JPH05112803A - Production of tb-containing rare-earth metal-transition metal-based alloy powder - Google Patents

Abstract

PURPOSE:To obtain the alloy powder having low contents of alkali (earth) metal and chlorine and appropriate for an alloying target for magnetic recording by using calcium oxide as the disintegration accelerator in the production of the powder by the reductive diffusion method. CONSTITUTION:One or more kinds of reducing agents among alkali (earth) metals, their hydrides and calcium oxide are added to the mixed powder of Tb oxide and transition metals contg. >=1 kind among iron, Ni and Co. The mixture is heated in an inert gas atmosphere or in vacuum to obtain a lumpy reaction product mixture. When the mixture is brought into contact with water, the unreacted reducing agent in the mixture, the by-produced oxides of the reducing agent, etc., are dissolved as the hydroxides, and the lumpy mixture is disintegrated. The formed slurry is agitated, and the hydroxides are removed from the obtained alloy powder by decantation. Meanwhile, metallic Ca is appropriately used as the reducing agent from the standpoint of handling and cost. Although the reducing agent is formed from the metallic Ca, the amt. is insufficient to accelerate disintegration.

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 rare earth-transition metal alloy powder containing Tb as a main element, which is particularly suitable for use in magneto-optical recording and alloy recording magnetic targets. The present invention relates to a method for producing a Tb-containing rare earth-transition metal alloy powder.

[0002]

2. Description of the Related Art In recent years, a magneto-optical recording medium has been developed as a recording medium capable of recording information at a high density and easily reproducing, erasing and re-recording, and an alloy for a magnetic metal thin film forming a recording layer thereof. As such, rare earth-transition metal type amorphous alloys (for example, Tb-Fe-Co, Gd-Tb-Co, etc.) are known. These have many advantages such as a small amount of energy required for recording, no occurrence of grain boundary noise, and the ability to make large-sized ones relatively easily.

In the field of magnetic recording media, γ-Fe ₂
A coating type magnetic recording medium in which a magnetic powder such as O ₃ is coated on a non-magnetic substrate using an organic binder to form a magnetic recording layer has been generally used, but in recent years, a purpose has been to increase recording density. As such, a metal thin film type magnetic recording medium in which a magnetic metal thin film containing Fe, Co and Ni as main components is formed on a non-magnetic support has been developed. Further, among these metal thin film magnetic recording media, those in which a metal thin film is formed on a flexible support are easily corroded because the magnetic metal is exposed to the outside air, and also have many holes. I had a problem, but Co
Alternatively, it is known that such a problem can be effectively improved by forming an alloy obtained by adding a rare earth element to Ni as a metal thin film.

Thus, thin films of rare earth-transition metal alloys have attracted attention in both magneto-optical recording media and magnetic recording media. As a method for forming such a thin film, a chemical plating method, a sputtering method, an ion plating method, a vacuum vapor deposition method and the like are known. From the viewpoint of the quality of the magnetic thin film obtained, the sputtering method, the ion plating method and the vacuum vapor deposition method. The method is preferably used.

The sputtering method requires a target, and the ion plating method and the vacuum evaporation method require a vapor deposition source. However, the yield is good, the composition change is small, and an alloy thin film having a target composition is easily obtained. The type is
It is advantageous as a target or vapor deposition source. Typical examples of rare earth elements used in the production of this alloy include Tb, Dy, Gd, Nd, etc., but they have excellent magnetic properties for use as recording media for magneto-optical disks. In many cases Tb is used as the main element.

[0006] As a method for producing a rare earth element-transition metal alloy used as a target or a vapor deposition source, there is a method of melting a rare earth element and a transition metal by arc discharge or the like to form an alloy, but the rare earth element is highly active. Because of this, the yield is poor, segregation is likely to occur, ingots containing vacancies are likely to occur, and an extremely brittle alloy of rare earth elements and transition metals has the characteristic of being an intermetallic compound, which is particularly large. There is a problem that cracks and cracks are likely to occur during the production of the alloy ingot.

On the other hand, a mixture of a rare earth element powder and a transition metal powder or an alloy powder containing a rare earth element and a transition metal in a predetermined composition is used as a raw material, and the raw material powder is sintered by powder metallurgy. Therefore, a method for producing a rare earth element-transition metal alloy is also known. With this manufacturing method, problems such as cracks and cracks can be effectively avoided.

