CA2900418A1 - Cathode block having an abrasion-resistant surface that can be wetted - Google Patents
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Abstract
The invention relates to a cathode block for an aluminum electrolytic cell composed, at least in some sections, of a material that can be obtained by burning a mixture, which mixture contains at least one material containing carbon having a degree of graphitization calculated in accordance with Maire and Mehring from the mean layer distance c/2 after a heat treatment at 2,800°C of at most 0.50 and at least one nonoxide ceramic.
Description
WO 2014/124970 Al Cathode block having an abrasion-resistant surface that can be wetted The present invention relates to a cathode block for an aluminium electrolysis cell, to a method for the production thereof, to the use thereof and to a cathode comprising it.
Electrolysis cells are used for example for the electrolytic production of aluminium, which is usually carried out industrially by the Hall-Fleroult process. In the Hall-Heroult process, a melt composed of aluminium oxide and cryolite is electrolysed. The cryolite, Na3[AlF6] serves to reduce the melting point from 2,045 C for pure aluminium oxide to approximately 950 C
for a mixture containing cryolite, aluminium oxide and additives such as aluminium fluoride and calcium fluoride.
The electrolysis cell used in this method comprises a cathode base which may be composed of a multiplicity of mutually adjacent cathode blocks which form the cathode.
To withstand the thermal and chemical conditions which prevail during the operation of the cell, the cathode is usually composed of a carbon-containing material. Usually, grooves are provided on each lower face of the cathode, in each of which at least one busbar is arranged through which the current supplied via the anodes is dissipated. An anode, in particular formed from individual anode blocks, is usually arranged approximately 3 to 5 cm above the layer of liquid aluminium, usually 15 to 50 cm high, which is located on the upper face of the cathode, the electrolyte, in other words the melt containing aluminium oxide and cryolite, being located between said anode and the surface of the aluminium. During the electrolysis, which is carried out at approximately 1,000 C, the aluminium formed is deposited below the electrolyte layer, in other words as an intermediate layer between the upper face of the cathode and the electrolyte layer, because of the density thereof, which is greater than that of the electrolyte. During the electrolysis, the aluminium oxide dissolved in the melt is split by an electrical current into aluminium and oxygen. In electrochemical terms, the layer of liquid aluminium is the actual cathode, since aluminium ions are reduced to elemental aluminium on the surface thereof. Nevertheless, in the following the term cathode refers not to the cathode in electrochemical terms, in other words the layer of liquid aluminium, but rather to the component, for example composed of one or more cathode blocks, which forms the electrolysis cell base.
Electrolysis cells are used for example for the electrolytic production of aluminium, which is usually carried out industrially by the Hall-Fleroult process. In the Hall-Heroult process, a melt composed of aluminium oxide and cryolite is electrolysed. The cryolite, Na3[AlF6] serves to reduce the melting point from 2,045 C for pure aluminium oxide to approximately 950 C
for a mixture containing cryolite, aluminium oxide and additives such as aluminium fluoride and calcium fluoride.
The electrolysis cell used in this method comprises a cathode base which may be composed of a multiplicity of mutually adjacent cathode blocks which form the cathode.
To withstand the thermal and chemical conditions which prevail during the operation of the cell, the cathode is usually composed of a carbon-containing material. Usually, grooves are provided on each lower face of the cathode, in each of which at least one busbar is arranged through which the current supplied via the anodes is dissipated. An anode, in particular formed from individual anode blocks, is usually arranged approximately 3 to 5 cm above the layer of liquid aluminium, usually 15 to 50 cm high, which is located on the upper face of the cathode, the electrolyte, in other words the melt containing aluminium oxide and cryolite, being located between said anode and the surface of the aluminium. During the electrolysis, which is carried out at approximately 1,000 C, the aluminium formed is deposited below the electrolyte layer, in other words as an intermediate layer between the upper face of the cathode and the electrolyte layer, because of the density thereof, which is greater than that of the electrolyte. During the electrolysis, the aluminium oxide dissolved in the melt is split by an electrical current into aluminium and oxygen. In electrochemical terms, the layer of liquid aluminium is the actual cathode, since aluminium ions are reduced to elemental aluminium on the surface thereof. Nevertheless, in the following the term cathode refers not to the cathode in electrochemical terms, in other words the layer of liquid aluminium, but rather to the component, for example composed of one or more cathode blocks, which forms the electrolysis cell base.
2 A major drawback of the Hall-Heroult process is that it is highly energy-intensive.
Approximately 12 to 15 kWh of electrical energy are needed to produce 1 kg of aluminium, and this constitutes up to 40 % of the production costs. To reduce the production costs, it is 'therefore desirable to reduce the specific energy consumption in this method as much as possible.
Therefore, recently graphite cathodes have increasingly been used, in other words ones consisting of cathode blocks containing graphite as a primary constituent. A
distinction is made between graphitic cathode blocks, in the production of which graphite is used as the starting material, and graphitised cathode blocks, for the production of which a graphite precursor, which contains a carbon and which is converted to graphite by a subsequent heat treatment known as graphitisation at 2,100 to 3,000 C, is used as a starting material. By comparison with amorphous carbon, graphite is distinguished by a much lower electrical resistivity and by a significantly higher thermal conductivity, meaning that the use of graphite cathodes during the electrolysis can reduce the specific energy consumption of the electrolysis and also makes it possible to carry out the electrolysis at a higher current intensity, making it possible to increase the aluminium production. However, cathodes or cathode blocks made of graphite, and in particular graphitised cathode blocks, are subjected to considerable wear during the electrolysis as a result of surface abrasion, this wear being much greater than the wear of cathode blocks made of amorphous carbon. Aside from this, cathodes or cathode blocks made of amorphous carbon or graphite have comparatively poor wettability with aluminium.
So as to increase the wettability of cathode blocks, and in particular of those made of graphite, with aluminium, and also to increase the wear resistance of cathode blocks made of graphite, it has previously been proposed to form at least the face of the cathode block forming the upper face thereof during operation of the cathode block from a graphite material containing for example titanium diboride. For example, WO 2012/107400 A2 discloses a cathode block for an aluminium electrolysis cell, which comprises a base layer and a cover layer, the base layer containing graphite and the cover layer containing a graphite composite material containing 1 to less than 50 % by weight hard material having a melting point of at least 1,000 C. Either a material containing carbon, such as coke, anthracite, soot or vitreous carbon, or alternatively a non-oxidic ceramic, preferably titanium diboride, may be used as the hard material. The addition of the hard material is intended to increase the wear-
Approximately 12 to 15 kWh of electrical energy are needed to produce 1 kg of aluminium, and this constitutes up to 40 % of the production costs. To reduce the production costs, it is 'therefore desirable to reduce the specific energy consumption in this method as much as possible.
Therefore, recently graphite cathodes have increasingly been used, in other words ones consisting of cathode blocks containing graphite as a primary constituent. A
distinction is made between graphitic cathode blocks, in the production of which graphite is used as the starting material, and graphitised cathode blocks, for the production of which a graphite precursor, which contains a carbon and which is converted to graphite by a subsequent heat treatment known as graphitisation at 2,100 to 3,000 C, is used as a starting material. By comparison with amorphous carbon, graphite is distinguished by a much lower electrical resistivity and by a significantly higher thermal conductivity, meaning that the use of graphite cathodes during the electrolysis can reduce the specific energy consumption of the electrolysis and also makes it possible to carry out the electrolysis at a higher current intensity, making it possible to increase the aluminium production. However, cathodes or cathode blocks made of graphite, and in particular graphitised cathode blocks, are subjected to considerable wear during the electrolysis as a result of surface abrasion, this wear being much greater than the wear of cathode blocks made of amorphous carbon. Aside from this, cathodes or cathode blocks made of amorphous carbon or graphite have comparatively poor wettability with aluminium.
So as to increase the wettability of cathode blocks, and in particular of those made of graphite, with aluminium, and also to increase the wear resistance of cathode blocks made of graphite, it has previously been proposed to form at least the face of the cathode block forming the upper face thereof during operation of the cathode block from a graphite material containing for example titanium diboride. For example, WO 2012/107400 A2 discloses a cathode block for an aluminium electrolysis cell, which comprises a base layer and a cover layer, the base layer containing graphite and the cover layer containing a graphite composite material containing 1 to less than 50 % by weight hard material having a melting point of at least 1,000 C. Either a material containing carbon, such as coke, anthracite, soot or vitreous carbon, or alternatively a non-oxidic ceramic, preferably titanium diboride, may be used as the hard material. The addition of the hard material is intended to increase the wear-
3 resistance of the cathode block made of graphite, whilst the use of preferably titanium boride is intended to improve the wettability for aluminium.
