WO2013068412A2

WO2013068412A2 - Cathode block having a domed and/or rounded surface

Info

Publication number: WO2013068412A2
Application number: PCT/EP2012/072046
Authority: WO
Inventors: Thomas Frommelt; Arash RASHIDI
Original assignee: Sgl Carbon Se
Priority date: 2011-11-09
Filing date: 2012-11-07
Publication date: 2013-05-16
Also published as: IN2014CN03395A; JP2014532816A; WO2013068412A3; CN103958740A; EP2776608A2; CA2854928A1; DE102011086044A1

Abstract

The invention relates to a cathode block for an aluminum electrolytic cell, in particular based on carbon and/or graphite, having at least one groove for accommodating a bus bar, said groove being arranged on one of the sides of the cathode block and extending in the longitudinal direction of the cathode block, wherein at least one section of the surface of the side of the cathode block opposite the side having the at least one groove is curved outwardly in the shape of an arch as viewed in the cross-section of the cathode block, wherein the vertex of the at least one section curved outwardly in the shape of an arch is arranged over the at least one groove, with respect to the direction extending perpendicularly to the side having the at least one groove in the cross-section of the cathode block. The invention further relates to a cathode block for an aluminum electrolytic cell, in particular based on carbon and/or graphite, which cathode block has a tub-shaped surface as viewed in the longitudinal section of the cathode block, wherein the tub has two edge regions and a bottom region, which is arranged between the edge regions and lowered relative to the edge regions as viewed in the longitudinal direction of the cathode, wherein a respective side wall region is provided between each edge region and the bottom region, which side wall region connects the respective edge region and the bottom region, wherein at least one of the two connecting regions between the edge regions and the side wall regions and/or at least one of the two connecting regions between the bottom region and the side wall regions is curved in the shape of an arch, wherein the at least one section curved in the shape of an arch has a length of more than 2 cm.

Description

Cathode block with curved and / or rounded surface

The present invention relates to a cathode block which is particularly suitable for use in an electrolytic cell for the production of aluminum.

Electrolysis cells are used, for example, for the electrolytic production of aluminum, which is usually carried out industrially by the Hall-Heroult process. In the Hall-Heroult process, a melt composed of aluminum oxide and cryolite is electrolyzed. It serves the

Cryolite, Na3 [AIF ₆ ], to lower the melting point from 2,045 ° C for pure alumina to about 950 ° C for a cryolite, alumina and additives such as aluminum fluoride and calcium fluoride containing mixture. The electrolytic cell used in this method has a cathode bottom, which may be composed of a plurality of adjacent, forming the cathode cathode blocks. In order to withstand the thermal and chemical conditions prevailing in the operation of the cell, the cathode is usually composed of a carbonaceous material. On the lower sides of the cathode, grooves are usually provided, in each of which at least one bus bar is arranged, through which the current supplied via the anodes is removed. About 3 to 5 cm above the located on the cathode top, usually 15 to 50 cm high, layer of liquid aluminum is formed, in particular of individual anode blocks formed anode, between the and the surface of the aluminum, the electrolyte, ie the Alumina and cryolite-containing melt is located. During the electrolysis carried out at about 1000 ° C., the aluminum formed is deposited below the electrolyte layer due to its greater density compared to that of the electrolyte, ie as an intermediate layer between the upper side of the cathode and the electrolyte layer. In the Electrolysis, the dissolved in the melt aluminum oxide is split by electric current flow to aluminum and oxygen. From an electrochemical point of view, the layer of liquid aluminum is the actual cathode because aluminum ions are reduced to elemental aluminum on its surface. Nevertheless, the term cathode will not be understood below to mean the cathode from an electrochemical point of view, ie the layer of liquid aluminum, but rather the component forming the base of the electrolytic cell, for example composed of one or more cathode blocks.

A major disadvantage of the Hall-Heroult process is that it is very energy intensive. To produce 1 kg of aluminum about 12 to 15 kWh of electrical energy is needed, which accounts for up to 40% of the manufacturing cost. In order to be able to reduce the production costs, it is therefore desirable to reduce the specific energy consumption in this process as much as possible.

Due to the relatively high electrical resistance of the melt, in particular in comparison with the layer of liquid aluminum and the cathode material, relatively high ohmic losses in the form of Joule dissipation occur, especially in the melt. In view of the relatively high melt specific losses, there is a desire to reduce as much as possible the thickness of the melt layer and thus the distance between the anode and the layer of liquid aluminum. However, owing to the electromagnetic interactions present in the electrolysis and the resulting formation of waves in the layer of liquid aluminum, if the thickness of the melt layer is too low, there is a risk that the layer of liquid aluminum will come into contact with the anode, resulting in short-circuiting of the layer Electrolysis cell and undesirable reoxidation of the aluminum formed and the electrical instability of the electrolysis plant, and in particular a fluctuation of the cell voltage can result. Occurring shorts also lead to increased wear and thus to a reduced service life of the electrolysis cell. For these reasons, the distance between the anode and the layer of liquid aluminum can not be arbitrarily reduced.

The driving force for the formation of waves in the layer of liquid aluminum is the inhomogeneous distribution of the electric current density and the magnetic flux density over the surface of the cathode, which leads to a corrugating distribution of the Lorentz force density in the layer of liquid aluminum. In this case, the Lorentz force density is defined as the vector product of the electrical current density present at a specific location and the magnetic flux density present at this location. The reason for the inhomogeneous distribution of the electric current density and the magnetic flux density at the top of the cathode, in turn, is that the current in the

Cathode and in the aluminum bath preferably follows the path of least electrical resistance. For this reason, the electric current flowing through the cathode typically concentrates primarily on the lateral edge regions of the cathode, at which the connection of the cathode with the busbars contacting the latter takes place, since the resulting electrical resistance in the flow of current across the edge regions to the surface of the Cathode is lower than the current flow through the center of the cathode to the surface of the cathode, in which a longer path or electrical path must be covered as in the flow of current over the edge regions to the surface of the cathode.

In addition to increased wave formation in the layer of liquid aluminum, the inhomogeneous current density distribution, and in particular the increased current density at the lateral edge regions of the cathode viewed in the transverse direction of the cathode, also increase in comparison with the current density in the center of the cathode an increased wear of the cathode in the lateral edge regions, which typically leads after prolonged operation of the electrolytic cell to a characteristic in cross-section of the cathode about W-shaped wear profile of the cathode.

