EP0102892B1 - Verfahren zur Herstellung von Metallen und Legierungen hoher Reinheit - Google Patents

Verfahren zur Herstellung von Metallen und Legierungen hoher Reinheit Download PDF

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Publication number
EP0102892B1
EP0102892B1 EP83401671A EP83401671A EP0102892B1 EP 0102892 B1 EP0102892 B1 EP 0102892B1 EP 83401671 A EP83401671 A EP 83401671A EP 83401671 A EP83401671 A EP 83401671A EP 0102892 B1 EP0102892 B1 EP 0102892B1
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Prior art keywords
metal
process according
chromium
metallic
alloy
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EP83401671A
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English (en)
French (fr)
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EP0102892A1 (de
Inventor
Laurent Lucien Boulier
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C Delachaux SA
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C Delachaux SA
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Priority to AT83401671T priority Critical patent/ATE24205T1/de
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/24—Binding; Briquetting ; Granulating
    • C22B1/242—Binding; Briquetting ; Granulating with binders
    • C22B1/244—Binding; Briquetting ; Granulating with binders organic
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/24—Binding; Briquetting ; Granulating
    • C22B1/2406—Binding; Briquetting ; Granulating pelletizing
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/24—Binding; Briquetting ; Granulating
    • C22B1/242—Binding; Briquetting ; Granulating with binders
    • C22B1/244—Binding; Briquetting ; Granulating with binders organic
    • C22B1/245—Binding; Briquetting ; Granulating with binders organic with carbonaceous material for the production of coked agglomerates
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B34/00—Obtaining refractory metals
    • C22B34/30—Obtaining chromium, molybdenum or tungsten
    • C22B34/32—Obtaining chromium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B5/00—General methods of reducing to metals
    • C22B5/02—Dry methods smelting of sulfides or formation of mattes
    • C22B5/04—Dry methods smelting of sulfides or formation of mattes by aluminium, other metals or silicon
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S75/00—Specialized metallurgical processes, compositions for use therein, consolidated metal powder compositions, and loose metal particulate mixtures
    • Y10S75/959—Thermit-type reaction of solid materials only to yield molten metal

