JP2018083964A - Iron nitride material and method of manufacturing iron nitride material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an iron nitride material which has, on a surface of an iron base material, a dense nitride layer containing α''-FeN.SOLUTION: An iron nitride material according to one embodiment of the present invention has a nitride layer containing FeNon a surface of an iron base material of 99 mass% in purity, and the nitride layer has a mean film thickness of 10-100 μm. The iron nitride material can be manufactured by a method of manufacturing the iron nitride material comprising: an electrolyte forming process of forming an electrolyte, for example, by dissolving nitride ions (N) in molten salt; and an electrolysis process of electrolytically depositing α''-FeNon a surface of an anode 51 through molten salt electrolysis using the anode 51 and a cathode 52 provided in the electrolyte 53. In the electrolysis process, the temperature of the electrolyte 53 is 250°C or lower, the anode 51 is an iron base material of 99 mass% or larger in purity, and a potential applied to the anode is 0.5-1.5 V based upon Li/Li.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an iron nitride material and a method for producing an iron nitride material.

Conventionally, rare earth magnets containing rare earth elements such as Nd (neodymium) and Sm (samarium) have been widely used as permanent magnets used in motors and generators. However, although rare earth magnets are excellent in magnetic properties, the rare earth elements contained in the magnets are rare elements, so that reduction of the amount used is required. As an alternative to rare earth magnets, magnets using iron nitride materials have attracted attention. In particular, α ″ -Fe ₁₆ N ₂ is known as an iron nitride material having very high saturation magnetization and excellent magnetic properties.

  Various methods for forming an iron nitride layer have been studied. For example, Non-Patent Document 1 describes a method of permeating and diffusing nitrogen into a steel material by gas nitriding the steel material. A method for forming an iron nitride layer by molecular beam epitaxy is described in Non-Patent Document 2, and a method for forming an iron nitride layer by sputtering is described in Non-Patent Document 3. In addition, there is a plating method. For example, Patent Document 1 describes a method of forming a nitride layer by performing molten salt electrolysis using a steel material as a working electrode in an electrolytic bath of molten salt containing nitride ions. Has been.

JP 2009-052104 A

Takaaki Umeda Kazuo Miyabe, “Development of production technology for nitriding treatment using nitriding potential control”, KOMATSU TECHNIC REPORT, 2014, VOL. 60, no. 167, pp17-23 M.M. Komuro et al. , “Epitaxial growth and magnetic properties of Fe16N2 films with high saturation magnetic density (invited)” Journal of Applied Py. 90. 67, no. 9, pp. 5126-5130 M.M. Takahashi et al. "Magnetic moment of α" -Fe16N2 films (invited) "Journal of Applied Physics, 1994, vol. 76, no. 10, pp. 6642-6647

The gas nitriding method described in Non-Patent Document 1 is a process in which NH ₃ gas is introduced into a furnace and heated to 500 ° C. to 580 ° C. to permeate and diffuse nitrogen into the steel material, and the ε phase (Fe ₃ N) And γ ′ phase (Fe ₄ N) are formed, but α ″ -Fe ₁₆ N ₂ cannot be formed. This is considered that α ″ -Fe ₁₆ N ₂ becomes unstable when it exceeds 250 ° C., and is therefore not generated by heat treatment at 500 ° C. to 580 ° C.
Further, according to the methods described in Non-Patent Document 2 and Non-Patent Document 3, although α ″ -Fe ₁₆ N ₂ can be formed, the growth rate is limited, and thus there is a problem that it takes time for film formation. Further, since an environment such as a vacuum is necessary, continuous processing is difficult, and it is not suitable for industrial production.

In the method described in Patent Document 1, a steel material (a steel material containing chromium, basically stainless steel) is placed in an electrolytic bath of a molten salt containing nitride ions, and is 415 ° C. or less, preferably 315 ° C. A molten salt electrolysis is performed with a steel material as a working electrode at the following bath temperature to form a nitride layer having excellent corrosion resistance. However, there is no description or suggestion regarding α ″ -Fe ₁₆ N ₂ formation in the formed nitride layer. According to the method described in Patent Document 1, molten salt electrolysis is performed at 415 ° C. or lower, preferably 315 ° C. or lower. However, even within this range, α ″ -Fe ₁₆ is used at temperatures higher than 250 ° C. This is probably because N ₂ cannot be formed. In addition, the material to be subjected to the surface nitriding treatment is steel (stainless steel), and since steel contains Cr and the like in addition to Fe, these elements react with N to generate nitrides. , Α ″ -Fe ₁₆ N ₂ cannot be formed. In addition, C is contained in the steel material, and C coexists with N to become stable Fe ₃ (C, N), which may affect the production of Fe ₁₆ N ₂ . In that case, it is considered that the magnetic characteristics change.

Accordingly, an object of the present invention is to provide an iron nitride material having a dense nitride layer containing α ″ -Fe ₁₆ N ₂ on the surface of an iron base. Furthermore, it aims at providing the manufacturing method of the iron nitride material which can manufacture the said iron nitride material easily in a comparatively short time.

