US20230099171A1

US20230099171A1 - L10 type iron-nickel ordered alloy and method of manufacturing l10 type iron-nickel ordered alloy

Info

Publication number: US20230099171A1
Application number: US17/950,431
Authority: US
Inventors: Hiroaki Kura; Takahiro NISHIO; Eiji Watanabe; Yoshiaki Hayashi; Takayuki Yamamoto; Hisashi MAEHARA; Takanori Matsuno
Original assignee: Nichia Corp; Denso Corp
Current assignee: Nichia Corp; Denso Corp
Priority date: 2021-09-27
Filing date: 2022-09-22
Publication date: 2023-03-30
Also published as: DE102022124393A1; CN115852204A

Abstract

An L1₀type iron-nickel (FeNi) ordered alloy has an L1₀type ordered structure and contains sulfur. The L1₀type FeNi ordered alloy may have a sulfur content in a range from 0.01% by mass to 10% by mass. A manufacturing method of an L1₀type FeNi ordered alloy includes performing a nitriding treatment to an FeNi alloy containing sulfur to obtain a nitride containing Fe and Ni.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority from Japanese Patent Application No. 2021-156936 filed on Sep. 27, 2021 and Japanese Patent Application No. 2022-118993 filed on Jul. 26, 2022. The entire disclosures of the above applications are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an L1₀type iron-nickel (FeNi) ordered alloy (hereinafter, also referred to as FeNi superlattice) having an L1₀type ordered structure and a method of manufacturing an L1₀type FeNi ordered alloy.

BACKGROUND

FeNi superlattices are expected as magnet materials having high heat resistance and magnetic device materials such as magnetic recording materials.

SUMMARY

According to an aspect of the present disclosure, an L1₀type FeNi ordered alloy has an L1₀type ordered structure and contains sulfur. According to another aspect of the present disclosure, a manufacturing method of an L1₀type FeNi ordered alloy includes performing a nitriding treatment to an FeNi alloy containing sulfur to obtain a nitride containing Fe and Ni.

BRIEF DESCRIPTION OF DRAWINGS

Objects, features and advantages of the present disclosure will become apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a schematic diagram showing a lattice structure of an L1₀type FeNi ordered structure;

FIG. 2 is a schematic diagram showing a lattice structure of FeNiN;

FIG. 3 is a flowchart showing a synthesis process of an FeNi superlattice according to a first embodiment;

FIG. 4 is a flow chart showing a synthesis process of an FeNi superlattice according to a second embodiment;

FIG. 5 is a diagram showing differences in FeNi superlattice manufacturing conditions, FeNiN formation rate, ammonia efficiency, and the like for each of Examples and Comparative Examples;

FIG. 6 is a diagram showing measurement results of powder X-ray diffraction (XRD) patterns of Comparative Example 2 and Example 3;

FIGS. 7A to 7D are diagrams showing results of cross-sectional TEM observation and composition image observation using a transmission electron microscope (TEM);

FIGS. 8A to 8D are diagrams showing results of cross-sectional TEM observation and composition image observation using the TEM;

FIG. 9 is a diagram showing differences in FeNi superlattice manufacturing conditions, FeNiN formation rate, ammonia efficiency, and the like for each of Examples and Comparative Examples;

FIG. 10 is a diagram showing differences in FeNi superlattice manufacturing conditions, FeNiN formation rate, ammonia efficiency, and the like for each of Examples and Comparative Examples;

FIG. 11 is a diagram showing magnetic characteristics of FeNi superlattice magnetic powder obtained by using FeNiN of Comparative Example 2, Example 3 and Example 7; and

FIG. 12 is a diagram showing X-ray absorption near edge spectra (XANES) for FeNi superlattice magnetic powder of each of Example 3 and Example 4.

