US3405043A - Method of producing silicon and electrolytic cell therefor - Google Patents

Method of producing silicon and electrolytic cell therefor Download PDF

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Publication number
US3405043A
US3405043A US476022A US47602265A US3405043A US 3405043 A US3405043 A US 3405043A US 476022 A US476022 A US 476022A US 47602265 A US47602265 A US 47602265A US 3405043 A US3405043 A US 3405043A
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silica
electrolyte
cell
silicon
cavity
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US476022A
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English (en)
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Barakat Dlawar
Keller Hans
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General Trustee Co Inc
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General Trustee Co Inc
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • 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
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/33—Silicon
    • 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
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof

Definitions

  • silicon can be obtained by electrolysis of a fused or molten bath of cryolite containing silica.
  • the purity of the silicon is dependent to a large extent upon the purity of the electrolytic bath or electrolyte.
  • Electrolytic reduction and deposition must be carried out above the melting point of cryolite, e.g., in a range between about 970 C. and 1050" C. Due to the high temperature involved, it is difficult to find materials for the construction of a suitable electrolytic cell which do not react with and contaminate the molten cryolite with resulting contamination of the silicon deposited electrolytically.
  • Graphite is recognized as a material which does not react chemically with fluorides or cryolites. However, it is difiicult to eliminate oxygen from the type of electro lyte used and from the atmosphere above the electrolytic bath, and when oxygen is present, combustion of the graphite takes place which causes deterioration of the cell and contaminates the bath with the combustion products of the graphite and/ or impurities contained in the graphite. Accordingly, cells formed of or having the inner walls of the cells lined with graphite deteriorate rapidly and have a very short operating life.
  • a cell which is formed of pure silica granules or sand packed in a jacket or container and having a cavity therein adapted to receive the molten electrolyte and an anode and a cathode by means of which silica is reduced to silicon and deposited on the cathode in the form of pure or substantially pure silicon.
  • the electrolyte contains silica as an essential component to enable the electro-deposition of silicon by reduction of the silica to silicon
  • the use of the silica cell will not introduce any contaminants so long as the silica or sand of which the cell is composed is of a high degree of purity.
  • the cell made of finely divided silica or sand does not have a great deal of initial wall strength, the molten electrolyte in the cavity will penetrate or seep into a zone of substantial thickness surrounding the cavity and due to the progressively decreasing temperature from the cavity to the outside of the cell, the electrolyte will solidify in a zone spaced between the cavity and the outside of the silica body with the result that a barrier wall is formed of a cemented mixture of the solidified electrolyte and 'ice silica which is form-retaining and provides other advantages as will be explained hereinafter.
  • FIGURE 1 illustrates schematically and in cross-Section a typical cell embodying the present invention
  • FIGURE 2 is a plan view of the cell.
  • a typical cell used for example, on a laboratory scale, includes a cylindrical container or jacket 10 formed of metal, such as, for example, steel, silica brick, or any other suitable material, and supported upon legs 11 or otherwise, as may be desired.
  • the cell may be formed in a cavity in the earth or the floor of a building.
  • a suitable procedure for forming the cell is to fill the bottom of the container with rammed sand and then insert a shell or tubular mold spaced from the wall of the container and fill the space between the shell and the container wall with sand.
  • the space Within the shell can be filled with finely divided solid cryolite or cryolite and silica.
  • the shell is removed and the top of the container is filled with sand or silica to form a non-removable cover 12 which is a continuation of the body 13.
  • This cover is made out of silica or sand to which was added 2% sodium silicate as a bonding agent to give it the necessary rigidity.
  • This cover 12 is provided with a series of openings 15, 16, 17, 18, 19 and 20 for receiving anodes 21, 22 and 23 and cathodes 24, 25 and 26 in the form of the invention illustrated.
  • the electrodes can be positioned in the cell during its formation so that the anodes are embedded in but movable relative to the cover and extend downwardly into the finely divided solid electrolyte. Larger openings are formed for the cathodes to enable their withdrawal.
  • Removable covers 35, 36 and 37 are made of regular refractory bricks and cover the cathodes openings 16, 17 and 20. For larger cells, a greater number of pairs of anodes and cathodes may be provided and for smaller cells, a relatively smaller number of anodes and cathodes may be provided.
  • the direct current which is supplied to the anode and cathode or anodes and cathodes is insufficient to maintain the temperature of the cell within the desired operating range, i.e., 970 C. to 1050 C., and for that reason, other electrodes 27 and 28 may extend through the cover 12 into contact with the electrolyte E in the cell for passage of alternating current therethrough to supply additional heat. In larger commercial production cells, alternating current heating is not required and these electrodes can be omitted.
  • the anodes and cathodes 21 to 26 may be formed of pure graphite and are connected by means of suitable bus bars or conductors 29 and 30 to a source of direct current.
  • the electrodes are short-circuited by means of graphite bricks or strips which may be placed in the cell during its formation and filling with electrolyte.
