EP0134162A1 - Alloys of neodymium and process for their production - Google Patents

Abstract

The present invention relates to alloys of neodymium and iron. It also relates to the process for manufacturing said alloys, characterized in that it consists in reducing a neodymium halide with a reducing metal, in the presence of iron. Neodymium can be partially replaced by a metal from another rare earth.

Description

The present invention relates to neodymium alloys and their manufacturing process.

Among the ceric rare earth metals, which includes lanthanum, cerium, praseodymium and neodymium, the latter is the only metal that cannot be manufactured industrially by the electrolysis of these salts. Indeed, it is mentioned in the article by T. KURITA (Denki Kagaku, 1967, 35 (7) p.496-501) that yields of 6 to 20% of pure neodymium are obtained by electrolysis in a molten bath - neodymium chloride, potassium chloride ~.

Consequently, obtaining neodymium alloys from metallic neodymium does not appear to be an industrially valid route.

One of the objectives of the present invention is to have available new neodymium alloys obtained according to an industrial manufacturing process.

The object of the present invention lies in new neodymium alloys characterized by the fact that they contain neodymium and iron.

A variant of the present invention resides in neodymium alloys characterized by the fact that they contain neodymium, iron, and at least one metal from another rare earth chosen from the group formed by yttrium, lanthanum, cerium, praseodymium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, lutetium.

The rare earth metal involved in said alloys is therefore any metal belonging to the group formed by yttrium and lanthanides, except samarium, europium and ytterbium.

In the following description of the invention, a metal of a rare earth or a mixture of rare earth metals chosen from the group defined above will be simplifiedly designated by "metal TR".

Another object of the present invention is the process for manufacturing said alloys, characterized in that it consists in reducing a neodymium halide and optionally a halide of a T.R. metal with a reducing metal, in the presence of iron.

As neodymium halide, neodymium fluoride or neodymium chloride or a mixture thereof is used.

Preferably, neodymium fluoride is used.

It is desirable that the halide used is of high purity, that is to say free of residual oxide and of oxyhalide and that it be dry: its water content must be less than 5% and preferably less than 2 X.

Neodymium fluoride is available in an anhydrous state because it is a low hygroscopic product.

On the other hand, neodymium chloride exists in the form of hydrates containing 6 to 7 moles of water per mole of neodymium chloride. It is generally prepared by the reaction of hydrochloric acid and neodymium sesquioxide.

The implementation of this chloride requires a drying step at a temperature between 100 ° C and 500 ° C but preferably between 200 ° C and 250 ° C. This operation can be done in air or under reduced pressure, for example between 1 mm of mercury (= 133,322 Pa) and 100 mm of mercury (= 13,332.2 Pa). This treatment is also suitable for neodymium fluoride.

The drying time can vary between 2 and 24 hours.

The conditions set out above for drying the neodymium halide are not critical and are given on a preferential basis.

The particle size of the neodymium halide may vary. It is commercially available in powder form, the particle size of which varies from 40 to 150 µm.

The particle size influencing the reduction speed, it is recommended that the powder is fine which can cause grinding operation so that the average particle diameter of the neodymium halide is less than 100 μm. There is no lower diameter limit.

As regards the metal halide TR, a metal fluoride TR, a metal chloride TR or a mixture thereof can be chosen.

Preferably, the fluoride of the metal TR is used.

The properties required and the conditions for using the metal halide TR are identical to those of the neodymium halide.

In view of what is mentioned above, it is possible to use a mixture of halides of different rare earth metals.

The reducing metal used in the process of the invention can be an alkali metal, an alkaline earth metal or a mixture thereof. Mention may be made, as alkali metal, of sodium, lithium or potassium and, as alkaline earth metal, of calcium or magnesium.

Calcium or magnesium is preferably used and even more preferably calcium.

The reducing metal is used in the form in which it is sold, whether it is in the solid state or in the form of pellets or balls.

As regards the iron which intervenes in the alloy with neodymium, it gives a fusible alloy at low temperature which makes the process industrially advantageous.

It is used in its form as sold, powder or flakes.

A preferred variant of the process of the invention consists in adding to the reaction medium calcium chloride or calcium fluoride as the case may be in order to lower the melting point and the density of the slag formed in the reaction so that the alloy formed neodymium-iron separates more easily.

