JP6778653B2 - Iron nitride based magnet - Google Patents

Description

The present invention relates to an iron nitride based magnet.

Currently, as a magnet having excellent magnetic characteristics, a rare earth magnet represented by a neodymium magnet is exemplified, and it is used in various fields such as various motors and generators.

However, among the rare earth elements that make up rare earth magnets, there are many elements with a small amount of reserves, elements with uneven distribution of reserve areas, etc., and the raw material price fluctuates greatly, making it difficult to supply stable raw materials. is there.

Therefore, research is being conducted to develop high-performance magnets using only the elements that are abundant on the earth without using rare earth elements.

As such a high-performance magnet, a ferromagnetic iron nitride-based magnet using an Fe—N-based compound is known. In particular, the iron nitride based magnet containing the Fe ₁₆ N _2- phase exhibits a huge saturation magnetization, and theoretically, the maximum energy product has a performance superior to that of the neodymium magnet.

For example, Patent Document 1 describes an iron nitride magnet that achieves a high degree of orientation by using iron nitride powder in which the abundance ratio of the number of iron nitride particles having a predetermined particle size is within a specific range. It is disclosed.

Japanese Unexamined Patent Publication No. 2016-17199

Patent Document 1 states that iron nitride-based particles can be densely arranged in the orientation direction by setting the abundance ratio of particles having a large particle diameter and particles having a small particle diameter within a specific range among the iron nitride-based particles. Is described. However, if not only the particle size but also the iron nitride-based particle shape is not taken into consideration, voids are likely to occur in the magnet. As a result, there is a problem that a magnet having a sufficient density cannot be obtained and the mechanical strength as a magnet is insufficient.

Further, by densely arranging the iron nitride-based magnetic particles, the magnetization tends to increase and the maximum energy product tends to increase. However, if the iron nitride-based magnetic particles are arranged more densely, it becomes difficult to magnetically separate the iron nitride-based magnetic particles, the coercive force is lowered, and conversely, the maximum energy product is lowered.

The present invention has been made in view of such an actual situation, and an object of the present invention is to provide an iron nitride based magnet capable of achieving both a good mechanical strength and a good maximum energy product.

In order to achieve the above object, the iron nitride based magnet of the present invention is used.
[1] An iron nitride based magnet containing _two phases of Fe ₁₆ N.
The iron nitride-based magnet has iron nitride-based magnetic particles and iron oxide-based particles.
The shape aspect ratio expressed as the ratio of the average particle major axis of the iron nitride-based magnetic particles to the average particle minor axis of the iron nitride-based magnetic particles is 3.0 or more and 10.0 or less.
The average particle size ratio of iron oxide-based particles, which is expressed as the ratio of the average particle size of iron oxide-based particles to the average particle minor size of iron nitride-based magnetic particles, is 50% or more and 100% or less.
Iron nitride expressed as the ratio of the area occupied by the iron nitride-based magnetic particles to the total area occupied by the iron nitride-based magnetic particles and the area occupied by the iron oxide-based particles in the cross section parallel to the orientation direction of the iron nitride-based magnet. It is an iron nitride-based magnet characterized in that the area ratio of the magnetic particles is 80.0% or more and 99.9% or less.

[2] The iron nitride-based magnet according to [1], wherein the iron nitride-based magnetic particles have an average particle diameter of 10 nm or more and 100 nm or less.

Since the iron nitride based magnet according to the present invention has the above characteristics, it is possible to provide an iron nitride based magnet capable of achieving both good mechanical strength and good maximum energy product.

FIG. 1A is a schematic diagram for explaining the particle major axis and the particle minor axis of the iron nitride based magnetic particles. FIG. 1B is a schematic diagram for explaining the particle size of the iron nitride based magnetic particles. FIG. 2 is a schematic cross-sectional view showing the existence state of the iron nitride-based magnetic particles and the iron oxide-based particles in the cross section parallel to the orientation direction of the iron nitride-based magnet according to the present embodiment.

Hereinafter, the present invention will be described in detail in the following order based on specific embodiments.
1. 1. Iron Nitride Magnet 1.1 Iron Nitride Magnetic Particles 1.2 Iron Oxide Particles 1.3 Existence of Iron Nitride Magnetic Particles and Iron Oxide Particles 2. Method for manufacturing iron nitride magnets 2.1 Manufacture of iron nitride magnetic particles 2.2 Manufacture of iron oxide particles 2.3 Manufacture of iron nitride magnets 3. Effect in this embodiment

(1. Iron nitride based magnet)
The iron nitride based magnet according to the present embodiment includes a Fe ₁₆ N ₂ phase, which is a ferromagnetic iron nitride phase. Further, the iron nitride-based magnet has iron nitride-based magnetic particles and iron oxide-based particles.