  • A.C. or DC. applied to the short-circuited electrodes will heat and melt the electrolyte and bring the cell up to operating temperature.
  • the electrodes then are withdrawn from contact with the short-circuiting strips or bricks and, if desired, the bricks or strips can be removed through the openings 16, 17 and 20.
  • the above-described procedure is more satisfactory than charging the cell with'molten electrolyte for the reason that the molten electrolyte damages the cell walls as it is introduced into the cell and also freezes and solidifies when the cell walls and bottom are cold.
  • the electrolyte is composed principally of cryolite and it may also contain silica in an amount between about 3% and depending upon the operating temperature of the cell.
  • the cell can operate at a temperature as high as 1400 C., the normal operating temperature is about 1040 C. At this temperature, the electrolyte will contain approximately 10% silica.
  • the electrolyte contains 3% silica which is added initially to the electrolyte and is dissolved therein.
  • the electrolyte When the electrolyte is in a molten condition, it flows into and permeates the silica or sand throughout a zone 32 which is proportional to the temperature of the electrolyte as it penetrates outwardly from the cavity.
  • the electrolyte solidifies at 950 C. and as a consequence, when the temperature of the electrolyte permeating the sand or silica is reduced to that temperature, it solidifies and forms, in effect, a barrier wall and also cements together the sand or silica grains.
  • the thickness of the zone of penetration 32 around the cavity 14 will vary, depending upon the temperature of the cell and the electrolyte therein, the thickness of the barrier zone decreasing at higher temperatures and increasing at lower temperatures. At a temperature of about 970 C., the wall is practically an isotherm,
  • the concentration of silica in the upper phase E1 decrease, due to deposition of silicon on the cathode or cathodes, the necessary amount of silica to bring up the level of silica concentration in its upper layer is dissolved from the lower phase E2.
  • the silica added from the top of the cell goes directly to the lower liquid phase E2 when phase E1 is already saturated with silica.
  • the lower phase E2 is about one-tenth the total volume of the electrolytic bath E.
  • the temperatures of the two layers E1 and E2 vary between 970 and 1050 C. As mentioned above, the temperature of the barrier zone 32 is always below 970 C. If this barrier zone 32 tends to move outwards due to an increase in temperature, the silica or sand of the barrier zone 32 goes into solution and is dissolved in layer E2. Thus, it is possible to maintain a state of equilibrium in the cell, by controlling the temperature and the silica concentration which will prolong the cell life indefinitely.
  • a direct current at about 7 volts and 400 amperes is supplied across the cathodes and anodes.
  • the anodic current density can be as high as 150 amperes per square decimeter. A 100 amperes per square decimeter anodic current density is adequate for most purposes.
  • the cathodic current density it varies with the size of the cathodic ball B and is difiicut to determine.
  • the temperature of the cell is maintained between 970 C. and 1050 C. and, in fact, close to 1040 C. by supplying additional heat with the alternating current electrodes 27 and 28 at about volts and a 4 200 amperes.
  • the current efiiciency for the cell illustrated is about 90%.
  • the silicon collects in the form of a pasty ball B or shell on the cathode or cathodes and is strip ed from the cathode periodically.
  • the silicon is separated from the electrolyte by leaching out or subliming off the electrolyte which clings to and is carried over with the ball B or shell.
  • the silicon crystal obtained are further treated, as may be required, for industrial and electronic purposes.
  • the cell life is prolonged indefinitely due to the fact that little or no silica is dissolved from the cell itself during the electrolytic reaction.
  • the formation of the cavity for receiving the electrolyte may be accomplished in various ways, such as, for example, by ramming the container 10 with sand or packing the sand in and scooping out a cavity or by bonding the sand together with suitable binders such as cryolite in order to avoid introduction of contaminants into the electrolyte adversely affecting the purity of the silicon deposited from the electrolytic bath.
  • suitable binders such as cryolite
  • a method of producing silicon comprising introducing an electrolyte comprising molten cryolite into a cavity in a mold composed principally of finely divided silica, dissolving approximately 3% to 10% silica in said molten cryolite and maintaining said molten cryolite and dissolved silica at a temperature between about 970 and 1400 C., passing a direct current through said electrolyte between an anode and a cathode immersed in said electrolyte to reduce said dissolved silica to silicon and deposit said silicon on said cathode.
  • a cell for producing silicon from silica comprising a container, a body principally of finely divided silica in said container, a cavity in said body of silica for receiving a molten cryolite electrolyte, at least one pair of electrodes extending into said cavity and a cover for said container.
  • a method of producing silicon comprising forming a cavity in a body composed principally of silica, filling the cavity at least partially with a finely divided, solid electrolyte of the class of cryolite or cryolite and silica, passing electrical current between interconnected electrodes in contact with said electrolyte to melt said electrolyte and heat it to between about 970 C. and 1400 C., disconnecting said electrodes from each other, maintaining in said electrolyte between about 3% and 10% of dissolved silica and passing a direct current from one electrode to another electrode immersed in the molten electrolyte to reduce said dissolved silica to silicon and deposit said silicon on one of said electrodes.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Sampling And Sample Adjustment (AREA)
US476022A 1965-06-15 1965-07-30 Method of producing silicon and electrolytic cell therefor Expired - Lifetime US3405043A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CH828765A CH426279A (fr) 1965-06-15 1965-06-15 Cellule électrolytique pour la fabrication de silicium