It has been shown in experiments that the addition of for example titanium diboride does increase the wettability of cathode blocks made of graphite, making it possible to reduce the thickness of the aluminium layer in the electrolysis cell and thus the anode-cathode distance in the electrolysis cell, leading to a reduction in the specific energy consumption of the electrolysis cell; however, the wear-resistance of these cathode blocks needs to be improved. As a result of the wear resistance which needs to be improved, cathodes composed of cathode blocks of this type are unsuitable or only sometimes suitable for modern electrolysis cells in particular, which are operated at high current intensities of up to 600 kA, because of the short service life thereof in these operating conditions.
The object of the present invention is therefore to provide a cathode block which is suitable in particular for use for an aluminium electrolysis cell and which not only has a low electrical resistivity and is highly wettable with aluminium melt, but is also distinguished in particular by a high wear-resistance towards the abrasive chemical and thermal conditions prevailing during the operation during melt-flow electrolysis, in particular including at high current intensities of for example 600 kA.
According to the invention, this object is achieved by a cathode block for an aluminium electrolysis cell which is composed at least in portions of a material which is obtainable by combusting a mixture which contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and at least one non-oxidic ceramic.
The cathode block according to the invention is preferably formed from a base layer and a cover layer, the at least one portion which contains the aforementioned mixture being part of the cover layer. Within the meaning of the invention, this portion may extend over the entire cover layer or the portion may merely form part of this cover layer.
This solution is based on the finding that the combined addition of material containing comparatively poorly or not at all graphitisable carbon, specifically of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the
It has been shown in experiments that the addition of for example titanium diboride does increase the wettability of cathode blocks made of graphite, making it possible to reduce the thickness of the aluminium layer in the electrolysis cell and thus the anode-cathode distance in the electrolysis cell, leading to a reduction in the specific energy consumption of the electrolysis cell; however, the wear-resistance of these cathode blocks needs to be improved. As a result of the wear resistance which needs to be improved, cathodes composed of cathode blocks of this type are unsuitable or only sometimes suitable for modern electrolysis cells in particular, which are operated at high current intensities of up to 600 kA, because of the short service life thereof in these operating conditions.
The object of the present invention is therefore to provide a cathode block which is suitable in particular for use for an aluminium electrolysis cell and which not only has a low electrical resistivity and is highly wettable with aluminium melt, but is also distinguished in particular by a high wear-resistance towards the abrasive chemical and thermal conditions prevailing during the operation during melt-flow electrolysis, in particular including at high current intensities of for example 600 kA.
According to the invention, this object is achieved by a cathode block for an aluminium electrolysis cell which is composed at least in portions of a material which is obtainable by combusting a mixture which contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and at least one non-oxidic ceramic.
The cathode block according to the invention is preferably formed from a base layer and a cover layer, the at least one portion which contains the aforementioned mixture being part of the cover layer. Within the meaning of the invention, this portion may extend over the entire cover layer or the portion may merely form part of this cover layer.
This solution is based on the finding that the combined addition of material containing comparatively poorly or not at all graphitisable carbon, specifically of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the
4 average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, and of non-oxidic ceramic to the material from which at least a portion of the cathode block is produced great)y increases the wear-resistance of the cathode block, and this is accompanied by excellent wettability of the cathode block with aluminium and outstanding electrical and thermal conductivity of the cathode block. Whilst the addition of non-oxidic ceramic, such as titanium diboride, because of the catalytic activity thereof for the graphitisation, increases both the electrical conductivity and the thermal conductivity of the cathode block as well as increasing the wettability of the of the cathode block with aluminium, the addition of material containing comparatively poorly or not at all graphitisable carbon greatly increases the wear-resistance of the cathode block. Therefore, the cathode block according to the invention can be used in particular even at high current intensities of for example 600 kA
and has a long service life even in operating conditions of this type. Meanwhile, the comparatively poor graphitisability of the carbon-containing material is also advantageous because it adjusts an excessively high electrical conductivity, which the mere addition of the non-oxidic ceramic might confer on the cathode block, into an acceptable range. In principle as high an electrical conductivity as possible is desirable for a cathode; however, an excessively high electrical conductivity is undesirable because it can lead for example to an inhomogeneous current distribution in the cathode block, and this can lead both to electrochemically induced corrosion resulting from aluminium carbide formation and to a decrease in energy efficiency resulting from increased horizontal currents in liquid aluminium and thus to reduced stability of the electrolysis cell. Overall, as a result of the combined addition of material containing comparatively poorly or not at all graphitisable carbon, specifically of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, and of non-oxidic ceramic to the material from which at least a portion of the cathode block is produced, the cathode block according to the invention not only has a low electrical resistivity and good wettability with aluminium melt, but is also distinguished in particular by a high wear-resistance towards the abrasive chemical and thermal conditions prevailing during the operation during melt-flow electrolysis, in particular including at high current intensities of for example 600 kA.
Within the meaning of the present invention, carbon material means in particular a material containing more than 60 % by weight, preferably more than 70 % by weight, particularly preferably more than 80 % by weight and more preferably more than 90 % by weight carbon, in particular coke.
As a result of the aforementioned properties and advantages, the cathode block according to the invention is preferably a graphite-based cathode block, in other words a cathode block obtainable by combusting and subsequently graphitising the material from which it is produced. As a result of the comparatively poor or completely absent graphitisability of the carbon-containing material used according to the invention, having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, only very limited transformation into a graphite structure takes place during the graphitisation, and none at all takes place in the non-oxidic ceramic, and so the graphite proportion of the cathode block in this embodiment stems virtually exclusively from the other constituents of the material, which are described in detail below.
To achieve the advantages, described above in relation to the addition of the material containing comparatively poorly or not at all graphitisable carbon, to a great extent, a development of the inventive idea proposes providing carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.40 and particularly preferably of at most 0.30 in the material of which the cathode block is composed at least in portions. This leads to a particularly good wear-resistance of the cathode block and makes the electrical conductivity particularly reliably controllable. In the context of the present invention, the graphitisability is determined according to Maire and Mehring as disclosed by J. Maire and J.
Mehring in "Graphitization of soft carbons" in Chemistry and Physics of Carbon, Vol. 6, Marcel Dekker, P.K. Walker Jr. (Ed.), New York 1970, pages 125 to 190. Briefly summarised, in this context the lattice spacing is determined from the diffraction peak of the (002) plane, and the graphitisation level is calculated therefrom by the formula g = [0.3440 ¨
d(002)]/0.0086, in which g is the graphitisation level and d(002) is the lattice spacing from the diffraction peak of the (002) plane in nm.
For the same reason, in a further preferred embodiment it is preferred for the at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 to be coke, particularly preferably coke having an average layer spacing c/2 of at least 0.339 nm as determined by X-ray diffraction interference. Coke of this type has a suitably low graphitisability, very good results being obtained in particular with coke which has an average layer spacing c/2 of 0.340 to 0.344 nm as determined by X-ray diffraction interference.
Preferably, particulate carbon material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 is used, the specific BET area of the particles of the carbon material preferably being 10 to 40 m2/g and particularly preferably 20 to 30 m2/g.
A preferred example of coke having a low graphitisability of the aforementioned type is coke which accumulates as a side product in the production of unsaturated hydrocarbons, in particular of acetylene, and which is referred to in the following as acetylene coke irrespective of the nature of the unsaturated hydrocarbon during the production of which it accumulates. Acetylene coke obtainable from the crude oil fractions or steam crack residues used when quenching reaction gas in the synthesis of unsaturated hydrocarbons, in particular of acetylene, has been found to be particularly suitable for this purpose. To produce this coke, the quenching oil or soot mixture is passed to a coker which is heated to approximately 500 C. In the coker, liquid components of the quenching oil evaporate, whilst the coke collects on the base of the coker. A corresponding method is described for example in DE 29 47 005 Al. In this way, a fine-grained onion-skin-like coke is obtained, which preferably has a carbon content of at least 96 % by weight and an ash content of at most 0.05 % by weight and preferably of at most 0.01 % by weight.
The acetylene coke preferably has an average layer spacing c/2, as determined by X-ray diffraction interference, of at least 0.34 nm, the crystallite size in the c direction Lc preferably being less than 20 nm and the crystallite size in the a direction La preferably being less than 50 nm and particularly preferably less than 40 nm.
In addition, it is preferred for the acetylene coke to be in the form of spherical particles having a grain size of more than 0.2 mm and preferably of more than 0.5 mm.
Good results are obtained in particular if the acetylene coke has a BET area of 20 to 40 m2/g.
A further preferred example of coke, which may be used in addition or as an alternative to acetylene coke, is coke produced in fluidised bed methods. With these methods, coke of a spherical to ellipsoid form is obtained, and is of an onion-skin-like construction.
Another further preferred example of coke, which may be used in addition or as an alternative to the above-disclosed acetylene coke and/or coke obtained by flexicoking methods, is shot coke, which is produced by delayed coking. The particles of this coke are of a spherical morphology. It is preferred for this coke to have an average layer spacing c/2, as determined by X-ray diffraction interference, of at least 0.339 nm and for the crystallite size in the c direction Lc to be less than 30 nm.
