EP1240364B1 - Anodes a base metallique pour cellules d'extraction electrolytique d'aluminium - Google Patents

Anodes a base metallique pour cellules d'extraction electrolytique d'aluminium Download PDF

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EP1240364B1
EP1240364B1 EP00977813A EP00977813A EP1240364B1 EP 1240364 B1 EP1240364 B1 EP 1240364B1 EP 00977813 A EP00977813 A EP 00977813A EP 00977813 A EP00977813 A EP 00977813A EP 1240364 B1 EP1240364 B1 EP 1240364B1
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Prior art keywords
nickel
anode
iron
surface layer
metal
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EP1240364A2 (fr
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Vittorio De Nora
Jean-Jacques Duruz
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Moltech Invent SA
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Moltech Invent SA
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
    • C25C3/12—Anodes

Definitions

  • This invention relates to non-carbon, metal-based, anodes for use in cells for the electrowinning of aluminium from alumina dissolved in a fluoride-containing molten electrolyte, methods for their fabrication, and electrowinning cells containing such anodes and their use to produce aluminium.
  • the anodes are still made of carbonaceous material and must be replaced every few weeks. During electrolysis the oxygen which should evolve on the anode surface combines with the carbon to form polluting CO 2 and small amounts of CO and fluorine-containing dangerous gases.
  • the actual consumption of the anode is as much as 450 Kg/Ton of aluminium produced which is more than 1/3 higher than the theoretical amount of 333 Kg/Ton.
  • metal anodes in aluminium electrowinning cells would drastically improve the aluminium process by reducing pollution and the cost of aluminium production.
  • US Patent 4,374,050 discloses inert anodes made of specific multiple metal compounds which are produced by mixing powders of the metals or their compounds in given ratios followed by pressing and sintering, or alternatively by plasma spraying the powders onto an anode substrate. The possibility of obtaining the specific metal compounds from an alloy containing the metals is mentioned.
  • US Patent 4,614,569 (Duruz/Derivaz/Debely/Adorian) describes non-carbon anodes for aluminium electrowinning coated with a protective coating of cerium oxyfluoride, formed in-situ in the cell or pre-applied, this coating being maintained by the addition of a cerium compound to the molten cryolite electrolyte. This made it possible to have a protection of the surface from the electrolyte attack and to a certain extent from the gaseous oxygen but not from the nascent monoatomic oxygen.
  • EP Patent application 0 306 100 (Nyguen/Lazouni/Doan) describes anodes composed of a chromium, nickel, cobalt and/or iron based substrate covered with an oxygen barrier layer and a ceramic coating of nickel, copper and/or manganese oxide which may be further covered with an in-situ formed protective cerium oxyfluoride layer.
  • US Patents 5,069,771, 4,960,494 and 4,956,068 disclose aluminium production anodes with an oxidised copper-nickel surface on an alloy substrate with a protective oxygen barrier layer. However, full protection of the alloy substrate was difficult to achieve.
  • US Patent 5,510,008 discloses an anode made from an inhomogeneous porous metallic body obtained by micropyretically reacting a metal powder mixture of nickel, iron, aluminium and optionally copper.
  • the porous metal is anodically polarised in-situ to form a dense iron-rich oxide outer portion whose surface is electrochemically active.
  • Bath materials such as cryolite which may penetrate the porous metallic body during formation of the oxide layer become sealed off from the electrolyte and from the active outer surface of the anode where electrolysis takes place, and remain inert inside the electrochemically-inactive inner metallic part of the anode.
  • Metal or metal-based anodes are highly desirable in aluminium electrowinning cells instead of carbon-based anodes. Many attempts were made to use metallic anodes for aluminium production, however they were never adopted by the aluminium industry for commercial aluminium production because their lifetime must still be increased.
  • a major object of the invention is to provide an anode for aluminium electrowinning which has no carbon so as to eliminate carbon-generated pollution and has a long life.
  • a further object of the invention is to provide an aluminium electrowinning anode material with a surface having a high electrochemical activity for the oxidation of oxygen ions and the formation of bimolecular gaseous oxygen and a low solubility in the electrolyte.
  • Another object of the invention is to provide an anode for the electrowinning of aluminium which is covered with an adherent electrochemically active layer.
  • Yet another object of the invention is to provide an improved anode for the electrowinning of aluminium which is made of readily available material(s).
  • Yet another object of the invention is to provide operating conditions for an aluminium electrowinning cell under which the contamination of the product aluminium is limited.
  • the invention relates to an anode of a cell for the electrowinning of aluminium from alumina dissolved in a fluoride-containing molten electrolyte.
