JP6485065B2 - Iron nitride magnetic powder and bonded magnet using the same - Google Patents

Description

The present invention relates to an iron nitride-based magnetic powder having a Fe ₁₆ N ₂ compound phase as a main phase and maintaining a high saturation magnetization and having a high coercive force. Furthermore, a bonded magnet using the iron nitride magnetic powder is provided.

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) that do not use rare earth 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. In Patent Document 1, a third element is added in order to obtain iron nitride having a high coercive force. However, since the obtained iron nitride powder has a low coercive force, it is difficult to use it as a magnetic material for motor applications that require high coercive force and high saturation magnetization.

Further, as Fe ₁₆ N ₂ is said to be a metastable compound, it is difficult to chemically synthesize this compound as an isolated powder. In Patent Document 2, iron nitride magnetic powder is synthesized by a technique of synthesizing iron oxide by a coprecipitation method and reducing and nitriding. However, since the obtained iron nitride powder has a low magnetization, it is difficult to use it as a magnetic material for motors that require a high coercive force and a high saturation magnetization.

JP 2009-249682 A JP 2009-84115 A

The present invention has been made in view of the above, and aims to provide an iron nitride magnetic powder having a saturation magnetization of 140 emu / g or more and a coercive force of 2.5 kOe or more, and a bonded magnet using the magnetic powder. To do.

The present invention is an iron nitride-based magnetic powder containing Fe ₁₆ N ₂ as a main component, and containing 0.1 to 4.5 at% P with respect to Fe ₁₆ N ₂ of the iron nitride-based magnetic powder. The present invention relates to a featured iron nitride magnetic powder and a bonded magnet using the iron nitride magnetic powder.

The present invention is an iron nitride-based magnetic powder containing Fe ₁₆ N ₂ as a main component, and contains 0.1 to 4.5 at% P with respect to Fe ₁₆ N ₂ of the iron nitride-based magnetic powder. Thereby, an iron nitride-based magnetic powder having a coercive force of 2.5 kOe or more can be obtained while maintaining a saturation magnetization of 140 emu / g or more. Furthermore, a magnet using the iron nitride magnetic powder can be obtained.

Although not clear about this reason, P enters between the lattice of _Fe 16 _{N 2,} or by P to replace a portion of the N constituting the _Fe 16 _{N 2,} the lattice distortion of the _Fe 16 _{N 2} Since the anisotropy of the iron nitride magnetic powder is increased, it is considered that a high coercive force could be obtained while maintaining a high saturation magnetization.

Hereinafter, preferred embodiments of the present invention will be described. 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.

The iron nitride magnetic powder according to the present embodiment is an iron nitride magnetic powder containing Fe ₁₆ N ₂ as a main component, and P is 0.1 to Fe ₁₆ N ₂ of the iron nitride magnetic powder. Contains 4.5 at%. If it is less than 0.1 at%, the lattice distortion due to penetration or substitution of P is small, so that it does not have sufficient crystal magnetic anisotropy and a high coercive force cannot be obtained. If it exceeds 4.5 at%, a part of Fe ₁₆ N ₂ is changed to Fe ₃ P as an impurity, and both the saturation magnetization and the coercive force are lowered. Further, P exists in the iron nitride particles, and there is no segregation of the surface or a specific portion.

The saturation magnetization σs of the iron nitride magnetic powder according to the present embodiment is 140 emu / g or more, and when the saturation magnetization is less than the above, it is difficult to say that the magnetic characteristics are sufficient as the magnetic powder.

The coercive force Hc of the iron nitride-based magnetic powder according to this embodiment is 2.5 kOe or more, and when the coercive force is less than the above, it is difficult to say that the magnetic characteristics are sufficient as the magnetic powder.

The average particle size of the iron nitride magnetic powder according to this embodiment is preferably 20 nm or more and 60 nm or less. If the average particle size is less than 20 nm, the ratio of the oxide film on the particle surface is increased, or superparamagnetism is exhibited when the particle size is small, so the coercive force tends to decrease. When the average particle size exceeds 60 nm, the particle size is large, so the proportion of particles having a single domain critical diameter or less is small, and the coercive force tends to decrease.

In the method for measuring the average particle diameter according to the present invention, the obtained powder is weighed in a Φ6 mm disk-shaped case, paraffin having a melting point of 50 to 52 ° C. is added, heated on a hot plate, and the paraffin is melted. Paraffin was allowed to cool and solidify to produce paraffin containing powder. The paraffin containing the obtained powder was cut out so that a cross section of the powder appeared, and the cross section was observed with a transmission electron microscope (TEM, JEM-2000FX manufactured by JEOL). The equivalent circular area diameter of 1000 particles was calculated from the TEM observation image, and the average was taken as the average particle diameter.

