CS216666B2 - Method of making the powder substances or easily pulverisable alloys of elements of noble earths - Google Patents

Abstract

1438091 Vacuum furnace TH GOLDSCHMIDT AG 7 Jan 1974 [26 Jan 1973] 00725/74 Heading F4B [Also in Division C7] A furnace contains a reaction chamber 1 holding two reaction vessels 2, 3, the chamber 1 being evacuated by pipe 4 to a vacuum of #10<SP>-2</SP> mm. Hg, and the furnace space outside the chamber being evacuated to the same pressure by means not shown. When the desired pressure is reached, the vessels 2, 3 are heated independently by coils 5, 6 respectively for the reaction between the contents of the vessels to occur. The furnace is lined with magnesite bricks 7.

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for the production of powdered or easily powdered rare earth alloys with cobalt.

By rare earths for use in the method of the invention are meant oxides of elements of the third group of the periodic system, i.e., yttrium of atomic mass 39 and series of elements lanthanum to lutecium of atomic masses 57 to 7.1.

Known melt and powder metallurgical processes are used for the production of cobalt rare earth rare earth alloys.

In the melt metallurgical process is based on a process that is under protective, gas or ^·: vacuum. the rare-earth melt is produced by cobalt, which is then converted into a new suitable compact casting by more or less expensive casting. The rods which are formed can easily be ground due to their physical properties. The pulverization. different grinding equipment is used and the alloys can be ground up to particles of 3 to 10 µm in size. However, the powder alloys thus obtained are very sensitive to oxidation effects, in particular to humid ambient air, and must therefore be further processed. protect against oxygen attack. or moisture.

The alloy powders are then incorporated into suitable compression molds in free-flowing and compared to a certain energetic densification in the magnetic field. This densification is carried out either isostatically or hydrostatically. The density of the compacts is 75 to 85% of the theoretical density of the alloy. This is followed by sintering of the powders into compact magnets at temperatures of 1180 to 1400 ° C under a shielding gas atmosphere or under vacuum.

A method for the production of intermetallic compounds for permanent magnets from fine particles, formed by at least one 3d-transition element and one or more rare earth metals, is known from German Patent No. 195S 380, characterized in that in stoichiometric ratio The mixture is then compressed into a crude compact which is then sintered at a temperature of 750 ° C to 125 ° C for 4 to 10 hours, eliminating the effects of nitrogen, oxygen and carbon. For example, it is based on a metal samarium which is converted into a samarium hydride at elevated temperatures under a stream of hydrogen. Like most metal hydrides, samarium hydride is also brittle and can be easily comminuted. If the fine-grained samarium hydride with cobalt powder and the saliva products are ground, permanent magnet alloys are also obtained in a compact state, which, like cast bars, must be comminuted, magnetized, compressed and sintered into permanent magnets.

It is also known in the art to produce metals from their oxides by calcium reduction. For example, since 1927 it has been known to reduce vanadium calcium in the presence of calcium chloride according to the equation

V2O5 + 5Ca + 5CaCl2 = (2V + 5CaO +: 5CaC12

The reduction is carried out in a steel bomb at temperatures between 90 ° C and 950 ° C. A metal of up to 99.80% is obtained. This method, according to the basic principle, although heavily modernized technologically, is still used today. Zirconium oxide, titanium, nickel and tungsten, has already been used instead of vanadium oxide.

The reduction of rare earth oxides by calcium is already known, but has not been applied significantly since the reaction heat is very weakly negative and from 1873 K it becomes weakly positive, so that the reaction proceeds with a considerable heat consumption, which causes it is difficult to obtain a larger quantity of the corresponding metal.

SUMMARY OF THE INVENTION It is an object of the present invention to provide cobalt rare earth alloys which are easy to powder or which are directly in the form of powders and in which the molar ratio of the alloy components can be precisely controlled so that the same reaction conditions then, alloys are obtained whose structure and structural components are reproducible in terms of type and quantity. This is of great importance for the production of permanent magnet alloys since the content of the magnetically active component of the structure is to be as large as possible.

