JP2017183323A - Iron nitride-based magnetic powder and bond magnet arranged by use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: iron nitride-based magnetic powder which enables the achievement of a high orientation degree and a high density; and an iron nitride-based bond magnet which enables the achievement of a high residual magnetic flux density (Br).SOLUTION: Iron nitride-based magnetic powder has an FeNcompound phase as a main phase 2. The iron nitride-based magnetic powder comprises: iron nitride-based particles 1; and a layer 3 formed on a surface layer part of each iron nitride-based particle, and including an iron sulfide having a main phase of FeS. The iron sulfide-containing layer 3 has an average thickness of 1.2-12 nm; and the rate of the average thickness of the iron sulfide-containing layer 3 to an average particle diameter of the magnetic powder is 2.4-13%.SELECTED DRAWING: Figure 1

Description

The present invention relates to an iron nitride magnetic powder having a Fe ₁₆ N ₂ compound phase as a main phase. Furthermore, the present invention provides a bonded magnet that can obtain a high residual magnetic flux density using the iron nitride magnetic powder.

  In recent years, Nd-Fe-B magnets have been widely used as motor magnets for electric vehicles and hybrid vehicles. However, rare earths typified by Nd are raw materials for high-value-added members that support the industrial field, and since demand is increasing in recent years, there are concerns that resource depletion and raw material prices are unstable. . Furthermore, there is a problem in securing a stable supply because the demand is growing significantly in developing countries and the dependence on specific producing countries is high due to its uneven distribution.

  In order to avoid the above problems, it is required to develop a high-performance magnet from elements (iron, nitrogen) which do not use rare earths and exist infinitely in nature.

Fe-N-based compounds, particularly Fe ₁₆ N _2, are attracting attention as one of materials exhibiting a larger saturation magnetization than Fe.

Patent Document 1 describes that iron oxyhydroxide is subjected to reduction treatment and nitriding treatment to produce an iron nitride-based magnetic powder containing an Fe ₁₆ N ₂ phase. There is no exemplification to obtain a bonded magnet by using it, and it is insufficient as a technique for obtaining a bonded magnet having a high residual magnetic flux density (Br) by utilizing the high saturation magnetization of the Fe ₁₆ N ₂ phase.

  In order to obtain a bonded magnet having a high residual magnetic flux density (Br), a high degree of orientation and a high density are required. In order to obtain a high degree of orientation with a bonded magnet, it is necessary to cover the magnetic powder with a resin. In this case, the amount of resin increases and the density decreases. On the other hand, if the amount of resin is reduced, the interparticle friction increases, so that rotation of the particles by an external magnetic field is hindered, and a high degree of orientation cannot be obtained. Therefore, it is difficult to obtain a bonded magnet having a high degree of orientation and a high density.

JP 2011-91215 A

The present invention has been made in view of the above, and an iron nitride based magnetic powder suitable for obtaining a high degree of orientation and high density, and an iron nitride based bonded magnet having a high residual magnetic flux density (Br) using the magnetic powder. The purpose is to provide.

That is, the present invention is an iron nitride-based magnetic powder comprising iron nitride-based magnetic particles whose main phase is Fe ₁₆ N ₂ compound phase, and a layer containing iron sulfide whose main phase is FeS in the surface layer portion of the magnetic particles. The average thickness of the iron sulfide-containing layer is 1.2 to 12 nm, and the ratio of the average thickness of the iron sulfide-containing layer to the average particle diameter of the magnetic powder is 2.4 to 13 The present invention relates to an iron nitride-based magnetic powder and a bonded magnet using the magnetic powder.

When the main phase of the iron sulfide-containing layer is FeS, a hexagonal layered structure having pores is formed. When a force is applied to the contact point between the magnetic particles, the frictional resistance between the magnetic particles can be reduced by sliding so that the layered structure is peeled off. Furthermore, liquids such as resins and solvents used in bonded magnets are supported in the pores formed in the iron sulfide-containing layer, and this support provides a lubricating action between the magnetic particles, thereby reducing frictional resistance. It can be reduced. By using such an iron nitride magnetic powder, if the frictional resistance between the magnetic particles is reduced, the magnetic particles can be easily filled even with a small amount of resin, and the rotation of the particles by an external magnetic field is facilitated. High degree of orientation and high density can be obtained.

Furthermore, the present invention relates to an iron nitride magnetic powder having an average thickness of the iron sulfide-containing layer of 1.5 to 10 nm and a bonded magnet using the magnetic powder.

Furthermore, the present invention provides an iron nitride magnetic powder and a bonded magnet using the magnetic powder, wherein the ratio of the average thickness of the iron sulfide-containing layer to the average particle diameter of the magnetic powder is 2.4 to 10.2%. It is about.

Furthermore, the present invention relates to an iron nitride magnetic powder and a bond magnet using the magnetic powder, wherein the magnetic powder has an average particle size of 20 to 130 nm.

