AU2007203614A1 - Method for producing solar grade silicon - Google Patents

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: General Electric Company Actual Inventor(s): Thomas Francis McNulty, Mark Philip D'Evelyn, John Thomas Leman, Roman Shuba Address for Service and Correspondence: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: METHOD FOR PRODUCING SOLAR GRADE SILICON Our Ref 807045 POF Code: 88428/141848 The following statement is a full description of this' invention, including the best method of performing it known to applicant(s): -1- METHOD FOR PRODUCING SOLAR GRADE SILICON This application claims priority from US Application No. 11/497,876 filed on 3 August 2006, the contents of which are to be taken as incorporated herein by this reference.

BACKGROUND

The invention relates generally to production of silicon, and in particular production of solar grade silicon.

Silicon is used in solar cells for the conversion of solar energy into electrical energy.

Silicon employed in solar cells is of a quality designated as "solar grade" which has a purity of greater than about 99.999 percent. It is particularly important for the solar grade silicon to have a very low amount of electrically active elements from group 111 and group V of the periodic table of elements, especially boron and phosphorus, as the presence of these impurities may adversely affect the performance of the solar cells.

The widespread usage of solar cells and devices based on solar cells depends to a large extent on the availability and cost of solar grade silicon. Over 15,000 metric tons of silicon was used by the photovoltaic industry in 2005, and is growing at a rate of about annually. Several methods for producing solar grade silicon are known, but most of these methods have one or more drawbacks related to processing. Some of these methods are based on a carbothermic reduction of a siliceous compound such as silica, and may require raw material to be of high purity to produce silicon of solar grade.

Accordingly, it is desirable to provide a method and apparatus that may address one or more of the foregoing problems in the production of solar grade silicon.

BRIEF DESCRIPTION According to an aspect of the present invention, there is provided an apparatus for producing silicon including: a housing including a wall having an inner surface defining a chamber; a thermal energy source proximate to the housing and operable to supply thermal energy to the chamber; a silica source inlet at one end of the apparatus and in communication with the chamber to introduce a silica source including a plurality of granules into the chamber; a hydrocarbon inlet at the one end of the apparatus and in communication with the chamber to introduce a hydrocarbon species into the chamber; a gas outlet at the one end of the apparatus and in communication with the chamber to outside of the chamber and being operable to vent gas from inside the chamber to outside the chamber; and a silicon outlet at an opposite end of the apparatus and in communication with the chamber to outside of the chamber and being operable to drain out the solar grade silicon formed.

According to embodiments of the invention, a method for producing silicon is provided.

The method includes providing a starting material comprising a plurality of granules, the granules comprising silica and a coating disposed on at least some of the granules, the coating comprising carbon. The method further includes heating the W ISASKIAM .fi SpmVRN807045-27 7 07do 206803-1 starting material to form an intermediate comprising silica and silicon carbide. The method further includes reacting the intermediate to form silicon.

DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: FIG. 1 is a flow chart of a method for producing silicon, according to embodiments of the invention; and FIG. 2 is an apparatus for producing silicon, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION In the following specification and the claims that follow, reference will be made to a number of terms that shall be defined to have the following meanings. The singular forms "an" and "the" include plural referents unless the context clearly dictates otherwise. As used herein, the term "total pressure" implies the sum of the partial pressures of all the components in a mixture. As used herein, the term "partial pressure" implies the pressure of that particular component to the total pressure.

The growth of silicon-based solar energy industry is to a certain extent limited by the cost of solar grade silicon. The cost of the solar grade silicon is attributable to the cost of the raw materials used for the manufacture as well as on the cost involved in the processing. Typical raw materials for silicon production include a siliceous source and a carbon source. The methods that employ cheaper raw material may require more expensive processing condition to purify the resultant silicon.

Embodiments of the present invention address these and other issues.

According to embodiments of the present invention, solar grade silicon is produced by the reduction of silica using a hydrocarbon species. The hydrocarbon species is 206803-1 comparatively less expensive when compared to other carbon sources such as, for

C

example, high purity carbon black. Moreover, liquid or gaseous hydrocarbon species are more-readily available in highly pure form. In yet another embodiment of the present invention, the packing of the raw materials in the reactor is improved by using raw material in granular form, which may further lower the processing cost.

