CA2805866C - Cathode block for an aluminium electrolysis cell and a process for the production thereof - Google Patents
Cathode block for an aluminium electrolysis cell and a process for the production thereof Download PDFInfo
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- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
- C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
- C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
- C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
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Abstract
The invention relates to a cathode block for an aluminium electrolysis cell, comprising a composite layer which contains graphite and a hard material, such as TiB2. According to the invention, the hard material is present in a monomodal particle size distribution, where d50 is between 10 and 20 µm, in particular between 12 and 18 µm, in particular between 14 and 16 µm.
Description
2 Al CATHODE BLOCK FOR AN ALUMINIUM ELECTROLYSIS CELL AND A
PROCESS FOR THE PRODUCTION THEREOF
The present invention relates to a cathode block for an aluminium electrolysis cell and a process for the production thereof.
A known process for producing metallic aluminium is the Hall-Heroult process. In this electrolytic process, the base of the electrolysis cell is typically formed by a cathode surface comprising individual cathode blocks.
The cathodes are contacted from beneath via steel bars, which are introduced into corresponding elongated recesses in the underside of the cathode blocks.
The production of cathode blocks conventionally takes place by mixing coke with carbon-containing particles, such as anthracite, carbon or graphite, compacting and carbonising. If need be, this is followed by a graphitising step at higher temperatures, at which the carbon-containing particles and the coke are converted at least partially into graphite.
Graphitised carbon and graphite are however poorly wetted or are not wetted at all by liquid aluminium.
The power requirement and therefore also the energy requirement of an electrolysis cell are thus increased.
In order to solve this problem, TiB2 is introduced into an upper layer of a cathode block in the prior art.
This is described for example in DE 112006004078. Such an upper layer, which represents a TiB2-graphite composite, is in direct contact with the aluminium melt and is therefore crucial for the current coupling from the cathode into the aluminium melt. TiB2 and similar hard materials effect an improvement in the wettability of the cathode in the graphitised state and therefore a better energy efficiency of the electrolysis process. Hard materials can moreover increase the bulk density and the hardness of cathodes, which leads to a better resistance to wear especially with respect to aluminium and cryolite melts.
TiB2 powder and similar hard material powders (also referred to as refractory hard material (RHM)) are however difficult to process. Cathode blocks produced with them, which represent a TiB2-graphite composite layer in their entirety or in their upper layer, tend moreover towards inhomogeneities.
The present invention relates to a TiB2-graphite composite cathode which is readily wettable with respect to aluminium melts, has good wear properties and is easy to produce, as well as a process for the production thereof.
In one product aspect, the invention relates to a cathode block for an aluminium electrolysis cell, comprising a composite layer which contains graphite and a hard material, wherein the hard material is present in a monomodal particle size distribution, and wherein d50 lies between 10 and 20 pm.
In one process aspect, the invention relates to a process for the production of a cathode block as defined above, comprising the steps of: providing starting materials, including coke and if appropriate a further carbon-containing material, and a hard material powder; mixing the starting materials; forming the cathode block; and carbonising and graphitising, and also cooling, wherein the hard material powder used has a monomodal particle size distribution and has a d50 between 10 and 20 pm.
- 2a -The cathode block for an aluminium electrolysis cell according to the invention, which contains a composite layer, graphite and a hard material, such as TiB2 example, is characterised in that the hard material is present in a monomodal particle size distribution, wherein the average particle size of distribution d50 lies between 10 and 20 pm, in particular between 12 and 18 pm, in particular between 14 and 16 pm.
Surprisingly, it has emerged within the scope of the invention that, with such a d50, the hard material powder on the one hand has a large active surface, which produces very good wettability of the cathode block after graphitising, but on the other hand does not have the drawbacks that have an adverse effect on
PROCESS FOR THE PRODUCTION THEREOF
The present invention relates to a cathode block for an aluminium electrolysis cell and a process for the production thereof.
A known process for producing metallic aluminium is the Hall-Heroult process. In this electrolytic process, the base of the electrolysis cell is typically formed by a cathode surface comprising individual cathode blocks.
The cathodes are contacted from beneath via steel bars, which are introduced into corresponding elongated recesses in the underside of the cathode blocks.
The production of cathode blocks conventionally takes place by mixing coke with carbon-containing particles, such as anthracite, carbon or graphite, compacting and carbonising. If need be, this is followed by a graphitising step at higher temperatures, at which the carbon-containing particles and the coke are converted at least partially into graphite.
Graphitised carbon and graphite are however poorly wetted or are not wetted at all by liquid aluminium.
The power requirement and therefore also the energy requirement of an electrolysis cell are thus increased.
In order to solve this problem, TiB2 is introduced into an upper layer of a cathode block in the prior art.
