JP3294645B2 - Nitride magnetic powder and its production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth-iron-nitrogen based magnetic material having high magnetic properties and excellent oxidation resistance, and particularly to a magnetic material most suitable for use in small motors and actuators.

[0002]

2. Description of the Related Art Magnetic materials are used in a wide range of fields from home appliances, audio products, automobile parts and peripheral devices of computers, and their importance as electronic materials is increasing year by year. In particular, recently, there has been a demand for miniaturization and high efficiency of various electric and electronic devices, so that a magnetic material with higher performance is required.

[0003] In response to the demands of this era, Sm-Co based, N
The demand for rare earth magnetic materials such as d-Fe-B is rapidly increasing. However, the Sm-Co system has a problem that the supply of the material is unstable and the cost of the material is high, and the Nd-Fe-B system has a problem in that the heat resistance and the corrosion resistance are inferior. On the other hand, as a new rare earth magnetic material, a rare earth-iron-nitrogen magnetic material has been invented. This material has a high magnetization, an anisotropic magnetic field, and a high Curie point.
It is expected as a magnetic material that compensates for the drawbacks of the d-Fe-B system.

However, when a rare earth-iron-nitrogen based magnetic material is used after being finely pulverized, the surface is oxidized and the coercive force is reduced, so that the high magnetic properties inherent to this material can be sufficiently exhibited. Can not. Therefore, the appearance of rare earth-iron-nitrogen based magnetic materials which are more excellent in oxidation resistance and have high magnetic properties is strongly desired.

[0005]

DISCLOSURE OF THE INVENTION The present invention relates to a rare-earth-iron-nitrogen-based material having a rhombohedral or hexagonal crystal structure in which a metal element M coexists to provide high magnetic properties and excellent oxidation resistance. The present invention provides a rare earth-iron-M-nitrogen composition magnetic material having the following characteristics:

[0006]

In order to obtain a rare earth-iron-nitrogen based magnetic material having high magnetic properties and oxidation resistance, the present inventors have conducted intensive studies on a system obtained by adding various elements (M) to a mother alloy. The present inventors have found a magnetic material having a composition having high magnetic properties and excellent oxidation resistance, and a rare earth (R) -iron (Fe) -M-nitrogen (N) composition, and have accomplished the present invention.

That is, the present invention relates to (1) a general formula R _α (Fe _(1-γ) M _γ )
A magnetic material represented by _{(100-α-β-δ} -ε) N β H δ O ε, R is Sm, at least one M of Nd is P,
At least one of the elements As, Sb and Be , α,
β, δ, ε are atomic percentages, 2.4 ≦ α ≦ 20 2.4 ≦ β ≦ 30 0.1 ≦ δ ≦ 10 0.1 ≦ ε ≦ 10 γ is an atomic ratio of 0.001 ≦ γ ≦ 0. 5, wherein the main phase contains a rhombohedral or hexagonal crystal structure, and (2) 0.01 to 50 of Fe in the general formula described in (1).
Characterized in that atomic% is replaced by Co (1)
(3) a general formula R _{α / (100-β-δ-ε)} (Fe
_(1-γ) M _γ ) An alloy represented by _{(100-α-β-δ-ε) / (100-β-δ-ε)} is mixed in an atmosphere containing at least one of nitrogen gas and ammonia gas. After the heat treatment in the range of 200 to 650 ° C., the pulverization is performed by controlling the oxygen and hydrogen concentrations in the pulverization gas or adjusting the dissolved oxygen and water contents in the pulverization solvent (1). Or a method for producing a magnetic material according to (2). However, R in the above general formula
Is at least one of Sm and Nd, M is P and A
at least one of the elements s, Sb and Be ,
α, β, δ, ε are atomic percentages 2.4 ≦ α ≦ 20 2.4 ≦ β ≦ 30 0.1 ≦ δ ≦ 10 0.1 ≦ ε ≦ 10 γ is an atomic ratio of 0.001 ≦ γ ≦ 0.5

Hereinafter, the present invention will be described in detail. As the rare earth (R), Y, La, Ce, Pr, Nd, P
m, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
m, Yb and Lu , among which Sm or
Must contain mainly one or more of Nd
No.

