JP2014502671A - Method and apparatus for producing silicon - Google Patents

Abstract

An instrument for producing pure silicon from an electrolyte, comprising: a first crucible for receiving an electrolyte; a heat source for heating the electrolyte in the first crucible to form a molten electrolyte; a molten electrolyte; Electrolysis can be applied to the molten electrolyte once a potential difference is provided between the anode and the cathode, suitable for electrical / ion exchange. The stirrer is suitable for stirring the molten electrolyte when electrolysis is applied, and the pure silicon produced in this way can be dissolved in the anode to form an alloy.
[Selection] Figure 3

Description

  [0001] The present invention relates to a method and apparatus for manufacturing silicon, and more particularly, to a method and apparatus for manufacturing silicon having a purity suitable for use in solar cell applications and the like.

  [0002] Solar cell technology is understood to be an environmentally friendly technology that replaces conventional forms of energy production, such as energy production using fossil fuels. Therefore, solar cell technology is one of the important commercial markets.

  [0003] At present, technology developed by Siemens ("Siemens method") is generally accepted as the most important process for producing silicon with a purity suitable for use in solar cell applications. ing. In the Siemens method, when a high-purity silicon rod is exposed to trichlorosilane at 1150 ° C., silicon is sequentially decomposed by the trichlorosilane gas and deposited on the rod, and the rod becomes large. However, the Siemens method is considered relatively expensive and not environmentally friendly. In terms of energy, the Siemens process is estimated to consume approximately 200 MW / hour of electricity to produce 1 ton of solar grade silicon.

  [0004] A carbothermal reduction method has also been developed as an alternative to the Siemens method. However, because such processes do not inherently remove carbon and other impurities such as boron and phosphites, they can not be brought to appropriate low levels (i.e. parts per million or parts per billion). Cannot produce grade quality silicon.

  [0005] Accordingly, it has been recognized that alternative methods are needed in an attempt to solve the problems associated with solar grade silicon manufacturing described above.

  [0006] The present invention aims to alleviate at least one of the above-mentioned problems.

  [0007] The present invention may include a variety of general forms. Embodiments of the invention may include one or any combination of the various general forms described herein.

[0008] In a first general form, the present invention provides a method of producing pure silicon from an electrolyte, wherein the method comprises the following steps:
(I) heating the electrolyte in a first crucible to form a molten electrolyte; and
(Ii) applying electrolysis to the molten electrolyte by providing a potential difference between an anode and a cathode suitable for electricity / ion exchange with the molten electrolyte;
Including
Here, during the electrolysis, the molten electrolyte is agitated and the pure silicon produced can dissolve with the anode to form an alloy.

  [0009] Advantageously, agitation of the molten electrolyte during electrolysis may serve to both generate a flow of ions in the molten electrolyte and to increase contact between the electrolyte and the molten alloy anode. is there. Thereafter, as discussed further below, pure silicon can be easily separated from the alloy using separation techniques.

  [0010] Preferably, the electrolyte may include cryolite, calcium oxide particles, and quartz particles. More preferably, the electrolyte may comprise approximately 82-94% cryolite particles based on the weight of the electrolyte. Also typically, the electrolyte may include approximately 3-15% calcium oxide particles based on the weight of the electrolyte. Also preferably, the electrolyte may include approximately 3% quartz particles based on the weight of the electrolyte. More preferably, the electrolyte may comprise approximately 87% cryolite particles, 10% calcium oxide particles, and 3% quartz particles based on the weight of the electrolyte. Also preferably, the present invention includes the step of adding quartz particles in a controlled manner to the molten electrolyte during electrolysis so that substantially about 3% quartz particles are maintained in the electrolyte based on the mass of the electrolyte. You may go out.

  [0011] Typically, the first crucible may include at least one of carbon, silicon nitride, and silicon carbide material. Preferably, the material of the first crucible may be such that it generates heat when placed in an induction furnace, or it conducts heat in a relatively efficient manner when placed in a direct furnace. But you can. Preferably, the first crucible may include a recess defined by an inner peripheral wall and a bottom for receiving the electrolyte. Typically, the recess may be a cylindrical recess.

  [0012] Preferably, the first crucible lining can be disposed between the first crucible and the electrolyte inside the recess of the first crucible. More preferably, the first crucible lining may be formed so as to substantially supplement the peripheral wall in a shape along the inner peripheral wall of the first crucible. Preferably, the first crucible lining may include a quartz material. Alternatively, the first crucible lining may include at least one of calcium oxide, magnesium fluoride, sodium fluoride, and silicon material. Preferably, the material used as the first crucible lining may have a temperature resistance at temperatures above at least about 1000 ° C. Preferably, the material used as the first crucible lining may further have corrosion resistance while being exposed to the electrolyte during the electrolysis process. Advantageously, the first crucible lining may help prevent absorption of electrolyte into the first crucible wall, which may reduce the efficiency of the electrolysis process to the alloy anode. In addition, the first crucible lining helps to block the absorption of electrolyte into the wall of the first crucible, which prevents a short circuit that can have a significant impact on the electrolysis efficiency of the silicon to the alloy anode. It will also be.

  [0013] Alternatively, the first crucible lining can also be formed from the molten electrolyte itself, in which case a temperature gradient is formed in the molten electrolyte and a portion of the molten electrolyte is disposed near the inner peripheral wall of the first crucible. A lining can be formed by solidification. Typically, electric arc heating can be used to create a temperature gradient between the cathode and the molten electrolyte in contact with the inner peripheral wall of the first crucible.

  [0014] Typically, the electrolyte can be heated using at least one of an arc furnace and an induction furnace.

  [0015] Typically, the molten electrolyte may be agitated by magnetically agitating the molten electrolyte with a mechanical stirrer using at least one induction furnace.

  [0016] Typically, the anode may include at least one of a copper, gold, silver, zinc, and magnesium material. Preferably, the anode includes a copper material. More preferably, the anode may comprise an alloy of copper and pure silicon. Typically, pure silicon constitutes approximately 3% by weight of the alloy.

  [0017] Preferably, prior to step (i) in the first general form, in the first crucible, the alloy is placed adjacent to the bottom of the first crucible to form the alloy in the first crucible. The electrolyte can be deposited on the molten alloy of the first crucible in preparation for step (i) in the first general form that may be melted and subsequently performed. Typically, the alloy may be melted at a temperature of approximately 950-980 ° C.

  [0018] Typically, step (i) in the first general form comprises heating the electrolyte in a first crucible to a temperature of at least about 900 ° C. to form a molten electrolyte. You may go out.

  [0019] Preferably, during step (ii) in the first general form, the molten electrolyte may be maintained at a temperature at which the molten electrolyte does not solidify. Typically, a temperature of approximately 900-1000 ° C. may be maintained to reduce solidification of the molten electrolyte. Preferably, a temperature of approximately 980 ° C. may be maintained to prevent solidification of the molten electrolyte.

[0020] Typically, the molten electrolyte during the electrolysis is applied, may be subjected to a current density of approximately 0.1A ^/ cm ² ~2.0A ^/ cm 2 in the first crucible.

  [0021] Typically, the cathode may include at least one of carbon, copper and platinum materials. Preferably, the cathode can also be formed by pressing purified carbon powder into a solid rod. More preferably, the carbon powder may be purified by removing the impurities by subjecting the carbon powder to acid cleaning and flushing with chlorine.

  [0022] Preferably, after the electrolyte is heated to form a molten electrolyte, the cathode may be disposed in the first crucible while the cathode is exchanging electricity / ions with the molten electrolyte.

  [0023] Preferably, the present invention may include the step of separating pure silicon from the alloy after step (ii). Typically, when pure silicon produced as a result of electrolysis cannot be dissolved with the alloy, a step of separating pure silicon from the alloy may be performed. Further, typically, when the temperature of the alloy is approximately 950 to 980 ° C., there is a possibility that the pure silicon cannot be dissolved with the alloy when the amount of pure silicon in the alloy is approximately 25% based on the mass of the alloy.