In order to reduce the specific energy consumption of an electrolytic cell, it has recently been proposed to use electrolysed cells with profiled surface cathodes, for example those whose upper side, viewed in cross-section of the cathode, is in the form of a V-shaped well are. In this case, the depression formed in the form of a V-shaped well in the cathode surface causes the current density in the lateral edge regions of the cathode to be reduced, thereby reducing the wave formation potential and also the wear in these regions. In WO 201 1/148347 cathodes are used, the upper side of which contain a recessed central area, wherein this recessed area can have a certain volume A. These pits have sloped surfaces, i. they are in the form of tubs. However, these cathodes and the cathode blocks composing these cathodes also do not solve the wave formation and wear problems satisfactorily.

The object of the present invention is therefore to provide a cathode block which, when used in a fused-salt electrolysis in an electrolytic cell, causes a reduced specific energy consumption and has an increased service life. In particular, a cathode block is to be provided which allows the thickness of the melt layer between the aluminum and the anode to be reduced in the electrolysis cell without causing instabilities, such as short circuits or reoxidations of the formed layer, in the layer of liquid aluminum as a result of increased wave formation tendency Aluminum or fluctuations of the electrolysis cell voltage occur. According to a first aspect of the present invention, this object is achieved by providing a cathode block, in particular for an aluminum electrolytic cell, having the features of claim 1 with at least one arranged on one of the sides of the cathode block and extending in the longitudinal direction of the cathode block groove for receiving a Conductor rail, wherein at least a portion of the surface of the at least one groove side having opposite side of the cathode block, as seen in cross section of the cathode block, arcuately outwardly curved, wherein the vertex of the at least one arcuate outwardly curved section, based on the in the cross section of the cathode block perpendicular to the at least one groove having side extending direction over which at least one groove is arranged.

According to the invention, it has been recognized that, as viewed in the cross-section of the cathode block, an arcuately outwardly curved configuration of the side of the cathode block which is opposite the side having at least one groove, i. when using the cathode block in a cathode of an electrolytic cell by an arcuately outwardly curved configuration of the top of the cathode block, a homogenization of the electric current density and the magnetic flux density at the surface of the cathode block is achieved. This is because the distance between the upper edge of the groove and the vertically overlying portion on the top of the cathode block by the arcuately outwardly curved configuration of the top of the cathode block, the distances between the underside of the cathode block next to the groove and vertically above lying

Sections on the top of the cathode block is adjusted and thereby the length of the electrical path of least resistance, which leads from the upper edge of the groove to the vertically above the groove arranged portion of the top of the cathode block, to the length of the electrical paths of the larger resistances is adjusted from the lower edge of the cathode block next to the portion comprising the groove of the bottom of the cathode block lead to the top of the cathode block. In a conventional rectangular configuration of the cathode block, the length of the electrical path between the upper edge of the groove of rectangular cross-section centered at the bottom of the cathode block and the portion vertically above it on the upper side of the cathode block is substantially shorter than the lengths of the electrical paths. which lead from the side surface of the groove to the top of the cathode block. Since the current in the cathode block follows the path of least electrical resistance, in a cathode block described above, the current flows predominantly in the region between the top of the groove and the vertically overlying portion on the top of the cathode block, whereas the current flow in the two adjacent sections of the cathode block is greatly reduced, so that - seen over the surface of the cathode block - results in an inhomogeneous current density, which leads in the operation of an electrolytic cell to a stronger closure above the groove than at the junctions of the blocks. As a result, the cathode surface assumes a wave-like shape, which can lead to increased wave formation in the layer of liquid aluminum arranged on the cathode block. Due to the embodiment of the cathode block surface according to the invention, the electrical path between the upper side of the groove and the cathode surface is increased and reduced between the side surface of the groove and the cathode surface. Thereby, the current flow is displaced to the sides directly above the groove, so that - seen over the surface of the cathode block - a uniform current density is present, so that in the operation of an electrolysis cell comprising the cathode block, the wave formation in the arranged on the cathode block layer of liquid aluminum is reduced and also the wear of the cathode block is uniform over its surface. Overall, a wave formation in the layer of liquid aluminum is thus effectively avoided in the operation of an electrolytic cell comprising the cathode block according to the invention and a high energy efficiency at the same time achieved high stability and reliability of electrolysis operation. Due to the reduction in undulation in the layer of liquid aluminum disposed above the cathode block, the distance between the anode and the layer of liquid aluminum can be reduced, resulting in additional energy savings in the operation of an electrolytic cell comprising the cathode block. It is particularly advantageous that the above-described measure used to equalize the electric current density on the cathode top, namely the provision of at least one arcuate outwardly curved portion, can be easily sized so that the cathode block according to the invention can be used in an electrolysis cell in that the same bath volume results-even with a reduced distance between the anode and the layer of liquid aluminum-as with the use of a conventional cathode. The intersecting curve defined by the cathode surface in the cross-section of the cathode block is, as seen in the cross-section of the cathode block, curved outwards in an arcuate manner, as seen in the cross-section of the cathode block, with a convex edge facing outward with respect to the cathode block Curvature comprises, wherein a curved section is a section of the cutting curve in which the direction changes continuously, but without that in the curved area an angular or angular or angular change in direction is present. Further, the term "vertex" of a curved portion in the present invention refers to the farthest point of the curved portion as seen perpendicularly from the bottom of the cathode block. Preferably, the cathode block is constructed on the basis of carbon and / or graphite, wherein the cathode block is particularly preferably at least 30 wt .-%, more preferably at least 40 wt .-%, particularly preferably at least 50 wt .-%, very particularly preferably at least 60% by weight and most preferably entirely composed of carbon and / or graphite.

Preferably, the carbon is amorphous carbon and the graphite is preferably graphitic or graphitized carbon. It is further preferred that mixtures of amorphous carbon and graphitic carbon, amorphous carbon and graphitized carbon, amorphous carbon, graphitic and graphitized carbon, or graphitic and graphitized carbon are used. According to a preferred embodiment of the first aspect of the present invention, the cathode block has exactly one groove for receiving bus bars, preferably a bus bar, with a rectangular cross-section, preferably at least that, relative to the cross-section of the cathode block perpendicular to the side having the groove extending direction, over the groove lying portion of the groove side facing the opposite side of the cathode block is curved arcuately outward. As a result, as described above, the lengths of the electrical paths between the upper edge of the groove and the regions of the surface of the cathode block arranged vertically above the groove on the one hand and the adjacent areas of the surface of the cathode block on the other hand are unified, so that the cathode block in the Use in an electrolytic cell has - seen over its surface - homogeneous current density.