The iron nitride-based magnet may contain components other than the iron nitride-based magnetic particles and the iron oxide-based particles, for example, a resin. Further, the iron nitride-based magnet may be a magnet that does not contain a resin component and maintains a bulk shape by iron nitride-based magnetic particles and iron oxide-based particles.

Further, in the present embodiment, the existence state of the iron nitride-based magnetic particles and the iron oxide-based particles is controlled inside the iron nitride-based magnet. By doing so, the iron nitride based magnet according to the present embodiment can have both good mechanical strength and good maximum energy product.

The iron nitride based magnet according to the present embodiment may contain transition metal elements such as manganese (Mn), nickel (Ni), cobalt (Co), titanium (Ti), and zinc (Zn). Further, the iron nitride based magnet may contain silicon (Si). The content of these transition metal elements with respect to the entire iron nitride based magnet is preferably 1% by mass or less in terms of elements. Further, the content of Si with respect to the entire iron nitride based magnet is preferably 5% by mass or less in terms of element. The iron nitride based magnet according to the present embodiment may contain a small amount of impurities and the like in addition to the above elements within the range in which the effect of the present invention can be obtained. In the present embodiment, it is preferable that the total amount of iron (Fe), nitrogen (N) and oxygen (O) is 70% by mass or more with respect to the entire iron nitride based magnet.

(1.1 Iron nitride based magnetic particles)
In the present embodiment, the iron nitride-based magnetic particles comprise a particle containing Fe ₁₆ N ₂ phase as the iron nitride phase, the particles containing the Fe ₁₆ N ₂ phase other than iron nitride phase, both. From the viewpoint of obtaining a high maximum energy product, the content of the particles containing the Fe ₁₆ N ₂ phase is preferably 95% or more of the total iron nitride based magnetic particles. It is more preferable that the iron nitride based magnetic particles are composed of particles containing Fe ₁₆ N ₂ phase.

As shown in FIG. 1A, in the iron nitride based magnetic particles 2, the particle major axis a and the particle minor axis b can be set. The particle major axis a is defined as the length a of the long side of the quadrangle T that circumscribes the particle 2 and has the smallest area, and the particle minor axis b is the short side of the quadrangle T that circumscribes the particle 2 and has the smallest area. Defined as length b.

The particle major axis a and the particle minor axis b are measured for a predetermined number of iron nitride-based magnetic particles, and their average values are taken as the average particle major axis and the average particle minor axis, respectively. In this embodiment, the number of particles for measuring the particle major axis a and the particle minor axis b is about 500 to 1500. Then, the average particle major axis with respect to the average particle minor axis is defined as the shape aspect ratio of the iron nitride based magnetic particles. That is, the shape aspect ratio = average particle major axis / average particle minor axis.

In this embodiment, the shape aspect ratio is 3.0 or more and 10.0 or less. By setting the shape aspect ratio within the above range, the degree of orientation can be increased and the maximum energy product can be improved. The shape aspect ratio is preferably 5.0 or more. On the other hand, the shape aspect ratio is preferably 7.0 or less. Therefore, the iron nitride-based magnetic particles 2 have an elongated shape, and the degree of orientation can be easily increased by substantially matching the longitudinal direction of the iron nitride-based magnetic particles 2 with the orientation direction of the magnet.

Further, in the present embodiment, the particle diameter c of the iron nitride based magnetic particles 2 is defined. The particle diameter c of the iron nitride-based magnetic particles is defined as the equivalent circle diameter of the particles, unlike the above-mentioned average particle major axis and average particle minor axis. That is, as shown in FIG. 1B, the diameter c of the circle A having the same area as the area of the iron nitride-based magnetic particles 2 is defined as the particle diameter c of the iron nitride-based magnetic particles 2. Then, the particle area is measured for a predetermined number of iron nitride-based magnetic particles, and the average value of the circle-equivalent diameter calculated from the area values is defined as the average particle diameter of the iron nitride-based magnetic particles. In this embodiment, the number of particles for which the particle area is measured is about 500 to 1500.

In the present embodiment, the average particle size of the iron nitride based magnetic particles is preferably 10 nm or more and 100 nm or less. By setting the average particle size within the above range, it is possible to achieve both the mechanical strength of the iron nitride based magnet and the maximum energy product at a high level. The average particle size is more preferably 30 nm or more. On the other hand, the average particle size is more preferably 70 nm or less.

(1.2 Iron oxide particles)
In the present embodiment, the iron oxide-based particles are not particularly limited as long as they are particles containing an iron oxide phase. Examples of the iron oxide phase include a wustite (FeO) phase, a hematite (Fe ₂ O ₃ ) phase, and a magnetite (Fe ₃ O ₄ ) phase. Further, as the iron oxide-based particles, particles having a wustite phase, particles having a hematite phase, particles having a magnetite phase, and the like may be mixed.

