JP2020015968A - Iron nitride based magnet - Google Patents

Abstract

To provide an iron nitride based magnet having high residual magnetic flux density, high coercive force, high mechanical strength and high electrical resistance.SOLUTION: The iron nitride based magnet includes a plurality of iron nitride based magnetic particles having a magnetic phase including iron nitride and a non-magnetic phase existing around the magnetic phase. The plurality of iron nitride based magnetic particles neck to each other, and when in any cut surface of the iron nitride based magnet, the cross sectional area of the magnetic phase is S1, the cross-sectional area of the non-magnetic phase is S2 and the cross sectional area of a space is S3, 0.10≤S2/S1≤0.30 and 0.50≤S3/S1≤0.70 are satisfied.SELECTED DRAWING: Figure 1

Description

   The present invention relates to an iron nitride-based magnet.

  In recent years, Nd-Fe-B magnets have been widely used as motor magnets. However, demand for rare earths (rare earth elements) represented by Nd has been increasing in recent years. Furthermore, they are highly dependent on specific countries of origin. Therefore, there is a concern about securing a stable supply, and there is a demand for the development of a high-performance magnet that reduces the amount of rare earth used.

As a material for a high-performance magnet in which the amount of rare earth used is reduced, an Fe-N-based compound, particularly an Fe ₁₆ N ₂ compound, has attracted attention. This is because the Fe ₁₆ N ₂ compound shows a larger saturation magnetization than Fe.

However, the Fe ₁₆ N ₂ compound is decomposed by prolonged exposure to a temperature exceeding 200 ° C. Therefore, a sintered magnet using the Fe ₁₆ N ₂ compound cannot be manufactured. Patent Literature 1 describes a bonded magnet using Fe ₁₆ N ₂ . However, since the content of the magnetic powder in the bonded magnet is smaller than that of the sintered magnet, it is difficult to secure a sufficient residual magnetic flux density as a high-performance component, for example, a magnet for a motor.

  In particular, when a magnet is used for a motor, it is preferable to sufficiently secure the mechanical strength and electric resistance of the magnet itself. It is preferable to secure the electric resistance in order to reduce the eddy current loss.

JP 2009-84115 A

  An object of the present invention is to provide an iron nitride-based magnet having high residual magnetic flux density, high coercive force, high mechanical strength, and high electric resistance.

The present invention is an iron nitride-based magnet having a plurality of iron nitride-based magnetic particles,
The iron nitride-based magnetic particles have a magnetic phase and a non-magnetic phase existing around the magnetic phase,
The magnetic phase includes iron nitride;
The plurality of iron nitride-based magnetic particles are necked with each other,
In any cross section of the iron nitride-based magnet, assuming that the cross-sectional area of the magnetic phase is S1, the cross-sectional area of the non-magnetic phase is S2, and the cross-sectional area of the void is S3, the following equations (1) and (2) Meet.
0.10 ≦ S2 / S1 ≦ 0.30 Expression (1)
0.50 ≦ S3 / S1 ≦ 0.70 Expression (2)

The iron nitride-based magnet according to the present invention may satisfy the following expression (1A).
0.15 ≦ S2 / S1 ≦ 0.25 (1A)

The iron nitride-based magnet according to the present invention may satisfy the following expression (2A).
0.55 ≦ S3 / S1 ≦ 0.65 Expression (2A)

  In the iron nitride-based magnet according to the present invention, an average equivalent circle diameter of the magnetic phase at the arbitrary cut surface may be 30 nm or more and 150 nm or less.

  According to the present invention, it is possible to provide an iron nitride-based magnet having higher residual magnetization, higher coercive force, higher mechanical strength, and higher electric resistance than conventional iron nitride-based magnets.

FIG. 1 is a schematic view of a cut surface obtained by cutting an iron nitride-based magnet according to an embodiment of the present invention in an arbitrary direction. FIG. 2 is a schematic view of the iron nitride-based magnetic particles in a necked state. FIG. 3 is a schematic diagram of iron nitride-based magnetic particles that are not in a necked state.

  Hereinafter, preferred embodiments of the present invention will be described based on the embodiments shown in the drawings. Note that the present invention is not limited to the contents of the embodiments and examples described below. Further, the components shown in the embodiments and examples described below may be appropriately combined or may be appropriately selected.

  As shown in FIG. 1, an iron nitride-based magnet 1 of the present embodiment has iron nitride-based magnetic particles 2. Further, the iron nitride-based magnetic particles 2 have a magnetic phase 2a and a non-magnetic phase 2b existing around the magnetic phase 2a. In the present embodiment, the portions other than the iron nitride-based magnetic particles 2 of the iron nitride-based magnet 1 are the voids 4. However, a substance other than the iron nitride-based magnetic particles 2 may be included, for example, a resin is included. May be.

  However, the content of the resin in the iron nitride-based magnet 1 may be 1.0 wt% or less, and it is preferable that the resin is not substantially contained. When the content of the resin is too large, the content of the iron nitride-based magnetic particles 2 decreases. As a result, in particular, the residual magnetic flux density tends to decrease. In addition, that it does not contain resin substantially means that the content of resin is 0.1 wt% or less.

