阅读说明：本技术 钐-铁-氮磁铁粉末及其制造方法 (Samarium-iron-nitrogen magnet powder and method for producing same ) 是由 冈田周祐 高木健太 榎戸靖 藤川佳则 桥本龙司 于 2018-05-29 设计创作，主要内容包括：本发明的一个形态为钐-铁-氮磁铁粉末,其中,钐-铁-氮磁相的表面上形成有非磁性相,并且算术平均粗糙度Ra为3.5nm以下。(One form of the present invention is samarium-iron-nitrogen magnet powder in which a nonmagnetic phase is formed on the surface of a samarium-iron-nitrogen magnetic phase and the arithmetic average roughness Ra is 3.5nm or less.)

1. A samarium-iron-nitrogen magnet powder characterized in that,

a non-magnetic phase is formed on the surface of the samarium-iron-nitrogen magnetic phase,

the arithmetic average roughness Ra is 3.5nm or less.

2. A samarium-iron-nitrogen magnet powder according to claim 1,

the non-magnetic phase is a samarium oxide phase.

3. A samarium-iron-nitrogen magnet powder according to claim 1,

if the average particle diameter and coercive force of the samarium-iron-nitrogen magnet powder are set to X [ mu ] m and Y [ kOe ], respectively, the formula is satisfied

Y＝a×ln(X)+b，

In the formula, a is-9 or more and-6 or less, and b is 22 or more.

4. A samarium-iron-nitrogen magnet powder according to claim 1,

if the X-ray diffraction pattern is caused by Sm₂Fe₁₇N₃The intensity of the phase peak is designated as c and will be derived from SmFe₅D represents the intensity of the phase peak, and satisfies the formula

d/c＜0.05。

5. A samarium-iron-nitrogen magnet powder according to claim 1,

if the X-ray diffraction pattern is caused by Sm₂Fe₁₇N₃The intensity of the phase peak is denoted as c and will be derived from Sm₂O₃The intensity of the phase peak is set to e, and the formula is satisfied

e/c≥0.05。

6. A method for producing samarium-iron-nitrogen magnet powder, comprising:

reducing and diffusing precursor powder of the samarium-iron alloy to prepare samarium-iron alloy powder;

nitriding the samarium-iron alloy powder;

a step of non-magnetizing a samarium-rich phase present on the surface of the nitrided samarium-iron alloy powder;

a step of washing the powder in which the samarium-rich phase is non-magnetized with a solvent capable of dissolving a calcium compound; and

and a step of dehydrogenating the washed powder.

Technical Field

The present invention relates to samarium-iron-nitrogen magnet powder and a method for producing samarium-iron-nitrogen magnet powder.

Background

Currently, neodymium-iron-boron magnets have been used for various purposes as high-performance magnets.

However, since neodymium-iron-boron magnets have a low Curie temperature (312 ℃) and low heat resistance, dysprosium (dysprosium) needs to be added to the magnets for use in environments where motors and the like are exposed to high temperatures. Here, the production amount of dysprosium is small, the production area is limited, and the supply is insufficient.

Therefore, samarium (samarium) -iron-nitrogen magnets have been developed as a high-performance magnet having high heat resistance without adding dysprosium.

Samarium-iron-nitrogen magnets have the same saturation magnetization (saturation magnetization) as neodymium-iron-boron magnets, have a high curie temperature of 477 ℃, have a small temperature change in magnetic properties, and have an extremely high value such as 260kOe which is about 3 times as high as that of neodymium-iron-boron magnets as an anisotropic magnetic field which is a theoretical value of coercive force (coercivity), and thus samarium-iron-nitrogen magnets are promising as magnets having high heat resistance (see, for example, patent documents 1 to 4 and non-patent documents 1 to 3).