As an alternative to the preceding embodiment, the cathode block can also have two grooves for receiving busbars, preferably in each case one current busbar. rail, each having a rectangular cross-section, wherein at least the, relative to the cross-section of the cathode block perpendicular to the grooves having the side extending direction (z), lying over the grooves portion of the side facing the two grooves side of the cathode block once curved arcuately outwards, or, wherein each of the two, relative to the cross-section of the cathode block perpendicular to the side having the two grooves extending direction over the grooves lying portions of the side facing the two grooves side of the cathode block arcuate outwardly is curved, wherein each of the vertexes of the two arcuate outwardly curved portions, relative to the cross-section of the cathode block perpendicular to the direction of the two grooves having side extending direction, disposed over in each case one of the two grooves. In this way, in a two-slot cathode block, the lengths of the electrical paths between the upper edge of each nearest groove and the vertically disposed areas of the surface of the cathode block on the one hand and the adjacently disposed areas of the surface of the cathode block on the other hand unified, so that the cathode block at the use in an electrolytic cell has a - seen over its surface - homogeneous current density.

Alternatively, it is also possible that the cathode block has two grooves for receiving busbars, preferably in each case a busbar, each having a rectangular cross-section, preferably at least the, relative to the cross-section of the cathode block perpendicular to the side having the grooves Direction, over the grooves lying portion of the side facing the grooves of the opposite side of the cathode block is curved once arcuately outwards, so there is an arcuate outwardly curved portion on the cathode top, which spans the two grooves. Good results in the uniformity of the distribution of the electric current density on the cathode block surface when using the cathode block in an electrolytic cell are particularly achieved when the vertex of the at least one arcuately outwardly curved portion of the surface of the cathode block, with respect to the cross-section of the cathode block perpendicular to which the direction having at least one groove side is arranged over a region of the at least one groove which extends from 20 to 80%, preferably from 40 to 60%, of the width of the at least one groove, and particularly preferably above the center the at least one groove is arranged. In this case, the range of 20 to 80% of the width of the groove, the portion of the groove, which viewed in the cross section of the cathode block, at 20% of the measured from a lateral end of the groove in the width direction of the cathode block extension of the groove begins and at 80% of from this lateral end of the groove ends in the width direction of the cathode block measured extension of the groove ends. In this context, the center of the groove is understood to be the point which, viewed in cross-section of the cathode block, is arranged in the center of the groove, ie 50% of the extension of the groove measured from a lateral end of the groove in the width direction of the cathode block.

In order to achieve a uniform distribution of the electric current density as possible over the entire region of the cathode block arranged vertically above the slot width of the cathode block, it is proposed in a development of the invention that the at least one arcuately outwardly curved region of the surface of the cathode block cover at least 20%. , Preferably over at least 40%, more preferably over at least 60%, most preferably over at least 80% and most preferably over 100% of the range extending, based on the cross-section of the cathode block perpendicular to the at least one groove having side Direction, is arranged over the width of the groove. With regard to a uniform distribution of the electric current density over the entire cathode block surface when using the cathode block in an electrolysis cell, it is particularly preferred that the at least one arcuately outwardly curved region of the surface of the cathode block be at least 20%, preferably at least 40 %, more preferably over at least 60%, and most preferably over at least 100%, of the cross-section of the cathode block extending from the side of the cathode block opposite the at least one groove.

If the cathode block has exactly one groove for receiving a bus bar, the cathode block surface viewed in the cross section of the cathode block preferably has exactly one curved area which fulfills the values described above with respect to the width of the cathode block. If the cathode block has two grooves for receiving a respective bus bar, the cathode block surface, viewed in cross-section of the cathode block, preferably has a curved region spanning the two grooves, which fulfills the values given above with respect to the width of the cathode block, or has two curved portions which, taken together, satisfy the values given above with respect to the width of the cathode block.

A comprehensive homogenization of the distribution of the electric current density results in the context of the invention in particular when the at least one arcuate outwardly curved portion of the surface of the cathode block, for example over at least 60%, preferably over at least 80%, more preferably over at least 90% and most preferably extends over at least 100% of the length of the cathode block. A particularly well adapted to the electrical flow conditions in the cathode block when using the same in an electrolytic cell cathode surface is achieved according to a further embodiment of the first aspect of the present invention, characterized in that the at least one arcuate outwardly curved portion of the surface of the cathode block, based on the cross section of the cathode block, oval-segment-shaped, in particular circular-arc-shaped, cosinusoidal, in the form of a Gaussian normal distribution, elliptical-segment-shaped, curved in the shape of a Bezier curve, parabolic section-shaped or in the form of a cosine curve of higher power.

According to the typically symmetrical electrical flow conditions in the cathode block when used in an electrolytic cell, it is preferred that the at least one arcuately outwardly curved portion of the surface of the cathode block be symmetrical to the mid-perpendicular plane of the at least one groove relative to the cross section of the cathode block is. This also achieves easy manufacturability of the cathode block and universal applicability of the cathode block in an electrolysis cell. In order to achieve a particularly homogeneous distribution of the current density over the cathode block surface and thereby particularly effectively reduce the formation of waves in a layer of liquid aluminum arranged above the cathode block when using the cathode block according to the invention in an electrolytic cell, it becomes known in the invention proposed, the cathode block surface in such a way that the at least one arcuate outwardly curved portion the shape of an ellipse segment with a width of the interval of the polar angle between 10 ° and 180 °, preferably between 30 ° and 160 °, more preferably between 50 ° and 140 ° and very particularly preferably between 70 ° and 120 °, and / or that the at least one arc-shaped curve curved outward has the shape of a cosine curve having a width of the interval of the angle between 10 ° and 180 °, preferably between 30 ° and 160 °, more preferably between 50 ° and 140 ° and most preferably between 70 ° and 120 °, and or that the at least one arcuately outwardly curved section is in the form of a circular arc segment having a width of the interval of the midpoint angle between 10 ° and 180 °, preferably between 30 ° and 160 °, particularly preferably between 50 ° and 140 ° and completely more preferably between 70 ° and 120 °, and / or that the at least one arcuate outwardly curved portion is in the form of a Gaussian normal distribution with a quotient of the half width of the Gaussian normal distribution and the width of the at least one groove of 0.5 to 1 .5, preferably from 0.6 to

1, 4, more preferably from 0.7 to 1.3, most preferably from 0.8 to 1.2, and most preferably from 0.9 to 1.1. According to another preferred embodiment of the present invention, it has been found advantageous that the quotient of the distance from the vertex of the at least one arcuately outwardly curved portion of the surface of the cathode block to the lowest point of the groove and the distance from the lowest point of the groove the side of the cathode block opposite the at least one groove side to the lowest point of the groove between more than 1: 1 to at most 2: 1, preferably 1, 0 to