The aim being to obtain a CaF ₂ -CaCl ₂ slag, the addition when the source of neodymium is neodymium fluoride or neodymium chloride, respectively calcium chloride or calcium fluoride. If the neodymium halide is a mixture of fluoride and chloride, a mixture of chloride and calcium fluoride is added in order to obtain a CaF ₂ -CaCl ₂ mixture having the composition defined later.

In the case where there is a metal halide TR, calcium chloride should be added when using neodymium fluoride and a metal fluoride TR and calcium fluoride when using uses neodymium chloride and a metal chloride TR. If the neodymium halide or the metal TR is a mixture of fluoride and chloride or if the halides of neodymium and the metal TR are of different nature, it is necessary to add a mixture CaF ₂ -CaCl _{2 in} order to have the desired composition.

Can be used, according to the invention, the calcium halides available on the market: calcium fluoride and anhydrous calcium chloride, calcium chloride dihydrate which must be dried between 300 ° C and 400 ° C under reduced pressure of the order from 1 mm of mercury (= 133,322 Pa) to 100 mm of mercury (= 13,332.2 Pa).

The method of the invention consists in mixing a neodymium halide, optionally a metal halide TR, a reducing metal, iron and optionally a calcium halide in the proportions given below.

The quantity of TR metal halide used is calculated according to the composition of the desired alloy. It will preferably be defined so that the metal TR represents from 0 to 50% of the weight of the mixture constituted by neodymium and the metal TR and even more preferably from 0 to 10%.

The amount of reducing metal can vary within wide limits. However, it is advantageous to use a quantity sufficient to reduce the neodymium halide and possibly the metal halide TR but it should not be too large if we do not want to find, in a significant way, in the final alloy. The amount of reducing metal is at least equal to the stoichiometric amount or even in slight excess, up to 20% of the stoichiometric amount.

The amount of iron is adjusted according to the desired composition of the alloy. It is such that a fusible alloy with neodymium and iron is obtained at the reaction temperature. It is calculated so that iron represents from 5 to 30% of the weight of the alloy obtained.

The amount of calcium halide added is adjusted in order to obtain a slag containing from 30 to 70% by weight of calcium chloride and preferably 60 to 70%.

The various halides of neodymium, of metal TR and of calcium and the abovementioned metals constitute "a filler" having the desired weight composition. The constituents of this charge can be reacted in any order: by simultaneous mixing of all the constituents or by making premixes, on the one hand, the halides of neodymium, calcium, optionally of metal TR and on the other hand the reducing metal and the iron.

The reaction is carried out at a temperature between 800 ° C and 1100 ° C. The upper limit of temperature is not critical and can reach a value as high as 1400 ° C. Preferably, a temperature between 900 ° C and 1100 ° C is chosen.

The reaction is carried out at atmospheric pressure but in an inert gas atmosphere. For this purpose, the air is excluded by lowering the pressure to a non-critical value, for example between 1 mm of mercury (= 133.322 Pa) and 100 mm of mercury (= 13.332.2 Pa) and then ensures inert gas sweeping: rare gases including argon. It is desirable to subject the rare gas to a dehydration and deoxygenation treatment carried out according to the usual techniques, for example by passage through a molecular sieve.

The inert atmosphere is maintained throughout the reduction.

The duration of the reaction depends on the capacity of the apparatus and its ability to rapidly rise in temperature. Generally, once the desired temperature is reached, it is maintained for a variable duration of approximately 30 minutes to 3 hours.

During heating, two phases are formed in the reaction medium: a metallic phase consisting of the neodymium-iron alloy on which floats a slag consisting of CaF ₂ -CaCl ₂ having a density lower than that of the alloy.

At the end of the above heating time, the heating is stopped.

The alloy can be immediately separated from the slag by hot casting or allowed to cool under an inert gas atmosphere at room temperature (15 to 25 ° C) so that the alloy solidifies and can then be removed from the mold.

It can be seen that the yield of neodymium in the alloy expressed relative to the neodymium contained in the halide varies from 80 to 96%.

In the case where the metallic phase also contains a metal of another rare earth, one obtains a yield of rare earth metals (neodymium + metal TR) expressed, compared to the rare earth metals contained in the committed halides varying from 75 95%.

