JPH07166203A - Anisotropy acicular magnetic powder and production thereof - Google Patents

Abstract

PURPOSE:To inexpensively obtain anisotropy acicular magnetic powder showing ferromagnetism by specifying the compsn. consisting of rare earth elements, Fe and N and specifying the shape dimension of powdery grains. CONSTITUTION:A circular iron powder having the shape that the length of an acicular grain is regulated to 0.05 to 10mum and the width to <=2.0mum, rare earth oxide powder and a reducing agent such as Ca are mixed in a specific ratio. Next, this mixture is heated to about 600 to 1200 deg.C in a inert gas atmosphere to alloy rare earths and iron. The obtd. alloy is continuously heated to about 250 to 800 deg.C in an gaseous atmosphere of N2 gas or compounds contg. nitrogen such as NH3 and is nitrided. After that, the compound as a reducing agent is dissolved away by water or weak acid from the obtd. rare earth-iron nitride. Thus, the longitudinal anisotropy acicular magnetic powder expressed by the formula REXFe100-X-YNY (RE denotes rare earth elements and, by atom, 3<=X<=30% and 0.01<=Y<=25% are satisfied) and whose grain length is regulated to 0.05 to 10mum and the width to <=2.0mum can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder as a raw material for a permanent magnet and a method for producing the same, and more particularly to an anisotropic needle-like magnetic powder exhibiting ferromagnetism and a method for producing the same.

[0002]

2. Description of the Related Art Generally, a series of permanent magnets called rare earth magnets exhibit a coercive force based on the high crystal magnetic anisotropy of an intermetallic compound as a raw material. On the other hand, there is also a permanent magnet having a shape magnetic anisotropy that develops a coercive force by arranging needle crystals in a specific direction, such as an alnico magnet or a coating type magnetic recording medium.

As described above, coercive force manifestation factors of permanent magnets include those based on crystalline magnetic anisotropy such as rare earth materials and those based on other shape magnetic anisotropy. If a needle-like powder having shape magnetic anisotropy can be obtained from a rare earth material having crystal magnetic anisotropy,
As a result, it is considered that a permanent magnet having higher magnetic properties can be produced. However, in general, the method for producing a rare earth compound powder is based on crushing an ingot, and it has been impossible to obtain a powder having a specific shape, especially an acicular powder.

[0004]

SUMMARY OF THE INVENTION Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rare earth compound raw material having crystalline magnetic anisotropy and shape magnetic anisotropy. It is intended to realize a permanent magnet having high magnetic characteristics by providing the manufacturing method.

[0005]

The needle-like magnetic powder of the present invention is a needle-like magnetic powder of an anisotropic rare earth compound and has a general formula of RE _X · Fe _{100 —XY} N _Y (provided that RE Is
At least one element selected from rare earth elements, X is 3 atomic% <X <30 atomic%, Y is 0.01 atomic%
<Y <25 atomic%. ), The length of each particle of the acicular magnetic powder is in the range of 0.05 to 10 μm, and the width is 2.0 μm or less (however, length> width).
It is characterized by However, the shape of the acicular particles is determined by measurement with an electron microscope or a microscope.

Further, in the production method of the present invention for obtaining the above-mentioned acicular magnetic powder, the acicular iron powder has a shape in which the length of each acicular particle is in the range of 0.05 to 10 μm and the width is 2.0 μm or less. A first step of alloying rare earth and iron by heating a mixture of a rare earth oxide powder and a reducing agent in a predetermined ratio in an inert gas atmosphere, and the obtained rare earth iron A second step of nitriding the alloy by continuously heating it in a nitrogen gas atmosphere or a gas atmosphere of a compound containing nitrogen, and dissolving the reducing agent compound with water or a weak acid from the obtained rare earth iron nitride. It is characterized by comprising a third step of removing by.

[0007]

In the first step, the rare earth oxide powder and the needle-shaped Fe are used as raw materials in a ratio according to the intended composition.
Powder and Ca powder as a reducing agent are mixed. The acicular Fe powder is obtained by dehydrating and reducing acicular α-FeOOH (goethite) formed by oxidizing a suspension of Fe (OH) ₂ . The acicular Fe powder can be obtained also by a method of evaporating iron in a low vacuum, but the former method is superior in that a powder of any size can be obtained. Examples of the reducing agent include C
It is possible to use a reducing agent that is a metal that is easily oxidized, such as a, Mg, and Sr, and that can be easily removed in the third step when it becomes an oxide or a nitride. Among them, Ca is preferable. To use. CaO and CaN rapidly react with water to form calcium hydroxide, which can be easily removed in the third step. The rare earth oxide powder is not particularly limited in particle size and shape, and a usual rare earth oxide powder having a particle size of 0.1 μm to several tens of μm can be used.

