EP1601820B1 - Method for the manufacture of an inert anode for the production of aluminium by means of fusion electrolysis - Google Patents

Method for the manufacture of an inert anode for the production of aluminium by means of fusion electrolysis Download PDF

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EP1601820B1
EP1601820B1 EP04718991A EP04718991A EP1601820B1 EP 1601820 B1 EP1601820 B1 EP 1601820B1 EP 04718991 A EP04718991 A EP 04718991A EP 04718991 A EP04718991 A EP 04718991A EP 1601820 B1 EP1601820 B1 EP 1601820B1
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Prior art keywords
process according
nickel
weight
phase
proportion
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German (de)
French (fr)
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EP1601820A2 (en
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Véronique LAURENT
Armand Gabriel
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Rio Tinto France SAS
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Aluminium Pechiney 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

  • the invention relates to the production of aluminum by igneous electrolysis. It relates more particularly to the anodes used for this production and the manufacturing processes that make it possible to obtain them.
  • Aluminum metal is produced industrially by igneous electrolysis, namely by electrolysis of alumina in solution in a bath based on molten cryolite, called an electrolyte bath, in particular according to the well-known Hall-Héroult process.
  • the electrolyte bath is contained in tanks, called “electrolysis cells”, comprising a steel box, which is coated internally with refractory and / or insulating materials, and a cathode assembly located at the bottom of the tank. Anodes are partially immersed in the electrolyte bath.
  • electrolysis cell normally designates the assembly comprising an electrolytic cell and one or more anodes.
  • the electrolysis current which circulates in the electrolyte bath and the liquid aluminum sheet through the anodes and cathode elements, operates the aluminum reduction reactions and also allows the bath to be maintained.
  • electrolyte at a temperature typically of the order of 950 ° C by Joule effect.
  • the electrolysis cell is regularly supplied with alumina so as to compensate for the consumption of alumina produced by the electrolysis reactions.
  • anodes are made of carbon material and are consumed by the aluminum reduction reactions.
  • the typical life of an anode made of carbonaceous material is 2 to 3 weeks.
  • inert anodes The environmental constraints and costs associated with the manufacture and use of carbon anodes have, for many decades, led aluminum producers to look for anodes made of non-consumable materials, called “inert anodes”.
  • inert anodes Several materials have been proposed, among which include composite materials containing a phase called “ceramic” and a metallic phase. These composite materials are known under the name "cermet”.
  • cermet materials have been the subject of many studies, such as cermet materials whose ceramic phase contains a mixed oxide of iron and nickel. These studies have particularly focused on cermet materials whose ceramic phase contains a mixed phase of nickel oxide (NiO) and nickel ferrite (NiFe 2 O 4 ) and whose metal phase contains, for example, iron, nickel nickel or copper. Subsequently, these cermets are referred to as "NiO-NiFe cermets 2 O 4 -M", where M denotes the metallic phase.
  • NiO-NiFe 2 O 4 -M cermets are typically obtained by a process comprising the preparation of a mixture of metal powders and powders of one or more iron and nickel oxides, a compression of the mixture so as to forming a shaped green body and sintering the green body at a temperature between 900 and 1500 ° C.
  • the initial iron oxide and nickel powders are typically a precalcined mixture of nickel oxide (NiO) and iron oxide (typically Fe 2 O 3 or Fe 3 O 4 ).
  • the US patent US 4,871,438 in the name of Battelle Memorial Institute, describes a manufacturing process in which the initial oxide powder is a NiO-NiFe 2 O 4 powder and the initial metal powder consists of a mixture of 10 to 30% by weight of copper powder and 2 to 4% by weight of nickel.
  • the mass ratio between NiO and NiFe 2 O 4 is between 2: 3 ( ⁇ 0.67) and 3: 2 ( ⁇ 1.5).
  • Copper and nickel form, during sintering, an alloy whose melting temperature is higher than the sintering temperature, which makes it possible to avoid the bleeding of the metal phase ("bleed out" in English) and thus to obtain a final amount of metal phase greater than 17% by weight.
  • the initial mixture does not include an organic binder.
  • the sintering is carried out in an argon or nitrogen atmosphere containing from 100 to 500 ppm oxygen.
  • the US patent US 5,794,112 on behalf of Aluminum Company of America, discloses a method of making a cermet in which the initial mixture contains a metal powder of copper and / or silver and between 2 and 10 parts by weight of a binder organic and in which the sintering is carried out under a controlled atmosphere of argon containing between 5 and 3000 ppm of oxygen.
  • the invention relates to a process for producing an inert cermet anode as described in claim 1, said cermet being designated by the formula "NiO-NiFe 2 O 4 -M” and comprising a metal phase M including copper and nickel, and a ceramic phase C, said mixed, comprising at least two distinct phases, namely a N phase called “nickel monoxide” and a so-called S phase "nickel spinel".
  • Nickel monoxide phase N typically corresponds to the formula NiO, which can be non-stoichiometric and which may optionally include elements other than nickel, such as iron.
  • the nickel S spinel phase typically corresponds to the NiFe 2 O 4 formula, which can be non-stoichiometric and which may optionally include elements other than nickel and iron.
  • the applicant has had the idea of dissociating the physico-chemical functions filled by the binder and the precursor of the metal phase.
  • she noted that was generally sufficient to use a small amount of organic binder to ensure the holding of the workpiece at the beginning of sintering (that is to say to substantially reduce, or even prevent its deformation) and that the chemical reducing role of said binder could be provided by the addition of metallic nickel in the precursor of the metal phase, which is preferably formed of metal powders.
  • the fact of dissociating the two functions - mechanical behavior of the part and control of the composition of the metallic phase - makes it possible to reduce the quantity of binder and consequently, to reduce the emissions of toxic volatile materials with low oxygen supply, to reduce the duration of debinding and to limit the risks of cracking and porosity production associated with the elimination of the binder in the gas phase and the volatile decomposition products of the binder in the large parts.
  • Adjusting the composition of the metal phase of the sintered material by the addition of nickel makes it possible not only to avoid the exudation of the metal phase during sintering, but also to better control the local chemistry of the ceramic and metallic phases. .
  • the adjustment of the composition of the metal phase according to the invention also makes it possible to ensure a greater homogeneity of the microstructure of the cermet of large parts.
  • Sintering causes the migration of a part of the metallic elements between the different phases.
  • nickel oxide is enriched in iron
  • nickel ferrite becomes non-stoichiometric
  • the metal phase is enriched in nickel and possibly iron, generally in smaller proportions. Consequently, the cermet resulting from the sintering can be more precisely described by the formula Ni 1 -x Fe x O 1 ⁇ ⁇ -Ni y Fe 3 -y O 4 ⁇ ⁇ -M ', where M' is an alloy including the metal M initial, iron and nickel (MFeNi).
  • the phases NiO (and more generally Ni 1 -x Fe x O) and NiFe 2 O 4 (and more generally Ni y Fe 3 -y O 4 ) will be, by the followed by the terms “monoxide phase” and “spinel phase” respectively.
  • the cermet will simply be designated by the formula "NiO-NiFe 2 O 4 -M", where NiO denotes the monoxide phase (N), NiFe 2 O 4 designates the spinel phase (S), and M the metal phase.
  • the inert anodes according to the invention are intended for the production of aluminum by igneous electrolysis. They may optionally be assembled to form anode assemblies comprising a plurality of individual anodes, such as clusters.
  • the figure 1 represents a preferred embodiment of the manufacturing method of the invention.
  • the Figure 2A is a micrograph of a typical cermet obtained by the manufacturing method of the invention.
  • the Figure 2B is a schematic reproduction of the micrograph of the Figure 2A .
  • the figure 3 is a NiO / NiFe 2 O 4 / M ternary diagram showing the preferred domains of the initial composition in a preferred embodiment of the invention.
  • the figure 4 is a truncated Ni / Cu / Oxide ternary diagram showing the preferred domains of the initial composition in a preferred embodiment of the invention.
  • the metal powder containing copper and nickel is typically a mixture of a metallic copper powder and a nickel metal powder. It is also possible according to the invention to use a metal powder comprising, in all or part, an alloy of copper and nickel. Preferably, at least 95% by weight of the grains of said metal powder have a size of between 3 and 10 ⁇ m.
  • the proportion of metal powder in the initial mixture is preferably greater than 15% by weight, and more preferably greater than 20% by weight. This proportion is preferably less than 35% by weight. It is typically between 15% and 30% by weight, and more typically between 20% and 25% by weight. These preferred proportions are represented in the ternary diagram of the figure 3 in the case where the precursor of said N and S spinel phases consists of nickel oxide NiO and nickel ferrite NiFe 2 O 4 .
  • the proportion of nickel in the metal powder of the precursor of the metal phase is preferably greater than or equal to 3% by weight, more preferably between 3 and 30% by weight, and typically between 5 and 25% by weight.
  • These preferred proportions are represented in the ternary diagram of the figure 4 in the case where the precursor of the metal phase consists of nickel and copper.
  • the preferred domains of the proportions of Ni and Cu are expressed in terms of Ni / Cu ratio (for example, the ratio 3/97 corresponds to 3% by weight Ni in the metal powder).
  • oxides denotes all the constituents of the precursor of the N-monoxide and S-spinel phases; the proportions of M given in this diagram correspond to the 100% difference with respect to the total proportion of the oxides.
  • the initial mixture may optionally further comprise at least one element capable of limiting the oxidation of the metal phase of the cermet, such as silver.
  • This anti-oxidation element is typically added in powder form. It can optionally be added to the initial metal powder.
  • Said anti-oxidation element may optionally be in an oxidized form, such as in an oxide (for example Ag 2 O), which will be reduced during sintering.
  • the anti-oxidation elements, in metallic or oxidized form, may be added at any stage of the preparation of the initial mixture.
  • the proportion of organic binder in the initial mixture is preferably between 0.5 and 1.5% by weight. Said binder is preferably capable of ensuring a green holding of the shaped part. It is not necessary according to the invention; to use an organic binder having chemical reducing properties because the function of reducing the oxidized phases is essentially provided by the metal powder (or mixture of metal powders) used in the initial mixture.
  • Said binder is typically APV (polyvinyl alcohol), but can be any known organic or organometallic binder, such as acrylic polymers, polyglycols (such as polyethylene glycol or PEG), polyvinyl acetates, polyisobutylenes, polycarbonates, polystyrenes, polyacrylates or stearates (such as stearic acid or zinc stearate).