[0009] The R may have a purity that can be obtained by industrial production, and impurities unavoidable in production, such as O, H,
C, Al, Si, F, Na, Mg, Ca, Li and the like may be present. Iron (Fe) is the basic composition of the present magnetic material that is responsible for ferromagnetism.
Up to 50 atomic% may be replaced by Co, in which case the Curie point, increase in magnetization, and improvement in oxidation resistance are expected. Hereinafter, when it is described as an iron component, it includes a case where Co is replaced by a maximum of 50 atomic%. With respect to each element (M) of P, As, Sb, and Be, which are essential components for exhibiting the effects of the present invention, one or more of M are added to the total amount of the iron component and M. , In atomic ratio 0.001 to
Coexist in the range of 0.5.

[0010] The composition of the R-Fe-MN-based magnetic material in the present invention is such that the content of the rare earth element is 3 to 20 atomic%, and
3.91 at%, M component must be within the range of 0.05 to 47 at%, and N must be within the range of 3 to 30 at%. When the R component is less than 3 atomic%, a soft magnetic phase containing a large amount of iron component is separated, and the coercive force of the nitride is reduced, so that a practical permanent magnet cannot be obtained. On the other hand, if the R component exceeds 20 atomic%, the residual magnetic flux density is undesirably reduced.

If the content of the M component exceeds 47 atomic%, the saturation magnetization decreases, which is not preferable. If the content of the M component is less than 0.05 atomic%, there is almost no effect of adding M on the oxidation resistance. Also, M
A preferable range of the component amount is 0.1 to 30 atomic%. In addition to P, As, Sb, and Be as M components,
Li, Na, K, Mg, Ca, Sr, Ba, Zr, T
i, Hf, V, Nb, Ta, Cr, Mo, W, Mn, N
i, Pd, Cu, Ag, Zn, B, Al, Ga, In,
One or more of the elements C, Sn, Pb, and Bi (M ′ component) may be added, but their contents do not exceed the total amount of P, As, Sb, and Be. In addition, the total amount of P, As, Sb, and Be must be within the range of the γ value.

Of the M ′ components, In, Cu, and Zn are particularly effective in mixing and adding the M component. By adding an appropriate amount of these elements together with the M component, the coercive force of the present magnetic material is stabilized against oxidation. Sex is further enhanced. The R-Fe-MN-based magnetic material according to the present invention exhibits high oxidation resistance when the main phase contains 50% or more of the entire volume fraction.

The main phase referred to here is at least R, Fe
And a phase containing N and a rhombohedral or hexagonal crystal structure, and a phase having another composition and crystal structure is called a subphase. For example, RFe _12-X M _X
It may contain a highly magnetic nitride phase that takes a tetragonal form, such as an N _y phase and an RFe _12-x M′N _y phase. It is desirable that the fraction does not exceed the volume fraction of the magnetic material of the present invention.
Further, when the volume fraction of the main phase exceeds 75%, the material becomes extremely preferable for practical use. However, the magnetic material of the present invention is not limited to the above volume fraction range.

However, only when M = Ge, the main phase must have a rhombohedral or hexagonal crystal structure, and the volume fraction of the main phase must exceed 50% of the whole. By introducing nitrogen between the crystal lattices of the R-Fe-M material alloy, one or more of the items of the oxidation resistance and the magnetic properties are improved, and the magnetic material becomes practically suitable.

The magnetic characteristics referred to herein include the saturation magnetization (4πIs), residual magnetic flux density (Br), magnetic anisotropic magnetic field (Ha), magnetic anisotropic energy (Ea), magnetic anisotropy ratio, Curie point (Tc), intrinsic coercive force (iHc), squareness ratio (Br / 4πIs), maximum energy product [(BH) m
ax], the thermal demagnetization rate (α), and the temperature change rate (β) of the coercive force. However, the magnetic anisotropy ratio is
The ratio (a / b) of the magnetization (a) in the difficult magnetization direction and the magnetization (b) in the easy magnetization direction when an external magnetic field of 15 kOe is applied. Is evaluated as high.

