U.S. patent application number 15/351290 was filed with the patent office on 2017-03-02 for flux composition useful in directional solidification for purifying silicon.
The applicant listed for this patent is Silicor Materials Inc.. Invention is credited to Christain Alfred, Alain Turenne, Chunhui Zhang.
Application Number | 20170057831 15/351290 |
Document ID | / |
Family ID | 48771740 |
Filed Date | 2017-03-02 |
United States Patent
Application |
20170057831 |
Kind Code |
A1 |
Zhang; Chunhui ; et
al. |
March 2, 2017 |
FLUX COMPOSITION USEFUL IN DIRECTIONAL SOLIDIFICATION FOR PURIFYING
SILICON
Abstract
The present invention provides for a flux composition, and the
use thereof in a directional solidification for the purification of
silicon.
Inventors: |
Zhang; Chunhui; (Oakville,
CA) ; Turenne; Alain; (Kitchener, CA) ;
Alfred; Christain; (Brampton, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Silicor Materials Inc. |
San Jose |
CA |
US |
|
|
Family ID: |
48771740 |
Appl. No.: |
15/351290 |
Filed: |
November 14, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14409546 |
Dec 19, 2014 |
9512008 |
|
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PCT/US13/47511 |
Jun 25, 2013 |
|
|
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15351290 |
|
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|
61663887 |
Jun 25, 2012 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C30B 9/12 20130101; C01B
33/037 20130101; C30B 11/00 20130101; C30B 29/06 20130101 |
International
Class: |
C01B 33/037 20060101
C01B033/037; C30B 9/12 20060101 C30B009/12; C30B 29/06 20060101
C30B029/06; C30B 11/00 20060101 C30B011/00 |
Claims
1. A composition comprising: (a) silicon dioxide (SiO.sub.2); (b)
sodium carbonate (Na.sub.2CO.sub.3); (c) optionally calcium oxide
(CaO); and (d) at least one of calcium fluoride (CaF.sub.2) and
calcium chloride (CaCl.sub.2).
2. The composition of claim 1, wherein the silicon dioxide is
present in about 35 wt. % to about 80 wt. % of the composition.
3. The composition of claim 1, wherein the sodium carbonate is
present in about 40 wt. % to about 60 wt. % of the composition.
4. The composition of claim 1, wherein the sodium carbonate is
present in about 40 wt. % to about 55 wt. % of the composition.
5. The composition of claim 1, wherein the calcium oxide is
absent.
6. The composition of claim 1, wherein e calcium fluoride is
present in about 0.50 wt. % to about 6.00 wt. % of the
composition.
7. The composition of claim 1, wherein the calcium chloride is
present in about 4.00 wt. % to about 6.00 wt. % of the
composition.
8. The composition of claim 1 wherein both the calcium fluoride and
the calcium chloride are present in the composition.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of and claims the benefit
of priority under 35 U.S.C. .sctn.120 to U.S. patent application
Ser. No. 14/409,546, filed on Dec. 19, 2014, which is a U.S.
National Stage Filing under 35 U.S.C, .sctn.371 from International
Application No. PCT/US2013/047511, entitled "FLUX COMPOSITION
USEFUL IN DIRECTIONAL SOLIDIFICATION FOR PURIFYING SILICON," filed
on Jun. 25, 2013, and published as WO 2014/004441 A 1 on Jan. 3,
2014, which claims the benefit of priority to U.S. Provisional
Application No. 61/663,887, filed Jun. 25, 2012, each of which is
hereby incorporated by reference in its entirety.
BACKGROUND
[0002] Solar cells are currently utilized as an energy source by
using their ability to convert sunlight to electrical energy.
Silicon is used almost exclusively as the semiconductor material in
such photovoltaic cells. A significant limitation currently on the
use of solar cells has to do with the cost of purifying silicon to
solar grade (SG). In view of current energy demands and supply
limitations, there is an enormous need for a more cost efficient
way of purifying metallurgical grade (MG) silicon (or any other
silicon having greater impurities than solar grade) to solar grade
silicon.
SUMMARY
[0003] The present invention provides a composition that includes:
(a) silicon dioxide (SiO.sub.2); (b) sodium carbonate
(Na.sub.2CO.sub.3); (c) optionally calcium oxide (CaO); and (d) at
least one of calcium fluoride (CaF.sub.2) and calcium chloride
(CaCl.sub.2).
[0004] The present invention also provides a composition that
includes: (a) silicon dioxide (SiO.sub.2), present in about 50 wt.
%, .+-.50%; (b) sodium carbonate (Na.sub.7CO.sub.3), present in
about 47 wt. %, .+-.20%; (c) optionally calcium oxide (CaO),
present in up to about 6 wt. %; and (d) at least one of calcium
fluoride (CaF.sub.2) and calcium chloride (CaCl.sub.2), when
present, each is independently present in up to about 5.00 wt.
%.
[0005] The present invention also provides a composition that
includes: (a) silicon dioxide (SiO.sub.2), present in about 42.70
wt. %, .+-.10%; (b) sodium carbonate Na.sub.2CO.sub.3), present in
about 50.60 wt. %, .+-.10%; (c) calcium oxide (CaO), present in
about 1.70 wt. %, .+-.10%; (d) at least one of calcium fluoride
(CaF.sub.2) and calcium chloride (CaCl.sub.2), when present, each
is independently present in about 5.00 wt. %, .+-.20%.
[0006] The present invention also provides a composition that
includes: (a) silicon dioxide (SiO.sub.2), present in about 35 wt.
% to about 80 wt. % of the composition; (b) sodium carbonate
(Na.sub.2CO.sub.3), present in about 40 wt. % to about 55 wt. % of
the composition; (c) optionally calcium oxide (CaO), present in up
to about 6 wt. % of the composition; and (d) at least one of
calcium fluoride (CaF.sub.2) and calcium chloride (CaCl.sub.2),
when present, each is independently present in about 0.50 wt. % to
about 6.00 wt. % of the composition.
[0007] The present invention also provides a composition that
includes: (a) silicon dioxide (SiO.sub.2), present in about 35 wt.