The present invention can provide an iron nitride magnetic powder suitable for obtaining a high degree of orientation and a high density. Furthermore, it is possible to provide an iron nitride bond magnet having a high residual magnetic flux density (Br) using the magnetic powder.

FIG. 1 is a cross-sectional view showing an iron nitride-based magnetic powder according to an embodiment of the present invention. FIG. 2 is a cross-sectional configuration diagram of a bonded magnet according to an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described based on the embodiments shown in the drawings. The present invention is not limited by the contents of the embodiments and examples described below. In addition, the constituent elements shown in the embodiments and examples described below may be appropriately combined or may be appropriately selected.

As shown in FIG. 1, the iron nitride magnetic powder according to the present invention is composed of iron nitride magnetic particles 1, and the magnetic particles 1 are composed of a main phase 2 composed of Fe ₁₆ N ₂ compound and the magnetic particles 1. The layer 3 containing iron sulfide is formed on the surface layer portion of.

The main phase 2 of the magnetic particle 1 is an Fe ₁₆ N ₂ compound phase, but may include a nitride phase such as an Fe ₄ N compound in addition to the Fe ₁₆ N ₂ compound. In addition to the nitride phase, it may have a trace amount of an oxide phase such as Fe ₂ O ₃ , Fe ₃ O ₄ and FeO, and a sulfide phase such as FeS. May have a phase. Further, the magnetic particle 1 may contain a transition metal such as Mn, Ni, Co, Ti, Zn.

The main phase of iron sulfide contained in the layer 3 containing iron sulfide is FeS, but contains the interface between the main phase 2 composed of the Fe ₁₆ N ₂ compound phase and the layer 3 containing iron sulfide or iron sulfide. Part of the layer 3 contains a trace amount of a sulfide phase such as FeS ₂ and Fe ₃ S ₄ , a nitride phase such as an Fe ₄ N compound, and an iron oxide phase such as Fe ₂ O ₃ , Fe ₃ O ₄ and FeO. You may go out. Further, the present invention is not limited to this, and other phases may be included as long as they are outside the range of hindering the effect.

The average particle size 4 of the magnetic powder 1 is preferably in the range of 15 to 155 nm. If the average particle diameter is not within this range, a sufficient residual magnetic flux density (Br) may not be obtained. More preferably, it is 20-130 nm.

The thickness 5 of the iron sulfide-containing layer has an average value of 1.2 to 12 nm, and the ratio of the average thickness of the iron sulfide-containing layer to the average particle diameter of the magnetic powder is 2.4 to 13%. A more preferable range of the thickness 5 of the layer containing iron sulfide is 1.5 to 10 nm. A more preferable range of the average thickness ratio is 2.4 to 10.2%.

When the thickness 5 of the layer containing iron sulfide is smaller than 1.2 nm, the formation of a hexagonal layered structure having pores is insufficient, so that a high degree of orientation and high density cannot be obtained. In addition, when the ratio of the average thickness of the iron sulfide-containing layer to the average particle diameter of the magnetic powder is lower than 2.4%, the effect of reducing the frictional resistance between the magnetic particles is too small, resulting in a high degree of orientation and high The density may not be obtained. On the other hand, if the ratio is larger than 12 nm or if the ratio of the average thickness of the iron sulfide-containing layer to the average particle diameter of the magnetic powder is higher than 13%, the structure of the surface layer becomes brittle or the foreign phase is excessively precipitated. It is difficult to obtain a high degree of orientation and high density, or the ratio of the main phase contained in the iron nitride-based magnetic particles is reduced, so that the saturation magnetization of the iron nitride-based magnetic powder is reduced. The density (Br) may not be obtained.

Below, the suitable manufacturing method of the iron nitride type magnetic powder which concerns on this embodiment is described. The iron nitride magnetic powder according to the present embodiment contains iron sulfide with respect to iron nitride magnetic particles obtained by synthesizing iron oxide particles and then subjecting the iron oxide particles to reduction treatment and nitriding treatment in order. It is obtained by performing a process for forming a layer.

The iron oxide particles can be produced by mixing an aqueous iron salt solution and an aqueous alkaline solution, aging and washing.

Examples of the iron salt include sulfates, chlorides and nitrates, and these may be used in appropriate combination. Moreover, those hydrates can be used.

As the alkaline aqueous solution, one or more of sodium hydroxide aqueous solution, ammonia water, ammonia salt aqueous solution, and urea aqueous solution can be used, but not limited thereto.

In addition, after the iron oxide production, an aging reaction in liquid such as hydrothermal treatment by an autoclave may be performed for improving crystallinity and controlling the particle size and particle shape.

After the iron oxide is produced, the aqueous solution is filtered, and the iron oxide particles can be recovered by performing a washing treatment such as washing with water as necessary.

The iron oxide particles may be coated with a Si compound in order to suppress sintering of the particles during heat treatment such as reduction. As the Si compound, colloidal silica, a silane coupling agent, a silanol compound, or the like can be used.