The magnetic phase 2a of the iron nitride-based magnetic particles 2 contains iron nitride. The magnetic phase 2a is mainly composed of a Fe ₁₆ N ₂ compound and preferably has ferromagnetism. However, the magnetic phase 2a may contain iron nitride other than the Fe ₁₆ N ₂ compound, such as a Fe ₄ N compound. Furthermore, the magnetic phase 2a may contain a transition metal element other than Fe as a metal element, for example, may contain Mn, Ni, Co, Ti and / or Zn. The content ratio of the Fe ₁₆ N ₂ compound as the main component in the magnetic phase 2a is preferably 95% by weight or more based on the entire magnetic phase 2a. The content of iron nitride other than the Fe ₁₆ N ₂ compound is preferably 4.0% by weight or less based on the entire magnetic phase 2a, and the content of the compound having a transition metal element other than Fe is preferably less than 4.0 wt%. It is preferably 1.0% by weight or less.

The non-magnetic phase 2b of the iron nitride-based magnetic particles 2 contains a metal oxide and has no ferromagnetism. The non-magnetic phase 2b includes, for example, oxides such as Fe ₂ O ₃ , Fe ₃ O ₄ and FeO. Furthermore, compounds other than metal oxides may be included. Examples of the compound other than the metal oxide include a Si compound. The content of the compound other than the metal oxide is arbitrary as long as the effects of the present invention are not hindered. For example, the amount of Si contained in the iron nitride-based magnetic particles 2 may be from 0.2 wt% to 2.1 wt% in terms of Si with respect to the entire iron nitride-based magnetic particles 2.

  Although not all iron nitride-based magnetic particles 2 need to have the nonmagnetic phase 2b, it is preferable that 90% or more of the iron nitride-based magnetic particles 2 on a number basis have the nonmagnetic phase 2b.

In the iron nitride-based magnet 1 according to the present embodiment, the cross-sectional area of the magnetic phase 2a is S1, the cross-sectional area of the non-magnetic phase 2b is S2, and the cross-sectional area of the void 4 is S3 at an arbitrary cut surface. ) And Equation (2) are satisfied.
0.10 ≦ S2 / S1 ≦ 0.30 Expression (1)
0.50 ≦ S3 / S1 ≦ 0.70 Expression (2)

When S2 / S1 <0.10, a sufficient magnetic separation effect by the non-magnetic phase 2b is not exhibited, so that the coercive force becomes insufficient. When S2 / S1> 0.30, the amount of the ferromagnetic magnetic phase 2a in the iron nitride-based magnetic particles 2 is reduced, so that the residual magnetization becomes insufficient and the residual magnetic flux density becomes insufficient. More preferably, the following formula (1A) is satisfied.
0.15 ≦ S2 / S1 ≦ 0.25 (1A)

When S3 / S1 <0.50, the ratio of the iron nitride-based magnetic particles 2 (magnetic phase 2a) having a lower electric resistance in the iron nitride-based magnet 1 than the gap 4 increases, and The electric resistance of the magnet 1 becomes insufficient. When S3 / S1> 0.70, the ratio of the iron nitride-based magnetic particles 2 (magnetic phase 2a) in the iron nitride-based magnet 1 decreases, the residual magnetization becomes insufficient, and the residual magnetic flux density becomes insufficient. Becomes Furthermore, the rate at which the plurality of iron nitride-based magnetic particles 2 are necked with each other decreases, and the mechanical strength (particularly, bending strength) becomes insufficient. More preferably, the following formula (2A) is satisfied.
0.55 ≦ S3 / S1 ≦ 0.65 Expression (2A)

  The size of each of the iron nitride-based magnetic particles 2 and the magnetic phase 2a is arbitrary. The average equivalent circle diameter of the magnetic phase 2a is preferably 30 nm or more and 150 nm or less. When the average circle equivalent diameter of the magnetic phase 2a is 30 nm or more and 150 nm or less, the residual magnetic flux density and the coercive force particularly tend to increase. The average equivalent circle diameter of the magnetic phase 2a is the average equivalent circle diameter of the plurality of magnetic phases 2a, that is, the diameter of a circle having the same area as the plurality of magnetic phases 2a.

  Hereinafter, a method for identifying the magnetic phase 2a, the non-magnetic phase 2b, and the voids 4 at an arbitrary cut surface of the iron nitride-based magnet 1, a method for calculating a cross-sectional area of each phase, a method for calculating an average circle equivalent diameter of the magnetic phase 2a, and the like. State about

