JPH05271852A - Rare earth magnet alloy manufacturing method - Google Patents

Abstract

(57) [Summary] [Objective] To provide an effective nitriding method for raw material powders of nitriding magnets. [Structure] A cake-like reaction product obtained by a reduction diffusion method of a rare earth oxide is directly subjected to a nitriding treatment, and then a target magnet alloy material is recovered by washing with water.

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 a rare earth magnet alloy material by a reduction diffusion method, and in particular, a rare earth magnet alloy material obtained by nitriding a reaction product mixture obtained by a reduction diffusion reaction. Manufacturing method.

[0002]

2. Description of the Related Art Rare earth magnets such as so-called samarium-cobalt magnets and neodiboron magnets are currently evaluated for their excellent magnetic characteristics such as high saturation magnetic flux density and high coercive force, and they are used in home appliances, electronics, automobile parts, etc. It is used in a wide range of fields and its demand is increasing rapidly. This is because the high saturation magnetic flux density and coercive force of rare earth magnets contribute to making the magnet parts lighter, thinner and smaller.

In recent years, it has been pointed out that nitriding a rare earth-iron-based alloy may yield a magnet alloy having magnetic properties superior to those of conventional rare earth-based magnet alloys, and the technology related thereto is being disclosed. For example, Japanese Patent Application Laid-Open No. 3-16102 discloses the nitrogen content and the type and amount of elements added to the nitride-based magnet alloy, and Japanese Patent Application Laid-Open No. 2-57663 discloses a method for manufacturing the nitride-based magnet. There are things that have been done.

For example, according to Japanese Patent Application Laid-Open No. 2-57663, the method of producing a rare earth nitriding magnet alloy proposed so far uses a rare earth metal and iron as raw materials, and these raw materials are subjected to arc melting or high frequency melting. An ingot of a master alloy having a rare earth metal and iron as a basic composition was prepared by melting, and once cooled, an average particle size of 0.5 m was used for nitriding the master alloy.
Coarsely crush it to about m, contact this powder with a reducing gas containing ammonia at around 400 ℃ to let in nitrogen, hydrogen, etc., and further pulverize it to about 20 microns to remove rare earth-iron-nitrogen. It was intended to obtain the nitriding magnet alloy powder which was the main component. On the other hand, although this is not a method for producing a nitriding magnet powder, a reduction diffusion method is known as a method for producing a rare earth magnet powder in addition to the above-mentioned melting method. See, for example, JP-A-60-106930.

This method is a method of using an inexpensive rare earth oxide as a starting material because the raw material rare earth metal required for the above-mentioned melting method is expensive, and rare earth oxides such as calcium and magnesium are used. Mixing a reducing agent with metals such as iron and cobalt, and placing this in a neutral atmosphere such as argon or a reducing atmosphere such as hydrogen at about 1000 ° C reduces the rare earth oxides and diffuses the constituent elements. This is a method of alloying by means of the so-called reduction and diffusion reaction. After completion of the reaction, the cake-like reaction product mixture formed by this reduction diffusion reaction is washed with water to remove substances other than the magnet alloy contained in the reaction product mixture, for example, oxides of calcium or magnesium or unreacted reducing agent. The magnet alloy is separated, and the recovered magnet alloy is dried and then pulverized to a size of several μm to finally obtain an alloy powder for magnet.

According to this method, after the reduction-diffusion reaction, a cake-like reaction product mixture in which the magnet alloy is mixed with metallic calcium, calcium oxide, etc. is obtained, and it decomposes by contacting with water. The reduction diffusion method is known as a method for obtaining an inexpensive magnet alloy because it has an advantage that the necessary coarse pulverization step can be omitted.

[0007]

As described above, although the rare earth nitriding magnet alloy produced by the melting method generally has excellent magnetic properties, it requires the above-mentioned expensive rare earth metal as a raw material, In addition, the reduction and diffusion method requires a step of coarse pulverization that is not necessary, so that the obtained magnet powder is expensive.