When coat | covering with Si compound, it is preferable that the coating amount is 0.1 to 20 mass% in conversion of Si with respect to iron oxide particles. When the amount is less than 0.1% by mass, the effect of suppressing the sintering of the particles during the heat treatment cannot be obtained sufficiently, and the finally obtained iron nitride magnetic particles become large. On the other hand, if it exceeds 20% by mass, the effect of suppressing the sintering of the particles during the heat treatment becomes excessive, and the finally obtained iron nitride-based magnetic particles become smaller.

The iron oxide particles preferably have an average particle diameter of 10 nm to 150 nm. By setting the average particle diameter within this range, the average particle diameter of the iron nitride-based magnetic particles finally obtained can be set to 15 to 155 nm.

Examples of the iron oxide particles include magnetite, γ-Fe ₂ O ₃ , α-Fe ₂ O ₃ , α-FeOOH, β-FeOOH, γ-FeOOH, and FeO, but are not limited thereto.

The particle shape of the iron oxide particles may be any of spherical shape, needle shape, granular shape, spindle shape, rectangular parallelepiped shape, and the like.

Next, the obtained iron oxide particles are subjected to reduction treatment to obtain iron particles. The temperature of the reduction treatment is 200 to 400 ° C. When the temperature of the reduction treatment is less than 200 ° C., the iron oxide particles are not sufficiently reduced. When the temperature of the reduction treatment exceeds 400 ° C., the iron oxide particles are sufficiently reduced, but this is not preferable because sintering between the particles proceeds. More preferably, it is 230-350 degreeC.

The time for the reduction treatment is not particularly limited, but is preferably 1 to 96 hours. If it exceeds 96 hours, the sintering proceeds depending on the reduction temperature, and the subsequent nitriding process is difficult to proceed. If it is less than 1 hour, the reduction does not proceed sufficiently. More preferably, it is 2 to 72 hours.

The atmosphere for the reduction treatment is a hydrogen gas atmosphere.

Next, the obtained iron particles are nitrided to obtain iron nitride-based magnetic particles. The temperature of the nitriding treatment is 100 to 200 ° C. When the nitriding temperature is less than 100 ° C., nitriding does not proceed sufficiently. When the temperature of the nitriding process exceeds 200 ° C., nitriding proceeds excessively, so that the magnetic characteristics are deteriorated. More preferably, it is 120-180 degreeC.

The nitriding time is not particularly limited, but is preferably 1 to 48 hours. If it exceeds 48 hours, the magnetic properties will deteriorate depending on the nitriding temperature. In many cases, sufficient nitriding cannot be performed in less than 1 hour. More preferably, it is 3 to 36 hours.

The atmosphere of the nitriding treatment is desirably an ammonia gas NH ₃ atmosphere, and in addition to NH ₃ , nitrogen gas N ₂ , hydrogen gas H _{2, and the} like may be appropriately mixed.

At this time, an iron oxide layer may be provided on the surface layer of the iron nitride magnetic particles.

Subsequent to the nitriding treatment, a sulfuration treatment is performed to obtain an iron nitride-based magnetic powder in which a layer containing iron sulfide is formed on the surface layer portion. The temperature of the sulfuration treatment is 100 to 200 ° C. When the temperature of the sulfuration treatment is less than 100 ° C., formation of the layer containing iron sulfide does not proceed sufficiently. When the temperature of the sulfiding treatment exceeds 200 ° C., the penetration of S and N proceeds excessively, so that the magnetic characteristics are deteriorated. More preferably, it is 120-180 degreeC.

The time for the sulfur treatment is not particularly limited, but is preferably 1 to 36 hours. By changing the treatment time, the thickness of the layer containing iron sulfide can be controlled. If it is less than 1 hour, the formation of a layer containing iron sulfide is insufficient. If it exceeds 36 hours, the penetration of S and N will proceed excessively depending on the processing temperature, so that the magnetic properties will deteriorate. More preferably, it is 2 to 24 hours.

The atmosphere of the sulfuration treatment is preferably a mixed atmosphere of hydrogen sulfide gas H ₂ S and NH _3, but is not limited to this, and N ₂ , H _2, etc. may be mixed in addition to the H ₂ S single atmosphere or NH _3. . By changing the mixing ratio of H ₂ S and NH ₃ , the thickness of the layer containing iron sulfide can be controlled. Desirably, the ratio of _{H 2} S in the mixed atmosphere is 10~60mol%.

A bonded magnet can be obtained using the iron nitride magnetic powder obtained according to the present embodiment. The bond magnet is manufactured by molding a mixture of magnetic powder and an organic binder such as a thermosetting resin or a thermoplastic resin into a desired shape. Compared to bulk magnets obtained by sintering, the magnetic properties are inferior, but there are advantages that magnets with complex shapes can be produced and that dimensional accuracy is excellent.