  [0024] Typically, the step of separating the pure silicon from the alloy may include adjusting the temperature of the alloy to approximately 800-850 ° C., whereby the pure silicon is removed from the alloy. It can be separated naturally. Also preferably, the alloy may be transferred to a second crucible before adjusting the temperature of the alloy to approximately 800-850 ° C. Preferably, the second crucible may comprise a material that is inert to the alloy and / or molten salt. Typically, pure silicon separated with a molten salt may be coated to reduce the reoxidation of pure silicon. Typically, once a predetermined percentage of pure silicon particles have been separated from the alloy based on the mass of the alloy, the alloy in the second crucible may be reintroduced into the first crucible. More typically, when the alloy in the second crucible is reintroduced into the first crucible, the percentage of pure silicon particles (based on the mass of the alloy) is approximately 11% pure silicon based on the mass of the alloy. It may be a particle.

[0025] Alternatively and / or in addition, after separating a predetermined percentage of pure silicon particles from the alloy in the second crucible, the alloy in the second crucible is reintroduced into the first crucible. Instead of the following steps:
(I) forming an alloy in the second crucible into at least one of a tape and a powder; and
(Ii) applying a second electrolysis to the tape or powder;
May be applied so that pure silicon particles can be separated from the alloy in the form of nano-sized pure silicon particles.

  [0026] Typically, the tape can also be formed by at least one of alloy casting or extrusion. Typically, the powder can also be formed by mechanically grinding or grinding the alloy. Preferably, the powder can also be formed by grinding the alloy in a controlled environment. Typically, the powder may contain micron to nano-sized alloy particles.

[0027] Preferably, the step of applying the second electrolysis may comprise immersing the tape or powder in the electrolyte. Typically, the electrolyte is hydrochloric acid (HCl), acetic anhydride, iodine solution (i.e. potassium iodine solution), hydrazoic acid (HN _3), acetone, at least one of high concentrations of alcohol and combinations thereof May be included. Preferably, the acidity of the electrolyte may be supplemented during the second electrolysis.

  [0028] During the second electrolysis, typically less than 1 A of current can be applied.

  [0029] Preferably, after the second electrolysis is performed, the electrolyte containing nano-sized pure silicon particles may be further processed to separate the nano-sized pure silicon particles from the electrolyte. Typically, nanosized pure silicon particles may be separated from the electrolyte by centrifugation. Also preferably, the separated nanosized pure silicon particles may then be stored in a material suitable for reducing reaction with free oxygen. Such materials typically include high concentrations of alcohol or absolute alcohol.

  [0030] Alternatively, as would be understood by those skilled in the art, any of the above steps of separating pure silicon from the alloy in the second crucible can be performed without moving to the second crucible. This can be done directly on the first crucible alloy.

  [0031] Alternatively, after step (ii) according to the first general form of the present invention, the step of separating pure silicon from the alloy produced in the first crucible may comprise It may include decomposing and reversing the polarity of the anode and cathode. Preferably, by reversing the polarity, the cathode can provide a positive node and the anode can provide a negative node during the second electrolysis. Typically, a second electrolysis can deposit a composite material comprising silicon and an electrolyte on the anode. The composite material formed on the anode may typically include silicon having a particle size of about 300 mesh.

  [0032] Preferably, the second electrolysis may be performed on the alloy in a crucible separate from the first crucible (which may typically include SiC material).

[0033] Typically, the second electrolysis is the electrolyte composition shown below (expressed in approximate weight percent):
(I) 10% K ₂ SiF ₆ , 25% AlF ₃ , 25% NaF, 35% BaF ₂ , 5% CaF ₂ ;
(Ii) 40 to 70% of _Na 3 _AlF 6, _5~20% of _K 2 _SiF 6, _5~15% of _CaF 2, 5 to 10% of CaO; and,
(Iii) 95-99% Na ₃ AlF ₆ , 1-5% SiO ₂ ,
You may carry out using at least 1 sort (s) of these.

  [0034] Preferably, the composite material deposited on the anode may be melted at a temperature of at least approximately 1450 ° C. or higher, followed by cooling in the electrolyte to agglomerate the silicon into pellets or ingots. Typically, the composite material may be melted by using an induction furnace or the like.

  [0035] Typically, during cooling, agglomerated silicon pellets or ingots may be filtered out of the electrolyte by using a filter (eg, a mesh or the like). Alternatively, the composite material may be melted back into the alloy, cooled at a controlled rate, and the silicon lifted up for easy recovery. Typically, the composite material may be melted back into the alloy at a temperature in accordance with a predetermined melting temperature shown in the phase equilibrium diagram shown in FIG.

[0036] In a second general form, the present invention provides an instrument for producing pure silicon from an electrolyte, the instrument comprising:
A first crucible for receiving electrolyte;
A heat source for heating the electrolyte in the first crucible to form a molten electrolyte;
An anode and cathode suitable for electrical / ion interaction with the molten electrolyte, where electrolysis can be applied to the molten electrolyte when a potential difference is formed between the anode and cathode; and
An agitation device for agitating the molten electrolyte when applying electrolysis, thereby producing pure silicon and melting with the anode to form an alloy;
including.

  [0037] Preferably, the electrolyte may include cryolite, calcium oxide particles, and quartz particles. More preferably, the electrolyte may comprise approximately 82-94% cryolite particles based on the weight of the electrolyte. Also typically, the electrolyte may include approximately 3-15% calcium oxide particles based on the weight of the electrolyte. Also preferably, the electrolyte may include approximately 3% quartz particles based on the mass of the electrolyte. More preferably, the electrolyte may comprise approximately 87% cryolite particles, 10% calcium oxide particles, and 3% quartz particles based on the weight of the electrolyte.

  [0038] Preferably, the present invention includes a dispenser for dispensing quartz particles to the electrolyte during electrolysis so that approximately 3% quartz particles are maintained in the electrolyte substantially based on the mass of the electrolyte. You may go out.

  [0039] Typically, the first crucible may include at least one of carbon, silicon nitride, and silicon carbide material. Preferably, the first crucible may include a recess surrounded by an inner peripheral wall and a bottom for receiving the electrolyte. Typically, the recess may include a cylindrical or rectangular recess.

  [0040] Preferably, the present invention may include a lining of the first crucible, the lining being disposed between the first crucible and the electrolyte inside the recess of the first crucible. Preferably, the lining of the first crucible may be formed so as to substantially supplement the peripheral wall in a shape along the inner peripheral wall of the first crucible. Typically, the first crucible lining may include at least one of quartz, calcium oxide, magnesium fluoride, sodium fluoride, and silicon material.

  [0041] Alternatively, the first crucible may include a lining of the first crucible, the lining of the first crucible being a part of the molten electrolyte as a result of forming a temperature gradient in the molten electrolyte. It is formed by solidifying the part. Typically, the present invention may include an electric arc heating device for creating a temperature gradient between the cathode and the molten electrolyte in contact with the inner peripheral wall of the first crucible.

  [0042] Typically, the heat source may include at least one of an arc furnace and an induction furnace. Preferably, the arc furnace may be a primary heat source.

  [0043] Typically, the molten electrolyte may be agitated by magnetically agitating the molten electrolyte with a mechanical stirrer using at least one induction furnace. Advantageously, the induction furnace can reduce production costs by providing two functions as a heat source and as a stirring device.

  [0044] Typically, the anode may include at least one of copper, silver, gold, zinc, and magnesium materials. Preferably, the anode may include a copper material. More preferably, the anode may comprise an alloy of copper and pure silicon. Typically, pure silicon may comprise approximately 3-7% by weight of the alloy.

  [0045] Preferably, in the first crucible, the alloy may be placed adjacent to the bottom of the first crucible to melt the alloy, and the electrolyte may be placed on the alloy. Typically, the heat source may be set to melt the alloy at a temperature of approximately 950-980 ° C.

  [0046] Typically, the heat source may be set to heat the electrolyte to a temperature of at least about 900 ° C. in the first crucible to form a molten electrolyte.

  [0047] Preferably, during electrolysis of the molten electrolyte, the heat source may be set to maintain the molten electrolyte at a temperature at which the molten electrolyte does not solidify. Typically, the heat source may be set to maintain the temperature of the molten electrolyte at approximately 900-1000 ° C to prevent solidification of the molten electrolyte. Preferably, in order to prevent solidification of the molten electrolyte, the heat source may be set to maintain the temperature of the molten electrolyte at approximately 980 ° C.

[0048] Typically, the molten electrolyte during the electrolysis is applied, may be subjected to a current density of approximately 0.1A ^/ cm ² ~2.0A ^/ cm 2 in the first crucible.