[0016]

The amount of nitrogen (N) to be introduced must be in the range of 3 to 30 atomic%. If it exceeds 30 atomic%, the magnetization is low, and its practicality is small as a magnet material. If it is less than 3 atomic%, the performance of the raw material alloy cannot be improved much, which is not preferable. More preferably as the amount of nitrogen,
It is 5 to 25 at%, particularly preferably 10 to 17 at%.

The R-Fe-MN magnetic material obtained by the present invention contains 0.01 to 15 atomic% of hydrogen (H) and 0.01 to 15 atomic% of oxygen (O). Is preferred. More preferred amounts of hydrogen and oxygen are 0.1 to
10 at% and 0.1 to 10 at%. Therefore, a particularly preferred composition of the R-Fe-MN-based material of the present invention is:
General formula Rα (Fe _(1- γ ₎ Mγ) _(100- α _- β _- δ _- ε
₎ When expressed as NβHδOε, α, β, δ, and ε are atomic%, and 2.4 ≦ α ≦ 20 2.4 ≦ β ≦ 30 0.1 ≦ δ ≦ 10 0.1 ≦ ε ≦ 10 γ is an atom The ratio is in the range of 0.001 ≦ γ ≦ 0.5.

The effect of adding the M component to the R-Fe-N-based magnetic material is mainly to improve the oxidation resistance. In particular,
In the deterioration of an R-Fe-N-based magnetic material due to oxidation, a decrease in coercive force is more problematic than a decrease in magnetization, and the magnetic material of the present invention is characterized by having excellent stability of coercive force against oxidation. The invention, R, such as near grain boundary, or RFe ₃ phase
In a material having an R-Fe-N composition such as a rich nitride phase and an α-Fe phase or a nitride phase thereof, the M component is condensed into a subphase exhibiting soft magnetism and is converted into a nonmagnetic phase. It also has the effect of improving the squareness ratio and coercive force of the nitride.

Hereinafter, the production method of the present invention will be exemplified. (1) Preparation of master alloy In the magnetic material of the present invention, R-Fe-
The main material phase of the M alloy has a structure in which the M component replaces the iron component site in the R-Fe alloy crystal, or the main material phase and the sub-material phase are different from the R-Fe two-component system due to the addition of M. composition,
It has a structure and exhibits the effects of the present invention. Therefore, it is desirable to add M at the stage of master alloy adjustment.

The main raw material phase referred to herein is a phase containing at least R and Fe but not containing N and having a rhombohedral or hexagonal crystal structure. And a phase containing no N is referred to as an auxiliary raw material phase. As a method for producing an R-Fe-M alloy, R, Fe,
M component is melted by high frequency, high frequency melting method for casting into molds, etc., each component is charged to a boat such as copper, arc melting method for melting by arc discharge, and high frequency melt is dropped on a rotated copper roll. A super-quenching method for obtaining a ribbon-shaped alloy, a gas atomizing method for spraying a high-frequency molten metal with a gas to obtain an alloy powder, an Fe and / or M powder or an Fe-M alloy powder, and an R and / or M oxide powder,
And reducing agent at a high temperature to reduce R or R and M, while converting R or R and M to Fe and or Fe
R / D method for diffusing into -M alloy powder, mechanical alloying method in which each metal component alone and / or alloy is reacted while finely pulverized with a ball mill or the like, or alloy obtained by any of the above methods is heated in a hydrogen atmosphere. However, any of the HDDR methods of decomposing into hydrides of R and / or M and Fe and / or M or Fe-M alloys and then recombining and alloying while purging hydrogen at a low pressure at high temperature is used. Good.

When the high frequency melting method or the arc melting method is used, a soft magnetic component mainly composed of Fe tends to precipitate from the molten state when the alloy is solidified, which causes a decrease in coercive force even after the nitriding step. Therefore, in order to eliminate the soft magnetic component or to improve the crystallinity, the temperature is set to 800 ° C. or less in an inert gas such as argon or helium or in a vacuum.
It is effective to perform annealing in a temperature range of 1300 ° C.
The alloy produced by this method has a large crystal grain size and good crystallinity, and has a high residual magnetic flux density, as compared with the case where a super-quenching method or the like is used.

