DE2350406A1 - PROCESS FOR MANUFACTURING AN ALLOY OF A RARE EARTH METAL - Google Patents

Description

UHESDNER BANK. Patentanwalts B O RO TELEPHONE: (0811) 8995

MONKS 4613703

DR. EGGERS

POST CHECK D-8033 KRAILLING AT MUNICH TELEGRAM:

MUNICH 43939-800 BLUMENSTRASSE 13 ULEGPAT MUNICH

Patent Attorney Office Dr. Eggers - 8033 Krallllng - Blumenstrasse 13 ·

DATE DATE '

Ö.0KI.1973

Your sign your message. Our mark S4 / Pt2 Your ref. Ybur communlc. Our ref. Votre ref. Votre communlc. '' 'Notre ref.

Shinetsu Chemical Company

6-1, Otemachi 2-chome, Chiyoda-ku

• Tokyo, Japan

Method of making an alloy of a rare

Earth metal

The invention relates to an improved method of making alloys containing rare earth metals. In particular, the invention relates to the manufacture of alloys of rare earth metals with light metals.

Alloys of rare earth metals and light metals such as Yttrium-aluminum or mixtures of light, rare earth metals (Mixed metal '} and magnesium, have found extensive use

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Mflnd'Ohe Ahra. ^ En only after schrlftHcbsr PlestS'loimn ys ''> inH "rh

as a mother alloy for the production of special iron and Non-ferrous alloys, and on the other hand, as an intermediate product, the extraction of pure rare earth metals that they contain are. The demand for such alloys has grown rapidly.

Containing rare earth metals in the electrolytic production Alloys like yttrium-cobalt and yttrium-manganese alloys, an oxide of yttrium, which is molten in one Slectrolytsalzbad is dissolved, using Kobaltbzw. Manganese cathodes as consuming electrodes, electrolytic reduced, resulting in the alloys of yttrium with the metals from which the electrode is formed. The use consumable electrodes is not applicable in the manufacture of alloys of rare earth metals with light metals like yttrium-aluminum and mischmetal-magnesium le ^ ierun, ·; «! because if aluminum or magnesium rods were used as consuming electrodes, they would melt and the metals float on the surface of the molten electrolyte bath due to their low melting point and low density became. .

According to the invention, an advantageous method of generating of alloys of rare earth metals with light metals, in particular, alloys of rare earth metals with magnesium and rare earth metals with aluminum are created.

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~ 3 -

According to the invention, alloys are made from rare earth metals Magnesium or made from rare earth metals with aluminum easily, by using an oxide of rare earth metal and a! '! or aluminum oxide is subjected to simultaneous electrolytic reduction in a molten salt bath, the latter consisting of the fluorides of a corresponding rare earth metal and des. Lithium, and optionally barium and / or magnesium or aluminum, whereby the reduced metals ciuf one Cathode are excreted. The alloys thus produced, which Have a relatively low melting point and melt in the Ead at the electrolysis device, can by means of a Samrael vessel which is attached below the cathode and into which the alloys fall.

The invention is directed to the simultaneous electrolytic reduction of an oxide of a rare earth metal and a magnesium or alumina, which is in a molten electrolyte salt bath are dissolved, whereby the salt bath the fluoride wines corresponding rare earth metals and lithium, and alloys of the rare earth metals can be formed with great ease form with magnesium or aluminum.

The oxides of the rare earth metals, in this case yttrium, as well as magnesium and aluminum, are all very stable Links. There is little difference among those oxides in terms of energies required for electrolytic induction

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are required because the free energies that are formed at 100O ⁰ G are very close to each other such as -250 or -220 or -200 Kcal./Mol O ₂ * From this theoretical consideration, the present invention resulted from the Experimental confirmation that, according to the electrolytic method described above, the rare earth metal and magnesium or aluminum are deposited at the same time on the cathode at a temperature of 800 C to 1200 C and thereby become one. Alloy of the rare earth metal and magnesium or aluminum with a relatively low melting point.

It is also an advantage of the method according to the invention that an alloy of magnesium produced according to the invention with a Rare earth metal can be used as an intermediate material for the extraction of metallic magnesium by using the Magnesium from the rare earth metal component by means of vacuum distillation separates.

Examples of oxides of rare earth metals, which in the invention Processes used are the oxides of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, prometheum, samarium, Europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and mixtures of these oxides. on it is more advantageous in some areas of application. Mixtures of Oxides of the rare earth metals to use because of their relatively low cost. For example, mixed oxides become lighter

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rare earth metals, which are naturally occurring monazite or bastnasite and which "usually more than 40% by weight Contain cerium oxide, with advantage for the production of mixed metal magnesium or misclimetal aluminum alloys are used. Mixed Oxides of heavy rare earth metals, which are derived from naturally occurring xenotime or ytspate and which are common contain more than 40 wt .- ^ yttrium oxide (known under the name Yttriam concentrate), are advantageous for the production * of. Yttrium-magnesium-'or. Yttrium-aluminum alloys in the cases used where the presence of small amounts of heavy rare earths other than yttrium has no deleterious effect. When such mixed rare earth metal oxides are used, of course, the composition of rare earths differs Earth metals in the resulting alloys of the composition of the mixed rare earth oxides used as the starting material were used.