Turning now to the figures, FIG 1 is a fow chart 10 of a method of producing solar IN grade silicon, according to embodiments of the present invention. At step 12, a starting material comprising a plurality of granules and a coating disposed on at least some of the granules is provided within a reactor. As used herein, the term "granules" refers to individual units of starting material, in contrast to, for example, a solid continuum of material such as a large block; the term as used herein encompasses units ranging from infinitesimal powder particulates with sizes on the micrometer scale (such as, for example, a 325 mesh powder) up to comparatively large pellets of material with sizes on the centimeter scale. The plurality of granules, in some embodiments, has a median granule size in the range of from about 1 micrometer to about 150 micrometers. The plurality of granules may comprise pure silica, and may be produced by milling of larger silica particles. The granules may additionally be washed in mineral acids, such as, but not limited to, nitric acid, hydrochloric acid, hydrofluoric acid, aqua regia, fluorosilicic acid, sulfuric acid, perchloric acid, phosphoric acid, and any combination thereoft to improve the purity of silica. In certain other embodiments, the granules are agglomerates, such as pellets. The median size of the pellets is typically on the centimeter scale. In some embodiments, the agglomerates are formed by mixing silica powder or particles with a binding agent to form a mixture, and subjecting the mixture to drying, partial decomposition, or decomposition of the binding agent by evaporation of solvent, or by baking, or by heating. Exemplary binding agents include hydrocarbons, sugars, cellulose, carbohydrates, polyethylene glycols, polysiloxanes, and polymeric materials. In some embodiments, the starting material has a median granule size in the range of from about 150 micrometers to about 1 millimeter. In certain embodiments, the starting material has a median granule size in the range of from about 1 millimeter to about 206803-1 millimeters. In other embodiments, the starting material has a median granule size in the range of from about 5 millimeters to about 5 centimeters.

The purity of the starting material may have a significant effect on the properties of the final solar grade silicon. In some embodiments, the starting material has a purity of about 99.999 percent. In another embodiment, the purity of the starting material is greater than about 99.9999 percent. It is also desirable that an amount of boron and phosphorus in the starting material is below certain limits. Typically such limits are in a range of about 50 parts per billion to about 500 parts per billion.

The step 12 of providing the starting material, in some embodiments, comprises decomposing a hydrocarbon species on at least some of the granules comprising silica. The decomposition of hydrocarbon species is also referred to as "cracking of the hydrocarbon species", wherein the hydrocarbon species decompose to form the coating comprising carbon at a surface of the granules. An example of one such decomposition reaction may be represented by the chemical equation, CH4 C 2H2 Here, methane, a hydrocarbon species, decomposes to form carbon, which is deposited as a coating on the granules with an accompanying release of hydrogen gas.

The hydrogen gas is removed, in some embodiments, by passing a sweep gas through an area at which the reaction occurs. Exemplary sweep gas comprises an inert gas such as, but not limited to, argon, helium, or hydrogen.

In some embodiments, the coating is deposited on the surface of at least some of the granules. In certain embodiments; the coating is deposited on the surface of substantially all of the granules. In particular embodiments, the coating substantially covers the entire surface of the granules that are coated. When the coating comprising carbon is deposited on the granules comprising silica, a surface area of carbon available for further reaction with silica is considerably higher than that available in conventional processes that do not employ this coating, and this may lead to a better yield of solar grade silicon. According to embodiments of the invention, a molar ratio 206803-1 O of silica to carbon in the starting material is about 1:2, in accordance with the chemistry of the overall decomposition reaction.

In some embodiments, decomposing the hydrocarbon species comprises heating the hydrocarbon species to a temperature greater than about 600 degrees Celsius. In certain embodiments, the hydrocarbon species decomposes at a temperature greater than about 1000 degrees Celsius. In some embodiments, the hydrocarbon species comprises a straight chain, a branched chain, or a cyclic isomer of hydrocarbons such as, alkanes, alkenes, alkynes and aromatic hydrocarbon compounds. Examples of suitable hydrocarbon species include, but are not limited to, natural gas, methane, C butane, propane, acetylene, or any combinations thereof. In some embodiments, the hydrocarbon species is a gas. In certain embodiments, the hydrocarbon species is a liquid at ambient pressure and temperature.

