KR101483319B1 - Method for forming rare earth metal hydride and method for forming rare earth metal-transition metal alloy powder using the same - Google Patents

Abstract

Thereby obtaining a rare earth metal-transition metal alloy powder. First, mixed rare earth metal oxide powder, transition metal nano powder or transition metal oxide powder, and alkaline earth metal hydride powder are mixed and milled to form mixed nano powder. The mixed nano powder is heat-treated in an inert gas atmosphere at a temperature lower than the melting temperature of the alkaline earth metal hydride to perform a first heat treatment for reducing the rare earth metal oxide to a rare earth metal hydride. The first heat-treated mixed nano powder is heat-treated in a vacuum atmosphere to perform a secondary heat treatment to form a rare-earth metal-transition metal alloy.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth metal hydride and a rare earth metal-transition metal alloy powder,

TECHNICAL FIELD The present invention relates to an alloy powder, and more particularly, to a method for producing a rare earth metal-transition metal alloy powder.

Sm-Fe-N type magnetic materials have attracted attention as a new permanent magnet material due to strong uniaxial magnetic anisotropy, high saturation magnetization value and excellent corrosion resistance. However, since the Curie temperature (Tc) is low, phase separation into Sm-nitride and Fe occurs at the temperature required for sintering, and thus it is largely limited to applications to sintered magnets which must be sintered at a temperature higher than Tc. For this reason, Sm-Fe-N type magnetic materials having high performance permanent magnet properties are currently used as bond magnets through bonding with resins.

Such a bonded magnet has a disadvantage in that the magnetic property is lowered as the amount of the magnetic material to be added is lower than that of the sintered magnet. Therefore, recent studies have been made to make a Sm-Fe-N magnet as a sintered magnet.

In order to make the Sm-Fe-N magnet as a sintered magnet, it is necessary to reduce the size of the Sm-Fe alloy powder. However, as a result of the research to date, the heat treatment temperature for forming the Sm-Fe alloy powder is as high as about 1000 ° C., which is a stumbling block in reducing the size of the Sm-Fe alloy powder.

A problem to be solved by the present invention is to prepare a Sm-Fe alloy nano powder through a heat treatment at a low temperature.

The technical objects of the present invention are not limited to the technical matters mentioned above, and other technical subjects not mentioned can be clearly understood by those skilled in the art from the following description.

According to one aspect of the present invention, there is provided a method of manufacturing a rare earth metal-transition metal alloy powder. First, the rare earth metal oxide and the alkaline earth metal hydride are first heat treated in an inert gas atmosphere at a temperature lower than the melting temperature of the alkaline earth metal hydride, thereby reducing the rare earth metal oxide to a rare earth metal hydride. The rare earth metal hydride and the transition metal or transition metal oxide are subjected to a secondary heat treatment in a vacuum atmosphere to form a rare earth metal-transition metal alloy.

The inert gas atmosphere may contain hydrogen gas. The primary heat treatment step and the secondary heat treatment step may be performed at a temperature of less than 500 degrees Celsius to less than 850 degrees Celsius degrees. The rare earth metal oxide may be Sm ₂ O ₃ , the transition metal may be Fe, and the alkaline earth metal hydride may be CaH ₂ .

The mixed nano powder can be formed by mixing and milling the rare earth metal oxide powder, the transition metal nano powder or the transition metal oxide powder, and the alkaline earth metal hydride powder before performing the first heat treatment. In this case, the first heat treatment is a step of heat-treating the mixed nano powder.

The mixed nano powder is formed by mixing and milling the rare earth metal oxide powder and the alkaline earth metal hydride powder to form a rare earth metal oxide-alkaline earth metal hydride mixed nano powder, and then mixing the rare earth metal oxide-alkaline earth metal hydride Mixing the mixed nano powder with the transition metal nanopowder to form a transition metal-rare earth metal oxide-alkaline earth metal hydride mixed nano powder. The transition metal nanopowder may be prepared by hydrogen reduction of the transition metal oxide nanopowder.