% to about 50 wt. % of the composition; (b) sodium carbonate
(Na.sub.2CO.sub.3), present in about 45 wt. % to about 55 wt. % of
the composition; (c) calcium oxide (CaO), present in about 1.50 wt.
% to about 1.90 wt. % of the composition; and (d) at least one of
calcium fluoride (CaF.sub.2) and calcium chloride (CaCl.sub.2),
when present, each is independently present in about 4.00 wt. % to
about 6.00 wt. % of the composition.
[0008] The present invention also provides a method that includes:
(a) forming a molten liquid from silicon and a flux, the flux
including the composition described herein; (b) forming a slag,
from the flux and impurities in the molten liquid and; and (c)
optionally removing at least a portion of the slag from the molten
liquid, to provide a purified molten liquid.
[0009] The present invention also provides a method that includes:
(a) forming a molten liquid from silicon and a flux, the flux
including the composition described herein; (b) forming a slag,
from the flux and impurities in the molten liquid; (c) optionally
removing at least a portion of the slag from the molten liquid; (d)
directionally solidifying the molten liquid, to form solid silicon;
and (e) removing a portion of the solid silicon, to provide
purified solid silicon. In specific embodiments, the molten slag
forms a protection layer on the surface of the furnace inner liner
to prevent contamination of impurities from the inner liner
refractory into the molten silicon.
BRIEF DESCIUPTION OF THE DRAWINGS
[0010] FIG. 1 illustrates a block flow diagram of a method for
purifying silicon.
[0011] FIG. 2 illustrates a block flow diagram of a method for
purifying silicon.
DETAILED DESCRIPTION
[0012] The following detailed description includes references to
the accompanying drawings, which form a part of the detailed
description. The drawings show, by way of illustration, specific
embodiments in which the invention may be practiced. These
embodiments, which are also referred to herein as "examples," are
described in enough detail to enable those skilled in the art to
practice the invention. The embodiments may be combined, other
embodiments may he utilized, or structural, and logical changes may
be made without departing from the scope of the present invention.
The following detailed description is, therefore, not to be taken
in a limiting sense, and the scope of the present invention is
defined by the appended claims and their equivalents.
[0013] In this document, the terms "a" or "an" are used to include
one or more than one and the term "or" is used to refer to a
nonexclusive "or" unless otherwise indicated, In addition, it is to
be understood that the phraseology or terminology employed herein,
and not otherwise defined, is for the purpose of description only
and not of limitation. Furthermore, all publications, patents, and
patent documents referred to in this document are incorporated by
reference herein in their entirety, as though individually
incorporated by reference. In the event of inconsistent usages
between this document and those documents so incorporated by
reference, the usage in the incorporated reference should be
considered supplementary to that of this document; for
irreconcilable inconsistencies, the usage in this document
controls.
[0014] In the methods of manufacturing described herein, the steps
can be carried out in any order without departing from the
principles of the invention, except when a temporal or operational
sequence is explicitly recited. Recitation in a claim to the effect
that first a step is performed, then several other steps are
subsequently performed, shall be taken to mean that the first step
is performed before any of the other steps, but the other steps can
be performed in any suitable sequence, unless a sequence is further
recited within the other steps. For example, claim elements that
recite "Step A, Step B, Step C, Step D, and Step E" shall be
construed to mean step A is carried out first, step E is carried
out last, and steps B, C, and D can be carried out in any sequence
between steps A and E, and that the sequence still falls within the
literal scope of the claimed process. A given step or sub-set of
steps may also be repeated.
[0015] Furthermore, specified steps can be carried out concurrently
unless explicit claim language recites that they be carried out
separately. For example, a claimed step of doing X and a claimed
step of doing Y can be conducted simultaneously within a single
operation, and the resulting process will fall within the literal
scope of the claimed process.
Definitions
[0016] As used herein, "silicon dioxide" also known as silica, is
an oxide of silicon with the chemical formula SiO.sub.2.
[0017] As used herein, "sodium carbonate" also known as washing
soda or soda ash, is a sodium salt of carbonic acid with the
chemical formula Na.sub.2CO. The sodium carbonate is employed in
the compositions (e.g., flux) and methods herein, to decompose with
heat in the molten liquid. Upon decomposition, the sodium carbonate
will evolve carbon dioxide. As such, it is appreciated that those
of skill in the art of chemistry understand and appreciate that in
various embodiments, reference to "sodium carbonate" can include
those compounds (e.g., carbonates or bicarbonates) that can
decompose with heat in the molten liquid, to provide sodium oxide
(Na.sub.2O) and/or to evolve carbon dioxide. Such compounds
include, e.g., sodium bicarbonate (NaHCO.sub.3).
[0018] As used herein, "calcium oxide" commonly known as quicklime
or burnt lime, is an inorganic compound with the chemical formula
CaO. The calcium oxide is employed in the compositions (e.g., flux)
and methods herein, to form an oxide anion (O.sup.-) in the molten
liquid. As such, it is appreciated that those of skill in the art
of chemistry understand and appreciate that in various embodiments,
reference to "calcium oxide" can include those compounds (e.g.,
metal oxides) that can form an oxide anion (O.sup.-) in the molten
liquid. Such compounds include, e.g., magnesium oxide (MgO).
[0019] As used herein, "calcium fluoride" is an inorganic compound
with the formula CaF.sub.2. The calcium fluoride is employed in the
compositions (e.g., flux) and methods herein, to provide a source
of calcium cation (Ca.sup.+) and/or fluorine anion (F.sup.-) in the
molten liquid. As such, it is appreciated that those of skill in
the art of chemistry understand and appreciate that in various
embodiments, reference to "calcium fluoride" can include those
compounds (e.g., calcium halides) that can form an alkali cation
(Ca.sup.+) and/or halogen anion (F.sup.-) in the molten liquid.
Such compounds include, e.g., calcium chloride (CaCl.sub.2) (e.g.,
calcium cation (Ca.sup.+) and chlorine anion (Cl.sup.+).
[0020] As used herein, "purifying" refers to the physical
separation of a substance of interest from one or more foreign or
contaminating substances. In contrast, "impurities" or "impurity"
refers to the one or more foreign or contaminating substances,
other than silicon, that are undesirable.
