JP2876761B2 - Method for producing rare earth metal powder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a rare earth metal element powder.

Scandium, a kind of rare-earth metal, is used in high-brightness, high-color-rendering metal halide lamps as a powder, and its demand is increasing. The present invention provides a method for efficiently producing a rare earth metal powder such as scandium.

[Conventional technology and problems]

Conventionally, the metal refining method of scandium is a calcium reduction method like yttrium, and a scandium oxide Sc ₂ O ₃ (melting point 2480) obtained by separating it from other elements by a solvent extraction method or an ion exchange resin method. ° C) into fluoride, which is reduced with calcium in the presence of zinc in a Ta-made crucible to form a low melting point Sc-Zn alloy, which is vacuum distilled to remove zinc by volatilization. We manufacture scandium. However, this method cannot obtain scandium metal powder. Conventionally, there is no method disclosed in patents and other documents for a method for directly producing scandium metal powder.

For a metal element having a very high boiling point, such as a rare earth element, a method usually considered as a method of directly producing this metal powder is to first react a rare earth metal with hydrogen gas at a high temperature to form a hydride, and then pulverize the hydride. This is a method for dehydrogenation in a vacuum. However, in this method, the hydride of the rare earth metal must first be produced first, and the production process is complicated since a dehydrogenation step is required after the hydride is formed. Further, since the rare earth metal and the hydrogen gas react violently at high temperatures, this reaction operation involves danger. Further, rare earth metals are generally very unstable and easily oxidized, so that there are various problems such as troublesome prevention of oxidation.

[Knowledge for problem solving]

The present inventors have conducted various studies on a method for completely and simply producing a metal scandium powder, and as a result, have noticed that Sc-Zn alloys and the like can be easily and uniformly pulverized.First, scandium and zinc, magnesium, etc. Forming an alloy of
It has been found that a metal scandium powder can be easily produced by volatilizing and removing the alloying elements such as zinc and magnesium after pulverizing the alloy, and a method for producing a rare earth metal powder based on this finding was proposed (Japanese Patent Application No. 63-63). 107633
issue).

The present inventors have further improved the above-mentioned method, and have developed a method capable of producing a rare earth metal powder excellent in dispersibility without powder sintering when the alloying element is volatilized and removed. An object of the present invention is to provide an improved method for producing a rare earth metal powder.

[Configuration of the invention]

According to the present invention, (1) an alloy-forming element selected from zinc, cadmium, magnesium or arsenic is added to a rare earth metal and heated and melted to produce a rare earth metal containing 5 to 80% by weight of the rare earth metal, and then oxygen is added. A thin oxide in which the above alloying elements are volatilized by grinding in a mixed atmosphere of gas and inert gas, or pulverizing in an inert gas atmosphere and then briefly exposing it to a mixed atmosphere of oxygen gas and inert gas. A method is provided for producing a rare earth metal powder by evaporating and removing zinc, cadmium, magnesium or arsenic of the above alloying elements by heating the alloy powder under vacuum after forming the alloy powder having a coating on the surface. ing.

In a preferred embodiment, (2) an alloy of rare earth metal with zinc, cadmium, magnesium or arsenic is pulverized to 200 mesh or less in an inert gas atmosphere, and then the powder is mixed with air or a mixture of oxygen and nitrogen. A manufacturing method is provided in which a thin oxide film is formed by allowing the film to stand in a gas for a short time, and further heated at 700 to 1000 ° C. in a vacuum vessel to volatilize and remove the alloy-forming element.

Hereinafter, the present invention will be described using scandium (hereinafter Sc) as an example.

