Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
  • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
  • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes

Definitions

• the present invention relates to a cathode block for an aluminum electrolysis cell, a process for its preparation, its use and a cathode comprising this.
• Electrolysis cells are used, for example, for the electrolytic production of aluminum, which is usually carried out industrially by the Hall-Heroult process.
• a melt composed of alumina and cryolite is electrolyzed.
• the cryolite, Na 3 [AIF 6 ] serves to lower the melting point from 2045 ° C. for pure aluminum oxide to approximately 950 ° C. for a mixture containing cryolite, aluminum oxide and additives such as aluminum fluoride and calcium fluoride.
• 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.
• the cathode is usually composed of a carbonaceous material.
• 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.
• layer of liquid aluminum is formed, in particular of individual anode blocks, anode, between the and the surface of the Aluminum is the electrolyte, so the alumina and cryolite containing melt is.
• 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.
• the dissolved in the melt aluminum oxide is split by electric current flow to aluminum and oxygen.
• the layer of liquid aluminum is the actual cathode because aluminum ions are reduced to elemental aluminum on its surface.
• 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 reduce the manufacturing costs, it is therefore desirable to reduce the specific energy consumption in this process as much as possible.
• graphite cathodes are increasingly used in recent times, ie those of cathode blocks, which contain graphite as the main component.
• graphitic cathode blocks for the production of which graphite is used as the starting material
• graphitized cathode blocks for the production of which a carbon-containing graphite precursor is used as starting material, which is replaced by a subsequent one Graphitization referred to heat treatment at 2,100 to 3,000 ° C is converted to graphite.
• graphite Compared to amorphous carbon, graphite is characterized by a considerably lower specific electrical resistance as well as a significantly higher thermal conductivity, which means that the use of graphite cathodes in electrolysis can reduce the specific energy consumption of the electrolysis and the electrolysis can be carried out at a higher current, which allows an increase in the production of aluminum.
• cathode or cathode blocks of graphite, and in particular graphitized cathode blocks undergo severe wear during electrolysis due to surface erosion, which is considerably greater than the wear of cathode blocks of amorphous carbon.
• cathode or cathode blocks of amorphous carbon or graphite have a comparatively poor wettability with aluminum.
• a cathode block for an aluminum electrolysis cell which comprises a base layer and a cover layer, wherein the base layer contains graphite and the cover layer 1 to less than 50 wt .-% hard material having a melting point of at least Contains 1 .000 ° C containing graphite composite material.
• a carbon-containing material such as coke, anthracite, carbon black or glassy carbon
• a non-toxic ceramic such as preferably titanium diboride
• the object of the present invention is therefore to provide a cathode block which is suitable, in particular, for use with an aluminum electrolysis cell, which not only has a low electrical resistivity and which is very readily wettable with molten aluminum, but which is also particularly resistant to wear due to high wear resistance characterized in the operation in a fused-salt electrolysis prevailing abrasive, chemical and thermal conditions, in particular at high currents of, for example, 600 kA.
• a cathode block for an aluminum electrolysis cell which is at least partially composed of a material which is obtainable by firing a mixture containing at least one carbon-containing material with a Maire and Mehring after a heat treatment at 2,800 ° C. from the middle Layer spacing c / 2 calculated graphitization degree of not more than 0.50 and at least one non-oxide ceramic contains.
• the cathode block according to the invention is preferably constructed from a base layer and a cover layer, wherein the at least one section which contains the abovementioned mixture is a constituent of the cover layer.
• this section can extend over the entire cover layer or the section represents only a part of this cover layer.
• the cathode block according to the invention can be used in particular even at high currents of, for example, 600 kA and has a long service life even under such operating conditions.
• the comparatively poor graphitizability of the carbon-containing material is also advantageous because it results in too high an electrical conductivity which is due to the cathode block alone Addition of non-oxide ceramics could be imparted within an acceptable range.
• the cathode block according to the invention due to the combined addition of comparatively poorly or not graphitierbarem carbon containing material, namely carbon-containing material with a Maire and Mehring after a heat treatment at 2,800 ° C from the average layer spacing c / 2 calculated degree of graphitization of not more than 0.50, as well as non-oxide ceramic to the material from which at least a portion of the cathode block is made, not only a low electrical resistivity and a good wettability with molten aluminum, but is characterized in particular by a high wear resistance over the abrasive, chemical and thermal conditions prevailing during operation in a fused-salt electrolysis, in particular even at high currents of, for example, 600 kA.