FIG. 2 shows a cross-sectional configuration diagram of a bonded magnet according to an embodiment of the present invention. As shown in FIG. 2, the bonded magnet 8 according to the present invention includes the resin (organic binder) 9 and the iron nitride magnetic particles 2. By forming the layer 4 containing iron sulfide on the surface layer portion of the magnetic particles 2, the frictional resistance between the magnetic particles is reduced, so that a bonded magnet having a high degree of orientation and a high density can be obtained.

Examples of the organic binder used for the bond magnet include a thermosetting resin and a thermoplastic resin. Examples of thermosetting resins include epoxy resins and phenol resins, and thermoplastic resins include polyolefin resins, polystyrene, polyurethane resins, polyester systems, polyamide (nylon) systems, acrylic resins, derivatives thereof, copolymers, and the like. Each is listed. The organic binder can be selected from various types of resins according to the desired moldability, heat resistance, mechanical strength, etc., and even if one type of resin is used alone, two or more types of resins can be selected. May be used in combination.

Below, an example of the manufacturing method of the bonded magnet using the iron nitride type magnetic powder obtained by this embodiment is demonstrated. The method for manufacturing a bonded magnet in the present embodiment includes a compounding (preparing a mixed composition of magnetic powder and resin) process and a molding process, and a bonded magnet can be manufactured through these processes.

In the compounding step, the resin and the iron nitride-based magnetic powder are mixed with, for example, a pressure heating kneader, a twin screw extruder, a Henschel mixer, or the like to produce a compound (composition) for a bond magnet. When producing a bonded magnet by compression molding, it is preferable to use a thermosetting resin, and more preferably an epoxy resin or a phenol resin. When producing a bonded magnet by injection molding, a thermoplastic resin is preferable.

Examples of the bonded magnet compound include powder, granules, and pellets, but the present invention is not limited to this and may be selected as appropriate.

The compound for the bond magnet may be in the form of a slurry or a paste. In this case, a liquid resin or a solution obtained by dissolving a resin in an organic solvent and an iron nitride-based magnetic powder are mixed and stirred using, for example, a ball mill or a rotation / revolution mixer to produce a compound for a bonded magnet. By mixing in the liquid, the mixing degree of the resin and the magnetic powder becomes better. The organic solvent is preferably one that can dissolve the resin used. For example, a single liquid or a mixed liquid using any one or more of alkanes such as hexane, cyclohexane and octane, and ketones such as cyclohexanone and MEK can be used, but this is not restrictive.

The content ratio of the iron nitride-based magnetic powder and the resin in the bonded magnet preferably includes, for example, 0.5% by mass or more and 20% by mass or less of the resin with respect to 100% by mass of the magnetic powder. When the resin content is less than 0.5% by mass, the magnetic powder is not sufficiently coated with the resin, so that the dispersion state of the magnetic powder is deteriorated, and the shape retention of the bonded magnet tends to be lowered. There is. On the other hand, when the resin content exceeds 20% by mass, the content of the magnetic powder in the bonded magnet is lowered, and thus there is a tendency that it is difficult to obtain sufficiently excellent magnetic properties.

  Moreover, you may add a coupling agent, a dispersing agent, and another additive to the compound for bonded magnets as needed. As the coupling agent, any one or more of a silane coupling agent, a titanate coupling agent and the like can be used, but not limited thereto. The dispersant may be any one or more of oleic acid, oleylamine, trioctylamine and the like, but is not limited thereto. The amount of the coupling agent or dispersant added may be 0.1% by mass or more and 5% by mass or less with respect to the magnetic powder.

A bonded magnet containing the magnetic powder and the resin can be obtained by producing the above-described bonded magnet compound and then compression-molding the bonded magnet compound. When producing a bonded magnet by compression molding, after producing the aforementioned compound for bonded magnet, the compound for bonded magnet is filled into a mold having a predetermined shape, and pressure is applied to obtain the predetermined shape from the mold. Take out the molded product (bonded magnet). When a bonded magnet compound is formed and taken out by a mold, it is performed using a compression molding machine such as a mechanical press or a hydraulic press. Then, a bonded magnet is obtained by putting in a furnace such as a heating furnace or a vacuum drying furnace and heating to cure the resin.

When producing a bonded magnet by compression molding, the molding pressure may be, for example, 0.29 to 1.96 MPa (3 to 20 kgf / cm ² ). When the molding pressure is less than 0.29 MPa (3 kgf / cm ² ), pressurization is insufficient and shape retention is difficult. On the other hand, when the molding pressure is greater than 1.96 MPa (20 kgf / cm ² ), the residual stress increases, so that a crack occurs in the iron nitride-based bond magnet or a mold breakage occurs.

Moreover, when volatilizing the solvent in the compound for bonded magnets, it is preferable to heat the mold to 50 to 200 ° C. When the temperature is lower than 50 ° C., the solvent cannot be volatilized sufficiently. Above 200 ° C., decomposition of the Fe ₁₆ N ₂ phase and thermal decomposition of the resin start, and the magnetic properties deteriorate.

