WO2024020979A1

WO2024020979A1 - Ferrite particles and method for producing ferrite particles

Info

Publication number: WO2024020979A1
Application number: PCT/CN2022/108810
Authority: WO
Inventors: Shaowei YANG; Minoru Tabuchi; Naoto Yagi; Jianjun Yuan; Xiao Sun; Wei Zhao; Jian Guo
Original assignee: Dic Corporation
Priority date: 2022-07-29
Filing date: 2022-07-29
Publication date: 2024-02-01
Also published as: JP2024531012A; TW202408969A

Abstract

Disclosed are ferrite particles containing molybdenum and a method for producing the ferrite particles, including firing a metal compound and an iron compound in the presence of a molybdenum compound.

Description

FERRITE PARTICLES AND METHOD FOR PRODUCING FERRITE PARTICLES

Technical Field

This invention relates to ferrite particles and a method for producing ferrite particles.

Background Art

Ferrite is a compound oxide mainly containing iron oxide (Fe ₂O ₃) and is used in various fields mainly as magnetic materials. In recent years, a demand for noise suppression sheets has been increasing along with the overcrowding of an electromagnetic environment inside vehicles caused by the increased use of electrical equipment in vehicles such as automobiles. Currently, while noise suppression sheets are mainly for car navigation and in-vehicle cameras, demand is expected for millimeter-wave radars in the future. In the telecommunications field, a demand for high shielding performance in noise suppression sheets for smartphones is increasing along with the shift to 5G.

PTL 1 discloses a method for producing a hexagonal ferrite powder in which an aqueous solution containing a hexagonal ferrite precursor is heated to 300℃ or higher and is pressurized to 20 MPa or higher to convert the precursor into a hexagonal ferrite, thereby obtaining a ferrite represented by a general formula AFe ₁₂O ₁₉. It is also disclosed that A in the general formula is a divalent metal atom, and the divalent metal atom is a metal atom that can be a divalent cation as an ion and includes alkaline earth metal atoms such as barium, strontium, and calcium and lead.

PTL 2 discloses a method for producing a hexagonal ferrite magnetic powder in which a raw material mixture containing a glass-forming component and a hexagonal ferrite-forming component is melted, the obtained molten substance is quenched to obtain a solid, and the obtained solid is subjected to heating treatment to precipitate hexagonal ferrite magnetic particles and a glass component.

Citation List

Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. 2016-222517

PTL 2: Japanese Unexamined Patent Application Publication No. 2020-100561

Summary of Invention

Technical Problem

However, conventional knowledge of ferrite particles and methods for producing them is limited, and there is still room for further study. In addition, conventional methods for producing ferrite particles usually use wet processes or sol-gel reactions, and it is difficult to control a particle size in wet processes or sol-gel reactions, and thus it is difficult to obtain ferrite particles having a certain particle size or certain particle size distribution according to application.

The present invention has been made in order to solve the problems, and an object thereof is to provide ferrite particles having excellent properties and a method for producing ferrite particles, which can easily produce the ferrite particles.

Solution to Problem

The inventors of the present invention have conducted earnest studies to solve the subjects to find out that using a molybdenum compound as a flux can easily produce ferrite particles by dry mixing and can easily produce ferrite particles containing molybdenum and to complete the present invention.

Specifically, the present invention has the following aspects.

[1] Ferrite particles containing molybdenum.

[2] The ferrite particles according to [1] above, in which the ferrite particles have a spinel structure.

[3] The ferrite particles according to [2] above, in which the spinel structure is represented by AFe ₂O ₄ (in the formula, A is one or a plurality of elements selected from Ni, Mn, Cu, Zn, Mg, Ca, and Co) .

[4] The ferrite particles according to [1] or [2] above, in which a molybdenum content in the ferrite particles is 0.1 to 30%by mass, a content (Mo ₁) in terms of MoO ₃ with respect to 100%by mass of the ferrite particles determined by performingX-ray fluorescence (XRF) analysis on the ferrite particles.

[5] The ferrite particles according to [1] or [2] above, in which a molybdenum content in surface layers of the ferrite particles is 2.0 to 95.0%by mass, a content (Mo ₂) in terms of MoO ₃ with respect to 100%by mass of the surface layers of the ferrite particles determined by performing X-ray photoelectron spectroscopy (XPS) surface analysis on the ferrite particles.

[6] The ferrite particles according to [1] or [2] above, in which the molybdenum is localized in surface layers of the ferrite particles.

[7] The ferrite particles according to [1] or [2] above, in which a molybdenum surface layer localization ratio (Mo ₂/Mo ₁) , which is a content (Mo ₂) in terms of MoO ₃ with respect to 100%by mass of the ferrite particles determined by performing X-ray photoelectron spectroscopy (XPS) surface analysis on the ferrite particles to a content (Mo ₁) in terms of MoO ₃ with respect to 100%by mass of the ferrite particles determined by performing XRF analysis on the ferrite particles, is 1.0 to 80.0.

[8] The ferrite particles according to [1] or [2] above, in which an average particle size of primary particles of the ferrite particles is 0.1 to 100 μm.

[9] The ferrite particles according to [1] or [2] above, in which the ferrite particles have a specific surface area measured by the BET method of 0.1 to 2.5 m ²/g.

[10] A method for producing the ferrite particles according to [1] , the method including firing a metal compound and an iron compound in the presence of a molybdenum compound.

[11] The method for producing the ferrite particles according to [10] above, the method including firing the metal compound and the iron compound with a zinc compound further added in the presence of the molybdenum compound.

[12] The method for producing the ferrite particles according to [10] or [11] above, in which the molybdenum compound is at least one compound selected from the group consisting of molybdenum trioxide, lithium molybdate, potassium molybdate, and sodium molybdate.

[13] The method for producing the ferrite particles according to [10] or [11] above, in which a firing temperature at the firing is 800 to 1,500℃.

Advantageous Effects of Invention

The present invention can provide ferrite particles having excellent properties and a method for producing ferrite particles, which can easily produce the ferrite particles.

Brief Description of Drawings

FIG. 1 is a SEM image of ferrite particles obtained in Example 1.

FIG. 2 is a SEM image of ferrite particles obtained in Example 2.

FIG. 3 is a SEM image of ferrite particles obtained in Example 3.

FIG. 4 is a SEM image of ferrite particles obtained in Example 4.

FIG. 5 is a SEM image of ferrite particles obtained in Example 5.

FIG. 6 is a SEM image of ferrite particles obtained in Example 6.

FIG. 7 is a SEM image of ferrite particles obtained in Example 7.

FIG. 8 is a SEM image of ferrite particles obtained in Example 8.

FIG. 9 is a SEM image of ferrite particles obtained in Example 9.

FIG. 10 is a SEM image of ferrite particles obtained in Example 10.

FIG. 11 is a SEM image of ferrite particles obtained in Example 11.

FIG. 12 is a SEM image of ferrite particles obtained in Comparative Example 1.

FIG. 13 is X-ray diffraction (XRD) patterns of the ferrite particles obtained in Examples 1 to 10 and Comparative Example 1.

FIG. 14 is an X-ray diffraction (XRD) pattern of the ferrite particles obtained in Example 11.

Description of Embodiments

The following describes an embodiment of the present invention in detail with reference to the accompanying drawings.

<<Ferrite Particles>>

The ferrite particles of the embodiment contain molybdenum. The ferrite particles of the embodiment contain molybdenum and have excellent properties such as magnetism derived from molybdenum.

The ferrite particles of the embodiment can also have the excellent property of the particle shape being controlled.

The ferrite particles of the embodiment can also have the excellent property of having a low degree of agglomeration or no agglomeration.

The ferrite particles of the embodiment can contain molybdenum derived from a molybdenum compound used in a method of production described below. The particle shape of the ferrite particles to be produced can be controlled by using the molybdenum compound in the method of production described below.

As to the molybdenum contained in the ferrite particles of the embodiment, its presence state and amount are not limited to particular ones, and it may be included in the ferrite particles as molybdenum metal, molybdenum oxides, partially reduced molybdenum compounds, or the like. Molybdenum is considered to be contained in the ferrite particles as MoO ₃ but may also be contained in the ferrite particles as MoO ₂, MoO, or the like other than MoO ₃.

The contained form of molybdenum is not limited to a particular form. It may be contained in the form of adhering to the surfaces of the ferrite particles, be contained in the form of substituting part of the crystal structure of the ferrite particles, be contained in the state of amorphous, or be a combination of these.

Thus, the ferrite particles of the embodiment can contain molybdenum and can, in particular, contain molybdenum derived from the molybdenum compound used in the method of production described below, and thus, improved magnetic performance can be expected compared to that by conventional ferrite particles.

In the present specification, controlling the particle shape of the ferrite particles means that the particle shape of the produced ferrite particles is not amorphous. In the present specification, the ferrite particles with their particle shape controlled means ferrite particles that are not amorphous in particle shape.

The ferrite particles of the embodiment may have a polygonal shape. The ferrite particles of the embodiment have a controlled crystal shape and can have a polygonal idiomorphic shape. The ferrite particles with their crystal shape controlled can be produced by the method of production described below.

An aggregate (powder) of the ferrite particles may contain ferrite particles of any shape other than the polygonal shape in any state. The content of the ferrite particles of the polygonal shape is preferably 80%or more, more preferably 90%or more, and even more preferably 95%or more on a weight basis or a number basis with respect to the total amount of the aggregate (powder) of the ferrite particles. The morphology of the ferrite particles can be determined with a scanning electron microscopy (SEM) .

For the ferrite particles of the embodiment, the particle size and the molybdenum content of the ferrite particles to be obtained can be controlled by controlling the use amount and the type of the molybdenum compound, a firing temperature, or the like in the method of production described below.