In the iron nitride magnetic powder according to this embodiment, the main phase is an Fe ₁₆ N ₂ compound phase, an iron oxide phase such as Fe ₂ O ₃ , Fe ₃ O ₄ and FeO, an iron nitride phase such as Fe ₄ N, Fe _An iron phosphide phase such as ₃ P may also be included.

A suitable method for producing the magnetic powder according to this embodiment will be described. The iron nitride magnetic powder of the present invention can be obtained by sequentially performing synthesis of iron oxide particles, reduction of iron oxide, and nitriding with a mixed gas of ammonia gas and phosphine gas. The P content can be controlled by changing the proportion of the phosphine gas in the mixed gas.

The iron oxide particles can be produced by mixing an aqueous iron salt solution containing ferrous salt and / or ferric salt and an alkaline aqueous solution, aging and washing.

Examples of the early iron salt include sulfate, chloride, nitrate, etc., and these may be used in appropriate combination. Moreover, those hydrates can be used.

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

The iron oxide has an average particle size of 5 to 25 nm.

Iron oxide having an average particle diameter of 5 to 10 nm can be prepared by controlling the aging reaction temperature in the liquid during the precipitation reaction. Moreover, the particle size control of the iron oxide having an average particle size of 10 to 25 nm is made by oxidizing a solution containing ferrous ions in the presence of an alkali of an equal amount or more in a solution to which ultrafine iron oxide particles are added. it can.

Further, after the iron oxide is produced, an aging reaction in liquid such as hydrothermal treatment by an autoclave may be performed for improving crystallinity and controlling the particle shape.

The iron oxide particles can be recovered by filtering the aqueous solution after the synthesis of iron oxide and subjecting it to a washing treatment such as washing as necessary.

After the iron oxide synthesis, if necessary, the surface of iron oxide may be coated with a Si compound in order to suppress sintering of the particles by reduction treatment. As the Si compound, sodium orthosilicate, sodium metasilicate, colloidal silica, silane coupling agent, silanol compound and the like can be used.

The coating amount of the Si compound is preferably 0.1% by mass or more and 20% by mass or less in terms of Si with respect to iron oxide. When the amount is less than 0.1% by mass, it is difficult to say that the effect of suppressing the sintering between particles during heat treatment is sufficient. When it exceeds 20 mass%, a nonmagnetic component will increase and it is not preferable. A more preferable surface coating amount is 0.15% by mass or more and 15% by mass or less, and further more preferably 0.2% by mass or more and 10% by mass or less.

The obtained iron oxide slurry can be dried at 85 ° C. for 20 hours to produce an iron oxide powder.

The iron oxide is not particularly limited, but magnetite, γ-Fe ₂ O ₃ , α-Fe ₂ O ₃ , α-FeOOH, β-FeOOH, γ-FeOOH, FeO, etc. can be used, but in this case Absent.

The particle shape of the iron oxide as a raw material is not particularly limited.

Next, a reduction process is performed. The temperature for the reduction treatment is preferably 200 to 400 ° C. When the temperature of the reduction treatment is less than 200 ° C., iron oxide is not sufficiently reduced to metallic iron. When the temperature of the reduction treatment exceeds 400 ° C., the iron oxide is sufficiently reduced, but this is not preferable because sintering between 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, depending on the reduction temperature, the sintering proceeds and the subsequent nitriding process becomes 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 preferably a hydrogen atmosphere.

After the reduction treatment, nitriding treatment is performed. By controlling the ratio of the phosphine gas in the mixed gas of ammonia and phosphine gas used for the nitriding treatment, the P content in the iron nitride magnetic powder of the present invention can be controlled.

The nitriding treatment uses a mixed gas of ammonia gas and phosphine gas. The proportion of phosphine gas in the mixed gas of ammonia gas and phosphine gas is preferably 0.8 to 29 mol%.

The temperature of the nitriding treatment is 100 to 200 ° C. When the nitriding temperature is less than 100 ° C., the nitriding does not proceed sufficiently. When the nitriding temperature exceeds 200 ° C., nitriding proceeds excessively, so that an iron nitride magnetic powder exhibiting desired Hc cannot be obtained. 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, depending on the nitriding temperature, an iron nitride magnetic powder exhibiting desired Hc cannot be obtained. In many cases, sufficient reduction cannot be achieved in less than 1 hour. More preferably, it is 3 to 24 hours.

An anisotropic bonded magnet can be obtained using the iron nitride magnetic powder obtained by the present embodiment. Hereinafter, the manufacturing method will be described.