  • APV polyvinyl alcohol
  • acrylic polymers such as polyethylene glycol or PEG
  • polyvinyl acetates such as polyethylene glycol or PEG
  • polyisobutylenes such as polycarbonates
  • polystyrenes such as polyacrylates or stearates (such as stearic acid or zinc stearate).
  • the precursor of the monoxide and spinel phases is typically a mixture of oxides or organometallic compounds capable of forming said phases during sintering. These oxides or compounds may optionally be added separately to the initial mixture, but it is advantageous to mix them together before adding them to the initial mixture.
  • the oxides and / or compounds of the initial mixture, in particular the precursor of the monoxide and spinel phases, are preferably in the form of powders. More preferably, at least 95% by weight of the grains of these powders have a size between 5 and 10 microns.
  • the precursor of the monoxide and spinel phases typically comprises a mixture of oxides comprising a nickel oxide (typically NiO) and a nickel ferrite (typically NiFe 2 O 4 ).
  • This mixture of oxides can be obtained in different ways. For example, it can be formed by mixing a nickel oxide powder (NiO) and a nickel ferrite powder (NiFe 2 O 4 ). It can also be obtained by calcining a mixture of a nickel oxide powder and an iron oxide powder (such as Fe 2 O 3 or Fe 3 O 4 ).
  • Said mixture of oxides is advantageously obtained by pyrolysis of iron and nickel compounds, which makes it possible to obtain an intimate mixture of the initial oxides and to avoid the impurities which are frequently found in the industrial iron and nickel oxides.
  • a process typically comprises the co-precipitation of salts in aqueous solution, a high temperature spraying of salts, grinding and calcination or champing at a sufficient temperature, typically above 900 ° C.
  • the proportion of nickel ferrite (NiFe 2 O 4 ) in the initial mixture is typically between 50 and 85% by weight, and more preferably between 60 and 85% by weight. In order to obtain a satisfactory densification of the cermet, the proportion of nickel oxide in the initial mixture is typically between 0.1% by weight and 25% by weight.
  • the ratio between the mass proportion of nickel oxide and the mass proportion of nickel ferrite (typically NiO / NiFe 2 O 4 ) is between 0.2 / 99.8 and 30/70, and preferably 0.2 / 99.8 and 30/70. 99.8 and 20/80.
  • the applicant has found that it is important to precisely adjust the different proportions to obtain a final product having the desired properties for use as an anode for the production of aluminum by electrolysis.
  • it noted the importance of the initial adjustment of the relative proportions of total iron and total nickel (ie all phases combined) and the relative proportions of nickel oxide and ferrite. nickel for obtaining a final cermet having the desired properties.
  • the proportions of the precursors of the monoxide, spinel and metal phases for example, the proportions of nickel oxide, nickel ferrite and metal
  • the sintering temperature and the oxygen content of the The sintering atmosphere is advantageously adjusted so as to obtain the desired atomic ratio between iron and nickel (Fe / Ni) in the spinel phase of the cermet.
  • This ratio is preferably greater than or equal to 2.4, and more preferably greater than or equal to 2.8.
  • the initial mixture i.e. the mixture to be shaped and sintered to obtain a cermet piece, typically comprises water and a dispersant to facilitate the mixing of the constituents and the shaping of the green parts.
  • the dispersant is preferably capable of not reacting chemically with the copper of the precursor of the metal phase.
  • the initial mixture is preferably dried before the shaping operation in order to remove the water contained therein. This drying is typically carried out by spray drying.
  • the shaping operation of the green part is typically carried out by cold isostatic pressing, that is to say by pressing at a temperature capable of preventing excessive evaporation or decomposition of the organic binder.
  • the cold pressing temperature is typically less than 200 ° C. Pressing pressures are typically between 100 and 200 MPa.
  • the sintering operation of the green part is typically performed in a controlled atmosphere containing at least one inert gas and oxygen .
  • the inert gas of the controlled atmosphere used during sintering is typically argon.
  • Said controlled atmosphere preferably comprises between 10 and 200 ppm of oxygen.
  • a minimum oxygen content is preferable in order to avoid the reduction of the oxides of the mixture.
  • a maximum content is advantageous because it avoids the oxidation of the metal powder or powders.
  • the sintering temperature is preferably between 1150 and 1400 ° C and more preferably between 1300 and 1400 ° C. It is typically 1350 ° C.
  • the holding time at the sintering temperature is not critical in the process of the invention. This holding time is typically about two hours in order to ensure the homogeneity of the sintering.
  • the process advantageously comprises a slow cooling step, at a cooling rate typically between -10 ° and -100 ° / hour, between the sintering temperature and an intermediate temperature between about 900 and about 1000 ° C; slow cooling, at the beginning of the cooling step, makes it possible to increase the electrical conductivity of the anode.
  • the proportion of the metal phase of the final cermet is preferably greater than 15% by weight, more preferably between 15 and 30% by weight, and typically between 15 and 25% by weight.
  • the proportion of nickel in the metal phase is preferably greater than or equal to 3% by weight, preferably between 3 and 30% by weight, and more preferably between 5 and 25% by weight, so as to increase the resistance to metal phase oxidation when using the cermet in a molten salt electrolysis process.
  • the proportion of spinel phase in the final cermet is preferably between 30 and 90% by weight, and typically between 40 and 90% by weight.
  • the spinel phase is preferably non-stoichiometric in order to increase the electrical conductivity.
  • the atomic ratio between iron and nickel (Fe / Ni) in the spinel phase is preferably greater than or equal to 2.4, and more preferably greater than or equal to 2.8.
  • the spinel phase may optionally comprise at least one substitution element capable of increasing its electrical conductivity, such as a tetravalent element (Ti, Zr, etc.).
  • a substitution element capable of increasing its electrical conductivity such as a tetravalent element (Ti, Zr, etc.).
  • the proportion of monoxide phase in the final cermet is preferably less than 40% by weight, in order to obtain sufficient resistance of the cermet to electrochemical corrosion.
  • the cermet obtained by the process of the invention comprises a developed spinel phase (S) which surrounds the metal phase islands (M) and forms a percolation network.
  • the monoxide phase (N) is discontinuous.
  • the Applicant hypothesizes that the high conductivity of the cermet comes largely from the percolation network of the spinel phase in close contact with the metal phase. It also assumes that the percolating character of the spinel phase can only be obtained for sufficient levels of Ni in the metal phase, typically greater than 5% by weight.
  • the porosity of the final cermet is typically less than or equal to 5%. Its electrical conductivity at a temperature between 900 ° C. and 1050 ° C. is preferably greater than 50 ⁇ -1 ⁇ cm -1 , and more preferably greater than 100 ⁇ -1 ⁇ cm -1 .
  • the process according to the invention is advantageously used for the production of inert anodes intended for the production of aluminum by igneous electrolysis.
  • the invention also relates to the use of inert anodes or inert anode assemblies obtained by the manufacturing method according to the invention for the production of aluminum by igneous electrolysis.
  • the invention also relates to an igneous electrolysis process for producing aluminum using the use of at least one inert anode produced by the manufacturing method according to the invention.
  • the subject of the invention is also an electrolysis cell intended for the production of aluminum by igneous electrolysis comprising at least one inert anode produced by the manufacturing method according to the invention.
  • cermet anodes have been prepared according to the prior art from mixtures of powders of Cu, NiFe 2 O 4 and NiO having the following proportions (by weight): 17% Cu, 61% NiFe 2 O 4 , 22 % NiO.
  • the mixture was bound by 5% by weight of APV in aqueous solution and shaped by cold isostatic pressing.
  • the green anodes were sintered at the maximum temperature of 1350 ° C under a controlled atmosphere (residual oxygen content between 10 and 100 ppm).
  • the density of sintered anodes was 6.10 g / cm 3 , a residual porosity of 2.84%.
  • the sintered material consisted of 28% by weight of metal phase containing 32% by weight of Ni, the proportions of spinel phase and monoxide phase being respectively 45.2% and 26.7% by weight.
  • the electrical conductivity of these anodes at 1000 ° C was about 77 ⁇ -1 .cm -1 .
  • cermet anodes have been prepared according to the invention from mixtures of powders of Cu, Ni, NiFe 2 O 4 and NiO having the following proportions (by weight): 16% Cu, 5% Ni, 57% NiFe 2 O 4 and 22% NiO.
  • the mixture was bound by 1% by weight of APV in aqueous solution and shaped by cold isostatic pressing.
  • the green anodes were sintered at the maximum temperature of 1350 ° C. under a controlled atmosphere (residual oxygen content between 10 and 100 ppm).
  • the density of the sintered anodes was 6.14, which is a residual porosity of 2%.
  • the sintered material consisted of 24% by weight of metal phase containing 28.5% by weight of Ni, the proportions of spinel phase ferrite and monoxide phase being respectively 40% and 36% by weight.
  • the electrical conductivity of these anodes at 1000 ° C was about 48 ⁇ -1 .cm -1 .
  • cermet anodes have been prepared according to the invention from mixtures of powders of Cu, Ni, NiFe 2 O 4 and NiO having the following proportions (by weight): 19% Cu, 6.4% Ni, 60% NiFe 2 O 4 and 14.6% NiO.
  • the mixture was bound by 1% by weight of APV in aqueous solution and shaped by cold isostatic pressing.
  • the green anodes were sintered at the maximum temperature of 1350 ° C. under a controlled atmosphere (residual oxygen content between 10 and 100 ppm).
  • the density of sintered anodes was 6.17, a residual porosity of 1.95%.
  • the sintered material consisted of 30.7% by weight of metal phase containing 32% by weight of Ni, the proportions of the spinel phase and the monoxide phase being respectively 41.6% and 27.7% by weight.
  • the electrical conductivity of these anodes at 1000 ° C was about 103 ⁇ -1 .cm -1 .
  • cermet anodes have been developed from mixtures of powders of Cu, Ni, NiFe 2 O 4 and NiO having the following proportions (by weight): 21% Cu, 4% Ni, 30% NiFe 2 O 4 , 45% NiO.
  • the mixture was bound with 1% by weight of APV in aqueous solution.
  • the green anodes were sintered at the maximum temperature of 1200 ° C. under a controlled atmosphere (residual oxygen content between 10 and 100 ppm).
  • the density of sintered anodes was 6.49, a residual porosity of 3.57%.
  • the sintered material consisted of 27.3% by weight of metal phase containing 24.8% by weight of Ni, the proportions of spinel phase and monoxide phase being respectively 21.7% and 51% by weight.
  • the electrical conductivity of these anodes at 1000 ° C was about 139 ⁇ -1 .cm -1 .
  • the corrosion rates measured are given in Table I.
  • the "number of tests” column corresponds to the number of anodes tested, an anode being tested at each test.
  • the column “Fe / Ni ratio” corresponds to the Fe / Ni atomic ratio in the spinel phase S measured by X-rays (lots 1, 3 and 4) or by microprobe (batch 2).