The average particle size of the primary particles of the ferrite particles of the embodiment may be 0.1 to 100 μm, 0.1 to 50 μm, 1.0 to 40 μm, or 1.5 to 30 μm.

As to the average particle size of the primary particles of the ferrite particles, the ferrite particles are photographed with a scanning electron microscope (SEM) , and for particles as the smallest unit on a two-dimensional image (that is, the primary particles) , the average of the measured maximum length among distances between two points on the contour line of 50 randomly selected primary particles is employed.

The median diameter D ₅₀ calculated by laser diffraction and scattering of the ferrite particles of the embodiment may be 0.5 to 50 μm, 1 to 40 μm, or 1.5 to 35 μm.

The median diameter D ₅₀ calculated by laser diffraction and scattering of the ferrite particles can be determined as, in particle size distribution measured in dry form using a laser diffraction particle size analyzer, a particle size at which the proportion of volume accumulation percentage is 50%.

The specific surface area determined by the BET method of the ferrite particles of the embodiment may be 0.1 to 2.5 m ²/g, 0.15 to 2.5 m ²/g, 0.1 to 2.0 m ²/g, or 0.2 to 2.0 m ²/g.

The specific surface area is measured with a specific surface area meter (BELSORP-mini manufactured by Microtrac Bell Corporation, for example) , and the surface area per gram of a sample measured from the adsorption amount of nitrogen gas by the Brunauer-Emmett-Teller method (the BET method) is calculated as the specific surface area (m ²/g) .

The ferrite particles of the embodiment contain ferrite. While the ferrite particles can take various crystal structures, such as the spinel structure and the garnet structure, it is preferred to have the spinel structure in the present embodiment. The spinel structure is represented by AFe ₂O ₄ (in the formula, A is one or a plurality of elements selected from Ni, Mn, Cu, Zn, Mg, Ca, and Co) , for example. The spinel structure is typically represented by AFe ₂O ₄ (in the formula, A is one or two elements selected from Ni, Mn, Cu, Zn, Mg, Ca, and Co) .

The ferrite particles of the embodiment preferably contain AFe ₂O ₄ in an amount of 65 to 99.95%by mass, more preferably contain it in an amount of 70 to 99.5%by mass, and even more preferably contain it in an amount of 90 to 99%by mass with respect to 100%by mass of the ferrite particles.

The ferrite particles may contain nickel. The nickel content contained in the ferrite particles can be measured by X-ray fluorescence (XRF) analysis. The nickel content in the ferrite particles of the embodiment is preferably 5 to 50%by mass, more preferably 10 to 40%by mass, and even more preferably 15 to 30%by mass, a content (Ni ₁) in terms of NiO with respect to 100%by mass of the ferrite particles determined by performing the XRF analysis on the ferrite particles.

The iron content contained in the ferrite particles can be measured by the XRF analysis. The iron content in the ferrite particles of the embodiment is preferably 35 to 80%by mass, more preferably 40 to 75%by mass, and even more preferably 45 to 70%by mass, a content (Fe ₁) in terms of Fe ₂O ₃ with respect to 100%by mass of the ferrite particles determined by performing the XRF analysis on the ferrite particles.

The molybdenum content contained in the ferrite particles can be measured by the XRF analysis. The molybdenum content in the ferrite particles of the embodiment is preferably 0.1%by mass or more, preferably 0.1 to 30%by mass, more preferably 0.5 to 25%by mass, and even more preferably 0.75 to 20%by mass, a content (Mo ₁) in terms of MoO ₃ with respect to 100%by mass of the ferrite particles determined by performing the XRF analysis on the ferrite particles.

The respective upper limit values and the respective lower limit values of the content (Ni ₁) , the content (Fe ₁) , and the content (Mo ₁) exemplified above in the ferrite particles of the embodiment can be freely combined with each other. The respective values of the content (Ni ₁) , the content (Fe ₁) , and the content (Mo ₁) can also be freely combined with each other.

An example of the ferrite particles of the embodiment, when the spinel structure is represented by NiFe ₂O ₄, may be ferrite particles having a content (Ni ₁) of 15 to 45%by mass, a content (Fe ₁) of 35 to 75%by mass, and a content (Mo ₁) of 0.1 to 30%by mass with respect to 100%by mass of the ferrite particles determined by performing the XRF analysis on the ferrite particles, ferrite particles having a content (Ni ₁) of 17.5 to 40%by mass, a content (Fe ₁) of 40 to 70%by mass, and a content (Mo ₁) of 0.5 to 25%by mass with respect to 100%by mass of the ferrite particles determined by performing the XRF analysis on the ferrite particles, or ferrite particles having a content (Ni ₁) of 20 to 35%by mass, a content (Fe ₁) of 45 to 65%by mass, and a content (Mo ₁) of 0.75 to 20%by mass with respect to 100%by mass of the ferrite particles determined by performing the XRF analysis on the ferrite particles.

The ferrite particles may further contain zinc. The zinc content contained in the ferrite particles can be measured by the XRF analysis. The zinc content in the ferrite particles of the embodiment is preferably 0.5 to 25%by mass, more preferably 0.75 to 20%by mass, and even more preferably 0.1 to 15%by mass, a content (Zn ₁) in terms of ZnO ₂ with respect to 100%by mass of the ferrite particles determined by performing the XRF analysis on the ferrite particles.

The respective upper limit values and the respective lower limit values of the content (Ni ₁) , the content (Fe ₁) , the content (Zn ₁) , and the content (Mo ₁) exemplified above in the ferrite particles of the embodiment can be freely combined with each other. The respective values of the content (Ni ₁) , the content (Fe ₁) , the content (Zn ₁) , and the content (Mo ₁) can also be freely combined with each other.

An example of the ferrite particles of the embodiment, when the spinel structure is represented by NiFe ₂O ₄, may be ferrite particles having a content (Ni ₁) of 10 to 40%by mass, a content (Fe ₁) of 45 to 60%by mass, a content (Zn ₁) of 0.5 to 20%by mass, and a content (Mo ₁) of 0 to 5%by mass with respect to 100%by mass of the ferrite particles determined by performing the XRF analysis on the ferrite particles, ferrite particles having a content (Ni ₁) of 12.5 to 35%by mass, a content (Fe ₁) of 47.5 to 57.5%by mass, a content (Zn ₁) of 0.75 to 17.5%by mass, and a content (Mo ₁) of 0.1 to 3%by mass with respect to 100%by mass of the ferrite particles determined by performing the XRF analysis on the ferrite particles, or ferrite particles having a content (Ni ₁) of 15 to 30%by mass, a content (Fe ₁) of 50 to 55%by mass, a content (Zn ₁) of 1.0 to 15%by mass, and a content (Mo ₁) of 0.5 to 2.5%by mass with respect to 100%by mass of the ferrite particles determined by performing the XRF analysis on the ferrite particles.

The ferrite particles may contain manganese in place of nickel. The manganese content contained in the ferrite particles can be measured by the XRF analysis. The manganese content in the ferrite particles of the embodiment is preferably 10 to 60%by mass, more preferably 20 to 50%by mass, and even more preferably 30 to 40%by mass, a content (Mn ₁) in terms of MnO ₂ with respect to 100%by mass of the ferrite particles determined by performing the XRF analysis on the ferrite particles.

The respective upper limit values and the respective lower limit values of the content (Mn ₁) , the content (Fe ₁) , and the content (Mo ₁) exemplified above in the ferrite particles of the embodiment can be freely combined with each other. The respective values of the content (Mn ₁) , the content (Fe ₁) , and the content (Mo ₁) can also be freely combined with each other.

An example of the ferrite particles of the embodiment, when the spinel structure is represented by MnFe ₂O ₄, may be ferrite particles having a content (Mn ₁) of 10 to 60%by mass, a content (Fe ₁) of 30 to 80%by mass, and a content (Mo ₁) of 0%by mass with respect to 100%by mass of the ferrite particles determined by performing the XRF analysis on the ferrite particles, ferrite particles having a content (Mn ₁) of 20 to 50%by mass, a content (Fe ₁) of 40 to 75%by mass, and a content (Mo ₁) of 0%by mass with respect to 100%by mass of the ferrite particles determined by performing the XRF analysis on the ferrite particles, or ferrite particles having a content (Mn ₁) of 30 to 40%by mass, a content (Fe ₁) of 50 to 70%by mass, and a content (Mo ₁) of 0%by mass with respect to 100%by mass of the ferrite particles determined by performing the XRF analysis on the ferrite particles.

For the XRF analysis, an X-ray fluorescence analyzer (Primus IV manufactured by Rigaku Corporation, for example) can be used.

The content (Ni ₁) in terms of NiO refers to the value of the nickel content determined by performing the XRF analysis on the ferrite particles determined from an NiO amount converted using a calibration line in terms of NiO.

The content (Fe ₁) in terms of Fe ₂O ₃ refers to the value of the iron content determined by performing the XRF analysis on the ferrite particles determined from an Fe ₂O ₃ amount converted using a calibration line in terms of Fe ₂O ₃.

The content (Mo ₁) in terms of MoO ₃ refers to the value of the molybdenum content determined by performing the XRF analysis on the ferrite particles determined from an MoO ₃ amount converted using a calibration line in terms of MoO ₃.

The content (Zn ₁) in terms of ZnO ₂ refers to the value of the zinc content determined by performing the XRF analysis on the ferrite particles determined from a ZnO ₂ amount converted using a calibration line in terms of ZnO ₂.

The content (Mn ₁) in terms of MnO ₂ refers to the value of the manganese content determined by performing the XRF analysis on the ferrite particles determined from an MnO ₂ amount converted using a calibration line in terms of MnO ₂.