As a method for producing samarium-iron-nitrogen magnet powder, there is a method in which samarium-iron oxide powder produced by a coprecipitation method or the like is subjected to reduction diffusion to form samarium-iron alloy powder, which is subjected to nitriding treatment, and then unreacted calcium and calcium oxide as a by-product are removed by washing. By this method, fine samarium-iron-nitrogen magnet powder can be produced without performing pulverization treatment. Accordingly, the edges (edges) of the samarium-iron-nitrogen magnet powder which can be the sources of the strain and/or the reversible magnetization region are small, so that the samarium-iron-nitrogen magnet powder having a high coercive force can be produced.

Disclosure of Invention

One aspect of the present invention is to provide a samarium-iron-nitrogen magnet powder having a high coercive force.

In the samarium-iron-nitrogen magnet powder according to one embodiment of the present invention, a nonmagnetic phase is formed on the surface of the samarium-iron-nitrogen magnetic phase (magnet phase), and the arithmetic average roughness Ra is 3.5nm or less.

In another embodiment of the present invention, a method for producing a samarium-iron-nitrogen magnet powder includes: a step of producing samarium-iron alloy powder by reducing and diffusing precursor powder of the samarium-iron alloy; nitriding the samarium-iron alloy powder; a step of non-magnetizing a samarium-rich phase (Sm-rich phase) present on the surface of the nitrided samarium-iron alloy powder; a step of washing the powder in which the samarium-rich phase is non-magnetized with a solvent capable of dissolving a calcium compound; and a step of dehydrogenating the cleaned powder.

According to an aspect of the present invention, a samarium-iron-nitrogen magnet powder having a high coercive force can be provided.

Drawings

Fig. 1 is an FE-SEM backscattered electron image of a cross section of the samarium-iron-nitrogen magnet powder of example 1.

Fig. 2 is an FE-SEM backscattered electron image of a cross section of the samarium-iron-nitrogen magnet powder of example 2.

FIG. 3 is an FE-SEM backscattered electron image of a cross section of the samarium-iron-nitrogen magnet powder of comparative example 1.

FIG. 4 is an FE-SEM backscattered electron image of a cross section of the samarium-iron-nitrogen magnet powder of comparative example 2.

Fig. 5 is a STEM image and line analysis result of a cross section of the samarium-iron-nitrogen magnet powder of example 1.

Fig. 6 is a STEM image and line analysis result of a cross section of the samarium-iron-nitrogen magnet powder of example 2.

Fig. 7 is a STEM image and line analysis result of a cross section of the samarium-iron-nitrogen magnet powder of comparative example 1.

Fig. 8 is a STEM image and line analysis result of a cross section of the samarium-iron-nitrogen magnet powder of comparative example 2.

Fig. 9 is an X-ray diffraction pattern of the samarium-iron-nitrogen magnet powder of example 1.

Fig. 10 is an X-ray diffraction pattern of the samarium-iron-nitrogen magnet powder of example 2.

Fig. 11 is an X-ray diffraction pattern of the samarium-iron-nitrogen magnet powder of comparative example 1.

Fig. 12 is an X-ray diffraction pattern of the samarium-iron-nitrogen magnet powder of comparative example 2.

Fig. 13 is a graph showing a relationship between the average particle diameter and the coercive force of the samarium-iron-nitrogen magnet powder.

Detailed Description

The inventors of the present invention have found, in the course of conducting studies on the production of high-performance samarium-iron-nitrogen magnet powder, that whether or not a layer is formed on the surface of the samarium-iron-nitrogen magnetic phase affects the surface smoothness of the samarium-iron-nitrogen magnet powder. Further, the inventors of the present invention have found that the surface smoothness of the samarium-iron-nitrogen magnet powder greatly affects the coercive force of the samarium-iron-nitrogen magnet powder. Further, the inventors of the present invention have found that the coercive force of samarium-iron-nitrogen magnet powder can be improved by forming a non-magnetic phase on the surface of the samarium-iron-nitrogen magnetic phase, and have completed the present invention.

It is known that, in order to increase the coercive force of the magnet powder, the size (size) and/or surface state of the magnet powder are important in addition to the crystal structure (crystal structure) of the magnet powder. In particular, if there are defects such as irregularities or strain on the surface of the magnet powder, the anisotropic magnetic field at the defective portion is lowered, and the coercive force of the magnet powder is also lowered. Therefore, the surface of the magnet powder is preferably a smooth surface with less defects.