The iron nitride material according to one aspect of the present invention is
Having a nitride layer containing α ″ -Fe ₁₆ N ₂ on the surface of an iron base having a purity of 99% by mass or more;
The nitride layer is an iron nitride material having an average film thickness of 10 nm or more and 100 μm or less.
In addition, the method for producing an iron nitride material according to one aspect of the present invention includes:
A method for producing the iron nitride material,
An electrolytic solution forming step of forming an electrolytic solution by dissolving nitride ions (N ³⁻ ) in the molten salt;
By performing molten salt electrolysis using an anode and a cathode provided in the electrolyte, iron nitride containing α ″ -Fe ₁₆ N ₂ is electrodeposited on the surface of the anode to form a nitride layer. An electrolysis process;
Have
In the electrolysis step, the temperature of the electrolytic solution is 250 ° C. or less, the anode is an iron base having a purity of 99% by mass or more, and the potential applied to the anode is 0.5 V or more on the basis of Li ⁺ / Li, It is a manufacturing method of the iron nitride material which is 1.5V or less.

According to the above invention, it is possible to provide an iron nitride material having a dense nitride layer containing α ″ -Fe ₁₆ N ₂ on the surface of an iron base. Furthermore, it is possible to provide a method for producing an iron nitride material, which can easily produce the iron nitride material in a relatively short time.

In the method of measuring the average film thickness of the nitride layer in an iron nitride material, it is the schematic showing an example of the state which defined areas AE on the iron nitride material. It is a conceptual diagram showing an example of the visual field (i) at the time of observing the area A of the iron nitride material shown in FIG. 1 with a scanning electron microscope. It is a conceptual diagram showing an example of the visual field (ii) at the time of observing the area A of the iron nitride material shown in FIG. 1 with a scanning electron microscope. It is a conceptual diagram showing an example of the visual field (iii) at the time of observing the area A of the iron nitride material shown in FIG. 1 with a scanning electron microscope. It is a figure showing the outline of an example of the electrolysis process in the manufacturing method of the iron nitride material which concerns on embodiment of this invention. It is a figure showing the outline of an example of composition of a gas electrode which can be used in an electrolytic solution formation process and an electrolysis process in a manufacturing method of an iron nitride material concerning an embodiment of the present invention. It is a figure showing the outline of another example of the structure of the gas electrode which can be used in the electrolyte solution formation process and electrolysis process in the manufacturing method of the iron nitride material which concerns on embodiment of this invention. It is a figure showing the outline of another example of the structure of the gas electrode which can be used in the electrolyte solution formation process and electrolysis process in the manufacturing method of the iron nitride material which concerns on embodiment of this invention. It is a figure showing the outline of another example of the structure of the gas electrode which can be used in the electrolyte solution formation process and electrolysis process in the manufacturing method of the iron nitride material which concerns on embodiment of this invention.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described.
(1) The iron nitride material according to one aspect of the present invention is
Having a nitride layer containing α ″ -Fe ₁₆ N ₂ on the surface of an iron base having a purity of 99% by mass or more;
The nitride layer is an iron nitride material having an average film thickness of 10 nm or more and 100 μm or less.
According to the aspect of the invention described in (1) above, it is possible to provide an iron nitride material having a dense nitride layer containing α ″ -Fe ₁₆ N ₂ on the surface of an iron base.

(2) It is preferable that the nitride layer according to the above (1) has a corrosion prevention layer on the surface.
(3) The anticorrosion layer according to (2) is preferably ε-Fe _2-3 N, iron carbide, or iron oxide.
According to the aspect of the invention described in the above (2) or (3), it is possible to provide an iron nitride material that is hardly affected by an atmosphere such as the air and is not easily deteriorated.

(4) A method for producing an iron nitride material according to an aspect of the present invention includes:
A method for producing the iron nitride material according to (1) above,
An electrolytic solution forming step of forming an electrolytic solution by dissolving nitride ions (N ³⁻ ) in the molten salt;
By performing molten salt electrolysis using an anode and a cathode provided in the electrolyte, iron nitride containing α ″ -Fe ₁₆ N ₂ is electrodeposited on the surface of the anode to form a nitride layer. An electrolysis process;
Have
In the electrolysis step, the temperature of the electrolytic solution is 250 ° C. or less, the anode is an iron base having a purity of 99% by mass or more, and the potential applied to the anode is 0.5 V or more on the basis of Li ⁺ / Li, It is a manufacturing method of the iron nitride material which is 1.5V or less.
According to the aspect of the invention described in the above (4), an iron nitride material having a dense nitride layer containing α ″ -Fe ₁₆ N ₂ on the surface of an iron base is easily produced in a relatively short time. It is possible to provide a method of manufacturing an iron nitride material that can be used.

(5) The method for producing an iron nitride material according to (4) above is:
It is preferable to have a pretreatment step of removing an oxide layer formed on the surface of the iron base used for the anode before the electrolysis step.
According to the aspect of the invention described in (5) above, since the iron oxide film can be removed by the pretreatment step, it is possible to manufacture an iron nitride material having a nitride layer with a small oxygen component.

(6) The method for producing an iron nitride material according to (4) or (5) above,
It is preferable to have an anticorrosion layer forming step of forming an anticorrosion layer on the surface of the nitride layer after the electrolysis step.
(7) The method for producing an iron nitride material according to (6) above is:
The anticorrosion layer is preferably ε-Fe _2-3 N, iron carbide or iron oxide.
According to the aspect of the invention described in the above (6) or (7), it is possible to provide a method for producing an iron nitride material that is hardly affected by an atmosphere such as the air and is not easily deteriorated.