DETAILED DESCRIPTION

A high-quality FeNi superlattice can be manufactured using a nitriding and denitriding method in which an FeNi alloy is nitrided by a nitriding treatment to obtain a nitride, and then nitrogen is desorbed from the nitride by a denitriding treatment.
However, in the nitriding and denitriding method, a large amount of ammonia (NH₃) is required in the nitriding treatment for the FeNi alloy as a raw material in order to synthesize FeNiN, which is a precursor of the FeNi superlattice, and a fact that a nitriding efficiency is low is one of factors that increase a production cost of FeNi superlattice magnetic powder.
The present inventors repeatedly studied to improve the nitriding efficiency and confirmed that the nitriding efficiency is lowered because the nitride generated in the nitriding process is decomposed by heat.
According to an aspect of the present disclosure, an L1₀type FeNi ordered alloy has an L1₀type ordered structure and contains sulfur.
When the L1₀type FeNi ordered alloy contains sulfur, that is, when forming the L1₀type FeNi ordered alloy using an FeNi alloy containing sulfur as a raw material, a high nitriding efficiency can be obtained.
According to another aspect of the present disclosure, a manufacturing method of an L1₀type FeNi ordered alloy includes performing a nitriding treatment to an FeNi alloy containing sulfur to obtain a nitride containing Fe and Ni.
In this way, when the FeNi alloy containing sulfur is subjected to the nitriding treatment, a high nitriding efficiency can be obtained.
Hereinafter, embodiments of the present disclosure will be described in detail. However, the embodiments described below are examples for embodying the technical idea of the present disclosure, and the present disclosure is not limited to the following embodiments. In the present disclosure, the term “process” is used not only as an independent process but also as a process included in other process as long as an intended purpose of the process is achieved even if it cannot be dearly distinguished from the other process. Further, the numerical range indicated by using “to” indicates a range including the numerical values before and after “to” as the minimum value and the maximum value, respectively. In the embodiments described hereinafter, the same or equivalent parts will be designated with the same reference numerals.
<L1₀Type FeNi Ordered Alloy>
An L1₀type FeNi ordered alloy of the present embodiment has an L1₀ordered structure and contains sulfur. The L1₀type ordered alloy referred to here means that the regularity is 0.1 or more, and can be preferably 0.5 or more. Further, the upper limit of the regularity may be 1 or less. The L1₀type FeNi ordered alloy according to the present embodiment is suitably used as a magnetic powder and a magnetic material. Examples of the magnetic material include magnetic materials such as sintered magnets, bonded magnets, and magnetic recording materials. The regularity S_regindicates the degree of the order in FeNi superlattice. The L1₀type ordered structure has a structure based on a face-centered cubic lattice, and has a lattice structure as shown in FIG. 1 . In FIG. 1 , an utmost upper layer in a stacking structure on a (001) plane of the face-centered cubic lattice is defined as site I, and a middle layer disposed between the utmost upper layer and an utmost lower layer is defined as site II. In this case, an existing ratio of metal A at site I is defined as x, and an existing ratio of metal B at site I is defined as (1−x). The existing ratio of metal A and metal B at side I is expressed as A_xB_1-x. Similarly, an existing ratio of metal at site II is defined as x, and an existing ratio of metal A at site II is defined as (1−x). The existing ratio of metal A and metal B at site II is expressed as A_1-xB_x. Here, x satisfies a relationship of 0.5≤x≤1. In this case, the regularity S_regis defined as S_reg=2x−1.
The estimation of the regularity S_regis performed using an estimation equation of the regularity S_regin the L1₀type FeNi ordered alloy shown in the following equation 1.
$\begin{matrix} S_{reg} = \sqrt{\frac{{(I_{\sup} / I_{fund})}^{obs}}{{(I_{\sup} / I_{fund})}^{cal}}} & (Equation 1) \end{matrix}$
Here, in the equation 1, “I_sup” is an integrated intensity of a diffraction peak (superlattice diffraction peak) peculiar to the L1₀type ordered alloy and found in an X-ray diffraction (XRD) pattern observed by an XRD method. “I_fund” is an integrated intensity of a diffraction peak (fundamental diffraction peak) appearing in both the FeNi alloy and the L1₀type FeNi ordered alloy. “(I_sup/I_fund)^obs” is a ratio of the integrated intensity of the superlattice diffraction peak and the integrated intensity of the fundamental diffraction peak in the X-ray diffraction pattern measured in each of Examples and Comparative Examples. Further, “(I_sup/I_fund)^cal” is a ratio of the integrated intensity of the superlattice diffraction peak of the FeNi ordered alloy having a regularity of 1 estimated from the Rietbelt simulation to the integrated intensity of the fundamental diffraction peak. As shown in the equation 1, the regularity S_regis obtained by calculating a square root of these two ratios. As an XRD device used here, a general device such as a SmartLab manufactured by Rigaku Co., Ltd. can be used, but the regularity S_regcan be estimated accurately by using Fe-kβ rays as an X-ray.
The lower limit of the sulfur (S) content in the L1₀type FeNi ordered alloy can be, for example, 0.01% by mass or more, preferably 0.03% by mass or more, and more preferably 0.1% by mass or more. The upper limit of the S content in the L1₀type FeNi ordered alloy can be, for example, 10% by mass or less, preferably 2.0% by mass or less, more preferably 1.5% by mass or less, more preferably 1.0% by mass or less, more preferably 0.75% by mass or less, and particularly preferably 0.53% by mass or less. The S content can be measured by a method described in Examples below.
The oxidation number of sulfur (S) in the L1₀type FeNi ordered alloy may include S²⁻ or S⁶⁺ or a mixed state of S²⁻ and S⁶⁺. The oxidation number of sulfur can be measured by XAFS measurement (that is, partial fluorescence yield measurement) described later. The absorption peak appearing at 2482.0±2 eV in the XAFS measurement can be regarded as the peak due to S⁶⁺, and the absorption peak appearing at 2471.5±2 eV can be regarded as the peak due to S²⁻. Based on the presence of these absorption peaks, it can be determined that S²⁻ and S⁶⁺ are present. Further, the oxidation number of sulfur contained in the FeNi superlattice may be other than S²⁻ and S⁶⁺ as long as the effect of improving ammonia efficiency can be obtained.
The L₁₀type FeNi ordered alloy may be composed of particles 100 having the L1₀type ordered structure, as shown in FIGS. 7 and 8 described later. In cases where the L1₀type FeNi ordered alloy is composed of particles 100 having the L1₀type ordered structure, S may be present throughout the particles, may be segregated inside the particles, or may be segregated on the particle surfaces. The state of S can be measured by a method described in Examples below.
In cases where the L1₀type FeNi ordered alloy is composed of particles having the L1₀type ordered structure, the lower limit of the average particle size can be, for example, 10 nm or more, preferably 50 nm or more, and more preferably 100 nm or more. Also, the upper limit of the average particle size can be, for example, 5000 nm or less, preferably 1000 nm or less, and more preferably 500 nm or less. The average particle size can be measured from scanning electron microscope (SEM) images.
The L1₀type FeNi ordered alloy may be composed of secondary particles in which primary particles are aggregated, and in that case, the lower limit of the average particle size of the primary particles may be, for example, 10 nm or more, preferably 30 nm, and more preferably 50 nm or more. Also, the upper limit of the average particle size of the primary particles can be, for example, 1000 nm or less, preferably 500 nm or less. The average particle size of primary particles can be calculated by analyzing the XRD pattern by the Williamson-Hall method.
The ratio of the number of moles of Fe to the total number of moles of Fe and Ni in the L1₀type FeNi ordered alloy may be 0.4 to 0.6, preferably 0.45 to 0.55, and more preferably 0.48 to 0.52. The number of moles of Fe and Ni can be measured by inductively coupled plasma (ICP) emission spectroscopy, energy dispersive X-ray spectroscopy (EDS) using an electron microscope, or the like.
<Manufacturing Method of L1₀Type FeNi Ordered Alloy>
A manufacturing method of the L1₀type FeNi ordered alloy according to the present embodiment includes performing a nitriding treatment to an FeNi alloy containing sulfur (S) to obtain a nitride containing Fe and Ni. According to the present embodiment, the FeNi alloy used in a nitriding process contains S, so that thermal decomposition of the FeNi nitrides generated in the nitriding process can be suppressed, which is thought to improve the nitriding efficiency. The L1₀type FeNi ordered alloy manufactured according to the present embodiment is suitably used as magnetic powder and magnetic material. Examples of the magnetic material include magnetic materials such as sintered magnets, bonded magnets, and magnetic recording materials.
