CA1162880A - Anode of dimensionally stable oxide-ceramic individual elements - Google Patents
Anode of dimensionally stable oxide-ceramic individual elementsInfo
- Publication number
- CA1162880A CA1162880A CA000366990A CA366990A CA1162880A CA 1162880 A CA1162880 A CA 1162880A CA 000366990 A CA000366990 A CA 000366990A CA 366990 A CA366990 A CA 366990A CA 1162880 A CA1162880 A CA 1162880A
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- Prior art keywords
- oxide
- anode
- anode according
- ceramic
- elements
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Classifications
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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
Abstract
ABSTRACT OF THE DISCLOSURE
An anode of a fusion electrolysis furnace for the production of aluminium consists of a plurality of individual oxide-ceramic elements of stable dimensions; the individual elements have linear cross-sectional dimensions of 2-12 cm.
on the current exit surface, the elements have a length which corresponds to 2-20 times the value of the mean linear cross-sectional dimension, they are arranged approximately parallel with a mean distance between outer surfaces of 1-20 mm. and are held together mechanically stably at the end facing the current entry with an electrically conductive device situated outside the molten electrolyte; the anode in bundle configuration, in com-parison with oxide-ceramic anodes of large format, has a lower corrosion, is simpler to produce ceramically and has a greater stability to temperature changes.
An anode of a fusion electrolysis furnace for the production of aluminium consists of a plurality of individual oxide-ceramic elements of stable dimensions; the individual elements have linear cross-sectional dimensions of 2-12 cm.
on the current exit surface, the elements have a length which corresponds to 2-20 times the value of the mean linear cross-sectional dimension, they are arranged approximately parallel with a mean distance between outer surfaces of 1-20 mm. and are held together mechanically stably at the end facing the current entry with an electrically conductive device situated outside the molten electrolyte; the anode in bundle configuration, in com-parison with oxide-ceramic anodes of large format, has a lower corrosion, is simpler to produce ceramically and has a greater stability to temperature changes.
Description
1~L6~
Anode of dimensionally stable oxide-ceramic individual ele~ents The present inven-tion relates to an anode of a fusion electrolysis furnace for the prcduction of aluminium, which anode consists of a plurality of indiYidual oxide-cera~ic elements of stable d~ensions.
The currently-used Hall-Heroult process for obtaining aluminium from alun~na dissolved in cryolite takes place at 940 - 1000 C, and electrolysis is carried out between a horizontal anode and a parallel liquid aluminium cathode. m e anodically precipitated oxygen reacts with ~ the anode carbon to form carbon dioxide and the carbon burns away. At the same rate as the linear burning away of the anode takes place, in the case of suitable cell geometry the build--up of the aluminium layer takes place cathodically, so that the interpolar distance is maintained. After the scooping of the liquid aluminium the interpolar distance must be freshly adjusted by lowering of the anodes, furthermore burned-away carbon anode blocks must be replaced at regular intervals. A special works, the anode factory, is necessary for the production of these anode blocks.
Replacement of the burning carbon anodes by an axide-ceramic anode of stable dimensions should, in camparison with the conventional Hall-He'roult process, bring a whole series of advantages:-Simplification of furnace operation, ~ 2 -~6~38G~
Reduction and improved detection of the furnace waste gases, Independence of the fluctuations of price and quality of the petroleum coke, Lower overall energy consumption of the process.
These factors should take effect in reduced metal productlon costs.
Oxide-ceramic anodes of stable dimensions which are used in cryolite melts are known and are disclosed for example in U.S. Patent 3,960,678, Hanspeter Alder, issued June 1, 1976. In further publications whole classes of substances for use as oxide-ceramic anodes axe described, for example spinel structures in U.S. Patent 4,039,401, Koichi Yameda et al, issued August 2, 1977, 3apanese Published Patent Specification 52-140 411, filed May 19, 1976, Sumitomo Chemical KK. Finally in Japanese Published Patent Specification 52-153-816, filed June 17, 1976, Sumitomo Chemical KK, an oxide mixture of the composition Znl 7Nio 3SnO4 is proposed which is applied to a wire mesh, whereby a gas-permeable porous electrode is formed.
The multiplicity of proposed metal oxide systems indicates that hitherto it has not been possible to find an icleal material which satisfies the many, in some cases contradictory, demands of cryolite electrolysis, and which is economical.
~ n the replacement of the currently utilised carbon blocks of large format of the Hall-Heroult electro-lytic cell by ceramic anodes of stable dimensions of good conductivity, three main difficulties arise:-38~
The production of ceramic bodies of large format, The insertion and manner of operation in the electrolytic cell without mechanical damage to the ceramic bodies, and The achievement of long life with minimum possible anode corrosion.
Replacement of the carbon anodes by ceramic anodes signifies that several tonnes of ceramic material must be mixed, ground, pressed and sintered. The i 10 resultant anode bodies should differ as little as possible in their physical properties. In U.S. Patent 3,960,678 it was therefor proposed to embed individually produced anode blocks of oxide-ceramic material in an electricall~ insulating carrier plate reslstant to the melt. me individual anode bIocks are in contact with a current-distributor plate. m e ceramic anodes can be inserted into the carrier plate in such a way that they are flush with the lower plane of the carrier plate or ~rotrude from it. The removal of the generated anode gas is facilitated-in that some apertures in the carrier plate are not fitted with anode blocks (Figures 5 and 6). m e Figures also show that the anodes are designed so that both the carrier plate and the oxide-ceramic material are dipped into the melt.