The process of the invention as described, can be implemented in an apparatus of conventional type, used in metallurgy.

The reduction is carried out in a crucible placed in a reactor made of a material resistant to hydrofluoric and hydrochloric vapors.

It can be chosen from refractory steel, for example, from steel containing 25 X of chromium and 20 X of nickel but preferably in inconel which is an alloy containing nickel, chromium (20%), iron (5%), molybdenum (8-10%).

Said reactor is equipped with a temperature control device (for example thermocouple), an inlet and an outlet for inert gases. It is provided in its upper part with a double envelope in which circulates a coolant.

This reactor is placed in an induction furnace or in an furnace heated by electrical resistances.

A crucible in which the temperature control device is immersed is placed at the bottom of the reactor. It must be made of a material resistant to neodymium halides or have a coating resistant to them. Preferably, a tantalum crucible is used.

Once the reaction is complete, the molten alloy can be cast in molds, for example, cast iron.

• - de 70 à 95 % de néodyme
• - de 5 à 30 % de fer.

The alloys obtained according to the present invention have the following weight composition:

• - from 70 to 95% of neodymium
• - from 5 to 30% iron.

Note the presence of a very small amount of reducing metal which varies between 0 and 3% by weight.

• - de 70 à 95 % d'un mélange de néodyme et de métal TR
• - de 5 à 30 % de fer.

According to the present invention, it is also possible to obtain alloys having the following weight composition:

• - from 70 to 95% of a mixture of neodymium and TR metal
• - from 5 to 30% iron.

In the mixture of neodymium and TR metal, the proportion of TR metal can represent from 0 to 50% of the weight of the mixture constituted by neodymium and TR metal and, preferably, from 0 to 10%.

We also note the presence of a very small amount of reducing metal ranging from 0 to 3% by weight.

• - alliage néodyme-fer
  • . de 83 à 91 % de néodyme
  • . de 9 à 16 % de fer
  • . de 0 à 1 % de calcium
• - alliage néodyme-fer-métal TR
  • . de 83 à 91 % d'un mélange de néodyme et de métal TR
  • . de 9 à 16 % de fer
  • . de 0 à 3 % de calcium

Preferred compositions of the alloys obtained are given below, by way of illustration and without limitation.

• - neodymium-iron alloy
  • . 83 to 91% neodymium
  • . 9 to 16% iron
  • . 0 to 1% calcium
• - neodymium-iron-metal TR alloy
  • . 83 to 91% of a mixture of neodymium and metal TR
  • . 9 to 16% iron
  • . 0 to 3% calcium

The alloys obtained according to the present invention are very rich in neodymium since they can contain up to 95%.

They can be used as master alloys in particular in the manufacture of permanent magnets.

• - le néodyme et l'autre métal d'une terre rare lorsqu'il est présent sont dosés, ensemble, selon la méthode chimique exposée ci-après et séparément, par fluorescence X. La méthode chimique de dosage consiste :
  • . à dissoudre l'échantillon d'alliage en milieu acide,
  • . à porter à ébullition la solution obtenue,
  • . à précipiter le métal réducteur, le fer et les terres rares sous la forme de leur hydroxyde à pH 9, par traitement à l'ammoniaque, puis à filtrer et laver les précipités obtenus,
  • . à redissoudre le précipité d'hydroxydes de terres rares en milieu acide, .
  • . à ajouter à ébullition à la solution obtenue, de l'oxalate d'ammonium afin d'obtenir les oxalates de terres rares,
  • à calciner les oxalates de terres rares à 900°C pendant 1 heure pour les transformer en oxyde,
  • à peser la quantité d'oxydes obtenus permettant ainsi de calculer la quantité de terres rares contenus dans l'alliage.
• ― les autres métaux, métal réducteur et fer sont titrés par absorption atomique.