In order to produce samarium-iron-nitrogen magnet powder, in the present embodiment, the samarium-iron oxide powder and/or samarium-iron hydroxide powder produced by the wet synthesis method is subjected to pre-reduction, reductive diffusion, nitridation, cleaning, and dehydrogenation. Thus, fine powder can be produced without performing a micronizing treatment such as pulverization treatment. As a result, the samarium-iron-nitrogen magnet powder having no surface defects and a high coercive force can be obtained because there is no damage caused by the pulverization treatment.

In particular, when the temperature for reducing and diffusing samarium oxide-iron powder is 950 ℃ or lower, submicron (submicron) size samarium-iron-nitrogen magnet powder having an average particle size of less than 1 μm can be produced. The finer the average particle diameter of the samarium-iron-nitrogen magnet powder is, the more the coercive force of the samarium-iron-nitrogen magnet powder can be improved. Specifically, the inventors of the present invention produced samarium-iron-nitrogen magnet powder having an average particle diameter of 0.65 μm and a coercive force of 24.7kOe (for example, see non-patent document 1).

In order to produce a samarium-iron-nitrogen magnet powder having a higher coercive force, the inventors of the present invention examined the influence of the coercive force given to the surface of the samarium-iron-nitrogen magnet powder and developed a method for controlling the surface.

Samarium-iron alloy powder can be obtained by alloying samarium and iron generated by reduction of samarium oxide after reduction diffusion of samarium oxide-iron powder. In this case, if an iron phase (soft magnetic phase) with high magnetization remains, the coercivity, remanence, squareness, and other magnet characteristics of the samarium-iron-nitrogen magnet powder are greatly reduced. For this reason, in general, it is necessary to add samarium in an excess amount larger than the Stoichiometric ratio (stoichimetric ratio), and the excess addition of samarium results in a samarium-rich phase.

Here, for the samarium-rich phase, the metal complex represented by the general formula

SmFe_xN_y(x is 7 and y is 0 to 3.)

Crystal structure represented by and represented by₂Zn₁₇、TbCu₇The expressed samarium-iron-nitrogen magnetic phase contains more samarium than samarium, but has inferior magnet characteristics compared with the samarium-iron-nitrogen magnetic phase. Therefore, the samarium-rich phase may be subjected to a dissolving treatment with a weak acid such as a dilute acetic acid aqueous solution having a pH of 5 to 7 (for example, see patent document 1).

The inventors of the present invention conducted detailed investigations on the influence of the samarium-rich phase, the influence of the samarium-rich phase on the surface of the samarium-iron-nitrogen magnet powder, and the influence of the surface of the samarium-iron-nitrogen magnet powder on the coercive force. As a result, it was found that SmFe exists on the surface of the samarium-iron-nitrogen magnetic phase in the case of producing the samarium-iron-nitrogen magnet powder by the conventional production method₅Phase (soft magnetic phase). It has also been found that if the samarium-rich phase is subjected to a dissolution treatment based on a weak acid having a pH of less than 7, the surface of the samarium-iron-nitrogen magnet powder becomes rough, resulting in a decrease in the coercive force of the samarium-iron-nitrogen magnet powder. It was thus found that, if the samarium-rich phase is made nonmagnetic and a nonmagnetic phase is formed on the surface of the samarium-iron-nitrogen magnetic phase, a samarium-iron-nitrogen magnet powder having an arithmetic average roughness Ra of 3.5nm or less and a high coercive force can be obtained.

The samarium-iron-nitrogen magnet powder and the method for producing the same according to the present embodiment will be described in detail below. Redundant description is appropriately omitted. Further, where the term "between" and "between" are used herein to indicate a range of values, the two values are also included in the range of values (i.e., inclusive of the endpoints).

[ samarium-iron-nitrogen magnet powder ]

In the case of the samarium-iron-nitrogen magnet powder of the present embodiment, a nonmagnetic phase is formed on the surface of the samarium-iron-nitrogen magnetic phase. That is, the samarium-iron-nitrogen magnet powder of the present embodiment has a core-shell structure (core-shell structure), and the nonmagnetic phase (shell) is formed on at least a part of the surface of the samarium-iron-nitrogen magnetic phase (core).

