US4214920A — Method for producing solar cell-grade silicon fro…

Claim 1

Independent Claim 64 words

A process for producing solar grade high purity silicon from common rice hulls comprising: leaching the rice hulls in acid and in water, coking the leached rice hulls to produce a composite of carbon and silica, adjusting the carbon to silica ratio of the coked rice hulls to less than about 2:1, thermally reducing the adjusted carbon and silica mixture to produce elemental silicon.

Claim 2

Dependent Claim 64 words

A process for producing solar grade high purity silicon from common rice hulls comprising: leaching the rice hulls in acid and in water, coking the leached rice hulls to produce a composite of carbon and silica, adjusting the carbon to silica ratio of the coked rice hulls to less than about 2:1, thermally reducing the adjusted carbon and silica mixture to produce elemental silicon.

Claim 3

Dependent Claim 26 words

The process set forth in claim 1 wherein the step of leaching comprises contacting said rice hulls with aqueous hydrochloric acid and rinsing in distilled water.

Claim 4

Dependent Claim 23 words

The process set forth in claim 2 wherein said leaching reduces the impurity level in the rice hulls to below about 400 ppm.

Claim 5

Dependent Claim 37 words

The process set forth in claim 2 wherein said leaching reduces the impurity level of calcium and magnesium to below about 50 ppm and reduces the impurity level of maganese and iron to below about 30 ppm.

Claim 6

Dependent Claim 20 words

The process set forth in claim 1 wherein the size of the rice hulls is decreased by grinding or milling.

Claim 7

Dependent Claim 50 words

The process set forth in claim 1 wherein said coking comprises pyrolyzing the rice hulls at a temperature of about 920° C. in a non-oxidizing atmosphere comprising a gaseous mixture of an inert gas and at least one of the group of anhydrous acids consisting of HCl, HBR, and HI.

Claim 8

Dependent Claim 17 words

The process set forth in claim 6 wherein the gaseous mixture comprises about 1% anhydrous hydrogen chloride.

Claim 9

Dependent Claim 17 words

The process set forth in claims 6 or 7 wherein said inert gas comprises argon or nitrogen.

Claim 10

Dependent Claim 29 words

The process set forth in claim 6 or claim 7 wherein said steps of leaching and coking reduces the impurity level of the rice hulls to about 100 ppm.

Claim 11

Dependent Claim 26 words

The process set forth in claim 1 or claim 8 wherein said steps of leaching and coking reduces the boron impurity level to about 5 ppm.

Claim 12

Dependent Claim 27 words

The process set forth in claim 1 or claim 8 wherein said steps of leaching and coking reduces the aluminum impurity level to below about 10 ppm.

Claim 13

Dependent Claim 27 words

The process set forth in claim 1 wherein the step of adjusting the carbon to silica ratio comprises adding high purity silica to the coked rice hulls.

Claim 14

Dependent Claim 17 words

The process set forth in claim 12 wherein the added silica comprises finely divided uniformly dispersed quartz.

Claim 15

Dependent Claim 32 words

The process set forth in claim 1 wherein the step of adjusting the carbon to silica ratio comprises the controlled partial combustion of the carbon content of the carbon and silica composite.

Claim 16

Dependent Claim 26 words

The process set forth in claim 14 wherein the controlled partial combustion is accomplished in the presence of a gaseous mixture of argon and carbon dioxide.

Claim 17

Dependent Claim 16 words

The process set forth in claim 15 wherein the gaseous mixture contains about 5% carbon dioxide.

Claim 18

Dependent Claim 19 words

The process set forth in claim 16 wherein the temperature of the controlled partial combustion is about 950° C.

Claim 19

Dependent Claim 25 words

The process set forth in claim 15 wherein the partial combustion of carbon produces a carbon to silica ratio controllably variable between 2.5:1 to 1.4:1.

Claim 20

Dependent Claim 33 words

The process set forth in claim 1 wherein the step of reducing the coked rice hulls comprises thermally reacting the carbon and silica in an arc furnace at a temperature of about 1900°.

Claim 21

Dependent Claim 105 words

A process for producing a silicon single crystal solar cell comprising: (a) leaching rice hulls in acid and water; (b) coking the leached rice hulls in a non-oxidizing atmosphere; (c) adjusting the carbon to silica content ratio to below about 2.5 to 1; (d) reducing the adjusted rice hulls at a temperature of about 1900° C. to form silicon and carbon monoxide; (e) growing a single crystal boule from said silicon; (f) sawing said single crystal boule into thin wafers; (g) providing a suitable junction in or on said wafers; (h) providing ohmic contacts to either side of said junction to form a solar cell.