[Nitriding Process]
In the nitriding process, an FeNi alloy containing S (hereinafter also referred to as FeNi—S) is nitrided to obtain a nitride containing Fe and Ni (hereinafter referred to as FeNi nitride). The nitriding treatment is not particularly limited as long as FeNi nitride can be obtained from FeNi—S, but examples the nitriding treatment include gas nitriding with ammonia gas or nitrogen, plasma nitriding, and nitriding using metal amide. Specifically, the nitriding treatment is performed by heat-treating prefabricated FeNi—S under an ammonia gas flow. The flow rate of the ammonia gas in the nitriding treatment can be 0.1 to 10 liters/min, preferably 0.5 to 5 liters/min, with respect to 1 g of FeNi—S. The heat treatment temperature can be, for example, 300 to 500° C., preferably 310 to 475° C., and more preferably 330 to 450° C. The heat treatment time can be, for example, 5 to 50 hours, preferably 10 to 20 hours. The FeNi nitride obtained in the nitriding process may be an S-containing FeNi nitride (hereinafter also referred to as FeNi nitride-S).
The S-containing FeNi alloy used in the nitriding process may have a disordered structure. The disordered structure referred to here may be one in which the arrangement of atoms is random without regularity, or the peak of the L1₀type ordered structure is not observed when measured by X-ray diffraction.
The FeNi—S used in the nitriding process can be produced by adding a compound containing a predetermined amount of sulfur element (hereinafter also referred to as a sulfur compound) to an FeNi alloy produced by a known method, as necessary. The FeNi—S can also be produced by mixing the FeNi alloy and the sulfur compound and then performing a heat treatment, or by reacting the FeNi alloy and the sulfur compound. The FeNi—S can also be produced by partially sulfurizing the FeNi alloy with hydrogen sulfide gas or the like. The sulfur compound should contain elemental sulfur, and examples of the sulfur compound include sulfur, organic sulfur compounds, metal sulfides such as iron sulfide and nickel sulfide, and sulfates such as ammonium sulfate, iron sulfate, and nickel sulfate.
FeNi—S used in the nitriding process may be synthesized during the nitriding process. Specifically, for example, FeNi nitride is formed by heat-treating the FeNi alloy under a mixed gas flow of ammonia gas and hydrogen sulfide so that synthesis and nitriding of FeNi nitride-S are performed in parallel (sulphonitriding).
The ratio of the number of moles of Fe to the total number of moles of Fe and Ni in FeNi—S used in the nitriding process may be 0.4 to 0.6, preferably 0.45 to 0.55, and more preferably 0.48 to 0.52.
The content of sulfur (S) in FeNi—S used in the nitriding process can be, for example, 0.01% by mass to 10% by mass, preferably 0.02% by mass to 2.0% by mass, more preferably 0.02% by mass to 1.5% by mass, more preferably 0.03% by mass to 1.0% by mass, and particularly preferably 0.05% by mass to 0.7% by mass. When the content of S in FeNi—S used in the nitriding process is within the above range, there is a tendency that the nitriding can be promoted while suppressing the deterioration of the magnetic performance of the finally obtained FeNi ordered alloy. The content of sulfur can be measured by the method described in Examples below.
Examples of FeNi nitride obtained in the nitriding process include FeNiN, Fe₂Ni₂N, and the like, and it is preferable that a ratio of FeNiN is large in order to obtain the L11 type FeNi ordered alloy. FeNiN has a crystal structure as shown in FIG. 2 and can be identified from an XRD diffraction pattern. The ratio of FeNi nitride contained after the nitriding process can be 90% by mass or more of the entire product. The ratio of FeNiN in the FeNi nitride can be 50% by mass or more, and preferably 80% by mass or more. The ratio of nitrides and the ratio of FeNiN after the nitriding process can be calculated by analyzing the XRD diffraction pattern by the reference intensity ratio (RIR) method.
The ratio of the number of moles of Fe to the total number of moles of Fe and Ni in the FeNi nitride obtained in the nitriding process may be 0.4 to 0.6, preferably 0.45 to 0.55, and more preferably 0.48 to 0.52. The number of moles of Fe and Ni can be measured by inductively coupled plasma (ICP) emission spectroscopy, energy dispersive X-ray spectroscopy (EDS) using an electron microscope, or the like.
The FeNi nitride obtained in the nitriding process may contain sulfur (S). In cases where the FeNi nitride contains S, the lower limit of the S content can be, for example, 0.01% by mass or more, preferably 0.03% by mass or more, and more preferably 0.05% by mass or more. The upper limit of the S content in the L1₀type FeNi ordered alloy can be, for example, 10% by mass or less, preferably 2.0% by mass or less, more preferably 1.5% by mass or less, more preferably 1.0% by mass or less, and particularly preferably 0.7% by mass or less. The S content can be measured by a method described in Examples below.
In cases where the FeNi nitride obtained in the nitriding process contains S, the FeNi nitride may be composed of particles. In cases where the FeNi nitride is composed of particles, S may be present throughout the particles, or may be segregated inside the particles. Further, S may be segregated on the particle surface. The state of S can be measured by a method described in Examples below.
In cases where the FeNi nitride obtained in the nitriding process is composed of particles, the lower limit of the average particle size can be, for example, 10 nm or more, preferably 50 nm or more, and more preferably 100 nm or more. Also, the upper limit of the average particle size can be, for example, 5000 nm or less, preferably 1000 nm or less, and more preferably 500 nm or less. The average particle size can be measured from scanning electron microscope (SEM) images.
The FeNi nitride obtained in the nitriding process may be composed of secondary particles in which primary particles are aggregated, and in that case, the lower limit of the average particle size of the primary particles can be, for example, 10 nm or more, preferably 30 nm or more, and more preferably 50 nm or more. Also, the upper limit of the average particle size can be, for example, 1000 nm or less, preferably 500 nm or less. The average particle size of primary particles can be calculated by analyzing the XRD pattern by the Williamson-Hall method.
In the nitriding process, the nitriding treatment is performed to FeNi—S. Accordingly, it is possible to obtain a high nitriding efficiency, as shown in Examples described later. The nitriding efficiency in the nitriding process can be greater than 4.7×10⁻⁵, preferably greater than 10×10⁻⁵, and more preferably greater than 20×10⁻⁵. The term “nitriding efficiency” used in the present disclosure means the number obtained by dividing the amount (g) of FeNiN formed by the nitriding treatment by the nitrogen raw material (g) consumed in the nitriding treatment. A nitriding efficiency in a case where ammonia is used as nitrogen source (hereinafter, referred to as an ammonia efficiency) indicates the number obtained by dividing the formation amount (g) of FeNiN by the amount (g) of consumed ammonia, and is the ammonia amount required for synthesizing FeNiN. A higher numerical value of ammonia efficiency means that FeNiN can be synthesized with a smaller amount of ammonia.
In the nitriding process, an L1₀type FeNi ordered alloy containing S may be used as the FeNi alloy. The L1₀type FeNi ordered alloy containing S can be obtained by adding a predetermined amount of sulfur compound as necessary to the L1₀type FeNi ordered alloy manufactured by a known method, in addition to the L1₀type FeNi ordered alloy containing S described in the present embodiment. The L1₀type FeNi ordered alloy containing S can also be produced by mixing an L1₀type FeNi ordered alloy and a sulfur compound and then performing a heat treatment, or by reacting an L1₀type FeNi ordered alloy with a sulfur compound. The L1₀type FeNi ordered alloy containing S can also be produced partially sulfurizing an L1₀type FeNi ordered alloy with hydrogen sulfide gas or the like. The sulfur compound is as described above. In cases where FeNi—S having the L1₀type ordered structure is used, an improvement in the regularity can be expected.
[Denitriding Process]
In the denitriding process, the FeNi nitride obtained in the above-described nitriding process is denitrided to obtain an L1₀type FeNi ordered alloy. Specifically, after pulverizing the FeNi nitride obtained in the nitriding process, a denitriding treatment can be performed by subjecting it to heat treatment in a hydrogen atmosphere. The flow rate of hydrogen in the denitriding treatment can be 0.01 to 10 liters/min, preferably 0.1 to 5 liters/min, with respect to 1 g of FeNi nitride-S. The heat treatment temperature can be, for example, 100 to 400° C., preferably 200 to 350° C. The heat treatment time can be, for example, 1 to 24 hours, preferably 2 to 10 hours. The L1₀type FeNi ordered alloy obtained in the denitriding process may be an L1₀type FeNi ordered alloy containing S.
Examples of a method for manufacturing the FeNi alloy containing S used in the nitriding process will be described below.