  • the anode comprises a nickel-iron alloy substrate having a nickel metal rich outer portion with an integral nickel-iron oxide containing surface layer which is pervious to electrolyte and adheres to the nickel metal rich outer portion of the nickel-iron alloy substrate.
  • the electrolyte-pervious surface layer in use is electrochemically active for the evolution of oxygen gas.
  • Cermet anodes which have been described in the past in relation to aluminium production have an oxide content which forms the major phase of the anode. Such anodes have an overall electrical conductivity which is higher than that of solid ceramic anodes but insufficient for industrial commercial production. Moreover, the uniformly distributed metallic phase is exposed to dissolution into the electrolyte.
  • anodes predominantly made of metal and protected with a thick oxide outer layer e.g. as disclosed in US Patent 5,510,008 (Sekhar/Liu/Duruz)
  • a thick oxide outer layer e.g. as disclosed in US Patent 5,510,008 (Sekhar/Liu/Duruz)
  • molten electrolyte may penetrate into cracks between the metallic inner part and the oxide layer.
  • the surfaces of the crack would then form a dipole between the metallic inner anode part and the oxide layer, causing electrolytic dissolution of the metallic inner part into the electrolyte contained in the crack and corrosion of the metallic anode part underneath the thick oxide layer.
  • the anode of the present invention provides a solution to this problem. Instead of being covered with a thick protective oxide layer, during use the nickel-iron alloy substrate contacts or virtually contacts molten electrolyte circulating through the electrolyte-pervious surface layer. As opposed to prior art anodes, the electrolyte close to the nickel-iron alloy substrate, typically at a distance of less than 10 micron, is continuously replenished with dissolved alumina. The electrolysis current does not dissolve the anode.
  • the entire electrolysis current passed at the anode surface is used for the electrolysis of alumina by oxidising oxygen-containing ions directly on the active surfaces or by firstly oxidising fluorine-containing ions that subsequently react with oxygen-containing ions, as described in PCT/IB99/01976 (Duruz/de Nora).
  • the overall electrical conductivity of the metal anode according to the present invention is substantially higher than that of prior art anodes covered with a thick oxide protective layer or made of bulk oxide.
  • the metal phase underlying the electrochemically active surface layer of this anode forms a matrix containing a minor amount of metal compound inclusions, in particular oxide inclusion resulting from a pre-oxidation treatment in an oxidising atmosphere, which matrix confers an overall high electrical conductivity to the anode.
  • the electrolyte-pervious electrochemically active surface layer of the invention is usually a very thin one, preferably having a thickness of less than 50, possibly less than 100 micron or at most 200 micron.
  • Such a thin electrolyte-pervious electrochemically active surface layer offers the advantage of limiting the width of possible pores and/or cracks present in the surface layer to a small size, usually below about a tenth of the thickness of the surface layer.
  • the electrochemical potential difference in the molten electrolyte across the pore and/or crack is below the reduction-oxidation potential of any metal oxide of the surface layer present in the molten electrolyte contained in the pore and/or crack. Therefore, such an electrolyte-pervious surface layer cannot be dissolved by electrolysis of its constituents within the pores and/or cracks.
  • the pores and/or cracks should be so small that when the surface layer is polarised, the potential differential through each pore or crack is below the potential for electrolytic dissolution of the oxide of the surface layer.
  • no or substantially no oxide of the surface layer should be able to dissolve electrolytically when the surface layer is polarised.
  • the thinness of the oxide surface layer is such that, when polarised during use, the voltage drop therethrough is below the potential for electrolytic dissolution of the oxide of the surface layer.
  • Another advantage which is derived from a thin electrochemically active and electrolyte-pervious surface layer can be observed when electrolyte contained in pores and/or cracks of the surface layer reaches the nickel metal rich outer portion of the nickel-iron alloy.
  • the thinness of the surface layer permits oxygen evolved on the surface layer to reach the nickel metal rich outer portion, which leads to the formation of a passive layer of nickel oxide on the nickel metal rich outer portion where contacted by molten electrolyte, avoiding the dissolution of nickel cations from the nickel metal rich outer portion into the molten electrolyte.
  • the anode Before use, the anode can have a Ni/Fe atomic ratio below 1 or of at least 1, in particular from 1 to 4.
  • the nickel metal rich outer portion may have a porosity obtainable by oxidation in an oxidising atmosphere before use.