[0021] As used herein, "flux" refers to a chemical cleaning agent,
flowing agent, or purifying agent. In the process of forming a
molten liquid in the melt of silicon, inorganic compounds (e.g.,
silicon dioxide, sodium carbonate, calcium oxide and calcium
fluoride) can be considered a "flux" when added to the molten
liquid, and of rendering slag. The slag is a mixture of impurities.
As such, the flux is used to remove impurities from the molten
liquid, and/or for adding desirable trace elements.
[0022] As used herein, a "slag" refers to a mixture of impurities
formed in a molten liquid. The slag is typically formed by the
addition of a flux to the molten liquid. As such, the slag can
include a reaction product formed from impurities in the molten
liquid (initially from the source silicon) and the flux. The slag
will typically form on the surface of the molten liquid, where it
can subsequently be removed.
[0023] As used herein, "molten" or "molten liquid" refers to one or
more substances, together, that are melted.
[0024] As used herein, "melting" refers to the process of heating
one or more solid substances to a point (called the melting point),
or above, where they turn into a liquid. As such, the "melting"
refers to a substance changing from a solid to a liquid, when
exposed to sufficient heat.
[0025] As used herein, a "reaction product" refers to a compound
formed by the chemical reaction of two or more substances. For
example, impurities in the molten liquid (from the initial silicon
source) can react with one or more substances in the flux, to form
one or more reaction products.
[0026] As used herein, "solidifying" refers to the process of
cooling one or more liquid substances (e.g., molten liquid) below a
point (called the freezing point), where they turn into a solid. As
such, the "solidifying" refers to a substance changing from a
liquid to a solid, upon cooling.
[0027] As used herein, "removing" refers to the process of
separating a substance from another substance (e.g., removing a
solid or a liquid from a mixture) or separating a portion of a
substance from another portion (e.g,, removing a part of a solid
from another part of the solid). The process can employ any
technique known to those of skill in the art, e.g., decanting the
mixture, skimming one or more liquids from the mixture,
centrifuging the mixture, filtering the solids from the mixture,
cutting a solid to remove a portion thereof, or a combination
thereof.
[0028] As used herein, "aluminum" refers to the chemical element
that has the symbol Al and atomic number 13. The term includes
metal aluminum or elemental aluminum (Al.sup.0), or an alloy
thereof.
[0029] As used herein, "boron" refers to the chemical element that
has the symbol B and atomic number 5. The term includes compounds
that include boron (i.e., boron-containing compounds that include
B.sup.3+, B.sup.2+, or B.sup.+), and combinations thereof.
[0030] As used herein, "silicon" refers to the chemical element
that has the symbol Si and atomic number 14. The term includes
metal or elemental silicon (Si.sup.0), or an alloy thereof.
[0031] As used herein, "metallurgical grade silicon" or "MG
silicon" refers to relatively pure (e.g., at least about 98.0 wt.
%) silicon.
[0032] As used herein, "upgraded metallurgical grade silicon" or
"UMG silicon" refers to a relatively intermediate pure (e.g., at
least about 99.0 wt. %) silicon.
[0033] As used herein, "solar grade silicon" or "SOG silicon"
refers to a relatively high pure (e.g., at least about 99.9999 wt.
%) silicon.
[0034] As used herein, "crystalline" includes the regular,
geometric arrangement of atoms in a solid. As such, "silicon
crystals" refers to silicon having regular, geometric arrangement
of the silicon atoms in a solid state.
[0035] As used herein, "directionally solidifying" refers to the
solidification of molten metal so that feed metal is continually
available for the portion undergoing solidification.
[0036] As used herein, "polycrystalline silicon" or "poly-Si"
refers to a material consisting of multiple silicon crystals.
[0037] As used herein, "monocrystalline silicon" refers to silicon
that has a single and continuous crystal lattice structure.
[0038] As used herein, "ingot" refers to a mass of material cast
into a shape which is relatively easy to handle and transport. For
example, metal heated past its melting point and molded into a bar
or block is referred to as an ingot.
[0039] As used herein, "boule" refers to a single-crystal ingot
synthetically produced. For example, in the Czochralski or "CZ"
process, a seed crystal is used to create a larger crystal, or
ingot. This seed crystal is dipped into the pure molten silicon and
slowly extracted. The molten silicon grows on the seed crystal in a
crystalline fashion. As the seed is extracted the silicon sets and
eventually a large, circular boule is produced.
[0040] As used herein, "contacting" refers to the act of touching,
making contact, or of bringing substances into immediate
proximity.
[0041] As used herein, "decanting" or "decantation" includes
pouring off a fluid, leaving a sediment or precipitate, thereby
separating the fluid from the sediment or precipitate. The sediment
or precipitate can be present as a slag.
[0042] As used herein, "filtering" or "filtration" refers to a
mechanical method to separate solids from liquids by passing the
feed stream through a porous sheet such as a ceramic or metal
membrane, which retains the solids and allows the liquid to pass
through. This can be accomplished by gravity, pressure or vacuum
(suction). The filtering effectively separates the sediment and/or
precipitate from the liquid. The solids can be present as a
slag.
[0043] Referring to FIG. 1, an example of a block flow diagram of a
method for purifying silicon 101 is shown, according to some
embodiments. A molten liquid that includes a slag 109 is formed by
heating 107 silicon 103 and a flux 105. The slag is removed 111
from the molten liquid, to provide purified molten liquid 113. The
purified molten liquid 113 is cooled (directional solidification)
115, to provide a solid silicon 117. A portion of the solid silicon
117 is removed 119, to provide purified solid silicon 121.
[0044] Referring to FIG. 2, an example of a block flow diagram of a
method for purifying silicon 201 is shown, according to some
embodiments. A molten liquid 208 is formed by heating 207 silicon
203. Flux 205 is added to the molten liquid 208, to allow slag to
form in the molten liquid 209. The slag is removed 211 from the
molten liquid, to provide a purified molten liquid 213. The
purified molten liquid 213 is cooled 215, to provide solid silicon
217. A portion of the solid silicon 217 is removed 219, to provide
purified solid silicon 221.