This is described for example in DE 112006004078. Such an upper layer, which represents a TiB2-graphite composite, is in direct contact with the aluminium melt and is therefore crucial for the current coupling from the cathode into the aluminium melt. TiB2 and similar hard materials effect an improvement in the wettability of the cathode in the graphitised state and therefore a better energy efficiency of the electrolysis process. Hard materials can moreover increase the bulk density and the hardness of cathodes, which leads to a better resistance to wear especially with respect to aluminium and cryolite melts.
TiB2 powder and similar hard material powders (also referred to as refractory hard material (RHM)) are however difficult to process. Cathode blocks produced with them, which represent a TiB2-graphite composite layer in their entirety or in their upper layer, tend moreover towards inhomogeneities.
The present invention relates to a TiB2-graphite composite cathode which is readily wettable with respect to aluminium melts, has good wear properties and is easy to produce, as well as a process for the production thereof.
In one product aspect, the invention relates to a cathode block for an aluminium electrolysis cell, comprising a composite layer which contains graphite and a hard material, wherein the hard material is present in a monomodal particle size distribution, and wherein d50 lies between 10 and 20 pm.
In one process aspect, the invention relates to a process for the production of a cathode block as defined above, comprising the steps of: providing starting materials, including coke and if appropriate a further carbon-containing material, and a hard material powder; mixing the starting materials; forming the cathode block; and carbonising and graphitising, and also cooling, wherein the hard material powder used has a monomodal particle size distribution and has a d50 between 10 and 20 pm.
- 2a -The cathode block for an aluminium electrolysis cell according to the invention, which contains a composite layer, graphite and a hard material, such as TiB2 example, is characterised in that the hard material is present in a monomodal particle size distribution, wherein the average particle size of distribution d50 lies between 10 and 20 pm, in particular between 12 and 18 pm, in particular between 14 and 16 pm.
Surprisingly, it has emerged within the scope of the invention that, with such a d50, the hard material powder on the one hand has a large active surface, which produces very good wettability of the cathode block after graphitising, but on the other hand does not have the drawbacks that have an adverse effect on
- 3 -the processability of the hard material powder as a composite component in a graphite-hard material composite. These possible drawbacks, which are not exhibited by the hard material powder used according to the invention, are:
- tendency towards dust formation, for example during filling into a mixing container or during transport of the powder, - agglomerate formation, in particular during mixing, such as for example wet mixing with coke (in this connection, wet mixing means in particular mixing with pitch as a liquid phase), - demixing on account of different material densities of hard material and coke.
Apart from the absence of these drawbacks, the hard material powder used according to the invention has a particularly good flowability or free flowability. This makes the hard material powder particularly easy to convey with conventional conveying devices, for example to a mixing apparatus.
The production of hard material powder composites for cathode blocks is greatly simplified by the good processability of the hard material powder with the d50 between 10 and 20 pm and a monomodal particle size distribution. The obtained cathode blocks have a very good homogeneity with respect to the distribution of the hard material powder in the coke in the green body and in the graphite in the graphitised cathode body.
The d90 of the refractory hard material preferably lies between 20 and 40 pm, in particular between 25 and 30 pm. The effect of this, advantageously, is that wetting
- tendency towards dust formation, for example during filling into a mixing container or during transport of the powder, - agglomerate formation, in particular during mixing, such as for example wet mixing with coke (in this connection, wet mixing means in particular mixing with pitch as a liquid phase), - demixing on account of different material densities of hard material and coke.
Apart from the absence of these drawbacks, the hard material powder used according to the invention has a particularly good flowability or free flowability. This makes the hard material powder particularly easy to convey with conventional conveying devices, for example to a mixing apparatus.
The production of hard material powder composites for cathode blocks is greatly simplified by the good processability of the hard material powder with the d50 between 10 and 20 pm and a monomodal particle size distribution. The obtained cathode blocks have a very good homogeneity with respect to the distribution of the hard material powder in the coke in the green body and in the graphite in the graphitised cathode body.
The d90 of the refractory hard material preferably lies between 20 and 40 pm, in particular between 25 and 30 pm. The effect of this, advantageously, is that wetting
4 and processing properties of the hard material powder are still better.
The (110 of the refractory hard material advantageously lies between 2 and 7 pm, in particular between 3 and 5 pm. The effect of this, advantageously, is that wetting and processing properties of the hard material powder are still better.
Moreover, to characterise the monomodal particle size distribution, its distribution breadth can be described by the so-called span value, which is calculated as follows:
Span = (d90- d10)/d50 The span of the refractory hard material powder advantageously lies between 0.65 and 3.80, in particular between 1.00 and 2.25. The effect of this, advantageously, is that wetting and processing properties of the hard material powder are still better.
Provision can advantageously be made such that the composite layer forms the whole cathode block. This has the advantage that a single green material composition and correspondingly only a single mixing step are required to produce the cathode block.
Alternatively, it may be advantageous for the cathode block to comprise at least two layers, wherein the composite layer forms the upper layer of the cathode block. This upper layer is in direct contact with the melt of the electrolysis cell during the use of the cathode block according to the invention.
The cathode block preferably comprises at least one further layer, which comprises less hard material ..