Description

Domaine de l'inventionField of the invention

L'invention concerne la production d'aluminium par électrolyse ignée. Elle concerne plus particulièrement les anodes utilisées pour cette production et les procédés de fabrication qui permettent de les obtenir.The invention relates to the production of aluminum by igneous electrolysis. It relates more particularly to the anodes used for this production and the manufacturing processes that make it possible to obtain them.

Etat de la techniqueState of the art

L'aluminium métal est produit industriellement par électrolyse ignée, à savoir par électrolyse de l'alumine en solution dans un bain à base de cryolithe fondue, appelé bain d'électrolyte, notamment selon le procédé bien connu de Hall-Héroult. Le bain d'électrolyte est contenu dans des cuves, dites « cuves d'électrolyse », comprenant un caisson en acier, qui est revêtu intérieurement de matériaux réfractaires et/ou isolants, et un ensemble cathodique situé au fond de la cuve. Des anodes sont partiellement immergées dans le bain d'électrolyte. L'expression « cellule d'électrolyse » désigne normalement l'ensemble comprenant une cuve d'électrolyse et une ou plusieurs anodes.Aluminum metal is produced industrially by igneous electrolysis, namely by electrolysis of alumina in solution in a bath based on molten cryolite, called an electrolyte bath, in particular according to the well-known Hall-Héroult process. The electrolyte bath is contained in tanks, called "electrolysis cells", comprising a steel box, which is coated internally with refractory and / or insulating materials, and a cathode assembly located at the bottom of the tank. Anodes are partially immersed in the electrolyte bath. The expression "electrolysis cell" normally designates the assembly comprising an electrolytic cell and one or more anodes.

Le courant d'électrolyse, qui circule dans le bain d'électrolyte et la nappe d'aluminium liquides par l'intermédiaire des anodes et des éléments cathodiques, opère les réactions de réduction de l'aluminium et permet également de maintenir le bain d'électrolyte à une température typiquement de l'ordre de 950 °C par effet Joule. La cellule d'électrolyse est régulièrement alimentée en alumine de manière à compenser la consommation en alumine produite par les réactions d'électrolyse.The electrolysis current, which circulates in the electrolyte bath and the liquid aluminum sheet through the anodes and cathode elements, operates the aluminum reduction reactions and also allows the bath to be maintained. electrolyte at a temperature typically of the order of 950 ° C by Joule effect. The electrolysis cell is regularly supplied with alumina so as to compensate for the consumption of alumina produced by the electrolysis reactions.

Dans la technologie standard, les anodes sont en matériau carboné et sont consommées par les réactions de réduction de l'aluminium. La durée de vie typique d'une anode en matériau carboné est de 2 à 3 semaines.In standard technology, the anodes are made of carbon material and are consumed by the aluminum reduction reactions. The typical life of an anode made of carbonaceous material is 2 to 3 weeks.

Les contraintes environnementales et les coûts associés à la fabrication et à l'utilisation des anodes en matériau carboné ont, depuis de nombreuses décennies, conduit les producteurs d'aluminium à rechercher des anodes en matériaux non-consommables, dites « anodes inertes ». Plusieurs matériaux ont été proposés, parmi lesquels figurent notamment les matériaux composites contenant une phase dite "céramique" et une phase métallique. Ces matériaux composites sont connus sous la dénomination « cermet ».The environmental constraints and costs associated with the manufacture and use of carbon anodes have, for many decades, led aluminum producers to look for anodes made of non-consumable materials, called "inert anodes". Several materials have been proposed, among which include composite materials containing a phase called "ceramic" and a metallic phase. These composite materials are known under the name "cermet".

Certains matériaux cermet ont fait l'objet de nombreuses études, tels que les matériaux cermet dont la phase céramique contient un oxyde mixte de fer et de nickel. Ces études ont particulièrement porté sur les matériaux cermet dont la phase céramique contient une phase mixte d'oxyde de nickel (NiO) et de ferrite de nickel (NiFe2O4) et dont la phase métallique contient, par exemple, du fer, du nickel ou du cuivre. Par la suite, ces cermets sont dénommés « cermets NiO-NiFe2O4-M », où M désigne la phase métallique.Certain cermet materials have been the subject of many studies, such as cermet materials whose ceramic phase contains a mixed oxide of iron and nickel. These studies have particularly focused on cermet materials whose ceramic phase contains a mixed phase of nickel oxide (NiO) and nickel ferrite (NiFe 2 O 4 ) and whose metal phase contains, for example, iron, nickel nickel or copper. Subsequently, these cermets are referred to as "NiO-NiFe cermets 2 O 4 -M", where M denotes the metallic phase.

Tel que décrit, par exemple, dans les brevets américains US 4 455 211 , US 4 454 015 et US 4 582 585 , les cermets NiO-NiFe2O4-M sont typiquement obtenus par un procédé comprenant la préparation d'un mélange de poudres de métal et de poudres d'un ou plusieurs oxydes de fer et de nickel, une compression du mélange de manière à former un corps cru de forme déterminée et le frittage du corps cru à une température comprise entre 900 et 1500 °C. Les poudres d'oxyde de fer et de nickel initiales sont typiquement un mélange précalciné d'oxyde nickel (NiO) et d'oxyde de fer (typiquement Fe2O3 ou Fe3O4).As described, for example, in US patents US 4,455,211 , US 4,454,015 and US 4,582,585 , NiO-NiFe 2 O 4 -M cermets are typically obtained by a process comprising the preparation of a mixture of metal powders and powders of one or more iron and nickel oxides, a compression of the mixture so as to forming a shaped green body and sintering the green body at a temperature between 900 and 1500 ° C. The initial iron oxide and nickel powders are typically a precalcined mixture of nickel oxide (NiO) and iron oxide (typically Fe 2 O 3 or Fe 3 O 4 ).

Le brevet américain US 4 871 438 , au nom de Battelle Mémorial Institute, décrit un procédé de fabrication dans lequel la poudre d'oxyde initiale est une poudre de NiO-NiFe2O4 et la poudre de métal initiale est constituée d'un mélange de 10 à 30 % en poids de poudre de cuivre et de 2 à 4 % en poids de nickel. Le rapport massique entre le NiO et le NiFe2O4 est compris entre 2 : 3 (≈ 0,67) et 3 : 2 (≈ 1,5). Le cuivre et le nickel forment, lors du frittage, un alliage dont la température de fusion est supérieure à la température de frittage, ce qui permet d'éviter l'exsudation de la phase métallique (« bleed out » en anglais) et d'obtenir ainsi une quantité finale de phase métallique supérieure à 17 % en poids. Le mélange initial ne comprend pas de liant organique. Le frittage est effectué dans une atmosphère d'argon ou d'azote contenant de 100 à 500 ppm d'oxygène.The US patent US 4,871,438 , in the name of Battelle Memorial Institute, describes a manufacturing process in which the initial oxide powder is a NiO-NiFe 2 O 4 powder and the initial metal powder consists of a mixture of 10 to 30% by weight of copper powder and 2 to 4% by weight of nickel. The mass ratio between NiO and NiFe 2 O 4 is between 2: 3 (≈ 0.67) and 3: 2 (≈ 1.5). Copper and nickel form, during sintering, an alloy whose melting temperature is higher than the sintering temperature, which makes it possible to avoid the bleeding of the metal phase ("bleed out" in English) and thus to obtain a final amount of metal phase greater than 17% by weight. The initial mixture does not include an organic binder. The sintering is carried out in an argon or nitrogen atmosphere containing from 100 to 500 ppm oxygen.

Plus récemment, le brevet américain US 5 794 112 , au nom d'Aluminum Company of America, décrit un procédé de fabrication d'un cermet dans lequel le mélange initial contient une poudre de métal constituée de cuivre et/ou d'argent et entre 2 et 10 parties en poids d'un liant organique et dans lequel le frittage est effectué sous atmosphère contrôlée d'argon contenant entre 5 et 3000 ppm d'oxygène.More recently, the US patent US 5,794,112 , on behalf of Aluminum Company of America, discloses a method of making a cermet in which the initial mixture contains a metal powder of copper and / or silver and between 2 and 10 parts by weight of a binder organic and in which the sintering is carried out under a controlled atmosphere of argon containing between 5 and 3000 ppm of oxygen.

Les procédés de fabrication connus présentent toutefois des problèmes pour la production de pièces en cermet NiO-NiFe2O4-M dont la phase métallique M contient du cuivre et du nickel, notamment pour la production de pièces de grande dimension (c'est-à-dire de pièces dont la plus petite dimension - typiquement le diamètre - est supérieure ou égale à environ 20 cm). La demanderesse a trouvé difficile de piloter et de contrôler de manière satisfaisante la composition et proportion relative de l'ensemble des phases du cermet. Or, lesdites composition et proportion affectent les propriétés d'usage du cermet. En outre, l'élimination des produits d'évaporation et de décomposition du liant lors du frittage dépend fortement de la nature de celui-ci, ce qui rend le procédé très sensible au choix du liant lorsque sa proportion dans le mélange initial est importante (comme dans le procédé décrit dans le brevet US 5 794 112 ). De surcroît, la combinaison d'une faible conductivité thermique et d'une grande dimension de la pièce crue conduit à une interruption de l'évacuation des gaz d'évaporation et de décomposition provoquée par la fermeture des pores en superficie. Les pièces peuvent également se fissurer. Ces dernières difficultés peuvent être partiellement résolues par un allongement de la phase de déliantage, mais cette solution réduit sensiblement la productivité du procédé.The known manufacturing processes, however, present problems for the production of NiO-NiFe 2 O 4 -M cermet parts whose metallic phase M contains copper and nickel, in particular for the production of large parts (ie that is to say pieces whose smallest dimension - typically the diameter - is greater than or equal to about 20 cm). The applicant has found it difficult to control and control satisfactorily the composition and relative proportion of all phases of the cermet. Now, said composition and proportion affect the properties of use of the cermet. In addition, the removal of the evaporation and decomposition products of the binder during sintering is highly dependent on the nature of the binder, which makes the process very sensitive to the choice of the binder when its proportion in the initial mixture is important ( as in the process described in the patent US 5,794,112 ). Moreover, the combination of a low thermal conductivity and a large dimension of the green part leads to an interruption of evaporation and decomposition gas evacuation caused by the closure of the surface pores. Parts can also crack. These last difficulties can be partially solved by an extension of the debinding phase, but this solution substantially reduces the productivity of the process.