The starting material is heated, at step 14, to form an intermediate comprising silicon carbide and silica. The starting material is heated to a temperature greater than about 1600 degrees Celsius. In some embodiments, the temperature is greater than about 1750 degrees Celsius. The reaction comprising the formation of intermediate may be illustrated by the chemical equation, 3Si0O2 6C SiO2 2SiC 4CO Here, silica reacts with carbon to form silicon carbide and silica, along with an accompanying release of carbon monoxide gas. In some embodiments, the silica consists essentially of liquid silica. According to embodiments of the invention, the reaction equilibrium may be shifted towards the intermediate formation (that is, the right side of the equation) by maintaining a partial pressure of carbon monoxide that is lower than that required by thermodynamic equilibrium conditions. In some embodiments, the partial pressure of carbon monoxide is at a pressure less than about kilo Pascal (kPa). In another embodiment, the partial pressure of carbon monoxide is at a pressure less than about 25 kilo Pascal. In one embodiment, the partial pressure of carbon monoxide is maintained by flowing a sweep gas, as described for the previous step, over the intermediate. The flow rate of the sweep gas may depend on 206803-1 8 the design and configuration of the reactor in which the process occurs, the packing of the materials within the reactor, and the like. In one embodiment,the total pressure of Z the reactor is in a range of from about 100 kilo Pascal to about 150 kilo Pascal. In another embodiment, the total pressure of the reactor is in a range of about 150 kilo Pascal to about 200 kilo Pascal. In yet another embodiment, the total pressure of the reactor is greater than about 200 kilo Pascal.

\0 The intermediate comprising silicon carbide and silica is reacted to form silicon, at step 16. The intermediate is generally heated to a temperature greater than about 2000 degrees Celsius. In some embodiments, the temperature is greater than about O 2100 degrees Celsius. The reaction comprising the formation of solar grade silicon may be illustrated by the chemical equation, SiO2 2SiC 3Si 2CO As in the previous step, maintaining a partial pressure of the carbon monoxide below a level specified by thermodynamic equilibrium may shift the reaction equilibrium towards the desired right side of the equation, here, the formation of solar grade silicon. In some embodiments, the partial pressure of carbon monoxide is maintained at a pressure of less than about 90 kPa. In certain embodiments, the partial pressure of carbon monoxide is maintained at a pressure of less than about 46 kPa. The partial pressure of carbon monoxide is maintained, in some embodiments, by flowing a sweep gas comprising an inert gas. In some embodiments, the solar grade silicon formed consists essentially of liquid silicon.

In some embodiments, the solar grade silicon undergoes further purification steps prior to use. For example, it may be desirable to reduce the level of carbon or of residual metals in the silicon. Exemplary purification steps may comprise at least one of removal of particulates in molten silicon by sedimentation, removal of particulates in molten silicon by filtration, refining by bubbling of oxygen through molten silicon, refining by bubbling of wet hydrogen through molten silicon, zone refining, directional solidification, or heating in vacuum.

206803-1 O In some embodiments, the purity of the solar grade silicon is greater than about 99.999 percent or greater. In certain embodiments, the purity of the solar grade ;Z silicon is in a range of about 99.999 percent to about 99.9999 percent. In some embodiments, the purity of the solar grade silicon may reflect the purity of the starting Smaterials.

In accordance with an embodiment, an exemplary apparatus 20 for the production of IN solar grade silicon is shown in FIG. 2. The apparatus 20, in some embodiments, is a O reactor configured to accept a starting material comprising a plurality of granules at one end of the reactor and to collect a product material comprising silicon at an Sopposite end of the reactor. The apparatus 20 may have a number of components such as, inlets, outlets, thermal energy sources, and the like. In some embodiments, apparatus 20 comprises a multiple zone furnace where the temperature of each of the multiple zones is independently controllable. The apparatus 20 includes a housing 22 having a wall 24. In some embodiments, the housing 22 may include one or more walls 24. The wall 24 has an inner surface 26 that defines a chamber 28. The wall 24 of the housing 22 may be made of a metal, a refractory material, graphite, silicon carbide, or fused silica that are compliant with materials requirements for solar grade silicon manufacturing. In the illustrated embodiment, the wall 24 of the apparatus is fabricated from graphite. Additionally, an inert liner (not shown) may be provided along the inner surface 26 of the wall 24. The liner material is chosen so as to avoid acting as a source of undesirable contaminants. The liner may prevent or reduce material deposition on the inner surface 26 of the wall 24. Advantageously, the liner may be removable so as to allow the deposited material to be stripped from the wall 24 during a cleaning process.