From the viewpoint of magnetic separation, the iron oxide-based particles are preferably composed of particles having a wustite phase, particles having a hematite phase, and the like.

Further, in the present embodiment, the particle size of the iron oxide-based particles is defined. The particle size of iron oxide-based particles is defined as the equivalent circle diameter of the particles. That is, it is defined by the same definition as the particle size of the iron nitride based magnetic particles described above. Further, the average particle size of the iron oxide-based particles is also calculated from the area values of a predetermined number of iron oxide-based particles by measuring the particle area in the same manner as the average particle size of the iron nitride-based magnetic particles. The average value of the equivalent circle diameters is taken as the average particle diameter of the iron oxide-based particles. In the present embodiment, the number of particles for which the particle area is measured is about 500 to 1500.

In this embodiment, the relationship between the average particle size of iron oxide-based particles and the average minor particle size of iron nitride-based magnetic particles is defined. That is, when the average particle size of the iron oxide-based particles is taken as the average particle size ratio of the iron oxide-based particles with respect to the average particle minor diameter of the iron nitride-based magnetic particles, the average particle size ratio of the iron oxide-based particles is 50%. More than 100% or less.

By setting the average particle size ratio within the above range, the voids in the iron nitride based magnet can be reduced, the mechanical strength of the iron nitride based magnet can be improved, and the maximum energy product can be improved. The average particle size ratio is preferably 65% or more. On the other hand, the average particle size ratio is preferably 85% or less.

The average particle size of the iron oxide-based particles is not particularly limited as long as the above average particle size ratio is satisfied, but in the present embodiment, it is preferably 3 nm or more and 40 nm or less.

(1.3 Existence state of iron nitride-based magnetic particles and iron oxide-based particles)
The existence state of the iron nitride-based magnetic particles and the iron oxide-based particles is controlled inside the iron nitride-based magnet according to the present embodiment. FIG. 2 schematically shows a cross section parallel to the orientation direction of the iron nitride based magnet 1.

As shown in FIG. 2, it is preferable that the iron nitride-based magnetic particles 2 are arranged so that their longitudinal directions substantially coincide with the orientation direction. Further, as described above, since the average particle size ratio of the iron oxide-based particles 4 is 100% or less, the iron oxide-based particles 4 are smaller than the iron nitride-based magnetic particles 2, and the iron oxide-based particles 4 are nitrided. It exists between the iron-based magnetic particles 2 and fills the voids between the iron nitride-based magnetic particles 2. In this way, by filling the space between the iron nitride-based magnetic particles having a predetermined shape aspect ratio with the iron oxide-based particles smaller than the iron nitride-based magnetic particles, the voids in the iron nitride-based magnet are reduced and the iron nitride-based magnet is used. Magnetic separation between magnetic particles is facilitated, and the coercive force is improved.

Such an effect is related not only to the average particle size ratio of the iron oxide-based particles 4 described above, but also to the abundance ratio of the iron nitride-based magnetic particles 2 and the iron oxide-based particles 4. In the present embodiment, the ratio of the area occupied by the iron nitride-based magnetic particles 2 to the total area occupied by the area occupied by the iron nitride-based magnetic particles 2 and the area occupied by the iron nitride-based particles 4 is defined as the area ratio of the iron nitride-based magnetic particles. Define. That is, even if a resin component is present in the cross section parallel to the orientation direction of the iron nitride based magnet 1, for example, the area occupied by the iron nitride based magnetic particles 2 and the iron oxide are not considered, without considering the area occupied by the resin component. The area ratio is calculated from the total area with the area occupied by the system particles 4.

The area ratio is 80.0% or more and 99.9% or less. By setting the area ratio within the above range, the voids of the iron nitride magnet are reduced and the mechanical strength is improved, and the magnetic separation between the iron nitride magnetic particles is facilitated, which is the maximum. The energy product can be improved. The area ratio is preferably 85.0% or more. On the other hand, the area ratio is preferably 95.0% or less.

The area ratio can be calculated as follows. First, the iron nitride based magnet is cut so that a cross section parallel to the orientation direction of the iron nitride based magnet appears. The iron nitride-based magnetic particles and the iron oxide-based particles are identified in a predetermined field of view obtained by observing the cut cross section with an electron microscope or the like. The predetermined visual field is preferably a visual field observed at a magnification of 30,000 to 300,000 times.

The method for identifying the iron nitride-based magnetic particles and the iron oxide-based particles is not particularly limited as long as it is a method that can obtain information on the abundance of the elements present in the visual field. In the present embodiment, a surface analysis is performed on a predetermined region using an energy dispersive X-ray Spectroscopy (EDS) device attached to a scanning transmission electron microscope (STEM). , Obtain information on the abundance (concentration) of each element at the measurement point in the region, and perform mapping of a predetermined element.