  The method for identifying the constituent phases of the iron nitride-based magnetic particles 2 having the magnetic phase 2a and the non-magnetic phase 2b present around the magnetic phase 2a is optional. For example, after the iron nitride-based magnet 1 is pulverized, X is determined by powder XRD. This can be done by obtaining a line diffraction profile. Further, the iron nitride-based magnet 1 may be cut so as to have a section, the section may be observed with a TEM (transmission electron microscope), and the element distribution may be mapped with EDS. From the elemental mapping image (magnification of 30,000 or more and 100,000 or less), a phase substantially containing at least Fe and N and substantially not containing O in the iron nitride-based magnetic particles 2 is defined as a magnetic phase 2a. The phase substantially containing at least Fe and O in the iron-based magnetic particles 2 can be identified as the nonmagnetic phase 2 b, and the portion other than the iron nitride-based magnetic particles 2 can be identified as the void 4. Further, the total of the cross-sectional areas of the magnetic phase 2a, the non-magnetic phase 2b, and the voids 4 included in the cross section of the iron nitride-based magnet 1 is measured by image analysis of the obtained element mapping image. S2 / S1 and S3 / S1 can be calculated, where S1 is the total cross-sectional area of the magnetic phase 2a, S2 is the total cross-sectional area of the nonmagnetic phase 2b, and S3 is the total cross-sectional area of the void. Also, the equivalent circle diameter of each magnetic phase 2a is calculated from the obtained cross-sectional area of each magnetic phase 2a and averaged, whereby the average equivalent circle diameter of the magnetic phase 2a can be obtained. When a cross section of the iron nitride magnet 1 is observed by SEM, a white portion is observed as the magnetic phase 2a, a gray portion is observed as the nonmagnetic phase 2b, and a black portion is observed as the void 4.

  Further, by performing a microstructure analysis on the nonmagnetic phase 2b of the plurality of iron nitride-based magnetic particles 2, the presence or absence of a necking state can be confirmed. The method of microstructure analysis is arbitrary. For example, there is a method using a TEM. The nonmagnetic phases 2b of the plurality of iron nitride-based magnetic particles 2 are sintered together, and the particle boundaries between the nonmagnetic phases 2b are also confirmed by TEM images (magnification of 100,000 to 200,000 times) as shown in FIG. The state where it cannot be performed is referred to as the necking state. That is, the necking state is different from the state in which the nonmagnetic phases 2b of the respective iron nitride-based magnetic particles 2 are simply in contact with each other at the particle boundaries 2c as shown in FIG.

  Here, in general, as the density of the iron nitride-based magnetic particles (magnetic phase 2a) increases, the electric resistance tends to decrease and the coercive force tends to decrease. Also, as the density of the iron nitride-based magnetic particles (magnetic phase 2a) decreases, the electric resistance increases, but the residual magnetic flux density tends to decrease.

  The iron nitride-based magnet 1 according to the present embodiment has a structure in which the nonmagnetic phase 2b exists around the magnetic phase 2a (surface), and further has a necking state. Since the non-magnetic phase 2b having a high electric resistance exists around the magnetic phase 2a having a low electric resistance, each magnetic phase 2a has a single magnetic domain structure. Therefore, even if the density of the iron nitride-based magnetic particles 2 (magnetic phase 2a) increases, the electric resistance is kept high, and the coercive force does not decrease. Then, the residual magnetic flux density is improved. Further, the ratio of the voids in the iron nitride-based magnetic particles 2 (magnetic phase 2a) decreases due to necking, and the mechanical strength of the iron nitride-based magnet also increases.

  The amount of Si contained in the iron nitride-based magnetic particles 2 can be measured by EDS.

  A preferred method for manufacturing the iron nitride-based magnet according to the present embodiment will be described. The method for producing the iron nitride-based magnetic particles according to the present embodiment is arbitrary. For example, after synthesizing the iron oxide particles, the iron nitride particles obtained by sequentially performing a reduction treatment and a nitriding treatment on the iron oxide particles are subjected to a slow oxidation heat treatment at a low temperature and a low oxygen partial pressure to obtain a surface of the iron nitride particles. Is formed by forming a non-magnetic phase on the substrate, forming a molded body with a mold, and performing necking heat treatment.

  The method for producing the iron oxide particles is arbitrary. For example, it can be produced by mixing an aqueous solution of an iron salt containing an iron (II) salt and / or an iron (III) salt and an aqueous alkali solution, then aging and washing. In the following description, iron (II) salt and iron (III) salt may be collectively referred to as iron salt.

  The type of iron salt is arbitrary. For example, iron sulfate, iron chloride, iron nitrate and the like can be mentioned, and these may be used in an appropriate combination. Also, their hydrates can be used.

  The type of the alkaline aqueous solution is arbitrary. For example, one or more selected from aqueous sodium hydroxide, aqueous ammonia, aqueous ammonium salt, and aqueous urea can be used.

  The aging method is optional. Aging can be performed to improve the crystallinity of the iron oxide particles, control the particle size and / or particle shape, and the like. The ripening method is optional. For example, it can be performed by a liquid aging reaction such as a hydrothermal treatment in an autoclave. In addition, aging can be omitted.

  After the production of the iron oxide particles (after aging), the aqueous solution containing the iron oxide particles is filtered, and if necessary, a washing treatment such as washing with water is performed to collect the iron oxide particles.

  The collected iron oxide particles may be partially or entirely coated with a Si compound before the reduction treatment in order to suppress sintering of the particles by the reduction treatment described below. The type of the Si compound used for coating is arbitrary. For example, colloidal silica, a silane coupling agent, and a silanol compound are mentioned.

