Classifications

• • 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
  • C01B33/08—Compounds containing halogen
  • C01B33/107—Halogenated silanes
  • C01B33/10705—Tetrafluoride
• • 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
  • 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
  • C01B33/021—Preparation
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B7/00—Halogens; Halogen acids
  • C01B7/19—Fluorine; Hydrogen fluoride
  • C01B7/20—Fluorine
• • 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
  • C25B1/24—Halogens or compounds thereof
  • C25B1/245—Fluorine; Compounds thereof
• • 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
  • C25C5/00—Electrolytic production, recovery or refining of metal powders or porous metal masses
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C5/00—Electrolytic production, recovery or refining of metal powders or porous metal masses
  • C25C5/04—Electrolytic production, recovery or refining of metal powders or porous metal masses from melts

Definitions

• the invention relates to technologies for the production of rare metals and non-metals, namely: to the production of electrolytically pure, suitable for use in solar energy and in semiconductor technology, silicon powder, more specifically, to methods for reducing silicon from gaseous silicon tetrafluoride, as well as to a technology for producing tetrafluoride silicon.
• Semiconductor silicon is obtained from a technical (metallurgical) material by chlorinating finely ground silicon powder with anhydrous hydrogen chloride, followed by purification of chlorosilanes formed during chlorination by rectification to the required purity (see the book by E. Falkevich, et al. Semiconductor silicon technology., M. : Metallurgy, 1992). In some countries, semiconductor silicon is obtained by fusion of industrial silicon with magnesium, decomposition of magnesium silicide, subsequent low-temperature distillation purification of monosilane and its thermal decomposition (see the book Belov I.P. et al. Monosilane in the technology of semiconductor materials.
• a known method of producing a fine silicon powder from gaseous silicon tetrafluoride see RU 2066296, IPC C01BZZ / 03, publ.
• SHEET 09/10/96 isolated from waste products of uranium hexafluoride, which is Na 2 SiF 6 .
• the basis of this method is the decomposition of gaseous silicon tetrafluoride under the action of laser radiation.
• powerful continuous radiation of a CO 2 laser (2-10 kW) was introduced into the reaction chamber (closed volume), in which gaseous silicon tetrafluoride and hydrogen circulating fluorine during the decay of SiF 4 are simultaneously circulated.
• the method of producing silicon from silicon tetrafluoride by laser technology using waste production of uranium hexafluoride allows you to get pure silicon at a relatively low cost.
• the purity of such silicon is approximately 99%, which is insufficient for its use in solar energy or in semiconductor technology.
• a known technology for producing semiconductor silicon, in particular silicon for solar cells (see RU 2035397, IPC C01B ⁇ / 02, publ. 05.20.1995), including a series of gas transport reactions using silicon tetrafluoride, from which, as a result of its interaction with deionized water, hydrofluoric acid. Silicon is obtained by reducing it at room temperature from fluorosilicic acid with atomic hydrogen.
• Replacement sheet low melting cathode which is used as a molten metal, in particular zinc.
• a mixture of fluorine and chlorine on the anode, a mixture of fluorine and chlorine, and the cathode, i.e. Zinc melt absorbs metallic silicon released from the aforementioned silicon-containing compounds and, as a solution of metallic silicon, is further processed to produce silicon as a commercial product.
• Another disadvantage of the prototype is the frequency of the process. In order to separate silicon from a liquid cathode melt, it is necessary at a certain stage characterized by sufficient saturation of the cathode melt with silicon particles, stop the electrolysis, direct the silicon melt to the silicon precipitation stage, and fill the electrolytic apparatus with a new zinc melt, and only after all these procedures to continue the process.
• the disadvantage of this method is that in addition to fluorine, chlorine gas is released on the anode.