Other oxides used together with the rare earth oxides are the oxides of magnesium and aluminum. These can have commercial quality and a special high quality Purity is not required. ...

The oxides of the rare. Earth and the magnesium or aluminum oxide are dissolved separately or as a mixture in the electrolyte. Before-, The oxides are preferably in powdery form, so that theirs Dissolution in a molten salt bath at electrolysis temperature

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is made easier. In some cases, lump shape is preferred, as this offers easy handling.

The molten electrolyte salt bath used in the invention Procedure is, consists essentially of or essentially contains the fluoride or the fluorides of a certain rare earth metal or certain rare earth metals and the fluoride an alkali metal such as lithium, and optionally the fluoride of an alkaline earth metal such as barium and the fluoride of magnesium or aluminum. The formulation of the mixed fluoride bath is in the range given below, with all Percentages relate to weight:

Rare earth fluoride: $ 20 to $ 80, preferably $ 40

to $ 70; Lithium fluoride: $ 80 to $ 20, preferably $ 50

to $ 20; Barium fluoride: $ 0 to $ 20, preferably $ 5

to $ 15; Magnesium or aluminum fluoride: 0 to 5 $.

The rare earth metals contained in the rare earth metal fluorides mentioned above should be considered the rare earth metals which are used in the preparation of the oxides. For example, if the rare earth metal, which with magnesium or aluminum is to be alloyed, yttrium, cerium, lanthanum or

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Is erbium, bq the fluorides are those of yttrium, gers, Lanthans or Erbiums. When the mixed rare earth metal oxides are used, the composition of rare earth metals should be the rare earth metal oxides and those of the mixed fans rare earth metal fluorides be the same.

The oxides of rare earth metals and magnesium and aluminum are in the electrolyte bath of the above-mentioned recipe at the electrolysis temperature easily resolved. Too high a content of rare earth metal fluoride in the composition of the electrolyte bath, night however, the view of the bath is higher than the density of the resulting one Alloy and consequently the alloy floats on the surface of the bath and interferes with the smooth electrolysis process. On the other hand, too high a content of "lithium fluoride" leads to a Reduction of the solubility of the oxides in the electrical bath.

The oxides of barium, magnesium and aluminum can be added to improve the electricity yield and at the same time to avoid the unfavorable reactions between the fluoride bath and the once to prevent alloys formed. One of the most important conditions in the formulation of the mixed fluoride bath is established refers to the density of the molten bath, which must be less than the density of the rare earth metal alloys Magnesium or rare earth metal with aluminum, which is produced should be.

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In a preferred embodiment of the invention, the Electrolysis is carried out in a stainless steel cell with graphite linings, with the added mixed Fluorides can be melted by heating by suitable means. Oxides of rare earth metals and magnesium and aluminum are added either separately or as a mixture to the molten fluoride bath, where they dissolve easily. In electrolysis, the graphite-lined electrolyte cell serves as the anode, while a refractory rod made of molybdenum, Tungsten or tantalum is intended to serve as a cathode. In some cases it is necessary to improve the surrounding atmosphere Keeping inert by using an inert gas such as nitrogen, argon or helium is used. When a graphite rod is applied as an anode is, it is preferred that the surface thereof is corrugated, thereby increasing the surface area.

As for the proportional use of the oxides of the rare earth metals and magnesium or aluminum, it is observed that too much magnesium or aluminum oxide to accumulate a large amount of undissolved residue at the bottom of the electrolytic cell during the course of the electrolysis, which makes the continuation of the electrolysis reactions very difficult. Also results too much magnesium or aluminum oxide a lower content of rare earth metal in the alloy being formed. on the other hand too much rare earth metal oxide causes the melting point of the resulting alloy to be higher than the electrolyte temperature

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temperature and consequently the resulting alloy is deposited in the solid state and not in the molten state on the cathode and does not fall down into a collecting vessel which is mounted below the cathode for recovery, thereby disrupting the desired, smooth course of the electrolysis . Usually the content of rare earth metal oxide in the mixed oxides is chosen in the range between 30 and 90% by weight, and the content of magnesium or aluminum oxide in the range between 70 and 10% by weight. ^x -