The walls 24 of the housing 22 may be configured shaped or sized) with reference to processing conditions. The configuration may depend on the size and number of components. In one embodiment, the housing 22 may be rectangular. In the illustrated embodiment, the apparatus 20 has a vertically oriented configuration with a cylindrical shape with an outer diameter in a range of from about centimeters to about 5 meter, and a length of from about I meter to about 10 meters, although apparatus 20 of differing size and/or shape may be used. The chamber 28 7 206803-1 may have a pre-determined volume. The chamber 28 of the apparatus 20 may be further divided to zones, first zone 32, second zone 34, and third zone 36, based on the reactions occurring in these zones, although there is no requirement for a physical barrier between the zones.

A set of thermal energy sources 40, 42 and 44 may be located proximate to the housing 22 to supply thermal energy to the chamber 28. In some embodiments, the thermal energy sources 40, 42 and 44 may be independently controllable. In certain embodiments, the first thermal energy source 40, the second thermal energy source 42, and the third thermal energy source 44 may provide a different temperature at the first zone 32, the second zone 34, and the third zone 36, respectively. In one embodiment, the thermal energy may be provided by a heater. The heater may provide thermal energy by resistive heating or by inductive heating. Exemplary heaters include, but are not limited to, a ceramic heater, a molybdenum heater, a split furnace heater, a three zone split furnace heater, or an induction heater. When an induction heater is employed, the walls 24 of the housing 22 may be susceptible for induction heating the chamber 28. In some embodiments, a single thermal energy source is provided proximate to the housing and may be configured to provide a different temperature at each of the reaction zones.

At the upper portion of the apparatus 20, just above the first zone 32, a set of inlets and an outlet is provided to flow materials in and out of the chamber 28. A silica source inlet 46 and a hydrocarbon inlet 48 extend through the wall 24 and are in communication with the chamber 28 to introduce a silica source and a hydrocarbon species, respectively. The silica source inlet 46 and the hydrocarbon inlet 48 may be fabricated from graphite, silicon carbide, or a refractory material.

The silica source inlet 46 may include at least one gate valve (not shown) in series, so that silica may be introduced to the chamber 28 without disruption of the atmosphere in the chamber 28. The upstream portion of the silica source inlet 46 may include provisions for evacuation, backfill, and controls, to control the conditions within the chamber 28.

206803-1 0 The hydrocarbon inlet 48 may terminate above zone 32, as shown in FIG. 2. In some embodiments, the hydrocarbon inlet 48 may terminate within zone 32. Further, the ;ZT hydrocarbon inlet 48 may include a nested tube (not shown), to suppress the decomposition of hydrocarbon in tilhe hydrocarbon inlet 48 by flowing a coolant 0 through the nested tube so as to lower the temperature within the hydrocarbon inlet 48. In one embodiment, the coolant comprises a flowing gas, such as argon or helium. In some embodiments, the coolant comprises a liquid, such as water,

ID

Ccn ethylene glycol, or propylene glycol.

The flow rate of the hydrocarbon species to the chamber 28 may be adjusted for an extensive, uniform formation of the carbon coating on the starting material. Typical flow rate of the gaseous hydrocarbon species is in a range of from about 1000 cubic centimeters per minute to about 100,000 cubic centimeters per minute, although for an apparatus of differing dimension the flow rate may be varied according to the silica feed rate. In some embodiments, an external pump may be supplied to pump in the hydrocarbon species to the chamber 28. The external pump may advantageously provide additional control on the flow rate of the hydrocarbon species.

A gas outlet 50 provided at the upper portion of the apparatus 20 extends through the wall 24 and is in communication with the chamber 28. The inlets 46, 48 and the gas outlet 50 may be fabricated from graphite, silicon carbide, or a refractory material.

Additionally, valves (not shown), with or without mass flow controllers, may be provided at the inlets 46, 48 and the gas outlet 50 to control a flow of the materials to the chamber. Optionally, driers and/or purifiers may be provided at the silica source inlet 46, and the hydrocarbon inlet 48 to further dry and/or purify the starting material.