The (110 of the refractory hard material advantageously lies between 2 and 7 pm, in particular between 3 and 5 pm. The effect of this, advantageously, is that wetting and processing properties of the hard material powder are still better.
Moreover, to characterise the monomodal particle size distribution, its distribution breadth can be described by the so-called span value, which is calculated as follows:
Span = (d90- d10)/d50 The span of the refractory hard material powder advantageously lies between 0.65 and 3.80, in particular between 1.00 and 2.25. The effect of this, advantageously, is that wetting and processing properties of the hard material powder are still better.
Provision can advantageously be made such that the composite layer forms the whole cathode block. This has the advantage that a single green material composition and correspondingly only a single mixing step are required to produce the cathode block.
Alternatively, it may be advantageous for the cathode block to comprise at least two layers, wherein the composite layer forms the upper layer of the cathode block. This upper layer is in direct contact with the melt of the electrolysis cell during the use of the cathode block according to the invention.
The cathode block preferably comprises at least one further layer, which comprises less hard material ..
- 5 -powder than the upper layer or comprises no hard material powder. This can reduce the quantity of cost-intensive hard material powder used. During the use of the cathode in an aluminium electrolysis cell, the further layer is not in direct contact with the aluminium melt and does not therefore have to have good wettability and wear resistance.
The upper layer can advantageously have a height amounting to 10 to 50%, in particular 15 to 45%, of the total height of the cathode block. A small height of the upper layer, such as for example 20%, may be advantageous, since a small quantity of cost-intensive hard material is required.
Alternatively, a large height of the upper layer, such as for example 40%, may be advantageous, since a layer comprising hard material has a high resistance to wear.
The greater the height of this highly wear-resistant material in relation to the total height of the cathode block, the greater the resistance to wear of the overall cathode block.
The cathode block according to the invention is preferably produced with a process comprising the steps of providing starting materials, including coke, a hard material, such as Ti32 for example, and if appropriate a further carbon-containing material, forming the cathode block, carbonising and graphitising, and also cooling. According to the invention, the coke comprises two types of coke which, during the carbonising and/or graphitising and/or cooling, have a different volume-change behaviour.
In the graphitising step, at least a fraction of carbon in the cathode block is converted into graphite.
CA 02805866 2013-01-17 .
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The upper layer can advantageously have a height amounting to 10 to 50%, in particular 15 to 45%, of the total height of the cathode block. A small height of the upper layer, such as for example 20%, may be advantageous, since a small quantity of cost-intensive hard material is required.
Alternatively, a large height of the upper layer, such as for example 40%, may be advantageous, since a layer comprising hard material has a high resistance to wear.
The greater the height of this highly wear-resistant material in relation to the total height of the cathode block, the greater the resistance to wear of the overall cathode block.
The cathode block according to the invention is preferably produced with a process comprising the steps of providing starting materials, including coke, a hard material, such as Ti32 for example, and if appropriate a further carbon-containing material, forming the cathode block, carbonising and graphitising, and also cooling. According to the invention, the coke comprises two types of coke which, during the carbonising and/or graphitising and/or cooling, have a different volume-change behaviour.
In the graphitising step, at least a fraction of carbon in the cathode block is converted into graphite.
CA 02805866 2013-01-17 .
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- 6 -Surprisingly, it has been shown that the useful life of the cathode blocks produced with such process is much longer than in the case of the cathode blocks produced with conventional processes.
A cathode block produced with a process according to the invention preferably has a bulk density of a carbon fraction of over 1.68 g/cm3, particularly preferably of over 1.71 g/cm3, in particular of up to 1.75 g/cm3.
A higher bulk density presumably contributes advantageously to a longer useful life. This may on the one hand be based on the fact that more mass is present per unit volume of a cathode block, which, with a given mass abrasion per unit of time, leads to a higher residual mass after a given abrasion period. On the other hand, it can be assumed that a higher bulk density with a corresponding lower porosity prevents an infiltration of electrolyte, which acts as a corrosive medium.
On account of the addition of REIN after graphitising, the second layer can have a bulk density of for example over 1.80 g/cm3.
The two types of coke advantageously include a first type of coke and a second type of coke, wherein the first type of coke exhibits a greater shrinkage and/or expansion than the second type of coke during the carbonising and/or graphitising and/or cooling. In this connection the greater shrinkage and/or expansion is an advantageous development of a different volume-change behaviour, which presumably is particularly well suited for leading to a greater compaction than when types of coke are mixed that possess an identical shrinkage and/or expansion. Thereby, the greater shrinkage and/or expansion relates to an arbitrary temperature range.
A cathode block produced with a process according to the invention preferably has a bulk density of a carbon fraction of over 1.68 g/cm3, particularly preferably of over 1.71 g/cm3, in particular of up to 1.75 g/cm3.