  When a part or the whole of the particle surface is coated with the Si compound, the amount of the Si compound used for coating is preferably 0.1 wt% or more and 20 wt% or less in terms of Si with respect to the iron oxide particles. If the amount is less than 0.1 wt%, it is difficult to suppress sintering between particles during heat treatment, and the finally obtained iron nitride-based magnetic particles tend to be coarse. If the content exceeds 20 wt%, sintering between the particles during heat treatment tends to be excessively suppressed, and the finally obtained iron nitride-based magnetic particles tend to be fine.

  The average particle size of the collected iron oxide particles is arbitrary, but is preferably from 10 nm to 150 nm. By setting the average particle diameter to 10 nm or more and 150 nm or less, it is easy to set the average circle equivalent diameter of the magnetic phase described later to 30 nm or more and 150 nm or less.

Further, the recovered iron oxide particles are composed of magnetite, γ-Fe ₂ O ₃ , α-Fe ₂ O ₃ , α-FeOOH, β-FeOOH, γ-FeOOH, FeO, etc. It may be configured.

  The shape of the collected iron oxide particles may be spherical, needle-like, granular, spindle-shaped, or rectangular parallelepiped.

  Next, the collected iron oxide particles are reduced to obtain iron particles. The temperature of the reduction treatment is arbitrary, but may be 200 ° C. or more and 400 ° C. or less. If the temperature of the reduction treatment is lower than 200 ° C., it is not preferable because the iron oxide particles are not sufficiently reduced. If the temperature of the reduction treatment exceeds 400 ° C., the iron oxide particles are sufficiently reduced, but the sintering between the particles tends to proceed excessively, which is not preferable. The temperature of the reduction treatment is more preferably 230 ° C or more and 350 ° C or less.

  The time of the reduction treatment is arbitrary, but is preferably 1 hour or more and 96 hours or less. If the time of the reduction treatment exceeds 96 hours, sintering proceeds depending on the temperature of the reduction treatment. Therefore, it becomes difficult for the nitriding treatment described later to proceed. If the time of the reduction treatment is less than 1 hour, the reduction will not sufficiently proceed. The time of the reduction treatment is more preferably 2 hours or more and 72 hours or less.

The atmosphere at the time of the reduction treatment is preferably an H ₂ atmosphere.

Next, the obtained iron particles are subjected to nitriding treatment to obtain iron nitride particles containing a Fe ₁₆ N ₂ compound as a main component. The temperature of the nitriding treatment is optional, but is preferably 100 ° C. or more and 200 ° C. or less. If the temperature of the nitriding treatment is lower than 100 ° C., the nitriding of the iron particles does not easily proceed sufficiently. If the temperature of the nitriding treatment exceeds 200 ° C., the nitriding of the iron particles tends to proceed excessively, and the magnetic properties tend to deteriorate. The temperature of the nitriding treatment is more preferably 120 ° C. or more and 180 ° C. or less.

  The nitriding time is optional. The time is preferably from 1 hour to 48 hours. If the nitriding time exceeds 48 hours, the magnetic properties of the finally obtained iron nitride-based magnet tend to deteriorate depending on the nitriding temperature. If the nitriding time is less than 1 hour, the iron particles may not be sufficiently nitrided depending on the nitriding temperature. The nitriding time is more preferably 3 hours or more and 24 hours or less.

The nitriding atmosphere is preferably an NH ₃ atmosphere. Alternatively, an atmosphere in which N ₂ , H _2, or the like is mixed with NH ₃ may be used.

  Next, by subjecting the obtained iron nitride particles to a gradual oxidation heat treatment, the surface of the iron nitride particles is oxidized, whereby a magnetic phase and a non-magnetic phase existing around the magnetic phase are provided. Get the particles. The temperature of the gradual oxidation heat treatment is arbitrary, but is preferably 40 ° C. or more and 100 ° C. or less. If the temperature of the gradual oxidation heat treatment is lower than 40 ° C., it is difficult to form a non-magnetic phase sufficiently, and the magnetic properties of the finally obtained iron nitride-based magnet tend to deteriorate. Further, when the temperature of the gradual oxidation heat treatment is 100 ° C. or more, an excessively non-magnetic phase is likely to be formed, and the magnetic properties of the finally obtained iron nitride-based magnet are likely to deteriorate. The temperature of the slow oxidation heat treatment is more preferably 50 ° C. or more and 80 ° C. or less.

  The time of the slow oxidation heat treatment is arbitrary. It is preferable that the time is 1 hour or more and 96 hours or less. If the annealing time exceeds 96 hours, the non-magnetic phase tends to be excessively formed depending on the annealing temperature and the annealing atmosphere, and the magnetic properties of the finally obtained iron nitride-based magnet tend to deteriorate. Become. If the annealing time is less than 1 hour, it is difficult to form a non-magnetic phase sufficiently depending on the annealing temperature and the annealing atmosphere, and the magnetic properties of the finally obtained iron nitride magnet deteriorate. Easier to do. The time of the slow oxidation heat treatment is more preferably 2 hours or more and 72 hours or less.