  [0049] Typically, the cathode may include at least one of carbon, copper, and platinum materials. Preferably, the cathode may include a solid rod formed from purified carbon powder. More preferably, the carbon powder may be purified by removing the impurities by subjecting the carbon powder to acid cleaning and flushing with chlorine. Preferably, the cathode is also suitable for being placed in the first crucible after the electrolyte is heated to form a molten electrolyte and the cathode is in electrical / ion exchange with the molten electrolyte. Good.

  [0050] Preferably, the present invention may include an instrument for separating pure silicon from an alloy. Preferably, the device for separating pure silicon from the alloy may be set to separate pure silicon from the alloy when the pure silicon produced as a result of electrolysis does not dissolve with the alloy. Also typically, when the alloy is at a temperature of approximately 950-980 ° C., pure silicon may not dissolve with the alloy (where the amount of pure silicon in the alloy is approximately 25 based on the mass of the alloy). %).

  [0051] Typically, an apparatus for separating pure silicon from an alloy may be adapted to adjust the temperature of the alloy to approximately 800-850 ° C., thereby separating pure silicon from the alloy. Is possible. Also preferably, the instrument for separating pure silicon from the alloy may be designed to transfer the alloy to a second crucible before adjusting the temperature of the alloy to approximately 800-850 ° C. Also preferably, the second crucible may comprise a material that may be inert to the alloy and / or molten salt. Preferably, in order to reduce reoxidation of pure silicon, pure silicon separated using a molten salt may be coated. Typically, the present invention may be suitable for reintroducing the alloy in the second crucible into the first crucible once a predetermined percentage of pure silicon particles are separated from the alloy based on the mass of the alloy. There is sex. More typically, the predetermined percentage of pure silicon particles based on the mass of the alloy may comprise approximately 11% pure silicon particles based on the mass of the alloy.

[0052] Alternatively and / or in addition, an apparatus for separating pure silicon from an alloy in a second crucible is:
(I) an instrument for forming the alloy in the second crucible into at least one of a tape and powder; and
(Ii) a device for applying a second electrolysis to the tape or powder;
May contain,
With such an instrument, pure silicon particles can be separated from the alloy in the form of nano-sized pure silicon particles.

  [0053] Typically, an instrument for forming an alloy into a tape may be designed to cast or extrude the alloy into a tape. Also typically, the powder forming device may be suitable for mechanically grinding or grinding the alloy into a powder in a controlled environment. Preferably, the powder can also be formed by grinding the alloy. Typically, the powder may contain micron to nano-sized alloy particles.

[0054] Preferably, the device for applying the second electrolysis may be suitable for immersing the tape or powder in the electrolyte. Typically, the electrolyte is hydrochloric acid (HCl), acetic anhydride, iodine solution (i.e. potassium iodine solution), hydrazoic acid (HN _3), acetone, at least one of high concentrations of alcohol and combinations thereof May be included. Preferably, the acidity of the electrolyte may be supplemented during the second electrolysis.

  [0055] Typically, an instrument for applying a second electrolysis may be suitable for applying a current of less than 1 A during the second electrolysis.

  [0056] Preferably, the present invention may include an instrument for separating nano-sized pure silicon particles in the electrolyte from the electrolyte after the second electrolysis is applied. Typically, this may include a centrifuge device for separating nanosized pure silicon particles from the electrolyte by centrifugation. Also preferably, the present invention may include a storage device for storing nano-sized pure silicon particles separated in a material suitable for reducing reaction with free oxygen. Such materials typically include high concentrations of alcohol.

  [0057] Alternatively, as would be understood by one of ordinary skill in the art, the instrument for separating pure silicon from the alloy in the second crucible is likewise not transferred to the second crucible. It is also suitable for separating pure silicon directly from the first crucible alloy.

  [0058] Alternatively, an apparatus for separating pure silicon from an alloy produced in a first crucible performs a second electrolysis on the alloy and reverses the polarity of the anode and cathode during the second electrolysis. It may be suitable for. Preferably, by reversing the polarity, the cathode can provide a positive node and the anode can provide a negative node. Typically, a second electrolysis can deposit a solid composite comprising silicon and an electrolyte on the anode. Typically, the silicon in the composite material formed on the anode may have a particle size of about 300 mesh.

  [0059] Preferably, the apparatus for separating pure silicon from the alloy may include a crucible separate from the first crucible, wherein the separate crucible performs a second electrolysis on the alloy. The polarity of the anode and cathode can be reversed. Typically, such a separate crucible may contain a SiC material.

[0060] Typically, instruments for separating pure silicon are the electrolytes shown below (shown in approximate mass percent):
(I) 10% K ₂ SiF ₆ , 25% AlF ₃ , 25% NaF, 35% BaF ₂ , 5% CaF ₂ ;
(Ii) 40 to 70% of _Na 3 _AlF 6, _5~20% of _K 2 _SiF 6, _5~15% of _CaF 2, 5 to 10% of CaO; and,
(Iii) 95-99% Na ₃ AlF ₆ , 1-5% SiO ₂ ,
The second electrolysis may be designed using at least one of the above.

  [0061] Preferably, the device is suitable for melting the composite material deposited on the anode at a temperature of at least about 1450 ° C or higher, followed by cooling in the electrolyte to agglomerate the silicon into pellets or ingots. A heating mechanism may be included. Typically, the heating mechanism for melting the composite material may include an induction furnace or the like.

  [0062] Preferably, the device may include a filter, such as a mesh filter, suitable for filtering out aggregated silicon pellets or ingots from the electrolyte as it cools.

  [0063] Alternatively, the instrument may include a mechanism that melts the composite material back into the alloy, cools the composite material at a controlled rate, and floats the silicon up for easy retrieval. . Typically, the composite material may be melted back into the alloy at a temperature in accordance with a predetermined melting temperature shown in the phase equilibrium diagram shown in FIG.

[0064] In a third general form, the present invention provides a method of producing pure silicon from an electrolyte, wherein the method comprises the following steps:
(I) heating the electrolyte in a first crucible to form a molten electrolyte; and
(Ii) applying electrolysis to the molten electrolyte by providing a potential difference between an anode and a cathode suitable for electricity / ion exchange with the molten electrolyte;
Including
Here, the lining of the first crucible is arranged inside the first crucible, so that when the electrolysis is applied, the inner peripheral wall of the first crucible and the molten electrolyte are substantially separated. Isolated and produced pure silicon can melt with the anode to form an alloy.

[0065] In a fourth general form, the present invention provides an instrument for producing pure silicon from an electrolyte, the instrument comprising:
A first crucible for receiving electrolyte;
A heat source for heating the electrolyte in the first crucible to form a molten electrolyte;
An anode and cathode suitable for electrical / ion interaction with the molten electrolyte, where electrolysis can be applied to the molten electrolyte when a potential difference is formed between the anode and cathode; and
Lining of the first crucible disposed inside the first crucible (thereby substantially isolating the inner peripheral wall of the first crucible from the molten electrolyte when electrolysis is applied to the molten electrolyte. Can)
Including
The pure silicon produced in this way melts with the anode to form an alloy.

[0066] In a fifth general form, the present invention separates pure silicon from an alloy comprising at least one of copper, gold, silver, zinc, and magnesium materials alloyed with pure silicon particles. A method is provided, the method comprising the steps of:
(I) forming the alloy into at least one of a tape and a powder; and
(Ii) applying electrolysis to the tape or powder;
Including
In this way, pure silicon particles can be isolated from the alloy in the form of nano-sized pure silicon particles.

  [0067] Typically, the tape can also be formed by at least one of alloy casting or extrusion. Typically, the powder can also be formed by mechanically grinding or grinding the alloy in a controlled environment. Preferably, the powder is formed by grinding the alloy. Typically, the powder may contain micron to nano-sized alloy particles.

[0068] Preferably, the step of performing the electrolysis may comprise immersing the tape or powder in an electrolyte. Typically, the electrolyte is hydrochloric acid (HCl), acetic anhydride, iodine solution (i.e. potassium iodine solution), hydrazoic acid (HN _3), acetone, at least one of high concentrations of alcohol and combinations thereof May be included. Preferably, the acidity of the electrolyte may be supplemented during electrolysis.

  [0069] During electrolysis, typically less than 1 A of current can be applied.

  [0070] Preferably, after the electrolysis is performed, the electrolyte containing nano-sized pure silicon particles may be further processed to separate the nano-sized pure silicon particles from the electrolyte. Typically, nanosized pure silicon particles may be separated from the electrolyte by centrifugation. Also preferably, the separated nano-sized pure silicon particles can then be stored in a material suitable for reducing reaction with free oxygen. Such materials typically include high concentrations of alcohol.