Alternatively, forming the mixed nano powder may include mixing and milling the rare earth metal oxide powder and the transition metal oxide powder to form a transition metal oxide-rare earth metal oxide mixed nano powder, and the transition metal oxide-rare earth metal oxide mixture Rare-earth metal-oxide mixed nano powder is mixed with and milled to form a transition metal-rare-earth metal oxide-alkali niobate powder mixed with the transition metal-rare earth metal oxide-alkali niobium powder, To form a ground metal hydride mixed nano powder.

According to another aspect of the present invention, there is provided a method of manufacturing a rare-earth metal-transition metal alloy powder. First, Sm ₂ O ₃ powder, Fe nano powder, and CaH ₂ powder are mixed and milled to form Fe-Sm ₂ O ₃ -CaH ₂ mixed nano powder. The Fe-Sm ₂ O ₃ -CaH ₂ mixed nano powder is subjected to a first heat treatment at a temperature lower than the melting temperature of CaH _{2 in} an inert gas atmosphere to reduce the Sm ₂ O ₃ to SmH ₂ . The mixed heat-treated nano powder is subjected to a secondary heat treatment in a vacuum atmosphere to form an Sm-Fe alloy.

According to another aspect of the present invention, there is provided a method for manufacturing a rare earth metal hydride. First, the rare earth metal oxide powder and the alkaline earth metal hydride powder are mixed and milled to form a mixed nano powder. The mixed nano powder is heat-treated at a temperature lower than the melting temperature of the alkaline earth metal hydride in an inert gas atmosphere to reduce the rare earth metal oxide to a rare earth metal hydride.

As described above, according to the present invention, since the primary heat treatment is performed at a temperature lower than the melting temperature of the alkaline earth metal hydride, the reaction may be performed at a solid phase, so that the crystal grains may not be coarsened. The rare earth metal hydride can be easily separated into rare earth metal and hydrogen in the vacuum atmosphere during the second heat treatment. Therefore, the reaction between the rare earth metal and the transition metal can be promoted, and a rare earth metal-transition metal alloy can be formed even at a relatively low heat treatment temperature. In addition, as the transition metal-rare earth metal oxide-alkaline earth metal hydrate mixed powder has nano-size, a rare-earth metal-transition metal alloy is formed even at a relatively low heat treatment temperature due to a short diffusion path and a high diffusion coefficient .

FIG. 1 is a flowchart of a process for producing a rare-earth metal-transition metal alloy powder according to an embodiment of the present invention.
2 is a graph showing the temperature-time of the first and second heat treatment steps in the Sm-Fe alloy nano powder production example.
Figure 3 is a Sm-Fe alloy nano powder production of the embodiment of the obtained Fe-Sm ₂ O ₃ -CaH ₂ mixing a scanning electron microscope (SEM) photographs (a) and Fe-Sm ₂ O ₃ taken nanopowder mixed -CaH ₂ (B) showing X-ray diffraction analysis results of the nano powder.
4 is a graph showing the results of X-ray diffraction analysis of powders obtained after the primary heat treatment in an atmosphere of an inert gas during the production of the Sm-Fe alloy nano powder production example.
FIG. 5 is a graph showing the results of X-ray diffraction analysis (a) of the powder obtained after the second heat treatment in a vacuum atmosphere during the execution of the Sm-Fe alloy nano powder production example and the result of the X- X-ray diffraction analysis (b).
6 is a scanning electron microscope (SEM) photograph of a Sm-Fe alloy nano powder obtained in a Sm-Fe alloy nano powder production example.
7 is a scanning electron microscope (SEM) photograph of the cross-section of the Sm-Fe alloy nano powder obtained in the production example of the Sm-Fe alloy nano powder, and the result of the component analysis using EDS (energy dispersive spectroscopy).
8 is a transmission electron microscope (TEM) photograph of a section of the Sm-Fe alloy nano powder obtained in the Sm-Fe alloy nano powder production example.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. In the drawings, where a layer is referred to as being "on" another layer or substrate, it may be formed directly on another layer or substrate, or a third layer may be interposed therebetween.

