EP0322326B1 - Protective coating for studs and emerging parts of prebaked anodes - Google Patents
Protective coating for studs and emerging parts of prebaked anodes Download PDFInfo
- Publication number
- EP0322326B1 EP0322326B1 EP19880420430 EP88420430A EP0322326B1 EP 0322326 B1 EP0322326 B1 EP 0322326B1 EP 19880420430 EP19880420430 EP 19880420430 EP 88420430 A EP88420430 A EP 88420430A EP 0322326 B1 EP0322326 B1 EP 0322326B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- anodes
- alumina
- anode
- logs
- protective coating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 239000011253 protective coating Substances 0.000 title claims description 4
- 239000000203 mixture Substances 0.000 claims description 21
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 18
- 239000004568 cement Substances 0.000 claims description 16
- 238000005868 electrolysis reaction Methods 0.000 claims description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 10
- 229910052782 aluminium Inorganic materials 0.000 claims description 9
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 9
- 238000005260 corrosion Methods 0.000 claims description 7
- 230000007797 corrosion Effects 0.000 claims description 7
- 229910052596 spinel Inorganic materials 0.000 claims description 7
- 239000011029 spinel Substances 0.000 claims description 7
- 239000000463 material Substances 0.000 claims description 5
- XFWJKVMFIVXPKK-UHFFFAOYSA-N calcium;oxido(oxo)alumane Chemical compound [Ca+2].[O-][Al]=O.[O-][Al]=O XFWJKVMFIVXPKK-UHFFFAOYSA-N 0.000 claims description 4
- 239000012535 impurity Substances 0.000 claims description 4
- 230000003647 oxidation Effects 0.000 claims description 4
- 238000007254 oxidation reaction Methods 0.000 claims description 4
- 238000009626 Hall-Héroult process Methods 0.000 claims description 3
- 239000011248 coating agent Substances 0.000 claims description 3
- 238000000576 coating method Methods 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 claims description 3
- 239000000843 powder Substances 0.000 claims 2
- 239000004411 aluminium Substances 0.000 claims 1
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 7
- 229910000831 Steel Inorganic materials 0.000 description 5
- 239000011777 magnesium Substances 0.000 description 5
- 238000005507 spraying Methods 0.000 description 5
- 239000010959 steel Substances 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 4
- QDOXWKRWXJOMAK-UHFFFAOYSA-N dichromium trioxide Chemical compound O=[Cr]O[Cr]=O QDOXWKRWXJOMAK-UHFFFAOYSA-N 0.000 description 4
- 229910052742 iron Inorganic materials 0.000 description 4
- 229910052749 magnesium Inorganic materials 0.000 description 4
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 3
- 235000011941 Tilia x europaea Nutrition 0.000 description 3
- 150000004645 aluminates Chemical class 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 239000000571 coke Substances 0.000 description 3
- 239000004571 lime Substances 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 239000004215 Carbon black (E152) Substances 0.000 description 2
- 239000000654 additive Substances 0.000 description 2
- RHZUVFJBSILHOK-UHFFFAOYSA-N anthracen-1-ylmethanolate Chemical compound C1=CC=C2C=C3C(C[O-])=CC=CC3=CC2=C1 RHZUVFJBSILHOK-UHFFFAOYSA-N 0.000 description 2
- 239000003830 anthracite Substances 0.000 description 2
- 229910052681 coesite Inorganic materials 0.000 description 2
- 229910052593 corundum Inorganic materials 0.000 description 2
- 229910052906 cristobalite Inorganic materials 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 238000000605 extraction Methods 0.000 description 2
- 239000012530 fluid Substances 0.000 description 2
- 238000009472 formulation Methods 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 239000010439 graphite Substances 0.000 description 2
- 230000009931 harmful effect Effects 0.000 description 2
- 229930195733 hydrocarbon Natural products 0.000 description 2
- 150000002430 hydrocarbons Chemical class 0.000 description 2
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
- 238000001465 metallisation Methods 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- NOTVAPJNGZMVSD-UHFFFAOYSA-N potassium monoxide Inorganic materials [K]O[K] NOTVAPJNGZMVSD-UHFFFAOYSA-N 0.000 description 2
- CHWRSCGUEQEHOH-UHFFFAOYSA-N potassium oxide Chemical compound [O-2].[K+].[K+] CHWRSCGUEQEHOH-UHFFFAOYSA-N 0.000 description 2
- 238000007493 shaping process Methods 0.000 description 2
- 239000000377 silicon dioxide Substances 0.000 description 2
- 235000012239 silicon dioxide Nutrition 0.000 description 2
- 239000007921 spray Substances 0.000 description 2