La demanderesse a donc recherché des solutions aux inconvénients des procédés de fabrication connus.The applicant has therefore sought solutions to the disadvantages of known manufacturing processes.

Description de l'inventionDescription of the invention

L'invention a pour objet un procédé de fabrication d'une anode inerte en cermet tel que décrit dans la revendication 1, ledit cermet étant désigné par la formule « NiO-NiFe2O4-M » et comportant une phase métallique M incluant du cuivre et du nickel, et une phase céramique C, dite mixte, comprenant au moins deux phases distinctes, à savoir une phase N dite "monoxyde de nickel" et une phase S dite "spinelle de nickel".The invention relates to a process for producing an inert cermet anode as described in claim 1, said cermet being designated by the formula "NiO-NiFe 2 O 4 -M" and comprising a metal phase M including copper and nickel, and a ceramic phase C, said mixed, comprising at least two distinct phases, namely a N phase called "nickel monoxide" and a so-called S phase "nickel spinel".

La phase monoxyde de nickel N correspond typiquement à la formule NiO, qui peut être non stoechiométrique et qui peut éventuellement comprendre des éléments autres que le nickel, tel que le fer. La phase spinelle de nickel S correspond typiquement à la formule NiFe2O4 qui peut être non stoechiométrique et qui peut éventuellement comprendre des éléments autres que le nickel et le fer.Nickel monoxide phase N typically corresponds to the formula NiO, which can be non-stoichiometric and which may optionally include elements other than nickel, such as iron. The nickel S spinel phase typically corresponds to the NiFe 2 O 4 formula, which can be non-stoichiometric and which may optionally include elements other than nickel and iron.

Selon l'invention, le procédé de fabrication d'une anode inerte en cermet de type NiO-NiFe2O4-M comprenant au moins une phase monoxyde de nickel N, une phase spinelle de nickel S, contenant du fer et du nickel, et une phase métallique M, contenant du cuivre et du nickel, est caractérisé en ce qu'il comprend :

  • la préparation d'un mélange initial comprenant au moins un précurseur des phases monoxyde N et spinelle S, un précurseur de la phase métallique M et un liant organique, la proportion de liant organique dans le mélange initial étant faible, à savoir moins de 2,0 % en poids, et le précurseur de la phase métallique comprenant une poudre métallique contenant du cuivre et du nickel,
  • une opération de mise en forme du mélange, typiquement par pressage ou compression isostatique, de manière à former une anode crue de forme déterminée,
  • une opération de frittage de l'anode crue, à une température typiquement supérieure à 900°C et dans une atmosphère contrôlée contenant une faible quantité d'oxygène, à savoir typiquement moins de 200 ppm d'O2.
According to the invention, the process for manufacturing an inert coke anode of the NiO-NiFe 2 O 4 -M type comprising at least one nickel N monoxide phase, a nickel S spinel phase containing iron and nickel, and a metallic phase M, containing copper and nickel, is characterized in that it comprises:
  • the preparation of an initial mixture comprising at least one precursor of the N-monoxide and S-spinel phases, a precursor of the metal phase M and an organic binder, the proportion of organic binder in the initial mixture being low, namely less than 2, 0% by weight, and the precursor of the metal phase comprising a metal powder containing copper and nickel,
  • a shaping operation of the mixture, typically by pressing or isostatic compression, so as to form a green anode of determined shape,
  • a sintering operation of the green anode, at a temperature typically above 900 ° C and in a controlled atmosphere containing a small amount of oxygen, typically less than 200 ppm O 2 .

La demanderesse a eu l'idée de dissocier les fonctions physico-chimiques remplies par le liant et le précurseur de la phase métallique. Dans ce contexte, elle a noté qu'il était généralement suffisant d'utiliser une faible quantité de liant organique pour assurer la tenue de la pièce au début du frittage (c'est-à-dire pour réduire sensiblement, voire éviter, sa déformation) et que le rôle de réducteur chimique dudit liant pouvait être assuré par l'ajout de nickel métallique dans le précurseur de la phase métallique, qui est de préférence formé de poudres métalliques.The applicant has had the idea of dissociating the physico-chemical functions filled by the binder and the precursor of the metal phase. In this context, she noted that was generally sufficient to use a small amount of organic binder to ensure the holding of the workpiece at the beginning of sintering (that is to say to substantially reduce, or even prevent its deformation) and that the chemical reducing role of said binder could be provided by the addition of metallic nickel in the precursor of the metal phase, which is preferably formed of metal powders.

Le fait de dissocier les deux fonctions - tenue mécanique de la pièce et contrôle de la composition de la phase métallique - permet de réduire la quantité de liant et par conséquent, de réduire les émissions de matières volatiles toxiques sous faible apport d'oxygène, de réduire la durée du déliantage et de limiter les risques de fissuration et production de porosité associés à l'élimination du liant en phase gazeuse et des produits volatiles de décomposition du liant dans les pièces de dimensions importantes. Le fait d'ajuster la composition de la phase métallique du matériau fritté par l'ajout de nickel permet non seulement d'éviter l'exsudation de la phase métallique durant le frittage, mais aussi de mieux contrôler la chimie locale des phases céramique et métallique. L'ajustement de la composition de la phase métallique selon l'invention permet également d'assurer une plus grande homogénéité de la microstructure du cermet des pièces de grandes dimensions.The fact of dissociating the two functions - mechanical behavior of the part and control of the composition of the metallic phase - makes it possible to reduce the quantity of binder and consequently, to reduce the emissions of toxic volatile materials with low oxygen supply, to reduce the duration of debinding and to limit the risks of cracking and porosity production associated with the elimination of the binder in the gas phase and the volatile decomposition products of the binder in the large parts. Adjusting the composition of the metal phase of the sintered material by the addition of nickel makes it possible not only to avoid the exudation of the metal phase during sintering, but also to better control the local chemistry of the ceramic and metallic phases. . The adjustment of the composition of the metal phase according to the invention also makes it possible to ensure a greater homogeneity of the microstructure of the cermet of large parts.

L'utilisation d'une faible quantité de liant organique permet de rendre le procédé plus fiable dans le cadre d'une production industrielle d'anodes (et plus généralement de pièces destinées à former des anodes). En particulier, elle permet de rendre le procédé moins sensible à la taille des pièces frittées.The use of a small amount of organic binder makes the process more reliable in the context of industrial production of anodes (and more generally of parts intended to form anodes). In particular, it makes the process less sensitive to the size of the sintered parts.

Le frittage provoque la migration d'une partie des éléments métalliques entre les différentes phases. Ainsi, typiquement, l'oxyde de nickel s'enrichit en fer, le ferrite de nickel devient non stoechiométrique et la phase métallique s'enrichit en nickel et éventuellement en fer, généralement en moindres proportions. Par conséquent, le cermet issu du frittage peut être plus précisément décrit par la formule Ni1-xFexO1±δ-NiyFe3-yO4±δ-M', où M' est un alliage incluant le métal M initial, du fer et du nickel (MFeNi). Toutefois, afin de simplifier la terminologie, les phases NiO (et plus généralement Ni1-xFexO) et NiFe2O4 (et plus généralement NiyFe3-yO4) seront, par la suite, simplement dénommées respectivement par les expressions « phase monoxyde » et « phase spinelle ». En outre, le cermet sera simplement désigné par la formule « NiO-NiFe2O4-M », où NiO désigne la phase monoxyde (N), NiFe2O4 désigne la phase spinelle (S), et M la phase métallique.Sintering causes the migration of a part of the metallic elements between the different phases. Thus, typically, nickel oxide is enriched in iron, nickel ferrite becomes non-stoichiometric and the metal phase is enriched in nickel and possibly iron, generally in smaller proportions. Consequently, the cermet resulting from the sintering can be more precisely described by the formula Ni 1 -x Fe x O 1 ± δ -Ni y Fe 3 -y O 4 ± δ -M ', where M' is an alloy including the metal M initial, iron and nickel (MFeNi). However, in order to simplify the terminology, the phases NiO (and more generally Ni 1 -x Fe x O) and NiFe 2 O 4 (and more generally Ni y Fe 3 -y O 4 ) will be, by the followed by the terms "monoxide phase" and "spinel phase" respectively. In addition, the cermet will simply be designated by the formula "NiO-NiFe 2 O 4 -M", where NiO denotes the monoxide phase (N), NiFe 2 O 4 designates the spinel phase (S), and M the metal phase.

Les anodes inertes selon l'invention sont destinées à la production d'aluminium par électrolyse ignée. Elles peuvent éventuellement être assemblées pour former des assemblages d'anodes comprenant plusieurs anodes individuelles, tels que des grappes.The inert anodes according to the invention are intended for the production of aluminum by igneous electrolysis. They may optionally be assembled to form anode assemblies comprising a plurality of individual anodes, such as clusters.

L'invention sera mieux comprise à l'aide des figures annexées et de la description détaillée qui suit.The invention will be better understood with the aid of the appended figures and the detailed description which follows.

La figure 1 représente un mode de réalisation préféré du procédé de fabrication de l'invention.The figure 1 represents a preferred embodiment of the manufacturing method of the invention.

La figure 2A est une micrographie d'un cermet typique obtenu par le procédé de fabrication de l'invention.The Figure 2A is a micrograph of a typical cermet obtained by the manufacturing method of the invention.

La figure 2B est une reproduction schématique de la micrographie de la figure 2A.The Figure 2B is a schematic reproduction of the micrograph of the Figure 2A .

La figure 3 est un diagramme ternaire NiO / NiFe2O4 / M montrant les domaines de préférence de la composition initiale dans un mode de réalisation préféré de l'invention.The figure 3 is a NiO / NiFe 2 O 4 / M ternary diagram showing the preferred domains of the initial composition in a preferred embodiment of the invention.

La figure 4 est un diagramme ternaire Ni / Cu / Oxydes tronqué montrant les domaines de préférence de la composition initiale dans un mode de réalisation préféré de l'invention.The figure 4 is a truncated Ni / Cu / Oxide ternary diagram showing the preferred domains of the initial composition in a preferred embodiment of the invention.

