a copper wire or a superconducting coil using a superconducting wire can be used. In particular, when a superconducting coil using a high-temperature superconducting wire is used, the excitation speed is high and the cooling cost can be reduced, so that the productivity is excellent.

  In the above-described method for producing iron carbide powder, the form in which iron oxide is used as the raw material (iron powder) has been described. However, pure iron can also be used. Nano-order fine pure iron powder (nano iron powder) can be produced by using a known method such as a coprecipitation method, a reverse micelle method, or a sol-gel method. Such nano iron powder is substantially composed of α-Fe. Moreover, as long as the body-centered cubic structure (BCC) can be maintained, elements other than Fe may be contained, and iron alloys such as Fe—Co and Fe—Mn can be used as raw materials. It is.

{Iron carbide powder compact}
The manufactured iron carbide powder can be molded to obtain an iron carbide powder molded body (iron carbide material). Examples of the molding method include solidification with a binder resin and compression molding. Specifically, a bonded magnet material can be manufactured by mixing iron carbide powder and a binder resin, filling this into a molding die, and compression molding. Alternatively, a dust magnet material can be produced by filling a molding die with iron carbide powder and compression molding.

In the case of a bonded magnet material, as the binder resin, for example, a thermosetting resin such as an acrylic resin, a polyimide resin, or an epoxy resin can be used. For example, the molding pressure may be 0.1 GPa or more and 1.0 GPa or less. The atmosphere during molding may be an inert gas atmosphere or a vacuum atmosphere. Compression molding can be performed with a magnetic field applied. In this case, the magnetic field strength is, for example, 0.1 T or more and 5 T or less. By shaping while applying a magnetic field, the Fe ₁₆ C ₂ crystal can be oriented in the direction in which the magnetic field is applied, and magnetic anisotropy can be imparted.

In the case of a dust magnet material, the molding pressure is, for example, 0.6 GPa or more and 1.5 GPa or less. The atmosphere during molding may be an inert gas atmosphere or a vacuum atmosphere. The compression molding can be performed in a state where a magnetic field is applied, similarly to the above-described bonded magnet material. By shaping while applying a magnetic field, the Fe ₁₆ C ₂ crystal can be oriented in the direction in which the magnetic field is applied, and magnetic anisotropy can be imparted.

{Method for producing iron carbide molded body}
The method for manufacturing an iron carbide molded body includes a preparation process, a mixing process, a pre-molding process, a carbonizing process, and a diffusion process. This iron carbide molded body manufacturing method is basically different from the above-described iron carbide powder manufacturing method in that it includes a pre-molding step. Below, it demonstrates centering around difference with the manufacturing method of iron carbide powder.

(Pre-molding process)
In the pre-molding step, the carbon-adhered iron powder produced in the mixing step is pressure-molded to produce an intermediate molded body. In the method for manufacturing an iron carbide molded body, a molded body is produced in advance by this pre-molding step, and a carbonized body and a diffusion process in the subsequent steps are performed in the state of being formed into a molded body, whereby an iron carbide molded body is finally obtained. In addition, since the diffusion process is performed in the state of the molded body, the synthesized Fe ₁₆ C ₂ crystals can be oriented in the direction of application of the magnetic field, and the finally obtained iron carbide molded body has magnetic anisotropy. Can be made. That is, in the diffusion step, magnetic anisotropy can be imparted to the iron carbide molded body simultaneously with the synthesis of Fe ₁₆ C ₂ .

In the pre-molding step, it is preferable to perform pressure molding so that the intermediate molded body is porous. Thereby, in the carbonization process of a post process, it is easy to distribute reducing gas from the surface of a molded object to the inside, a reducing gas penetrate | invades to an internal iron oxide particle, and it becomes easy to reduce | restore iron oxide particles. To obtain a preform porous, the molding pressure, and be, for example, 10kgf ^/ cm 2 (0.98MPa) above 200kgf ^/ cm 2 (19.6MPa) or less.

For example, the porosity of the intermediate molded body may be 20% by volume or more and 50% by volume or less. The porosity represents the ratio of the volume of voids contained in the intermediate molded body to the volume of the intermediate molded body as a percentage. Specifically, it can be obtained by dividing the bulk density (molding density) of the intermediate molded body by the theoretical density (true density) to obtain the relative density, and substituting the obtained relative density into the following formula.
Formula: Porosity (%) = (1−relative density) × 100

(Carbonization process)
In the carbonization step, Fe ₃ C is generated by reduction heat treatment, and the precursor particles containing Fe and Fe ₃ C are synthesized in the same manner as the iron carbide powder manufacturing method described above. The difference is that a grain boundary phase of carbon is formed. In the method for producing an iron carbide molded body, in the carbonization step, carbon particles corresponding to excess reaction with Fe react and bond to form a carbon grain boundary phase. This carbon grain boundary phase contributes to the bonding between Fe ₁₆ C ₂ particles.