In the insertion of the anodes into the melt and in the case of temperature fluctuations in operation, axial and radial temperature gradients occur which cause 7, z~
mechanical tensile stresses which can even lead to tearing of the carrier plate fitted with oxide-ceramic blocks.
The erosion of the ceramic metal oxide is effected substantially by the aluminium present in the cryolite. Thus the anode corrosion is dependent upon the passage of substance from the melt-to the solid body, which is mainly a function of the escape of the anodically generated gas. The desired gas outflow is only partially achieved by the arrangement of regularly distributed holes in the carrier plate according to U.S. Patent 3,960,678, especially with ceramic anodes protruding from the electrically insulating carrier plate~
The inventors have therefore faced the problem of producing an anode of large format consisting of individual oxide-ceramic elements of stable dimensions, which leads to satisfactory metal production with long life, good stability to temperature changes and minimum erosion.
In accordance with the invention the problem is solved in that the individual elements, having linear cross-sectional dimensions of 2-12 cm. on the current exit surface, have a length which corresponds to 2-20 times the value of the mean linear cross-sectional dimension, are arranged approximately parallel with a mean distance between the outer surface of 1-20 mm., and are mechanically stably held ~, .
together at the end facing the current entry with an electrically conductive device situated outsi~e the molten electrolyte.
Although the individual oxide-ceramic elements are preferably made cylindrical or prismatic, especially- with hexagonal, sguare or rectangular cross-section, they can also be made as cone frusta or as pyra~id frusta, in which case however the narrowing in the direction of the electric current should be only slight.
In principle the individual elements can have any desired geometric form, if their linear cross-section dimensions, their ratio of length to mean linear cross-sectional dimension and the mean distance between their outer surfaces lie in the range of the prescribed values.
The linear cross-sectional dimensions on the current exit surface of the oxide-ceramic individual ele~ents lie preferably between . 3 and 10 cm. The length of the individual elements advantageously corresponds to 3~10 times the value of the mean linear cross-sectional dimension. m e mean d~stance between adjacent individual elements preferably lies in the range of 2~5 m~ metres.
The geometric forms and the cross-sections of the Qxide-ceramic individual elements can be made equal or egually can be made different. Expecially in the case of individual elements with rour~ cross~section, still further elements ~ 6 -~L Ei28~a~
of substantially smaller cross~sectional dimension can be arranged in the relatively large cavities.
Edges or corners o~ the oxide-ceramic individual elements can be left, rounded off or chamfered.
~ ~ geome~ric cross-sectional form of the entire bundle is preferably rectangular or square, and individual or several separate elements on the corners can be omitted.
A superficial dimension for the stability to temperature change of the oxide-ceramic material is the ratic of thermal expansion (d~) to the coeffic;ent of thermal conductivity (k) at the corresponding temperature.
For t~o ceramic materials having greatly different stability to temperature change, the ratio of ~o~/k) at 900C can be calculated as follows:-SnO2 Fe2O3 m ermal expansion ~ 6 o -1~ 4 5 14 m ermal conductlvity k: (W~m K) 7.6 3.5 Quotient~ O.6 4.0 For a given temperat~re on the outer surface of an oxide-ceramic individual element thus the stressing occurring in the interior is sub-stantially variably:~
For haematite it is for example 6.7 times greater than for tin oxide. If no~ the thermal tensile stressing exceeds the local bending strength, then the ceramic body splits.
~ 7 -l, m ere are restrictions on the sizes in which anode bodies of oxide-ceramic materials can be produced because the bending strength cannot ~e increased at will. It is therefore preferred - especially in the case of larger individual oxide-ceramic elements ~ to form a cavity closed a~ainst the molten electrolyte. The individual oxide~ceramic elements are formed and fitted so that they can yield freely to the thermal tensile stressing, for example ~n that the current supply conductor is merely pressed against the upper edge of the anode.
Ho~ever the edge -thickness of the elements cannot be reduced at will, with regard to the bending strength, because otherwise the voltage drop for the anodic current issuing at the exit surface with a current intensity of 0.1 - 3.0 A/sq.cm. would have too great a value.
The material used for the production of the individual oxide~
ceramic elements consists for 90% or more by weight of at least one oxide of the metals Cr, Mo, W, Mn, Fe, Co, Ni, Zn, Sn, Pb. To these oxides or oxide mixtures, called basic material, there are added less than 10% by weight of at least one oxide of the following metals: Rare earths, Ti, Zr, Hf, V, Nb, Ta, Mg, Ca, Sr, Ba, Al, Ga, Si, Ge, Cu, As, Sb, Bi.
me individual oxide-Geramic elements are produced according to known methods of ceramic technology.
8~
The invention will ke explained in greater detail with reference to the drawing. The single figure shows diagrammatically a vertical section through a bundle anode dipped into the molten electrolyte.
me prismatic anode rods 10 with square cross~section of oxide-ceramic material with electronic conductlhvity have a diameter of 8 cm.
and a length of 40 cm. The edges at the ends are chamfered.