Good results are obtained in particular if the at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 consists of particles having a grain size of 0.2 mm to 3 mm and preferably of 0.5 mm to 20 mm.
A development of the inventive idea proposes to provide carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, which is composed of particles having a spherical morphology, in other words a spherical to ellipsoidal form, in the mixture. Because of the high flowability thereof, a carbon material consisting of particles of this type leads to a material having a higher bulk density, and this contributes to an increase in the wear-resistance. Preferably, the particles of the carbon material have a length-to-diameter ratio of 1 to 5, particularly preferably of 1 to 3. This is because the flowability of the carbon material and thus the bulk density and wear-resistance of the cathode block increases more the closer the form of the particles is to an ideal spherical shape.
In a further preferred embodiment of the present invention, the individual particles of the carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 have an onion-skin structure, referring within the meaning of the invention to a multilayer construction in which an inner layer of particles of spherical or ellipsoid form is covered completely or at least in part by at least an intermediate layer and an outer layer.
To achieve the advantages, described above in relation to the addition of the material containing comparatively poorly or not at all graphitisable carbon, to a particularly great extent, a development of the inventive idea proposes providing carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 in an amount of 1 to 25 % by weight, particularly preferably of 10 to 25 % by weight and most preferably of 10 to 20 `)/0 by weight in the mixture from which the material of which the cathode block is composed at least in portions is obtained by combusting and preferably graphitising. As a result, a particularly high wear-resistance of the cathode block is achieved at the same time as excellent wettability with aluminium and sufficiently high electrical and thermal conductivity.
In a preferred embodiment of the present invention, the non-oxidic ceramic is a non-oxidic ceramic which is composed of at least one metal from the 4th to 6th transition groups and at least one element from the 31-d or 4th main group of the periodic table of elements.
Particularly preferred examples of ceramics of this type are titanium diboride, zirconium diboride, tantalum diboride, titanium carbide, boron carbide, titanium carbonitride, silicon carbide, tungsten carbide, vanadium carbide, titanium nitride, boron nitride, silicon nitride and any desired chemical combinations and/or mixtures of two or more of said compounds.
Particularly good results are obtained if the at least one non-oxidic ceramic is titanium diboride and/or zirconium diboride, in particular titanium diboride.
A development of the inventive idea proposes for the at least one non-oxidic ceramic contained in the cathode block to have a monomodal particle size distribution, the volume-average particle size (d3,50) as determined by random light scattering pursuant to International Standard ISO 13320-1, being 10 to 20 pm.
In the context of the present invention, it has been found that non-oxidic ceramic having an above-defined monomodal particle size distribution not only brings about very good wettability of the surface of the cathode block with aluminium, but, by way of combination with the at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, in particular also leads to a cathode block having excellent wear-resistance. In addition, in the context of the present invention it has surprisingly been found that this effect is achieved in particular even at comparatively small amounts of added non-oxidic ceramic. As a result, a high concentration of non-oxidic ceramic in the cathode block, which leads to a brittle cathode block surface, can be dispensed with. Non-oxidic ceramic 'having an above-defined monomodal particle size distribution is also distinguished by very good workability. In particular, the dust formation of a non-oxidic ceramic of this type is sufficiently low, for example during filling into a mixing container or during transport of powder containing this ceramic, and at most slight agglomerate formation occurs during the mixture. Moreover, a powder of this type containing this ceramic has a sufficiently high flowability and pourability, in such a way that it can be conveyed to a mixing device for example using a conventional conveyor device.
Preferably, the at least one non-oxidic ceramic provided in the cathode block has a monomodal particle size distribution, the volume-average particle size (d3,50), determined as above, being 12 to 18 pm and particularly preferably 14 to 16 pm.
As an alternative to the aforementioned embodiment, the non-oxidic ceramic contained in the cathode block may have a monomodal particle size distribution, the volume-average particle size (d3,50) as determined by random light scattering pursuant to International Standard ISO 13320-1, being 3 to 10 pm and preferably 4 to 6 pm. In this embodiment too, particularly preferably a non-oxidic titanium ceramic and most preferably titanium diboride having an above-defined monomodal particle size distribution is used.
A development of the inventive idea proposes that the at least one non-oxidic ceramic has a volume-average d3,90 Particle size, determined as above, of 20 to 40 pm and preferably of 25 to 30 pm. Preferably, the non-oxidic ceramic has a d3,90 value of this type in combination with an above-defined d3,50 value. In this embodiment too, the non-oxidic titanium ceramic and particularly preferably titanium diboride. As a result, the advantages and effects mentioned for the above embodiment are actually achieved to an increased extent.
As an alternative to the aforementioned embodiment, the non-oxidic ceramic contained in the cathode block may have a volume-average d3,90 particle size, determined as above, of to 20 pm and preferably of 12 to 18 pm. Preferably, the non-oxidic ceramic has a d3,90 value of this type in combination with an above-defined d3,50 value. In this embodiment too, particularly preferably a non-oxidic titanium ceramic and most preferably titanium diboride having an above-defined monomodal particle size distribution is used.
In a further preferred embodiment of the present invention, the non-oxidic ceramic has a volume-average d3,10 particle size, determined as above, of 2 to 7 pm and preferably 3 to 5 µpm. Preferably, the non-oxidic ceramic has a d3,10 value of this type in combination with an above-defined d3,90 value and/or d3,50 value. In this embodiment too, the non-oxidic ceramic is preferably a non-oxidic titanium ceramic and particularly preferably titanium diboride. As a result, the advantages and effects mentioned for the above embodiments are actually achieved to an increased extent.
As an alternative to the aforementioned embodiment, the non-oxidic ceramic contained in the cathode block may have a volume-average d3,10 particle size, determined as above, of 1 to 3 pm and preferably of 1 to 2 pm. Preferably, the non-oxidic ceramic has a d3,10 value of this type in combination with an above-defined d3,90 value and/or d3,50 value.
In this embodiment too, particularly preferably a non-oxidic titanium ceramic and most preferably titanium diboride having an above-defined monomodal particle size distribution is used.
In addition, it is preferred for the non-oxidic ceramic, in particular a non-oxidic titanium ceramic and particularly preferably titanium diboride, to have a particle size distribution characterised by a span value calculated by the following equation:
span = (d3,90 ¨ d3,10)/c13,50 of 0.65 to 3.80 and particularly preferably of 1.00 to 2.25. Preferably, the non-oxidic ceramic has a span value of this type in combination with an above-defined d3,90 value and/or d3,50 value and/or d3,10 value. As a result, the advantages and effects mentioned for the above embodiments are actually achieved to an increased extent.
To achieve the advantages described above, in particular sufficiently high electrical conductivity and wettability of the cathode block with aluminium, to a particularly great extent, a development of the inventive idea proposes providing non-oxidic ceramic in an amount of 1 to 45 % by weight in the mixture from which the material of which the cathode block is composed at least in portions is obtained by combusting and preferably graphitising.
Particularly good results are obtained in this regard if the amount of non-oxidic ceramic is 10 to 40 % by weight and particularly preferably 15 to 35 % by weight.
Preferably, the total of the amount of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and the amount of non-oxidic ceramic in the mixture from which the material of which the cathode block is composed at least in portions is obtained by combusting and preferably graphitising is 2 to 70 % by weight, preferably 20 to 65 % by weight and particularly preferably 25 to 55 % by weight. As a result, the cathode block according to the invention has a particularly good wear-resistance towards the abrasive chemical and thermal conditions prevailing during the operation during melt-flow electrolysis, in particular including at high current intensities of for example 600 kA, at the same time as a low electrical resistivity and a good wettability with aluminium melt.
In a further preferred embodiment of the present invention, the proportion of non-oxidic ceramic is 20 to 95 % by weight, particularly preferably 50 to 75 % by weight, based on the total of non-oxidic ceramic and carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50.
In addition to the at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and in addition to the at least one non-oxidic ceramic, the mixture from which the material of which the cathode block is composed at least in portions is obtained by combusting and preferably graphitising preferably contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of more than 0.50, preferably of at least 0.60, particularly preferably of at least 0.65 and most preferably of at least 0.70. During the graphitisation which is preferably carried out after the combusting, this carbon forms a graphite structure which subsequently significantly contributes to the excellent electrical and thermal conductivity of the cathode block according to the invention.
In addition to or instead of the at least one carbon-containing material having a comparatively high graphitisability, the mixture from which the material of which the cathode block is composed at least in portions is obtained by combusting and preferably graphitising preferably contains at least one binder. The binder may for example be pitch, in particular coal tar pitch and/or petroleum pitch, tar, bitumen, phenol resin or furan resin. A particularly preferred binder is pitch.