Will sense the problem is solved by the invention In a manner producing pulverulent or obtainable easily dustable alloys of rare earths with cobalt, characterized in that it -with a mixture of fine-grained oxides of rare earth elements and cobalt reduced at temperatures of 1000 -to 1400, ^OI C and a pressure of gl 3.33 Pa with calcium gas, the reaction product is mechanically pulverized - into particles - sizes < 100 .mu.m, and the resulting rare earth and cobalt alloy is separated from the reaction by-products by aqueous acid treatment or magnetically or by extraction.

Here, different thermodynamic ratios of rare earth oxides and cobalt are utilized. While, as mentioned above, the calcium-thermal reduction of rare-earth elements is slightly exothermic, the reduction of cobalt oxide or oxides is strongly exothermic, the heat balance becomes positive and the oxide mixture can be reduced quickly, quantitatively and at tolerable thermal conditions. This dual-reaction calcium-thermal process is novel.

Suitable cobalt oxides are, in particular, cobalt dioxide CO 2 O 3 and cobalt oxide cobalt oxide CO 3 O 4.

The mixture of rare earth metal oxides with cobalt is chosen according to the desired alloy structure and structure. Since, in principle, the compounds of rare earth metal C07, rare earth metal Cos and - rare earth metal C017 are desirable - it is expedient according to the advantageous component - structure - to reduce the mixture of metal oxides - rare - earth and cobalt in such ratio so that the resulting atomic ratio was 1: 3 to 1: 9. Since - as a rule - the rare earth metal phase -Cos is preferred, the atomic ratio of the rare earth metal to cobalt is also 1: 5.

Regarding the choice of the rare earth element, it depends on the price of the energy product of the resulting magnetic materials, - whether it is used as the rare earth element oxides of relatively - cheap lanthanum and cerium oxides or other oxides rare-earth elements or - pure - or near-pure salmonium oxide, - which - is - particularly suitable for - the production of permanent magnet materials.

The reaction proceeds at - temperatures -. ^: 1000- - to 140O ° C, while pressure is maintained - maximum 1,333- Pa.

Calciothermal reduction is carried out with calcium in the gaseous state. Once the reaction has started, its course in the mixture of oxides is easy and quantitative at the temperatures indicated. A powdery to compact reaction product is formed. If the product is compact, it is easy to powder. In addition to the resulting rare earth alloy with cobalt, the product contains - as a contaminant - mainly calcium oxide. - This contaminant can be easily removed with - rare earth compounds with - cobalt. After mechanical comminution of the reaction product - _to: particle size «-lOiOi microns, the oxide leaches vápenatý- dilute acid such as dilute hydrochloric acid or - acetic acid, - or dissociates magnet, or a known separators - extraction procedure.

It is already known from numerous earlier German patents that - certain - parts - of cobalt in alloys - rare earth elements with cobalt - can be replaced by one or - more - elements such as iron, nickel, manganese and copper. The production of such modified alloys is also possible in the novel reduction process according to the invention, in which up to 60 mole percent of cobalt oxide is replaced by one or more. more elements such as iron, nickel, manganese, copper or their oxides.

The reduction according to the invention produces very fine powders in the particle size range> 0 to <20 μΐη. This range is practically determined by the different proportions of rare earth oxide, cobalt oxide and calcium. Depending on the circumstances, thickening of the powder may also be advantageous for further processing and for achieving other properties of the powders. The coarseness of the powder can be achieved, for example, by three different measures, either individually or in combination. One of these measures is the partial replacement of cobalt oxide with cobalt ¹ powder. The larger the amount of cobalt oxide you replace with cobalt powder, the more coarser the grain will be. However, the replacement of cobalt oxide with cobalt-powder is - within the limits of the thermodynamics of the process - the production of powders, so that virtually no more than 80 masses can be replaced. -% of cobalt oxide by powdered cobalt. The powder particles coarsen to about -200 to about 300 tum.

A second possibility of increasing the coarseness of the powder consists in adding up to -50% by volume of calcium chloride to the rare-earth oxide-cobalt oxide mixture. The calcium chloride forms during the reduction of the liquid phase and therefore promotes the growth of grains.

Yet another option is the addition of up to 10 vol% sulfur. -to <- mixtures - oxides. This is justified by the fact that the exothermic forms calcium sulfide, thereby increasing the temperature accordingly.

Both the calcium chloride and the resulting calcium sulfide can be easily separated from the reaction product or otherwise separated.

