JP3049874B2 - Method for producing alloy powder containing rare earth metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an alloy powder containing a rare earth metal, and more particularly to a method for producing an alloy powder containing a rare earth metal by a direct reduction diffusion method.

[0002]

2. Description of the Related Art Alloys containing rare earth metals (including intermetallic compounds) include permanent magnet alloys, hydrogen storage alloys, magneto-optical recording alloys, magnetostrictive alloys, magnetic sensor alloys, and alloys for magnetic refrigeration work. It is known to be useful as Incidentally, these alloy materials are often put to practical use in the form of powder. For example, typical permanent magnet materials include a samarium-cobalt-based magnet and a neodymium-iron-boron-based magnet, and these are used as sintered magnets or resin-molded magnets using the alloy powder. In addition, hydrogen storage alloys, mainly lanthanum-nickel-based materials, have recently been used for negative electrodes as active materials for negative electrodes of alkaline secondary batteries. For example, hydrogen storage alloy powders have been used by filling and molding a porous current collector into a porous current collector. I have. Further, the magneto-optical recording alloy is used as an alloy thin film of terbium-iron-cobalt or the like.In many cases, a physical vapor deposition method such as a sputtering method or an ion plating method is used. A sintered alloy target made using an alloy powder is used as a necessary evaporation source.

[0003] As a method for producing such an alloy powder containing a rare earth metal, a melting / pulverizing method and a direct reduction diffusion method can be mentioned. In the melting and pulverizing method, a rare earth metal constituting an alloy and a master alloy block made of various metals serving as other alloy components are prepared into a required composition, melted by a high frequency melting furnace or the like, cast, and cast. And pulverizing it to obtain an alloy powder having a required particle size. This method is disadvantageous in that expensive and active rare earth metals are used, segregation during casting is inevitable, and grinding is indispensable.

[0004] In the direct reduction diffusion method, a rare earth oxide powder and another metal component powder are blended so as to have a required alloy composition.
This is a method of directly producing an alloy powder having a desired composition by mixing and heating a reducing agent such as an alkaline earth metal or the like to carry out a reduction diffusion reaction, and subjecting the obtained reaction product to wet treatment. This method has the advantage that an inexpensive and chemically stable rare earth metal oxide can be used.Also, a powdery alloy having an average particle size of 100 μm or less can be obtained, and alkali metal chlorides can be obtained. When an alkaline earth metal chloride is added as a flux to perform a reductive diffusion reaction, an alloy powder having an even smaller particle size and having less residual reducing agent component can be obtained. Thus, depending on the desired particle size, no milling step is required at all. When alloy powder with a smaller particle size is required, pulverization is performed,
The dissolution and pulverization method requires coarse pulverization and fine pulverization, but the direct reduction diffusion method has an advantage that at least coarse pulverization is unnecessary.

[0005]

However, in the case of the direct reduction diffusion method described above, some of the alloy components may droop to the lower part of the reaction vessel. Not only cannot be obtained, but also it is difficult to take out the reaction product from the reaction vessel, and the deterioration of the reaction vessel becomes remarkable. The present inventors have studied the problem of the direct reduction diffusion method, and as a result, such dripping is common when producing an alloy powder having a melting point phase (low melting point phase) lower than the reduction temperature. It was found that such a low-melting phase dripped. For example, when metal calcium is used as the reducing agent, the Ca reduction reaction of the rare earth metal oxide starts at about 800 ° C, and when the temperature of the furnace reaches 851 ° C or higher due to the heating of the furnace and the reaction heat, the reduction reaction starts quickly. Although proceeding, it is generally maintained at a temperature of 900 to 1300 ° C. in order to sufficiently reduce, diffuse and homogenize. Here, the melting point of the structure in the alloy powder of the target composition is
If there is an alloy phase below 850 ° C, the phase will droop to the lower part of the reaction vessel without being sufficiently diffused, or even if it has diffused sufficiently, the lower part of the reaction product will have drastic dripping of the low melting point phase. The falling causes an alloy lump that cannot be recovered as a powder. The term “uniform” as used herein refers to eliminating the presence of a metal phase or an alloy phase that does not contain a rare earth metal component, which is generated when the diffusion of the rare earth metal component is insufficient. It is not meant to consist of a single phase.