1 .5, more preferably 1, 0 to 1, 3 and most preferably 1, 0 to 1, 2. In order to maximize the cathode block surface useful for electrolysis, it is preferred that the at least one groove be at least 40%, preferably at least 60%, more preferably at least 80%, most preferably at least 90%, and most preferably above entire length of the cathode block extends. In order to further increase the achievable equalization of the distribution of the electric current density at the cathode block surface, it is proposed in a development of the invention that the at least one groove, in particular rectangular in cross-section, has a depth varying over its length, the at least one groove particularly preferably has a smaller depth at its longitudinal ends than in its center. In this case, the groove can in particular have a course approximately triangular in longitudinal section of the cathode block. By means of such a configuration, an increase in the electric current density at the longitudinal end regions of the cathode surface, which usually takes place in the region of the longitudinal ends of the groove, is effectively prevented from contacting the surface regions located further inside. At the same time both in the transverse direction and in the longitudinal direction of

Cathode blocks to achieve a uniform distribution of the electric current density at the cathode block surface when it is used in an electrolytic cell, it is preferred if the surface of the side facing the at least one groove side, viewed in longitudinal section of the cathode block, is designed trough-shaped. It is particularly preferred when the cathode block is configured with the trough-shaped surface according to the second aspect of the present invention described below. In this respect, the advantageous embodiments and advantages described below in relation to the second aspect of the present invention also apply correspondingly to the first aspect of the present invention.

According to a second aspect of the present invention, the object described above is achieved by providing a cathode block for an aluminum electrolytic cell, which has a trough-shaped surface viewed in a longitudinal section of the cathode block, wherein the trough has two edge regions and a, seen in the longitudinal direction of the cathode block, arranged between the edge regions and lowered relative to the edge regions bottom region, wherein between the two edge regions and the bottom region in each case a corresponding edge region and the bottom region connecting side wall region is provided, wherein at least one of the two connection regions between the Edge regions and the side wall portions and / or at least one of the two connecting portions between the bottom portion and the side wall portions is arcuately curved, wherein the at least one arcuately curved portion has a length of more than 2 cm.

It is preferred if the cathode block is based on carbon and / or graphite, wherein the cathode block is particularly preferably at least 30 wt .-%, more preferably at least 40 wt .-%, particularly preferably at least 50 wt. %, more preferably at least 60% by weight and most preferably entirely composed of carbon and / or graphite.

Preferably, the carbon is amorphous carbon and the graphite is preferably graphitic or graphitized carbon. It is further preferred that mixtures of amorphous carbon and graphitic carbon, amorphous carbon and graphitized carbon, amorphous carbon, graphitic and graphitized carbon, or graphitic and graphitized carbon are used.

The trough-shaped surface is preferably the surface of the cathode block, which is arranged opposite the surface of the cathode block which has the at least one groove for receiving busbars, preferably in each case one busbar. In other words, the trough-shaped surface of the cathode block according to the invention is located on the - im With regard to the use of the cathode block in an electrolytic cell - top of the cathode block, that is the side of the cathode block on which the layer of liquid aluminum is provided. According to the invention, it has been recognized that it is achieved by an arcuately curved configuration of at least one of the connection regions of a trough-shaped cathode block, ie by an arcuately curved configuration of at least one of the connection regions which are provided between the edge regions and the sidewall regions and between the bottom region and the sidewall regions in that the electric current density and the magnetic flux density are made uniform in the use of the cathode block in an electrolytic cell. This is because in a trough-shaped embodiment of the cathode block, the current - in contrast to a cuboid cathode block - not primarily flows in the lateral edge regions of the cathode block, but the current flow, because in the trough-shaped configuration realized as described above, the electrical resistance of the edge regions due to greater height of the edge areas is increased in relation to the height of the bottom area with respect to the electrical resistance of the bottom portion of the cathode block, is homogeneously distributed over the surface of the cathode block. This, in turn, is a consequence of the fact that the current in the cathode block follows the path of least electrical resistance. In addition, at least one of the connecting regions is achieved by the arcuately curved configuration that no inhomogeneously distributed current densities occur even in the region of the at least one connecting region, which runs at an angle in a trough-shaped configuration known from the prior art. Rather, the arcuately curved configuration, the occurring during the use of the cathode block in an electrolytic cell at the surface of the cathode block distribution of electric current density is compared in comparison to a cathode block with a winkeligen design even in the connecting areas, so that wave formation in the layer of liquid aluminum during operation of the electrolytic cell and concomitant instabilities of the electrolysis operation can be effectively avoided. This is because due to the arcuately curved configuration of at least one of the connecting regions in contrast to an angled configuration of the connecting regions at these regions peaks or valleys of flowing through the surface of the cathode block electric current density are avoided, which in an angular configuration of the connecting portions as Consequence of the fact that the current follows the path of least electrical resistance. Overall, in the operation of an electrolysis cell comprising the cathode block according to the invention, a wave formation in the layer of liquid aluminum is effectively avoided and a high energy efficiency is achieved while high stability and reliability of the electrolysis operation are achieved. Due to the reduction in the formation of waves in the layer of liquid aluminum disposed above the cathode block, the distance between the anode and the layer of liquid aluminum can be reduced, resulting in additional energy savings in the operation of an electrolysis cell comprising the cathode block. As in the first aspect of the present invention, an arcuate portion is understood to mean a portion where the sectional curve defined in the cross section of the cathode block by the cathode surface has a convex curvature with respect to the cathode block interior, with a portion below the curved portion Intersection curve is understood, in which the direction changes continuously, but without that in the curved area an angular change in direction is present.

In this case, the length of the arc-shaped curved section in the sense of the present invention designates the extension, measured in the longitudinal direction of the cathode block, of the arc-shaped curved section from its beginning up to its end, ie from the point of transition of the preferably rectilinear edge region in the arcuately curved connecting portion to the point of its transition into a preferably rectilinear portion of the side wall portion or from the point of transition of a preferably rectilinear portion of the side wall portion in the arcuately curved connecting portion to the point of its transition into the preferably rectilinearly shaped bottom portion.

Good results with regard to the equalization of the current density are obtained, in particular, if the at least one arcuately curved section has a length of more than 2 cm to 100 cm, preferably 3 to 50 cm, particularly preferably 4 to 30 cm, particularly preferably 5 to 20 cm, most preferably from 7 to 15 cm and most preferably 10 cm, since peaks or valleys of the electric current density above the curved portion are particularly reliably avoided by such a dimensioning of the curved portion.

When the arc-shaped curved portion is provided in at least one of the joint portions between the bottom portion and the sidewall portions of the trough-shaped surface of the cathode block, the arcuate portion is preferably arcuately curved inwardly with respect to the cathode block as viewed in the longitudinal section, whereas if the arcuate portion Section is provided in at least one of the connecting portions between the edge regions and the side wall portions of the trough-shaped surface of the cathode block, preferably outwardly arcuately curved. Thus, according to a preferred embodiment of the present invention, at least one of the two connection regions is between the bottom region and the side wall regions and are preferably both connection regions between the bottom region and the side wall regions, with respect to the cathode layer considered in longitudinal section. block, designed curved inwards in an arcuate manner. Alternatively or in addition to this, at least one of the two connection regions between the edge regions and the sidewall regions and preferably both connection regions between the edge regions and the sidewall regions are / is configured outwardly arched with respect to the cathode block viewed in longitudinal section.