(8) The method for producing an iron nitride material according to (4) to (7) above,
The molten salt is preferably an alkali metal halide, an alkaline earth metal halide, or a mixture thereof.
(9) The method for producing an iron nitride material according to (8) above is:
The alkali metal halide is preferably an alkali metal bromide, iodide or a mixture of bromide and iodide.
(10) The method for producing an iron nitride material according to (8) or (9) above,
The alkaline earth metal halide is preferably an alkaline earth metal bromide, iodide or a mixture of bromide and iodide.
(11) The method for producing an iron nitride material according to any one of (8) to (10) above,
The alkali metal is preferably at least one selected from the group consisting of Li, K, and Cs.
(12) The method for producing an iron nitride material according to any one of (8) to (11) above,
The alkaline earth metal is preferably at least one selected from the group consisting of Mg, Ca, Sr and Ba.
(13) The method for producing an iron nitride material according to any one of (4) to (12) above,
The molten salt is preferably LiBr-KBr-CsBr or LiI-KI-CsI.
(14) The method for producing an iron nitride material according to any one of (4) to (13) above,
The molten salt contains Li ⁺ , K ⁺ and Cs ⁺ , the Li ⁺ content is 40 mol% or more and 80 mol% or less, the K ⁺ content is 5 mol% or more and 30 mol% or less, and the Cs ⁺ content is It is preferable that it is 10 mol% or more and 40 mol% or less.
According to the aspect of the invention described in any one of (8) to (14) above, a molten salt having a stable temperature range of α ″ -Fe ₁₆ N ₂ is relatively easily obtained, Moreover, it can form with the kind of material with easy handling.

(15) The method for producing an iron nitride material according to any one of (4) to (14) above,
It is preferable to add Li ₃ N to the molten salt to form an electrolytic solution in which nitride ions (N ³⁻ ) are dissolved.
According to the aspect of the invention described in (15) above, nitride ions can be easily dissolved in the molten salt.

(16) The method for producing an iron nitride material according to any one of (4) to (15) above,
Preferably, the molten salt is provided with a nitrogen gas reducing electrode, and an electrolytic solution in which nitride ions (N ³⁻ ) are dissolved is formed by supplying nitrogen gas to the nitriding gas reducing electrode and electrochemically reducing it. .
According to the aspect of the invention described in (16) above, nitride ions can be continuously supplied into the molten salt.

[Details of the embodiment of the present invention]
Specific examples of the iron nitride material and the manufacturing method thereof according to the embodiment of the present invention will be described below. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to the claim are included.

<Iron nitride material>
The iron nitride material according to the embodiment of the present invention has a dense nitride layer containing α ″ -Fe ₁₆ N ₂ on the surface of iron as a base material.
(Iron base)
The iron substrate may be iron having a purity of 99% by mass or more.
Moreover, if it is 1 mass% or less, components other than iron may be intentionally or unavoidably contained in the iron base material. For example, components other than iron may include Ni, Cu, and the like.
The shape of the iron substrate is not particularly limited, and may be appropriately selected depending on the purpose, such as a flat plate shape.

(Nitride layer)
Since the nitride layer is formed by molten salt electrolysis as will be described later, the nitride layer is firmly adhered to the surface of the iron base and is formed as a dense layer.
The nitride layer may have an average film thickness of 10 nm or more and 100 μm or less. When the average thickness of the nitride layer in the iron nitride material is 10 nm or more, the characteristics of α ″ -Fe ₁₆ N ₂ having a high saturation magnetization can be sufficiently exhibited. Further, when the average thickness of the nitride layer is 100 μm or less, a thin magnetic film that can be used for a recording medium or the like can be obtained. From these viewpoints, the average thickness of the nitride layer is more preferably 20 nm or more and 10 μm or less, and further preferably 50 nm or more and 1 μm or less.

The average film thickness of a nitride layer shall mean what is measured by observing the cross section of a nitride layer with an electron microscope as follows. The outline of the measuring method of an average film thickness is shown in FIGS.
First, an iron nitride material having a nitride layer is arbitrarily divided into areas, and five locations (area A to area E) are selected as measurement locations. And the cross section of the nitride layer in each area is observed with a scanning electron microscope (SEM). The magnification of the SEM is set so that the entire thickness direction of the nitride layer can be confirmed and the thickness direction can be seen as large as possible within one field of view. Then, the maximum thickness and the minimum thickness of the nitride layer are measured at three locations in each area while changing the field of view, and the average is referred to as the average thickness of the nitride layer.
As an example, FIG. 1 shows a schematic diagram of an iron nitride material 1 having a nitride layer on the surface of a substantially square iron substrate, with the four corners being area A to area D and the center being area E. FIG. 2 shows a conceptual diagram of the visual field (i) when the area A of the iron nitride material 1 shown in FIG. 1 is observed by SEM. Similarly, FIG. 3 shows a conceptual diagram of the visual field (ii) of the area A, and FIG. 4 shows a conceptual diagram of the visual field (iii) of the area A.
Thickness (maximum thickness A (i), maximum thickness A (ii), maximum thickness) in which nitride layer 3 is maximum in the field of view (i) to field of view (iii) when area A of iron nitride material 1 is observed with an SEM A (iii)) and the minimum thickness (minimum thickness a (i), minimum thickness a (ii), minimum thickness a (iii)) of nitride layer 3 are measured. The thickness of the nitride layer 3 refers to the length of the nitride layer 3 extending in the vertical direction from the iron base 2. As a result, the maximum thickness A (i) to the maximum thickness A (iii) and the minimum thickness a (i) to the minimum thickness a (iii) of the three visual fields in the area A are determined. For areas B, C, D, and E, the maximum thickness and the minimum thickness of the nitride layer in the three visual fields are measured in the same manner as area A.
The average thickness of the nitride layer is determined by averaging the maximum thickness A (i) to maximum thickness E (iii) and the minimum thickness a (i) to minimum thickness e (iii) of the nitride layer measured as described above. That's it.