A plurality of anode rods is assembled into a bundle with three outer elements, the mean distance 10a between thP circumferential surfaces of adjacent anode rods amounting to 3 mm. m is distance serves on the one hand for drawing off the anode gas and on the other provides that the thermal expansion of the rods can ke taken up flexibly.
On their undersides the anode rods dip into the molten electrolyte 12 which lies on the liquid metal 14 forming the cathode. The crust formed frcm solidified electrolyte material and the alunLI~a tipped on to the crust are not illustrated, for the sake of simplicity.
m e anode rods are drilled through a few centimetres below the upper end face and penetrated by a suspension of rod 16 of corresponding diam-eter consisting of highly refractory steel. The t~ ends of the rod pro-truding from the outer anodes are mounted on carrier plates 18 which in turn are mounted on horizontal inward flanges 20 of an outer tube 22. This outer tube 22, formed in conformity with the bundle of anode rods, is secured through electric insulators to the furnace lid or anode carrier (not shown).
The carrier plate 18 i5 adjusted by bolts or screws 24 on the bottom plate 25 of the inner tube 30.
The electrical contact between the presser plate 26 and the flat-ground upper end fac:e of the anode rods 10 is produced either mechanically, by pressing with 0.05-1.0 MP_ pressure alone or in combination with an intermediate layer 10 2~3 of good electrical conductivity. This intermediate layer 28 consists of one or more layers of metal wire mesh, pre-ferably nickel wire mesh, which is used either untreated or oxidised in the flame after thermal treatment. In place of a metal wire mesh there may be employed a composition con-sisting of metal particles and low-sintering ceramics, known as a Cermet, and in this way the metal-oxide-ceramic current transmission is facilitated, in a preferred e~odi-ment the metal wire mesh is employed with the Cermet com-position.
In order to maintain the most favourable application pressure upon the anode rods 10, the presser plate 26 of the current supply conductor 32 can be pressed on by a suitable device, for example, a spring.
The current supply conductor 32 is situated in the interior tube 30 of the anode mounting (not shown) which is used as counterpiece for the presser device. The bottom plate 25 of the inner tube 30 - through the central bore of which the current supply conductor 32 is conducted 2l~
freely and which is connected by means of threaded bolts 24 with the carrier plate - here serves on the one hand for the positioning of the anode rods lO and on the other as basis for the a.pplication pressure.
The cavity 34 between inner and outer tubes is sealed off, for example by an alumina filling, to prevent the escape of the anode gases.
It is self-evident that the anode rods can also be suspended in a m~nner differing from Figure l. Thus the upper region of the anodes can be drilled through cross-wise at different levels, whereup~n the suspension rods consisting of highly refractory steel can be drawn in at right angles to one another. Likewise a notching preferably of semi-circular cross-section can be formed laterally of the anodes and the securing rods can be pushed ~l.
The production of the individual axide-ceramic elements lO for the anode according to the invention and their use in a fusion electrolytic furnace for the production of.aluminium are to be explained in greater detail by reference to the following examples.
Example 1 40 kg of spray-roasted iron oxide (Fe2O3, haematite) with a purity of about 99.6~ and a mean particle size of approximately 40~ m are mixed with 1.05 kg. of titanium dioxide and pre-calcined at 1020 C. Then the pcwder is camminu~ed in a ball ...~
~L6Z8~
mill during 125 hours to a ~ean grain of 2.5 ~m. The material is charged into a latex rubber mould of parallelepipedic form and put into the pressure chamber of an isostatic press The pressure is raised during 3 minutes from 0 to 1250 kg/sq.cm., kept at this value for 1 ~in. and then reduced again.
The pressed and worked blanks are sintered in an electric furnace, where the temperature is raised during 80 hours from room temperature to 1000, then increased during ten hours from 1000 to 1250C., left at this value for 30 hours and then reduced again.
m e sintered oxide-ceramic rods have a square end area with an edge length of 3.4 cm. and a length of 24 cm. m ese rods are assembled as bundles so that a square is produced having three rods for each edge, the interspace between the rods amounting to 2-3 mm.
m e rows of three are drilled through parallel with the end faces in one direction, at abou-t 3 cm. away from the upper end faces, with a diamond drill of appro~Imately 1.2 cm. diameter along the side faces lying one upon the other. Then a notching of half-round cross-section with a diameter of about 1.2 cm. is produced on two opposite side faces of each rod. Four rods of approximately 1 cm. diameter and 13 cm.
length consist~ng o~ highly refractory chromium-n;ckel steel are used as suspension rods and utilised, as represented in Figure 1, for th~ securing of the individual elements or rod form. The ~ 12 ~
1~L6Z~381~
applicati4n pressure of the current sup~ly conductor is adjusted to 0.24 MPa.
m e bundle electrode is dipped into a carbon tank and heated to looo&. during 50 hours. Then cryolite wIth 3.75% AlF3, 5~ CaF2 and 6.9% A12O3 is added and melted until the immerslon depth of the anodes amounts to about 2 cm. m e interpolar distance from the anodes to the liquid aluminium used as cathode and lying on the bottom of the cell amounts to 6-8 cm. The anodic current intensity is increased by stages until it amounts to 1.25 A~sq,cm.; after 190 hours of work at this current intensity the anode bundle is withdrawn. me individual elements of rod form after cooling display no damage and are free from cracks.