  Furthermore, when volatilizing the solvent, the solvent can be volatilized in a shorter time by reducing the pressure using a vacuum pump or the like in addition to heating. The vacuum pump may be a dry pump or a rotary pump, but is not limited thereto.

After producing the bonded magnet compound as described above, the bonded magnet compound containing the magnetic powder and the resin can be obtained by injection molding the bonded magnet compound. When producing a bonded magnet by injection molding, the bonded magnet compound is heated to the melting temperature of the binder (thermoplastic resin) as necessary to obtain a fluid state, and then the bonded magnet compound has a predetermined shape. Injection into the mold and molding. Then, it cools and the molded article (bond magnet) which has a predetermined shape is taken out from a metal mold | die. In this way, a bonded magnet is obtained.

The shape of the bonded magnet obtained by molding is not particularly limited, and can be changed, for example, in a plate shape, a column shape, or a cross-sectional shape in a ring shape, depending on the shape of the mold to be used. In addition, the obtained bonded magnet may be plated or painted in order to prevent the formation of an oxide layer or the deterioration of the resin layer on the surface.

The bonded magnet compound may be molded while applying a magnetic field when it is molded into a desired shape. Thereby, since the iron nitride magnetic powder is oriented in a specific direction, an anisotropic bonded magnet having more excellent magnetic properties can be obtained. The applied magnetic field at this time may be about 398 to 1989 kA / m (5 to 25 kOe), for example.

The manufacture of the bonded magnet may be performed in the air or in an atmosphere having a low oxygen concentration, such as in an N ₂ atmosphere or an Ar atmosphere. By setting the oxygen concentration to a low oxygen atmosphere such as less than 0.1%, it is possible to suppress oxidative deterioration of the magnetic powder and resin.

Next, the iron nitride magnetic powder and the bonded magnet described in 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
<Production of iron nitride magnetic powder>
167 g of iron chloride hexahydrate (FeCl ₃ · 6H ₂ O) and 85 g of iron sulfate heptahydrate (FeSO ₄ · 7H ₂ O) were dissolved in ion-exchanged water to prepare an iron salt aqueous solution. After maintaining 600 g of 2.5 mol ammonia aqueous solution at 30 ° C. and adding the previously prepared iron salt aqueous solution, the temperature was controlled to be constant at 70 ° C. as a ripening reaction in the liquid, stirred for 30 minutes, and then centrifuged. Was washed 3 times with 2 L of ion exchange water to prepare an iron oxide slurry.

To the iron oxide slurry, 10.0 g of tetraethoxysilane and 9.0 g of ethanol were added and subjected to Si deposition treatment. This iron oxide slurry was dried at 85 ° C. for 24 hours to produce iron oxide particles containing Fe ₂ O ₃ .

3 g of the iron oxide particles were placed in a firing boat and left in a heat treatment furnace. After filling the furnace with nitrogen gas, the flow rate was 1 L / min. In a hydrogen gas stream at 5 ° C./min. The temperature was increased to 270 ° C. at a rate of temperature increase of and maintained for 48 hours for reduction treatment. After the reduction treatment, the supply of hydrogen gas was stopped and the flow rate was 2 L / min. The temperature was lowered to 140 ° C. in a nitrogen gas stream. After reaching 140 ° C., the supply of nitrogen gas was stopped, and the flow rate was 0.2 L / min. In an ammonia gas stream, nitriding was performed for 22 hours. Following the nitriding treatment, the flow rate was 0.04 L / min. Hydrogen sulfide gas and a flow rate of 0.16 L / min. In a mixed gas stream of ammonia gas, the sulfurating treatment was performed at 140 ° C. for 4 hours. After the sulfur treatment, the flow rate is 2 L / min. The temperature was lowered to 50 ° C. in a nitrogen gas stream and air replacement was performed for 24 hours to obtain an iron nitride magnetic powder.

<Production of bonded magnet>
9.5 g of the obtained iron nitride magnetic powder was mixed with 0.5 g of bisphenol A type epoxy resin and 0.25 g of an aliphatic polyamine type epoxy resin curing agent, and 0.1 g of oleylamine was further added as a dispersant. A compound containing a magnetic powder was prepared. The obtained compound was filled in a 10 mm square mold, and 0.98 MPa (10 kgf / cm ² ) in a magnetic field of 796 kA / m (10 kOe) while heating the mold to 50 ° C. using a 40-t hydraulic molding machine. An anisotropic bonded magnet molded body was produced by pressurizing with a molding pressure. The obtained molded body was heated in vacuum at 80 ° C. to obtain an anisotropic bonded magnet.

<Constituent phase of iron nitride magnetic powder>
The constituent phase of the obtained iron nitride magnetic powder was measured using a powder X-ray diffractometer (XRD, a powerful X-ray diffractometer RINT-2000 manufactured by Rigaku Corporation, CuKα, 2θ scan rate = 2 ° / min.). It was identified from the measured XRD diffraction pattern.