[0045] Silicon 103 or 203 for processing may be obtained from a
number of sources. The silicon 103 or 203 may be scrap or discarded
silicon from manufacturing solar cell panels, semiconductor wafers
or shaping ingots, for example. Often the silicon 103 or 203 is
part of a slurry. The slurry may include water, polyethylene glycol
(PEG), silicon carbide, iron, aluminum, calcium, copper and other
contaminants. The silicon 103 or 203 may be removed from the slurry
(e.g., separated) and dried to remove excess water. The powder may
be separated from the slurry by centrifuge, settling or other
processes. Adding water to the slurry can lower the specific
gravity to help improve the settling or centrifuging. The silicon
103 or 203 may undergo further processing to remove contaminants,
such as by undergoing an acid treatment, for example. For example,
hydrochloric acid can be used to dissolve the metals, such as iron,
off of the surface of the silicon powder. Hydrofluoric acid,
hydrochloric acid, nitric acid or a combination thereof may be used
to dissolve silicon dioxide off of the surface of the powder or to
dissolve the surface of the powder. Alternatively, potassium
hydroxide, sodium hydroxide or a combination thereof may be used to
dissolve the surface of the powder. The powder may also be treated
with a magnetic separating process to remove iron and other
magnetic elements.
[0046] Specifically, the silicon 103 or 203 can include
metallurgical grade (MG) silicon. Alternatively, the silicon 103 or
203 can be of a grade or quality that is below metallurgical grade
(MG) silicon. Employing less pure silicon (e.g., silicon of a grade
or quality that is below metallurgical grade (MG) silicon) can
provide cost-savings, as well as allowing for the use of silicon
that would otherwise not be feasible or practical.
[0047] The molten liquid and slag 109 or 209 can be formed by: (i)
heating silicon sufficient to form a molten liquid, and
subsequently adding the flux (FIG. 2), or (ii) forming a molten
liquid by heating a combination of silicon and flux (FIG. 1).
Either way, a molten liquid that includes a slag 109 or 209 can be
formed. As such the silicon 103 and flux 105 can be present, and
together they can be heated 107 to form the molten liquid and slag
109 (FIG. 1). Alternatively (FIG. 2), the molten liquid 209 can be
formed from silicon 203, wherein the flux 205 can subsequently be
added to the molten liquid 208, thereby forming the molten liquid
and slag 209.
[0048] The molten liquid 208 can be formed from silicon 203, such
as by feeding into a vortex using a rotary degasser, molten metal
pump, rotary furnace or by induction currents. Likewise, the molten
liquid and slag 109 or 209 can be formed from silicon 103 or 203,
and flux 105 or 205. The silicon 103 or 203 (and optionally flux
105 or 205) may be substantially dried and fed consistently into
the vortex, thus limiting its contact with oxygen. The silicon 103
or 203 (and optionally flux 105 or 205) may be sheared into
individual grains, such as by setting the mixer settings for high
shear. The melting may occur under submersion in a molten bath. For
example, the bath may be below the liquidus temperature and above
the solidus temperature, so that it is easier to put more shear on
the powder and easier to keep the powder submerged in the bath due
to the increased viscosity of the bath. The furnace refractory may
be low in contaminates, such as by having little to no phosphorus
or boron in the material. Fused silica may be an example of an
acceptable refractory. Similarly, if a rotary degasser or molten
metal pump is utilized, they may be manufactured with little
phosphorus or boron to minimize contamination.
[0049] The silicon 103 or 203 (and optionally flux 105 or 205) may
be kept submerged by utilizing melt turbulence. The melting may
occur under mixing conditions in which the temperature is
maintained above the solidus temperature.
[0050] The heating 107 or 207 can be carried out in a suitable
manner to achieve a temperature that will effectively form a molten
liquid 208, or a molten liquid and slag 109 or 209. For example,
the molten liquid and slag 109 or 209 (or molten liquid 208) can be
formed at a temperature above the solidus temperature.
Specifically, the molten liquid and slag 109 or 209 (or molten
liquid 208) can be formed at a temperature of at least about
1450.degree. C.
[0051] Any suitable amount or ratio of silicon 103 (or 203) and
flux 105 (or 205) can be employed, provided the slag is formed and
can effectively be removed from the molten liquid. For example, the
silicon 103 (or 203) and flux 105 (or 205) can be employed, in a
weight ratio of about 15:1 to about 10:1, silicon to flux.
[0052] The flux 105 or 205 will typically be used to remove
impurities e.g., boron-containing impurities and/or aluminum) from
the silicon 103 or 203. As such, silicon 103 or 203 can be purified
from boron, such that at least some of the boron is removed from
the silicon 103 or 203. For example, the silicon 103 or 203 can be
purified from boron, to provide purified solid silicon 121 or 221
with at least about a 30 wt. % reduction in boron. Additionally,
the silicon 103 or 203 can be purified from boron, to provide
purified solid silicon 121 or 221 that includes less than about
0.30 ppmw boron.
[0053] The silicon 103 or 203 can be purified from aluminum, such
that at least some of the aluminum is removed from the silicon 103
or 203. For example, the silicon 103 or 203 can be purified from
aluminum, to provide purified solid silicon 121 or 221 with at
least about a 99.5 wt. % reduction in aluminum. Additionally, the
silicon 103 or 203 can be purified from aluminum, to provide
purified solid silicon 121 or 221 that includes less than about 10
ppmw aluminum.
[0054] The slag is allowed to form in the molten liquid (slag and
molten liquid 109 or 209), where it can be removed 111 or 211. In
specific embodiments, the slag will move toward the top of the
surface of the molten liquid. In such embodiments, the slag can be
removed, e.g., by skimming off the slag from the molten liquid.
[0055] The slag is allowed to form in the molten liquid. It is
appreciated that those of skill in the art of metallurgical
chemistry understand that in the process of forming slag in the
molten liquid, matter is not being created. Instead, at least a
portion of the impurities present in the molten liquid (from the
silicon 103 or 203) will complex or react with the flux 105 or 205,
in the molten liquid. These impurities will be transformed to a
slag, that can be removed from the molten liquid.