  • This porosity may contain cavities, in particular round or elongated cavities, which are partly or completely filled with iron compounds, in particular oxides resulting from an oxidation treatment in an oxidising atmosphere, and possibly also nickel compounds, such as nickel oxides or iron-nickel oxides, to form inclusions of iron compounds or iron and nickel compounds.
  • the inclusions may be iron-rich nickel-iron oxides, typically containing oxidised iron and oxidised nickel in an Fe/Ni atomic ratio above 2.
  • the nickel metal rich outer portion has a decreasing concentration of iron metal towards the electrochemically active surface layer.
  • the nickel metal rich outer portion, where it reaches the surface layer may comprise nickel metal and iron metal in an Ni/Fe atomic ratio of about 3 or more.
  • the nickel-iron alloy may further comprise a non-porous inner portion which is oxide-free.
  • the electrochemically active surface layer usually comprises iron-rich nickel-iron oxide, such as nickel-ferrite, in particular non-stoichiometric nickel-ferrite.
  • the surface layer may comprise nickel-ferrite having an excess of iron or nickel and/or an oxygen-deficiency.
  • the nickel-iron alloy usually comprises nickel metal and iron metal in a total amount of at least 65 weight%, usually at least 80, 90 or 95 weight%, of the alloy, and further alloying metals in an amount of up to 35 weight%, in particular up to 5, 10 or 20 weight%, of the alloy. Minor amounts of further elements, such as carbon, boron, sulphur, phosphorus or nitrogen, may be present in the nickel-iron alloy, usually in a total amount which does not exceed 2 weight% of the alloy.
  • the nickel-iron alloy can comprise at least one further metal selected from chromium, copper, cobalt, silicon, titanium, tantalum, tungsten, vanadium, zirconium, yttrium, molybdenum, manganese and niobium in a total amount of up to 5 or 10 weight% of the alloy.
  • the nickel-iron alloy may also comprise at least one catalyst selected from iridium, palladium, platinum, rhodium, ruthenium, tin or zinc metals, Mischmetals and their oxides and metals of the Lanthanide series and their oxides as well as mixtures and compounds thereof, in a total amount of up to 5 weight% of the alloy.
  • the nickel-iron alloy may comprise aluminium in an amount less than 20 weight%, in particular less than 10 weight%, preferably from 1 to 5 or even 6 weight% of the alloy.
  • the aluminium may form an intermetallic compound with nickel which is known to be mechanically and chemically well resistant.
  • the anode of the invention may comprise an inner core made of an electronically conductive material, such as metals, alloys, intermetallics, cermets and conductive ceramics, which core is covered with the nickel-iron alloy substrate as a layer.
  • the core may comprise at least one metal selected from copper, chromium, nickel, cobalt, iron, aluminium, hafnium, molybdenum, niobium, silicon, tantalum, tungsten, vanadium, yttrium and zirconium, and combinations and compounds thereof.
  • the core may consist of an alloy comprising 10 to 30 weight% of chromium, 55 to 90 weight% of at least one of nickel, cobalt and/or iron and up to 15 weight% of at least one of aluminium, hafnium, molybdenum, niobium, silicon, tantalum, tungsten, vanadium, yttrium and zirconium.
  • the core is a non-porous nickel rich nickel-iron alloy, having a nickel/iron weight ratio that is close to or higher than the nickel/iron weight ratio of the nickel-iron alloy substrate, for example from 1 to 4 or higher, in particular above 3. Thus, during use, little or no iron diffuses from the inner core.
  • Another aspect of the invention relates to a method of manufacturing an anode as described above.
  • the method comprises providing a nickel-iron alloy substrate and oxidising the nickel-iron alloy substrate to produce the electrolyte-pervious electrochemically active nickel-iron oxide containing surface layer which adheres to the nickel metal rich outer portion.
  • the oxidation of the nickel-iron alloy substrate comprises one or more steps at a temperature of 800° to 1200°C, in particular 1050° to 1150°C, for up to 60 hours in an oxidising atmosphere.
  • the nickel-iron alloy substrate is oxidised in an oxidising atmosphere for a short period of time, such as 0.5 to 5 hours.
  • the oxidising atmosphere may consist of oxygen or a mixture of oxygen and one or more inert gases, such as argon; having an oxygen content of at least 10 molar% of the mixture.
  • the oxidising atmosphere can be air.
  • the nickel-iron alloy substrate may be subjected to a thermal-mechanical treatment for modifying its microstructure before oxidation. Alternatively, it may be cast, before oxidation, with known casting additives.
  • the oxidation of the nickel-iron alloy substrate in an oxidising atmosphere may be followed by a heat treatment in an inert atmosphere at a temperature of 800° to 1200°C for up to 60 hours.