FIG. 1 is a flowchart of a process for producing a rare-earth metal-transition metal alloy powder according to an embodiment of the present invention.

Referring to FIG. 1, a rare earth metal oxide powder, a transition metal nano powder or transition metal oxide powder, and alkaline earth metal hydride powder are prepared (S10).

In the rare earth metal oxide powder, the rare earth metal may be, for example, Sm, Nd, or Pr. A specific example of the rare earth metal oxide powder may be Sm ₂ O ₃ .

In the transition metal nano powder or the transition metal oxide powder, the transition metal may be Fe, Co, Cu, or Zr. The transition metal nanopowder can be obtained by hydrogen reduction of the transition metal oxide nanopowder. A specific example of the transition metal nanopowder may be Fe nanopowder, and a specific example of the transition metal oxide powder may be Fe ₂ O ₃ powder.

In the alkaline earth metal hydride powder, the alkaline earth metal hydride is a substance in which an alkaline earth metal and hydrogen are ionically bonded and serves as a reducing agent. The alkaline earth metal hydride may be, for example, CaH ₂ or MgH _2.

The raw material powders are mixed and milled to form a mixed nano powder (S20).

In the case of using raw material powders which are rare earth metal oxide powders, transition metal nano powders and alkaline earth metal hydride powders, the rare earth metal oxide powders and the alkaline earth metal hydride powders are mixed and then milled to prepare rare earth metal oxide-alkaline earth metal hydrate mixed nano- Powder, and then the transition metal nano powder may be mixed to form a transition metal-rare earth metal oxide-alkaline earth metal hydrate mixed nano powder. In the transition metal-rare earth metal oxide-alkaline earth metal hydrate mixed nano powder, the transition metal can maintain aggregated form of nanoparticles aggregated, and the rare earth metal oxide can be located only on the outer surface of the transition metal nano powder aggregate .

On the other hand, in the case of using the rare earth metal oxide powder, the transition metal oxide powder, and the alkaline earth metal hydride powder as raw material powders, the rare earth metal oxide powder and the transition metal oxide powder are mixed and then milled to prepare a transition metal oxide- Nano powder can be formed. The transition metal oxide-rare earth metal oxide mixed nano powder may exhibit the form of agglomerates in which the transition metal oxide nano powder and the rare earth metal oxide nano powder are uniformly mixed through mixing and milling. Thereafter, the transition metal oxide-rare earth metal oxide mixed nano powder is subjected to hydrogen reduction. At this time, the transition metal oxide is reduced to a transition metal, while a rare earth metal having excellent affinity with oxygen can be maintained as a rare earth metal oxide without being reduced. Thus, a transition metal-rare earth metal oxide mixed nano powder can be formed. Thereafter, the transition metal-rare earth metal hydrate mixed nano powder can be formed by mixing the transition metal-rare earth metal oxide mixed nano powder with an alkaline earth metal hydride powder and then milling the mixture.

The mixing step and the milling step may be performed in an inert gas atmosphere, for example, an argon gas atmosphere of 99.999%. By performing mixing and milling in an inert gas atmosphere as described above, the raw material powders can be kept in their respective compositions without being oxidized or phase-changed.

The mixed nano powder is composed of nano-sized powders, and nano-sized powders may have the form of agglomerated aggregates.

The mixed nano powder is subjected to a first heat treatment in an inert gas atmosphere (S30).

In the first heat treatment step in this inert gas atmosphere, the rare earth metal hydride may be generated as the rare earth metal oxide is reduced by the alkaline earth metal hydride (see the following reaction formula).