[0071] In a sixth general form, the present invention is for separating pure silicon from an alloy comprising at least one of copper, gold, silver, zinc, and magnesium materials alloyed with pure silicon particles. This instrument provides:
(I) an instrument for forming the alloy into at least one of a tape and powder; and
(Ii) a device for applying electrolysis to the tape or powder;
Including
In this way, pure silicon particles can be separated from the alloy in the form of nano-sized pure silicon particles.

  [0072] Typically, an instrument for forming an alloy into a tape may be designed to cast or extrude the alloy into a tape. Also typically, the device for forming the powder may be suitable for mechanically grinding or grinding the alloy into a powder. Preferably, the powder can also be formed by grinding the alloy in a controlled environment. Typically, the powder may contain micron to nano-sized alloy particles.

[0073] Preferably, the electrolysis device may be suitable for dipping a tape or powder in an electrolyte. Typically, the electrolyte is at least one of hydrochloric acid (HCl), acetic anhydride, iodine solution (ie, potassium iodide solution), hydrazoic acid (HN ₃ ), acetone, high concentration alcohol, and combinations thereof. May be included. Preferably, the acidity of the solution may be supplemented during electrolysis.

  [0074] Typically, an instrument that performs electrolysis may be suitable for applying a current of less than 1 A during electrolysis.

  [0075] Preferably, the present invention may include a device for separating nanosized pure silicon particles in the electrolyte from the electrolyte. Typically, this may include a centrifuge device for separating nanosized pure silicon particles from the electrolyte by centrifugation. Also preferably, the present invention may include a storage device for storing the separated nano-sized pure silicon particles in a material suitable for reducing reaction with free oxygen. Such materials typically include high concentrations of alcohol.

  [0076] In any one of the general aspects of the invention described above, the second crucible lining may be disposed in the first crucible between the alloy and the first crucible lining. Typically, the second crucible lining may include at least one of SiN or SiC material, so that the lifetime of the first lining is such that SiC and SiN are wear resistant. Can be extended. Preferably, the second crucible lining may include a substantially non-porous surface.

  [0077] Typically, the second crucible lining may be submerged substantially below the upper surface of the alloy (if melted) in the first crucible, and further in the first crucible. During the electrolysis of the electrolyte, it is maintained substantially below the upper surface of the alloy so that the absorption of electrolyte into the second crucible lining is reduced.

[0078] In a seventh general form, the present invention provides a method of producing pure silicon, the method comprising the following steps:
(I) a step of electrolyzing an electrolyte containing quartz in a crucible to form a solid composite material containing silicon and an electrolyte;
(Ii) melting the composite material and subsequently aggregating silicon particles in the composite material in the electrolyte while cooling;
(Iii) a step of filtering out the agglomerated silicon from the electrolyte when the temperature of the melted composite material falls below approximately 1414 ° C .;
including.

  [0079] Typically, in step (i), the electrolyte may comprise a combination of quartz pellets / blocks and powdered quartz. Preferably, step (i) of performing electrolysis includes maintaining the supply of silicon particles during electrolysis by periodically adding powdered quartz to the crucible.

  [0080] Typically, the formed composite material may include approximately 20 weight percent silicon particles and approximately 80 weight percent electrolyte particles.

  [0081] Preferably, the electrolysis may be performed using two carbon electrodes containing an appropriate amount of raw material that can be subjected to an electrolysis process.

[0082] In an eighth general form, the present invention provides an instrument for producing pure silicon, the instrument;
(I) a crucible suitable for containing an electrolyte containing quartz;
(Ii) an electrolysis system suitable for electrolyzing the electrolyte in the crucible and depositing a solid composite material of silicon and electrolyte in the crucible;
(Iii) a heating mechanism suitable for aggregating the silicon particles in the composite in the electrolyte while melting the composite and subsequently cooling; and
(Iv) a filter suitable for filtering out aggregated silicon from the electrolyte when the temperature of the melted composite material drops below approximately 1414 ° C .;
including.

  [0083] Typically, the electrolyte may comprise a combination of quartz pellets / blocks and powdered quartz. Preferably, the present invention includes a mechanism for delivering periodically powdered quartz to the crucible during electrolysis to maintain a supply of silicon particles during electrolysis.

  [0084] Typically, a composite material formed by electrolyte electrolysis may include approximately 20 weight percent silicon particles and approximately 80 weight percent electrolyte particles.

  [0085] Preferably, the electrolysis system may include two carbon electrodes containing an appropriate amount of raw material that can be subjected to an electrolysis process.

  [0086] In a ninth general form, the present invention provides pure silicon produced according to any one of the general forms of the invention described herein.

  [0087] In a tenth general form, the present invention provides a solar cell comprising pure silicon produced according to any one of the general aspects of the invention described herein.

  [0088] In an eleventh general form, the invention provides a battery comprising pure silicon produced according to any one of the general forms of the invention described herein. Typically, the battery anode is formed from pure silicon.

  [0089] In a twelfth general form, the present invention provides a crucible lining suitable for use in accordance with any one of the general forms of the invention described herein. In a thirteenth general form, the present invention provides an electrical equipment grade silicon material suitable for use in forming an integrated circuit device, wherein said electrical equipment grade silicon material. Are produced according to any one of the general forms of the invention described herein.

  [0090] The invention will be better understood from the following detailed description of a preferred, non-limiting embodiment of the invention described in connection with the accompanying drawings.

FIG. 1 shows a flow chart of a method for producing pure silicon from an electrolyte according to an embodiment of the present invention. FIG. 2 shows a flowchart of an embodiment method for separating pure silicon from an alloy formed according to the method steps shown in FIG. FIG. 3 shows a cutaway side view of an instrument for producing pure silicon in accordance with an embodiment of the present invention. FIGS. 4a and 4b show an EDX chart and corresponding SEM image of a first sample taken from an alloy containing pure silicon after the first electrolysis in the first crucible. 5a and 5b show an EDX chart and corresponding SEM image of a second sample taken from an alloy containing pure silicon after the first electrolysis in the first crucible. Figures 6a and 6b show an EDX chart and corresponding SEM image of a third sample taken from an alloy containing pure silicon after the first electrolysis in the first crucible. Figures 7a and 7b show an EDX chart and corresponding SEM image of a fourth sample taken from an alloy containing pure silicon after the first electrolysis in the first crucible. FIG. 8 shows EDX data and corresponding SEM images of a sample of pure silicon naturally separated from an alloy transferred from a first crucible to a second crucible according to an embodiment of the present invention. FIG. 9 shows EDX data of a sample of nanosized pure silicon separated from the alloy in the second crucible during a second electrolysis using a 10% hydrochloric acid (HCl) electrolyte according to an embodiment of the present invention. And the SEM image corresponding to it is shown. FIG. 10 shows EDX data of a sample of nanosized pure silicon separated from the alloy in the second crucible during the second electrolysis using a 20% hydrochloric acid (HCl) electrolyte according to an embodiment of the present invention. And the SEM image corresponding to it is shown. FIG. 11 shows additional EDX data and corresponding SEM images of an additional sample of nano-sized pure silicon separated from the alloy in the second crucible during the second electrolysis according to an embodiment of the present invention. Indicates. FIG. 12 shows an amorphous tape cast from the alloy remaining in the second crucible after some of the pure silicon particles in the alloy naturally separated in accordance with an embodiment of the present invention. FIG. 13 includes pure silicon in a first crucible in accordance with an embodiment of the present invention in which a direct furnace and induction furnace are variably used in heating an electrolyte in a first electrolysis as described herein. Data of test parameters and test results observed during alloy production are shown. FIG. 14 shows a cutaway view of an alternative embodiment of an instrument for separating silicon from an alloy. FIG. 15 shows a cutaway side view of an alternative embodiment of an instrument for separating silicon from an alloy. FIG. 16 shows a cutaway side view of an embodiment of the present invention in which a second crucible lining is disposed in the first crucible between the first crucible lining and the alloy anode. FIG. 17 shows a cut-away view of a further embodiment of the present invention. FIG. 18 shows experimental data showing tests performed on samples of silicon produced in accordance with an embodiment of the present invention. FIG. 19 shows a phase equilibrium diagram of an alloy of copper and silicon.

  [0091] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.