An example of a method for producing an anisotropic bonded magnet using the iron nitride-based magnetic powder obtained by the present embodiment will be described. A resin binder containing resin and magnetic powder are kneaded by a pressure kneader such as a pressure kneader to prepare a compound (composition) for a bond magnet. Resins include thermosetting resins such as epoxy resins and phenol resins, styrene, olefin, urethane, polyester and polyamide elastomers, ionomers, ethylene propylene copolymer (EPM), ethylene-ethyl acrylate copolymer There are thermoplastic resins such as coalescence. Among them, the resin used for compression molding is preferably a thermosetting resin, and more preferably an epoxy resin or a phenol resin. The resin used for injection molding is preferably a thermoplastic resin. Moreover, you may add a coupling agent and another additive to the compound for bonded magnets as needed.

Moreover, it is preferable that the content ratio of the magnetic powder and resin in a bond magnet contains 0.5 mass% or more and 20 mass% or less of resin with respect to 100 mass% of magnetic powder. If the resin content is less than 0.5% by mass with respect to 100% by mass of the magnetic powder, the shape retention tends to be impaired. If the resin exceeds 20% by mass, sufficiently excellent magnetic properties are obtained. It tends to be difficult to obtain.

After preparing the above-described bonded magnet compound, the bonded magnet compound containing magnetic powder and 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 method of manufacturing the bonded magnet is not limited to the above-described method by injection molding. For example, a bonded magnet containing magnetic powder and resin may be obtained by compression molding a bonded magnet compound. In the case of producing a bonded magnet by compression molding, after preparing the above-mentioned bonded magnet compound, the bonded magnet compound is filled into a mold having a predetermined shape, and pressure is applied to form the predetermined shape from the mold. Take out the molded product (bonded magnet). When forming and taking out a bonded magnet compound with a mold, a compression molding machine such as a mechanical press or a hydraulic press is used. Then, a bonded magnet is obtained by making it harden | cure by putting in furnaces, such as a heating furnace and a vacuum drying furnace, and applying heat.

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

When the bonded magnet compound is molded into a desired predetermined shape, a molded body obtained by molding by applying a magnetic field may be oriented in a certain direction. Thereby, since a bonded magnet orientates in a specific direction, an anisotropic bonded magnet with stronger magnetism is obtained.

Hereinafter, although this invention is demonstrated further in detail using an Example and a comparative example, this invention is not limited to the aspect shown in an Example.

(Explanation of measurement method)
The constituent phases of the obtained iron nitride magnetic powder were identified by an X-ray diffractometer (XRD, RINT-2500, manufactured by Rigaku) and a Mossbauer spectrometer. Mossbauer measurement was performed in a state where a magnetic powder was put in a laminate pack and sealed in a glove box in an argon atmosphere. In the peak analysis of the Mossbauer spectrum, curve fitting was performed on the assumption that the spectrum was an ideal linear addition, the peak position was determined, and the peak area of each component was calculated. The peaks were assumed to be symmetrical Lorentz type, and the peak half-value widths for each component were all equal, and the peak heights at the symmetrical positions were assumed to be equal. The magnetic properties of the iron nitride magnetic powder were measured in a magnetic field of 0 to 20000 Oe at 296K using a vibrating sample magnetometer (VSM, VSM-5-20 manufactured by Toei Kogyo). As a sample for measuring magnetic properties, the obtained powder is weighed in a Φ6 mm disk-type case, paraffin having a melting point of 50 to 52 ° C. is added, heated on a hot plate, and the paraffin is melted. Solidified to produce paraffin containing iron nitride magnetic powder. The average particle size of the iron nitride-based magnetic powder is such that the paraffin containing the iron nitride-based magnetic powder is cut out so that the cross-section of the iron nitride-based magnetic powder appears, and the cross-section is transmitted through a transmission electron microscope (TEM, manufactured by JEOL JEM-2000FX). The equivalent circular area diameter of 1000 particles was calculated from the TEM observation image, and the average was taken as the average particle diameter.
Next, elemental mapping is performed on the cross section using an energy dispersive X-ray analyzer (STEM-EDS, JEM2100F manufactured by JEOL) using a scanning transmission electron microscope, and the distribution of P in the iron nitride magnetic powder particles is uniform. After confirming that, the average value of the element ratio of iron and P was calculated for 1000 particles. Furthermore, the element ratio of iron, nitrogen, and P was calculated using the results of the Mossbauer spectroscopy. Bonded magnets can also be measured by the same method as for powders. However, the B—H tracer is used for measuring the magnetic properties, and the average particle size and the distribution and amount of P are measured by cutting out the cross section of the bonded magnet.

Example 1
<Manufacture of iron oxide powder>
600 mL of 1 mol / L ferrous sulfate aqueous solution and 300 mL of 1 mol / L ferric chloride aqueous solution were mixed and stirred at 30 ° C., and 500 mL of 5 mol / L sodium hydroxide aqueous solution was added thereto, followed by aging in the liquid As a reaction, the temperature was controlled to be constant at 70 ° C., and the mixture was stirred for 30 minutes, filtered and washed with water to prepare an iron oxide slurry having an average particle size of 10 nm.

