JP6618858B2 - Iron nitride magnet - Google Patents

Description

  The present invention relates to an iron nitride magnet.

An iron nitride magnet made of Fe ₁₆ N ₂ has attracted attention from the viewpoint of its high magnetic properties and environmental considerations that do not use rare earths. _However, iron nitride magnet consisting of _Fe 16 _{N 2,} it is difficult to sinter _{for Fe} 16 _{N 2} phase is decomposed at elevated temperatures. For this reason, as an iron nitride magnet, a compacted magnet only by compression molding and a bonded magnet solidified by resin have been proposed.

  For example, in the following Patent Document 1, although it is described in the specification as a bond magnet and a dust magnet, there is no specific description including examples.

JP 2013-80922 A

In iron nitride magnet consisting of _{Fe 16 N 2, Fe 16 N} 2 from being metastable compounds, there is a case where an impurity phase is generated such Fe ₄ N and alpha-Fe by sintering at high temperatures. Thereby, magnetic characteristics such as coercive force and magnetization are deteriorated. In addition, when a resin is added like a bond magnet, a Fe ₁₆ N ₂ iron nitride magnet having a high coercive force is composed of very fine iron nitride magnetic particles. The magnetic characteristics are deteriorated as compared with the magnet. Furthermore, it cannot be said that the mechanical strength and moisture resistance are sufficient. On the other hand, a powder magnet densified by simple compression molding is not suitable as a magnet product because sufficient mechanical strength cannot be obtained.

  The present invention has been made in view of the above, and an object thereof is to provide an iron nitride magnet having both high mechanical strength and high magnetic properties.

The iron nitride magnet according to the present invention is an iron nitride magnet containing Fe ₁₆ N ₂ as a main component, and Sn or Sn alloy is added between iron nitride magnetic particles in the iron nitride magnet in an amount of 1 for the weight of the iron nitride magnet. It is an iron nitride magnet characterized by containing not less than 30% by weight.

Since the iron nitride magnet according to the present invention can be densified at a relatively low temperature due to the effect of Sn or Sn alloy, high mechanical strength and high magnetic properties can be obtained without impairing the properties of Fe ₁₆ N _2. Can be combined. The reason for using Sn is that it is excellent in workability and mechanical strength, and is excellent from the viewpoint of influence on price and environment.

According to the present invention, an iron nitride magnet made of Fe ₁₆ N ₂ can be densified, and high mechanical strength and high magnetic properties can be combined.

  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 magnet according to the present embodiment is mainly composed of Fe ₁₆ N _{2, and} may include Fe ₄ N, Fe ₃ N, α-Fe, iron oxide, nonmagnetic oxide, resin, etc. in part. good. The particle diameter of the iron nitride magnetic particles constituting the iron nitride magnet is about 10 nm to 200 nm, and the particle diameter of the iron nitride magnetic particles as a raw material is maintained as the iron nitride magnet.

  The iron nitride magnet according to the present embodiment preferably has a maximum magnetic energy product (BH) max of 3 MGOe or more. More preferably, the maximum magnetic energy product is 3.5 MGOe or more. Moreover, it is preferable that bending strength is 30 Mpa or more as an index of mechanical strength. More preferably, the bending strength is 40 MPa or more, and still more preferably 50 MPa or more.

The iron nitride magnet according to the present embodiment is an iron nitride magnet mainly composed of Fe ₁₆ N _2, and Sn or Sn alloy is added between iron nitride magnetic particles in the iron nitride magnet with respect to the weight of the iron nitride magnet. 1 to 30% by weight is contained. If the content of Sn or Sn alloy is less than 1% by weight, sufficient densification cannot be performed and sufficient mechanical strength cannot be obtained. On the other hand, if the Sn or Sn alloy content exceeds 30% by weight, the maximum energy product decreases, and satisfactory magnetic properties cannot be obtained.