- 229910052682 stishovite Inorganic materials 0.000 description 2
- 229910052905 tridymite Inorganic materials 0.000 description 2
- 229910001845 yogo sapphire Inorganic materials 0.000 description 2
- 244000000626 Daucus carota Species 0.000 description 1
- 235000002767 Daucus carota Nutrition 0.000 description 1
- HIGRAKVNKLCVCA-UHFFFAOYSA-N alumine Chemical compound C1=CC=[Al]C=C1 HIGRAKVNKLCVCA-UHFFFAOYSA-N 0.000 description 1
- 150000001491 aromatic compounds Chemical class 0.000 description 1
- 229910021383 artificial graphite Inorganic materials 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000004939 coking Methods 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 230000000295 complement effect Effects 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 229910001610 cryolite Inorganic materials 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 239000003822 epoxy resin Substances 0.000 description 1
- LNEPOXFFQSENCJ-UHFFFAOYSA-N haloperidol Chemical compound C1CC(O)(C=2C=CC(Cl)=CC=2)CCN1CCCC(=O)C1=CC=C(F)C=C1 LNEPOXFFQSENCJ-UHFFFAOYSA-N 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 235000011837 pasties Nutrition 0.000 description 1
- 230000001766 physiological effect Effects 0.000 description 1
- 229920000647 polyepoxide Polymers 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 238000004416 surface enhanced Raman spectroscopy Methods 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
- 230000004580 weight loss Effects 0.000 description 1
Classifications
-
- 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
- C25C3/125—Anodes based on carbon
-
- 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
- C25C7/025—Electrodes; Connections thereof used in cells for the electrolysis of melts
Definitions
- the invention relates to a coating for protection against corrosion and hot oxidation for pre-baked anode logs and the emerging carbonaceous part of these anodes used in aluminum production tanks by electrolysis of alumina dissolved in the cryolite melted using the Hall-Héroult process.
- anode plugs are introduced into the upper part of the anode, into which logs (or steel plates) will be introduced and sealed. ) which will serve both to suspend the anode from the anode frame and to supply it with current.
- the sealing is carried out by casting iron or more rarely by means of a carbonaceous paste of special composition.
- the steel logs are subjected both to a high temperature and to the corrosive effect of the fluorinated effluents emitted by the tank in operation.
- the molten cryolithic bath can come into contact with the base. steel logs.
- the emerging part of the anodes that is to say the upper part which, in normal operation of the electrolytic cell, is not immersed in the molten electrolyte, undergoes degradation by combustion, that l 'It is sought to avoid by covering a solidified and ground electrolysis bath, possibly mixed with alumina, or by metallization obtained by spraying liquid aluminum.
- SERS European patent application EP 0 269 534
- This composition is essentially characterized by a carbon aggregate such as coke, artificial graphite, waste anodes or semi-graphite electrodes with a low ash content (preferably ⁇ 2%) bound by a lime aluminate cement, to low content of annoying impurities (SiO2, Fe2O3, TiO2, K2O, Cr2O3, total content preferably less than 1%) having an alumina content at least equal to 70% and, preferably, at least equal to 80%, the together being linked by addition of water.
- a carbon aggregate such as coke, artificial graphite, waste anodes or semi-graphite electrodes with a low ash content (preferably ⁇ 2%) bound by a lime aluminate cement, to low content of annoying impurities (SiO2, Fe2O3, TiO2, K2O, Cr2O3, total content preferably less than 1%) having an alumina content at least equal to 70% and, preferably, at least equal to 80%, the together being linked by addition of water.
- a complementary addition of magnesium spinel (Al2O3, MgO), whose thermal conductivity is high, makes it possible to lower the temperature of the surface of the anode, thus delaying oxidation.
- alumina for example alumina for electrolysis or globular alumina, at a content which can constitute up to 50% of the total weight of the aggregate.
- the cement content by weight, expressed in weight percent of the aggregate (carbon product + additives) is between 10 and 60% and, preferably, from 15 to 50%. It is appropriate to denote by "dry matter” the whole of the aggregate (carbonaceous product, alumina, additives) and the cement.
- the same compositions are suitable, but it is then preferable to apply them by spraying with a gun.