In addition, the samarium-iron-nitrogen magnet powder of the present embodiment does not substantially form SmFe on the surface thereof₅And (4) phase(s).

The samarium-iron-nitrogen magnet powder of the present embodiment has an arithmetic average roughness Ra of 3.5nm or less, preferably 2nm or less, more preferably 1nm or less.

Here, in the case where a nonmagnetic phase is not formed on the surface of the samarium-iron-nitrogen magnetic phase, since irregularities are formed on the surface by oxidation or the like in the samarium-iron-nitrogen magnetic powder, the arithmetic average roughness Ra exceeds 3.5nm, which leads to a decrease in the coercive force of the samarium-iron-nitrogen magnetic powder.

On the other hand, in the case where the nonmagnetic phase is formed on the surface of the samarium-iron-nitrogen magnetic phase, the surface smoothness of the samarium-iron-nitrogen magnetic phase can be maintained regardless of the thickness of the nonmagnetic phase. Therefore, the thickness of the nonmagnetic phase does not particularly affect the coercive force of the samarium-iron-nitrogen magnet powder. Here, if the nonmagnetic phase becomes thick, the magnetization of the samarium-iron-nitrogen magnet powder decreases, so the nonmagnetic phase is preferably thin.

Note that the arithmetic average roughness Ra of the samarium-iron-nitrogen magnet powder can be measured by a Transmission Electron Microscope (TEM) or a Scanning Transmission Electron Microscope (STEM).

When the surface (hereinafter referred to as "measurement surface") on which the arithmetic average roughness Ra is measured is a cross section, the arithmetic average roughness Ra can be determined according to the definition of the arithmetic average roughness Ra of JIS B0601.

Specifically, the roughness curve can be obtained by obtaining an average line (expansion curve) from the profile curve of the measurement surface and then subtracting the average line from the profile curve, that is, replacing the average line with a straight line. Next, according to the coordinate system defined in JIS B0601, a direction coinciding with the average line after the substitution into a straight line is taken as an X-axis, and a direction perpendicular to the X-axis and parallel to the cross section is taken as a Z-axis. The reference length l is extracted from the roughness curve in the X-axis direction, and the average line of the extracted portion can be represented by the following formula (1).

[ formula 1]

At this time, the arithmetic average roughness Ra is Z (x) and Z₀The average of the absolute values of the deviations (c) can be obtained by the following equation (2).

[ formula 2]

Specifically, for example, a measurement plane of the cross section is observed using a microscope capable of high-magnification observation such as TEM, and an average line and a roughness curve are obtained from the cross section curve. A region of 150nm was arbitrarily selected on the X-axis, and 50X values (X) were extracted at regular intervals in the selected region₁～X₅₀) And for each X value, a Z value (Z (X)₁)～Z(x₅₀) To perform the measurement. Then, from the measured Z value, Z can be obtained by the following formula (3)₀。

Z₀＝(1/50)×{Z(x₁)+Z(x₂)+Z(x₃)+···+Z(x₅₀) } -formula (3)

Then, the obtained Z is used₀The arithmetic average roughness Ra can be obtained by the following formula (4).

Ra＝(1/50)×{|Z(x₁)-Z₀|+|Z(x₂)-Z₀|+···+|Z(x₅₀)-Z₀Equation (4)

There is a correlation (i.e., there is a relationship) between the coercive force of the samarium-iron-nitrogen magnet powder and the surface smoothness of the samarium-iron-nitrogen magnet powder. For this reason, the nonmagnetic phase may be formed on at least a part of the surface of the samarium-iron-nitrogen magnetic phase.

The coverage of the nonmagnetic phase of the samarium-iron-nitrogen magnet powder is preferably 50% or more, more preferably 60% or more, and still more preferably 80% or more, from the viewpoint of the coercive force of the samarium-iron-nitrogen magnet powder.