• both of the elements released on the anode are transported to release silicon from a silicon-containing raw material, i.e. these elements are negotiable, the need to separate one element from another complicates the technology, increases its hardware support and, as a result, leads to an increase in the cost of the final product.
• a known method of producing silicon tetrafluoride from a solution of hydrofluoric acid see patent RU 2046095, IPC COl B 33/10, publ. 20.10.95, including the interaction of a solution of this acid with a solution of an organic base with the formation of salts of hydrofluoric acid.
• the resulting salt is washed, dried and decomposed by treatment with concentrated mineral acid, and after the decomposition step, the obtained silicon terrafluoride is separated from hydrogen fluoride.
• the main disadvantage of the prototype is the environmental insecurity of the technology, as well as the fact that the silicon tetrafluoride obtained is characterized by a high content of impurities, which makes it unsuitable for use in semiconductor silicon production technology.
• the problem to which the claimed group of inventions is directed is to develop an effective and environmentally safer technology for producing electrolytically pure and relatively inexpensive semiconductor silicon with the simultaneous production of high-purity silicon tetrafluoride and elemental fluorine, which can be used as in the inventive method for producing semiconductor silicon as a reverse chemical compounds and chemical elements, and can be commercial products with high quality tween characteristics.
• the problem is solved in that in the method for producing silicon from silicon tetrafluoride with the simultaneous production of elemental fluorine by electrolysis and with the release of elemental fluorine at the anode, according to the claimed invention, electrolysis of the eutectic melt of ternary alkali metal fluoride salts systems saturated with silicon tetrafluoride is electrolytically decomposed. Silicon released in the form of a suspension of silicon powder and electrolyte, which is the above-mentioned eutectic melt of ternary systems of alkali metal fluoride salts, is removed from the electrolyzer. After withdrawal of said suspension, i.e. outside the electrolyzer, silicon powder is separated from the eutectic melt of the ternary systems of alkali metal fluoride salts.
• the technical result of the claimed method is the ability to realize the production of silicon in a continuous mode, with a high yield of finished products and its high quality. This result is due to the following distinctive features.
• a distinctive feature of the proposed method is that in the process of producing high-purity silicon, the eutectic melt of ternary systems of fluoride salts of certain alkali metals is used, i.e. chemical compounds containing fluorine, and the saturation of this melt is carried out with silicon tetrafluoride, i.e. a chemical compound that also contains fluorine. This allows one stage to obtain high quality electrolytically pure semiconductor
• Another distinctive feature of the proposed method for producing silicon is that for the selection of the product does not need to stop the electrolysis process, the withdrawal of silicon powder in a mixture with molten electrolyte can be continuous.
• the method in which the eutectic melt of the ternary systems of alkali metal fluoride salts after separation of the silicon powder is sent for reuse in the electrolysis process, thereby closing the process and ensuring waste-free production.
• the withdrawal of electrolytically obtained silicon is accompanied by a drain of the electrolyte and its constant replenishment, i.e. the electrolyte is essentially flowing, but due to the fact that the suspension is taken in the inter-pole gap of the electrolyte, the electrolyte is not subject to “flow” in full, but to the “chosen” part, i.e. the volume (that part) that represents the suspension with the highest concentration of the released powder is constantly withdrawn from the process.
• the continuity of the withdrawal of the suspension by silicon and electrolyte powders is also facilitated by the fact that the density of the electrolyte with the released silicon powder is less than the density of the electrolyte without powder, i.e. the suspension is extruded by a column of electrolyte.
• the inventive method is the most technologically advanced if the eutectic melt of the following composition is used as a melt eutectic of ternary systems of alkali metal fluoride salts: LiF-KF-NaF, and electrolysis is carried out at a temperature of 450 ° C-600 ° C.
