JP2000038608A - Rare earthmetal-iron-nitrogen based magnetic powder and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To moreover improve rare earthmetal-iron-nitrogen based magnetic powder prepd. by a reducing diffusion method and to furthermore improve the magnetic properties such as coercive force, magnetization or the like of a bond magnet using it. SOLUTION: In the method for producing rare earthmetal-iron-nitrogen based magnetic powder in which raw material powder contg. rare earth oxides is subjected to reducing diffusion and nitriding to obtain an alloy block, the alloy block is immersed into water and is collapsed, and after that, washing and acid treatment are executed, the acid treatment is composed of treatment by weak acid and treatment by acid contg. acid comprising the group 5B elements and oxygen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing not only rare earth transition metal alloy powder but also an intermetallic compound of rare earth transition metal, and more particularly to a method for producing an alloy powder having good magnetic properties. It is.

[0002]

2. Description of the Related Art Rare earth elements and transition metals (iron, cobalt,
An alloy or a compound of (nickel) is an extremely important material in industry. For example, SmCo5 is a permanent magnet, L
aNi5 is used for a hydrogen storage alloy. Also, compounds comprising rare earth-transition metal-boron, for example, Nd2Fe14B, are rapidly expanding the market as super-strong magnets. on the other hand,
Rare earth-transition metal-nitrogen compound (Sm2Fe17
N3) is expected as a next-generation permanent magnet material, and researches particularly on bond magnets have been made.

[0003] By the way, as a form of an alloy or a compound composed of these rare earth elements and a transition metal, a powder of several μm is often required. In order to obtain such an alloy powder, a rare-earth element oxide powder and a transition metal powder are mixed, and the mixture is heated in calcium vapor to reduce the rare-earth element oxide and diffuse into the transition metal. Diffusion methods are known. The reduction diffusion method has an advantage that an inexpensive rare earth element oxide can be used and that an alloy can be obtained at the same time as reduction. This method is widely used in the production of SmCo5 intermetallic compounds for permanent magnets or Sm2Co17-based alloys. ing.

[0004] The product obtained by the reduction diffusion step is a porous alloy block, which contains a reducing agent such as metal Ca together with the desired reduced alloy material. In order to obtain a magnetic powder, the porous block is put into water, collapsed and powdered.
In order to finish this into a magnetic powder product, conventionally, washing with water by decantation or the like, acid treatment, and finally, separation and drying have been performed to obtain a target magnetic powder. The particle properties of the magnetic powder obtained by the reduction diffusion method depend on the particle size, particle size distribution, and particle shape of the oxide of the transition metal or rare earth element selected as the raw material, and the oxide particles having a uniform size are mixed. Thereby, a magnetic powder of small particles having a relatively sharp particle size distribution can be obtained without a pulverizing step.

[0005] The rare earth iron-nitrogen based magnetic powder obtained by applying this reduction diffusion method has excellent magnetic properties, and is particularly promising for application to bonded magnets.

[0006]

The compound for a bonded magnet mainly comprises a magnetic powder and a resin. This compound is mechanically kneaded in a temperature range of 150 to 350 ° C. so that the magnetic powder is homogeneously mixed throughout. If the compound has poor fluidity during the kneading, shear heat is generated, and the magnetic powder particles and the resin are thermally degraded. In addition, stress is applied to the particles due to the agglomeration of the particles, and the magnetic characteristics are deteriorated. Further, at the time of magnetic field molding, there is a problem that the orientation is deteriorated because the particles are hard to move.

Accordingly, an object of the present invention is to further improve the rare earth iron-nitrogen based magnetic powder prepared based on this reduction diffusion method, and to further improve the magnetic properties such as the coercive force and magnetization of the bonded magnet using the same. To improve.