Xu atmosphere oxidizing heat treatment is preferably _{N 2} atmosphere containing 10ppm or 500ppm or less _{O 2,} may be in addition to mixed with an inert gas such as He or Ar in _{N 2.} When the content of O ₂ is less than 10 ppm, it is difficult to form a non-magnetic phase sufficiently depending on the gradual oxidation temperature, and the magnetic properties of the finally obtained iron nitride-based magnet tend to decrease. On the other hand, if the O ₂ content exceeds 500 ppm, an excessively non-magnetic phase is likely to be formed depending on the gradual oxidation temperature, and the magnetic properties of the finally obtained iron nitride-based magnet are likely to deteriorate. The content of O ₂ during the slow oxidation heat treatment is more preferably 30 ppm or more and 100 ppm or less.

Next, iron nitride-based magnetic particles having a magnetic phase and a non-magnetic phase existing around the magnetic phase are charged into a mold having an arbitrary shape and size, preferably from 30 kgf / cm ^{2 to} 300 kgf / cm. A load of ² or less is applied to produce a molded body. 30 kgf / cm ² or more 300 kgf / cm ² by the following load, it is possible to suppress the crack molded body has sufficient shape retention, and generates the molded body. Load more preferably 100 kgf / cm ² or more 300 kgf / cm ² or less.

  The molded body may be manufactured by applying a magnetic field when molding into a predetermined shape. Thereby, the iron nitride-based magnetic particles contained in the finally obtained iron nitride-based magnet are oriented in a specific direction, so that an iron nitride-based magnet having more excellent magnetic properties can be obtained.

A molded body made of iron nitride-based magnetic particles having the obtained magnetic phase and a non-magnetic phase existing around the magnetic phase is subjected to necking heat treatment at a temperature of 300 ° C. or less using RHK (roller hearth kiln). By performing the above, the plurality of iron nitride-based magnetic particles are necked together to obtain the iron nitride-based magnet according to the present embodiment. When the necking heat treatment is performed at a temperature exceeding 300 ° C., the Fe ₁₆ N ₂ compound which is a main component of the magnetic phase may be decomposed even in a short time, and the magnetic properties may be significantly reduced. The temperature of the necking heat treatment by RHK is more preferably 200 ° C. or less.

The time of the necking heat treatment using RHK is arbitrary, but is preferably 1 minute or more and 10 minutes or less. When the time of the necking heat treatment using RHK is less than 1 minute, necking between a plurality of iron nitride-based magnetic particles becomes insufficient, and mechanical strength tends to decrease. If the necking heat treatment time exceeds 10 minutes, the Fe ₁₆ N ₂ compound which is the main component of the magnetic phase may be decomposed, and the magnetic properties may be significantly reduced. The time of the necking heat treatment is more preferably 1 minute or more and 5 minutes or less.

The atmosphere at the time of necking heat treatment by RHK is arbitrary. For example, it is an inert atmosphere such as N ₂ , He, or Ar or a vacuum.

  The necking heat treatment method is optional. In addition to the above method using RHK, a hot press method, HIP (hot isostatic pressing method), SPS (discharge plasma sintering method) and the like can be mentioned. The conditions of the necking heat treatment, particularly the time and atmosphere, may be appropriately selected depending on the method of the necking heat treatment. However, a normal heat treatment, such as that performed in a stationary batch furnace, hardly causes a necking state.

  The obtained iron nitride-based magnet may be plated or painted on its surface in order to prevent the oxide layer and the resin from deteriorating.

  The application of the iron nitride-based magnet according to the present embodiment is arbitrary. Examples include motors (especially for electric vehicles and hybrid vehicles), generators for generators, voice coil motors, actuators for robots, and the like.

  Next, the iron nitride-based magnet of the present invention will be described in more detail using examples and comparative examples, but the present invention is not limited to the embodiments shown in the examples.

(Example 1) was dissolved in iron sulfate heptahydrate _{(FeSO 4 · 7H 2 O)} 167g iron chloride hexahydrate _(FeCl 3 _· 6H 2 O) Ion exchange water 248g and 85 g, the iron salt solution Produced. Next, 600 g of a 2.5 mol aqueous ammonia solution was maintained at 30 ° C., and 500 g of the previously adjusted iron salt aqueous solution was added. The temperature was controlled so as to be constant at 70 ° C. as an in-solution aging reaction, followed by stirring for 30 minutes. . Thereafter, the resultant was washed three times with 2 L of ion-exchanged water using a centrifuge to prepare an iron oxide slurry.

To 1000 g of the iron oxide slurry, 5.0 g of tetraethoxysilane, 21 g of ethanol, and 78 g of diethylene glycol monobutyl ether were added, and a Si coating treatment was performed. This iron oxide slurry was dried at 85 ° C. for 24 hours to produce iron oxide particles containing Fe ₂ O ₃ .