First Embodiment

As shown in FIG. 3 , a manufacturing method according to a first embodiment includes a reduction process of reducing an FeNi oxide containing S (hereinafter, also referred to as FeNi oxide-S) to obtain an FeNi—S.
A reduction method in the reduction process is not particularly limited, but for example, the FeNi—S can be obtained by heat-treating the FeNi oxide containing S in a reducing gas atmosphere. The flow rate of the reducing gas can be 1 liter/min, preferably 0.5 to 10.0 liters/min, with respect to 8.5 g of the FeNi oxide-S. The heat treatment temperature can be, for example, 300 to 700° C., and preferably 450 to 700° C. The heat treatment time can be, for example, 1 to 10 hours, preferably 1.5 hours. Examples of the reducing gas include hydrogen and carbon monoxide, and hydrogen is preferred from the viewpoint of reducing properties.
The ratio of the number of moles of Fe to the total number of moles of Fe and Ni in the FeNi oxide-S may be 0.4 to 0.6, preferably 0.45 to 0.55, and more preferably 0.48 to 0.52.
The FeNi oxide-S used in the reduction process may contain an Fe oxide, a Ni oxide, or an oxide containing Fe and Ni. Further, the Fe oxide, the Ni oxide, and the oxide containing Fe and Ni may each contain S. The oxide containing Fe and Ni as used herein means containing Fe element and Ni element in one oxide particle.
The FeNi oxide-S used in the reduction process can be produced by adding a predetermined amount of sulfur compound as necessary to the FeNi oxide manufactured by the present embodiment or a known method. The FeNi oxide-S can also be produced by mixing the FeNi oxide and the sulfur compound and then performing a heat treatment, or by reacting an FeNi oxide and a sulfur compound. The FeNi oxide-S can also be produced by partially sulfurizing the FeNi oxide with hydrogen sulfide gas or the like. The sulfur compound is as described above.
The FeNi oxide-S used in the reduction process may be synthesized during the reduction process. Specifically, for example, an FeNi oxide is heat-treated under a mixed gas flow of hydrogen gas and hydrogen sulfide so that synthesis and reduction of the FeNi oxide-S are performed in parallel.
The Fe oxide is not particularly limited. Examples of the Fe oxide include FeO, Fe₂O₃, Fe₃O₄, and oxides obtained by oxidizing iron metal, iron hydroxide, iron carbonate, iron chloride, iron iodide, iron bromide, iron sulfate, iron nitrate, iron phosphate, and iron oxalate. Among them, iron sulfate is preferable because it serves as a sulfur source for the Fe oxide containing S. The Fe oxide containing S may be produced by the preparing method of the FeNi oxide-S described above.
The Ni oxide is not particularly limited. Examples of the Ni oxide include NiO, and oxides obtained by oxidizing nickel metal, nickel hydroxide, nickel carbonate, nickel chloride, nickel iodide, nickel bromide, nickel sulfate, nickel nitrate, nickel phosphate, and nickel oxalate. Among them, nickel sulfate is preferable because it serves as a sulfur source for the Ni oxide containing S. The Ni oxide containing S may be produced by the preparing method of the FeNi oxide-S described above.
The oxide containing Fe and Ni can be produced by mixing a solution containing Fe and Ni with a precipitant to obtain a precipitate containing Fe and Ni (precipitation process), and heat-treating the precipitate to obtain the oxide containing Ni and Ni (oxidation process). According to this method, it is easy to control the average particle size and particle size distribution of the resulting oxide containing Fe and Ni, and the distribution of the Fe element and the Ni element in the oxide containing Fe and Ni tends to be uniform.
[Precipitation Process]
In the precipitation process, Fe raw material and Ni raw material are dissolved in a strongly acidic solution to prepare a solution containing Fe and Ni.
The Fe raw material and Ni raw material are not limited as long as they can be dissolved in an acidic solution. Examples of the Fe raw material include iron metal, iron oxide, iron hydroxide, iron carbonate, iron chloride, iron iodide, iron sulfate, iron nitrate, iron phosphate, iron oxalate, and the like. It is preferable to use iron metal, iron carbonate, iron sulfate or iron chloride, and it is more preferable to use iron sulfate because it serves as a sulfur source for the precipitate containing S. Examples of the Ni raw material include nickel metal, nickel oxide, nickel hydroxide, nickel carbonate, nickel chloride, nickel iodide, nickel sulfate, nickel nitrate, nickel phosphate, and nickel oxalate. It is preferable to use nickel metal, nickel carbonate, nickel sulfate or nickel chloride, and it is more preferable to use nickel sulfate because it serves as a sulfur source for the precipitate containing S. Examples of the acidic solution include sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, and the like. Among them, sulfuric acid is preferred because it serves as a sulfur source for the precipitate containing S, Fe and Ni. The concentration of the solution containing Fe and Ni can be appropriately adjusted within a range in which the Fe raw material and the Ni raw material are substantially dissolved in the acidic solution.
The ratio of the number of moles of Fe to the total number of moles of Fe and Ni in the solution containing Fe and Ni may be 0.4 to 0.6, preferably 0.45 to 0.55, and more preferably 0.48 to 0.52.
The precipitate containing Fe and Ni is obtained by reacting the solution containing Fe and Ni with the precipitant. In the reaction between the solution containing Fe and Ni and the precipitant, the precipitant may be added to the solution containing Fe and Ni, or the solution containing Fe and Ni may be added to the precipitant. The solution containing Fe and Ni referred to here may be a solution containing Fe and Ni when reacted with the precipitant. Raw materials containing Fe and Ni may be prepared as separate solutions, and the solutions may be added to react with the precipitant. Even in cases where they are prepared as separate solutions, adjustments are produced as appropriate within the range in which each raw material is substantially dissolved in the acidic solution. The precipitant is not limited as long as it reacts with the solution containing Fe and Ni to obtain the precipitate. Examples of the precipitant include oxalic acid and alkaline solutions such as an aqueous sodium hydroxide solution, an aqueous sodium hydrogen carbonate solution, an aqueous potassium hydroxide solution, and an aqueous lithium hydroxide solution. The precipitate can also be obtained by blowing carbon dioxide into the solution containing Fe and Ni. Examples of the precipitate include oxalate, carbonate, hydroxide, and the like.
The precipitation process may include a process of separating and washing the precipitate. As a method for separating the precipitate, for example, after adding a solvent (preferably water) to the obtained precipitate and mixing it, a filtration method, a decantation method, or the like can be used. In addition, washing can be performed by repeating the same process for the precipitate that has once been separated.
After separating the precipitate, in order to prevent the precipitate from re-dissolving in the remaining solvent in the heat treatment of the subsequent oxidation process and aggregating the precipitate when the solvent evaporates, it is preferable to remove the solvent from the precipitate. As a specific example of a method for removing the solvent, for example, in cases where water is used as the solvent, the precipitate may be dried in an oven at a temperature in a range from 70 to 200° C. for 5 to 12 hours. After drying, if necessary, the particles may be crushed or pulverized to adjust the particle size.
The precipitate containing S, Fe and Ni can be obtained by adding a predetermined amount of a sulfur compound as necessary during or after the reaction between the solution containing Fe and Ni and the precipitant, and can be obtained by adding a sulfur compound in the process of separating and washing. The precipitate containing S, Fe and Ni can also be produced by adding a predetermined amount of a sulfur compound to the obtained precipitate, or by reacting the precipitate with the sulfur compound, as necessary. The reaction between the precipitate and the sulfur compound can be performed, for example, by mixing the precipitate and the sulfur compound and then heat-treating the mixture. The precipitate containing S, Fe and Ni can also be produced by sulfurizing a part of the precipitate with hydrogen sulfide gas or the like. The sulfur compound is as described above.
[Oxidation Process]
The oxidation process is a process of obtaining an oxide containing Fe and Ni by heat-treating the precipitate containing Fe and Ni obtained in the precipitation process. The oxidation process can convert the precipitate to the oxide, for example, by heat treatment. When the heat treatment of the precipitate is performed, the heat treatment must be performed in the presence of oxygen, and can be performed, for example, in an air atmosphere. Moreover, since the heat treatment must be performed in the presence of oxygen, it is preferable that the non-metallic portion of the precipitate contains an oxygen atom. When the precipitate containing S, Fe and Ni is used in the oxidation process, the FeNi oxide-S can be obtained. The obtained FeNi oxide-S may be pulverized or pulverized to adjust the particle size, as necessary.
The heat treatment temperature in the oxidation process (hereinafter referred to as oxidation temperature) is not particularly limited, but the heat treatment temperature can be, for example, 200 to 800° C., preferably 350 to 450° C. The heat treatment time can be, for example, 4 to 24 hours, preferably 8 hours.
The obtained oxide is an oxide particle in which Fe and Ni are sufficiently microscopically mixed, and the shape of the precipitate, particle size distribution and the like are reflected.
The precipitate containing S, Fe and Ni used in the oxidation process may be synthesized during the oxidation process. Specifically, for example, the precipitate containing Fe and Ni is heat-treated under a mixed gas flow of air and hydrogen sulfide so that synthesis and oxidation of the precipitate containing S, Fe, and Ni are performed in parallel.

Second Embodiment

The following describes a second embodiment. The present embodiment is different from the first embodiment in a manufacturing method of FeNiN, and the other parts are similar to those of the first embodiment. Therefore, only a part different from the first embodiment will be described below. Hereinafter, a manufacturing method of an FeNi superlattice according to the present embodiment will be described with reference to the flowchart showing in FIG. 4 .
First, as shown in FIG. 4 , an FeNi alloy to which S is added is produced. Specifically, first, FeNi powder is prepared. It is preferable to prepare FeNi powder having a composition ratio of Fe:Ni=50:50. The composition ratio of Fe:Ni may be about 50:50. For example, it is sufficient that the proportion of Fe is 50±3% and the proportion of Ni is the remaining {100−(50±3)}%. As such FeNi powder, for example, FeNi nanoparticles synthesized by the thermal plasma method manufactured by Nisshin Engineering Co., Ltd., FeNi powder synthesized by the gas atomization method manufactured by Epson Atmix, and the like can be used.
Next, the FeNi powder is reacted in a mixed gas of H₂S gas and nitrogen (N₂) gas. As a result, FeNi—S, which is the FeNi alloy to which S is added, is obtained. For example, 3% H₂S gas+97% N₂gas is used as the mixed gas, and a heat treatment is performed at 200 to 500° C. for 2 to 24 hours to obtain the FeNi—S.
After that, a nitriding process is performed in the same manner as in the first embodiment to synthesize the FeNiN—S, and then a denitriding treatment is further performed to obtain the FeNi superlattice. The FeNi superlattice obtained as described above also contains S. Also in this case, as shown in Examples described later, it is possible to obtain high ammonia efficiency.
Hereinafter, Examples in which FeNi—S is produced by various methods including the manufacturing methods of the above-described embodiments and then subjected to the nitriding and denitriding treatment will be compared with Comparative Examples using FeNi containing no sulfur.
FIG. 5 is a diagram showing how the differences in the manufacturing conditions of the FeNi superlattice, the formation rate of FeNiN, the ammonia efficiency, and the like changed in each Example and Comparative (COMP) Example. In a S doping method in FIG. 5 , (1) means the manufacturing method of the first embodiment, (2) means the manufacturing method of the second embodiment, and the details of Examples 1 to 5 will be described later. Example 6 shows a case where the FeNi—S is synthesized by reacting the FeNi alloy particles produced by the gas atomization method of the second embodiment with ammonium sulfate. Example 7 shows a case where the FeNi—S is synthesized by reacting ammonium sulfate with FeNi alloy particles produced by the thermal plasma method in the second embodiment. Comparative Examples 1 and 2 show cases where FeNi produced by the thermal plasma method is subjected to the nitriding and denitriding treatment without reacting with ammonium sulfate.
Note that a sulfur content (mass %) shown in FIG. 5 , that is, the mass ratio of S to the total mass of Fe, Ni, and S is evaluated using a generally used elemental mass analysis method. For example, the sulfur content can be identified by inductively coupled plasma (ICP) emission spectroscopy, energy dispersive X-ray spectroscopy (EDS) using an electron microscope, or the like. The sulfur content (mass %) is substantially the same before and after the nitriding and denitriding treatment. The FeNiN formation rate is the ratio of the amount of FeNiN formed after the nitriding treatment to the amount of FeNi alloy before the nitriding treatment, and is calculated from the reference intensity ratio (RIR) method by measuring the powder XRD pattern. More specifically, the FeNiN formation rate is a rate of the amount of FeNiN actually obtained with respect to the ideal formation amount of FeNiN when it is assumed that the total amount of FeNi alloy contained in the raw material before the nitriding treatment is obtained as FeNiN by the nitriding treatment. The RIR values of FeNiN, Fe₂Ni₂N, and FeNi alloy stored in the database of the analysis software (PDXL2) attached to the XRD device (SmartLab manufactured by Rigaku Corporation) were used for the analysis of the formation rate by the RIR method. Further, the efficiency improvement rate indicates the rate of the ammonia efficiency in each of Comparative Example 1 and Examples 1 to 7 in cases where Comparative Example 2 is used as a reference (REF).
Hereinafter, Examples 1 to 7, 9, 10, 12, and 13 will be described in detail. Unless otherwise specified, “%” is based on mass.