A higher bulk density presumably contributes advantageously to a longer useful life. This may on the one hand be based on the fact that more mass is present per unit volume of a cathode block, which, with a given mass abrasion per unit of time, leads to a higher residual mass after a given abrasion period. On the other hand, it can be assumed that a higher bulk density with a corresponding lower porosity prevents an infiltration of electrolyte, which acts as a corrosive medium.
On account of the addition of REIN after graphitising, the second layer can have a bulk density of for example over 1.80 g/cm3.
The two types of coke advantageously include a first type of coke and a second type of coke, wherein the first type of coke exhibits a greater shrinkage and/or expansion than the second type of coke during the carbonising and/or graphitising and/or cooling. In this connection the greater shrinkage and/or expansion is an advantageous development of a different volume-change behaviour, which presumably is particularly well suited for leading to a greater compaction than when types of coke are mixed that possess an identical shrinkage and/or expansion. Thereby, the greater shrinkage and/or expansion relates to an arbitrary temperature range.
- 7 -Thus, for example, only a greater shrinkage of the first coke may be present during carbonising. On the other hand, for example, a greater expansion may be present, additionally or instead, in a transition zone between carbonising and graphitising. Instead or in addition, a different volume-change behaviour may be present during cooling.
The shrinkage and/or expansion of the first type of coke during the carbonising and/or graphitising and/or cooling related to the volume is preferably at least 10% higher than that of the second type of coke, in particular at least 25% higher, in particular at least 50% higher. Thus, for example, in the case of a 10%
higher shrinkage of the first type of coke, the shrinkage from room temperature to 2000 C in the case of the second type of coke is 1.0% by volume, but in the case of the first type of coke 1.1% by volume.
The shrinkage and/or the expansion of the first type of coke during the carbonising and/or graphitising and/or cooling related to the volume is advantageously at least 100% higher than that of the second type of coke, in particular at least 200% higher, in particular at least 300% higher. Thus, for example, in the case of a 300% higher expansion of the first type of coke, the expansion from room temperature to 1000 C in the case of the second type of coke is 1.0% by volume, whereas in the case of the first type of coke it is 4.0% by volume.
The case where the first type of coke experiences a shrinkage, but the second type of coke experiences an expansion in the same temperature range, is also covered by the process according to the invention. A
300% higher shrinkage and/or expansion thus also includes, for example, the case where the second type
The shrinkage and/or expansion of the first type of coke during the carbonising and/or graphitising and/or cooling related to the volume is preferably at least 10% higher than that of the second type of coke, in particular at least 25% higher, in particular at least 50% higher. Thus, for example, in the case of a 10%
higher shrinkage of the first type of coke, the shrinkage from room temperature to 2000 C in the case of the second type of coke is 1.0% by volume, but in the case of the first type of coke 1.1% by volume.
The shrinkage and/or the expansion of the first type of coke during the carbonising and/or graphitising and/or cooling related to the volume is advantageously at least 100% higher than that of the second type of coke, in particular at least 200% higher, in particular at least 300% higher. Thus, for example, in the case of a 300% higher expansion of the first type of coke, the expansion from room temperature to 1000 C in the case of the second type of coke is 1.0% by volume, whereas in the case of the first type of coke it is 4.0% by volume.
The case where the first type of coke experiences a shrinkage, but the second type of coke experiences an expansion in the same temperature range, is also covered by the process according to the invention. A
300% higher shrinkage and/or expansion thus also includes, for example, the case where the second type
- 8 -of coke shrinks by 1.0% by volume, whereas the first type of coke expands by 2.0% by volume.
Alternatively, instead of the first type of coke, the second type of coke can exhibit a greater shrinkage and/or expansion in at least one arbitrary temperature range of the process according to the invention, as described above for the first type of coke.
The cathode block according to the invention is preferably produced with a process comprising the steps of providing starting materials, including coke, forming the cathode block, carbonising and graphitising, and also cooling. Thereby, the coke preferably comprises two types of coke which, with a different volume-change behaviour during the carbonising and/or graphitising and/or cooling, lead to a compaction of the cathode block of over 1.68 g/cm3.
Different volume-change behaviours of the two types of coke presumably lead to a situation where, in a compaction process during the carbonising and/or graphitising and/or cooling, jamming or other kind of blocking of individual coke particles with one another due to similar shrinkage properties can be prevented.
Presumably, individual particles are thus able to migrate to more favourable positions for a compaction and so a higher packing density of the coke particles or of the particles arising therefrom in the further process is achieved than in the case of conventional production processes.
With this variant, the advantages of a multi-layer block, in which the layer facing the anode contains a hard material, are combined with the use of two types of coke with different volume-change behaviour. The small differences in the thermal expansion behaviour during the heat treatment steps reduce production times
Alternatively, instead of the first type of coke, the second type of coke can exhibit a greater shrinkage and/or expansion in at least one arbitrary temperature range of the process according to the invention, as described above for the first type of coke.