'A development of the inventive idea proposes for the material of which the cathode block is composed at least in portions to be obtainable by combusting and preferably subsequently graphitising a mixture which contains:
- 1 to 25 % by weight of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, - 1 to 45 % by weight of at least one non-oxidic ceramic, - 10 to 70 % by weight of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of more than 0.50, preferably of at least 0.60, particularly preferably of at least 0.65 and most preferably of at least 0.70, and - 10 to 25 % by weight binder, the total of the amount of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and the amount of non-oxidic ceramic preferably being 5 to 70 %
by weight, and the total of the individual constituents being 100 % by weight.
Particularly preferably, the material of which the cathode block is composed at least in portions is obtainable by combusting and preferably subsequently graphitising a mixture which contains:
- 10 to 25 % by weight, and preferably 10 to 20 % by weight, of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.40 and preferably of at most 0.30, - 10 to 40 % by weight, and preferably 15 to 35 % by weight, of at least one non-oxidic ceramic, - 20 to 40 % by weight, and preferably 25 to 35 % by weight, of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at least 0.60, and preferably of at least 0.70, and - 10 to 25 % by weight binder, the total of the amount of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800. C, of at most 0.40 and the amount of non-oxidic ceramic preferably being 20 to 65 %
'by weight and particularly preferably 25 to 55 % by weight, and the total of the individual constituents being 100 % by weight.
As set out above, it is particularly preferred for the material of which the cathode block is composed at least in portions to be obtainable by combusting and subsequently graphitising the above-described mixture. It is preferred for the graphitisation of the mixture to take place at a temperature of more than 1,800 to 3,000 C, preferably of 2,000 to 3,000 C and particularly preferably of 2,200 to 2,700 C.
As mentioned previously, the cathode block preferably comprises a base layer and a cover layer, the cover layer being composed at least in portions of the material which is obtainable by combusting and preferably subsequently graphitising the above-described mixture. In this context, the addition of the non-oxidic ceramic and of the carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 is limited to the at least one portion of the cover layer of the cathode block. The cover layer is the layer which is exposed to the aluminium melt during operation of the electrolysis cell.
In this context, it is preferred for the thickness of the cover layer to be 1 to 50 %, preferably 5 to 40 %, particularly preferably 10 to 30 % and most preferably 15 to 25 % of the total height of the cathode block.
In this context, an addition of non-oxidic ceramic and of the carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 into the base layer is superfluous. Therefore, a preferred embodiment of the present invention proposes for the base layer merely to consist of graphitised, graphitic or graphitisable materials for the purpose of achieving a high electrical and thermal conductivity. Preferably the base layer is at least 80 % by weight, preferably at least 90 % by weight, more preferably at least 95 % by weight, more preferably at least 99 % by weight and most preferably completely composed of graphite and binder or the carbonisation and/or graphitisation product thereof.
The cover layer may comprise a plurality of portions, two or more of the portions being composed of respectively different materials. In this way, each surface region of the cathode block can be tailored with respect to the desired wear-resistance, electrical conductivity, 'thermal conductivity and wettability with aluminium. In this embodiment, it is possible in particular to take into account the fact that individual surface portions of the cathode block are exposed to higher wear than others during the melt-flow electrolysis, in such a way that the surface portions which are subject to particularly high wear are selectively composed of a material comprising a correspondingly large amount of carbon, having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, whilst the other surface portions which are subject to low wear are composed of a material containing less carbon, having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50.
In an example variant of the above embodiment of the present invention, the at least two portions are composed of different materials, which are each obtainable by combusting a mixture which contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and at least one non-oxidic ceramic.
Alternatively, however, it is also possible for only one or more of the at least two portions to be composed of different materials, which are each obtainable by combusting a mixture which contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and at least one non-oxidic ceramic, whilst at least one of the at least two portions is composed of a material which contains no carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and/or no non-oxidic ceramic.
In principle, the cathode block according to the invention is not limited as regards the number of different portions in the cover layer. However, good results are obtained in particular when the cover layer of the cathode block according to the invention comprises 3 to 7, preferably 3 to 5, particularly preferably 3 to 4 and most preferably 3 different portions, preferably one or two of the portions respectively being composed of a material which is obtainable by combusting a mixture which contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and at least one non-oxidic ceramic.
'A further subject matter of the present invention is a method for producing a cathode block according to at least one of the preceding claims, comprising the following steps:
a) producing a mixture which contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and at least one non-oxidic ceramic, b) shaping the mixture to form at least one portion of a cathode block, and c) combusting the mixture at a temperature of 600 to less than 1,500 C.
Preferably, in method step a) a mixture is produced which contains:
- 10 to 25 % by weight of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, - 10 to 40 % by weight of at least one non-oxidic ceramic, - 20 to 40 % by weight of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at least 0.60, and - 10 to 25 % by weight binder, the total of the amount of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and the amount of non-oxidic ceramic preferably being 20 to 65 %
by weight, and the total of the individual constituents being 100 % by weight.
Particularly preferably, in method step a) a mixture is produced which contains:
- 10 to 20 % by weight of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.40, - 15 to 35 % by weight of at least one non-oxidic ceramic, - 25 to 35 % by weight of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at least 0.70, and - 10 to 25 % by weight binder, the total of the amount of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,806 C, of at most 0.40 and the amount of non-oxidic ceramic preferably being 30 to 50 %
by weight, and the total of the individual constituents being 100% by weight.
In a development of the inventive idea, it is proposed for the mixture produced in method step a) to be applied by a vibration method to a second mixture which preferably contains - 40 to 90 % by weight of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of more than 0.50, and - 10 to 25 % by weight binder, the total of the individual constituents being 100 % by weight, and the overall mixture thus produced being shaped into a cathode block in method step b), the second mixture forming the base layer and the other mixture forming the cover layer of the cathode block, before the cathode block is combusted in method step c) and subsequently preferably graphitised.
Preferably, the combustion in method step c) takes place at a temperature of 600 to less than 1,500 C, preferably of 800 to 1,200 C and particularly preferably of 900 to 1,100 C.
In a development of the inventive idea, it is proposed to graphitise the combusted cathode block after method step c) at a temperature of more than 1,800 to 3,000 C, preferably of 2,000 to 3,000 C and particularly preferably of 2,200 to 2,700 C.
A further subject matter of the present invention is a cathode which contains at least one above-disclosed cathode block.
The present invention further relates to the use of an above-disclosed cathode block or an above-disclosed cathode to carry out a melt-flow electrolysis to produce metal, preferably to produce aluminium.
In the following, purely by way of example, the present invention is described by way of advantageous embodiments and with reference to the accompanying drawings, in which:
Fig. 1 is a schematic perspective view of a cathode block in accordance with a first embodiment of the present invention, and Fig. 2 is a schematic perspective view of a cathode block in accordance with a second embodiment of the present invention.
Fig. 1 is a schematic perspective view of a cathode block 10 in accordance with a first embodiment of the present invention. The cathode block 10 consists of a lower base layer 12 and a cover layer 14 arranged above and rigidly connected thereto. The boundary surface between the base layer 12 and the cover layer 14 is planar. While the base layer 12 of the cathode block 10 has a graphite material structure, the cover layer 14 is composed of a graphite composite material containing acetylene coke and titanium diboride.
The cathode block 10 has a length of 3,100 mm, a width of 420 mm and a height of 400 mm, the base layer 12 having a height of 260 mm and the cover layer 14 having a height of 140 mm.
Finally, the cathode block 10 comprises, on the lower face thereof, a groove 16 having a right-angled, specifically substantially rectangular cross section.
In practice, a cathode for an aluminium electrolysis cell is composed of 12 to 28 cathode blocks of this type, a steel busbar (not shown) having a likewise right-angled or substantially rectangular cross section being inserted into each of the grooves 16. The gap between the busbars and the walls defining the groove 16 is filled with cast iron (not shown), thereby connecting the busbars to the walls defining the groove 16.
The cathode block 10 in accordance with a second embodiment of the present invention shown in Fig. 2 differs from that shown in Fig. 1 in that the cover layer 14 consists of three different portions 18, 18', 18". The portions 18, 18" are each composed of the same material, which differs from the material of which the portion 18' is composed and from the material of which the base layer 12 is composed. Whilst the portions 18, 18"
are composed of a graphite composite material containing 20 % by weight acetylene coke and 20 % by weight titanium diboride, the portion 18' is composed of a graphite composite material containing 10 % by weight acetylene coke and 30 % by weight titanium diboride, and the base layer 12 has a graphite material structure. In this way, the individual surface portions are adapted to the cover layer 14 in such a way that the portions 18, 18', 18"
of the cathode block 10 which are exposed to a higher wear than other parts during the melt-flow electrolysis have a correspondingly higher wear resistance.
In the following, purely by way of example, the present invention is disclosed by way of an example, which does not limit the invention.
'Example A cathode block 10 as shown in Fig. 1 was produced by filling a mixture A, forming the base layer 12, and a mixture B, forming the cover layer 14, into a correspondingly dimensioned vibration mould.