Example 1

[Precipitation Process]
First, 0.34 liters of a 5% by mass iron sulfate aqueous solution and 0.2 liters of a 9% by mass nickel sulfate aqueous solution were added to 3 liters of a 10% by mass oxalic acid aqueous solution that is being stirred so that the molar ratio of iron and nickel becomes 50:50. Accordingly, an oxalate slurry containing Fe, Ni and S was obtained. After the obtained slurry was washed with pure water by decantation, an oxalate containing Fe and Ni was separated into solid and liquid. The separated oxalate containing Fe and Ni was dried in an oven at 100° C. for 10 hours. The S contained in the oxalate is considered to be due to the sulfate ions of iron sulfate or nickel sulfate as raw materials.
[Oxidation Process]
Subsequently, 50 g of the resulting oxalate containing Fe, Ni and S was heat-treated at 400° C. for 8 hours in air. After cooling, an oxide containing Fe, Ni and S was obtained.
[Reduction Process]
Subsequently, 8.5 g of the oxide containing Fe, Ni and S was heat-treated at 450° C. for 1.5 hours in a hydrogen gas atmosphere (hydrogen flow rate 1 liter/min). After cooling, an FeNi alloy containing S was obtained. The sulfur content in the alloy was 0.03% by mass. The sulfur content was determined by dissolving the FeNi alloy containing S in hydrochloric acid and measuring the mass ratio of S to the total mass of Fe, Ni, and S by the ICP-AES method using an apparatus named Optima 8300.
[Nitriding Process]
Subsequently, 0.4 g of the FeNi alloy containing S was heat-treated at 335° C. for 40 hours in an ammonia gas atmosphere (ammonia flow rate: 1 liter/min) to obtain an FeNiN. The FeNiN formation rate was 95%. The FeNiN formation rate was measured by an X-ray diffraction method (apparatus name: Smartlab, tube current: 200 mA, tube voltage: 45 kV) using kβ rays of Fe (wavelength: 1.75653 Å), and was defined as the ratio of the integrated intensity of the FeNiN peak (40°) to the sum of the integrated intensity of the FeNiN peak and the integrated intensity of the Fe₂Ni₂N peak (41.5°). The FeNiN formation rate was calculated using the reference intensity ratio (RIR) method by measuring the powder XRD pattern in addition to the mass of the FeNi alloy as the raw material and the mass of the obtained FeNi nitride.
[Denitriding Process]
The obtained FeNiN was heat-treated at 250° C. for 20 hours in a hydrogen gas atmosphere (hydrogen flow rate: 1 liter/min) to obtain an L1₀type FeNi ordered alloy. It was confirmed that the sulfur content in the L1₀type ordered alloy was 0.03% by mass, which was almost the same amount as in the FeNi alloy containing S obtained in the reduction process. The sulfur content was measured by the ICP-AES method after dissolving the obtained FeNi alloy in hydrochloric acid, and defined as the mass ratio of S to the total mass of Fe, Ni, and S.

Example 2

The same processes as in Example 1 were performed except that the heat treatment temperature in the nitriding process was changed to 415° C.

Example 3

The same processes as in Example 2 were performed except that ammonium sulfate was added and a heat treatment was performed to the oxalate containing Fe, Ni and S obtained in Example 1. Ammonium sulfate was added in an amount of 0.02% by mass with respect to the oxalate. As a result, the sulfur content in the alloy particles was 0.05% by mass.

Example 4

The same processes as in Example 2 were performed except that ammonium sulfate was added and a heat treatment was performed to the oxalate containing Fe, Ni and S obtained in Example 1. Ammonium sulfate was added in an amount of 0.11% by mass with respect to the oxalate. As a result, the sulfur content in the alloy particles was 0.14% by mass.