The iron nitride-based magnetic particles and the iron oxide-based particles are identified from the obtained element mapping image. That is, a region containing iron (Fe) and nitrogen (N) in a predetermined amount or more is determined to be iron nitride-based magnetic particles, and a region containing iron (Fe) and oxygen (O) in a predetermined amount or more is determined to be iron oxide-based particles. .. The predetermined amounts of Fe, N, and O may be determined according to the composition of the magnet, the composition of each particle, and the like.

Subsequently, in a predetermined region, the total area of the regions determined to be iron nitride-based magnetic particles is defined as the area occupied by the iron nitride-based magnetic particles, and the total area of the regions determined to be iron oxide-based particles is oxidized. The area occupied by iron-based particles. The area ratio of the iron nitride-based magnetic particles can be calculated from the area occupied by the obtained iron nitride-based magnetic particles and the area occupied by the iron oxide-based particles.

Further, the particle major axis, minor axis and particle diameter of the iron nitride-based magnetic particles described above and the particle diameter of the iron oxide-based particles are also the same as the above-mentioned method for calculating the area ratio of the iron nitride-based magnetic particles. The cross section parallel to the orientation direction of the iron nitride based magnet 1 shown in FIG. 2 can be measured in a predetermined field obtained by observing with an electron microscope or the like.

These measurements may be calculated by performing image processing on the element mapping image to identify the iron nitride-based magnetic particles and the iron oxide-based particles.

(2. Manufacturing method of iron nitride based magnet)
Next, an example of a method for manufacturing an iron nitride based magnet will be described below.

(2.1 Manufacture of iron nitride based magnetic particles)
In the present embodiment, the iron nitride-based magnetic particles are produced by producing iron oxide particles and then nitriding the produced iron oxide particles. Iron oxide particles are aged after mixing an aqueous iron salt solution containing an iron (II) salt and / or an iron (III) salt (hereinafter, may be simply referred to as "iron salt") and an alkaline aqueous solution. It can be produced by advancing the reaction and further performing an oxidation treatment.

In the present embodiment, the iron oxide constituting the iron oxide particles is not particularly limited, and for example, ustite (FeO), hematite (α-Fe ₂ O ₃ ), maghemite (γ-Fe ₂ O ₃ ), and magnetite (γ-Fe ₂ O ₃ ) Examples thereof include Fe ₃ O ₄ ) and iron oxyhydroxide. Examples of iron oxyhydroxide include Gecite (α-FeOOH), β-FeOOH, and γ-FeOOH.

The iron salt is not particularly limited, and examples thereof include sulfates, chlorides, nitrates, and hydrates thereof, and these may be appropriately combined.

The alkaline aqueous solution is not particularly limited, and examples thereof include sodium carbonate aqueous solution, sodium hydroxide aqueous solution, ammonia water, ammonia salt aqueous solution, urea aqueous solution and the like, and these may be appropriately combined.

The conditions of the aging reaction are not particularly limited, and can be appropriately selected depending on the type of iron salt and the type of alkaline aqueous solution. Further, the conditions of the oxidation treatment are not particularly limited, and the temperature and the aeration time may be appropriately set.

Further, from the viewpoint of improving the crystallinity of iron oxide obtained after the aging reaction, controlling the particle size, and facilitating the control of the particle shape, the aging reaction may be an in-liquid aging reaction such as hydrothermal treatment by an autoclave. preferable.

The iron oxide particles obtained by the aging reaction can be recovered by filtering the aqueous solution after the aging reaction. Further, an iron oxide slurry containing iron oxide particles may be obtained by subjecting the aqueous solution after the aging reaction to a washing treatment such as washing with water using a centrifuge or the like.

In order to prevent the iron oxide particles from sintering each other by the reduction treatment described later, a part of the surface of the iron oxide particles may be coated with a Si compound. The Si compound is not particularly limited, and examples thereof include colloidal silica, a silane coupling agent, and a silanol compound.

When coated with a Si compound, the coating amount of the Si compound is preferably 0.1% by weight or more and 20% by weight or less in terms of Si with respect to the iron oxide particles. By setting the coating amount of the Si compound within the above range, the sintering between the iron oxide particles during the heat treatment can be controlled, and the average particle size of the iron nitride-based magnetic particles can be easily set within the above range. ..

Further, the step of coating with the Si compound may be performed on the iron oxide particles obtained by filtration, or may be performed on the iron oxide slurry. Further, after the step of coating the iron oxide slurry with the Si compound, the iron oxide particles can be recovered by filtering the iron oxide slurry.

The average particle size of the obtained iron oxide particles is not particularly limited, and is preferably 10 nm or more and 150 nm or less when the average particle size of the iron nitride-based magnetic particles is within the above range.