[0008]

Means for Solving the Problems The present inventors have improved the affinity between a magnetic powder synthesized by reduction diffusion and a resin, so that no extra energy is added during kneading in the preparation of a compound for a bonded magnet. As a result, we thought that the deterioration of the magnetic powder due to heat or mechanical stress can be prevented, and as a result of intensive examination of various surface treatments on the magnetic powder obtained after the reduction diffusion step, Improvements could be made.

That is, according to the method for producing a rare earth iron-nitrogen based magnetic material of the present invention, a raw material powder containing a rare earth oxide is subjected to reduction diffusion and nitridation to obtain an alloy block, and the alloy block is immersed in water and collapsed. In a method for producing a rare earth iron-nitrogen based magnetic powder, which is then subjected to water washing and acid treatment, the acid treatment comprises:
It is characterized by comprising a treatment with a weak acid, followed by a treatment with an acid containing an acid comprising a Group 5B element and oxygen.

The weak acid used is preferably at least one of formic acid, acetic acid and propionic acid.

The acid comprising a Group 5B element and oxygen is phosphoric acid,
Arsenic acid, antimonic acid and bismuth acid can be preferably used.

[0012] The concentration of the acid consisting of a Group 5B element and oxygen used in the acid treatment is preferably in the range of 0.005 to 1.0% by weight.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic powder to which the production method of the present invention is applicable is a rare earth iron-nitrogen-based material, and as rare earth elements, Y, Nd, Pr, La, Ce, Tb, Dy, Ho,
It may be at least one of Er, Eu, Sm, Gd, Er, Tm, Yb, and Lu. A typical example is Sm2Fe17N3, and its magnetic properties such as residual magnetization, coercive force, and Curie temperature are particularly superior to those of the body material.

The raw material to be subjected to the reduction diffusion step is a rare earth element whose oxide is, for example, Y 2 O 3, Nd 2 O 3, Pr 2
O3, La2O3, CeO2, Tb4O7, Dy2O3, Ho2
O3, Er2O3, Eu2O3, Sm2O3, Gd2O3, Er2
O3, Tm2O3, Yb2O3, Lu2O3 and the like are used. The iron raw material is based on metallic iron, but FeO, Fe3O
4. Fe2O3 or the like may be used, and a double oxide of a rare earth element and iron oxide may be used.

These raw material powders need to have an average particle diameter of 5 μm or less. More preferably, the average particle size is 0.2
It is preferably in the range from μm to 2 μm and the maximum particle size should not exceed 10 μm. If the average particle size is 5 μm or more, the particle size of the finally obtained magnetic powder also exceeds 5 μm, and the particle size is particularly important for Sm · Fe · N magnetic materials.

As the reducing agent used in the reduction diffusion method, granular metallic calcium having a particle size of 4 mesh or less can be suitably used.
These reducing agents have a reaction equivalent (the stoichiometric amount necessary to reduce the rare earth oxide, and if the transition metal is used in the form of an oxide, it contains the amount necessary to reduce it. )
1.1 to 3.0 times, preferably 1.5 to 2.0 times
Use at twice the rate.

The alloy block (reaction product) obtained in the reduction diffusion step is a mixture of CaO by-produced, unreacted excess calcium, and produced alloy powder, and is in a sintered mass state in which these are combined. This product mixture is then poured into cooling water to separate CaO and metallic calcium from the alloy powder as a Ca (OH) 2 suspension.