[Reaction Scheme]

L ₂ O ₃ + 3MH ₂ ? 2LH ₂ + 3MO + H _2? (Where L is a rare earth metal and M is an alkaline earth metal)

The primary heat treatment is performed at a temperature lower than the melting temperature of the alkaline earth metal hydride. In this case, since the reaction may be performed at a solid phase, the crystal grains may not coarsen. For example, when the alkaline earth metal hydride is CaH ₂ , considering that the melting temperature of CaH ₂ is 850 ° C, the primary heat treatment may be performed at a temperature lower than 850 ° C. As an example, the primary heat treatment may be performed at a temperature of less than 500 ° C to less than 850 ° C.

The inert gas atmosphere may contain H ₂ . In this case, H ₂ in the atmosphere can prevent the transition metal from being oxidized or reduce the oxidized transition metal again. However, when the inert gas atmosphere contains too much H ₂ , the reaction rate shown in the above reaction formula can be reduced. Therefore, the H ₂ may be contained in an amount of 1 to 30 vol%, specifically 5 to 15 vol%, based on the total atmosphere.

The first heat-treated mixed nano powder is subjected to a secondary heat treatment in a vacuum atmosphere (S40).

In the second heat treatment step in the vacuum atmosphere, the rare earth metal hydride reacts with the transition metal to form a rare earth metal-transition metal alloy.

In the vacuum atmosphere, the rare earth metal hydride can be easily separated into rare earth metal and hydrogen. Therefore, the reaction between the rare earth metal and the transition metal can be promoted, and a rare earth metal-transition metal alloy can be formed even at a relatively low heat treatment temperature. Further, when the inert gas atmosphere contains H ₂ and the transition metal is prevented from being oxidized in the first heat treatment step, a rare earth metal-transition metal alloy may be formed even at a relatively low heat treatment temperature because the transition metal participating in the reaction is increased have. In addition, as the transition metal-rare earth metal oxide-alkaline earth metal hydrate mixed powder has nano-size, a rare-earth metal-transition metal alloy is formed even at a relatively low heat treatment temperature due to a short diffusion path and a high diffusion coefficient .

In order to separate the rare earth metal hydride into rare earth metal and hydrogen in the vacuum atmosphere, the second heat treatment temperature may be 500 ° C or higher. Therefore, a rare-earth metal-transition metal alloy can be formed even if the heat treatment is performed at a temperature lower than 500 ° C to 850 ° C lower than conventionally reported.

The first heat treatment step and the second heat treatment step may proceed without vacuum breakdown.

The reaction by-products are removed from the secondary heat treatment reaction (S40).

The alkaline earth metal oxide formed through the reaction shown in the above reaction formula can be easily removed by a washing process using distilled water as a reaction by-product. As a result, a rare-earth metal-transition metal alloy powder finally remains.

Hereinafter, preferred examples will be given to facilitate understanding of the present invention. It should be understood, however, that the following examples are for the purpose of promoting understanding of the present invention and are not intended to limit the scope of the present invention.

<Experimental Examples> examples>

<Production example of Fe nano powder>

The ball milled Fe ₂ O ₃ (99.9%) powder with a diameter of 20 nm was subjected to hydrogen reduction at 450 ° C. for 50 min in a horizontal tubular furnace to obtain an Fe nanopowder having an aggregate size of about 150 nm to 20 nm .

<Production example of Sm-Fe alloy nano powder>

Sm ₂ O ₃ powder and CaH ₂ powder were prepared in amounts of 1.07 times and 4.5 times excess of the theoretical equivalent, respectively. Then, SPEX mill (800M Spex Mixer / Mill, Spex Indurstries, Edison, NJ, USA) for 1 h at 1060 cycles / min to obtain a Sm ₂ O ₃ -CaH ₂ mixed powder. Fe nanopowder The Fe nanopowder and the obtained Sm ₂ O ₃ -CaH ₂ mixed powder obtained through the preparation of the Fe nanopowder were again mixed in a 3D turbular mixer for ₃₀ minutes to obtain Fe-Sm ₂ O ₃ -CaH ₂ mixed nano powder &Lt; / RTI &gt; The handling and mixing of all the powders proceeded in a glove box with oxygen (O ₂ ) and water (H ₂ O) contents of 300 ppm or less in an Ar gas (99.999%) atmosphere for reoxidation and phase change prevention Respectively.