The particle shape of the obtained iron oxide particles is not particularly limited, and may be, for example, spherical, needle-shaped, granular, spindle-shaped, rectangular parallelepiped, or the like. Further, the iron oxide particles may be dried, if necessary, before the obtained iron oxide particles are subjected to the reduction treatment described later. There are no particular restrictions on the drying conditions.

Subsequently, the obtained iron oxide particles are subjected to a reduction treatment to obtain iron particles. Then, by subjecting the obtained iron particles to nitriding treatment, iron nitride-based magnetic particles can be obtained. Further, if necessary, the iron nitride-based magnetic particles may be subjected to a slow oxidation treatment to form an oxide phase on the surface of the iron nitride-based magnetic particles.

Hereinafter, the reduction treatment, the nitriding treatment and the slow oxidation treatment will be described.

The temperature of the reduction treatment is not particularly limited, and is preferably 200 ° C. or higher and 400 ° C. or lower, for example. By setting the temperature of the reduction treatment to 200 ° C. or higher, the iron oxide particles can be sufficiently reduced. By setting the temperature of the reduction treatment to 400 ° C. or lower, the iron oxide particles can be sufficiently reduced, and sintering between the particles can be appropriately suppressed. More preferably, the temperature of the reduction treatment is 230 ° C. or higher and 350 ° C. or lower.

The time of the reduction treatment is not particularly limited, and is preferably 1 hour or more and 96 hours or less, for example. When the reduction treatment time is 96 hours or less, it becomes difficult to appropriately proceed with sintering between particles even if the temperature of the reduction treatment is raised. As a result, the nitriding process described later becomes easy to proceed. If the reduction treatment time is 1 hour or more, the reduction can easily proceed. The time of the reduction treatment is more preferably 2 hours or more and 72 hours or less.

Atmosphere reduction treatment, a reducing atmosphere, for example, may be set to an H ₂ atmosphere.

Next, the iron particles obtained by the reduction treatment are subjected to nitriding treatment to obtain iron nitride-based magnetic particles. The iron nitride phase contained in the resulting iron nitride-based magnetic particles, although Fe ₁₆ N ₂ phase is preferred, it may be included iron nitride phases other than Fe ₁₆ N ₂ phase.

The temperature of the nitriding treatment is preferably 100 ° C. or higher and 200 ° C. or lower. When the temperature of the nitriding treatment is 100 ° C. or higher, nitriding easily proceeds sufficiently. When the temperature of the nitriding treatment is 200 ° C. or lower, nitriding is less likely to proceed excessively, and it becomes easier to suppress a decrease in magnetic characteristics. The temperature of the nitriding treatment is more preferably 120 ° C. or higher and 180 ° C. or lower.

The nitriding treatment time is not particularly limited, and is preferably 1 hour or more and 48 hours or less, for example. When the nitriding treatment time is 48 hours or less, the magnetic characteristics are less likely to deteriorate even if the nitriding treatment temperature is raised. When the nitriding treatment time is 1 hour or more, nitriding easily proceeds sufficiently. The nitriding treatment time is more preferably 3 hours or more and 24 hours or less.

Atmosphere of the nitriding treatment, NH ₃ atmosphere is preferred. Further, the atmosphere may be a mixture of N ₂ and / or H _{2 with} respect to NH ₃ .

The temperature of the slow oxidation treatment is preferably 40 ° C. or higher and 100 ° C. or lower. By setting the temperature of the slow oxidation treatment to 40 ° C. or higher, the oxide phase is likely to be sufficiently formed on the particle surface, and the magnetic properties are less likely to deteriorate. Further, when the temperature of the slow oxidation treatment is 100 ° C. or lower, it becomes easy to control so that the ratio of the oxide phase does not become excessive, and the magnetic characteristics are less likely to deteriorate. The temperature of the slow oxidation treatment is more preferably 50 ° C. or higher and 80 ° C. or lower.

The time of the slow oxidation treatment is not particularly limited, but is preferably 1 hour or more and 96 hours or less. If the time of the slow oxidation treatment is 96 hours or less, the ratio of the oxide phase is unlikely to become excessive and the magnetic characteristics are unlikely to deteriorate even when the slow oxidation temperature is high or the oxygen concentration in the slow oxidation atmosphere is high. .. If the time of the slow oxidation treatment is less than 1 hour, the oxide phase is likely to be sufficiently formed and the magnetic properties are less likely to deteriorate. The time of the slow oxidation treatment is more preferably 2 hours or more and 72 hours or less.