After the reduction reaction by reduction diffusion is completed, before moving to the collapse step, nitrogen gas,
Alternatively, nitriding can be performed by introducing a compound gas capable of supplying nitrogen by being decomposed by heating. Since the rare-earth iron-based alloy is obtained in the form of a porous mass in the reduction diffusion step, heat treatment can be immediately performed in a nitrogen atmosphere without pulverization, whereby nitriding is performed uniformly, and a rare-earth iron-nitrogen alloy is obtained. This nitriding treatment is performed at a temperature of 150 to 800 ° C. by lowering the temperature from the heating temperature range for the reduction.
It is preferably in the range of 300 to 600 ° C, particularly 400 to 55 ° C.
A temperature of 0 ° C. is optimal. Nitriding can be performed by setting the atmosphere in this temperature range to a nitrogen atmosphere. For example, when the nitriding temperature is lower than 150 ° C., diffusion of nitrogen into the rare-earth iron-based alloy becomes insufficient, and it becomes difficult to perform uniform nitriding. Further, when the nitriding temperature exceeds 800 ° C.,
Since the rare-earth iron-based alloy is decomposed into the rare-earth / nitrogen-based compound and α-iron, the magnetic properties of the obtained alloy powder are significantly reduced. The heat treatment time is set to such an extent that the nitriding is performed sufficiently uniformly, and generally, this time is about 2 to 20 hours.

When the alloy block obtained in the nitriding treatment step is immersed in pure water, the alloy block collapses, and Ca components (calcium oxide, calcium hydroxide, calcium nitride) and calcium nitride, which are by-products of the alloy powder, are removed. Separation begins. Repeat decantation several times to remove some by-products.

A feature of the present invention is that in the subsequent weak acid treatment, the surface is treated with a weak acid treatment followed by an acid containing an acid composed of an element of group 5B and oxygen.

<Weak Acid Treatment> This step aims at dissolving Ca, which could not be removed by decantation, with an acid and dissolving unreacted rare earth metals and transition metals. For this dissolution, formic acid, acetic acid,
Weak acids such as propionic acid and citric acid can be preferably used. If a strong acid such as hydrochloric acid or sulfuric acid is used, not only dissolution of Ca or a different phase on the surface, but also dissolution of the internal magnetic material structure, as a result, a decrease in magnetic properties is induced. It is. Among weak acids,
In particular, acetic acid can be preferably used, including its low cost.

The concentration of the weak acid aqueous solution is preferably from 0.005% to 5%, more preferably from 0.05% to 0.1%. If it is less than 0.005%, the dissolution is insufficient and the Ca cleaning effect is hardly recognized. Conversely, 5.
If it exceeds 0%, the surface is oxidized, which is not preferable. The amount of the weak acid aqueous solution may be such that the rare-earth transition metal nitride-based magnetic powder can be sufficiently stirred therein and may be used in excess of the required amount. What is easy to handle in the working process is in the range of 3 times to 50 times the volume of the rare earth transition metal nitride-based magnetic powder.

<Treatment with an acid containing an acid consisting of a group 5B element and oxygen> The acid consisting of a group 5B element and oxygen is an element excluding N among the group 5B elements N, P, As, Sb, and Bi And an acid obtained by bonding oxygen and oxygen, and phosphoric acid, arsenic acid, antimonic acid and bismuth acid can be used. Here, the phosphoric acid means an acid formed by hydration of diphosphorus pentoxide P2O5, and includes metaphosphoric acid, pyrophosphoric acid, orthophosphoric acid, triphosphoric acid, tetraphosphoric acid and the like. Arsenic acid refers to an acid formed by the hydration of arsenic pentoxide As2 O5, and orthoarsenic acid can be used as an aqueous solution. Antimonic acid refers to a hydrate of diantimony pentoxide, and includes orthoantimonic acid, metaantimonic acid, pyroantimonic acid and triantimonic acid. An acid consisting of N and oxygen has an oxidizing effect and cannot be used.

The concentration of the acid consisting of the Group 5B element and oxygen is as follows:
The content is preferably 0.005% or more and 1% or less, more preferably 0.01% or more and 0.1% or less. If it is less than 0.005%, the surface treatment is insufficient, and if it exceeds 1.0%, the surface is oxidized, which is not preferable. This chemical conversion treatment with an acid comprising a Group 5B element and oxygen may be performed either in a suspension or by adding it to a cake before drying. In the case of (1), it is sufficient that the amount is such that the suspending operation can be performed in the same manner as in the case of the weak acid described above.
In either case, too much does not adversely affect the properties.