- a gun it is necessary, depending on the type of gun used, to control the particle size of the aggregate and the cement (less than 1 mm and, preferably, less than 0.5 mm) and significantly increase the quantity of water.
- This amount of water will be fixed, for example, between 10 and 70% by weight relative to the dry matter (as defined above) for use in the form of collar paste and, up to 60% by weight for use in the form of a fluid paste to be sprayed on with a spray gun.
- the object of the present invention is a protective composition which does not have the drawbacks of carbonaceous pastes or comprising a carbonaceous aggregate, and which provides effective protection of the base of the steel logs and possibly of the carbonaceous part emerging from the anodes throughout the lifespan of the anodes (about twenty days on average).
- This composition is characterized by a mixture of dry materials made up of lime aluminate cement, magnesium spinel, possibly fine powdered alumina and water.
- the lime aluminate cement has an alumina content of at least 70% and preferably 80% by weight. It preferably contains less than 1% of annoying impurities (SiO2, Fe2O3, TiO2, K2O, Cr2O3)
- composition of the dry matter mixture is located in the following ranges:
- the amount of water is between 10 and 80% of the total weight of the dry matter, the contents between 10 and about 50% corresponding to a pasty composition, usable as flange paste, and the contents going up to 80% corresponding to a fluid paste usable by spraying with a gun, with, in this case, a particle size of the dry materials less than 1 mm and preferably less than 0.5 mm.
- the protective coating of the emerging part of prebaked anodes was implemented according to three formulations for application by spraying with a spray gun, which is adapted - by reducing the water content - for the use of paste paste.
- the carbon substrate for the tests consists of a core 30 mm in diameter and 120 mm high.
- the different compositions A, B, C are applied to a group of samples and a certain number of controls are kept without coating. All the samples are treated for 1 hour at 1000 ° C. under nitrogen to remove all traces of water.
- a 2 hour carboxyreactivity test is then carried out at 1000 ° C. under a CO2 flow rate of 50 liters / hour.
- the samples are cooled under a stream of nitrogen and each carrot is weighed to determine its weight loss.
- the results are expressed in milligrams related to an area of 1 cm2 and for a duration of 1 hour. The result is therefore given in mg.cm ⁇ 2.h ⁇ 1.
- the following results were obtained:
- the optimal compositions expressed in Secar Cement / Secar cement + Al2O3 + Spinel ratio being between 5 and 50%.
- the percentage of water to be added depends on the cement content and the particle size of the alumina. It is between 30 and 50 and preferably between 35 and 45% by weight relative to dry matter (that is to say 35 to 45 grams of water per 100 grams of the mixture of Secar cement + alumina + magnesium spinel ).
- the reduction in corrosion of the anode logs is evident from the first cycle and is accentuated during the following cycles. It can be estimated that the useful life of the anode logs is extended by at least 30%.
- Secar cement based on calcium aluminate having an alumina content at least equal to 70% and preferably at least equal to 80%.
- the composition of Secar 80 and 71 cements from the company LAFARGE FONDU INTERNATIONAL and Spinel of Magnesium, from PEM (PECHINEY ELECTROMETALLURGY) are recalled below:
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electrolytic Production Of Metals (AREA)
- Prevention Of Electric Corrosion (AREA)
- Furnace Housings, Linings, Walls, And Ceilings (AREA)
- Preventing Corrosion Or Incrustation Of Metals (AREA)
Description
L'invention concerne un revêtement de protection contre la corrosion et l'oxydation à chaud destiné aux rondins d'anodes précuites et à la partie carbonée émergeante de ces anodes utilisées dans les cuves de production d'aluminium par électrolyse d'alumine dissoute dans de la cryolithe fondue selon le procédé Hall-Héroult.The invention relates to a coating for protection against corrosion and hot oxidation for pre-baked anode logs and the emerging carbonaceous part of these anodes used in aluminum production tanks by electrolysis of alumina dissolved in the cryolite melted using the Hall-Héroult process.
La plupart des cuves modernes pour la production électrolytique selon le procédé Hall-Héroult utilisent des anodes carbonées dites "précuites" obtenues par mise en forme à 120-160°C environ d'une pâte carbonée essentiellement constituée de coke (et/ou anthracite) et de brai, puis cuisson pendant une centaine d'heures à 1150/1200°C.Most modern tanks for electrolytic production according to the Hall-Héroult process use carbonaceous anodes called "precooked" obtained by shaping at around 120-160 ° C a carbonaceous paste essentially consisting of coke (and / or anthracite) and pitch, then baking for a hundred hours at 1150/1200 ° C.
