EP0931182B1 - Anoden mit hoher stabilität für aluminiumproduktionszellen - Google Patents

Anoden mit hoher stabilität für aluminiumproduktionszellen Download PDF

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EP0931182B1
EP0931182B1 EP97942654A EP97942654A EP0931182B1 EP 0931182 B1 EP0931182 B1 EP 0931182B1 EP 97942654 A EP97942654 A EP 97942654A EP 97942654 A EP97942654 A EP 97942654A EP 0931182 B1 EP0931182 B1 EP 0931182B1
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aluminum
elements
iron
nickel
additive element
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French (fr)
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EP0931182A1 (de
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Jainagesh A. Sekhar
Vittorio De Nora
James Jenq Liu
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Moltech Invent SA
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Moltech Invent SA
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/23—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces involving a self-propagating high-temperature synthesis or reaction sintering step
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/047—Making non-ferrous alloys by powder metallurgy comprising intermetallic compounds
    • 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
    • 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
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • C25C7/02—Electrodes; Connections thereof

Definitions

  • This invention relates to cell components, particularly anodes, for use in the electrowinning of aluminum by the electrolysis of alumina in a molten fluoride electrolyte, in particular cryolite.
  • the invention is more particularly concerned with the production of cell components, particularly anodes, of aluminum production cells made of composite materials by the micropyretic reaction of a mixture of reactive powders, which reaction mixture when ignited undergoes a micropyretic reaction to produce a reaction product.
  • US Patent 4,948,676 (Darracq et al) describes a ceramic/metal composite material for use as an anode for aluminum electrowinning particularly when coated with a protective cerium oxyfluoride based coating, comprising mixed oxides of cerium and one or more of aluminum, nickel, iron and copper in the form of a skeleton of interconnected ceramic oxide grains interwoven with a metallic network of an alloy or an intermetallic compound of cerium and one or more of aluminum, nickel, iron and copper.
  • US Patent 4,909,842 discloses the production of dense, finely grained composite materials with ceramic and metallic phases by self-propagating high temperature synthesis (SHS) with the application of mechanical pressure during or immediately after the SHS reaction.
  • SHS high temperature synthesis
  • US Patent 5,217,583 (Sekhar et al) describes the production of ceramic or ceramic-metal electrodes for electrochemical processes, in particular for aluminum electrowinning, by micropyretic reaction of particulate or fibrous reactants with particulate or fibrous fillers and binders.
  • the reactants included aluminum usually with titanium and boron; the binders included copper and aluminum; the fillers included various oxides, nitrides, borides, carbides and silicides.
  • the described composites included copper/aluminum oxide-titanium diboride etc.
  • US Patent 5,316,718 (Sekhar et al) describes an improvement of US Patent 5,217,583 with specific fillers.
  • the described reactants included an aluminum nickel mixture, and the binder could be a metal mixture including aluminum, nickel and up to 5 weight % copper.
  • US Patents 4,374,050 (Ray) and 4,374,761 (Ray) disclose anodes for aluminum electrowinning composed of a family of metal compounds including oxides. It is stated that the anodes could be formed by oxidizing a metal alloy substrate of suitable composition. However, it has been found that oxidized alloys do not produce a stable, protective oxide film but corrode during electrolysis with spalling off of the oxide. US patent 4,620,905 (Tarcy et al) also discloses oxidized alloy anodes.
  • This teaching provided an anode for aluminum production where the problem of poor adherence due partly to thermal mismatch between a metal substrate and an oxide coating formed from the metal components of the substrate was resolved, the metal electrode being covered with an oxide layer which remained stable during electrolysis and protected the substrate from corrosion by the electrolyte.
  • Such an anode for the production aluminum by the electrolysis of alumina in a molten fluoride electrolyte comprises a porous micropyretic reaction product derived from particulate nickel, aluminum and iron, or particulate nickel, aluminum, iron and copper, optionally with small quantities of doping elements such as chromium, manganese, titanium, molybdenum, cobalt, zirconium, niobium, cerium, oxygen, boron and nitrogen included in a quantity of up to 5 wt% in total.
  • doping elements such as chromium, manganese, titanium, molybdenum, cobalt, zirconium, niobium, cerium, oxygen, boron and nitrogen included in a quantity of up to 5 wt% in total.
  • the porous micropyretic reaction product contained metallic and/or intermetallic phases, and a composite oxide surface formed in-situ from the metallic and intermetallic phases contained in the porous micropyretic reaction product, by anodically polarizing the micropyretic reaction product in a molten fluoride electrolyte containing dissolved alumina.
  • the in-situ formed composite oxide surface comprised an iron-rich relatively dense outer portion, and an aluminate-rich relatively porous inner portion.