As already mentioned, calcium reduction is carried out in a gaseous state. In this case, it is expedient to produce - gaseous - calcium in the reaction space, in which the reduction of the rare earth oxide mixture with the cobalt oxide also takes place. In doing so, however, the production of gaseous; of calcium in the reaction space will use a separate reaction vessel. The reaction of fine-grained calcium oxide with powdered aluminum is suitable for releasing calcium in larger quantities at temperatures of 100 to 15 ° C. The simultaneous production of calcium prior to the reduction of rare earth oxides-cobalt elements - or during reduction is particularly advantageous for carrying out the process of the invention.

This advantageous reduction process is preferably carried out in a special furnace comprising an oven closed to the outside atmosphere and preferably equipped with a centrally located reaction space exhausted by a vacuum pump to a pressure of <1.333 Pa - up to 0.1333 Pa, which contains two - - separately - separated, heated top open reaction vessels. - One is used to place - a mixture of oxides - of rare earth elements with cobalt, - the other - to place a mixture of calcium oxide and aluminum.

It is particularly advantageous if the reaction vessel - for the reaction - of calcium oxide with aluminum - is arranged below the reaction vessel containing a mixture of oxides of rare earth elements with cobalt. The reaction space is conveniently made of chromium-nickel steel and also contains a reaction vessel containing - mixtures of oxides - rare earth elements and cobalt oxide. Preferably, the reaction vessel is lined with calcium oxide. This will prevent the rare earth elements from attacking the walls of the vessel. On the other hand, it is sufficient if the reaction vessel in which calcium is produced by reacting calcium oxide with aluminum is made of iron.

The reaction space has a diameter depending on the size of the reaction vessels contained therein. - - - - The suction line, extending from the reaction space to the pump, should have a small internal diameter, not more than 10 mm, relative to the diameter of the reaction space. Release 6 '6 6 6

-li. In the reaction of the calcium oxide with the powdered aluminum, the gaseous calcium condenses some of the calcium in the colder part of the suction line until it finally closes the reaction space exhausted to a pressure of 50 psi with a small calcium plug so that the system self-sealing. Suitably, the suction line is surrounded in the upper part of the furnace by cooling components such as heat shields.

In order to counteract the deformation of the reaction space by the vacuum in which it is maintained, it is expedient to place the furnace surrounding the reaction vessels in a space evacuated to a vacuum of 13.33 Pa.

An exemplary embodiment of the device according to the invention is shown schematically in the drawing.

The reduction furnace has inside the reaction space 1, in which two reaction vessels 2 and 3 are arranged, of which the upper reaction vessel 2 is lined with calcium oxide and serves to accommodate a mixture of the rare earth and cobalt oxides expediently compressed into shaped parts. The lower reaction vessel 3 serves to receive a mixture of calcium oxide and powdered aluminum. Through a thin suction line 4 made of steel and located at the upper end of the reaction space 1, the reaction space can be evacuated to a pressure. · 1.333 Pa. The furnace is gas-tight and is sealed to the outside atmosphere by a seal 8 located in the outlet of the exhaust duct 4. In the upper part of the furnace there are protective shields 9, which reflect resp. they absorb heat from the reaction space so that the suction line 4 can be cooler than the reaction space 1. Two independent heating systems 5, 6 are arranged outside the reaction space for heating the upper reaction vessel 2 and the lower reaction vessel 3. Furnace lining 7 is expediently made up of magnesite bricks joined without joints.

The furnace according to the invention operates as follows.

