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 method of manufacturing a cathode block for an aluminum electrolytic cell and a cathode block.
• One known method of producing metallic aluminum is the Hall-Heroult process.
• the bottom of an electro-lyse cell is formed by a cathode surface consisting of individual cathode blocks. From below, the cathodes are contacted via steel ingots, which are placed in corresponding elongated recesses in the bottom of the cathode blocks.
• Cathode blocks are conventionally made by mixing coke with carbonaceous particles such as anthracite, carbon or graphite, compacting and carbonizing.
• carbonaceous particles such as anthracite, carbon or graphite
• a graphitization step follows at higher temperatures where the carbonaceous particles and coke are at least partially converted to graphite.
• TiB 2 is introduced into an upper layer of a cathode block.
• a top layer which is a TiB 2 graphite composite
• TiB 2 and similar hard ceramic materials cause an improvement in the wettability of the cathode in the graphitized state and thus a better energy efficiency of the electrolysis process.
• Ceramic hard materials can also increase the density and increase the hardness of cathodes, which results in better wear resistance, in particular compared with aluminum and cryolite melts. Hard materials are also referred to as RHM (refractory hard material).
• the object of the present invention is therefore to provide a simple process for producing a TiB 2 graphite composite cathode, which is readily wettable to aluminum melts and has good wear properties, and a corresponding cathode block.
• the object is achieved by a method according to claim 1.
• a method for producing a cathode block according to the invention comprises the steps of providing starting materials comprising coke and a hard material powder such as TiB 2 , and optionally another carbonaceous material, mixing the starting materials, forming a cathode block, carbonizing and graphitizing, and cooling characterized in that the step of graphitizing at temperatures between 2300 and 3000 ° C, in particular between 2400 and 2900 ° C is performed.
• the graphitization step is carried out at an average heating rate between 90 K / h and 200 K / h.
• the graphitization step is carried out at an average heating rate between 90 K / h and 200 K / h.
• the graphitization step is carried out at an average heating rate between 90 K / h and 200 K / h.
• a duration of the temperature treatment may be 10 to 28 hours up to the time of commencement of the cooling.
• graphitized carbon forms the entire cathode block. This has the advantage that a single green mass composition is necessary, and accordingly only a single mixing step.
• the cathode block may have at least two layers, wherein the composite layer forms the second layer of the cathode block. This second layer is in direct contact with the melt of the electrolysis cell.
• the cathode block preferably has at least one further layer (referred to below as the first layer) which has less hard material powder than the upper layer or no hard material powder. This can reduce the amount of expensive hard material powder used.
• the first layer is not in direct contact with the aluminum melt and therefore does not have to have good wettability and wear resistance.
• the second layer may have a height which is 10 to 50%, in particular 15 to 45%, of the total height of the cathode block.
• a small height of the second layer such as about 20%, may be advantageous because a small amount of expensive hard material is needed.
• a larger height of the second layer, such as 40% may be advantageous since a layer having a hard material has high wear resistance. The greater the height of this highly wear-resistant material relative to the overall height of the cathode block, the higher the wear resistance of the entire cathode block.
• the coke comprises two types of coke, which have a different volume change behavior during carbonation and / or graphitization and / or cooling.
• the carbon content of the cathode block preferably condenses to a bulk density of more than 1.68 g / cm 3 , in particular of more than 1.71 g / cm 3 , in particular up to 1.75 g / cm 3 .
• a higher apparent density advantageously contributes to a longer service life. This may be due to the fact that more mass is present per unit volume of a cathode block, resulting in a given mass removal per unit time to a higher residual mass after a given removal period. On the other hand, it can be assumed that a higher bulk density with a corresponding corresponding lower porosity hampers an infiltration of electrolyte, which acts as a corrosive medium.
• the second layer always has a high apparent density of, for example, more than 1.80 g / cm 3 , because of the addition of hard material after graphitization, it is advantageous if the first layer also has a high density after graphitization Bulk density of the invention over 1.68 g / cm 3 .
• the small differences in thermal expansion behavior and bulk densities during the heat treatment steps reduce production times and reject rates of the cathode blocks. Furthermore, therefore, advantageously the resistance to thermal stresses and resulting damage in the application is also increased.
• the two types of coke comprise a first type of coke and a second type of coke, the first type of coke having a greater shrinkage and / or expansion during the carbonizing and / or graphitizing and / or cooling than the second type of coke.
• the increased shrinkage and / or expansion is an advantageous embodiment of a different volume change behavior, which is probably particularly well suited to lead to a greater compression than when mixed cokes that have the same shrinkage and / or expansion.
• the stronger shrinkage and / or expansion refers to any temperature range.