Accordingly, an object of the present invention is to provide a method for producing an alloy powder containing a rare earth metal and having a melting point lower than the reduction temperature by a direct reduction diffusion method, whereby dripping of the low melting point phase is effectively suppressed. It is to provide a method that can do it.

[0007]

According to the present invention, a rare earth metal oxide, another alloying element powder, and a reducing agent are mixed, and the mixture is subjected to a reduction diffusion reaction in an inert gas atmosphere. In a method for producing an alloy powder containing a metal and having a melting point phase (low melting point phase) lower than the reduction temperature, the initial reduction diffusion is performed under conditions where the rare earth metal oxide is effectively reduced. A method is provided, wherein the second reduction diffusion is performed by lowering the reduction temperature before dripping of the low melting point phase generated by the reduction diffusion.

[0008]

In the present invention, the above-mentioned alloy composition having a low melting point phase is often found in an alloy system of a rare earth metal and a 3d transition metal of the periodic table or a rare earth metal and a noble metal, and generally has a high rare earth metal component concentration. For example, in an Nd-Co binary alloy, the melting point of Nd ₃ Co as an intermetallic compound is 640 ° C., and Nd ₃ Co and NdCo
The eutectic temperature is close to 650 ° C, which is considerably lower than the temperature at which Ca reduction proceeds rapidly. An alloy powder having such a low melting point phase is suitable for a case where an alloy powder having a high rare earth metal content is required, or as described above, when used as a sintered alloy using an alloy powder containing a rare earth metal. It is used when it is necessary to realize liquid phase sintering and improve the sintering density by blending an alloy powder containing an amount of a low melting point phase.

As the rare earth metal oxide component used in the present invention, any one can be used as long as the above-mentioned low melting point phase is formed. For example, rare earth metals include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), and dysprosium (Dy). ), Holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), ruthenium (Lu), promethium (Pm), yttrium (Y), and scandium
(Sc). These rare earth metal oxides can be used alone or in combination of two or more. If it is a small amount, a part thereof may be chloride.

The other metal component which forms the target alloy together with the rare earth metal is not particularly limited as long as it is hardly volatile at the heating temperature (about 1300 ° C.) of the general direct reduction diffusion method. As typical examples of the metal elements forming the low melting point phase described above, cobalt (Co), iron (F
e), nickel (Ni), manganese (Mn), iridium (Ir), rhodium (Rh), magnesium (Mg), platinum (Pt), silver (Ag), gold
(Au), copper (Cu) and the like can be exemplified, and these can be used alone or in combination of two or more. Further, other metal elements and semimetal elements such as boron (B) and silicon (Si) can be added as necessary. These components other than the rare earth metal can be used as oxides and chlorides in a small amount.

In the present invention, the above-mentioned rare earth metal oxide and other alloying element components are mixed according to the desired alloy composition, and a reducing agent is further blended to perform initial reduction diffusion.
Examples of the reducing agent used include alkali metals, alkaline earth metals and hydrides thereof, and specific examples thereof include lithium, sodium, potassium, calcium, magnesium and hydrides thereof. Calcium metal is most preferred in terms of handling safety and cost. These reducing agents are used in the form of particles or powder. These reducing agents are generally used in a ratio of 1.1 to 2.0 times the stoichiometric amount required to reduce rare earth metal oxides.

In the present invention, a flux may be mixed together with the reducing agent in order to improve the difficulty in disintegration in a wet process by fusing and coarsening the alloy powder in the heat reaction product. it can. Such fluxes include, for example, chlorides of alkali metals such as lithium, sodium and potassium, and chlorides of alkaline earth metals such as magnesium and calcium, which are usually anhydrous containing no hydrate. Are preferably used. Most preferably, anhydrous calcium chloride is used, which exhibits little volatility when heated and is also advantageous in terms of cost. The amount of these fluxes used is relative to the rare earth metal oxide.
It is desirable that the content be 3 to 20% by weight.