Definitions

  • the present invention relates to a method for manufacturing metals or metal alloys of high purity, in particular metallic chromium.
  • the superalloys concerned require extremely careful and sophisticated processing from very high quality raw materials, both in chemical purity and in regularity. This is in particular the case for pure metallic chromium which is used as an alloying element providing the superalloys with resistance to hot oxidation.
  • a first technique, electrolytic, makes it possible to obtain a metallic chromium of very good chemical purity which however contains too many gases which are very harmful for superalloys, in particular oxygen, hydrogen and nitrogen.
  • a reductive degassing is then carried out under vacuum, so that the oxygen content of the chromium falls from 2000 to 5000 ppm for the crude product of electrolysis to 300-500 ppm for the metallic chromium obtained after treatment.
  • This treatment also makes it possible to significantly lower the hydrogen and nitrogen contents as well as the contents of certain volatile metals such as lead or certain metalloids such as sulfur.
  • a second technique known as aluminothermic, consists of reducing chemically pure chromium oxide (99.5 to 99.7% Cr 2 0 3 ) at very high temperatures, ie above 2000 ° C. aluminum powder.
  • aluminothermic consists of reducing chemically pure chromium oxide (99.5 to 99.7% Cr 2 0 3 ) at very high temperatures, ie above 2000 ° C. aluminum powder.
  • the igneous elaboration used inevitably leads to the presence in the pure metallic chromium obtained, returned to ambient temperature, of non-metallic oxidized inclusions of alumina and chromium oxide.
  • the oxygen content which is the consequence thereof and which varies inversely with the content of residual reducing agent in metallic chromium, in this case the aluminum content, is then prohibitive for the noblest aeronautical uses which, moreover, cannot tolerate very low residual aluminum contents.
  • a third technique for manufacturing metallic chromium consists in carrying out a reduction of chromium oxide using carbon.
  • granules are prepared from a mixture of finely divided chromium oxide, finely divided carbon, and a binder. Then these granules, transported by a gas stream, are passed through a plasma torch.
  • the metallic chromium obtained is then preferably subjected to an additional refining, either by heating to at least 1200 ° C. in a vacuum oven, or by irradiation of the product with a plasma torch under a protective atmosphere.
  • the process of the invention makes it possible to manufacture different metals, in particular chromium, and different alloys, with high purity.
  • the process of the invention is based essentially on a primary production of a metal or a metal alloy essentially containing non-metallic inclusions oxidized from the base metal, easily reducible, which is then ground and agglomerated before being subjected to a vacuum reducing treatment.
  • the primary production of the metal or of the metal alloy is preferably obtained by an unbalanced aluminothermic reaction allowing the content of difficultly reducible aluminous inclusions to be reduced to a minimum, but this production can also be obtained by other techniques, for example by silicothermia, by reduction in an electric oven, etc., provided that the characteristics of the non-metallic inclusions make it possible to reproduce the subsequent stages of grinding and reducing treatment under vacuum.
  • the metals or metallic alloys which can be obtained with high purity by means of the process of the invention are those capable of comprising reducible non-metallic inclusions which can be practically eliminated at the end of the grinding and reduction steps under vacuum, i.e. essentially the base metal's own oxides.
  • the metals which can be produced with the process of the invention mention may in particular be made of chromium, titanium, vanadium, molybdenum, manganese, niobium and tungsten.
  • the alloys envisaged in the context of the invention are alloys comprising at least one of the preceding metals, and / or boron, these alloys also comprising ferro-alloys in general.
  • step a) comprises an aluminothermic reaction between at least one metal oxide and divided aluminum, the reaction being unbalanced by an aluminum defect relative to the quantity necessary for the complete aluminothermic reaction, to produce a metal or a metal alloy containing reducible non-metallic inclusions, mainly consisting of inclusions of the basic metal oxide, the appearance of inclusions of alumina Al z 0 3 being minimized.
  • This defect in aluminum which can represent from 0.5 to 8%, preferably from 2 to 5% by weight of the quantity necessary for the complete aluminothermic reaction is essential to lower to the minimum the inclusions of alumina which are the most difficult to reduce. .
  • the preferred metal for carrying out the process of the invention is chromium.
  • the metallic chromium will advantageously be prepared by an unbalanced aluminothermic reaction, of the type indicated above, between chromium oxide, optionally an additive such as potassium dichromate, and divided aluminum.
  • aluminothermic reaction of the type indicated above