Example 2 40 kg. of tin oxide (SnO2) with a purity of above 99.9%
and a nean particle size of less than 5~m are mixed with 0.8 kg. of copper oxide (CuO) and 0.4 kg. of antimony o~ide (Sb2O3). m e material is charged into a latex r~bber mould of parallelepipedic form and put into the pressure cham~er of an isostatic press. During 3 minutes the pressure is increased form 0 to 1250 kg/sq.cm., kept for one minute at this value and then reduced again.
m e pressed and worked blanks are sintered in an electric furnace, the temperature being increased during 80 hours frQm room temperature to 1250 C., left at this value for 24 hours and then lowered to 150C. during 48 hours.
~L~L6Z88t~
The sintered oxide-ceramic rods of square end face have an edge length of 5.0 cm. and a length of 24 cm. Nine rods are assembled as in Example l into a bundle anode, producing an effective anode area of 225 sq.cm.
In an electrolysis arrangement corresp~nding to Example l the bundle anode is used witR an anodic current intensity of 1.20 A/sq.cm.
for 216 Rours. At the end of tRe electrolysis the total anode erosion amounts to 14.6 cc., which corresponds to a mean erosion of 3~ m/h, in relation to the bottom area~ This corrosion however occurs mainly on the corners of the bundle, while three of the four middle anode rods display no erosion of any kind.
Ccmparative experiments have shown that the inherently already slight erosion of individual oxide-ceramic anodes of large format can be further reduced if tRey are formed as bundle anodes with equal working area. The withdrawal of anode gas permits of r~educing the anode corrosion of bundles by about a factor 5. This constitutes a further advantage in addition to the simpler ceramic production and the improved stability to temperature change.
The experiments have further shcwn that with an increase of the number of the anode rods contained in the bundle the reduct~ of corrosion can be improved still further, because the number of enclosed anodes is increased.
~ 14
Anode of dimensionally stable oxide-ceramic individual ele~ents The present inven-tion relates to an anode of a fusion electrolysis furnace for the prcduction of aluminium, which anode consists of a plurality of indiYidual oxide-cera~ic elements of stable d~ensions.
The currently-used Hall-Heroult process for obtaining aluminium from alun~na dissolved in cryolite takes place at 940 - 1000 C, and electrolysis is carried out between a horizontal anode and a parallel liquid aluminium cathode. m e anodically precipitated oxygen reacts with ~ the anode carbon to form carbon dioxide and the carbon burns away. At the same rate as the linear burning away of the anode takes place, in the case of suitable cell geometry the build--up of the aluminium layer takes place cathodically, so that the interpolar distance is maintained. After the scooping of the liquid aluminium the interpolar distance must be freshly adjusted by lowering of the anodes, furthermore burned-away carbon anode blocks must be replaced at regular intervals. A special works, the anode factory, is necessary for the production of these anode blocks.
Replacement of the burning carbon anodes by an axide-ceramic anode of stable dimensions should, in camparison with the conventional Hall-He'roult process, bring a whole series of advantages:-Simplification of furnace operation, ~ 2 -~6~38G~
Reduction and improved detection of the furnace waste gases, Independence of the fluctuations of price and quality of the petroleum coke, Lower overall energy consumption of the process.
These factors should take effect in reduced metal productlon costs.
Oxide-ceramic anodes of stable dimensions which are used in cryolite melts are known and are disclosed for example in U.S. Patent 3,960,678, Hanspeter Alder, issued June 1, 1976. In further publications whole classes of substances for use as oxide-ceramic anodes axe described, for example spinel structures in U.S. Patent 4,039,401, Koichi Yameda et al, issued August 2, 1977, 3apanese Published Patent Specification 52-140 411, filed May 19, 1976, Sumitomo Chemical KK. Finally in Japanese Published Patent Specification 52-153-816, filed June 17, 1976, Sumitomo Chemical KK, an oxide mixture of the composition Znl 7Nio 3SnO4 is proposed which is applied to a wire mesh, whereby a gas-permeable porous electrode is formed.
The multiplicity of proposed metal oxide systems indicates that hitherto it has not been possible to find an icleal material which satisfies the many, in some cases contradictory, demands of cryolite electrolysis, and which is economical.
~ n the replacement of the currently utilised carbon blocks of large format of the Hall-Heroult electro-lytic cell by ceramic anodes of stable dimensions of good conductivity, three main difficulties arise:-38~
The production of ceramic bodies of large format, The insertion and manner of operation in the electrolytic cell without mechanical damage to the ceramic bodies, and The achievement of long life with minimum possible anode corrosion.
Replacement of the carbon anodes by ceramic anodes signifies that several tonnes of ceramic material must be mixed, ground, pressed and sintered. The i 10 resultant anode bodies should differ as little as possible in their physical properties. In U.S. Patent 3,960,678 it was therefor proposed to embed individually produced anode blocks of oxide-ceramic material in an electricall~ insulating carrier plate reslstant to the melt. me individual anode bIocks are in contact with a current-distributor plate. m e ceramic anodes can be inserted into the carrier plate in such a way that they are flush with the lower plane of the carrier plate or ~rotrude from it. The removal of the generated anode gas is facilitated-in that some apertures in the carrier plate are not fitted with anode blocks (Figures 5 and 6). m e Figures also show that the anodes are designed so that both the carrier plate and the oxide-ceramic material are dipped into the melt.