The cathode block according to the invention is preferably produced with a process comprising the steps of providing starting materials, including coke, forming the cathode block, carbonising and graphitising, and also cooling. Thereby, the coke preferably comprises two types of coke which, with a different volume-change behaviour during the carbonising and/or graphitising and/or cooling, lead to a compaction of the cathode block of over 1.68 g/cm3.
Different volume-change behaviours of the two types of coke presumably lead to a situation where, in a compaction process during the carbonising and/or graphitising and/or cooling, jamming or other kind of blocking of individual coke particles with one another due to similar shrinkage properties can be prevented.
Presumably, individual particles are thus able to migrate to more favourable positions for a compaction and so a higher packing density of the coke particles or of the particles arising therefrom in the further process is achieved than in the case of conventional production processes.
With this variant, the advantages of a multi-layer block, in which the layer facing the anode contains a hard material, are combined with the use of two types of coke with different volume-change behaviour. The small differences in the thermal expansion behaviour during the heat treatment steps reduce production times
- 9 -and reject rates of the cathode blocks. Furthermore, the resistance to thermal stresses and to resultant damage in use is therefore advantageously also increased.
At least one of the two types of coke is preferably a petroleum coke or coal-tar-pitch coke.
The quantity fraction in percentage by weight of the second type of coke in the total quantity of coke preferably amounts to between 50% and 90%. In these quantity ranges, the different volume-change behaviour of the first and second type of coke has a particularly good effect on a compaction during the carbonising and/or graphitising and/or cooling. Conceivable quantity ranges of the second type of coke can be 50 to 60%, but also 60 to 80%, as well as 80 to 90%.
At least one carbon-containing material and/or pitch and/or additives are advantageously added to the coke.
This can be advantageous both with regard to the processability of the coke as well as the subsequent properties of the produced cathode block.
The further carbon-containing material preferably contains graphite-containing material; in particular, the further carbon-containing material comprises graphite-containing material, such as for example graphite. The graphite can be synthetic and/or natural graphite. The effect of such a further carbon-containing material is that the necessary shrinkage of the cathode material, which is dominated by the coke, is reduced.
The carbon-containing material related to the total quantity of coke and carbon-containing material is
At least one of the two types of coke is preferably a petroleum coke or coal-tar-pitch coke.
The quantity fraction in percentage by weight of the second type of coke in the total quantity of coke preferably amounts to between 50% and 90%. In these quantity ranges, the different volume-change behaviour of the first and second type of coke has a particularly good effect on a compaction during the carbonising and/or graphitising and/or cooling. Conceivable quantity ranges of the second type of coke can be 50 to 60%, but also 60 to 80%, as well as 80 to 90%.
At least one carbon-containing material and/or pitch and/or additives are advantageously added to the coke.
This can be advantageous both with regard to the processability of the coke as well as the subsequent properties of the produced cathode block.
The further carbon-containing material preferably contains graphite-containing material; in particular, the further carbon-containing material comprises graphite-containing material, such as for example graphite. The graphite can be synthetic and/or natural graphite. The effect of such a further carbon-containing material is that the necessary shrinkage of the cathode material, which is dominated by the coke, is reduced.
The carbon-containing material related to the total quantity of coke and carbon-containing material is
- 10 -advantageously present at 1 to 40% by weight, in particular at 5 to 30% by weight.
In addition to the quantity of coke and, as appropriate, carbon-containing material, said quantity representing a total of 100% by weight, pitch in quantities of 5 to 40% by weight, in particular 15 to 30% by weight (related to 100% by weight of the total green mixture), can preferably be added. Pitch acts as a binder and serves to produce a dimensionally stable body during the carbonising.
Advantageous additives can be oil, such as auxiliary pressure oil, or stearic acid. These facilitate mixing of the coke and, if appropriate, the further components.
The coke in at least one of the two layers, i.e. in the first and/or the second layer, preferably comprises two types of coke which, with a different volume-change behaviour during the carbonising and/or graphitising and/or cooling, lead to a compaction of the emerging graphite of over 1.68 g/cm3. Depending on what is desired and/or required, both layers or one of the two layers can therefore be produced, according to the invention, with two different types of coke. The possibility thus arises of adjusting bulk densities and bulk density ratios, as required or desired. According to the invention, solely the first layer can for example be produced with two types of coke, whilst the second layer is produced with only one type of coke, but additionally contains TiB2 as a hard material. The bulk densities and/or expansion behaviours of the two layers are thus made similar, which can advantageously increase the resistance of the layer bond.
In addition to the quantity of coke and, as appropriate, carbon-containing material, said quantity representing a total of 100% by weight, pitch in quantities of 5 to 40% by weight, in particular 15 to 30% by weight (related to 100% by weight of the total green mixture), can preferably be added. Pitch acts as a binder and serves to produce a dimensionally stable body during the carbonising.
Advantageous additives can be oil, such as auxiliary pressure oil, or stearic acid. These facilitate mixing of the coke and, if appropriate, the further components.