[0008]

Conventionally, the raw material powder to be subjected to the above-mentioned powder metallurgy method has been manufactured by crushing an alloy ingot obtained by melting the component metals, for example. (See Sho 60-230903, etc.). However, since rare earth elements have the property of being easily oxidized in air, the oxygen content of the alloy powder obtained during pulverization becomes large, and as a result, the oxygen content of the sintered body obtained by sintering this is high. Increasing the content is unavoidable. By the way, oxygen in this sintered alloy significantly deteriorates the magneto-optical characteristics and magnetic characteristics of the thin film formed by the sputtering method, the ion plating method and the vacuum evaporation method. In order to reduce the amount of oxygen in the sintered alloy, the crushing step may be performed in an organic solvent or in an inert atmosphere, but in this case, the crushing step becomes complicated and costly. There are some disadvantages.

On the other hand, as a method for producing a raw material alloy powder to be subjected to powder metallurgy, there is also known a method in which a reduction diffusion method is used to prevent the process from becoming complicated and to reduce the production cost (JP-A-63). -105909 publication). However, according to this method, the produced alloy powder contains impurities such as alkali metal, alkaline earth metal and chlorine. Particularly, chlorine has a problem that it deteriorates the weather resistance of a thin film formed by a sputtering method or the like.

Therefore, an object of the present invention is to contain Tb for producing a sintered alloy having a low oxygen and chlorine content and useful for forming a metal thin film which becomes a recording layer of a magneto-optical recording medium or a magnetic recording medium. It is to provide a method for producing an alloy powder.

[0011]

According to the present invention, terbium (Tb) oxide powder, transition metal powder containing at least one of iron, nickel and cobalt, alkali metal, alkaline earth metal and After mixing at least one selected from these hydrides with calcium oxide and heating the mixture in an inert gas atmosphere or under vacuum,
Provided is a method for producing a Tb-containing rare earth-transition metal based alloy powder, which comprises wet treating a reaction product mixture.

[0012]

In the present invention, it is extremely important to mix calcium oxide prior to the heat treatment of the mixed powder containing Tb oxide. This calcium oxide has an action of suppressing the metal powder and the produced alloy particles used as raw materials from being welded and bonded to each other, or from being mixed with oxide particles such as by-produced alkali metal oxides. In addition, it has an action of promoting the disintegration of the heated reaction product obtained as a lump mixture during wet treatment.

Originally, using a reducing agent such as metallic calcium
When the mixed powder containing Tb oxide is reduced, calcium oxide is produced, and the product is disintegrated by the wet treatment. It is sufficient, it takes a long time to disintegrate, and there are some particles that are not disintegrated and remain as coarse particles, so that the yield as a product decreases.

Further, in the method disclosed in the above-mentioned JP-A-63-105909, an alkaline earth metal salt such as calcium chloride is used as a material for promoting the disintegration. According to this method, the disintegration property is improved and the product yield is also improved, but since the salt-forming component of the alkaline earth metal salt added with chlorine or the like remains in the product, the product is sintered. When the obtained alloy powder is used for a magnetic recording material such as a magneto-optical disk, the characteristics such as durability of the magneto-optical disk are significantly impaired.

According to the present invention, by using calcium oxide as a disintegration promoter, it is possible to effectively prevent not only chlorine but also impurities such as oxygen and carbon from being mixed into the product, and to obtain the powder product obtained. Even when used as a magnetic recording material, deterioration of the properties of the product is effectively prevented. In the present invention, the above-mentioned calcium oxide is used in an amount of 1 to 30% by weight, especially 5% by weight or more, based on the rare earth oxide.

Raw Material Powder The main rare earth element used in the present invention is Tb. The oxides of Tb include Tb ₄ O ₇ and Tb ₂ O ₃ ,
Tb ₂ O ₃ is preferably used in the present invention. That is,
The heat generated upon reduction with an alkali metal or the like, Tb ₂
By using it in the form of O ₃ , it can be suppressed more effectively than when it is used in the form of Tb ₄ O ₇ . Therefore, it is possible to effectively avoid the sintering of particles caused by this heat generation and the trapping of alkali metal or the like into the particles, and as a result, it is possible to suppress the content of impurities such as oxygen or alkali metal to be low. Becomes

As for Tb ₂ O ₃ , Tb ₄ O ₇ (the oxide of Tb is usually present in this form) is put in a crucible such as alumina, and the temperature is set to 700 in a vacuum or an inert atmosphere such as argon. ~
It is obtained by roasting at a temperature of 1100 ° C. for 1 to 3 hours. Although Tb ₂ O ₃ does not immediately oxidize in air to become Tb ₄ O ₇ , it is generally preferable to store it in a vacuum aluminum pack. The Tb oxide used preferably has an average particle size of 1 to 50 μm (Fischer-Subsieve-Sizer method, the same applies hereinafter). still,
In the present invention, an oxide powder of a rare earth element other than Tb can be used together.