In the insertion of the anodes into the melt and in the case of temperature fluctuations in operation, axial and radial temperature gradients occur which cause 7, z~
mechanical tensile stresses which can even lead to tearing of the carrier plate fitted with oxide-ceramic blocks.
The erosion of the ceramic metal oxide is effected substantially by the aluminium present in the cryolite. Thus the anode corrosion is dependent upon the passage of substance from the melt-to the solid body, which is mainly a function of the escape of the anodically generated gas. The desired gas outflow is only partially achieved by the arrangement of regularly distributed holes in the carrier plate according to U.S. Patent 3,960,678, especially with ceramic anodes protruding from the electrically insulating carrier plate~
The inventors have therefore faced the problem of producing an anode of large format consisting of individual oxide-ceramic elements of stable dimensions, which leads to satisfactory metal production with long life, good stability to temperature changes and minimum erosion.
In accordance with the invention the problem is solved in that the individual elements, having linear cross-sectional dimensions of 2-12 cm. on the current exit surface, have a length which corresponds to 2-20 times the value of the mean linear cross-sectional dimension, are arranged approximately parallel with a mean distance between the outer surface of 1-20 mm., and are mechanically stably held ~, .
together at the end facing the current entry with an electrically conductive device situated outsi~e the molten electrolyte.
Although the individual oxide-ceramic elements are preferably made cylindrical or prismatic, especially- with hexagonal, sguare or rectangular cross-section, they can also be made as cone frusta or as pyra~id frusta, in which case however the narrowing in the direction of the electric current should be only slight.
In principle the individual elements can have any desired geometric form, if their linear cross-section dimensions, their ratio of length to mean linear cross-sectional dimension and the mean distance between their outer surfaces lie in the range of the prescribed values.
The linear cross-sectional dimensions on the current exit surface of the oxide-ceramic individual ele~ents lie preferably between . 3 and 10 cm. The length of the individual elements advantageously corresponds to 3~10 times the value of the mean linear cross-sectional dimension. m e mean d~stance between adjacent individual elements preferably lies in the range of 2~5 m~ metres.
The geometric forms and the cross-sections of the Qxide-ceramic individual elements can be made equal or egually can be made different. Expecially in the case of individual elements with rour~ cross~section, still further elements ~ 6 -~L Ei28~a~
of substantially smaller cross~sectional dimension can be arranged in the relatively large cavities.
Edges or corners o~ the oxide-ceramic individual elements can be left, rounded off or chamfered.
~ ~ geome~ric cross-sectional form of the entire bundle is preferably rectangular or square, and individual or several separate elements on the corners can be omitted.
A superficial dimension for the stability to temperature change of the oxide-ceramic material is the ratic of thermal expansion (d~) to the coeffic;ent of thermal conductivity (k) at the corresponding temperature.
For t~o ceramic materials having greatly different stability to temperature change, the ratio of ~o~/k) at 900C can be calculated as follows:-SnO2 Fe2O3 m ermal expansion ~ 6 o -1~ 4 5 14 m ermal conductlvity k: (W~m K) 7.6 3.5 Quotient~ O.6 4.0 For a given temperat~re on the outer surface of an oxide-ceramic individual element thus the stressing occurring in the interior is sub-stantially variably:~
For haematite it is for example 6.7 times greater than for tin oxide. If no~ the thermal tensile stressing exceeds the local bending strength, then the ceramic body splits.
~ 7 -l, m ere are restrictions on the sizes in which anode bodies of oxide-ceramic materials can be produced because the bending strength cannot ~e increased at will. It is therefore preferred - especially in the case of larger individual oxide-ceramic elements ~ to form a cavity closed a~ainst the molten electrolyte. The individual oxide~ceramic elements are formed and fitted so that they can yield freely to the thermal tensile stressing, for example ~n that the current supply conductor is merely pressed against the upper edge of the anode.
Ho~ever the edge -thickness of the elements cannot be reduced at will, with regard to the bending strength, because otherwise the voltage drop for the anodic current issuing at the exit surface with a current intensity of 0.1 - 3.0 A/sq.cm. would have too great a value.
The material used for the production of the individual oxide~
ceramic elements consists for 90% or more by weight of at least one oxide of the metals Cr, Mo, W, Mn, Fe, Co, Ni, Zn, Sn, Pb. To these oxides or oxide mixtures, called basic material, there are added less than 10% by weight of at least one oxide of the following metals: Rare earths, Ti, Zr, Hf, V, Nb, Ta, Mg, Ca, Sr, Ba, Al, Ga, Si, Ge, Cu, As, Sb, Bi.
me individual oxide-Geramic elements are produced according to known methods of ceramic technology.
8~
The invention will ke explained in greater detail with reference to the drawing. The single figure shows diagrammatically a vertical section through a bundle anode dipped into the molten electrolyte.
me prismatic anode rods 10 with square cross~section of oxide-ceramic material with electronic conductlhvity have a diameter of 8 cm.
and a length of 40 cm. The edges at the ends are chamfered.