Since the nitriding rate is very slow in the course of this coarse pulverization process, the reaction surface area of the master alloy is pulverized to a diameter of about 0.5 mm so as to be as large as possible, and the nitriding process is carried out within a time period which does not cause much problems in industry. This is a process required to complete the nitriding reaction. Especially in the melting method, since the mother alloy is obtained in the form of a large ingot, even if an attempt is made to nitride without coarse pulverization, only the surface of the ingot is nitrided,
This crushing step is indispensable and cannot be omitted.

In order to end the nitriding reaction as described above, it is better to pulverize the mother alloy as finely as possible, but if it is made too fine, the metal powders will sinter during nitriding and the particles will become large, resulting in fine particles. Not only does the meaning of crushing disappear, but the particles are oxidized before nitriding to make it difficult to nitrify, and the oxidation deteriorates the magnetic properties of the magnet alloy. Therefore, in the nitriding treatment, it does not mean that the mother alloy should be just roughly crushed, and the mother alloy is not too large,
In addition, it is necessary to make the particle size uniform so that it is not too small, which is a manufacturing difficulty.

An object of the present invention is to provide a method for solving the drawbacks in manufacturing the conventional nitriding magnet alloy by the melting method. Specifically, an object of the present invention is to provide a method for producing an inexpensive nitriding magnet alloy powder having excellent magnetic properties for producing a rare earth magnet.

[0011]

Means for Solving the Problems The present inventor has conducted various studies in order to achieve such an object, and has obtained the following findings. Since the magnet alloy obtained by the above-mentioned reduction diffusion method includes the step of contacting with water as described above, some degree of oxidation is unavoidable, and there is a drawback that magnetic properties are inferior as compared with the magnet alloy produced by the melting method. there were. However, the reaction product mixture of the reduction diffusion method itself has a structure that easily collapses,
It does not require the above-mentioned coarse grinding step, which is one of the major drawbacks of the dissolution method. Since the reaction product mixture has a cake-like and porous structure, the surface area is very large, and the surface is activated particularly at the stage of completion of the reaction,
Not only the oxidation reaction but also the nitriding reaction can easily occur.

Therefore, by nitriding such a reaction product mixture in advance before washing with water, it is possible to prevent the oxidation of particles during washing with water, which is a drawback of the reduction and diffusion method, and to utilize the advantage of omitting the step of coarse pulverization. With the idea in mind, when the reaction product mixture was actually subjected to nitriding treatment by the reduction diffusion method, not only did the magnetic properties not deteriorate even if such nitriding was performed in advance, but rather, oxidation in the washing process could be prevented. ， Unknown that the improvement can be planned unexpectedly,
The present invention has been completed.

Here, the present invention is characterized in that a nitrogen-containing gas is brought into contact with a cake-like reaction product mixture obtained by a reduction diffusion method using a rare earth oxide, a reducing agent and a metal as a starting material for nitriding. Is a method for producing a rare earth magnet alloy material.

Further, the present invention is a method for producing a rare earth magnet alloy powder, which comprises nitriding the cake-like reaction product mixture obtained as described above and pulverizing the recovered magnet alloy material. .. In the present invention, the reduction diffusion method may use a conventional method, and the present invention is not limited to the specific conditions thereof, and a reaction product mixture containing a magnet alloy powder by diffusion of a rare earth metal and an appropriate metal component. Should be generated.

[0015]

The present invention provides a cake-like reaction product mixture comprising a reducing agent, an oxide of the reducing agent, and a magnet alloy obtained by the reduction diffusion reaction in a reduction diffusion method which is one of the methods for producing a magnet alloy. For example, when performing a water washing treatment to separate the magnet alloy, it is brought into contact with a gas containing nitrogen at a stage before the water washing treatment, and the magnet alloy that is a reaction product is nitrided. It is a manufacturing method of a system magnet alloy.

The present invention will be described in detail below in the order of its concrete steps. FIG. 1 is a process diagram showing each processing condition in the reduction diffusion reaction process, the nitriding process, the water washing process, the fine pulverization and the molding process according to the present invention.

Reduction / diffusion reaction step: This is the step until a reaction product mixture in the form of a cake is obtained by the reduction / diffusion method. The steps up to this point are the same as those in the conventional reduction / diffusion method, and rare earth oxides such as salium and neodymium. In addition to iron, cobalt, and other main elements, boron, gallium, chromium, titanium, copper, and transition metals such as vanadium and tungsten are added as additional elements to improve magnetic properties, if necessary. In this case, each element is used alone or in the form of an alloy such as ferroboron.