The nickel content contained in the surface layers of the ferrite particles can be measured by X-ray photoelectron spectroscopy (XPS) surface analysis. The nickel content in the surface layers of the ferrite particles of the embodiment is preferably 0 to 65%by mass, more preferably 0 to 60%by mass, and even more preferably 0 to 55%by mass, a content (Ni ₂) in terms of NiO with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles.

The iron content contained in the surface layers of the ferrite particles can be measured by the X-ray photoelectron spectroscopy (XPS) surface analysis. The iron content in the surface layers of the ferrite particles of the embodiment is preferably 5 to 65%by mass, more preferably 10 to 60%by mass, and even more preferably 12.5 to 57.5%by mass, a content (Fe ₂) in terms of Fe ₂O ₃ with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles.

The molybdenum content contained in the surface layers of the ferrite particles can be measured by the X-ray photoelectron spectroscopy (XPS) surface analysis. The molybdenum content in the surface layers of the ferrite particles of the embodiment is preferably 1%by mass or more, preferably 2.0 to 95%by mass, more preferably 2.5 to 90%by mass, and even more preferably 3.0 to 87.5%by mass, a content (Mo ₂) in terms of MoO ₃ with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles.

The respective upper limit values and the respective lower limit values of the content (Ni ₂) , the content (Fe ₂) , and the content (Mo ₂) exemplified above in the ferrite particles of the embodiment can be freely combined with each other. The respective values of the content (Ni ₂) , the content (Fe ₂) , and the content (Mo ₂) can also be freely combined with each other.

An example of the ferrite particles of the embodiment, when the spinel structure is represented by NiFe ₂O ₄, may be ferrite particles having a content (Ni ₂) of 0 to 60%by mass, a content (Fe ₂) of 5 to 65%by mass, and a content (Mo ₂) of 2.5 to 90%by mass with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles, ferrite particles having a content (Ni ₂) of 3 to 57.5%by mass, a content (Fe ₂) of 10 to 60%by mass, and a content (Mo ₂) of 5 to 87.5%mass with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles, or ferrite particles having a content (Ni ₂) of 5 to 55%by mass, a content (Fe ₂) of 12.5 to 55%by mass, and a content (Mo ₂) of 7.5 to 85%mass with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles.

As described above, the ferrite particles may further contain zinc. The zinc content contained in the ferrite particles can be measured by the X-ray photoelectron spectroscopy (XPS) surface analysis. The zinc content in the surface layers of the ferrite particles of the embodiment is preferably 0.1 to 10%by mass, more preferably 0.25 to 8%by mass, and even more preferably 0.5 to 6%by mass, a content (Zn ₂) in terms of ZnO ₂ with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles.

The respective upper limit values and the respective lower limit values of the content (Ni ₂) , the content (Fe ₂) , the content (Zn ₂) , and the content (Mo ₂) exemplified above in the ferrite particles of the embodiment can be freely combined with each other. The respective values of the content (Ni ₂) , the content (Fe ₂) , the content (Zn ₂) , and the content (Mo ₂) can also be freely combined with each other.

An example of the ferrite particles of the embodiment, when the spinel structure is represented by NiFe ₂O ₄, may be ferrite particles having a content (Ni ₂) of 0.5 to 25%by mass, a content (Fe ₂) of 20 to 70%by mass, a content (Zn ₂) of 0.1 to 10%by mass, and a content (Mo ₂) of 20 to 75%by mass with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles, ferrite particles having a content (Ni ₂) of 1.0 to 20%by mass, a content (Fe ₂) of 25 to 65%by mass, a content (Zn ₂) of 0.25 to 8%by mass, and a content (Mo ₂) of 25 to 70%by mass with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles, or ferrite particles having a content (Ni ₂) of 1.5 to 10%by mass, a content (Fe ₂) of 30 to 60%by mass, a content (Zn ₂) of 0.5 to 6%by mass, and a content (Mo ₂) of 30 to 65%by mass with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles.

When the ferrite particles contain manganese in place of nickel, the manganese content contained in the ferrite particles can be measured by the X-ray photoelectron spectroscopy (XPS) surface analysis. The content in the surface layers of the ferrite particles of the embodiment is preferably 10 to 80%by mass, more preferably 20 to 70%by mass, and even more preferably 30 to 60%by mass, a content (Mn ₂) in terms of MnO ₂ with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles.

The respective upper limit values and the respective lower limit values of the content (Mn ₂) , the content (Fe ₂) , and the content (Mo ₂) exemplified above in the ferrite particles of the embodiment can be freely combined with each other. The respective values of the content (Mn ₂) , the content (Fe ₂) , and the content (Mo ₂) can also be freely combined with each other.

An example of the ferrite particles of the embodiment, when the spinel structure is represented by MnFe ₂O ₄, may be ferrite particles having a content (Mn ₂) of 10 to 80%by mass, a content (Fe ₂) of 5 to 75%by mass, and a content (Mo ₂) of 10 to 95%by mass with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles, ferrite particles having a content (Mn ₂) of 20 to 70%by mass, a content (Fe ₂) of 7.5 to 65%by mass, and a content (Mo ₂) of 12.5 to 90%by mass with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles, or ferrite particles having a content (Mn ₂) of 30 to 60%by mass, a content (Fe ₂) of 10 to 60%by mass, and a content (Mo ₂) of 15 to 87.5%by mass with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles.

For the XPS analysis, a scanning X-ray photoelectron spectral analyzer (QUANTERA SXM manufactured by ULVAC Phi, Inc., for example) can be used.

The content (Ni ₂) refers to a value determined as the content of NiO with respect to 100%by mass of the surface layers of the ferrite particles by performing the XPS surface analysis on the ferrite particles by X-ray photoelectron spectroscopy (XPS) to acquire presence proportions (atom%) for respective elements and determining a nickel content in terms of oxide.

The content (Fe ₂) refers to a value determined as the content of Fe ₂O ₃ with respect to 100%by mass of the surface layers of the ferrite particles by performing the XPS surface analysis on the ferrite particles by X-ray photoelectron spectroscopy (XPS) to acquire presence proportions (atom%) for respective elements and determining an iron content in terms of oxide.

The content (Mo ₂) refers to a value determined as the content of MoO ₃ with respect to 100%by mass of the surface layers of the ferrite particles by performing the XPS surface analysis on the ferrite particles by X-ray photoelectron spectroscopy (XPS) to acquire presence proportions (atom%) for respective elements and determining a molybdenum content in terms of oxide.

The content (Mn ₂) refers to a value determined as the content of MnO ₂ with respect to 100%by mass of the surface layers of the ferrite particles by performing the XPS surface analysis on the ferrite particles by X-ray photoelectron spectroscopy (XPS) to acquire presence proportions (atom%) for respective elements and determining a manganese content in terms of oxide.

In the ferrite particles of the embodiment, the molybdenum is preferably localized in the surface layers of the ferrite particles.

The "surface layers" in the present specification refer to the region within 10 nm of the surfaces of the ferrite particles of the embodiment. This distance corresponds to XPS detection depth used for measurement in the examples.

Being "localized in the surface layers" refers to a state in which the mass of molybdenum or the molybdenum compound per unit volume in the surface layers is larger than the mass of molybdenum or the molybdenum compound per unit volume in other than the surface layers.

The fact that molybdenum is localized in the surface layers of the ferrite particles in the ferrite particles of the present embodiment can be determined by the fact that the molybdenum content (Mo ₂) in terms of MoO ₃ with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles is larger than the molybdenum content (Mo ₁) in terms of MoO ₃ with respect to 100%by mass of the ferrite particles determined by performing the X-ray fluorescence (XRF) analysis on the ferrite particles as shown in the examples described below.

In the ferrite particles of the embodiment, as an indicator of molybdenum being localized in the surface layers of the ferrite particles, the ferrite particles of the embodiment has a molybdenum surface layer localization ratio (Mo ₂/Mo ₁) , which is a content (Mo ₂) in terms of MoO ₃ with respect to 100%by mass of the surface layers of the ferrite particles determined by performing the XPS surface analysis on the ferrite particles to a content (Mo ₁) in terms of MoO ₃ with respect to 100%by mass of the ferrite particles, of preferably 1.0 to 80, more preferably 3.0 to 60, and even more preferably 5.0 to 50.

By localizing molybdenum or the molybdenum compound in the surface layers of the ferrite particles, excellent properties such as catalytic activity can be imparted more efficiently than a case in which molybdenum or the molybdenum compound is caused to be uniformly present not only in the surface layers but also in other than the surface layers (inner layers) .

The ferrite particles of the embodiment can be provided as an aggregate of ferrite particles, and for the values of the nickel content, the iron content, and the molybdenum content described above, for example, values determined with the aggregate as a sample can be employed. Similarly, for the values of the nickel content, the iron content, the zinc content, and the molybdenum content described above, values determined with the aggregate as a sample can be employed. Furthermore, for the values of the manganese content, the iron content, and the molybdenum content described above, values determined with the aggregate as a sample can be employed.

In addition to molybdenum, the ferrite particles of the present embodiment may further contain lithium, potassium, or sodium.

The method for producing ferrite particles of the embodiment includes firing a metal compound and an iron compound in the presence of the molybdenum compound. More specifically, the method of production of the present embodiment is a method for producing the ferrite particles and may include mixing together the metal compound, the iron compound, and the molybdenum compound to make a mixture and firing the mixture.

By firing the metal compound and the iron compound in the presence of the molybdenum compound, the formation reaction efficiency of ferrite particles can be improved compared to a case in which the molybdenum compound is not used. Thus, high-quality ferrite particles with the content of impurities reduced can be efficiently produced, and furthermore, ferrite particles with a low degree of agglomeration can be easily produced.