A plurality of anode rods is assembled into a bundle with three outer elements, the mean distance 10a between thP circumferential surfaces of adjacent anode rods amounting to 3 mm. m is distance serves on the one hand for drawing off the anode gas and on the other provides that the thermal expansion of the rods can ke taken up flexibly.
On their undersides the anode rods dip into the molten electrolyte 12 which lies on the liquid metal 14 forming the cathode. The crust formed frcm solidified electrolyte material and the alunLI~a tipped on to the crust are not illustrated, for the sake of simplicity.
m e anode rods are drilled through a few centimetres below the upper end face and penetrated by a suspension of rod 16 of corresponding diam-eter consisting of highly refractory steel. The t~ ends of the rod pro-truding from the outer anodes are mounted on carrier plates 18 which in turn are mounted on horizontal inward flanges 20 of an outer tube 22. This outer tube 22, formed in conformity with the bundle of anode rods, is secured through electric insulators to the furnace lid or anode carrier (not shown).
The carrier plate 18 i5 adjusted by bolts or screws 24 on the bottom plate 25 of the inner tube 30.
The electrical contact between the presser plate 26 and the flat-ground upper end fac:e of the anode rods 10 is produced either mechanically, by pressing with 0.05-1.0 MP_ pressure alone or in combination with an intermediate layer 10 2~3 of good electrical conductivity. This intermediate layer 28 consists of one or more layers of metal wire mesh, pre-ferably nickel wire mesh, which is used either untreated or oxidised in the flame after thermal treatment. In place of a metal wire mesh there may be employed a composition con-sisting of metal particles and low-sintering ceramics, known as a Cermet, and in this way the metal-oxide-ceramic current transmission is facilitated, in a preferred e~odi-ment the metal wire mesh is employed with the Cermet com-position.
In order to maintain the most favourable application pressure upon the anode rods 10, the presser plate 26 of the current supply conductor 32 can be pressed on by a suitable device, for example, a spring.
The current supply conductor 32 is situated in the interior tube 30 of the anode mounting (not shown) which is used as counterpiece for the presser device. The bottom plate 25 of the inner tube 30 - through the central bore of which the current supply conductor 32 is conducted 2l~
freely and which is connected by means of threaded bolts 24 with the carrier plate - here serves on the one hand for the positioning of the anode rods lO and on the other as basis for the a.pplication pressure.
The cavity 34 between inner and outer tubes is sealed off, for example by an alumina filling, to prevent the escape of the anode gases.
It is self-evident that the anode rods can also be suspended in a m~nner differing from Figure l. Thus the upper region of the anodes can be drilled through cross-wise at different levels, whereup~n the suspension rods consisting of highly refractory steel can be drawn in at right angles to one another. Likewise a notching preferably of semi-circular cross-section can be formed laterally of the anodes and the securing rods can be pushed ~l.
The production of the individual axide-ceramic elements lO for the anode according to the invention and their use in a fusion electrolytic furnace for the production of.aluminium are to be explained in greater detail by reference to the following examples.
Example 1 40 kg of spray-roasted iron oxide (Fe2O3, haematite) with a purity of about 99.6~ and a mean particle size of approximately 40~ m are mixed with 1.05 kg. of titanium dioxide and pre-calcined at 1020 C. Then the pcwder is camminu~ed in a ball ...~
~L6Z8~
mill during 125 hours to a ~ean grain of 2.5 ~m. The material is charged into a latex rubber mould of parallelepipedic form and put into the pressure chamber of an isostatic press The pressure is raised during 3 minutes from 0 to 1250 kg/sq.cm., kept at this value for 1 ~in. and then reduced again.
The pressed and worked blanks are sintered in an electric furnace, where the temperature is raised during 80 hours from room temperature to 1000, then increased during ten hours from 1000 to 1250C., left at this value for 30 hours and then reduced again.
m e sintered oxide-ceramic rods have a square end area with an edge length of 3.4 cm. and a length of 24 cm. m ese rods are assembled as bundles so that a square is produced having three rods for each edge, the interspace between the rods amounting to 2-3 mm.
m e rows of three are drilled through parallel with the end faces in one direction, at abou-t 3 cm. away from the upper end faces, with a diamond drill of appro~Imately 1.2 cm. diameter along the side faces lying one upon the other. Then a notching of half-round cross-section with a diameter of about 1.2 cm. is produced on two opposite side faces of each rod. Four rods of approximately 1 cm. diameter and 13 cm.
length consist~ng o~ highly refractory chromium-n;ckel steel are used as suspension rods and utilised, as represented in Figure 1, for th~ securing of the individual elements or rod form. The ~ 12 ~
1~L6Z~381~
applicati4n pressure of the current sup~ly conductor is adjusted to 0.24 MPa.
m e bundle electrode is dipped into a carbon tank and heated to looo&. during 50 hours. Then cryolite wIth 3.75% AlF3, 5~ CaF2 and 6.9% A12O3 is added and melted until the immerslon depth of the anodes amounts to about 2 cm. m e interpolar distance from the anodes to the liquid aluminium used as cathode and lying on the bottom of the cell amounts to 6-8 cm. The anodic current intensity is increased by stages until it amounts to 1.25 A~sq,cm.; after 190 hours of work at this current intensity the anode bundle is withdrawn. me individual elements of rod form after cooling display no damage and are free from cracks.