  • Comparative anodes of similar compositions i.e. similar to those of the anodes of U.S. Patent 5,510,008 and WO 96/12833, Sekhar et al
  • Comparative anodes of similar compositions show poor performance. This is believed to be a result of the mismatch in thermal expansion between the oxide layer and the metallic substrate with the alloy anodes.
  • the differences in thermal expansion coefficients allow cracks to form in the oxide layer, or the complete removal of the oxide layer from the alloy, which induced corrosion of the anode by penetration of the bath materials, leading to short useful lifetimes.
  • porous anodes according to U.S. Patent 5,510,008 and WO 96/12833 (Sekhar et al) accommodate the thermal expansion, leaving the dense protective oxide layer intact.
  • Bath materials such as cryolite which may penetrate the porous metal 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 did not lead to corrosion but remain inert inside the electrochemically inactive inner part of the anode.
  • Patent 5,510,008 and WO96/12833 were not successful, in that such additives were found either not to have an effect of limiting the growth rate of the thickness of the oxide layer, or a thickness limiting effect was achieved but to an inadequate amount and/or this effect would be offset by problems of contamination of the product aluminum.
  • the invention is based on the discovery that the performance of the anodes of U.S. Patent 5,510,008 and WO96/12833 is unexpectably improved by certain additive elements.
  • the invention relates to a cell component, preferably an anode, for the electrowinning of aluminum by the electrolysis of alumina dissolved in a molten fluoride electrolyte, comprising a porous micropyretic reaction product of particulate nickel, aluminum, iron and optionally, copper, and of at least one additive element in an effective amount usually up to 8 wt% of the total, the porous micropyretic reaction product containing metallic and intermetallic phases which preferably form a composite oxide surface layer, more preferably comprising an iron-rich relatively dense outer portion and an aluminate-rich relatively porous inner portion, wherein said layer is formed when the porous micropyretic reaction product is anodically polarized in a molten fluoride electrolyte containing dissolved alumina, or is oxidised by being subjected to contact with oxygen at high temperatures.
  • the product comprises a porous core and the composite oxide surface.
  • the product can be characterized as a "graded" material.
  • the overall performance of the prior art electrodes of U.S. Patent 5,510,008 and WO96/12833 is greatly enhanced by using, as an additive element, at least one element from the group consisting of silicon, tin, zinc, vanadium, indium, hafnium, tungsten, elements from the lanthanide series starting from praesodymium and misch metal.
  • the combustion behavior of the reactant mixture is improved considerably as will be explained in greater detail below.
  • composition of the micropyretic reaction product is important to the formation of a dense composite oxide surface preferably comprising an iron-rich relatively dense outer portion which is associated with an aluminate-rich relatively porous inner portion by diffusion of the metals/oxides during the in-situ production of the oxide surface.
  • the micropyretic reaction product is preferably produced from the particulate nickel, aluminum, iron, copper and the additive element in the amounts 50-90 wt% nickel, 3-20 wt% aluminum, 5-20 wt% iron, 0-15 wt% copper and 0.5-5 wt% of said at least one additive element from the group consisting of silicon, tin, zinc, vanadium, indium, hafnium, tungsten, elements from the lanthanide series starting from praesodymium and misch metal and optionally other additives. More preferably still, the micropyretic reaction product is produced from 60-80 wt% nickel, 3-10 wt% aluminum, 5-20 wt% iron and 5-15 wt% copper, plus 0.5-5 wt% of the selected additive element(s).
  • the ignition temperature T i and the combustion temperature T c are important processing parameters. See, for example, Processing of Composite Materials by the Micropyretic Synthesis Method, M. Fu and J.A. Sekhar, Key Eng. Mat., Trans. Tech Publications, vol. 108-110, pp. 19-44 (1995)). It has bee noted when using the compositions of the present invention that the combustion temperature decreased with the presence of iron, copper and zinc, which do not contribute to the energy developed during the reaction. Contrarily the combustion temperature increased with the presence of nickel, aluminum, silicon or tin, because these elements participate in the micropyretic reaction.
  • Preferred embodiments of the invention include silicon, tin or zinc as additive element in an amount of 0.5 to 3 wt% of the total.
  • Preferred elements from the lanthanide series are praesodymium, neodymium and ytterbium as well as misch metal which is a mixture of cerium, lanthanum, neodymium and other rare-earth metals. These elements are also preferably included as additive element in an amount of 0.5 to 3 wt% of the total.
  • the micropyretic reactions product was tested in the absence of the additive elements for effect of the aluminum content.
  • the resulting composites have good adherence with cerium oxyfluoride coatings when such coatings are used for protection, and the lowest corrosion rate.
  • the composites still have low corrosion, but surface spalling is found after testing.