2 g of the iron oxide particles were placed in a firing boat and left in a heat treatment furnace (batch furnace). After filling the furnace with N ₂ gas, the temperature was raised to 250 ° C. at a rate of 5 ° C./min while flowing H ₂ gas at a flow rate of 1 L / min, and the reduction treatment was performed by holding for 48 hours. . Thereafter, the supply of H ₂ gas was stopped, and the temperature was lowered to 140 ° C. while flowing nitrogen gas at a flow rate of 2 L / min. Subsequently, the nitriding treatment was performed at 140 ° C. for 24 hours while stopping the supply of the N ₂ gas and flowing the NH ₃ gas at a flow rate of 0.2 L / min. Thereafter, the supply of NH ₃ gas was stopped, and the temperature was lowered to 50 ° C. while flowing N ₂ gas at a flow rate of ₂ L / min. Subsequently, a slow oxidation heat treatment was performed at 50 ° C. for 24 hours while flowing N ₂ gas containing 50 ppm of O ₂ at a flow rate of ₂ L / min. Thereafter, the supply of various atmosphere gases was stopped, and the temperature was lowered to room temperature to obtain iron nitride-based magnetic particles having a nonmagnetic phase composed of Fe ₃ O _{4 on the} surface of the particles.

A mold is filled with iron nitride-based magnetic particles having a nonmagnetic phase of Fe ₃ O _{4 on the} surface of the obtained particles, and a pressure of 150 kgf / cm ² is applied at room temperature to form particles of Fe ₃ O _{4 on the} surface. A molded body made of iron nitride-based magnetic particles having a non-magnetic phase was obtained. The molded bodies for measuring magnetic properties and electric resistance and the molded bodies for measuring bending strength were filled in separate molds to obtain separate molded bodies. This is because the size of the test sample used for the measurement is different.

  Each of the obtained molded bodies was subjected to necking heat treatment with an RHK (roller hearth kiln) flowing Ar gas to produce an iron nitride-based magnet. At this time, the Ar gas flow rate was 2 L / min, and heat treatment was performed at 200 ° C. for 5 minutes.

  (Example 2) An iron nitride-based magnet was produced in the same manner as in Example 1, except that the amount of tetraethoxysilane added to the iron oxide slurry was 4.0 g.

(Example 3) An iron nitride-based material was prepared in the same manner as in Example 1 except that the amount of tetraethoxysilane added to the iron oxide slurry was 2.5 g, and the molding pressure at the time of producing a molded body was 150 kgf / cm ^2. A magnet was made.

  (Example 4) An iron nitride-based magnet was produced in the same manner as in Example 1 except that the amount of tetraethoxysilane added to the iron oxide slurry was 1.8 g.

  Example 5 An iron nitride-based magnet was produced in the same manner as in Example 1, except that the amount of tetraethoxysilane added to the iron oxide slurry was 0.8 g.

  (Example 6) An iron nitride magnet was produced in the same manner as in Example 1, except that the amount of tetraethoxysilane added to the iron oxide slurry was 0.6 g.

  (Comparative Example 1) An iron nitride-based magnet was produced in the same manner as in Example 3, except that the annealing time was set to 0.5 hour.

  (Example 11) An iron nitride-based magnet was produced in the same manner as in Example 3, except that the gradual oxidation heat treatment was performed for 1 hour.

  (Example 12) An iron nitride-based magnet was produced in the same manner as in Example 3, except that the annealing treatment was gradually performed for 12 hours.

  (Example 13) An iron nitride-based magnet was produced in the same manner as in Example 3, except that the gradual oxidation heat treatment was performed for 30 hours.

  (Example 14) An iron nitride-based magnet was produced in the same manner as in Example 3, except that the gradual oxidation heat treatment was performed for 36 hours.

  (Comparative Example 2) An iron nitride-based magnet was produced in the same manner as in Example 3, except that the annealing treatment was gradually performed for 40 hours.

(Comparative Example 11) An iron nitride-based magnet was produced in the same manner as in Example 3, except that the molding pressure at the time of producing a molded body was 350 kgf / cm ² .

(Example 21) An iron nitride-based magnet was produced in the same manner as in Example 3, except that the molding pressure at the time of producing the molded body was 300 kgf / cm ² .

(Example 22) An iron nitride-based magnet was produced in the same manner as in Example 3, except that the molding pressure at the time of producing the molded body was 200 kgf / cm ² .

(Example 23) An iron nitride-based magnet was produced in the same manner as in Example 3, except that the molding pressure at the time of producing the molded body was 100 kgf / cm ² .

(Example 24) An iron nitride-based magnet was produced in the same manner as in Example 3, except that the molding pressure at the time of producing the molded body was 30 kgf / cm ² .

(Comparative Example 12) An iron nitride-based magnet was produced in the same manner as in Example 3, except that the molding pressure at the time of producing the molded body was 20 kgf / cm ² .

  (Comparative Example 21) An iron nitride-based magnet was produced in the same manner as in Example 3 except that the heat treatment of the molded body was performed at 200 ° C for 1 minute using a batch furnace instead of RHK.

  (Example 31) An iron nitride-based magnet was produced in the same manner as in Example 3, except that the condition for necking heat treatment of the molded body with RHK was set to 200 ° C for 1 minute.

  (Example 32) An iron nitride-based magnet was produced in the same manner as in Example 3, except that the condition for necking heat treatment of the molded body with RHK was set to 200 ° C for 10 minutes.