Example 2 40 kg. of tin oxide (SnO2) with a purity of above 99.9%
and a nean particle size of less than 5~m are mixed with 0.8 kg. of copper oxide (CuO) and 0.4 kg. of antimony o~ide (Sb2O3). m e material is charged into a latex r~bber mould of parallelepipedic form and put into the pressure cham~er of an isostatic press. During 3 minutes the pressure is increased form 0 to 1250 kg/sq.cm., kept for one minute at this value and then reduced again.
m e pressed and worked blanks are sintered in an electric furnace, the temperature being increased during 80 hours frQm room temperature to 1250 C., left at this value for 24 hours and then lowered to 150C. during 48 hours.
~L~L6Z88t~
The sintered oxide-ceramic rods of square end face have an edge length of 5.0 cm. and a length of 24 cm. Nine rods are assembled as in Example l into a bundle anode, producing an effective anode area of 225 sq.cm.
In an electrolysis arrangement corresp~nding to Example l the bundle anode is used witR an anodic current intensity of 1.20 A/sq.cm.
for 216 Rours. At the end of tRe electrolysis the total anode erosion amounts to 14.6 cc., which corresponds to a mean erosion of 3~ m/h, in relation to the bottom area~ This corrosion however occurs mainly on the corners of the bundle, while three of the four middle anode rods display no erosion of any kind.
Ccmparative experiments have shown that the inherently already slight erosion of individual oxide-ceramic anodes of large format can be further reduced if tRey are formed as bundle anodes with equal working area. The withdrawal of anode gas permits of r~educing the anode corrosion of bundles by about a factor 5. This constitutes a further advantage in addition to the simpler ceramic production and the improved stability to temperature change.
The experiments have further shcwn that with an increase of the number of the anode rods contained in the bundle the reduct~ of corrosion can be improved still further, because the number of enclosed anodes is increased.
~ 14
Claims (15)
1. An anode of a fusion electrolysis furnace for the production of aluminium, consisting of a plurality of individual oxide-ceramic elements of stable dimensions, characterized in that the individual elements, having linear cross-sectional dimensions of 2-12 cm. at the current exit surface:
have a length which corresponds to 2-20 times the value of the mean linear cross-sectional dimension, are arranged approximately parallel with a mean distance between outer surfaces of 1-20 mm, and are held together mechanically stably at the end facing the current entry with an electrically con-ductive supporting device situated outside the molten electrolyte.
have a length which corresponds to 2-20 times the value of the mean linear cross-sectional dimension, are arranged approximately parallel with a mean distance between outer surfaces of 1-20 mm, and are held together mechanically stably at the end facing the current entry with an electrically con-ductive supporting device situated outside the molten electrolyte.
2. An anode according to claim 1, wherein the individual elements have linear cross-sectional dimensions of 3-10 cm, a length corresponding to 3-10 times the value of the mean linear cross-sectional dimension and a mean distance between outer surfaces of 2-5 mm.
3. An anode according to claim 1 or 2, wherein the individual elements are made cylindrical or prismatic.
4. An anode according to claim 1 or 2, wherein the individual elements are made cylindrical or prismatic with a hexagonal, square or rectangular cross-section.
5. An anode according to claim 1 or 2, wherein the individual elements are made in frusto-conical or frusto-pyramidal form, the degree of taper being however only slight in the direction of the electric current.
6. An anode according to claim 1 or 2, wherein the individual elements are made in frusto-conical or frusto-pyramidal form with a hexagonal, square or rectangular cross-section, the degree of taper being however only slight in the direction of the electric current.
7. An anode according to claim 1 or 2, wherein the bundle is made rectangular or square in cross-section.
8. An anode according to claim 1 or 2, wherein single or several corner individual elements are omitted in the bundle.
9. An anode according to claim 1 or 2, wherein the supporting device comprises a presser plate electrically conductively connected with a supply conductor pressed with 0.5 - 1.0 MPa upon the upper ends of the ceramic elements.
10. An anode according to claim 1 or 2, wherein between the end faces of the oxide-ceramic elements and the supporting device an intermediate layer is arranged which consists of at least one layer of metal wire mesh.
11. An anode according to claim 1 or 2, wherein between the end faces of the oxide-ceramic elements and the supporting device an intermediate layer is arranged which consists of at least one layer of metal wire mesh of bright or oxidized nickel, or of a metallic-ceramic composition (Cermet).
12. An anode according to claim 1, wherein the oxide-ceramic elements comprise at least one oxide of the metals Cr, Mo, W, Mn, Fe, Co, Ni, Zn, Sn and Pb.
13. An anode according to claim 2, wherein the oxide-ceramic elements comprise at least one oxide of the metals Cr, Mo, W, Mn, Fe, Co, Ni, Zn, Sn and Pb.
14. An anode according to claim 12 or 13, wherein the oxide-ceramic elements contain less than 10% of at least one oxide of the metals:rare earths, Ti, Zr, Hf, V, Nb, Ta, Mg, Ca, Sr, Ba, Al, Ga, Si, Ge, As, Sb, Cu and Bi.