Claim 22

Dependent Claim 105 words

A process for producing a silicon single crystal solar cell comprising: (a) leaching rice hulls in acid and water; (b) coking the leached rice hulls in a non-oxidizing atmosphere; (c) adjusting the carbon to silica content ratio to below about 2.5 to 1; (d) reducing the adjusted rice hulls at a temperature of about 1900° C. to form silicon and carbon monoxide; (e) growing a single crystal boule from said silicon; (f) sawing said single crystal boule into thin wafers; (g) providing a suitable junction in or on said wafers; (h) providing ohmic contacts to either side of said junction to form a solar cell.

Claim 23

Dependent Claim 57 words

A process for producing a high purity feedstock of carbon and silica from common rice hulls which feedstock is capable of being reduced to high purity elemental silicon, said process comprising the steps of leaching the rice hulls in acid and in water then coking the leached rice hulls to provide a composite of carbon and silica.

Claim 24

Dependent Claim 57 words

A process for producing a high purity feedstock of carbon and silica from common rice hulls which feedstock is capable of being reduced to high purity elemental silicon, said process comprising the steps of leaching the rice hulls in acid and in water then coking the leached rice hulls to provide a composite of carbon and silica.

Claim 25

Dependent Claim 28 words

The process set forth in claim 21 wherein the step of leaching the rice hulls comprises contacting the hulls with aqueous hydrochloric acid and rinsing in distilled water.

Claim 26

Dependent Claim 23 words

The process set forth in claim 21 wherein said leaching reduces the impurity level of the rice hulls to below about 400 ppm.

Claim 27

Dependent Claim 36 words

The process set forth in claim 21 wherein said leaching reduces the impurity level of calcium and magnesium to below about 50 ppm and reduces the impurity level of manganese and iron below about 30 ppm.

Claim 28

Dependent Claim 50 words

The process set forth in claim 21 wherein said coking comprises pyrolyzing the rice hulls at a temperature of about 920° C. in a non-oxidizing atmosphere comprising a gaseous mixture of an inert gas and at least one of the group of anhydrous acids consisting of HCl, HBR, and HI.

Claim 29

Dependent Claim 17 words

The process set forth in claim 25 wherein the gaseous mixture comprises about 1% anhydrous hydrochloric acid.

Claim 30

Dependent Claim 17 words

The process set forth in claims 25 or 26, wherein said inert gas comprises argon or nitrogen.

Claim 31

Dependent Claim 29 words

The process set forth in claim 25 or claim 26 wherein said steps of leaching and coking reduces the impurity level of the rice hulls to about 100 ppm.

Claim 32

Dependent Claim 27 words

The process set forth in claim 21 or claim 27 where said steps of leaching and coking reduces the boron impurity level to below about 5 ppm.

Claim 33

Dependent Claim 27 words

The process set forth in claim 21 or claim 27 wherein said steps of leaching and coking reduces the aluminum impurity level to below about 10 ppm.

Claim 34

Dependent Claim 87 words

A process for producing a carbon and silica feedstock from common rice hulls capable of being reduced to high purity elemental silicon comprising steps of: leaching the rice hulls in acid solution containing from 10% to 50% by volume HCl followed by rinsing the hulls in distilled deionized water, coking the leached rice hulls at a temperature of about 920° C. in an atmosphere of argon containing 1% anhydrous HCl to produce a composite of carbon and silica having an impurity content less than about 100 ppm.

Claim 35

Dependent Claim 87 words

A process for producing a carbon and silica feedstock from common rice hulls capable of being reduced to high purity elemental silicon comprising steps of: leaching the rice hulls in acid solution containing from 10% to 50% by volume HCl followed by rinsing the hulls in distilled deionized water, coking the leached rice hulls at a temperature of about 920° C. in an atmosphere of argon containing 1% anhydrous HCl to produce a composite of carbon and silica having an impurity content less than about 100 ppm.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1983-07-29	1984-01-28	1984-07-29	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1987-07-29	1988-01-28	1988-07-29	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1991-07-29	1992-01-28	1992-07-29	$7700.00	Window Closed / Lapsed

Method for producing solar cell-grade silicon from rice hulls

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