JPH10106820A - Manufacturing method of rare earth-iron-nitrogen magnetic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relax the shock acting on magnetic powder at the time of collision of the powder and restrain the stress acting on a crystal structure at the time of pulverization, by adding and mixing a lubricant to a magnetic material and then pulverizing the mixture. SOLUTION: Magnetic powder of a magnetic material expressed by a formula RaFe(100-a-b-c)MbNc is prepared (with R contains at least one type of rare earth element including Y and Sm as an essential element at approximately 50at% or more, and M is at least one of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W, while a, b and c represent atomic percentages having the relations of 5<=a<=20, 0<=b<=5 and 3<=c<=30, with the remaining portion being Fe). Then, fatty acid as a lubricant is added to and mixed with the magnetic powder. The mixture is then pulverized by using a jet mill, more preferably, an airstream jet mill. Thus, the fatty acid film is caused to exist between colliding substances at the time of collision, thereby providing good lubricity. Thus, the shock acting on the magnetic powder at the time of collision is relaxed, thereby reducing the quantity of defects introduced by pulverization and exhibiting excellent magnetic property.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a rare earth-iron-nitrogen based magnetic material applicable to bonded magnets and the like.

[0002]

2. Description of the Related Art In recent years, it has been found that a rare-earth-iron-nitrogen-based alloy produced by dissolving nitrogen in an alloy of a rare earth and iron in an interstitial form as a new magnetic material exhibits excellent magnetic properties. Was done. This rare earth-iron-nitrogen based alloy exhibits uniaxial magnetic anisotropy when Sm is selected as the rare earth, and has a composition of Sm2 Fe17 N2.1,
It has been reported to exhibit high magnetic properties with a Curie temperature of 470 ° C., a saturation magnetization of 15.4 kG, and an anisotropic magnetic field of> 60 kOe (J.M.D. Volume 87 (1990) Chapter 25
1 page (JMDCoye and H.Sun, JMMM87 (1990) L251)
reference).

[0003] As a method for producing the above-mentioned rare earth-iron-nitrogen based magnetic material, the following steps can be mentioned.

[0004] 1) Preparation of master alloy 2) Coarse pulverization 3) Nitriding 4) Fine pulverization (single magnetic domain particle formation) Rare earth-iron-nitrogen based magnetic material is a strong uniaxial magnet by introducing nitrogen into the mother alloy in an interstitial manner. It is known that Curie temperature and saturation magnetization are improved while exhibiting anisotropy. Nitriding is performed by heat treatment of the rare-earth-iron-based material powder in an atmosphere gas such as a nitrogen gas, an ammonia gas, a hydrogen-nitrogen mixed gas, or a hydrogen-ammonia mixed gas. The coercive force manifesting mechanism of the rare earth-iron-nitrogen based alloy is a nucleation type, and it is necessary to pulverize the rare earth-iron-nitrogen alloy to a single magnetic domain particle diameter of 3 μm or less in order to increase the coercive force. Various ball mills such as a rotary ball mill, a vibrating ball mill, and an attritor, or a jet mill are used as a method of pulverization.

[0005]

In the rare earth-iron-nitrogen based magnetic material, in order to produce a magnetic powder having high magnetic properties, it is necessary to minimize defects such as processing strain introduced during pulverization. is important. If the amount of defects introduced at the time of pulverization is large, the saturation magnetization is greatly reduced and the squareness ratio is reduced. The squareness here means a value obtained by dividing the external magnetic field strength Hk when the magnetic flux density in the second quadrant of the magnetic hysteresis loop becomes 90% of the residual magnetic flux density by the coercive force iHc. The closer this value is to 1.0, the better the squareness ratio. This squareness ratio is closely related to the maximum energy product (BH) max, and the lower the squareness ratio, the higher the maximum energy product.
The product (BH) max cannot be obtained. Therefore, in the rare earth-iron-nitrogen based magnetic material, it is important to reduce the amount of defects introduced during pulverization and to make the powder into fine powder in order to produce a magnetic powder having high magnetic properties.