The mixture A was composed as follows:
- 80 % by weight petroleum coke having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of 0.7, and - 20 % by weight coal tar pitch having a Kramer-Sarnow softening point of 90 C as a binder.
Further, the mixture B was composed as follows:
- 24 % by weight titanium diboride, - 16 % by weight acetylene coke having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of 0.3, - 40 % by weight petroleum coke having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of 0.7, and - 20 % by weight coal tar pitch having a Kramer-Sarnow softening point of 90 C as a binder.
List of reference numerals cathode block 12 base layer 14 cover layer 16 groove 18, 18', 18" portions of the cover layer
and has a long service life even in operating conditions of this type. Meanwhile, the comparatively poor graphitisability of the carbon-containing material is also advantageous because it adjusts an excessively high electrical conductivity, which the mere addition of the non-oxidic ceramic might confer on the cathode block, into an acceptable range. In principle as high an electrical conductivity as possible is desirable for a cathode; however, an excessively high electrical conductivity is undesirable because it can lead for example to an inhomogeneous current distribution in the cathode block, and this can lead both to electrochemically induced corrosion resulting from aluminium carbide formation and to a decrease in energy efficiency resulting from increased horizontal currents in liquid aluminium and thus to reduced stability of the electrolysis cell. Overall, as a result of the combined addition of material containing comparatively poorly or not at all graphitisable carbon, specifically of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, and of non-oxidic ceramic to the material from which at least a portion of the cathode block is produced, the cathode block according to the invention not only has a low electrical resistivity and good wettability with aluminium melt, but is also distinguished in particular by a high wear-resistance towards the abrasive chemical and thermal conditions prevailing during the operation during melt-flow electrolysis, in particular including at high current intensities of for example 600 kA.
Within the meaning of the present invention, carbon material means in particular a material containing more than 60 % by weight, preferably more than 70 % by weight, particularly preferably more than 80 % by weight and more preferably more than 90 % by weight carbon, in particular coke.
As a result of the aforementioned properties and advantages, the cathode block according to the invention is preferably a graphite-based cathode block, in other words a cathode block obtainable by combusting and subsequently graphitising the material from which it is produced. As a result of the comparatively poor or completely absent graphitisability of the carbon-containing material used according to the invention, having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, only very limited transformation into a graphite structure takes place during the graphitisation, and none at all takes place in the non-oxidic ceramic, and so the graphite proportion of the cathode block in this embodiment stems virtually exclusively from the other constituents of the material, which are described in detail below.
To achieve the advantages, described above in relation to the addition of the material containing comparatively poorly or not at all graphitisable carbon, to a great extent, a development of the inventive idea proposes providing carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.40 and particularly preferably of at most 0.30 in the material of which the cathode block is composed at least in portions. This leads to a particularly good wear-resistance of the cathode block and makes the electrical conductivity particularly reliably controllable. In the context of the present invention, the graphitisability is determined according to Maire and Mehring as disclosed by J. Maire and J.
Mehring in "Graphitization of soft carbons" in Chemistry and Physics of Carbon, Vol. 6, Marcel Dekker, P.K. Walker Jr. (Ed.), New York 1970, pages 125 to 190. Briefly summarised, in this context the lattice spacing is determined from the diffraction peak of the (002) plane, and the graphitisation level is calculated therefrom by the formula g = [0.3440 ¨
d(002)]/0.0086, in which g is the graphitisation level and d(002) is the lattice spacing from the diffraction peak of the (002) plane in nm.
For the same reason, in a further preferred embodiment it is preferred for the at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 to be coke, particularly preferably coke having an average layer spacing c/2 of at least 0.339 nm as determined by X-ray diffraction interference. Coke of this type has a suitably low graphitisability, very good results being obtained in particular with coke which has an average layer spacing c/2 of 0.340 to 0.344 nm as determined by X-ray diffraction interference.
Preferably, particulate carbon material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 is used, the specific BET area of the particles of the carbon material preferably being 10 to 40 m2/g and particularly preferably 20 to 30 m2/g.
A preferred example of coke having a low graphitisability of the aforementioned type is coke which accumulates as a side product in the production of unsaturated hydrocarbons, in particular of acetylene, and which is referred to in the following as acetylene coke irrespective of the nature of the unsaturated hydrocarbon during the production of which it accumulates. Acetylene coke obtainable from the crude oil fractions or steam crack residues used when quenching reaction gas in the synthesis of unsaturated hydrocarbons, in particular of acetylene, has been found to be particularly suitable for this purpose. To produce this coke, the quenching oil or soot mixture is passed to a coker which is heated to approximately 500 C. In the coker, liquid components of the quenching oil evaporate, whilst the coke collects on the base of the coker. A corresponding method is described for example in DE 29 47 005 Al. In this way, a fine-grained onion-skin-like coke is obtained, which preferably has a carbon content of at least 96 % by weight and an ash content of at most 0.05 % by weight and preferably of at most 0.01 % by weight.
The acetylene coke preferably has an average layer spacing c/2, as determined by X-ray diffraction interference, of at least 0.34 nm, the crystallite size in the c direction Lc preferably being less than 20 nm and the crystallite size in the a direction La preferably being less than 50 nm and particularly preferably less than 40 nm.
In addition, it is preferred for the acetylene coke to be in the form of spherical particles having a grain size of more than 0.2 mm and preferably of more than 0.5 mm.
Good results are obtained in particular if the acetylene coke has a BET area of 20 to 40 m2/g.
A further preferred example of coke, which may be used in addition or as an alternative to acetylene coke, is coke produced in fluidised bed methods. With these methods, coke of a spherical to ellipsoid form is obtained, and is of an onion-skin-like construction.
Another further preferred example of coke, which may be used in addition or as an alternative to the above-disclosed acetylene coke and/or coke obtained by flexicoking methods, is shot coke, which is produced by delayed coking. The particles of this coke are of a spherical morphology. It is preferred for this coke to have an average layer spacing c/2, as determined by X-ray diffraction interference, of at least 0.339 nm and for the crystallite size in the c direction Lc to be less than 30 nm.
Good results are obtained in particular if the at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 consists of particles having a grain size of 0.2 mm to 3 mm and preferably of 0.5 mm to 20 mm.
A development of the inventive idea proposes to provide carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, which is composed of particles having a spherical morphology, in other words a spherical to ellipsoidal form, in the mixture. Because of the high flowability thereof, a carbon material consisting of particles of this type leads to a material having a higher bulk density, and this contributes to an increase in the wear-resistance. Preferably, the particles of the carbon material have a length-to-diameter ratio of 1 to 5, particularly preferably of 1 to 3. This is because the flowability of the carbon material and thus the bulk density and wear-resistance of the cathode block increases more the closer the form of the particles is to an ideal spherical shape.
In a further preferred embodiment of the present invention, the individual particles of the carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 have an onion-skin structure, referring within the meaning of the invention to a multilayer construction in which an inner layer of particles of spherical or ellipsoid form is covered completely or at least in part by at least an intermediate layer and an outer layer.
To achieve the advantages, described above in relation to the addition of the material containing comparatively poorly or not at all graphitisable carbon, to a particularly great extent, a development of the inventive idea proposes providing carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 in an amount of 1 to 25 % by weight, particularly preferably of 10 to 25 % by weight and most preferably of 10 to 20 `)/0 by weight in the mixture from which the material of which the cathode block is composed at least in portions is obtained by combusting and preferably graphitising. As a result, a particularly high wear-resistance of the cathode block is achieved at the same time as excellent wettability with aluminium and sufficiently high electrical and thermal conductivity.
In a preferred embodiment of the present invention, the non-oxidic ceramic is a non-oxidic ceramic which is composed of at least one metal from the 4th to 6th transition groups and at least one element from the 31-d or 4th main group of the periodic table of elements.
Particularly preferred examples of ceramics of this type are titanium diboride, zirconium diboride, tantalum diboride, titanium carbide, boron carbide, titanium carbonitride, silicon carbide, tungsten carbide, vanadium carbide, titanium nitride, boron nitride, silicon nitride and any desired chemical combinations and/or mixtures of two or more of said compounds.
Particularly good results are obtained if the at least one non-oxidic ceramic is titanium diboride and/or zirconium diboride, in particular titanium diboride.
A development of the inventive idea proposes for the at least one non-oxidic ceramic contained in the cathode block to have a monomodal particle size distribution, the volume-average particle size (d3,50) as determined by random light scattering pursuant to International Standard ISO 13320-1, being 10 to 20 pm.
