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WO2009108061A1 - Composition d'un alliage d'anode et procédé d'utilisation de ladite composition - Google Patents

Composition d'un alliage d'anode et procédé d'utilisation de ladite composition Download PDF

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Publication number
WO2009108061A1
WO2009108061A1 PCT/NO2009/000061 NO2009000061W WO2009108061A1 WO 2009108061 A1 WO2009108061 A1 WO 2009108061A1 NO 2009000061 W NO2009000061 W NO 2009000061W WO 2009108061 A1 WO2009108061 A1 WO 2009108061A1
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Prior art keywords
weight
anode
alloy
metal
group
Prior art date
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Ceased
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PCT/NO2009/000061
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English (en)
Inventor
Espen Olsen
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Sinvent AS
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Sinvent AS
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Filing date
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Publication of WO2009108061A1 publication Critical patent/WO2009108061A1/fr
Anticipated expiration legal-status Critical
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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
    • C01B33/037—Purification
    • 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

Definitions

  • composition of an anode alloy and method for using said composition is a composition of an anode alloy and method for using said composition.
  • the present invention comprises a composition of an anode alloy for use in a three layer electrorefining of silicon and a method for producing silicon with a purity in the range of 99,99-99,999% by weight in a three layer electrochemical refining process using an anode alloy and an electrolyte.
  • Super purity aluminium is today produced commercially by the so called three layer refining process. This is an electrochemical process comprising three molten layers where impure metal is alloyed with a heavy, noble metal (Cu) and placed in the bottom as anode of an electrochemical cell. Over this, a liquid layer of electrolyte with intermediate density is positioned. Liquid super purity aluminium with density of 2.3 g/cm 3 is deposited cathodically on top of this by sending electric current through the system. This principle may also be used for purifying other less-noble metals as Si and Mg, and may yield a product with ultra high purity.
  • Cu heavy, noble metal
  • Yoshikawa et al. [1] describe removal of B by metallurgical solidification refining of Si using an Al-Si alloy in which precipitation of stabile substances in a liquid phase is followed by solidification refining of the contaminates between two phases in which one of the phases (Al) has a higher affinity for the undesirable contaminate (B) than the other phase (Si).
  • the objective of the present invention is to provide a composition of an anode alloy and method for producing silicon with a purity in the range of 99,99-99,999% by weight for use in a three layer electrorefining process involving an anode alloy and an electrolyte.
  • an object of the invention is to obtain an anode alloy and a method involving said anode alloy for producing super purified silicon with a high yield and reduce the problems with contaminants.
  • addition of a metal to the anode alloy in a three layer electrorefining cell resulted in the possibility of widening of the electrochemical window and allowing the use of higher current densities and subsequently higher yield, along with lower content of contaminants and a purity of the refined Si in the range of 99,99- 99,999% by weight.
  • the invention provides in an aspect an anode alloy composition for use in an anode that constitutes a lower layer in a three layer arrangement for electrorefining of silicon, said composition comprising the following components: 60-90 weight% Si, 0-40 weight% Cu, 0-10 weight% B, 0-10 weight% AI, wherein the composition comprises at least one of the following components: 0-40weight% of a metal from group 8 of the transition metals, 0-10 weight% of a metal from group 4 of the transition metals, 0-10 weight% of a metal from group 5 of the transition metals, and possibly at least one precipitated intermetallic compound.
  • the density of said anode alloy is in the range of from 2,7-6 g/cm 3 , more preferably in the range of from 2,7-4,4 g/cm 3 .
  • the intermetallic compounds are at least one compound comprising metal boride.
  • the present invention comprises a method for producing silicon with a purity in the range of 99,99-99,999% by weight in an electrorefining process using a three layer arrangement comprising an anode, an electrolyte, and a cathode, said electrolyte comprising at least one alkaline earth metal fluoride, said anode being a metal alloy anode, the alloy comprising the following components: 60-90 weight% Si, 0-40 weight% Cu, 0-10 weight% B, 0-10 weight% Al, wherein at least one of the following components is added to said anode alloy: 0-40 weight% of a metal from group 8 of the transition metals, 0-10 weight% of a metal from group 4 of the transition metals, 0
  • At least one of the components added to said anode alloy is chosen from the transitions metals: Ti, Fe and V.
  • a further aspect of the present invention is to keep the hydrostatic pressure high at the bottom of the cell in order to avoid contact between the intermetallic particles and the electrolyte. This can be obtained by keeping the height of the column of the anode alloy in the range of from 20-100cm, preferably 20-80cm and most preferably 20-50cm.
  • the added metal component is formed into at least one compound having a densitiy p ⁇ Panodeaiioy , and at least one compound with a densitiy p ⁇ P a n odea ii o y is removed from the upper part of the forwell.
  • the added metal component is formed into at least one compound having a densitiy p > Panodeaiioy - and at least one compound having a density p > P anodea ii o y is precipitated. Said at least one compound is precipitated at the bottom of a forwell.
