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WO2008115072A2 - Électrolyte et procédé pour le raffinage électrochimique de silicium - Google Patents

Électrolyte et procédé pour le raffinage électrochimique de silicium Download PDF

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Publication number
WO2008115072A2
WO2008115072A2 PCT/NO2008/000105 NO2008000105W WO2008115072A2 WO 2008115072 A2 WO2008115072 A2 WO 2008115072A2 NO 2008000105 W NO2008000105 W NO 2008000105W WO 2008115072 A2 WO2008115072 A2 WO 2008115072A2
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WO
WIPO (PCT)
Prior art keywords
electrolyte
silicon
weight
electrochemical
layer
Prior art date
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Ceased
Application number
PCT/NO2008/000105
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English (en)
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WO2008115072A3 (fr
Inventor
Espen Olsen
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Sinvent AS
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Sinvent AS
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Publication of WO2008115072A3 publication Critical patent/WO2008115072A3/fr
Anticipated expiration legal-status Critical
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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
    • C25C3/34—Electrolytic production, recovery or refining of metals by electrolysis of melts of metals not provided for in groups C25C3/02 - C25C3/32
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • C25C7/005—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells of cells for the electrolysis of melts

Definitions

  • the invention discloses an electrolyte for electrochemical refining of a material containing silicon at a temperature above the melting point of silicon in a three layer electrochemical cell.
  • the invention also comprises the method and the electrochemical cell involved in the electrochemical refining of silicon.
  • metallurgical (MG) methods are being developed, but these have not yet been shown to exhibit significantly lower production costs compared with the Siemens process, combined with acceptable purity.
  • the continued growth of the PV industry is invariably dependent on further reductions in the price of solar electricity, and there is a need for a low-cost silicon production process which is capable of producing larger amounts of silicon with an acceptable quality and to a substantially lower price than can be achieved today.
  • the quality requirements are in general considered to be 99.99% (metals base) and with a particular emphasis on impurities of boron (B) and phosphorous (P) which should be below 0.5 and 1 ppmw, respectively.
  • B boron
  • P phosphorous
  • These elements are characterized by distribution coefficients close to 1 which makes them difficult, if not impossible, to remove by zone refining.
  • this particular trait is used during the doping process of silicon, yielding a low gradient in dopant concentration through the solidified ingot due to the small segregation effects.
  • Electrochemical refining of aluminium is carried out in the so called "3-layer process" invented by Hoopes in the 1920s, where metallurgical grade Al is alloyed with Cu to give a heavy alloy which is polarized anodically under a layer of a chloride and/or fluoride based electrolyte. On top of this, a layer of pure Al is deposited cathodically.
  • the process runs at ⁇ 750°C and is shown schematically in figure 1. Three molten layers; - alloy at the bottom, an intermediate layer of fluoride electrolyte and a top layer of refined metal is maintained by differences in density (p).
  • the process yields a product with purity in the range of 99.999% by weight in industrial scale electrochemical cells (10-5OkA).
  • the present invention is based on this technical principle. Electrochemical refining of silicon (Si) has been performed with a successful result.
  • the mechanism can be described by the following: A molten alloy of impure metallurgical grade silicon (MG-Si) and a heavy, noble metal (i.e. Cu) is placed at the bottom of a reactor with a layer of molten fluoride based electrolyte on top. On top of this, a layer of the molten, pure solar grade silicon is positioned.
  • the heavy alloy in the bottom of the cell is polarized anodically. This causes the silicon in the alloy to dissolve anodically into the electrolyte as electrons are extracted from the system, as described by equation [1].
  • the two main differences when substituting aluminium with silicon will then be the temperature (>1412°C vs. 750 0 C) and the density of the product (2.6 g/cm 3 vs. 2.2 g/cm 3 ).
  • the challenges to be met are related to the temperature tolerance and chemical inertness of the construction materials in the reactor and finding an electrolyte with the right density, viscosity and low electric and chemical losses.
  • the 3-layer principle has primarily been used for the refining of aluminium.
  • Norwegian Patent NO 156 172 (T. Grong and J. K. Tuset, Ha og Lilleby smelteverk 1984) describes a method for refining silicon, by use of the three-layer process.
  • the electrolyte is an oxide-based electrolyte containing SiO 2 , CaO and BaO with small additions of CaF 2 and BaF 2 to enhance the low ionic electrical conductivity of the oxide based melt.
  • Fluoride-based electrolyte is specifically mentioned not to be suitable due to formation of SiF 4 .
  • Refined silicon is produced and the 3-layer approach is demonstrated as feasible in the oxide-based electrochemical system. This electrolyte is however associated with a number of fundamental problems.