The surface of the magnetic particles is modified as follows by the above-described two-stage composite treatment of a weak acid, a group 5B element and oxygen. 1) First, Ca components (calcium oxide, calcium hydroxide, calcium nitride), iron oxide, samarium nitride, and the like adhering to the surface of the rare earth iron-nitrogen magnetic powder by weak acid treatment are dissolved, and these are separated from the magnetic powder. 2) As a result, a relatively clean magnetic powder surface appears. If left as it is, it reacts with oxygen and moisture in the air and becomes mottled by oxides, and N and H easily escape from the surface of the magnetic powder based on that, and the crystal structure becomes unstable. Become. As a result, not only the coercive force but also the magnetization decreases. 3) In order to suppress this, immediately after the magnetic powder surface is cleaned, treatment is performed with an acid of a 5B group element. By the action of the acid, a dense and extremely thin film is formed on the surface of the magnetic powder, and closes the holes from which N and H easily escape. The unstable portion on the crystal is filled with the same group 5B element as nitrogen, and the outermost surface of the magnetic powder is stabilized with an extremely thin film. 4) By stabilizing the surface layer, the generation of reverse magnetic buds can be suppressed, and a uniform film based on the group 5B element on the surface acts as pinning to make the domain wall hard to move. It is considered that the coercive force is improved for the above two reasons.

[0026]

[Example 1] Average particle size 1.5 μm, purity 9
135.7 g of 9.9% iron oxide (Fe2O3) powder is placed in a mild steel tray and subjected to a reduction treatment at 600 ° C. in a hydrogen stream. The hydrogen flow rate is 2 L / min and the processing time is 5 hours. As a result of oxygen analysis, the obtained reduced iron oxide had an oxygen removal rate of 90.5% and an average particle diameter of 1.9 μm. This powder had an average particle size of 1.0 μm and a purity of 99.9%.
34.9 g of samarium oxide (Sm2O3) powder of
Mix with high speed mixer for 10 minutes. Next, 43.29 g of granular metallic calcium is added to this mixed powder, mixed well, and then put into a mild steel crucible. After inserting the crucible into the gas-replaceable electric furnace, the pressure inside the electric furnace was 1 × 1.
Evacuate to 0 ^-2 Torr. Thereafter, the pressure is restored to the atmospheric pressure with argon gas.
Distribute at L / min.

When the temperature of the electric furnace is raised to 1050 ° C., this state is maintained for 1 hour, and thereafter cooled to 50 ° C. in argon gas. Here, the inside of the furnace is evacuated to a pressure of 1 × 10 ⁻² Torr, and then the evacuation is stopped and the pressure is restored to the atmospheric pressure by nitrogen gas, and nitrogen gas is allowed to flow at 5 L / min. Here, when the temperature of the electric furnace is raised again to 450 ° C., this state is maintained for 5 hours, and then the heating is stopped and the mixture is allowed to cool.

The obtained reaction product is in the form of a porous block and can be easily taken out of the crucible. When this is poured into 3000 cc of ion-exchanged water, CaO (calcium oxide) as a reaction product becomes fine Ca (O
H) 2 (calcium hydroxide), which results in the blocks breaking down into a slurry. This slurry is stirred for 10 minutes, and then allowed to stand for 5 minutes, and the supernatant in which fine Ca (OH) 2 is floating is discarded. The above operation is repeated five times. Thereafter, 2.5 ml of 90% acetic acid (acetic acid concentration 0.0
(75%) and stirred for about 3 minutes, followed by decantation. The calcium-derived components adhering to the product were washed.

To 3000 cc of pure water, 2.5 ml of 85% orthophosphoric acid (phosphoric acid concentration: 0.071%) was added and added.
After stirring for about 3 minutes, decantation was performed. PH at this time
Was 5.3. After solid-liquid separation, the cake was replaced with ethanol to obtain a dehydrated cake. Next, this was added at 170 ° C for 2
Vacuum drying was performed for a time to obtain a rare earth transition metal nitride-based magnetic powder of the present invention.