When the ultra-quenching method is used, fine crystal grains are obtained, and submicron particles can be prepared depending on conditions. However, when the cooling rate is high, the alloy becomes amorphous, and magnetic properties such as magnetization are reduced even after nitriding. Also in this case, annealing after alloy preparation is effective.
The alloy obtained by the gas atomization method often takes a spherical form, and can be prepared from a fine powder to a coarse powder. Also in this case, depending on the conditions, it is necessary to perform annealing to improve the crystallinity. In addition to this method, R / D
The alloy prepared by the method, the mechanical alloying method, or the HDDR method can adjust fine crystal grains or have a distribution in the composition of the M component. It is possible to

Incidentally, the crystal phase of the alloy may be different depending on the annealing conditions. For example, depending on the R component,
Depending on the case of annealing and the case of rapid cooling, there are cases where rhombohedral crystals are formed and cases where hexagonal crystals are formed. Therefore, the conditions for annealing require careful attention, and the desired crystal phase can be selected by controlling the annealing conditions. (2) Coarse pulverization and classification It is possible to directly nitride the alloy ingot produced by the above method. However, if the crystal grain size is larger than 500 μm, the nitriding treatment time becomes longer. It is efficient.

The coarse crushing is performed by using a jaw crusher, a hammer,
This is performed using a stamp mill, a rotor mill, a pin mill, a coffee mill, or the like. Further, even if a pulverizer such as a ball mill or a jet mill is used, an alloy powder suitable for nitriding can be prepared depending on conditions. Also, after coarse grinding,
Adjusting the particle size using a sieve, a vibratory or sonic classifier, a cyclone, or the like is also effective for performing more uniform nitriding.

Annealing in an inert gas or hydrogen after coarse pulverization and classification can remove structural defects, which is effective in some cases. In the above, the preparation method of the powder material or the ingot material of the rare earth-iron alloy as the material of the magnetic material of the present invention has been exemplified, but depending on the crystal grain size, crushed grain size, microstructure, surface state, etc. of these materials. There is a difference in the following optimum conditions for nitriding. (3) Nitriding and annealing Nitriding involves contacting a gas containing at least one of ammonia gas and nitrogen gas with the R-Fe-M alloy powder or ingot obtained in the above (1) or (1) and (2). Then, nitrogen is introduced into the crystal structure.

At this time, it is preferable to coexist a hydrogen gas in the nitriding atmosphere gas since nitriding efficiency is high and nitriding can be performed with a stable crystal structure. In addition, an inert gas such as argon, helium, or neon may be allowed to coexist in order to control the reaction. The nitriding reaction can be controlled by gas composition, heating temperature, heat treatment time, and pressure. The heating temperature varies depending on the mother alloy composition and the nitriding atmosphere.
It is selected in the range of 200 to 650 ° C. At 200 ° C. or lower, the rate of nitrogen penetration is low, and the reaction takes too much time, which is not preferable. At 650 ° C. or higher, the high magnetic property phase including the main phase is decomposed and the magnetic properties deteriorate. A more preferred heating temperature range is 250 to 600 ° C.

After nitriding, annealing in an inert gas and / or hydrogen gas is preferable from the viewpoint of improving magnetic properties. Examples of the nitriding / annealing apparatus include horizontal and vertical tubular furnaces, rotary reactors, and closed reactors. In any of the apparatuses, the magnetic material of the present invention can be adjusted. However, in order to obtain a powder having a uniform nitrogen composition distribution, it is preferable to use a rotary reactor.

The gas used for the reaction may be a gas flow system in which a gas stream of 1 atm or more is fed into the reaction furnace while keeping the gas composition constant, a gas sealing system in which the gas is sealed in a container at a pressure of 0.01 to 70 atm, or Supplied in combination. As a method for producing the magnetic material, a step of preparing a master alloy having an R-Fe-M composition by the method exemplified in (1) and (2) and then nitriding by the method shown in (3) is used. According to this method, the M component can coexist in a desired region or crystal lattice position of the present magnetic material, which is particularly effective for improving oxidation resistance.