La poudre métallique contenant du cuivre et du nickel est typiquement un mélange d'une poudre de cuivre métallique et d'une poudre de nickel métallique. Il est également possible selon l'invention d'utiliser une poudre métallique comprenant, en tout ou partie, un alliage de cuivre et de nickel. De préférence, au moins 95 % en poids des grains de ladite poudre métallique ont une taille comprise entre 3 et 10 µm.The metal powder containing copper and nickel is typically a mixture of a metallic copper powder and a nickel metal powder. It is also possible according to the invention to use a metal powder comprising, in all or part, an alloy of copper and nickel. Preferably, at least 95% by weight of the grains of said metal powder have a size of between 3 and 10 μm.

La proportion de poudre métallique dans le mélange initial est de préférence supérieure à 15 % en poids, et de préférence encore supérieure à 20 % en poids. Cette proportion est de préférence inférieure à 35 % en poids. Elle est typiquement comprise entre 15 % et 30 % en poids, et plus typiquement entre 20 % et 25 % en poids. Ces proportions préférentielles sont représentées dans le diagramme ternaire de la figure 3 dans le cas où le précurseur desdites phases monoxyde N et spinelle S est constitué d'oxyde de nickel NiO et de ferrite de nickel NiFe2O4.The proportion of metal powder in the initial mixture is preferably greater than 15% by weight, and more preferably greater than 20% by weight. This proportion is preferably less than 35% by weight. It is typically between 15% and 30% by weight, and more typically between 20% and 25% by weight. These preferred proportions are represented in the ternary diagram of the figure 3 in the case where the precursor of said N and S spinel phases consists of nickel oxide NiO and nickel ferrite NiFe 2 O 4 .

La proportion de nickel dans la poudre métallique du précurseur de la phase métallique (c'est-à-dire dans la quantité de poudre métallique) est de préférence supérieure ou égale à 3 % en poids, de préférence encore comprise entre 3 et 30 % en poids, et typiquement entre 5 et 25 % en poids. Ces proportions préférentielles sont représentées dans le diagramme ternaire de la figure 4 dans le cas où le précurseur de la phase métallique est constitué de nickel et de cuivre. Les domaines préférentiels des proportions de Ni et Cu sont exprimés en terme de rapport Ni/Cu (par exemple, le rapport 3/97 correspond à 3 % pds Ni dans la poudre métallique). L'expression "Oxydes" désigne l'ensemble des constituants du précurseur des phases monoxyde N et spinelle S; les proportions de M donnés dans ce diagramme correspondent à la différence à 100 % par rapport à la proportion totales des oxydes.The proportion of nickel in the metal powder of the precursor of the metal phase (that is to say in the amount of metal powder) is preferably greater than or equal to 3% by weight, more preferably between 3 and 30% by weight, and typically between 5 and 25% by weight. These preferred proportions are represented in the ternary diagram of the figure 4 in the case where the precursor of the metal phase consists of nickel and copper. The preferred domains of the proportions of Ni and Cu are expressed in terms of Ni / Cu ratio (for example, the ratio 3/97 corresponds to 3% by weight Ni in the metal powder). The expression "oxides" denotes all the constituents of the precursor of the N-monoxide and S-spinel phases; the proportions of M given in this diagram correspond to the 100% difference with respect to the total proportion of the oxides.

Le mélange initial peut éventuellement comprendre en outre au moins un élément apte à limiter l'oxydation de la phase métallique du cermet, tel que de l'argent. Cet élément anti-oxydation est typiquement ajouté sous forme de poudre. Il peut éventuellement être ajouté à la poudre métallique initiale. Ledit élément anti-oxydation peut optionnellement se trouver sous une forme oxydée, tel que dans un oxyde (par exemple Ag2O), qui sera réduite lors du frittage. Les éléments anti-oxydation, sous forme métallique ou oxydée, peuvent être ajoutés à toute étape de la préparation du mélange initial.The initial mixture may optionally further comprise at least one element capable of limiting the oxidation of the metal phase of the cermet, such as silver. This anti-oxidation element is typically added in powder form. It can optionally be added to the initial metal powder. Said anti-oxidation element may optionally be in an oxidized form, such as in an oxide (for example Ag 2 O), which will be reduced during sintering. The anti-oxidation elements, in metallic or oxidized form, may be added at any stage of the preparation of the initial mixture.

La proportion de liant organique dans le mélange initial est de préférence comprise entre 0,5 et 1,5 % en poids. Ledit liant est de préférence apte à assurer une tenue à cru de la pièce mise en forme. Il n'est pas nécessaire, selon l'invention; d'utiliser un liant organique possédant des propriétés de réducteur chimique car la fonction de réduction des phases oxydées est essentiellement assurée par la poudre métallique (ou le mélange de poudres métalliques) utilisée dans le mélange initial. Ledit liant est typiquement de l'APV (alcool polyvinylique), mais peut être tout liant organique ou organométallique connu, tel que les polymères acryliques, les polyglycols (tels que le polyéthylène de glycol ou PEG), les acétates de polyvinyle, les polyisobutylènes, les polycarbonates, les polystyrènes, les polyacrylates ou les stéarates (tels que l'acide stéarique ou le stéarate de zinc).The proportion of organic binder in the initial mixture is preferably between 0.5 and 1.5% by weight. Said binder is preferably capable of ensuring a green holding of the shaped part. It is not necessary according to the invention; to use an organic binder having chemical reducing properties because the function of reducing the oxidized phases is essentially provided by the metal powder (or mixture of metal powders) used in the initial mixture. Said binder is typically APV (polyvinyl alcohol), but can be any known organic or organometallic binder, such as acrylic polymers, polyglycols (such as polyethylene glycol or PEG), polyvinyl acetates, polyisobutylenes, polycarbonates, polystyrenes, polyacrylates or stearates (such as stearic acid or zinc stearate).

Le précurseur des phases monoxyde et spinelle est typiquement un mélange d'oxydes ou de composés organométalliques aptes à former lesdites phases lors du frittage. Ces oxydes ou composés peuvent éventuellement être ajoutés séparément au mélange initial, mais il est avantageux de les mélanger ensemble avant de les ajouter au mélange initial.The precursor of the monoxide and spinel phases is typically a mixture of oxides or organometallic compounds capable of forming said phases during sintering. These oxides or compounds may optionally be added separately to the initial mixture, but it is advantageous to mix them together before adding them to the initial mixture.

Les oxydes et/ou composés du mélange initial, notamment le précurseur des phases monoxyde et spinelle, se présentent de préférence sous la forme de poudres. De préférence encore, au moins 95 % en poids des grains de ces poudres ont une taille comprise entre 5 et 10 µm.The oxides and / or compounds of the initial mixture, in particular the precursor of the monoxide and spinel phases, are preferably in the form of powders. More preferably, at least 95% by weight of the grains of these powders have a size between 5 and 10 microns.

Le précurseur des phases monoxyde et spinelle comprend typiquement un mélange d'oxydes comprenant un oxyde de nickel (typiquement NiO) et un ferrite de nickel (typiquement NiFe2O4). Ce mélange d'oxydes peut être obtenu de différentes façons. Par exemple, il peut être formé par mélange d'une poudre d'oxyde de nickel (NiO) et d'une poudre de ferrite de nickel (NiFe2O4). Il peut également être obtenu par calcination d'un mélange d'une poudre d'oxyde nickel et d'une poudre d'un oxyde de fer (tel que Fe2O3 ou Fe3O4).The precursor of the monoxide and spinel phases typically comprises a mixture of oxides comprising a nickel oxide (typically NiO) and a nickel ferrite (typically NiFe 2 O 4 ). This mixture of oxides can be obtained in different ways. For example, it can be formed by mixing a nickel oxide powder (NiO) and a nickel ferrite powder (NiFe 2 O 4 ). It can also be obtained by calcining a mixture of a nickel oxide powder and an iron oxide powder (such as Fe 2 O 3 or Fe 3 O 4 ).

Ledit mélange d'oxydes est avantageusement obtenu par pyrolyse de composés de fer et de nickel, ce qui permet d'obtenir un mélange intime des oxydes initiaux et d'éviter les impuretés qui se trouvent fréquemment dans les oxydes de fer et de nickel industriels. Un tel procédé (connu sous l'appellation « spray pyrolysis ») comprend typiquement la co-précipitation de sels en solution aqueuse, une pulvérisation à haute température des sels, un broyage et une calcination ou chamottage à une température suffisante, typiquement supérieure à 900 °C.Said mixture of oxides is advantageously obtained by pyrolysis of iron and nickel compounds, which makes it possible to obtain an intimate mixture of the initial oxides and to avoid the impurities which are frequently found in the industrial iron and nickel oxides. Such a process (known as "spray pyrolysis") typically comprises the co-precipitation of salts in aqueous solution, a high temperature spraying of salts, grinding and calcination or champing at a sufficient temperature, typically above 900 ° C.

La proportion de ferrite de nickel (NiFe2O4) dans le mélange initial est typiquement comprise entre 50 et 85 % en poids, et de préférence encore entre 60 et 85 % en poids. Afin d'obtenir une densification satisfaisante du cermet, la proportion d'oxyde de nickel du mélange initial est typiquement comprise entre 0,1 % en poids et 25 % en poids. Le rapport entre la proportion massique d'oxyde de nickel et la proportion massique de ferrite de nickel (typiquement NiO/NiFe2O4) est compris entre 0,2/99,8 et 30/70, et de préférence 0,2/99,8 et 20/80.The proportion of nickel ferrite (NiFe 2 O 4 ) in the initial mixture is typically between 50 and 85% by weight, and more preferably between 60 and 85% by weight. In order to obtain a satisfactory densification of the cermet, the proportion of nickel oxide in the initial mixture is typically between 0.1% by weight and 25% by weight. The ratio between the mass proportion of nickel oxide and the mass proportion of nickel ferrite (typically NiO / NiFe 2 O 4 ) is between 0.2 / 99.8 and 30/70, and preferably 0.2 / 99.8 and 30/70. 99.8 and 20/80.