• a different volume change behavior may be present during cooling.
• the shrinkage and / or expansion of the first type of coke during carbonation and / or graphitization and / or cooling based on the volume is at least 10% higher than that of the second coke variety, in particular at least 25% higher, in particular at least 50% higher.
• the shrinkage and / or expansion of the first type of coke during carbonation and / or graphitization and / or cooling based on the volume at least 100% higher than that of the second coke, in particular at least 200% higher, in particular at least 300% higher.
• the first type of coke undergoes shrinkage the second coke variety, however, an expansion in the same temperature interval, is detected by the inventive method.
• a 300% higher shrinkage and / or expansion also includes the case that the second type of coke shrinks by 1, 0 vol .-%, the first Koksorte, however, by 2.0 vol .-% expands.
• the second type of coke may have a greater shrinkage and / or expansion, as described above for the first coke variety.
• At least one of the two types of coke is preferably a petroleum or coal-tar coke.
• the weight percent of the second coke variety in the total amount of coke is between 50% and 90%.
• the different volume change behavior of the first and second types of coke has a particularly good effect on compression during carbonization and / or graphitization and / or cooling.
• Conceivable advantageous quantitative ranges of the second type of coke can be 50 to 60%, but also 60 to 80%, and 80 to 90%.
• At least one carbonaceous material and / or pitch and / or additives are added to the coke. This can be advantageous both with regard to the processability of the coke and the subsequent properties of the cathode block produced.
• the further carbonaceous material contains graphite-containing material;
• the further carbonaceous material is graphite-containing material, such as graphite.
• the graphite may be synthetic and / or natural be phit.
• the carbonaceous material is advantageously 1 to 40% by weight, in particular from 5 to 30% by weight, based on the total amount of coke and carbonaceous material.
• pitch in addition to the amount of coke and optionally carbonaceous material, which represents a total of 100 wt .-%, pitch in amounts of 5 to 40 wt .-%, in particular 15 to 30 wt .-% (based on 100 wt .-% the entire green mix). Pitch acts as a binder and serves to create a dimensionally stable body during carbonation.
• Advantageous additives may be oil, such as press auxiliary oil, or stearic acid. These facilitate mixing of the coke and optionally the other components.
• the coke comprises at least in one of the two layers, ie in the first and / or the second layer, two types of coke, which have a different volume change behavior during carbonation and / or graphitization and / or cooling.
• This can presumably lead to a densification of the resulting graphite of more than 1.70 g / cm 3 , in particular more than 1.71 g / cm 3 .
• both layers or one of them can be used
• Layers are produced according to the invention with two different types of coke.
• only the first layer can be produced according to the invention with two types of coke, while the second layer is produced with only one type of coke, but additionally contains TiB 2 as hard material.
• the expansion behavior of the two layers are adjusted, which can advantageously increase the life of the layers.
• the multilayer block has more than two layers.
• one can any number of layers are produced according to the invention each with two types of coke different volume change behavior.
• a first and a second coke are milled separately, separated into grain size fractions and mixed together with pitch together with, for example, 15 to 25 wt%, such as 20 wt% TiB 2 .
• the weight fraction of the first coke may be, for example, 10 to 20% by weight or 40 to 45% by weight of the total amount of coke.
• the mixture is filled into a mold that largely corresponds to the later shape of the cathode blocks and vibration-compressed or block-pressed.
• the resulting green body is heated to a final temperature in a range of 2300 to 3000 ° C, such as 2600 or 2800 ° C, with a graphitization step, and then cooled.
• the resulting cathode block has a bulk density of 1.68 g / cm 3 and a very high resistance to wear compared to liquid aluminum and cryolite. Due to the average degree of graphitization achieved, thermal and electrical conductivity are high. A loss of TiB 2 could not be determined by X-ray diffractometry. The wettability of the cathode block by liquid aluminum is very good.
• a single coke variety is used.
• the wetting behavior of the resulting cathode block is largely the same as in the first embodiment.
• the thermal and electrical conductivity are similar to those in the first embodiment.
• graphite powder or carbon particles are added to the coke mixture.

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)

Priority Applications (6)

Applications Claiming Priority (2)

Publications (1)

Family

ID=44546387

Family Applications (1)

Country Status (9)

Cited By (1)

Families Citing this family (1)

Citations (4)

Family Cites Families (6)

• 2010
  • 2010-07-29 DE DE102010038665A patent/DE102010038665A1/de not_active Withdrawn
• 2011
  • 2011-07-29 EP EP11738711.8A patent/EP2598674B1/de active Active
  • 2011-07-29 RU RU2013108752/02A patent/RU2556192C2/ru active
  • 2011-07-29 JP JP2013521156A patent/JP5631492B2/ja active Active
  • 2011-07-29 WO PCT/EP2011/063077 patent/WO2012013769A1/de active Application Filing
  • 2011-07-29 CN CN2011800374644A patent/CN103069053A/zh active Pending
  • 2011-07-29 UA UAA201302501A patent/UA109020C2/uk unknown
  • 2011-07-29 NO NO11738711A patent/NO2598674T3/no unknown
  • 2011-07-29 CA CA2805562A patent/CA2805562C/en active Active

Patent Citations (4)

Also Published As

Similar Documents

Legal Events