In the context of the present invention, it has been found that non-oxidic ceramic having an above-defined monomodal particle size distribution not only brings about very good wettability of the surface of the cathode block with aluminium, but, by way of combination with the at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, in particular also leads to a cathode block having excellent wear-resistance. In addition, in the context of the present invention it has surprisingly been found that this effect is achieved in particular even at comparatively small amounts of added non-oxidic ceramic. As a result, a high concentration of non-oxidic ceramic in the cathode block, which leads to a brittle cathode block surface, can be dispensed with. Non-oxidic ceramic 'having an above-defined monomodal particle size distribution is also distinguished by very good workability. In particular, the dust formation of a non-oxidic ceramic of this type is sufficiently low, for example during filling into a mixing container or during transport of powder containing this ceramic, and at most slight agglomerate formation occurs during the mixture. Moreover, a powder of this type containing this ceramic has a sufficiently high flowability and pourability, in such a way that it can be conveyed to a mixing device for example using a conventional conveyor device.
Preferably, the at least one non-oxidic ceramic provided in the cathode block has a monomodal particle size distribution, the volume-average particle size (d3,50), determined as above, being 12 to 18 pm and particularly preferably 14 to 16 pm.
As an alternative to the aforementioned embodiment, the non-oxidic ceramic contained in the cathode block may have a monomodal particle size distribution, the volume-average particle size (d3,50) as determined by random light scattering pursuant to International Standard ISO 13320-1, being 3 to 10 pm and preferably 4 to 6 pm. In this embodiment too, particularly preferably a non-oxidic titanium ceramic and most preferably titanium diboride having an above-defined monomodal particle size distribution is used.
A development of the inventive idea proposes that the at least one non-oxidic ceramic has a volume-average d3,90 Particle size, determined as above, of 20 to 40 pm and preferably of 25 to 30 pm. Preferably, the non-oxidic ceramic has a d3,90 value of this type in combination with an above-defined d3,50 value. In this embodiment too, the non-oxidic titanium ceramic and particularly preferably titanium diboride. As a result, the advantages and effects mentioned for the above embodiment are actually achieved to an increased extent.
As an alternative to the aforementioned embodiment, the non-oxidic ceramic contained in the cathode block may have a volume-average d3,90 particle size, determined as above, of to 20 pm and preferably of 12 to 18 pm. Preferably, the non-oxidic ceramic has a d3,90 value of this type in combination with an above-defined d3,50 value. In this embodiment too, particularly preferably a non-oxidic titanium ceramic and most preferably titanium diboride having an above-defined monomodal particle size distribution is used.
In a further preferred embodiment of the present invention, the non-oxidic ceramic has a volume-average d3,10 particle size, determined as above, of 2 to 7 pm and preferably 3 to 5 µpm. Preferably, the non-oxidic ceramic has a d3,10 value of this type in combination with an above-defined d3,90 value and/or d3,50 value. In this embodiment too, the non-oxidic ceramic is preferably a non-oxidic titanium ceramic and particularly preferably titanium diboride. As a result, the advantages and effects mentioned for the above embodiments are actually achieved to an increased extent.
As an alternative to the aforementioned embodiment, the non-oxidic ceramic contained in the cathode block may have a volume-average d3,10 particle size, determined as above, of 1 to 3 pm and preferably of 1 to 2 pm. Preferably, the non-oxidic ceramic has a d3,10 value of this type in combination with an above-defined d3,90 value and/or d3,50 value.
In this embodiment too, particularly preferably a non-oxidic titanium ceramic and most preferably titanium diboride having an above-defined monomodal particle size distribution is used.
In addition, it is preferred for the non-oxidic ceramic, in particular a non-oxidic titanium ceramic and particularly preferably titanium diboride, to have a particle size distribution characterised by a span value calculated by the following equation:
span = (d3,90 ¨ d3,10)/c13,50 of 0.65 to 3.80 and particularly preferably of 1.00 to 2.25. Preferably, the non-oxidic ceramic has a span value of this type in combination with an above-defined d3,90 value and/or d3,50 value and/or d3,10 value. As a result, the advantages and effects mentioned for the above embodiments are actually achieved to an increased extent.
To achieve the advantages described above, in particular sufficiently high electrical conductivity and wettability of the cathode block with aluminium, to a particularly great extent, a development of the inventive idea proposes providing non-oxidic ceramic in an amount of 1 to 45 % by weight in the mixture from which the material of which the cathode block is composed at least in portions is obtained by combusting and preferably graphitising.
Particularly good results are obtained in this regard if the amount of non-oxidic ceramic is 10 to 40 % by weight and particularly preferably 15 to 35 % by weight.
Preferably, the total of the amount of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and the amount of non-oxidic ceramic in the mixture from which the material of which the cathode block is composed at least in portions is obtained by combusting and preferably graphitising is 2 to 70 % by weight, preferably 20 to 65 % by weight and particularly preferably 25 to 55 % by weight. As a result, the cathode block according to the invention has a particularly good wear-resistance towards the abrasive chemical and thermal conditions prevailing during the operation during melt-flow electrolysis, in particular including at high current intensities of for example 600 kA, at the same time as a low electrical resistivity and a good wettability with aluminium melt.
In a further preferred embodiment of the present invention, the proportion of non-oxidic ceramic is 20 to 95 % by weight, particularly preferably 50 to 75 % by weight, based on the total of non-oxidic ceramic and carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50.
In addition to the at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and in addition to the at least one non-oxidic ceramic, the mixture from which the material of which the cathode block is composed at least in portions is obtained by combusting and preferably graphitising preferably contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of more than 0.50, preferably of at least 0.60, particularly preferably of at least 0.65 and most preferably of at least 0.70. During the graphitisation which is preferably carried out after the combusting, this carbon forms a graphite structure which subsequently significantly contributes to the excellent electrical and thermal conductivity of the cathode block according to the invention.
In addition to or instead of the at least one carbon-containing material having a comparatively high graphitisability, the mixture from which the material of which the cathode block is composed at least in portions is obtained by combusting and preferably graphitising preferably contains at least one binder. The binder may for example be pitch, in particular coal tar pitch and/or petroleum pitch, tar, bitumen, phenol resin or furan resin. A particularly preferred binder is pitch.
'A development of the inventive idea proposes for the material of which the cathode block is composed at least in portions to be obtainable by combusting and preferably subsequently graphitising a mixture which contains:
- 1 to 25 % by weight of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, - 1 to 45 % by weight of at least one non-oxidic ceramic, - 10 to 70 % by weight of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of more than 0.50, preferably of at least 0.60, particularly preferably of at least 0.65 and most preferably of at least 0.70, and - 10 to 25 % by weight binder, the total of the amount of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and the amount of non-oxidic ceramic preferably being 5 to 70 %
by weight, and the total of the individual constituents being 100 % by weight.
Particularly preferably, the material of which the cathode block is composed at least in portions is obtainable by combusting and preferably subsequently graphitising a mixture which contains:
- 10 to 25 % by weight, and preferably 10 to 20 % by weight, of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.40 and preferably of at most 0.30, - 10 to 40 % by weight, and preferably 15 to 35 % by weight, of at least one non-oxidic ceramic, - 20 to 40 % by weight, and preferably 25 to 35 % by weight, of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at least 0.60, and preferably of at least 0.70, and - 10 to 25 % by weight binder, the total of the amount of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800. C, of at most 0.40 and the amount of non-oxidic ceramic preferably being 20 to 65 %
'by weight and particularly preferably 25 to 55 % by weight, and the total of the individual constituents being 100 % by weight.
As set out above, it is particularly preferred for the material of which the cathode block is composed at least in portions to be obtainable by combusting and subsequently graphitising the above-described mixture. It is preferred for the graphitisation of the mixture to take place at a temperature of more than 1,800 to 3,000 C, preferably of 2,000 to 3,000 C and particularly preferably of 2,200 to 2,700 C.
As mentioned previously, the cathode block preferably comprises a base layer and a cover layer, the cover layer being composed at least in portions of the material which is obtainable by combusting and preferably subsequently graphitising the above-described mixture. In this context, the addition of the non-oxidic ceramic and of the carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 is limited to the at least one portion of the cover layer of the cathode block. The cover layer is the layer which is exposed to the aluminium melt during operation of the electrolysis cell.
In this context, it is preferred for the thickness of the cover layer to be 1 to 50 %, preferably 5 to 40 %, particularly preferably 10 to 30 % and most preferably 15 to 25 % of the total height of the cathode block.
In this context, an addition of non-oxidic ceramic and of the carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 into the base layer is superfluous. Therefore, a preferred embodiment of the present invention proposes for the base layer merely to consist of graphitised, graphitic or graphitisable materials for the purpose of achieving a high electrical and thermal conductivity. Preferably the base layer is at least 80 % by weight, preferably at least 90 % by weight, more preferably at least 95 % by weight, more preferably at least 99 % by weight and most preferably completely composed of graphite and binder or the carbonisation and/or graphitisation product thereof.
The cover layer may comprise a plurality of portions, two or more of the portions being composed of respectively different materials. In this way, each surface region of the cathode block can be tailored with respect to the desired wear-resistance, electrical conductivity, 'thermal conductivity and wettability with aluminium. In this embodiment, it is possible in particular to take into account the fact that individual surface portions of the cathode block are exposed to higher wear than others during the melt-flow electrolysis, in such a way that the surface portions which are subject to particularly high wear are selectively composed of a material comprising a correspondingly large amount of carbon, having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, whilst the other surface portions which are subject to low wear are composed of a material containing less carbon, having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50.