The electrolysis voltage is preferably kept below 15 volts with regard to the energy yield and safety. Any Voltages as low as 3 volts can be used, although these are undesirable because of poor productivity are. The electric current of the electrolysis is largely depending on: the dimensions and construction of the electro-1-ytic Cell and electrodes. For example, one applies a current of 50 to. 150 A for a cell with a diameter of is as large as 100 mm; and a current of 500 A is applied to a cell which is 200 mm in diameter. . '

The temperature at which the electrolysis is carried out is selected depending on the composition of the alloys to be produced and the composition of the electrolyte salt bath used in the range between 800 and 1200 ^° C. At such a temperature

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the resulting alloy deposited on the cathode is in a molten state and falls slightly downward into a collecting vessel, which is placed below the cathode in the salt bath. The collecting vessel consists of a fire-proof one Metal such as molybdenum, which does not react with the fluoride bath or with the alloys produced in the electrolyte bath.

The composition of the process according to the invention The alloys produced are determined by (a) the ratio of the rare earth metal oxide to magnesium or aluminum oxide, (b) the Composition of the mixed fluoride bath and (c) the electrolysis conditions in terms of temperature, voltage and current density. Satisfactory results can be obtained by doing this Selects characteristic values in the areas mentioned above.

Exemplary of the effects of the method according to the invention are the following specific examples where all percentages relate to weight.

Example 1 -

A graphite crucible (100 mm diameter and 150 mm deep) with a cathode made of a molybdenum rod in the middle and a receptacle made of molybdenum, which is located below the cathode is on the bottom of the pan, you load with about 3 kg of remisclitez Fluoride from 50 $ yttrium fluoride, 45 $ lithium fluoride and 5 '' barium

fluoride and it is kept in the molten state at 95O ° C. Mixed things

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Oxide powder made from $ 60 yttrium oxide and $ 40. Magnesium oxide goes into the molten bath at a rate of 2 g / min. The electrolytic heduction is then carried out for 2 hours the mean voltage of 5.5 volts and the mean current of 110 amps. Collect them in the receiving vessel or collecting vessel 80 g yttrium-magnesium alloy with an yttrium content of $ 73.

Example 2,

A mixed fluoride bath of 50 $ yttrium fluoride, 45 $ lithium fluoride and 5 $ barium fluoride is formed in a graphite crucible similar to that used in Example 1. While the bath is kept ^{in the molten state at 115O 0} C, the mixed oxide powder of 40 $ yttrium oxide and 60 $ aluminum oxide is introduced into the molten bath at a rate of 1.0 g / min. The electrolysis is carried out for 2 "hours with an average voltage of 5.2 volts and an average current of 120 amperes. 55 g of yttrium-aluminum alloy with a content of 30% yttrium are obtained.

Example 3 '

A mixed fluoride bath of 60 $ cerium fluoride, 20 $ lithium fluoride, 15 $ barium fluoride and 5 $ magnesium fluoride is formed in a graphite crucible similar to that used in Example 1. The bath is maintained at 850 ⁰ G in a molten state and the mixed oxide powder aua 60 $ ceria and $ 40 Magnesium oxide is introduced into the molten bath at a rate of 1.5 g / min, a. ■ L> he electrolysis is 1.5 hours with the mean voltage of

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5.8 volts and the mean current of 150 amperes. 83 g of cerium-magnesium alloy with a 7- ^f n '·' cerium content are obtained.

Example 4

In a graphite crucible similar to that used in Example 1, a mixed fluorine bath of 50 $ lanthanum fluoride, 40 $ lithium fluoride, and 10% barium fluoride is formed. The bath is kept in the molten state at 1100 ° C. and the mixture of oxide powder of 30 $ lanthanum oxide and 70 $ aluminum oxide is introduced into the molten bath at a rate:. 1.0 g / min., A. Me electrolysis is 1.5 hours with the mean voltage of t>, 3 volts and. the mean current of 125 amps. 40 g of lanthanum-aluminum alloy containing 37% of lanthanum are obtained.

Example 5

In a graphite crucible similar to that used in Example 1, about 3 kg of a fluoride bath is formed from 63 '/' mixed fluorides of rare earth metals (consisting of about 60 $ yttrium, about 10 $ dysprosium, about 8 $ erbium and ytterbium and about 22 $ other rare earth elements), 21 $ Lithiurafluorid, 14 $ Bar-iumf luorid and 2 $ Magne siumf luorid. Maintaining the fluoride bath then in a molten state at 1OOO ⁰ C. Liun a Oxydpulvergemisch of 65 $ mixed oxides of rare earth metals ( "consisting of about 60 $ yttrium, about 10 $ dysprosium, erbium about $ 8

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and ytterbium and about 22% other rare earth elements) and 35% magnesia in the fluoride bath at one speed of 1.0 g / min. The electrolysis is carried out for 2 hours with the mean voltage of 5.6 volts and the mean current of 160 amps. 82 g of an alloy from rare Earth metals and magnesium, the alloy being 66% of the mixed contains rare earth metals.