  • additives of this kind is well known in the field of aluminothermics to provide additional oxygen and to heat the aluminothermic reaction.
  • the grinding step b) is advantageously carried out by means of an impact mill, for example a hammer mill.
  • the grinding of the metal or of the metal alloy is a so-called “purifying” grinding which makes it possible to produce a certain flow of sweeping air in order to partially entrain the non-metallic inclusions released during grinding.
  • This purification associated with grinding is not compulsory, but of course preferred, since it allows a first physical separation of the non-metallic inclusions before the reducing treatment of step c).
  • the non-metallic inclusions released during the purifying grinding seem to be preferably the inclusions of base metal oxide, for example the inclusions of Cr Z 0 3 in the case of the production of metallic chromium.
  • the purifying grinding is advantageously supplemented by elimination by sieving or any other selective separation of the finest particles from the ground product in which almost all of the non-metallic inclusions released by the grinding are found concentrated.
  • the ground product thus obtained, from which part of the non-metallic inclusions will have been eliminated, is then agglomerated with a binder and a reducing agent to form balls.
  • the binder will advantageously consist of an organic compound or a mixture of organic compounds capable of leaving, during the heating of step c), a carbon skeleton which completes the reducing action of the reducing agent.
  • the binder can be constituted by a mixture of bakelite and furfuraldehyde and the reducing agent will advantageously be constituted by carbon black.
  • the balls are shaped in a conventional compacting press and then baked at a set temperature, for example between 200 and 230 ° C to avoid any oxidation of the metal or metals constituting the balls, while obtaining satisfactory cohesion.
  • the reducing treatment is carried out in a vacuum oven and is optionally supplemented by sweeping using a non-oxidizing or reducing gas which is not soluble in the metal or the alloy.
  • the metal product obtained after reducing the vacuum treatment is cooled in a neutral atmosphere and can then be used in the manufacture of metal parts.
  • Chromium oxide (Cr 2 0 3 ) potassium dichromate (Cr 2 o 7 K 2 ) and divided aluminum are introduced into an aluminothermic crucible, lined with a refractory material. Chromium oxide and potassium dichromate are tagging commercial products having a particle size between 0 and 15 ⁇ m, while the divided aluminum consists of grains less than 1 mm.
  • Chromium oxide and potassium dichromate are present in the proportions of the classic aluminothermic reaction, while aluminum is present with a defect compared to the proportion of the classic aluminothermic reaction. As indicated above, this defect in aluminum can represent from 0.5 to 8%, preferably from 2 to 5% by weight of the usual amount.
  • the three constituents are mixed thoroughly and the reaction is initiated in the crucible as appropriate.
  • the reaction temperature quickly reaches a value of about 2200 ° C., and at the end of the reaction, the metal is collected at the bottom of the crucible, and a supernatant slag.
  • the analysis of the metallic chromium obtained shows that by deliberately choosing to remain below the usual proportions, with the consequence of not reaching the optimum extracting yield, the residual aluminum content in the metallic chromium drops to very low levels below 0.01% (100 ppm). This analysis also shows that the content of non-metallic inclusions rises very quickly to reach high levels of 0.40 to 0.80%, or even more, but that these non-metallic inclusions are almost entirely composed of chromium oxide. not reduced (Cr 2 0 3 ) with very little Al 2 O 3 .
  • the residual aluminum is in an amount large enough to be able to reduce all of the chromium oxide or dissolved oxygen and there is even an unused excess in chromium.
  • the non-metallic inclusions which remain trapped in the solid metal are then almost entirely formed of Al 2 O 3 alumina.
  • the operation is carried out, in accordance with the process of the invention, with an aluminum defect with respect to the previous usual quantity, the residual aluminum present is in insufficient quantity to be able to reduce all of the chromium oxide or of the dissolved oxygen.
  • All or almost all of the aluminum present is oxidized by the oxygen present (phase equilibrium during slow cooling) and the excess of chromium oxide or unreduced dissolved oxygen precipitates in the form of non-metallic inclusions Cr 2 0 3 .
  • step a) The unbalanced aluminothermic reaction of step a) obviously gives a slightly less good yield than in conventional aluminothermic processes.
  • the elemental chromium is nevertheless reduced and the final product obtained is a metallic chromium of high purity, identical to normal aluminothermic metallic chromium of good quality, except that it contains a very high oxygen content ( 2000 to 3000 ppm or more), but in the almost exclusive form of non-metallic Cr Z 0 3 inclusions (0.40 to 0.80% or more) with the presence of very few Al 2 O 3 aluminous inclusions (100 to 400 ppm corresponding to 50 to 200 ppm of oxygen bound to aluminum).