In the first step, iron oxide such as Fe ₂ O ₃ or Fe ₃ O ₄ may be substituted in the range of up to 30 atomic% with respect to the acicular iron powder. Due to the heat of reaction when these iron oxides are reduced by the reducing agent, a uniform reaction can be carried out as a whole, leading to the saving of external energy and the improvement of the yield. Regarding the amount of the reducing agent mixed, it is sufficient to reduce the rare earth oxides (when iron oxides for self-heating are added, the iron oxides are also reduced).
It is necessary. Preferably, the mixing amount of the reducing agent is about 1.5 times the equivalent amount of oxygen atoms of the total of the rare earth oxide and the iron oxide such as Fe ₂ O ₃ or Fe ₃ O ₄ to be additionally mixed. Is desirable.

The mixed powder obtained by mixing the raw materials is placed in a heating container that can be evacuated. After evacuating the inside of the heating container,
While passing an inert gas, the acicular iron powder as a mixed powder and the rare earth oxide are subjected to a reduction reaction to form an alloy. As the inert gas, any gas such as Ar and Ne may be used as long as it does not react with the used raw material, and Ar is preferably used. The heating condition is not particularly limited as long as it is a temperature at which the rare earth oxide and the acicular iron powder are alloyed, but 600 ° C to 12 ° C.
Heating is performed within a range of 00 ° C., preferably within a range of 800 ° C. to 1200 ° C. for several hours, preferably about 2 to 5 hours. 6
If the temperature is lower than 00 ° C, the reduction reaction of the oxide is difficult to proceed, and if it is 1200 ° C or higher, the rare earth element and the reducing agent tend to be evaporated, which is not preferable. Further mixed powder,
That is, when an appropriate amount of Fe ₂ O ₃ or Fe ₃ O ₄ is contained in the starting system, self-heating occurs during the temperature rise, and a uniform reaction can be efficiently performed, but at least 30 atomic% with respect to Fe. If a considerable amount of Fe ₂ O ₃ or Fe ₃ O ₄ is mixed, an extremely large amount of heat will cause an explosion or scattering, which is not preferable.

Next, in the second step, the rare earth iron alloy obtained in the first step is continuously heated in a gas atmosphere of nitrogen or a compound containing nitrogen to form a nitride. The heating temperature is not particularly limited as long as it is a temperature at which the alloy is nitrided. Preferably, the heating in the first step is stopped, and subsequently, in an inert gas atmosphere, 250 ° C to 800 ° C.
After cooling to a constant temperature within the range of 300 ° C., preferably within the range of 300 ° C. to 600 ° C., this temperature is kept constant, the heating container is evacuated again, and then a means for introducing nitrogen gas is provided. Can be used. The gas to be introduced is not limited to nitrogen and may be a gas containing nitrogen atoms, for example, ammonia or hydrazine. The nitriding condition is several hours, preferably 3 to 10 while passing nitrogen gas or the like at a pressure higher than atmospheric pressure.
The alloy can be nitrided by heating for about an hour and then stopping the heating and allowing it to cool.

Next, in the third step, since the reducing agent added first is an oxide or a nitride, the reducing agent compound such as an oxide or a nitride is washed with water or a weak acid such as acetic acid. It can be easily removed by dissolving. By pouring the obtained reaction product into water, the reaction product immediately disintegrates, and the separation of the alloy powder and the reducing agent component begins. The reducing agent component is completely separated by repeating stirring in water, standing, and removal of the supernatant several times, and finally treating with a weak acid such as acetic acid. The alloy powder thus obtained has a sharp particle size and is fluid.

In the method of the present invention, the nitriding treatment in the second step is carried out prior to the water washing step in the third step, so that an alloy powder containing no oxygen component can be obtained in the third step. To help. That is, Ca as a reducing agent
Conventionally, when CaO is used, the reaction product CaO rapidly reacts with water to form Ca (OH) ₂ , but unreacted C
Since a reacts relatively slowly, it took a lot of time to remove it and, in turn, caused a decrease in purity.
According to the present invention, since nitriding is performed, most of unreacted Ca becomes a nitride of calcium such as CaN,
This calcium nitride such as CaN reacts rapidly with water similarly to CaO, and is extremely convenient for this removal.

As a result, the anisotropic needle-like magnetic powder RE _X .Fe100- _XY N _Y thus obtained contains nitrogen in a range of more than 0.01 atom% and less than 25 atom%. By reducing the nitriding time, the nitrogen content was reduced to 0.
Although it can be reduced to less than 01 atom%, if it is less than 0.01 atom%, chemical stability in the atmosphere cannot be obtained, and if it is more than 25 atom%, a non-ferromagnetic rare earth nitride. Are generated, which deteriorates the magnet characteristics, which is not preferable.