Example β '-

In a graphite crucible similar to that used in Example 1, about 5 kg of fluoride bath is formed from 70% mixed fluorides of rare earth metals (consisting of about 50% cerium, about 20% lanthanum, about 10% iFeodymium and about 20% other elements rare earths), 24% lithium fluoride, 5% barium fluoride and 1% aluminum fluoride. The eluoride bath is now kept in the molten state ^{at 95O 0 O.} Then, a Öxydpulvergemisch of 85% of mixed oxides is rare earth metals (consisting of rare of approximately 50% cerium, approximately 20% lanthanum, about 10% neodymium, and about 20% of other elements earth) and 15% ^A iuminiumöxyd in daa Fluöridbäd at a rate of 1 , 3 g / min, introduced * The electrolysis is carried out for 1.5 hours with an average voltage of 5 * 5 volts and an average current of 130 amperes % of mixed rare earth metals.

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Example 7

In a graphite crucible, which is used in the Seispiel 1 similar forms is about 3 kg of a mixed fluoride bath Removing 60 $ erbium fluoride, lithium fluoride $ 35 and $ 5 Bariurafluorid. The bath is maintained at 1GOO ⁰ C in a molten state. An oxide powder mixture of 60 $ erbium oxide and 4-0 $ magnesium oxide is poured into the molten fluoride bath at a rate of 1.0 g / min. fed. The electrolysis is carried out for 1.5 hours with an average voltage of 5-7 volts and an average current of 120 amperes. 73 g of Srbiura-Ca ^ nesiuin alloy are obtained, which contains 70 $ erbium.

- patent claims -

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Claims (13)

Claims 1 «Process for making an alloy of a rare earth metal with a light metal, this light metal being magnesium and / or aluminum, characterized in that a salt bath is used in a molten state, the latter being composed of fluorides of a rare earth metal and lithium is; that an oxide of the same light metal and an oxide of the same rare earth metal are introduced into the salt bath; and that one then the oxides of the light metal and the rare metal for the purpose of producing the predetermined alloy, which is based on a Cathode is deposited in contact with the salt bath, subjected to a simultaneous electrolytic reduction. 2. The method according to claim 1, characterized in that nan a yttrium oxide, a cerium oxide, a lanthanum oxide and / or an erbium oxide are used as the oxide of a rare earth metal. 3. The method according to claim 1 and 2j, characterized in that that the rare earth metal oxide is a mixture of oxides seldom used earth metals, which more than 40 wt .- ^ S Geroxyd contains. 4. The method according to any one of the preceding claims, characterized in that one is used as the oxide of the rare earth metals. Mixture of oxides of heavy rare earth metals used, which 409816/0890. Contains more than 50 percent by weight of yttrium oxide. 5. The method according to any one of the preceding claims, characterized in that the oxide of the rare earth metal is the ■ Oxides of scandium, praseodymium, neodymium, prometheum, samarium, Europium, gadolinium ,. Terbium, dysprosium, holmium, thulium, Ytterbium, lutetium or mixtures of two or more of these oxides are used. 6. The method according to any one of the preceding claims, characterized in that a salt bath is used, which consists of 20 to 80 wt .- ^ of the fluoride of this rare earth metal and 80 to 20 wt .- $ lithium fluoride is composed. 7. The method according to any one of the preceding claims, characterized in that a salt bath is used which additionally contains 0 to 20 wt.% - ° / o barium fluoride. 8. The method according to any one of the preceding claims, characterized in that a salt bath is used which additionally contains 0 to 5 wt. Fo of the fluoride of this light metal. 9. The method according to any one of the preceding claims, characterized characterized in that a salt bath is used which additionally contains 0 to 20 wt .- ^ barium fluoride and 0 to 5 wt .- / »of the fluoride this light metal contains " 4 i »; J" 3 i ο ν VI <Qi Tj U 10. The method according to any one of the preceding claims, characterized characterized in that the oxides of the rare earth metals ^ and the light metal in the form of an oxide mixture in the salt bath introduces. 11. The method according to claim 10, characterized in that an oxide mixture is used, which consists of 30 to 90 wt of the rare earth metal oxide and 70 to 10% by weight of the light metal oxyds is composed. 12. The method according to any one of the preceding claims, characterized in that the simultaneous electrolytic reduction is carried out at a temperature in the range from 800 to 1200 ⁰ C and at a voltage in the range from 3 to 15 volts. 13. The method according to any one of the preceding claims, thereby characterized in that the alloy deposited on the cathode is collected by placing the alloy in a collecting vessel drops, which consists of refractory, non-reactive metal and which is stored below the cathode.