• carbon material is in particular a material containing more than 60% by weight, preferably more than 70% by weight, more preferably more than 80% by weight and most preferably more than 90% by weight of carbon understood, especially coke.
• the cathode block according to the invention is preferably a cathode block based on graphite, ie a cathode block which is formed by firing and subsequently graphitizing the magnet. tenals from which it is produced, is available. Due to the comparatively poor or even completely lacking graphitizability of the carbonaceous material according to the invention with a degree of graphitization of not more than 0.50 calculated according to Maire and Mehring after a heat treatment at 2,800 ° C.
• the at least one carbon-containing material having a graphitization degree of maximum 0.50 coke calculated according to Maire and Mehring after a heat treatment at 2,800 ° C from the average layer pitch c / 2 is particularly coke having an average layer spacing c / 2 of at least 0.339 nm determined by X-ray diffraction interference.
• Such coke has a suitably low graphitizability, in particular very good results being obtained with coke, which has a mean layer spacing c / determined by X-ray diffraction interference. 2 from 0.340 to 0.344 nm.
• particulate carbon material having a degree of graphitization of not more than 0.50 calculated according to Maire and Mehring after a heat treatment at 2,800 ° C. from the average layer spacing c / 2 is used, the specific BET surface area of the particles of the carbon material preferably being 10 to 40 m 2 / g and more preferably 20 to 30 m 2 / g.
• a preferred example of coke with a low graphitization capacity mentioned above is coke which is obtained as a by-product in the production of unsaturated hydrocarbons, in particular of acetylene and subsequently, regardless of the type of unsaturated hydrocarbon in whose production it is obtained, is referred to as Acetylenkoks.
• Acetylene coke which is obtainable from the crude oil fractions or steam cracking residues used in the quenching of reaction gas in the synthesis of unsaturated hydrocarbons, in particular acetylene, has proven particularly suitable for this purpose.
• the quench oil or carbon black mixture is passed to a coker heated to about 500.degree.
• the acetylene coke preferably has an average layer spacing c / 2 of at least 0.34 nm determined by X-ray diffraction interference, wherein the crystallite size in c-direction L c is preferably less than 20 nm and the crystallite size in a-direction L a is preferably less than 50 nm and more preferably less than 40 nm.
• the acetylene coke is present in the form of spherical particles having a grain size of greater than 0.2 mm and preferably greater than 0.5 mm.
• coke which can be used in addition to or as an alternative to acetylene coke is coke, which is made by fluid bed processes. With this method coke is obtained with spherical to ellipsoidal shape, which is constructed onion-shell-like.
• a still further preferred example of coke which may be used in addition to or as an alternative to the previously described coke and / or coke made by flexocrossing is a coke formed by delayed coke formation
• the particles of this coke have a spherical morphology it is preferred that this coke has an average layer spacing c / 2 of at least 0.339 nm determined by X-ray diffraction interference and that the crystallite size in the c-direction L c is less than 30 nm.
• the at least one carbon-containing material with a Maire and Mehring after a heat treatment at 2,800 ° C from the average layer spacing c / 2 calculated graphitization degree of 0.50 maximum consists of particles having a grain size of 0 , 2 mm to 3 mm and preferably from 0.5 mm to 2 mm.
• the mixture carbon-containing material with a calculated according to Maire and Mehring after a heat treatment at 2,800 ° C from the average layer spacing c / 2 graphitization degree of not more than 0.50, which consists of particles with a spherical morphology , ie spherical to ellipsoidal shape, is composed. Due to its high flowability, a carbon material consisting of such particles results in a material having a higher bulk density, which contributes to an increase in wear resistance.
• the particles of the carbon material have a length to diameter ratio of 1 to 5, more preferably 1 to 3. This is due to the fact that the flowability of the carbon material and thus the bulk density and wear resistance of the cathode block increases all the more, the more the shape of the particles approach an ideal spherical shape.
• the individual particles of the carbonaceous material having a degree of graphitization of not more than 0.50, calculated according to Maire and Mehring after a heat treatment at 2,800 ° C. from the average layer spacing c / 2, have an onion shell structure, in the sense of the present invention is understood to mean a multilayer construction in which an inner layer of particles with spherical to ellipsoidformiger shape is completely or at least partially covered by at least one intermediate layer and an outer layer.