The coke in at least one of the two layers, i.e. in the first and/or the second layer, preferably comprises two types of coke which, with a different volume-change behaviour during the carbonising and/or graphitising and/or cooling, lead to a compaction of the emerging graphite of over 1.68 g/cm3. Depending on what is desired and/or required, both layers or one of the two layers can therefore be produced, according to the invention, with two different types of coke. The possibility thus arises of adjusting bulk densities and bulk density ratios, as required or desired. According to the invention, solely the first layer can for example be produced with two types of coke, whilst the second layer is produced with only one type of coke, but additionally contains TiB2 as a hard material. The bulk densities and/or expansion behaviours of the two layers are thus made similar, which can advantageously increase the resistance of the layer bond.
- 11 -Further advantageous embodiments and developments of the invention are explained below with the aid of a preferred example of embodiment and the figure.
Single figure 1 shows a grain size distribution of a TiB2 powder used according to the invention: a) as a volume density distribution q3 and b) as a cumulative volume distribution Q3.
For the production of a cathode block according to the invention, coke is mixed with pitch, mixed with TiB2 powder with a monomodal particle size distribution and a d50 of 15 pm, a d90 of 30 pm and a dlo of 5 pm. The span value for this particle size distribution amounts to 1.67. The proportion by weight of TiB2 powder in the green material amounts for example to 10 to 30% by weight, such as for example 20% by weight. The mixture is filled into a mould, which largely corresponds to the subsequent shape of the cathode blocks, and is compacted by vibration or block-pressed. The emerging green body is heated up to a final temperature in a range from 2300 to 3000 C, in particular 2500 to 2900 C, such as 2800 C for example, a carbonising step and then a graphitising step taking place, and is subsequently cooled. The emerging cathode block has a very good wettability behaviour and a very high wear resistance to liquid aluminium and cryolite.
Alternatively, two types of coke with different volume-change behaviour are used instead of a single type of coke. This different volume-change behaviour of the two cokes leads to a high bulk density of the graphite in the composite and therefore to a still higher wear resistance of the obtained cathode blocks than with the TiB2 powder alone.
Single figure 1 shows a grain size distribution of a TiB2 powder used according to the invention: a) as a volume density distribution q3 and b) as a cumulative volume distribution Q3.
For the production of a cathode block according to the invention, coke is mixed with pitch, mixed with TiB2 powder with a monomodal particle size distribution and a d50 of 15 pm, a d90 of 30 pm and a dlo of 5 pm. The span value for this particle size distribution amounts to 1.67. The proportion by weight of TiB2 powder in the green material amounts for example to 10 to 30% by weight, such as for example 20% by weight. The mixture is filled into a mould, which largely corresponds to the subsequent shape of the cathode blocks, and is compacted by vibration or block-pressed. The emerging green body is heated up to a final temperature in a range from 2300 to 3000 C, in particular 2500 to 2900 C, such as 2800 C for example, a carbonising step and then a graphitising step taking place, and is subsequently cooled. The emerging cathode block has a very good wettability behaviour and a very high wear resistance to liquid aluminium and cryolite.
Alternatively, two types of coke with different volume-change behaviour are used instead of a single type of coke. This different volume-change behaviour of the two cokes leads to a high bulk density of the graphite in the composite and therefore to a still higher wear resistance of the obtained cathode blocks than with the TiB2 powder alone.
- 12 -In a further variant, the mould is first partially filled with a mixture comprising coke, graphite and TiB2 and, if appropriate, compacted by vibration. A
mixture of coke and graphite is then filled onto the resultant initial layer, which in the subsequent cathode represents the upper layer which is facing the anode and will thus have direct contact with the aluminium melt, and is again compacted. The resultant upper initial layer represents, in the subsequent cathode, the lower layer which is facing away from the anode. This two-layer block is carbonised and graphitised as in the case of the first example of embodiment.
In a further alternative, two types of coke with different volume-change behaviour are used as coke of the lower layer. The wear resistance of the cathode block thus obtained with respect to aluminium is particularly high. This is due to the smaller bulk density difference between the upper and lower cathode layer than in the case of conventional TiB2 composite blocks.
All the features mentioned in the description, the examples and claims can contribute to the invention in any combination. The invention is not however limited to the stated examples, but can also be performed in modifications that are not specifically described here.
In particular, other hard material powders apart from T1B2 are also covered, such as for example ZrB2, HfB2 or other transition metal borides.
mixture of coke and graphite is then filled onto the resultant initial layer, which in the subsequent cathode represents the upper layer which is facing the anode and will thus have direct contact with the aluminium melt, and is again compacted. The resultant upper initial layer represents, in the subsequent cathode, the lower layer which is facing away from the anode. This two-layer block is carbonised and graphitised as in the case of the first example of embodiment.
In a further alternative, two types of coke with different volume-change behaviour are used as coke of the lower layer. The wear resistance of the cathode block thus obtained with respect to aluminium is particularly high. This is due to the smaller bulk density difference between the upper and lower cathode layer than in the case of conventional TiB2 composite blocks.