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US3405043A true US3405043A (en) 1968-10-08

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US (1) US3405043A (no)
CH (1) CH426279A (no)
FR (1) FR1461092A (no)
GB (1) GB1080589A (no)
NL (1) NL6512726A (no)
NO (1) NO116216B (no)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3711386A (en) * 1969-12-04 1973-01-16 Us Interior Recovery of metals by electrodeposition
US3779699A (en) * 1973-03-15 1973-12-18 Aluminum Co Of America Furnace structure
US3983013A (en) * 1973-07-26 1976-09-28 Mark Borisovich Gutman Method of electrolytic borating of articles
US4292145A (en) * 1980-05-14 1981-09-29 The Board Of Trustees Of Leland Stanford Junior University Electrodeposition of molten silicon
FR2533547A1 (fr) * 1982-09-24 1984-03-30 Rice George Compose d'hydrures de silicium et de metal, leur procede de preparation, procede d'electrodeposition de silicium sur un element cathodique et bain d'electrodeposition
FR2567915A1 (fr) * 1984-07-20 1986-01-24 Wedtech Corp Procede de traitement des roches par electrolyse
US5076902A (en) * 1989-01-12 1991-12-31 Toshiba Ceramics Co., Ltd. Electrolysis apparatus
WO1995033870A1 (en) * 1994-06-07 1995-12-14 Jan Stubergh Method for the production of silicium metal, silumin and aluminium metal
WO2002068719A1 (en) * 2001-02-26 2002-09-06 Norwegian Silicon Refinery As Process for preparing silicon by electrolysis and crystallization, and preparing low-alloyed and high-alloyed aluminum silicon alloys
US20040108218A1 (en) * 2001-02-26 2004-06-10 Stubergh Jan Reidar Process for preparing silicon and optionally aluminum and silumin (aluminum-silicon alloy)
US20100000875A1 (en) * 2005-05-13 2010-01-07 Wulf Naegel Low-temperature fused salt electrolysis of quartz
CN103103552A (zh) * 2011-11-15 2013-05-15 北京有色金属研究总院 一种采用熔盐电解制取硅的方法

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4142947A (en) * 1977-05-12 1979-03-06 Uri Cohen Electrodeposition of polycrystalline silicon from a molten fluoride bath and product
FR2480796A1 (fr) * 1980-04-21 1981-10-23 Extramet Sarl Procede de production de silicium de haute purete par voie electrochimique