Of technical anhydrous calcium oxide with a maximum grain size of 50 μ and fine - grained powder. aluminum, 75% of which have a grain size <60. μ. moldings are pressed with a pressure of 392 MPa, diameter 310 mm and height · 30 · mm. These moldings are laminated into a lower reaction vessel 3, which is inserted into the reaction space. The upper reaction vessel 2 is lined with calcium oxide and then filled with moldings of a mixture of rare earth oxide and cobalt oxide. This upper reaction vessel 2 is placed on the lower reaction vessel 3 and then the entire reaction space is sealed by vacuum flanges of the upper furnace lid. The internal vacuum in the reaction space · 1 and · the external vacuum in the furnace · are formed simultaneously, the internal vacuum should be about 1.333 Pa, if possible up to 0.333 Pa. Once the prescribed vacuum has been reached, the heating system 6 of the lower reaction vessel 3 is switched on 1 the heating system 5 of the upper reaction vessel 2. In the lower reaction vessel 3, the reaction already starts at 600 ° C, at which calcium is formed. With constant evacuation of the reaction space, the temperatures of both heating systems continue to rise. Depending on the pressure in the lower reaction vessel 3, from 900 ° C calcium vapors are formed which rise to the upper part of the reaction space and, since there is an excess of reducing agent, slowly close the thin feed line because calcium vapors are within the temperature range 600 to 620 · · ° C condense. . After condensation of calcium vapors, there is a high vacuum in the reaction space 1. Since calcium vapors are present everywhere, an additional gettering of calcium begins to act, leading to the binding of gaseous residues.

The effective reaction time is about 2 hours. After this effective period, the heating is switched off and the entire furnace system is cooled to room temperature. The furnace lid is then opened, the heat shields removed and the reaction vessels removed from the reaction chamber. The reaction space of the vessel is opened and the reaction product in the upper vessel 2 can be fed for further processing. It is a fluffy to medium-hard porous cake and can be easily removed from the reaction vessel.

The properties of the sintered powder produced by the process according to the invention are shown in the following tables containing the results of the tests performed.

Table 1 Calcium Calcium. . Excess hydrochloric acid was then. removed by additional washing with distilled water.

Properties of cobalt sintered samarium powder, chemically wet processed. The product was ground. and washed with dilute hydrochloric acid until

Test no. Samaria content % Cobalt content% Calcium content mass % Oxygen content (PPmj 1 33.12 66.03 0.011 1280 2 32.94 67.00 0.280 830 3 33.18 66.00 0.180 940 4 33.15 66.49 0,045 650 5 33.05 66.30 0,072 610 6 33.45 66.39 0.145 780 7 33.40 66.26 0,070 500 8 32.92 66.70 0,063 1240 9 '. 33.18 66.31 0.710 1000 10 33.28 66.14 0.130 590

From the results of the analysis it can be immediately concluded that a relatively good reproducibility of the alloy composition can be achieved.

Larger variations are only in the calcium content.

The calcium content varies from 630 to 600

2800 ppm, while there are no very large variation ranges for the oxygen contents. This is due to the use of a self-closing reaction space and reduction through the calcium vapor environment.

Table 2

Properties of the sintered samarium powder with a cO In this case, the powder reaction probalt, treated with a magnet separator, was separated by means of a magnet separator by separation.

Test no. Samaria content % Cobalt content % Calcium content mass % Oxygen content (PPm) 1 32.84 66.34 0.284 2820 2 33.09 66.16 0.650 1940 3 32.75 66.40 0,123 1130 4 32.98 66.10 0.134 2000 5 32.75 66.26 0.298 1660 6 33.18 66.10 0.359 1540 7 33,00 65.95 0,099 980 8 32.91 65.92 0,834 1900 9 32.78 66.30 0.810 1530 10 32.77 66.48 0.243 1400

The results of tests with magnetic separation of the alloy components from the non-magnetized fraction show that the calcium oxide content is higher than in alloyed powders chemically wet. In addition, there are also larger variations in the samarium and cobalt contents.

The difficulty of achieving greater degrees of purity of the alloy powder is that in spite of the intensive comminution of the reaction products, alloy powders containing oxide inclusions are formed again.

If this oxide fraction is small or far less than the magnetizable metal fraction, the magnetic fraction is assigned to the metal fraction upon magnetic field separation and will naturally reappear in the cobalt or cobalt rare earth element during the analysis. in Samaria alloy with cobalt.

Table 3 shows the other physical properties of the cobalt-samarium alloys that have been chemically extracted from the reduction products by wet treatment. It is important, as is well known, that metallic compressible and sinterable powders that are processed into compact sintered products have bulk bulk properties _; the tap density and average particle size can be determined by known test methods.

Table 3

Physical properties of samarium-cobalt alloys, chemically wet-processed.