  • corrosion increases gradually, and above about 20 wt% aluminum the composites have low porosity due to the increase of combustion temperature. It is expected that these effects would continue even with the inclusion of the additive elements of the present invention.
  • micropyretic reaction products were also tested in the absence of the additive elements for effect of iron content. Below 5 wt% iron or no iron, the samples have higher corrosion and a nonconducting layer is found after testing. Above 20 wt% iron, results in surface spalling after oxidation, 15 wt% being a preferred upper limit. It is expected that these effects would continue even with the inclusion of the additive elements.
  • micropyretic reaction products were further tested in the absence of the additive elements for effect of copper content. Below 5 wt% copper down to 0 wt% copper results in anodes with higher corrosion rate but which are nevertheless acceptable, and more than 15 wt%, in particular more than 20 wt% copper, results in surface spalling after oxidation. In the cell components tested as anodes, it was found that the composite oxide layer is depleted in copper, whereas the unoxidized portion of the micropyretic reaction product adjacent to the aluminate rich inner portion of the oxide surface is rich in copper. It is expected that these effects would continue even with addition of the additive elements.
  • the particulate nickel may advantageously have a larger particle size than the particulate aluminum, iron and copper.
  • Large particle size nickel for example up to about 150 micrometers, is preferred.
  • Fine nickel particles smaller than 10 micrometers, tend to lead to very fine NiAl, Ni 3 Al or NiOx particles which may increase corrosion when the finished product is used as anode.
  • Using large nickel particles enhances the formation of aluminates such as NiA10, NiAlFeO or FeA10 phases on the surface, which inhibits corrosion and also promotes a porous structure.
  • good results have also been obtained with nickel particles in the range 10 to 20 micrometers, these small nickel particles leading to a finer and more homogenous porous microstructure.
  • Aluminum particles in the size range 5 to 20 micrometers. Very large aluminum particles (100 mesh) tend to react incompletely. Very fine aluminum particles, below 5 micrometers, tend to have a strong oxidation before the micropyretic reaction, which may result in corrosion when the finished product is used as an anode.
  • the powder mixture may be compacted preferably by uniaxial pressing usually at about 200-250 Mpa, or cold isostatic pressing (CIP), and the micropyretic reaction may be ignited in air or an inert atmosphere such as argon.
  • CIP cold isostatic pressing
  • the thermal explosion mode of micropyretic synthesis is preferred, at about 1000°C. Excellent results have been obtained with combustion in air.
  • the powder mixture is preferably compacted dry, such as by ball milling. Alternatively, liquid binders may be used for compaction.
  • the micropyretic reaction (also called self propagating high temperature synthesis or combustion synthesis), can be initiated by applying local heat to one or more points of the reaction body by a convenient heat source such as an electric arc, electric spark, flame, welding electrode, microwaves or laser to initiate a reaction which propagates through the reaction body along a reaction front which may be self propagating or assisted by a heat source, as in a furnace. Reaction may also be initiated by heating the entire body to initiate reaction throughout the body in a thermal explosion mode.
  • the reaction atmosphere is not critical, and reaction can take place in ambient conditions without the application of pressure.
  • the micropyretic reaction product has a porous structure comprising at least two metallic and/or intermetallic phases.
  • the micropyretic reaction product comprises at least one intermetallic compound from the group consisting of nickel-iron, nickel-aluminum, nickel-copper, aluminum-iron, nickel-aluminum-copper and nickel-aluminum-iron-copper containing intermetallic compounds.
  • the porosity and microstructure of the micropyretic reaction product are important for the in-situ formation of the preferred surface oxide layer since the pores accommodate for thermal expansion, leaving the outer oxide layer intact during electrolysis.
  • the porous micropyretic reaction product may comprise nickel aluminide (Ni 3 Al), in solid solution with copper, and possibly also in solid solution with other metals and oxides, including silicon, tin, zinc and compounds thereof (including oxides), or of the other additive elements, and mixtures.
  • the core of the preferred cell component/anode material comprises a major amount of Ni and Ni 3 Al and minor amounts of NiCu and NiFe in the substrate and a major amount of NiO and a minor amount of NiFe 2 O 4 , ZnO and NiZnFe 2 O 4 (nickel zinc ferrite) in the mixed oxide surface layer. It is believed that the surface of such materials contains non-stoichiometric conductive oxides wherein lattice vacancies are occupied by the metals, providing an outstanding conductivity while retaining the property of ceramic oxides to resist oxidation.
  • the aluminum is depleted from the core of the cell component/anode material, with the Ni 3 Al being replaced by Ni 3 Fe.
  • the aluminum migrates to the surface.