The content of α ″ -Fe ₁₆ N ₂ in the nitride layer is preferably as high as possible. When the content of α ″ -Fe ₁₆ N ₂ in the nitride layer is 30% by mass or more, the characteristics of α ″ -Fe ₁₆ N ₂ having high saturation magnetization can be sufficiently exhibited. The content of α ″ -Fe ₁₆ N ₂ in the nitride layer is more preferably 50% by mass or more, and further preferably 80% by mass or more. Components other than α ″ -Fe ₁₆ N ₂ may be intentionally or unavoidably contained in the nitride layer. As components other than α ″ -Fe ₁₆ N ₂ , for example, Fe, Fe ₄ N, Fe ₃ N, FeO, Fe ₂ O ₃ , Fe ₃ O ₄ , FeOH and the like may be included.

(Anti-corrosion layer)
The iron nitride material according to the embodiment of the present invention preferably has an anticorrosion layer on the surface of the nitride layer in order to suppress deterioration due to the atmosphere. As the anticorrosion layer, for example, iron nitride having a composition different from that of α ″ -Fe ₁₆ N ₂ can be considered. For example, ε-Fe _2-3 N having high corrosion resistance can be used. Since iron nitride as the anticorrosion layer is a phase having a different nitriding rate from α ″ -Fe ₁₆ N ₂ , it can be generated by changing the nitriding conditions. Although details will be described later, when the nitride layer is formed by molten salt electrolysis as in the method of manufacturing an iron nitride material according to the embodiment of the present invention, α ″ -Fe ₁₆ N is controlled by controlling the potential of the anode. ₂ and a phase having a different nitridation rate can be generated. For this reason, it is also possible to continuously generate the anticorrosion layer after the nitride layer containing α ″ -Fe ₁₆ N ₂ by continuously changing the generation conditions of the nitride layer.
As other anticorrosion layers, iron carbide and iron oxide can be applied. In the case of iron oxide, it can be formed by performing a mild oxidation treatment after the formation of the nitride layer. In addition to the iron-based material, the anticorrosion layer can be formed by providing SiO ₂ or Al ₂ O ₃ on the surface of the nitride layer.
Moreover, it is preferable that the thickness of a corrosion prevention layer is 0.5 nm or more and 20 nm or less. When the thickness of the anticorrosion layer is 0.5 nm or more, deterioration of the nitride layer due to an atmosphere such as air can be suppressed. Moreover, when the thickness of the anticorrosion layer is 20 nm or less, it is possible to suppress the influence of strain and the like on the nitride layer, and it is possible to generate the anticorrosion layer without much effort and time. The thickness of the anticorrosion layer is more preferably 1 nm or more and 10 nm or less.

<Manufacturing method of iron nitride material>
The manufacturing method of the iron nitride material which concerns on embodiment of this invention is a method of manufacturing the iron nitride material which concerns on said embodiment of this invention, has an electrolyte solution formation process, an electrolysis process, Furthermore, a pre-processing process And an anticorrosion layer forming step selectively. The electrolytic solution forming step is a step of forming an electrolytic solution by dissolving nitride ions (N ³⁻ ) in the molten salt. As shown in FIG. 5, the electrolytic process is performed by performing molten salt electrolysis by connecting the anode 51 and the cathode 52 provided in the electrolytic solution 53 to a power source 54, so that α ″ -Fe ₁₆ N ₂ is formed on the surface of the anode 1. In this step, a nitride layer is formed by electrodepositing an iron nitride containing iron. The power source 54 may be any power source that can control the potential. For example, a potentio galvanostat can be preferably used. A pretreatment process is a process performed before an electrolysis process, and is a process of removing the oxide layer currently formed in the surface of the iron base material used for an anode. The anticorrosion layer forming step is a step performed after the electrolysis step, and is a step of forming the anticorrosion layer on the surface of the nitride layer formed in the electrolysis step. Each step will be described in detail below.

(Electrolyte formation process)
As described above, this step is a step of forming an electrolytic solution by dissolving nitride ions (N ³⁻ ) in the molten salt.
-Molten salt-
What is necessary is just to select a molten salt which becomes a liquid by melting at 250 ° C. or lower. The molten salt having a low melting point and relatively easily available is preferably, for example, an alkali metal halide, an alkaline earth metal halide, or a mixture thereof. In general, the molten salt has a lower melting point when a multi-component salt is used than when a single-component salt is used. Therefore, it is preferable to use a mixture of a plurality of types of salts. The alkali metal halide is preferably bromide, iodide or a mixture of bromide and iodide. Similarly, the alkaline earth metal halide is preferably bromide, iodide or a mixture of bromide and iodide. Iodide and bromide salts are preferred because they can be melted at low temperatures and are easy to handle.