The transition metal used in the present invention is Fe,
It is necessary to contain at least one of Co and Ni, but especially when the obtained alloy powder is used for forming a metal thin film of a magnetic recording medium, use either Co or Ni. is necessary. It is also possible to use transition metals other than Fe, Co and Ni, such as Mn, Cr, V, and Ti, in combination.

These transition metals can also be used in the form of metal or alloy powders or mixtures of these forms. Also, a part of the metal or alloy powder can be used as an oxide. In particular, when the amount of the metal used is small compared to the amount of the entire transition metal, the total amount of the metal can be used in the form of oxide. The particle size of the transition metal powder and the like is not particularly limited, but it is desirable that the particle size is 100 mesh or less (Tyler standard, the same applies hereinafter) in view of the particle size of the produced alloy powder and the uniformity of the alloy composition.

In the present invention, the mixed powder of the above Tb oxide powder and the transition metal powder is used as the raw material powder. The mixing ratio of the two is appropriately set according to the composition of the intended alloy powder. The particle size of this raw material powder is preferably 1/2 or less of the target particle size. For example, in order to produce fine alloy powder of 100 mesh or less, which is suitable as a powder metallurgy raw material, a mixed powder of 200 mesh or less Is preferably used.

Reducing Agent In the present invention, a reducing agent is added to the above mixed powder. As the reducing agent, at least one selected from alkali metals, alkaline earth metals and their hydrides is used. Typical examples thereof include lithium, sodium, potassium, calcium, magnesium and hydrides thereof, but metallic calcium is preferable from the viewpoint of handling safety and cost. Further, these reducing agents are used in the form of particles or powder, and in view of cost, granular metal calcium having a particle size of 4 mesh or less is particularly preferable. These reducing agents are equivalent to the reaction (the stoichiometric amount required to reduce the rare earth oxide, and when the transition metal is used in the form of an oxide, include the amount necessary to reduce it). ) 1.1 to 3.0 times, preferably 1.5 to 2.0 times.

Reduction Reaction In the present invention, the above-mentioned raw material powder, a reducing agent, and the above-mentioned calcium oxide acting as a disintegration accelerator are mixed to reduce the mixture. Mixing of each component is performed under conditions such as a dry inert gas atmosphere that does not cause moisture absorption.
In the present invention, the reduction of the mixture is performed by heat treatment in an inert gas atmosphere or in vacuum. When performing in vacuum, it is desirable that the degree of vacuum is 10 ⁻³ torr or less. Argon or the like is preferably used as the inert gas. The temperature of heat treatment is 900 ~ 13
A suitable range is 00 ° C., particularly 950 to 1100 ° C. The heat treatment time is not particularly limited, but it is preferably 1 to 10 hours in order to obtain an alloy powder having a uniform composition. The product obtained by this reduction reaction is a massive mixture containing the target rare earth-transition metal, an oxide such as an alkali metal as a reducing agent, and an unreacted alkali metal.

Wet Treatment According to the invention, the agglomerated mixture obtained above is subjected to a wet treatment. This wet treatment may be carried out by bringing the mixture into water and stirring the mixture, or the like. That is, when the massive mixture is brought into contact with water, the unreacted reducing agent and the by-produced reducing agent oxide contained therein react with water to form a hydroxide such as Ca (OH) _2. And dissolve. Therefore,
The bulk mixture disintegrates easily. In the present invention, this disintegration is completed in 1 to 2 hours, but if calcium oxide is not used, it takes 20 to 30 hours.

After stirring the slurry produced by disintegration,
By removing the hydroxide such as the alkali metal on the upper portion by decantation and repeating the operations of water injection-stirring-decantation, the hydroxide can be removed from the obtained alloy powder. Further, the partially remaining hydroxide is completely removed by acid washing with an acid such as acetic acid or hydrochloric acid in the range of pH 3 to 6, preferably pH 4 to 5. After completion of such wet treatment, for example, after washing with water, washing with an organic solvent such as alcohol or acetone,
After dehydration, vacuum drying may be performed.