  • reaction bonded silicon nitride as a construction material in areas of the cell where magnesia or chamotte does not provide enough chemical inertness.
  • Silicon nitride ceramic bodies of high purity and chemical inertness can be reaction sintered to ⁇ 20% porosity.
  • This material exhibits properties which through the invention, has been shown to be well suited for the use as construction material for an electrochemical reactor (cell) based on the three-layer principle for refining of Si above 1400 0 C.
  • the object of the present invention is to produce refined silicon of high purity while avoiding problems with high electrolyte viscosity, chemical attack of the reactor construction materials and the formation of SiO (g).
  • a fluoride based electrolyte capable of dissolving SiF 4 (g) in the form of stable SiF 6 2" -ions can be used.
  • the electrolyte may contain a Si-bearing species. This may be added as SiO 2 in small amounts to lower the loss of SiO, or as M x SiF 6 , which will eliminate formation of SiO.
  • the first aspect of this invention is an electrolyte for electrochemical refining of a material containing silicon at a temperature above the melting point of silicon, wherein the electrolyte comprises 50-100% by weight of at least one alkaline earth metal fluoride selected from BaF 2 , CaF 2 , SrF 2 and MgF 2 .
  • One preferred embodiment of the invention is an electrolyte for electrochemical refining of a material containing silicon at a temperature above the melting point of silicon, wherein the electrolyte comprises 80-100% by weight of at least one alkaline earth metal fluoride selected from BaF 2 , CaF 2, SrF 2 and MgF 2 .
  • the electrolyte mixture must exhibit the following features:
  • the formation of SiF 4 will not create a problem, since SiF 4 will dissolve easily as the ion SiF 6 2" in fluorides exhibiting basic (non-acidic) properties.
  • BaF 2 and SrF 2 both show higher densities in the molten state than silicon and may be used in their pure, molten state.
  • MgF 2 and CaF 2 have lower densities than Si in their molten state and must, subsequently, be mixed with a heavier component to be used as the intermediate electrolyte layer in three-layer refining.
  • the electrolyte comprises a mixture based on at least one of the following compounds; BaF 2 , CaF 2, SrF 2 and MgF 2 .
  • Sr, Ba in an amount of 50-80% , preferably 60-80% and with the possible addition of from 0 to 50 % by weight, preferably 0-20% of one or more of the other three.
  • the melting point of Si is 1412°C and thus, the temperature of the electrolyte should be in the range from 1412°C to the boiling point of the electrolyte.
  • the boiling point of the electrolyte may be in the range from around 2000 to 2300 0 C.
  • a silicon bearing species may be added to the electrolyte to enhance the process kinetics from the start. This may also be omitted, in which case the product deposited from the start will be contaminated by impurities until sufficient amounts of Si-carrying ions have been transported from the bottom anode to the top cathode.
  • the silicon bearing species can be K 2 SiF 6 , Na 2 SiF 6 , CaSiF 6 , BaSiF 6 , SrSiF 6 or
  • the silicon bearing species is added in an amount from 0 to 20 % by weight of the electrolyte, preferably from 0.1 to 10% by weight.
  • Another aspect of the invention is a method for electrochemical refining of a material containing silicon wherein at least one fluoride from the alkaline earth metals is used.
  • the electrochemical refining is performed in a three-layer process comprising a molten bottom layer of silicon and a heavy, noble metal which is polarized anodically, a pure, molten layer of silicon polarized catiodically and an intermediate electrolyte layer.
  • a third aspect with the invention is an electrochemical cell (or reactor) for electrochemical refining of a material containing silicon at a temperature above the melting point of silicon, wherein the electrochemical cell possesses a lining comprised of reaction bonded SJsN 4 .
  • the porosity of the reaction bonded Si 3 N 4 is in the range from 10 to 60% of the theoretical value, preferably within the range from 20 to 40% of the theoretical value where low cost methods may be employed to make the ceramic bodies.
  • Figure 1 shows a cell for three-layer refining
  • Figure 2 shows schematically the principle for three layer refining of silicon
  • FIG. 3 is a schematic drawing of the electrochemical cell used in the experiments.
  • the furnace was evacuated before being filled with Ar (Ar 4.6, AGA).
  • Ar Ar 4.6, AGA
  • the molten alloy was quenched by pouring it into graphite crucibles kept at room temperature and with a diameter smaller than the inner diameter of the cell.
  • the anode alloy was cut into the right weight before being transferred to the electrochemical cell container consisting of a graphite crucible with a high purity reaction sintered Si 3 N 4 tubular lining.
  • the electrolyte was pre-mixed and melted down under argon (Ar 5.0) before being crushed and filled on top of the anode alloy.
  • 100 g Si was cut from an undoped multicrystalline ingot in the form of a cylinder and put on top of the crushed electrolyte. The aim of this large amount was to form a stable layer of Si covering the whole surface area of the underlying electrolyte to trap potential SiO being formed in the electrolyte.
  • the cell was placed in a tubular furnace and melted down under Ar atmosphere (Ar 5.0). Mo current leads were screwed into the graphite crucible from the top and a graphite cathode which was lowered into the molten Si after melting.
  • the pure Si obtained was analyzed.
  • the impurity level was surprisingly low.
  • the results were: Al ⁇ 900 ppm, B ⁇ 11 ppm; Ca ⁇ 22ppm; Fe ⁇ 5ppm; P ⁇ 1ppm; Ti ⁇ 20ppm