Before detailing the examples embodying the practical implementation of the invention, the methods for assaying the various constituents of the alloy will be explained briefly by the following techniques:

• - the neodymium and the other rare earth metal when it is present are assayed together, according to the chemical method set out below and separately, by X-ray fluorescence. The chemical assay method consists:
  • . dissolving the alloy sample in an acid medium,
  • . bring the solution obtained to a boil,
  • . to precipitate the reducing metal, iron and rare earths in the form of their hydroxide at pH 9, by treatment with ammonia, then to filter and wash the precipitates obtained,
  • . redissolving the precipitate of rare earth hydroxides in an acid medium,.
  • . adding ammonium oxalate to the solution obtained in boiling in order to obtain the rare earth oxalates,
  • calcining the rare earth oxalates at 900 ° C for 1 hour to transform them into oxide,
  • weighing the quantity of oxides obtained, thus making it possible to calculate the quantity of rare earths contained in the alloy.
• - the other metals, reducing metal and iron are titrated by atomic absorption.

In the following description of the invention, an example of the preparation of a neodymium-iron alloy is given (example 1) and two examples of the preparation of a neodymium-praseodymium-iron alloy (examples 2 and 3).

EXAMPLE 1 - Preparation of a neodymium-iron alloy containing 12% iron.

We start by grinding, roughly, 382.2 g of calcium chloride and then drying it for 3 hours, at a temperature of 350 ° C-400 ° C and under reduced pressure of 1 mm of mercury (= 133,322 Pa).

A premix is then made containing 382.2 g of calcium chloride in the dry state and 281.4 g of neodymium fluoride having an average particle diameter of 60 μm. The drying of the said mixture is carried out for 24 hours in a vacuum oven at a temperature of 225 ° C. and under a pressure reduced by 1 mm of mercury (= 133.322 Pa). The previously defined load is then ready for use.

The calciothermic reduction reaction of neodymium fluoride is carried out in a tantalum crucible of about 1 liter placed at the bottom of an inconel reactor which is equipped with an inlet and an outlet for argon and a thermocouple introduced. in a thermometric sheath which is immersed in the reaction medium contained in the crucible: the upper part of the reactor is provided with a double jacket in which cold water circulates (approximately 10 ° C).

• - que l'on obtienne un alliage contenant 12 % de fer
• - que l'on ait un excès de calcium de 20 % par rapport au poids stoechiomètrique requis
• - que l'on forme une scorie contenant 70 % de chlorure de calcium.

The proportion of the constituents of the filler is defined so that the conditions set out below are met:

• - that we obtain an alloy containing 12% iron
• - that there is an excess of calcium of 20% compared to the required stoichiometric weight
• - that a slag containing 70% calcium chloride is formed.

27.5 g of iron in the form of scales, 101 g of calcium in the form of pellets and the abovementioned charge containing 382.2 g of calcium chloride and 281.4 g of neodymium fluoride are successively introduced at the bottom of the crucible .

Once the crucible has been replaced in the closed reactor, the pressure is lowered to around 100 mm of mercury (= 13,332.2 Pa) to expel the air, then a dry argon sweep is established, which will be maintained throughout the reaction.

A temperature rise is carried out at the same time until the temperature fixed at 1100 ° C. is obtained; this temperature being kept constant for another 30 minutes.

562 g of slag are collected and 188 g of a neodymium-iron alloy are recovered by hot casting in a cast iron ingot mold. The neodymium yield in the alloy expressed relative to the neodymium contained in the neodymium fluoride is 81%.

• - 87,4 X de néodyme
• - 12 X de fer
• - 0,6 X de calcium.

The analysis of the alloy obtained is as follows:

• - 87.4 X of neodymium
• - 12 X of iron
• - 0.6 X of calcium.

EXAMPLE 2 - Preparation of a neodymium-praseodymium-iron alloy containing 13% iron.

We begin by grinding, roughly, 530.8 g of calcium chloride and then drying it for 3 hours, at a temperature of 350 ° C-400 ° C and under reduced pressure of 1 mm of mercury (= 133.322 Pa).

A premix containing 530.8 g of calcium chloride in the dry state and 390.8 g of a mixture containing 96.4 X of neodymium fluoride and 3.6% of praseodymium fluoride is then made: said mixture having an average particle diameter of 60 µm. The drying of the said mixture is carried out for 24 hours in a vacuum oven at a temperature of 225 ° C. and under a pressure reduced by 1 mm of mercury (= 133.322 Pa). The previously defined load is then ready for use.