In the present invention, the reduction diffusion reaction of the raw material powder mixture is carried out in an inert gas atmosphere such as argon gas in two stages in a high temperature region and subsequently in a low temperature region. The temperature range and holding time in each region vary depending on the type of reducing agent used, the particle size of the raw material powder, the presence or absence of flux, and the like, and cannot be specified unconditionally, but the initial reduction diffusion reaction performed in the high temperature region Is carried out to such an extent that the reduction is sufficiently performed, a certain degree of diffusion is performed, and the dripping of the low melting point phase does not occur. For example, the temperature range is desirably about the melting point of the reducing agent or higher, but if the temperature is too high, the low-melting-point phase droops quickly. If the holding time in the temperature range is too short, the reduction is insufficient even if the low-melting-point phase does not sag. The second reduction-diffusion reaction in the low-temperature region that is performed subsequent to the initial reduction-diffusion reaction sufficiently diffuses and homogenizes the generated rare-earth metal component in addition to the reduction reaction. That is, the low-melting-point phase generated by the initial reduction-diffusion reaction exists as a melt, and the higher the temperature, the lower the viscosity and the more likely it is to hang. In the present invention, the viscosity of the low-melting-point phase is increased by performing the second reduction-diffusion reaction in a low-temperature region, and the dripping thereof is effectively suppressed. This second reduction diffusion reaction is performed at a temperature equal to or higher than the melting point of the low melting point phase. If the temperature is lower than this melting point, the low melting point phase exists as a solid, and the reduction diffusion is not effectively performed, which is inappropriate.

Hereinafter, the present invention will be described in the case of using neodymium-iron-cobalt ternary alloy powder by using metallic calcium as a reducing agent, neodymium as a rare earth element, and iron and cobalt as other alloying elements. This will be specifically described with reference to an example. Generally, in a composition consisting of 40 to 50% by weight of neodymium, 6 to 11.5% by weight of cobalt and the balance being iron, a low melting point phase of Nd ₃ (Co—Fe) phase having a melting point of 640 ° C. and a high melting point phase of about 1185 ° C. Nd ₂ (Co-Fe) ₁₇ phase is formed.

In the present invention, in the production of such an alloy powder, the raw material mixed powder containing metallic calcium as a reducing agent is heated at 800 to 940 ° C., preferably 850 to 940 ° C.
The initial reduction diffusion is performed by heating and maintaining the temperature in the range of 940 ° C. For example, if the heating temperature is higher than 940 ℃,
Even if the holding time is as short as about 1 hour, no phase in which the rare earth metal component is insufficiently diffused is not observed, and there is no quality problem with the obtained alloy powder. However, Nd ₃ (Co−
The Fe) phase dripped drastically to the lower part of the reaction vessel, making it difficult to remove the reaction product from the reaction vessel. In addition, the reaction vessel (usually made of stainless steel) and the Nd ₃ (Co-Fe) phase melted. It causes significant deterioration of the reaction vessel due to deposition, reaction and alloying. Nd ₃ (Co-Fe) generated
Since the phase drips at the same time as the metallic calcium in the melt, an insufficiently reduced portion is formed at the top of the reaction mixture due to calcium deficiency. Furthermore, even if part of the reaction product could be taken out of the reaction vessel, the drooping part at the bottom of the reaction vessel is in the form of an alloy lump, and this part can no longer be recovered as alloy powder, There is also a disadvantage that the recovery rate of the alloy powder is reduced. If the temperature is lower than 800 ° C., reduction of neodymium oxide cannot be effectively performed. Therefore, the lower limit of the temperature condition of the initial reduction diffusion is set to 800 ° C., preferably, to 850 ° C., more preferably, 870 ° C. for the melting point of metallic calcium as a reducing agent.