  The alkali metal is preferably at least one selected from the group consisting of Li, K and Cs. The alkaline earth metal is preferably at least one selected from the group consisting of Mg, Ca, Sr and Ba. These alkali metal and alkaline earth metal halides can be melted at a low melting point and are relatively easily available.

From the above viewpoint, the molten salt is preferably, for example, LiBr-CsBr, LiBr-KBr-CsBr, Li-KI, Li-CsI, Li-KI-CsI, or the like.
Further, when the molten salt contains Li ⁺ , K ⁺ and Cs ⁺ , the Li ⁺ content is 40 mol% or more and 80 mol% or less, the K ⁺ content is 5 mol% or more and 30 mol% or less, Cs ⁺ It is preferable that the content rate of is 10 mol% or more and 40 mol% or less. Thereby, it can be set as a low melting-point molten salt.
The content of Li ^{+ in} the molten salt is more preferably 45 mol% or more and 75 mol% or less, and further preferably 50 mol% or more and 70 mol% or less.
The content of K ^{+ in} the molten salt is more preferably 7 mol% or more and 25 mol% or less, and further preferably 9 mol% or more and 20 mol% or less.
The content of Cs ^{+ in} the molten salt is more preferably 15 mol% or more and 35 mol% or less, and further preferably 20 mol% or more and 30 mol% or less.

-Formation of nitride ions-
The method for dissolving nitride ions in the molten salt is not particularly limited. For example, it is possible to generate nitride ions in the molten salt by adding and dissolving Li ₃ N in the molten salt. For example, the amount of nitride ions added may be such that Li ₃ N is added to the molten salt so that the concentration of Li ₃ N is 0.05 mol% or more and 5 mol% or less. By setting the concentration of Li ₃ N to be 0.05 mol% or more, a sufficient amount of nitride to deposit α ″ -Fe ₁₆ N ₂ in the electrolysis step that follows the electrolytic solution formation step Ions can be generated in the molten salt. Further, since the concentration of Li 3 _N is set to be less 5 mol%, it is possible to suppress an increase in melting point of the molten salt. From these viewpoints, the amount of Li ₃ N added is more preferably such that the concentration of Li ₃ N is 0.1 mol% or more and 3 mol% or less, and is 0.2 mol% or more and 2 mol% or less. More preferably.
Note that when α ″ -Fe ₁₆ N ₂ begins to be electrodeposited in the electrolysis process described later, nitride ions in the electrolytic solution are consumed, so a large amount of nitride layer containing α ″ -Fe ₁₆ N ₂ is used. In the case of forming in a molten salt, Li ₃ N may be appropriately added to the molten salt also in the electrolysis step.

  Nitrogen gas is generated in the molten salt by providing a nitrogen gas reducing electrode (hereinafter simply referred to as “gas electrode”) in the molten salt, supplying nitrogen gas, and electrochemically reducing the nitrogen. Can do. Any known gas electrode can be used as long as it can supply a gas containing nitrogen gas to the electrode surface, but the gas electrode is preferably a gas electrode having a structure shown in FIGS. .

The gas electrode shown in FIG. 6 is a gas electrode including a cylindrical electrode member 62 having an internal space serving as a flow path for a gas containing nitrogen gas. The lead wire 61 is connected to the cylindrical electrode member 62 and connected to the cathode side of the power source, the counter electrode is connected to the anode side of the power source, and the potential is applied to the anode. Then, by supplying a gas containing nitrogen gas to the internal space of the cylindrical electrode member 62, the nitrogen gas is reduced on the surface of the internal space and dissolved in the molten salt as nitride ions (N ³⁻ ). it can.

Further, like the gas electrode shown in FIG. 7, it is preferable to dispose a conductive porous member 73 at the tip of the internal space of the cylindrical electrode member 72. The porous member 73 only needs to have a large number of communication holes communicating between one surface and the other surface. Since the porous member 73 has the communication hole, the gas supplied to the internal space of the gas electrode can be made to flow outside the gas electrode. The communication hole may be, for example, a hole that goes straight from one surface of the porous member 73 to the other surface, or a hole formed by a complicated structure such as a three-dimensional network structure. It may be. When the gas electrode provided with the porous member 73 at the tip of the internal space is arranged in the molten salt, the inside of the communication hole is filled with the molten salt. The lead wire 71 may be connected to the cylindrical electrode member 72 and connected to the cathode side of the power source, the counter electrode may be connected to the anode side of the power source, and the potential may be applied to the anode. Since the porous member 73 is conductive, the nitrogen gas is reduced on the surface of the communication hole of the porous member 73 by supplying a gas containing nitrogen gas to the internal space of the gas electrode. Thereby, nitride ions (N ³⁻ ) can be dissolved in the molten salt.

  The cylindrical electrode members (62, 72) and the porous member 73 are preferably made of an inert material in the molten salt. For example, platinum, gold, or an alloy thereof, glassy carbon, graphite, stainless steel, nickel, or a nickel-based alloy can be preferably used. The cylindrical electrode member 72 and the porous member 73 may be made of the same material or different materials.