As the metal compound, a metal compound containing any element selected from Ni, Mn, Cu, Zn, Mg, Ca, and Co can be used. Examples thereof include nickel compounds, manganese compounds, copper compounds, zinc compounds, magnesium compounds, calcium compounds, and cobalt compounds.

By firing the metal compound and the iron compound with the zinc compound further added in the presence of the molybdenum compound, a certain proportion of a paramagnetic substance is added, thus enabling the magnetism of the A site to be moderately reduced and the magnetism derived from the A-B site interaction to be increased.

A case in which a compound containing molybdenum and nickel, such as nickel molybdate, is used is also considered to be a case in which the molybdenum compound and the nickel compound are used.

The method for producing ferrite particles of the embodiment can easily produce the ferrite particles of the embodiment described above.

A preferred method for producing ferrite particles includes a step of mixing together the metal compound containing any element selected from Ni, Mn, Cu, Zn, Mg, Ca, and Co, the iron compound, and the molybdenum compound to make a mixture (amixing step) and a step of firing the mixture (a firing step) . The following describes a case in which the nickel compound is used as an example of the metal compound taken as an example.

[Mixing Step]

The mixing step is a step of mixing together the nickel compound, the iron compound, and the molybdenum compound to make a mixture. The following describes the contents of the mixture.

(Nickel Compound)

The type of the nickel compound is not limited to a particular type. Examples of the nickel compound include nickel hydroxide, nickel oxide, nickel carbonate, nickel molybdate, nickel chloride, nickel nitrate, nickel sulfate, and nickel acetate. Nickel oxide, nickel hydroxide, or nickel carbonate is preferred, and from the viewpoint of reactivity and the viewpoint of not generating toxic gases, nickel oxide or nickel hydroxide is more preferred.

The shape of the ferrite particles after firing hardly reflects the shape of the raw material nickel compound, and thus, as the nickel compound, spherical one, amorphous one, structures with a high aspect ratio (awire, a fiber, a ribbon, a tube, and the like) , a sheet, and the like can also be suitably used.

(Iron Compound)

The type of the iron compound is not limited to a particular type, and any known ones can be used. Specific examples of these include iron (II) oxide (FeO) , or what is called wüstite, black iron (II, III) oxide (Fe ₃O ₄) , and red or brown iron (III) oxide (Fe ₂O ₃) . Examples of iron (III) oxide include α-Fe ₂O ₃, β-Fe ₂O ₃, γ-Fe ₂O ₃, and ε-Fe ₂O ₃. Examples of iron oxyhydroxide include α-iron oxyhydroxide, β-iron oxyhydroxide, γ-iron oxyhydroxide, and δ-iron oxyhydroxide. Examples of iron hydroxide include iron (II) hydroxide (Fe (OH) ₂) and iron (III) hydroxide (Fe (OH) ₃) . As iron oxide, iron (III) oxide (Fe ₂O ₃) is preferred.

The shape of the iron compound is not limited to a particular shape, and spherical, rod-like, or plate-like shape can be suitably used, for example.

(Molybdenum Compound)

Examples of the molybdenum compound include molybdenum oxides, molybdic acid, molybdenum sulfide, molybdenum silicide, and molybdate compounds, and molybdenum oxides or molybdate compounds are preferred.

Examples of the molybdenum oxides include molybdenum dioxide (MoO ₂) and molybdenum trioxide (MoO ₃) , and molybdenum trioxide is preferred.

The molybdate compound is not limited so long as it is a salt compound of a molybdenum oxoanion such as MoO ₄ ^2-, Mo ₂O ₇ ^2-, Mo ₃O ₁₀ ^2-, Mo ₄O ₁₃ ^2-, Mo ₅O ₁₆ ^2-, Mo ₆O ₁₉ ^2-, Mo ₇O ₂₄ ^6-, or Mo ₈O ₂₆ ^4-. The molybdate compound may be an alkali metal salt, an alkaline earth metal salt, or an ammonium salt of the molybdenum oxoanion.

The molybdate compound is preferably an alkali metal salt of the molybdenum oxoanion, more preferably lithium molybdate, potassium molybdate, or sodium molybdate, even more preferably potassium molybdate or sodium molybdate, and particularly preferably sodium molybdate.

In the method for producing ferrite particles of the embodiment, the molybdate compound may be a hydrate.

The molybdenum compound is preferably at least one compound selected from the group consisting of molybdenum trioxide, lithium molybdate, potassium molybdate, and sodium molybdate, more preferably at least one compound selected from the group consisting of molybdenum trioxide, potassium molybdate, and sodium molybdate, and even more preferably molybdenum trioxide and/or sodium molybdate.

(Zinc Compound)

In the mixing step, the nickel compound, the iron compound, and the molybdenum compound are mixed together, and a zinc compound may be further added to make a mixture.

The type of the zinc compound is not limited to a particular type. Examples of the zinc compound include zinc hydroxide, zinc oxide, zinc carbonate, zinc molybdate, zinc acetate, zinc chloride, zinc nitrate, and zinc sulfate, and from the viewpoint of reactivity and the viewpoint of not generating toxic gases, zinc hydroxide or zinc oxide is preferred.

(Manganese Compound)

In the mixing step, a manganese compound may be used in place of the nickel compound, and the manganese compound, the iron compound, and the molybdenum compound may be mixed together to form a mixture.

The type of the manganese compound is not limited to a particular type. Examples of the manganese compound include manganese carbonate, manganese oxide, manganese acetate, manganese chloride, manganese nitrate, manganese sulfate, and their hydrates, and from the viewpoint of reactivity and the viewpoint of not generating toxic gases, manganese carbonate or manganese oxide is preferred.

The method for producing ferrite particles of the embodiment may include a step of firing the nickel compound and the iron compound in the presence of the molybdenum compound and a sodium compound and/or a potassium compound.

The method for producing ferrite particles of the embodiment can include, prior to a firing step, a step of mixing together the nickel compound, the iron compound, the molybdenum compound, and the sodium compound and/or the potassium compound to make a mixture (amixing step) and can include a step of firing the mixture (the firing step) .

In the method of production of the embodiment, by using the sodium compound and/or the potassium compound, it is easy to adjust the particle size of the ferrite particles to be produced, and ferrite particles having a low degree of agglomeration or no agglomeration can be produced.

In place of at least part of the molybdenum compound and the sodium compound, a compound containing molybdenum and sodium, such as sodium molybdate, can also be used. Similarly, in place of at least part of the molybdenum compound and the potassium compound, a compound containing molybdenum and potassium, such as potassium molybdate, can also be used.

Thus, a step of mixing together the nickel compound, the iron compound, and a compound containing molybdenum and potassium and/or sodium to make a mixture is also regarded as a step of mixing together the nickel compound, the iron compound, the molybdenum compound, the potassium compound and/or the sodium compound to make a mixture.

The compound containing molybdenum and sodium, which is suitable as a flux agent, can be produced in the process of firing with the molybdenum compound and the sodium compound, which are lower in price and more readily available, as raw materials, for example. In this example, both a case in which the molybdenum compound and the sodium compound are used as the flux agent and a case in which the compound containing molybdenum and sodium is used as the flux agent are collectively regarded as a case in which the molybdenum compound and the sodium compound are used as the flux agent, that is, in the presence of the molybdenum compound and the sodium compound.

The compound containing molybdenum and potassium, which is suitable as the flux agent, can be produced in the process of firing with the molybdenum compound and the potassium compound, which are lower in price and more readily available, as raw materials, for example. In this example, both a case in which the molybdenum compound and the potassium compound are used as the flux agent and a case in which the compound containing molybdenum and potassium is used as the flux agent are collectively regarded as a case in which the molybdenum compound and the potassium compound are used as the flux agent, that is, in the presence of the molybdenum compound and the potassium compound.

The molybdenum compound described above may be used alone or used in combination of two or more.

Sodium molybdate (Na ₂Mo _nO _3n+1, n = 1 to 3) contains sodium and can also have the function as the sodium compound described below.

Potassium molybdate (K ₂Mo _nO _3n+1, n = 1 to 3) contains potassium and can also have the function as the potassium compound described below.

(Sodium Compound)

The sodium compound is not limited to a particular compound. Examples thereof include sodium carbonate, sodium molybdate, sodium oxide, sodium sulfate, sodium hydroxide, sodium nitrate, sodium chloride, and metallic sodium. Among these, it is preferable to use sodium carbonate, sodium molybdate, sodium oxide, and sodium sulfate from the viewpoints of industrial availability and ease of handling.

The sodium compound described above may be used alone or used in combination of two or more.

In the same manner as the above, sodium molybdate contains molybdenum and can thus also have the function as the molybdenum compound described above.

(Potassium Compound)

The potassium compound is not limited to a particular compound. Examples thereof include potassium chloride, potassium chlorite, potassium chlorate, potassium sulfate, potassium hydrogen sulfate, potassium sulfite, potassium hydrogen sulfite, potassium nitrate, potassium carbonate, potassium bicarbonate, potassium acetate, potassium oxide, potassium bromide, potassium bromate, potassium hydroxide, potassium silicate, potassium phosphate, potassium hydrogen phosphate, potassium sulfide, potassium hydrogen sulfide, potassium molybdate, and potassium tungstate. In this case, the potassium compound includes isomers as with the case of the molybdenum compound. Among these, it is preferable to use potassium carbonate, potassium bicarbonate, potassium oxide, potassium hydroxide, potassium chloride, potassium sulfate, and potassium molybdate, and it is more preferable to use potassium carbonate, potassium bicarbonate, potassium chloride, potassium sulfate, and potassium molybdate.

The potassium compound described above may be used alone or used in combination of two or more.

In the same manner as the above, potassium molybdate contains molybdenum and can thus also have the function as the molybdenum compound described above.