同 定 Identification of the constituent phases in the cross section of the iron nitride magnet, calculation of the cross-sectional area ratio of each constituent phase, and calculation of the average circle equivalent diameter of the iron nitride magnetic particles≫
The prepared iron nitride-based magnetic particles having a nonmagnetic phase on the particle surface were obtained by crushing an iron nitride-based magnet and obtaining an X-ray diffraction profile by powder XRD (Rigaku RINT-2500) to identify constituent phases. Further, the obtained iron nitride-based magnet was cut so as to have a section, the section was observed with a TEM (JEM-2100FCS, manufactured by JEOL Ltd.), and the element distribution was mapped by ESD. From the elemental mapping image (magnification: 50,000 times), a phase substantially containing at least Fe and N and substantially not containing O in the iron nitride-based magnetic particles was defined as a magnetic phase, A phase substantially containing at least Fe and O was defined as a nonmagnetic phase, and portions other than the iron nitride-based magnetic particles were identified as voids. The measurement range of the cross-section observation may be a range including at least 100 or more magnetic phase 2a, nonmagnetic phase 2b, and void 4, respectively, and preferably a range including 200 or more. Further, by image analysis of the obtained element mapping image, 500 cross-sectional areas of the magnetic phase, the non-magnetic phase, and the voids included in the cross section of the iron nitride-based magnet were measured. S2 / S1 and S3 / S1 were calculated assuming that the sectional area of the magnetic phase is S1, the sectional area of the nonmagnetic phase is S2, and the sectional area of the void is S3. Further, the equivalent circle diameter of each magnetic phase was calculated from the obtained cross-sectional area of each magnetic phase, and averaged to obtain an average equivalent circle diameter.

  The microstructure of the non-magnetic phase was analyzed using a TEM at a magnification of 100,000 and the presence or absence of necking was confirmed.

  The amount of Si contained in the iron nitride-based magnetic particles was measured by EDS.

<< Measurement of residual magnetization (Br) and coercive force (Hc) of iron nitride magnet >>
The Br and Hc of the iron nitride-based magnet were measured using a BH tracer (TRF-5BH, manufactured by Toei Kogyo) for the iron nitride-based magnet for measuring magnetic properties. Br and Hc were determined from demagnetization curves obtained by changing the externally applied magnetic field from +25 kOe to -25 kOe. An iron nitride-based magnet having Br of 3.0 kG or more and Hc of 2.0 kOe or more was allowed. Further, Br is preferably 4.0 kG or more, and Hc is preferably 2.5 kOe or more.

≫Measurement of bending strength of iron nitride magnet 磁石
The bending strength of the iron nitride magnet was prepared by preparing a test sample in which an iron nitride magnet for bending strength measurement was processed into a size of 80 mm × 10 mm × 4 mm, and a bending strength tester (Instron Japan Company) in accordance with JIS K7171 standard. It was measured using INSTRON5543 manufactured by Limited. Five test samples were prepared for each standard, the bending strength was measured, and the average value was calculated. An iron nitride-based magnet having a bending strength of 25 MPa or more was allowed. Further, the bending strength is preferably 35 MPa or more.

≫Measurement of electric resistance of iron nitride magnet 磁石
The electric resistance of the iron nitride-based magnet was measured using a four-deep needle method for the iron nitride-based magnet for measuring electric resistance after necking heat treatment. The electric resistance of five iron nitride-based magnets per level was measured, and the average value was calculated. An iron nitride-based magnet having an electric resistance of 1.0E + 00Ω · cm or more was allowed. Further, the electric resistance is preferably 1.0E + 01Ω · cm or more.

In all Examples and Comparative Examples, in the iron nitride-based magnet, a magnetic phase containing Fe ₁₆ N ₂ , a non-magnetic phase containing Fe ₃ O ₄ , and voids were observed on the cut surface. In addition, it was confirmed that the amount of Si contained in the iron nitride-based magnetic particles was 0.2 to 2.1 wt%. Furthermore, it was confirmed that a plurality of iron nitride-based magnetic particles were in a necking state in all Examples and Comparative Examples except for Comparative Example 21 in which RHK was not used.

  The necking state was confirmed, and in all the examples where S2 / S1 and S3 / S1 satisfy Expressions (1) and (2), Br, Hc, bending strength, and electric resistance were all within allowable ranges.

  Table 1 shows Examples in which the equivalent circle diameter of the magnetic phase was changed. Table 1 shows that, even when the equivalent circle diameter of the magnetic phase was changed, Br, Hc, bending strength, and electric resistance were all within the allowable ranges in all Examples. Further, Examples 2 to 5 in which the equivalent circle diameter of the magnetic phase was 30 nm or more and 150 nm or less had better Br than Example 1 in which the equivalent circle diameter was 23 nm. In addition, Hc was superior to Example 6 in which the equivalent circle diameter was 161 nm.