In the present invention, the initial reduction diffusion is performed to such an extent that the Nd ₃ (Co—Fe) phase does not sag. The reduction diffusion of neodymium oxide proceeds as the temperature is maintained in the above-mentioned temperature range for a long time. However, when the temperature is maintained in the temperature range for an excessively long time, dripping of the generated Nd ₃ (Co—Fe) phase is promoted. Therefore, in general, the holding time in the temperature range is preferably 0.5 to 3 hours, particularly preferably 1 to 2 hours.

According to the present invention, following the initial reduction diffusion, the second reduction diffusion is performed in a lower temperature region. This second reduction diffusion is carried out by heating and holding at 640 to 800 ° C, preferably 640 to 700 ° C. For example, at a temperature of 850 ° C. or higher, an excessive amount of calcium metal is a melt with respect to the equivalent of oxide reduction, and the volume of the melt existing in the entire system increases, so that dripping easily occurs. In the range of 800 to 850 ° C, excess metal calcium solidifies and exists as a solid, so dripping is slightly improved, but dripping also occurs due to low viscosity of the low melting point phase. Will be. If the temperature is lower than 640 ° C., the Nd ₃ (Co—Fe) phase, which is a low-melting phase, solidifies and becomes a solid, so that its diffusion cannot be performed effectively. The holding time in the temperature range of the second reduction diffusion is determined in consideration of, for example, the degree of the initial reduction diffusion, the particle size of the raw material powder used, the target particle size of the target product alloy powder, and the uniformity of the alloy composition. It is determined as appropriate.

In the above-described present invention, the conditions for the initial reduction diffusion in the high temperature region and the second reduction diffusion in the low temperature region are as follows:
For example, the temperature conditions and the like can be appropriately changed without departing from the object of the present invention of preventing the low melting point phase from dripping. For example, when a flux such as calcium chloride is added, the reduction start temperature may shift to a lower temperature. Further, after the initial reduction diffusion is performed, the temperature may be once lowered to a temperature lower than the melting point of the low melting point phase, and then the temperature may be raised again to perform the second reduction diffusion. Further, from the initial reduction diffusion temperature region to the second reduction diffusion temperature region,
It is also possible to continuously lower the temperature with a smooth heat pattern.

After completion of the above-mentioned reduction diffusion treatment, the obtained reaction mixture is taken out of the reaction vessel and subjected to a wet treatment. That is, the reaction mixture taken out of the reaction vessel is
It is thrown into water, easily disintegrated to form a slurry, and the alloy particles and the reducing agent (for example, calcium metal) are completely released. Since the upper part of the slurry generated by this collapse is a suspension of a hydroxide such as calcium hydroxide, most of the slurry can be removed by repeating decantation-water injection-decantation. In order to remove a small amount of hydroxide remaining and oxides on the surface of the alloy powder, it is preferable to perform cleaning with a dilute acid. The dilute acid washing is performed at pH 4 to 7 using, for example, acetic acid, hydrochloric acid, or the like. The alloy powder after acid cleaning is washed with an organic solvent such as alcohol or acetone, and the organic solvent is removed by vacuum drying or the like to obtain a product.

[0020]

【Example】

Example 1: Nd-Fe-Co respective pure preparation of the alloy powder is more than 99.9 wt% Nd ₂ O ₃ (average particle size 3
μm) 335.6 g, iron powder (particle size 200 mesh or less) 308.2
g, cobalt powder (particle size 200 mesh or less) 38.3 g, metallic calcium (particle size 4 mesh or less) 179.6 g and anhydrous calcium chloride (particle size 100 mesh or less) 33.6 g are blended and thoroughly mixed, and then the mixture is made of stainless steel. And heated to 860 ° C. in about 40 minutes in a high-purity argon gas stream. After holding at 860 ° C for 1 hour,
Cool down to 650 ° C in 0 minutes, hold at 650 ° C for 3 hours,
After cooling to room temperature, the produced reaction product was taken out of the reaction vessel. This removal was easy, without fusion between the reaction product and the bottom of the reaction vessel, and no dripping was seen below the reaction product. The reaction product taken out is roughly crushed into a lump having a diameter of 1 cm, poured into 12 liters of pure water, stirred for about 1 hour, disintegrated in water, and then formed from the resulting slurry to obtain an upper layer of calcium hydroxide (Ca (OH)). ₂ ) Separate the white suspension containing as a main component by decantation,
The slurry was further poured into water and the slurry was stirred for 5 minutes, and decantation was performed again. This water injection-stirring-decantation operation is repeated, and after the remaining Ca component is sufficiently removed,
After washing the alloy powder obtained by filtration with ethanol,
It was vacuum dried at 40 ° C. and 1 × 10 ⁻² Torr for 10 hours.