  • oxidation in an oxidising atmosphere is partial, it may be completed by oxidation in-situ at the beginning of electrolysis.
  • the nickel-iron alloy substrate may be formed as a layer on an inner core made of an electronically conductive material, such as a nickel-rich nickel-iron alloy core.
  • Nickel and iron metal may be deposited as such onto the core, or compounds of nickel and iron may be deposited on the core and then reduced, for example one or more layers of Fe(OH) 2 and Ni(OH) 2 are deposited onto the core, e.g. as a colloidal slurry, and reduced in a hydrogen atmosphere.
  • Nickel and iron and/or compounds thereof may be co-deposited onto the inner core or deposited separately in different layers which are then interdiffused, e.g. by heat treatment.
  • This heat treatment may take place in an inert atmosphere, such as argon, if the nickel and iron are applied as metals, or a reducing atmosphere, such as hydrogen, if nickel and iron compounds are applied onto the core.
  • the nickel and iron metals and/or compounds may be deposited by electrolytic or chemical deposition, arc or plasma spraying, painting, dipping or spraying.
  • a further aspect of the invention concerns a cell for the electrowinning of aluminium from alumina dissolved in a fluoride-containing molten electrolyte.
  • the cell according to the invention comprises at least one anode as described above which faces and is spaced from at least one cathode.
  • the invention also relates to a method of producing aluminium in such a cell.
  • the method comprises passing an ionic current in the molten electrolyte between the cathode(s) and the electrochemically active surface layer of the anode(s), thereby evolving at the anode(s) oxygen gas derived from the dissolved alumina and producing aluminium on the cathode(s).
  • the nickel metal rich outer portion of the anode(s) may be further oxidised in-situ by atomic and/or molecular oxygen formed on its electrochemically active surface layer, in particular if the anode comprises a surface which is partly oxide-free when immersed into the molten electrolyte, until the oxidised nickel metal rich outer portion of the anode forms an impervious barrier to oxygen.
  • the method includes substantially saturating the molten electrolyte with alumina and species of at least one major metal, usually iron and/or nickel, present in the electrochemically active surface layer of the anode(s) to inhibit dissolution of the anode(s).
  • the molten electrolyte may be operated at a temperature sufficiently low to limit the solubility of the major metal species thereby limiting the contamination of the product aluminium to an acceptable level.
  • a “major metal” refers to a metal which is present in the surface of the metal-based anode, in an amount of at least 25 atomic% of the total amount of metal present in the surface of the metal based anode.
  • the cell can be operated with the molten electrolyte at a temperature from 730° to 910°C, in particular below 870°C.
  • the electrolyte may contain AlF 3 in such a high concentration that fluorine-containing ions predominantly rather than oxygen ions are oxidised on the electrochemically active surface, however, only oxygen is evolved, the evolved oxygen being derived from the dissolved alumina present near the electrochemically active anode surface.
  • aluminium is produced on an aluminium-wettable cathode, in particular on a drained cathode, for instance as disclosed in US Patent 5,683,559 (de Nora) or in PCT application WO99/02764 (de Nora/Duruz).
  • the nickel of the nickel-iron alloy in particular of the integral oxide containing surface layer, is wholly or predominantly substituted by cobalt.
  • An anode was made by pre-oxidising in air at 1100°C for 1 hour a substrate of a nickel-iron alloy consisting of 60 weight% nickel and 40 weight% iron, to form a very thin oxide surface layer on the alloy.
  • the surface-oxidised anode was cut perpendicularly to the anode operative surface and the resulting section of the anode was subjected to microscopic examination.
  • the anode before use had an outer portion that comprised an electrolyte-pervious, electrochemically active iron-rich nickel-iron oxide surface layer having a thickness of up to 10-20 micron and, underneath, an iron-depleted nickel-iron alloy having a thickness of about 10-15 micron containing generally round cavities filled with iron-rich nickel-iron oxide inclusions and having a diameter of about 2 to 5 micron.
  • the nickel-iron alloy of the outer portion contained about 75 weight% nickel.
  • the nickel-iron alloy had remained substantially unchanged.
  • Example 1 An anode prepared as in Example 1 was tested in an aluminium electrowinning cell containing a molten electrolyte at 870°C consisting essentially of NaF and AlF 3 in a weight ratio NaF/AlF 3 of about 0.7 to 0.8, i.e. an excess of AlF 3 in addition to cryolite of about 26 to 30 weight% of the electrolyte, and approximately 3 weight% alumina.