Obtained in the Fe-Sm ₂ O ₃ -CaH ₂ and then charged into the mixing nano powder in a crucible made of stainless steel (STS 304), due to the volatile to prepare the cover closed, so the quality and out of the atmospheric gas loss achieved with CaH ₂ Phase changes are minimized. The Fe-Sm ₂ O ₃ -CaH ₂ mixed nano powder in the crucible thus prepared was cooled at a rate of 5 ° C / min in an atmosphere of Ar-H ₂ mixed gas (99.999%, Ar 95 vol% / H ₂ 5 vol%) using a horizontal tubular furnace The temperature was raised to 800 DEG C at a rate of 3 hours and then subjected to a first heat treatment. After that, the first heat-treated Fe-Sm ₂ O ₃ -CaH ₂ mixed nano powder was subjected to a second heat treatment in a vacuum atmosphere of ~ 1 Pa for 2 hours. Figure 2 is a temperature-time graph of the primary and secondary heat treatment steps.

After that, the primary and secondary heat treated powders were washed with distilled water to remove CaO as a reaction gas.

Figure 3 is a Sm-Fe alloy nano powder production of the embodiment of the obtained Fe-Sm ₂ O ₃ -CaH ₂ mixing a scanning electron microscope (SEM) photographs (a) and Fe-Sm ₂ O ₃ taken nanopowder mixed -CaH ₂ (B) showing X-ray diffraction analysis results of the nano powder.

Referring to FIG. 3, the Fe-Sm ₂ O ₃ -CaH ₂ mixed nano powder forms a spherical agglomerate having a size of 5 to 50 mm. This aggregate was observed to consist of spherical Sm ₂ O ₃ -CaH ₂ powder milled to a few tens of nm or less by milling and Fe nanopowder having an average size of 150 nm.

4 is a graph showing the results of X-ray diffraction analysis of powders obtained after the primary heat treatment in an atmosphere of an inert gas during the production of the Sm-Fe alloy nano powder production example.

Referring to FIG. 4, it is confirmed that SmH ₂ is formed through the first heat treatment.

FIG. 5 is a graph showing the results of X-ray diffraction analysis (a) of the powder obtained after the second heat treatment in a vacuum atmosphere during the execution of the Sm-Fe alloy nano powder production example and the result of the X- X-ray diffraction analysis (b).

Referring to FIG. 5, Sm ₂ Fe ₁₇ phase and SmFe ₃ phase, which are Sm-Fe alloys, are observed. The reaction by-product, CaO, can also be identified (a). It can be seen that the CaO was removed through a subsequent step of distilled water washing (b).

6 is a scanning electron microscope (SEM) photograph of a Sm-Fe alloy nano powder obtained in a Sm-Fe alloy nano powder production example.

Referring to FIG. 6, the powder thus prepared was found to have a size of 10 to 100 mm in the form of agglomerate, and despite the low temperature region where it was previously reported that Sm-Fe alloying was difficult to occur, due to the reaction of Sm and Fe separated from SmH ₂ , It was confirmed that the crystal grains of the Sm-Fe alloy phase were present on the surface. The grain size of the Sm-Fe alloy phase on the powder surface was observed to be less than 1 mm at several hundred nm.

FIG. 7 is a scanning electron microscope (SEM) photograph of the cross-section of the Sm-Fe alloy nano powder obtained in the production example of the Sm-Fe alloy nano powder and the result of the analysis using the energy dispersive spectroscopy (EDS).