In the present invention, as a Sc raw material, a halide of Sc,
In particular, fluoride (ScF ₃ ) or chloride (ScCl ₃ ) is used. Generally, rare earth metals are oxides (in the case of Sc, Sc ₂ O ₃ )
Is very stable and separated from the ore is obtained in the form of oxides, but is converted to more reactive halides to produce elemental metals. Commonly used are fluorides or chlorides. In the case of Sc, ScF ₃ or ScCl ₃ is reduced to Sc metal with a simple metal of Ca, Mg, Na or K. If an alloying element such as zinc is added during this reduction reaction, a Sc—Zn alloy is formed. Since Sc forms an alloy with Ca and Mg, excess Ca exceeds the theoretical equivalent required for reduction.
Alternatively, Mg may be added. As other alloying elements
As can be used. The content of Sc in the alloy is not particularly limited, but it is necessary that the alloy be easily crushed. For example, the amount of Sc is 5 to 80%, preferably 5 to 40%.
It is. If the Sc is less than 5%, the amount of separated and removed Zn will be excessive.
The purity of Sc decreases. If Sc is 80% or more, Sc−Zn
The yield of the alloy decreases.

The production temperature of the alloy is basically set to be equal to or higher than the melting point of the alloy formed by the reduction reaction. Generally, the reaction temperature is lowered by adding a melting point depressant such as lithium fluoride (LiF). Since rare earth elements and alloys are liable to produce oxides, the processing for forming the alloy is performed in an inert gas atmosphere. Specifically, the raw material ScF ₃ or ScCl ₃ , the reducing agent Ca and the like, and the alloying element Zn and the like are charged into a Ta crucible, placed in a stainless steel vacuum vessel, and the air inside is exhausted. Then, the mixture is evacuated, filled with an inert gas, and heated and melted in an inert gas atmosphere.

The heating temperature is preferably from 900 ° C. to 1100 ° C., and the heating time is preferably from 15 minutes to 1 hour.

After the completion of the reduction alloying reaction, the flux is separated, and the obtained Sc alloy (Sc-Zn) is pulverized. Sc-Zn alloys are very brittle and can be easily crushed by grinding in a mortar. After or during pulverization, a thin oxide film is formed on the powder surface. The oxide film prevents powder sintering when the alloy is subsequently heated to volatilize low melting point Zn and the like. The thickness of the oxide film is a thickness at which the alloy-forming components such as zinc are volatilized in the heating step. In order to form an oxide film during the pulverization of the Sc-Zn alloy or the like, the pulverization is performed in an inert gas atmosphere with a reduced oxygen content in order to prevent excessive oxidation of the alloy powder. Alternatively, when pulverizing in the air, the pulverization is completed in a short time. When an oxide film is formed after the pulverization, the pulverized alloy powder is briefly exposed to an oxygen-containing gas, for example, air or a mixed gas flow of an oxygen gas and an inert gas to form an oxide film.

The pulverized alloy is put again in a Ta crucible, which is charged into a vacuum vessel, heated and heated under an inert gas atmosphere, and evacuated to remove alloy components other than Sc, or Zn in the case of Sc-Zn alloy. Volatile removal and separation from Sc. The temperature and time for vacuum separation are appropriately adjusted depending on the metal to be separated and removed. In the case of a Sc-Zn alloy, treatment at 700 to 1000 ° C. for about 1 to 3 hours is required. The alloy powder having been subjected to the surface oxidation treatment does not sinter each other at the time of the above-mentioned heating, and a Sc metal powder which is well dispersed can be obtained.

When the oxide film is not formed, when the alloy powder is heated to volatilize and separate alloy components other than Sc, the powder sinters, and even if the powder is crushed again, the powder has a desired particle size. Becomes difficult. If the oxide film is too thick, metal Sc
As worthless.

〔The invention's effect〕

According to the production method of the present invention, a rare earth metal which was conventionally obtained only in the form of a sponge or the like can be directly produced as a metal powder, and the obtained powder has excellent dispersibility. Moreover, the method of the present invention can be manufactured at a lower temperature than the conventional refining method, and the manufacturing process is simple and easy to implement.

〔Example〕

Hereinafter, examples of the present invention will be described. Note that the present embodiment does not limit the scope of the present invention.