The above is the description of the method for producing the R—Fe—M—N magnetic material of the present invention. In particular, when the magnetic material of the present invention is applied as a practical hard magnetic material, (4)
Fine grinding, (5) magnetic field shaping, and (6) magnetization may be performed. Hereinafter, the example is shown simply. (4) Pulverization For example, among R-Fe-MN-based magnetic materials of a single magnetic domain type, particularly when a large crystal grain size is to be maintained and a large coercive force is desired to be developed after nitriding, Fine grinding is performed, for example, when the polycrystalline grains are kept after the treatment and anisotropic hard magnetic material is desired.

As a method of pulverization, a rotary ball mill,
A vibration ball mill, a planetary ball mill, a wet mill, a jet mill, a cutter mill, a pin mill, an automatic mortar and a combination thereof are used. The pulverization method is selected according to the adjustment of the amount of hydrogen or oxygen and the target pulverized particle size.

As a method for controlling the amounts of hydrogen and oxygen within the particularly preferred ranges of the present invention, for example, when a jet mill is used, the oxygen and water vapor concentrations in the pulverized gas are maintained at a predetermined concentration, and an attritor or the like is used. When wet pulverization is used, a method of adjusting the amount of dissolved oxygen or the amount of water in the solvent may be used. (5) Magnetic field molding For example, when the magnetic powder obtained in (3) or (4) is applied to an anisotropic bonded magnet, compression molding is performed in a magnetic field after mixing with a thermosetting resin or a metal binder, After kneading with thermoplastic resin, injection molding is performed in a magnetic field,
Form a magnetic field.

The magnetic field shaping is preferably performed at 10 kOe in order to sufficiently orient the R-Fe-MN-based magnetic material in a magnetic field.
Above, more preferably in a magnetic field of 15 kOe or more. (6) Magnetization The anisotropic bonded magnet material and sintered magnet material obtained in (5) are usually magnetized to enhance magnet performance.

Magnetization is performed, for example, by an electromagnet that generates a static magnetic field,
This is performed by a condenser magnetizer that generates a pulse magnetic field. The magnetic field strength for sufficiently magnetizing is preferably 15 kOe or more, more preferably 30 kOe or more.

[0035]

The present invention will be described below in detail with reference to examples. The evaluation method is as follows. (1) Magnetic properties An R-Fe-MN-based magnetic material having an average particle size of about 3 μm was prepared by subjecting an external magnetic field of 15 kOe to 12 ton / cm ² at 5 mm × 1.
After shaping to about 0 mm × 2 mm and pulse magnetizing at room temperature with a magnetic field of 60 kOe, the intrinsic coercive force (iHc / kOe) was measured using a vibrating sample magnetometer (VSM). (2) Nitrogen amount, nitrogen amount and hydrogen amount Si ₃ N ₄ (including SiO ₂ quantified) as a standard sample,
The amounts of nitrogen and oxygen were determined by an inert gas melting method. The amount of hydrogen was determined by an inert gas melting method using high-purity hydrogen gas (99.999% or more) as a standard gas. (3) Average particle size It was evaluated using a Lee Nurse specific surface area meter. (4) Oxidation resistance The powder molded product having an average particle size of 3 μm evaluated in (1) was
It was placed in a thermostat at 10 ° C., and the intrinsic coercive force after 200 hours was measured in the same manner as in (1), and the retention rate (%) of the intrinsic coercive force was determined by comparing with the result of (1). The higher the retention, the higher the oxidation resistance. In addition, in this test, since the evaluation was performed using a green compact containing no binder, the retention was 70%.
If the material exceeds, for example, it can be determined that the material has oxidation resistance enough to be practically used for a bonded magnet material or the like. (5) Oxidation test 10 mg of a coarse powder sample adjusted to an average particle size of 15 μm was placed in a thermobalance and heated in a 50 ml / min air stream at a heating rate of 1 μm.
The rate of weight change (% by weight) from 50 ° C. to 250 ° C. was measured at 0 ° C./min. The smaller the rate of weight change, the less likely it is to be oxidized.

[0036]

REFERENCE EXAMPLE 1 Sm of 99.9% purity, Fe of 99.9% purity and Si of 99.9% purity were melt-mixed in a high-frequency melting furnace under an argon gas atmosphere, and then the molten metal was cast into a pure iron mold. Pour it in, cool it, and in an argon atmosphere,
By annealing at 1050 ° C. for 30 hours, Sm
An alloy having a composition of _9.5 (Fe _0.9 Si _0.1 ) _90.5 was prepared.