These magnet alloy raw materials are mixed with reducing agents such as calcium and magnesium, or their hydrides and chlorides. In the present invention, these compounding elements are not particularly limited. It is also possible to change it as needed. Put these starting materials in a furnace and
It is heated at a heating rate of 1 minute and kept at about 1000 ° C in vacuum or in a reducing atmosphere or in a neutral atmosphere such as argon to reduce the rare earth oxides and to diffuse the reduced rare earth metal and other elements. Make a magnet alloy.
This reduction-diffusion reaction usually requires several hours, for example, 4 hours.

Nitriding Step After completion of the reduction diffusion, it is usually cooled to around room temperature in a neutral atmosphere such as argon or a reducing atmosphere such as hydrogen at a rate of 4 ° C./minute while avoiding oxidation. In this case, after cooling to a certain extent, the nitriding treatment is performed at a high temperature of 450 ° C., for example. Of course, depending on the case, as long as oxidation is appropriately prevented, the material may be once cooled to room temperature and then reheated to perform the next nitriding treatment. The nitriding conditions at this time are not particularly limited, but as the nitriding atmosphere,
For example, an atmosphere of H ₂ 0.1 atm and N ₂ 0.9 atm is preferable.

As described above, in the reaction product mixture taken out from the reduction treatment furnace, the magnet alloy, the oxide of the reducing agent, that is, calcium oxide, and the reducing agent left unreacted are intermingled. It has a cake shape. The microstructure of this cake is porous and has a structure that allows gas to pass through very easily.

For example, when calcium is used as a reducing agent, when the microstructure is observed in detail with a microscope, the particles of the amorphous magnet alloy are separated by calcium oxide, and the calcium oxide portion is very porous. Is. Such a porous shape is formed
The melting point of calcium oxide produced by the reduction-diffusion reaction is as high as 2500 ° C., which is much higher than the temperature of the reduction-diffusion reaction, and it is speculated that calcium oxide is produced as a solid.

In the present invention, by utilizing the porous structure of the cake, it is possible to easily nitride the cake without crushing it as in the conventional melting method. Preferably, as described above, the time for nitriding this cake is preferably around 450 ° C., which is in the middle of the cooling step in the reduction diffusion method. Although the cake once cooled to room temperature can be heated and nitrided again, preferably in order to minimize the oxidation of the magnet alloy and to save the heating energy, preferably during the reduction-diffusion cake cooling. It is better to nitride.

That is, once the material is cooled to room temperature and then heated to the nitriding temperature, the time of the whole process is extended, and the amount of oxidation of the magnet alloy is increased accordingly. If the nitriding is performed during the cooling of the cake, the total time required for the process is shortened, and further, the nitriding can be continued in the atmosphere deoxidized by the reducing agent, so that the oxidation can be minimized.

The gas for nitriding may be any gas containing a nitrogen component, and may be nitrogen, ammonia gas or the like, or a mixed gas of these with hydrogen or an inert gas. A gas pressure of about 1 atm is sufficient. For example, as mentioned above, H ₂
An atmosphere of 0.1 atm and N _{2 at} 0.9 atm can be mentioned.

The nitriding temperature does not have to be kept strictly constant, but since the speed of nitriding varies depending on the temperature, the time allotted to the nitriding step can be accurately estimated if the temperature is controlled to be substantially constant, which is industrially convenient. After nitriding is completed, it is preferable to cool to room temperature in a reducing atmosphere or a neutral atmosphere so as not to oxidize. This is because oxidation and the like easily proceed in a high temperature atmosphere.

Washing step with water: After the nitriding treatment is completed, the reaction product mixture taken out is washed with water if necessary to wash away unnecessary substances other than the magnet alloy to recover magnet alloy powder. The magnet alloy produced by the conventional reduction diffusion method was oxidized in this washing process, which was a cause of deteriorating the magnet characteristics.However, if the alloy is nitrided before washing as in the present invention, the alloy surface Becomes extremely difficult to oxidize.