7, the powder was observed in a core-shell structure in which Fe was surrounded by an Sm-Fe alloy layer, and the first outer phase identified as white had an atomic ratio of Sm to Fe of 1: satisfying the 3 SmFe _3-phase, two atomic ratio of the second external phase Sm and Fe is observed by light gray is 1: each was confirmed by Sm ₂ Fe ₁₇ phase to meet the 8.5 degree. On the other hand, the deep gray internal phase was identified as 100% Fe. The average thickness of the alloy layer on the SmFe ₃ phase was 1.9 mm and the average thickness of the alloy layer on the Sm ₂ Fe ₁₇ was 3.5 mm.

8 is a transmission electron microscope (TEM) photograph of a section of the Sm-Fe alloy nano powder obtained in the Sm-Fe alloy nano powder production example.

Referring to FIG. 8, it can be seen that several hundreds of nm of Sm ₂ Fe ₁₇ crystal grains and SmFe ₃ crystal grains are formed.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, This is possible.

Claims (10)

A first heat treatment step of heat treating the rare earth metal oxide and the alkaline earth metal hydride at a temperature lower than the melting temperature of the alkaline earth metal hydride in an atmosphere containing an inert gas to reduce the rare earth metal oxide to a rare earth metal hydride; And
And a second heat treatment step of forming a rare earth metal-transition metal alloy by heat-treating the rare earth metal hydride and the transition metal in a vacuum atmosphere. The method according to claim 1,
Wherein the atmosphere containing the inert gas further contains hydrogen gas. The method according to claim 1,
Wherein the first heat treatment step and the second heat treatment step are performed at a temperature of not less than 500 degrees and not more than 850 degrees. The method according to claim 1,
The rare earth metal oxide Sm ₂ O _3, and wherein said at least one transition metal is Fe, and the alkaline earth metal hydride CaH ₂ is a rare earth metal-transition metal alloy powder method. The method according to claim 1,
Further comprising mixing and milling the rare earth metal oxide powder, the transition metal powder, and the alkaline earth metal hydride powder to form a mixed powder before the first heat treatment step,
Wherein the mixed powder is heat-treated in the first heat treatment step. 6. The method of claim 5,
The step of forming the mixed powder
Mixing and milling the rare earth metal oxide powder and the alkaline earth metal hydride powder to form a rare earth metal oxide-alkaline earth metal hydride mixed powder; And
And mixing the rare earth metal oxide-alkaline earth metal hydride mixed powder with the transition metal powder to form a mixed powder of transition metal-rare earth metal oxide-alkaline earth metal hydride powder. 6. The method of claim 5,
Wherein the transition metal powder is produced by hydrogen reduction of a transition metal oxide powder. 8. The method of claim 7,
The step of forming the mixed powder
Mixing and milling the rare earth metal oxide powder and the transition metal oxide powder to form a transition metal oxide-rare earth metal oxide mixed powder;
Reducing the transition metal oxide-rare earth metal oxide mixed powder to form a transition metal-rare earth metal oxide mixed powder; And
And mixing and milling the transition metal-rare earth metal oxide mixed powder with the alkaline earth metal hydride powder to form a mixed powder of transition metal-rare earth metal oxide-alkaline earth metal hydride powder . Mixing and milling Sm ₂ O ₃ powder, Fe powder, and CaH ₂ powder to form Fe-Sm ₂ O ₃ -CaH ₂ mixed powder;
A first heat treatment step of heat-treating the Fe-Sm ₂ O ₃ -CaH ₂ mixed powder at a temperature lower than the melting temperature of CaH ₂ in an atmosphere containing an inert gas to reduce the Sm ₂ O ₃ to SmH ₂ ; And
And a second heat treatment step of forming a Sm-Fe alloy by heat-treating the mixed powder containing SmH ₂ in a vacuum atmosphere. Mixing and milling the rare earth metal oxide powder and the alkaline earth metal hydride powder to form a mixed powder; And
And heat treating the mixed powder in an atmosphere containing an inert gas at a temperature lower than the melting temperature of the alkaline earth metal hydride to reduce the rare earth metal oxide to a rare earth metal hydride.

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