  • Metallic chromium is therefore obtained with non-metallic inclusions mainly constituted by Cr 2 O 3 inclusions which are easy to remove and secondarily by alumina inclusions, which are more difficult to remove, but in small quantities.
  • the metallic chromium coming from stage a) is ground in an impact mill advantageously constituted by a high energy mill of the hammer type (mobile hammers / against fixed hammers) until a fine powder passing entirely through is obtained. a 200 ⁇ m sieve opening of mesh.
  • the high impact energy of the grinder causes the grains to burst, which releases, at least in large part, the non-metallic inclusions Al z 0 3 and Cr 2 0 3 contained in the metal, the inclusions Cr 2 0 3 appearing preferentially released. .
  • the grinding is a purifying grinding which produces ventilation, that is to say a certain flow of purge air.
  • This ventilation can be produced directly by the crusher itself or indirectly by an additional device, such as a blower.
  • This sweeping air makes it possible to ventilate the product during grinding, which on the one hand prevents the product from overheating, and therefore possibly its oxidation and nitriding by ambient air, and on the other hand causes the most fractions. fine and lighter in the sweeping air stream, that is to say preferably the non-metallic inclusions released, the density of which is lower.
  • the air flow can be adjusted voluntarily to accentuate, if desired, the purifying effect.
  • this purifying effect can be supplemented by elimination by sieving or any other selective separation of the finest particles from the ground product where almost all of the non-metallic inclusions released by the grinding are found concentrated.
  • the purified chromium powder thus obtained is then intimately mixed with a reducing agent and a binder.
  • a reducing agent and a binder are advantageously constituted by a mixture of bakelite and furfuraldehyde.
  • the purpose of the furfuraldehyde is to facilitate cold agglomeration, the bakelite dissolved in the furfuraldehyde forming cold glue, as well as the subsequent polymerization of the hot bakelite.
  • other thermosetting agglomerants and other solvents can be used.
  • the reducer for its part, is advantageously constituted by carbon black which complements the carbon of the bakelite.
  • the respective amounts of these products are variable but are generally adjusted, with a slight excess, to the residual oxygen content of the ground product.
  • the reducing / caking mixture may consist of 0.1% bakelite, 0.3% of furfuraldehyde and 0.05 to 0.2% of carbon black, these percentages being based on weight of the ground product.
  • the mixture obtained is shaped into balls or pellets by means of a conventional compacting press, such as a ball press with tangential wheels or a tableting press. After agglomeration, the mixture is steamed at the appropriate temperature (200 to 230 ° C approximately) to remove the volatile furfuraldehyde and polymerize the bakelite which forms a binder and gives resistance to the balls or pellets.
  • a conventional compacting press such as a ball press with tangential wheels or a tableting press.
  • oven temperature must be limited to the minimum necessary to avoid any oxidation of the product.
  • the balls or pellets obtained in the previous step are then subjected to a reducing treatment under vacuum at 1100 ° -1400 ° C under high vacuum of the order of 10- 4 mm of mercury.
  • the bakelite decomposes at around 600 ° C, leaving a carbon skeleton which is added to the carbon black introduced as a reducing agent in the mixture. Once it has reached the processing temperature, this carbon reacts on the oxygen of the Cr 2 0 3 remaining in the product but practically not on the oxygen of the alumina A1 2 0 3 because to reduce the alumina it would be necessary to operate at higher temperature and reach deeper voids.
  • the vacuum is brought into the processing furnace to 10- 1 mm Hg scan controlled by a non-oxidizing or reducing gas, such as hydrogen, which has the particularity of being substantially insoluble in the solid chromium.
  • a non-oxidizing or reducing gas such as hydrogen
  • a product containing at most 300 to 400 ppm of total oxygen in the form of 200 to 300 ppm of alumina approximately containing 100 to 150 ppm of oxygen and approximately 500 ppm maximum of unreduced chromium oxide containing about 150 ppm of oxygen. It is therefore a chromium of high purity which makes it possible to develop superalloys which can be used in particular in the manufacture of the noble parts of aeronautical turbo-engines.
  • step a the use of a conventional starting product without imbalance in step a) would necessarily lead, insofar as it is desired to lower the oxygen content to the required level of about 300 ppm, treatment allowing the reduction of A1 2 0 3 by carbon which, in addition to the preceding drawbacks, would bring a rise in the residual aluminum content of the finished product to levels not acceptable by the users preparing the superalloys.
  • step a) can be carried out other than by aluminothermy, for example by silicothermal or else by reduction in an electric furnace, to obtain a metal or alloy comprising oxidized non-metallic inclusions of the base metal.