Here, if the nonmagnetic phase is not formed but the iron phase, SmFe, is formed on the surface of the samarium-iron-nitrogen magnetic phase₅The coercivity of the samarium-iron-nitrogen magnet powder is lowered with an equivalent soft magnetic phase.

The non-magnetic phase refers to a phase obtained by non-magnetizing a samarium-rich phase, although it is a magnetic strength ratio SmFe₅The phase is also low, but the magnetization is preferably low.

In the specification and claims of the present application, a samarium-iron-nitrogen magnet means a magnet containing samarium, iron, and nitrogen.

The elemental composition and/or crystal phase of the nonmagnetic phase is not particularly limited, but the nonmagnetic phase is preferably a samarium oxide phase.

If the average particle diameter and coercive force of the samarium-iron-nitrogen magnet powder of the present embodiment are set to X [ mu ] m and Y [ kOe ], respectively, the formula is satisfied

Y＝a×ln(X)+b

(in the formula, a is-9 or more and-6 or less, and b is 22 or more.)

Is preferred. Accordingly, the coercive force of the samarium-iron-nitrogen magnet powder can be improved.

If Sm is originated from Sm in the X-ray diffraction pattern of the samarium-iron-nitrogen magnet powder of the present embodiment₂Fe₁₇N₃The intensity of the phase peak is set as c and will be derived from SmFe₅D represents the intensity of the phase peak, and satisfies the formula

d/c＜0.05

Is preferred. Accordingly, the coercive force of the samarium-iron-nitrogen magnet powder can be improved.

If Sm is originated from Sm in the X-ray diffraction pattern of the samarium-iron-nitrogen magnet powder of the present embodiment₂Fe₁₇N₃The intensity of the peak of the phase is designated as c and is derived from Sm₂O₃Intensity of phase peakSet to e, then the formula is satisfied

e/c≥0.05

Is preferred. Accordingly, the coercive force of the samarium-iron-nitrogen magnet powder can be improved.

The samarium-iron-nitrogen magnet powder according to the present embodiment may further contain a rare earth element such as neodymium or praseodymium (praseodymium) and an iron group element other than iron. In addition, the crystal structure of samarium-iron-nitrogen magnet may be Th₂Zn₁₇Structure and TbCu₇Any one of the structures.

[ method for producing samarium-iron-nitrogen magnet powder ]

The manufacturing method of samarium-iron-nitrogen magnet powder comprises: reducing and diffusing precursor powder of the samarium-iron alloy so as to prepare samarium-iron alloy powder; nitriding samarium-iron alloy powder; and a step of non-magnetizing a samarium-rich phase present on the surface of the nitrided samarium-iron alloy powder. Further, the method for producing the samarium-iron-nitrogen magnet powder further comprises: a step of washing the powder in which the samarium-rich phase is non-magnetized with a solvent capable of dissolving a calcium compound; and a step of dehydrogenating the washed powder. Thus, a fine samarium-iron-nitrogen magnet powder having a high coercive force can be produced without performing a pulverization treatment.

[ preparation of precursor powder of samarium-iron alloy ]

The precursor powder of the samarium-iron alloy is not particularly limited as long as it can produce samarium-iron alloy powder by reduction diffusion, but examples thereof include samarium-iron oxide powder and/or samarium-iron hydroxide powder, and two or more kinds thereof may be used simultaneously.

In the specification and claims of the present application, samarium-iron alloy powder means alloy powder containing samarium and iron.

The samarium-iron alloy powder may further contain rare earth elements such as neodymium and praseodymium, and iron group elements other than iron.

Precursor powder of samarium-iron alloy can be produced by coprecipitation. Specifically, first, a precipitant such as alkali (alkali) is added to a solution containing a samarium salt and an iron salt to precipitate a precipitate composed of samarium and iron compounds (mainly hydroxide), and then the precipitate is recovered by filtration, centrifugation, or the like. Next, the precipitate is washed and dried in a hot air furnace, whereby samarium-iron (hydr) oxide can be obtained. Then, samarium-iron (water) oxide is coarsely pulverized by a blade mill (blademill) or the like, and then finely pulverized by a bead mill or the like, whereby samarium-iron oxide powder and/or samarium-iron hydroxide powder can be produced.