A particularly advantageous embodiment of the cathode block according to the second aspect of the invention, with regard to a very homogeneous distribution of the electrical current density, provides that the two connection regions between the bottom region and the side wall regions are configured curved inwards in relation to the cathode block viewed in longitudinal section as well as the two connecting regions between the edge regions and the side wall regions, based on the cathode block viewed in longitudinal section, are configured curved in an arc-shaped outward direction.

In a further development of the inventive concept, it is proposed that at least one arcuately curved section has a minimum radius of curvature of at least 2 cm, preferably of at least 10 cm and particularly preferably of at least 20 cm. As a result, a particularly gentle course of the cathode block surface is achieved within the curved portion, whereby a particularly uniform distribution of the electric current density is achieved when using the cathode block in an electrolytic cell. According to a further preferred embodiment of the second aspect of the present invention provides that at least one arcuate portion, with respect to the longitudinal section of the cathode block, oval segment, in particular circular arc, cosinus, in the form of a Gaussian distribution, elliptical segmental or in the shape of a Bezier curve is configured. In view of the above-described effects to be achieved with the second aspect of the present invention, it has also been found to be particularly advantageous to determine the ratio between the greatest height in the edge regions relative to the cross-sectional plane extending in the longitudinal direction lowest height in the bottom region of the cathode block between 1, 1 and 4, preferably between 1, 1 and 2.5 and more preferably between 1, 1 and 2.1 set. In this case, the cross-sectional plane extending in the longitudinal direction denotes the vertical plane running perpendicular to the width direction of the cathode block and parallel to the longitudinal direction of the cathode block.

Particularly good results with regard to the distribution of the electric current density at the surface of the cathode block are furthermore achieved if the angle between the one end and the other end of the at least one arcuately curved section of the at least one connecting region of the cathode block 95 to 175 ° is preferred 1 is 10 to 160 ° and more preferably 125 to 150 °. The angle between the two ends of the curved portion denotes the larger of the two angles, the two fictitious, at the two ends of the section and starting, considered in the longitudinal section of the cathode block, each tangent to the curved portion extending straight lines.

In order to achieve a uniform distribution of the electric current density, in particular within the edge regions of the cathode block, it is proposed in development of the invention that at least one of the two edge regions and preferably both edge regions, viewed in longitudinal section of the cathode block, in the longitudinal direction of the cathode block to the center of the Cathode block sloping sloping runs / run, with the inclination angle of the edge region or the edge regions relative to this level preferred is between 1 ° and 30 °, more preferably between 2 ° and 15 ° and most preferably between 3 ° and 10 °.

In this embodiment, it is preferred that at least one of the two edge regions and preferably both of the edge regions over at least 30%, preferably over at least 50%, more preferably over at least 75% and most preferably over 100% of the length measured in the longitudinal direction of the cathode block Edge region or the edge regions, viewed in a longitudinal section of the cathode block in the longitudinal direction of the cathode block, sloping towards the center of the cathode block extends / run.

According to a further preferred embodiment of the second aspect of the invention, it is provided that the bottom region extends at least in regions in a straight line, wherein the surface of the bottom region, with respect to the longitudinal direction an angle between -20 ° and 20 °, preferably between -10 ° and 10 ° and more preferably of 0 °.

A homogeneous distribution of the electric current density over the surface of the cathode block resulting from the use of the cathode block according to the invention in an electrolysis cell is achieved in particular if each of the two edge regions is more than 5 to 40%, preferably 10 to 35% and particularly preferably 15 to 30 % of the length of the cathode block extends and / or the bottom region extends over 10 to 90%, preferably 20 to 70% and particularly preferably 30 to 60% of the length of the cathode block.

In order to increase the flexibility in terms of the design of the cathode surface, it is proposed in development of the invention that the cathode block has a, seen in the longitudinal direction of the cathode block, varying material composition, wherein the material in the two edge regions preferably has a higher electrical resistivity has as the material in the bottom portion of the cathode block. Thus, already by the material used of the cathode block, a favoring of the current flow in the middle of the cathode block is achieved with respect to the edge regions, so that the height difference between the edge regions and the bottom portion of the cathode block surface can be comparatively small to the desired equalization of the current density over the To reach cathode block surface.

In this embodiment, good results are obtained in particular if the cathode block contains 5 to 50% by weight and preferably between 10 to 30% by weight of acetylene coke in the two edge regions. The Acetylenkoks does not change its electrical properties at the carried out during the production of the cathode block Graphitierungsschritt not or only slightly, so that the edge portions of the cathode block graphite with a lower degree of graphitization and thus with a greater electrical resistivity than in the case of graphitization without addition of the acetylene coke.

Further, it is preferred that the cathode block in the bottom regions contain from 5 to 50% by weight and preferably between 10 to 40% by weight of titanium diboride, silica and / or chromium oxide. The titanium diboride, silica or chromium oxide promotes in the process performed during the preparation of the cathode block

Graphitierungsschritt the formation of the graphite structure, so that the bottom portion of the cathode block contains graphite with a higher degree of graphitization and thus with a lower electrical resistivity than in the case of graphitization without the addition of titanium diboride, silica or chromium oxide.

The second aspect of the present invention can be combined with the first aspect of the present invention, that is, according to a particularly preferred embodiment of the present invention, the cathode block has the in Related to the features described in the first aspect of the present invention as well as the features described in relation to the second aspect of the present invention. Another object of the present invention is a cathode assembly, in particular for an aluminum electrolysis cell, which comprises at least two configured as described above cathode blocks.

In addition, the present invention relates to an electrolysis cell, in particular for the production of aluminum, which comprises a previously described cathode arrangement, a layer of liquid aluminum arranged on the top side of the cathode arrangement, a melt layer thereon and an anode above the melt layer. Hereinafter, the present invention will be described purely by way of example with reference to advantageous embodiments with reference to the accompanying drawings. Show it:

1 is a perspective sectional view of a cathode block according to the prior art,

FIG. 2 is a perspective sectional view of a cathode block according to an embodiment of the first aspect of the present invention. FIG.