  [0092] FIGS. 1 and 2 show a flow chart of steps in accordance with an embodiment of a method for producing pure silicon. In the embodiments described herein, the term “pure silicon” means solar grade silicon. FIG. 3 shows an instrument (1) used in carrying out the steps of the method shown in FIGS. 1 and 2, which comprises a first crucible (2) for receiving electrolyte, a first To heat the first crucible lining (3) and the first crucible (2) disposed in the first crucible (2) for separating the electrolyte from the inner peripheral wall (2a) of the crucible (2). A heat source, an electrolysis device for applying electrolysis to the electrolyte (4) after melting the electrolyte (4) by the heat source, and a device for stirring the molten electrolyte (4) during electrolysis. Pure silicon produced by electrolysis forms an alloy with the anode (5). Thereafter, pure silicon can be extracted from the alloy by use of separation tools and processes as described in more detail below.

[0093] The electrolyte used in the embodiments described herein comprises approximately 87% cryolite particles, 10% calcium oxide particles, and 3% quartz particles based on the mass of the electrolyte (4). Including. Prior to placing the electrolyte (4) in the first crucible (2), the electrolyte (4) was melted together with cryolite, calcium oxide and quartz particles at a temperature of 1200 ° C., followed by melting the material. Manufactured by solidification. The resulting density of this electrolyte (4) is approximately 3 g / cm ³ .

  [0094] The first crucible (2) is formed of a carbon material and has an internal recess (2c) for receiving the electrolyte (4). The recess (2c) has a cylindrical shape and is surrounded by the inner peripheral wall (2a) and the bottom (2b). In an alternative embodiment, the first crucible (2) and the internal recess (2c) need not necessarily be cylindrical. Alternatively, the first crucible (2) may be formed from a material such as a silicon nitride or silicon carbide material. Whatever material is used, the first crucible (2) material is a material that can generate heat when placed in an induction furnace or is relatively efficient when placed in a direct furnace. It is desirable that the material be able to conduct heat in a manner.

  [0095] The electrolyzer includes an anode (5) and a cathode (7), which are coupled to an anode terminal and a cathode terminal (not shown) of a power source. When the cathode (7) and the anode (5) are arranged in contact with the molten electrolyte (4) and a potential difference is formed between the anode (5) and the cathode (7), the molten electrolyte (4) is electrolyzed. To receive. This produces pure silicon.

  [0096] The anode (5) comprises an alloy of copper and approximately 3% pure silicon particles based on the mass of the alloy. Such alloys are formed by first melting copper at a temperature of approximately 1200 ° C. and combining with approximately 3% pure silicon particles. Inclusion of 3% pure silicon particles in the alloy anode helps to set the melting temperature of the alloy to the temperature applied during electrolysis. It is conceivable that more than 3% by weight of pure silicon is combined with copper to form an alloy anode, but this amount is considered to be an appropriate minimum level for setting an appropriate melting point.

  [0097] The cathode (7) includes a carbon rod formed by pressing purified carbon powder. Prior to pressing, the carbon powder is purified by removing any impurities in the carbon powder using acid cleaning and flushing with chlorine. The carbon rod may be arranged to be controllable, and after the electrolyte (4) is heated to form the molten electrolyte (4), it is lowered into the recess of the crucible so as to contact the electrolyte (4). In large scale production, the placement of the carbon cathode (7) is expected to be made by some automated mechanical positioning system well known to those skilled in the art. In the course of testing the embodiments described herein, the carbon rod was manually lowered into contact with the molten electrolyte.

  [0098] The first crucible lining (3) has a cylindrical tube structure that fits inside the recess of the first crucible. The first crucible lining (3) is attached to the first crucible lining (2a) so as to compensate for the inner peripheral wall (2a) of the recess (2c) of the first crucible. Therefore, during use, the first crucible lining (3) becomes a barrier for separating the electrolyte (4) in the recess (2c) from the inner peripheral wall (2a) of the recess (2c) of the first crucible. Notably, the presence of the first crucible lining (3) causes the electrolyte (4) to absorb into the first crucible wall (2a), which otherwise reduces the efficiency of the electrolysis process. Is expected to prevent). In addition, the first crucible lining (3) serves to block the absorption of the electrolyte (4) into the wall (2a) of the first crucible so that more electrolyte (4) is directed to the alloy anode. As a result, the efficiency of the electrolysis process can be further improved.

  [0099] In this embodiment, the first crucible lining (3) is formed from quartz. Since the quartz lining (3) is gradually corroded by the electrolyte (4) during electrolysis, the time that electrolysis can take place is limited, and therefore the total time available to produce pure silicon by electrolysis. Is also limited. In an attempt to extend the electrolysis time, other relatively less corrosive materials such as calcium oxide, magnesium fluoride and sodium fluoride may be used instead of quartz. When quartz material is used as the first crucible lining (3), the quartz material is necessary to maintain the ratio of quartz particles in the molten electrolyte (4) at a predetermined level throughout the time electrolysis is performed. Any suitable amount of additional quartz particles can be provided.

  [0100] Alternatively, pure material has the property that it does not melt at the temperature applied in the electrolysis process and the property that it does not corrode upon interaction with the electrolyte (4), so this material is the first crucible. Can be used to form the lining (3). Since the first crucible lining (3) of pure silicon has the property of not corroding, the selected thickness of the first crucible lining (3) of pure silicon is the same as that of the first crucible lining (3) of quartz. It is not as important a consideration as when such a corrosive first crucible lining (3) is used. Since the first crucible lining of pure silicon (3) is reusable and can save current production costs, it is therefore possible to use such a lining in large scale production of pure silicon. It is expected to be particularly advantageous. Further, in practical use, when the corrosive first crucible lining (3) is used, it is necessary to periodically reinsert the first first crucible lining (3) into the first crucible (2). As expected, using pure silicon first crucible lining (3) is expected to help reduce the operational complexity associated with corrosive first crucible lining (3). In testing embodiments of the present invention, a quartz lining with a diameter of approximately 9.5 cm was used.

  [0101] Alternatively and / or in addition, the natural lining of the first crucible in the first crucible (2) by appropriately adjusting the temperature of the region in the first crucible (2) It is also possible to produce (3). For example, this can be done by creating a suitable temperature gradient, whereby the cathode (7) rather than the electrolyte present in contact with the inner peripheral wall (2a) of the first crucible (2). Can be set to a relatively high temperature. Electric arc heating is expected to be particularly suitable for forming an appropriate temperature gradient because a relatively high temperature is generated at the cathode (7) compared to the electrolyte in contact with the inner peripheral wall of the first crucible (2). . When the temperature of the cathode (7) is set to 980 ° C., for example, and the temperature of the electrolyte (4) in contact with the inner peripheral wall (2a) of the first crucible is set to 900 ° C. or lower, the first crucible The natural lining (3) of the first crucible in contact with the inner peripheral wall (2a) of (2) solidifies, but the electrolyte (4) remaining inside the first crucible (2) is at the temperature of the cathode (7). Therefore, it seems to remain in a molten state. The production of the natural lining (3) of the first crucible is in that it reduces the production costs and complexity of carrying out the process by eliminating the need to provide a stand-alone first crucible lining (3). Is advantageous.

  [0102] When testing the embodiments described herein, as a primary heat source for heating the first crucible (2), the electrolyte (4) and the alloy in the first crucible (2), A direct furnace was used. However, in an alternative embodiment, it is also conceivable to use electric arc heating, in which heat is generated by the electrical resistance of the anode (5) and the cathode (7) in the electrolyte medium as an alternative heat source. As may be easily understood, the further distance between the anode (5) and the cathode (7) is expected to result in greater resistance, and therefore a greater amount of heat is transferred to the first crucible ( 2) It is expected to shift to the electrolyte (4). Alternatively and / or in addition, an induction furnace may be used to provide induction heating.

  [0103] The molten electrolyte (4) may be continuously stirred during electrolysis using a stirring device. Agitation of the molten electrolyte (4) serves both to create a flow of ions in the electrolyte (4) and to increase contact between the electrolyte (4) and the molten alloy anode (5). Conveniently, if an induction furnace is used, the inherent nature of the induction furnace provides a stirring action within the molten electrolyte during electrolysis. Therefore, in addition to being able to be used as a second heat source for temperature control, the induction furnace can also be used as a mechanism for stirring the molten electrolyte (4) during electrolysis. This is expected to help reduce the cost of introducing a separate specialized stirrer. Furthermore, the stirring provided by the induction furnace is due to electromagnetic forces rather than direct mechanical interaction with the molten electrolyte (4), so the time and cost required to repair the mechanical stirring device. Can be reduced. The induction furnace can be designed to stir the molten electrolyte (4) with a pulse of current. In other embodiments of the invention, it will be appreciated that a mechanical stirrer may be utilized if desired.