In an example variant of the above embodiment of the present invention, the at least two portions are composed of different materials, which are each obtainable by combusting a mixture which contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and at least one non-oxidic ceramic.
Alternatively, however, it is also possible for only one or more of the at least two portions to be composed of different materials, which are each obtainable by combusting a mixture which contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and at least one non-oxidic ceramic, whilst at least one of the at least two portions is composed of a material which contains no carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and/or no non-oxidic ceramic.
In principle, the cathode block according to the invention is not limited as regards the number of different portions in the cover layer. However, good results are obtained in particular when the cover layer of the cathode block according to the invention comprises 3 to 7, preferably 3 to 5, particularly preferably 3 to 4 and most preferably 3 different portions, preferably one or two of the portions respectively being composed of a material which is obtainable by combusting a mixture which contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and at least one non-oxidic ceramic.
'A further subject matter of the present invention is a method for producing a cathode block according to at least one of the preceding claims, comprising the following steps:
a) producing a mixture which contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and at least one non-oxidic ceramic, b) shaping the mixture to form at least one portion of a cathode block, and c) combusting the mixture at a temperature of 600 to less than 1,500 C.
Preferably, in method step a) a mixture is produced which contains:
- 10 to 25 % by weight of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50, - 10 to 40 % by weight of at least one non-oxidic ceramic, - 20 to 40 % by weight of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at least 0.60, and - 10 to 25 % by weight binder, the total of the amount of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.50 and the amount of non-oxidic ceramic preferably being 20 to 65 %
by weight, and the total of the individual constituents being 100 % by weight.
Particularly preferably, in method step a) a mixture is produced which contains:
- 10 to 20 % by weight of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at most 0.40, - 15 to 35 % by weight of at least one non-oxidic ceramic, - 25 to 35 % by weight of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of at least 0.70, and - 10 to 25 % by weight binder, the total of the amount of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,806 C, of at most 0.40 and the amount of non-oxidic ceramic preferably being 30 to 50 %
by weight, and the total of the individual constituents being 100% by weight.
In a development of the inventive idea, it is proposed for the mixture produced in method step a) to be applied by a vibration method to a second mixture which preferably contains - 40 to 90 % by weight of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of more than 0.50, and - 10 to 25 % by weight binder, the total of the individual constituents being 100 % by weight, and the overall mixture thus produced being shaped into a cathode block in method step b), the second mixture forming the base layer and the other mixture forming the cover layer of the cathode block, before the cathode block is combusted in method step c) and subsequently preferably graphitised.
Preferably, the combustion in method step c) takes place at a temperature of 600 to less than 1,500 C, preferably of 800 to 1,200 C and particularly preferably of 900 to 1,100 C.
In a development of the inventive idea, it is proposed to graphitise the combusted cathode block after method step c) at a temperature of more than 1,800 to 3,000 C, preferably of 2,000 to 3,000 C and particularly preferably of 2,200 to 2,700 C.
A further subject matter of the present invention is a cathode which contains at least one above-disclosed cathode block.
The present invention further relates to the use of an above-disclosed cathode block or an above-disclosed cathode to carry out a melt-flow electrolysis to produce metal, preferably to produce aluminium.
In the following, purely by way of example, the present invention is described by way of advantageous embodiments and with reference to the accompanying drawings, in which:
Fig. 1 is a schematic perspective view of a cathode block in accordance with a first embodiment of the present invention, and Fig. 2 is a schematic perspective view of a cathode block in accordance with a second embodiment of the present invention.
Fig. 1 is a schematic perspective view of a cathode block 10 in accordance with a first embodiment of the present invention. The cathode block 10 consists of a lower base layer 12 and a cover layer 14 arranged above and rigidly connected thereto. The boundary surface between the base layer 12 and the cover layer 14 is planar. While the base layer 12 of the cathode block 10 has a graphite material structure, the cover layer 14 is composed of a graphite composite material containing acetylene coke and titanium diboride.
The cathode block 10 has a length of 3,100 mm, a width of 420 mm and a height of 400 mm, the base layer 12 having a height of 260 mm and the cover layer 14 having a height of 140 mm.
Finally, the cathode block 10 comprises, on the lower face thereof, a groove 16 having a right-angled, specifically substantially rectangular cross section.
In practice, a cathode for an aluminium electrolysis cell is composed of 12 to 28 cathode blocks of this type, a steel busbar (not shown) having a likewise right-angled or substantially rectangular cross section being inserted into each of the grooves 16. The gap between the busbars and the walls defining the groove 16 is filled with cast iron (not shown), thereby connecting the busbars to the walls defining the groove 16.
The cathode block 10 in accordance with a second embodiment of the present invention shown in Fig. 2 differs from that shown in Fig. 1 in that the cover layer 14 consists of three different portions 18, 18', 18". The portions 18, 18" are each composed of the same material, which differs from the material of which the portion 18' is composed and from the material of which the base layer 12 is composed. Whilst the portions 18, 18"
are composed of a graphite composite material containing 20 % by weight acetylene coke and 20 % by weight titanium diboride, the portion 18' is composed of a graphite composite material containing 10 % by weight acetylene coke and 30 % by weight titanium diboride, and the base layer 12 has a graphite material structure. In this way, the individual surface portions are adapted to the cover layer 14 in such a way that the portions 18, 18', 18"
of the cathode block 10 which are exposed to a higher wear than other parts during the melt-flow electrolysis have a correspondingly higher wear resistance.
In the following, purely by way of example, the present invention is disclosed by way of an example, which does not limit the invention.
'Example A cathode block 10 as shown in Fig. 1 was produced by filling a mixture A, forming the base layer 12, and a mixture B, forming the cover layer 14, into a correspondingly dimensioned vibration mould.
The mixture A was composed as follows:
- 80 % by weight petroleum coke having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of 0.7, and - 20 % by weight coal tar pitch having a Kramer-Sarnow softening point of 90 C as a binder.
Further, the mixture B was composed as follows:
- 24 % by weight titanium diboride, - 16 % by weight acetylene coke having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of 0.3, - 40 % by weight petroleum coke having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 C, of 0.7, and - 20 % by weight coal tar pitch having a Kramer-Sarnow softening point of 90 C as a binder.
List of reference numerals cathode block 12 base layer 14 cover layer 16 groove 18, 18', 18" portions of the cover layer
Claims (15)
1. Cathode block (10) for an aluminium electrolysis cell, the cathode block (10) being composed at least in portions of a material which is obtainable by combusting a mixture which contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 °C, of at most 0.50 and at least one non-oxidic ceramic.
2. Cathode block (10) according to claim 1, characterised in that the at least one carbon-containing material has a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 °C, of at most 0.40 and preferably of at most 0.30.
3. Cathode block (10) according to either claim 1 or claim 2, characterised in that at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 °C, of at most 0.50 is contained in the mixture in an amount of 1 to 25 % by weight, particularly preferably of 10 to 25 % by weight and most preferably of 10 to 20 % by weight.
4. Cathode block (10) according to at least one of the preceding claims, characterised in that the at least one non-oxidic ceramic is selected from the group consisting of titanium diboride, zirconium diboride, tantalum diboride, titanium carbide, boron carbide, titanium carbonitride, silicon carbide, tungsten carbide, vanadium carbide, titanium nitride, boron nitride, silicon nitride and any desired chemical combinations and/or mixtures of two or more of said compounds.
5. Cathode block (10) according to claim 4, characterised in that the at least one non-oxidic ceramic is titanium boride and/or zirconium diboride, and preferably titanium diboride.
6. Cathode block (10) according to at least one of the preceding claims, characterised in that the at least one non-oxidic ceramic is contained in the mixture in an amount of 1 to 45 % by weight, preferably 10 to 40 % by weight and particularly preferably 15 to 35 % by weight.
7. Cathode block (10) according to at least one of the preceding claims, characterised in that the total of the amount of one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 °C, of at most 0.50 and the amount of non-oxidic ceramic in the mixture is 2 to 70 % by weight, preferably 20 to 65 % by weight and particularly preferably 25 to 55 %
by weight.
by weight.
8. Cathode block (10) according to at least one of the preceding claims, characterised in that the material of which the cathode block (10) is composed at least in portions is obtainable by combusting a mixture which contains, in addition to the at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 °C, of at most 0.50 and in addition to the at least one non-oxidic ceramic, i) at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 °C, of more than 0.50, preferably of at least 0.60, particularly preferably of at least 0.65 and most preferably of at least 0.70 and/or ii) at least one binder, which is preferably pitch.