  • contaminants such as at least one metal component is added to the anode alloy in the forewell.
  • the anode alloy primarily consists of SiCu, SiCuFe or SiFe.
  • the contaminants have a residence time previous to the formation of different borides which is precipitated and settled at the bottom and is further removed from the forewell. Possibly lighter precipitated compounds will rise to the top of the forewell where it is removed.
  • a definite anode alloy and further contaminants such as preferably at least one of the following components Ti, Fe and V is added to the anode alloy in order to remove active boron of the anode alloy in the main cell which again lead to widening of the electrochemical window.
  • the effect of the widening of the electrochemical window is that the current density is increased simultaneously as achieving high purity of the product Si at the cathode.
  • the addition of contaminants in a three layer electrorefining process results in the widening of the electrochemical window, the increase in the current density and the production of super purity Si which is a surprising and unexpected feature.
  • the precipitated particles of intermetallic compounds will settle at the bottom of the cell.
  • the hydrostatic pressure at the bottom of the cell must be kept high enough in order to prevent the electrolyte from forming a film below the anode alloy. This is achieved having a layer of the anode alloy in the range of from 20 - 100cm. Further, it is required to collect the precipitated particles and segregation crystals/compounds in the forewell. This can be achieved by constructing the forewell with a depressed bottom compared to the main area of the cell. The particles and contaminants will be collected in the forewell which makes removal of these more easily.
  • Figure 1 The principle of three-layer electrorefining depicted schematically.
  • Figure 2 X-ray diffractogram of particles collected from the top of the anode alloy. Densities: alloy, 4.0 g/cm 3 , electrolyte 3.0 g/cm 3 .
  • AI 2 Cu has been oxidized to AI 2 CuO 4 due to air exposure.
  • Figure 3 Schematic drawing of a cell for electrorefining of Si. lntermetallic particles of Ti, Fe, Al, B etc. form in the anode alloy. Particles lighter than the alloy will float up in the forewell while heavy particles will accumulate on the bottom.
  • Figure 4 The relationship between the content of B and the content of Ti in a Si+20wt%Cu molten alloy.
  • Figure 5 The relationship between the content of B and the content of Fe in a Si+20wt%Cu molten alloy.
  • the electrolyte may be based on different anions such as F “ , Cl “ , SO 4 2" or O 2" , to mention some.
  • fluoride based electrolytes is utilized for the refining of Al.
  • oxide based electrolytes has been investigated, but without success due to a number of reasons, most notably the high viscosity of these melts.
  • Silicon may, however, be refined in a three layer process above its melting point by incorporating a Si-Cu alloy as anode under a fluoride based electrolyte based on CaF 2 with additions of BaF 2 (density modifyer) and SiF 4 as Si-carrying agent.
  • the electrochemical series in the fluoride system is listed in Table 1.
  • the elements with E° ⁇ E°(Si) will thermodynamically be more stable than Si and so not go anodically into solution during polarization of the Si-Cu alloy.
  • the elements with E°>E°(Si) will be less stable than Si and enter the electrolyte in the form of fluorides together with Si during polarization.
  • the difference in E 0 between Si and its neighbours is termed the electrochemical window in the refining of Si.
  • E°-values is modified and the actual potential where the process starts is termed E rev . This effect is described by Eq. 2 and arises due to chemical activities deviating from unity.
  • E > - " ⁇ G and E rev E° - — ⁇ n ⁇ - ⁇ [2] nF nF a B - a,
  • Table 1 Gibbs free energy and related electrochemical potential for the dissolution of metals in fluoride media at 1700K.
  • 13mV may be tolerated in a high-temperature three-layer electrorefining process by keeping the anodic current density low, it is desirable to keep the activity of B in the anode alloy low in order to push the E rev -value for the dissolution of B away from that of Si-dissolution. This in order to increase the anodic current density employed and thereby the yield from the reactor. This may be accomplished by using feedstock without or very low in B. This is not easily accomplished since B is inherently difficult to remove from Si due to its high segregation coefficient (0.8- 1.0). If low-B feedstock may be found, boron will never the less accumulate in the anode alloy until it reaches activities approaching unity in the long term.
  • the present method is carried out in a three layer electrorefining cell in which the density of the bottom layer, the anode alloy, is in the range of from 2,7 g/cm 3 to 6 g/cm 3 , the middle layer, the electrolyte, is in the range of from 2,6 g/cm 3 to 4 g/cm 3 , and the top layer Si, the product, has a density of 2,57 g/cm 3 .
  • a range of intermetallic compounds may form in the anode alloy at the bottom of the cell.
  • Boron and aluminium are known to form very stable borides and aluminates with Ti, Fe and Cu.
  • the anode alloy comprised of mainly Si and Cu will, invariably, contain substantial amounts of other metallic impurities more electropositive than Si during long term operation of an industrial cell.
  • Fe and Ti will be the most abundant as these are the main impurity elements in metallurgical Si used as feedstock.
  • Ti and B will have a high affinity for each other and the reaction described by Eq. 4 will proceed in the molten alloy.
  • the boride-forming mechanism can be described by Eq. 5.
  • Table 2 Intermetallic phases detected in particles collected from the top and bottom of the anode alloy layer and their respective densities.
  • the solid intermetallic phases being formed in the anode alloy will exhibit a fundamental, characteristic solubility product K sp both in the alloy and in the electrolyte.
  • K sp fundamental, characteristic solubility product