However, in the above prior art,
When various ball mills such as a rotary ball mill, a vibrating ball mill and an attritor are used, they are easily pulverized, but give a large stress to the crystal structure, so that a large amount of defects are introduced and the saturation magnetization is reduced. Is remarkable. As a method of pulverizing without giving a large stress to the crystal structure, pulverization by a jet mill is effective. Jet mills are roughly classified into collision type and air flow type based on their pulverizing mechanism. In both methods, the sample powder is moved at a high speed by a high-pressure pulverizing gas and crushed by colliding with a target in the collision type, and finely pulverized by the mutual collision of the sample powders mainly in the air flow type.
With respect to the crushing ability, the collision type is more effective and can be finely crushed. However, in terms of suppressing the stress applied to the crystal structure, pulverization by an air jet mill is more effective, and an air jet jet mill is the most suitable pulverization method for the rare earth-iron-nitrogen based magnetic material. It is a grinding method. However, even when finely pulverized by an air jet mill, it is difficult to completely eliminate defects introduced during fine pulverization. As a production method for reducing the amount of strain introduced during the fine pulverization, a production method in which the fine pulverization is performed in a non-aqueous solvent by wet pulverization over a long period of time has been proposed (JP-A-6-96920). However, wet pulverization is a batch process and therefore has low productivity.
In addition, since a non-aqueous solvent is used, it is necessary to install a local exhaust system from the viewpoint of preserving the working environment, which increases the cost.

[0007]

In order to solve the above-mentioned problems, the present invention provides a compound of the general formula RaFe (100-abc) M
R is at least one kind of rare earth element including Y, and contains Sm as an essential element in an amount of 50 at% or more, and M is Ti, Zr, Hf, V, Nb, Ta, Cr, M
at least one of o and W, wherein a, b and c are atomic percentages, and 5 ≦ a ≦ 200 ≦ b ≦ 53 ≦ c ≦ 30, and the balance is Fe. The present invention proposes a method for producing a rare earth-iron-nitrogen based magnetic material, characterized in that a lubricant is added to a magnetic material, mixed and then finely pulverized by jet mill pulverization.

Further, the present invention relates to a compound represented by the general formula:
abc) MbNc, R is at least one of rare earth elements including Y, and 50
at% or more, M is Ti, Zr, Hf, V, Nb, T
a, Cr, Mo, W, at least one of a, b,
c is an atomic percentage, 5 ≦ a ≦ 200 ≦ b ≦ 53 ≦ c ≦ 30, and the balance is made of Fe. In the method for producing a magnetic material, a coating layer made of a lubricant is provided on the inner wall of the grinding chamber. The present invention proposes a method for producing a rare earth-iron-nitrogen based magnetic material, which comprises pulverizing using a provided jet mill.

Further, in the above method for producing a rare earth-iron-nitrogen based magnetic material, the lubricant is at least one kind selected from fatty acids, wherein the lubricant is at least one kind selected from fatty acids.

The reasons for limiting the composition of the rare earth-iron-nitrogen based magnetic material in the present invention are as follows.

R is an element that plays an essential role in expressing magnetic anisotropy and generating coercive force. R contains Sm as an essential element, contains 50% or more in atomic percentage, and may be used as one or a combination of two or more elements selected from rare earth elements containing Y. R needs to be in the range of 5 to 20% in atomic percentage. When R <5%, a large amount of soft magnetic phase αFe is present in the alloy, making it difficult to obtain a coercive force.
If it is> 20%, the volume of the magnetic phase decreases and the saturation magnetization decreases, which is not preferable.