The calciothermic reduction reaction of neodymium fluoride and praseodymium fluoride is carried out in a tantalum crucible of about 1 liter placed at the bottom of an inconel reactor which is equipped with an inlet and an outlet for argon and a thermocouple introduced into a thermometric sheath which is immersed in the reaction medium contained in the crucible: the upper part of the reactor is provided with a double jacket in which circulates cold water (approximately 10 ° C.).

• - que l'on obtienne un alliage contenant 13 % de fer
• - que l'on ait un excès de calcium de 20 % par rapport au poids stoechiomètrique requis
• - que l'on forme une scorie contenant 70 % de chlorure de calcium.

The proportion of the constituents of the filler is defined so that the conditions set out below are met:

• - that we obtain an alloy containing 13% iron
• - that there is an excess of calcium of 20% compared to the required stoichiometric weight
• - that a slag containing 70% calcium chloride is formed.

38.2 g of iron in the form of scales, 140.3 g of calcium in the form of pellets and the abovementioned charge containing 530.8 g of calcium chloride and 390.8 g of a mixture of neodymium fluoride and praseodymium fluoride.

Once the crucible has been replaced in the closed reactor, the pressure is lowered to around 100 mm of mercury (= 13,332.2 Pa) to expel the air, then a dry argon sweep is established, which will be maintained throughout the reaction.

A temperature rise is carried out at the same time until the temperature fixed at 1100 ° C. is obtained; this temperature being kept constant for another 30 minutes.

717.2 g of slag are collected and 296 g of a neodymium-praseodymium-iron alloy are recovered by hot casting in a cast iron ingot mold. The yield of rare earths in the alloy expressed relative to the rare earths contained in neodymium and praseodymium fluorides is 90%.

• - 86 % d'un mélange contenant 96,4 % de néodyme et 3,6 % de praséodyme
• - 13 % de fer
• - 1 % de calcium.

The analysis of the alloy obtained is as follows:

• - 86% of a mixture containing 96.4% of neodymium and 3.6% of praseodymium
• - 13% iron
• - 1% calcium.

EXAMPLES - Preparation of a neodymium-praseodymium-iron alloy containing 13% iron.

Example 2 is reproduced, except that a mixture of neodymium fluoride and praseodymium fluoride is used, but a mixture containing 58% of neodymium chloride and 42% of praseodymium chloride. In this case, the neodymium and praseodymium chlorides are dried for 3 hours in a vacuum oven at a temperature of 220 ° C. and under pressure reduced by 1 mm of mercury (= 133.322 Pa).

• - 39,3 g de fer
• - 144 g de calcium
• - 142,7 g de fluorure de calcium
• - 498,6 g d'un mélange de chlorure de néodyme et de chlorure de praséodyme

The charge implemented according to the same operating mode is as follows:

• - 39.3 g of iron
• - 144 g of calcium
• - 142.7 g of calcium fluoride
• - 498.6 g of a mixture of neodymium chloride and praseodymium chloride

At the end of the reaction, 519 g of slag and 275 g of a neodymium-praseodymium-iron alloy are obtained, which corresponds to a rare earth yield of 81%.

• - 84 % d'un mélange contenant 58 % de néodyme et 42 % de praséodyme
• - 13 % de fer
• - 3 % de calcium

The alloy obtained contains:

• - 84% of a mixture containing 58% neodymium and 42% praseodymium
• - 13% iron
• - 3% calcium

Claims (27)