Examples of a preferred combination of raw materials in the method for producing ferrite particles of the embodiment, when the spinel structure in the ferrite particles is represented by NiFe ₂O ₄, include using nickel oxide, iron (III) oxide, and molybdenum trioxide.

Similarly, examples of the preferred combination of raw materials in the method for producing ferrite particles of the embodiment include use of nickel oxide, iron (III) oxide, and sodium molybdate or hydrates thereof.

Similarly, examples of the preferred combination of raw materials in the method for producing ferrite particles of the embodiment include use of nickel oxide, iron (III) oxide, molybdenum trioxide, and sodium molybdate or hydrates thereof.

Similarly, examples of the preferred combination of raw materials in the method for producing ferrite particles of the embodiment include use of nickel oxide, iron (III) oxide, zinc oxide, molybdenum trioxide, and sodium molybdate or hydrates thereof.

In addition, examples of the preferred combination of raw materials in the method for producing ferrite particles of the embodiment, when the spinel structure in the ferrite particles is represented by MnFe ₂O ₄, include use of manganese carbonate or hydrates thereof, iron oxyhydroxide, and sodium molybdate or hydrates thereof.

By firing the nickel compound and the iron compound in the presence of the molybdenum compound and the sodium compound or in the presence of the molybdenum compound and the potassium compound, it is easy to adjust the particle size of the ferrite particles to be produced, and ferrite particles having a low degree of agglomeration or no agglomeration can be produced. Although the reasons for this are not clear, the following reasons are conceivable. K ₂MoO ₄ and Na ₂MoO ₄, for example, are stable compounds and are difficult to volatilize by the firing step, and thus they are less likely to involve a rapid reaction during a volatilization step, making it easier to control the growth of the ferrite particles. It is also considered that molten K ₂MoO ₄ and Na ₂MoO ₄ exhibit functions like those of a solvent and can increase the value of the particle size by increasing the reaction time, for example. It is also considered that molten K ₂MoO ₄ and Na ₂MoO ₄ exhibit functions like those of a solvent, and thus the ferrite particles are dispersed, making it difficult for agglomeration to occur.

In the method for producing ferrite particles of the present embodiment, the molybdenum compound is used as the flux agent. In the present specification, this method of production using the molybdenum compound as the flux agent may be hereinafter simply referred to as the "flux method. " It is considered that after the nickel compound, the iron compound, and the molybdenum compound react with each other at a high temperature by such firing to form iron molybdate and nickel molybdate, when the iron molybdate and nickel molybdate further decompose into a nickel-iron compound oxide and molybdenum oxides at a higher temperature, the molybdenum compound is incorporated into the ferrite particles. It is considered that molybdenum oxides sublimate to be removed from the system, and in this process, the molybdenum compound and the nickel-iron compound oxide react with each other to form the molybdenum compound in the surface layers of the ferrite particles.

As to the formation mechanism of the molybdenum compound contained in the ferrite particles, more specifically, it is considered that the formation of Mo-O-Ni and Mo-O-Fe by the reaction of molybdenum with nickel atoms and iron atoms occurs in the surface layers of the ferrite particles, that Mo is desorbed by performing high-temperature firing, and that molybdenum oxides or compounds having Mo-O-Ni-O-Fe bonds and the like are formed in the surface layers of the ferrite particles.

Molybdenum oxides that are not incorporated into the ferrite particles can be recovered by sublimating them and reused. In this way, the amount of molybdenum oxides adhering to the surfaces of the ferrite particles can be reduced, and the original properties of the ferrite particles can be imparted to the maximum.

On the other hand, the alkali metal salt of the molybdenum oxoanion does not vaporize even in the firing temperature range and can be easily recovered by washing after firing, thus reducing the amount of the molybdenum compound released outside a firing furnace and significantly reducing production costs.

In the flux method, it is considered that when the molybdenum compound and the sodium compound are used in combination, for example, the molybdenum compound and the sodium compound first react with each other to form sodium molybdate. It is considered that at the same time the molybdenum compound reacts with the iron compound to form iron molybdate. It is considered that nickel molybdate and iron molybdate decompose in the presence of liquid sodium molybdate to be caused to grow crystals, for example, whereby ferrite particles having a low degree of agglomeration or no agglomeration can be easily obtained while controlling the evaporation of the flux (the sublimation of MoO ₃) described above.

(Other Metal Compounds)

Other metal compounds can be used during firing if desired. The method for producing ferrite particles of the embodiment can include, prior to a firing step, a step of mixing together the nickel compound, the iron compound, the molybdenum compound, the sodium compound and/or the potassium compound, and the other metal compound to make a mixture (amixing step) and can include a step of firing the mixture (the firing step) .

The other metal compound, which is not limited to a particular metal compound, preferably contains at least one selected from the group consisting of Group II metal compounds and Group III metal compounds.

Examples of the Group II metal compounds include calcium compounds, strontium compounds, and barium compounds.

Examples of the Group III metal compounds include scandium compounds, yttrium compounds, lanthanum compounds, and cerium compounds.

The other metal compound described above means an oxide, a hydroxide, a carbonate, and a chloride of metal elements. Examples of the yttrium compounds include yttrium oxide (Y ₂O ₃) , yttrium hydroxide, and yttrium carbonate. Among these, the metal compound is preferably an oxide of metal elements. Note that these metal compounds include isomers thereof.

Among these, the other metal compound is preferably a metal compound of third period elements, a metal compound of fourth period elements, a metal compound of fifth period elements, or a metal compound of sixth period elements, more preferably a metal compound of fourth period elements or a metal compound of fifth period elements, and even more preferably a metal compound of fifth period elements. Specifically, it is preferable to use calcium compounds, yttrium compounds, and lanthanum compounds, it is more preferable to use calcium compounds and yttrium compounds, and it is particularly preferable to use yttrium compounds.

The other metal compound is preferably used at a proportion of 0 to 1.2%by mass (0 to 1 mol%, for example) , for example, with respect to the total amount of the metal compound used in the mixing step.

In the method for producing ferrite particles of the present embodiment, the blending amounts of the nickel compound, the iron compound, and the molybdenum compound used are not limited to particular blending amounts. In the raw material, or in the mixture, for example, the ratio of the total mass of the nickel compound and the iron compound to the mass of the molybdenum compound may be 0.1 to 40, 0.2 to 20, or 0.4 to 10.

In the method for producing ferrite particles of the present embodiment, when the zinc compound is further blended, the blending amounts of the nickel compound, the iron compound, the zinc compound, and the molybdenum compound used are not limited to particular blending amounts. In the raw material, or in the mixture, for example, the ratio of the total mass of the nickel compound, the iron compound, and the zinc compound to the mass of the molybdenum compound may be 0.1 to 40, 0.2 to 20, or 0.4 to 10.

In the method for producing ferrite particles of the present embodiment, the blending amounts of the manganese compound, the iron compound, and the molybdenum compound used are not limited to particular blending amounts. In the raw material, or in the mixture, for example, the ratio of the total mass of the manganese compound and the iron compound to the mass of the molybdenum compound may be 0.1 to 40, 0.2 to 20, or 0.4 to 10.

In the method for producing ferrite particles of the present embodiment, the molar ratio of nickel to iron (Ni/Fe) in the raw material, or in the mixture, for example, may be 0.2 to 0.6 or 0.25 to 0.5.

[Firing Step]

The firing step is a step of firing the mixture. As described above, the method of production of the present embodiment includes firing the nickel compound and the iron compound in the presence of the molybdenum compound. Alternatively, when a mixture containing the zinc compound is obtained in the mixing step, firing the nickel compound and the iron compound with the zinc compound further added in the presence of the molybdenum compound may be included.

When a mixture containing the nickel compound, the manganese compound, the copper compound and/or the cobalt compound is obtained in the mixing step, firing the nickel compound, the manganese compound, the iron compound, the copper compound and/or the cobalt compound in the presence of the molybdenum compound may be included.

In the mixing step, the manganese compound may be used in place of the nickel compound. When a mixture containing the manganese compound and the copper compound and/or the cobalt compound is obtained, firing the manganese compound, the iron compound, and the copper compound and/or the cobalt compound in the presence of the molybdenum compound may be included.

The ferrite particles according to the embodiment are obtained by firing the mixture. As described above, this method of production is called the flux method.

The flux method is classified as the solution method. The flux method, more specifically, is a method of crystal growth using the fact that a crystal-flux two-component state diagram shows a eutectic type one. The mechanism of the flux method is presumed to be as follows. That is, when a mixture of a solute and a flux is heated, the solute and the flux become a liquid phase. In this process, the flux is a melting agent, or in other words, a solute-flux two-component state diagram shows a eutectic type one, and thus the solute melts at a temperature lower than its melting point to form a liquid phase. When the flux is evaporated in this state, the concentration of the flux decreases, or in other words, the effect of lowering the melting point of the solute by the flux reduces, and the evaporation of the flux acting as driving force causes the crystal growth of the solute (the flux evaporation method) . Note that the solute and the flux can cause the crystal growth of the solute also by cooling the liquid phase (the slow cooling method) .

The flux method has advantages such as the ability to grow crystals at temperatures much lower than the melting point, the ability to precisely control a crystal structure, and the ability to form crystal bodies having their idiomorphic shape.

In the production of ferrite particles by the flux method using the molybdenum compound as the flux, although the mechanism is not necessarily clear, it is presumed to be due to the following mechanism, for example. That is, when the nickel compound and the iron compound are fired in the presence of the molybdenum compound, nickel molybdate and iron molybdate are first formed. In this process, the nickel molybdate and the iron molybdate grow nickel ferrite crystals at a lower temperature than the melting point of nickel oxide and iron oxide or nickel ferrite as their compound oxide as can be understood from the above explanation. Then, by evaporating the flux, for example, nickel molybdate and iron molybdate decompose and grow crystals to yield ferrite particles. That is, the molybdenum compound functions as a flux, and nickel ferrite particles are produced via intermediates, or nickel molybdate and iron molybdate.