[0056] The purified molten liquid 113 or 213 can be cooled 115 or
215 to form solid silicon 117 or 217. The cooling 115 or 215 can be
carried out in any suitable manner, provided the solid silicon 117
or 217 is obtained. For example, the cooling 115 or 215 can include
directionally solidifying the purified molten liquid. The
directional solidification can be carried out by cooling 115 or 215
the purified molten liquid. For example, the directional
solidification can be carried out by cooling 115 or 215 a bottom
portion of the purified molten liquid. Additionally, the
directional solidification can be carried out by cooling 115 or 215
a bottom portion of the purified molten liquid, while continuing to
heat a top portion of the purified molten liquid.
[0057] Upon cooling 115 or 215, a solid silicon 117 or 217 is
provided. A portion of the solid silicon 117 or 217 can be removed
119 or 219, to provide purified solid silicon 121 or 221.
[0058] In those specific embodiments in which the impurities will
move toward the top of the vessel containing the purified molten
liquid 113 or 213, the top portion of the solid silicon 117 or 217
can be removed (i.e., the portion of the solid silicon 117 or 217
including a significant amount of the impurities). That portion of
the solid silicon 117 or 217 can be removed by any suitable means.
For example, that portion of the solid silicon 117 or 217 can be
mechanically removed, for example, by cutting the solid silicon 117
or 217.
[0059] In specific embodiments, the method for purifying silicon
101 or 201 can be carried out once. In alternative specific
embodiments, the method for purifying silicon 101 or 201 can be
carried out two or more (e.g., 2, 3 or 4) times.
[0060] Specific ranges, values, and embodiments provided below are
for illustration purposes only and do not otherwise limit the scope
of the disclosed subject matter, as defined by the claims. The
specific ranges, values, and embodiments described below encompass
all combinations and sub-combinations of each disclosed range,
value, and embodiment, whether or not expressly described as
such.
Specific Ranges, Values, and Embodiments
[0061] In specific embodiments, the calcium chloride is absent from
the composition. In additional specific embodiments, the calcium
chloride is present in the composition. In additional specific
embodiments, the calcium chloride is present in up to about 6.00
wt. % of the composition. In additional specific embodiments, the
calcium chloride is present in about 4.00 wt. % to about 6.00 wt. %
of the composition. In additional specific embodiments, the calcium
chloride is present in about 5.00 wt. %, .+-.20% of the
composition. In additional specific embodiments, the calcium
chloride is present in about 5.00 wt. %, .+-.10% of the
composition.
[0062] In specific embodiments, the silicon dioxide is present in
about 35 wt. % to about 80 wt. % of the composition. In additional
specific embodiments, the silicon dioxide is present in about 35
wt. % to about 50 wt. % of the composition. In additional specific
embodiments, the silicon dioxide is present in about 42.70 wt. %,
.+-.10% of the composition. In additional specific embodiments, the
silicon dioxide is present in about 42.70 wt. %, .+-.5% of the
composition.
[0063] In specific embodiments, the sodium carbonate is present in
about 45 wt. % to about 55 wt. % of the composition. In additional
specific embodiments, the sodium carbonate is present in about
50.60 wt. %, .+-.10% of the composition. In additional specific
embodiments, the sodium carbonate is present in about 50.60 wt. %,
.+-.5% of the composition.
[0064] In specific embodiments, the calcium oxide is absent. In
alternative specific embodiments, the calcium oxide is present. In
additional specific embodiments, the calcium oxide is present in
about 1.50 wt. % to about 1.90 wt. % of the composition. In
additional specific embodiments, the calcium oxide is present in
about 1.50 wt. % to about 1.90 wt. % of the composition. In
additional specific embodiments, the calcium oxide is present in
about 1.70 wt. %, .+-.10% of the composition. In additional
specific embodiments, the calcium oxide is present in about 1.70
wt. %, .+-.5% of the composition.
[0065] In specific embodiments, the calcium fluoride is absent from
the composition. In additional specific embodiments, the calcium
fluoride is present in about 4.00 wt. % to about 6.00 wt. % of the
composition. In additional specific embodiments, the calcium
fluoride is present in up to about 6.00 wt. % of the composition.
In additional specific embodiments, the calcium fluoride is present
in about 5.00 wt. %, .+-.20% of the composition. In additional
specific embodiments, the calcium fluoride is present in about 5.00
wt. %, .+-.10% of the composition.
[0066] In specific embodiments, the method is a method for
purifying silicon. In additional specific embodiments, the method
at least partially purifies silicon from aluminum. In additional
specific embodiments, the method purifies silicon from aluminum. In
additional specific embodiments, the method provides for silicon
with at least about a 98 wt. % reduction in aluminum. In additional
specific embodiments, the method provides for silicon with at least
about a 99.5 wt. % reduction in aluminum. In additional specific
embodiments, the method provides for silicon with at least about a
99.8 wt. % reduction in aluminum. In additional specific
embodiments, the method provides for purified silicon that includes
less than about 20 ppmw aluminum. In additional specific
embodiments, the method provides for purified silicon that includes
less than about 10 ppmw aluminum. In additional specific
embodiments, the method provides for purified silicon that includes
less than about 5 ppmw aluminum.
[0067] In specific embodiments, the method purifies silicon from
boron. In additional specific embodiments, the method provides for
silicon with at least about a 20 wt. % reduction in boron, In
additional specific embodiments, the method provides for silicon
with at least about a 30 wt. % reduction in boron. In additional
specific embodiments, the method provides for silicon with at least
about a 40 wt. % reduction in boron. In additional specific
embodiments, the method provides for purified silicon that includes
less than about 0.40 ppmw boron. In additional specific
embodiments, the method provides for purified silicon that includes
less than about 0.30 ppmw boron. In additional specific
embodiments, the method provides for purified silicon that includes
less than about 0.20 ppmw boron.
[0068] In specific embodiments, the method employs metallurgical
grade (MG) silicon, e.g., the silicon that forms the molten liquid
includes metallurgical grade (MG) silicon. In additional specific
embodiments, the method employs upgraded metallurgical grade (UMG)
silicon, e.g., the silicon that forms the molten liquid includes
upgraded metallurgical grade (UMG) silicon. In additional specific
embodiments, the method employs solar grade (SOG) silicon, e.g.,
the silicon that forms the molten liquid includes solar grade (SOG)
silicon. In additional specific embodiments, the method employs a
grade or quality of silicon that is below metallurgical grade (MG)
silicon.