As shown in FIG. 8, the gas electrode may include an electrode member 83 and a cylindrical member 82. The cylindrical member 82 has an internal space serving as a flow path for a gas containing nitrogen gas, and the electrode member 83 may be disposed in the internal space of the cylindrical member 82. Then, the lead wire 81 is connected to the electrode member 83 and connected to the cathode side of the power source, the counter electrode is connected to the anode side, and the potential is applied to the anode. At this time, by supplying a gas containing nitrogen gas to the internal space of the cylindrical member 82, the nitrogen gas is reduced on the surface of the electrode member 82 and dissolved as nitride ions (N ³⁻ ) in the molten salt. Can do.

  Further, as the electrode member 83, as shown in FIG. 9, it is preferable to use a porous body 93 having a skeleton having a three-dimensional network structure. Thereby, the surface area of an electrode can be enlarged and the melt | dissolution efficiency to the molten salt of the nitrogen gas supplied to the space inside the cylindrical member 92 can be improved more.

The cylindrical members (82, 92) are not particularly required to be conductive, and may be any material that is stable in the molten salt. On the other hand, it is desirable that the electrode member 83 and the porous body 93 are electrically conductive and inactive in the molten salt. As the electrode member 83, for example, platinum, gold, or an alloy thereof, glassy carbon, graphite, stainless steel, nickel, or a nickel-based alloy can be preferably used. Examples of the porous body 93 include a nickel porous body having a three-dimensional network structure skeleton.
The gas electrode is more efficient as there are more parts that form a three-phase interface of nitrogen gas, molten salt, and the current-carrying part of the gas electrode. For this reason, the gas electrode of the aspect shown in FIG.7 and FIG.9 which uses a porous member for an electricity supply part is more effective.

As described above, a gas containing nitrogen gas is supplied to the gas electrode. As a result, nitrogen gas is reduced on the electrode surface and dissolved as nitride ions in the molten salt.
As a gas supplied to the gas electrode, a mixed gas of a gas that does not affect the molten salt and the nitrogen gas can be used in addition to the nitrogen gas. As a gas to be mixed with nitrogen gas, for example, argon (Ar) gas can be preferably used. In the case of supplying a mixed gas of nitrogen gas and another gas, it is preferable that the concentration of nitrogen gas is high in consideration of the reaction efficiency on the electrode surface. That is, it is desirable to adjust the concentration to supply the maximum amount of nitrogen gas that can be reacted with the electrode used.

The flow rate of the gas containing nitrogen gas is preferably set to a flow rate at which the maximum amount of nitrogen gas that can be reacted with the electrode can be supplied from the viewpoint of increasing the generation efficiency of nitride ions.
Further, unreacted gas discharged from the gas electrode may be collected and circulated so as to be supplied again to the gas electrode.

(Electrolysis process)
This step is a step in which molten salt electrolysis is performed using the electrolytic solution prepared in the above-described electrolytic solution forming step, and iron nitride containing α ″ -Fe ₁₆ N ₂ is electrodeposited on the surface of the anode. In the electrolysis process, as shown in FIG. 5, the anode 51 and the cathode 52 are provided in the electrolytic solution 53, and the anode 51 is connected to the anode side of the power source 4 and the cathode 52 is connected to the cathode side of the power source 54. Then, by applying a potential to the anode 51, α ″ -Fe ₁₆ N ₂ can be electrodeposited on the surface of the anode 51.

-Electrolyte-
As the electrolytic solution, the electrolytic solution prepared in the above-described electrolytic solution forming step is used. When the temperature of the electrolytic solution exceeds 250 ° C., α ″ -Fe ₁₆ N ₂ becomes unstable and cannot be electrodeposited. Therefore, the temperature of the electrolytic solution is set to 250 ° C. or lower. Further, since the salt does not become liquid at a temperature lower than the melting point of the molten salt used as the electrolytic solution, the temperature may be higher than the melting point of the molten salt of the electrolytic solution.

-Anode-
An iron base having a purity of 99% by mass or more is used for the anode. The iron base material may contain components other than iron intentionally or unavoidably as long as it is 1% by mass or less. However, a component that is more easily nitrided than iron or α ″ -Fe ₁₆ N It is preferable that the component affecting the magnetic characteristics of ₂ is not contained as much as possible. For example, light metals such as Ti, V, Cr, Mn, lanthanoids, and Al and Si are more easily nitrided than iron. Therefore, they inhibit nitrogen diffusion during electrolysis and inhibit the production of α ″ -Fe ₁₆ N _2. End up.
The shape of the iron substrate is not particularly limited, and may be appropriately selected depending on the purpose, such as a flat plate shape.

-Cathode-
A cathode that is conductive and stable in the electrolytic solution may be used. For example, platinum, gold, or an alloy thereof, glassy carbon, graphite, stainless steel, alumina, nickel, or a nickel-based alloy can be preferably used.
Moreover, the above-mentioned gas electrode can also be used for a cathode. By using the gas electrode, nitride ions can be continuously supplied to the electrolyte during molten salt electrolysis. The configuration of the gas electrode may be the same as the gas electrode described in the above-described electrolytic solution forming step.