This alloy was pulverized by a jaw crusher and then further pulverized by a rotor mill in a nitrogen atmosphere, and the particle size was adjusted by a sieve to obtain a powder having an average particle diameter of about 50 μm. This Sm-Fe-Si alloy powder was charged into a horizontal tubular furnace, and at 465 ° C, an ammonia partial pressure of 0.3 a.
Heat treatment was performed for 2.5 hours in a mixed gas flow of tm and 0.7 atm of hydrogen gas, followed by annealing for 30 minutes in a flow of argon, and then adjusted to an average particle size of about 15 μm. Next, the powder was pulverized to a mean particle size of about 3 μm by a jet mill using a gas mainly containing nitrogen and partially mixed with oxygen and water vapor.

Table 1 shows the composition, oxidation resistance and oxidation test results of the obtained Sm-Fe-Si-N powder. Also,
The coercive force of the compact of the Sm—Fe—Si—N-based magnetic material pulverized to 3 μm is 6.5 kOe, and the residual magnetic flux density is 8.3 k.
G. As a result of analysis by the X-ray diffraction method, the crystal structure of this material was mainly rhombohedral, and no diffraction line corresponding to Si alone was found.

[0039]

Reference Examples 2 to 4 and Examples 1 to 7
R-Fe-MN-based powder was obtained by the same operation as in Reference Example 1 except that the composition ratio was changed to the composition shown in Table 1 . Table 1 shows the results. As a result of X-ray diffraction, the material of Reference Example 2 was a material in which a rhombohedral substance was a main component and a tetragonal substance was partially mixed. Further, the crystal structure of the material of Reference Example 3 was mainly rhombohedral.

[0040]

Comparative Example 1 Sm-F was prepared in the same manner as in Reference Example 1 except that Fe was added by the amount (atomic%) without adding Si.
An eN powder was obtained. Table 1 shows the results.

Nd-F was prepared in the same manner as in Reference Example 2 except that Fe was added by the amount (atomic%) without adding Ge.
An eN powder was obtained. Table 1 shows the results.

[0042]

[0043]

[Table 1]

[0044]

As described above, according to the present invention, rare earth-iron-M- has excellent oxidation resistance and high magnetic properties.
A nitrogen-based magnetic material can be provided.

Claims (3)

(57) [Claims] 1. The general formula R _α (Fe _(1-γ) M _γ )
A magnetic material represented by _{(100-α-β-δ} -ε) N β H δ O ε, R is Sm, at least one M of Nd is P, As, S
At least one of the elements b and Be, α, β, δ, and ε are represented by atomic percentages: 2.4 ≦ α ≦ 20 2.4 ≦ β ≦ 30 0.1 ≦ δ ≦ 10 0.1 ≦ ε ≦ 10 γ Is a magnetic material having an atomic ratio of 0.001 ≦ γ ≦ 0.5 and a main phase having a rhombohedral or hexagonal crystal structure. 2. The amount of Fe in the general formula according to claim 1.
2. The magnetic material according to claim 1, wherein 01 to 50 atomic% is substituted by Co. 3. The method of claim 1, wherein R _{α / (100-β-δ-ε)} (Fe
_(1-γ) M _γ ) An alloy represented by _{(100-α-β-δ-ε) / (100-β-δ-ε)} is mixed in an atmosphere containing at least one of nitrogen gas and ammonia gas. After heat treatment in the range of 200 to 650 ° C., pulverizing by controlling the oxygen and hydrogen concentrations in the pulverizing gas or adjusting the amount of dissolved oxygen and water in the pulverizing solvent. 3. The method for producing a magnetic material according to 1 or 2. Where R in the above general formula is S
m, at least one of Nd, M is P, As,
At least one element of Sb and Be , wherein α, β, δ, and ε are represented by atomic percentages: 2.4 ≦ α ≦ 20 2.4 ≦ β ≦ 30 0.1 ≦ δ ≦ 10 0.1 ≦ ε ≦ 10 γ is atomic ratio 0.001 ≦ γ ≦ 0.5