The same can be said about the rare earth-transition metal powders. When the rare earth metal (RE) is less than 3 atom%, most of the Fe content is Fe, which cannot be practically used, and the rare earth metal is 30 atom. If it is more than%, the rare earth metal precipitates and becomes unstable in the atmosphere, which is inconvenient.

If the length of each acicular particle is less than 0.05 μm, coercive force will not be generated due to the influence of the oxide film and the like.
If it exceeds 0 μm, the particle size exceeds the single domain particle size and no coercive force is generated. If the width of the acicular particles exceeds 2.0 μm, the coercive force due to the shape anisotropy, which is a feature of the present invention, is not effectively generated, and only magnetic characteristics equivalent to those having a random particle shape can be obtained. . In the present invention, the shape and size of the Fe particles used as the raw material are directly inherited by the product. Therefore, the needle-like Fe powder as a raw material is required to have a limited size, that is, a length of 0.05 to 10 μm and a width of 2 μm or less.

[0016]

EXAMPLES Hereinafter, specific examples of the present invention will be described in comparison with conventional ones. [Example 1] 26.85 g of Sm ₂ O ₃ powder having an average particle size of 1 μm
And needle-like Fe powder 73.10 g having an average length of about 1.5 μm and an average width of about 0.1 μm are mixed, and further granular Ca1
Add 3.88 g and mix well. Ca equivalent is Sm
It is 1.5 times the equivalent of oxygen atoms in ₂ O ₃ . The mixture is placed in a mild steel crucible and set in a heating vessel. The inside of the heating container is evacuated to 1 × 10 ^-2 Torr or less, and then argon gas is introduced and allowed to flow at atmospheric pressure.

When the heating container is heated to 1150 ° C., it is kept in this state for 5 hours, and thereafter cooled while keeping the argon gas flowing. When the temperature reaches 500 ° C., holding at this temperature is started, the circulation of argon gas is stopped, and the inside of the heating container is immediately evacuated. After the inside of the heating container has been evacuated to 1 × 10 ^-2 Torr or less, the evacuation is stopped, nitrogen gas is introduced, and nitrogen gas is allowed to flow at atmospheric pressure.
After that, heat treatment is performed for 5 hours, heating is stopped, and the mixture is allowed to cool.

The reaction product obtained is in the form of a porous block and can be easily taken out from the crucible. When the reaction product is put into 3000 cc of ion-exchanged water, it is immediately disintegrated. At this time, most of CaO in the reaction product and unreacted Ca which is a nitride of calcium such as CaN.
And become fine Ca (OH) ₂ . 1 of this slurry
After stirring for 0 minutes, let stand for 10 minutes to obtain fine Ca (O
H) Discard the supernatant liquid in which ₂ is floating. Here again 3
The same operation as above is carried out by adding 000 cc of ion-exchanged water. After repeating this operation several times, the mixture is stirred for 15 minutes in an aqueous acetic acid solution initially adjusted to pH 4.5, and left to stand to discard the supernatant. After that, washing with water is repeated several times to complete the removal of Ca. Finally, the alloy powder from which the Ca content has been removed is separated from water while the alcohol is being replaced with a Nutsche, and the separated cake is vacuum dried at 80 ° C., whereby Sm-
An Fe-N alloy powder is obtained.

The alloy powder thus obtained weighed 98.7 g and was an acicular particle having an average length of about 1.5 μm and an average width of about 0.2 μm. According to chemical analysis, Sm22.4%,
Fe 74.1%, N 3.05%, Ca 0.07% and O
(Oxygen atom) was 0.22%. That is, the obtained alloy had a general formula of Sm22.5Fe74.4N3.1. The yield based on Sm and Fe as starting materials is 9
It was 9.0%.

Next, a bond magnet was produced using the obtained alloy powder by the following procedure. First, 3 wt% of alloy powder
The epoxy resin of No. 1 was mixed, and this was compression-molded at a pressure of 5 ton / cm ² while applying a magnetic field of 20 kOe. After magnetizing this compact with a pulsed magnetic field of 50 kOe, VS
Magnetic properties were measured with M. As a result, a bonded magnet having the following excellent magnetic properties was obtained. Br 11.0 kG, bHc 8.8 kOe, (BH) max 27 MGOe