All the features mentioned in the description, the examples and claims can contribute to the invention in any combination. The invention is not however limited to the stated examples, but can also be performed in modifications that are not specifically described here.
In particular, other hard material powders apart from T1B2 are also covered, such as for example ZrB2, HfB2 or other transition metal borides.
Claims (29)
1. A cathode block for an aluminium electrolysis cell, comprising a composite layer which contains graphite and a hard material, wherein the hard material is present in a monomodal particle size distribution, and wherein d50 lies between 10 and 20 µm.
2. The cathode block according to claim 1, wherein the hard material is TiB2.
3. The cathode block according to claim 1 or 2, wherein the d50 lies between 12 and 18 µm.
4. The cathode block according to claim 3, wherein the d50 lies between 14 and 16 µm.
5. The cathode block according to any one of claims 1 to 4, wherein d90 of the hard material lies between 20 and 40 µm.
6. The cathode block according to claim 5, wherein the d90 lies between 25 and 30 µm.
7. The cathode block according to any one of claims 1 to 6, wherein d10 of the hard material lies between 2 and 7 µm.
8. The cathode block according to claim 7, wherein the d10 lies between 3 and 5 µm.
9. The cathode block according to any one of claims 1 to 8, wherein the span = (d90 - d10)/d50 of the particle size distribution of the hard material powder lies between 0.65 and 3.80.
10. The cathode block according to claim 4, wherein the span lies between 1.00 and 2.25.
11. The cathode block according to any one of claims 1 to 10, wherein the composite layer forms the whole cathode block.
12. The cathode block according to any one of claims 1 to 10, wherein the cathode block comprises at least two layers, and wherein the composite layer forms the upper layer of the cathode block.
13. The cathode block according to claim 12, wherein the cathode block comprises at least one further layer, which comprises less hard material powder than the upper layer or no hard material powder.
14. The cathode block according to claim 12 or 13, wherein the upper layer has a thickness which amounts to 10 to 50% of the total thickness of the cathode block.
15. The cathode block according to claim 14, wherein the thickness amounts to 15 to 45%.
16. The cathode block according to any one of claims 1 to 15, wherein the bulk density in at least one layer of the cathode block related to the carbon fraction is greater than 1.68 g/cm3.
17. The cathode block according to claim 16, wherein the bulk density is greater than 1.71 g/cm3.
18. A process for the production of a cathode block according to any one of claims 1 to 17, comprising the steps of: providing starting materials, including coke and if appropriate a further carbon-containing material, and a hard material powder; mixing the starting materials; forming the cathode block; and carbonising and graphitising, and also cooling, wherein the hard material powder used has a monomodal particle size distribution and has a d50 between 10 and 20 µm.
19. The process according to claim 18, wherein the d50 is between 12 and 18 µm.
20. The process according to claim 19, wherein the d50 is between 14 and 16 µm.
21. The process according to any one of claims 18 to 20, wherein the hard material powder has a d90 between 20 and 40 µm.
22. The process according to claim 21, wherein the d90 is between 25 and 30 µm.
23. The process according to any one of claims 18 to 22, wherein the hard material powder has a d10 between 2 and 7 µm.
24. The process according to claim 23, wherein the d10 is between 3 and 5 µm.
25. The process according to any one of claims 18 to 24, wherein the particle size distribution of the hard material powder has a span = (d90 - d10)/d50 between 0.65 and 3.80.
26. The process according to claim 25, wherein the span is between 1.00 and 2.25.
27. The process according to any one of claims 18 to 26, wherein the coke used comprises two types of coke, which have a different volume-change behaviour during the carbonising and/or graphitising and/or cooling.
28. The process according to claim 27, wherein a cathode block with a bulk density of a carbon fraction of over 1.68 g/cm3 is obtained.