In the present invention, M may not be contained,
By adding M, higher magnetic characteristics can be achieved. M
Is to improve the material of the rare earth-iron-nitrogen based magnetic material and has the effect of improving brittleness. As a result, the grindability is improved, and the amount of defects introduced at the time of fine pulverization can be reduced, so that the magnetic properties can be improved. M is Ti, Zr, H
It may be used as one or a combination of two or more elements selected from f, V, Nb, Ta, Cr, Mo, and W. M
When M is added, M may be in the range of 0.05 to 5% in atomic percentage in order to exert the above effect. M <0.0
At 5%, brittleness cannot be improved, and at M> 5%, a compound phase having a high M concentration precipitates and brittleness cannot be improved.

N is an important element in a rare earth-iron-nitrogen based magnetic material for improving magnetic properties. By introducing N into the mother alloy in an interstitial manner, strong uniaxial magnetic anisotropy is exhibited, and the saturation magnetization and Curie temperature are increased. To exert the above effect, N needs to be in the range of 3 to 30% in atomic percentage. N <3%
In this case, the improvement of the magnetic properties by nitriding is poor, and when N> 30%, the crystal structure of the magnetic phase becomes unstable, which is not preferable.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for producing a rare earth-iron-nitrogen based magnetic material of the present invention will be described in detail. The rare earth-iron-nitrogen based magnetic material in the present invention is prepared by the steps of 1) preparation of a master alloy, 2) coarse pulverization, 3) nitriding, and 4) fine pulverization.

1) Preparation of Master Alloy The preparation method of the mother alloy is not particularly limited. For example, R metal, M metal, and iron are blended at a predetermined ratio, and a melting method of preparing a master alloy ingot using a high-frequency induction heating melting furnace or an arc melting furnace, or R metal, M metal, and iron are used. It is prepared by using a master alloy prepared by the above-mentioned melting method by blending at a predetermined ratio or melting and spraying a molten metal onto a copper roll rotating at a high speed to form an alloy, or by using various atomizing methods. It is possible. When prepared by various atomizing methods, it is possible to omit the subsequent coarse grinding step by controlling the particle size. If the alloy prepared by the above means has a non-uniform structure or poor crystallinity, a heat treatment step is provided as a next step to prepare an alloy having uniform and high crystallinity.

2) Coarse pulverization The coarse pulverization method is not particularly limited. For example, it can be pulverized using various types of pulverizers such as a jok crusher and a stamp mill. The rare earth-iron master alloy absorbs hydrogen and decomposes by performing a heat treatment in a range of 100 to 300 ° C. in hydrogen. Although this hydrogen absorption / pulverization occurs even in a hydrogen gas flow, it is preferable to perform it under pressure in order to shorten the time. The higher the hydrogen pressure, the better, but from the viewpoint of the safety of the material of the container and the like, the hydrogen pressure is preferably 80 kgf / cm2 or less. Hydrogen in the powder after hydrogen absorption and pulverization may be used as it is, or hydrogen may be released by a dehydrogenation treatment. In the case of releasing hydrogen, the pressure is reduced to 350
The heat treatment may be performed in a temperature range of up to 550 ° C. The pulverized particle size is preferably a particle size that allows nitrogen to uniformly penetrate during the nitriding treatment, and is preferably 1000 μm or less, more preferably 200 μm or less.

3) Nitriding treatment The nitriding method is not particularly limited. For example, nitriding can be performed by heat treatment in a nitriding gas atmosphere.
Examples of the nitriding gas include a nitrogen gas, a nitrogen-hydrogen mixed gas, an ammonia gas, and an ammonia-hydrogen mixed gas. The processing temperature is preferably in the range of 400 to 600 ° C. If the temperature is lower than the above-mentioned temperature range, the nitriding speed is unfavorably low. Further, since the rare earth-iron-nitrogen based magnetic material is decomposed into rare earth nitride and iron at 650 ° C. or higher, it is not preferable to perform the heat treatment at a temperature higher than the above temperature range. In addition, although nitriding can be performed sufficiently even in a nitriding gas stream, the nitriding speed can be increased by setting the atmosphere in a pressurized atmosphere.