-Electrolysis conditions-
The potential applied to the anode during molten salt electrolysis may be about 0.5 V or more and 1.5 V or less on the basis of Li ⁺ / Li. By setting the potential to 0.5 V (vs. Li ⁺ / Li) or higher, α ″ -Fe ₁₆ N ₂ can be favorably formed on the surface of the iron base material used as the anode. On the other hand, by setting the potential to 1.5 V (vs. Li ⁺ / Li) or less, α ″ -Fe ₁₆ N ₂ can be formed without dissolving the iron of the anode. The potential applied to the anode is more preferably about 0.55 V to 1.2 V, more preferably about 0.6 V to 1.0 V, based on Li ⁺ / Li.
The time for performing the molten salt electrolysis is not particularly limited, and may be a time for sufficiently forming the target α ″ -Fe ₁₆ N ₂ .
In some cases, heat treatment is performed on the iron nitride material after electrolysis of molten salt to promote the production of α ″ -Fe ₁₆ N ₂ . In this case, the generation of α ″ -Fe ₁₆ N ₂ may be further promoted by quenching by rapid cooling from the heat treatment temperature after the heat treatment.
The heat treatment of the iron nitride material is preferably performed at room temperature or higher and lower than the molten salt electrolysis temperature, for example, at about 15 ° C. or more and 200 ° C. or less. Moreover, the atmosphere which heat-processes is not specifically limited, You may carry out in electrolyte solution and may carry out in a gas atmosphere.

(Pretreatment process)
This step is a step performed before the electrolysis step, and is a step of removing the oxide layer formed on the surface of the iron base used for the anode.
A method for removing the oxide layer formed on the surface of the iron base is not particularly limited, and examples thereof include a method of removing by dissolving the anode by electrolysis and a method of removing by chemicals.
In order to remove the oxide layer by anodic dissolution, for example, as in the above-described electrolysis step, a cathode and an anode made of an iron base are provided in the electrolytic solution, and a potential of 2.0 V or higher on the basis of Li ⁺ / Li. Is applied to the anode to dissolve and remove the oxide layer on the anode surface. Note that after the oxide layer is removed, the electrolysis step can be performed by setting the potential to 0.5 V or more and 1.5 V or less on the basis of Li ⁺ / Li.
The removal of the oxide layer can also be performed by dissolving the oxide layer of the iron substrate with an acid chemical. For example, nitric acid, hydrochloric acid, sulfuric acid or the like can be used as the acid chemical.

(Anti-corrosion layer forming process)
The anticorrosion layer forming step is a step performed after the electrolysis step, and is a step of forming the anticorrosion layer on the surface of the nitride layer formed by the electrolysis step. The anticorrosion layer formed on the surface of the nitride layer is preferably ε-Fe _2-3 N, iron carbide or iron oxide.
When forming an iron nitride having a phase different from that of α ″ -Fe ₁₆ N ₂ , such as ε-Fe _2-3 N, as the anticorrosion layer, for example, changing the electrolysis conditions in the electrolysis step Can be formed. That is, by controlling the anode to a noble potential from the potential at which α ″ -Fe ₁₆ N ₂ was generated after the electrolysis step, an anticorrosion layer made of iron nitride containing ε-Fe _2-3 N having excellent corrosion resistance was formed. It can be formed on the surface of the nitride layer.
Further, without using electrolytic treatment, the surface can be irradiated with nitrogen plasma to form an anticorrosion layer made of iron nitride.
In the case of forming iron carbide as the anticorrosion layer, for example, after nitriding, carbide ions (C ₂ ²⁻ ) are added to the molten salt and the surface of iron nitride is carbonized by electrolysis, or after cleaning, a carbonized material (liquid carbonization) Hydrogen or the like) may be applied and baked in an inert atmosphere furnace, or heat treatment may be performed in a CO atmosphere.
When iron oxide is formed as the anticorrosion layer, an iron nitride material having a nitride layer formed on the anode surface may be oxidized under mild conditions. As a mild oxidation treatment condition, for example, Fe ₃ O ₄ may be formed by a heat treatment at about 100 ° C. after cleaning.
In addition, as the anticorrosion layer, Cr ions may be reacted to form a chromium nitride layer, or SiO ₂ or Al ₂ O ₃ may be formed.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, these Examples are illustrations, Comprising: The iron nitride material of this invention and its manufacturing method are not limited to these. The scope of the present invention is defined by the scope of the claims, and includes meanings equivalent to the scope of the claims and all modifications within the scope.

[Example 1]
-Electrolytic solution formation process-
LiBr, KBr, and CsBr were mixed at a molar ratio of 56.1: 18.9: 25.0 and heated to 250 ° C. to prepare a molten salt. Li ₃ N was added to the molten salt so as to have a concentration of 1.0 mol%, thereby preparing an electrolytic solution.
-Electrolytic process-
Molten salt electrolysis was performed in a glove box with an Ar flow atmosphere.
A 5 mm × 5 mm × 1 mmt Fe plate as an anode and a glassy carbon rod as a cathode were disposed in the electrolyte. An Al—Li alloy was used as a reference electrode. The temperature of the electrolytic solution was 240 ° C.
Iron nitride material by connecting the anode and cathode to a potentio galvanostat as a power source capable of controlling the potential, applying a potential of 0.8 V to the anode based on Li ⁺ / Li, and performing molten salt electrolysis at a constant potential for 3 hours No. 1 was produced.

[Example 2]
In Example 1, except that the temperature of the electrolytic solution was 245 ° C., the iron nitride material No. 2 was produced.

[Comparative example]
In Example 1, except that the temperature of the electrolytic solution was 255 ° C., the iron nitride material No. 3 was produced.