<Adhesion of sintering inhibitor>
To the iron oxide slurry prepared above, 2.5 g of tetraethoxysilane, 21 g of ethanol, and 78 g of diethylene glycol monobutyl ether were added to perform Si deposition treatment. This iron oxide slurry was dried at 85 ° C. for 24 hours to produce iron oxide powder.

<Reduction treatment of iron oxide powder>
2 g of the powder obtained above was placed in a firing boat and allowed to stand in a heat treatment furnace. After filling the furnace with nitrogen gas, the temperature was raised to 250 ° C. at a temperature rising rate of 5 ° C./min while flowing hydrogen gas at a flow rate of 1 L / min, and the reduction treatment was performed for 48 hours. Thereafter, the supply of hydrogen gas was stopped, and the temperature was lowered to 140 ° C. while flowing nitrogen gas at a flow rate of 2 L / min to produce iron powder.

<Nitride treatment of iron powder>
Subsequently, a mixed gas of 198 mL / min of ammonia gas and 2 mL / min of phosphine gas was flowed, and nitriding was performed at 140 ° C. for 24 hours. Thereafter, the temperature was lowered to 50 ° C. while flowing nitrogen gas at a flow rate of 2 L / min, and air substitution was carried out for 24 hours to produce an iron nitride magnetic powder.

(Example 2)
It was produced in the same manner as in Example 1 except that the ammonia gas was 188 mL / min and the phosphine gas was 12 mL / min.

(Example 3)
It was produced in the same manner as in Example 1 except that ammonia gas was 180 mL / min and phosphine gas was 20 mL / min.

Example 4
It was produced in the same manner as in Example 1 except that ammonia gas was 169 mL / min and phosphine gas was 31 mL / min.

(Example 5)
It was produced in the same manner as in Example 1 except that ammonia gas was 142 mL / min and phosphine gas was 58 mL / min.

(Example 6)
It was produced in the same manner as in Example 4 except that the amount of tetraethoxysilane added was 1.0 g.

(Example 7)
It was produced in the same manner as in Example 4 except that the amount of tetraethoxysilane added was 2.0 g.

(Example 8)
It was produced in the same manner as in Example 4 except that the amount of tetraethoxysilane added was 3.0 g.

Example 9
It was produced in the same manner as in Example 4 except that the amount of tetraethoxysilane added was 3.5 g.

(Comparative Example 1)
It was produced in the same manner as in Example 1 except that the ammonia gas was 200 mL / min and the phosphine gas was 0 mL / min.

(Comparative Example 2)
It was produced in the same manner as in Example 1 except that ammonia gas was 199 mL / min and phosphine gas was 1 mL / min.

(Comparative Example 3)
It was produced in the same manner as in Example 1 except that the ammonia gas was 138 mL / min and the phosphine gas was 62 mL / min.

≪Evaluation≫
Table 1 shows the results of the P content, saturation magnetization, and coercivity of the samples obtained in Examples 1 to 5 and Comparative Examples 1 to 3.

When 0.1 to 4.5 at% of P was contained with respect to Fe ₁₆ N ₂ , it was confirmed that the saturation magnetization of the iron nitride magnetic powder was 140 emu / g or more and the coercive force was 2.5 kOe or more. This is probably because a part of N in Fe ₁₆ N ₂ was replaced with P and the lattice was distorted, so that a high coercive force could be obtained while maintaining a high saturation magnetization.

Further, when Fe is contained in an amount of 0.1 to 4.5 at% with respect to Fe ₁₆ N ₂ and the average particle diameter is 20 to 60 nm, the saturation magnetization is 150 emu / g or more and the coercive force is 2.8 kOe or more. The characteristic was able to be confirmed.

In Comparative Example 1, nitriding is performed only with ammonia gas, and since P is not contained, the coercive force is low.

In Comparative Example 2, the coercive force decreased because the P content was less than 0.1 at%.

In Comparative Example 3, the P content exceeded 4.5 at%, and the saturation component and coercive force were reduced by decreasing the ferromagnetic component and increasing the impurity component Fe ₃ P.

As described above, since the iron nitride magnetic powder according to the present invention has sufficient saturation magnetization and coercive force, it can be used for high-performance magnets that do not use rare earths.

Claims (3)

An iron nitride magnetic powder containing a ferromagnetic phase represented by Fe ₁₆ N ₂ and containing 0.1 to 4.5 at% P with respect to the Fe ₁₆ N ₂ . The iron nitride magnetic powder according to claim 1, wherein an average particle diameter of Fe ₁₆ N ₂ particles constituting the iron nitride magnetic powder is 20 nm to 60 nm. A bonded magnet using the iron nitride-based magnetic powder according to claim 1.