• a salt melt is preferable on the basis that the melting temperature of the initial components of the melt is lower than the melting temperature of silicon, while the temperature regime is most optimal for electrolysis and the process of separation of silicon powder.
• the melt of the eutectic of fluoride salts LiF-KF-NaF is saturated with silicon tetrafluoride in the range of 2-35% of May. according to SiF 4.
• a parameter below 2% requires a very high voltage, which is not economically feasible, and a parameter above 35% will increase the melting point of the eutectic of fluoride salts, which is also undesirable.
• the electrolysis efficiency increases if the saturation of the eutectic melt of ternary systems of alkali metal fluoride salts is carried out by bubbling silicon tetrafluoride into the melt. This is because bubbling ensures uniform saturation of the molten electrolyte with higher fluoride of the starting element in the gas phase.
• the inventive method for separating silicon from molten salts solves the same problem as the method described above for producing high-purity semiconductor silicon and elemental fluorine, i.e. the task of obtaining high-purity semiconductor silicon of low cost.
• Replacement sheet NaF in the form of a liquid phase and from silicon particles, which are a solid phase, is filtered to separate the solid phase in the form of silicon powder, and the liquid phase is directed to the distillation of hydrogen fluoride, which is used in the dissolution stage.
• the solidified melt with silicon particles is crushed before dissolution, and the dissolution process is carried out at a temperature of from -5 ° C to +12 0 C, with the preferred result of the dissolution process being the resulting composition with a solid phase to liquid phase ratio of 1 : 23, i.e. 23 parts of HF + (Li-KF-NaF) contain one part of solid silicon particles.
• This ratio predetermined by the supply of an appropriate amount of anhydrous hydrogen fluoride to a certain amount of melt with silicon particles, is most optimal for further filtering the composition and separating the silicon powder.
• the filtration is carried out by centrifugation using centrifuges produced by the industry, or the same centrifuges, structurally modified based on specific production conditions.
• the proposed method it is applicable to purify silicon powder from metal impurities by washing it with a solution of a mixture of inorganic acids, in particular of the following composition: 2-3 MH 2 SO 4 + OD-0.2 M HF at a temperature of 5 ° C-75 ° C, followed by drying of silicon powder in an inert medium and at 80 0 C - 120 ° ⁇ .
• a solution of a mixture of inorganic acids in particular of the following composition: 2-3 MH 2 SO 4 + OD-0.2 M HF at a temperature of 5 ° C-75 ° C, followed by drying of silicon powder in an inert medium and at 80 0 C - 120 ° ⁇ .
• the melt of the eutectic of fluoride salts LiF-KF-NaF is used in the method of producing high-purity silicon powder from silicon tetrafluoride with the simultaneous production of elemental fluorine, i.e. in the first of the claimed group of the invention set forth in claim l of the formula.
• electrolytically pure silicon which is characterized by the content of the following components: silicon with a weight content of C 1 , metal impurities with a weight content of C 2 and non-metal impurities with a weight content of C 3 .
• electrolytically pure silicon is obtained by fluoride technology according to the method according to claim 1, i.e. during electrolytic decomposition of the eutectic melt of ternary systems of alkali metal fluoride salts saturated with silicon tetrafluoride, it is removed from the electrolyzer in the form of a suspension with an electrolyte, isolated from the electrolyte melt according to the method of claim 8, and is characterized by the above composition provided that:
• the claimed solutions provide highly pure elemental fluorine, including fluorine with a mass content of C 4 and impurities with their mass content of C 5 , which is obtained by fluoride technology according to the method according to claim 1 of the formula, i.e. isolated on the anode during electrolytic decomposition of the eutectic melt of ternary systems of alkali metal fluoride salts saturated with silicon tetrafluoride, and is characterized by the above composition under the condition:
• the problem of obtaining high-purity silicon powder is also solved by a method for producing silicon tetrafluoride used in the above technology, which includes the use of silicon dioxide as the starting compound, and which differs from the known solutions for the production of silicon tetrafluoride in that silicon dioxide is fluorinated by exposure to elemental fluorine, the fluorination process lead in two stages, of which: at the first stage, silicon dioxide is treated with elemental fluorine at a temperature of HOO 0 C - 1200 0 C, while the supply of elemental fluorine is carried out from May 20-30%. excess relatively stoichiometrically necessary amount and the gas phase is sent to the 2nd stage of the process, at the 2nd stage carry out the fluorination of silicon dioxide when it is supplied with 70-
• Replacement sheet May 80th. excess, while using an excess of elemental fluorine of the 1st stage with its complete absorption.
• fluorination is carried out in a flame of a flame reactor.
• fluorine obtained by the method for producing high-purity silicon powder by electrolysis of a melt eutectic of ternary systems of alkali metal fluoride salts saturated with silicon tetrafluoride i.e. fluorine obtained by the method described in paragraph l of the formula of the claimed group of inventions.
• the proposed methods serve one purpose and provide the possibility of recirculation of the chemical elements and compounds obtained during the process, thereby causing the closure of the technological cycle for producing high-purity silicon, which, along with solving the problem by means of a set of characteristics set forth in independent clauses, is also aimed at reducing the cost of the final product - high purity semiconductor silicon.
• the possibility of returning the spent substance back to the process solves the problem of waste of harmful substances, eliminates their release into the atmosphere, eliminates the need for their disposal and cleaning, etc.
• the claimed group of inventions is so interconnected that these inventions form a single common inventive concept, and there is a technical relationship between the inventions.
• FIG. 1 is a flowchart showing a process (part I) for producing high-purity silicon powder and elemental fluorine, including a set of process steps (part II) for separating silicon powder from molten salts;
• FIG. 2 is a flowchart illustrating a method for producing silicon tetrafluoride;
• equipment and hardware complexes used at the enterprises of the chemical industry and in metallurgy are used, namely: electrolyzers or similar reactors, flare (flame) reactors; bubbling plants, equipment for flotation, flushing, etc., drying units, transport systems designed to supply gas, liquid or solid reagents, known control equipment, etc.
• the electrolyte saturated with silicon tetrafluoride is continuously supplied to electrolyzer 2, either with a liquid metal cathode or with a solid cathode (stainless steel, silicon) and with inert anodes (carbide, silicon nitride, graphite).
• electrolyzer 2 either with a liquid metal cathode or with a solid cathode (stainless steel, silicon) and with inert anodes (carbide, silicon nitride, graphite).
• the design of the electrolyzer should be carried out taking into account the continuous withdrawal of the suspension of the released silicon powder and electrolyte from the pole gap of the electrolyzer.
• Si F 6 2 " dissociates into ions: positive Si 4+ ions and negative fluorine ions (6F " ), which are reduced: positive silicon ions on the cathode are reduced to metal silicon powder (Si), negative fluorine ions - on the anode to elemental fluorine ( ⁇ F ⁇ )
• silicon is obtained in the form of a suspension of Si powder in the electrolyte melt in a ratio of 2: 8 parts, i.e. 2 parts of silicon powder and 8 parts of electrolyte.
• Silicon powder mixed with an electrolyte melt i.e., a suspension including silicon powder and LiF-KF-NaF eutectic melt) is discharged from the cell.
• the silicon powder is separated from the molten electrolyte. This can be done by any known methods, or by the claimed method of separating silicon from molten salts (see Fig. 1, part II).
• the process is carried out in accordance with the claimed method of separating silicon from a salt melt, namely from a melt of the eutectic of fluoride salts LiF-KF-NaF.
• the solidified molten electrolyte with silicon powder is crushed in a known manner using a crusher 3.
• the crushed composition in the reactor 4 is dissolved with hydrogen fluoride HF, dissolve with stirring and at a temperature of from -5 0 C to + 12 ° C.
• a suspension is obtained from the electrolyte and silicon powder dissolved in hydrogen fluoride and the suspension is filtered to separate the Si powder using a centrifuge 5.