Example 5

The same processes as in Example 2 were performed except that ammonium sulfate was added and a heat treatment was performed to the oxalate containing Fe, Ni and S obtained in Example 1. Ammonium sulfate was added in an amount of 0.45% by mass with respect to the oxalate. As a result, the sulfur content in the alloy particles was 0.48% by mass.
In each of Comparative Examples 1 and 2, since the FeNi superlattice was manufactured by a conventional manufacturing method in which sulfur was not added to FeNi, the doping method of sulfur (S Doping method) and the sulfur content (mass %) are indicated by “-” that means “no”. In a case where the amount of NH₃was 5 liters/min and the nitriding was performed at 300° C. for 40 hours as in Comparative Example 2, the formation rate of FeNiN was 99%, which is almost 100%, so the ammonia efficiency at this time was 4.7 (×10⁻⁵) is used as the reference. On the other hand, when the amount of NH₃is 1 liter/min, which is smaller than that in Comparative Example 2, as in Comparative Example 1, the formation rate of FeNiN is only 15%. The ammonia efficiency was only 3.6 (×10⁻⁵), and the efficiency improvement rate was 0.76, which is significantly lower than that of Comparative Example 2, which serves as the reference.
From this, it can be seen that in cases where FeNi to which sulfur is not added is subjected to the nitriding and denitriding treatment, the amount of NH₃cannot be reduced, and unless the amount of NH₃is about 5 liters/min, the FeNiN formation rate cannot be increased and the ammonia efficiency decreases.
The temperature during the nitriding treatment was set to 300° C. In cases of FeNi to which sulfur is not added, when the temperature exceeds 300° C., the FeNiN formation rate is not stabilized, and the ammonia efficiency similarly decreases. The time for the nitriding treatment was set to 40 hours. If the time is shorter than 40 hours, the FeNiN formation rate is not stabilized, and the ammonia efficiency similarly decreases. The sample amount was set to 400 mg. If the amount of FeNi to be nitrided at one time is increased, the FeNiN formation rate is not stabilized, and the ammonia efficiency similarly decreases. Therefore, as described above, if the amount of NH₃is reduced, the nitriding treatment is shortened, or the amount of FeNi to be nitrided at one time is increased, the ammonia efficiency decreases, and pure FeNiN cannot be obtained.
On the other hand, in each of Examples 1 to 7, FeNi to which sulfur was added was subjected to the nitriding and denitriding treatment, and in all cases of Examples 1 to 7, the ammonia efficiency higher than the reference was obtained.
In Example 1, the sulfur was as small as 0.03 (mass %), but even if the amount of NH₃was reduced to 1 liter/min under nitriding conditions at 335° C. for 40 hours, the FeNiN formation rate was a high value of 95% and the ammonia efficiency was a high value of 22.9 (×10⁻⁵). The efficiency improvement rate was also a high value of 4.8.
In Example 2, with the same sulfur content as in Example 1, only the nitriding temperature was increased to 415° C. Although the FeNiN formation rate decreased to 43%, the ammonia efficiency was 10.4 (×10⁻⁵) which is higher than the reference. The efficiency improvement rate was also a high value of 2.2.
In Example 3, the sulfur content was set to 0.05 (mass %), which was higher than in Example 1, FeNiN The formation rate was as high as 97%, and the ammonia efficiency was a high value of 23.6 (×10⁻⁵). The efficiency improvement rate was also a high value of 4.9. As will be described later, it has been confirmed that the FeNiN formation rate can be increased by changing the temperature of the nitriding treatment according to the sulfur content. In Example 3, the nitriding temperature was set to 415° C. so as to increase the FeNiN formation rate. Therefore, the FeNiN formation rate could be a particularly high value, and a higher ammonia efficiency was obtained.
In Example 4, the sulfur content was increased to 0.14 (mass %), which is higher than in Example 3, and the nitriding conditions were the same as in Example 3. The FeNiN formation rate was maintained at a high value of 90%, and the ammonia efficiency was maintained at a high value of 21.8 (×10⁻⁵). The efficiency improvement rate was also a high value of 4.6. In Examples 5 to 7, the sulfur content was increased more than in Example 4, and the same nitriding conditions as in Examples 3 and 4 were used. In Example 5, the sulfur content was set to 0.48 (mass %), the FeNiN formation rate was 94%, the ammonia efficiency was 22.8 (×10⁻⁵), and the efficiency improvement rate was 4.8, all of which were high values. In Example 6, the sulfur content was set to 1.05 (mass %), the FeNiN formation rate was 92%, the ammonia efficiency was 22.1 (×10⁻⁵), and the efficiency improvement rate was 4.7, all of which were high values. In Example 7, the sulfur content was set to 2.26 (mass %), the FeNiN formation rate was 88%, the ammonia efficiency was 21.2 (×10⁻⁵), and the efficiency improvement rate was 4.5, all of which were high values.
For reference, FIG. 6 shows the XRD pattern measurement results for Comparative Example 2 and Example 3. Circles shown in FIG. 6 are XRD diffraction peaks attributable to FeNiN. It can be seen that in both Comparative Example 2 and Example 3, high-purity FeNiN was obtained.
From these Examples 1 to 7, in cases where the FeNi superlattice is produced by adding sulfur to FeNi and then performing the nitriding and denitriding treatment, the FeNiN formation rate can be increased and the ammonia efficiency can be increased compared to the conventional manufacturing method in which sulfur is not added.
Specifically, by setting the sulfur content to 0.03 (mass %) or more, the ammonia efficiency can be improved by a factor of 2 or more compared to the conventional manufacturing method. Therefore, in the FeNi superlattice of the present embodiment, by increasing the ammonia efficiency, at least one of reducing the amount of NH₃, shortening the nitriding time, and increasing the amount of material to be nitrided at one time can be performed, which reduces costs.
Further, as in Examples 1 to 5, the FeNi superlattice produced by the manufacturing method of the first embodiment was subjected to cross-sectional TEM observation and composition image observation using a TEM, and the results shown in FIGS. 7A to 7D were obtained. FIG. 7A shows the result of cross-sectional TEM observation, FIG. 7B shows a S composition image, FIG. 7C shows an Fe composition image, and FIG. 7D shows a Ni composition image.
In a case where the particles 100 of the FeNi superlattice are distributed as shown in FIG. 7A, FeNi is uniformly present as shown in the composition images of Fe and Ni shown in FIG. 7C and FIG. 7D, and the FeNi superlattice is formed in good condition. Then, as shown in FIG. 7B, it can be seen that S is present in a state distributed throughout, corresponding to the distribution of the particles 100 of the FeNi superlattice. The fact that S is present throughout the particles 100 of the FeNi superlattice means that S is present in the entire FeNi alloy or FeNiN particles 100 even in the manufacturing process of the FeNi superlattice. In this way, it can be seen that a high ammonia efficiency can be obtained in cases where S is present throughout the particles 100 of the superlattice, in other words, in cases where S is present throughout the particles 100 in the FeNi alloy or the FeNiN in the manufacturing process of the FeNi superlattice.
As shown in FIG. 7A, FIG. 7C and FIG. 7D, in each Examples 1 to 5, a particle diameter of the FeNi superlattice was about 100 nm, but the particle diameter can be appropriately changed according to the purpose of applying the FeNi superlattice, and can be changed, for example, in the range of 100 nm to several μm. According to experiments, the particle diameter of the FeNi superlattice changes according to the sintering temperature for obtaining the FeNi oxide and the reduction temperature for obtaining the FeNi alloy, and there is a tendency that the particle diameter tends to increase with increase in temperature. Since changes in particle diameter affect magnetic properties and environmental resistance, the sintering temperature and reduction temperature should be set according to the purpose of application of the FeNi superlattice so that the desired magnetic properties and environmental resistance can be obtained.
On the other hand, as in Examples 6 and 7, the FeNi superlattice manufactured by the manufacturing method of the second embodiment was also subjected to cross-sectional TEM observation and composition image observation. Then, the results with a large particle diameter were extracted, and are shown in FIG. 8A to FIG. 8D. FIG. 8A shows the result of cross-sectional TEM observation, FIG. 8B shows a S composition image, FIG. 8C shows an Fe composition image, and FIG. 8D shows a Ni composition image.
Even in a case where the FeNi superlattice with a large particle size is confirmed as shown in FIG. 8A, FeNi is uniformly present in the particles 100 as shown in the composition images of Fe and Ni shown in FIG. 8C and FIG. 8D, and the FeNi superlattice is formed in good condition. Then, as shown in FIG. 8B, it can be seen that S is segregated and present on the surface of the particles 100 of the FeNi superlattice. The fact that S is segregated on the surface of the particles 100 of the FeNi superlattice means that S is segregated on the surface of the FeNi alloy or FeNiN particles even in the manufacturing process of the FeNi superlattice. Thus, in cases where S is segregated on the surface of the particles 100 of the FeNi superlattice, in other words, even if S is segregated on the particle surface of the FeNi alloy or FeNiN in the manufacturing process of the FeNi superlattice, a high ammonia efficiency can be obtained.
Next, the FeNiN formation rate, the ammonia efficiency, and the efficiency improvement rate were examined by changing the temperature during the nitriding treatment while keeping the sulfur content. Specifically, in the case where the sulfur content was set to 0.14 (mass %) as in Example 4 described above, the experiment was conducted by changing the temperature of the nitriding treatment. Moreover, as comparative examples, a similar experiment was conducted with respect to the conventional manufacturing method. FIG. 9 is a diagram showing the results. In FIG. 9 , Example 4 is the same as Example 4 in FIG. 5 . Examples 9 and 10 and Comparative Examples 9 and 10 show cases in which only the temperature of the nitriding treatment is changed from Example 4. Further, Comparative Example 2 is the same as Comparative Example 2 in FIG. 5 . Comparative Examples 3 to 6 show cases in which only the temperature of the nitriding treatment is changed from Comparative Example 2, and the NH₃flow rate remains at 5 liters/min.
In cases where the heat treatment temperatures of the nitriding treatment were 375° C. and 450° C. as shown in Examples 9 and 10, the FeNiN formation rates were 76% and 80%, respectively, but the ammonia efficiencies were high values of 18.4 (×10⁻⁵) and 19.2 (×10⁻⁵), respectively. In addition, the efficiency improvement rates were also high values of 3.9 and 4.1, respectively. Furthermore, even in a case where the temperature of the nitriding treatment was set to 415° C., which is a temperature between Examples 9 and 10, as in Example 4, the ammonia efficiency and the efficiency improvement rate were high.