It has been well known that nitriding an iron-based material increases the oxidation resistance, but by appropriately specifying the nitriding time in the reduction diffusion method as in the present invention, the conventional problem is solved. Oxidation of the magnet alloy, which has been described above, during washing with water is significantly reduced. That is, if it is just nitriding, it may be an alloy after washing with water, but by performing nitriding before washing with water as in the present invention, oxidation during washing with water is prevented, and as a result, a magnet with good magnetic properties is obtained. A powder is obtained. It should be noted that this water washing step can be omitted when the magnetic alloy is selected by magnetic separation.

Milling step: Finally, the washed magnet alloy is dried and, if necessary, milled to obtain magnet alloy powder. This fine pulverization process is usually carried out by a jet mill, and the size is set to about several μm. Also in this case, it is preferable to carry out fine pulverization in a nitrogen atmosphere in order to prevent oxidation. The magnet alloy powder thus obtained is then appropriately shaped by a conventional means and used as a magnet. Hereinafter, the present invention will be described in detail with reference to examples.

[0029]

EXAMPLE In the present example, the present invention was carried out according to the processing pattern shown in FIG. Sm ₂ O ₃ powder with an average particle size of 10 μm 302
After mixing 398 g of pure iron powder having an average particle size of 50 μm with 100 g of granular calcium having an average particle size of 15 mm or less, a reduction diffusion reaction was performed in an atmosphere and a temperature pattern as shown in FIG. As shown in Fig. 1, the cake-like reaction product mixture prepared here was maintained at a temperature of 450 ± 10 ° C during the cooling process before the water washing process, nitrogen gas of 0.9 atm was introduced, and it was held for 25 minutes.
It was cooled to room temperature and removed from the furnace. This was poured into water, repeatedly washed, and vacuum dried to recover the magnet alloy.

Next, this magnet alloy was jet milled for 3.
Finely pulverize to 7 μm, add zinc as a binder, and
It was press molded in a magnetic field of kOe with a molding pressure of ² t / cm ² . Then, the magnetic characteristics of this molded body were measured by a vibrating sample magnetometer. As a comparative example, after reductive diffusion, the magnet alloy once cooled to room temperature, washed with water and dried was heated again, and a magnet alloy nitrided at the same temperature and atmosphere as the example was molded under the same conditions as the example. , Its magnetic properties were measured.

Table 1 shows the magnetic properties of the magnet alloys obtained in Examples and Comparative Examples and the oxygen concentration of the magnet alloys immediately before press molding. An example of the conventional dissolution method is also shown for reference. As can be seen from the results shown in Table 1, the present invention improved the residual magnetic flux density Br from about 9 kG to about 11 kG and the coercive force from 8 to 9 kOe to 11 kOe. This is because, as shown in Table 1, the degree of oxidation of the magnet alloy before being molded into a magnet was remarkably reduced from about 0.9 wt% to about 0.1 wt%. It is considered that this is because in the present invention, the alloy powder is less likely to be oxidized because it is nitrided before being washed with water, and the amount of oxidation is reduced in the steps of washing with water and fine pulverization. Further, in the conventional melting method, the oxygen concentration in the alloy is low and the coercive force is excellent, but since the alpha iron tends to remain unreacted, the residual magnetic flux density is not so high.

[0032]

[Table 1]

[0033]

As described above, in obtaining a rare earth-based nitrided magnet alloy, it is possible to perform nitriding treatment without crushing by using a cake obtained by a reduction diffusion method instead of an ingot or alloy powder, and before washing with water. By nitriding the magnet alloy, the oxidation resistance of the magnet alloy is improved, and even if it is washed with water, the alloy will not be oxidized and the magnetic properties will not deteriorate, and extremely high quality magnet powder can be manufactured without complicated steps. can do.

[Brief description of drawings]

FIG. 1 is a process diagram for manufacturing a magnet powder by a reduction diffusion method according to the present invention.

Claims (2)

[Claims] 1. A rare earth magnet alloy characterized in that a nitrogen-containing gas is brought into contact with a cake-like reaction product mixture obtained by a reduction diffusion method using a rare earth oxide, a reducing agent and a metal as starting materials for nitriding. Material manufacturing method. 2. A method for producing a rare earth magnet alloy powder, which comprises nitriding the cake-like reaction product mixture obtained in claim 1 and pulverizing the recovered magnet alloy material.