Lors de la mise en forme de la pâte, on ménage, à la partie supérieure de l'anode, un certain nombre de cavités souvent appelées "bouchons d'anode" dans lesquelles on introduira et scellera des rondins (ou des plaques d'aciers) qui serviront à la fois à suspendre l'anode au cadre anodique et à l'alimenter en courant. Le scellement est effectué par coulée de fonte ou plus rarement au moyen d'une pâte carbonée de composition spéciale.During the shaping of the dough, a number of cavities, often called "anode plugs", are introduced into the upper part of the anode, into which logs (or steel plates) will be introduced and sealed. ) which will serve both to suspend the anode from the anode frame and to supply it with current. The sealing is carried out by casting iron or more rarely by means of a carbonaceous paste of special composition.
Les rondins d'acier sont soumis à la fois à une température élevée et à l'effet corrosif des effluents fluorés émis par la cuve en fonctionnement. En outre, lors de certaines opérations, par exemple lors d'une descente d'anodes destinée à faire cesser un "effet anodique", ou lors de "vagues" dans l'électrolyte, du bain cryolithique fondu peut entrer en contact avec la base des rondins d'acier.The steel logs are subjected both to a high temperature and to the corrosive effect of the fluorinated effluents emitted by the tank in operation. In addition, during certain operations, for example during an anode descent intended to stop an "anodic effect", or during "waves" in the electrolyte, the molten cryolithic bath can come into contact with the base. steel logs.
Ces diverses causes font que la teneur en fer de l'aluminium produit dans la cuve est sensiblement augmentée par la corrosion de base des rondins. Cette corrosion a aussi pour effet nocif de réduire la durée de vie de l'ensemble de suspension des anodes (rondins + barres de liaison entre les rondins et la tige d'anode) qui sont normalement récupérés et réutilisés après extraction de la cuve des anodes uséesThese various causes cause the iron content of the aluminum produced in the tank to be appreciably increased by the basic corrosion of the logs. This corrosion also has the harmful effect of reducing the service life of the anode suspension assembly (logs + connecting bars between the logs and the anode rod) which are normally recovered and reused. after extraction of the spent anode tank
De même, la partie émergeante des anodes, c'est-à-dire la partie supérieure qui, en fonctionnement normal de la cuve d'électrolyse, n'est pas immergée dans l'électrolyte fondu, subit une dégradation par combustion, que l'on cherche à éviter par un recouvrement de bain d'électrolyse solidifié et broyé, éventuellement mélangé d'alumine, ou encore par une métallisation obtenue par projection d'aluminium liquide.Similarly, the emerging part of the anodes, that is to say the upper part which, in normal operation of the electrolytic cell, is not immersed in the molten electrolyte, undergoes degradation by combustion, that l 'It is sought to avoid by covering a solidified and ground electrolysis bath, possibly mixed with alumina, or by metallization obtained by spraying liquid aluminum.
On a également cherché à protéger la base des rondins par différents procédés tels que la métallisation par projection d'aluminium liquide ou la mise en place, autour des rondins, d'une collerette en aluminium laissant avec le rondin (ou la plaque) un espace de 10 à 30 mm que l'on remplit d'une pâte carbonée coulée à chaud. On a proposé pour cela des pâtes carbonées classiques (coke et/ou anthracite et/ou graphite + brai) ou des compositions plus complexes comportant des produits organiques polymérisables et cokéfiables tels que résines époxy, résines furfuryliques, etc... (demande de brevet allemand DE-AS 25 47 061).We have also sought to protect the base of the logs by various methods such as metallization by projection of liquid aluminum or the installation, around the logs, of an aluminum flange leaving with the log (or the plate) a space from 10 to 30 mm which is filled with a carbonaceous paste poured hot. For this, conventional carbonaceous pastes (coke and / or anthracite and / or graphite + pitch) have been proposed or more complex compositions comprising polymerizable and coking organic products such as epoxy resins, furfuryl resins, etc. (patent application German DE-AS 25 47 061).