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Claims (19)

1. Verfahren zur Herstellung von Metallen oder Metalllegierungen von hoher Reinheit, gekennzeichnet durch die folgenden Verfahrensschritte:
a) Erschmelzen eines Metalles oder einer Metalllegierung, deren nichtmetallische Einschlüsse im wesentlichen Oxide des Basismetalles sind,
b) Mahlen des so erhaltenen Metalles oder der so erhaltenen Metalllegierung und Verdichten des gemahlenen Metalles oder der gemahlenen Metalllegierung mit einem Binde- und einem Reduktionsmittel zur Bildung von Briketts, und
c) Unterwerfen der Briketts einer reduzierenden Behandlung im Vakuum unter Regelung von Druck und Temperatur, so dass das Reduktionsmittel mit den nichtmetallischen Einschlüssen reagiert, ohne dass eine wesentliche Sublimation von behandeltem Metall oder von behandelten Legierungsmetallen erfolgt.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass das Metall aus Chrom, Titan, Vanadium, Molybdän, Mangan, Niob und Wolfram ausgewählt wird, und dass die Legierung zumindest eines der vorgenannten Metalle und/ oder Bor enthält, wobei die Legierung auch die Eisenlegierungen im allgemeinen einschliesst.
3. Verfahren nach einem der Ansprüche 1 und 2, dadurch gekennzeichnet, dass Schritt a) eine aluminothermische Reaktion zwischen zumindest einem metallischen Oxid und zerkleinertem Aluminium umfasst, wobei die Reaktion durch einen Aluminiumunterschuss in bezug auf herkömmlich verwendete Mengen im Gleichgewicht verschoben wird, um ein Metall oder eine Metalllegierung zu erzeugen, die reduzierbare nichtmetallische Einschlüsse enthält, die hauptsächlich aus Einschlüssen von Oxiden des Basismetalles bestehen, wobei die Bildung von Einschlüssen aus Aluminiumoxid Alz03 auf ein Minimum reduziert wird.
4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, dass der Aluminiumunterschuss 0,5-8 Gew.% der zur vollständigen aluminothermischen Reaktion erforderlichen Menge beträgt.
5. Verfahren nach Anspruch 4, dadurch gekennzeichnet, dass der Aluminiumunterschuss 2-5 Gew.% der zur vollständigen aluminothermischen Reaktion erforderlichen Menge beträgt.
6. Verfahren zur Herstellung von metallischem Chrom hoher Reinheit nach einem der Ansprüche 3-5, dadurch gekennzeichnet, dass man die aluminothermische Reaktion zwischen Chromoxid und zerkleinertem Aluminium durchführt.
7. Verfahren nach Anspruch 6, dadurch gekennzeichnet, dass man die aluminothermische Reaktion zwischen Chromoxid und einem Additiv und zerkleinertem Aluminium durchführt.
8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, dass das Additiv Kaliumbichromat ist.
9. Verfahren nach einem der Ansprüche 1-8, dadurch gekennzeichnet, dass man das Mahlen des Metalls oder der Metalllegierung in einer Prallmühle, z.B. einer Hammermühle, durchführt.
10. Verfahren nach einem der Ansprüche 1-9, dadurch gekennzeichnet, dass das Mahlen des Metalls oder der metallischen Legierung ein reinigendes Mahlen ist, bei dem eine Menge Spülluft zum teilweisen Fortspülen der während des Mahlens freigesetzten nichtmetallischen Einschlüsse erzeugt wird.
11. Verfahren nach Anspruch 10, dadurch gekennzeichnet, dass auf das reinigende Mahlen eine selektive Abtrennung der freigesetzten nichtmetallischen Einschlüsse erfolgt.
12. Verfahren nach einem der Ansprüche 1-11, dadurch gekennzeichnet, dass das Bindemittel ein Bakelit/Furfurylaldehyd-Gemisch ist.
13. Verfahren nach einem der Ansprüche 1-12, dadurch gekennzeichnet, dass das Reduktionsmittel Russ ist.
14. Verfahren nach einem der Ansprüche 1-10, dadurch gekennzeichnet, dass die Briketts in einer Verdichtungspresse geformt werden und anschliessend, um jegliche Oxidation von Metall oder von Metallen, die die Briketts bilden, zu vermeiden, unter Temperaturregelung erwärmt werden, um dabei eine ausreichende Festigkeit zu erhalten.
15. Verfahren nach Anspruch 14, dadurch gekennzeichnet, dass die Erwärmungstemperatur zwischen 200 und 230°C liegt.
16. Verfahren nach einem der Ansprüche 1-15, dadurch gekennzeichnet, dass man die reduzierende Behandlung in einem Vakuumofen durchführt, und dass man eine Begasung mit Hilfe eines im Metall oder der Legierung nicht löslichen, nicht oxidierenden oder reduzierenden Gases anwendet.
17. Verfahren zur Herstellung von metallischem Chrom von hoher Reinheit nach Anspruch 16, dadurch gekennzeichnet, dass man die Chromoxid und Aluminiumoxid enthaltenden Chrombriketts einer reduzierenden Behandlung im Hochvakuum bei einer Temperatur von 1100-1400°C unterwirft und im Verlauf der Behandlung den Druck durch Belüftung mit einem nicht oxidierenden oder reduzierenden Gas wie Wasserstoff auf den eines geringeren Vakuums herabsetzt.
18. Verfahren nach Anspruch 17, dadurch gekennzeichnet, dass das nicht oxidierende oder reduzierende Gas Wasserstoff ist.
19. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass das nach der reduzierenden Vakuumbehandlung erhaltene metallische Produkt in neutraler Atmosphäre abgekühlt wird.
EP83401671A 1982-08-20 1983-08-17 Verfahren zur Herstellung von Metallen und Legierungen hoher Reinheit Expired EP0102892B1 (de)