• the non-oxidic ceramic is a non-oxide ceramic composed of at least one metal of the 4th to 6th subgroups and at least one element of the 3rd or 4th main group of the Periodic Table of the Elements.
• Such ceramics are titanium diboride, zirconium diboride, tantalum boride, titanium carbide, boron carbide, titanium carbonitride, silicon carbide, tungsten carbide, vanadium carbide, titanium nitride, boron nitride, silicon nitride and any chemical combinations and / or mixtures of two or more of the aforementioned compounds.
• the at least one non-oxide ceramic is titanium diboride and / or zirconium diboride, in particular titanium diboride.
• the at least one non-oxide ceramic contained in the cathode block has a monomodal particle size distribution, the average volume-weighted particle size determined by static light scattering in accordance with International Standard ISO 13320-1 (d3, see above) being from 10 to 20 ⁇ amounts.
• non-oxide ceramic having a monomodal particle size distribution defined above not only causes very good wettability of the surface of the cathode block with aluminum, but by combination with the at least one carbon-containing material according to Maire and Mehring after heat treatment at 2,800 ° C from the average layer spacing c / 2 calculated graphitization degree of 0.50 in particular also leads to a cathode block with excellent wear resistance.
• this effect is achieved in particular even with comparatively small amounts of added non-oxidic ceramic.
• a high concentration of non-oxide ceramic in the cathode block which leads to a brittle cathode block surface, can be dispensed with.
• non-oxide ceramic with a monomodal particle size distribution as defined above is also characterized by very good processability.
• the dusting tendency of such a non-oxide ceramic for example, when filling in a mixing container or during the transport of this ceramic-containing powder is sufficiently low and occurs, for example, when mixing at most a small agglomeration.
• such a powder containing this ceramic has a sufficiently high flowability and Rieselfä- ability, so that this can be promoted, for example, with a conventional conveying device to a mixing device.
• the at least one nonoxidic ceramic provided in the cathode block preferably has a monomodal particle size distribution, the average volume-weighted particle size (d3, 5 o) determined above being from 12 to 18 ⁇ m and more preferably from 14 to 16 m.
• the non-oxide ceramic contained in the cathode block may have a monomodal particle size distribution, wherein the average volume-weighted particle size (d3, 5 o) determined by static light scattering according to International Standard ISO 13320-1 is 3 to 10 ⁇ m and preferably 4 to 6 ⁇ amounts.
• the average volume-weighted particle size (d3, 5 o) determined by static light scattering according to International Standard ISO 13320-1 is 3 to 10 ⁇ m and preferably 4 to 6 ⁇ amounts.
• the at least one non-oxidic ceramic has a volume-weighted d3.90 particle size of from 20 to 40 ⁇ and preferably from 25 to 30 ⁇ as determined above.
• the non-oxide ceramic has such a d3, go value in combination with a previously defined d3, 5 o value.
• the non-oxidic titanium ceramic and more preferably titanium diboride.
• the non-oxide ceramic contained in the cathode block may have a volume-weighted d3, 90 particle size of from 10 to 20 ⁇ m, and preferably from 12 to 18 ⁇ m, as determined above.
• the non-oxide ceramic preferably has such a d3, go Value in combination with a previously defined d3, 5 o value.
• the non-oxidic ceramic has a volume-weighted d3, io particle size of from 2 to 7 ⁇ m, and preferably from 3 to 5 ⁇ m, as determined above.
• the non-oxide ceramic has such a d3, io value in combination with a previously defined d3, go value and / or d3, 5 o value.
• the non-oxide ceramic is preferably a non-oxide titanium ceramic, and more preferably titanium diboride.
• the non-oxide ceramic contained in the cathode block may have a volume-weighted d3, io particle size of from 1 to 3 ⁇ m and preferably from 1 to 2 ⁇ m, as determined above.
• the non-oxide ceramic has such a d3, io value in combination with a previously defined d3, go value and / or d3, 5 o value.
• the non-oxide ceramic in particular a non-oxidic titanium ceramic and more preferably titanium diboride, has a particle size distribution which is determined by a span value calculated according to the following equation:
• the non-oxide ceramic has such a span value in combination with a previously defined d3, go value and / or d3, 5 o value and / or d3, io value.
• the sum of the amount of carbon-containing material with a Maire and Mehring after a heat treatment at 2,800 ° C from the average layer spacing c / 2 calculated graphitization of maxi times 0.50 and the amount of non-oxide ceramic in the mixture, from which the material from which the cathode block is at least partially assembled is obtained by firing and preferably graphitizing, 2 to 70 wt .-%, preferably from 20 to 65 wt .-% and particularly preferably 25 to 55 wt .-%.
• the cathode block according to the invention has a particularly good resistance to wear in relation to the abrasive, chemical and thermal conditions prevailing during operation in a fused-salt electrolysis, in particular even at high currents of, for example, 600 kA, at the same time low specific electrical resistance and a good Wettability with aluminum melt.