  The reduction heat treatment in the carbonization step may be performed in a state where the intermediate molded body is pressurized. For example, the intermediate molded body is housed in a mold capable of uniaxial pressing, and reduction heat treatment is performed while pressing the intermediate molded body. In the pre-molding step, it is difficult to increase the molding density because the iron oxide powder that is hardly plastically deformed is pressure-molded. On the other hand, during the carbonization process, Fe that easily undergoes plastic deformation is generated in part by the reduction heat treatment, so it is easy to increase the molding density by reducing heat treatment while applying pressure, and the density of the iron carbide compact that is finally obtained Can be improved. In addition, by performing a reduction heat treatment while applying pressure, the aspect ratio of the particles can be improved, and the coercive force and magnetic anisotropy (shape magnetic anisotropy) can be improved. The pressurizing pressure is preferably 100 MPa or more, more preferably 150 MPa or more, and further preferably 250 MPa or more, from the viewpoint of improving the aspect ratio of the particles. Here, in the post-diffusion process, the magnetic anisotropy can be further improved if the direction in which the magnetic field is applied is perpendicular to the pressurizing direction during the reduction heat treatment.

(Post-molding process)
Further, after the carbonization step, a post-molding step for pressure-molding the precursor compact may be added. In the pre-molding step, it is difficult to increase the molding density because the iron oxide powder that is hardly plastically deformed is pressure-molded. On the other hand, since the precursor compact after the carbonization step contains Fe which is easily plastically deformed, it is easy to increase the molding density by pressure molding, and the density of the iron carbide compact finally obtained is improved. be able to. Therefore, when such an iron carbide molded body is used as a magnet material, the magnet density is high and the magnetic properties can be improved.

  In the manufacturing method of the iron carbide molded body described above, the pre-molding step can be omitted and only the post-molding step can be performed. That is, in the same manner up to the carbonization step in the iron carbide powder manufacturing method described above, after the carbonization step, the precursor powder is pressure-molded to produce a precursor molded body, and the diffusion step is performed on this molded body. May be. Also in this case, as described in the post-forming step described above, the density of the finally obtained iron carbide formed body can be improved.

<Test Example 1>
A sample of iron carbide powder was produced by the following procedure, and its magnetic properties were evaluated.

(Preparation process)
As a raw material, a sintered body of γ-Fe ₂ O ₃ produced by a solid phase reaction method was used. This γ-Fe ₂ O ₃ sintered body was mechanically pulverized until the particle size of the particles became about 1 to 5 μm to obtain γ-Fe ₂ O ₃ powder.

(Mixing process)
Next, commercially available activated carbon powder (average particle size 100 nm) was added to the powder of γ-Fe ₂ O ₃ and mixed and ground. In this test, the mixture was pulverized using a bead mill until the average particle size of the γ-Fe ₂ O ₃ particles reached about 80 nm. As media for the bead mill, zirconia beads having a diameter of 0.5 mm were used. The addition amount of activated carbon (C addition amount) was 3% by mass with respect to the Fe content in the γ-Fe ₂ O ₃ powder. The secondary aggregate of gamma-Fe ₂ O ₃ particles which graphene particles adhere to the surface (carbon deposition iron powder) was produced.

(Carbonization process)
The produced secondary aggregate was subjected to a reduction heat treatment at 750 ° C. for 5 hours in a CO gas atmosphere.

(Diffusion process)
Next, after CO gas was exhausted and Ar gas was introduced, diffusion heat treatment was performed at 205 ° C. for 20 hours in an Ar gas atmosphere. The diffusion heat treatment was performed in a state where a 5T magnetic field was applied. Then, to produce the iron carbide powder with a carbon coating layer on the surface of the Fe ₁₆ C ₂ particles.

  The obtained iron carbide powder aggregate was press-molded at 2.0 GPa to produce an iron carbide powder compact, and the magnetic properties of the iron carbide powder compact were evaluated. Specifically, the iron carbide powder compact was magnetized with a pulse magnetic field of 4000 kA / m to form a magnet, and then examined using a BH tracer (DCBH tracer manufactured by Riken Denshi Co., Ltd.). Here, saturation magnetic flux density Bs (T) and intrinsic coercive force iHc (kA / m) were measured as magnetic characteristics.