La demanderesse a constaté qu'il était important d'ajuster précisément les différentes proportions pour obtenir un produit final ayant les propriétés souhaitées pour l'utilisation en tant qu'anode pour la production d'aluminium par électrolyse. En particulier, elle a noté l'importance de l'ajustement initial des proportions relatives du fer total et du nickel total (c'est-à-dire toutes phases confondues) et des proportions relatives de l'oxyde de nickel et du ferrite de nickel pour l'obtention d'un cermet final ayant les propriétés souhaitées. En particulier, les proportions des précurseurs des phases monoxyde, spinelle et métallique (par exemple, les proportions d'oxyde de nickel, de ferrite de nickel et de métal) dans le mélange initial, la température de frittage et la teneur en oxygène de l'atmosphère de frittage sont avantageusement ajustées de manière à obtenir le rapport atomique souhaité entre le fer et le nickel (Fe/Ni) dans la phase spinelle du cermet. Ce rapport est de préférence supérieur ou égal à 2,4, et de préférence encore supérieur ou égal à 2,8.The applicant has found that it is important to precisely adjust the different proportions to obtain a final product having the desired properties for use as an anode for the production of aluminum by electrolysis. In particular, it noted the importance of the initial adjustment of the relative proportions of total iron and total nickel (ie all phases combined) and the relative proportions of nickel oxide and ferrite. nickel for obtaining a final cermet having the desired properties. In particular, the proportions of the precursors of the monoxide, spinel and metal phases (for example, the proportions of nickel oxide, nickel ferrite and metal) in the initial mixture, the sintering temperature and the oxygen content of the The sintering atmosphere is advantageously adjusted so as to obtain the desired atomic ratio between iron and nickel (Fe / Ni) in the spinel phase of the cermet. This ratio is preferably greater than or equal to 2.4, and more preferably greater than or equal to 2.8.

Le mélange initial, c'est-à-dire le mélange destiné à être mis en forme et fritté de manière à obtenir une pièce en cermet, comprend typiquement de l'eau et un dispersant afin de faciliter le mélange des constituants et la mise en forme des pièces crues.The initial mixture, i.e. the mixture to be shaped and sintered to obtain a cermet piece, typically comprises water and a dispersant to facilitate the mixing of the constituents and the shaping of the green parts.

Selon un mode de réalisation préféré de l'invention, le mélange initial est préparé suivant un procédé comprenant :

  • la préparation d'une barbotine contenant de l'eau (typiquement 40 % en poids), un dispersant apte à éviter l'agglomération des poudres (de préférence moins de 1 % en poids) et la poudre d'oxyde(s) initiale ;
  • une opération de désagglomération de la barbotine, typiquement par brassage, de manière à obtenir une viscosité déterminée (typiquement comprise entre 0,1 et 0,2 Pa.sec);
  • l'ajout de la poudre de précurseur de la phase métallique et du liant organique.
According to a preferred embodiment of the invention, the initial mixture is prepared according to a process comprising:
  • the preparation of a slip containing water (typically 40% by weight), a dispersant capable of preventing agglomeration of the powders (preferably less than 1% by weight) and the initial oxide powder (s);
  • a deagglomeration operation of the slip, typically by stirring, so as to obtain a determined viscosity (typically between 0.1 and 0.2 Pa.sec);
  • the addition of the precursor powder of the metallic phase and the organic binder.

Le dispersant est de préférence apte à ne pas réagir chimiquement avec le cuivre du précurseur de la phase métallique.The dispersant is preferably capable of not reacting chemically with the copper of the precursor of the metal phase.

Le mélange initial est de préférence séché avant l'opération de mise en forme afin d'éliminer l'eau qu'il contient. Ce séchage est typiquement réalisé par atomisation (« spray drying »).The initial mixture is preferably dried before the shaping operation in order to remove the water contained therein. This drying is typically carried out by spray drying.

L'opération de mise en forme de la pièce crue est typiquement effectuée par pressage isostatique à froid, c'est-à-dire par pressage à une température apte à éviter l'évaporation excessive ou la décomposition du liant organique. La température de pressage à froid est typiquement inférieure à 200 °C. Les pressions de pressage sont typiquement comprises entre 100 et 200 MPa.The shaping operation of the green part is typically carried out by cold isostatic pressing, that is to say by pressing at a temperature capable of preventing excessive evaporation or decomposition of the organic binder. The cold pressing temperature is typically less than 200 ° C. Pressing pressures are typically between 100 and 200 MPa.

L'opération de frittage de la pièce crue (c'est-à-dire de l'anode crue ou de l'élément d'anode cru) est typiquement effectuée dans une atmosphère contrôlée contenant au moins un gaz inerte et de l'oxygène. Le gaz inerte de l'atmosphère contrôlée utilisée lors du frittage est typiquement de l'argon. Ladite atmosphère contrôlée comprend de préférence entre 10 et 200 ppm d'oxygène. Une teneur en oxygène minimale est préférable afin d'éviter la réduction des oxydes du mélange. Une teneur maximale est avantageuse car elle permet d'éviter l'oxydation de la ou des poudres métalliques.The sintering operation of the green part (i.e. the green anode or the raw anode element) is typically performed in a controlled atmosphere containing at least one inert gas and oxygen . The inert gas of the controlled atmosphere used during sintering is typically argon. Said controlled atmosphere preferably comprises between 10 and 200 ppm of oxygen. A minimum oxygen content is preferable in order to avoid the reduction of the oxides of the mixture. A maximum content is advantageous because it avoids the oxidation of the metal powder or powders.

La température de frittage est de préférence comprise entre 1150 et 1400°C et de préférence encore comprise entre 1300 et 1400°C. Elle est typiquement de 1350°C. Le temps de maintien à la température de frittage n'est pas critique dans le procédé de l'invention. Ce temps de maintien est typiquement de deux heures environ afin d'assurer l'homogénéité du frittage. Après une étape de maintien à la température de frittage, le procédé comprend avantageusement une étape de refroidissement lent, à une vitesse de refroidissement typiquement comprise entre -10° et -100°/heure, entre la température de frittage et une température intermédiaire comprise entre environ 900 et environ 1000 °C; un refroidissement lent, au début de l'étape de refroidissement, permet d'augmenter la conductivité électrique de l'anode.The sintering temperature is preferably between 1150 and 1400 ° C and more preferably between 1300 and 1400 ° C. It is typically 1350 ° C. The holding time at the sintering temperature is not critical in the process of the invention. This holding time is typically about two hours in order to ensure the homogeneity of the sintering. After a step of maintaining the sintering temperature, the process advantageously comprises a slow cooling step, at a cooling rate typically between -10 ° and -100 ° / hour, between the sintering temperature and an intermediate temperature between about 900 and about 1000 ° C; slow cooling, at the beginning of the cooling step, makes it possible to increase the electrical conductivity of the anode.

La proportion de la phase métallique du cermet final est de préférence supérieure à 15 % en poids, de préférence encore entre 15 et 30 % en poids, et typiquement entre 15 et 25 % en poids. La proportion de nickel dans la phase métallique est de préférence supérieure ou égale à 3 % en poids, de préférence entre 3 et 30 % en poids, et de préférence encore entre 5 et 25 % en poids, de manière à augmenter la résistance à l'oxydation de phase métallique lors de l'utilisation du cermet dans un procédé d'électrolyse en sel fondu.The proportion of the metal phase of the final cermet is preferably greater than 15% by weight, more preferably between 15 and 30% by weight, and typically between 15 and 25% by weight. The proportion of nickel in the metal phase is preferably greater than or equal to 3% by weight, preferably between 3 and 30% by weight, and more preferably between 5 and 25% by weight, so as to increase the resistance to metal phase oxidation when using the cermet in a molten salt electrolysis process.

La proportion de phase spinelle dans le cermet final est de préférence comprise entre 30 et 90 % en poids, et typiquement comprise entre 40 et 90 % en poids. La phase spinelle est de préférence non stoechiométrique afin d'en augmenter la conductivité électrique. Dans ce but, le rapport atomique entre le fer et le nickel (Fe/Ni) dans la phase spinelle est de préférence supérieur ou égal à 2,4, et de préférence encore supérieur ou égal à 2,8.The proportion of spinel phase in the final cermet is preferably between 30 and 90% by weight, and typically between 40 and 90% by weight. The spinel phase is preferably non-stoichiometric in order to increase the electrical conductivity. For this purpose, the atomic ratio between iron and nickel (Fe / Ni) in the spinel phase is preferably greater than or equal to 2.4, and more preferably greater than or equal to 2.8.

La phase spinelle peut éventuellement comprendre au moins un élément de substitution apte à augmenter sa conductivité électrique, tel qu'un élément tétravalent (Ti, Zr,...).The spinel phase may optionally comprise at least one substitution element capable of increasing its electrical conductivity, such as a tetravalent element (Ti, Zr, etc.).

La proportion de phase monoxyde dans le cermet final est de préférence inférieure à 40 % en poids, afin d'obtenir une résistance suffisante du cermet à la corrosion électrochimique.The proportion of monoxide phase in the final cermet is preferably less than 40% by weight, in order to obtain sufficient resistance of the cermet to electrochemical corrosion.

La demanderesse a constaté que, comme le montre les figures 2A et 2B, le cermet obtenu par le procédé de l'invention comprend une phase spinelle (S) développée qui entoure les îlots de phase métallique (M) et forme un réseau de percolation. La phase monoxyde (N) est discontinue. La demanderesse émet l'hypothèse que la conductivité élevée du cermet provient en grande partie du réseau de percolation de la phase spinelle en contact étroit avec la phase métallique. Elle émet également l'hypothèse que le caractère percolant de la phase spinelle ne peut être obtenu que pour des teneurs de Ni dans la phase métallique suffisantes, soit typiquement supérieures à 5 % en poids.The plaintiff has found that, as shown by the Figures 2A and 2B the cermet obtained by the process of the invention comprises a developed spinel phase (S) which surrounds the metal phase islands (M) and forms a percolation network. The monoxide phase (N) is discontinuous. The Applicant hypothesizes that the high conductivity of the cermet comes largely from the percolation network of the spinel phase in close contact with the metal phase. It also assumes that the percolating character of the spinel phase can only be obtained for sufficient levels of Ni in the metal phase, typically greater than 5% by weight.

La porosité du cermet final est typiquement inférieure ou égale à 5%. Sa conductivité électrique à une température comprise entre 900°C et 1050°C est de préférence supérieure à 50 Ω-1.cm-1, et de préférence encore supérieure à 100 Ω-1.cm-1.The porosity of the final cermet is typically less than or equal to 5%. Its electrical conductivity at a temperature between 900 ° C. and 1050 ° C. is preferably greater than 50 Ω -1 · cm -1 , and more preferably greater than 100 Ω -1 · cm -1 .

Le procédé selon l'invention est avantageusement utilisé pour la fabrication d'anodes inertes destinées à la production d'aluminium par électrolyse ignée.The process according to the invention is advantageously used for the production of inert anodes intended for the production of aluminum by igneous electrolysis.