<Calculation of average particle diameter of iron nitride magnetic powder and average thickness of iron sulfide-containing layer>
The average particle size of the obtained iron nitride-based magnetic powder was determined from a particle image observed with a transmission electron microscope (TEM, JEM-200FX manufactured by JEOL Ltd.). The sample for observation was prepared by kneading the obtained iron nitride-based magnetic powder into an epoxy resin, curing the resin, and then slicing it. With respect to 100 iron nitride magnetic particle cross sections arbitrarily selected from TEM observation images, point analysis of the inside of the particle and the surface layer of the particle was performed by EDS (energy dispersive spectroscopic analysis). Fe was detected from the inside and surface portion of the iron nitride magnetic particles, S was detected from the surface portion, and N was detected from the inside of the particles. Next, each element of Fe, S, and N was subjected to element mapping by EDS, and the distribution state of each element of Fe, S, and N was analyzed with respect to a cross section of 1000 iron nitride magnetic particles. The location where Fe was detected was an iron nitride magnetic particle, and the location where both Fe and S were detected was an iron sulfide-containing layer. The average particle diameter D of the iron nitride-based magnetic powder was obtained by calculating the average value after determining the equivalent circle diameter d in the region where Fe was detected for each particle. In addition, the average thickness T of the iron sulfide-containing layer is obtained by obtaining, for each particle, a circle-equivalent diameter d ′ in a region where Fe is detected but S is not detected, and the thickness t = (dd ′) / for each particle. The average value of 2 was calculated.

<Measurement of residual magnetic flux density (Br) and orientation degree of anisotropic bonded magnet>
Using the obtained anisotropic bonded magnet, the residual magnetic flux density (Br = residual magnetic polarization Jr) and the degree of orientation were measured. Residual magnetic flux density (Br) was measured in a 23 ° C. atmosphere using a BH tracer (TRF-5BH manufactured by Toei Kogyo Co., Ltd., applied magnetic field ± 20 kOe). The degree of orientation was calculated by the ratio (Br / Js) × 100 of the residual magnetic flux density (Br) to the saturation magnetic polarization Js, which is the maximum value in the first quadrant of the magnetic hysteresis curve.

<Calculation of magnetic powder filling rate in anisotropic bonded magnet>
The magnetic powder filling rate in the obtained anisotropic bonded magnet was determined as follows. After the cured anisotropic bonded magnet was included to cure the resin, the cross section of the bonded magnet obtained by mirror polishing and Ar ion milling was scanned with a scanning electron microscope (FE-SEM, JSM-manufactured by JEOL Ltd.). 6700F). About 10 field of the observation image, respectively, and measuring the area S _P and the observation field total area S _A of the portion occupied by the iron nitride-based magnetic powder by image processing, an average value of the ratio S _{P /} S _A in the bonded magnet The magnetic powder filling rate was used.

(Example 2)
In the production of the iron nitride magnetic powder, the nitriding treatment time in the ammonia gas stream was set to 20 hours, and the sulfurating treatment time in the mixed stream of hydrogen sulfide gas and ammonia gas was set to 8 hours. Similarly, an iron nitride-based magnetic powder and a bonded magnet were produced and evaluated.

(Example 3)
Example 1 except that the nitriding time in the ammonia gas stream was 18 hours and the sulfurating time in the mixed gas stream of hydrogen sulfide gas and ammonia gas was 12 hours in the production of the iron nitride magnetic powder. Similarly, an iron nitride-based magnetic powder and a bonded magnet were produced and evaluated.

Example 4
In the production of the iron nitride-based magnetic powder, Example 1 and Example 1 were performed except that the nitriding time in the ammonia gas stream was set to 16 hours and the sulfurating time in the mixed stream of hydrogen sulfide gas and ammonia gas was set to 16 hours. Similarly, an iron nitride-based magnetic powder and a bonded magnet were produced and evaluated.

(Example 5)
Example 1 except that the nitriding time in the ammonia gas stream was set to 14 hours and the sulfurating time in the mixed stream of hydrogen sulfide gas and ammonia gas was set to 20 hours in the production of the iron nitride magnetic powder. Similarly, an iron nitride-based magnetic powder and a bonded magnet were produced and evaluated.

(Example 6)
In the production of the iron nitride magnetic powder, an iron nitride magnetic powder and a bonded magnet were produced in the same manner as in Example 1 except that the addition amount of tetraethoxysilane was 15.0 g and the addition amount of ethanol was 13.5 g. And evaluated.

(Example 7)
In the production of the iron nitride magnetic powder, the addition amount of tetraethoxysilane was 13.0 g, the addition amount of ethanol was 11.7 g, and the sulfurization time in a mixed gas stream of hydrogen sulfide gas and ammonia gas was 6 hours. Except for the above, an iron nitride magnetic powder and a bonded magnet were produced and evaluated in the same manner as in Example 1.