Toutefois, ces compositions hydrocarbonées ont pour inconvénient majeur de provoquer, dès la mise en service de l'anode, qui atteint progressivement sa température d'équilibre, un dégagement de vapeurs d'hydrocarbures provenant du craquage de la pâte carbonée. Certains composés aromatiques ainsi formés sont soupçonnés d'effets physiologiques néfastes, et, en outre, ils polluent et favorisent l'obstruction des circuits d'aspiration et de lavage d'effluents sur les cuves d'électrolyse. Pour toutes ces raisons, les "pâtes de collerettes" composées uniquement de produits carbonés ne satisfont plus les exploitants de cuves d'électrolyse à anodes précuites. Or, la tendance actuelle est, précisément, de produire dans les cuves un aluminium primaire de pureté aussi élevée que possible. La corrosion de la base des rondins étant une des sources de fer dans l'aluminium produit, il importait donc de trouver un moyen de protection efficace et qui, de préférence, s'applique également à la partie carbonée émergeante des anodes.However, these hydrocarbon compositions have the major drawback of causing, as soon as the anode is put into service, which gradually reaches its equilibrium temperature, a release of hydrocarbon vapors from the cracking of the carbonaceous paste. Certain aromatic compounds thus formed are suspected of harmful physiological effects, and, in addition, they pollute and favor the obstruction of the suction and washing circuits of effluents on the electrolytic cells. For all these reasons, "flange pastes" composed solely of carbonaceous products no longer satisfy the operators of electrolysis tanks with prebaked anodes. However, the current trend is, precisely, to produce in the primary primary aluminum of as high a purity as possible. Corrosion of the base of the logs being one of the sources of iron in the aluminum produced, it was therefore important to find an effective means of protection which, preferably, also applies to the carbonaceous part emerging from the anodes.
La demande de brevet européen EP 0 269 534 (SERS) a pour objet une composition de pâte de collerette ne présentant pas les inconvénients des pâtes carbonées, et assurant une protection efficace de la base des rondins d'acier et éventuellement de la partie carbonée émergeante des anodes pendant toute la durée de vie des anodes (soit une vingtaine de jours en moyenne). Cette composition est essentiellement caractérisée par un agrégat carboné tel que coke, graphite artificiel, déchets d'anodes ou d'électrodes semi-graphite à faible teneur en cendre (de préférence < 2%) lié par un ciment d'aluminate de chaux, à faible teneur en impuretés gênantes (SiO₂, Fe₂O₃, TiO₂, K₂O, Cr₂O₃, teneur totale de préférence inférieure à 1%) ayant une teneur en alumine au moins égale à 70% et, de préférence, au moins égale à 80%, l'ensemble étant lié par addition d'eau.The subject of European patent application EP 0 269 534 (SERS) is a flange paste composition which does not have the drawbacks of carbonaceous pastes, and which provides effective protection of the base of the steel logs and possibly of the carbonaceous part emerging from the anodes during the entire life of the anodes (about twenty days on average). This composition is essentially characterized by a carbon aggregate such as coke, artificial graphite, waste anodes or semi-graphite electrodes with a low ash content (preferably <2%) bound by a lime aluminate cement, to low content of annoying impurities (SiO₂, Fe₂O₃, TiO₂, K₂O, Cr₂O₃, total content preferably less than 1%) having an alumina content at least equal to 70% and, preferably, at least equal to 80%, the together being linked by addition of water.
Ces impuretés sont qualifiées de gênantes car, introduites dans le bain d'électrolyse, elles sont réduites et les métaux correspondants Si, Fe, Ti, Cr, Mn, K s'allient à l'aluminium liquide.These impurities are classified as troublesome because, introduced into the electrolysis bath, they are reduced and the corresponding metals Si, Fe, Ti, Cr, Mn, K are combined with liquid aluminum.
Une addition complémentaire de spinelle de magnésium (Al₂O₃, MgO), dont la conductivité thermique est élevée, permet d'abaisser la température de la surface de l'anode, retardant ainsi l'oxydation.A complementary addition of magnesium spinel (Al₂O₃, MgO), whose thermal conductivity is high, makes it possible to lower the temperature of the surface of the anode, thus delaying oxidation.
On peut également effectuer dans la pâte une addition d'alumine, par exemple de l'alumine pour électrolyse ou de l'alumine globulaire, à une teneur pouvant constituer jusqu'à 50 % du poids total de l'agrégat.It is also possible to add alumina to the paste, for example alumina for electrolysis or globular alumina, at a content which can constitute up to 50% of the total weight of the aggregate.
La teneur pondérale en ciment, exprimée en pour-cent en poids de l'agrégat (produit carboné+additifs) est comprise entre 10 et 60 % et, de préférence, de 15 à 50 %. On convient de désigner par "matière sèche" l'ensemble de l'agrégat (produit carboné, alumine, additifs) et du ciment.The cement content by weight, expressed in weight percent of the aggregate (carbon product + additives) is between 10 and 60% and, preferably, from 15 to 50%. It is appropriate to denote by "dry matter" the whole of the aggregate (carbonaceous product, alumina, additives) and the cement.