L'invention a également pour objet l'utilisation d'anodes inertes ou d'assemblages d'anodes inertes obtenues par le procédé de fabrication selon l'invention pour la production d'aluminium par électrolyse ignée. En d'autres termes, l'invention a également pour objet un procédé production d'aluminium par électrolyse ignée comportant l'utilisation d'au moins une anode inerte produite par le procédé de fabrication selon l'invention.The invention also relates to the use of inert anodes or inert anode assemblies obtained by the manufacturing method according to the invention for the production of aluminum by igneous electrolysis. In other words, the invention also relates to an igneous electrolysis process for producing aluminum using the use of at least one inert anode produced by the manufacturing method according to the invention.

L'invention a encore pour objet une cellule d'électrolyse destinée à la production d'aluminium par électrolyse ignée comportant au moins une anode inerte produite par le procédé de fabrication selon l'invention.The subject of the invention is also an electrolysis cell intended for the production of aluminum by igneous electrolysis comprising at least one inert anode produced by the manufacturing method according to the invention.

Essais comparatifsComparative tests Lot 1Lot 1

Plusieurs anodes en cermet ont été élaborées selon l'art antérieur à partir de mélanges de poudres de Cu, de NiFe2O4 et de NiO ayant les proportions suivantes (en poids) : 17 % Cu, 61 % NiFe2O4, 22 % NiO. Le mélange a été lié par 5 % en poids d'APV en solution aqueuse et mis en forme par pressage isostatique à froid. Les anodes crues ont été frittées à la température maximale de 1350°C sous atmosphère contrôlée (teneur résiduelle en oxygène entre 10 et 100 ppm). La densité des anodes frittées était de 6,10 g/cm3, soit une porosité résiduelle de 2,84 %. Le matériau fritté était constitué de 28 % en poids de phase métallique contenant 32 % en poids de Ni, les proportions de phase spinelle et de phase monoxyde étant respectivement de 45,2 % et de 26,7 % en poids. La conductivité électrique de ces anodes à 1000 °C était de 77 Ω-1.cm-1 environ.Several cermet anodes have been prepared according to the prior art from mixtures of powders of Cu, NiFe 2 O 4 and NiO having the following proportions (by weight): 17% Cu, 61% NiFe 2 O 4 , 22 % NiO. The mixture was bound by 5% by weight of APV in aqueous solution and shaped by cold isostatic pressing. The green anodes were sintered at the maximum temperature of 1350 ° C under a controlled atmosphere (residual oxygen content between 10 and 100 ppm). The density of sintered anodes was 6.10 g / cm 3 , a residual porosity of 2.84%. The sintered material consisted of 28% by weight of metal phase containing 32% by weight of Ni, the proportions of spinel phase and monoxide phase being respectively 45.2% and 26.7% by weight. The electrical conductivity of these anodes at 1000 ° C was about 77 Ω -1 .cm -1 .

Lot 2Lot 2

Plusieurs anodes en cermet ont été élaborées selon l'invention à partir de mélanges de poudres de Cu, de Ni, de NiFe2O4 et de NiO ayant les proportions suivantes (en poids) : 16 % Cu, 5 % Ni, 57 % NiFe2O4 et 22 % NiO. Le mélange a été lié par 1 % en poids d'APV en solution aqueuse et mis en forme par pressage isostatique à froid. Les anodes crues ont été frittées à la température maximale de 1350°C sous atmosphère contrôlée (teneur résiduelle en oxygène comprise entre 10 et 100 ppm). La densité des anodes frittées était égale à 6,14, soit une porosité résiduelle de 2 %. Le matériau fritté était constitué de 24 % en poids de phase métallique contenant 28,5 % en poids de Ni, les proportions de ferrite de phase spinelle et de phase monoxyde étant respectivement de 40 % et de 36 % en poids. La conductivité électrique de ces anodes à 1000 °C était de 48 Ω-1.cm-1 environ.Several cermet anodes have been prepared according to the invention from mixtures of powders of Cu, Ni, NiFe 2 O 4 and NiO having the following proportions (by weight): 16% Cu, 5% Ni, 57% NiFe 2 O 4 and 22% NiO. The mixture was bound by 1% by weight of APV in aqueous solution and shaped by cold isostatic pressing. The green anodes were sintered at the maximum temperature of 1350 ° C. under a controlled atmosphere (residual oxygen content between 10 and 100 ppm). The density of the sintered anodes was 6.14, which is a residual porosity of 2%. The sintered material consisted of 24% by weight of metal phase containing 28.5% by weight of Ni, the proportions of spinel phase ferrite and monoxide phase being respectively 40% and 36% by weight. The electrical conductivity of these anodes at 1000 ° C was about 48 Ω -1 .cm -1 .

Lot 3Lot 3

Plusieurs anodes en cermet ont été élaborées selon l'invention à partir de mélanges de poudres de Cu, de Ni, de NiFe2O4 et de NiO ayant les proportions suivantes (en poids) : 19 % Cu, 6,4 % Ni, 60 % NiFe2O4 et 14,6 % NiO. Le mélange a été lié par 1 % en poids d'APV en solution aqueuse et mis en forme par pressage isostatique à froid. Les anodes crues ont été frittées à la température maximale de 1350°C sous atmosphère contrôlée (teneur résiduelle en oxygène comprise entre 10 et 100 ppm). La densité des anodes frittées était de 6,17, soit une porosité résiduelle de 1,95 %. Le matériau fritté était constitué de 30,7 % en poids de phase métallique contenant 32 % en poids de Ni, les proportions de phase spinelle et de phase monoxyde étant respectivement de 41,6 % et de 27,7 % en poids. La conductivité électrique de ces anodes à 1000 °C était de 103 Ω-1.cm-1 environ.Several cermet anodes have been prepared according to the invention from mixtures of powders of Cu, Ni, NiFe 2 O 4 and NiO having the following proportions (by weight): 19% Cu, 6.4% Ni, 60% NiFe 2 O 4 and 14.6% NiO. The mixture was bound by 1% by weight of APV in aqueous solution and shaped by cold isostatic pressing. The green anodes were sintered at the maximum temperature of 1350 ° C. under a controlled atmosphere (residual oxygen content between 10 and 100 ppm). The density of sintered anodes was 6.17, a residual porosity of 1.95%. The sintered material consisted of 30.7% by weight of metal phase containing 32% by weight of Ni, the proportions of the spinel phase and the monoxide phase being respectively 41.6% and 27.7% by weight. The electrical conductivity of these anodes at 1000 ° C was about 103 Ω -1 .cm -1 .

Lot 4Lot 4

Plusieurs anodes en cermet ont été élaborées à partir de mélanges de poudres de Cu, de Ni, de NiFe2O4 et de NiO ayant les proportions suivantes (en poids) : 21 % Cu, 4 % Ni, 30 % NiFe2O4, 45 % NiO. Le mélange a été lié par 1 % en poids d'APV en solution aqueuse. Les anodes crues ont été frittées à la température maximale de 1200 °C sous atmosphère contrôlée (teneur résiduelle en oxygène comprise entre 10 et 100 ppm). La densité des anodes frittées était de 6,49, soit une porosité résiduelle de 3,57 %. Le matériau fritté était constitué de 27,3 % en poids de phase métallique contenant 24,8 % en poids de Ni, les proportions de phase spinelle et de phase monoxyde étant respectivement de 21,7 % et de 51 % en poids. La conductivité électrique de ces anodes à 1000 °C était de 139 Ω-1.cm-1 environ.Several cermet anodes have been developed from mixtures of powders of Cu, Ni, NiFe 2 O 4 and NiO having the following proportions (by weight): 21% Cu, 4% Ni, 30% NiFe 2 O 4 , 45% NiO. The mixture was bound with 1% by weight of APV in aqueous solution. The green anodes were sintered at the maximum temperature of 1200 ° C. under a controlled atmosphere (residual oxygen content between 10 and 100 ppm). The density of sintered anodes was 6.49, a residual porosity of 3.57%. The sintered material consisted of 27.3% by weight of metal phase containing 24.8% by weight of Ni, the proportions of spinel phase and monoxide phase being respectively 21.7% and 51% by weight. The electrical conductivity of these anodes at 1000 ° C was about 139 Ω -1 .cm -1 .

Les anodes élaborées dans les lots 1, 3 et 4 ont été mises à l'essai dans une cellule d'électrolyse d'essai dans les conditions suivantes :

  • durée de l'électrolyse : 10 heures;
  • température d'électrolyse : 960 °C;
  • composition du bain : bain de cryolithe de ratio molaire NaF/AlF3 égal à 2,2 (soit avec un excès d'AlF3 de 11 % en poids) saturée en alumine;
  • densité du courant d'électrolyse : 1,5 A/cm2.
The anodes elaborated in lots 1, 3 and 4 were tested in a test electrolysis cell under the following conditions:
  • duration of the electrolysis: 10 hours;
  • electrolysis temperature: 960 ° C;
  • composition of the bath: cryolite bath of molar ratio NaF / AlF 3 equal to 2.2 (or with an excess of AlF 3 of 11% by weight) saturated with alumina;
  • density of the electrolysis current: 1.5 A / cm 2 .

Les vitesses de corrosion mesurées sont données au tableau I. La colonne "nombre d'essais" correspond aux nombres d'anodes testées, une anode étant testée à chaque essai. La colonne "rapport Fe/Ni" correspond au rapport atomique Fe/Ni dans la phase spinelle S mesuré par rayons X (lots 1, 3 et 4) ou par microsonde (lot 2).The corrosion rates measured are given in Table I. The "number of tests" column corresponds to the number of anodes tested, an anode being tested at each test. The column "Fe / Ni ratio" corresponds to the Fe / Ni atomic ratio in the spinel phase S measured by X-rays (lots 1, 3 and 4) or by microprobe (batch 2).