[0069] In additional specific embodiments, the method employs a
grade or quality of silicon that is below about 98 wt. % pure. In
additional specific embodiments, the method employs a grade or
quality of silicon that is below about 95 wt. % pure. In additional
specific embodiments, the method employs a grade or quality of
silicon that is below about 90 wt. % pure. In additional specific
embodiments, the method employs a grade or quality of silicon that
is below about 85 wt. % pure. In additional specific embodiments,
the method employs a grade or quality of silicon that is below
about 80 wt. % pure. In additional specific embodiments, the method
employs a grade or quality of silicon that is below about 75 wt. %
pure. In additional specific embodiments, the method employs a
grade or quality of silicon that is below about 70 wt. % pure. In
additional specific embodiments, the method employs a grade or
quality of silicon that is below about 65 wt. % pure. In additional
specific embodiments, the method employs a grade or quality of
silicon that is below about 60 wt. % pure.
[0070] In specific embodiments, the silicon that forms the molten
liquid includes silicon recycled from a silicon purification
process.
[0071] In specific embodiments, the method employs silicon 201 can
include metallurgical grade (MG) silicon. In additional specific
embodiments, the silicon 201 can include upgraded metallurgical
grade (UMG) silicon.
[0072] In specific embodiments, forming the molten liquid from the
silicon and the flux is carried out, such that a molten liquid of
silicon is initially formed, and the flux is subsequently added to
the molten silicon. In additional specific embodiments, forming the
molten liquid from the silicon and the flux is carried out, such
that solid silicon is initially contacted with the flux, and
together they are heated to form the molten liquid.
[0073] In specific embodiments, the silicon and flux can be
employed, in a weight ratio of about 25:1 to about 5:1, of silicon
to flux. In additional specific embodiments, the silicon and flux
can be employed, in a weight ratio of about 20:1 to about 7:1, of
silicon to flux. In additional specific embodiments, the silicon
and flux can be employed, in a weight ratio of about 15:1 to about
10:1, of silicon to flux.
[0074] In specific embodiments, the silicon and flux can be
employed, in a weight ratio of at least about 5:1, of silicon to
flux. In additional specific embodiments, the silicon and flux can
be employed, in a weight ratio of at least about 10:1, of silicon
to flux. In additional specific embodiments, the silicon and flux
can be employed, in a weight ratio of at least about 15:1, of
silicon to flux. In additional specific embodiments, the silicon
and flux can be employed, in a weight ratio of at least about 20:1,
of silicon to flux. In additional specific embodiments, the silicon
and flux can be employed, in a weight ratio of at least about 25:1,
of silicon to flux.
[0075] In specific embodiments, the silicon and flux can be
employed, in a weight ratio of up to about 25:1, of silicon to
flux. In additional specific embodiments, the silicon and flux can
be employed, in a weight ratio of up to about 20:1, of silicon to
flux. In additional specific embodiments, the silicon and flux can
be employed, in a weight ratio of up to about 15:1, of silicon to
flux. in additional specific embodiments, the silicon and flux can
be employed, in a weight ratio of up to about 10:1, of silicon to
flux. In additional specific embodiments, the silicon and flux can
be employed, in a weight ratio of up to about 5:1, of silicon to
flux.
[0076] In specific embodiments, the molten liquid is formed at a
temperature of at least about 1420.degree. C. In additional
specific embodiments, the molten liquid is formed at a temperature
of at least about 1450.degree. C. In additional specific
embodiments, the molten liquid is formed at a temperature of at
least about 1500.degree. C. In additional specific embodiments, the
molten liquid is formed at a temperature of at least about
1550.degree. C.
[0077] In specific embodiments, the molten liquid is formed at a
temperature above the solidus temperature. In additional specific
embodiments, the molten liquid is formed at a temperature above the
liquidus temperature. In specific embodiments, the slag includes a
product of the flux and impurities from the silicon. In additional
specific embodiments, the slag includes a reaction product of the
flux and itnputities from the silicon. In additional specific
embodiments, the slag includes impurities from the silicon.
[0078] In specific embodiments, the slag forms on the surface of
the molten liquid. In additional specific embodiments, the slag
forms on the surface of the molten liquid, and is subsequently
removed from the molten liquid.
[0079] In specific embodiments, the method further includes
directionally solidifying the purified molten liquid, to form solid
silicon. In additional specific embodiments, the directional
solidification is carried out by cooling the purified molten
liquid. In additional specific embodiments, the directional
solidification is carried out by cooling the purified molten
liquid, to a temperature of less than the liquidus temperature of
the purified molten liquid. In additional specific embodiments, the
purified molten liquid is cooled to above the solidus temperature
of the purified molten liquid and below the liquidus temperature of
the purified molten liquid.
[0080] In specific embodiments, a top portion of the purified
molten liquid is maintained above the melting point, while a
bottom. portion of the purified molten liquid is cooled below the
melting point. In additional specific embodiments, a top portion of
the purified molten liquid is heated, while a bottom portion of the
purified molten liquid is cooled.
[0081] In specific embodiments, the directional solidification is
carried out by cooling the purified molten liquid at a bottom
portion of a directional solidification mold. In additional
specific embodiments, the directional solidification is carried out
by cooling the purified molten liquid at a bottom portion of a
directional solidification mold, and by heating the purified molten
liquid at a top portion of a directional solidification mold. In
additional specific embodiments, the directional solidification is
carried out by cooling the purified molten liquid at a bottom
portion of a directional solidification mold, at a rate of less
than about 75.degree. C./hr.
[0082] In specific embodiments, the directional solidification is
carried out by cooling the purified molten liquid, to within about
125.degree. C. above the solidus temperature of the purified molten
liquid. In additional specific embodiments, the directional
solidification is carried out by cooling the purified molten
liquid, to within about 125.degree. C. above the melting point of
the purified molten liquid. In additional specific embodiments, the
directional solidification is carried out by cooling the purified
molten liquid, over a period of time of at least about 18
hours.