  • Most of the copper is also present in the core as is the iron, because both copper and iron are highly soluble in nickel. It has been observed that Ni 3 Al and Ni 3 Fe are both considerably superior to NiAl and NiFe, respectively, in terms of corrosion resistance and oxidation resistance.
  • the preferred cell components of the present invention have a predominance of Ni 3 Al and Ni 3 Fe versus NiAl and NiFe.
  • the micropyretic reaction product can also be produced from a mixture containing, in addition to said at least one additive element from the group consisting of silicon, tin, zinc, vanadium, indium, hafnium, tungsten, elements from the lanthanide series starting from praesodymium, and misch metal (preferably in an amount of 05. to 3 wt% of the total), an optional additional additive element from the group consisting of chromium, manganese, titanium, molybdenum, cobalt, zirconium, niobium, tantalum, yttrium, cerium, lanthanum, oxygen, boron and nitrogen.
  • an optional additional additive element from the group consisting of chromium, manganese, titanium, molybdenum, cobalt, zirconium, niobium, tantalum, yttrium, cerium, lanthanum, oxygen, boron and nitrogen.
  • additional additive elements are not as effective as silicon, tin, zinc, vanadium, indium, hafnium, tungsten, elements from the lanthanide series starting from praesodymium, and misch metal in reducing the thickness of the oxide layer, they may be included as additional "dopants"in small quantities with favorable effects.
  • the total of the main and the additional additive elements preferably should not exceed 7 wt% of the total.
  • the composite oxide surface usually comprises an iron-rich relatively dense outer portion, and an aluminate-rich relatively porous inner portion which integrate into the porous structure of the substrate. Analysis of some of the specimens has shown that there is present between the iron-rich outer portion and the aluminate-rich inner portion, an aluminum-depleted intermediate portion comprising predominantly oxides of nickel and iron.
  • the outermost iron-rich oxide layer when present, is a homogenous, dense layer usually comprising oxides of aluminum, iron and nickel with predominant quantities of iron, usually mainly nickel ferrite and nickel-zinc ferrite (NiZnFe 2 O 4 ) doped with aluminum (when zinc is the additive element).
  • Nickel-zinc ferrite has been observed to have excellent properties as an anode coating material for aluminum production, even being superior to nickel ferrite.
  • the composite oxide surface comprises nickel oxide, nickel ferrite, zinc oxide and nickel-zinc ferrite.
  • the aluminum-depleted intermediate oxide layer when present, usually comprises oxides of nickel and iron, with nickel highly predominant, for example iron-doped nickel oxide which provides good electrical conductivity of the anode and contributes to good resistance during electrolysis.
  • the innermost aluminate-rich oxide part which is usually present, is slightly more porous that the two preceding oxide layers and is essentially an oxide of aluminum, iron and nickel, with aluminum highly predominant.
  • This aluminate-rich part may be a homogenous phase of aluminum oxide with iron and nickel in solid solution, and usually comprises mainly iron nickel aluminate.
  • the porous metal substrate close to the oxide layer, often comprises nickel in solution with copper and iron and also includes small quantities of aluminum.
  • the substrate is usually largely depleted in aluminum as the aluminum is used to create the preferred aluminate-rich part on it.
  • the substrate is also depleted in iron.
  • the metallic and intermetallic core deeper inside the substrate is also preferably depleted of aluminum as a result of internal oxidation in the open pores of the material and diffusion of the oxidized aluminum to the surface.
  • the metallic and intermetallic core (deep down in the sample), can have a similar composition to the metallic core nearer the oxide surface.
  • Interconnecting pores in the metal substrate may be filled with cryolite by penetration during formation of the oxide layer, but the penetrated material becomes sealed off from the electrolyte by the dense oxide coating and does not lead to corrosion inside the anode.
  • the invention also provides a method of manufacturing a cell component, preferably an anode, for the production of aluminum by the electrolysis of alumina in a molten fluoride electrolyte, comprising reacting a micropyretic reaction mixture of particulate nickel, aluminum, iron and optionally copper, and at least one additive element selected from the group consisting of silicon, tin, zinc, vanadium, indium, hafnium, tungsten, elements from the lanthanide series starting from praesodymium, and misch metal in an amount up to 8 wt% of the total reactants, to produce a porous micropyretic reaction product containing metallic and intermetallic phases, and preferably anodically polarizing the micropyretic reaction product in a molten fluoride electrolyte containing dissolved alumina, or subjecting it to contact with oxidizing gas at high temperatures, to produce, from the metallic and intermetallic phases contained in the porous micropyretic reaction product, an in-situ or ex-sit
  • the electrowinning method comprises providing a starter anode, which is a porous micropyretic reaction product comprising metallic and intermetallic phases produced by reacting a micropyretic reaction mixture of particulate nickel, aluminum, iron and optionally copper, and at least one additive element from the group comprising silicon, tin, zinc, vanadium, indium, hafnium, tungsten, elements from the lanthanide series starting from praesodymium, and misch metal in an amount up to 8 wt% of the total reactants, and anodically polarizing it in a molten fluoride electrolyte containing dissolved alumina, or subjecting it to contact with oxidizing gas at high temperatures, to produce a composite oxide surface usually comprising an iron-rich relatively dense outer portion and an aluminate-rich relatively porous inner portion.