La comparaison des résultats sur les lots 1 et 3 montre que les anodes peuvent être fabriquées selon l'invention avec de faibles quantités de liant organique tout en maintenant une faible vitesse de corrosion et tout en obtenant une valeur élevée pour la conductivité électrique à chaud. La comparaison des résultats des lots 3 et 4 montre qu'une teneur excessive de phase NiO dans le cermet fritté conduit à une mauvaise tenue à la corrosion électrochimique. Tableau I Lot Nombre d'essais Conductivité électrique à 1000°C (Ω-1.cm-1) Vitesse de corrosion (cm/an) Rapport Fe/Ni 1 4 77 6,4 ± 1 3,039 2 - 48 - 2,88 3 2 103 7,2 ± 1,5 3,087 4 2 139 12,8 ± 1,5 2,73 The comparison of the results on batches 1 and 3 shows that the anodes can be manufactured according to the invention with small amounts of organic binder while maintaining a low rate of corrosion and while obtaining a high value for electrical conductivity when hot. Comparison of the results of lots 3 and 4 shows that an excessive NiO phase content in the sintered cermet leads to poor resistance to electrochemical corrosion. Table I Lot Number of trials Electrical conductivity at 1000 ° C (Ω -1 .cm -1) Corrosion rate (cm / year) Fe / Ni ratio 1 4 77 6.4 ± 1 3,039 2 - 48 - 2.88 3 2 103 7.2 ± 1.5 3,087 4 2 139 12.8 ± 1.5 2.73

Claims (24)

  1. Process for manufacturing an inert cermet anode of the NiO-NiFe2O4-M type comprising at least a nickel monoxide phase N, a nickel spinel phase S containing iron and nickel, and a metallic phase M, containing copper and nickel, the said process being characterised in that it comprises:
    - preparation of an initial mixture including at least one precursor of the said monoxide phase N and the spinel phase S, a precursor of the metallic phase M and an organic binder, the proportion of the organic binder in the initial mixture being less than 2.0% by weight, the precursor of the metallic phase comprising a metallic powder containing copper and nickel, the precursor of the monoxide and spinel phases comprising a mixture of oxides comprising a nickel oxide and a nickel ferrite, the ratio between the proportion by mass of nickel oxide and the proportion by mass of nickel ferrite being between 0.2/99.8 and 30/70,
    - a mixture shaping operation, so as to form a green anode with a determined shape,
    - a green anode sintering operation, at a temperature higher than 900°C in a controlled atmosphere containing at least an inert gas and oxygen, and in that the proportion of the monoxide phase in the cermet is less than 40% by weight.
  2. Process according to claim 1, characterised in that the said metallic powder is a mixture of a metallic copper powder and a metallic nickel powder.
  3. Process according to claim 1, characterised in that the said metallic powder consists partly or entirely of a copper and nickel alloy.
  4. Process according to any one of claims 1 to 3, characterised in that the size of at least 95% by weight of the grains of the said metallic powder is between 3 and 10 µm.
  5. Process according to any one of claims 1 to 4, characterised in that the proportion of metallic powder in the initial mixture is more than 15% by weight, and preferably more than 20% by weight.
  6. Process according to any one of claims 1 to 5, characterised in that the proportion of nickel in the metallic powder of the precursor for the metallic phase is more than or equal to 3% by weight, and preferably between 3 and 30% by weight.
  7. Process according to any one of claims 1 to 6, characterised in that the proportion of the organic binder in the initial mixture is between 0.5 and 1.5% by weight.
  8. Process according to any one of claims 1 to 7, characterised in that the precursor of the monoxide and spinel phases is a powder for which the size of at least 95% by weight of the grains is between 5 and 10 µm.
  9. Process according to any one of claims 1 to 8, characterised in that the proportion of nickel ferrite in the initial mixture is between 50 and 85% by weight.
  10. Process according to any one of claims 1 to 8, characterised in that the proportion of nickel ferrite in the initial mixture is between 60 and 85% by weight.
  11. Process according to any one of claims 1 to 10, characterised in that the proportion of nickel oxide in the initial mixture is between 0.1% by weight and 25% by weight.
  12. Process according to any one of claims 1 to 11, characterised in that the ratio between the proportion by mass of nickel oxide and the proportion by mass of nickel ferrite is between 0.2/99.8 and 20/80.
  13. Process according to any one of claims 1 to 12, characterised in that the proportions of the precursors of the monoxide, spinel and metallic phases in the initial mixture and the sintering temperature are adjusted so as to obtain the atomic ratio between iron and nickel (Fe/Ni) in the spinel phase S of the cermet greater than or equal to 2.4, and preferably greater than or equal to 2.8.
  14. Process according to any one of claims 1 to 13, characterised in that the shaping operation of the green part is done by cold isostatic pressing.
  15. Process according to any one of claims 1 to 14, characterised in that the said controlled atmosphere comprises between 10 and 200 ppm of oxygen.
  16. Process according to any one of claims 1 to 15, characterised in that the sintering temperature is between 1150 and 1400°C and preferably between 1300 and 1400°C.
  17. Process according to any one of claims 1 to 16, characterised in that it includes a slow cooling step at a rate of between -10° and -100°/hour, between the sintering temperature and an intermediate temperature between 900 and 1000°C, after a step in which the sintering temperature is maintained.
  18. Process according to any one of claims 1 to 17, characterised in that the initial mixture also comprises at least one element for limiting oxidation of the metallic phase of the cermet, such as silver.
  19. Process according to any one of claims 1 to 18, characterised in that the spinel phase also comprises at least one substitution element capable of increasing its electrical conductivity.
  20. Process according to claim 19, characterised in that the said substitution element is a tetravalent element.
  21. Process according to any one of claims 1 to 20, characterised in that the electrical conductivity of the cermet at a temperature of between 900°C and 1050°C is higher than 50 Ω-1.cm-1, and is preferably higher than 100 Ω-1.cm-1.
  22. Use of the process according to any one of claims 1 to 21, for the fabrication of inert anodes to be used for the production of aluminium by fused bath electrolysis.
  23. Use of an inert anode or an assembly of inert anodes, obtained by the process according to any one of claims 1 to 21, for the production of aluminium by fused bath electrolysis.
  24. Electrolytic cell intended for the production of aluminium by fused bath electrolysis comprising at least one inert anode produced by the manufacturing process according to any one of claims 1 to 21.
EP04718991A 2003-03-12 2004-03-10 Method for the manufacture of an inert anode for the production of aluminium by means of fusion electrolysis Expired - Lifetime EP1601820B1 (en)

Priority Applications (1)

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SI200430790T SI1601820T1 (en) 2003-03-12 2004-03-10 Method for the manufacture of an inert anode for the production of aluminium by means of fusion electrolysis

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FR0303045 2003-03-12
FR0303045A FR2852331B1 (en) 2003-03-12 2003-03-12 PROCESS FOR PRODUCING AN INERT ANODE FOR ALUMINUM PRODUCTION BY IGNEE ELECTROLYSIS
PCT/FR2004/000563 WO2004082355A2 (en) 2003-03-12 2004-03-10 Method for the manufacture of an inert anode for the production of aluminium by means of fusion electrolysis

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EP1601820B1 true EP1601820B1 (en) 2008-05-21

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AU (1) AU2004222545B2 (en)
DE (1) DE602004013935D1 (en)
ES (1) ES2305745T3 (en)
FR (1) FR2852331B1 (en)
IS (1) IS2627B (en)
NO (1) NO20054641L (en)
RU (1) RU2336369C2 (en)
SI (1) SI1601820T1 (en)
WO (1) WO2004082355A2 (en)
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CN101255570B (en) * 2007-12-07 2010-07-07 东北大学 Inert anode material for aluminium electrolysis and method for manufacturing same

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CN101713083B (en) * 2008-06-02 2011-09-28 王飚 Molten-salt electrolytic aluminum inert anode, preparation method and application thereof
MY153924A (en) 2008-09-08 2015-04-15 Rio Tinto Alcan Int Ltd Metallic oxygen evolving anode operating at high current density for aluminium reduction cells.
CN102489700B (en) * 2011-12-23 2013-06-19 长沙理工大学 Cu-Ni-Al alloy powder and preparation method thereof
CN102732765A (en) * 2012-07-18 2012-10-17 武汉科技大学 Metal ceramic matrix used as aluminium electrolyzing inert anode and preparation method thereof
AU2014248631B2 (en) 2013-03-13 2016-07-21 Alcoa Usa Corp. Systems and methods of protecting electrolysis cell sidewalls
CN103556184B (en) * 2013-11-13 2016-01-20 昆明冶金研究院 A kind of full moist type nano-Ni/Fe 2o 4the preparation method of-NiO-Cu-Ni cermet inert anode
FR3022917B1 (en) * 2014-06-26 2016-06-24 Rio Tinto Alcan Int Ltd ELECTRODE MATERIAL AND ITS USE IN THE MANUFACTURE OF INERT ANODE
CN104047035A (en) * 2014-06-27 2014-09-17 中国铝业股份有限公司 Inert anode for fused salt electrolysis and preparation method thereof
RU2590362C1 (en) * 2015-01-22 2016-07-10 Федеральное государственное автономное образовательное учреждение высшего&nbsp Method of producing inert anode of cast composite material
GB2535338B (en) * 2015-02-06 2017-01-25 Ceres Ip Co Ltd Electrolyte forming process
GB2524638B (en) 2015-02-06 2016-04-06 Ceres Ip Co Ltd Electrolyte forming process
FR3034433B1 (en) 2015-04-03 2019-06-07 Rio Tinto Alcan International Limited CERMET MATERIAL OF ELECTRODE
CN110282966A (en) * 2019-06-26 2019-09-27 北京信息科技大学 A kind of New Nickel ferrite ceramic material and preparation method thereof
CN113215429A (en) * 2021-04-30 2021-08-06 中南大学 Preparation method of high-density metal ceramic inert anode material for aluminum electrolysis
CN117362068B (en) * 2023-10-31 2024-05-03 昆明理工大学 Preparation method of spinel-based porous heat-insulating cover plate for aluminum electrolysis

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US5865980A (en) * 1997-06-26 1999-02-02 Aluminum Company Of America Electrolysis with a inert electrode containing a ferrite, copper and silver
US6423204B1 (en) * 1997-06-26 2002-07-23 Alcoa Inc. For cermet inert anode containing oxide and metal phases useful for the electrolytic production of metals

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AU2004222545A1 (en) 2004-09-30
FR2852331A1 (en) 2004-09-17
RU2336369C2 (en) 2008-10-20
ES2305745T3 (en) 2008-11-01
FR2852331B1 (en) 2005-04-15
WO2004082355A2 (en) 2004-09-30
IS8063A (en) 2005-10-06
NO20054641D0 (en) 2005-10-10
CN100507090C (en) 2009-07-01
SI1601820T1 (en) 2008-10-31
DE602004013935D1 (en) 2008-07-03
ZA200508244B (en) 2007-01-31
NO20054641L (en) 2005-12-12
WO2004082355A3 (en) 2004-10-28
CN1759207A (en) 2006-04-12
AU2004222545B2 (en) 2009-03-26
AR043490A1 (en) 2005-08-03
ATE396290T1 (en) 2008-06-15
RU2005131580A (en) 2006-02-10
IS2627B (en) 2010-05-15

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