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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)
  • Silicon Compounds (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Electrolytic Production Of Metals (AREA)

Abstract

La présente invention concerne une composition d'un alliage d'anode destinée à être utilisée dans un électroaffinage en trois couches de silicium, et un procédé d'électroaffinage en trois couches utilisant un alliage d'anode et un électrolyte pour produire du silicium dont la pureté se situe dans la plage de 99,99 à 99,999 % en poids. La composition comprend les composants suivants : 60 à 90 % en poids de Si, 0 à 40 % en poids de Cu, 0 à 10 % en poids de B, 0 à 10 % en poids d'Al. La composition comprend au moins l'un des composants suivants : 0 à 40 % en poids d'un métal du groupe 8 des métaux de transition, 0 à 10 % en poids d'un métal du groupe 4 des métaux de transition, 0 à 10 % en poids d'un métal du groupe 5 des métaux de transition et, éventuellement, au moins un composé intermétallique précipité.
PCT/NO2009/000061 2008-02-26 2009-02-24 Composition d'un alliage d'anode et procédé d'utilisation de ladite composition Ceased WO2009108061A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NO20080977 2008-02-26
NO20080977A NO332874B1 (no) 2008-02-26 2008-02-26 Fremgangsmate for fremstilling av silisium med en renhet i omradet 99,99-99,999 vekt-% i en elektroraffineringsprosess

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WO2009108061A1 true WO2009108061A1 (fr) 2009-09-03

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NO (1) NO332874B1 (fr)
WO (1) WO2009108061A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019126208A1 (fr) * 2017-12-22 2019-06-27 Sila Nanotechnologies, Inc. Séparateur pourvu d'une couche de séparateur comprenant une céramique

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3442622A (en) * 1964-09-15 1969-05-06 Gen Trustee Co Inc The Refining of silicon
NO156172B (no) * 1984-02-13 1987-04-27 Ila Lilleby Smelteverker Fremgangsmaate ved fremstilling av renset silicium ved elektrolytisk raffinering.
EP0855367A1 (fr) * 1997-01-22 1998-07-29 Kawasaki Steel Corporation Méthode d'élimination du bore contenu dans du silicium de qualité métallurgique et son dispositif
US20070215483A1 (en) * 2006-03-10 2007-09-20 Elkem As Method for electrolytic production and refining of metals

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3442622A (en) * 1964-09-15 1969-05-06 Gen Trustee Co Inc The Refining of silicon
NO156172B (no) * 1984-02-13 1987-04-27 Ila Lilleby Smelteverker Fremgangsmaate ved fremstilling av renset silicium ved elektrolytisk raffinering.
EP0855367A1 (fr) * 1997-01-22 1998-07-29 Kawasaki Steel Corporation Méthode d'élimination du bore contenu dans du silicium de qualité métallurgique et son dispositif
US20070215483A1 (en) * 2006-03-10 2007-09-20 Elkem As Method for electrolytic production and refining of metals

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019126208A1 (fr) * 2017-12-22 2019-06-27 Sila Nanotechnologies, Inc. Séparateur pourvu d'une couche de séparateur comprenant une céramique

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NO20080977L (no) 2009-08-27
NO332874B1 (no) 2013-01-28

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