The alloy powder thus obtained has a weight of 59
0.3g, the composition is 42.1% by weight of neodymium, 5.9% by weight of cobalt, the balance is iron, and as other unavoidable impurities, 0.06% by weight of calcium, 0.14% by weight of oxygen,
The carbon content was 0.031% by weight. The Fisher average particle size of this alloy powder was 26.4 μm. Further EPMA
As a result of observing the structure by Nd, almost no particles with insufficient diffusion of neodymium were observed, and Nd ₃ (Co-Fe) phase and Nd ₂ (Co-
Fe) It is a powder having an alloy structure composed of ₁₇ phases, and was confirmed to be a good alloy powder.

Comparative Example 1: Production of Nd-Fe-Co alloy powder A raw material powder mixture was prepared in exactly the same manner as in Example 1. The mixture was placed in a stainless steel reaction vessel and heated to 1000 ° C. in a high-purity argon gas stream in about 65 minutes. After maintaining at 1000 ° C. for 3 hours, the mixture was cooled to room temperature, and the reaction product was taken out of the reaction vessel. At this time, the lower part of the reaction product and the bottom of the reaction vessel and a part of the lower part of the side face of the reaction vessel were fused, and the reaction product could not be completely removed. The taken out reaction product was subjected to crushing, disintegration in water, and pouring-stirring-decantation in the same manner as in Example 1. In addition, the reaction product mixture remaining in the reaction vessel is directly poured into the reaction vessel to disintegrate in water, and mixed during the first decantation of the wet treatment of the reaction product that could be taken out of the reaction vessel. ,
Both were processed together. Thus, 521.4 g of an alloy powder was obtained.

The composition of the obtained alloy powder is neodymium 39.2
Weight%, cobalt 5.2% by weight, balance iron, and other unavoidable impurities, calcium 0.06% by weight, oxygen
0.15% by weight and 0.033% by weight of carbon. The Fisher average particle size of this alloy powder was 28.6 μm. Further, as a result of observing the structure by EPMA, particles with insufficient diffusion of neodymium were hardly observed, and the powder was an alloy structure composed of a Nd ₃ (Co—Fe) phase and a Nd ₂ (Co—Fe) ₁₇ phase.
Although it was confirmed that the alloy powder was of good quality, the recovered amount of the alloy powder was smaller and the Nd content was lower than that of Example 1. In addition, the weight of the reaction vessel after the recovery of the alloy powder was increased by 43.4 g as compared with that before the production of the alloy, and the Nd ₃ (Co—Fe) phase was dripping at the bottom of the reaction vessel.

Example 2: Production of Nd-Dy-Fe-Co alloy powder Nd ₂ O ₃ (average particle size: 59.9% by weight or more)
μm) 597.1 g, Dy ₂ O ₃ (average particle size 8 μm) 42.2 g,
366.8 g of iron powder (particle size 200 mesh or less), 148.2 g of cobalt powder (particle size 200 mesh or less), 339.8 g of metallic calcium (particle size 4 mesh or less), and 63.9 g of anhydrous calcium chloride (particle size 100 mesh or less) After mixing, the mixture was placed in a stainless steel reaction vessel and heated to 900 ° C. in a high-purity argon gas stream in about 45 minutes. After holding at 900 ℃ for 1 hour, it takes about 25 minutes to reach 700 ℃
After cooling to 700 ° C. for 3 hours, the reaction product was cooled to room temperature, and the produced reaction product was taken out of the reaction vessel. This removal was easy, without fusion between the reaction product and the bottom of the reaction vessel, and no dripping was seen below the reaction product. The reaction product taken out was crushed and wet-processed in the same manner as in Example 1 to obtain 918.6 g of an alloy powder.