3 shows a front view of the cathode block section shown in FIG. 2,

4 is a cross-sectional view of a cathode block according to another embodiment of the first aspect of the present invention; 5 is an illustration of possible embodiments of the arcuate outwardly curved portion of a cathode block according to various embodiments of the first aspect of the invention;

6 is a longitudinal sectional view of a cathode block according to the prior art,

7 is a longitudinal sectional view of a cathode block according to an embodiment of the second aspect of the present invention;

8 is a longitudinal sectional view of a cathode block according to another embodiment of the second aspect of the present invention;

9a-e are schematic representations of the distribution of the electric current density at the surface of different cathode blocks when the respective cathode block is used in an electrolysis cell,

10 is a perspective view of the cathode block shown in FIG. 6 according to the prior art,

1 1 is a perspective view of a cathode block according to a

Embodiment of the second aspect of the present invention

12 is a perspective view of a cathode block according to another embodiment of the second aspect of the present invention and a perspective view of a cathode block according to another embodiment of the second aspect of the present invention. Fig. 1 shows a perspective sectional view of a cathode block according to the prior art. The cathode block has a groove 12a arranged on one side 10a of the cathode block and extending in the longitudinal direction y of the cathode block for receiving a bus bar. The cathode block also has an opposite side 14a, which has the groove 12a, with a surface 16a which, when the cathode block is used in an electrolysis cell, faces the layer of liquid aluminum arranged above the cathode block. In the embodiment of the cathode block illustrated in FIG. 1, the surface 16a is flat. In the operation of such a cathode block in an electrolytic cell results in the surface 16a a - seen in particular in the width direction x of the cathode block - uneven distribution of the electric current density, whereby a wave formation is favored in the overlying layer of liquid aluminum. In Fig. 1, as in the other prior art figures, the numerals _{a are} provided with the subscript _a to distinguish these reference numerals from the corresponding reference numerals of the figures representing the present invention.

Fig. 2 is a perspective sectional view of a cathode block according to an embodiment of the first aspect of the invention. The width Bi measured in the width direction x of the cathode block shown in FIG. 2 is about 42 cm and the width B _{2 of} the groove 12 is about 20 cm. The length L of the cathode block measured in the longitudinal direction y may be, for example, 2.5 to 4.0 m. The cathode block shown in FIG. 2 differs from that shown in FIG. 1 in that a portion of the surface 16 of the side 14 of the side opposite the side 10 having the at least one groove 12 Cathode block, seen in cross-section of the cathode block, is arcuately curved outward. The sectional curve of the surface 16 resulting in the cross section of the cathode block is identified by reference numeral 18 in FIG. This sectional curve 18 is arc-shaped over its entire width Bi measured in the width direction x and thus represents an arcuately curved section 20 of the cross-sectional surface 16. As also shown in FIG. 1, the apex 22 of the arcuate outwardly curved section 20 relative to the in the cross section of the cathode block perpendicular to the at least one groove 12 having side 10 extending direction z is arranged vertically above the groove 12. The region of the surface 16 arranged in the direction z above the groove 12 is identified by the reference numeral 24 in FIG. Due to the arcuate configuration of the surface 16, the distribution of the electric current density in the use of the cathode block in an electrolytic cell compared to the cathode block shown in Fig. 1 is made uniform and thereby reduces a wave formation in the arranged above the cathode block layer of liquid aluminum.

FIG. 3 shows the cross section of the cathode block cutout shown in FIG. 2. As can be seen in FIG. 3, the quotient of the distance hi from the apex 22 of the curved section 20 to the lowest point of the groove 12 and the distance h ₂ from the lowest point of the side 14 facing the groove 12 is equal to 14 the lowest point of the groove 12 in this embodiment is about 1.4: 1.

4, a cathode block according to a further embodiment of the first aspect of the invention is shown in cross-section. The cathode block shown in FIG. 4 has two grooves 12, 12 'for receiving in each case one bus bar and the surface 16 of the cathode block has, seen in cross-section, two arcuately outwardly curved sections 20, 20', wherein the plate telpunkt 22, 22 'of each arcuate outwardly curved portion 20, 20' in the direction perpendicular to the grooves 12, 12 'having side 10 oriented direction z above the corresponding groove 12, 12' is arranged. In this way, even with a cathode block with two grooves 12, 12 'in the use of the cathode block in an electrolytic cell over the entire width B of the cathode block uniform distribution of the electric current density at the surface 16 of the cathode block can be achieved.

Fig. 5 shows an illustration of possible embodiments of the arcuate outwardly curved portion of a cathode block according to various embodiments of the first aspect of the invention. More precisely, FIG. 5 shows possible sectional curves 18a-e which can form an arcuately curved section of the cathode block surface in the cross section of the cathode block. The x values range from (-0.5) times the cathode block width to 0.5 times the cathode block width and the y values indicate the height of the cathode surface relative to a fictitious middle horizontal. In this case, the cut curve 18a has the shape of a semicircle, the cut curve 18b the shape of a parabolic section, the cut curve 18c the shape of a half ellipse, the cut curve 18d the shape of a cosine curve, and the cut curve 18e the shape of a cosine curve in the fourth power , ie the function cos ⁴ (x).

FIG. 6 shows a section of a cathode block shown in longitudinal section according to the prior art. The cathode block according to FIG. 6 has a trough-shaped surface 16a, which, viewed in a longitudinal section of the cathode block, faces in the use of the cathode block in an electrolysis cell the layer of liquid aluminum arranged above the cathode block and carried by the cathode block. In this case, the trough comprises two edge regions 26a, of which only one is shown in the sectional illustration of FIG. 6, and one, arranged in the longitudinal direction y of the cathode block, arranged between the edge regions 26a and with reference to FIG Edge regions 26a lowered bottom portion 28a, wherein between the two edge regions 26a and the bottom portion 28a each one of the corresponding edge portion 26a and the bottom portion 28a connecting side wall portion 30a is provided. As shown in FIG. 6, the edge regions 26a and the bottom region 28a in each case pass over angled transitions into the sidewall regions 30a. Values in the distribution of the electric current density in the region of the angular transitions between the edge regions 26a 'and the corresponding side wall region 30a of the surface 16a and peaks in the distribution of the electric current density in the region of the angled transitions between occur when the cathode block is used in an electrolysis cell the bottom portion 28a and the corresponding side wall portions 30a. These peaks and valleys lead to an inhomogeneous distribution of the electric current density over the cathode surface and thereby to an undesirable wave formation in the provided on the cathode surface layer of liquid aluminum.