  • Electrolysis is then continued, using the same electrolyte (in which the in-situ oxide layer was formed) or a different molten fluoride electrolyte containing dissolved alumina, to produce aluminum using the in-situ oxidized starter anode.
  • the composite oxide surface would be formed in a cerium-free molten fluoride electrolyte containing alumina, then cerium would be added to deposit a cerium oxyfluoride based protective coating upon the composite oxide layer.
  • the preferred final stage of production (formation of the composite oxide layer on the anode surface) will be performed in-situ in the aluminum production cell during production of aluminum.
  • Yet another aspect of the present invention is a precursor of a cell component of an aluminum production cell which is ignitable to produce by micropyretic reaction, a cell component made of a composite material, said precursor comprising particulate nickel, aluminum, iron and, optionally copper, and at least one additive element selected from the group consisting of silicon, tin, zinc, vanadium, indium, hafnium, tungsten, elements from the lanthanide series starting from praesodymium, and misch metal, said additive element being present in an amount of up to 8 weight percent of the total precursor, possibly with other additives as explained above.
  • a coating may be applied to the preferred in-situ formed oxide layer; a preferred coating being in-situ formed cerium oxyfluoride according to US Patent No. 4,614,569 (Duruz et al).
  • the cerium oxyfluoride may optionally contain additives such as compounds of tantalum, niobium, yttrium, praesodymium and other rare earth elements; this coating being maintained by the addition of cerium and possibly other elements to the molten cryolite-based electrolyte. Production of such a protective coating in-situ leads to dense and homogeneous cerium oxyfluoride.
  • a powder mixture was prepared from 73 wt% (68 atomic %) nickel, 100 mesh ( ⁇ 149 micrometer), 6 wt% (12 atomic %) aluminum, 325 mesh ( ⁇ 42 micrometer), 11 wt% (11 atomic %) iron, 10 micrometers particle size, and 10 wt% (9 atomic %) copper, 5-10 micrometers particle size.
  • the dry mixture i.e. without any liquid fiber
  • the pressed samples were then ignited in a furnace at 900°C or 1050°C to initiate a micropyretic reaction in air.
  • the specimens were then used as anodes in a cryolite-based electrolyte containing 7 wt% alumina and 1 wt% cerium fluoride at 980°C.
  • a typical test for a specimen with an anode surface area of 22.4 cm 2 ran for a first period of 48 hours at a current density of 0.3 A/cm 2 , followed by a second period of 54 hours at a current density of 0.5 A/cm 2 .
  • the cell voltage was from 2.9 to 2.5 Volts
  • the cell voltage was from 3.3 to 4.4 Volts.
  • the anode specimens were removed.
  • the specimens showed no signs of dimensional change, and the metallic substrate of dense appearance was covered by a coarse, dense, uniform and well adhering layer of cerium oxyfluoride.
  • the cerium oxyfluoride coating appeared homogeneous and very dense, with no apparent porosity.
  • the outermost oxide layer was a homogeneous, dense, oxide-only layer devoid of fluoride.
  • This oxide layer comprised oxides of nickel, aluminum and iron with predominant quantities of iron.
  • the quantities of metals present in atomic % were 32% nickel, 21% aluminum, 45% iron and 2% copper. It is believed that this phase comprises nickel ferrite doped with aluminum.
  • the intermediate oxide layer was composed of large grains which interpenetrated with the outermost layer. Analysis showed no detectable fluoride, and the intermediate oxide layer comprised oxides of nickel and iron, with nickel highly predominant. The quantities of metals present in atomic % were 83% nickel, 3% aluminum, 13% iron and 1 % copper. It is believed that this phase is iron-doped nickel oxide which would explain the good electrical conductivity of the cell component/anode and its resistance to dissolution during electrolysis.
  • the oxide layer below the intermediate layer was slightly more porous that the top two oxide layers. Analysis identified it is an oxide of nickel, aluminum and iron with aluminum highly predominant. A small quantity of fluoride was detected in the pores. The quantities of metals present in atomic % were 22.6% nickel, 53.87% aluminum, 21.54% iron and 1.99% copper. It is believed that this phase may be a homogeneous phase of aluminum oxide with iron and nickel in solid solution, forming an aluminate-rich layer such as an iron nickel aluminate.