The composition is 44.1% by weight of neodymium, 3.35% by weight of dysprosium, 14.1% by weight of cobalt, the balance being iron, and 0.04% by weight of calcium as another unavoidable impurity component.
% Of oxygen, 0.16% by weight of oxygen and 0.034% by weight of carbon.
The average particle size of this alloy powder is 24.8μm.
Met. Further observation of the tissue by EPMA,
There are few particles with insufficient diffusion of neodymium (Nd
-Dy) ₃ (Co-Fe) phase, (Nd-Dy) ₂ (Co-Fe) ₁₇ phase,
(Nd-Dy) (Co-Fe) ₂ phase, powder of alloy structure consisting of (Nd-Dy) (Co-Fe) ₃ phase, low inevitable impurity component as rare earth alloy powder, good quality alloy powder It was recognized that there was.

Comparative Example 2 Production of Nd-Dy-Fe-Co Alloy Powder A raw material powder mixture was prepared in exactly the same manner as in Example 2. The mixture was placed in a stainless steel reaction vessel and heated to 900 ° C. in a high-purity argon gas stream in about 45 minutes. After maintaining at 900 ° C. for 1 hour, the mixture was cooled to room temperature, and the reaction product was taken out of the reaction vessel. This removal can be easily performed, and (Nd-D
y) No dripping of the ₃ (Co-Fe) phase was observed. The reaction product thus taken out was subjected to crushing and wet treatment in the same manner as in Example 1 to obtain 886.1 g of an alloy powder. When the inside of the reaction product was observed during the crushing, pale green neodymium oxide remaining unreduced was observed inside the reaction product.

The composition of the alloy powder is 43.9% by weight of neodymium,
Dysprosium was 3.26% by weight, cobalt was 13.6% by weight, and the balance was iron. Other unavoidable impurities were 0.06% by weight of calcium, 0.22% by weight of oxygen, and 0.034% by weight of carbon. The Fisher average particle size of this alloy powder is 2
It was 2.9 μm. Further, as a result of observing the structure by EPMA, it was confirmed that the diffusion of neodymium and dystrosium was insufficient, and many particles having an Fe phase or an Fe-Co phase were present.
The other phases mainly consisted of four kinds of phases similar to those in Example 2. In this example, an alloy powder having almost the same composition as that of Example 2 was obtained. However, the amount of recovered alloy powder was smaller than that of Example 2 due to insufficient reduction and insufficient diffusion. , And Fe phase and Fe-Co phase existed systematically, and the quality was rejected.

[0028]

According to the present invention, the production of a rare earth metal-containing alloy powder having an alloy phase having a melting point lower than the reduction temperature in a part of its structure is performed by a direct reduction diffusion method. This can be performed while effectively suppressing the inconvenience caused thereby. Generally, the low-melting-point phase composition region of an alloy containing a rare-earth metal is in a composition range in which the rare-earth component is high. Therefore, according to the present invention, an alloy powder having a higher rare earth metal content than before can be produced by a direct reduction diffusion method, which is extremely useful industrially.

Claims (2)

(57) [Claims] 1. A rare-earth metal oxide, another alloying element powder, and a reducing agent are mixed and reduced and diffused in an inert gas atmosphere to contain a rare-earth metal and have a temperature lower than the reduction temperature. In a method for producing an alloy powder having a melting point phase (low melting point phase), an initial reduction diffusion is performed under conditions in which the rare earth metal oxide is effectively reduced, and the low melting point phase generated by the initial reduction diffusion is The method, wherein the second reduction diffusion is performed by lowering the reduction temperature before dripping occurs. 2. The method of claim 1, wherein said second reductive diffusion is performed at a temperature higher than the melting point of said low melting point phase.