Further, in cases where the heat treatment temperature of the nitriding treatment was 325° C. and 500° C. as shown in Comparative Examples 9 and 10, the FeNiN formation rates were 12% and 3%, respectively, and the ammonia efficiencies were 2.9 (×10⁻⁵) and 0.72 (×10⁻⁵), respectively. The efficiency improvement rates were 0.61 and 0.15, respectively. From these results, it can be seen that, in cases where 0.14% by mass of S is added, the ammonia efficiency and efficiency improvement rate are increased by setting the temperature of the nitriding treatment to a temperature range higher than 325° C. and lower than 500° C. More preferably, it can be seen that the ammonia efficiency and efficiency improvement rate can be increased by setting the nitriding temperature in the temperature range from 375 to 450° C.
On the other hand, in Comparative Examples 2 and 4, the FeNiN formation rates, ammonia efficiencies, and efficiency improvement rates were relatively high values, but in Comparative Examples 3, 5, and 6, the FeNiN formation rates, ammonia efficiencies, and efficiency improvement rates were relatively low or zero.
Specifically, in cases where the temperatures of the nitriding treatment were 300° C. and 325° C. as in Comparative Examples 2 and 4, the FeNiN formation rates were 99% and 95%, respectively, and the ammonia efficiencies were 4.7 (×10⁻⁵) and 4.6 (×10⁻⁵). The efficiency improvement rates were 1 and 0.98, respectively.
When the temperature of the nitriding treatment was 275° C., which is lower than 300° C., as in Comparative Example 3, the FeNiN formation rate was 0%, the ammonia efficiency was 0, and the efficiency improvement rate was 0. Similarly, in cases where the temperatures of the nitriding treatment were 375° C. and 415° C. as in Comparative Examples 5 and 6, the FeNiN formation rates were 9% and 0%, respectively, and the ammonia efficiencies were 0.43 (×10⁻⁵) and 0, respectively, and the efficiency improvement rates were low values of 0.09 and 0, respectively. These results show that in cases where S is not added, the desired ammonia efficiency and efficiency improvement rate cannot be obtained unless the temperature of the nitriding treatment is in the range from 300 to 325° C.
As described above, in cases where S is added, the desired ammonia efficiency and efficiency improvement rate can be obtained by setting the temperature of the nitriding treatment to at least a temperature range from 375 to 450° C. On the other hand, in the case of the conventional manufacturing method in which S is not added, the desired ammonia efficiency and efficiency improvement rate cannot be obtained unless the temperature of the nitriding treatment is at least in the temperature range from 300 to 325° C. Therefore, by adding S, it is possible to widen the temperature range in which the desired ammonia efficiency and efficiency improvement rate can be obtained, and it is also possible to raise the process temperature and expand the process window. If the process temperature can be raised, the FeNiN—S can be synthesized at a higher temperature, so that the crystallinity of the FeNi superlattice can be improved. Accordingly, properties of the FeNi superlattice can be improved. Further, if the process window can be expanded, the temperature of the nitriding treatment can be set within the range of the process window, which facilitates temperature control.
The above has described examples in which the sulfur content is 0.14 mass % as in Example 4, and the temperature of the nitriding treatment should be at least in the temperature range from 375 to 450° C. based on the results of Examples 4, 9 and 10. However, this is only one example, for example, as shown in Example 1, by setting the temperature of the nitriding treatment to at least 335° C. or higher, a high ammonia efficiency and a high efficiency improvement rate can be obtained. Therefore, in cases where the sulfur content is 0.03 mass % or more and 2.26 mass % or less, the temperature of the nitriding treatment may be set in a range from 335 to 450° C., so that the process window can be further expanded.
Further, the FeNiN formation rate, ammonia efficiency, and efficiency improvement rate were investigated by changing the nitriding treatment time while keeping the sulfur content. Specifically, in a case where the sulfur content was set to 0.05 (mass %) as in Example 3 described above, the experiment was conducted by changing the time of the nitriding treatment. Moreover, as comparative examples, a similar experiment was conducted with respect to the conventional manufacturing method. FIG. 10 is a diagram showing the results. In FIG. 10 , Example 3 is the same as Example 3 in FIG. 5 . Examples 12 and 13 show cases in which only the time of the nitriding treatment is changed from Example 3. Further, Comparative Example 2 is the same as Comparative Example 2 in FIG. 5 . Comparative Examples 7 and 8 show cases in which only the time of the nitriding treatment is changed from Comparative Example 2.
Even in cases where the times of the nitriding treatment were 10 hours and 20 hours, which were shorter than 40 hours, as shown in Examples 12 and 13, the FeNiN formation rates were 88% and 93%, respectively, and the ammonia efficiency were high values of 84.6 (×10⁻⁵) and 44.9 (×10⁻⁵), respectively. In addition, the efficiency improvement rates were also high values of 17.9 and 9.5, respectively. Therefore, it can be said that in cases where S is added, the ammonia efficiency and efficiency improvement rate can be improved even if the time of the nitriding treatment is shortened.
On the other hand, in cases where the times of the nitriding treatment were 10 hours and 20 hour as in Comparative Examples 7 and 8, the FeNiN formation rates were 5% and 40%, respectively, and the ammonia efficiencies were 0.97 (×10⁻⁵) and 3.9 (×10⁻⁵), respectively. The efficiency improvement rates were 0.20 and 0.82, respectively. These results show that in cases where S is not added, the desired ammonia efficiency and efficiency improvement rate cannot be obtained unless the time of the nitriding treatment is 40 hours or longer.
As described above, in cases where S is added, even if the time of the nitriding treatment is shortened from 40 hours, a high ammonia efficiency and a high efficiency improvement rate can be obtained.
For reference, regularities and magnetic properties of FeNi superlattice magnet powders obtained by denitriding the FeNiN of Comparative Example 2, Example 3, and Example 7 at 250° C. for 4 hours were examined. The regularity of the FeNi superlattice obtained by denitriding the FeNi nitride of Comparative Example 2 was 0.71, whereas the regularity of the FeNi superlattice obtained by denitriding the FeNi nitride of Example 3 was 0.68, which was almost the same. The regularity of Example 7 was 0.60. FIG. 11 shows respective hysteresis curves. The coercive force of Comparative Example 2 was 142 kA/m. On the other hand, the coercive force of Example 3 was 135 kA/m, and the coercive force of Example 7 was 120 kA/m. The saturation magnetization of Comparative Example 2 was 139 Am²/kg and the saturation magnetization of Example 3 was also 139 Am²/kg. The saturation magnetization of Example 7 was 91 Am²/kg. From these results, it can be seen that the FeNi superlattice to which an appropriate amount of S is added as in Example 3 has the same performance as the FeNi superlattice to which S is not added as in Comparative Example 2. Since an excessive amount of sulfur causes a decrease in saturation magnetization as in Example 7, the sulfur content is preferably 2% by mass or less from the viewpoint of magnetic performance.
From these results and the measurement results of the XRD patterns of Comparative Example 2 and Example 3 shown in FIG. 5 , no effect of doping with an appropriate amount of sulfur on the crystal structure and magnetic properties was observed. Therefore, it can be said that even if sulfur is doped, it is possible to improve the ammonia efficiency during the manufacture of the FeNi superlattice without deteriorating the performance, and it is possible to increase the production efficiency of the FeNi superlattice.
In addition, the inventors examined the oxidation number of sulfur contained in the FeNi superlattice magnetic powders obtained in Examples 3 and 4, respectively. Specifically, XAFS measurement (that is, partial fluorescence yield measurement) was performed at Aichi Synchrotron Light Center BL6N1 in the following procedure.
(1) Energy Calibration
SK-edge XANES measurement of K₂SO₄, which is a standard sample, was performed before measuring the sample. Energy calibration was performed so that the peak top at that time was 2481.70 eV.
(2) Sample Preparation
The sample was embedded in an indium sheet and attached to a sample holder using conductive carbon tape. The sample holder to which the sample was attached was introduced into the He atmospheric pressure chamber, and He substitution was performed for about 30 minutes before measurement.
(3) Main Measurement
Partial fluorescence yield measurements were performed in the measurement range of 2440 to 2550 eV. The incident angle of the incident light was 20° with respect to the sample plate.
(4) Analysis of Measurement Results
The present inventors analyzed the measurement results using “Athena” as analysis software. Flattening and normalization were performed by setting the end E0 of 2471 eV, the pre-edge range of 2440 to 2470 eV, and the normalization range of 2508 to 2547 eV. Then, the presence or absence of an absorption peak due to S⁶⁺ and an absorption peak due to S²⁻ was determined by comparison with standard samples. The presence or absence of the absorption peaks was determined by the rise of the absorption intensity at 10 times or more the noise level (that is, the S/N ratio of 10 or more). This noise level is the mean value of the absolute value of the deviation of the signal in the range of 2440 to 2460 eV in the pre-edge range. (NH₄)₂SO₄was used as the S⁶⁺ standard sample. FeS was used as the S²⁻ standard sample. The absorption peak appearing at 2482.0±2 eV is the peak due to S⁶⁺. The absorption peak appearing at 2471.5±2 eV is the peak due to S²⁻. Based on the presence of these absorption peaks, it was determined that the S²⁻ and S⁶⁺ states are present.
As a result of measurement and analysis, the results shown in FIG. 12 were obtained. FIG. 12 is a diagram showing X-ray absorption near edge spectra (XANES) for FeNi superlattice magnetic powder of each of Example 3 and Example 4. FIG. 12 also shows the X-ray absorption near-edge spectra of (NH₄)₂SO₄and FeS as the standard samples. As shown in FIG. 12 , in both Examples 3 and 4, the oxidation number of sulfur was a mixture of S²⁻ and S⁶⁺. Example 3 contained more S⁶⁺ than Example 4. Example 4 contained more S²⁻ than Example 3. Incidentally, although not shown, it has been confirmed that the oxidation numbers of sulfur before and after the denitriding treatment are substantially the same in each of Examples 3 and 4.
From the results shown in FIG. 12 , it was found that the sulfur contained in the FeNi superlattice was not in the state of elemental sulfur but in the state of being combined with other elements. Further, from the results shown in FIG. 12 and the ammonia efficiency results of Examples 3 and 4 shown in FIG. 5 , it can be said that even if the oxidation number of sulfur differs, the effect of improving the ammonia efficiency can be obtained. In Examples 3 and 4, the oxidation number of sulfur was in the mixed state of S²⁻ and S⁶⁺, but even if the oxidation number of sulfur is only one of S²⁻ and S⁶⁺, the effect of improving ammonia efficiency is obtained. Further, the oxidation number of sulfur contained in the FeNi superlattice may be other than S²⁻ and S⁶⁺ as long as the effect of improving ammonia efficiency can be obtained.