  • the alumina concentration was maintained at a substantially constant level throughout the test by adding alumina at a rate adjusted to compensate the cathodic aluminium reduction.
  • the test was run at a current density of about 0.6 A/cm 2 , and the electrical potential of the anode remained substantially constant at 4.2 volts throughout the test.
  • the anode was cut perpendicularly to the anode operative surface and the resulting section of the used anode was subjected to microscopic examination, as in Example 1.
  • anode had an electrochemically active surface covered with a discontinuous, non-adherent, macroporous iron oxide external layer of the order of 100 to 500 micron thick, hereinafter called the "excess iron oxide layer".
  • the excess iron oxide layer was pervious to and contained molten electrolyte, indicating that it had been formed during electrolysis.
  • the excess iron oxide layer resulted from the excess of iron contained in the portion of the nickel-iron alloy underlying the electrochemically active surface and which diffuses therethrough.
  • the excess iron oxide layer resulted from an iron migration from inside to outside the anode during the beginning of electrolysis.
  • Such an excess iron oxide layer has no or little electrochemical activity. It slowly diffuses and dissolves into the electrolyte until the portion of the anode underlying the electrochemically active surface reaches an iron content of about 15-20 weight% corresponding to an equilibrium under the operating conditions at which iron ceases to diffuse, and thereafter the iron oxide layer continues to dissolve into the electrolyte.
  • the anode's aforementioned outer portion had been transformed during electrolysis. Its thickness had grown from 10-20 micron to about 300 to 500 micron and the cavities had also grown in size to vermicular form but were only partly filled with iron and nickel compounds. No electrolyte was detected in the cavities and no sign of corrosion appeared throughout the anode.
  • the shape and external dimensions of the anode had remained unchanged after electrolysis which demonstrated stability of this anode structure under the operating conditions in the molten electrolyte.
  • An anode having a generally circular active structure of 210 mm outer diameter was made of three concentric rings spaced from one another by gaps of 6 mm.
  • the rings had a generally triangular cross-section with a base of about 19 mm and were connected to one another and to a central vertical current supply rod by six members extending radially from the vertical rod and equally spaced apart from one another around the vertical rod.
  • the gaps were covered with chimneys for guiding the escape of anodically evolved gas to promote the circulation of electrolyte and enhance the dissolution of alumina in the electrolyte as disclosed in PCT publication WO00/40781 (de Nora).
  • the anode and the chimneys were made from cast nickel-iron alloy containing 50 weight% nickel and 50 weight% iron that was heat treated as in Example 1. The anode was then tested in a laboratory scale cell containing an electrolyte as described in Example 2 except that it contained approximately 4 weight% alumina.
  • the electrolyte was periodically replenished with alumina to maintain the alumina content in the electrolyte close to saturation. Every 100 seconds an amount of about 5 g of fine alumina powder was fed to the electrolyte. The alumina feed was periodically adjusted to the alumina consumption based on the cathode efficiency, which was about 67%.
  • the anode was cut perpendicularly to the anode operative surface and the resulting section of a ring of the active structure was subjected to microscopic examination, as in Example 1.
  • porous outer alloy portion had grown inside the anode ring to a depth of about 7 mm leaving only an inner portion of about 5 mm diameter unchanged, i.e. consisting of a non-porous alloy of 50 weight% nickel and 50 weight% iron.
  • the porous outer portion of the anode had a concentration of nickel varying from 85 to 90 weight% at the anode surface to 70 to 75 weight% nickel close to the non-porous inner portion, the balance being iron.
  • the iron depletion in the openly porous outer portion corresponded about to the accumulation of iron present as oxide on the surface of the anode, which indicated that the iron oxide had not substantially dissolved into the electrolyte during the test.
  • the anode showed no sign of corrosion which demonstrated that the pores and/or cracks in the electrolyte-pervious electrochemically active oxide layer were sufficiently small that, when polarised during use, the voltage drop through the pores and/or cracks was below the potential of electrolytic dissolution of the oxide of the surface layer.

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Claims (45)

  1. Anode d'une cuve pour l'électro-obtention d'aluminium à partir d'alumine dissoute dans un électrolyte en fusion contenant du fluorure, ladite anode comprenant un substrat en alliage nickel-fer ayant une partie externe riche en métal de nickel avec une couche de surface contenant de l'oxyde nickel-fer intégré qui adhère à la partie externe riche en métal de nickel du substrat en alliage nickel-fer et qui est perméable à l'électrolyte par la présence de pores et/ou de criques dans celui-ci, la couche de surface en utilisation étant électrochimiquement active pour le dégagement de gaz oxygène et contenant de l'électrolyte dans lesdits pores et/ou criques qui sont petits de sorte que, quand la couche de surface est polarisée, le différentiel de potentiel par les pores et/ou les criques contenant de l'électrolyte est au-dessous du potentiel pour la dissolution électrolytique de l'oxyde de la couche de surface.
