Method and apparatus for producing silicon

Abstract

An apparatus for producing pure silicon from an electrolyte including a first crucible for receiving the electrolyte, a heat source for heating the electrolyte in the first crucible to form a molten electrolyte, an anode and a cathode which are adapted for electrical/ionic communication with the molten electrolyte wherein electrolysis is able to be applied to the molten electrolyte when a potential difference is provided between the anode and the cathode. A stirring device is adapted for stirring the molten electrolyte when electrolysis is being applied whereby pure silicon is produced which is soluble with the anode to form an alloy.

1 . A method of producing pure silicon from an electrolyte wherein the method includes the steps of:
 (i) heating the electrolyte in a first crucible to form a molten electrolyte; and   (ii) applying electrolysis to the molten electrolyte by providing a potential difference between an anode and a cathode which are adapted for electrical/ionic communication with the molten electrolyte;   wherein the molten electrolyte is stirred as electrolysis is being applied and pure silicon produced as a result of the electrolysis is soluble with the anode to form an alloy.   
     
     
         2 . A method as claimed in  claim 1  wherein the electrolyte comprises cryolite, calcium oxide particles and quartz particles. 
     
     
         3 . A method as claimed in  claim 2  wherein the electrolyte comprises approximately between 82-94% cryolite particles by weight of the electrolyte. 
     
     
         4 . A method as claimed in  claim 2 , wherein the electrolyte comprises approximately between 3-15% calcium oxide particles by weight of the electrolyte. 
     
     
         5 . A method as claimed in  claim 2 , wherein the electrolyte comprises approximately 3% quartz particles by weight of the electrolyte. 
     
     
         6 . A method as claimed in  claim 2 , wherein the electrolyte comprises approximately 87% cryolite particles, 10% calcium oxide particles and 3% quartz particles by weight of the electrolyte. 
     
     
         7 . A method as claimed in  claim 2 , including a step of controllably adding quartz particles to the electrolyte during electrolysis to substantially maintain approximately 3% quartz particles in the electrolyte by weight of the electrolyte. 
     
     
         8 . A method as claimed in  claim 1 , wherein the first crucible includes at least one of a carbon, silicon nitrate and silicon carbide material. 
     
     
         9 . A method as claimed in  claim 1 , wherein the first crucible includes a recess defined by an inner peripheral wall and a base for receiving the electrolyte. 
     
     
         10 . A method as claimed in  claim 9  including the step of arranging a first crucible lining inside the first crucible recess between the first crucible and the electrolyte. 
     
     
         11 . A method as claimed in  claim 1  including the step of arranging a second crucible lining inside the first crucible recess between the alloy anode and the first crucible lining. 
     
     
         12 . A method as claimed in  claim 11 , wherein the second crucible lining includes at least one of an SiC and an SiN material. 
     
     
         13 . A method as claimed in  claim 11 , wherein the second crucible lining is submerged beneath the anode during electrolysis in the first crucible. 
     
     
         14 . A method as claimed in  claim 1 , wherein silicon is segregated from the alloy after step (ii) by performing a secondary electrolysis upon the alloy whereby a solid composite of silicon and electrolyte is formed. 
     
     
         15 . A method as claimed in  claim 14 , wherein the polarities of the anode and cathode are reversed. 
     
     
         16 . A method as claimed in  claim 14 , wherein the secondary electrolysis is performed in a crucible separate to the first crucible. 
     
     
         17 . A method as claimed in  claim 14 , wherein the separate crucible includes an SiC material. 
     
     
         18 . A method as claimed in  claim 14 , wherein the secondary electrolysis is performed using at least one of the following electrolyte compositions: 
       (i) 10% K 2 SiF 6 , 25% AlF 3 , 25% NaF, 35% BaF 2 , 5% CaF 2 ; 
       (ii) 40-70% Na 3 AlFe, 5-20% K 2 SiF 6 , 5-15% CaF 2 , 5-10% CaO; and 
       (iii) 95-99% Na 3 AlF 6 , 1-5% SiO 2 . 
     
     
         19 . A method as claimed in  claim 14 , wherein the composite that is deposited on the anode is melted at a temperature of at least approximately 1450° C. whereby silicon conglomerates into pellets or ingots within the electrolyte upon cooling. 
     
     
         20 . A method as claimed in  claim 19 , wherein the conglomerated silicon pellets or ingots are filtered from the electrolyte using a filter. 
     
     
         21 . A method of producing pure silicon including the steps of:
 (i) performing an electrolysis upon a quartz-containing electrolyte in a crucible wherein a solid composite is formed containing silicon and the electrolyte;   (ii) thereafter, melting the composite wherein the silicon particles in the composite conglomerates in the electrolyte upon cooling;   (iii) thereafter, when the temperature of the melted composite falls below approximately 1414° C., filtering the conglomerated silicon from the electrolyte.   
     
     
         22 . A method as claimed in  claim 21  including the step of periodically adding powdered quartz to the crucible to maintain a supply a silicon particles during the electrolysis. 
     
     
         23 . A method as claimed in  claim 21 , wherein two carbon nodes are used in the electrolysis.