29. The process according to claim 28, wherein the bulk density is over 1.71 g/cm3.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE201010038669 DE102010038669A1 (en) | 2010-07-29 | 2010-07-29 | Cathode block for an aluminum electrolysis cell and a method for its production |
| DE102010038669.3 | 2010-07-29 | ||
| PCT/EP2011/063082 WO2012013772A1 (en) | 2010-07-29 | 2011-07-29 | Cathode block for an aluminium electrolysis cell and a process for the production thereof |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2805866A1 CA2805866A1 (en) | 2012-02-02 |
| CA2805866C true CA2805866C (en) | 2015-07-21 |
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| CA2805866A Active CA2805866C (en) | 2010-07-29 | 2011-07-29 | Cathode block for an aluminium electrolysis cell and a process for the production thereof |
Country Status (8)
| Country | Link |
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| EP (1) | EP2598675B1 (en) |
| JP (1) | JP5714108B2 (en) |
| CN (1) | CN103038396B (en) |
| CA (1) | CA2805866C (en) |
| DE (1) | DE102010038669A1 (en) |
| RU (1) | RU2533066C2 (en) |
| UA (1) | UA109019C2 (en) |
| WO (1) | WO2012013772A1 (en) |
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|---|---|---|---|---|
| DE102011004014A1 (en) * | 2011-02-11 | 2012-08-16 | Sgl Carbon Se | Cathode block with a covering layer containing hard material |
| DE102011004013A1 (en) * | 2011-02-11 | 2012-08-16 | Sgl Carbon Se | Graphitized cathode block with an abrasion resistant surface |
| DE102012201468A1 (en) * | 2012-02-01 | 2013-08-01 | Sgl Carbon Se | A method of making a cathode block for an aluminum electrolytic cell and a cathode block |
| DE102013202437A1 (en) * | 2013-02-14 | 2014-08-14 | Sgl Carbon Se | Cathode block with a wettable and abrasion resistant surface |
| CN107429414A (en) * | 2015-04-23 | 2017-12-01 | 俄铝工程技术中心有限责任公司 | Electrode of aluminum electrolysis cell (variant) |
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| NL129768C (en) * | 1965-01-06 | |||
| JPS5849483B2 (en) * | 1976-04-02 | 1983-11-04 | 東洋カ−ボン株式会社 | Cathode carbon block manufacturing method for aluminum electrolyzer |
| US4308114A (en) * | 1980-07-21 | 1981-12-29 | Aluminum Company Of America | Electrolytic production of aluminum using a composite cathode |
| US4308115A (en) * | 1980-08-15 | 1981-12-29 | Aluminum Company Of America | Method of producing aluminum using graphite cathode coated with refractory hard metal |
| US4376029A (en) * | 1980-09-11 | 1983-03-08 | Great Lakes Carbon Corporation | Titanium diboride-graphite composits |
| US4526669A (en) * | 1982-06-03 | 1985-07-02 | Great Lakes Carbon Corporation | Cathodic component for aluminum reduction cell |
| JPS59500974A (en) * | 1982-06-03 | 1984-05-31 | グレ−ト レ−クス カ−ボン コ−ポレ−シヨン | Cathode element of aluminum reduction electrolyzer |
| US4582553A (en) * | 1984-02-03 | 1986-04-15 | Commonwealth Aluminum Corporation | Process for manufacture of refractory hard metal containing plates for aluminum cell cathodes |
| JPH05263285A (en) * | 1992-03-17 | 1993-10-12 | Nippon Light Metal Co Ltd | Electrode for electrolyzing aluminum |
| WO1994013861A1 (en) * | 1992-12-17 | 1994-06-23 | Comalco Aluminium Limited | Electrolysis cell for metal production |
| JP3977472B2 (en) * | 1997-01-23 | 2007-09-19 | 新日本テクノカーボン株式会社 | Method for producing high density isotropic graphite material having low thermal expansion coefficient |
| DE19714433C2 (en) * | 1997-04-08 | 2002-08-01 | Celanese Ventures Gmbh | Process for producing a coating with a titanium boride content of at least 80% by weight |
| RU2232211C2 (en) * | 1998-11-17 | 2004-07-10 | Алкан Интернешнел Лимитед | Carbon composite materials capable of wetting, erosion \ oxidation resistant |
| US7462271B2 (en) * | 2003-11-26 | 2008-12-09 | Alcan International Limited | Stabilizers for titanium diboride-containing cathode structures |
| US20050253118A1 (en) * | 2004-05-17 | 2005-11-17 | Sgl Carbon Ag | Fracture resistant electrodes for a carbothermic reduction furnace |
| CN100491600C (en) | 2006-10-18 | 2009-05-27 | 中国铝业股份有限公司 | Method for preparing carbon block of cathode capable of being humidified |
| WO2008078679A1 (en) * | 2006-12-22 | 2008-07-03 | Toyo Tanso Co., Ltd. | Graphite material and method for manufacturing the same |
| 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 |
| RU2371523C1 (en) * | 2008-06-23 | 2009-10-27 | Федеральное государственное образовательное учреждение высшего профессионального образования "Сибирский федеральный университет" | Composite material for moistened cathode of aluminium electrolytic cell |
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2010
- 2010-07-29 DE DE201010038669 patent/DE102010038669A1/en not_active Ceased
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- 2011-07-29 WO PCT/EP2011/063082 patent/WO2012013772A1/en active Application Filing
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| CA2805866A1 (en) | 2012-02-02 |
| CN103038396B (en) | 2016-08-03 |
| UA109019C2 (en) | 2015-07-10 |
| DE102010038669A1 (en) | 2012-02-02 |
| RU2013108797A (en) | 2014-09-10 |
| CN103038396A (en) | 2013-04-10 |
| WO2012013772A1 (en) | 2012-02-02 |
| RU2533066C2 (en) | 2014-11-20 |
| EP2598675B1 (en) | 2017-03-08 |
| JP5714108B2 (en) | 2015-05-07 |
| EP2598675A1 (en) | 2013-06-05 |
| JP2013532773A (en) | 2013-08-19 |
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