Dry conversion of high purity ultrafine silicon powder to densified pellet form for silicon melting applications

Abstract

A bulk silicon material for making silicon ingots, consisting of silicon pellets, and a method for making the pellets from an agglomerate-free source of high purity, ultra fine silicon powder by feeding a controlled amount of silicon powder into a pellet die, and dry compacting the powder at ambient temperature with pressure to produce a pellet that has a density of about 50-85% of the theoretical density of elemental silicon, a weight within a range of about 1.0 gram to about 3.0 grams, a diameter in the range of 10 mm to 20 mm and preferably of about 14 mm, and a height in the range of 5 mm to 15 mm and preferably of about 10 mm.

1 . A silicon pellet for making silicon ingots, consisting of a dry compacted volume of silicon powder, said silicon powder having a median particle size within a range of up to about 100 micrometers and a range of particle size of not greater than about 1000 micrometers.  
     
     
         2 . The silicon pellet according to  claim 1 , said powder being free of intentional additives and binders.  
     
     
         3 . The silicon pellet for making silicon ingots according to  claim 1 , said silicon powder having a median particle size within a range of up to about 10 micrometers and a range of particle size of not greater than about 1000 micrometers.  
     
     
         4 . The silicon pellet for making silicon ingots according to  claim 1 , said silicon powder having a bulk density within a range of about 0.60 g/cc to about 0.75 g/cc and preferably about 0.68 g/cc.  
     
     
         5 . The silicon pellet for making silicon ingots according to  claim 1 , said silicon powder having a bulk density of about 0.68 g/cc.  
     
     
         6 . The silicon pellet for making silicon ingots according to  claim 1 , said pellet having a density of about 50-85% of the theoretical density of elemental silicon, and having a weight within a range of about 1 gram to about 3 grams.  
     
     
         7 . The silicon pellet for making silicon ingots according to  claim 1 , said pellet having a diameter in the range of 10 mm to 20 mm, and a height in the range of 5 mm to 15 mm.  
     
     
         8 . The silicon pellet for making silicon ingots according to  claim 1 , wherein said powder comprises substantially pure silicon particles.  
     
     
         9 . The silicon pellet for making silicon ingots according to  claim 8 , wherein said powder is compacted with a force sufficient to cause adhesion between said particles.  
     
     
         10 . The silicon pellet for making silicon ingots according to  claim 8 , wherein said powder is compacted with a force of at least approximately 10,000 Newton's.  
     
     
         11 . A silicon pellet for making silicon ingots, comprising a dry compacted volume of silicon powder compacted by a force of at least approximately 10,000 Newton's, said powder having a median particle size of up to about 10 micrometers, said pellet having a density of about approximately 60-75% of the theoretical density of elemental silicon and a weight of about approximately 2.3 grams, said pellet having a diameter of about approximately 14 mm, and a height of about approximately 10 mm.  
     
     
         12 . The silicon pellet of  claim 11 , said pellet being free of additives and binders.  
     
     
         13 . A method for making a silicon pellet comprising: 
 providing a source of high purity silicon powder having a median particle size within a range of up to about 100 micrometers and a range of particle size of not greater than about 1000 micrometers;    feeding a controlled amount of said powder from said source into a pellet die;    compacting with pressure said controlled amount of said powder in said die thereby forming a dry pellet of high purity silicon; and    discharging said pellet from said die.    
     
     
         14 . The method for making a silicon pellet according to  claim 13 , said compacting being done at about ambient temperature.  
     
     
         15 . The method for making a silicon pellet according to  claim 13 , said powder being free of intentional additives and binders.  
     
     
         16 . The method for making a silicon pellet according to  claim 13  wherein said step of dry compressing comprises applying a force greater than or equal to about approximately 10,000 Newton's to said powder.  
     
     
         17 . A silicon pellet for the making of silicon ingots produced by a process comprising the steps of: 
 providing an agglomerate, additive and binder free source of high purity silicon powder having a median particle size within a range of up to about 100 micrometers and a range of particle size of not greater than about 1000 micrometers;    feeding a controlled amount of said powder from said source into a pellet die;    dry compacting with pressure said controlled amount of said powder in said die thereby forming a dry pellet of high purity silicon; and    discharging said pellet from said die.    
     
     
         18 . The silicon pellet according to  claim 17 , said dry compacting being done at about ambient temperature.  
     
     
         19 . The silicon pellet according to  claim 17  wherein said step of dry compaction comprises applying a force of greater than or equal to 10,000 Newton's to said powder.  
     
     
         20 . The method for making a silicon pellet of  claim 17 , further comprising: 
 adding an organic binder to said silicon powder to form a mixture of binder and silicon, said controlled amount of said powder comprising a controlled amount of said mixture, said dry compacting with pressure comprising adding sufficient heat whereby said binder is evaporated.