(Example 8)
In the production of the iron nitride magnetic powder, the addition amount of tetraethoxysilane was 6.5 g, the addition amount of ethanol was 5.5 g, and the sulfurization treatment time in a mixed gas flow of hydrogen sulfide gas and ammonia gas was 16 hours. Except for the above, an iron nitride magnetic powder and a bonded magnet were produced and evaluated in the same manner as in Example 1.

Example 9
In the production of the iron nitride magnetic powder, the addition amount of tetraethoxysilane was 5.0 g, the addition amount of ethanol was 4.5 g, and the sulfurization time in a mixed gas flow of hydrogen sulfide gas and ammonia gas was 20 hours. Except for the above, an iron nitride magnetic powder and a bonded magnet were produced and evaluated in the same manner as in Example 1.

(Example 10)
In the production of the iron nitride magnetic powder, the amount of tetraethoxysilane added was 4.0 g, the amount of ethanol added was 3.5 g, and the sulfurization time in a mixed gas stream of hydrogen sulfide gas and ammonia gas was 24 hours. Except for the above, an iron nitride magnetic powder and a bonded magnet were produced and evaluated in the same manner as in Example 1.

(Example 11)
In the production of the iron nitride magnetic powder, the addition amount of tetraethoxysilane was 3.0 g, the addition amount of ethanol was 2.5 g, and the sulfurization time in a mixed gas flow of hydrogen sulfide gas and ammonia gas was 30 hours. Except for the above, an iron nitride magnetic powder and a bonded magnet were produced and evaluated in the same manner as in Example 1.

(Comparative Example 1)
In the production of the iron nitride magnetic powder, the nitriding time in the ammonia gas stream was set to 24 hours, and the sulfurating process in the mixed gas stream of hydrogen sulfide gas and ammonia gas was not performed. An iron nitride magnetic powder and a bonded magnet were prepared and evaluated.

(Comparative Example 2)
In the production of the iron nitride magnetic powder, Example 3 and Example 3 were performed except that the nitriding time in the ammonia gas stream was set to 10 hours and the sulfurating time in the mixed stream of hydrogen sulfide gas and ammonia gas was set to 24 hours. Similarly, an iron nitride-based magnetic powder and a bonded magnet were produced and evaluated.

(Comparative Example 3)
In the production of the iron nitride magnetic powder, an iron nitride magnetic powder and a bond magnet were produced in the same manner as in Example 7, except that the sulfurating treatment time in the mixed gas flow of hydrogen sulfide gas and ammonia gas was 2 hours. Evaluation was performed.

(Comparative Example 4)
In the production of the iron nitride magnetic powder, an iron nitride magnetic powder and a bond magnet were produced in the same manner as in Example 9, except that the sulfurating treatment time in the mixed gas flow of hydrogen sulfide gas and ammonia gas was 30 hours, Evaluation was performed.

≪Evaluation results≫
The average particle diameter of the iron nitride-based magnetic powder obtained in Examples 1 to 11 and Comparative Examples 1 to 4, the average thickness of the iron sulfide-containing layer, the ratio of the average thickness of the iron sulfide-containing layer to the average particle diameter, and the bond magnet Table 1 shows the residual magnetic flux density (Br), the degree of orientation, and the magnetic powder filling rate. The residual magnetic flux density (Br) is 300 mT or more as good magnetic properties.

From the phase identification results by XRD, it was confirmed that the Fe ₁₆ N ₂ phase was the main phase in all Examples and Comparative Examples. Moreover, from the result of analyzing the distribution state of each element of Fe, S, and N by elemental mapping by TEM-EDS, the presence of an iron sulfide-containing layer was confirmed in all Examples and Comparative Examples except Comparative Example 1. It was done.

As shown in all Examples and Comparative Examples, the average thickness of the iron sulfide-containing layer formed on the surface layer portion of the iron nitride magnetic particles constituting the iron nitride magnetic powder is 1.2 to 12 nm. When the ratio of the average thickness of the iron sulfide-containing layer to the average particle diameter of the magnetic powder is 2.4 to 13%, the degree of orientation and the magnetic powder filling rate are improved, and the residual magnetic flux density (Br) is 300 mT. It was confirmed that this was the case.

In particular, as shown in Example 3 and Examples 7 to 10, when the average thickness of the iron sulfide-containing layer is 1.5 to 10 nm, good magnetic properties with a residual magnetic flux density (Br) of 400 mT or more can be obtained. It was.

In particular, as shown in Examples 1 to 4, when the ratio of the average thickness of the iron sulfide-containing layer to the average particle diameter of the iron nitride-based magnetic powder is 2.4 to 10.2%, the residual magnetic flux density (Br ) Good magnetic properties of 400 mT or more were obtained.