According to the present invention described above, it is possible to obtain a sintering alloy powder in which the content of impurities is extremely effectively suppressed. For example, calcium chloride as a disintegration promoter and Tb oxide
When alloy powder is produced by using Tb ₄ O ₇ and calcium as a reducing agent, the impurity content (shown by weight%) of the obtained alloy powder is Ca: 0.2% or less, C: 0.02% or less, O:
₂ : 0.2% or less, Cl: 0.01 to 0.03%. On the other hand, Tb ₄ O ₇ is used as the Tb oxide, and calcium is used as the reducing agent (the disintegration promoter as the disintegration accelerator).
Taking CaO as an example, the obtained alloy powder has an impurity content of Ca: 0.2% or less, C: 0.02% or less, O ₂ : 0.2% or less, Cl: 0.001% or less. Furthermore, when Tb ₂ O ₃ is used as the Tb oxide in the above, Ca: 0.15% or less, C: 0.02% or less, O ₂ : 0.15%
Below, Cl: 0.001% or less.

Thus, according to the present invention, the impurity content,
For example, the chlorine content is extremely low, and a very useful alloy powder can be obtained as a raw material powder for a target for magneto-optical recording.
That is, the alloy powder obtained as described above is subjected to sintering by, for example, a powder metallurgy method, and thereby a sintered alloy is obtained. In this case, the alloy powder can be used alone, or if necessary, the composition can be adjusted by mixing an appropriate amount of transition metal powder such as Fe, Co and Ni.

Sintering by the powder metallurgy method can be carried out under conditions known per se, for example, alloy powder at room temperature at 0.5
~5t / cm ² of either simple compression pressure, after forming in an isostatic press at a pressure of 0.5~2t / cm ^2, a vacuum or Ar,
Atmospheric pressure sintering method of sintering at a temperature of 900 to 1300 ℃ for 1 to 5 hours in an atmosphere, 800 to 120 at a pressure of 0.1 to 0.5t / cm ^{2 in} a vacuum.
Hot pressing method that sinters at a temperature of 0 ℃ for 1 to 5 hours, and after encapsulating in an elastic body, temperature of 800 to 1200 ℃, 0.1 to 2t / cm ²
It can be carried out by a hot isostatic pressing method or the like in which sintering is performed for 1 to 5 hours. After being targeted by such a powder metallurgy method, a thin film for, for example, a magneto-optical disk is formed by a sputtering method, an ion plating method or a vacuum evaporation method.

[0028]

EXAMPLES In the following examples, "%" means "% by weight" unless otherwise specified. In addition, all of the following examples and comparative examples were manufactured (target composition: Tb 4
9.85%, Fe 44.46%, Co 5.69%).

Example 1 Tb ₄ O _{7 with} a purity of 99.9% or more (average particle size of 3 μm or less) 60.4
4g, iron powder (particle size 325 mesh or less) 44.46g, cobalt powder (particle size 300 mesh or less) 5.96g, metallic calcium (particle size 4 mesh or less) 29.63g, and calcium oxide (particle size 100 mesh or less) 6.04g, Mix well in an inert atmosphere. This mixture was placed in a stainless steel reaction vessel, heated to 1050 ° C. in a high-purity Ar gas atmosphere in about 1 hour, held at that temperature for 5 hours, and then cooled to room temperature.

The resulting lumpy mixture was crushed to a square of about 1 cm and then poured into about 15 liters of water. After 1.5 hours, the mixture had completely disintegrated and the resulting slurry was
The Ca (OH) ₂ suspension was separated by decantation and after pouring water, the slurry was stirred for 5 minutes and decanted again. This operation of water injection-stirring-decantation was repeated to sufficiently separate unreacted calcium, calcium hydroxide and calcium oxide from the alloy powder.
Next, the pH of the slurry obtained by adding water to the alloy powder is 5.0.
Dilute acetic acid is added dropwise with stirring to maintain the temperature for 5 minutes, then filtered. The alloy powder obtained is washed with water and then with ethanol, and vacuumed at 50 ° C and 1 × 10 ^-2 torr for 12 hours. Dried.

The composition of the alloy powder thus obtained was as follows. Tb 49.83%, Fe 44.2%, Co 5.66% The impurity concentrations were as follows. Ca: 0.14%, C: 0.015%, O ₂ : 0.15%, Cl: 0.001
Less than%, there was no roasted product that could not pass through the 48-mesh screen.

Example 2 Tb ₂ O _{3 having} a purity of 99.9% or more (average particle size of 3 μm or less) 59.1
5g, iron powder (particle size 325 mesh or less) 44.46g, cobalt powder (particle size 300 mesh or less) 5.96g, metallic calcium (particle size 4 mesh or less) 29.10g, and calcium oxide (particle size 100 mesh or less) 5.92g, When thoroughly mixed in an inert atmosphere and subjected to heat treatment and wet treatment in the same manner as in Example 1, the time required for disintegrating the massive mixture was
It was 1.5 hours. Water injection-stirring-as in Example 1.
The operation of decantation was repeated to carry out pickling, ethanol washing and vacuum drying.