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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)

Abstract

L'invention porte sur un électrolyte pour le raffinage électrochimique d'une matière contenant du silicium à une température supérieure au du point de fusion du silicium dans une cellule électrochimique à trois couches. L'électrolyte comprend 50-100 % en poids d'au moins un fluorure de métal alcalino-terreux choisi parmi BaF<SUB>2</SUB>, CaF<SUB>2</SUB>, SrF<SUB>2</SUB> et MgF<SUB>2</SUB>. L'invention concerne également le procédé et la cellule électrochimique mise en jeu dans le raffinage électrochimique de silicium.
PCT/NO2008/000105 2007-03-21 2008-03-17 Électrolyte et procédé pour le raffinage électrochimique de silicium Ceased WO2008115072A2 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
NO20071496 2007-03-21
NO20071496A NO328263B1 (no) 2007-03-21 2007-03-21 Elektrolytt og fremgangsmate for elektrokjemisk raffinering av silisium
US92430407P 2007-05-08 2007-05-08
US60/924,304 2007-05-08

Publications (2)

Publication Number Publication Date
WO2008115072A2 true WO2008115072A2 (fr) 2008-09-25
WO2008115072A3 WO2008115072A3 (fr) 2008-11-13

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/NO2008/000105 Ceased WO2008115072A2 (fr) 2007-03-21 2008-03-17 Électrolyte et procédé pour le raffinage électrochimique de silicium

Country Status (2)

Country Link
NO (1) NO328263B1 (fr)
WO (1) WO2008115072A2 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2399698C1 (ru) * 2009-11-16 2010-09-20 Учреждение Российской академии наук Институт высокотемпературной электрохимии Уральского отделения РАН Способ получения кремния нано- или микроволокнистой структуры
WO2010137555A1 (fr) * 2009-05-26 2010-12-02 住友化学株式会社 Procédé de production d'un métal ou d'un métalloïde raffiné
CN115305508A (zh) * 2021-05-08 2022-11-08 郑州大学 利用高硅含铝资源生产金属铝和多晶硅的方法
WO2025219160A1 (fr) * 2024-04-15 2025-10-23 Rheinisch-Westfälische Technische Hochschule Aachen, abgekürzt RWTH Aachen, Körperschaft des öffentlichen Rechts Procédé de traitement de corps solides contenant du silicium

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4292145A (en) * 1980-05-14 1981-09-29 The Board Of Trustees Of Leland Stanford Junior University Electrodeposition of molten silicon
US4448651A (en) * 1982-06-10 1984-05-15 The United States Of America As Represented By The United States Department Of Energy Process for producing silicon
NO156172C (no) * 1984-02-13 1987-08-12 Ila Lilleby Smelteverker Fremgangsmaate til fremstilling av renset silisium ved elektrolytisk raffinering.
NO20010963D0 (no) * 2001-02-26 2001-02-26 Norwegian Silicon Refinery As FremgangsmÕte for fremstilling av silisium og/eller aluminium og silumin (aluminium-silisium-legering)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2010137555A1 (fr) * 2009-05-26 2010-12-02 住友化学株式会社 Procédé de production d'un métal ou d'un métalloïde raffiné
DE112010004425T5 (de) 2009-05-26 2012-11-29 Sumitomo Chemical Co., Ltd. Verfahren zur Herstellung von gereinigtem Metall oder Halbmetall
RU2399698C1 (ru) * 2009-11-16 2010-09-20 Учреждение Российской академии наук Институт высокотемпературной электрохимии Уральского отделения РАН Способ получения кремния нано- или микроволокнистой структуры
CN115305508A (zh) * 2021-05-08 2022-11-08 郑州大学 利用高硅含铝资源生产金属铝和多晶硅的方法
WO2025219160A1 (fr) * 2024-04-15 2025-10-23 Rheinisch-Westfälische Technische Hochschule Aachen, abgekürzt RWTH Aachen, Körperschaft des öffentlichen Rechts Procédé de traitement de corps solides contenant du silicium

Also Published As

Publication number Publication date
NO20071496L (no) 2008-09-22
NO328263B1 (no) 2010-01-18
WO2008115072A3 (fr) 2008-11-13

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