• the silicon powder separated by centrifugation is sent to flotation machine b, and
• the silicon powder is washed first in a solution of inorganic acids of the composition 2-3 MH 2 SO 4 + 0.1-0.2 M HF, and in the washing installation 8 with condensate (demineralized water).
• the silicon powder washed with demineralized water on the unit 9 is filtered off from water and dried in a dryer 10 in an inert medium at a temperature of 80 ° C-120 ° C. Ready high-purity, suitable for use in solar energy and in semiconductor technology, silicon powder is packaged.
• the electrolytically pure silicon powder obtained by the above method is characterized by a composition comprising silicon with a weight content of C 1 , metal impurities with a weight content of C 2 and non-metal impurities with a weight content of C 3 , under the condition:
• silicon tetrafluoride is used, which is obtained using a complex of equipment 13 and the claimed method for producing silicon tetrafluoride, an example of which is given below (see Fig. 2).
• the starting material for producing silicon tetrafluoride is natural quartzite, silica sand or other raw materials containing a large amount of silicon dioxide.
• this raw material is characterized by the following composition: SiO 2 ⁇ 97%, macroimpurity: Fe 2 O 3 , CaO, Al 2 O 3
• silicon dioxide SiO 2 is treated with elemental fluorine F 2 (obtained by the method according to claim 1) at a temperature of HOO 0 C - 1200 ° C, while the treatment is carried out in a flame of a flame reactor 14.
• the elemental fluorine is fed into the reactor 14 with excess (20-30%) relative to the stoichiometrically necessary amount.
• the gaseous phase including gaseous silicon tetrafluoride SiF 4 , and also including the oxygen obtained in the reaction process and the excess fluorine (02 + F2) not involved in the reaction process.
• a slurry containing macroimpurity fluorides is removed from reactor 14: aluminum trifluoride (AlF 3 ), calcium difluoride (CaF 2 ), iron trifluoride (FeF 3 ).
• AlF 3 aluminum trifluoride
• CaF 2 calcium difluoride
• FeF 3 iron trifluoride
• silicon dioxide is simultaneously fed into it, which is supplied from May 70-80%. in excess.
• the excess of elementary fluorine of the 1st stage is completely absorbed, the silicon tetrafluoride obtained is used as a reagent to saturate the electrolyte in the method for producing high-purity silicon powder and elemental fluorine, or it is removed from the process as a finished product, and the excess of silicon dioxide is sent into the first reactor 14, thus closing the process.
• the inventive method for producing silicon tetrafluoride ensures the full use of elemental fluorine in the technological process, including it may be fluorine obtained by electrolytic production of silicon powder.
• the inventive inventions forming a fluoride technology for producing high-purity semiconductor silicon are energy and
• SHEET resource-saving while the technology is characterized by environmental friendliness due to the fact that the process is conducted in a closed cycle using fluorine obtained during electrolysis to obtain silicon tetrafluoride, and also due to the fact that the spent electrolyte is returned completely to the process.
• the resulting products (silicon, fluorine, silicon tetrafluoride) are characterized by a very small amount of impurities, and the cost of silicon as a finished product is much lower than by other known technologies.

Landscapes

• 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)

Priority Applications (4)

Applications Claiming Priority (2)

Related Child Applications (1)

Publications (1)

Family

ID=35907667

Family Applications (1)

Country Status (7)

Families Citing this family (9)

Citations (3)

Family Cites Families (8)

• 2004
  • 2004-08-12 RU RU2004124626/15A patent/RU2272785C1/ru not_active IP Right Cessation
• 2005
  • 2005-01-08 UA UAA200700624A patent/UA80662C2/uk unknown
  • 2005-08-01 WO PCT/RU2005/000400 patent/WO2006019334A1/ru active IP Right Grant
  • 2005-08-01 ES ES200750013A patent/ES2319072B1/es not_active Expired - Fee Related
  • 2005-08-01 DE DE112005001969T patent/DE112005001969T5/de not_active Withdrawn
  • 2005-08-01 CN CN2005800271905A patent/CN101090862B/zh not_active Expired - Fee Related
• 2007
  • 2007-02-12 US US11/673,788 patent/US20070209945A1/en not_active Abandoned

Patent Citations (3)

Also Published As

Similar Documents

Legal Events