The counter ion (counter ion) in the samarium salt and the iron salt may be an inorganic ion such as a chloride ion, a sulfate ion, a nitrate ion, or an organic ion such as an alcohol (alkoxide).

As the solvent contained in the solution containing the samarium salt and the iron salt, an organic solvent such as water or ethanol (ethanol) may be used.

As the base, for example, a hydroxide of an alkali metal or an alkaline earth metal and/or ammonia (ammonia) can be used.

In addition to the alkali, a compound such as urea that can be decomposed by an external action such as heating to generate an alkali can be used as the precipitant.

Further, in addition to drying using an air heater, vacuum drying may be performed.

As the precursor powder of the samarium-iron alloy other than the samarium-iron oxide powder and/or the samarium-iron hydroxide powder, iron (hydr) oxide-samarium compound powder prepared by adding a samarium salt to a suspension containing iron hydroxide particles or iron oxide particles and evaporating the samarium salt to dry or adding a precipitant may be used.

As the precursor powder of the samarium-iron alloy, iron (hydr) oxide-samarium compound powder prepared by adding iron salt to a suspension containing samarium compound particles whose particle size is controlled and evaporating the iron salt to dry, or adding a precipitant can be used.

[ reduction diffusion ]

The method for reducing and diffusing the precursor powder of the samarium-iron alloy is not particularly limited, and examples thereof include a method in which calcium or calcium hydride is used and the precursor powder is heated to a temperature (about 850 ℃) equal to or higher than the melting point of calcium in an inert gas atmosphere. At this time, samarium reduced by calcium diffuses into the calcium melt and reacts with iron, whereby samarium-iron alloy powder can be produced.

The reduction diffusion temperature and the particle size of the samarium-iron alloy powder have a correlation, and the higher the reduction diffusion temperature is, the larger the particle size of the samarium-iron alloy powder is.

For example, Sm having an average particle size of 1 μm or less₂Fe₁₇The powder can be reduced and diffused in an inert gas atmosphere at a temperature of 850 to 950 ℃ for about 30 minutes to 2 hours.

[ Pre-reduction ]

In the case where the precursor powder of the samarium-iron alloy contains iron oxide or an iron compound, it is preferable to perform pre-reduction for reduction to iron before performing reduction diffusion. Accordingly, the particle size of the samarium-iron alloy powder can be reduced.

The method of pre-reducing the precursor powder of the samarium-iron alloy is not particularly limited, and examples thereof include a method of performing a heat treatment at a temperature of 400 ℃ or higher in a reducing atmosphere such as hydrogen.

For example, in order to obtain a composite powder having an average particle diameter of 1 μm or less and consisting of iron, samarium-iron oxide and samarium oxide by using a heat treatment furnace, pre-reduction may be performed in a hydrogen atmosphere at a temperature of 500 to 800 ℃.

[ nitriding ]

The method for nitriding the samarium-iron alloy powder is not particularly limited, and examples thereof include a method of performing a heat treatment at a temperature of 300 to 500 ℃ in an atmosphere of ammonia, a mixed gas of ammonia and hydrogen, a mixed gas of nitrogen, nitrogen and hydrogen, or the like.

The nitrogen content in the samarium-iron-nitrogen magnetic phase affects the magnetic properties of the samarium-iron-nitrogen magnetic powder. It is known that in order to improve the coercive force of samarium-iron-nitrogen magnet powder, the optimum samarium-iron-nitrogen magnetic phase is Sm₂Fe₁₇N₃And (4) phase(s). For this reason, it is very important to control the nitrogen content in the samarium-iron-nitrogen magnetic phase. To be explainedThat is, in the case of nitriding samarium-iron alloy powder using ammonia, although nitriding can be performed in a short time, the nitrogen content in the samarium-iron-nitrogen magnetic phase is present more than Sm₂Fe₁₇N₃The case of the phase. In this case, it is known that excess nitrogen can be discharged from the crystal lattice by nitriding the samarium-iron alloy powder and then annealing (annealing) the nitrided samarium-iron alloy powder in hydrogen gas. Therefore, to form single-phase Sm in a short time₂Fe₁₇N₃As the phase, a method of nitriding samarium-iron alloy powder with ammonia is preferable.