Example 2 26.85 g of Sm ₂ O ₃ powder having an average particle size of 1 μm, an average length of about 2.0 μm and an average width of about 0.8 μm.
69.45 g of needle-like Fe powder having a particle diameter of 05 μm, and an average particle diameter of 0.
3.42 g of 1 μm Fe ₂ O ₃ powder is mixed. Of the Fe atoms in these raw materials, those derived from Fe ₂ O ₃ are 5.0
It is atomic%. Further, 19.77 g of granular Ca is added and mixed well. The equivalent of Ca is Sm ₂ O ₃ and Fe ₂ O ₃
It is 1.5 times the equivalent of oxygen atoms in the inside. The mixture is placed in a mild steel crucible and set in a heating vessel. After evacuating the inside of the heating container to 1 × 10 ^-2 Torr or less,
Argon gas is introduced and flowed at atmospheric pressure. Thereafter, the heat treatment with argon gas was performed in the same manner as in Example 1,
Nitrogen treatment and post-treatment were performed, but 620 ° C during initial temperature rise
From this, a rapid self-heating is observed, and the temperature of the reaction system instantaneously reaches 870 ° C.

The resulting Sm-Fe-N alloy powder was 99.
6 g, average length about 2.0 μm, average width about 0.1
The particles were needle-shaped particles of μm. According to chemical analysis, Sm2
3.1%, Fe73.3%, N2.99%, Ca0.0
It was 9% and O (oxygen atom) 0.12%. That is, the obtained alloy had a general formula of Sm23.2Fe73.7N3.1. In addition, the yield based on Sm and Fe as starting materials was 99.8%.

Next, using the obtained alloy powder, Example 1
A bonded magnet was produced in the same manner as in. The magnetic properties were as follows. Br 11.0 kG, bHc 9.2 kOe, (BH) max 29 MGOe

[Comparative Example 1] A powder having the same composition as the alloy obtained in Example 1 was produced through steps such as high frequency melting of Sm and Fe, heat treatment, pulverization and nitriding. However, the shape of the powder was random because it was crushed, and the average particle size was 2.5 μm. A bonded magnet was produced from this powder in the same manner as in Example 1. The magnetic properties were as follows. Br 9.2 kG, bHc 6.7 kOe, (BH) max 18 MGOe.

[0025]

The magnetic powder obtained by the method of the present invention is a needle-like rare earth alloy powder having anisotropy. By using the acicular powder having a certain shape, the packing rate of the powder in the magnet is higher than that of the pulverized powder in the magnetic field orientation, so that the residual magnetization is high. In addition, the coercive force also increases due to the shape anisotropy. Therefore, at the (BH) max value, a high performance magnet of 25 MGOe or more, which is extremely high as a bonded magnet, can be obtained.

In the production method according to the present invention, rare earth oxides, which are generally cheaper than rare earth metals, can be used as a raw material without using a rare earth metal as a raw material, which is industrially advantageous. is there. Further, according to the production method of the present invention, the reduction diffusion reaction and the nitriding treatment can be performed by changing the reaction atmosphere and the reaction temperature in one reaction container without moving the reaction product.

As described above, according to the present invention, it is possible to provide a ferromagnetic powder having a shape anisotropy of a type that has never been obtained. A bonded magnet produced using this powder has a high characteristic of (BH) max25MGOe or more. Moreover, since the raw material thereof is a rare earth oxide, which is cheaper than a rare earth metal, or an industrially produced iron powder, the present invention is industrially very useful.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C22C 38/00 303 DH 01F 1/06

Claims (3)

[Claims] 1. An acicular magnetic powder having anisotropy, comprising:
General formula: RE _X · Fe _100-XY N _Y (where RE is at least one element selected from rare earth elements, X is 3 atom% <X <30 atom%, Y is 0.01 atom) % <Y <25 atomic%.), The length of each particle of the acicular magnetic powder is in the range of 0.05 to 10 μm, and the width is 2.0 μm or less (however, An anisotropic acicular magnetic powder characterized in that length> width). 2. The length of each acicular particle is 0.05 to 10 μm.
heating a mixture of acicular iron powder having a shape of 2.0 μm or less in width in the range of m, a rare earth oxide powder, and a reducing agent in a predetermined ratio in an inert gas atmosphere. A first step of alloying rare earth and iron with, and a second step of nitriding the obtained rare earth iron alloy by continuously heating in a nitrogen gas atmosphere or a gas atmosphere of a compound containing nitrogen, And a third step of removing the compound of the reducing agent by dissolving it with water or a weak acid from the obtained rare earth iron nitride, and manufacturing the anisotropic acicular magnetic powder. 3. The anisotropic acicular magnetic powder according to claim 2, wherein in the first step, the iron oxide powder is mixed in a range of up to 30 atom% of the acicular iron powder. Production method.