The powder thus obtained was a dispersed powder having good fluidity, and the following analysis results were obtained. Alloy powder weight: 125.5 g Average particle diameter: 2.0 μm Maximum particle diameter: 7.5 μm Minimum particle diameter: 0.8 μm Composition analysis Sm: 23.5 wt% Fe: 72.9 wt% N: 3.13 wt% Ca: 0.01 wt% O: 0.16 wt% PO4: 0.31 wt%

The magnetic characteristics of the obtained Sm—Fe—N alloy powder were measured by a VSM (vibrating sample magnetometer) having a maximum magnetic field of 20 kOe. At this time, the alloy powder was packed in a sample case together with paraffin wax, the paraffin wax was melted by a drier, the axes of easy magnetization were aligned with an orientation magnetic field of 20 kOe, and pulse magnetization was performed with a magnetization magnetic field of 40 kOe. The true density of the Sm2Fe17N3 intermetallic compound was 7.66 g / ml and evaluated without demagnetizing field correction. As a result of measurement of the sample, the residual magnetization was 127 emu / g, and the coercive force was 20 kOe.

Next, a bonded magnet was manufactured by the following procedure using the obtained Sm.Fe.N alloy powder. First, 10 parts of a polyamide resin (nylon 12) is mixed with 100 parts by weight of the powder using a mixer, and mixed with a twin-screw mixer.
The compound obtained by kneading at 30 ° C. is subjected to an orientation magnetic field of 9K.
Injection molding was performed at Oe and 230 ° C. to obtain a cylindrical bonded magnet molded product of 10 mmφ × 7 mm. 50k
After magnetization with a pulse magnetic field of Oe, the magnetic properties were measured with a BH tracer. As a result, a bonded magnet having the following excellent magnetic properties was obtained. Br: 7.5 kG iHc: 15.0 kOe (BH) max: 13.0 MGOe

Example 2 The same raw material as in Example 1 was reduced and diffused under the same conditions, followed by nitriding to obtain a porous block. This was disintegrated under the same conditions, further washed with water and treated with a weak acid.

83% in 3000 cc of pure water Antimony pentoxide manufactured by Nissan Chemical Industries (trade name: San-Epoque NA-103)
0) in an amount of 2.5 g (orthoantimonic acid concentration 0.069).
%) And decanted after stirring for about 3 minutes. After solid-liquid separation, the cake was replaced with ethanol to obtain a dehydrated cake. Next, this was vacuum dried at 170 ° C. for 2 hours to obtain a rare earth transition metal nitride-based magnetic powder of the present invention.

The powder thus obtained was a dispersed powder having good fluidity, and the following analysis results were obtained. Alloy powder weight: 125.7 g Average particle diameter: 2.2 μm Maximum particle diameter: 7.7 μm Minimum particle diameter: 0.9 μm Composition analysis Sm: 23.5 wt% Fe: 72.9 wt% N: 3.13 wt% Ca: 0.01 wt% O: 0.11 wt% Sb2O5: 0.21 wt%

As a result of measurement of the obtained Sm-Fe-N alloy powder in the same manner, the residual magnetization was 126 emu / g and the coercive force was 19.3 kOe.

Next, using the obtained Sm · Fe · N alloy powder, a bonded magnet was produced in the same manner as in Example 1,
When measured under the same conditions, the following measurement results were obtained. Br: 7.5 kG iHc: 15.5 kOe (BH) max: 13.0 MGOe

Comparative Example 1 The same raw material as in Example 1 was reduced and diffused under the same conditions, followed by nitriding to obtain a porous block. This was disintegrated under the same conditions, further washed with water, subjected to a weak acid treatment, and a magnetic powder was obtained in the same manner as in Example 1 except that the phosphoric acid treatment was not performed.