  [0104] In an alternative embodiment, a special magnetic stirrer may be used to magnetically stir the alloy in the first crucible (2).

  [0105] Hereinafter, a method of using the above-described apparatus for producing pure silicon will be described according to embodiments of the present invention.

  [0106] First, the quartz lining (3) of the first crucible is slid into the recess to mount the lining inside the recess of the crucible. This process is indicated by block (100) in FIG. Subsequently, the alloy anode (5) is placed in the recess (2c) of the crucible so as to be in contact with the bottom (2) of the first crucible. Subsequently, the first crucible (2) is heated in a direct-fired furnace at a temperature of about 950 to 980 ° C. so that the alloy melts. This step is indicated by block (110) in FIG.

  [0107] As soon as the alloy (5) is melted, the solid electrolyte (4) is placed on the melted alloy (5) in the recess (2c) of the first crucible, followed by the first crucible (2). Further, heating is performed at a temperature of at least 900 ° C. to melt the electrolyte into a molten electrolyte (4). These steps are indicated by blocks (120) and (130) described in FIG.

  [0108] Thereafter, the carbon rod is lowered and brought into contact with the molten electrolyte (4) to start electrolysis of the molten electrolyte (4). This step is indicated by block (140) in FIG. The cathode (7) is electrically connected directly to the negative terminal of the power supply, and the alloy anode is electrically connected to the positive terminal of the power supply via the first crucible (2) (which itself is a conductive material). Then, a potential difference between the anode and the cathode (7) is generated, and electrolysis is promoted.

[0109] In a test of the embodiments described herein, a voltage in the range of 6-8V was applied across the anode (5) and cathode (7), and the anode (5) and A current of approximately 40-60 A was generated between the cathodes (7). Molten electrolyte (4) is placed in a crucible of quartz having a diameter of approximately 9.5cm, exposed to approximate current density of 70.8800938Cm ² overall for approximately 1A / cm ² of the surface area of the electrolyte.

[0110] It should be noted that if the current density is set too high, damage to the first crucible lining (3) and / or the first crucible (2) may be promoted. As will be appreciated by those skilled in the art, it will be described herein by varying the dimensions of the first crucible (2), the magnitude of the applied current density, and the surface of the electrolyte. The yield level of pure silicon produced according to the embodiment to be varied. Yield can generally be estimated according to the following formula:
Yield = Current (A) x [Electrolysis constant (0.262g / Ah)] x [Electrolysis time (h)] u
[0111] To prevent solidification of the molten electrolyte (4) during electrolysis, the molten electrolyte (4) is maintained at a temperature of approximately 900-1000 ° C. Generally, when the molten electrolyte (4) is maintained at a relatively high temperature during electrolysis, the production efficiency of pure silicon is improved. However, it should also be noted that there are certain limitations regarding the selected temperature. First of all, when testing the embodiments described herein, maintaining the temperature of the molten electrolyte (4) at a temperature of approximately 980 ° C. during electrolysis may yield particularly desirable results. It was found. If the temperature is higher than 980 ° C., the molten electrolyte (4) tends to evaporate and the viscosity increases, thereby reducing the production efficiency of pure silicon and eventually stopping the electrolysis. When the temperature is 980 ° C. or lower, the tendency to cause evaporation of the molten electrolyte (4) and increase in viscosity is expected to be low, but the molten electrolyte (4) is expected to solidify at temperatures below 900 ° C. Therefore, the temperature should not be lowered below 900 ° C.

  [0112] When electrolysis occurs, the molten electrolyte (4) is agitated and the flow of pure silicon particles produced during electrolysis increases and comes into contact with the alloy anode (5). In the test, automatic mechanical stirring was used. However, in order to magnetically stir the molten electrolyte (4) by applying a pulse of (4) current to the molten electrolyte, it is convenient to use an induction furnace. This step is indicated by block (150) in FIG.

  [0113] During electrolysis, the proportion of quartz particles in the electrolyte (4) should be maintained at approximately 3% based on the mass of the electrolyte (4). To achieve this requirement, the quartz particles in the electrolyte (4) are periodically measured using a sensor, and the quartz particles in the molten electrolyte (4) are compensated to compensate for the reduced amount if necessary. A dispensing means is used to dispense while controlling the additional amount. As described above, when a quartz material is used as the first crucible lining (3), the amount of quartz particles in the molten electrolyte (4) decreased during the electrolysis by using the quartz particles for the lining. It is possible to maintain the required ratio of quartz particles. This step is indicated by block (160) in FIG.

  [0114] FIGS. 5 and 6 show pure silicon (6) that forms an alloy with the anode (5) by using the embodiment described above. Pure silicon (6) can be separated from alloy (5) by using a separation technique.

  [0115] When pure silicon reaches the solubility limit in the alloy after a certain period of time, the electrolysis in the first crucible (2) is expected to stop. This step is indicated by block (170) in FIG. When testing embodiments of the present invention, when alloy (5) is heated at a temperature of approximately 950-980 ° C., pure silicon (6) in alloy (5) is approximately 25% by weight of alloy (5). Once reached, pure silicon (6) was found to be insoluble (5) with the alloy. The time required to reach the solubility limit is expected to depend on various factors such as the surface area of the molten electrolyte (4) that undergoes electrolysis. However, when testing the embodiments described herein, it has been found that this solubility limit is achieved in about 8 hours. Naturally, it is expected that significant improvements over existing production methods will be shown in terms of yield and purity of pure silicon (6) produced in accordance with the embodiments described herein.

  [0116] In this embodiment, referring to FIG. 2, first the molten alloy (5) is moved to a second crucible by using a suction device or any other suitable mechanical extraction means ( Not shown) initiates separation of pure silicon from alloy. The second crucible can be made from any material suitable for exposure to temperatures of approximately 800-1000 ° C. However, the material used to form the second crucible is expected to be inert to the alloy and / or molten salt, ie, a material that does not chemically react with the alloy or any other molten salt. Is expected. This step is indicated by block (200) in FIG.

  [0117] In a second crucible, maintaining the molten alloy at a temperature of approximately 800-850 ° C. at a cooling rate of approximately 2-3 ° C./min to obtain pure silicon (6 ) Is expected to spontaneously separate from the alloy (5) as a thermodynamic result. Pure silicon (6) has a lower density than copper, but floats on naturally molten alloy (5). This step is indicated by block (210) in FIG. In testing embodiments of the present invention, it was found that approximately 11% pure silicon (6) particles, based on the mass of the alloy (5), float as solid pure silicon (6) on top of the melt. . The pure silicon (6) floating in this way can be remelted into an ingot.

  [0118] This form of naturally isolated pure silicon (6) has been found to be suitable for solar grade applications and is expected to provide at least about 18% efficiency. (This efficiency is consistent with the performance of solar grade polysilicon produced by Siemens in the past). In order to reduce the reoxidation of the solid pure silicon (6) floating in this way, the molten alloy (5) in the second crucible is coated with a molten salt.

  [0119] In certain embodiments, once approximately 11% by weight of pure silicon (6) of the molten alloy from the alloy in the second crucible has spontaneously separated, the remaining alloy in the second crucible is removed from the first crucible. It may be reintroduced into the crucible. It is expected that the reintroduced molten alloy will sink to the bottom of the first crucible (2) and contribute to the further electrolysis process.

  [0120] Alternatively, instead of reintroducing the remaining alloy in the second crucible into the first crucible after a predetermined percentage of pure silicon particles have been separated from the alloy in the second crucible. The alloy remaining therein may be cast or extruded into amorphous tape, or may be mechanically ground or ground into a powder of micron to nano-sized alloy particles. As would be recognized by one skilled in the art, mechanical grinding of alloys is relatively prone to incorporating significant amounts of impurities. In previous tests of the embodiment of the present invention, instead of casting on tape, mechanical grinding of the alloy in a second crucible was performed. This step is indicated by block (220) in FIG.

  [0121] Processes and instruments used in casting amorphous tapes can be designed so that the microstructure of nano-sized pure silicon particles contained in the tape itself can be controlled according to the cooling rate during tape casting. it can. Nano-sized pure silicon particles may range from approximately 10 nm to 60 nm, and such particles can later be separated from the tape according to the embodiments described herein. FIG. 12 shows an amorphous tape cast from an alloy.