Pour la protection de la partie émergeante de l'anode, les mêmes compositions conviennent, mais il est alors préférable de les appliquer par projection au pistolet. Pour cela, il est nécessaire, en fonction du type de pistolet utilisé, de contrôler la granulométrie de l'agrégat et du ciment (inférieure à 1 mm et, de préférence, inférieure à 0,5 mm) et d'augmenter sensiblement la quantité d'eau.For the protection of the emerging part of the anode, the same compositions are suitable, but it is then preferable to apply them by spraying with a gun. For this, it is necessary, depending on the type of gun used, to control the particle size of the aggregate and the cement (less than 1 mm and, preferably, less than 0.5 mm) and significantly increase the quantity of water.
Cette quantité d'eau sera fixée, par exemple, entre 10 et 70 % en poids par rapport à la matière sèche (telle que définie ci-dessus) pour l'utilisation sous forme de pâte de collerette et, jusqu'à 60% en poids pour l'utilisation sous forme de pâte fluide à projeter au pistolet.This amount of water will be fixed, for example, between 10 and 70% by weight relative to the dry matter (as defined above) for use in the form of collar paste and, up to 60% by weight for use in the form of a fluid paste to be sprayed on with a spray gun.
L'objet de la présente invention est une composition de protection ne présentant pas les inconvénients des pâtes carbonées ou comportant un agrégat carboné, et assurant une protection efficace de la base des rondins d'acier et éventuellement de la partie carbonée émergeante des anodes pendant toute la durée de vie des anodes (soit une vingtaine de jours en moyenne). Cette composition est caractérisée par un mélange de matières sèches constituées de ciment d'aluminate de chaux, de spinelle de magnésium, éventuellement d'alumine en poudre fine et d'eau.The object of the present invention is a protective composition which does not have the drawbacks of carbonaceous pastes or comprising a carbonaceous aggregate, and which provides effective protection of the base of the steel logs and possibly of the carbonaceous part emerging from the anodes throughout the lifespan of the anodes (about twenty days on average). This composition is characterized by a mixture of dry materials made up of lime aluminate cement, magnesium spinel, possibly fine powdered alumina and water.
Le ciment d'aluminate de chaux a une teneur en alumine égale au moins à 70 % et de préférence à 80% en poids. Il contient de préférence moins de 1 % d'impuretés gênantes (SiO₂, Fe₂O₃, TiO₂, K₂O, Cr₂O₃)The lime aluminate cement has an alumina content of at least 70% and preferably 80% by weight. It preferably contains less than 1% of annoying impurities (SiO₂, Fe₂O₃, TiO₂, K₂O, Cr₂O₃)
La composition du mélange de matières sèches est située dans les intervalles suivants :
La quantité d'eau se situe entre 10 et 80% du poids total des matières sèches, les teneurs entre 10 et environ 50 % correspondant à une composition pâteuse, utilisable comme pâte de collerette, et les teneurs allant jusqu'à 80% correspondant à une pâte fluide utilisable par projection au pistolet, avec, dans ce cas, une granulométrie des matières sèches inférieure à 1mm et de préférence inférieure à 0,5 mm.The amount of water is between 10 and 80% of the total weight of the dry matter, the contents between 10 and about 50% corresponding to a pasty composition, usable as flange paste, and the contents going up to 80% corresponding to a fluid paste usable by spraying with a gun, with, in this case, a particle size of the dry materials less than 1 mm and preferably less than 0.5 mm.
Le revêtement protecteur de la partie émergeante d'anodes précuites a été mis en oeuvre selon trois formulations pour application par pulvérisation au pistolet, que l'on adapte - en diminuant la teneur en eau - pour l'utilisation en pâte de collerettes.
Les conditions de pulvérisation ont été les suivantes : le substrat carboné pour les tests est constitué par une carotte de 30 mm de diamètre et de 120 mm de haut.
On applique les différentes compositions A,B,C sur un groupe d'échantillons et on conserve un certain nombre de témoins sans revêtement. L'ensemble des échantillons est traité 1 heure à 1000°C sous azote pour enlever toute trace d'eau. On effectue ensuite un test de carboxyréactivité de 2 heures à 1000°C sous un débit de CO₂ de 50 litres/heure. En fin de test, on refroidit les échantillons sous courant d'azote et on pèse chaque carotte pour déterminer sa perte de poids. Les résultats sont exprimés en milligrammes rapportés à une surface de 1 cm² et à une durée de 1 heure. Le résultat est donc donné en mg.cm⁻².h⁻¹.