The flux method can produce ferrite particles containing molybdenum in which the molybdenum is localized in the surface layers of the ferrite particles.

The method of firing is not limited to a particular method and can be performed by any known and customary method. It is considered that when the firing temperature is higher than 800℃, the nickel compound, the iron compound, and the molybdenum compound react with each other to form nickel molybdate and iron molybdate. Furthermore, it is considered that when the firing temperature reaches 950℃ or higher, nickel molybdate and iron molybdate decompose to form the nickel ferrite particles. It is considered that in the nickel ferrite particles, when nickel molybdate and iron molybdate decompose to be nickel ferrite and molybdenum oxides, the molybdenum compound is incorporated into the nickel ferrite particles.

The state of the nickel compound, the iron compound, and the molybdenum compound during firing is not limited to a particular state, and the molybdenum compound is only required to be present in the same space so that it can act on the nickel compound and the iron compound. Specifically, the state may be simple mixing in which the powder of the molybdenum compound, the powder of the nickel compound, and the powder of the iron compound are mixed together, mechanical mixing using a pulverizer or the like, or mixing using a mortar or the like and may be mixing in a dry state or a wet state.

The state of the nickel compound, the iron compound, the zinc compound, and the molybdenum compound when the mixture containing the zinc compound is fired is not limited to a particular state, and the molybdenum compound is only required to be present in the same space so that it can act on the nickel compound, the iron compound, and the zinc compound. Specifically, the state may be simple mixing in which the powder of the molybdenum compound, the powder of the nickel compound, the powder of the iron compound, and the powder of the zinc compound are mixed together, mechanical mixing using a pulverizer or the like, or mixing using a mortar or the like and may be mixing in a dry state or a wet state.

There are no particular limitations on the condition of the firing temperature, which is determined as appropriate, taking into consideration the particle size of the target ferrite particles, the formation of the molybdenum compound in the ferrite particles, the shape of the ferrite particles, and the like. The firing temperature may be 950℃ or higher, which is close to the decomposition temperature of nickel molybdate and iron molybdate, 1,000℃ or higher, 1,050℃ or higher, or 1,100℃ or higher.

A higher firing temperature tends to be more likely to obtain ferrite particles with their particle shape controlled and with a large particle size. From the viewpoint of efficiently producing such ferrite particles, the firing temperature is preferably 950℃ or higher, more preferably 1,000℃ or higher, even more preferably 1, 050℃ or higher, and particularly preferably 1,100℃ or higher.

Generally, when it is attempted to control the shape of ferrite particles obtained after firing or to improve magnetism, high-temperature firing at higher than 1,200℃ or preferably higher than 1,500℃ is required to be performed. However, there are significant challenges to industrial use in terms of a burden on a firing furnace and energy costs.

One embodiment of the present invention can perform the formation of the ferrite particles efficiently at low cost even under the condition of the maximum firing temperature for firing the nickel compound and the iron compound being 1,500℃or lower, for example, contributing to a reduction in energy costs and an environmental load reduction.

The method for producing ferrite particles of the embodiment can form ferrite particles having an idiomorphic shape regardless of the shape of the precursor even when the firing temperature is 1,500℃ or lower, which is lower than the melting point of iron oxide. From such a viewpoint, the firing temperature is preferably 1,500℃ or lower, more preferably 1,400℃ or lower, even more preferably 1,300℃ or lower, and particularly preferably 1,200℃ or lower.

The numerical range of the firing temperature for firing the nickel compound and the iron compound in the firing step may be 800 to 1,500℃, 900 to 1,500℃, 950 to 1,400℃, 1,000 to 1,300℃, or 1,000 to 1,200℃, as an example.

The temperature rising rate may be 20 to 600℃/h, 40 to 500℃/h, or 80 to 400℃/h from the viewpoint of production efficiency.

As to the time of firing, the temperature rising time to a certain firing temperature is preferably performed in a range of 15 minutes to 10 hours. The holding time at the firing temperature can be 5 minutes or more, is preferably performed in a range of 5 minutes to 1,000 hours, and is more preferably performed in a range of 1 to 30 hours. To efficiently perform the formation of the ferrite particles, the firing temperature holding time being 2 hours or more is even more preferred, and the firing temperature holding time being 2 to 24 hours is particularly preferred.

As an example, by selecting the conditions of a firing temperature of 800 to 1,500℃ and a firing temperature holding time of 2 to 24 hours, the ferrite particles containing molybdenum can be easily obtained.

The atmosphere of firing, which is not limited to a particular atmosphere so long as the effects of the present invention can be obtained, is preferably an oxygen-containing atmosphere such as air or oxygen or an inert atmosphere such as nitrogen, argon, or carbon dioxide, for example, and is more preferably an air atmosphere, considering the aspect of cost.

The apparatus for firing is not necessarily limited, and what is called a firing furnace can be used. The firing furnace is preferably formed of a material that does not react with sublimated molybdenum oxides, and furthermore, it is preferable to use a highly sealed firing furnace so that molybdenum oxides can be efficiently used.

[Cooling Step]

The method for producing ferrite particles may include a cooling step. The cooling step is a step of cooling the crystal-grown ferrite particles in the firing step.

The cooling rate, which is not limited to a particular rate, is preferably 1 to 1,000℃/hour, more preferably 5 to 500℃/hour, and even more preferably 50 to 100℃/hour. The cooling rate being 1℃/hour or more is preferred because the production time can be shortened. On the other hand, the cooling rate being 1,000℃/hour or less is preferred because a firing container is less likely to break due to heat shock and can be used longer.

The method of cooling, which is not limited to a particular method, may be natural cooling or use a cooling apparatus.

[Molybdenum Removal Step]

The method for producing ferrite particles of the present embodiment may further include a molybdenum removal step of removing at least part of molybdenum as needed after the firing step.

Examples of the method include washing and high-temperature treatment. These can be done in combination.

As described above, molybdenum involves sublimation during firing, and thus by controlling the firing time, the firing temperature, or the like, the molybdenum content present in the surface layers of the ferrite particles can be controlled, and the molybdenum content and its presence state present in other than the surface layers (inner layers) of the ferrite particles can be controlled.

Molybdenum can adhere to the surfaces of the ferrite particles. As means other than the sublimation, the molybdenum can be removed by washing it with water, an aqueous ammonia solution, an aqueous sodium hydroxide solution, or the like.

In this process, the molybdenum content in the ferrite particles can be controlled by changing the concentration and the use amount of water, the aqueous ammonia solution, or the aqueous sodium hydroxide solution used, a washing site, a washing time, and the like as appropriate.

Examples of the method of high-temperature treatment include a method of raising the temperature up to the sublimation point or the boiling point of the molybdenum compound or higher.

[Pulverization Step]

In a fired product obtained through the firing step, the ferrite particles may agglomerate, and a suitable particle size range in applications to be considered is not necessarily satisfied. Thus, the ferrite particles may be pulverized to satisfy the suitable particle size range as needed.

The method for pulverizing the fired product is not limited to a particular method, and conventionally known methods of pulverization such as ball mills, jaw crushers, jet mills, disk mills, spectromills, grinders, and mixer mills can be used.

[Classification Step]

The fired product containing the ferrite particles obtained by the firing step may be subjected to classification processing as appropriate in order to adjust the particle size range. The "classification processing" refers to an operation to group particles according to the size of the particles.

Classification may be either wet form or dry form, but dry classification is preferred from the viewpoint of productivity.

The dry classification includes classification with a sieve and wind power classification, in which classification is performed by the difference between centrifugal force and fluid drag force. From the viewpoint of classification accuracy, wind power classification is preferred, which can be performed using classifiers such as an air flow classifier using the Coanda effect, a swirling air flow classifier, a forced vortex centrifugal classifier, and a semi-free vortex centrifugal classifier.

The pulverization step and the classification step can be performed at necessary stages. By the presence or absence of the pulverization and the class ification and the selection of conditions therefor, the average particle size of the ferrite particles to be obtained can be adjusted, for example.

The ferrite particles of the embodiment or the ferrite particles obtained by the method of production of the embodiment have a small degree of agglomeration or no agglomeration and are thus preferred from the viewpoints that they easily exhibit their original properties, that they are superior in their own handleability, and that they have better dispersibility when used dispersed in a medium in which they are dispersed.

The method for producing ferrite particles of the embodiment can easily produce ferrite particles having a small degree of agglomeration or no agglomeration and thus has the excellent advantage that ferrite particles having the desired excellent properties can be produced with high productivity even without performing the pulverization step or the classification step.

The method for producing ferrite particles of the embodiment described above can produce ferrite particles containing molybdenum and with high quality with their shape controlled easily and with high efficiency.

[Examples]

The following describes the present invention in more detail with reference to examples. The present invention is not limited to the following examples.

[Example 1]

Into an 80 ml zirconia pot, 5.63 g of nickel oxide (manufactured by Kanto Chemical Co., Inc. ) , 12.45 g of iron (III) oxide (manufactured by Kanto Chemical Co., Inc. ) , 3.6 g of molybdenum trioxide (manufactured by Nippon Inorganic Colour & Chemical Co., Ltd. ) , and 100 g of

zirconia beads were charged, which were mixed together and pulverized using a planetary ball mill (P-5 manufactured by Fritsch) at 200 rpm for 60 minutes to obtain a mixture. The obtained mixture was put into a crucible and was fired in a ceramic electric furnace at 1,100℃ for 10 hours. The temperature rising was performed at 5℃/min. After the temperature was lowered, the crucible was taken out to obtain a black powder.