  2. Anode selon la revendication 1, dans laquelle la couche de surface électrochimiquement active a une épaisseur inférieure à 50 micromètres.
  3. Anode selon la revendication 1, dans laquelle la couche de surface électrochimiquement active a une épaisseur inférieure à 100 micromètres.
  4. Anode selon la revendication 1, dans laquelle la couche de surface électrochimiquement active a une épaisseur inférieure à 200 micromètres.
  5. Anode selon une quelconque revendication précédente, qui a un rapport atomique Ni/Fe en dessous de 1 avant utilisation.
  6. Anode selon une quelconque des revendications 1 à 4, qui a un rapport atomique Ni/Fe au-dessus de 1, en particulier de 1 à 4, avant utilisation.
  7. Anode selon une quelconque revendication précédente, dans laquelle la partie externe riche en métal de nickel a une porosité contenant des cavités qui sont partiellement ou complètement remplies de composés de fer et de nickel, ladite porosité pouvant être obtenue par oxydation dans une atmosphère oxydante avant utilisation.
  8. Anode selon une quelconque revendication précédente, dans laquelle la partie externe riche en métal de nickel a une concentration décroissante de métal de fer vers la couche de surface électrochimiquement active.
  9. Anode selon la revendication 8, dans laquelle la partie externe riche en métal de nickel comprend du métal de nickel et du métal de fer dans un rapport atomique Ni/Fe de plus de 3 quand il atteint la couche de surface électrochimiquement active.
  10. Anode selon une quelconque revendication précédente, dans laquelle l'alliage nickel-fer comprend une partie interne non poreuse qui est exempte d'oxyde.
  11. Anode selon une quelconque revendication précédente, dans laquelle la couche de surface électrochimiquement active comprend de l'oxyde nickel-fer riche en fer.
  12. Anode selon la revendication 11, dans laquelle la couche de surface électrochimiquement active comprend du nickel-ferrite.
  13. Anode selon la revendication 12, dans laquelle le nickel-ferrite de la couche de surface électrochimiquement active contient du nickel-ferrite non stoechiométrique ayant un excès de fer ou de nickel, et/ou un manque d'oxygène.
  14. Anode selon une quelconque revendication précédente, dans laquelle l'alliage nickel-fer comprend du métal de nickel et du métal de fer dans une quantité totale d'au moins 65% en poids, en particulier au moins 80% en poids, de préférence au moins 90% en poids de l'alliage.
  15. Anode selon la revendication 14, dans laquelle l'alliage nickel-fer comprend au moins un autre métal choisi à partir du chrome, du cuivre, du cobalt, du silicium, du titane, du tantale, du tungstène, du vanadium, du zirconium, de l'yttrium, du molybdène, du manganèse et du niobium dans une quantité totale de jusqu'à 10% en poids de l'alliage.
  16. Anode selon la revendication 14 ou 15, dans laquelle l'alliage nickel-fer comprend au moins un catalyseur choisi à partir d'iridium, de palladium, de platine, de rhodium, de ruthénium, d'étain ou de zinc comme métaux, de mischmétaux et leurs oxydes et de métaux de la série des lanthanides et leurs oxydes ainsi que des mélanges et composés de ceux-ci, dans une quantité totale de jusqu'à 5% en poids de l'alliage.
  17. Anode selon la revendication 14, 15 ou 16, dans laquelle l'alliage nickel-fer comprend de l'aluminium dans une quantité inférieure à 20% en poids, en particulier inférieure à 10% en poids, de préférence de 1 à 6% en poids de l'alliage.
  18. Anode selon une quelconque revendication précédente, comprenant un noyau réalisé en un matériau électroniquement conducteur qui est recouvert du substrat en alliage nickel-fer.
  19. Anode selon la revendication 18, dans laquelle le noyau est réalisé en métaux, alliages, composés intermétalliques, cermets et céramiques conductrices.