Priority Applications (1)

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AT83401671T ATE24205T1 (de) 1982-08-20 1983-08-17 Verfahren zur herstellung von metallen und legierungen hoher reinheit.

Applications Claiming Priority (2)

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FR8214386A FR2531978B1 (fr) 1982-08-20 1982-08-20 Procede de fabrication de metaux ou d'alliages de purete elevee
FR8214386 1982-08-20

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EP0102892A1 EP0102892A1 (de) 1984-03-14
EP0102892B1 true EP0102892B1 (de) 1986-12-10

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US (1) US4504310B1 (de)
EP (1) EP0102892B1 (de)
JP (1) JPS5956540A (de)
AT (1) ATE24205T1 (de)
DE (1) DE3368288D1 (de)
FR (1) FR2531978B1 (de)
ZA (1) ZA835957B (de)

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FR1019752A (fr) * 1949-06-24 1953-01-26 Electric Furnace Prod Co Procédé de réduction des oxydes chromiques par le carbone
US2839379A (en) * 1955-08-19 1958-06-17 Union Carbide Corp Metal aggregate
JPS537369A (en) * 1976-07-09 1978-01-23 Seiko Instr & Electronics Ltd Electronic watch
JPS5372718A (en) * 1976-12-10 1978-06-28 Showa Denko Kk Manufacture of ferrochromium
US4148628A (en) * 1977-02-18 1979-04-10 Toyo Soda Manufacturing Co., Ltd. Process of producing metallic chromium

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FR2531978B1 (fr) 1985-07-12
US4504310B1 (en) 1994-03-15
JPS5956540A (ja) 1984-04-02
ATE24205T1 (de) 1986-12-15
JPH0261531B2 (de) 1990-12-20
DE3368288D1 (en) 1987-01-22
EP0102892A1 (de) 1984-03-14
FR2531978A1 (fr) 1984-02-24
ZA835957B (en) 1984-04-25
US4504310A (en) 1985-03-12

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