  As a result, Bs was 1.8 T and iHc was 1.1 kOe (87.5 kA / m). The iron carbide powder of Test Example 1 has high saturation magnetization and excellent magnetic properties, and can be suitably used for magnetic materials such as magnets.

Furthermore, an iron carbide powder was produced in the same procedure as in Test Example 1 described above, and the structure of the iron carbide powder was observed. Specifically, the obtained carbonized powder aggregate was embedded in a resin, and then the structure of the cut and polished cross section was observed. For tissue observation, TEM (Transmission Electron Microscope) -EDX (Energy Dispersive X-ray spectroscopy) was used. As a result, the Fe ₁₆ C ₂ particles were substantially composed of Fe ₁₆ C ₂ and the average particle size was 50 nm. The average particle size of Fe ₁₆ C ₂ particles, an equal area circle equivalent diameter measured for _Fe 16 _{C 2} particles in the observation field of view and is the average. Moreover, the average thickness of the carbon coating layer on the surface of Fe ₁₆ C ₂ particles was 3 nm. The average thickness of the carbon coating layer was determined by measuring the thicknesses of three points of the carbon coating layer in the Fe ₁₆ C ₂ particles in the observation field.

<Test Example 2>
Sample No. of iron carbide molded body was changed by changing the production conditions. 1-No. 30 were produced and their magnetic properties were evaluated.

(Preparation process)
As the raw material, commercially available γ-Fe ₂ O ₃ powder (average particle size 5 μm) was used.

(Mixing process)
Next, commercially available activated carbon powder (average particle size 100 nm) was added to the powder of γ-Fe ₂ O ₃ and mixed and ground. In this test, the mixture was pulverized using a bead mill until the average particle size of the γ-Fe ₂ O ₃ particles reached about 80 nm. As media for the bead mill, zirconia beads having a diameter of 0.5 mm were used. The addition amount (C addition amount) of the activated carbon was 1.0% by mass to 10.0% by mass with respect to the Fe content in the powder of γ-Fe ₂ O ₃ . Then, the activated carbon particles to prepare a carbon deposition of iron powder were γ-Fe ₂ O ₃ particles adhere to the surface.

(Pre-molding process)
The produced carbon-adhered iron powder was pressure-molded with a hand press to produce an intermediate molded body. The molding pressure at this time was 200 kgf / cm ² (19.6 MPa).

(Carbonization process)
The produced intermediate molded body was subjected to a reduction heat treatment at 750 ° C. for 3 hours in a CO gas atmosphere. In this test, the reduction heat treatment was performed in a state where the intermediate molded body was housed in a mold capable of uniaxial pressing and the intermediate molded body was pressurized. The pressure applied during the reduction heat treatment was 0 to 500 MPa. The pressurization pressure of “0” means that no pressurization is performed.

(Diffusion process)
Next, after CO gas was exhausted and Ar gas was introduced, diffusion heat treatment was performed in an Ar gas atmosphere with a magnetic field applied. The temperature of the diffusion heat treatment was 150 ° C. to 250 ° C., and the time of the diffusion heat treatment was 20 hours. The strength of the magnetic field was 0 to 5 T, and the direction of application of the magnetic field was perpendicular to the pressurizing direction during the reduction heat treatment in the carbonization step. Then, to produce iron carbide molded body having a carbon grain boundary phase between Fe ₁₆ C ₂ particles. The magnetic field strength of “0” means that no magnetic field is applied.

Sample No. of the obtained iron carbide molded article. 1-No. As for Test No. 25, after magnetizing with a pulse magnetic field of 4000 kA / m as in Test Example 1, the magnetic characteristics were evaluated using a BH tracer. Here, saturation magnetic flux density Bs (T), squareness ratio Br / Bs (ratio of residual magnetic flux density Br and saturation magnetic flux density Bs), intrinsic coercive force iHc (kA / m), maximum energy product (BH) max ( kJ / m ³ ) was measured. The results are shown in Table 1 together with the production conditions.