  20. Anode selon la revendication 19, dans laquelle le noyau est un alliage nickel-fer riche en nickel non poreux.
  21. Procédé pour fabriquer une anode selon une quelconque revendication précédente pour une utilisation dans une cuve pour l'électro-obtention d'aluminium, consistant à prévoir un substrat en alliage nickel-fer et à oxyder le substrat en alliage nickel-fer pour produire ladite couche de surface contenant de l'oxyde nickel-fer électrochimiquement active perméable à l'électrolyte qui adhère à la partie externe riche en métal de nickel, l'oxydation du substrat en alliage nickel-fer comprenant une ou plusieurs étapes à une température de 800°C à 1200°C pendant jusqu'à 60 heures dans une atmosphère oxydante.
  22. Procédé selon la revendication 21, consistant à oxyder le substrat en alliage nickel-fer dans une atmosphère oxydante pendant 0,5 à 5 heures.
  23. Procédé selon la revendication 21 ou 22, dans lequel l'atmosphère oxydante se compose d'oxygène ou d'un mélange d'oxygène et d'un ou de plusieurs gaz inertes ayant une teneur en oxygène d'au moins 10% molaire du mélange.
  24. Procédé selon la revendication 21, 22 ou 23, dans lequel l'atmosphère oxydante est de l'air.
  25. Procédé selon une quelconque des revendications 21 à 24, dans lequel l'alliage nickel-fer est oxydé à une température de 1050°C à 1150°C.
  26. Procédé selon une quelconque des revendications 21 à 25, consistant à soumettre le substrat en alliage nickel-fer à un traitement thermique-mécanique pour modifier sa microstructure avant oxydation.
  27. Procédé selon une quelconque des revendications 21 à 26, consistant à couler le substrat en alliage nickel-fer avec des additifs pour fournir une microstructure pour accroítre l'oxydation.
  28. Procédé selon une quelconque des revendications 21 à 27, dans lequel l'oxydation dans l'atmosphère oxydante est suivie par un traitement thermique dans une atmosphère inerte à une température de 800°C à 1200°C pendant jusqu'à 60 heures.
  29. Procédé selon une quelconque des revendications 21 à 28, dans lequel l'oxydation dans l'atmosphère oxydante est partielle et achevée in situ par oxydation au départ de l'électrolyse.
  30. Procédé selon une quelconque des revendications 21 à 29, consistant à former le substrat en alliage nickel-fer sur un noyau.
  31. Procédé selon la revendication 30, consistant à déposer des métaux de nickel et de fer sur le noyau.
  32. Procédé selon la revendication 30, consistant à déposer des composés de nickel et de fer sur le noyau et ensuite à réduire les composés.
  33. Procédé selon la revendication 32, dans lequel les composés de nickel et de fer sont Fe(OH)2 et Ni(OH)2 qui sont réduits dans une atmosphère d'hydrogène.
  34. Procédé selon une quelconque des revendications 30 à 33, consistant à co-déposer du nickel et du fer et/ou des composés de ceux-ci sur le noyau.
  35. Procédé selon une quelconque des revendications 30 à 33, consistant à déposer au moins une couche de fer et/ou d'un composé de fer et au moins une couche de nickel et/ou d'un composé de nickel sur le noyau, et ensuite à mêler intimement les couches.
  36. Procédé selon une quelconque des revendications 30 à 35, consistant à déposer électrolytiquement ou chimiquement au moins l'un du nickel, du fer et des composés de ceux-ci sur le noyau.
  37. Procédé selon une quelconque des revendications 30 à 35, consistant à soumettre à une projection à l'arc ou à une projection au plasma au moins l'un du nickel, du fer et des composés de ceux-ci sur le noyau.
  38. Procédé selon l'une des revendications 30 à 35, consistant à appliquer au moins l'un du nickel, du fer et des composés de ceux-ci par peinture, immersion ou pulvérisation sur le noyau.
  39. Cuve pour l'électro-obtention d'aluminium à partir d'alumine dissoute dans un électrolyte en fusion contenant du fluorure, la cuve comprenant au moins une anode telle que définie dans l'une quelconque des revendications 1 à 20, faisant face à au moins une cathode et espacée de celle-ci.
  40. Procédé pour produire de l'aluminium dans une cuve selon la revendication 39 contenant de l'alumine dissoute dans un électrolyte en fusion, le procédé consistant à faire passer un courant ionique dans l'électrolyte en fusion entre la cathode(s) et la couche de surface électrochimiquement active de l'anode(s), en émettant ainsi au niveau de l'anode(s) du gaz oxygène dérivé de l'alumine dissoute et en produisant de l'aluminium sur la cathode(s).
  41. Procédé selon la revendication 40, consistant de plus à oxyder ladite partie externe riche en métal de nickel d'au moins une anode in situ par oxygène atomique et/ou moléculaire formé sur sa couche de surface électrochimiquement active, en particulier quand l'anode comprend une surface qui est partiellement exempte d'oxyde quand elle est immergée dans l'électrolyte en fusion, jusqu'à ce que la partie externe riche en métal de nickel oxydé de l'anode forme une barrière imperméable à l'oxygène.