As the Sn alloy, Sn and alloys such as Cu, Ag, Zn, Bi, Sb, and In can be used. As a general low melting point metal as a simple substance, Zn, Ga, In, Bi, Pb and the like can be cited in addition to Sn. However, when used for an iron nitride magnet made of Fe ₁₆ N ₂ , these low melting point metals are insufficient in reducing the melting point, which is not preferable from the viewpoint of cost and environmental impact.

  Next, the suitable manufacturing method of the iron nitride magnet which concerns on this embodiment is described.

  The iron nitride magnetic particles according to the present embodiment can be obtained by performing a reduction treatment using iron oxide as a raw material and subsequently performing a nitriding treatment.

The raw material iron oxide is not particularly limited, and examples thereof include magnetite, γ-Fe ₂ O ₃ , α-Fe ₂ O ₃ , α-FeOOH, β-FeOOH, γ-FeOOH, and FeO.

  The method for synthesizing the raw material iron oxide is not particularly limited, and examples thereof include a coprecipitation method, an air oxidation method, a hydrothermal synthesis method, and a gas phase method.

  In the present embodiment, if necessary, the surface of iron oxide as a raw material may be coated with a compound such as Si in order to suppress sintering of the particles by reduction treatment.

  The raw iron oxide whose surface is coated with Si is adjusted by adjusting the pH of the aqueous suspension obtained by dispersing the iron oxide particles, and then adding the Si compound and mixing and stirring, or if necessary, mixing It is obtained by adjusting the pH value after stirring, and then washing, drying and pulverizing.

  As the Si compound, sodium orthosilicate, sodium metasilicate, colloidal silica, silane coupling agent and the like can be used.

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

  The temperature of the reduction treatment is preferably 200 to 600 ° 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 600 ° C., iron oxide is sufficiently reduced, but sintering between particles also proceeds, which is not preferable. A more preferable reduction temperature is 250 to 450 ° C.

  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. In many cases, sufficient reduction cannot be achieved in less than 1 hour. 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. 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., since nitriding proceeds excessively, Fe ₁₆ N ₂ cannot be obtained. A more preferable nitriding temperature is 120 to 180 ° C.

The nitriding time is not particularly limited, but is preferably 1 to 48 hours. If it exceeds 48 hours, depending on the nitriding temperature, the proportion of heterogeneous phases that are not Fe ₁₆ N ₂ compound phases will increase. In many cases, sufficient nitriding cannot be performed in less than 1 hour. More preferably, it is 3 to 24 hours.

The atmosphere of the nitriding treatment is desirably an NH ₃ atmosphere, and N ₂ , H ₂ or the like may be mixed in addition to NH ₃ .

  Next, an example of a method for producing an iron nitride magnet using the iron nitride magnetic particles obtained by the present embodiment will be described.

  Sn or Sn alloy is deposited on the surface of the iron nitride magnetic particles obtained by the present embodiment in an amount of 1 wt% to 30 wt% with respect to the iron nitride magnet weight. As a method for depositing Sn or Sn alloy, vapor deposition, plating, powder mixing, paste addition, mechanical alloy, or the like can be used.

Next, iron nitride magnetic particles are filled in a mold and densified at a temperature of 150 to 250 ° C. while being pressurized at a pressure of 1 to 30 t / cm ² . The pressurization time is 1 to 3600 seconds. As a forming method, either a uniaxial pressing method or an isotropic pressing method such as CIP may be used. As a heating method, heater heating, microwave heating, plasma heating or the like can be used.

  When the iron nitride magnetic particles are formed into a desired shape, they may be formed while applying a magnetic field, and the resulting formed body may be oriented in a certain direction. Thereby, since the iron nitride magnet is oriented in a specific direction, an iron nitride magnet having stronger magnetic anisotropy can be obtained. The intensity of the applied magnetic field is preferably 20 kOe or more.

  The shape of the iron nitride 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. Further, the obtained iron nitride magnet may be plated or painted on its surface in order to prevent deterioration of the oxide layer, the resin layer and the like.

  Although the iron nitride magnet and the manufacturing method thereof according to the present embodiment have been described above, the present invention is not limited to the above embodiment.

  Hereinafter, the present invention will be described more specifically based on examples and comparative examples.