Xu atmosphere oxidation treatment is preferably _{N 2} atmosphere containing 10ppm or 500ppm or less _{O 2,} may be mixed with an inert gas such as He or Ar in addition to _{N 2} and _{O 2.} When O ₂ is 10 ppm or more, the oxide phase is easily formed sufficiently and the magnetic properties are less likely to deteriorate. Further, when O ₂ is 500 ppm or less, the ratio of the oxide phase is unlikely to be excessive even if the slow oxidation temperature is high, and the magnetic characteristics are unlikely to deteriorate. The content of O ₂ is more preferably 30 ppm or more and 100 ppm or less.

Through the above steps, iron nitride-based magnetic particles can be obtained.

(2.2 Production of iron oxide particles)
In the present embodiment, the iron oxide-based particles can be produced by the same method as the method for producing the iron oxide particles used for producing the iron nitride-based magnetic particles described above. The production conditions may be the same as or different from the production conditions of the iron oxide particles used for producing the iron nitride-based magnetic particles. In the present embodiment, the iron oxide-based particles are produced under the production conditions different from the production conditions of the iron oxide particles used for producing the iron nitride-based magnetic particles.

(2.3 Manufacture of iron nitride magnets)
A mixed powder in which the iron nitride-based magnetic powder composed of the iron nitride-based magnetic particles obtained above and the iron oxide-based powder composed of the iron oxide-based particles obtained above are mixed in a predetermined ratio, a resin, a solvent, and the like. If necessary, an additive selected from various dispersants, plasticizers and the like is kneaded with a ball mill or the like to obtain a slurry for iron nitride-based magnets.

A sheet for iron nitride magnets is obtained by applying the obtained slurry for iron nitride magnets and drying the slurry. When producing the iron nitride-based magnet sheet, the magnetic orientation treatment may be performed using a magnet or the like after the iron nitride-based magnet slurry is applied and before it is dried. The method of applying the slurry is not particularly limited, and examples thereof include a doctor blade method.

Next, the iron nitride magnet sheets obtained by the above steps are laminated to obtain a laminated body. Subsequently, the obtained laminate is pressurized from both sides in the lamination direction to obtain an iron nitride based magnet. The pressure at the time of pressurization is preferably 1 MPa or more and 100 MPa or less.

Further, when pressurizing the laminated body, the laminate may be pressurized while applying a magnetic field. By pressurizing while applying a magnetic field, the magnetic particles contained in the iron nitride based magnet are further oriented in a specific direction, so that an iron nitride based magnet having more excellent magnetic characteristics can be obtained.

Alternatively, as a method for molding an iron nitride-based magnet, an iron nitride-based magnetic powder composed of iron nitride-based magnetic particles, an iron oxide-based powder composed of iron oxide-based particles, and a lubricant are filled in a mold and a magnetic field is applied. While pressurizing may be used. The pressure at the time of pressurization in this case is preferably 100 MPa or more and 2 GPa or less. The lubricant is not particularly limited as long as it is a known lubricant, but in the present embodiment, stearic acid-based or lauric acid-based lubricants are preferable.

The surface of the obtained iron nitride based magnet may be plated or painted in order to prevent oxidation of the surface and deterioration of the resin and the like.

Through the above steps, the iron nitride based magnet according to the present embodiment can be obtained.

(3. Effect in this embodiment)
In the present embodiment, the iron nitride-based magnet containing the Fe ₁₆ N _2- phase contains iron nitride-based magnetic particles having a shape aspect ratio within a specific range and iron oxide-based particles smaller than the iron nitride-based magnetic particles. By doing so, the voids formed between the needle-shaped iron nitride-based magnetic particles are filled with the iron oxide-based particles, and the magnetic separation between the iron nitride-based magnetic particles becomes easy. As a result, both the mechanical strength of the iron nitride based magnet and the maximum energy product can be achieved at the same time.

The above effect can be obtained when the area ratio of the iron nitride-based magnetic particles, the shape aspect ratio of the iron nitride-based magnetic particles, and the average particle diameter ratio of the iron oxide-based particles are within the above-mentioned ranges.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and may be modified in various ways within the scope of the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

(Example 1)
First, an iron nitride-based magnetic powder composed of iron nitride-based magnetic particles was produced as follows. While stirring at a stirring speed of 600 rpm, 1 L of 1.60 mol / L Na ₂ CO ₃ aqueous solution was put into the reaction vessel, and then 1 L of ferrous sulfate aqueous solution having Fe ²⁺ concentration of 0.8 mol / L was added and mixed. A suspension containing FeCO ₃ was produced. Atmosphere in the reaction vessel, by a flow rate of 1L / min continuous flow of N ₂ gas into the reaction vessel, and a non-oxidizing atmosphere.