• the proportion of non-oxide ceramic is 20 to 95 wt .-%, particularly preferably 50 to 75 wt .-%, based on the sum of non-oxide ceramic and carbon-containing material with a according to Maire and Mehring a heat treatment at 2,800 ° C calculated from the average layer spacing c / 2 graphitization degree of a maximum of 0.50.
• the mixture from which the Material from which the cathode block is at least partially assembled is obtained by firing and preferably graphitizing, preferably at least one carbon-containing material having a comparatively good graphitization, namely at least one carbon with a Maire and Mehring after a heat treatment at 2,800 ° C from the average layer spacing c / 2 calculated graphitization degree of more than 0.50, preferably of at least 0.60, more preferably of at least 0.65 and most preferably of at least 0.70.
• This carbon forms in the graphitization preferably carried out after firing a graphite structure, which then contributes significantly to the excellent electrical and thermal conductivity of the cathode block according to the invention.
• the mixture from which the material of which the cathode block is at least partially composed is obtained by firing and preferably graphitizing, preferably at least one binder.
• the binder may, for example, be pitch, in particular coal tar pitch and / or petroleum pitch. pitch, tar, bitumen, phenolic resin or furan resin. A particularly preferred binder is pitch.
• the material from which the cathode block is at least partially assembled is obtainable by firing and preferably subsequently graphitizing a mixture which contains:
• the sum of the amount of carbon-containing material having a degree of graphitization of not more than 0.50 calculated from Maire and Mehring after a heat treatment at 2,800 ° C. from the average layer spacing c / 2 and the amount of non-oxide ceramic is preferably from 5 to 70% by weight and the sum of the individual constituents is 100% by weight.
• the material from which the cathode block is at least partially assembled is obtainable by firing and preferably subsequently graphitizing a mixture which contains:
• the material of which the cathode block is at least partially assembled is obtainable by firing and then graphitizing the mixture described above. It is preferred that the graphitization of the mixture at a temperature of more than 1 .800 to 3,000 ° C, preferably from 2,000 to 3,000 ° C and more preferably from 2,200 to 2,700 ° C.
• the cathode block preferably comprises a base layer and a cover layer, wherein the cover layer is at least partially composed of the material which is obtainable by firing and preferably subsequently graphitizing the mixture described above.
• the cover layer is the layer which is exposed to the aluminum melt during operation of the electrolysis cell.
• the thickness of the cover layer is 1 to 50%, preferably 5 to 40%, more preferably 10 to 30% and most preferably 15 to 25% of the total height of the cathode block.
• the base layer consists of graphitized, graphitic and / or graphitizable materials in order to achieve a high electrical and thermal conductivity.
• the base layer is from at least 80% by weight, more preferably at least 90% by weight, most preferably at least 95% by weight, further preferably at least 99% by weight and most preferably entirely from graphite and binder or their carbonation and / or graphitization product.
• the cover layer may include a plurality of sections, with two or more of the sections being composed of different materials, respectively.
• each surface area of the cathode block can be tailored to the desired wear resistance, electrical conductivity, thermal conductivity and wettability with aluminum.
• particular account can be taken of the fact that individual surface portions of the cathode block are subjected to higher wear than others in fused-salt electrolysis, so that specifically those surface sections which are subject to particularly high wear are composed of a material containing a corresponding amount of carbon with a graphitization degree of not more than 0.50 calculated according to Maire and Mehring after a heat treatment at 2,800 ° C.
• the at least two sections are composed of different materials, each being obtainable by firing a mixture comprising at least one carbonaceous material having a Maire and Mehring heat treatment at 2,800 ° C average layer spacing c / 2 calculated graphitization degree of not more than 0.50 and contains at least one non-oxide ceramic.
• the cathode block according to the invention is not limited with regard to the number of different sections in the cover layer.
• the cover layer of the cathode block according to the invention comprises 3 to 7, preferably 3 to 5, particularly preferably 3 to 4, and most preferably 3 different sections, wherein preferably one or two of the sections each consist of one material which is obtainable by firing a mixture which contains at least one carbon-containing material having a degree of graphitization of not more than 0.50 and calculated according to Maire and Mehring after a heat treatment at 2,800 ° C. from the average layer spacing c / 2 contains non-oxidic ceramic.