4) Fine pulverization The fine pulverization is desirably performed using a jet mill, preferably an air jet mill. Further, as a pulverizing gas in the jet mill pulverization, an inert gas is preferably used, and preferably an inexpensive nitrogen gas is used because rare-earth-iron-nitrogen-based magnetic materials deteriorate magnetic properties due to oxidation. When a jet mill, particularly an air jet mill, is used for the fine pulverization, the stress applied to the crystal structure during the fine pulverization is suppressed, and the amount of defects such as processing strain introduced is reduced. However, it is difficult to completely eliminate them. It is important to reduce the number of defects as much as possible in order to develop more excellent magnetic properties. The present invention solves this problem, and further reduces the amount of defects introduced at the time of pulverization, thereby realizing more excellent magnetic characteristics.

The fine pulverization method of the present invention is a method in which a fatty acid is added as a lubricant to the magnetic powder prepared in the above step, and the mixture is pulverized using a jet mill, preferably a gas jet mill. Jet mill pulverization mainly involves pulverization by powder collision with a target in the collision type, and pulverization by mutual collision of powders in the air flow type, but also pulverization by collision with the inner wall of the pulverization chamber. In the present invention, by adding a fatty acid as a lubricant, a fatty acid film is present between the colliding objects at the time of these collisions, and the lubricity is improved, so that the impact force applied to the powder at the time of these collisions is reduced. For this reason, stress applied to the crystal structure during pulverization is further suppressed, and the amount of defects introduced into pulverization is further reduced, so that more excellent magnetic properties can be exhibited.

The fatty acid used in the present invention is not particularly limited, but is preferably a saturated fatty acid represented by the general formula RCOOH and R = Cn H2n + 1, R = Cn H2n-1 R = Cn H2n-3 R = Cn H2n-5 is an unsaturated fatty acid.

When a liquid fatty acid is used, the amount of addition is preferably in the range of 0.1 to 20 parts by weight based on 100 parts by weight of the magnetic powder. If the amount is less than 0.1 part by weight, it is difficult to coat the whole powder, and the above effect is poor.
If the added amount exceeds 20 parts by weight, the powder adheres to the inner wall of the jet mill pulverizing chamber, and continuous pulverization becomes difficult. When a solid fatty acid is used, the amount added is desirably in the range of 0.1 to 40 parts by weight. If the amount is less than 0.1 part by weight, it is difficult to coat the whole powder, and the above effect is poor. When a solid fatty acid is used, it does not adhere to the inner wall of the pulverizing chamber, but if the added amount exceeds 40 parts by weight, the probability of mutual collision between powders, the probability of collision of the powder with the target and the inner wall of the pulverizing chamber decreases, and the pulverizing is performed. Decrease efficiency.

Further, the pulverization method of the present invention is to perform pulverization using a jet mill provided with a coating layer made of a fatty acid as a lubricant on the inner wall of the pulverization chamber (including the target in the collision type). By providing a coating layer made of a fatty acid on the inner wall of the pulverizing chamber, the impact force when the powder collides with the inner wall of the pulverizing chamber is reduced by the same effect as in the case where the fatty acid is added to the powder and mixed and then finely pulverized. When the powder collides with the inner wall of the crushing chamber, the fatty acid is adsorbed to the powder. Therefore, even in the case of mutual collision between powders, the same effect as when finely pulverized after adding and mixing a fatty acid to the powder can be obtained.

The fatty acid used in the coating layer is not particularly limited, but is preferably the above-mentioned saturated fatty acid and unsaturated fatty acid.

