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US3666654A - Furnaces with bipolar electrodes for the production of metals, particularly aluminum, through electrolysis of molten salts, equipped with auxiliary heating facilities - Google Patents

Furnaces with bipolar electrodes for the production of metals, particularly aluminum, through electrolysis of molten salts, equipped with auxiliary heating facilities Download PDF

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Publication number
US3666654A
US3666654A US859790A US3666654DA US3666654A US 3666654 A US3666654 A US 3666654A US 859790 A US859790 A US 859790A US 3666654D A US3666654D A US 3666654DA US 3666654 A US3666654 A US 3666654A
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furnace
resistors
electrolysis
aluminum
graphite
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Expired - Lifetime
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US859790A
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English (en)
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Giorgio Olah De Garab
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    • 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

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  • ABSTRACT [30] Foreign Application Priority Data A furnace with bipolar electrodes for the production of metals, particularly aluminum, through the electrolysis of mo]- Sept. 24, ten Salt baths. Electrical heating resistors selected from g phite fabrics, tapes and felts, are placed in the cold" zones of [52] US. Cl. ..204/243 R, 204/274 said furnace [51] Int. Cl. .C22d 3/02, BOlk 3/00 [58] Field of Search ..204/243-247, 274 7 Claims, 2 Drawing Figures e 7 5 5 7 j A 5 7 9 7%?
  • the present invention concerns equipment for heating the bottom and/or the walls of furnaces for the production of metals, and particularly of aluminum, through electrolysis in molten salt baths. It is known that conventional furnaces for producing aluminum through the so-called igneous electrolysis require no external heat. Consequently there is no problemfor their heating.
  • zones are to be considered as cold zones or, more properly, zones too cold to keep the aluminum gathered in the collecting pit or pits in sufi'iciently flowable condition and to keep the molten salt layers neighboring said molten aluminum in liquid and fluid state without any exceptional thermal insulation or supply of external heat.
  • cold zones are meant zones which have a temperature equal to or lower than the temperature at which a bath, having a given composition, starts solidifying, that is at a temperature at which the bath tends to thicken and/or solidify.
  • cryolite baths which are commonly used for the electrolytic aluminum production and which have specific gravity lower or higher than the molten aluminum, according to whether they are in liquid, solid, semi-solid state, the zones at a temperature between 800 and 900 C or lower, can be considered cold as above meant.
  • continuous aluminum layers in this case, can form on the furnace bottom, correspondingly with two or several bipolar electrodes, in consequence of which a current by-pass or shunt occurs through the same aluminum layers.
  • the present invention obviates the above specified inconveniences by supplying with additional heat the bottom and/or the walls of the furnace of the type as above and intended to produce aluminum or other metals by means of resistors chemically inert towards the electrolytic baths, having practically neglectable overall dimensions and practically unlimited flexibility, which allows their adjustment to the sometimes heavy deformation sufiered by the materials of the walls and the bottom of the furnace pot.
  • electrical resistors to embody in the furnace structures, corresponding to the zones where the additional heat is required according to the present invention, particularly fabrics, tapes or felts made of graphite fibers, sandwiched between refractory material layers, are foreseen.
  • Graphite fabrics, tapes and felts are known commercial products and consist of woven or felted filaments made of graphite with 99.9 percent or higher purity, obtained through heat treatment of suitably selected and prepared organic fibers at temperatures reaching about 2,700 C.
  • graphite fabrics, tapes or felts according to the present invention an important technical problem and remarkable technical prejudices have been now overcome.
  • FIG. 1 shows a longitudinal section of a furnace of the type described in de Varda et al. patent application Ser. No. 809,852, filed Mar. 24, 1969, provided with the heating equipment according to the present invention
  • FIG. 2 shows a cross section taken along line A-A in FIG. 1.
  • a refractory material pot l with double flight stepped down bottom having in the center a pit 2 where liquid aluminum 4, produced by the electrolysis of molten salts 6 in cells 7 formed by bipolar electrodes 5 and terminal electrodes 8, 9 and falling from overflow edges 3, collects.
  • the bottom of this furnace has a special refractory lining 10.
  • This special refractory can be, for example, silicon nitride bonded silicon carbide.
  • the bottom of pit 2 has two thicker layers 11 and 12 made of refractory material, with a thin tape of fibrous graphite 13, approximately as wide as pit 2, interposed between the thicker layers.
  • the direct or alternating current feeding is shown at 14 in FIG. 2.
  • a temperature ranging from 920 to 930 C and sufficient to keep both the aluminum as well as the neighboring molten salts in molten and. fluid state is thus obtained within pit 2 wherein aluminum collects.
  • the pit 2 is in the less thermally insulated zone of the furnace, which zone is the thinnest and nearest to the external shell of the furnace. This is important to prevent the danger of bath thickening or freezing (i.e. solidification), which consequently causes clogs in the tapping system for the produced aluminum.
  • the tapping system has been omitted because of the schematic nature of the drawing.
  • the heating resistors to be used in conformity with this invention consist of fibrous graphite in the form of fabrics, tapes or felts of commercial type.
  • the resistors can for example be high purity graphite fabric, having a percentage of ashes of about 0.04 percent, woven with 1,440 filaments y'arn, each filament having a diameter of 8 microns, the weight of the fabric being'2-3 g/m
  • the electrical features are functions of known parameters, i.e. the characteristics of the graphite fabric and the characteristics of the furnace as well as the electrolysis bath.
  • the power taken may indicatively, but not limitatively, amount to about 6 kW/30 dm, i.e.
  • the installation consists in laying the graphite fabric, tape or felt on the refractory layer or bricks duringthe erection of the refractory pot, thereon superimposing then the other refractory layer and supplying the suitable electric connections.
  • a furnace provided with two 30 cm wide pits it is for example suitable to insert two tapes 13 (one for every pit) between refractory layers 11 and '12, connecting them electrically in series, each tape consisting of three graphite fabric layers superimposed one upon another. This is only an example of absolutely non-limiting nature.
  • one or several layers of some millimeters thickness, of silicon carbide of fine grit quality can be advantageously inserted in order to prevent molten aluminum coming from the pit from seeping downwards and consequently making contact with the disclosed resistor.
  • silicon carbide grit to prevent the escaping of aluminum is described in Italian Pat. No. 790,333.
  • the paste shall in this case be smeared between the graphite fabric and the carbon blocks, to improve the electrical contact.
  • Graphite, pitch and tar can be its chemical base; an example of suitable compound, always exemplifying but non-limiting, is:

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  • 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)
  • Accessories For Mixers (AREA)
US859790A 1968-09-24 1969-09-22 Furnaces with bipolar electrodes for the production of metals, particularly aluminum, through electrolysis of molten salts, equipped with auxiliary heating facilities Expired - Lifetime US3666654A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
IT2158468 1968-09-24

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US3666654A true US3666654A (en) 1972-05-30

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US859790A Expired - Lifetime US3666654A (en) 1968-09-24 1969-09-22 Furnaces with bipolar electrodes for the production of metals, particularly aluminum, through electrolysis of molten salts, equipped with auxiliary heating facilities

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US (1) US3666654A (xx)
BR (1) BR6912694D0 (xx)
DE (1) DE1947880A1 (xx)
ES (1) ES371776A1 (xx)
FR (1) FR2018739A1 (xx)
NO (1) NO122559B (xx)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4049530A (en) * 1974-09-30 1977-09-20 Sony Corporation Electrolyzer
US4093524A (en) * 1976-12-10 1978-06-06 Kaiser Aluminum & Chemical Corporation Bonding of refractory hard metal
US5876584A (en) * 1995-05-26 1999-03-02 Saint-Gobain Industrial Ceramics, Inc. Method of producing aluminum
CN103774181A (zh) * 2012-10-23 2014-05-07 贵阳铝镁设计研究院有限公司 防侵蚀与抑制水平电流的阴极钢棒结构

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2773825A (en) * 1944-04-28 1956-12-11 Frank A Newcombe Electrolysis apparatus
US3271277A (en) * 1962-04-30 1966-09-06 Leonard F Yntema Refractory metal production
US3382166A (en) * 1963-05-29 1968-05-07 Montedison Spa Method and apparatus for starting up multicell electrolytic furnaces for aluminum production
US3514520A (en) * 1967-02-01 1970-05-26 Montedison Spa Linings of electrolysis,remelting,and similar furnaces,containing molten metals,alone or together with molten salts

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2773825A (en) * 1944-04-28 1956-12-11 Frank A Newcombe Electrolysis apparatus
US3271277A (en) * 1962-04-30 1966-09-06 Leonard F Yntema Refractory metal production
US3382166A (en) * 1963-05-29 1968-05-07 Montedison Spa Method and apparatus for starting up multicell electrolytic furnaces for aluminum production
US3514520A (en) * 1967-02-01 1970-05-26 Montedison Spa Linings of electrolysis,remelting,and similar furnaces,containing molten metals,alone or together with molten salts

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4049530A (en) * 1974-09-30 1977-09-20 Sony Corporation Electrolyzer
US4093524A (en) * 1976-12-10 1978-06-06 Kaiser Aluminum & Chemical Corporation Bonding of refractory hard metal
US5876584A (en) * 1995-05-26 1999-03-02 Saint-Gobain Industrial Ceramics, Inc. Method of producing aluminum
CN103774181A (zh) * 2012-10-23 2014-05-07 贵阳铝镁设计研究院有限公司 防侵蚀与抑制水平电流的阴极钢棒结构

Also Published As

Publication number Publication date
BR6912694D0 (pt) 1973-02-08
NO122559B (xx) 1971-07-12
FR2018739A1 (xx) 1970-06-26
ES371776A1 (es) 1971-11-16
DE1947880A1 (de) 1970-04-23

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