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US920893A (en) * 1903-09-12 1909-05-04 Henry Spencer Blackmore Art of extracting aluminum and other metals.
US1980378A (en) * 1932-01-16 1934-11-13 Burgess Louis Method of making beryllium and light alloys thereof
US2892763A (en) * 1957-04-12 1959-06-30 American Potash & Chem Corp Production of pure elemental silicon
US3254010A (en) * 1962-03-14 1966-05-31 Gen Trustee Company Inc Refining of silicon and germanium

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US920893A (en) * 1903-09-12 1909-05-04 Henry Spencer Blackmore Art of extracting aluminum and other metals.
US1980378A (en) * 1932-01-16 1934-11-13 Burgess Louis Method of making beryllium and light alloys thereof
US2892763A (en) * 1957-04-12 1959-06-30 American Potash & Chem Corp Production of pure elemental silicon
US3254010A (en) * 1962-03-14 1966-05-31 Gen Trustee Company Inc Refining of silicon and germanium

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3711386A (en) * 1969-12-04 1973-01-16 Us Interior Recovery of metals by electrodeposition
US3779699A (en) * 1973-03-15 1973-12-18 Aluminum Co Of America Furnace structure
US3983013A (en) * 1973-07-26 1976-09-28 Mark Borisovich Gutman Method of electrolytic borating of articles
US4292145A (en) * 1980-05-14 1981-09-29 The Board Of Trustees Of Leland Stanford Junior University Electrodeposition of molten silicon
FR2533547A1 (fr) * 1982-09-24 1984-03-30 Rice George Compose d'hydrures de silicium et de metal, leur procede de preparation, procede d'electrodeposition de silicium sur un element cathodique et bain d'electrodeposition
FR2567915A1 (fr) * 1984-07-20 1986-01-24 Wedtech Corp Procede de traitement des roches par electrolyse
US4569733A (en) * 1984-07-20 1986-02-11 Wedtech Corp. Method of treating rock to recover metal, oxygen, and water
US5076902A (en) * 1989-01-12 1991-12-31 Toshiba Ceramics Co., Ltd. Electrolysis apparatus
WO1995033870A1 (en) * 1994-06-07 1995-12-14 Jan Stubergh Method for the production of silicium metal, silumin and aluminium metal
US5873993A (en) * 1994-06-07 1999-02-23 Stubergh; Jan Method and apparatus for the production of silicium metal, silumin and aluminium metal
WO2002068719A1 (en) * 2001-02-26 2002-09-06 Norwegian Silicon Refinery As Process for preparing silicon by electrolysis and crystallization, and preparing low-alloyed and high-alloyed aluminum silicon alloys
US20040094428A1 (en) * 2001-02-26 2004-05-20 Stubergh Jan Reidar Process for preparing silicon by electrolysis and crystallization and preparing low-alloyed and high-alloyed aluminum silicon alloys
US20040108218A1 (en) * 2001-02-26 2004-06-10 Stubergh Jan Reidar Process for preparing silicon and optionally aluminum and silumin (aluminum-silicon alloy)
US6974534B2 (en) 2001-02-26 2005-12-13 Norwegian Silicon Refinery As Process for preparing silicon and optionally aluminum and silumin (aluminum-silicon alloy)
US7101470B2 (en) 2001-02-26 2006-09-05 Norwegian Silicon Refinery As Process for preparing silicon by electrolysis and crystallization and preparing low-alloyed and high-alloyed aluminum silicon alloys
US20100000875A1 (en) * 2005-05-13 2010-01-07 Wulf Naegel Low-temperature fused salt electrolysis of quartz
CN103103552A (zh) * 2011-11-15 2013-05-15 北京有色金属研究总院 一种采用熔盐电解制取硅的方法
CN103103552B (zh) * 2011-11-15 2016-04-13 国联汽车动力电池研究院有限责任公司 一种采用熔盐电解制取硅的方法

Also Published As

Publication number Publication date
FR1461092A (fr) 1966-12-10
NL6512726A (no) 1966-12-16
GB1080589A (en) 1967-08-23
CH426279A (fr) 1966-12-15
NO116216B (no) 1969-02-17

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