FIG. 7 shows a section of a cathode block shown in longitudinal section according to an embodiment of the second aspect of the present invention. The cathode block shown in FIG. 7 differs from the cathode block shown in FIG. 6 in that, viewed in the longitudinal section of the cathode block, the connection region 32 between the edge region 26 and the sidewall region 30 is arcuately outwardly curved, which is arcuate curved section 34 has a length Li of more than 2 cm measured in the longitudinal direction y of the cathode block. This curved transition between the edge region 26 and the sidewall region 30 avoids an electric current density valley in this region of the cathode block surface 16 when the cathode block is used in an electrolysis cell and thus reduces the formation of waves in the layer of liquid aluminum. In the cathode block shown in FIG. 7, the quotient of the highest height h ₃ in the edge region 26 and the lowest height h in is the bottom portion 28 of the cathode block about 2: 1. Further, the angle α between the one end and the other end of the arc-shaped curved portion 34 is about 120 °. 8 shows a section of a cathode block shown in longitudinal section according to a further embodiment of the second aspect of the present invention. The cathode block shown in FIG. 8 differs from that shown in FIG. 7 in that, viewed in the longitudinal section of the cathode block, instead of the connection region 32 between the edge region 26 and the side wall region 30, the connection region 36 between the side wall region 30 and the Bottom portion 28 is designed as an arcuate inwardly curved portion 34, wherein the arcuate curved portion 34 has a measured in the longitudinal direction y of the cathode block length Li of more than 2 cm. This curved transition between the sidewall region 30 and the bottom region 28 avoids a peak in the electric current density in this region of the cathode block surface 16 when the cathode block is used in an electrolysis cell and thus further reduces the formation of waves in the layer of liquid aluminum. The embodiments shown in FIGS. 7 and 8 can also be combined in such a way that both the transition between the edge regions 26 and the side wall regions 30 and the transitions between the side wall regions 30 and the bottom region 28 are curved in an arc shape. This makes it possible to achieve a particularly homogeneous distribution of the electric current density at the surface 16 of the cathode block with regard to the formation of waves in the layer of liquid aluminum.

FIGS. 9a-e show a schematic representation of the distribution of the electric current density occurring on the surface of different cathode blocks when the respective cathode block is used in an electrolysis cell. overall In more detail, FIGS. 9a-e respectively show the distribution of the electrical current density, which is projected into the horizontal plane, on the surface of the respective cathode block during operation of the electrolysis cell. The legend 38 shown in FIGS. 9a-e indicates which hatching in FIGS. 9a-e corresponds in each case to which electrical current density.

FIG. 9a shows the distribution of current density using a prior art trough-shaped cathode block as shown in FIGS. 6 and 10.

In Fig. 9b, the distribution of the electric current density using a cathode block as shown in Fig. 2 according to the first aspect of the present invention having an outwardly curved surface 16 (see Fig. 2) and otherwise the same configuration as the cathode block of Fig. 10. As highlighted in FIG. 9b by the dashed boxes 40, the curvature of the cathode block surface, especially in the central region viewed in the longitudinal direction y of the cathode block, results in a substantially more homogeneous distribution of the electric current density across the width (x direction) of the cathode block as in the cathode block shown in Fig. 9a.

In Fig. 9c is shown the distribution of the electric current density using a cathode block as shown in Fig. 11, which is formed simultaneously according to the first aspect of the invention and also formed according to the second aspect of the invention. More specifically, the surface 16 of the cathode block according to the second aspect of the invention has a longitudinally-trough-shaped surface 16 (see FIG. 11), the trough having two edge regions 26, 26 'and one seen in the longitudinal direction y of the cathode block between the edge regions 26, 26 'arranged and based on the edge regions 26, 26' lowered bottom portion 28, wherein between the Edge regions 26, 26 'and the bottom region 28 is provided in each case a side wall region 30, 30' connecting the corresponding edge region 26, 26 'and the bottom region 28. In the embodiment shown in FIG. 11, viewed in the longitudinal section of the cathode block, both the connection regions 32, 32 between the edge regions 26, 26 'and the sidewall regions 30, 30' and the two connection regions 36, 36 'are located between the bottom region 28 and the side wall portions 30, 30 'arcuately curved configured, wherein the two arcuate curved portions 34, 34' have a length of more than 2 cm. The connecting regions 32, 32 'between the edge regions 26, 26' and the side wall regions 30, 30 'are curved in an arc outward and the connecting regions 36, 36' between the bottom region 28 and the side wall regions 30, 30 'are curved in an arcuate manner inwardly , In addition, the embodiment shown in FIG. 11 has an outwardly directed curvature of the surface 16, viewed in cross-section of the cathode block, but not shown in FIG. 11 for the sake of simplicity. As can be seen from FIG. 9c, the embodiment of the cathode block surface 16 shown in FIG. 11 leads to a further homogenization of the distribution of the electric current density, in particular in the region of the boxes 40 drawn in FIG. 9c.

Fig. 9d shows the distribution of the electric current density using a cathode block as shown in Fig. 12. The cathode block shown in FIG. 12 substantially corresponds to the embodiment shown in FIG. 11, wherein in FIG. 12 the edge regions 26, 26 ', viewed in a longitudinal section of the cathode, are viewed at an angle β to the center of the horizontal Cathode block inclined towards. As can be seen from FIG. 9d, the distribution of the electric current density in the region of the boxes 40, ie, at the longitudinal end of the cathode block, is thereby additionally clearly homogenized. Fig. 9e shows the distribution of the electric current density using a cathode block as shown in Fig. 13. The cathode block shown in FIG. 13 essentially corresponds to the embodiment shown in FIG. 12, the cathode block shown in FIG. 13 having a locally varying material composition, specifically the cathode block sections 42, 42 arranged below the edge regions 26, 26 '', ie the areas hatched in simple hatched areas 42, 42' of the cathode block, acetylene coke are added and the arranged below the bottom portion 28, in Fig. 13 double hatched marked area 44 of the cathode block titanium diboride is added. As shown in FIG. 9e, the distribution of the electric current density in the middle area of the cathode surface identified by the box 40 is once again additionally homogenized compared to the distribution shown in FIG. 9d by this measure.

LIST OF REFERENCE NUMBERS

10, 10a (bottom) side of the cathode block

12, 12 ', 12a groove

14, 14a (upper) side of the cathode block

16, 16a surface of the cathode block

18 cutting curve

20, 20 'arcuately curved section

22, 22 'vertex of the arcuate curved portion 24, 24' above the groove arranged area

26, 26 ', 26a edge area

28, 28a floor area

30, 30 ', 30a sidewall region

32, 32 'connection area

34, 34 'arcuately curved section

36, 36 'connection area

38 legend

40 box

42, 42 'areas with added acetylene coke

44 areas with added titanium diboride

B, Bi width

hrh distance, height

L, Li length

x, y, z width, length and height direction

α, ß angle

Claims

claims

Cathode block for an aluminum electrolytic cell with at least one arranged on one of the sides (10, 14) of the cathode block and in the longitudinal direction (y) of the cathode block extending groove (12, 12 ') for receiving a busbar, wherein at least a portion (20, 20 ') of the surface (16) of the at least one groove (12, 12') having side (10) opposite side (14) of the cathode block, as seen in cross section of the cathode block, arcuately outwardly curved, wherein the vertex (22, 22 ') of the at least one curved outwardly curved portion (20, 20'), based on the cross-section of the cathode block perpendicular to the at least one groove (12, 12 ') having side (10) extending direction (z) over the at least one groove (12, 12 ') is arranged.