15. An anode according to claim 1 or 2, wherein the oxide-ceramic elements consist of 90% or more, by weight, of at least one oxide of the metals Cr, Mo, W, Mn, Fe, Co, Ni, Zn, Sn, Pb, and include less than 10%, by weight, of at least one oxide of the metals:rare earths, Ti, Zr, Hf, V, Nb, Ta, Mg, Ca, Sr, Ba, Al, Ga, Si, Ge, Cu, As, Sb and Bi.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CH1119879A CH642402A5 (en) | 1979-12-18 | 1979-12-18 | ANODE OF DIMENSIONAL STABLE OXIDE CERAMIC INDIVIDUAL ELEMENTS. |
| CH11198/79-3 | 1979-12-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1162880A true CA1162880A (en) | 1984-02-28 |
Family
ID=4371039
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000366990A Expired CA1162880A (en) | 1979-12-18 | 1980-12-17 | Anode of dimensionally stable oxide-ceramic individual elements |
Country Status (11)
| Country | Link |
|---|---|
| JP (1) | JPS5698490A (en) |
| AU (1) | AU538726B2 (en) |
| CA (1) | CA1162880A (en) |
| CH (1) | CH642402A5 (en) |
| DE (1) | DE3003922C2 (en) |
| FR (1) | FR2472038A1 (en) |
| GB (1) | GB2065708B (en) |
| IT (1) | IT1201938B (en) |
| NO (1) | NO803793L (en) |
| NZ (1) | NZ195853A (en) |
| ZA (1) | ZA807764B (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3102776A1 (en) * | 1981-01-28 | 1982-08-26 | C. Conradty Nürnberg GmbH & Co KG, 8505 Röthenbach | ELECTRODE FOR ARC FURNACE |
| US4609249A (en) * | 1985-04-25 | 1986-09-02 | Aluminum Company Of America | Electrically conductive connection for an electrode |
| DE3537575A1 (en) * | 1985-10-22 | 1987-04-23 | Conradty Nuernberg | INERT COMPOSITE ELECTRODE, ESPECIALLY ANODE FOR MELTFLOW ELECTROLYSIS |
| NO20024049D0 (en) * | 2002-08-23 | 2002-08-23 | Norsk Hydro As | Material for use in an electrolytic cell |
| US7762486B2 (en) | 2007-01-30 | 2010-07-27 | Staples The Office Superstore, Llc | Shredder |
| CN103088367A (en) * | 2011-10-31 | 2013-05-08 | 贵阳铝镁设计研究院有限公司 | Continuous prebaked anode combination structure of aluminum electrolysis tank |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2958641A (en) * | 1958-05-20 | 1960-11-01 | Reynolds Metals Co | Anode for alumina reduction cells |
| DE1121340B (en) * | 1959-11-25 | 1962-01-04 | Du Pont | Anode structure for fused metal electrolysis cells, especially for the production of sodium |
| CH575014A5 (en) * | 1973-05-25 | 1976-04-30 | Alusuisse | |
| EP0022921B1 (en) * | 1979-07-20 | 1983-10-26 | C. CONRADTY NÜRNBERG GmbH & Co. KG | Regenerable, shape-stable electrode for use at high temperatures |
| DE2929346C2 (en) * | 1979-07-20 | 1985-10-17 | C. Conradty Nürnberg GmbH & Co KG, 8505 Röthenbach | Stable high temp. electrodes which can be regenerated - and have very long life when used in mfg. metals by electrolysis of molten salts |
-
1979
- 1979-12-18 CH CH1119879A patent/CH642402A5/en not_active IP Right Cessation
-
1980
- 1980-02-04 DE DE3003922A patent/DE3003922C2/en not_active Expired
- 1980-12-11 ZA ZA00807764A patent/ZA807764B/en unknown
- 1980-12-16 IT IT26669/80A patent/IT1201938B/en active
- 1980-12-16 NO NO803793A patent/NO803793L/en unknown
- 1980-12-16 NZ NZ195853A patent/NZ195853A/en unknown
- 1980-12-17 CA CA000366990A patent/CA1162880A/en not_active Expired
- 1980-12-17 AU AU65474/80A patent/AU538726B2/en not_active Ceased
- 1980-12-17 GB GB8040442A patent/GB2065708B/en not_active Expired
- 1980-12-18 FR FR8026947A patent/FR2472038A1/en active Pending
- 1980-12-18 JP JP17967880A patent/JPS5698490A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| AU538726B2 (en) | 1984-08-23 |
| NZ195853A (en) | 1983-04-12 |
| GB2065708B (en) | 1983-03-23 |
| JPS5698490A (en) | 1981-08-07 |
| FR2472038A1 (en) | 1981-06-26 |
| NO803793L (en) | 1981-06-19 |
| IT8026669A0 (en) | 1980-12-16 |
| CH642402A5 (en) | 1984-04-13 |
| ZA807764B (en) | 1981-12-30 |
| GB2065708A (en) | 1981-07-01 |
| DE3003922A1 (en) | 1981-06-25 |
| DE3003922C2 (en) | 1982-06-16 |
| AU6547480A (en) | 1981-06-25 |
| IT1201938B (en) | 1989-02-02 |
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