Other Embodiments

While the present disclosure has been described in accordance with the embodiments described above, the present disclosure is not limited to the embodiments and includes various modifications and equivalent modifications. In addition, while the various elements are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the present disclosure.
For example, S is doped to the FeNi oxide in the first embodiment, and S is doped to the FeNi alloy in the second embodiment, but the doping of S may be performed during the nitriding treatment. In the first embodiment, S may be doped at the stage of the Fe, Ni salt or the FeNi alloy. S may be doped during the nitriding treatment. Further, the doping method of S is not limited to the methods described in the first and second embodiments, and any method can be used. For example, ammonium sulfate may be added to the raw material and then a heat treatment may be performed, or H₂S may be applied to the raw material. For example, FeNi—S can be synthesized by any method, such as adding ammonium sulfate to metal FeNi or performing immersion nitriding by mixing H₂S with NH₃gas during nitriding.
In the second embodiment described above, as an example of cases where S segregates in the FeNi superlattice, S segregates on the surface of the particles of the FeNi superlattice. However, S may segregate to a portion other than the surface. For example, S may be segregated inside the particles of the FeNi superlattice.
The present disclosure is not limited to the above described embodiments and may be suitably modified. In each of the above-described embodiments, individual elements or features of a particular embodiment are not necessarily essential unless it is specifically stated that the elements or the features are essential, or unless the elements or the features are obviously essential in principle. Further, in each of the above-described embodiments, when numerical values such as the number, quantity, range, and the like of the constituent elements of the embodiment are referred to, except in the case where the numerical values are expressly indispensable in particular, the case where the numerical values are obviously limited to a specific number in principle, and the like, the present disclosure is not limited to the specific number.
Various aspects of the present disclosure will be described below. According to a first aspect, an L1₀type FeNi ordered alloy has an L1₀type ordered structure and contains sulfur.
According to a second aspect, a sulfur content of the L1₀type FeNi ordered alloy according to the first aspect is 0.01% by mass or more.
According to a third aspect, the sulfur content of the L1₀type FeNi ordered alloy according to the first aspect or the second aspect is 10% by mass or less.
According to a fourth aspect, the L1₀type FeNi ordered alloy according to any one of the first to third aspects is composed of particles 100 having the L1₀type ordered structure, and the sulfur is present throughout the particles.
According to a fifth aspect, the L1₀type FeNi ordered alloy according to any one of the first to third aspects is composed of particles 100 having the L1₀type ordered structure, and the sulfur is segregated to the particles.
According to a sixth aspect, in the L1₀type FeNi ordered alloy according to the fifth aspect, the sulfur is segregated on surfaces of the particles.
According to a seventh aspect, in the L1₀type FeNi ordered alloy according to any one of the first to sixth aspects, an oxidation number of the sulfur includes S²⁻ or S⁶⁺ or a mixed state of S²⁻ and S⁶⁺.
According to an eighth aspect, a manufacturing method of an L1₀type FeNi ordered alloy includes performing a nitriding treatment to an FeNi alloy containing sulfur to obtain a nitride containing Fe and Ni.
According to a ninth aspect, in the manufacturing method of the L1₀type FeNi order alloy according to claim 8, a sulfur content in the FeNi alloy is 0.01% by mass or more.
According to a tenth aspect, in the manufacturing method of the L1₀type FeNi ordered alloy according to the eighth aspect or the ninth aspect, a sulfur content in the FeNi alloy is 10% by mass or less.
According to an eleventh aspect, in the manufacturing method of the L1₀type FeNi ordered alloy according to any one of the eighth to tenth aspects, the nitriding treatment includes a heat treatment at a temperature in a range from 300 to 500° C.
According to a twelfth aspect, in the manufacturing method of the L1₀type FeNi ordered alloy according to any one of the eighth to eleventh aspects, the nitriding treatment includes a heat treatment at a temperature in a range from 330 to 450° C.
According to a thirteen aspect, in the manufacturing method of the L1₀type FeNi ordered alloy according to any one of eighth to twelfth aspects, a nitriding efficiency in the nitriding treatment to obtain the nitride containing Fe and Ni is greater than 4.7×10⁻⁵.

Claims

What is claimed is:

1. An L1₀type iron-nickel (FeNi) ordered alloy having an L1₀type ordered structure and containing sulfur.

2. The L1₀type FeNi ordered alloy according to claim 1, wherein a sulfur content is 0.01% by mass or more.

3. The L1₀type FeNi ordered alloy according to claim 1, wherein a sulfur content is 10% by mass or less.

4. The L1₀type FeNi ordered alloy according to claim 1, wherein the L1₀type FeNi ordered alloy is composed of particles having the L1₀type ordered structure, and the sulfur is present throughout the particles.

5. The L1₀type FeNi ordered alloy according to claim 1, wherein the L1₀type FeNi ordered alloy is composed of particles having the L1₀type ordered structure, and the sulfur is segregated to the particles.

6. The L1₀type FeNi ordered alloy according to claim 5, wherein the sulfur is segregated on surfaces of the particles.

7. The L1₀type FeNi ordered alloy according to claim 1, wherein an oxidation number of the sulfur includes S²⁻ or S⁶⁺ or a mixed state of S²⁻ and S⁶⁺.

8. A manufacturing method of an L1₀type iron-nickel (FeNi) ordered alloy comprising performing a nitriding treatment to an FeNi alloy containing sulfur to obtain a nitride containing Fe and Ni.

9. The manufacturing method according to claim 8, wherein a sulfur content in the FeNi alloy is 0.01% by mass or more.

10. The manufacturing method according to claim 8, wherein a sulfur content in the FeNi alloy is 10% by mass or less.

11. The manufacturing method according to claim 8, wherein the nitriding treatment includes a heat treatment at a temperature in a range from 300 to 500° C.

12. The manufacturing method according to claim 8, wherein the nitriding treatment includes a heat treatment at a temperature in a range from 330 to 450° C.

13. The manufacturing method according to claim 8, wherein a nitriding efficiency in the nitriding treatment to obtain the nitride containing Fe and Ni is greater than 4.7×10⁻⁵.