Cathode block according to claim 1,

By doing so, that is

this is at least 30 wt .-%, preferably at least 40 wt .-%, more preferably at least 50 wt .-%, most preferably at least 60 wt .-% and most preferably completely composed of carbon and / or graphite ,

Cathode block according to claim 1 or 2,

By doing so, that is

the vertex (22, 22 ') of the at least one arcuately outwardly curved section (20, 20') of the surface (16) of the cathode block, relative to the cross section of the cathode block perpendicular to the at least one groove (12, 12 ') page (10). (z), over a region of the at least one groove (12, 12 ') is arranged, which is from 20 to 80% of the width (Bi) of the at least one groove (12, 12'), and preferably from 40 to 60 % of the width (Bi), which extends at least one groove (12, 12 '), and particularly preferably over the center of the at least one groove (12, 12') is arranged.

Cathode block according to at least one of the preceding claims, characterized in that

the at least one curved outwardly curved region (20, 20 ') of the surface (16) of the cathode block over at least 20%, preferably over at least 40%, more preferably over at least 60%, most preferably over at least 80% and most preferably over 100% of the area (24, 24 ') which, relative to the cross-section of the cathode block perpendicular to the at least one groove (12, 12') having side (10) extending direction (z), over the width ( Bi) of the groove (12, 12 ') is arranged.

the at least one curved outwardly curved portion (20, 20 ') is in the form of an ellipse segment having a width of the interval of the polar angle between 10 ° and 180 °, preferably between 30 ° and 160 °, more preferably between 50 ° and 140 ° and completely particularly preferably between 70 ° and 120 °, and / or

the at least one curved outwardly curved portion (20, 20 ') in the form of a cosine curve with a width of the interval of the angle between 10 ° and 180 °, preferably between 30 ° and 160 °, more preferably between 50 ° and 140 ° and most preferably between 70 ° and 120 °, and / or the at least one curved outwardly curved portion (20, 20 ') the shape of a circular arc segment having a width of the interval of the midpoint angle between 10 ° and 180 °, preferably between 30 ° and 160 °, more preferably between 50 ° and 140 ° and all particularly preferably between 70 ° and 120 °, and / or

the at least one arcuately outwardly curved section (20, 20 ') has the form of a Gaussian normal distribution with a quotient of the half-width of the Gaussian normal distribution and the width of the at least one groove of 0.5 to 1 .5, preferably of 0, 6 to 1, 4, more preferably from 0.7 to 1, 3, most preferably from 0.8 to 1, 2 and most preferably from 0.9 to 1, 1.

the quotient of the distance (hi) from the vertex (22, 22 ') of the at least one arcuately outwardly curved portion (20, 20') of the surface (16) of the cathode block to the lowest point of the groove (12, 12 ') and the distance (h ₂ ) from the lowest point of the side (14) of the cathode block opposite the at least one groove (12, 12 ') side (14) to the lowest point of the groove (12, 12') between more than 1: 1 to a maximum of 2: 1, preferably 1, 0 to 1, 5, more preferably 1, 0 to 1, 3 and very particularly preferably 1, 0 to 1, 2.

the at least one preferably rectangular cross-section groove (12, 12 ') has a varying depth over its length, wherein the at least one groove (12, 12') particularly preferably at their longitudinal ends has a smaller depth than in its center. Cathode block for an aluminum electrolysis cell, which has a trough-shaped surface (16), viewed in the longitudinal section of the cathode block, wherein the trough has two edge regions (26, 26 ') and one, seen in the longitudinal direction (y) of the cathode block, between the edge regions (26, 26 ') and lowered relative to the edge regions (26, 26') lowered bottom region (28), wherein between the two edge regions (26, 26 ') and the bottom region (28) in each case a corresponding edge region (26, 26') and at least one of the two connecting regions (32, 32 ') between the edge regions (26, 26') and the side wall regions (30, 30 ') and / or at least one of the two connecting regions (36, 36 ') between the bottom portion (28) and the side wall portions (30, 30') is arcuately curved, wherein the at least one arcuately curved portion (34, 34 ') Lä length (Li) of more than 2 cm to 100 cm, preferably from 3 to 50 cm, particularly preferably from 4 to 30 cm, particularly preferably from 5 to 20 cm, very particularly preferably from 7 to 15 cm and most preferably 10 cm having.

Cathode block according to claim 8,

By doing so, that is

Cathode block according to claim 8 or 9,

characterized in that at least one of the two connecting regions (36, 36 ') between the bottom region (28) and the side wall regions (30, 30') and preferably both connecting regions (36, 36 ') between the bottom region (28) and the side wall regions (30, 30'). ), based on the viewed in longitudinal section cathode block, is designed inwardly arcuate curved / is.

11. Cathode block according to at least one of claims 8 to 10,

By doing so, that is

at least one of the two connection regions (32, 32 ') between the

Edge regions (26, 26 ') and the side wall portions (30, 30') and preferably both connecting portions (32, 32 ') between the edge regions (26, 26') and the side wall portions (30, 30 '), based on the longitudinal section considered cathode block, outwardly arcuately curved is configured / are.

Cathode block according to at least one of claims 8 to 11,

By doing so, that is

the ratio between the maximum height (h ₃ ) in the edge regions (26, 26 ') and the lowest height (h) in the bottom region (28) of the cathode block between 1, in the longitudinal direction (y), 1 and 4, preferably between 1.1 and 2.5, and more preferably between 1.1 and 2.1.

Cathode block according to at least one of claims 8 to 12,

By doing so, that is

the cathode block has a varying material composition, viewed in the longitudinal direction (y) of the cathode block, wherein the material in the two edge regions (26, 26 ') preferably has a higher specific see resistance as the material in the bottom portion (28) of the cathode block.

14. Cathode block according to claim 13,

By doing so, that is

the cathode block in the two edge regions (26, 26 ') contains 5 to 50% by weight and preferably between 10 to 30% by weight of acetylene coke.

15. Cathode block according to claim 13 or 14,

By doing so, that is

the cathode block in the bottom region (28) contains from 5 to 50% by weight and preferably between 10 to 40% by weight of titanium diboride, silica and / or chromium oxide.