  • the porous metal substrate in contact with the oxide layer is comprised of nickel with small quantities of copper, iron and aluminum. It is largely depleted in aluminum, as the aluminum is used to create the aluminate layer on top of it.
  • the composition of the porous substrate in atomic % was 77.8% nickel, 5.3% aluminum, 3.5% iron and 13.5% copper.
  • the metallic core deeper inside the substrate is also depleted of aluminum as a result of internal oxidation in the open pores of the material and diffusion of the oxidized aluminum.
  • the composition in atomic % was 77.2% nickel, 1.8% aluminum, 9.7% iron and 11.3% copper.
  • Example 1 The procedure of Example 1 was repeated varying the proportions in the starting mixture and with zirconium, chromium, titanium, yttrium or niobium as an extra component in a total amount up to 5 wt% of the total reactants.
  • the particle size of the chromium was 325 mesh ( ⁇ 425 micrometer).
  • the composition was nickel 73 wt%, aluminum 6 wt%, iron 6 wt%, copper 10 wt% and chromium or other additive up to 5 wt%. Results comparable to those for the samples of Example 1 were obtained.
  • samples prepared according to comparative Examples 1 and 2 i.e. according to U.S. Patent 5,510,008 and WO96/12833 (Sekhar et al), have shown outstanding properties as dimensionally stable anodes or anode substrates for aluminum production in the Hall-Héroult process, i.e. electrolysis of alumina dissolved in molten cryolite at temperatures of about 950°.
  • the anodes also show outstanding long term resistance to oxidation when subjected to oxidation tests in air or oxygen at 950°C.
  • the oxide surface layer was much thinner, i.e. it grew at a much slower rate than that for comparative examples 1 and 2.
  • the added metals, in particular zinc are well tolerated in small quantities as impurities in the product aluminum.
  • the oxidation testing was carried out as follows: Samples prepared according to the preceding Examples were subjected to oxidation testing in a tube furnace at 1000°C or 1150°C in air under static conditions or with a high airflow rate (0.2 1/min), for a time of about 24 hours.
  • zinc is relatively better tolerated as an impurity in aluminum, than the additives of the prior art such as titanium and chromium.
  • zinc is also better tolerated as an impurity than silicon and tin.
  • All of the samples with silicon, tin and zinc additives has a reduced oxide layer thickness compared to the samples without additives.
  • the no-additives samples had a considerably thicker oxide layer thickness (about 5 to 10 times greater). It is believed that the lower growth rates of the samples with the additives of the present invention would allow aluminum production cells including such components as anodes, to be operated at much greater current densities than the traditional current densities of 0.3 to 0.5 A/cm2. It is believed that current densities of up to 8 A/cm2 would be possible.
  • FIGS. 1 and 2 show the Two-Theta X-ray diffraction spectra of two samples, one with a composition Ni(73)Al(6)Cu(10)Fe(11) wt%, the other with a composition Ni(73)Al(6)Cu(10)Fe(11)Zn(3) parts by weight, before and after oxidation.
  • Theta is half the angle between the diffracted X-ray beam and the original X-ray beam direction.
  • a moving X-ray detector records the 2 Theta angles at which the X-ray beams is diffracted, giving a characteristic diffraction pattern as seen in Figs. 1 and 2.
  • a textbook such as The Science and Engineering of Materials , D.R. Askeland, PWS Publishing Company (1994), may be consulted.
  • the primary phases of the metallic/intermetallic substrate are Ni and Ni 3 Al, which indicates that the major reactions during the synthesis process are between Ni and Al particles.
  • Cu and Fe have high solubility in Ni and Ni 3 Al, and exist in solid solution in these phases or form minor amounts of copper and iron compounds such as NiCu and NiFe (not detected by the X-ray diffraction).
  • the mixed oxide layer is the part of the anode which contacted the cryolite alumina electrolyte during electrolytic testing.
  • this layer is primarily made up of NiO and NiFe 2 O 4 , which have low solubility in cryolite.
  • Zn has a high solubility in the Ni and the Ni 3 Al and exists in solid solution or as zinc compounds in small amounts that are not detected by the X-ray diffraction.
  • the mixed oxide layer formed with the zinc-containing specimen is significantly different, with formation of complex mixed oxides.
  • the oxides include NiO, NiFe 2 O 4 , NiZnFe 2 O 4 and ZnO. It is believed that the complex oxides density the mixed oxide layer and enhance the oxidation resistance, especially NiZnFe 2 O 4 .