Exam Bulk density Shake density poi Average size no. (g.cm-3) (g.cm-3) of particles (μΐη) 1 2.85 3.24 2 5 4- 15 2 3.24 3.86 35 + 17 3 4.25 4.64 10+ 3 4 4.30 4.73 12+ 4 5 2, '915 3.90 29 + 13 6 3.86 4.19 103 + 28. 7 3.20 3.60 150 + 35 8 4ДО 4.45 210 + 43 9 4.22 4.48 155 + 25 10 3, '46 3.88 160 + 20

Experiments 1 to 5 were carried out with material 1. samaria and 5 cobalt grammoms,. which were . reduced - in shape - their. experiments 6 to - 10, on the other hand, with 1 grammatome of samaria in the form of oxide, se - 4. metal · cobalt gramamatomes about - an oxygen-shaped cobalt grammatome. Therefore, also here, larger average particle sizes have been found.

Table 4 shows the values of - the physical - metal powders - processed magnetically.

Table 4

Physical properties of magnetically processed samarium- cobalt alloys.

Exam Bulk density Shake density Average size no. (g.cm- ³ ) (g.cmr ³ ) particle (jum) 1 3.10 3.65 60 + 10 2 3.60 3.93 '41 + 8 3 4,2S 4.75 30+ 6 4 3.00: 3.35 25 + - 5 -5 3,110 ' 3.55 19 + 3 6 4.00 4, i25 48+ '5 7 4.25 4.76 +9 + 7 8 3,9) 5 4.35 75 + 8 9 4.10 4.40 '53' + 6 10 4.65 4.90 44 + 5

Test values 1 to 5 were also obtained by reducing the mixtures of oxides consisting of 1-gram-samarium and 5 gram-cobalt tu, based on oxygen. In tests 6 to 10, 4 gram-oxylic cobalt were replaced with powder-cobalt powder.

Claims (13)

A process for the manufacture of powdered or. - easily práškovate-lných alloys of rare earth elements -s -kobaltem, characterized in that · the - mixture of fine oxides of elements vzácných- earths with cobalt calcium reducing gas at temperatures up to 1400 IOOO C and a pressure ^{of 4} g - 1330 Pa, the reaction product is mechanically comminuted to a particle size < 100 μ aη and the resulting cobalt rare earth alloy is separated from the byproducts by treatment with aqueous acid or magnetically or by extraction. 2. A process according to claim 1, characterized in that the mixtures of rare earth oxide and cobalt are mixed with each other in such a ratio that the resulting atomic ratio of the resulting alloy is 1: 3 to 1: 9, preferably 1: 5. 3. The process according to claim 1, wherein the oxide of the rare earth elements is treated with samarium oxide. 4. A method according to any one of claims 1 to 3, characterized in that it is treated with a mixture in which it is at most 80; % - mass, cobalt oxide - replaced by powder: cobalt ·. 5. Process according to one of Claims 1 to 4, characterized in that the mixture is admixed with up to 50% by volume of calcium chloride. 6. A process as claimed in any of claims 1 to -5, characterized in that the mixture is treated with an additive of up to 10% by volume of sulfur. 7. A method according to any one of claims 1 to -6, characterized in that a mixture is processed in which it is finally reimbursed. . 60. mole% of cobalt oxide by one or more elements of the series. -. iron, nickel, manganese and copper, or their oxides. 8. Apparatus for carrying out the process according to claim 1, characterized in that it consists of a furnace which is enclosed against an &quot; external &quot; atmosphere and which preferably contains a centrally located reaction space exhausted by a vacuum pump. -up. . at a vacuum of 1.333 Pa to 0.1333 Pa, in which are located two separate, top-open heated reaction vessels (2, 3). Device according to Claim 8, characterized in that the reaction vessel (3) for reacting calcium oxide with aluminum is. placed under the reaction vessel. (2), -containing. a mixture of rare-earth elements of acobalt. 10. Apparatus according to Claims 8 and 9, characterized in that the reaction vessel (2) containing a mixture of rare earth oxide and cobalt is lined with calcium oxide. Device according to Claim 8, characterized in that the neck of the suction line (4) of the reaction chamber of the furnace has a maximum clear diameter of 10 mm. Device according to - claim 11, characterized in that the suction pipe connection (4) is surrounded by cooling components, such as heat shields (9). Apparatus according to claim 8, characterized in that the furnace surrounding the reaction vessels (2, 3, 3) is located in a vacuum evacuated space at 13.33 Pa.