At the lower end of the apparatus 20, below the third zone 36, a silicon outlet 52, and a gas inlet 54 are provided. The gas inlet 54 is optional, in some embodiments. The silicon outlet 52, and the gas inlet 54 extend through the wall 24 and are in communication with the chamber 28 through the third zone 36. In some embodiments, the gas inlet 54 may be supplied with an external pump to flow in a sweep gas to the chamber 28. The silicon outlet 52 and the gas inlet 54 are fabricated from graphite, silicon carbide, silica, or other refractory material suitable for solar 9 206803-1 grade silicon manufacturing. Valves (not shown), with or without mass flow controllers, apertures, and baffles may be provided at the silicon outlet 52 and the gas inlet 54 to control a flow of the materials to and from the chamber 28. The chamber 28 may contain one or more of baffles, apertures, frits, and the like, in order to promote mixing. Additionally, a dryer and/or point of use purifier may be provided at the gas inlet 54 and at the silicon outlet 52 to further dry and/or purify the sweep gas and the solar grade silicon, respectively.

The silica source inlet 46 introduces the granules comprising silica to the chamber 28.

Typical packing density of the granules in the chamber 28 is in a range of about to about 50% by volume. The first thermal energy source 40, proximate to the first zone 32 is activated to raise the temperature within the chamber 28. Activating the first thermal energy source 40 increases the temperature within the chamber 28, and in particular at the first zone 32 to a pre-determined level and at a pre-determined rate of temperature increase. In some embodiments, the pre-determined level is greater than about 600 degrees Celsius. In certain embodiments, the pre-determined level is greater than about 1000 degrees Celsius.

The hydrocarbon species is introduced in the chamber 28 through the hydrocarbon inlet 48. When the pre-determined temperature is reached, the hydrocarbon species decomposes at a surface of the granules to form a coating comprising carbon, particularly at the first zone 32. In some embodiments, as the granules flows down from the first zone 32 to the second zone 34 most of' the granules have a coating comprising carbon. The granules in the second zone 34 and the third zone 36 may also have a coating comprising carbon. In some embodiments, the carbon is essentially in the solid form.

Following the formation of the coating, the temperature of the granules is raised by providing thermal energy at the second zone 34 by activating the second thermal energy source 42. In some embodiments, the temperature at the second zone 34 is greater than about 1600 degrees Celsius. In certain embodiments, the temperature at the second zone 34 is greater than about 1750 degrees Celsius. The granules comprising silica and carbon form arn intermediate comprising silica and silicon 206803-1 carbide. The intermediate formation may also release silicon monoxide in the second zone 34, in some embodiments. In one embodiment, the partial pressure of carbon monoxide is maintained at a pressure of less than about 50 kPa by flowing in the sweep gas through the gas inlet 54. In another embodiment, the partial pressure of carbon monoxide is maintained at a pressure of' less than about 25 kPa by flowing in the sweep gas through the gas inlet 54. The sweep gas removes the carbon monoxide formed in the chamber 28 through the gas outlet 50. The sweep gas may also carry other unwanted gaseous species such as hydrogen and silicon monoxide along with it.

The flow rate of the sweep gas may be adjusted to maintain the desired partial pressure of carbon monoxide. Additionally, the flow rate of the sweep gas is controlled such that any gaseous silicon monoxide formed in the second zone 34 condenses on the coated granules present in the first zone 32, so that they remain available for further conversion to solar grade silicon. Optionally, the gas outlet may be monitored to detect the concentration of carbon monoxide gas that comes out through the gas outlet 50, which may indicate the reaction condition within the chamber 28. In some embodiments, where the apparatus 20 does not include a gas inlet 54, the sweep gas is not introduced in the chamber 28 to control the reaction, instead other techniques may be utilized.

The temperature at the third zone 36 is raised by providing thermal energy by activating the third thermal energy source 44. In some embodiments, the temperature at the third zone 36 is greater than about 2000 degrees Celsius. In certain embodiments, the temperature at the third zone 36 is greater than about 2100 degrees Celsius. The intermediate reacts to form the solar grade silicon with the release of carbon monoxide. In some embodiments, the reaction of the intermediate also releases silicon monoxide in the third zone 36. In one embodiment, the partial pressure of carbon monoxide is maintained at a pressure of less than about 90 kPa by flowing in the sweep gas through the gas inlet 54. In another embodiment, the partial pressure of carbon monoxide is maintained at a pressure of less than about 46 kPa by flowing in the sweep gas through the gas inlet 54. The sweep gas removes the carbon monoxide formed from the chamber 28 through the gas outlet 50. Moreover, the flow rate of the sweep gas may be controlled such that any gaseous silicon monoxide 206803-1 formed in the third zone 36 condenses on the coated granules present in the first zone 32, thereby making it available for conversion to solar grade silicon. The intermediate comprising silica and silicon carbide reacts to form silicon- In some embodiments, the silicon is in a liquid form. 'The silicon collects at the lower end of the apparatus 20, below the third zone 36 and may be drained out through the silicon outlet 52. The method may be a continuous process, where the starting material may be continuously fed at the upper portion of the apparatus 20 and the product material comprising solar grade silicon may be collected at the lower end of the apparatus through the silicon outlet 52.