表１の結果より、溶融塩電解時に電解液の温度を２５０℃以下とすることでα’’−Ｆｅ_１６Ｎ_２を含有する窒化物層が得られるが、２５０℃を超えると得られないことがわかる。 -Evaluation-
(Generation phase)
Formation of a nitride layer on the surface of the anode Fe plate was observed under all conditions of Example 1, Example 2, and Comparative Example.
The product phase of the obtained nitride layer was analyzed by an X-ray diffractometer. The results are shown in Table 1.

From the results in Table 1, a nitride layer containing α ″ -Fe ₁₆ N ₂ can be obtained by setting the temperature of the electrolytic solution to 250 ° C. or less during molten salt electrolysis, but it cannot be obtained when the temperature exceeds 250 ° C. I understand.

(Average film thickness)
The iron nitride material No. obtained as described above. 1-No. The average film thickness of 3 was measured by cross-sectional observation.
As a result, the iron nitride material No. 1 has an average film thickness of 80 nm. 2 is 80 nm. 3 was 80 nm.

(Content of α ″ -Fe ₁₆ N ₂ )
The iron nitride material No. obtained as described above. 1, no. The content of α ″ -Fe ₁₆ N ₂ in the two nitride layers was measured with an X-ray diffractometer.
As a result, the iron nitride material No. The content of α ″ -Fe ₁₆ N ₂ in the nitride layer of No. 1 is 55% by mass. 2 was 32 mass%.

A Any area on the iron nitride material B Any area on the iron nitride material C Any area on the iron nitride material D Any area on the iron nitride material E Any area on the iron nitride material 1 Iron nitride material 2 Iron base material 3 Nitride Membrane 51 Anode 52 Cathode 53 Electrolyte 54 Power supply 61 Lead wire 62 Cylindrical electrode member 71 Lead wire 72 Cylindrical electrode member 73 Porous member 81 Lead wire 82 Cylindrical member 83 Electrode member 91 Lead wire 92 Cylindrical member 93 Porous body

Claims (16)

Having a nitride layer containing α ″ -Fe ₁₆ N ₂ on the surface of an iron base having a purity of 99% by mass or more;
The nitride layer is an iron nitride material having an average film thickness of 10 nm or more and 100 μm or less.   The iron nitride material according to claim 1, further comprising an anticorrosion layer on a surface of the nitride layer. The anticorrosion _layer, ε-Fe 2-3 _N, is iron carbide or iron oxide, nitride iron according to claim 2. A method for producing the iron nitride material according to claim 1,
An electrolytic solution forming step of forming an electrolytic solution by dissolving nitride ions (N ³⁻ ) in the molten salt;
By performing molten salt electrolysis using an anode and a cathode provided in the electrolyte, iron nitride containing α ″ -Fe ₁₆ N ₂ is electrodeposited on the surface of the anode to form a nitride layer. An electrolysis process;
Have
In the electrolysis step, the temperature of the electrolytic solution is 250 ° C. or less, the anode is an iron base having a purity of 99% by mass or more, and the potential applied to the anode is 0.5 V or more on the basis of Li ⁺ / Li, The manufacturing method of the iron nitride material which is 1.5V or less.   The manufacturing method of the iron nitride material of Claim 4 which has the pre-processing process of removing the oxide layer currently formed in the surface of the said iron base material used for the said anode before the said electrolysis process.   6. The method of manufacturing an iron nitride material according to claim 4, further comprising an anticorrosion layer forming step of forming an anticorrosion layer on a surface of the nitride layer after the electrolysis step. The anticorrosion _layer, ε-Fe 2-3 _N, is iron carbide or iron oxide, method for producing a nitride iron according to claim 6.   The method for producing an iron nitride material according to any one of claims 4 to 7, wherein the molten salt is an alkali metal halide, an alkaline earth metal halide, or a mixture thereof.   9. The method for producing an iron nitride material according to claim 8, wherein the alkali metal halide is an alkali metal bromide, iodide, or a mixture of bromide and iodide.   The method for producing an iron nitride material according to claim 8 or 9, wherein the alkaline earth metal halide is an alkaline earth metal bromide, iodide, or a mixture of bromide and iodide.   The method for producing an iron nitride material according to any one of claims 8 to 10, wherein the alkali metal is at least one selected from the group consisting of Li, K, and Cs.   The said alkaline earth metal is a manufacturing method of the iron nitride material as described in any one of Claims 8-11 which is 1 or more types selected from the group which consists of Mg, Ca, Sr, and Ba.   The method for producing an iron nitride material according to any one of claims 4 to 12, wherein the molten salt is LiBr-KBr-CsBr or LiI-KI-CsI. The molten salt contains Li ⁺ , K ⁺ and Cs ⁺ , the content of Li ⁺ is 40 mol% or more and 80 mol% or less, the content of K ⁺ is 5 mol% or more and 30 mol% or less, and the content of Cs ⁺ is The method for producing an iron nitride material according to any one of claims 4 to 13, which is 10 mol% or more and 40 mol% or less. The method for producing an iron nitride material according to any one of claims 4 to 14, wherein Li ₃ N is added to the molten salt to form an electrolytic solution in which nitride ions (N ^3- ) are dissolved. A nitrogen gas reducing electrode is provided on the molten salt, and an electrolytic solution in which nitride ions (N ³⁻ ) are dissolved is formed by supplying nitrogen gas to the nitriding gas reducing electrode and performing electrochemical reduction. The method for producing an iron nitride material according to any one of claims 4 to 15.

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