The obtained black powder was transferred to a beaker, with 200 g of 0.5%ammonia water added thereto, was stirred, and was washed for 3 hours to dissolve remaining molybdenum trioxide. Then, particles obtained by filtering out by suction filtration using 5C filter paper was dried at 120℃to obtain 17.1 g of a white powder. The obtained particles were NiFe ₂O ₄.

[Example 2]

A black powder was obtained in the same manner as in Example 1 except that the charged amount of molybdenum trioxide was 1.8 g.

[Example 3]

Into a 100 ml polypropylene bottle, 3.19 g of nickel oxide (manufactured by Kanto Chemical Co., Inc. ) , 6.81 g of iron (III) oxide (manufactured by Kanto Chemical Co., Inc. ) , 13.94 g of sodium molybdate dihydrate (manufactured by Kanto Chemical Co., Inc. ) , 8.23 g of molybdenum trioxide (manufactured by Nippon Inorganic Colour & Chemical Co., Ltd. ) , and 100 g of

zirconia beads were charged, which were mixed together and pulverized using a paint shaker (manufactured by Toyo Seiki Seisaku-sho, Ltd. ) for 120 minutes to obtain a mixture. The obtained mixture was put into a crucible and was fired in a ceramic electric furnace at 1,300℃for 10 hours. The temperature rising was performed at 5℃/min. After the temperature was lowered, the crucible was taken out to obtain a black powder.

The obtained black powder was transferred to a beaker, with 200 g of ion-exchanged water added thereto, was stirred, and was washed for 3 hours to dissolve remaining sodium molybdate. Then, particles obtained by filtering out by suction filtration using 5C filter paper was dried at 120℃to obtain 9.2 g of a black powder. The obtained particles were NiFe ₂O ₄.

[Example 4]

A black powder was obtained in the same manner as in Example 3 except that the firing temperature was 1,500℃ and the temperature rising rate was 2℃/min.

[Example 5]

A black powder was obtained in the same manner as in Example 3 except that the firing temperature was 900℃ and the temperature rising rate was 2℃/min.

[Example 6]

A black powder was obtained in the same manner as in Example 3 except that the firing temperature was 1,100℃.

[Example 7]

A black powder was obtained in the same manner as in Example 6 except that the charged amount of nickel oxide was 3.02 g, and 0.17 g of zinc oxide was further added to nickel oxide, iron (III) oxide, sodium molybdate dihydrate, and molybdenum trioxide (the molar ratio of ZnO to (NiO + ZnO) : 0.05) . The obtained particles were particles mainly containing NiZnFe ₂O ₄.

[Example 8]

A black powder was obtained in the same manner as in Example 7 except that the charged amount of nickel oxide was 2.86 g, and that the charged amount of zinc oxide was 0.35 g (the molar ratio of ZnO to (NiO + ZnO) : 0.1) .

[Example 9]

A black powder was obtained in the same manner as in Example 7 except that the charged amount of nickel oxide was 2.23 g, and that the charged amount of zinc oxide was 1.04 g (the molar ratio of ZnO to (NiO + ZnO) : 0.3) .

[Example 10]

A black powder was obtained in the same manner as in Example 7 except that the charged amount of nickel oxide was 1.59 g, and that the charged amount of zinc oxide was 1.73 g (the molar ratio of ZnO to (NiO + ZnO) : 0.5) .

[Example 11]

Into a 100 ml polypropylene bottle, 6.65 g of manganese carbonate-n-hydrate (manufactured by Kanto Chemical Co., Inc. ) , 8.89 g of iron oxyhydroxide (manufactured by Kanto Chemical Co., Inc. ) , 15.5 g of sodium molybdate dihydrate (manufactured by Kanto Chemical Co., Inc. ) , 100 g of

zirconia beads, and 20 g of ion-exchange water were charged, which were mixed together and pulverized using a paint shaker for 120 minutes in wet form to obtain a mixture. The obtained mixture was dried at 120 degrees, and the mixture was put into a crucible, and was fired with an atmospheric electric furnace in a nitrogen atmosphere at 800℃ for 10 hours. The temperature rising was performed at 5℃/min. After the temperature was lowered, the crucible was taken out to obtain a black powder.

The obtained black powder was transferred to a beaker, with 200 g of ion-exchanged water added thereto, was stirred, and was washed for 3 hours to dissolve remaining sodium molybdate. Then, particles obtained by filtering out by suction filtration using 5C filter paper was dried at 120℃to obtain a black powder. The obtained particles were particles mainly containing MnFe ₂O ₄.

[Comparative Example 1]

Into an 80 ml zirconia pot, 5.63 g of nickel oxide (manufactured by Kanto Chemical Co., Inc. ) , 12.45 g of iron (III) oxide (manufactured by Kanto Chemical Co., Inc. ) , and 100 g of

zirconia beads were charged, which were mixed together and pulverized using a planetary ball mill (P-5 manufactured by Fritsch) at 200 rpm for 60 minutes to obtain a mixture. The obtained mixture was put into a crucible and was fired in a ceramic electric furnace at 1,100℃ for 10 hours. The temperature rising was performed at 5℃/min. After the temperature was lowered, the crucible was taken out to obtain 17.5 g of a black powder. The obtained particles were NiFe ₂O ₄ with a small amount of unreacted matter contained.

The powders obtained in Examples 1 to 11 and Comparative Example 1 were used as sample powders to perform the following evaluations.

[Crystal Structure Analysis: X-Ray Diffraction (XRD) ]

The sample powder was filled into a 0.5 mm-deep sample holder for measurement, which was set in a wide-angle X-ray diffraction (XRD) apparatus (Ultima IV manufactured by Rigaku Corporation) , and measurement was performed under the conditions of Cu/Kα radiation, 40 kV/40 mA, a scan speed of 2°/min, and a scanning range of 10 to 70°.

[Specific Surface Area Measurement of Ferrite Particles]

The specific surface area of the ferrite particles was measured with a specific surface area meter (BELSORP-mini manufactured by Microtrac Bell Corporation) , and the surface area per gram of a sample measured from the adsorption amount of nitrogen gas by the BET method was calculated as the specific surface area (m ²/g) .

[Primary Particle Size]

The ferrite particles were photographed with a scanning electron microscope (SEM) , for particles as the smallest unit on a two-dimensional image (that is, the primary particles) , the average of the measured maximum length among distances between two points on the contour line of 50 randomly selected primary particles was defined as a primary particle size of the ferrite particles.

[Particle Size Distribution Measurement]

The particle size distribution of the sample powder was measured in dry form using a laser diffraction dry particle size analyzer (HELOS (H3355) & RODOS manufactured by Japan Laser Corporation) under the conditions of a dispersion pressure of 3 bar and a drawing pressure of 90 mbar. The particle size at a point at which a distribution curve of volume accumulation percentage intersects a horizontal axis at 50%was determined as D ₅₀.

[X-Ray Fluorescence (XRF) Analysis]

Using an X-ray fluorescence analyzer (Primus IV manufactured by Rigaku Corporation) , about 70 mg of the sample powder was placed on filter paper, was covered with PP film, and was subjected to X-ray fluorescence (XRF) analysis under the following conditions.

Measurement Conditions

EZ scan mode

Measured elements: F to U

Measurement time: standard

Measurement diameter: 10 mm

Residual (balance component) : none

The nickel content, the iron content, the zinc content, and the molybdenum content of the ferrite particles obtained by the XRF analysis were determined in terms of oxide to acquire the results of the NiO content (Ni ₁) with respect to 100%by mass of the ferrite particles, the Fe ₂O ₃ content (Fe ₁) with respect to 100%by mass of the ferrite particles, the ZnO ₂ content (Zn ₁) with respect to 100%by mass of the ferrite particles, and the MoO ₃ content (Mo ₁) with respect to 100%by mass of the ferrite particles.

The manganese content, the iron content, and the molybdenum content of the ferrite particles obtained by the XRF analysis were determined in terms of oxide to acquire the MnO ₂ content (Mn ₁) with respect to 100%by mass of the ferrite particles, the Fe ₂O ₃ content (Fe ₁) with respect to 100%by mass of the ferrite particles, and the MoO ₃ content (Mo ₁) with respect to 100%by mass of the ferrite particles.

[XPS Surface Analysis]

For surface elemental analysis of the sample powder, the measurement of X-ray photoelectron spectroscopy (XPS) was performed using an X-ray photoelectron spectral analyzer (QUANTERA SXM manufactured by ULVAC Phi, Inc. ) using monochromatized Al-Kα as an X-ray source. The average of n = 3 measurement was acquired for each element in atom%by 1,000 μm square area measurement.

The nickel content in the surface layers of the ferrite particles, the iron content in the surface layers, and the molybdenum content in the surface layers obtained by the XPS analysis were determined in terms of oxide to determine the NiO content (Ni ₂) (%by mass) with respect to 100%by mass of the surface layers of the ferrite particles, the Fe ₂O ₃ content (Fe ₂) (%by mass) with respect to 100%by mass of the surface layers of the ferrite particles, and the MoO ₃ content (Mo ₂) (%by mass) with respect to 100%by mass of the surface layers of the ferrite particles.

The manganese content in the surface layers of the ferrite particles, the iron content in the surface layers, and the molybdenum content in the surface layers obtained by the XPS analysis were determined in terms of oxide to determine the MnO ₂ content (Mn ₂) (%by mass) with respect to 100%by mass of the surface layers of the ferrite particles, the Fe ₂O ₃ content (Fe ₂) (%by mass) with respect to 100%by mass of the surface layers of the ferrite particles, and the MoO ₃ content (Mo ₂) (%by mass) with respect to 100%by mass of the surface layers of the ferrite particles.