Sample No. shown in Table 1 1-No. From the result of the magnetic characteristics of No. 6, it can be seen that the magnetic characteristics are improved as the C addition amount is increased. In particular, Sample No. having a C addition amount of 2.6 mass% to 4.0 mass%. 4-No. 6 has Bs of 1.75T (especially 1.80T) T or more, iHc is 350 kA / m (especially 400 kA / m) or more, and (BH) max is 100 kJ / m ³ (especially 150 kJ / m ³ ) or more. It has excellent magnetic properties. Furthermore, sample no. 4-No. No. 6 has Br / Bs of 0.8 or more and high magnetic anisotropy. However, Sample No. 7-No. As shown in FIG. 10, when the amount of added C is excessively increased, the improvement in magnetic properties (particularly Br / Bs and (BH) max) tends to be reduced.

Sample No. 1-No. As in Test Example 1, the cross-sectional structure of 10 was observed using TEM-EDX. As a result, sample no. 4-No. In No. 6, Fe ₁₆ C ₂ particles were substantially composed of Fe ₁₆ C ₂ . In contrast, sample no. 1-No. 3, Fe remained, and sample No. 4-No. Compared to 6, Fe ₁₆ C ₂ contained fewer components. On the other hand, fee No. 7-No. 10, Fe ₃ C remains. 4-No. Compared to 6, Fe ₁₆ C ₂ contained fewer components.

From these results, it is considered that when the amount of addition of C is insufficient, the soft magnetic Fe remains, and the improvement width of the magnetic characteristics such as the coercive force becomes small. On the other hand, when the amount of addition of C is excessive, Fe ₃ C, which is inferior in magnetic properties as compared with Fe ₁₆ C ₂ , remains, so that the improvement width of the magnetic properties is considered to be small.

Sample No. 5, the average particle diameter of the Fe ₁₆ C ₂ particles and the average thickness of the carbon grain boundary phase were determined. The average particle diameter of the Fe ₁₆ C ₂ particles was 60 nm, and the average thickness of the carbon grain boundary phase. Was 5 nm. _Here, the average particle size of the _Fe 16 _{C 2} particles, an equal area circle equivalent diameter measured for _Fe 16 _{C 2} particles in the observation field of view and is the average. The average thickness of the carbon grain boundary phase was determined by measuring the thicknesses of three points of the carbon grain boundary phase between adjacent Fe ₁₆ C ₂ grains in the observation field.

Sample No. shown in Table 1 5 and no. 11-No. It can be seen from the result of the magnetic properties of 17 that the magnetic properties are improved as the pressure applied during the reduction heat treatment in the carbonization step is increased. In particular, when the pressurizing pressure is 100 MPa or more, more preferably 150 MPa or more, and even more preferably 250 MPa or more, the improvement range of magnetic characteristics is large. For example, sample No. with a pressurization pressure of 100 MPa is used. Sample No. 5 with Br / Bs of 0.85 or more, iHc of 450 kA / m or more, and pressurization pressure of 150 MPa. Sample No. 13 with Bs of 1.85 T or more, (BH) max of 200 kJ / m ³ or more, and a pressure of 250 MPa. No. 15, Bs is 1.9 T or more, Br / Bs is 0.9 or more, and iHc is 500 kA / m or more. This is thought to be due to the fact that the coercive force and squareness ratio (magnetic anisotropy) were improved by increasing the aspect ratio of the particles in the carbonization process by increasing the pressure applied during the reduction heat treatment. .

Sample No. shown in Table 1 5 and no. 18-No. From the result of 25 magnetic properties, it is understood that the temperature of the diffusion heat treatment in the diffusion step is preferably 200 ° C. or more and 210 ° C. or less. This is because when the temperature of the diffusion heat treatment is set to 200 ° C. or higher, the reaction for synthesizing Fe ₁₆ C ₂ further proceeds, and the amount of Fe ₁₆ C ₂ generated is increased. On the other hand, the temperature of the diffusion heat treatment is less than 210 ° C. Thus, it is considered that the stabilization of Fe ₃ C is suppressed and the production amount of Fe ₁₆ C ₂ is increased.

Sample No. shown in Table 1 5 and no. 26-No. From the results of the magnetic characteristics of 30, it can be seen that the magnetic characteristics are improved as the magnetic field strength in the diffusion process is increased. In particular, when the magnetic field strength is 3T or more, the improvement range of the magnetic characteristics is large. This is considered to be due to the fact that the reaction for synthesizing Fe ₁₆ C ₂ further proceeds and the production amount of Fe ₁₆ C ₂ increases by setting the magnetic field strength to 3T or more.

Sample No. As for No. 26, a cross-sectional structure was observed using TEM-EDX, and composition analysis was performed. As a result, Fe ₁₆ C ₂ was hardly detected.