Example 1 Scandium fluoride ScF ₃ 40 g, calcium Ca 34 g, zinc
137.7 g of Zn and 42 g of lithium fluoride LiF with 500 ml of T
a) into a stainless steel vacuum reaction vessel, evacuate the air in the vessel to ^10-4 mmHg with a vacuum pump, fill with argon gas, and degas again to ^10-4 mmHg. Again, the inside of the container was filled with argon gas to 1 atm. The temperature of the reaction vessel was raised to 900 ° C. in 2 hours, and the temperature was maintained for 1 hour to melt and alloy the raw materials. Thereafter, the inside of the vessel was allowed to cool, the crucible was taken out, and the alloy phase and the flux phase were separated. Next, the alloy phase was pulverized to 200 mesh or less in a glow box in an argon atmosphere. The pulverized alloy powder was oxidized by leaving it in a mixed gas stream of air 100 ml / min and nitrogen 300 ml / min for 30 minutes to form a thin oxide film on the surface of the powder. The oxidized alloy powder was placed again in a Ta crucible and charged in a vacuum vessel, and zinc was volatilized and removed at 1000 ° C. for 5 hours.

Microscopic observation confirmed that the powder thus obtained was not sintered, was in the same dispersion state as at the time of pulverization, and had substantially the same particle size as that at the time of pulverization. Further, the obtained powder was confirmed to be metallic scandium from the result of X-ray diffraction. 0.005% zinc residue in this powder
It was below.

Example 2 40 g of holmium fluoride HoF ₃ , 41 g of calcium Ca, zinc Zn
50 g and 48 g of lithium fluoride LiF were put into a 500-ml Ta crucible with an internal volume of 500 ml, and this was charged into a stainless steel vacuum reaction vessel.The air in the vessel was evacuated to 10 ^-4 mmHg with a vacuum pump, and then filled with argon gas. Then, the vessel was degassed again to 10 ^-4 mmHg, and again filled with argon gas to make the inside of the vessel 1 atm. The temperature of the reaction vessel was raised to 1050 ° C. in 2 hours, and the temperature was maintained for 1 hour to melt and alloy the raw materials. Thereafter, the inside of the vessel was allowed to cool, the crucible was taken out, and the alloy phase and the flux phase were separated. Next, the alloy phase was pulverized to 200 mesh or less in a glow box in an argon atmosphere. The alloy powder obtained by the pulverization was left to stand in a mixed gas stream of 10 ml / min of oxidation and 400 ml / min of nitrogen for 60 minutes to perform oxidation treatment, and a thin oxide film was formed on the surface of the powder. The oxidized alloy powder is again
The mixture was placed in a crucible and charged in a vacuum vessel, and zinc was volatilized and removed at 1000 ° C for 5 hours.

Microscopic observation confirmed that the powder thus obtained was not sintered, was in the same dispersion state as at the time of pulverization, and had substantially the same particle size as that at the time of pulverization. Further, the obtained powder was confirmed to be metal holmium from the result of X-ray diffraction. The residual amount of zinc in this powder was 0.005% or less.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-263904 (JP, A) JP-A-59-190289 (JP, A) JP-A-58-55393 (JP, A) 37402 (JP, B2) Special Table Hei 1-503310 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B22F 9/02 C22B 59/00

Claims (2)

(57) [Claims] 1. A rare earth metal, to which an alloying element selected from zinc, cadmium, magnesium or arsenic is added and heated and melted to produce a rare earth alloy containing 5 to 80% by weight of the rare earth metal, and then oxygen gas and inert gas are added. By pulverizing in a mixed gas atmosphere or pulverizing in an inert gas atmosphere and then briefly exposing it to a mixed atmosphere of oxygen gas and an inert gas, a thin oxide film in which the alloying elements are volatilized is coated on the surface. After having an alloy powder having, the alloy powder is heated under vacuum to form the alloy forming elements zinc, cadmium,
A method for producing rare earth metal powder by volatilizing and removing magnesium or arsenic. 2. An alloy of a rare earth metal and zinc, cadmium, magnesium or arsenic in an inert gas atmosphere.
After pulverizing to a mesh or smaller, this powder is allowed to stand for a short time in air or a mixed gas of oxygen and nitrogen to form a thin oxide film, and further heated in a vacuum vessel at 700 to 1000 ° C. to remove the alloy-forming element. The production method according to claim 1, wherein volatilization is removed.