An embodiment of the present invention will be described below. (Example 1) As raw materials, Sm having a purity of 99.9% and electrolytic iron having a purity of 99.99% were melted in a high frequency melting furnace.
An ingot was prepared by pouring into a mold. The obtained ingot is heated at 1100 to 1200 ° C. in an Ar atmosphere for 10 to 10 minutes.
The mother alloy was prepared by performing homogenization treatment for 24 hours. Put the adjusted master alloy in a stainless steel high-pressure vessel with an inner diameter of 1 inch,
After replacing the inside of the container with hydrogen, the internal pressure is increased to 20 to 60 kgf / cm.
2 and then raise the temperature to 150-200 ° C.
Heat treatment for 5 to 1 h and hydrogen absorption and pulverization to obtain a particle size of 20
A sample powder of 0 μm or less was prepared. The obtained sample powder was placed in a stainless steel high-pressure vessel and subjected to nitriding treatment at 470 ° C. for 12 hours in a high-pressure nitrogen atmosphere of 50 kgf / cm 2. The nitrogen gas used had a purity of 99.9999%. After the nitriding treatment, oleic acid was added as a lubricant to the sample powder and mixed, and the mixture was pulverized using an air jet mill. The pulverization was carried out in a glove box which was purged with nitrogen until the oxygen concentration became 100 ppm or less. Nitrogen gas having a purity of 99.99% is used as the pulverizing gas, and the pulverizing gas pressure is 6 k.
gf / cm2. After the obtained sample was washed with hexane to remove oleic acid, the magnetic properties were measured using a sample vibration magnetometer (VSM). Table 1 shows the measurement results. The composition of the prepared sample was Sm9.1 Fe77.3N1
3.6.

[0025]

[Table 1]

Example 2 A sample was prepared in the same manner as in Example 1 except that after the nitriding treatment, stearic acid was added as a lubricant. Table 1 shows the magnetic properties of the prepared samples.

Example 3 Example 1 was repeated except that oleic acid was applied to the inner wall of the pulverization chamber and a jet mill provided with a coating layer was used, and that oleic acid was not added to the sample powder after nitriding. A sample was prepared in the same manner. Table 1 shows the magnetic properties of the prepared samples.

Comparative Example 1 A sample was prepared in the same manner as in Example 1 except that oleic acid was not added after the nitriding treatment. Table 1 shows the magnetic properties of the prepared samples.

[0029]

As described above, in the process of producing a rare earth-iron-nitrogen based magnetic material, a fatty acid is added to a magnetic powder as a lubricant and mixed and then finely pulverized by a jet mill, or as a lubricant on the inner wall of the pulverization chamber. By finely pulverizing with a jet mill provided with a coating layer made of a fatty acid, when the magnetic powders collide with each other at the time of the fine powder, or when the magnetic powders collide with the target or the inner wall of the pulverizing chamber, the collision between these colliding substances occurs. The presence of a coating layer made of a fatty acid makes the lubricity good and reduces the impact force at the time of collision. For this reason, the stress applied to the crystal structure during the fine pulverization is suppressed, the amount of defects introduced by the fine pulverization can be reduced, and excellent magnetic characteristics can be exhibited.

Claims (3)

[Claims] 1. A compound of the general formula: RaFe (100-abc) Mb
A magnetic material represented by Nc, wherein R is at least one rare earth element including Y, and
And M is Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,
At least one of W; a, b, and c are atomic percentages; 5 ≦ a ≦ 200 ≦ b ≦ 53 3 ≦ c ≦ 30, and the balance being Fe, rare earth-iron-nitrogen A method for producing a rare-earth-iron-nitrogen-based magnetic material, comprising adding a lubricant to the magnetic material, mixing the mixture, and pulverizing the mixture with a jet mill. 2. The general formula RaFe (100-abc) Mb
A magnetic material represented by Nc, wherein R is at least one rare earth element including Y, and
And M is Ti, Zr, Hf, V, Nb, Ta, Cr, Mo,
At least one of W; a, b, and c are atomic percentages; 5 ≦ a ≦ 200 ≦ b ≦ 53 3 ≦ c ≦ 30, and the balance being Fe, rare earth-iron-nitrogen A method for producing a rare earth-iron-nitrogen based magnetic material, which comprises finely pulverizing with a jet mill provided with a coating layer made of a lubricant on the inner wall of a grinding chamber. 3. The rare earth element according to claim 1, wherein the lubricant is at least one selected from fatty acids.
A method for producing an iron-nitrogen based magnetic material.