On a obtenu les résultats suivants :
The different compositions A, B, C are applied to a group of samples and a certain number of controls are kept without coating. All the samples are treated for 1 hour at 1000 ° C. under nitrogen to remove all traces of water. A 2 hour carboxyreactivity test is then carried out at 1000 ° C. under a CO₂ flow rate of 50 liters / hour. At the end of the test, the samples are cooled under a stream of nitrogen and each carrot is weighed to determine its weight loss. The results are expressed in milligrams related to an area of 1 cm² and for a duration of 1 hour. The result is therefore given in mg.cm⁻².h⁻¹.
The following results were obtained:
On note l'efficacité particulière des formulations A et B qui réduisent la réactivité au CO₂ de près de 25 % .Note the particular effectiveness of formulations A and B which reduce the reactivity to CO₂ by almost 25%.
Des tests de longue durée ont été effectués en condition industrielle, sur la partie émergeante des anodes d'un certain nombre de cuves d'électrolyse Hall-Héroult. Les résultats sont moins précis du fait que les mégots d'anodes usées sont après leur retrait de la cuve, enrobés de bain d'électrolyse dont la séparation n'est jamais parfaite, mais ils confirment l'ordre de grandeur de 25% de diminution de l'oxydation de la partie émergeante des anodes précuites.Long-term tests were carried out under industrial conditions, on the emerging part of the anodes of a number of Hall-Héroult electrolysis cells. The results are less precise since the spent anode butts are coated with an electrolysis bath after their removal from the tank, the separation of which is never perfect, but they confirm the order of magnitude of 25% reduction. oxidation of the emerging part of the prebaked anodes.
Pour la protection des rondins d'anodes, le revêtement protecteur est mis en place à l'état de pâte. Les conditions de corrosion en cours d'électrolyse étant difficiles à simuler, on a procédé aux tests en conditions réelles, par mesure de la diminution du diamètre des rondins après extraction des anodes usées (soit après environ 3 semaines de séjour dans la cuve d'électrolyse).
Les compositions, pour cet usage, sont comprises dans les limites suivantes:
- Ciment
- : 10 à 95 %
- Alumine
- : 0 à 80 %
- Spinelle de Mg
- : 5 à 10 %
The compositions for this use are included within the following limits:
- Cement
- : 10 to 95%
- Alumina
- : 0 to 80%
- Mg Spinel
- : 5 to 10%
Les compositions optimales exprimées en rapport Ciment Secar/ciment Secar+Al₂O₃+Spinelle étant situées entre 5 et 50%. Le pourcentage d'eau à ajouter dépend de la teneur en ciment et de la granulométrie de l'alumine. Il se situe entre 30 et 50 et de préférence entre 35 et 45% en poids par rapport aux matières sèches (c'est-à-dire 35 à 45 grammes d'eau pour 100 grammes du mélange ciment Secar + alumine + spinelle de magnésium). La diminution de corrosion des rondins d'anode est évidente dès le premier cycle et s'accentue au cours des cycles suivants. On peut estimer que la durée de vie utile des rondins d'anodes est prolongée d'au moins 30 %.The optimal compositions expressed in Secar Cement / Secar cement + Al₂O₃ + Spinel ratio being between 5 and 50%. The percentage of water to be added depends on the cement content and the particle size of the alumina. It is between 30 and 50 and preferably between 35 and 45% by weight relative to dry matter (that is to say 35 to 45 grams of water per 100 grams of the mixture of Secar cement + alumina + magnesium spinel ). The reduction in corrosion of the anode logs is evident from the first cycle and is accentuated during the following cycles. It can be estimated that the useful life of the anode logs is extended by at least 30%.