  The following additional notes are disclosed in relation to the embodiment of the present invention described above.

[Appendix]
(Appendix 1)
A preparation step of preparing iron powder containing iron oxide particles;
Carbon powder containing carbon particles is added to the iron powder, the iron powder and the carbon powder are mixed, and the carbon particles are adhered to the surface of the iron oxide particles to produce a carbon-attached iron powder. Process,
The carbon-adhered iron powder is subjected to a reduction heat treatment in a reducing gas atmosphere, and a part of Fe produced by reducing the iron oxide is reacted with the carbon to produce Fe ₃ C, and the remaining Fe A carbonization step of synthesizing precursor particles containing Fe ₃ C and forming a precursor powder by forming a coating layer of carbon on the surface of the precursor particles;
The precursor powder is subjected to diffusion heat treatment with a magnetic field applied to synthesize Fe ₁₆ C ₂ particles from the remainder of Fe and Fe ₃ C, and the coating layer is formed on the surface of the Fe ₁₆ C ₂ particles. A diffusion step of producing an iron carbide powder comprising:
A molding step of forming the iron carbide powder by molding the iron carbide powder,
The manufacturing method of the iron carbide material provided with this.

  According to the method for manufacturing the iron carbide material of Supplementary Note 1 described above, a molded body of iron carbide powder (iron carbide powder molded body) can be obtained. Examples of the method for forming the iron carbide powder include solidification with a binder resin and compression molding.

(Appendix 2)
A preparation step of preparing iron powder containing iron oxide particles;
Carbon powder containing carbon particles is added to the iron powder, the iron powder and the carbon powder are mixed, and the carbon particles are adhered to the surface of the iron oxide particles to produce a carbon-attached iron powder. Process,
The carbon-adhered iron powder is subjected to a reduction heat treatment in a reducing gas atmosphere, and a part of Fe produced by reducing the iron oxide is reacted with the carbon to produce Fe ₃ C, and the remaining Fe A carbonization step of synthesizing precursor particles containing Fe ₃ C and forming a precursor powder by forming a coating layer of carbon on the surface of the precursor particles;
A molding step of pressure-molding the precursor powder to produce a precursor molded body; and
The precursor compact is subjected to diffusion heat treatment with a magnetic field applied to synthesize Fe ₁₆ C ₂ particles from the remaining Fe and the Fe ₃ C, and the grain boundaries between the Fe ₁₆ C ₂ particles. A diffusion step of producing an iron carbide molded body comprising a phase;
The manufacturing method of the iron carbide material provided with this.

  According to the method for producing an iron carbide material of Supplementary Note 2 above, since the precursor powder after the carbonization step contains Fe that is easily deformed, it is easy to increase the molding density in the case of pressure molding, and finally obtained. The density of the formed iron carbide molded body can be improved. As a result, when such an iron carbide molded body is used as a magnet material, the magnet density is high and the magnetic properties can be improved.

(Appendix 3)
A preparation step of preparing iron powder containing iron oxide particles;
Carbon powder containing carbon particles is added to the iron powder, the iron powder and the carbon powder are mixed, and the carbon particles are adhered to the surface of the iron oxide particles to produce a carbon-attached iron powder. Process,
A pre-molding step of pressure-molding the carbon-attached iron powder to produce a first intermediate molded body;
The intermediate molded body is subjected to a reduction heat treatment in a reducing gas atmosphere, and a part of Fe produced by reducing the iron oxide is reacted with the carbon to produce Fe ₃ C, and the remaining Fe and the Synthesizing precursor particles containing Fe ₃ C, and forming a precursor grain by forming a grain boundary phase of the carbon between the precursor particles; and
A post-molding step in which the precursor molded body is further pressure-molded to produce a second intermediate molded body;
A diffusion heat treatment is performed in a state where a magnetic field is applied to the second intermediate molded body to synthesize Fe ₁₆ C ₂ particles from the remaining Fe and the Fe ₃ C, and the particles between the Fe ₁₆ C ₂ particles are synthesized. A diffusion process for producing an iron carbide molded body having a boundary phase;
The manufacturing method of the iron carbide material provided with this.

  According to the method for manufacturing the iron carbide material of Supplementary Note 3 described above, since the precursor compact after the carbonization step contains Fe that is easily deformed, it is easy to increase the molding density by press molding, and finally The density of the obtained iron carbide molded body can be improved. As a result, when such an iron carbide molded body is used as a magnet material, the magnet density is high and the magnetic properties can be improved.