While the suspension generated at a flow rate of 1L / min flow of _{N 2} gas, after ripening to 2 hours at a temperature 55 ° C., the temperature of the suspension and 40 ° C., and the flow rate of 50L / min The resulting air was aerated in the suspension for 4 hours to generate gasite. Then, a gesite slurry was prepared by washing with 2 L of ion-exchanged water three times using a centrifuge.

50 mL of pure water equivalent to 50 mL of pure water was added to 1 g of the prepared Gecite slurry, and an aqueous sodium orthosilicate aqueous solution was added so that Si was 1.0% by mass while stirring. The obtained dispersion was allowed to stand for several hours to remove the supernatant. Subsequently, the operation of adding 200 mL of pure water to 1 g of the obtained sample and removing the supernatant was repeated 7 times, dried in a vacuum dryer at 85 ° C., and crushed using a mortar and pestle. Was done. The hematite powder composed of hematite particles was heat-treated in air at 750 ° C. to obtain a hematite powder composed of hematite particles.

5 g of hematite powder was placed in a firing boat and allowed to stand in a heat treatment furnace. After filling the furnace with nitrogen gas, the temperature is raised to 250 ° C. at a heating rate of 5 ° C./min while flowing hydrogen gas at a flow rate of 1 L / min, and the temperature is maintained at 250 ° C. for 48 hours for reduction treatment. It was. After the reduction treatment, the temperature was lowered to 140 ° C. while the supply of hydrogen gas was stopped and nitrogen gas was flowed at a flow rate of 2 L / min. Subsequently, while flowing ammonia gas at a flow rate of 0.2 L / min, the nitriding treatment was carried out by holding at 140 ° C. for 24 hours. After the nitriding treatment, the temperature was lowered to 50 ° C. while flowing nitrogen gas at a flow rate of 2 L / min to obtain an iron nitride-based magnetic powder composed of iron nitride-based magnetic particles.

Next, an iron oxide-based powder composed of iron oxide-based particles was produced as follows. And iron sulfate heptahydrate _{(FeSO 4 · 7H 2 O)} 162g iron chloride hexahydrate _{(FeCl 3 · 6H 2 O)} 83g was dissolved in ion-exchanged water 500 mL, to prepare an iron salt solution. 500 mL of a 2.4 mol / L sodium hydroxide aqueous solution prepared separately from the prepared iron salt aqueous solution was maintained at 30 ° C., and 500 g of the prepared iron salt aqueous solution was added to the sodium hydroxide aqueous solution. Then, the temperature of the mixed solution of the aqueous sodium hydroxide solution and the aqueous iron salt solution was controlled to be constant at 70 ° C., and the mixture was stirred for 30 minutes to advance the aging reaction in the solution to generate iron oxide.

Then, an iron oxide slurry was prepared by washing with 2 L of ion-exchanged water three times using a centrifuge. In order to control the particle size, if necessary, the following grain growth reaction and classification operation by centrifugation were performed to obtain an iron oxide-based powder composed of iron oxide-based particles.

The grain growth reaction was carried out as follows. Iron sulfate heptahydrate _{(FeSO 4 · 7H 2 O)} 28g was dissolved in ion-exchanged water 400 mL, to prepare an iron salt solution. After adding 400 mL of 0.4 mol / L sodium hydroxide aqueous solution to 100 mL of the 1000 mL of iron oxide slurry obtained above to the prepared iron salt aqueous solution, the temperature is constant at 70 ° C. while flowing air at a flow rate of 1 L / min. The temperature was controlled so as to be the same, and the aging reaction was allowed to proceed for 30 minutes to grow iron oxide particles.

The classification operation was performed by changing the rotation speed and time of a centrifuge (CR22GIII manufactured by Hitachi, Ltd.) to classify the iron oxide slurry.

Next, a resin and a solvent to be kneaded with the obtained iron nitride-based magnetic powder and iron oxide-based powder were prepared. Urethane resin was prepared as the resin, and xylene, methyl ethyl ketone and cyclohexanone were prepared as the solvent. The molecular weight of the urethane resin was 23000. The solvent used was a mixture of xylene, methyl ethyl ketone and cyclohexanone in a weight ratio of 4: 4: 2.

Weigh 10 g of mixed powder, 4.7 g of urethane resin, and 30 g of solvent, which are a mixture of iron nitride-based magnetic powder and iron oxide-based powder so that 9.7% by mass of iron oxide-based powder is contained, and diameter. The mixture was kneaded with 2 mm zirconia balls in a ball mill for 20 hours to obtain a slurry for iron nitride-based magnets.

The obtained slurry for iron nitride magnets was applied onto a PET film by a doctor blade method to obtain a sheet for iron nitride magnets.

The prepared iron nitride magnet sheet was peeled from the PET film and laminated. A sample of an iron nitride based magnet was obtained by molding the obtained laminate by applying a pressure of 20 MPa from both sides in the lamination direction.