In one embodiment, a fourth zone (not shown) is provided between the third zone 36 and the silicon outlet 52, allowing for a controlled cooling down of the molten silicon prior to exiting from the chamber.

In some embodiments, the axis of the reactor is tilted instead of being vertically oriented. When the reactor is oriented at an angle with respect to a vertical orientation, the silica source inlet, the hydrocarbon inlet, the gas outlet are provided above the gas inlet and silicon outlet. In a specific embodiment, the silica source inlet, the hydrocarbon inlet, the gas outlet are provided at one end of the reactor and at the other end of the reactor, the gas inlet and silicon outlet are provided. In some embodiments, the reactor may be rotated to promote mixing of the silica and the added hydrocarbon species, and to facilitate the transportation of the coated granules downstream the reactor.

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

206803-1 ELEMENT LIST flow chart of a method 12 provide a starting material 14 heat the starting material to form an intermediate 16 react the intermediate to form silicon apparatus 22 housing 24 wall 26 inner surface of the wall 28 chamber 32 first zone 34 second zone 36 third zone first thermal energy source 42 second thermal energy source 44 third thermal energy source 46 silica source inlet 48 hydrocarbon inlet gas outlet 52 silicon outlet 54 gas inlet

Claims (10)

1. An apparatus for producing silicon including: ;Z a housing including a wall having an inner surface defining a chamber; a thermal energy source proximate to the housing and operable to supply thermal energy IDto the chamber; a silica source inlet at one end of the apparatus and in communication with the chamber to introduce a silica source including a plurality of granules into the chamber; a hydrocarbon inlet at the one end of the apparatus and in communication with the chamber to introduce a hydrocarbon species into the chamber; a gas outlet at the one end of the apparatus and in communication with the chamber to outside of the chamber and being operable to vent gas from inside the chamber to outside the chamber; and a silicon outlet at an opposite end of the apparatus and in communication with the chamber to outside of the chamber and being operable to drain out the solar grade silicon formed.

2. The apparatus of claim 1 further including a first thermal energy source, a second thermal energy source, and a third thermal energy source, wherein the first thermal energy source is configured to raise a temperature at a first zone to greater than about 600 degrees Celsius, wherein the second thermal energy source is configured to raise a temperature at a second zone to greater than about 1600 degrees Celsius, and wherein the third thermal energy source is configured to raise a temperature at a third zone to greater than about 2000 degrees Celsius.

3. The apparatus of claim 1, wherein the apparatus includes a multiple zone furnace, wherein a temperature of each of the multiple zone is independently controllable. W ASKIA\P~rcnl SpMIRNS0704S.27 7 07 dm 14

4. The apparatus of any one of claims 1 to 3, further including a gas inlet at the opposite end of the apparatus to flow in a sweep gas.

5. The apparatus of any one of claims 1 to 4, wherein the hydrocarbon inlet further includes a nested tube configured to flow in a coolant through the nested tube.

6. The apparatus of any one of claims 1 to 5, wherein the hydrocarbon species includes alkanes, alkenes, alkynes, aromatic hydrocarbons, or any combinations thereof.

7. The apparatus of any one of claims 1 to 6, wherein the apparatus is configured to decompose the hydrocarbon species to form a coating including carbon on the plurality of granules, wherein the plurality of granules comprises silica.

8. The apparatus of any one of claims 1 to 7, wherein the plurality of granules has a median granule size in the range of from about 1 micrometer to about 5 centimeters.

9. The apparatus of claim 7 or 8, wherein a molar ratio of the silica to the carbon in the plurality of granules is about 1:2. The apparatus of any one of claims 1 to 9, wherein the hydrocarbon species and the silica source are continuously fed into one end of the apparatus and the solar grade silicon produced is collected at the opposite end of the apparatus.

11. An apparatus for producing silicon substantially as hereinbefore described with reference to Figure 2. W:%SASKIAP2aten SpeCURNS07045O-27 7 07 doc