  Table 2 shows Examples and Comparative Examples in which S2 / S1 was changed. According to Table 2, Br, Hc, bending strength, and electric resistance were all within the allowable ranges in all the examples in which S2 / S1 satisfied the expression (1). In particular, Examples 3, 12 and 13 satisfying the formula (1A) were superior in Hc as compared with Example 11 in which S2 / S1 was relatively low. Further, Br was superior to Example 14 in which S2 / S1 was relatively high. In Comparative Example 1 where S2 / S1 was too low and did not satisfy the expression (1), Hc was below the allowable range. In Comparative Example 2 where S2 / S1 was too high and did not satisfy the expression (1), Br was below the allowable range.

  Table 3 shows Examples and Comparative Examples in which S3 / S1 was changed. According to Table 3, Br, Hc, bending strength, and electric resistance were all within the allowable ranges in all the examples where S3 / S1 satisfied the expression (2). In particular, Examples 3, 22, and 23 satisfying the formula (2A) were superior in Hc and electric resistance as compared with Example 21 in which S3 / S1 was relatively low. In addition, Br and bending strength were superior to Example 24 in which S3 / S1 was relatively high. In Comparative Example 11 where S3 / S1 was too low and did not satisfy the expression (2), the electric resistance was lower than the allowable range. Further, in Comparative Example 12 in which S3 / S1 was too high and did not satisfy the expression (2), Br and bending strength were below the allowable range.

  Table 4 shows Examples and Comparative Examples in which the presence or absence of RHK and the time of the heat treatment using RHK were changed. From Table 4, heat treatment using RHK was performed, and in all the examples in which a plurality of iron nitride-based magnetic particles were confirmed to be in a necked state, Br, Hc, bending strength, and electric resistance were all within allowable ranges. Was. Further, as the time of the heat treatment using RHK becomes longer, the ratio of the iron nitride-based magnetic particles in the necking state increases, and the Br and the bending strength tend to increase. Conversely, as the time of the heat treatment using RHK becomes shorter, the ratio of the iron nitride-based magnetic particles in the necked state increases, and Hc and electric resistance tend to be improved. On the other hand, in Comparative Example 21 in which the heat treatment using RHK was not performed, no iron nitride-based magnetic particles in a necked state were confirmed, and the bending strength was high despite satisfying the formulas (1A) and (2A). Below the allowable range.

  When S2 / S1 is too small as in Comparative Example 1, the ratio of the non-magnetic phase in the iron nitride-based magnetic particles is small, so that the iron nitride-based magnetic particles are not sufficiently magnetically separated and Hc is reduced. it is conceivable that.

  When S2 / S1 is too large as in Comparative Example 2, the ratio of the nonmagnetic phase in the iron nitride-based magnetic particles is large, so that the ferromagnetic component in the iron nitride-based magnet decreases and Br decreases. it is conceivable that.

  If S3 / S1 is too small as in Comparative Example 11, the ratio of the voids in the iron nitride-based magnet becomes small, and the contact between the iron nitride-based magnetic particles becomes remarkable. Can be

  When S3 / S1 is too large as in Comparative Example 12, the ratio of the magnetic phase in the iron nitride-based magnet is reduced, and the ferromagnetic component is reduced. In addition, it is considered that the bending strength of the iron nitride-based magnet was lowered as a result of the reduced proportion of the iron nitride-based magnetic particles in the necking state.

  When the iron nitride-based magnetic particles in the iron nitride-based magnet are not in the necking state as in Comparative Example 21, the bonding strength between the non-magnetic phases existing on the surface of the iron nitride-based magnetic particles is small. It is considered that the shape retention was reduced, and as a result, the bending strength was reduced.

  As described above, since the iron nitride-based magnet according to the present invention has high residual magnetization, high coercive force, high mechanical strength (particularly bending strength), and electric resistance even without substantially including rare earth, It is useful as a magnet that does not substantially use.

DESCRIPTION OF SYMBOLS 1 Iron nitride magnet 2 Iron nitride magnetic particles 2a Magnetic phase 2b Nonmagnetic phase 2c Particle boundary 4 Void

Claims (4)

An iron nitride-based magnet having a plurality of iron nitride-based magnetic particles,
The iron nitride-based magnetic particles have a magnetic phase and a non-magnetic phase existing around the magnetic phase,
The magnetic phase includes iron nitride;
The plurality of iron nitride-based magnetic particles are necked with each other,
In any cross section of the iron nitride-based magnet, assuming that the cross-sectional area of the magnetic phase is S1, the cross-sectional area of the non-magnetic phase is S2, and the cross-sectional area of the void is S3, the following equations (1) and (2) An iron nitride magnet that satisfies.
0.10 ≦ S2 / S1 ≦ 0.30 Expression (1)
0.50 ≦ S3 / S1 ≦ 0.70 Expression (2) The iron nitride-based magnet according to claim 1, wherein the following formula (1A) is satisfied.
0.15 ≦ S2 / S1 ≦ 0.25 (1A) The iron nitride-based magnet according to claim 1 or 2, wherein the following formula (2A) is satisfied.
0.55 ≦ S3 / S1 ≦ 0.65 Expression (2A) The iron nitride-based magnet according to any one of claims 1 to 3, wherein an average equivalent circle diameter of the magnetic phase at the arbitrary cut surface is 30 nm or more and 150 nm or less.

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