[0122] Subsequently, the tape or powder is immersed in an electrolyte and a second electrolysis is applied to the tape or powder. In the embodiments described herein, electrolytes containing 10% hydrochloric acid (HCl) and 20% hydrochloric acid (HCl) were used in different cases, and the results of these variations are shown in FIGS. 9 and 10, respectively. Indicated. Second by pumping the HCl gas in the electrolytic solution suitable pH during electrolysis and Cl ^- by maintaining levels were periodically adjust the acidity of the electrolyte. Those skilled in the art will naturally understand that in alternative embodiments, acetic anhydride, iodine solution (ie, potassium iodide solution), hydrazoic acid (HN ₃ ), acetone, high concentration alcohol Alternatively, the alloy may be immersed in another electrolytic solution containing a combination thereof. This step is indicated by block (230) in FIG.

[0123] A current of less than approximately 1 A is applied during the second electrolysis, thereby properly removing copper from the alloy. After the second electrolysis is applied, the electrolyte contains Cu / Cu ⁺ / Cu ⁺⁺ and nano-sized pure silicon particles. Subsequently, nano-sized pure silicon particles are separated from the electrolytic solution by a rotational motion using a centrifugal separator. This step is indicated by block (240) in FIG. In an alternative embodiment, a current greater than 1 A may be applied during the second electrolysis, which may result in silicon oxidation. In such a case, for example, an oxide layer of silicon (quartz) can be corroded using an acid such as HF (hydrofluoric acid) to obtain nano-sized silicon.

  [0124] Because nano-sized pure silicon particles have a relatively strong tendency to react with oxygen, nano-sized pure silicon particles are stored in materials that reduce reaction with free oxygen, such as high concentrations of alcohol. The This step is indicated by block (250) in FIG.

  [0125] Re-introducing copper extracted from the alloy tape or powder cast after the separation process into the first crucible (2) to facilitate the electrolysis process in the first crucible (2). Can be used. As will be appreciated by those skilled in the art, the molten alloy already separated is 800-850 ° C., and energy equivalent to 100-150 ° C. is required to continue the electrolysis in the first crucible (2). This can be viewed as a more efficient method in terms of saving energy since it only needs to be added.

[0126] In another embodiment, the copper or copper by flushing the tape or powder with HCl gas or chlorine gas in a closed environment free of oxygen that allows the reaction of the tape or powder with HCl gas or chlorine gas. May be removed from the alloy in the second crucible. Subsequently, it is expected that the CuCl ₂ must be removed by mechanical methods or by rinsing with a suitable solution in which the CuCl ₂ can be dissolved. Subsequently, nano-sized pure silicon particles may be removed. As would be recognized by one skilled in the art, CuCl ₂ is paramagnetic. Therefore, by applying a magnetic field to the powder containing CuCl _2, it is possible to remove the CuCl ₂ from the powder, at the same time, it is also possible to reduce the introduction of contaminants when rinsing with a solution containing oxygen. Advantageously, CuCl ₂ formed as a result of flushing tape or powder with HCl gas or chlorine gas is readily soluble in any high concentration of alcohol used to reduce the reoxidation of nano-sized pure silicon particles. That is expected.

  [0127] As will be appreciated by those skilled in the art, in yet other alternative embodiments, the process and apparatus for separating pure silicon from the alloy in the second crucible described above is similarly: Even if the alloy in the first crucible (2) is not transferred to the second crucible in advance or the pure silicon is not naturally separated from the alloy in advance, it can be directly performed on the alloy in the first crucible. it can. Therefore, by applying electrolysis to the tape or powder obtained by molding the alloy in the first crucible (2) containing 25% pure silicon particles based on the mass of the alloy into a tape or powder, The separation tools and processes described above can be processed, and then the formed nanosized pure silicon particles can be separated from the electrolyte.

  [0128] Further, as would be recognized by one skilled in the art, an apparatus and method for separating pure silicon from the alloys described above is provided by pure silicon formed according to the embodiments described herein. It can be used not only for alloys containing, but also for alloys produced according to alternative instruments and methods.

  [0129] Figures 4 (a) -4 (b), 5 (a) -5 (b), 6 (a) -6 (b) and 7 (a) -7 (b) are described herein. Figure 2 shows EDX data and corresponding SEM images for four different sample regions of an alloy produced in a first crucible after first electrolysis according to an embodiment of the present invention. As will be appreciated by those skilled in the art, the variation in the ratio of pure silicon to copper in the alloy for each analyzed sample depends on the location on the alloy where the sample was measured. For example, FIGS. 5 (a) and 5 (b) show a relatively high pure silicon content (ie, 100%) compared to copper (a very small amount), which is an alloy composed mostly of pure silicon. Collected in the area. 4 (a) and 4 (b), on the other hand, show that the sample was measured at or near the interface between silicon and copper in the alloy, so that a relatively low pure silicon content ( That is, 68.83%).

  [0130] FIG. 8 shows the EDX data and the corresponding SEM image of pure silicon naturally separated from the alloy in the second crucible due to the difference between the density of pure silicon in the alloy and the density of copper. The pure silicon shown in FIG. 8 is suitable for melting into an ingot.

  [0131] FIGS. 9, 10 and 11 show EDX data and corresponding SEM images of nano-sized pure silicon particles produced and separated from the alloy after the second electrolysis and processing described herein. Show. The nano-sized pure silicon particles shown in FIG. 9 were produced using an electrolyte containing 10% hydrochloric acid (HCl), while the nano-sized particles shown in FIG. And an electrolyte containing 20% hydrochloric acid (HCl). The presence of aluminum indicated in the EDX data was introduced during the mechanical grinding process of the alloy and could be substantially removed by processing the alloy with higher precision grinding in future experiments. it can. Contained oxygen can also be substantially removed by storing nanosized pure silicon particles separated in further experiments in high concentrations of alcohol to reduce reoxidation to quartz. Therefore, considering the above, it is considered that silicon having a purity substantially exceeding 99% can be obtained.

  [0132] Figure 13 shows data obtained when testing embodiments of the present invention in pure silicon production. An average efficiency of approximately 71% and 75% was achieved using direct heating and induction heating, respectively, during the first electrolysis in the first crucible. The fourth column (“g (front)”) in FIG. 13 shows the amount of pure silicon in the alloy anode before the first electrolysis begins, while the fifth column (“g (back)”) , Shows the amount of pure silicon in the alloy after the first electrolysis in the first crucible (2) occurs. Efficiency can be measured by the net yield of pure silicon relative to the energy expended in this process.

  [0133] In an alternative embodiment, after electrolysis is performed in the first crucible (2), the alloy (5) is placed in a second crucible (7) made of SiC, and the second crucible (7 ) To separate the silicon (6) from the alloy (5) by subjecting the alloy (5) to a second electrolysis. The second electrolysis is performed by reversing the polarity of the anode (5) and the cathode (10). The second crucible (7) should not be made of carbon since silicon is expected to react with the carbon material to form SiC. FIG. 14 shows a typical separation device.

[0134] The second electrolysis is performed using a current in the range of 600-800A and a voltage of approximately 6-7V. The current density employed is about ^{0.1A / cm 2 ~2.0A / cm 2} .

[0135] The second electrolysis is the second crucible (7), with the electrolyte composition (8) shown below (shown in approximate weight percent):
(I) 10% K ₂ SiF ₆ , 25% AlF ₃ , 25% NaF, 35% BaF ₂ , 5% CaF ₂ ;
(Ii) 40 to 70% of _Na 3 _AlF 6, _5~20% of _K 2 _SiF 6, _5~15% of _CaF 2, 5 to 10% of CaO; and,
(Iii) 95-99% Na ₃ AlF ₆ , 1-5% SiO ₂ ,
Is performed using at least one of the following.

  [0136] The second electrolysis yields a solid composite (11) comprising silicon and electrolyte, which are deposited on an approximately 300 mesh alloy anode (5). The ratio of silicon to electrolyte in the composite material (11) is expected to increase the closer the composite material is to the anode (5). However, on average, the composite material (11) is expected to contain approximately 20-30 wt% silicon and approximately 70-80 wt% electrolyte.