For example, the nitrogen content in the samarium-iron-nitrogen magnetic phase can be optimized (optimization) by first nitriding in an ammonia-hydrogen mixed gas flow at a temperature of 350 ℃ to 450 ℃ for 10 minutes to 2 hours, then switching to a hydrogen gas flow at the same temperature, and then annealing for 30 minutes to 2 hours. Then, the flow is switched to argon gas flow and heat treatment is performed at the same temperature for 0 to 1 hour, thereby removing hydrogen.

[ non-magnetization of samarium-rich phase ]

Samarium-rich phases are present on the surface of the nitrided samarium-iron alloy powder. When the nitrided samarium-iron alloy powder is cleaned, vacuum-dried and dehydrogenated in the same manner as in the conventional method, SmFe is formed on the surface of the samarium-iron-nitrogen magnetic phase₅Phase, resulting in a decrease in the coercive force of the samarium-iron-nitrogen magnet powder. For this purpose, the nitrided samarium-iron alloy powder may be exposed to, for example, an oxidizing atmosphere to slowly oxidize the samarium-rich phase before being cleaned. Accordingly, a samarium oxide phase can be formed on the surface of the samarium-iron-nitrogen magnetic phase, and as a result, samarium-iron-nitrogen magnet powder having a high coercive force can be obtained.

The oxidizing atmosphere is not particularly limited, but an inert gas atmosphere containing moisture and/or an inert gas atmosphere containing a trace amount of oxygen can be used.

In addition to the slow oxidation of the samarium-rich phase, an element capable of making the samarium-rich phase nonmagnetic by a reaction with the samarium-rich phase may be added to the surface of the nitrided samarium-iron alloy powder by a wet treatment such as an impregnation method or a dry treatment such as a sputtering method, and then heat-treated.

[ cleaning ]

The powder in which the samarium-rich phase is non-magnetized contains calcium compounds such as calcium oxide, unreacted metal calcium, calcium nitride obtained by nitriding metal calcium, and calcium hydride. For this reason, in order to produce samarium-iron-nitrogen magnet powder, it is preferable to wash the powder in which the samarium-rich phase is non-magnetized with a solvent capable of dissolving a calcium compound to remove the calcium compound. Accordingly, the magnetization of the samarium-iron-nitrogen magnet powder can be improved.

The solvent capable of dissolving the calcium compound is not particularly limited, but water, alcohol, and the like can be exemplified. Among them, water is preferably used from the viewpoint of cost and good solubility of the calcium compound.

For example, the powder in which the samarium-rich phase is non-magnetized is first added to water, and then stirred and decanted (decantation) is continuously performed, whereby most of the calcium compounds can be removed. Then, the powder from which most of the calcium compound has been removed is added to water, and a dilute acetic acid aqueous solution or the like is added while stirring to adjust the pH to 7, whereby the remaining calcium compound can be removed.

[ vacuum drying ]

In order to remove the solvent which can dissolve the calcium compound, it is preferable to vacuum-dry the washed powder.

The temperature for vacuum drying the washed powder is preferably from room temperature to 100 ℃. This can suppress oxidation of the powder after cleaning.

The washed powder may be replaced with an organic solvent having high volatility and being miscible with water, such as alcohol, and then vacuum-dried.

[ dehydrogenation ]

When samarium-iron alloy in which the samarium-rich phase is non-magnetized is cleaned, dehydrogenation of the cleaned powder is required in order to remove hydrogen that enters the crystal lattice. Accordingly, the coercive force of the samarium-iron-nitrogen magnet powder can be improved.

The method for dehydrogenating the powder after cleaning is not particularly limited, and examples thereof include a method of heat treatment in vacuum or an inert gas atmosphere.