  The iron carbide material (powder or molded body) of the present invention can be suitably used for a magnetic material such as a magnet. For example, the present invention can be used as a material for permanent magnets provided in various motors, in particular, motors such as hybrid vehicles (HEV) and hard disk drives (HDD). In addition, the iron carbide material (powder or molded body) of the present invention can also be used for magnetic materials such as magnetic heads, reactors (transformers), motor cores, magnetic shields, and noise filters. Moreover, the manufacturing method of the iron carbide material (powder or molded object) of this invention can be utilized suitably for manufacture of the iron carbide material (powder or molded object) excellent in a magnetic characteristic.

Claims (16)

An iron carbide material, which is a powder comprising Fe ₁₆ C ₂ particles and a carbon coating layer on at least a part of the surface of the particles.   The iron carbide material according to claim 1, wherein an average particle diameter of the particles is 50 nm or more and 100 nm or less.   The iron carbide material according to claim 1 or 2, wherein an average thickness of the coating layer is 2.5 nm or more.   An iron carbide material obtained by molding the iron carbide material powder according to claim 1. An iron carbide material which is a formed body including Fe ₁₆ C ₂ particles and a carbon grain boundary phase between the particles.   The iron carbide material according to claim 5, wherein an average particle diameter of the particles is 50 nm or more and 100 nm or less.   The iron carbide material according to claim 5 or 6, wherein an average thickness of the grain boundary phase is 5 nm or more.   The iron carbide material according to any one of claims 5 to 7, wherein the squareness ratio is 0.8 or more. A preparation step of preparing iron powder containing iron oxide particles;
Carbon powder containing carbon particles is added to the iron powder, the iron powder and the carbon powder are mixed, and the carbon particles are adhered to the surface of the iron oxide particles to produce a carbon-attached iron powder. Process,
The carbon-adhered iron powder is subjected to a reduction heat treatment in a reducing gas atmosphere, and a part of Fe produced by reducing the iron oxide is reacted with the carbon to produce Fe ₃ C, and the remaining Fe A carbonization step of synthesizing precursor particles containing Fe ₃ C and forming a precursor powder by forming a coating layer of carbon on the surface of the precursor particles;
The precursor powder is subjected to diffusion heat treatment with a magnetic field applied to synthesize Fe ₁₆ C ₂ particles from the remainder of Fe and Fe ₃ C, and the coating layer is formed on the surface of the Fe ₁₆ C ₂ particles. A diffusion step of producing an iron carbide powder comprising:
The manufacturing method of the iron carbide material provided with this. A preparation step of preparing iron powder containing iron oxide particles;
Carbon powder containing carbon particles is added to the iron powder, the iron powder and the carbon powder are mixed, and the carbon particles are adhered to the surface of the iron oxide particles to produce a carbon-attached iron powder. Process,
A pre-molding step of pressure-molding the carbon-attached iron powder to produce an intermediate molded body;
The intermediate molded body is subjected to a reduction heat treatment in a reducing gas atmosphere, and a part of Fe produced by reducing the iron oxide is reacted with the carbon to produce Fe ₃ C, and the remaining Fe and the Synthesizing precursor particles containing Fe ₃ C, and forming a precursor grain by forming a grain boundary phase of the carbon between the precursor particles; and
The precursor compact is subjected to diffusion heat treatment with a magnetic field applied to synthesize Fe ₁₆ C ₂ particles from the remaining Fe and the Fe ₃ C, and the grain boundaries between the Fe ₁₆ C ₂ particles. A diffusion step of producing an iron carbide molded body comprising a phase;
The manufacturing method of the iron carbide material provided with this. The method for producing an iron carbide material according to claim 9 or 10, wherein the iron oxide is γ-Fe ₂ O ₃ .   The iron carbide material production according to any one of claims 9 to 11, wherein the amount of carbon added is 2.6 mass% or more and 4.0 mass% or less with respect to the Fe content in the iron powder. Method.   The method for producing an iron carbide material according to any one of claims 9 to 12, wherein the reducing gas in the carbonization step is CO gas.   The method for producing an iron carbide material according to any one of claims 9 to 13, wherein a temperature of the diffusion heat treatment in the diffusion step is set to 200 ° C or higher and 210 ° C or lower.   The method for manufacturing an iron carbide material according to any one of claims 9 to 14, wherein the magnetic field in the diffusion step is 3T or more.   The magnet which magnetized the iron carbide material of any one of Claim 1, Claim 4, and Claim 5.