• a further subject of the present invention is a method for producing a cathode block according to at least one of the preceding claims, which comprises the following steps:
• a mixture which contains:
• the sum of the amount of carbon-containing material having a degree of graphitization of not more than 0.50 calculated from Maire and Mehring after a heat treatment at 2,800 ° C. from the average layer spacing c / 2 and the amount of non-oxide ceramic is preferably from 20 to 65% by weight and the sum of the individual constituents is 100% by weight.
• the sum of the amount of carbon-containing material with a Maire and Mehring after a heat treatment at 2,800 ° C from the average layer spacing c / 2 calculated graphitization degree of not more than 0.40 and the amount of non-oxide ceramic is preferably from 30 to 50% by weight and the sum of the individual constituents is 100% by weight.
• the mixture produced in process step a) is applied by a shaking method to a second mixture, which is preferred
• step b) wherein the sum of the individual constituents is 100% by weight, and the total mixture thus produced in step b) is formed into a cathode block, the second mixture forming the base layer and the other mixture forming the cover layer of the cathode block before the cathode block is burned in the process step c) and then preferably graphitized.
• the firing in process step c) preferably takes place at a temperature of from 600 to less than 1, 500 ° C., preferably from 800 to 1, 200 ° C., and particularly preferably from 900 to 1, 100 ° C.
• Another object of the present invention is a cathode containing at least one cathode block described above. Furthermore, the present invention relates to the use of a previously described cathode block or a previously described cathode for performing a fused-salt electrolysis for the production of metal, preferably for the production of aluminum.
• Figure 1 is a schematic perspective view of a cathode block according to a first embodiment of the present invention.
• Figure 2 is a schematic perspective view of a cathode block according to a second embodiment of the present invention.
• the cathode block 10 consists of a lower base layer 12 and an overlying and thus firmly bonded cover layer 14. The interface between the base layer 12 and the cover layer 14 is planar. While the base layer 12 of the cathode block 10 has a graphite material structure, the cover layer 14 is composed of an acetylene coke and titanium diboride-containing graphite composite.
• the cathode block 10 has a length of 3,100 mm, a width of 420 mm and a height of 400 mm, wherein the base layer 12 has a height of 260 mm and the cover simply 14 has a height of 140 mm. Finally, the cathode block 10 comprises on its underside a groove 16 with a rectangular, namely substantially rectangular cross-section.
• a cathode for an aluminum electrolytic cell is assembled, wherein in each of the grooves 16, a bus bar (not shown) made of steel with a likewise rectangular or substantially rectangular cross section is used.
• the space between the busbar and the groove 16 delimiting walls is poured with cast iron (not shown), whereby the busbar is connected to the groove 16 delimiting walls.
• the cathode block 10 shown in Fig. 2 according to a second embodiment of the present invention differs from that shown in Fig. 1 in that the cover layer 14 consists of three different sections 18, 18 ', 18 " , 18 "are each composed of the same material, which is different from the material of which the portion 18 'is composed, as well as the material of which the base layer 12 is composed.
• sections 18, 18 " are composed of a 20 wt% acetylene coke and 20 wt% titanium diboride graphite composite
• section 18 ' is comprised of a 10 wt% acetylene coke and 30 wt% titanium diboride
• the individual surface portions of the cover layer 14 are adapted such that the portions 18, 18 ', 18 "of the cathode block 10 which are subjected to higher wear in fused-salt electrolysis than others, have a correspondingly higher wear resistance.
• a cathode block 10 as shown in FIG. 1 was produced by filling a mixture A forming the base layer 12 and a mixture B forming the cover layer 14 into a correspondingly dimensioned vibrating mold.
• the mixture A was composed as follows:
• mixture B was composed as follows:

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrolytic Production Of Metals (AREA)
• Inert Electrodes (AREA)
• Battery Electrode And Active Subsutance (AREA)

Priority Applications (6)

Applications Claiming Priority (2)

Publications (1)

Family

ID=50073212

Family Applications (1)

Country Status (8)

Families Citing this family (3)

Citations (6)

Family Cites Families (7)

• 2013
  • 2013-02-14 DE DE201310202437 patent/DE102013202437A1/de not_active Withdrawn
• 2014
  • 2014-02-12 RU RU2015138609A patent/RU2015138609A/ru not_active Application Discontinuation
  • 2014-02-12 UA UAA201508810A patent/UA115170C2/uk unknown
  • 2014-02-12 CA CA2900418A patent/CA2900418C/en not_active Expired - Fee Related
  • 2014-02-12 EP EP14703885.5A patent/EP2956573A1/de not_active Withdrawn
  • 2014-02-12 CN CN201480008980.8A patent/CN105026619A/zh active Pending
  • 2014-02-12 JP JP2015557413A patent/JP2016514204A/ja not_active Ceased
  • 2014-02-12 WO PCT/EP2014/052731 patent/WO2014124970A1/de not_active Ceased

Patent Citations (6)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events