  [0137] When the composite (11) is subsequently melted at a temperature of at least about 1450 ° C or higher using an induction furnace (12) or other suitable heating element and cooled in the electrolyte, the silicon becomes pellets or Aggregates into ingots. Subsequently, upon cooling, the agglomerated silicon pellets or ingots can be filtered out of the electrolyte by using a mesh filter (13) as shown in FIG. A sample of silicon produced according to this embodiment of the invention was tested (results shown in FIG. 18B).

  [0138] Alternatively, the composite material (11) may be melted at approximately 1000 ° C to return to an alloy of copper and silicon, with a silicon content of a minimum of 50 wt%. Of course, the melting temperature of the alloy is expected to vary depending on the specific weight percent of silicon in the alloy. A controlled cooling process can then be performed so that the silicon floats up due to solubility limits and density differences. The cooling rate may be 2-3 ° C./min or approximately 2-3 ° C./min (up to approximately 800 ° C.), depending on the weight percent of the given silicon in the alloy melt. At 300 ° C. or approximately 300 ° C., the alloy is still in the liquid phase, where the silicon itself is already separated from the alloy melt and can be obtained by pouring. After separating pure silicon, the remaining alloy is expected to contain approximately 13-15% by weight silicon. Separation by growing with silicon as a nucleus requires at least about 50 mass% silicon particles in the alloy. Examples of factors expected to affect how much silicon can be separated from the alloy based on the specific controlled cooling rate used include nucleation equations, crystal growth equations, Examples include the free energy of silicon particles.

  [0139] In any of the embodiments described herein above, the second crucible lining (9) made of a non-porous SiN or SiC material is formed in the first crucible (2) with an alloy ( 5) and the first crucible lining (3). The presence of the second crucible lining (9) between the alloy (5) and the first crucible lining (3) helps to extend the electrolysis process in the first crucible (2).

  [0140] The second crucible lining (9) is maintained immersed below the top level of the substantially molten alloy (5) during electrolysis in the first crucible (2). The By sinking the second crucible lining (9) below the upper surface of the molten alloy (5), the absorption of the electrolyte (4) into the second crucible lining (9) is reduced.

[0141] FIG. 17 illustrates a further embodiment for producing pure silicon. This embodiment includes an instrument for performing electrolysis with an electrolyte (15) comprising quartz in a crucible (14) without using any crucible lining. Electrolysis is performed in the electrolyte using two carbon rods (17a, 17b) as electrodes, where the two carbon electrodes contain an appropriate amount of raw material that can undergo an electrolysis process. In this embodiment, a material such as carbon or Al ₂ O ₃ should not be used as it is expected to tend to react with the electrolyte material to form a contaminant.

  [0142] First, quartz blocks or pellets are placed inside the crucible (14), and the powdered quartz is periodically added during electrolysis to ensure that silicon particles are supplied during electrolysis. By electrolysis, a compressed solid composite material (16) is deposited in the crucible (14), which comprises approximately 20% by weight silicon and 80% by weight electrolyte based on the weight of the composite material. Including. The silicon in the composite material (16) has a particle size of approximately 300 mesh.

  [0143] An induction furnace (18) or other suitable heating mechanism is used to melt the composite material (16) and agglomerate the silicon while cooling in the electrolyte to form a small ingot. Subsequently, when the temperature of the composite material falls below about 1414 ° C. (ie, the freezing point of silicon), the silicon ingot is filtered from the electrolyte using, for example, a mesh filter (13) such as that shown in FIG. It can be taken out. Alternatively, it has been found that 40 to 100% concentration of ethanol can be used to separate the silicon from the composite material (16) and subsequently the composite material (16) can be ground and rinsed with ethanol. It is expected that the solid electrolyte will float and the silicon will remain sunk.

  [0144] Boron and phosphorus-based compounds have been found to evaporate by forming compounds with electrolytes during electrolysis. A sample of silicon produced according to this embodiment of the invention was tested (results shown in FIG. 18A).

  [0145] As will be understood by those skilled in the art, the invention described herein is not limited to those specifically described, and variations and modifications may be made without departing from the scope of the invention. Modifications can be made. All such variations and modifications apparent to those skilled in the art are deemed to be within the spirit and scope of the invention as outlined above. Of course, the present invention includes all such changes and modifications. The invention also includes all steps and features mentioned or designated in the specification, individually or collectively, and further includes any two or more and any combination of the steps or features.

  [0146] All prior art cited herein is not to be construed as an approval or any form of suggestion that the prior art forms part of a common general knowledge and Will not be interpreted as such.

Claims (23)

A method for producing pure silicon from an electrolyte, the method comprising:
(I) heating the electrolyte in a first crucible to form a molten electrolyte; and
(Iii) applying electrolysis to the molten electrolyte by providing a potential difference between an anode and a cathode suitable for electricity / ion exchange with the molten electrolyte;
Including
The method described above, wherein the molten electrolyte is agitated while the electrolysis is being performed, and the pure silicon produced as a result of the electrolysis melts with the anode to form an alloy.   The method of claim 1, wherein the electrolyte comprises cryolite, calcium oxide particles, and quartz particles.   The method of claim 2, wherein the electrolyte comprises approximately 82-94% cryolite particles based on the weight of the electrolyte.   4. A method according to claim 2 or 3, wherein the electrolyte comprises approximately 3-15% calcium oxide particles based on the weight of the electrolyte.   The method according to any one of claims 2 to 4, wherein the electrolyte comprises approximately 3% quartz particles based on the mass of the electrolyte.   6. The method of any one of claims 2-5, wherein the electrolyte comprises approximately 87% cryolite particles, 10% calcium oxide particles, and 3% quartz particles based on the weight of the electrolyte.   7. The method of any one of claims 2 to 6, comprising adding controlled addition of quartz particles to the electrolyte during electrolysis to maintain approximately 3% quartz particles in the electrolyte substantially based on the mass of the electrolyte. The method according to one item.   The method according to any one of claims 1 to 7, wherein the first crucible comprises at least one of carbon, silicon nitride, and silicon carbide material.   9. A method according to any one of the preceding claims, wherein the first crucible includes a recess defined by an inner peripheral wall and a bottom for receiving the electrolyte.   The method according to claim 9, comprising disposing a first crucible lining between the first crucible and the electrolyte inside the recess of the first crucible.   The method according to any one of claims 1 to 10, comprising disposing a second crucible lining between the alloy anode and the first crucible lining inside the recess of the first crucible.   The method of claim 11, wherein the second crucible lining comprises at least one of SiC and SiN materials.   13. The method according to claim 11 or 12, wherein the second crucible lining is submerged below the anode during electrolysis in the first crucible.   14. After step (ii), said alloy is subjected to a second electrolysis to form a solid composite material of silicon and electrolyte to separate silicon from said alloy. The method described in 1.   The method of claim 14, wherein the polarity of the anode and the cathode is reversed.   The method according to claim 14 or 15, wherein the second electrolysis is performed in a crucible separate from the first crucible.   17. A method according to any one of claims 14 to 16, wherein the separate crucible comprises a SiC material. The second electrolysis is the electrolyte composition shown below:
(I) 10% K ₂ SiF ₆ , 25% AlF ₃ , 25% NaF, 35% BaF ₂ , 5% CaF ₂ ;
(Ii) 40 to 70% of _Na 3 _AlF 6, _5~20% of _K 2 _SiF 6, _5~15% of _CaF 2, 5 to 10% of CaO; and,
(Iii) 95-99% Na ₃ AlF ₆ , 1-5% SiO ₂ ,
The method as described in any one of Claims 14-17 performed using at least 1 sort (s) of these.   19. A method according to any one of claims 14 to 18, wherein the composite material deposited on the anode is melted at a temperature of at least approximately 1450 [deg.] C and subsequently cooled in an electrolyte to agglomerate silicon into pellets or ingots. .   20. The method of claim 19, wherein the agglomerated silicon pellets or ingot are filtered from the electrolyte using a filter. The following steps:
(I) a step of electrolyzing an electrolyte containing quartz in a crucible to form a solid composite material containing silicon and an electrolyte;
(Ii) melting the composite material and subsequently aggregating silicon particles in the composite material in the electrolyte while cooling;
(Iii) a step of filtering out the agglomerated silicon from the electrolyte when the temperature of the melted composite material falls below approximately 1414 ° C .;
A method for producing pure silicon.   The method of claim 21, comprising maintaining a supply of silicon particles during electrolysis by periodically adding powdered quartz to the crucible.   23. A method according to claim 21 or 22, wherein two carbon electrodes are used during electrolysis.