1 - Neodymium alloys characterized by the fact that they contain neodymium and iron. 2 - Neodymium alloys according to claim 1 characterized in that they contain at least one rare earth metal chosen from the group formed by yttrium, lanthanum, cerium, praseodymium, gadolinium, terbium , dysprosium, holmium, erbium, thulium, lutetium. 3 - Neodymium alloys according to claim 2 characterized in that the metal TR is praseodymium. 4 - Neodymium alloys according to claim 1, characterized in that they contain: - from 70 to 95% of neodymium - 5 to 30% iron - from 0 to 3% of reducing metal 5 - Neodymium alloys according to claim 4, characterized in that they contain: - from 83 to 91% of neodymium - from 9 to 16% iron - from 0 to 1% calcium 6 - Neodymium alloys according to claim 2, characterized in that they contain: - from 70 to 95% of a mixture of neodymium and TR metal - 5 to 30% iron - from 0 to 3% of reducing metal. 7 - Neodymium alloys according to claim 6, characterized in that they contain: - from 83 to 91% of a mixture of neodymium and metal TR - from 9 to 16% iron - 0 to 3% calcium 8 - Neodymium alloys according to one of claims 2, 6 and 7 characterized in that the proportion of metal TR represents from 0 to 50% of the weight of the mixture consisting of neodymium and metal TR. 9 - Neodymium alloys according to claim 8 characterized in that the proportion of metal TR represents from 0 to 10% of the weight of the mixture consisting of neodymium and metal TR. 10 - A method of manufacturing the alloys described in one of claims 1 to 9 characterized in that it consists in reducing a neodymium halide with a reducing metal, in the presence of iron. It - Method according to claim 10 characterized in that the neodymium halide is neodymium fluoride, neodymium chloride or a mixture thereof. 12 - Process according to claim 11 characterized in that the neodymium halide is subjected to drying between 100 ° C and 500 ° C, in air or under reduced pressure between 1 mm of mercury (= 133,322 Pa) and 100 mm of mercury (= 13,332.2 Pa). 13 - Process according to claim 10 characterized in that the reducing metal is an alkali metal such as sodium, lithium, potassium or an alkaline earth metal such as calcium or magnesium. 14 - Process according to claim 13 characterized in that the reducing metal is calcium. 15 - Process according to claim 10 characterized in that one adds a metal halide TR. 16 - Method according to claim 15 characterized in that the metal halide TR is subjected to drying between 100 ° C and 500 ° C, in air or under reduced pressure between 1 mm of mercury (= 133.322 Pa ) and 100 mm of mercury (= 13,332.2 Pa). 17 - Method according to one of claims 10 to 14 characterized in that one adds to the reaction medium calcium chloride, calcium fluoride or their mixture according to whether the neodymium halide is respectively neodymium fluoride, neodymium chloride or a mixture thereof. 18 - Method according to one of claims 15 and 16 characterized in that one adds to the reaction medium calcium chloride when using neodymium fluoride and a metal fluoride TR; calcium fluoride when doing use of neodymium chloride and a metal chloride TR; a mixture of calcium fluoride and calcium chloride if the neodymium or metal TR halide is a mixture of fluoride or chloride or if the neodymium and TR metal halides are of different nature. 19 - Method according to one of claims 17 and 18 characterized in that the calcium halide is subjected to drying between 300 ° C and 400 ° C, under reduced pressure of 1 mm of mercury (= 133,322 Pa) to 100 mm of mercury (= 13,332.2 Pa). 20 - Method according to one of claims 10 to 19 characterized in that the amount of metal halide TR is such that an alloy is obtained in which the proportion of metal TR represents from 0 to 50% by weight of the mixture consisting of neodymium and metal TR. 21 - Process according to claim 20 characterized in that the quantity of metal halide TR is such that an alloy is obtained in which the proportion of metal TR represents from 0 to 10% of the weight of the mixture consisting of neodymium and the metal TR. 22 - Method according to one of claims 10 to 21 characterized in that the amount of reducing metal is equal to the stoichiometric amount or in slight excess up to 20% of the stoichiometric amount. 23 - Method according to one of claims 10 to 22 characterized in that the amount of iron is such that an alloy containing 5 to 30% iron is obtained. 24 - Method according to one of claims 10 to 23 characterized in that the amount of calcium halide added is such that one obtains a slag containing 30 to 70% of calcium chloride. 25 - A method according to claim 24 characterized in that the amount of calcium halide added is such that one obtains a slag containing from 60 to 70 y calcium chloride. 26 - Method according to one of claims 10 to 25 characterized in that the reaction is carried out between 800 ° C and 1100 ° C under atmospheric pressure, but in an inert gas atmosphere. 27 - Process according to claim 26 characterized in that the reaction is carried out between 900 ° C and 1100 ° C. 28 - A method according to claim 26 characterized in that one carries out an inert gas atmosphere by excluding air, then by sweeping dry argon. 29 - The method of claim 26 or 27 characterized in that one maintains the selected temperature for a period ranging from 30 minutes to 3 hours. 30 - Method according to one of claims 10 to 29 characterized in that one separates, at the end of the reaction, the alloy obtained from the slag, either by hot casting, or by demolding after cooling under gas atmosphere inert.