As shown in Comparative Example 1, when the iron sulfide-containing layer was not formed on the surface layer portion of the iron nitride-based magnetic particles, a high residual magnetic flux density (Br) was not obtained. This is considered that the residual magnetic flux density (Br) was lowered because the effect of improving the degree of orientation and the magnetic powder filling rate did not appear due to the absence of the iron sulfide-containing layer. Therefore, as shown in Examples 1 and 6, the average thickness of the iron sulfide-containing layer is 1.2 nm or more, and the ratio of the average thickness of the iron sulfide-containing layer to the average particle diameter of the magnetic powder is 2.4%. This is necessary for obtaining a residual magnetic flux density (Br) of 300 mT or more.

As shown in Comparative Example 2, even when the average thickness of the iron sulfide-containing layer formed on the surface layer portion of the iron nitride-based magnetic particles is in the range of 1.2 to 12 nm, the average particle diameter of the magnetic powder is When the average thickness ratio of the iron sulfide-containing layer was 16.0%, a high residual magnetic flux density (Br) could not be obtained. This is because the effect of improving the degree of orientation and the magnetic powder filling rate due to the formation of the iron sulfide-containing layer is expressed, but the ratio of Fe ₁₆ N ₂ phase in the iron nitride-based magnetic particles is reduced, so that the iron nitride-based layer It is considered that the residual magnetic flux density (Br) was lowered because the saturation magnetization of the magnetic powder was reduced. Therefore, as shown in Example 5, in order to obtain a residual magnetic flux density (Br) of 300 mT or more, the ratio of the average thickness of the iron sulfide-containing layer to the average particle diameter of the magnetic powder is 13% or less. is necessary.

As shown in Comparative Example 3, even if the ratio of the average thickness of the iron sulfide-containing layer to the average particle diameter of the iron nitride-based magnetic powder is in the range of 2.4 to 13%, the average thickness of the iron sulfide-containing layer When the thickness became 0.9 nm, a high residual magnetic flux density (Br) could not be obtained. This is considered that the residual magnetic flux density (Br) was lowered because the effect of improving the degree of orientation and the magnetic powder filling rate due to the formation of the iron sulfide-containing layer was not sufficiently exhibited at such an average thickness. Therefore, as shown in Example 6, it is necessary that the average thickness of the iron sulfide-containing layer is 1.2 nm or more in order to obtain a residual magnetic flux density (Br) of 300 mT or more.

Further, as shown in Comparative Example 4, even when the ratio of the average thickness of the iron sulfide-containing layer to the average particle diameter of the iron nitride-based magnetic powder is in the range of 2.4 to 13%, the iron sulfide-containing layer When the average thickness was 13.0 nm, a high residual magnetic flux density (Br) could not be obtained. Although the effect of improving the degree of orientation and the magnetic powder filling rate due to the formation of the iron sulfide-containing layer is manifested, the ratio of the Fe ₁₆ N ₂ phase in the iron nitride-based magnetic particles is reduced, so that the iron nitride-based magnetism is reduced. It is considered that the residual magnetic flux density (Br) was lowered because the saturation magnetization of the powder was reduced. Therefore, as shown in Examples 4, 5, and 12, it is necessary for the iron sulfide-containing layer to have an average thickness of 12 nm or less in order to obtain a residual magnetic flux density (Br) of 300 mT or more.

In particular, as shown in Example 3 and Examples 7 to 10, when the average particle diameter was 20 to 130 nm, good magnetic properties with a residual magnetic flux density (Br) of 400 mT or more were obtained.

As described above, the iron nitride magnetic powder according to the present invention has a sufficiently high residual magnetic flux density (Br) by obtaining a high degree of orientation and a high magnetic powder filling rate. Useful as.

DESCRIPTION OF SYMBOLS 1 Iron nitride type magnetic particle 2 Main phase 3 Layer containing iron sulfide 4 Particle diameter of iron nitride type magnetic powder 5 Thickness of layer containing iron sulfide 6 Bond magnet 7 Resin (organic binder)

Claims (5)

An iron nitride-based magnetic powder having a Fe ₁₆ N ₂ compound phase as a main phase, and a layer containing iron sulfide having FeS as a main phase is formed on a surface layer portion of an iron nitride-based magnetic particle constituting the magnetic powder. The average thickness of the iron sulfide-containing layer is 1.2 to 12 nm, and the ratio of the average thickness of the iron sulfide-containing layer to the average particle diameter of the iron nitride-based magnetic powder is 2.4 to An iron nitride magnetic powder characterized by being 13%. 2. The iron nitride magnetic powder according to claim 1, wherein the iron sulfide-containing layer has an average thickness of 1.5 to 10 nm. The ratio of the average thickness of the iron sulfide-containing layer to the average particle diameter of the iron nitride magnetic powder is 2.4 to 10.2%, and the iron nitride system according to claim 1 or 2, Magnetic powder. The iron nitride magnetic powder according to claim 1, wherein an average particle diameter of the magnetic powder is 20 to 130 nm. A bonded magnet using the iron nitride magnetic powder according to claim 1.

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