9. Cathode block (10) according to claim 8, characterised in that the material of which the cathode block (10) is composed at least in portions is obtainable by combusting a mixture which contains:
- 10 to 25 % by weight, and preferably 10 to 20 % by weight, of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 °C, of at most 0.40 and preferably of at most 0.30, - 10 to 40 % by weight, and preferably 15 to 35 % by weight, of at least one non-oxidic ceramic, - 20 to 40 %by weight, and preferably 25 to 35 % by weight, of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 °C, of at least 0.60, and preferably of at least 0.70, and - 10 to 25 % by weight binder, the total of the amount of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 °C, of at most 0.40 and the amount of non-oxidic ceramic being 20 to 60 % by weight and preferably 30 to 50 % by weight, and the total of the individual constituents being 100 %
by weight
- 10 to 25 % by weight, and preferably 10 to 20 % by weight, of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 °C, of at most 0.40 and preferably of at most 0.30, - 10 to 40 % by weight, and preferably 15 to 35 % by weight, of at least one non-oxidic ceramic, - 20 to 40 %by weight, and preferably 25 to 35 % by weight, of at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 °C, of at least 0.60, and preferably of at least 0.70, and - 10 to 25 % by weight binder, the total of the amount of carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 °C, of at most 0.40 and the amount of non-oxidic ceramic being 20 to 60 % by weight and preferably 30 to 50 % by weight, and the total of the individual constituents being 100 %
by weight
10. Cathode block (10) according to at least one of the preceding claims, characterised in that it comprises a base layer (12) and a cover layer (14), the cover layer (14) being composed of the material obtainable by combusting the mixture.
11. Cathode block (10) according to claim 10, characterised in that the thickness of the cover layer (14) is 1 to 50 %, preferably 5 to 40 %, particularly preferably 10 to 30 % and most preferably 15 to 25 % of the total height of the cathode block (10).
12 Cathode block (10) according to either claim 10 or claim 11, characterised in that the cover layer (14) comprises a plurality of potions (18, 18', 18"), at least two of the portions (18, 18', 18") being composed of different materials which are each obtainable by combusting a mixture which contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 °C, of at most 0 50 and at least one non-oxidic ceramic.
13. Method for producing a cathode block (10) according to at least one of the preceding claims, comprising the following steps a) producing a mixture which contains at least one carbon-containing material having a graphitisation level, calculated according to Maire and Mehring from the average layer spacing c/2 after a heat treatment at 2,800 °C, of at most 0.50 and at least one non-oxidic ceramic, b) shaping the mixture to form at least one portion of a cathode block (10), and c) combusting the mixture at a temperature of 600 to less than 1,500 °C.
14. Method according to claim 13, characterised in that the combustion in method step c) takes place at a temperature of 600 to less than 1,500 °C, preferably of 800 to 1,200°C and particularly preferably of 900 to 1,100 °C.
15. Method according to either claim 13 or claim 14, characterised in that the combusted mixture is graphitised after method step c) at a temperature of more than 1,800 to 3,000 °C, preferably of 2,000 to 3,000 °C and particularly preferably of 2,200 to 2,700 °C.
Applications Claiming Priority (3)
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|---|---|---|---|
| DE102013202437.1 | 2013-02-14 | ||
| DE201310202437 DE102013202437A1 (en) | 2013-02-14 | 2013-02-14 | Cathode block with a wettable and abrasion resistant surface |
| PCT/EP2014/052731 WO2014124970A1 (en) | 2013-02-14 | 2014-02-12 | Cathode block having an abrasion-resistant surface that can be wetted |
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| CA2900418A1 true CA2900418A1 (en) | 2014-08-21 |
| CA2900418C CA2900418C (en) | 2018-01-02 |
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|---|---|---|---|
| CA2900418A Expired - Fee Related CA2900418C (en) | 2013-02-14 | 2014-02-12 | Cathode block having an abrasion-resistant surface that can be wetted |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP2956573A1 (en) |
| JP (1) | JP2016514204A (en) |
| CN (1) | CN105026619A (en) |
| CA (1) | CA2900418C (en) |
| DE (1) | DE102013202437A1 (en) |
| RU (1) | RU2015138609A (en) |
| UA (1) | UA115170C2 (en) |
| WO (1) | WO2014124970A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2018019888A1 (en) * | 2016-07-26 | 2018-02-01 | Sgl Cfl Ce Gmbh | Cathode current collector/connector for a hall-heroult cell |
| WO2018019910A1 (en) * | 2016-07-26 | 2018-02-01 | Sgl Cfl Ce Gmbh | Cathode assembly for the production of aluminum |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP7556048B2 (en) | 2020-04-30 | 2024-09-25 | ノルスク・ヒドロ・アーエスアー | Cathode block for aluminum electrolysis and method for manufacturing same |
Family Cites Families (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2947005C2 (en) | 1979-11-22 | 1983-08-04 | Basf Ag, 6700 Ludwigshafen | Process for the production of acetylene from hydrocarbons |
| US4333813A (en) * | 1980-03-03 | 1982-06-08 | Reynolds Metals Company | Cathodes for alumina reduction cells |
| US4376029A (en) * | 1980-09-11 | 1983-03-08 | Great Lakes Carbon Corporation | Titanium diboride-graphite composits |
| JPH05263285A (en) * | 1992-03-17 | 1993-10-12 | Nippon Light Metal Co Ltd | Electrode for electrolyzing aluminum |
| JP2002266091A (en) * | 2001-03-09 | 2002-09-18 | Sec Corp | Graphit cathode block for smelting aluminum |
| ATE486355T1 (en) * | 2007-02-15 | 2010-11-15 | Sgl Carbon Se | POROUS COKE |
| CN101158048A (en) * | 2007-08-03 | 2008-04-09 | 中国铝业股份有限公司 | Graphitized wetable cathode carbon block for aluminium electrolysis bath and production method thereof |
| JP5554117B2 (en) * | 2010-03-30 | 2014-07-23 | 日本電極株式会社 | Cathode carbon block for aluminum refining and method for producing the same |
| DE102010029538A1 (en) * | 2010-05-31 | 2011-12-01 | Sgl Carbon Se | Carbon body, process for producing a carbon body and its use |
| DE102010038665A1 (en) * | 2010-07-29 | 2012-02-02 | Sgl Carbon Se | A method of manufacturing a cathode block for an aluminum electrolytic cell and a cathode block |
| DE102010038669A1 (en) * | 2010-07-29 | 2012-02-02 | Sgl Carbon Se | Cathode block for an aluminum electrolysis cell and a method for its production |
| DE102011004013A1 (en) | 2011-02-11 | 2012-08-16 | Sgl Carbon Se | Graphitized cathode block with an abrasion resistant surface |
| DE102011004012A1 (en) * | 2011-02-11 | 2012-08-16 | Sgl Carbon Se | Surface profiled graphite cathode block with an abrasion resistant surface |
-
2013
- 2013-02-14 DE DE201310202437 patent/DE102013202437A1/en not_active Withdrawn
-
2014
- 2014-02-12 CN CN201480008980.8A patent/CN105026619A/en active Pending
- 2014-02-12 WO PCT/EP2014/052731 patent/WO2014124970A1/en active Application Filing
- 2014-02-12 UA UAA201508810A patent/UA115170C2/en unknown
- 2014-02-12 RU RU2015138609A patent/RU2015138609A/en not_active Application Discontinuation
- 2014-02-12 JP JP2015557413A patent/JP2016514204A/en not_active Ceased
- 2014-02-12 EP EP14703885.5A patent/EP2956573A1/en not_active Withdrawn
- 2014-02-12 CA CA2900418A patent/CA2900418C/en not_active Expired - Fee Related
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2018019888A1 (en) * | 2016-07-26 | 2018-02-01 | Sgl Cfl Ce Gmbh | Cathode current collector/connector for a hall-heroult cell |
| WO2018019910A1 (en) * | 2016-07-26 | 2018-02-01 | Sgl Cfl Ce Gmbh | Cathode assembly for the production of aluminum |
| RU2723867C1 (en) * | 2016-07-26 | 2020-06-17 | Токай КОБЕКС ГмбХ | Cathode current collector/connector for hall-héroult electrolyzer |
| US11242604B2 (en) | 2016-07-26 | 2022-02-08 | Cobex Gmbh | Cathode assembly for the production of aluminum |
| US11286574B2 (en) | 2016-07-26 | 2022-03-29 | Tokai Cobex Gmbh | Cathode current collector/connector for a Hall-Heroult cell |
Also Published As
| Publication number | Publication date |
|---|---|
| EP2956573A1 (en) | 2015-12-23 |
| CA2900418C (en) | 2018-01-02 |
| UA115170C2 (en) | 2017-09-25 |
| WO2014124970A1 (en) | 2014-08-21 |
| RU2015138609A (en) | 2017-03-20 |
| CN105026619A (en) | 2015-11-04 |
| DE102013202437A1 (en) | 2014-08-14 |
| JP2016514204A (en) | 2016-05-19 |
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