[Magnetic Analysis]

A vibrating sample magnetometer (BHV-50 manufactured by Riken Denshi Co., Ltd. ) was used to perform measurement for a specimen with an area of 30 mm ², a thickness of 2.5 mm, and a mass of about 0.15 g with a magnetic field strength of 7.96 × 10 ⁴ A/m and a measurement cycle of 5 min.

Table 1 lists respective values obtained by the evaluations. Note that "N.D. " is an abbreviation for "not detected" and indicates that the absence of detection.

[Table 1]

FIGS. 1 to 12 illustrate SEM images of the powders of the examples and the comparative example obtained by performing photographing with a scanning electron microscopy (SEM) .

In the powders of the respective examples of Examples 1 to 10, many beautiful polygonal particles were identified, and the crystal shape of the particles was controlled during the production process (FIG. 1 to FIG. 10) . In the powder of Example 11, many beautiful polygonal particles were also identified, and the crystal shape of the particles was controlled during the production process (FIG. 11) .

On the other hand, in the powders of Comparative Example 1, amorphous particles with no specific shape observed were observed (FIG. 12) .

FIG. 13 illustrates the results of the XRD analysis for Examples 1 to 10 and Comparative Example 1. Peaks (unmarked peaks) derived from ferrite (Ni ₂Fe ₂O ₄) were identified in the samples of the examples and the comparative example.

FIG. 14 illustrates the result of the XRD analysis for Example 11. Peaks (unmarked peaks) derived from ferrite (Mn ₂Fe ₂O ₄) were identified in the sample of the present example.

From the results of the SEM observation and the XRD analysis, it was confirmed that the powders obtained in the examples and the comparative example were ferrite particles containing ferrite.

In the sample powders of Examples 1 to 11, few peaks derived from impurities were identified (FIG. 13 and FIG. 14, detection of impurities in Table 1 "-" ) .

On the other hand, in the sample powder of Comparative Example 1, detection of peaks (peaks with a circle "●" in FIG. 13) derived from impurities such as nickel oxide and iron oxide, that is, unreacted raw materials were conspicuous (detection of impurities in Table 1 "+" ) . From this result, it was inferred that in the sample powders of Comparative Examples 1, the ferrite formation reaction was not complete and unreacted matter remained.

From this result, it was shown that in the examples, in which the nickel compound and the iron compound were fired in the presence of the molybdenum compound, even at relatively low firing temperatures of 900℃ to 1,500℃, the ferrite formation reaction favorably proceeded, and high-quality ferrite particles with the content of the impurities reduced and with their shape controlled were able to be produced with high efficiency.

The degree of agglomeration of the particles was evaluated from the SEM images of the respective ferrite particles based on the following criteria.

++: Agglomeration of particles is identified.

+: Some agglomeration of particles is identified.

-: No conspicuous agglomeration of particles is identified.

In the ferrite particles of Comparative Example 1, conspicuous agglomeration fusion between particles was identified (degree of agglomeration: +) , whereas no conspicuous agglomeration was identified in the ferrite particles of Examples 1 to 11 (degree of agglomeration: -) .

From this result, it was indicated that in the examples, in which either the nickel compound or the manganese compound and the iron compound were fired in the presence of the molybdenum compound, ferrite particles having a low degree of agglomeration or no agglomeration were able to be easily produced.

In the examples (refer to Examples 3, 5, and 6, for example) , a higher firing temperature tended to give ferrite particles with a larger particle size.

Thus, it was found that by controlling the firing temperature, the particle size of the ferrite particles was able to be controlled and ferrite particles having a desired particle size were able to be produced.

Table 1 lists the values of the NiO content (Ni ₁) , the Fe ₂O ₃ content (Fe ₁) , the ZnO ₂ content (Zn ₁) , the MoO ₃ content (Mo ₁) , the NiO content (Ni ₂) , the Fe ₂O ₃ content (Fe ₂) , the ZnO ₂ content (Zn ₂) , and the MoO ₃ content (Mo ₂) .

Table 1 also lists the values of the MnO ₂ content (Mn ₁) , the Fe ₂O ₃ content (Fe ₁) , the MoO ₃ content (Mo ₁) , the MnO ₂ content (Mn ₂) , the Fe ₂O ₃ content (Fe ₂) , and the MoO ₃ content (Mo ₂) .

From the result of the MoO ₃ content (Mo ₁) , it was confirmed that ferrite particles containing molybdenum were obtained.

From the result of the MoO ₃ content (Mo ₂) , the ferrite particles of Examples 1 to 11 contain molybdenum in the surface layers thereof, and it can be expected that various actions by molybdenum, such as magnetic properties, are exhibited.

Table 1 lists the calculation results of the surface layer localization ratio (Mo ₂/Mo ₁) of the MoO ₃ content (Mo ₂) with respect to the MoO ₃ content (Mo ₁) .

From the results of the surface layer localization ratio (Mo ₂/Mo ₁) , in the ferrite particles of Examples 1 to 11, the molybdenum content of the surface layers of the ferrite particles determined by the XPS surface analysis is larger than the molybdenum content determined by the XRF analysis. From this result, it is confirmed that molybdenum is localized in the surface layers of the ferrite particles, and it can be expected that various actions by molybdenum are effectively exhibited.

In the ferrite particles obtained in Examples 1 and 2, in which MoO ₃ was used in the raw material, the molybdenum content determined by the XRF analysis tended to decrease as the ratio of (Ni compound + Fe compound) /Mo compound in the raw material increased. In Examples 3 to 6, in which Na ₂MoO ₄ was used in combination in the raw material, when the ratio of (Ni compound + Fe compound) / (Mo compound) in the raw material was constant at 1/2, the molybdenum content determined by the XRF analysis and the molybdenum content in the surface layers of the ferrite particles determined by the XPS surface analysis changed along with a change in the firing temperature.

Thus, by controlling the amount and the type of the molybdenum compound used or the firing temperature, the amount of molybdenum contained in the ferrite particles can be controlled, and ferrite particles containing a desired amount of molybdenum can be produced.

In Examples 7 to 10, in which Na ₂MoO ₄ was used in combination in the raw material, and ZnO was also used, when the ratio of (Ni compound + Fe compound + Zn compound) / (Mo compound) in the raw material was constant at 1/2, the molybdenum content determined by the XRF analysis and the molybdenum content in the surface layers of the ferrite particles determined by the XPS surface analysis changed along with a change in Ni/Fe.

Table 1 lists the values of coercivity measured in Examples 2, 10, and 11 as representatives. The ferrite particles of Examples 2, 10, and 11 had a coercivity of 1.4 × 10 ³ A/m or less, the coercivity being as low as about 1/2 to 1/4 of that of Comparative Example 1, in which MoO ₃ was not used in the raw material, and it was revealed that suitable ones as soft ferrite (asoft magnetic material) were obtained.

On the other hand, the ferrite particles of Comparative Example 1 had a coercivity of 2.5 × 10 ³ A/m, which was a higher value than those in Examples 2, 10, and 11, and it was revealed that it was unsuitable as soft ferrite.

Each configuration and a combination thereof and the like in each embodiment are by way of example, and additions, omissions, substitutions, and other changes of the configuration can be made without departing from the gist of the present invention. The present invention is not limited by each embodiment but is limited only by the scope of the claims.

Claims

Ferrite particles comprising molybdenum.
The ferrite particles according to claim 1, wherein the ferrite particles have a spinel structure.
The ferrite particles according to claim 2, wherein the spinel structure is represented by AFe ₂O ₄ (in the formula, A is one or a plurality of elements selected from Ni, Mn, Cu, Zn, Mg, Ca, and Co) .
The ferrite particles according to claim 1 or 2, wherein a molybdenum content in the ferrite particles is 0.1 to 30%by mas s, a content (Mo ₁) in terms of MoO ₃ with respect to 100%by mas s of the ferrite particles determined by performing X-ray fluorescence (XRF) analysis on the ferrite particles.
The ferrite particles according to claim 1 or 2, wherein a molybdenum content in surface layers of the ferrite particles is 2.0 to 95.0%by mass, a content (Mo ₂) in terms of MoO ₃ with respect to 100%by mass of the surface layers of the ferrite particles determined by performing X-ray photoelectron spectroscopy (XPS) surface analysis on the ferrite particles.
The ferrite particles according to claim 1 or 2, wherein the molybdenum is localized in surface layers of the ferrite particles.
The ferrite particles according to claim 1 or 2, wherein a molybdenum surface layer localization ratio (Mo ₂/Mo ₁) , which is a content (Mo ₂) in terms of MoO ₃ with respect to 100%by mass of surface layers of the ferrite particles determined by performing X-ray photoelectron spectroscopy (XPS) surface analysis on the ferrite particles to a content (Mo ₁) in terms of MoO ₃ with respect to 100%by mass of the ferrite particles determined by performing XRF analysis on the ferrite particles, is 1.0 to 80.
The ferrite particles according to claim 1 or 2, wherein an average particle size of primary particles of the ferrite particles is 0.1 to 100 μm.
The ferrite particles according to claim 1 or 2, wherein the ferrite particles have a specific surface area measured by the BET method of 0.1 to 2.5 m ²/g.
A method for producing the ferrite particles according to claim 1, the method comprising firing a metal compound and an iron compound in presence of a molybdenum compound.
The method for producing the ferrite particles according to claim 10, the method comprising firing the metal compound and the iron compound with a zinc compound further added in the presence of the molybdenum compound.
The method for producing the ferrite particles according to claim 10 or 11, wherein the molybdenum compound is at least one compound selected from the group consisting of molybdenum trioxide, lithium molybdate, potassium molybdate, and sodium molybdate.
The method for producing the ferrite particles according to claim 10 or 11, wherein a firing temperature at the firing is 800 to 1,500℃.