(Examples 2 to 20 and Comparative Examples 1 to 7)
In the production of iron nitride-based magnetic powder, except that the aeration time of the aging reaction, the aeration temperature and reaction time of the oxidation treatment, the temperature and time of the reduction treatment, and the temperature and time of the nitriding treatment were set as the conditions shown in Table 1. An iron nitride based magnetic powder was produced in the same manner as in Example 1.

Further, an iron oxide-based powder was produced in the same manner as in Example 1 except that the amount of iron oxide slurry added in the grain growth reaction and the rotation speed and time of the centrifuge in the classification operation were set as the conditions shown in Table 1. The manufacturing conditions are shown in Table 1.

A sample of an iron nitride-based magnet was obtained by the same method as in Example 1 except that a mixed powder obtained by mixing the iron nitride-based magnetic powder and the iron oxide-based powder obtained above in the ratios shown in Table 1 was used.

The cross section of the obtained iron nitride based magnet sample was observed using a scanning transmission electron microscope, and an energy dispersive X-ray analyzer (STEM-EDS, JEM2100F manufactured by JEOL Ltd.) was used for a field view with a magnification of 100,000 times. ) Was used for element mapping to identify iron nitride-based magnetic particles and iron oxide-based particles. The areas of the identified iron nitride-based magnetic particles and iron oxide-based particles were calculated, and the area ratio of the iron nitride-based magnetic particles was calculated.

Further, for each of 1000 iron nitride-based magnetic particles and iron oxide-based particles, 1000 particles are selected, the equivalent circle diameter is calculated from the areas of the iron nitride-based magnetic particles and the iron oxide-based particles, and the average value thereof is averaged. The particle size was used.

Further, for the iron nitride-based magnetic particles, the average particle major axis and the average particle minor axis were calculated from the average values of the particle major axis and the particle minor axis, respectively, and the shape aspect ratio was calculated.

For the iron oxide-based particles, the average particle size ratio of the iron oxide-based particles was calculated from the average particle minor diameter of the needle-shaped iron nitride-based magnetic particles and the average particle diameter of the iron oxide-based particles. Image analysis software (Mac-View manufactured by Mountech) was used to calculate each particle area, equivalent circle diameter, particle major axis, and particle minor axis. The results are shown in Table 2.

For the obtained sample, the bending strength as the mechanical strength and the maximum energy product were measured as follows.

The bending strength of the iron nitride based magnet was measured as follows. The obtained iron nitride magnet sample was processed to a size of 80 × 10 × 4 mm, and calculated by the average value of 5 measurement samples using a bending strength tester (AGS manufactured by Shimadzu Corporation) according to JIS K7171 standard. .. In this example, a sample having a bending strength of 25 MPa or more was judged to be good. The results are shown in Table 2.

Further, the maximum energy product of the iron nitride based magnet was calculated from the average value of 5 measurement samples using a BH tracer (TM-BH25 manufactured by Tamagawa Seisakusho). In this example, a sample having a maximum energy product of 4.0 MGOe or more was judged to be good. The results are shown in Table 2.

From Table 2, when the area ratio of the iron nitride-based magnetic particles, the shape aspect ratio of the iron nitride-based magnetic particles, and the average particle diameter ratio of the iron nitride-based particles are within the above-mentioned ranges, the mechanical strength of the iron nitride-based magnet It was confirmed that both and the maximum energy product can be achieved at the same time.

Since the iron nitride based magnet according to the present invention can achieve both high mechanical strength and high maximum energy product, it can be suitably used as a high-performance magnet in various fields.

1 ... Iron nitride-based magnet 2 ... Iron nitride-based magnetic particles 4 ... Iron nitride-based particles

Claims (2)

An iron nitride based magnet containing _two Fe ₁₆ N _two phases.
The iron nitride-based magnet has iron nitride-based magnetic particles and iron oxide-based particles.
The shape aspect ratio expressed as the ratio of the average particle major axis of the iron nitride-based magnetic particles to the average particle minor axis of the iron nitride-based magnetic particles is 3.0 or more and 10.0 or less.
The average particle size ratio of the iron oxide-based particles expressed as the ratio of the average particle size of the iron oxide-based particles to the average particle minority of the iron nitride-based magnetic particles is 50% or more and 100% or less.
In the cross section parallel to the orientation direction of the iron nitride magnet, the ratio of the area occupied by the iron nitride magnetic particles to the total area occupied by the iron nitride magnetic particles and the area occupied by the iron oxide particles is shown. An iron nitride-based magnet characterized in that the area ratio of the iron nitride-based magnetic particles to be formed is 80.0% or more and 99.9% or less. The iron nitride-based magnet according to claim 1, wherein the iron nitride-based magnetic particles have an average particle diameter of 10 nm or more and 100 nm or less.

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