Bien que l'invention ait été décrite dans le cas particulier de l'utilisation de ciment Secar, elle s'applique de la même façon avec tout ciment à base d'aluminate de calcium ayant une teneur en alumine au moins égale à 70% et de préférence au moins égale à 80%. On rappelle ci-après la composition des ciments Secar 80 et 71 de la Société LAFARGE FONDU INTERNATIONAL et du Spinelle de Magnésium, de PEM (PECHINEY ELECTROMETALLURGIE):
Claims (2)
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR878718452A FR2624886B2 (en) | 1986-11-14 | 1987-12-22 | IMPROVEMENT IN PROTECTIVE COATINGS FOR PRE-COOKED ANODES AND THE EMERGING PART OF THESE ANODES |
| FR8718452 | 1987-12-22 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0322326A1 EP0322326A1 (en) | 1989-06-28 |
| EP0322326B1 true EP0322326B1 (en) | 1992-08-12 |
Family
ID=9358501
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP19880420430 Expired - Lifetime EP0322326B1 (en) | 1987-12-22 | 1988-12-21 | Protective coating for studs and emerging parts of prebaked anodes |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0322326B1 (en) |
| AU (1) | AU610964B2 (en) |
| BR (1) | BR8806778A (en) |
| CA (1) | CA1340408C (en) |
| DE (1) | DE3873713T2 (en) |
| ES (1) | ES2043877T3 (en) |
| IN (1) | IN169360B (en) |
| IS (1) | IS1465B6 (en) |
| NO (1) | NO885645L (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2606796B1 (en) * | 1986-11-14 | 1989-02-03 | Savoie Electrodes Refract | PROTECTIVE COATING FOR PRE-COOKED ANODE ROUND |
| NO930957L (en) * | 1993-03-17 | 1994-09-19 | Norsk Hydro As | Marterial composite for oxidation and corrosion protection of anode nipples |
| US6818106B2 (en) * | 2002-01-25 | 2004-11-16 | Alcoa Inc. | Inert anode assembly |
| WO2004035870A1 (en) * | 2002-10-18 | 2004-04-29 | Moltech Invent S.A. | Anode current feeding connection stem |
| ES2644864T3 (en) * | 2002-11-25 | 2017-11-30 | Alcoa Inc. | Inert Anode Assembly |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1365820A (en) * | 1972-02-15 | 1974-09-04 | Zirconal Processes Ltd | Coating composition suitable for use at high temperatures |
| FR2411166A1 (en) * | 1977-12-12 | 1979-07-06 | Lafarge Fondu Int | REFRACTORY HYDRAULIC BINDER BASED ON CALCIUM ALUMINATE AND ITS PREPARATION PROCESS |
| US4354918A (en) * | 1981-01-14 | 1982-10-19 | Martin Marietta Corporation | Anode stud coatings for electrolytic cells |
| JPS61111983A (en) * | 1984-11-02 | 1986-05-30 | ミサワホ−ム株式会社 | Manufacture of foamed concrete |
| BR8500347A (en) * | 1985-01-25 | 1986-09-09 | Ardal Og Sunndal Verk | PRE-COOKED ANODE WITH REDUCED CARBON LOSS FOR EMPLOYMENT IN ALUMINUM PRODUCTION BY REDUCTION BY ELECTROLYTIC FUSION AND THE PROCESS TO PRODUCE THE SAME |
-
1988
- 1988-11-21 IN IN814/MAS/88A patent/IN169360B/en unknown
- 1988-12-19 CA CA 586322 patent/CA1340408C/en not_active Expired - Fee Related
- 1988-12-20 NO NO88885645A patent/NO885645L/en unknown
- 1988-12-21 AU AU27429/88A patent/AU610964B2/en not_active Ceased
- 1988-12-21 DE DE19883873713 patent/DE3873713T2/en not_active Expired - Fee Related
- 1988-12-21 IS IS3424A patent/IS1465B6/en unknown
- 1988-12-21 EP EP19880420430 patent/EP0322326B1/en not_active Expired - Lifetime
- 1988-12-21 BR BR8806778A patent/BR8806778A/en not_active Application Discontinuation
- 1988-12-21 ES ES88420430T patent/ES2043877T3/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| NO885645L (en) | 1989-06-23 |
| DE3873713D1 (en) | 1992-09-17 |
| NO885645D0 (en) | 1988-12-20 |
| IN169360B (en) | 1991-09-28 |
| EP0322326A1 (en) | 1989-06-28 |
| CA1340408C (en) | 1999-02-23 |
| BR8806778A (en) | 1989-08-29 |
| IS1465B6 (en) | 1991-03-26 |
| AU610964B2 (en) | 1991-05-30 |
| ES2043877T3 (en) | 1994-01-01 |
| IS3424A7 (en) | 1989-06-23 |
| DE3873713T2 (en) | 1993-02-11 |
| AU2742988A (en) | 1989-06-22 |
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