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
  • C25C3/12—Anodes
  • C25C3/125—Anodes based on carbon
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/042—Electrodes formed of a single material
  • C25B11/043—Carbon, e.g. diamond or graphene
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/042—Electrodes formed of a single material
  • C25B11/043—Carbon, e.g. diamond or graphene
  • C25B11/044—Impregnation of carbon
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B7/00—Heating by electric discharge
  • H05B7/02—Details
  • H05B7/06—Electrodes
  • H05B7/08—Electrodes non-consumable
  • H05B7/085—Electrodes non-consumable mainly consisting of carbon

Definitions

• This application relates to the production of carbon electrodes for the electrolysis of molten salts. More particularly, it relates to the production of carbon anodes used in the electrolytic production of aluminum metal. Our invention is of particular importance when the anode is of the self-baking or so-called Soederberg type, but it is also useful with other types of electrodes such as the so-called prebaked types.
• the carbon anode serves for introducing the electric current into the bath and at the same time acts as a reductant.
• the oxygen liberated by electrolysis at the anode reacts with the carbon of the anode to form a mixture of carbon dioxide and carbon monoxide which leaves the furnace as the anode gas.
• the consumption of anode carbon is fairly high and amounts in commercial operation to 50 to 60% of the weight of the produced aluminum metal.
• the carbon anode consists of pitch coke, petroleum coke, purified anthracite or the like known as the dry material of the electrode. This dry material is crushed and screened to a suitable size and then mixed with a binder such as coal tar, coal tar pitch or the like. The resulting mixture is then shaped and carbonized to transform the binder into coke thus producing a coherent carbon anode.
• a binder such as coal tar, coal tar pitch or the like.
• the mixture of dry material and binder is compressed to shape and then carbonized in a special furnace made for that purpose.
• Such electrodes are known as prebaked electrodes.
• the mixture of dry material and paste is used for forming continuous electrodes which are self-baking or Soederberg electrodes.
• the present invention is of particular value in connection with the latter type of electrodes.
• the first of these characteristics is the behavior of the coke when the so-called anode effect occurs. It is well recognized that as the quantity of alumina dissolved in the bath is regradually reached at which the bath does not adequately wet the electrode and the voltage necessary to cause the current to have found that in electrodes now in use the anode eifect occurs more rapidly with the particles of coke introduced into the electrode as the dry material than with the coke resulting from the baking of the binder. Thus there is a period when virtually all of the activity of the electrode is working through the binder coke due to the fact that the bath is no longer wetting the bound particles. This tends to cause the binder coke to be eaten away more rapidly than the other particles, with the result that dust is released.
• the second characteristic has to do with the difference in anodic electro-chemical over-voltage between the two types of coke.
• the overvoltage in a bath of this type means the voltage over and above the theoretical necessary to produce the desired electrolysis.
• a greater over-voltage is required with the usual particles of coke introduced as dry material than with the coke resulting from baking of the binder. Again, this causes more rapid disintegration of the binder coke.
• the third. characteristic i the difference between thet wocokesin ,-.reactiv ity toward carbon dioxide.
• the oxygen is disassociated from the alumina in the bath it tends to form carbon dioxide with the carbon of the electrode mass and this carbon dioxide tends to act on additional quantities of carbon present to form carbon monoxide.
• jls a d ifierence in the reactivity toward carbon dioxide .of the coke resulting from the dry material and the coke resulting from the baking of the binder.
• This difference in reactivity ordinarily is quite appreciable, with the binder coke showing the greater reactivity so that again it tends to be eaten away more rapidly.
• the coke used as the dry material is calcined at a temperature or" 1400" C. to 1500 C. and it must be remembered that in producing aluminum :by the Soederberg system of continuous electrodes the temperature at which the binder i c lcined n ver ex ds 950 C. As a -I$ t the e i a great difieren e in the charac e sti of e t yp s of .coke found at the operating surfaces of the electrode. Even .the case of prebaked electrodes the calcining temperature of the finished electrode does not exceed about 1300 C. so that in this case also there is a marked difference in the coke characteristics.
• a known volume of the coke to be tested is crushed and screened between sieves of values of and 35 on the Iyler screen scale.
• This coke is placed inside a closed silica tube (the one which we employed was 1'7 mm. inside diameter), the coke resting on a perforated disk of alloy metal.
• the tube is heated to a temperature of 950 C. in a vertical tube furnace, the temperature being measured by a thermocouple in the center of the sample.
• a stream of pure carbon dioxide is passed through the bed of coke at a known rate. Eor example 100 mg. cf 00.2 are passed through in 5 minutes. This rate of flow of CO2 going into the tube we call a.
• the electrode ordinarily consists of pitch coke, petroleum coke .or purified anthracite coal.
• the binders are made of such materials as coal tar, coal tar pitch or the like all of which may be classified as bituminous pitches.
• the desired material for the dry coke is calcined at a temperature of between 1000 C. and 1200 C.
• a sample of binder material is then calcined at the temperature at which the electrode is to be formed, which in the case of a continuous electrode will be 950 C.
• the relative reactivities of the tWo cokes are then tested. If the coke from the dry material has a reactivity of at least 75% of the test sample of binder material coke, then the selected binder and coke can be combined and used in the usual manner.
• Paste made in this manner is a great improvement on the pastes now being used and when these instructions are followed, it will be found that the resulting electrode will have an appreciably greater life than those heretofore formed and will result in much less carbon dust being formed in the electrode bath.
• a method of preparing miXes for use in electrodes which comprises selecting bituminous pitch as a binder material, carbonizing a sample of such binder material at approximately the temperature at which the electrode is to be carbonized, testing the reactivity of such sample to CO2 as herein defined, calcining dry material selected from the group consisting of pitch coke, petroleum coke and purified anthracite at a temperature below 1200 C. and at a temperature low enough so that the reactivity thereof to CO2 as herein defined is at least 75% of the reactivity of the test sample of binder material and combining such dry material in powdered form with the binder material.
• a method of preparing so-called paste for use in electrodes which comprises combining together bituminous pitch as binder material and dry pulverulent carbonaceous material selected from the group consisting of pitch coke, petroleum coke and purified anthracite, such dry material having been calcined at a temperature not in excess of 1200 C. and having a reactivity to CO2 as herein defined equal to at least 75% of the reactivity to CO2 of a sample of the binder material carbonized at 950 C.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Electrolytic Production Of Metals (AREA)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=19904601

Family Applications (1)

Country Status (8)

Cited By (15)

Families Citing this family (1)

Citations (4)

• 1949
  • 1949-09-27 CH CH280174D patent/CH280174A/de unknown
  • 1949-09-28 BE BE491391D patent/BE491391A/xx unknown
  • 1949-10-03 SE SE856449A patent/SE137425C1/sv unknown
  • 1949-10-07 AT AT169326D patent/AT169326B/de active
  • 1949-10-11 FR FR997122D patent/FR997122A/fr not_active Expired
  • 1949-10-21 DE DEE79A patent/DE840921C/de not_active Expired
  • 1949-10-31 GB GB27810/49A patent/GB687146A/en not_active Expired
  • 1949-11-18 US US128252A patent/US2653878A/en not_active Expired - Lifetime

Patent Citations (4)

Also Published As

Similar Documents