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Claims (13)

  1. Zellenkomponente zum Elektrogewinnen von Aluminium durch die Elektrolyse von in einem geschmolzenen Fluoridelektrolyten gelöstem Aluminiumoxid, mit:
    einem porösen mikropyretischen Reaktionsprodukt von partikulärem Nickel, Aluminium, Eisen und gegebenenfalls Kupfer, und aus mindestens einem Additivelement ausgewählt aus der Gruppe bestehend aus Silicium, Zinn, Zink, Vanadium, Indium, Hafnium, Tungsten, Elementen der Lanthanserien beginnend mit Präsodymium und Mischmetall, in einer Menge von bis 8 Gew.-% des Gesamtgewichts, wobei das poröse mikropyretische Reaktionsprodukt metallische und intermetallische Phasen enthält, wobei die Additivelemente in Gestalt von Elementpulver, Oxiden der Elemente, anderer Verbindungen der Elemente oder Mischungen davon zugeführt werden.
  2. Zellenkomponente nach Anspruch 1, mit einer Kompositoxidoberfläche, die in situ durch anodisches Polarisieren des mikropyretischen Reaktionsprodukts in einem geschmolzenen Fluoridelektrolyten gebildet wird, der gelöstes Aluminiumoxid enthält, oder durch situ durch Oxidieren der Oberfläche des mikropyretischen Reaktionsproduktes in einem oxidierenden Gas bei hoher Temperatur.
  3. Zellenkomponente nach Anspruch 2, bei der die Kompositoxidoberfläche einen eisenreichen, relativ dichten äußeren Teil und einen aluminiumreichen, relativ porösen inneren Teil umfasst.
  4. Zellenkomponente nach Anspruch 2, die eine Anode ist.
  5. Zellenkomponente nach Anspruch 1, bei der das mikropyretische Reaktionsprodukt hergestellt ist aus partikulärem Nickel, Aluminium, Eisen, Kupfer und dem Additivelement in den Mengen 50 bis 90 Gew.-% Nickel, 3 bis 20 Gew.-% Aluminium, 5 bis 20 Gew.-% Eisen, 0 bis 15 Gew.-% Kupfer und 0,5 bis 5 Gew.-% von mindestens einem Additivelement aus der Gruppe bestehend aus Silicium, Zinn, Zink, Vanadium, Indium, Hafnium, Tungsten, Elementen der Lanthanserien beginnend mit Präsodymium und Mischmetall.
  6. Zellenkomponente nach Anspruch 5, bei der das mikropyretische Reaktionsprodukt hergestellt ist aus 60 bis 80 Gew.-% Nickel, 3 bis 10 Gew.-% Aluminium, 5 bis 20 Gew.-% Eisen, 5 bis 15 Gew.-% Kupfer und 0,5 bis 5 Gew.-% von mindestens einem Additivelement aus der Gruppe bestehend aus Silicium, Zinn, Zink, Vanadium, Indium, Hafnium, Tungsten, Elementen der Lanthanserien beginnend mit Präsodymium und Mischmetall.
  7. Zellenkomponente nach Anspruch 1, hergestellt aus einer Mischung enthaltend mindestens ein Additivelement aus der Gruppe bestehend aus Silicium, Zinn, Zink, Vanadium, Indium, Hafnium, Tungsten, Elementen der Lanthanserien beginnend mit Präsodymium, und Mischmetall, in einer Menge von 0,5 bis 5 Gew.-% des Gesamtgewichts, und mindestens ein weiteres Additivelement aus der Gruppe bestehend aus Chrom, Mangan, Titan, Molybdän, Kobalt, Zirkonium, Niob, Tantal, Yttrium, Cer, Lanthan, Sauerstoff, Bor und Stickstoff, wobei die Menge aller Additive nicht 8 Gew.-% des Gesamtgewichts übersteigt.
  8. Zellenkomponente nach Anspruch 1, hergestellt aus einer Mischung umfassend Silicium als Additivelement in einer Menge von 0,5 bis 5 Gew.-% des Gesamgewichts.
  9. Zellenkomponente nach Anspruch 1, hergestellt aus einer Mischung umfassend Zinn als additives Element in einer Menge von 0,5 bis 5 Gew.-% des Gesamtgewichts.
  10. Zellenkomponente nach Anspruch 1, hergestellt aus einer Mischung umfassend Zink als additives Element in einer Menge von 0,5 bis 5 Gew.-% des Gesamtgewichts.