(Example 1)
<Production process of iron nitride magnetic particles>
Using iron oxide γ-Fe ₂ O ₃ (particle size 30 nm) manufactured by Sigma-Aldrich, reduction was performed in a heat treatment furnace under conditions of hydrogen gas 2 L / min, 350 ° C., 50 hours, and then ammonia gas was reduced to 0. Iron nitride magnetic particles were obtained by performing nitriding treatment at 160 ° C. for 12 hours while flowing 1 L / min.

<Sn deposition process>
Sn was deposited on the obtained iron nitride magnetic particles using a vacuum deposition apparatus. The degree of vacuum was 1 × 10 ⁻⁴ Pa, and the weight to be deposited was adjusted by the deposition time.

<Manufacturing process of iron nitride magnet>
The obtained Sn-coated iron nitride magnetic particles were filled into a 90 mm × 12 mm sample-shaped mold and subjected to hydraulic press molding at a pressure of 20 t / cm ² by applying a transverse magnetic field of 25 kOe. During the pressure molding, a densification treatment was performed in a nitrogen atmosphere under the condition that the maximum temperature reached by the sample was 200 ° C. The iron nitride magnet of Example 1 was obtained through the above steps.

<Bending strength test>
The bending strength of the iron nitride magnet was measured by processing the iron nitride magnet into a size of 80 × 10 × 4 mm and using a bending strength tester according to JIS K7171 standard. An average value of five measurement samples was defined as bending strength, and a universal testing machine (AGS) manufactured by Shimadzu Corporation was used for the measurement. The results are shown in Table 1.

<Evaluation of magnetic properties>
The magnetic properties of the iron nitride magnet were evaluated with a BH tracer. As a magnetic characteristic, the maximum energy product was calculated by an average value of five measurement samples. A BH tracer (TM-BH25) manufactured by Tamagawa Seisakusho was used for the measurement. The results are shown in Table 1.
<Measurement of content of added metal>
The content of the added metal relative to the weight of the iron nitride magnet was measured by an ICP analyzer (ICPS-8100CL) manufactured by Shimadzu Corporation. The average value of the number of times of measurement was calculated, and the results are shown in Table 1.

(Examples 2 to 10, Comparative Example 4, Comparative Example 5)
By applying the additive metal shown in Table 1 to the iron nitride magnetic particles produced in the same manner as in Example 1 so as to have a desired deposition amount, Examples 2 to 10 and Comparative Examples 4 and 5 An iron nitride magnet was obtained.

(Comparative Examples 1-3)
An iron nitride magnet of Comparative Example 1 was obtained by the same production method as Example 1 except that there was no Sn deposition step. Moreover, the iron nitride magnets of Comparative Examples 2 and 3 were obtained in the same manner as in Example 1 except that the Sn deposition amount was changed to the amount shown in Table 1 in the Sn deposition step.

  In the same manner as in Example 1, the bending strength test, magnetic property evaluation, and additive metal content of each of the iron nitride magnets of Examples 2 to 10 and Comparative Examples 1 to 5 were measured. Table 1 shows the results of measurement of bending strength, magnetic property evaluation, and content of added metal.

  The bending strength was 30 MPa or more, and the maximum energy product was 3 MGOe or more.

  From the results shown in Table 1, the samples of Comparative Examples 1 and 2 have insufficient bending strength because Sn is not added, or even if added, the content is insufficient. In Comparative Example 3, the maximum energy product is insufficient because the Sn content is excessive. Furthermore, in Comparative Example 4 and Comparative Example 5, Zn and Bi are less effective in lowering the melting point compared to Sn, so that sufficient densification is not achieved and bending strength is insufficient. On the other hand, in the present invention, it can be seen that a sample having a high bending strength and a good maximum energy product is obtained.

Claims (1)

An iron nitride magnet mainly composed of Fe ₁₆ N _2, and containing Sn or Sn alloy between iron nitride magnetic particles in the iron nitride magnet in an amount of 1 wt% or more and 30 wt% or less based on the weight of the iron nitride magnet An iron nitride magnet characterized by