The composition of the alloy powder thus obtained was as follows. Tb 49.63%, Fe 44.2%, Co 5.94% The impurity concentrations were as follows. Ca: 0.12%, C: 0.013%, O ₂ : 0.10%, Cl: 0.001
Less than%, there was no roasted product that could not pass through the 48-mesh sieve.

Comparative Example 1 In Example 1, the components were mixed in the same manner as in Example 1 except that calcium oxide was not used, and heat treatment and wet treatment were carried out.
It took 30 hours. Further, as in Example 1, water injection-stirring-
The operation of decantation was repeated to carry out pickling, ethanol washing and vacuum drying.

The composition of the alloy powder thus obtained was as follows. Tb 48.48%, Fe 45.30%, Co 5.72% The impurity concentrations were as follows. Ca: 0.28%, C: 0.014%, O ₂ : 0.21%, Cl: 0.001
Less than% It is understood that the oxygen and calcium impurity concentrations are higher than in the examples. In addition, there were 11.2 g of roasted products that could not pass through the 48-mesh screen, and the product yield was poor.

Comparative Example 2 In Example 2, the components were mixed in the same manner as in Example 2 except that calcium oxide was not used, and heat treatment and wet treatment were carried out.
It took 30 hours. Further, as in Example 2, water injection-stirring-
The operation of decantation was repeated to carry out pickling, ethanol washing and vacuum drying.

The composition of the alloy powder thus obtained was as follows. Tb 48.41%, Fe 45.45%, Co 5.74% The impurity concentrations were as follows. Ca: 0.21%, C: 0.016%, O ₂ : 0.17%, Cl: 0.001
Less than% The oxygen and calcium impurity concentrations are higher than in the examples. In addition, there was 5.4 g of roasted product that could not pass through the 48-mesh screen, and the product yield was poor. However, it is understood that the impurity concentration and the yield are improved as compared with Comparative Example 1.

Comparative Example 3 Tb ₄ O _{7 with} a purity of 99.9% or more (average particle size 3 μm or less) 302.19 g, iron powder (particle size 325 mesh or less) 222.30 g, cobalt powder (particle size 300 mesh or less) 2
9.79 g, metallic calcium (particle size 4 mesh or less) 148.17
g and calcium chloride (particle size 100 mesh or less) 3
0.22g, thoroughly mixed in an inert atmosphere, Example 1
When heat treatment and wet treatment were carried out in the same manner as above, the time required for disintegration was 1.5 hours. Further, in the same manner as in Example 1, the operations of water injection-stirring-decantation were repeated to carry out pickling, ethanol washing and vacuum drying.

The composition of the alloy powder thus obtained was as follows. Tb 49.35%, Fe 44.6%, Co 5.73% The impurity concentrations were as follows. Ca: 0.15%, C: 0.018%, O ₂ : 0.15%, Cl: 0.015
% The impurity concentrations of oxygen, calcium and chlorine are higher than those in the examples. There was no roasted product that could not pass through the 48-mesh screen.

[0040]

According to the present invention, it is possible to obtain a Tb-containing rare earth-transition metal alloy powder in which the Ca content, the oxygen content and the chlorine content are effectively suppressed and the composition is uniform. In particular, according to the method of the present invention, since the lumpy product mixture produced by reduction has extremely high disintegration property (fine powderization), it is possible to easily produce an alloy powder having a target particle size in a short time.
Further, since the chlorine content, which adversely affects the magnetic properties, is effectively suppressed, after the alloy powder obtained by the present invention is targeted by the powder metallurgy method, using this, the sputtering method, the ion plating method or A magnetic metal thin film formed by a vacuum vapor deposition method, for example, a thin film for a magneto-optical disk is excellent in characteristics such as weather resistance.

Claims (2)

[Claims] 1. A terbium (Tb) oxide powder, iron,
A powder of a transition metal containing at least one of nickel and cobalt, at least one selected from alkali metals, alkaline earth metals and hydrides thereof, and calcium oxide are mixed, and the mixture is placed in an inert gas atmosphere. Alternatively, a method for producing a Tb-containing rare earth-transition metal alloy powder, which comprises subjecting the reaction product mixture to wet treatment after heating under vacuum. 2. The production method according to claim 1, wherein Tb ₂ O ₃ is used as the oxide of Tb.