The powder thus obtained had the following analysis results. Alloy powder weight: 125.0 g Average particle diameter: 2.1 μm Maximum particle diameter: 7.6 μm Minimum particle diameter: 0.9 μm Composition analysis Sm: 23.5 wt% Fe: 72.9 wt% N: 3.13 wt% Ca: 0.01 wt% O: 0.13 wt%

The obtained Sm-Fe-N alloy powder was measured in the same manner. As a result, the residual magnetization was 122 emu / g and the coercive force was 14 kOe.

Next, using the obtained Sm · Fe · N alloy powder, a bonded magnet was produced in the same manner as in Example 1,
When measured under the same conditions, the following measurement results were obtained. Br: 6.9 kG iHc: 9.5 kOe (BH) max: 10.1 MGOe

[Comparative Example 2] The same raw material as in Example 1 was reduced and diffused under the same conditions and subjected to nitriding treatment to obtain a porous block. This was disintegrated under the same conditions, and further washed with water in the same manner. However, a weak acid treatment was not performed, and a phosphoric acid treatment was performed under the same conditions as in Example 1 to obtain a magnetic powder.

The powder thus obtained obtained the following analysis results. Alloy powder weight: 125.8 g Average particle diameter: 2.3 μm Maximum particle diameter: 7.8 μm Minimum particle diameter: 1.1 μm Composition analysis Sm: 23.5 wt% Fe: 72.9 wt% N: 3.13 wt% Ca: 0.01 wt% O: 0.16 wt% PO4: 0.36 wt%

As a result of measurement of the obtained Sm-Fe-N-based alloy powder in the same manner, the residual magnetization was 127 emu / g and the coercive force was 13 kOe.

Next, using the obtained Sm · Fe · N alloy powder, a bonded magnet was prepared in the same manner as in Example 1,
When measured under the same conditions, the following measurement results were obtained. Br: 6.9 kG iHc: 8.5 kOe (BH) max: 9.8 MGOe

[0046]

As described above, by applying the present invention, of the magnetic characteristics, in particular, the coercive force is greatly improved. According to a comparison of magnetic powders, according to the conventional method, 14
What was about kOe is greatly improved to about 20 kOe.

This is because, by applying the present invention, a clean and extremely thin film is formed on the surface of the cleaned magnetic powder by the acid of the group 5B element, and the pores from which N and H easily escape are closed. Instable portions on the crystal are filled with the same Group 5B element as nitrogen, and the outermost surface of the magnetic powder is stabilized with an extremely thin film, and the surface layer is stabilized to capture the birth of reverse magnetic buds. It is presumed that the uniform film based on the 5B group element on the surface acts as pinning and makes the domain wall hard to move.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Keiji Ichinomiya 491-1 Kagaminakacho, Anan-shi, Tokushima Pref. HB09 HB15 HB17 NN17

Claims (5)

[Claims] An alloy block is obtained by subjecting a raw material powder containing a rare earth oxide to reduction diffusion and nitridation. The alloy block is immersed in water and collapsed, and then washed with water and subjected to an acid treatment. In the production method, the acid treatment comprises a treatment with a weak acid and a subsequent treatment with an acid containing an acid composed of a Group 5B element and oxygen. 2. The method according to claim 1, wherein the weak acid is at least one of formic acid, acetic acid, propionic acid, and citric acid. 3. The method for producing a rare-earth iron-nitrogen based magnetic powder according to claim 1, wherein the acid comprising the group 5B element and oxygen is phosphoric acid, arsenic acid, antimonic acid, or bismuthic acid. . 4. The rare earth iron according to claim 1, wherein the concentration of the acid consisting of a Group 5B element and oxygen used in the acid treatment is in the range of 0.005 to 1.0% by weight. A method for producing a nitrogen-based magnetic powder. 5. A rare-earth iron-nitrogen-based magnetic powder obtained by the method for producing a rare-earth iron-nitrogen-based magnetic powder according to claim 1.