[0083] In specific embodiments, the flux is present on an internal
surface of a vessel used to form a molten liquid that includes
silicon. In additional specific embodiments, the flux is present on
an internal surface of a furnace refractory. In additional specific
embodiments, the flux is present on an internal surface of a vessel
used to heat silicon. In additional specific embodiments, the flux
is present on an internal surface of a vessel used to form a molten
liquid of silicon.
[0084] In specific embodiments, the method further includes
removing a portion of the solid silicon. In additional specific
embodiments, the portion of the solid silicon is removed by cutting
the solid silicon.
[0085] In specific embodiments, any one or more steps are
independently carried, out multiple times.
[0086] In specific embodiments, the method provides for at least
about 1,000 kg silicon.
[0087] In specific embodiments, the method provides for purified
silicon which is suitable for the manufacture of a solar panel.
[0088] Specific enumerated embodiments [1] to [61] provided below
are for illustration purposes only, and do not otherwise limit the
scope of the disclosed subject matter, as defined by the claims.
These enumerated embodiments encompass all combinations,
sub-combinations, and multiply referenced (e.g., multiply
dependent) combinations described therein.
Enumerated Embodiments
[0089] [1.] A composition comprising: [0090] (a) silicon dioxide
(SiO.sub.2); [0091] (b) sodium carbonate (Na.sub.2CO.sub.3); [0092]
(c) optionally calcium oxide (CaO); and [0093] (d) at least one of
calcium fluoride (CaF.sub.2) and calcium chloride (CaCl.sub.2).
[0094] [2.] The composition of embodiment [1], wherein the silicon
dioxide is present in about 35 wt. % to about 80 wt. % of the
composition.
[0095] [3.] The composition of any one of the above embodiments,
wherein the silicon dioxide is present in about 40 wt. % to about
60 wt. % of the composition.
[0096] [4.] The composition of any one of the above embodiments,
wherein the silicon dioxide is present in about 50 wt. %,
.+-.50%.
[0097] [5.] The composition of any one of the above embodiments,
wherein the silicon dioxide is present in about 50 wt. %,
.+-.20%.
[0098] [6.] The composition of any one of the above embodiments,
wherein the sodium carbonate is present in about 40 wt. % to about
60 wt. % of the composition.
[0099] [7.] The composition of any one of the above embodiments,
wherein the sodium carbonate is present in about 40 wt. % to about
55 wt. % of the composition.
[0100] [8. ] The composition of any one of the above embodiments,
wherein the sodium carbonate is present in about 45 wt. % to about
55 wt. % of the composition.
[0101] [9.] The composition of any one of the above embodiments,
wherein the sodium carbonate is present in about 50.60 wt. %,
.+-.10%.
[0102] [10.] The composition of any one of the above embodiments,
wherein the calcium oxide is present.
[0103] [11.] The composition of any one of the above embodiments,
wherein the calcium oxide is absent.
[0104] [12.] The composition of any one of the above embodiments,
wherein the calcium oxide is present in about 1.50 wt. % to about
5.5 wt. % of the composition.
[0105] [13.] The composition of any one of the above embodiments,
wherein the calcium oxide is present in about 1.50 wt. % to about
1.90 wt. % of the composition.
[0106] [14.] The composition of any one of the above embodiments,
wherein the calcium oxide is present in about 1.70 wt. %,
.+-.10%.
[0107] [15.] The composition of any one of the above embodiments,
wherein the calcium fluoride is present in about 0.50 wt. % to
about 6.00 wt. % of the composition.
[0108] [16.] The composition of any one of the above embodiments,
wherein the calcium fluoride is present in about 4.00 wt. % to
about 6.00 wt. % of the composition.
[0109] [17.] The composition of any one of the above embodiments,
wherein the calcium fluoride is present in about 5.00 wt. %,
.+-.20%.
[0110] [18.] The composition of any one of the above embodiments,
wherein the calcium chloride is present in about 400 wt. % to about
6.00 wt. % of the composition.
[0111] [19.] The composition of any one of the above embodiments,
wherein the calcium chloride is present in about 5.00 wt. %,
.+-.20%.
[0112] [20.] The composition of any one of the above embodiments,
wherein both the calcium fluoride and the calcium chloride are
present in the composition.
[0113] [21.] A composition comprising: [0114] (a) silicon dioxide
(SiO.sub.2), present in about 50 wt. %, .+-.50%; [0115] (b) sodium
carbonate (Na.sub.2CO.sub.3), present in about 47 wt. %, .+-.20%;
[0116] (c) optionally calcium oxide (CaO), present in up to about 6
wt. %; and [0117] (d) at least one of calcium fluoride (CaF.sub.2)
and calcium chloride (CaCl.sub.2), when present, each is
independently present in up to about 5.00 wt. %.
[0118] [22.] A composition comprising: [0119] (a) silicon dioxide
(SiO.sub.2), present in about 42.70 wt. %, .+-.10%; [0120] (b)
sodium carbonate (Na.sub.7CO.sub.3), present in about 50.60 wt. %,
.+-.10%; [0121] (c) oxide (CaO), present in about 1.70 wt. %,
.+-.10%; [0122] (d) at least one of calcium fluoride (CaF.sub.2)
and calcium chloride (CaCl.sub.7), when present, each is
independently present in about 5.00 wt. %, .+-.20%.
[0123] [23.] A composition comprising: [0124] (a) silicon dioxide
(SiO.sub.2), present in about 35 wt. % to about 80 wt. % of the
composition; [0125] (b) sodium carbonate (Na.sub.2CO.sub.3),
present in about 40 wt. % to about 55 wt. % of the composition;
[0126] (c) optionally calcium oxide (CaO), present in up to about 6
wt. % of the composition; and [0127] (d) at least one of calcium
fluoride (CaF.sub.2) and calcium chloride (CaCl.sub.2), when
present, each is independently present in about 0.50 wt. % to about
6.00 wt. % of the composition.
[0128] [24.] A composition comprising: [0129] (a) silicon dioxide
(SiO.sub.7), present in about 35 wt. % to about 50 wt. % of the
composition; [0130] (b) sodium carbonate (Na.sub.2CO.sub.3),
present in about 45 wt. % to about 55 wt. % of the composition;
[0131] (c) calcium oxide (CaO), present in about 1.50 wt. % to
about 1.90 wt. % of the composition; [0132] (d) at least one of
calcium fluoride (CaF.sub.2) and calcium chloride (CaCl.sub.2),
when present, each is independently present in about 4.00 wt. % to
about 6.00 wt. % of the composition.