  42. Procédé selon la revendication 40 ou 41, consistant sensiblement à saturer de façon permanente et uniforme l'électrolyte en fusion avec l'alumine et une espèce d'au moins un métal principal présent dans la couche de surface électrochimiquement active de l'anode(s) pour inhiber la dissolution de l'anode(s).
  43. Procédé selon la revendication 40, 41 ou 42, dans lequel la cuve fonctionne avec l'électrolyte en fusion à une température suffisamment basse pour limiter la solubilité de ladite espèce de métal principal en limitant ainsi la contamination de l'aluminium produit à un niveau acceptable.
  44. Procédé selon une quelconque des revendications 40 à 43, dans lequel la cuve fonctionne avec l'électrolyte en fusion à une température de 730°C à 910°C.
  45. Procédé selon la revendication 44, dans lequel l'aluminium est produit sur une cathode mouillable par l'aluminium, en particulier une cathode de drainage.
EP00977813A 1999-12-09 2000-12-06 Anodes a base metallique pour cellules d'extraction electrolytique d'aluminium Expired - Lifetime EP1240364B1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
IB9901977 1999-12-09
WOPCT/IB99/01977 1999-12-09
PCT/IB2000/001814 WO2001042534A2 (fr) 1999-12-09 2000-12-06 Anodes a base metallique pour cellules d'extraction electrolytique d'aluminium

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EP1240364A2 EP1240364A2 (fr) 2002-09-18
EP1240364B1 true EP1240364B1 (fr) 2005-03-02

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EP (1) EP1240364B1 (fr)
AT (1) ATE290106T1 (fr)
AU (1) AU1544401A (fr)
CA (1) CA2393426A1 (fr)
DE (1) DE60018464T2 (fr)
ES (1) ES2234697T3 (fr)
NO (1) NO20022714D0 (fr)
WO (1) WO2001042534A2 (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003006716A2 (fr) * 2001-07-13 2003-01-23 Moltech Invent S.A. Structures d'anodes a base d'alliage pour la production d'aluminium
WO2013056363A1 (fr) * 2011-10-20 2013-04-25 Institut National De La Recherche Scientifique Anodes inertes pour l'électrolyse de l'aluminium et leur procédé de production
FR3022917B1 (fr) * 2014-06-26 2016-06-24 Rio Tinto Alcan Int Ltd Materiau d'electrode et son utilisation pour la fabrication d'anode inerte
KR101913757B1 (ko) 2015-04-21 2018-10-31 주식회사 엘지화학 산화 텅스텐의 제조 방법
EP3839084A1 (fr) * 2019-12-20 2021-06-23 David Jarvis Alliage métallique

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4374050A (en) * 1980-11-10 1983-02-15 Aluminum Company Of America Inert electrode compositions
US4582585A (en) * 1982-09-27 1986-04-15 Aluminum Company Of America Inert electrode composition having agent for controlling oxide growth on electrode made therefrom
US4541912A (en) * 1983-12-12 1985-09-17 Great Lakes Carbon Corporation Cermet electrode assembly
AU2428988A (en) * 1987-09-02 1989-03-31 Eltech Systems Corporation Non-consumable anode for molten salt electrolysis
US5284562A (en) * 1992-04-17 1994-02-08 Electrochemical Technology Corp. Non-consumable anode and lining for aluminum electrolytic reduction cell
US5510008A (en) * 1994-10-21 1996-04-23 Sekhar; Jainagesh A. Stable anodes for aluminium production cells
US5865980A (en) * 1997-06-26 1999-02-02 Aluminum Company Of America Electrolysis with a inert electrode containing a ferrite, copper and silver
AU740270B2 (en) * 1998-01-20 2001-11-01 Moltech Invent S.A. Non-carbon metal-based anodes for aluminium production cells

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DE60018464T2 (de) 2005-07-28
NO20022714L (no) 2002-06-07
WO2001042534A2 (fr) 2001-06-14
NO20022714D0 (no) 2002-06-07
ATE290106T1 (de) 2005-03-15
DE60018464D1 (de) 2005-04-07
AU1544401A (en) 2001-06-18
CA2393426A1 (fr) 2001-06-14
ES2234697T3 (es) 2005-07-01
EP1240364A2 (fr) 2002-09-18
WO2001042534A3 (fr) 2002-01-17

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