  11. Verfahren zur Herstellung einer Zellenkomponente zum Elektrogewinnen von Aluminium durch die Elektrolyse von Aluminiumoxid in einem geschmolzenen Fluoridelektrolyten, umfassend:
    Initiieren einer mikropyretischen Reaktion von einer Mischung aus partikulärem Nickel, Aluminium, Eisen, und gegebenenfalls Kupfer und mindestens einem Additivelement ausgewählt aus der Gruppe bestehend aus Silicium, Zinn, Zink, Vanadium, Indium, Hafnium, Tungsten, Elementen der Lanthanserien beginnend mit Präsodymium, und Mischmetall in einer Menge von bis zu 8 Gew.-% der Gesamtreaktionsmischung, um ein poröses mikropyretisches Reaktionsprodukt herzustellen, das metallische und intermetallische Phasen enthält, wobei die Additivelemente in Gestalt von Elementpulver, Oxiden der Elemente, anderen Verbindungen der Elemente oder Mischungen davon zugeführt werden.
  12. Verfahren zum Elektrogewinnen von Aluminium durch die Elektrolyse von Aluminiumoxid in einem geschmolzenen Fluoridelektrolyten, umfassend:
    Bereitstellen einer Starteranode, die ein poröses mikropyretisches Reaktionsprodukt ist, das metallische und intermetallische Phasen umfasst, die durch Reagieren einer mikropyretischen Reaktionsmischung aus partikulärem Nickel, Aluminium, Eisen und gegebenenfalls Kupfer und mindestens einem Additivelement aus der Gruppe bestehend aus Silicium, Zinn, Zink, Vanadium, Indium, Hafnium, Tungsten, Elemente der Lanthanserie beginnend mit Präsodymium, und Mischmetall in einer Menge von bis zu 8 Gew.-% des Gesamtgewichts hergestellt ist, wobei die Additivelemente in Gestalt von Elementpulver, Oxiden der Elemente, anderer Verbindungen der Elemente oder Mischungen davon zugeführt werden;
    Oxidieren der Oberfläche der Starteranode, um aus den metallischen und intermetallischen Phasen, die in dem porösen mikropyretischen Reaktionsprodukt enthalten sind, eine Kompositoxidoberfläche herzustellen, in situ in einem geschmolzenen Fluoridelektrolyten oder durch Exposition gegenüber einem oxidierenden Gas; und
    anodischem Polarisieren der Anode in einem geschmolzenen Fluoridelektrolyten, der gelöstes Aluminiumoxid enthält, um Aluminium in einer Aluminiumproduktionszelle herzustellen.
  13. Vorläufer einer Zellenkomponente einer Aluminiumproduktionszelle, der entzündlich ist, um durch eine mikropyretische Reaktion die Zellenkomponente herzustellen, wobei der Vorläufer aus einem Kompositmaterial hergestellt ist, das partikuläres Nickel, Aluminium, Eisen und gegebenenfalls Kupfer und mindestens ein Additivelement ausgewählt aus der Gruppe bestehend aus Silicium, Zinn, Zink, Vanadium, Indium, Hafnium, Tungsten, Elementen aus der Lanthanserien beginnend mit Präsodymium und Mischmetall umfasst, wobei das Additivelement in einer Menge bis 8 Gew.-% des gesamten Vorläufers vorhanden ist, wobei die Elemente in Gestalt von Elementpulver, Oxiden der Additivelemente, andere Verbindungen der Elemente oder Mischungen davon zugeführt werden.
EP97942654A 1996-09-23 1997-09-23 Anoden mit hoher stabilität für aluminiumproduktionszellen Expired - Lifetime EP0931182B1 (de)

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PCT/US1997/016865 WO1998012363A1 (en) 1996-09-23 1997-09-23 Ultrastable anodes for aluminum production cells

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003078695A2 (en) * 2002-03-15 2003-09-25 Moltech Invent S.A. Surface oxidised nickel-iron metal anodes for aluminium production

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6423195B1 (en) * 1997-06-26 2002-07-23 Alcoa Inc. Inert anode containing oxides of nickel, iron and zinc useful for the electrolytic production of metals
AU1404100A (en) * 1999-12-09 2001-06-18 Moltech Invent S.A. Aluminium electrowinning cells operating with metal-based anodes
IN2015DN00217A (de) * 2012-06-11 2015-06-12 Inner Mongolia United Ind Co Ltd
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
CN115849419B (zh) * 2022-11-22 2024-03-29 贵州大学 一种载氟氧化铝的生产方法及生产的载氟氧化铝的应用

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WO1994024321A1 (en) * 1993-04-19 1994-10-27 Moltech Invent S.A. Micropyretically-produced components of aluminium production cells
US5510008A (en) * 1994-10-21 1996-04-23 Sekhar; Jainagesh A. Stable anodes for aluminium production cells

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003078695A2 (en) * 2002-03-15 2003-09-25 Moltech Invent S.A. Surface oxidised nickel-iron metal anodes for aluminium production
WO2003078695A3 (en) * 2002-03-15 2003-11-27 Moltech Invent Sa Surface oxidised nickel-iron metal anodes for aluminium production

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DE69708903T2 (de) 2002-06-27

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