[0133] [25.] A method comprising: [0134] (a) forming a molten
liquid from silicon and a flux, the flux comprising the composition
of any one of embodiments [1]-[24]; [0135] (b)) forming a slag,
from the flux and impurities in the molten liquid and; and [0136]
(c) optionally removing at least a portion of the slag from the
molten liquid, to provide a purified molten liquid.
[0137] [26.] The method of embodiment [25], which is a method for
purifying silicon.
[0138] [27.] The method of any one of the above embodiments, which
purifies silicon from aluminum.
[0139] [28.] The method of any one of the above embodiments, which
provides for silicon with at least about a 99.5 wt. % reduction in
aluminum.
[0140] [29.] The method of any one of the above embodiments, which
provides for silicon comprising less than about 10 ppmw
aluminum.
[0141] [30.] The method of any one of the above embodiments, which
purifies silicon from boron.
[0142] [31.] The method of any one of the above embodiments, which
purifies silicon from aluminum.
[0143] [32.] The method of any one of the above embodiments, which
provides for silicon with at least about a 30 wt. % reduction in
boron.
[0144] [33.] The method of any one of the above embodiments, ch
provides for silicon comprising less than about 0.30 ppmw
boron.
[0145] [34.] The method of any one of the above embodiments,
wherein the silicon that forms the molten liquid comprises
metallurgical grade (MG) silicon.
[0146] [35.] The method of any one of the above embodiments,
wherein the silicon that forms the molten liquid comprises solar
grade (SOG) silicon.
[0147] [36.] The method of any one of the above embodiments,
wherein the silicon that forms the molten liquid comprises silicon
recycled from a silicon purification process.
[0148] [37.] The method of any one of the above embodiments,
wherein forming the molten liquid from the silicon and the flux is
carried out, such that a molten liquid of silicon is initially
formed, and the flux is subsequently added to the molten
silicon.
[0149] [38.] The method of any one of the above embodiments,
wherein forming the molten liquid from the silicon and the flux is
carried out, such that solid silicon is initially contacted with
the flux, and together they are heated to form the molten
liquid.
[0150] [39.] The method of any one of the above embodiments,
wherein the molten liquid is formed at a temperature of at least
about 1450.degree. C.
[0151] [40.] The method of any one of the above embodiments,
wherein the molten liquid is formed at a temperature above the
solidus temperature.
[0152] [41.] The method of any one of the above embodiments,
wherein the slag comprises a reaction product of the flux and
impurities from the silicon.
[0153] [42.] The method of any one of the above embodiments,
wherein the slag comprises impurities from the silicon.
[0154] [43.] The method of any one of the above embodiments,
wherein slag forms on the surface of the molten liquid.
[0155] [44.] The method of any one of the above embodiments,
wherein slag forms on the surface of the molten liquid, and is
subsequently removed from the molten liquid.
[0156] [45.] The method of any one of the above embodiments,
further comprising (d) directionally solidifying the purified
molten liquid, to form solid silicon.
[0157] [46.] The method of any one of the above embodiments,
wherein the flux is present on an internal surface of a furnace
refractory, which is configured to protect molten silicon from
contamination by impurities from the furnace refractory.
[0158] [47.] The method of any one of the above embodiments,
wherein the directional solidification is carried out by cooling
the purified molten liquid.
[0159] [48.] The method of any one of the above embodiments,
wherein the directional solidification is carried out by cooling
the purified molten liquid, to a temperature of less than the
liquidus temperature of the purified molten liquid.
[0160] [49.] The method of any one of the above embodiments,
wherein the purified molten liquid is cooled to above the solidus
temperature of the purified molten liquid and below the liquidus
temperature of the purified molten liquid.
[0161] [50.] The method of any one of the above embodiments,
wherein a top portion of the purified molten liquid is maintained
above the melting point, while a bottom portion of the purified
molten liquid is cooled below the freezing point.
[0162] [51.] The method of any one of the above embodiments,
wherein the directional solidification is carried out by cooling
the purified molten liquid, to within about 125.degree. C. above
the solidus temperature of the purified molten liquid.
[0163] [52.] The method of any one of the above embodiments,
wherein the directional solidification is carried out by cooling
the purified molten liquid, to within about 125.degree. C. above
the melting point of the purified molten liquid.
[0164] [53.] The method of any one of the above embodiments,
wherein the directional solidification is carried out by cooling
the purified molten liquid at a bottom portion of a directional
solidification mold.
[0165] [54.] The method of any one of the above embodiments,
wherein the directional solidification is carried out by cooling
the purified molten liquid at a bottom portion of a directional
solidification mold, at a rate of less than about 75.degree.
C./hr.
[0166] [55.] The method of any one of the above embodiments,
wherein the directional solidification is carried out by cooling
the purified molten liquid, over a period of time of at least about
18 hours.
[0167] [56.] The method of any one of the above embodiments,
further comprising (e) removing a portion of the solid silicon, to
provide purified solid silicon.
[0168] [57.] The method of any one of the above embodiments,
wherein the portion of the solid silicon is removed by cutting the
solid silicon.
[0169] [58.] The method of any one of the above embodiments,
wherein any one or more steps is independently carried out multiple
times.
[0170] [59.] The method of any one of the above embodiments, ch
provides for at least about 1,000 kg silicon.
[0171] [60.] The method of any one of the above embodiments,
wherein the purified solid silicon is employed in the manufacture
of a solar panel.
[0172] [61.] A method comprising: [0173] (a) forming a molten
liquid from silicon and a flux, the flux comprising the composition
of any one of embodiments [1]-[24]; [0174] (b) forming a slag, from
the flux and impurities in the molten liquid; [0175] (c) optionally
removing at least a portion of the slag from the molten liquid;
[0176] (d) directionally solidifying the molten liquid, to form
solid silicon; and [0177] (e) removing a portion of the solid
silicon, to provide purified solid silicon.
* * * * *